Session K1 - Poster Session II.
POSTER session, Tuesday afternoon, March 23
, Palais des Congres

[K1.001] Semiconductor I

This abstract not available.

[K1.002] Electronic Structure at Semiconductor-Vacuum Interface

The impressive success of density-functional theory for describing the ground state properties of metals is largely related to its local density approximation for the exchange correlation potential. However, in semiconductors this method underestimates the band gaps 30-50% compared to the experimental values. Sham developed a semiconductor form of exchange correlation energy, which is related, via an integral equation, to the non-local self energy as obtained from many-body perturbation theory. We perform a self consistent local density-functional calculation in which the zero-temperature form of the exchange correlation potential is used, but full account is taken through the Fermi distribution function of the finite-temperature occupancy effects. We also apply the effective mass approximation to our method.

[K1.003] Ultrafast time-resolved photoluminescence study of Self-Assembled ZnTe/ZnSe Quantum Dots

We use the ultrafast time-resolved photoluminescence upconversion technique, with temporal resolution better than 200 fs, to study the carrier capture and carrier recombination of several different sizes of ZnTe/ZnSe Type II quantum dots without wetting layers. The time-integrated photoluminescence showed two peaks at the energy below the bandgap of ZnTe and these peaks corresponded to the emission energies of large and small sizes of QDs. We found that the carrier capture times for those photoluminescence peaks were all within 2~3 ps for these QDs with different sizes. These observations were faster than the carrier capture times of the Type I QDs studied by others. The carrier capture time increases slightly as the size of QDs increases. The lifetime of the photoluminescence for large sizes of QDs was longer than that of small sizes of QDs and they were all within few hundreds of picoseconds. The energy state of small sizes of QDs situated inside the dot is closed to the energy level of the barriers and results in short lifetimes of photoluminescence and faster carrier capture of carriers.

[K1.004] Electron coupling and strain relaxation in stacked self-assembled InAs/GaAs quantum dots

We studied tenfold stacked layers of InAs/GaAs quantum dots by photoluminescence (PL) in pulsed magnetic fields B [1]. The sample with an interlayer distance d of 9.8 nm behaves very much like the single layered sample. When d is reduced to 5.5 nm, a doubling of the PL energy shift for B perpendicular to [001] is observed, indicating the onset of electron coupling between the dots in the stack. On reducing d to 3.1 nm a lower exciton effective mass is seen. For d this small, the GaAs layer in between two successive dots becomes strained, while the strain in the InAs dot is more relaxed, reducing the exciton effective mass. This work was supported by the FWO-Vlaanderen, the Flemish GOA and Belgian IUAP programmes, the VIS 00/001 project of the KU Leuven and the NANOMAT project of the Growth Programme of the EC, contract number G5RD-CT-2001-00545. [1] J. Maes et al., Appl. Phys. Lett. 81 (2002) 1480.

[K1.005] Photoluminescence in MoS_2

Photoluminescence in MoS_2 and other layered transition metal dichalcogenide semiconductors was recently documented [1]. The near infrared radiative emission originates from bound exciton recombination processes due to halogen impurities intercalated between the layers of the materials. Intercalation of the halogen molecules occurs during crystal growth thus limiting the radiative properties to synthetic crystals. However, recent studies performed on several commercial MoS_2 powders, produced from natural MoS_2 in a process involving chlorine, also revealed PL emission in the same spectral region ( \sim 0.8 to 1.2 eV) as for the synthetic MoS_2 single crystals. Present efforts to intercalate natural MoS_2 single crystals with halogen molecules and thus inducing PL will be described. Photoconductivity measurements on synthetic MoS_2 and WS_2 single crystals will also be presented and compared to their PL spectra providing further insight to the nature of the radiative processes.

1. L. Kulyuk, L. Charron, E. Fortin, Phys. Rev. B 68, 075314 (2003).

[K1.006] Structural and electronic properties of CdTe clusters

Due to their great importance in the microelectronics industry, semiconductor clusters have been studied extensively. The majority of semiconductor clusters studied to date, however, have focused on group III-V and IV-IV semiconductors. Here we present a density functional study on the structural and electronic properties of II-VI semiconductor clusters: Cd_mTe_m (m = 1-8). The HOMO-LUMO orbital gaps, binding energies and dipole moments are calculated. The clusters with 6 to 12 atoms have relatively higher energy gaps. We also find a correlation between the gaps and binding energies. All calculations have been done with Gaussian 03 program.

[K1.007] Optical and magnetic properties of Fe and Co substituted ZnO and TiO_2 films prepared by metalorganic decomposition

Metalorganic decomposition (MOD) is a very versatile and a low cost spin coating method for fabrication of oxide films. Fe and Co substituted TiO_2 and ZnO films (1-2 mm thick) have been prepared on sapphire substrates using Ti(IV)-ethylhexoxide, Zn-ethylhexanoate, Fe-ethylhexanoate, and Co-neodecanoate precursor solutions. X-ray diffraction and Raman spectra of Fe and Co (less than 10%) substituted TiO_2 films annealed at 550 ^oC show anatase phase whereas the samples annealed at 700 ^oC show a rutile structure. The analysis of optical transmission data measured in the UV-Visible region show an optical bandgap of \sim3.1 eV for Fe and Co-TiO_2 anatase films. Similarly Fe and Co-ZnO films, annealed at 550-700 ^oC, have wurtzite crystal structure with an optical energy bandgap of \sim3.3 eV. All the films are highly insulating at room temperature. Magnetic measurements show that while both Fe-TiO2 anatase and Fe-ZnO films exhibit weak ferromagnetic behavior, Co-substituted films did not show any ferromagnetic behavior. The effect of annealing in vacuum (to create oxygen vacancies) and additional doping with Cu ions on the electrical and magnetic properties on Fe and Co substituted TiO_2 and ZnO films will be presented. Supported by NSF-REU Grant # EEC0097736

[K1.008] Non local effects in the Casimir force: B-exciton in CdS

We present a study of the spatial dispersion effects in the Casimir force in parallel excitonic semiconductor slabs. We apply the Green's function method to calculate the Casimir force F which depends on the reflectivity of the electromagnetic waves of S and P polarizations in the free space between the slabs. The dielectric constants of the semiconductors are frequency and wave vector dependent. The reflection amplitudes contain the effects of the multiple transverse and longitudinal modes excited within the slabs which are generated due to the B_n=1-exciton in CdS.. Results of F as function of the thickness of the vacuum gap between the slabs and the incidence angle of light are reported in this work. Local theory calculations are included for comparisons. Our results show that excitonic transitions modify significantly both S and P polarization reflectivities which in turn induce an enhancement of the Casimir force.

[K1.009] Transport measurements in InAsN/InGaAs two-dimensional electron systems

For optoelectronic applications in the mid-infrared wavelengths, the InAs-based heterostructures are very promising. It has been shown that a better heterointerface and a better carrier confinement can be achieved by replacing InAs with InAsN alloys. Hence the study on InAsN alloys improves device qualities and broadens our knowledge of III-N-V alloys. Here, we present our investigation of Shubnikov-de Haas (SdH) oscillations of two-dimensional electron gas formed in composition-dependent InAsN/InGaAs single quantum wells (QW). The samples are grown using gas source molecular beam epitaxy. The photoluminescence (PL) peak energy decreases after nitrogen is incorporated. This agrees with the bowing effect due to the incorporation of nitrogen atoms. The nitrogen content can be determined by PL peak positions as well as X-ray diffraction. The largest nitrogen content is estimated to be 0.004. The composition-dependent effective mass value is determined from the SdH measurements. For the sample with nitrogen composition 0.004, a large effective mass of 0.1 \mathop m\nolimits_0 is found. The enhancement of the effective mass is mainly due to the incorporation of nitrogen atoms in the InAs lattice, which is consistent with a recent study on InAsN bulk alloys. The large increase of the effective mass cannot be explained by the simple band anti-crossing model. Our result is useful for reexamining the validity of assumptions in different theoretical approaches and for the optimization of devices based on InAsN/InGaAs QWs.

[K1.010] Lateral contraction of a traveling exciton packet

A near-resonant optical probing method is used to determine the spatial extent of a traveling high-density exciton packet. The packet is initially created by an intense laser pulse illumination (\lambda =532nm) incident on a natural single crystal of Cu_2O (at T=1.8K) having (100) symmetry. The traveling packet is laterally probed by a laser pulse tuned in the vicinity of the 1S orthoexciton resonance (\lambda =609.51nm), where the probing beam is additionally attenuated upon being transmitted through the excitonic packet. In order to measure the packet's longitudinal and transversal density profiles, the additional attenuation (NDA) is determined at various probing beam positions relative to the perpendicularly propagating packet. The transversal width of the exciton packet was found to be significantly reduced with respect to its initial width (pump beam diameter). Such a result provides an indication that the packet experiences a lateral contraction leading to a filament-like structure as it travels through the crystal.

[K1.011] electron's self trapping at the field-effect junction of a molecular crystal

We consider the interface of a molecular crystal with a polar dielectrics. Coulomb interaction of free electrons in the molecular crystal with surface polar phonons of the dielectrics can lead to the selftrapping of carriers. For typical parameters of molecular field effect transistors the binding energy is found to be high enough to allow for the formation of a strongly coupled polaron. The effect is further enhanced at presence of the bias electric field.

[K1.012] First principles total energy studies of the adsorption of disilane on Ge(001)-c(2x4)

We perform first principles total energy calculations to investigate the energetics and the atomic structure of the adsorption of silane (SiH_4) and disilane (Si_2H_6) on the Ge(001)-c(2\times 4) surface. The adsorption of Si_2H_6 is a dissociative process which first yields SiH_3 and then SiH_2 fragments. We first study the adsorption of SiH_2 considering two different models; the intra-row and the on-dimer geometries. Our results show that the on-dimer site is more stable than the intra-row geometry. This is not a surprise since in the absence of H atoms adsorption in the on-dimer site leaves no dangling bonds. In contrast, when the SiH_2 fragment is considered together with two H atoms, the intra-row geometry is favored energetically as compared with the on-dimer site. Similar results have been previously obtained for the adsorption of SiH_2 on Si(001). Disilane adsorption is explored according to two different geometries. In the first one, we have considered the adsorption as two SiH_3 fragments, while in the second, we have considered the adsorption as two SiH_2 fragments plus 2 H fragments. It is found that the later geometry is energetically more favorable.

[K1.013] Optical properties of GaMnAs thin films measured by spectroscopic ellipsometry

We have investigated the optical properties of a series of GaMnAs thin films using spectroscopic ellipsometry. The GaMnAs films were grown directly on GaAs (100) substrates using molecular-beam-epitaxy. A rotating analyzer spectroscopic ellipsometer was used to measure the complex reflection ratio for each of the films in the energy range between 0.7-6.0eV. By modeling the ellipsometric data, the dielectric functions for GaMnAs films were determined. All of the dielectric functions displayed the critical point structures related to the higher order electronic transitions. We fitted these critical point structures using standard analytical expressions to obtain various characteristics (i.e., energy, width, strength, excitonic contribution) associated with each of these points. This allowed us to predict the electronic structure variance of GaMnAs alloys as Mn is incorporated in to the lattice.

[K1.014] Characteristics of a two-dimensional electron-hole gas in a GaSb/InAs/AlSb heterostructure

The electronic states of a two-dimensional electron-hole gas (2DEHG) in GaSb/InAs/AlSb heterostructures with a GaSb cap layer has been calculated self-consistently. The electronic structure, densities and transport properties of the 2DEHG are expected to depend on the thickness of the GaSb and the density of the intrinsic interface deep donor which causes Fermi level pinning. Low-field magnetotransport data and the observation of Shubnikov-de Haas oscillations in the magnetoresistivity confirm the existence of a 2DEHG at the GaSb/InAs interface. The dependence of the observed magnetotransport properties and the calculated electronic structure of the 2DEHG on the thickness of the GaSb cap layer will be discussed.

[K1.015] Self-consistent approach and effective renormalization of band edge in quantum wells

We develop a new self-consistent approach to calculations of exciton properties in quantum well (QW) structures. In this approach, we solve the system of three coupled integro-differential equations for functions, which describe a single-particle one-dimensional motion for an electron and a hole across the QW, and a relative motion of an electron-hole pair in the plane of QW. As a result, the effective Coulomb interaction is treated self-consistently and appears in all three equations. Initial QW potential in this approach is renormalized by electron-hole Coulomb interaction. This renormalization gives rise to an infinite number of discrete energy levels extending from the initial single-particle ground states up to the points of accumulation, which are the barriers' heights. This happens due to Coulomb tails of the effective QW potential at large z. Experimentally this effect would manifest itself as an effective renormalization of the barrier band edge.

[K1.016] PHOTO-INDUCED CHANGES IN FARADAY ROTATION OF DOPED-InP

We report on the investigation of light induced changes in Faraday rotation (FR) conducted at several different wavelengths of several doped-InP samples, at room temperature. Appreciable FR, yielding Verdet constant values at 980, 1064, 1320 and 1550 nm has been previously reported. We have also investigated the role played by dopants in FR for this class of materials. In this study we focus on the changes in the magnitude and sign of FR when the sample is illuminated by a pump beam in addition to a probe beam. The FR experiment is conducted in the conventional geometry but a pump beam is also employed. This pump beam usually has a wavelength greater than the wavelength corresponding to the InP:Fe band gap. Results will be presented for various choices of the pump wavelength for a given choice of probe wavelength. Additionally, the changes in the FR levels as a function of the angle of the pump beam are also investigated.

[K1.017] Multiple Magnesium Donor Impurities in Silicon

It is well known that the group-II magnesium, when diffused into silicon, enters the silicon lattice interstitially and behaves as a helium-like double donor. The ionization energy determined from the excitation spectrum measured at liquid helium temperature is 107.50 meV for neutral magnesium donor. Several additional spectral lines have been observed from high-resolution FT-IR absorption spectrum measured at low temperature. Comparison of line spacings and relative intensities of these additional spectral lines and those observed for neutral magnesium donor suggests that they are due to several shallower donor impurities. This clearly indicates that there are multiple neutral donor centers for interstitial magnesium impurities in silicon.

[K1.018] Magnetoexcitons in type–II semiconductor quantum dots

We present a theoretical investigation of excitons in type-II semiconductor quantum dots (QD). In these systems the confinement of electrons inside the QD and the hole outside the QD produces a ring-like structure [1-2]. Recently, Ribeiro et al [3], in a magnetophotoluminescence study of type-II InP/GaAs self-assembled quantum dots, observed Aharonov-Bohm-type oscillations characteristic of the ring topology for neutral excitons. Using a simple model they have derived the groundstate hole energy as a function of the magnetic field, and obtained values for the ring parameters which are in good agreement with the measured values. However, some of the features observed experimentally, in the photoluminescence intensity, can not be well explained under that approach. In this work we present a more realistic model which considers the finite width of the ring and the electron-hole interaction included via a perturbative approach. The calculations are performed within the oneparticle formalism using the effective mass approximation. The confinement potential for electrons is modelled as the superposition of a quantum well potential along the axial direction, and a parabolic lateral confinement potential. The energies for the hole in the ring plane are calculated using the method of reference [4]. Theoretical calculations are in good agreement with the experimental results of reference [3] provided that excitonic effects are properly taken into account. References 1. A.O. Govorov et al., Physica E 13 , 297 (2002). 2. K. L. Janssens et al. Phys. Rev B64, 155324 (2001), and Phys. Rev. B66, 075314 (2002). 3. E. Ribeiro, G. Medeiros-Ribeiro, and W.Carvalho Jr., and A.O. Govorov, condmat/0304092 (2003). 4. Z. Barticevic, G. Fuster, and M. Pacheco,Phys. Rev. B 65, 193307 (2002).

[K1.019] Semiconductor II

This abstract not available.

[K1.020] NMR investigation of atomic ordering in Al_xGa_1-xAs thin films

Nuclear magnetic resonance is used to study the local cation ordering in thin films of Al_xGa_1-xAs (0 < x < 0.5) grown by metal organic vapor phase epitaxy. A quantitative analysis of the ^75As resonance intensities and the quadrupole coupling constants of all nuclei reveal no deviations from a random arrangement.

[K1.021] Optical and electrical properties of Titania thin films doped with In3+ and grown by sol-gel process.

Using the sol-gel process were prepared Titania (TiO2) thin films formed on glass substrates by dip-coating method. The samples were grown starting from Titanium Isopropoxide and changing the concentration of In3+ ions from Indium Nitrate. The results of the characterization of the samples by UV-VIS spectroscopy , IR , thermopotency and conductivity will be reported.

[K1.022] Modulated beam study of adsorption-induced-desorption reaction, H + D/Si(100) → D2

We have studied the kinetics mechanism of the adsorption-induced-desorption (AID) reaction, H + D/Si(100) \to D_2. Using a modulated H beam, two different types of AID reactions are revealed: one is the fast AID and the other is the slow AID reaction, occurring only at the beam on- and even at the beam off-cycles, respectively. Both the fast and slow AID reactions show the different dependence on surface temperature T_s, suggesting that their kinetics mechanisms are different. The fast AID reaction overwhelms the slow one in the desorption yield for all over the tested region 300K\le T_s \ge 650K. It proceeds along a first-order kinetics with respect to the incident H flux. Based on the experimental results, both two AID reactions are suggested to occur only on the 3\times 1 di-hydride phase accumulated under surface exposure to H atoms. Possible mechanisms for the two AID reactions are discussed.

[K1.023] Angular distributions of H-induced HD and D2 desorptions on Si(100) surfaces

Abstractin of D adatms by H atoms on Si(100) can be categorizes as,

Direct abstraction(ABS): H+D/Si\to HD, or

Adsorption-induced-desorption(AID): H+D/Si\to D_2.

We have measured the angular distributions y(\theta _f) of desorbing HD and D_2 molecules.We have found that y(\theta _f) for both ABS and AID reactions have a peak at \theta _f=0^o or along the surface normal. The width of y(\theta _f) is found to be broader for ABS than for AID. The dynamical mechanism for ABS and AID are discussed

[K1.024] Coverage dependence of the desorption dynamics of hydrogen from the Si (100) surface

We^ have studied the coverage (\Theta ) dependence of D_2 desorption from the Si(100) surface by time-of-flight (TOF) measurement. The translational energy tends to^ weakly decrease with increasing \Theta . It is revealed that desorption through 2H or 2H* process mainly takes place at low coverage, and 4H process takes place at high coverage around \Theta =1ML. Two rates along the 2H (2H*) and 4H processes cross over at 0.9 ML. Our result seems to support recent theoretical model for the interdimer mechanism, but 2H-4H crossing over occurs at much higher coverages than its prediction. The coverage dependence of the mean energy barrier (E_0) and distribution of barrier widths (W) were estimated from the analysis using the principle of detailed balance.

[K1.025] Growth and Characterization of GaN using high temperature AlN:Si as buffer layer by RF Plasma-assisted Molecular Beam Epitaxy

The GaN grown on c-plane sapphire using Si doped high temperature AlN as buffer layer by RF-MBE has been studied. The polarity of GaN film grown on high temperature AlN:Si buffer layer was determined by NaOH solution. The influence of high temperature AlN:Si buffer layer were investigated by reflection high-energy electron diffraction, photoluminescence, symmetric and asymmetric high-resolution x-ray diffraction, field-emission scanning electron microscopy and Hall measurement.

[K1.026] Erbia-containing electrospun titania nanofibers as selective emitters for low temperature thermophotovoltaic energy conversion

Tetraisopropyl titanate (TPT) has been mixed with a soluion of polyvinylpyrrolidone (PVP) and electrospun into nanofibers. The PVP is pyrolyzed, leaving nanofibers of rutile phase titania as shown by scanning electron microscopy and X-ray diffraction analysis. In order to obtain erbia containing titania nanofibers, erbium(III) oxide particles are added to the solution before electrospinning. After pyrolysis the titania nanofibers encapsulate the smaller erbia particles. Temperature-dependent emission spectra show that the erbia containing nanofibers emit selectively in the near-infrared when convectionally heated. The electrical power generated by a GaSb photodetector placed in line-of-sight geometry with respect to the heated nanofibers is also measured as a function of temperature. These nanofibers have potential as selective emitters for low temperature ( less than 600 degrees Celcius) thermophotovoltaic applications.

*Corresponding author: rex@uakron.edu Presenting author: Randy Teye-Mensah

[K1.027] First-Principles Studies of Titanium Overlayer Epitaxy on Diamond (100) Surface: the Earliest Stages

We use \textitab initio total energy calculations to study the adsorption and diffusion of Ti atom on diamond (100) surface at different coverage beyond one monolayer. Two interesting findings are reported in our calculations. First, we find that the most stable adsorption sites are very sensitive to the coverage of Ti atom and we predicted that there exists a transition when Ti atoms epitaxy on the diamond (100) surface in the earliest stages. By studying the diffusion of Ti atom on diamond (100) surface, we find a new diffusion mechanism for Ti atom on diamond (100) surface: not Ti atom “\textithopping” on the diamond surface but the “\textitC-C dimer bond opening”.

[K1.028] Light scattering in fractional quantum Hall regime

Light scattering measurements of GaAs at a magnetic field of 6-11 T and a temperature of 50 mK are examined. Peaks are found at the cyclotron frequency as well as at certain fractions of the same. These fractions have certain spin dependence and symmetry corresponding to two signs of the spin, +- s. Many properties have been examined and found to be in agreement with the theory of angular momentum[1]. Pan et al[2] have shown that the theory of CF is not satisfactory. We find that spin and orbital angular momenta of the electron are sufficient to explain the data but "associating strongly interacting electrons with even number of vortices called CF is not likely on the basis of probability theory. Hence the claim of flux attachment[3] of Herjibehedin et al[3] are not justified.

[1] K. N. Shrivastava, Introduction to quantum Hall effect, Nova Sci. N.Y. (2002);cond-mat/0302610. [2] W. Pan, H. L. Stormer, D. C. Tsui, et al, Phys. Rev. Lett. 90, 016801(2003). [3] C.F.Hirjibehedin, A. Pinczuk et al, PRL, 91, 186802(2003)

[K1.029] One-dimensional proton conductor with strong short-range interactions

Lately there has been great interest in objects with proton conductivity (superionic conductors, some biological systems, etc.). The problem of studying the mechanism of proton transport in these systems is important. However it is hard to take into account all of the microscopic processes that act in a proton subsystem, since they include proton transfer, interactions between protons, proton-phonon interactions, etc., although some work has examined the problem of short-range proton interactions. We aim to study their influence on the one-dimensional proton conductor described by a fermionic model which takes into account the proton transfer in the spirit of a two-stage Grotthuss mechanism as well as a strong short-range proton interaction. While performing the one-particle Green's function expansion, we introduce the irreducible parts, which arise due to the presence of interactions in the zero-order Hamiltonian. We have calculated the proton energy spectrum in the first-order scattering approximation, which takes into account the simplest contributions of proton scattering. In this approximation the behaviour of the chemical potential and the edges of the bands at different proton concentrations is investigated

[K1.030] Oscillations in the current-voltage characteristic of an asymmetric ballistic junction

Nonlinear effects in three- and four-terminal ballistic devices have attracted growing interest in the last few years. We fabricated a four-terminal asymmetric junction from a two-dimensional electron system confined in an InGaAs quantum well. Two contacts are available at each branch of the junction, allowing for four-contacts measurements of the resistances of each branch. Measurements are performed at low temperature, in the ballistic regime of transport. We apply a (longitudinal) current between opposite branches of the junction and measure the resulting transverse voltage between the two other contacts, as well as the change of longitudinal resistance. When the longitudinal current grows, we observe changes of slope and even oscillations in the transverse voltage, coinciding with abrupt changes of the longitudinal resistance. We discuss our results in light of Landauer-Büttikker simulations of the device (H.Q. Xu, Appl. Phys. Lett., 78, 2064 (2001)).

[K1.031] ¡§Mobility gap¡¨ of a spin-split GaAs two-dimensional electron system

We have performed magnetotransport measurements of the electron g factor in a two-dimensional GaAs electron gas. In order to obtain the spin gap \bigtriangleup_s, we measure the spin-split longitudinal resistivity minima which shows an activated behavior \rho_xx \sim \exp (-\bigtriangleup_s/2k_BT), where k_B is the Boltzmann constant and T is the temperature, respectively. We are able to determine the spin gaps at the different odd filling factors \nu=1, 3, 5, and 7 from Arrhenius plots. The spin gap is expected to have the form \begineqnarray \bigtriangleup_s=g_0\mu_BB+E_ex=g^\ast\mu_BB \endeqnarray where E_ex is the many-body exchange energy which lifts the g factor from its bare value (g_0 = 0.44 in GaAs) to its enhanced value g*. Using Eq 1, the enhanced g factor can be obtained from the linear fit of the spin gaps at the different odd filling factors as 9.28, almost 20 times greater than the bare value (0.44). This enhancement is due to electron-electron interactions. The measured g factor is larger than that previously reported in GaAs by studying the activation energy, which emphasizes the low level of the disorder in our system. Our experimental results provide compelling evidence that conventional activation energy studies yield a "mobility gap" which can be very different from the real spin gap in the energy spectrum.

[K1.032] Electron transport through Mn-O-Mn junction

We examine electron conduction properties of Mn-O-Mn atomic chain with account of oxigen oscillations in the double-well potential formed by Mn ions. The voltage and temperature dependencies of electron current through the structure are determined. Our theoretical results are compared with experimental data of diluted manganite materials.

[K1.033] Self-assembly of coherent quantum-dots of ZnO semiconductor

We studied growth dynamics of fabricated ZnO quantum-dot on the lattice mismatched substrate. The ZnO quantum dots grown by RF-magnetron sputtering method were formed on bare substrate surface for the Volmer-Weber growth or on the well-aligned wetted surface for the Stranski-Krastanov growth. Discrete self assembled ZnO quantum dot were undergone Ostwald ripening and coalescences processes above certain critical size. Therefore, discrete ZnO quantum dots changed to the continuous planer layer. We measured the epitaxy c-axis orientation on the surface normal direction of ZnO quantum dots by the synchrotron x-ray scattering method.

[K1.034] Step and terrace structure of the Ge(001) surface

Using a simple SOS model we describe the faceting behaviour of <010> steps on the Ge(001) surface. In contrast to Si(001), where <010> oriented steps tend to facet into local S_A and S_B steps, <010> steps on Ge(001) meander along the <010> direction. The faceting behaviour of these steps turns out to be fully governed by the next-nearest neighbour interaction. We also discuss how Ge(001) goes through the c(4\times2) to (2\times1) phase transition. As the result of an anisotropic surface stress component, the strain relaxation energy outweighs the energy to form domain boundaries between the two phases. The energy balance of strain relaxation energy vs. domain boundary energy induces a coexistence region around room temperature where a one-dimensional domain structure develops. It consists of alternating c(4\times2) and (2\times1) domains. In both cases, steps and terraces, we compare our model calculations with experimental observations and find good quantitative agreement.

[K1.035] Semiconductor III

This abstract not available.

[K1.036] Temperature Stable Hall Effect Sensors

Magnetic field sensors are needed for high accuracy position, angle, force, strain, torque, and current flow measurements. Molecular beam epitaxy was used to grow tellurium-doped indium gallium antimonide thin films. Hall effect sensors made from these films have been studied for their magnetic sensitivity and thermal stability. For a range of alloy composition and n-type doping levels, high magnetic sensitivity from -40°C to +200°C was found with a resolution of better than +/- 0.5 percent over the entire temperature range.

[K1.037] Point defects and defect complexes in ZnGeP_2

ZnGeP_2 is a chalcopyrite semiconductor of interest for nonlinear optical frequency conversion and as host for dilute magnetic semiconductor applications. The point defects in this material are not yet well understood. Here we present a study of some of the native point defects and several complexes related to them. Local spin density functional full-potential LMTO calculations of 64 supercells are used to calculate energies of formation and local densities of states of the defects. Calculations were performed for the V_Zn, V_Ge, V_P, Ge_Zn, and Zn_Ge point defects. We show that contrary to previous assignments in the literature the AL1 EPR center, which is commonly observed in as grown samples, cannot be assigned to the V_Zn point defect because the ENDOR measurements indicate localization of the wavefunction on only two equivalent P atoms whereas the V_Zn would require four P atoms. Symmetry breaking distortions of the V_Zn are not supported by our relaxation calculations. The Zn_Ge is also excluded for the same reason. The V_Ge is found to be unstable towards formation of a Zn_Ge and V_Zn pair. A new EPR center recently discovered in irradiated material could correspond to the V_Zn but disappears after annealing while AL1 grows suggesting complex formation. Supported by AFOSR.

[K1.038] Optical phonons in strained epilayers of GaN_yAs_1-y on GaAs(100)

Pseudomorphically strained 33 nm-thick films of the ternary alloy GaN_yAs_1-y have been grown by molecular beam epitaxy on GaAs(100) with y ranging from 0.006 to 0.05. Raman scattering studies in quasibackscattering geometry were performed on these uncapped alloys using 457.9 nm excitation to avoid substrate contributions. The optical phonon Raman spectrum displays a two-mode like behavior. The GaAs-like (GaN-like) first-order modes are represented at y = 0.05 by the stronger longitudinal optic (LO) mode at 288.4 (474.8) cm^-1 and the weaker transverse optic (TO) mode at 268.2 (458.4) cm^-1. Two very broad acoustic phonon bands are observed at 80 and 170 cm^-1 due to atomic disorder within the anion sublattice. As the nitrogen concentration increases, the GaAs-like LO mode shifts linearly towards lower wave number from the y = 0 limit of 291.2 cm^-1 while the GaN-like LO mode unexpectedly shifts up nonlinearly from 468.4 cm^-1 at y = 0.006. In addition, the GaN-like phonon band showed a proportional increase in its intensity and line width. Second order GaAs-like peaks were also observed at 334, 355, 371, 420, 452, 507, 521, 537, 560, and 578 cm^-1 for y = 0.05.

[K1.039] Influence of Arsenic and Silicon doping on the electrical properties of GaN epitaxial layers grown by MOCVD

Electrical properties of arsenic and silicon-doped GaN films grown on sapphire substrates by low metalorganic chemical vapor deposition have been investigated using temperature dependent Hall-effect measurements. The Hall data measured from the GaN layers shows that the concentration decreases with arsine flow (4, 40, and 400 sccm) at all temperatures, whereas, in general, the mobility increases for temperatures below 300 K. The carrier concentration of the Si-doped GaN, on the other hand, increases with the incorporation of arsine flow. This indicates that arsine flow enhances the efficiency of Si doping in GaN. The mobility, however, decreases with the incorporation of arsine in Si doped GaN at all temperatures

[K1.040] Observation of ring defects in high Indium content InGaN/GaN MQW

We report here on the observation of GaN islands in the barrier layer of high In content MQW structures which are surrounded by nanometer scale V-defects. These defects form nearly hexagonal rings when InGaN based multiquantum well (MQW) active layers are deposited under hydrogen free conditions or at growth temperatures below 800 o^C. Mechanical properties of the areas enclosed and outside of the ring defects as examined by ultrasonic force microscopy (UFM) show small variation in the material composition. Chemical etching of the MQW structure showed a slight difference in the etch rate of the ring defect against its surrounding regions, ruling out the possibility of growth of N-polar GaN in a Ga-polar GaN matrix. We did not observe formation of any ring defects at higher growth temperatures above 800o or when hydrogen is added.

[K1.041] CVD diamond films: a dosimeter material for the future

Recent advancements in CVD techniques have been important in providing high quality diamond films for dosimetric applications in an extended UV range and ionizing radiation. A review of the most significant developments on doped and non-doped diamond film used in thermally stimulated luminescence dosimetry (TLD) is presented. The main advantage of diamond films over the current and commercial dosimeter materials is that diamond is biologically compatible with human tissue, since it has a Zeff = 6.0 very close to Zeff = 7.5 of human tissue. Also it is non toxic and CVD technology available today permits to grow diamond films on large areas, important in developing re-usable medical radiography plates. The small size of diamond film, along with a strong thermally stimulated luminescence response of radiation exposed samples; open a wide range of application in medical radiotherapy and in situ monitoring of well localized regions inside the human body.

[K1.042] Ion beam characterization of GaAs1-xNx and GaAs1-x-yNxBiy epitaxial layers

GaAs_1-xN_x and GaAs_1-x-yN_xBi_y epitaxial layers, grown by Metal Organic Vapor Phase Epitaxy and Molecular Beam Epitaxy, respectively, were characterized by Rutherford Backscattering Spectrometry (RBS), Nuclear Reaction Analysis (NRA) and Elastic Recoil Detection (ERD) in random and channeling geometries using 2 - 3.73 MeV He beams and 50 MeV Cu beam respectively. The total amount of incorporated Bi and N in the layers was quantified by means of RBS (for Bi) and NRA/ERD (for N) in random orientation. The substitutional fraction of Bi and N in the samples can be estimated by using RBS and NRA along channeling directions. The results reveal that for these high quality layers all the Bi atoms are located at subsititutional sites with a total Bi concentration up to 2 at.% while 70\sim 80% of total N atoms in the layer are located at substitutional sites for the samples with 1 at.% N in GaAs_1-x-yN_xBi_y and higher N content (3 at.%) in GaAs_1-xN_x.

[K1.043] Deep level transient spectroscopy study of particle irradiation induced defects in n-6H-SiC

Neutron and electron irradiation induced deep level defects in n-type 6H-SiC have been investigated using deep level transient spectroscopy (DLTS) combined with annealing experiments. Deep levels ED1, E1/E2, Ei, and Z1/Z2 were observed in n-type 6H-SiC material irradiated with neutron. Thermal annealing studies of these deep levels revealed that ED1 and Ei annealed at a temperature below 350^oC, Z1/Z2 levels annealed out at 900^oC, while the intensity of the E1/E2 peaks increased with annealing temperature, reached a maximum at about 500-750^oC, and finally annealed out at 1400^oC. Upon further annealing at 1600^oC, four deep levels labeled NE1 at EC-0.44eV, NE2 EC-0.53eV, NE3 EC-0.64eV, and NE4 EC-0.68eV are produced. Ionization energies of these levels are similar to E1/E2 and Z1/Z2 respectively, but their capture cross sections are different. Samples were irradiated with electrons with different energies ranging from 0.2MeV to 1.7MeV. No deep level was detected in samples irradiated with 0.2MeV electron and deep levels ED1, E1/E2, and Ei were induced with electron energy larger than 0.3MeV.

[K1.044] Spatial distribution of carrier concentration in un-doped GaN film grown on sapphire

The depth and lateral dependent carrier concentration of un-intentionally doped GaN film grown on sapphire substrate have been studied by temperature-dependent Hall effect measurement, confocal micro-Raman spectroscopy and capacitance-voltage (C-V) measurements. The depth-dependent free carrier concentration extracted from the depth-profiled Raman spectra confirms a non-uniform spatial distribution of free carriers in the GaN film with a highly conductive layer of ~1 m thickness near the GaN/sapphire boundary. The temperature dependent Hall data have been analyzed using two-layer model to extract the carrier concentration in the GaN bulk film and in the parallel conduction channel adjacent to the GaN/sapphire boundary. The carrier concentrations of the two layers derived from the Raman technique and the Hall measurements agree with each other. The lateral-dependent carrier concentration of the 2-inch GaN epitaxial wafer has also been studied by micro-Raman spectroscopy and C-V measurements. The line-shape fitting of the Raman A1(LO) coupled modes taken from horizontal lateral-different positions on the wafer yielded a rudimentary spatial map of the carrier concentration. These data are compared well with a lateral-dependent carrier concentration map of the wafer revealed by C-V measurements. The study in the article indicates that Raman spectroscopy of the LO phonon-plasmon mode can be used as a nondestructive and reliable, in situ diagnostic for GaN wafer production.

[K1.045] TEM investigation of Si nanocrystals formed by ion implantation

\textitThe small size of silicon nanocrystals (Si-nc) is responsible for the photoluminescence (PL) of this material. Transmission electron microscopy has been used to study Si-nc formed by ion implantation into an amorphous silicon oxide (SiO_2\textit) film. Si-ions were implanted at the energy of 100 keV into the SiO_2\textit film at different implantation doses (2.10^16;8.10^16;3.10^17 \textitSi^+\textit/cm^2\textit). The material was then submitted to an annealing at 1100 ^oC for 1 or 4 h in an N_2\textit atmosphere and to a passivation of 500 ^oC for 1 h in a forming gas (5% H_2\textit and 95% N_2\textit). High resolution TEM micrographs were used to determine the shapes of the Si-nc and the inter planar distances. This latter is in accord with the Si structure. The size (2-5 nm) of Si-nc were measured on dark field TEM micrographs and found to vary according to different doses. The quantum confinement model can give the PL spectrum associated to a mean theoretical grain size and a width of the nanograin size distribution. This model contains a constant C whose values are found in the literature. With the mean grain size observed by TEM and the actual size distribution an experimental value of C was obtained.

[K1.046] Complex Materials II

This abstract not available.

[K1.047] Magnetoacoustic resonance in magnetoelectric bilayers

Layered composites of ferrite and ferroelectric single crystal thin films are of interest for studies on magnetoelectric interactions [1,2]. Such interactions result in unique and novel effects that are absent in single phase materials. For example, in a single crystal composite it is possible to control the ferromagnetic resonance (FMR) parameters for the ferrite by means of hypersonic oscillations induced in the ferroelectric phase. The absorption of acoustic oscillations by the ferrite results in variation in FMR line shape and power absorbed. One anticipates resonance absorption of elastic waves when the frequency of elastic waves coincides with the precession frequency of magnetization vector. This work is concerned with the nature of FMR under the influence of acoustic oscillations with the same frequency as FMR. Bilayers of ferrite and piezoelectric single crystals are considered. Hypersonic waves induced in the piezoelectric phase transmit acoustic power into ferrite due to mechanical connectivity between the phases. That transmission depends strongly on interface coupling [3]. We estimate the resulting variations in ferromagnetic resonance line shape. Estimates of magnetoelectric effect at magnetoacoustic resonance are also given. In addition, dependence of absorption of acoustic power on sample dimensions and compliances, electric and magnetic susceptibilities, piezoelectric and magnetostriction coefficients is discussed. The theory provided here is important for an understanding of interface coupling and the nature of magnetoelastic interactions in the composites.

1. M. I. Bichurin and V. M. Petrov, Zh. Tekh. Fiz. 58, 2277 (1988) [Sov. Phys. Tech. Phys. 33, 1389 (1988)]. 2. M.I. Bichurin, I. A. Kornev, V. M. Petrov, A. S. Tatarenko, Yu. V. Kiliba, and G. Srinivasan. Phys. Rev. B 64, 094409 (2001). 3. M. I. Bichurin, V. M. Petrov, and G. Srinivasan, J. Appl. Phys. 92, 7681 (2002).

This work was supported by grants from the Russian Ministry of Education (Å02-3.4-278), the Universities of Russia Foundation (UNR 01.01.007), and the National Science Foundation (DMR-0322254).

[K1.048] Influence of constant and ac electric fields on ferromagnetic resonance in magnetoelectric composites

A composite of ferromagnetic and ferroelectric phases is expected to show magnetoelectric coupling that is mediated by mechanical deformation. For such composites, we proposed a model to treat the magnetoelectric (ME) coupling at frequencies corresponding to ferromagnetic resonance (FMR) [1,2]. The effect manifests as a shift in the resonance field when subjected to a constant electric field. Here we discuss a theory for the influence of both dc and high frequency electric fields on FMR in the composites. The model predicts a significant increase in the strength of ME coupling when the electric field is tuned to the electromechanical resonance (EMR) frequency. We assume the composite to be a homogeneous medium. By solving combined elastostatics, electrostatics and magnetostatics equations, we estimate the ME constants using effective parameters. The calculations are for 3-0, 0-3 and 2-2 connectivities. Expressions for ME coefficients are obtained as a function of interface coupling and the volume fraction for the piezoelectric phase. Under the influence of a constant electric field E, our model predicts a shift in the ferromagnetic resonance field that is proportional to ME constants. In the presence of an ac electric field, we estimate a strong ME coupling when the frequency is tuned to EMR. As an example, the FMR field shift at 9.3 GHz due an ac electrical field tuned to EMR at 350 kHz is determined for multilayer and bulk composites of nickel ferrite - lead zirconate titanate. It is shown that ME interactions are enhanced by several orders of magnitude compared to off resonance values.

1. M.I. Bichurin, I. A. Kornev, V. M. Petrov, A. S. Tatarenko, Yu. V. Kiliba, and G. Srinivasan. Phys. Rev. B 64, 094409 (2001). 2. M.I. Bichurin, V. M. Petrov, Yu. V. Kiliba, and G. Srinivasan. Phys. Rev. B 66, 134404 (2002).

- supported by grants from the Russian Ministry of Education (Å02-3.4-278), the Universities of Russia Foundation (UNR 01.01.007), and the National Science Foundation (DMR-0322254).

[K1.049] Theory of magnetoelectric effects in ferromagnetic/piezoelectric bulk composites

Bulk and layered composites of piezoelectric and magnetostrictive phases show magnetoelectric (ME) properties. But bulk composites are desirable over layered samples due to superior mechanical strength. Here we discuss a model that considers less-than-ideal boundary conditions for ME interactions in a bulk composite. The composite is assumed to be a homogeneous medium with piezoelectric and magnetostrictive subsystems [1]. We solve combined elastostatics, electrostatics and magnetostatics equations to obtain composite effective parameters (piezoelectric modules, magnetostriction factors, compliances, ME coefficients) for 3-0 and 0-3 connectivities. Expressions for longitudinal and transverse low-frequency ME voltage coefficients have been obtained for unclamped and clamped samples. The strength of ME interactions and the volume fraction for maximum ME coefficient are shown to be dependent on mechanical connectivity for the two phases. It is shown that for 3-0 connectivity the longitudinal ME voltage coefficient is three times higher than the transverse coefficient. Volume fractions corresponding to peak low-frequency effective ME voltage coefficients depend on connectivity type. In addition, peak ME voltage coefficients are determined by degree of sample clamping. Clamping leads to significant variation of ME voltage coefficients. The calculated ME coefficients are compared with data.

1. M.I. Bichurin, V.M. Petrov, G. Srinivasan, Ferroelectrics, 280, 165 (2002); J. Appl. Phys. 92, 7681 (2002).

- supported by grants from the Russian Ministry of Education (Å02-3.4-278), the Universities of Russia Foundation (UNR 01.01.007) and the National Science Foundation (DMR-0302254).

[K1.050] Maxwell-Wagner relaxation in magnetoelectric composites

Magnetoelectric interactions in ferrite-piezoelectric composites are caused by magnetic and electric field coupling through elastic deformations [1]. Magnetostriction in the ferrite due to an applied magnetic field results in polarization in the piezoelectric phase. The addition of charges at the interface between the two phases results in dielectric dispersion and losses, namely, the Maxwell-Wagner relaxation. Past studies on the phenomenon include layered ferroelectric - polymer composites and polar dielectrics [2]. The present work focuses on the theory of Maxwell-Wagner relaxation in magnetoelectric parameters for ferrite-piezoelectric composites. We consider a multilayer composite of nickel ferrite-lead zirconate titanate and used an averaging procedure to obtain the composite and ME parameters. Our model predicts a giant relaxation in ME susceptibility and ME voltage coefficient. The relaxation is of the normal type in the susceptibility and is of the inverse type in the voltage coefficient. The relaxation time and frequency vary in a wide range and are dependent on volume fraction for the two phases, interface coupling parameters and the composite parameters. The estimated peak ME susceptibility exceeds any reported values for ME materials. The estimates are useful for engineering ME materials with maximum ME coefficients for specific frequency bands.

1. M. I. Bichurin, V. M. Petrov and G. Srinivasan. Phys. Rev. B. 68, 054402 (2003). 2. A.V.Turik and G.S.Radchenko. J. Phys. D. Appl. Phys. 35, 1188 (2003).

- supported by grants from the Russian Ministry of Education (Å02-3.4-278), the Universities of Russia Foundation (UNR 01.01.007) and the National Science Foundation (DMR-0302254).

[K1.051] Mechanical and Thermal Properties of a Natural Nanocomposite: Ivory

Ivory is a natural composite, composed of inorganic material (mostly calcium hydroxyapatite) in an organic (collagen) matrix. Type I collagen is formed by three protein chains which are wound together to form a triple helical structure. The crosslinking of the collagen molecules gives the structure a high tensile strength and stiffness. Hydroxyapatite crystals, 30 nm x 20 nm x 3 nm, embedded in the periodic gaps in the collagen fibrils, provide compressional strength. The tripartite organization of hydroxyapatite and collagen leads to an anisotropic structure for an ivory tusk, usually defined in terms of the radial, circumferential and transverse planes. In this study, the flexural strength, elastic modulus and thermal conductivity were determined along the transverse and radial planes of ivory.

[K1.052] Electronic properties of carbon nanotubes rings: Effects of electric and magnetic fields

Carbon nanotubes and correlated structures like carbon toroids, present a variety of electronic properties depending upon their intrinsic geometric formation. In this work, we analyze the electronic properties of a toroidal carbon-nanotube under an external magnetic field threading the toroid and an external electric field applied in different configurations. Our calculations are based on the electron single-orbital tight binding approximation, and two types of model-calculations are adopted: real-space renormalization techniques, based on Green function formalism, and straight diagonalization calculation. The magnetic field is considered through the Peierls-phase and the effect of the electric field is included into the on-site energies of the carbon atoms. By applying electric and magnetic fields a gap modulation can be induced which changes the electronic and transport properties of the structure.

[K1.053] Laser-based synthesis, nanostructure and electrical properties of networks of single wall carbon nanotube bundles

We have developed an ``all-laser'' synthesis approach for the controlled growth of Single-wall nanotubes (SWNTs) on various substrates. This original two-step growth process uses the same KrF excimer laser to deposit, in a first step, the Co/Ni nanoparticle catalysts on the patterned substrates and, in a subsequent step, to grow the carbon SWNTs. By using the appropriate laser ablation conditions of the Co/Ni target, it is shown that the mean diameter of the as-deposited Co/Ni nanoparticles can be controlled in the 0.5-2.5 nm range. On the other hand, a furnace temperature of 1000 ^oC and a laser intensity of \sim 3 x 10^8 W/cm^2 have been identified as the optimal conditions that lead to the growth of carbon SWNTs by means of a KrF UV laser.

The laser-grown SWNT bundle networks were characterized by means of AFM/STM, TEM and microRaman spectroscopy. These analyses have revealed that the ``all-laser'' process leads to the formation of lateral random networks of SWNT bundles. The diameter of the SWNTs was found to be of 1.1 \pm 0.1 nm, while that of the bundles is typically of \sim 10 nm. It is shown that the laser-synthesized random networks of SWNT bundles exhibit a typical field effect transistor behavior. Conductance--gate voltage curves not only demonstrated that transport through the nanotube networks is dominated by holes but also that the bundles consist of a mixture of semiconducting and metallic SWNTs.

[K1.054] Insulating to metallic transition in mats of SWNT under pressure

We report Resistance vs Temperature measurements, R(T), performed in mats of Single-Walled Carbon Nanotubes (SWNT) at high quasi-hydrostatic pressure, from room temperature to about 1.6 K. At atmospheric pressure SWNT mats show a semiconducting-like behavior that can be fitted to a Luttinger liquid model. From 0.5 to about 2.0 GPa the R(T) characteristic changes to a Kondo-like feature, which may be related to the magnetic impurities used to catalyze the nanotube formation. Above 2.0 GPa the minimum of the Kondo feature decreases in temperature until at higher pressure disappears and the resistance decreases precipitously suggesting a superconducting transition below 2K [1].

[1] R. Falconi, J. A. Azamar, and R. Escudero, Solid State Communications (in press). We acknowledge financial support from DGAPA-UNAM project IN102101, and CONACyT-México project G0017. We also thanks R. Rangel for the TEM studies.

[K1.055] Well-Dispersed Single Walled Carbon Nanotube Growth from Iron Nanoparticles Created from Poly(styrene-b-ethylmethylferrocenylsilane) Thin Films

Well dispersed single walled carbon nanotubes (SWNTs) have been grown directly from a diblock copolymer thin film, poly(styrene-b-ethylmethylferrocenylsilane), determined to be random spheres of polyethylmethylferrocenylsilane (PEMFS) in polystyrene (PS). When the spin cast block copolymer was heated in a chemical vapor deposition oven (CVD), iron nanoparticles formed from the ferrocene containing polymer block, acting as metal catalysts for SWNT growth. The SWNTs in this study were over 10 µm in length, and grew in bundles ca. 2-10 nm in diameter, with individual nanotube diameters of 0.66 to 1.1 nm. Optimum nanotube growth occurred in polymer film thicknesses of 24 to 36 nm, corresponding to one monolayer of PEMFS spheres on the surface. By selectively crosslinking regions of the polymer film with UV, SWNTs can be grown from single lines of polymer only 3 to 20 µm in width.

[K1.056] Non-linear conductance in quantum point contacts of noble metals

We studied the non-linear property of the electronic conductance of the noble metal nanocontact. Specimens were cleaned by Ar ion sputtering in UHV(`2\sim10|7[Pa]) at room temperature. Current vs voltage curves (I-V curves) were obtained, while the metal contact was stretched by STM. The bias voltage at the contact was changed within 2V (using the triangle wave voltage 3`5kHz). Au, Pt, Ag and Cu quantum point contacts showed non-linear I-V curves. These metallic contacts presented the quantized conductance of the quantum unit G0(=2e2/h). I-V curves are fitted to a cubic function ( IaV+cV3 ). The value of c/a does not depend on the zero-bias conductance value, a. However, c/a values depend on metals (c/a ; Au=0.58 0.02, Ag=0.33 0.02, Cu= 0.40 0.03). The present result indicates that metals of lower resistance (higher mobility) give lower values of c/a.

[K1.057] Magnetic anisotropy and de Haas - van Alphen oscillations in Bi microwire and nanowire arrays via cantilever magnetometry

We report measurements of the low temperature (T = 0.5 K) oscillatory magnetization in a high-density array of 50 micron diameter wires of polycrystalline Bi utilizing a high sensitivity silicon cantilever magnetometer. We find that the magnetic response is strongly anisotropic, being much larger for magnetic field perpendicular than for fields parallel to the wire-axis. We argue that this is a geometric effect caused by the large aspect ratio of the individual microwires in the array. The magnetic response of the microwires is dominated by the light electrons due to the larger cyclotron orbits in comparison with the heavier holes. We find that de Haas - van Alphen oscillations are easily resolved. Preliminary measurements on Bi nanowires are also presented and discussed in light of a possible confinement-induced modification of the Fermi surface (Huber et al., Phys. Rev. B 67, 245317 (2003)).

[K1.058] Enhanced sensitivity of a gas sensor using singlewalled carbon nanotubes-polypyrrole nanocomposites

A nanocomposite of polypyrrole (Ppy)/single walled carbon nanotubes (SWNTs) prepared by in situ chemical polymerization shows improves the conductivity of the polypyrrole. It's application to the chemical sensor by a simple spin-casting shows a drastic increase in the sensitivity. Chemical polymerization was simple and straightforward to have a uniform coating of Ppy on SWNTs. Ppy was uniformly coated on the wall of SWNTs to increase the specific surface area. The measured resistivity was greatly reduced due to the presence of the conductive SWNT network, whereas the specific surface area was increased by about three times. The sensitivity of the gas sensor fabricated with the SWNT/Ppy nanocomposite upon NO2 gas which was measured by a direct voltage divider at room temperature was very high, similar to that of the individually fabricated SWNTs. We obtained the SWNT sensor that behaved as an n-type. This was explained by an ambient presence of metallic tubes in SWNT mat that governed the transport of the SWNT sensor. The prepared Ppy and SWNT/Ppy also showed an n-type behavior, which was explained by anion doping in Ppy during chemical polymerization process.

[K1.059] Edge effect in the field emission properties on vertically aligned carbon nanotube arrays

We have synthesized vertically aligned carbon nanotubes (CNTs) on the patterned Ni thin films using thermal chemical vapor deposition (CVD) and investigated their field emission (EFE) properties. Ni thin films patterned with a form of dot-arrays were prepared using an comventional grid mask. In order to investigate the EFE properties, the tungsten tip as a current collector was used in field emission secondary electron microscopy (FESEM). In the central part CNTs with a high density, turn-on field was higher than those of edge parts CNTs and even intermediate parts without CNTs. Because of screening effect of electrons in central parts CNTs, electrons were merely emitted from the CNTs, resulted to high turn-on field and low enhancement factor. The relatively high current density in the intermediate parts without CNTs indicated that electrons emitted from edge parts CNTs near the intermediate parts could be widely spread, resulted to cross talk of electron to the anode materials. Because cross talk phenomena is one of the lacks to overcome for the application of FE display, research of edge field effect in the FE properties is very essential and important.

[K1.060] Development of Ultra-High Vacuum Transmission Electron Microscope (UHV-TEM) Combined with STM for Simultaneous Observation of the Structure and Electric Conductance of the Nanowire

Electric conductance of metal nanowires is quantized even at room temperature. An ultra-high vacuum transmission electron microscope (UHV-TEM) combined with an STM has been developed to observe the structure and electric conductance of the nanowires simultaneously. Nanomotor is used for coarse motion of 3 mm range for approaching (retracting) the tip to (from) the thin film sample for TEM observation. A piezotube (PZT) is used for fine motion of the tip in X, Y, Z directions. Using the system, the conductance can be measured in UHV condition (10^-8 - 10^-9 Pa) for each clean nanowire formed between the sample and the tip and characterized well by TEM. Long range of the fine motion of the nanomotor is effective to make a long silver nanowire (100 - 300 nm long) using an ionic conductor, AgI.

[K1.061] One Phonon Resonant Raman Scattering in Quantum Wires and Free Standing Wires

We have developed a theory of one phonon resonant Raman scattering in a semiconductor quantum wire (QWW) and free standing wire (FSW) of cylindrical geometry. We present a complete description of the phonon modes of cylindrical structures embedded in another material, including a correct treatment of the mechanical and electrostatic matching conditions at the surface. We consider the Fröhlich interaction for resonance Raman scattering. Electron states are considered confined within the QWW and the FSW. We also assume T=0K, a single parabolic conduction and valence bands. The spectra are discussed for different laser energies and the selection rules for the processes are also studied. Singularities in the spectra are found and interpreted.

[K1.062] Directed Self-Assembly of Carbon Nanotube Wires for Electronics

Carbon nanotubes are desirable for future micro and nanotechnologies due to their unique electronic/mechanical properties, with possible applications as highly selective chemical sensors, field emitters, and conducting wires. Fabricating these systems will require precise and controlled placement and orientation of nanotubes; mass-production will require scalable batch techniques and reproducibility. Our group is exploring self-assembly methods as a route to guided nanotube placement. We propose to utilize complementary chemical interactions to direct the assembly of carbon nanotubes onto specifically patterned surfaces. Our main process combines dip-pen nanolithography (DPN) and functionalization of carbon nanotubes to selectively bind nanotubes into targeted locations. We are currently focused on fabricating carbon nanotube wires with precise locations and orientations on a silicon substrate.

[K1.063] Frictional Energy Loss of Charged Particles to a Cylindrical Nanotube

We consider the motion of a charged particle near the surface of a single-walled cylindrical nanotube. We formulate the problem by considering the case when the charged particle moves parallel to the axis of the nanotube and also when its trajectory has a radial component of velocity. We calculate the frictional force on the particle due to the electrostatic interaction with the electrons on the surface of the nanotube in terms of its inverse dielectric function and surface response function. We generalize our formalism to a multi-walled nanotube and present numerical results as a function of the particle velocity and impact parameter. We analyze the contributions to the energy loss from the plasmon and single-particle excitations.

[K1.064] The Effect of Magnetic and Electric Fields on the Plasmon and Single-Particle Excitations for a Metallic Nanotube

We present calculations for the collective plasmon excitations of an electron gas confined to the surface of a cylindrical nanotube in a (a) magnetic field perpendicular to the axis of the cylinder, (b) a terahertz electric field along the axis, and (c) a spatially varying electric field due to a helical coil of charge cladding the nanotube. The single-particle eigenstates are calculated in each case and the results are used in the polarization function to obtain the dispersion equation.Numerical results for the plasmon dispersion are presented for (1) various magnetic field strengths, (2) different magnitudes of the terahertz field, and (c) several distributions of electric charge on the helix..

[K1.065] The Development of the High-Resolution Transmission Electron Microscope (HRTEM)�@Combined with AFM for Simultaneous Observation of Structure and Force of the Nanocontact

A high-resolution transmission electron microscope combined with an atomic force microscope (HRTEM-AFM) has been developed. It enables us to observe mechanical force and atomic structure of nanowires formed at the nanocontact simultaneously. And the self-sensing piezoresistive cantilever is used as an AFM probe in the�@HRTEM-AFM. It has high spatial resolution of 0.2nm and high force sensitivity of sub-nN. The HRTEM has also ability to work on ultra high vacuum(UHV) which is necessary to keep the nanocontact clean. The present system could never be developed without total redesigning of the goniometer stage of UHV-TEM which operates at 10^-8 Pa.

[K1.066] Spectroscopic Techniques

This abstract not available.

[K1.067] Antisymmetric Raman tensor: theory and experimental measurements

We report here a theory that corrects the earlier theoretical reports on magnitude, origin, and frequency dependence of the antisymmetric Raman tensor. Our theory is verified with the experimental results obtained with double-resonance infrared-visible sum-frequency generation spectroscopy from the isotropic chiral solution of 1,1^\prime-bi-2-naphthol where the strength of the vibrational peaks is directly proportional to the antisymmetric Raman tensor.

[K1.068] Artificially Structured Materials

This abstract not available.

[K1.069] Nanometric patterning of PLD-grown ferroelectric oxides

Under certain conditions the initial growth stages of thin films do not produce a continuous films but islands that are organised in regular patterns. Although self-organised structures do have a regular order, they are not arranged regularly enough to be used in integrated micro- or nanoelectronics. However, since island growth can be induced by defects, a regular pattern of defects with spacings in the tens of nanometer range induces the growth of islands with the periodicity and geometry of the defect lattice. Functional ferroelectric oxide nanostructures were deposited by pulsed laser deposition (PLD), on top of a substrate prepared in such a way that a network of defects exist on its surface. The self-organised ferroelectric nanostructures were characterized using different techniques such as X-ray diffraction, electron microscopy, and scanning probe microscopy. Preliminary investigations of the ferroelectric properties of these nanostructures using piezoresponse force microscopy show that they preserve their functionality i.e. they posses a spontaneous polarization that can be switched by an external electric field

[K1.070] two-to-three dimensional transition in the InAs/GaAs(001) heteroepitaxial growth

Atomic Force Microscopy (AFM) and Scanning Tunneling Microscopy have been used to study subsequent stages of the heteroepitaxy of InAs on GaAs(001), from the initial formation of the pseudomorphic strained two-dimensional wetting layer up to the self-assembling of three-dimensional quantum dots (QDs). We provide evidence of structural features that play a crucial role in the two-to-three-dimensional transition and discuss their contribution to the final morphology of the self-assembled nanoparticles. The features to be considered, close to the 2D-3D transition, are: large and small 2D-islands one-monolayer high, small quasi-3D islands of height £2 nm, 3D QD of height 3-4 nm. Although reported several times, definite conclusion on the role of these features in QD nucleation is not yet achieved. 2D-features contribute only as step edge by supplying nucleation sites. Statistical data show clearly separated distributions for the quasi-3D QD and the 3D-QD and the gap between them does not fill in at any InAs deposition. These observations are consistent with the existence of two equilibrium sizes for the 3D islands, one of which (quasi-3D QD) is stable only for a limited range of InAs thickness. No clear evidence exists that the nucleation of quasi-3D QD is the first step of the self-assembling QD. A model is suggested for the strained phase at the critical thickness consisting of an intermixed In_xGa_1-xAs and InAs ``floating'' on top. Such ``floating'' phase participate to the large mass-transport along the surface during the two-to-three-dimensional transition that accounts for the total volume of dots.

[K1.071] Silicon patterning using ion blistering and e-beam lithography

We explore the limits of silicon patterning using ion blistering in conjunction with e-beam lithography. In a first approach, we implanted 3.5E16 H/cm**2 at 5 keV through variable width (0.1–10 micron) e-beam written PMMA masks. The resist was then removed and the samples were rapid-thermal-annealed (RTA) up to 650°C. In the wider trenches, round blisters with 800-900 nm diameter and 15 nm height and a few exfoliations are observed, which are similar to those observed on an unmasked surface. In submicron trenches (500–1000 nm), there is a transition in morphology created by the proximity to the border; the blisters are smaller and they are densely aligned along the trench direction ("pearl-string" pattern). No effect is observed in the lowest dimension trenches. The results are discussed in terms of stress/strain fields, defect configuration, and mask shadowing and charging effects. Ultimate pattern resolution will be limited by lateral straggling of the ions in and by the mechanics of lateral crack propagation.

[K1.072] Stark effect of hydrogenic impurities in a quantum box

We extend the model of a cubic quantum box proposed by Ribeiro and Latge to carry out a variational calculation of the bindingenergy of impurities in such a structure as function of anelectric field.The binding energy of the impurities increases with the electric field. In addition, the electric field splits the energy of impurities on the faces of the box which are equivalent in the absence of the electric field.

[K1.073] Transport Through Disordered Silicon Oxide Quantum Structures

Silicon and oxygen semiconductor-atom structures (SAS) are built by alternating layers, creating structures similar to the traditional superlattices. These SAS have good electro-and photo-luminescence and may therefore form the basis of all-Si optoelectronic devices. Their I-V curves are only qualitatively understood. TEM images show that SAS have stacking faults and dislocations in substantial quantities as to affect response time and transmission. Experimental work has been done to understand why silicon may grow epitaxially after the oxygen barrier. This is never the case in Si/SiO2. If, during growth, the oxygen valve is left open, a large number of defects is generated in bulk silicon. By controlling the oxygen rate, it is possible to produce silicon on both sides of the oxygen interface with defect densities below 109/cm2. Nevertheless, the oxygen layer itself is typically broken up in islands. What is clear is that it is technically possible to produce SAS with negligible bulk defects but that still present strain and disorder at the oxygen interface. We have studied the effect of interface disorder and strain on SAS current-voltage curves. Their quality factor is extremely sensitive to the presence of imperfections. We will show the dependence of the spectrum on disorder. Work supported by Research Corporation.

[K1.074] Phasor-like interpretation of tight-binding electronic motion in the single-band approximation

We present a specific interpretation of a previously derived general method [1] for studying electronic wave-packet evolution within the single-band approximation. As a result of analytical properties of Bessel functions, it is shown that in a homogeneous time-dependent electric field an electron´s motion in a one-dimensional nearest-neighbor tight-binding band can be described in terms of a phasor (polygonal) construction in the complex plane. Based upon our polygonal construction, an analogy is established between motion in a constant or in a linearly time-dependent electric field and the optical phenomena of Fraunhofer or Fresnel diffraction, respectively. The first type of diffraction, associated to the figure of a “circumference”, leads to the usual Bloch oscillation effect, while -associated to the mathematical properties of the Cornu spiral- the second one leads to “asymptotic localization” of the electron. Furthermore, for periodically driven fields dynamical localization can also be elucidated within our complex-plane representation. Finally, a phasor-like generalized formula for inhomogeneous applied electric fields, general band structure and dimensionality of electronic motion is given in terms of a multidimensional integral of appropriate discrete Fourier transforms of the corresponding applied potential. [1] D. Sanjinés and J.-P. Gallinar, J. Phys. Condens. Matter 11, 3729 (1999).

[K1.075] DIELECTRIC AND PYROELECTRIC PROPERTIES OF FERROMAGNETIC - PIEZOELECTRIC LAYERED STRUCTURES

Results of our investigations on dielectric and pyroelectric properties of multilayer ferromagnetic-piezoelectric are presented here. Lead zircinate-titanate PbZr0.52Ti0.48O3 (PZT) was used for the piezoelectric phase in all the structures. The following materials were used for the ferromagnetic component: nickel-zinc ferrites Ni1.9Zn0.1Fe2O4 (NFO1) and Ni1.8Zn0.2Fe2O4 (NFO2), cobalt ferrite (CFO), lithium ferrite (LFO), lanthanum strontium manganite La0.7Sr0.3MnO3 (LSMO), and lanthanum-calcium manganite La0.7Ca0.3MnO3 (LCMO). The pyroelectric effect was studied by measuring the current J flowing through a closed loop containing the sample and an electrometer as the sample temperature T was slowly varied at the rate 0.1 K/s. Polarized PZT layers generate a pyroelectric current as the temperature changes. The main indicator of pyroelectric nature of the current is the sign reversal when the thermal cycle is switched from heating to cooling. Almost all of the multilayer structures showed a pyroelectric current, but the pyroelectric coefficient varied in a wide range. (i) For NFO1-PZT system the coefficient was in the range 0.01 - 10 nC/(cm2×K), depending on the temperature. (ii) CFO-PZT and LFO-PZT structures showed a large thermal current and a weak pyroelectric effect. (ii) Thermal currents, however, were absent in LCMO-PZT within the temperature range from the room temperature to 400 K. (iv) In LSMO-PZT, the thermal current exceeded the pyroelectric current. A model is proposed for an understanding of these results.

- work at Oakland University supported by a grant from the National Science Foundation (DMR-0302254)

[K1.076] Current Driven Electromagnetic Wave Amplification by a Double-Quantum-Wire Superlattice

We analyze the interaction of a THz EM wave with a current-carrying lateral double-quantum-wire superlattice. The superlattice (in the x-y plane) is taken to consist of two identical parallel quantum-wire sublattices shifted with respect to each other in the transverse y-direction. The two sublattices are taken to carry equal steady currents in opposite directions, and are coupled by Coulomb forces. We recently showed [G.R. Aizin, et al.,Phys.Rev.B,65,241311 (2002)] that quasi-1D plasmons of such double-quantum-wire SL systems become unstable when the electron drift velocity falls between the phase velocities of the acoustic and optical plasmon modes of the Coulomb-coupled wire subsystems. Here, we describe the electrodynamic interaction of an external linearly polarized THz EM wave with the SL electron system. Coupling of the EM wave with the plasmon excitations is provided by introducing a metal grating with the grating stripes oriented perpendicular to the quantum wires. We have determined the transmission, absorption and reflection coefficients for an EM wave propagating through the grating-superlattice system at normal incidence, demonstrating that amplification of the THz electromagnetic radiation occurs in the region of plasma instability. Our numerical calculations show that this effect occurs at experimentally achievable drift velocities in GaAs-based structures.

[K1.077] Optical Phonon Coupling Effects in Drifted Double-Quantum-Wire Plasmon Instabilities

We have examined the coupled plasmon-phonon modes of a double-quantum-wire system embedded in a semi-infinite medium, subject to instability due to equal and opposite steady currents passing through the wires. In particular, we analyze the effects of the coupling of optical phonons to the double-quantum-wire plasmons on the drift velocity limits of current-driven instability in terms of the acoustic and optical plasmon phase velocities as they are modified by the phonons. This examination of unstable modes is carried out as a function of wavenumber, distance of the first quantum wire from the bounding surface and on the separation of the quantum wires.

[K1.078] Resonance-forerunners in superlattices

An exact analytic solution of the time-dependent Schrödinger equation is used to explore the propagation phenomena of transmitted quantum waves in superlattices. Our approach deals with an initial condition consisting on a quantum shutter situated to the left edge of the structure, which separates the incident plane wave from the potential. The sudden opening of the shutter at t=0 enables the incident wave to interact with the superlattice giving rise to transmitted quantum waves to the right of the system. For incidence energies E below the first resonance, we find a series of propagating pulses (forerunners) at the transmission side of the structure traveling faster than the main wavefront. In particular, it is shown that each forerunner propagates at the speed v(\cal E_n)=[2m\cal E_n/\hbar^2]^1/2 associated to the n-th resonance \cal E_n, establishing a link between the sequence of forerunners and the resonance spectrum of the system.

[K1.079] An approach to transport measurement of gold nanoparticles chain

Electrical characterization of individual molecules and nanoparticles has received considerable attention recently in the scientific and engineering communities. Electron transport through these nanostructures and nanoparticles is strongly affected by electron¡Velectron repulsion and energy level quantization, and transport experiments can provide detailed insight into the electron dynamics. An approach to transport measurement of gold nanoparticles chain has been presented. The gold nanoparticles are trapped into a small trench of PMMA defined by electron beam lithography using AC-electrophoresis so that the gold nanoparticles chain is very easy to be measured. The interesting evaluation behaviors of I-V characterization of the nanoparticles chain have been measured.

[K1.080] Carrier Injection and Transport in Arrays of Monolayer-protected Gold Nanocrystals

We report on fabrication and electrical characterization of self-assembled 1.7 nm diameter gold nanocrystal (NC) array devices. Electrochemical data for surface-immobilized NCs reveal quantized charging effects indicating that the NCs are discrete entities with characteristic charging energies governed by their small capacitances (\sim 0.3 aF). Self-assembled NC array devices show activated transport from 70-200 K (E_a\sim 110 meV), consistent with sub-aF individual NC capacitances. At low temperatures, current suppression is observed below a threshold voltage (V_T), again indicating that charging of the individual NCs dominates the transport. Scaling behavior of the current above V_T indicates that the dimensionality of the transport network is >2D, consistent with the NC array preparation method. Thus, the unique characteristics of individual NCs are not compromised during device fabrication, thereby offering the possibility to exploit these ``artificial atoms'' in solid-state device formats.

[K1.081] Spin-dependent conductance of two-dimensional mesoscopic structures in the presence of spin-orbit interaction

The conductance of semiconductor mesoscopic structures becomes spin-dependent in the presence of spin-orbit interaction. The spin-filtering effect in these structures occurs due to the spin-polarized multi-beam reflection from potential barrier walls. In the presence of spin-orbit interaction, a single non-polarized beam scattered from a potential barrier becomes three beams with different spin polarizations. The trajectories of electron beams and conductance are numerically calculated in a weak magnetic field using several different geometries. One example is a triangular billiard with two symmetric or asymmetric leads. The weak magnetic field is utilized to tune the propagation and trajectories of electron beams. The initial electron beam becomes a series of spin-polarized beams due to multiple spin-dependent reflections and, therefore, the conductance becomes strongly spin-dependent. Parameters of InAs and InSb heterostructures are used for the numerical calculations. Mesoscopic ballistic structures in the presence of spin-orbit interaction represent a novel class of spintronic devices in which the conductance is strongly spin-dependent.

[K1.082] Stark effect of carriers in spherical quantum dots

We calculate the effects of electric fields of arbitrary intensity in the groundstate level of spherical quantum dots. We model the confinement by infinite hard-wall potential. We used a variational procedure and compared our results to previous perturbative calcultations and to Stark effect behaviour in similar cubic quantum dots.

[K1.083] Tuning quantum interference in a three-well semiconductor system

Phase interference of three-well quantum states was investigated by solving four coupled equations describing the quantum bound states interacting with photon beams. The general expression of optical absorption of a three-well quantum system delineates its dependence on the photon energy and the decay rate of each state resulting from tunneling to the continuum. We explicitly demonstrated this result by specializing to a three-well system composed of a deep 7.3-nm-thick GaAs well coupled to a two- shallow 6.8-nm-thick Al_0.165Ga_0.835As -well system by a 3.5-nm-thick Al_0.33Ga_0.67As barrier, where two shallow wells are separated by a Al_0.33Ga_0.67As barrier. Compared to a two-well system, the three-well case possesses a much richer structure in quantum interference. An additional zero absorption valley was found in the three-well system due to destructive interference. In this case, we can obtain a much higher absorption peak together with longer life time than in the two-well case, which can serve as the basis for laser operated without population inversion.

[K1.084] Optical properties of a dielectric-metallic superlattice: the complex photonic bands

We have studied theoretically the photonic bands in a periodic dielectric-metallic superlattice. In the calculations the absorption in the metallic layers was taken into account using the well-known Drude model for the dielectric function. Due to the absorption in the metallic films, the Bloch vector becomes complex for all frequencies, and the waves are evanescent. The photonic band structure is strongly modified as compared to the band structure of the nonabsorbent superlattice, mainly in the region of low frequencies where bands of odd behavior appear. We also have studied the absorption, reflection and transmission spectra of light incident on a finite superlattice. The spectra show that the complex bands, with complex wave vector and real frequency, are an appropriate resource to describe the optical properties of periodic absorbent structures.

[K1.085] Coherent control of Bloch oscillations by means of optical pulse shaping

We excite excitonic wavepackets in biased semiconductor superlattices with spectrally-shaped ultrashort optical pulses. We tailor the shape and phase of the pulse spectrum in order to control the coherent dynamics of the excitonic wavepackets formed from a superposition of three excitonic states. Via careful shaping, we are able to excite either wavepackets that exhibit standard Bloch oscillations (BOs) or breathing mode (BM) motion. These two type of motion are characterized by the presence (BOs) or absence (BM) of an internal intraband polarization caused by the electron-hole separation within the excitonic wavepacket. The wavepacket evolution is monitored using spectrally-resolved four wave mixing. This ability to control the BOs provides a way to control the emitted THz radiation.

[K1.086] Characteristics of silicon nanowire single electron transistor pairs as readout devices in impurity spin qubit structures

Quantum computer schemes based on electron and nuclear spins of single dopant atoms in silicon are attractive candidates for large scale quantum information processing. Silicon based Single Electron Transistors (SET) promise to enable single spin readout through spin dependent charge measurements. We present results from our development of silicon SET structures that are designed as pairs for integration with two P atoms. Devices with undoped, 10 nm wide silicon wires are formed by electron beam lithography without size reduction by stress limited oxidation. Device characterization at 4.2 K shows charging energies of 5-10 meV and total capacitances of ~10 aF. We will discuss Si-SET fabrication yields, critical performance criteria (offset charges, random telegraph signals), and the coupling of Si-SETs to radio frequency tank circuits in light of the very stringent requirements posed by qubit devices.

[K1.087] Rydberg States on the Surface of Liquid Helium as a Quantum Computer

Electrons localized on the surface of liquid helium reside in a dielectric image potential, which quantizes motion normal to the surface. These levels have been proposed as the basis of a quantum computer (QC). The decoherence (T_1) times of a QC composed of electrons on liquid helium have been estimated to be of order 100 microseconds due to the stability of the system at very low temperatures (~10 mK) which should allow 10000 operations. Microwave spectroscopic techniques have been employed to measure the decoherence time of the excited state for a large number of electrons floating on ^4He. Power broadening of the absorption line provides a measure of the Rabi frequency. We are presently conducting similar experiments with a ^3He substrate. Measurements on a ^3He substrate are of interest because the ripplon contribution to T_1 should be suppressed due to the large viscosity of he liquid. Discussion of these experiments and current results are given.

[K1.088] Small metallic contact/isolating barrier/semiconductor structure as a qubit

We consider an energy spectrum and wave functions for single-electron quantum states formed by a positive potential of a small metallic contact (SMC) placed on an isolating barrier over a semiconductor surface. The considered states are localized in the semiconductor around the SMC and near the barrier/semiconductor interface.Their spectrum depends on the SMC potential, shape and sizes (in comparison to the barrier thickness). We show that two low-lying levels can be formed, which are separated by a wide gap from higher-lying single-electron levels and also from two-electron states. Alongside the above-mentioned simplest structure, we consider a more complicated two-barrier structure with a quantum well between a main outer barrier and an additional thinner inner barrier. The studied two-level states controlled by the SMC potential can serve as qubits interacting with each other by dipolar forces. Such a qubit structure is analogous to that suggested for electrons floating on liquid helium [1]. We have considered Si dioxide/Si and AlGaAs/GaAs variants. [1] M.I. Dykman, P.M.Platzman,and P.Seddighard, Phys.Rev.B67, 155402 (2003).

[K1.089] Temperature-tuning of transmission spectra of 2D photonic crystals made of a semiconductor with free electrons.

We have studied theoretically the electromagnetic transmittance in finite samples of InSb-based 2D photonic crystals. Due to the temperature dependence of the intrinsic carrier concentration in this semiconductor, the triangular and square arrays of parallel InSb cylinders in air - or vice versa, parallel hole cylinders in InSb - give rise to tunable transmission spectra. As the temperature increases from 200 to 300 K the mid-gap frequencies move up in frequency while the widths of the gaps diminish in agreement with the bulk band structure.[1] The wave transmittance was calculated taking into account the dispersion due to phonons, as well as free charge carriers; absorptive mechanisms due to phonons, holes and electrons were also considered. We also studied tuning of localized modes due to linear defects. The corresponding transmittance peaks reveal considerable dependence on the temperature. This work was financially supported by CONACyT, Mexico, Grant No. 41195-F. [1] P. Halevi and F. Ramos-Mendieta, Phys. Rev. Lett. 85, 1875 (2000)

[K1.090] Oxidation of glancing angle deposited silicon rugate filters

Increased visible transmittance and control of ageing behavior of evaporated porous silicon rugate filters is critical to optical applications. We report experimental results of optical properties of rugate filters evaporated in vacuum and subsequently oxidized. The filters were fabricated with the glancing angle deposition technique, employing oblique vapor incidence and substrate rotation. With constant rapid substrate rotation, the vapor incidence angle was varied sinusoidally between 51 and 81 degrees from the substrate normal. The resulting morphology was characterized by scanning electron microscopy and optical transmittance spectra were measured periodically during thermal and ozone oxidation. Oxidation shifted the filter stop-band to shorter wavelengths, and increased visible transmittance. While some films delaminated during oxidation, in general is appears feasible to convert porous thin films of silicon into silica to change optical response of glancing angle deposited thin film filters.

[K1.091] Modulated Laser Action from Dye Containing Holographic Polymer Dispersed Liquid Crystals

Holographic polymerization of liquid crystal containing photopolymerizable resins enables one-step, rapid formation of multi-phase structures that exhibit partial photonic band gaps. Holographic polymer dispersed liquid crystals (H-PDLCs) provide a versatile platform for diffractive optical elements because the structures are not limited by multi-phase equilibrium but are controlled by the interference of multiple lasers at discrete angles. By incorporating optically active components (coumarin, pyrromethene, quantum dots) into acrylate polymer and nematic liquid crystal H-PDLCs we create optically pumped distributed feedback lasers. The lattice structure of the H-PDLC determines the wavelength, number and propagation direction of laser action from the embedded chromophores. Unlike one-dimensional Bragg stacks made from H-PDLCs where just one propagation direction exists, higher dimensional structures generate multiple laser beams creating electric field modulated laser arrays.

[K1.092] Exciton transfer in close-packed arrays of quantum dots

Colloidal semiconductor quantum dots (QD), such as close-packed CdSe and InP offer a promising route to new kind of artificial solids which provide media for potential novel optoelectronic applications. Optical properties of densely packed QD have attracted much attention recently [1,2]. The long-range energy transfer was investigated in pure (mono “atomic” QD arrays) and mixed (binary QD arrays) close-packed CdSe solids. It was pointed out that the data for luminescence may be fit by the Förster’s decay law. Meanwhile, it is well-known that the Förster’s law has been established for diluted systems. Thereupon, an intriguing question arises about the application of Förster approach to the dense media. We present here a theory for exciton transfer in pure and mixed close-packed QD arrays. Our approach is based on the master equation for the calculation of the density of excitons in two-dimensional lattices. The transfer rate between two dots has been calculated from a microscopic theory by using a spherical model of QD. The random parameters have been used to describe the dot-size variations. For mixed QD’s a random binary model has been used. We have found an exact solution of the master equation for a perfect lattice, which gives a non-Förster’s decay law. The master equation has been investigated numerically on 2D-disordered lattices. It was established that in the formation of the decaying law, the random walk of excitons on a disordered lattice plays a similar role as the exciton’s random-abandon of molecules in solutions. It has been demonstrated that with an increase of the disorder the time-dependence of exciton density is more and more similar to the Förster’s decaying function. We discuss the correspondence between our numerical results and experimental data [1]. 1. C. R. Kagan, C. B. Murray, and M. G. Bawendi, Phys. Rev. Lett. 76, 1517 (1996). 2. S. A.Crooker, J. A.Hollingsworth, S. Tretiak, and V. I. Klimov, Phys. Rev. Lett. 89, 186802 (1996).

*Supported by the Indiana 21st Century Research and Technology Fund

[K1.093] Hydrogen and Physisorbed Materials

This abstract not available.

[K1.094] The optical response of thin Pd films in a hydrogen atmosphere

The effect of hydrogen on the reflectivity of Pd films is studied. The optical response from optically thin Pd films deposited on Al_2O_3 substrates was measured as a function of hydrogen pressure. Samples were grown via magnetron sputtering and the interface roughness characterized with x-ray reflectivity. Optical reflectivity measurements were carried out with the sample mounted in a miniature vacuum chamber allowing controlled hydrogen loading. For 10.0 nm Pd films the reflectivity decreases by 16% when exposed to 140 Torr of hydrogen. The effect is fully reversed when vacuum is restored. In contrast no change in reflectivity is observed with N_2 gas. The reflectivity change is attributed to a change in the films’ index of refraction known to occur upon hydrogen loading. This is studied as a function of Pd thickness and the hydrogen diffusion constant in Pd is deduced from the measurements.

[K1.095] Coaxial impact collision ion scattering spectroscopy study of the adsorption of ethylene on the Si(001)(2x1) surface

The adsorption of ethylene (C2H4) on Si(001)(2x1) surface has been focused on a simple model system - small and unsaturated hydrocarbon molecules on Si(001)(2x1). Despite a variety of experimental and theoretical studies, the adsorption sites (so called the di-¥ò structure and tetra-¥ò structure) are still debated. Moreover, there is other argument whether the Si dimers are intact or cleaved after ethylene adsorption on Si(001)(2x1). In order to elucidate this controversial issues clearly, ethylene has been non-dissociatively chemisorbed on the Si(001)(2x1) at room temperature in the exposure range of 100-200L, and ethylene on Si(001)(2x1) surface was investigated by coaxial impact collision ion scattering spectroscopy (CAICISS). To confident out results definitely, the computer simulations with a two-dimension trajectory count method were performed and compared with experimental results.

[K1.096] Initial adsorption of diethylsilane on Si (100) studied by XPS and TPD

Diethylsilane dosed onto Si (100) surfaces at 100K were chosen to investigate the epitaxial film growth of Si on Si substrate at low temperature under non-thermal processes. However, it is not possible to understand these processes without studying the initial adsorbed species from gas phase of DES on Si surfaces at 100 K before non-thermal treatment. X-ray Photoelectron Spectroscopy and Temperature Programmed Desorption techniques were used to analyze the chemical species of adsorbed components and desorbed ones when the sample was heated from 100 K to 1130 K. Experimental results will be reported and discussed.

[K1.097] Electron induced decomposition of trimethylamine on Si(100) studied by TPD and HREELS

The decomposition of trimethylamine on Si(100) by electron irradiation at 100 K was investigated using temperature programmed desorption (TPD) and high resolution electron energy loss spectroscopy (HREELS). TPD data shows the cleavage of methyl groups from the parent molecule following electron irradiation of the TMA/Si(100) surface. The appearance of mass 42 in the TPD spectrum after electron irradiation suggests the production of reaction intermediates similar to those observed in gas-phase decomposition of TMA at high temperature. Electron-induced cleavage of C-H bonds is demonstrated by the appearance of a Si-H stretch peak at 2020 cm-1 in the HREELS spectrum of electron-irradiated TMA/Si(100) surface.

[K1.098] Adsorption Studies of Triethylsilane on the Si(100) Surface at 100K

The adsorption of triethylsilane at 100K on the Si(100) surface has been studied using temperature programmed desorption (TPD) and time-of-flight electron stimulated desorption (TOFESD). The effect of electron and photon irradiation on the adsorbed layer will be discussed. Evidence for a beta hydride elimination process accompanying ethyl group desorption will be presented. Results of the effect of electron and photon irradiation of the adsorbed layer on TPD and TOFESD spectra will be presented and discussed.

[K1.099] Ternary mixtures with photosensitive chemical reactions: The effect of hydrodynamic interactions.

We study the structural evolution of an A/B/C ternary mixture in which the A and B components can undergo reversible chemical reaction and form the C component. We assume that reactions are photosensitive: they can be activated by the light of appropriate wavelength. We formulate two-order parameters model and adopt a lattice Boltzmann algorithm to simulate evolution of the above mixtures. We study two different cases.

Case 1: C component acts like a surfactant and is localized mostly on the interface between the A and B components; the presence of C leads to the lower interfacial tension between the A and B fluids. We analyzed the growth of the A(B) domain as well as saturation of the A/B interface for different reaction rates and we compare these results for the fluid in the diffusive and viscous regimes.

Case 2: Ternary fluid is “symmetric”: the cost of A/C (and B/C) interfaces is about the same as the cost of A/B interface. Therefore, all three components are phase separating, i.e. C component also forms domains within the mixture. We show that by switching on and off the reactions at the appropriate stages of mixture evolution we can precisely control morphology and sizes of all domains within the system.

[K1.100] Surface, Interface, and Thin Films

This abstract not available.

[K1.101] Surface and thin film study of initial palladium silicide formation on 6H-SiC

SiC is a robust wide band gap semiconductor suitable for fabricating gas sensors. The simplest of these are Pd Schottky diodes whose electrical characteristics change as gases are absorbed. Device characterization studies have shown long-term degradation due to the formation of metal silicides. In present studies, thin Pd films are deposited and thermally annealed on 6H-SiC under ultra high vacuum conditions and characterized using an in-situ Auger electron spectroscopy. Ex-situ atomic force microscopy was used to characterize the surface before and after Pd deposition and after thermal annealing. These studies show atomically stepped surfaces produced by high-temperature hydrogen etching 6H-SiC, before Pd deposition, suppress silicide formation.

[K1.102] On the critical radius of spiral-shaped islands in YBa_2Cu_3O_7-\delta thin films morphology

Spiral-shaped island morphology of YBa_2Cu_3O_7-\delta films deposited on (001) SrTiO_3 by DC sputtering, display wide terraces towards the core of the spiral, while subsequent terraces are much narrower. A polar representation of the obtained spirals by atom force microscopy (AFM) measurements shows two growth regimes: the first one for large angles with a critical radius corresponding to the Burton-Cabrera-Frank theory (BCF), the second one, for small polar angles with steeper slope. The critical radius corresponding to this second growth mode is much larger than the nucleation radius of the islands observed on sub-monolayer films. This critical radius has not been discussed sufficiently in the literature. In order to study the behaviour of this critical radius, experimental values have been obtained from AFM images of spirals for films with different thicknesses. We discuss the experimental results in the framework of the thermodynamically conditions for the occurrence of hollow cores caused by stress screw dislocations.

[K1.103] Studies of Surface Morphology Evolution on Si during Ar+ Ion Bombardment

The evolution of Si surface morphology during Ar+ ion bombardment has been studied using atomic force microscopy (AFM) and synchrotron-based real-time grazing incidence small-angle x-ray scattering (GISAXS). The dependence of surface morphology on ion energy (300 - 1500 eV), substrate orientation, crystallinity (single-crystal vs. amorphous) and temperature has been systematically investigated. We find that for a wide range of process variables, ion bombardment causes the formation of structures on the Si surface with two distinct lateral length scales. These surface patterns show different behaviors in their evolution kinetics. The AFM analysis show that the shorter length scale pattern (``dots'' for normal incidence bombardment), that have a lateral wavelength range of 20 ¡V 50 nm, coarsen significantly during growth. In contrast, the longer length scale corrugations (\sim130 nm) appear to remain relatively constant as a function of time and ion energy. The AFM analysis of 60a off-axis sputtered samples show the formation of two ripple structures that are oriented perpendicular to each other and with different periodicities. The length scales or periodicities of the ripples are similar to those of the two roughness scales in the normal incidence samples, which suggest that similar mechanisms are operating. These observations will be discussed within the context of existing theory.

[K1.104] Diffusion barrier properties of ALD deposited TaN in Cu/TaN/SiO2/Si stack structure

The diffusion barrier properties of TaN layer grown by atomic layer deposition (ALD) has been investigated for the Cu/TaN(10 and 5 nm)/SiO_2/Si structure. The deposition of the TaN thin films has been performed using pentakis (ethylmethlyamino) tantalum (PEMAT) and ammonia as precursors at a substrate temperature range of 250^oC. The growth rate of TaN film was about 0.75Åper cycle. The thickness of films was linear with the number of cycles, which is a typical feature of ALD process. The N : Ta ratio for TaN film was 44 : 37 in composition and the film contained approximately 8-10 at.% carbon and 11 at.% oxygen impurity, as determined by Rutherford backscattering spectroscopy and auger electron spectroscopy. The stabilities of both 10 and 5 nm thick TaN films were tested through thermal annealing for 30 minutes in N_2 ambient and characterized by the help of XRD, sheet resistance, etch pit analysis, and capacitance-voltage analysis, which proves the ALD grown 10 nm thick TaN film to maintain a role of diffusion barrier against Cu up to 600^oC. However, through the C-V measurement, a 5 nm thick TaN film maintains the diffusion barrier properties against Cu diffusion up to 400^oC.

[K1.105] Initial stages of Pt growth on Ge(001) surface studied by STM and DFT

In an effort to understand and properly model the Pt nanowires forming on Ge(001) surface, we have studied the adsorption of Pt atoms onto Ge(001) surface using STM and DFT. We have experimentally identified the stable and the meta-stable adsorption configurations of Pt atoms on the surface and we confirmed these by total energy calculations. Our calculations also showed that Pt atoms are capable of breaking the surface dimer bonds during adsorption. Our STM experiments indicate the ejection of Ge atoms onto the surface during the intermixing of Pt with Ge at room temperature. Besides we have observed the spontaneous generation of 2+1dimer vacancy defects on the surface during the intermixing process again at room temperature. High temperature molecular dynamics simulations show that Pt atoms adsorbed at different sites progress to different surface/subsurface positions. STM data taken on high temperature annealed (Pt deposited) substrates are indicative of subsurface Pt atoms.

[K1.106] Self organization of Pt atoms on Ge(001): Germanide and nanowire formation

We have studied the Pt growth on Ge(001) surface using STM, STS and RHEED. Our experiments show that, although Pt intermixes with Ge even at room temperature and tends to dive under the surface, annealing the Pt deposited Ge(001) substrate results in the creation of metallic nanowires. These wires are defect and kink free and they can have aspect ratios up to 1000. We have also identified the alteration of the (2x1) and (4x2) reconstructed Ge(001) terraces and studied a previously unreported surface confined phase of platinum-germanide. Depending on the annealing temperature and the deposited Pt amount, Ge(001) surface becomes flatter with increased step-step distances, prior to nanowire formation. Besides the nanowires we have observed several anomalous formations on the surface such as the formation of stepped (Mayan) pyramids.

[K1.107] First-Principles Studies of Titanium Epitaxy on a Diamond (100) Surface at Submonolayer Coverages*

An atomic scale understanding of behavior of metal atoms on diamond surfaces is important in view of the huge applications of diamond-related devices. We use first-principles total energy calculations within density functional theory to study the energetic and kinetic properties of the initial stages of growth of Ti on a diamond (100)-2¡Á1 surface. For a Ti adatom, all the adsorption sites and the diffusion barriers between these sites are identified. The pedestal site at the center of two consecutive C dimers is the most stable adsorption site for a Ti adatom. As the coverage increases, the most stable adsorption sites change from pedestal to hollow sites. We predict the existence of two well-defined Ti nanowire structures at half monolayer coverage, and identify the kinetic pathways through which the metastable one converts into the stable configuration. *Supported by US DOE, US NSF, amp; NNSF of China.

[K1.108] Enhanced Vibrational Entropy contribution on Cu_3Au vicinal surfaces

We present a theoretical study of the local vibrational dynamics and thermodynamics of three vicinal surfaces of Cu_3Au which have similar terrace width. The local vibrational density of states are evaluated using a real space method with the force constants calculated from a many-body potential based on the embedded atom method. Our calculations show that the local vibrational properties of the three vicinal surfaces are sensitive to their local atomic environment. Surface Au atom are responsible for a large softening of the force field at the surface yielding a substantial shift toward low frequencies of the vibrational densities of states associated with Au surface atoms. As a consequence, the excess local free energy of the Au rich atoms are about 40 meV at 663K. We will also present other thermodynamical quantities on these three surfaces and rationalize the results in terms of coordination and chemical composition.

[K1.109] Nanostructures, Formation, and Characterization

This abstract not available.

[K1.110] Characterization of Pd Nanoparticles Produced by One and Two Phase Methods

We have compared the characteristics of Pd particles synthesized by two different techniques, a one-phase method and a two-phase method. Transmission electron microscopy determined that the particle sizes were 4 nm and 2 nm for the one and two-phase methods respectively. Electron diffraction from the particles confirmed that their structure was FCC with a lattice constant of ao=3.9 which is the same as the bulk value. The particles where also deposited at the air water interface in a Langmuir trough.where it was found that only the two phase samples wet the water surface indicasting that their thiol coverage is lower. The particles were also examined with EXAFS where we found that they contained an unusually large amount of Pd-S bonds. Simulation of the particles with a truncated icosahedron gave diameters that were consistently smaller than the TEM micrographs by a factor of two. Careful examination of the data indicated that much of Pd-S intensity was coming from Pd atoms that were not incorporated in the crystals. A re-examination of the EXAFS data indicated that the particles could also be modeled as cuboctahedrons. In this case, we could reproduce the diameter and the EXAFS intensity only if we assume that 50% of the Pd remains in the ionic form or complexed to S and not participating in the nanoparticles. Analysis of the LB sample indicated a much lower fraction of Pd-S bonds. Here, agreement between the EXAFS and TEM results could only be obtained by assuming an oblate particle shape. The major difference between the synthetic methods is the existence of a net magnetic moment of the particles, which persists at room temperature, and could only be observed in the two phase samples.

[K1.111] Synthesis and Characterization of Alkanethiolate Gold Nanoparticles

Two-phase (Brust1) method had been employed to synthesize thiol-functionalized gold nanoparticles, which could be spread at the air/water interface to produce a monolayer film. We characterized the film by using Transmission Electron Microscope (TEM) and X-ray reflectivity (XR) measurements. The XR data, which could be fitted with a four layer model, SiO2, thiol, Au/thiol, thiol, showed that (1) the thicknesses of the both thiol layers were 0.8 nm with the bulk dispersion number in x-ray index of refraction and (2) the thickness of the Au/thiol layer was 1.3 nm, while the diameter of Au particles was estimated to be 2.6 nm from TEM analysis, indicating that the gold cores of the particles had oblate shape. In addition, the volume fraction of the Au cores in the layer of Au/Thiol and the number of attached chains per gold core were estimated to be 2580, respectively. The size, shapes and thiol graft density of the nanoparticles in both solid and thin film states are being studied by EXAFS, which will be presented in the meeting.

References (1) Brust, M.; Walker, M.; Bethell, D.; Schiffrin, J.; Whyman, R. J. Chem. Soc., Chem. Commun., 1994, 801.

[K1.112] Brillouin Scattering Studies of Polymeric Nanostructures

For a range of applications, polymers are now being patterned into nanometer-sized features. In these applications, robust mechanical properties of the nanostructures are critical for performance and stability. Brillouin light scattering is presented as a non-destructive, non-contact tool to quantify the elastic constants in such nanostructures. We demonstrate this through a series of thin films and parallel ridges and spacings (gratings) with ridge widths from 180 nm down to 80 nm. For the set of films and structures presented here, the room temperature elastic moduli did not change with either decreasing film thickness or grating ridge width, implying that 1-D and 2-D confinement-induced changes of the mechanical properties are not significant down to feature sizes of 80 nm. Additionally, Brillouin spectra of submicron gratings reveal new modes that are not present in the spectra of thin films. The possible origin of these modes is discussed.

[K1.113] Search for positron trapping at quantum-dot like Cu nano particles on the surface of Fe using Positron Annihilation induced Auger Electron Spectroscopy (PAES)

This paper presents preliminary results and experimental details of a search using positron annihilation induced Auger electron spectroscopy for evidence of trapping of positrons at quantum-dot like particles of Cu at the surface of Fe. In PAES energetic electron emission results from Auger transitions initiated by annihilation of core electrons with positrons trapped in a image-potential well at the surface. The further localization of positrons at aggregates of Cu atoms at the Fe surface should be signaled by a sharp enhancement of the Cu PAES intensities relative to Fe. Preliminary studies of PAES intensities as a function of the amount of Cu deposited on a sputtered Fe surface provide evidence for such an enhancement.

[K1.114] Structures and Magic Numbers of Adatom Clusters on Metal fcc(001) Surfaces

With a genetic algorithm, the lowest-energy structures of adatom clusters on a series of metal fcc(001) surfaces are determined. The atomic interactions are modeled by the realistic model potentials including embedded-atom method potential, surface-embedded-atom method potential, and Rosato-Guillop¨¦-Legrand potential. The results show that the adatom clusters of sizes n=6,9,...,36 have the same structures on the different surfaces. Their special stability indicates that they are magic number clusters. For clusters of other sizes, the structures are generally different on the different surfaces. The change of the cluster structure with surfaces can be interpreted in terms of the relative interaction range and the compensation effect from the adatom-substrate interaction. When the interaction range becomes long and/or the compensation effect becomes strong, the shape of the lowest-energy structure tends to change from square to rectangle or even to one-dimensional chain.

[K1.115] Synthesis and characterizations of large quantity single crystal germanium nanowires

Single crystalline germanium nanowires have been synthesized with high yield and high purity using a vacuum thermal evaporation process mediated by vapor-liquid-sold crystal growth mechanism and gold as the catalyst. Germanium powder was evaporated at 1000 ¡ãC and deposited onto silica powder homogeneously mixed with gold nanoparticles (10 nm) at 400 ¡ãC using argon as carrier gas. SEM images showed the diameter of the germanium nanowires ranging from 40 to 60 nm. This narrow distribution may be related to the homogeneous diameter distribution of well-separated gold nanoparticles. Microstructure characterization and properties of germanium nanoparticles will be reported. The synthesis of these single crystalline semiconductor nanowires is expected to open up new possibilities for nanoelectronics and high figure-of-merit thermoelectrics applications.

[K1.116] Shape transition and dislocation nucleation in strained epitaxial islands

We study numerically the equilibrium shape and dislocation nucleation of strained epitaxial islands with a two-dimensional atomistic model, using interatomic potentials of Lennard-Jones type. Relaxation processes from coherent to incoherent states for different transition paths are studied using a systematic saddle point and transition path search based on the Nudged Elastic Band method. We obtain the phase diagram for island shapes, as a function of island size and lattice misfit with the substrate, as well the energy barrier for first order shape transitions. The minimum energy barrier and transition path for dislocation nucleation is also obtained for different island shapes. It is found that dislocations can nucleate spontaneously at the edges of the adsorbate-substrate interface above a critical size.

[K1.117] Electronic and Magnetic Properties of Thin Films and Nanostructures

This abstract not available.

[K1.118] Roughness dependence of the manganite thin films properties

A quantitative statistical study was done on digitized Atomic Force Microscope (AFM) images of La_2/3Ca_1/3MnO_3 thin films grown on (100) oriented SrTiO_3 substrates. The films were grown by a sputtering technique at high oxygen pressures and at substrate temperatures of 850^oC. From the AFM-images the roughness parameters: interface width, correlation length and roughness exponent using a specific designed algorithm have been determined. We addressed a systematic study to correlate roughness parameters with growth parameters such as thickness of the layer, substrate temperature, and magnetic properties such the Curie temperature determined by resistivity transition from paramagnetic to ferromagnetic phase. This work presents a detailed description of an algorithm and the procedure to the statistical analysis to extract the roughness parameters and the dependence with the thickness of the layer.

Acknowledgements This work was supported by Colciencias project No 1106 –05–11458 CT-046-2002

[K1.119] Superconductivity and Magnetism in Nb/Pd/Fe proximity multilayers.

The theory of the proximity effect in Superconductor/Ferromagnet (SC/FM) multilayers defines a parameter, I, proportional to the moment density and the exchange constant in the FM. However, using different FM materials to vary I makes it difficult to experimentally isolate the proximity effects from other changes. In order to change I, and avoid altering any other intrinsic properties, a spacer layer of Pd was grown between sputtered SC (Nb) and FM (Fe) layers. Pd becomes spin-polarised by proximity with the Fe, and will also become superconducting by proximity with the Nb. Nb/Pd systems show a SC coherence length in the Pd of ~4.5 nm, this is drastically reduced by the addition of an Fe layer. As Pd is made thicker, the Tc of the Nb rises as the interface polarisation drops – the relevant lengthscale is ~1.5 nm. As expected, the mean moment per atom decays over the same distance. A total thickness of Pd corresponding roughly to the sum of these two lengths is needed for the SC to experience no FM proximity effect, so that the Pd layer is large enough to contain full superconducting and ferromagnetic proximity regions.

[K1.120] Ferromagnetism in Co doped TiO2 films grown by RF magnetron sputtering

Structural and magnetic properties of epitaxial Co_xTi_1-xO_2 films with x about 10 %, grown by RF magnetron sputtering from composite oxide targets on matching LaAlO_3(001) substrates have been investigated. The films were sputtered at a deposition rate of \sim 0.14 Ås for a range of substrate temperatures from 300\r C to 750\r C, followed by UHV annealing for 1 hour at 400\r C. XRD experiments determine the best quality of highly oriented anatase (001) phase in films deposited at 500-750\r C. Magnetic hysteresis loops at 5K and 300K and thermoremanence measurements at 5- 365 K show ferromagnetism in all samples in the whole temperature range. Annealing leads to an increase of spontaneous moment an order of magnitude up to \sim 0.16 \mu _B/Co atom at 300 K. Both as-grown and annealed films were found to be highly resistive (>10^9 \quad Ømega /square at room temperature). AFM/MFM studies demonstrate changes both in surface morphology and distribution of spontaneous magnetization in the annealed films. Possible mechanisms of the ferromagnetic behavior of such dielectric transition metal-doped oxides will be discussed.

[K1.121] Magnetoresistance in exchange biased La_1/3Ca_2/3MnO_3/La_2/3Ca_1/3MnO_3 superlattices

We have measured the magnetoresistance of [La_1/3Ca_2/3MnO_3(FM) 20u.c./La_2/3Ca_1/3MnO_3(AF) nu.c.]_N superlattices varying systematically the thickness of the FM layer. FM-AF superlattices were grown by a high-pressure sputtering technique on (001) oriented SrTiO_3 substrates. The existence of an exchange bias effect at temperatures below the Neel temperature T_N of the AF layer was revealed by magnetoresistance data for n = 5 unit cell of FM layer, after field cooling. From this measurement, between 15 and 150 K (/simT_N) the observed exponential thermal decay of exchange biasing (H_ex) was fitted by H_ex=H_ex(o)exp(-T/T_0) function, with a T_o parameter value of 27 K approximately. This result is in close agreement with the temperature dependence of H_ex obtained from magnetization hysteresis loop, where the T_o value calculated is around 28 K for several multilayers with n ranging between 5 and 20 unit cell of the FM layer. This is an indicative that T_o parameter seems to be independent of the FM layer thickness.

[K1.122] Thin-Film Field Effect Transistors Based on La-doped SrTiO3 Heterostructures

Strontium titanate is one of the more interesting materials in nature. It has a relative dielectric constant 300 at room temperature and the value reaches a few thousands at low temperatures where the dielectric "constant" also becomes electric field dependent. The n-type doped SrTiO_3 is a wide bandgap semiconductor and superconductor with a T_c below 1 K. Due to its dielectric properties, electrical properties and lattice compatibility with high T_c superconductors, it has become a widely considered material for various applications. Field effect transistors were fabricated from epitaxial perovskite strontium titanate heterostrutures. Lanthanum-doped SrTiO_3 has been used as the semiconducting channel while insulating SrTiO_3 is used as a gate insulator. Both depletion and accumulation effects in the channel have been studied from 300 K to 4 K. Hall effect measurements indicate temperature independent n-type carrier density around 4-7 \times 10^19 cm^-3. At 300 K, typical mobilities are 2-3 cm^2V^-1s^-1 while low temperature mobilities are as high as 15 cm^2V^-1s^-1.

[K1.123] Resistance of Ta/PtMn/Ta thin films

Anomalous electrical resistance as a function of temperature has been observed for IrMn exchange-biased spin valves and Ti/IrMn/Ti trilayers (1). We have followed up with a study of Pt_50Mn_50 thin films with structure Ta/PtMn/Ta. In the past, resistance of PtMn alloys has been studied by Sarkissian (2) and Kastner (3) with Mn concentration ranging from 0.05-18%. These studies have found resistance minima, which vary depending on Mn concentration. We have found similar resistance curves for the PtMn structures, which depend on the thickness of the film and whether the film has been annealed. This work was supported by the Parsons Foundation, The Office of Naval Research, and the Harvey Mudd College Faculty Research Committee.

References:

(1) J. C. Eckert, N. P. Stern, D. S. Snowden, and P. D. Sparks, J. Appl. Phys. \textbf93, 6608

(2003)

(2) B. V. B. Sarkissian and R. H. Taylor, J. Phys. F \textbf4, L243 (1974)

(3) J. Kastner, E. F. Wassermann, K. Matho, and J. L. Tholence, J. Phys. F \textbf8, 103 (1974)

[K1.124] The zero-voltage conductance of short gold nanowires

Using the Landauer formula, we calculate the zero-voltage conductance of short gold wires with a self-consistent tight-binding method and with a combination of tight-binding and density functional theory (DFT). The gold wires considered are of single-atom diameter with a variable number N=1...,5 of atoms. With tight-binding, we find considerable conductance variations with one conductance quantum being the upper limit. Our combination of tight-binding (for the contacts) and Kohn-Sham DFT (for the wires) yields results that are qualitatively similar to the tight-binding calculations.

[K1.125] Semi-Classical Conduction of Charged and Neutral Particles in Finite Lattices

Because models of semi-classical dynamics and conduction in energy band systems are approximate, applying them in finite systems remains a challenging problem. In fact, although no formal justification of these kinds of theories exists, in general,beginning from an ordered ground state, it is possible to formally justify when the associated treatment of conductivity can apply either for charged or neutral particles, based on a microscopic theory, in a finite lattice. The essential physics of the associated argument is that when the Ground State is ordered, the lowest energy forms of reaction are initiated in "bulk regions" through perfectly elastic processes (similar to lattice recoil in the Mossbauer effect), in which the bulk region moves rigidly. From this starting point, it is possible to relate the semi-classical dynamical equations relating band state group velocity and band state time evolution to changes in the zero of momentum of the bulk. Implications of these results in areas related to transport of particles in finite, optical (and other) lattices are presented.

[K1.126] Positive charge creation, stabilization and recombination in solid Ar induced by low-energy electron bombardment

Hole creation, stabilization and recombination induced by low-energy (5-30 eV) electron impact in Ar films of 20-180 monolayers, is studied by measuring the desorption yield function of neutral species (metastables and UV photons). Positive charge accumulation occurs principally at the film/vacuum interface and the holes are long-lived and do not migrate from their original position once Ar over-layers are added to the film. Positively charged Ar films can be discharged by electron bombardment and recombination is especially strong when the incident electron energy corresponds to the threshold energy of Ar exciton states, since under this condition the exciton formation simultaneously produces a thermal-energy electron that is efficiently captured by Ar2+ centers.

[K1.127] Strain Effects in PCMO Films

The perovskite manganites based on Pr_1-xCa_xMnO3 have a rich phase diagram displaying highly sensitive characteristics dependent on doping. Stoichiometry near x=0.3 is of special interest because of the novel pressure, light, electric field, and magnetic field dependence of the transport. The effect of strain on the combined structural, transport and magnetic properties of films in this system have not been systematically explored. We have conducted studies of films of varying thickness for system on substrates with varying lattice parameter. The coupling between the substrate and the films is being explored. The changes in magnetic transport and structural properties will be discussed.

[K1.128] Instrumentation and Techniques

This abstract not available.

[K1.129] Deconvolution of SIMS Depth Profiles of As Multiple Delta Layers in Silicon

Two samples with the spacing of 50 nm and 5/10 nm between the arsenic doped silicon delta layers with the thickness of 1.0 nm and 0.5 nm, respectively, were used for the study. TOF-SIMS analysis with sputtering of 0.5 keV cesium ion has been performed to get the SIMS depth profile. We observed clearly separated five peaks in the 50 nm spacing sample, whereas we found poorly separated eight peaks in the 5/10 nm spacing sample. After deconvolution, however, we could obtain very thin and clearly separated sharp peaks in both samples. An improvement of the depth resolution of a factor of about 3 and a gain of the maximum peak intensity of a factor of about 4 were achieved. We could not find any significant loss or gain of peak intensity during the deconvolution procedure. The physical validity of the deconvolution method is supported by the non-destructive MEIS analysis, which can measure the thickness of the arsenic doped silicon delta layer in a silicon matrix quantitatively.

[K1.130] A microcantilever-based system for measuring surface stress changes induced in thin films by electrochemical reactions.

A microcantilever-based system capable of measuring surface stress changes in thin films which occur during electrochemical reactions is presented. In this system, the microcantilever provides both physical support and electrical contact to the thin film deposited on the metal coated face of the lever. The microcantilever serves as the working electrode (in a conventional three-electrode cell configuration) and as the mechanical transducer, for simultaneous, in situ and real-time measurements of the current and interfacial stress changes generated by the electrochemical transformations in the thin film. This micromechanical cantilever sensor has a surface stress sensitivity of 1x10-4 N/m and a dynamic range up to 50 N/m. This system has been characterized by performing measurements of interfacial stress changes on gold in the potential region associated with the electrical double layer and during ion doping/dedoping of dodecyl benzenesulfonate-doped polypyrrole (PPy(DBS)) films in an aqueous solution of Na(DBS).

[K1.131] Simulation of Complex Materials

This abstract not available.

[K1.132] Simulation of Nanoscale Spheres and Rods in Multicomponent Mixtures

Using large scale simulations of a microscopic model that accounts for hydrodynamic effect and excluded volume interactions, we systematically investigated the effect of solid nanoscale spheres and nanorods in phase-separating binary fluids. We found that nanospheres and nanorods that interact more attractively with one of the two components, lead to a reduction of growth rate of phase separation that is intensified as either the volume fraction of the nanoparticles or their diffusivity is increased. However, the generic characteristics of the kinetics is found to be identical to that of the binary mixture. Our results thus suggest that nanoparticles may not be considered as an effective compatibilizing agent of multicomponent blends. We will also present simulation results of multicomponent thin films containing nanoparticles.

[K1.133] Multiscale simulation of a liquid crystal biosensor

Recent experiments have shown that liquid crystals permit the detection of ligand-receptor binding by optical amplification. The optimal design of LC-based biosensors requires understanding the effects of the presence of biomolecules on the structure and dynamics of nematic liquid crystals. The underlying phenomena span multiple lenghtscales from a few angstroms to 100 nm, therefore we adopt a multiscale approach. At the atomic level, from Molecular Dynamics simulations, we determine the anchoring properties of liquid crystals at several biomimetic interfaces, e.g. a phospholipid bilayer. After establishing the proper anchoring, we can enforce it in molecular level Monte Carlo simulations and mesoscopic coarse-grained theories, which are used to investigate interactions of dilute colloidal particles and the structure of topological defects associated with them. Both descriptions agree down to separations comparable to the molecular length. The mesoscale modeling of the multi-particle sensor shows that the adsorbed biomolecules modify the relaxation dynamics in the device. These results are compared with the experimental observations of the nematic response in biosensors.

[K1.134] Quantum Fluids and Solids: Techniques and Applications

This abstract not available.

[K1.135] A novel approach for magnet leads

A frequent complication for cryogenic experiments results from the need to supply relatively large currents for magnets while minimizing the sizable heat which these leads can generate. Conventional approaches for magnet leads remove this heat by direct contact to the evaporated coolant gas. This requires relativly large surface areas for the leads themselves, often involving an isolated gas path. It is difficult for such leads, however,to minimize the heat load for both zero and high current states. We have developed an approach for heatsink magnet leads by utilizing the surface area afforded by cryostat baffles.Our discussion of this approach includes a computer model of the thermal process including the thermal resistance of all elements, joule heat of the leads, and contact to the helium gas and liquid. This baffle based approach is highly optimizable over a range of currents and can be extended to graded leads and superconducting sections. An overview of this approach including results of the model, an electrically isolated heatsink design, and associated measurements will be presented.

[K1.136] Transport properties of bulk hydrogen and hydrogen-helium slush at 4MHz using NMR measurements.

The most promising large-scale advance in rocket propulsion is the use of atomic propellants, stabilized in cryogenic environments. The high energy atomic propellants must be stored in a stabilizing medium to inhibit or delay their combination into molecules. We report studies of a suitable cryogenic matrix for atomic propellants consisting of a slush of small grains of solid hydrogen floating in liquid helium. Using NMR techniques, transport properties for bulk samples of solid hydrogen at 4 MHz have been studied as a function of ortho concentration and temperature. In an earlier experiment we determined the stability, transport and thermal properties of a solid hydrogen-liquid helium stabilizer. The nuclear spin-spin and spin-lattice relaxation times of the stabilizer were observed to be appreciably shorter than that expected for bulk samples. We anticipate that the solid-liquid surface relaxation could be the critical path for relaxation towards equilibrium. To address this question, data on relaxation processes for hydrogen –helium slush prepared by different methods will be compared.

[K1.137] Spin Relaxation in Hyperpolarized He-3 Fermi Liquids

In the past few years, attention has been drawn towards the hyperpolarized gases of Xenon-129 and Helium-3 isotopes. Medical research has explored the possibilities of using these isotopes for magnetic resonance imaging (MRI) of the lungs in both human and animal test subjects. Because the atoms of hyperpolarized gas are forced into a specific spin state, the MRI signal is enhanced. While the spin relaxation times of Helium-3 can be calculated in the high and low temperature limits, there exists no exact analytic solution for intermediate temperatures. The intention of this research was to numerically connect these limits with an accurate approximation. To do this, various analytic and numerical methods were used to reduce the spin relaxation time to a function of temperature, chemical potential, and particle number. Additional numerical methods were then used to calculate the chemical potential of Helium-3. The data show that a minimum occurs in the spin relaxation time at the order of the Fermi temperature, after which the classical limit is rapidly approached. These computational results seem to coincide with those expected.

[K1.138] Kirkwood Phase Transition for Boson and Fermion Hard-Sphere Systems

We construct the crystalline branch in quantum hard-sphere systems to study the freezing transition. We use the London ground-state energy formula as a function of number density \rho for a system of boson hard spheres of diameter c at zero temperature, corrected for the reduced mass of a pair of particles in a "sphere-of-influence" picture, and generalized to fermion hard-sphere systems with two and four intrinsic degrees of freedom. The fluid branch is taken from exact, low-density equation-of-state expansions for many-boson and -fermion systems, appropriately extrapolated to intermediate densities. Crystallization and melting densities for bosons and fermions are then determined via double-tangent constructions. Results agree well with available variational Monte Carlo, density-functional, and Green-Function Monte Carlo calculations. The viability of this approach to the quantum freezing transition is explored for popular examples of strongly-interacting quantum systems, including bulk atomic Helium-4 and Helium-3 systems, pure neutron matter, and symmetrical nuclear matter.

[K1.139] Insulators and Dielectrics

This abstract not available.

[K1.140] High-k titanium silicate dielectric thin films for CMOS applications

We report on the deposition of high-k titanium silicate (TiSiO_4) dielectric thin films by means of two different techniques, namely the pulsed laser deposition (PLD) and rf-magnetron sputtering. The bonding states and microstructure of the deposited films were characterized as a function of growth conditions. XPS and FTIR characterizations have provided clear evidence for the presence of Si-O-Ti bonds in the deposited films indicating thereby the formation of the titanium silicate phase. The electrical properties of the TiSiO_4 films (including dielectric constant, dielectric loss, leakage current and breakdown voltage) were systematically determined through their integration into Pt/TiSiO_4/Pt metal-insulator-metal devices. Deposition conditions that yield TiSiO_4 thin films with excellent dielectric properties are thus identified. These silicate films were found to exhibit a high-k value of \sim 30, a dissipation factor as low as \sim 0.01, and a leakage current lower than 10^-6 A/cm^2 at 1~MV/cm. Finally, predominant conduction mechanisms in these TiSiO_4 insulating films are discussed.

[K1.141] Spatially coherent coexistence of three phases of a mixed dielectric crystal

>From a quinary melt KBr:RbCl:RbBr:KI:RbI were grown a crystal in equimolar concentrations using the Czochralski technique. A very wide optical absorption F band were obtained coloring a sample. The structure and the texture of large crystals were determined by using powder and single plate difractometry and also Laue photography. It was found that these crystals are microcrystalline aggregates of three different fcc mixed alkali halide phases where Bravais lattices are all spatially coherent to each other whithin the aggregate. These phases were identified by applying standard powder X ray diffraction matching procedures together with ion balance equations and the Vegard's law, as pure RbBr, binary KI(0.39):RbI(0.61)and ternary KBr(0.47):RbCl(0.39):RbBr(0.14). Unit cell sizes of about 6.889, 7.23 and 6.631 Angtroms, respectively were measured for these phases.

[K1.142] Optical absorption spectrum in a dimerized extended antiferromagnetic Hubbard chain

We give an expression for the optical absorption spectrum of a dimerized antiferromagnetic and half-filled extended Hubbard chain. The calculation of this spectrum takes into account a nearest-neighbor interaction plus a doubly occupied site energy. The resulting two-band spectrum exhibits an interesting structure with a particular asymmetry, both in the excitonic absorption peaks -of which there can be at most four and at least two- and in the two extended absorption bands. Both of these have the same width, which is dependent upon dimerization only. As the nearest neighbor electronic repulsion is increased, intensity is leaked to the excitonic peaks which move downward in frequency, and may interact resonantly with the extended absorption bands. On the other hand, the increase in dimerization results in a narrowing and separation of the extended bands, as well as large excitonic absorption. Finally, a brief comparison is made with related theoretical work in the literature.

[K1.143] Direct observation and characterization of domain-patterned ferroelectrics by UV Photo-Electron Emission Microscopy (PEEM)

Electron emission from ferroelectric surfaces with polarity patterned domains of LiNbO3 (LNO) crystals and PbZrTiO3 (PZT) thin films was investigated using in situ UV-photo-electron emission microscopy (PEEM). The photo-electrons were excited with UV-light from the tunable (4.0 to 6.5eV) UV free electron laser (FEL) at Duke University. Brightness contrast between opposite polar domains was observed through the difference of the photoelectric yields. Domain polarity was confirmed by piezoresponse force microscopy (PFM) and by chemical etching. In both LNO and PZT, bright emission was observed from the negative domain ends (negative domains), indicating that the emission threshold of the negative domain is lower than that of the positive domain. For LNO, the photo-threshold of the negative domains measured by PEEM was less than 4.6eV, while for PZT, the threshold of the negative domains was less than 4.3eV. The PEEM polarity contrast is discussed in terms of a surface dipole between the bound polarization charge and the screening charge. The surfaces were examined at both room temperature and at elevated temperatures, and it was found that the brightness contrast was reduced at elevated temperatures, which is attributed to a reduction in bound polarization charges. The PEEM results allow for a measurement of the local electronic band structure of domain patterned ferroelectrics at the nanoscale. These results are compared with local surface potential measurements obtained by scanning Kelvin probe microscopy (SKPM). *Research supported by the ONR, the NSF and the AFOSR through the MFEL programs.

[K1.144] TL and OSL processes in KCl and KBr crystals doped with Eu^2+

The TL and OSL techniques are mainly used for dating and dosimetry purposes. Besides, KCl:Eu^2+ and KBr:Eu^2+ single crystals have been successfully used as both environment UV detectors and imaging plate in digital radiography by taking advantage of their optical and thermo-stimulated luminescent behaviors. The present work reports a comparative study of TL and OSL UV response and dosimetry properties. We have found that TL and OSL emissions around 420 nm are quite similar for each crystal. It may establish a link between TL and OSL recombination mechanisms which addresses the participation of Eu^2+ through F (KCl and KBr) and F_Z (KCl) centers as the main activator. These situations should be taken into account when we use KCl:Eu^2+ in UV light monitoring and dose measurements.

[K1.145] Numerical simulation method for exciton energy estimation of one- and two-sub-lattice orientationally disorded molecular crystal

The method of projecting operator is used for study of topological ranked many-sub-lattice crystal with admixtures. Quasipartial hamiltonian of such crystalline systems contains as diagonal, so and nondiagonal disorder. The account their configurationally dependencies and use the diagram technique has allowed us to select and sum up all corresponding to kinematical addend in the locator function without some approximation for the hamiltonian. The diagram method of the summation of corrections for frequentative filling the lattice sites is generalized for systems with arbitrary number of sub-lattice and is used at calculation of averaged resolvent in one-site approach. Exciton energy of one- and two-sub-lattice orientationally disorded molecular crystal with different corners of molecule reorientations are calculated by means of resolvent. Found (by means of the numerical calculation) concentration dependency of specified energies can be used for interpreting the wide circle optical experiment and determinations of orientation features of the considered crystalline systems.

[K1.146] EPR and ENDOR of chromium in congruent and stoichiometric lithium niobate

Observed difference of coloration and optical spectra of Li-deficient and Li-rich lithium niobate crystals doped with chromium was clarified with the help of the EPR and ENDOR. Li-deficient crystals (including conventional congruent ones) contain always great number of intrinsic defects (Li and Nb vacancies, antisite ions). Our EPR and ENDOR study has shown that chromium in Li-deficient crystals substitutes for Li and creates a family of similar centers with the crystal field splitting about 0.7-0.8 1/cm. Dominating axial center has no intrinsic defects in the nearest neighborhood (distant charge compensation of the positive charge excess), whereas other satellite centers have low C1 symmetry due to the presence of cation vacancies. In the crystals of stoichiometric or Li-rich composition the new axial chromium centers with the crystal field splitting 0.043 1/cm were found. In this case trivalent chromium substitute for Nb and the positive charge deficit is compensated by incorporated hydrogen ions or by additional Li ions. A comparison of the EPR/ENDOR and optical spectra for Li-deficient and Li-rich crystals allowed us to make reliable identification of optical absorption bands.

[K1.147] TiO_2-rich Reconstructions of SrTiO_3 (001): A Theoretical Study of Structural Patterns

We have recently reported structure solutions for the (2x1) and c(4x2) reconstructions of SrTiO_3 (001) based on high-resolution electron microscopy, direct methods analysis of diffraction data and density functional theory. Both reconstructions were found to be TiO_2-rich and feature a single overlayer of TiO_2 stoichiometry on top of bulk-like TiO_2 layer. Qualitatively, the two reconstruction geometries differ in the cation sub-lattice of the overlayer only, where Ti atoms distribute differently over twice as many 5-fold cation sites. Other cation distribution patterns are conceivable and may indeed correspond to observable reconstructions. This present work uses density functional theory to generate a number of such structural variations in search of patterns of stability. We find a reliable predictor for the reconstruction energy in the ability of oxygen atoms to relax vertically out of the overlayer plane. This ability in turn is modulated by the number and relative position of coordinating Ti atoms, which yields simple empirical rules as to how cations are distributed in low energy reconstructions. We find these rules to be transferable to other perovskite surfaces such as CaTiO_3 and BaTiO_3.

[K1.148] Low Frequency Magnetoelectric Interactions in Single Crystal YIG/PMN-PT Bilayers

This work is concerned with magnetoelectric (ME) coupling in novel layered ferromagnetic-ferroelectric composites. The heterostructures are capable of electric-to-magnetic field conversion that is mediated by mechanical stress [1]. We recently developed a theoretical model for low frequency effects that predicts an order of magnitude enhancement in ME coupling in single crystals compared to polycrystalline samples [2]. Use of single crystals is critical for probing the influence of piezomagnetism, ac magnetostriction, and ferroelasticity of the magnetic component and similar parameters for the ferroelectric component. The studies are also important for the creation of an optimal interface to accomplish strong ME interactions. Bilayers were prepared by bonding epitaxial (100), (110), and (111) films of YIG and (001) single crystals of PMN-PT. Low frequency ME voltage coefficients were measured for transverse (dc magnetic field H and ac field in-plane) and longitudinal (magnetic fields out-of-plane) fields. Important results are as follows. (i) The ME voltage coupling is the largest for H along <111> of YIG and is the weakest for H along <100>. (ii) The voltage coefficient increases with increasing volume of YIG. (iii) The transverse coefficient is an order of magnitude higher than the longitudinal coefficient. (iv) Studies on bilayers with (111) YIG films reveal a significant influence of in-plane anisotropy on ME coupling.

1. G. Srinivasan, E. T. Rasmussen, and R. Hayes, Phys. Rev. B. 67, 014418 (2003). 2. M. I. Bichurin, V. M. Petrov, and G. Srinivasan, Phys. Rev. B 68, 054402 (2003).

This work was supported by a grant from the National Science Foundation (DMR-0322254)

[K1.149] Structural and magnetic characterization of electrodeposited iron-containing oxide films

We describe structural and magnetic characteristics of thin iron-containing oxide films, such as the Fe_3O_4 (magnetite) and \gamma-Fe_2O_3 (maghemite) spinel-related phases, prepared by electrochemical methods in aqueous electrolytes. Phase identification and deposit crystallinity are monitored by X-ray diffraction, in conjunction with morphological information from scanning electron microscopy. Substrate influences are assessed by comparing film characteristics on polycrystalline substrates as well as low index single crystal gold surfaces.

[K1.150] Metals

This abstract not available.

[K1.151] Sublattice Analysis of Elastic Stability in Intermetallic Compounds

The fundamental basis for understanding the mechanical stability of alloys is not only one of the central issues in elasticity, it is also essential consideration in the analysis of structural response in alloys, ranging from polymorphism, amorphization, and melting to fracture. The mechanical stability of homogeneous intermetallics under isotropic tensile stress is discussed. We introduce an elastic-stability criterion on the basis of the sublattice analysis to predict the instability volume at isotherm expansion process. The onset of the instability is realized when the bulk-modulus instability of the sublattice is reached, and it coincides with the molecular dynamics results. It is found that the elastic instability is induced by the decrease of the potential contribution in the elastic constant. We discuss the role of the atomic size ratio and the lattice structure in the sublattice analysis. It is also studied when the impurity is incorporated into the alloys. Contrary to the homogeneous systems, the instability is introduced by the increase of pressure-fluctuation contribution in the elastic constant. The pressure fluctuation is facilitated by the atomic relaxation induced by the impurities, and it gives the instability. This idea is applied to understand the occurrence of the Hydrogen-Induced Amorphization (HIA).

[K1.152] Deposition geometry and substrate motion effects on crystal texture of copper thin films

Copper thin films were deposited by electron-beam evaporation onto SiO2/Si(100) substrates. Varying deposition geometry and substrate motion were utilized to investigate geometrical effects on crystal texture. Films were deposited onto stationary substrates inclined between 0 and 80 degrees from the incoming vapor flux; zigzag (periodic 180 degree substrate rotations) and helical films (continuous substrate rotation) were fabricated at 60 and 80 degree tilts. Stationary films with near-normal incidence exhibit a [111] fiber texture with a secondary [200] orientation. For incidence angles greater than 60 degrees, a powder-like texture is observed, with some preferred orientation. Substrate rotation induces weak [220] and [311] fiber texture, while zigzag motion induces weak oriented texture. X-ray diffraction pole figures and scanning electron microscope images show a film morphology and texture that varies greatly with substrate/vapor geometry.

[K1.153] A new universal analytical pseudopotential for the alkalis

A new universal analytical pseudopotential depending of only two parameters, parameters which are the same for all the alkalis, is proposed to study the properties of the alkalis. We calculated here the phonon dispersion curves, lattice specific heat and electric resistivity of Li, Na, K, Rb and Cs. We found a good agreement of our predictions and experimental results.

[K1.154] Renormalization of the width of electronic band by interactions

Using the model of electronic band with a sharp edge we show that interactions of electrons with impurities or phonons lead to an increase of the band width. The self consistent calculation of the electron self energy is essential in this problem.

[K1.155] Pressure induced structural phase transitions and mechanical properties of PtX alloys (X= Sc, Y) investigated by ab initio calculations

In this work we present ab initio structural and electronic calculations for the A_c, B1, B2, L1_0, L1_1, and B32 structures of the PtX alloys. The calculations are based on the Density Functional Theory within the Local Density Approximation (LDA) using the Troullier-Martins pseudopotentials. Our predicted geometries for the ground state of PtSc and PtY alloys are the B2 and A_c structures, respectively, in agreement to the experimental phase diagram. The energy and enthalpy curves show a phase transition from B2 to B32 structure at 59 GPa approximately, for the PtSc alloy, and two phase transitions for the PtY alloy: B1 to L1_0 at 27 GPa and B2 to B32 at 47 GPa. Additionally, we calculate the theoretical tensile strength for the B2 phase of PtX alloys along the [001] and [111] directions.

[K1.156] Structure properties and local order in liquid and supercooled metals by computer simulation

In this work we present calculations by molecular dynamics, modeling the interatomic interactions through a n-body Gupta semiempirical potential. The pair distribution function (PDF) of liquid and supercooled metals (Ni and Ag) is obtained to investigate structure properties. The steepest-descent method is used to find the inherent structures of the multidimensional potencial energy surface. The PDF obtained by our simulations is in agreement with experimental measurements. A comparison between the structural properties of liquid and supercooled metals shows that the general features in the supercooled metals are similar to those of the liquid state, except for the shoulder of the second peak in the PDF. Inherent structures abundances in the liquid and supercooled phases are characterized by the presence of the icosahedral and distorted icosahedral structures, also observing the presence of crystalline order.

[K1.157] Electronic structures of barium overlayers on crystalline tungsten.

The effect of barium coverage on the electronic structures of low index tungsten-barium-vacuum interfaces is investigated by measuring the total energy distributions (TEDs) of the field and photofield emission current. The TEDs obtained from density functional calculations of the surface electronic structures based on supercell models of the ordered interfaces are used to interpret features observed in the experimental data. The adsorbate-induced charge shifts at the interface are deduced, and are found to be consistent with the observed decrease in the work function.

[K1.158] Numerical study of resistivity escalation and saturation in disordered three-dimensional metals.

We calculate the zero-temperature resistivity of model 3-dimensional disordered metals described by tight-binding Hamiltonians. Two different mechanisms of disorder are considered – diagonal disorder (random on-site potentials) and off-diagonal disorder (random hopping integrals). The non-equilibrium Green function formalism provides a Landauer-type formula for the conductance of arbitrary mesoscopic systems. We use this formula to calculate the resistance of finite-size disordered samples of different lengths. The resistance averaged over disorder configurations is linear in sample length and resistivity is found from the coefficient of proportionality. Two structures are considered: (1) a simple cubic lattice with one s-orbital per site, (2) a simple cubic lattice with two d-orbitals. For small values of the disorder strength, our results agree with those obtained from the Boltzmann equation. Large off-diagonal disorder causes the resistivity to saturate, whereas increasing diagonal disorder causes the resistivity to increase faster than the Boltzmann result. The crossover toward localization starts when the Boltzmann mean free path is a few lattice constants.

[K1.159] Photoemission from clean Al(110): experiment and ab-initio theory

The angle-resolved energy distributions of photoelectrons from clean Al(110) have been measured for photon energies in the range 10-60 eV. Previously unknown structures in the spectra are identified as being due to emission from a surface state band and several surface resonance bands. The experimental results are interpreted by means of ab-initio calculations of the surface electronic structure based on density functional theory, in which the experimentally-observed oscillatory surface relaxation is taken into account. The calculated surface electronic structure is found to be in good overall agreement with the experimental data. The calculation is also used to investigate the effects of oscillatory surface relaxation on the surface electronic structure.

[K1.160] Spectroscopy of the optically excited mercury indium excimer

Pulsed laser excitation at the resonance line of indium at 410.1 nm was used to study the spectroscopy of the mercury indium excimer. The spectrum shows broad emission peaks at 5226.6 nm, 499.4 nm and satellite bands at 454.2 nm and 413.2 nm to the indium atomic lines at 451.1 and 410.3 nm. The emitter of these bands is the diatomic HgIn. Time resolved fluorescence spectra following the pulsed excitation; and the intensity dependence of the bands as a function of mercury and indium densities were obtained to derive kinetic information. Preliminary results and analysis of this study will be reported.

[K1.161] EPR vs. Electrical Methods of Monitoring Ferroelectric Switching Properties of Potassium Di-hydrogen Phosphate, a Comparative Study

Because ferroelectric materials remember electric fields, they have the potential of replacing conventional volatile random access memory (RAM). Further understanding of ferroelectric properties is vital to making such transitions possible. Past studies have utilized Electron Paramagnetic Resonance and Electrical Switching in the exploration of ferroelectric properties of various materials. However, it is the goal of this study to use both methods simultaneously so that relationships and discrepancies between their results can studied in detail. To do this comparison, we will use Potassium Dihydrogen Phosphate (KDP) because it has a relatively simple molecular structure, which has been characterized in past studies utilizing both methods (non-simultaneous) yielding differing results that have yet to be reconciled. An analysis of the results from the former method, which monitors the surface of the KDP crystal, and the latter method, which monitors the bulk of the material, we expect to show some correlations. If that is indeed the case, one may then go back to previous studies and “transform” data obtained from one method to data one would obtain using the other method. However, in the case where correlations are not found, one must investigate the nature of any discrepancies whether it is differing physical phenomena between the bulk and surface of the KDP crystal, or the possibility of the measurement techniques having differing effects on the domain characteristics of the crystal.

Aknowledgments: NASA GRANT NUMBER 0051-0078, Department of Defense (DOD) Control No.ISP02-EUG15, ISP02-EUG15, National Science Foundation (NSF) DMR-0116744.

[K1.162] Applications

This abstract not available.

[K1.163] Nanosecond Thermal Processing for Self-Aligned Silicon-On-Insulator Technology

Future radar and communications systems will have the need to use CMOS integrated circuits to provide increased analog and digital functions. Conventional CMOS technology has been locked into designing processes around polysilicon gate material because of the need for self-alignment. Low resistance metal gates are superior for high-speed devices. However, their low melting point prevented their use in a self-aligned structure that experiences high temperature processing (>700oC). Silicon-On-Insulator (SOI) technology, non-refractory metal gates, and nanosecond laser processing were used to fabricate a self-aligned structure. These techniques will allow further scaling of CMOS devices and enable mixed-mode devices to be integrated on the same substrate. The laser is used to rapidly, on the order of nanoseconds, melt and redistribute the implanted dopants for the source and drain with minimal lateral diffusion which lowers parasitic gate to drain and source overlap capacitance. Gate resistance can be lowered by at least an order of magnitude and optimal threshold control of PMOS and NMOS devices can be achieved by using an aluminum metal gate instead of a poly gate. This process allows high performance, low power digital technology to be integrated with high Fmax, low noise RF devices.

[K1.164] Electric Field Directed Collection and Metering of DNA in Microfluidic Devices

Microfluidic technology is a key component in the development of microfabricated lab-on-a-chip systems for use in bioanalytical and biosensing applications. These devices continue to be developed to perform a variety of DNA analysis assays, however many of these applications deal with such minute amounts of DNA that it must first be pre-concentrated to a detectable level. On the macroscale, this pre-concentration is typically performed using centrifugation processes which are difficult to miniaturize and interface with other microfluidic components. In order to address this issue, we have developed microfluidic devices incorporating arrays of on-chip electrodes to locally increase the concentration of DNA in solution. By applying a low voltage between neighboring electrodes positioned inside a microfluidic channel, the negatively charged DNA fragments are induced to migrate toward and collect the anode, thereby allowing the quantity of accumulated DNA to be precisely metered. We demonstrate the application of this technique in electrophoresis microchips to inject a narrow and well-defined DNA plug into an electrophoresis gel. This loading scheme both increases the concentration of the sample to be separated and significantly reduces the degradation in separation resolution due the size of the injected sample plug.

[K1.165] Dense hydrogen adsorption on carbon sub-nano pores at 77 K

Hydrogen adsorption measurements on two types of different carbon nano materials were carried out at 77 K up to hydrogen pressures of 2 MPa using the volumetric method modified for low-temperature experiments. The adsorption property was concluded as dense hydrogen physisorption in sub-nano meter sized pores because of the the Langmuir type isotherm, reversible adsorption/desorption and large hydrogen uptake exceeding 2 wtadsorbed hydrogen was comparable to the density of bulk liquid hydrogen, indicating that hydrogen filling would be attainable when both chemical potential of hydrogen and adsorption potential of carbon were optimized.

[K1.166] Novel Flow Geometries to Achieve Passive Mixing in Microfluidic Devices

Mixing of fluids at the microscale poses a variety of challenges, many of which arise from the fact that diffusion is the only available mechanism to achieve mixing in the laminar flow regime. While considerable progress has been made toward developing strategies achieve improved mixing in microfluidic systems, many of these techniques introduce additional complexity to device fabrication and/or operation processes. In this work, we explore the use of devices incorporating curved and spiral-shaped flow geometries designed to achieve efficient mixing in a format that can be constructed using only a single planar soft lithography step without the need for multilayer alignment. These channel designs have cross-sectional dimensions of 200 x 29 microns, and include a series of spiral-shaped curved segments arrayed along the flow path. Mixing studies are carried out by imaging the interface between parallel streams of blue and yellow dye at Reynolds numbers ranging from 0.1 to 15. We find that these curved channel geometries offer enhanced mixing in considerably shorter distances as compared with conventional straight channel designs. We investigate the influence of spiral curvature and pitch, and show further improvements can be achieved by incorporating arrays of barriers to alter the flow path within the curved channel segments.

[K1.167] Information Transfer During Quantum Measurement

``The progress in quantum measurement theory has increased the need for a physical theory of information transfer during quantum measurement. Using the RPI --Restricted Path Integrals- approach to quantum measurement, we discuss on equivalence of information transfer and measurement. It is possible to understand the nature of measurement process by working on the phenomenon of information transfer. I show that in contrary with today information theory, for a conscious observer the amount of information gained in a measurement is not an absolute amount but related to his or her previous knowledge of the system. The knowledge, the observer has about the history of the system interactions and entanglements with other systems. The more intelligent the observer is, the more information it gains in a measurement. This means that the difficulties in quantum measurement can have roots in consciousness -the intuitive belief of many physicists. And it directs our attention to work on a general theory of consciousness. At the end I will make a model for the amount of transferred information during an observation. ''

[K1.168] Detectors, Sensors, Transducers

This abstract not available.

[K1.169] Elaboration of adaptive photodetectors in the near IR-region

There is demand for IR detectors that are sensitive both for amplitude and phase changes. It allows to elaborate highly sensitive detectors of weak vibrations. In this work a titled geometry was realized that allows two-dimensional monitoring of the vibration source. A transient photocurrent was investigated in photorefractive CdTe and CdHgTe crystals doped with V and Ti atoms using IR-line (1.15 micron ) of He-Ne laser. In our experiment the sinosoidal modulation of an interference pattern on the crystal surface which was formed by two mutually coherent beams, was realized. This leads to the appearence of the non-steady-state EMF and electric current in the crystal and in external circuit. The photocurrent signal was registered in short circuit regime by a synchronons detectors .The dependence of the holographic current (EMF measurements ) on the modulation frequency, on the form of modulation wave and also titling angle were measured. To our knowledge, for the first time the photo-EMF measurements were carried out using the photogeneration of carriers from deep impurity centers ( early the appearance of photo-EMF was a result of the band-to-band transitions). This made it possible to measure the photo-EMF under the laser excitation in the near IR-region. The energy structure of impurity centers and mechanisms of the photogeneration of carriers from impurity states are also investigated by the optical and photoelectric measurements of investigations crystals.

[K1.170] Piezoresistive microsensors for detection of volatile organic compounds in water

Piezoresistive microcantilever (PMT) technology is used to develop small, rugged sensors capable of detecting both chemical and biological species. Using PMT in conjunction with organic polymers, polymer blends, or polymer composites, sensor arrays have been fabricated for the detection of organic pollutants in water, including carbon tetrachloride, TCE, and MTBE. These sensor arrays are small, require only inexpensive support electronics, and may be networked for remote operation. Individual sensor elements may also be configured for the detection of certain biological molecules, both in solution and in aerosol deliveries.

[K1.171] Development of a Gd-Converter GEM Neutron Detector

The Gaseous Electron Multiplier (GEM) was invented by Sauli in 1997 and is under consideration for a number of particle detection applications.(F. Sauli, “GEM: a new concept for electron amplification in gas detectors”, Nucl. Inst. and Meth. A386 (1997) 531-534.) One of the advantages of the GEM is that the functions of particle detection, signal amplification and signal pickup can be separated and each individually optimized. Monte-Carlo simulation calculations for and the design of a Gd-CsI neutron converter GEM detector will be presented. A prototype multi-GEM amplifier position sensitive 10 x 10 cm^2 device with a 1 x 1 mm^2 dual charge-division pickup plane is currently under construction. Sub-mm resolution is anticipated with the optimum 5 \mum Gd converter screen covered with a “spongy” CsI secondary electron emitter. Alternative detector configurations and preliminary detector test results will be presented.

[K1.172] Signal Processing and Analysis

This abstract not available.

[K1.173] Power spectral analysis for optical tweezers: Wavelength dependence in detection

In a typical optical tweezers detection system, laser light is impinging on a quadrant photodiode, and the signal from the four quadrants of the diode is used to determine the position of a trapped object. Often, this signal is processed using a power spectral analysis. In previous work, the detection system of a Si-PIN photodiode and a 1064 nm laser was modelled and shown to act as a first order filter with a 3dB frequency of order ten kHz (Berg-Sørensen et al, J.\ Appl.\ Phys., 93, 3167--3176 (2003)). This effect is due to the transparency of silicon to 1064 nm light. With an InGaAs diode, and with different wavelengths of the laser, the filtering effect has been shown to disappear (Peterman et al, Rev.\ Sci.\ Ins., July 2003). Here, we further explore the wavelength dependence of the detection system, and explore the simple model to its limits. The method of choice is precise power spectral analysis and our results are important for the further development of optical tweezers as a tool of precision.

[K1.174] Superconductivity: Electronic Properties, Spectroscopy, and Josephson Junctions

This abstract not available.

[K1.175] Interplay between gap sysmmetry and electronic structure in thermodynamics and ARPES

The interplay between gap symmetries and the electronic structure is studied. By considering three scenarios: 1. a single band with van Hove singularities, 2. two bands, both with van Hove singularities, and 3. two bands in which one of the bands presents van Hove singularities and the other can be described according to the free electron approximation, the consequences of a specific gap symmetry in specific heat and in the spectral function of ARPES experiment is explored. In both cases the BCS mean field expression for the specific heat and the spectral function have been used. In the later one a finite lifetime effect has been also introduced. The effect of dispersion along the direction perpendicular to superconducting layers is studied by appealing either to a tight binding approach or to a free electron picture. A special attention has been paid on the effect of topology of the isoenergetic contour on physical properties of superconductors. A comparison with experimental results has been included.

[K1.176] Infrared Studies of Single Crystal Single-Layer Bi_2Sr_2CuO_6

We present infrared reflectance measurements and calculated ab-plane conductivity for single-layer Bi_2Sr_2CuO_6 single crystals for temperatures from 300K to 10K. The far-infrared reflectance increases with decreasing temperature. A broad maxima is observed at 500 cm^-1 in the room temperature conductivity, which shifts to lower frequencies with decreasing temperature. From 70K to 10K, the conductivity decreases monotonically with frequency with no obvious maximum observed. These conductivity properties are quite different from those of double-layer high-T superconductors. We attribute the depression of the conductivity below the maximum as a pseudogap. Our observations support the scenario applied to stripe-phase NCCO cuprates, in which free and bound charges might coexist in Bi_2Sr_2CuO_6. We believe that the shifts of the maximum in the conductivity spectra above 100K and the disappearance of the maximum below 100K reflect a redistribution of charge carriers with temperature.

[K1.177] Raman phonons and possible ordering in (Ca,Sr)SiAl superconductors: Experiment and theory

CaSiAl and SrSiAl both crystallize in a hexagonal structure derived from MgB2 by substituting Ca/Sr for Mg and Si/Al for B. They both are superconductors, but superconducting properties differe substantially between two materials. It is possible that partial ordering of Si and Al plays a role in superconductivity. Raman scattering is a good tool to investigate this, because in fully disordered structure there is only one Raman active phonon, while ordering brings additional Raman modes. We measured Raman spectra for CaSiAl and SrSiAl and calculated from the first principles the Raman active phonons for different types of ordering. We discuss possible implications of our measurements combined with the calculations for the possibility of Si/Al ordering in these materials.

[K1.178] Temperature Effect and Fermi Surface Investigation in the Scanning Tunneling Microscopy of Bi_2Sr_2CaCu_2O_8

Based on a Fermi liquid picture, the temperature effect on the impurity-induced spatial modulation of local density of states (LDOS) in the d-wave superconductor Bi_2Sr_2CaCu_2O_8, is investigated in the context of scanning tunneling microscopy (STM). It is found that stripe-like structure exists even in the normal state due to a local-nesting mechanism, which is different from the octet scattering mechanism proposed by McElroy et al. [Nature 422, 592 (2003)] in the d-wave superconducting (dSC) state. The normal-state spectra when Fourier-transformed into the reciprocal space, can reveal the information of the entire Fermi surface at a single measuring bias, in contrast to the point-wise tracing proposed by McElroy et al. This may serve as another way to check the reality of Landau quasiparticles in the normal state. We have also re-visited the spectra in the dSC state and pointed out that, due to the Umklapp symmetry of the lattice, there should exist additional peaks in the reciprocal space, but experimentally yet to be found.

[K1.179] Gauge-invariant propagators in QED_3

We discuss properties of various gauge-invariant propagators in QED_3. The frequently-encountered Schwinger propagator G_S(x-y)=\langle \exp(-i\int_x^y a^\mu ds_\mu) \psi(x)\bar\psi(y)\rangle, where the integral in the phase factor is calculated along a straight line, is shown to be an exponentially decreasing function of separation G_S\sim \exp(-|x-y|/\xi) in 3-\epsilon dimensions rather than being described by a simple power-law. Near d=3, the correlation length \xi vanishes as (d-3), rendering G_S an ill-defined object. We explicitly demonstrate that G_S(|x-y|) factorizes into a product of an average of Wilson phase factor involving the transverse component of a gauge field only, and Landau gauge-invariant propagator \langle \exp(-i\int_x^y a^\mu_L ds_\mu)\psi(x)\bar\psi(y)\rangle to the leading order in 1/N expansion. The root-cause of the problem is thus revealed as severe UV divergence in the gauge invariant Wilson factor. In contrast, we show that the appropriately regularized Brown propagator is a well-defined, gauge invariant object whose power-law decay is characterized by a positive anomalous dimension 16/(3\pi^2 N).

[K1.180] Phonons and electron-phonon coupling in nickel borocarbides

Superconductivity in nickel borocarbides exhibits various unusual properties [1], which raises the question if electron-phonon coupling is the main source of pairing in this class of materials. To elucidate this subject, we present first principles density-functional calculations of the bandstructure, the phonon dispersion, and the electron-phonon coupling for superconducting YNi_2B_2C (T_c=15.5\,K) and compare them with results for the non-superconducting reference compounds LaNi_2B_2C and Y(Ni_.75Co_.25)_2B_2C. The calculations reproduce a pronounced phonon anomaly in the vicinity of the wave vector (0.6,0,0) in a low frequency branch of \Delta_4 symmetry that has been observed experimentally both in YNi_2B_2C and LuNi_2B_2C [2]. We find that the magnitude of the anomaly and of the electron-phonon coupling depend very sensitively on the chosen structural parameters (volume, c/a ratio). Another pronounced anomaly is predicted in an optic branch of the same symmetry with predominant B and C elongations. Although the low frequency phonon spectrum is strongly dominated by the vibrations of the heavy metal ions we find that B and C contribute more than 50% to the electron-phonon coupling constant \lambda.

[1] K. Izawa et al., Phys. Rev. Lett. 89, 137006 (2002). [2] C. Stassis et al., Physica C 317-318, 127 (1999).

[K1.181] Structural and Moessbauer characterization of the GdSr_2Ru_1-xFe_xCu_2O_8 system

The well known antagonism between superconductivity and long range magnetism has been one of the most studied problems in Condensed Matter Physics. The 1999 discovery that GdSr_2RuCu_2O_8, in which the Ru atoms order antiferromagnetically at a Neel temperature of T_N = 133 K, became superconductor with a critical temperature T_C = 46 K, without loosing its antiferromagnetic properties, renewed the interest in this problem, specially because it was the first known material with T_N>T_C. The substitution of a small fraction of the Ru atoms (and/or Cu atoms) with Fe atoms allows the use of Moessbauer spectroscopy to sense the environment around the sites that these atoms occupy in the crystal structure. We present resistance vs. temperature, X-ray and Moessbauer results in GdSr_2Ru_1-xFe_xCu_2O_8 with x = 0.025, 0.05, 0.075, 0.10 and 0.20, together with a discussion of which sites of the structure do the Fe atoms occupy.

[K1.182] On the origin of photogenerated terahertz radiation from current-biased superconducting YBa_2Cu_3O_7-\delta thin films

The origin of photogenerated terahertz radiation pulse from current-biased superconducting YBa_2Cu_3O_7-\delta thin films excited by femtosecond optical laser pulses is delineated. By investigating the performances of the transient terahertz radiation generated under different operating parameters, pulse reshaping in the measured terahertz electric field caused by the kinetic inductance of the superconducting charge carriers is identified. After recovering the original waveforms of the emitted terahertz pulses, the transient supercurrent density directly correlated to the optically excited quasiparticle dynamics is obtained. A fast decreasing component of about 1.0 ps and a slower recovery process with a value of 2.5 ps are unambiguously delineated in the optically induced supercurrent modulation. The radiation mechanism of the transient terahertz pulse related to nonequilibrium superconductivity is discussed.

[K1.183] Spatial Symmetry of Superconducting Gap and Pseudogap in Oxygen-deficient YBCO Obtained from Femtosecond Spectroscopy

The spatial symmetry of temperature-dependent gap and temperature-independent gap, which are generally associated with the superconducting gap \Delta(T) and pseudogap \Delta_p, respectively, in near optimally doped and underdoped YBCO are clearly delineated by the orientation- and time-resolved femtosecond spectroscopy. For the slightly oxygen-deficient (100) YBCO thin films, the coexistence of superconducting gap and pseudogap were evidently observed along b-axis, which is extremely different from the near optimal doping cases, where only superconducting gap is observed. Combing the well-textured samples, (110) and (100) YBCO thin films, the intrinsic symmetries (d_xy in near optimal doping and d_x^2_-y^2 in underdoped region) of pseudogap in YBCO have been disclosed.

[K1.184] Evidence for a metal-insulator transition in overdoped cuprates: new Raman results

Transport properties play a major role in the characterization of correlated metals such as the cuprates. The usual dc and optical conductivity measurements, however, suffer from the missing momentum resolution in the strongly anisotropic CuO_2 plane. The problem can be partially solved by using electronic Raman scattering. Here, the response is proportional to the conductivity. Additionally, different parts of the Fermi surface can be projected out by using polarized light. With this technique we study the electron dynamics in the normal state of cuprates over a wide range of doping. The strong anisotropy of the electron relaxation which evolves below a doping level of 0.22 holes/CuO_2 is interpreted in terms of an unconventional metal-insulator-transition with an anisotropic gap. A phenomenology is developed which allows a quantitative understanding of the Raman results and provides a scenario which links single- and many-particle properties.

[K1.185] Structural, magnetic and superconducting properties of the Fe doped MgCNi_3

Band structure calculation showed that the Fermi level for MgCNi_3 (T_c\approx 8K) is located in the slope descending from a sharp peak originating mainly from d states of Ni. These calculations also suggest that introducing hole dopants (e.g. Fe) into MgCNi_3 will result in an increase of the density of states at the Fermi level N(E_F), and consequently, one may expect an increase of T_c. However, a large N(E_F) is not always beneficial for superconductivity, because can induce spin fluctuation or magnetic order, which should destroy the superconducting pairing. The MgC(Ni_1-x Fe_x)_3 (0 \leq x \leq 0.7) system has been investigated by x-ray, magnetization and ^57Fe Mossbauer spectroscopy. The Fe doping quickly depress the T_c, leading to a complete destruction of the superconducting state for x\approx 0.04. However the establishment of a magnetic state is observed only for x \geq 0.3, far away from that for which the superconductivity is completely destroyed. As the Fe content is increased an expansion of the lattice was observed, leading to a decreasing of the charge transfer between Fe and C atoms. The magnetic moment of the Fe increases as the Fe concentration increases.

[K1.186] Relation between the increased transmission in the EXAFS region of X-ray absorption and the increase in the number of Abrikosov Vortices as cuprate superconductors go through Tc

The increased flux expulsion as T->Tc (observed as the external magnetic field, Bz = +/- 0.75 oe. goes through zero [1]) is related to the increased transmission as T->Tc (observed in all cuprate superconductors in the EXFAS region of X-ray absorption [2]). The expulsion of Abrikosov vortices as T->Tc is a cooperative dynamic phenomenon that affects only the EXAFS region of the spectrum. When the flux expulsion diverges beyond a critical value, we propose the EXAFS transmission increases because photoelectrons are involved in the Abrikosov Vortex. The phenomenon is similar to the increased transmission observed in He 4 by the formation of supercritical vortices [3]. [1] J.V. Acrivos, Lei Chen, C.M. Burch, P. Metcalf, J.M.Honig, R.S.Liu and K.K.Singh, Phys. Rev. B 50, 13710 (1994), [2] J.V. Acrivos, L.Nguyen, T.Norman, C.T. Lin, W.Y.Liang, J.M Honig and P.Somasundaram, Microchemical Journal, 71, 117 (2002), [3] E.J.Yarmchuk, M.J.V.Gordon, R.E.Packard, Phys.Rev.Lett. 43, 214 (1979)

[K1.187] Spontaneous supercurrent in superconducting pi ring

The free energy of a superconducting loop interrupted by a pi-junction is a double potential well with a degenerate ground state. Provided LIc/f0>>1, the phase difference generated by the pi-junction is compensated by the circulation of spontaneous supercurrents. We present two phase sensitive experiments to evidence the existence of such currents. In one case, a non-linear ferromagnetic pi ring is directly coupled to a linear SQUID by sharing one half of its perimeter. Given the pi-ring critical temperature lower than the SQUID one, the appearance of spontaneous supercurrents in the pi-ring is revealed as a shift in the SQUID interference pattern. In the second case, a Josephson junction is directly coupled to a ferromagnetic junction by sharing one electrode. Spontaneous vortices are generated at the transition of the ferromagnetic junction, producing a shift in the coupled Josephson junction pattern. They may result from roughness inducing the alteration of 0-pi regions at the S/F interface.

[K1.188] Measurements on Perforated Superconducting Films with Nano-size Periodicity*

Ultrathin superconducting films near the superconductor to insulator transition (SIT) exhibit interesting behavior caused by enhanced amplitude fluctuations. In particular, the resistive transitions and the peak in the tunneling density of states both broaden [1]. The fluctuations can be induced by either disorder or quantum effects. With the goal of understanding the relative importance of the disorder and quantum contributions to the fluctuations, we are fabricating films with periodic, sub-coherence length, nanoscale structure. The magneto-transport properties of these structures can yield insight into the different mechanisms. Our latest data will be presented.

*Supported by NSF-DMR0203608

[1] Fluctuation Effects in High Sheet Resistance Superconducting Films, (J. M. Valles, Jr., J. A. Chervenak, S. –Y. Hsu, and T. J. Kouh) Uspekhi Fizicheskikh Nauk 171, 104 (2001).

[K1.189] Enhanced resonant soft X-ray scattering of YBa2Cu3O7-x (YBCO) 50 nm c-axis film on bi-crystalline substrates

The disorder induced by the grain boundary in Josepshon junctions fabricated with 50 nm YBCO films deposited on SrTiO3 bi-crystalline substrates [1] has been investigated by YBCO [001] enhanced resonant soft X-ray scattering. Spectra have been collected in the back scattering geometry near the O(K), Cu(L3,2) and Ba(M5,4) edges at three different positions across the grain boundary. The experiments were performed at the 6.3.1-Jeff B. Kortright station of the Advanced Light Source, LBNL. The strain fields of dislocations perturb the grain boundary local structure, mainly the YBCO oxygen sublattice leading to non-superconducting zones near the grain boundary. By comparison to published spectra near the Cu(L3,2) and Ba(M5,4) edges [2] the oxygen content 7-x is greater than 6.5 at any position in the film. The decrease in the relative intensity of the Cu(L3,2) main peaks in the spectra observed at positions close to the grain boundary suggest a high concentration of holes in the CuO2 layers in this region. Information on the oxygen composition across the grain boundary can be obtained by comparison of the O(K) edge spectra with data previously published on YBCO single crystal with different oxygen content [3]. [1] M. A. Navacerrada, M. L. Lucía and F. Sánchez Quesada, Europhys. Lett. 54, 387 (2001); [2] N. Nücker, E.Pellegrin, P. Schweiss, J. Fink, S. L. Molodtsov, C.T. Simmons, G. Kaindl, A. Erb and G. Müller Vogt, Phys. Rev. B 51, 8529 (1995); [3] J.- H. Guo, S. M. Butorin, N. Wassdahl and J. Nordgren, Phys. Rev. B 61, 9140 (2000) and references therein.

[K1.190] Chemical Physics

This abstract not available.

[K1.191] Structure, stability, and reactions of complexes of the Criegee intermediate with water H2COO-(H2O)n, n=1-3: density functional theory investigation

The Criegee intermediate (CI) is a key intermediate in ozonolysis reactions of unsaturated hydrocarbons in atmosphere. The reactions of CI and water are suggested to lead to the formation of HO, H_2O_2 and organic peroxides, which are of great importance in the oxidative potential of the Earth atmosphere. The complexes of CI with water can alter these reactions significantly. In this work, the density functional theory calculations have been performed for several possible structures of CI-water complexes. The most stable geometries were found and its stabilisation energies were estimated. Intra-cluster reactions were studied as well. It has been found that reaction barrier decreases with increasing of number of water molecules complexed with CI.

[K1.192] The Influence of Cluster Formation on the Photodissociation of SO^2

Oxidation of atmospheric sulfur dioxide (SO^2) ultimately results in the formation of acid rain. As such, significant interest has been directed to understanding the photochemical processes of this atmospheric pollutant. We have recently and are currently devoting efforts to elucidating the dynamics of the photodissociation processes of SO^2 as well as the solvated system. Here we report results obtained from femtosecond pump-probe experiments of SO^2 as well as (SO^2)m clusters and (SO^2)m(H^2O)n binary clusters. The ensuing dynamics are found to proceed by a bi-exponential decay consisting of a fast component, 230 fs, and a slower component, which decays on a picosecond timescale. Studies employed to determine the effect of probe fluence on the excited state dynamics have enabled us to attribute the fast component to the amp;#7868; state dissociation that produces the SO product. Studies of (SO^2)m, m=1-4, indicate the larger species hinder dissociation of SO^2 through the neutral excited state. In addition, decay rates decrease sequentially as the cluster size increases, a trend that is also present in the binary cluster systems. While excitation is achieved through the SO^2 chromophore, the detected dissociation products indicate a charge transfer to water is operative. The binary cluster system appears to dissipate energy by charge transfer and evaporization processes rather than dissociation through the neutral excited state. Our experimental results, as well as our explanation of the data will be discussed in detail. Acknowledgements. Financial support by the Department of Energy, Grant No. DE-FG02-97ER13258 and the National Science Foundation, grant No. ATM-0089233, is gratefully acknowledged.

[K1.193] Transfer matrices for surface adsorption on terraces and nanotubes with first and higher order neighbor interactions

A simple method is presented for the recursive construction of the exact transfer matrix (T-matrix) associated with surface adsorption of monomers on terraces and nanotubes. First and higher order neighbor adsorbate-adsorbate interactions are taken into account, and the lattices considered are made of parallelograms, equilateral triangles, and hexagons, with different orientations. The T-matrix is constructed first for terraces with adsorbate-substrate interaction on edge sites being the same as that on bulk sites (free edges). Simple modifications of this T-matrix are possible to then describe either, terraces distinguishing between edge and bulk sites (edge effects), or nanotubes, for which the planar lattice is wrapped around a cylinder, corresponding to a periodic boundary. This provides an optimized algorithm for use on terascale supercomputers. While recovering previous adsorption results on fcc and bcc surfaces, it allows the study of more complicated adsorption problems, including adsorption on-top, hollow, and bridge sites, as well as a straightforward extension to adsorption studies on nanotubes.

[K1.194] Recent Developments with Local and Nonlocal Functionals in Magnetic Field Density Functional Theoru

Recent developments in test-case applications and further construction of functionals within Magnetic Field Density functional theory will be discussed. This theory allows, in principles, for the construction of functionals for the computation of NMR parameters requiring only the zero-field electron density. Further work towards this ideal will be presented, focussing on the nonlocal functionals developed by Harris and Salsbury

[K1.195] Mixed Quantum/Classical Dynamics of Electronically Excited Molecular Systems: A Model of Near Resonant Electron Transfer

One approach is to begin with the quantum mechanical density operator and the Liouville-von Neumann equation, and use the partial Wigner transform to derive a mixed quantum/classical description of the system which couples quasiclassical nuclear evolution to quantal electronic motion.^1 Our formulation introduces an effective potential to guide trajectories in phase space, and a time-propagation method suitable for different time scales of the nuclear and electronic motion. We present numerical results for a model of near resonant electron transfer in alkali atom-metal surface interactions, with two coupled quantum states and one quasiclassical degree of freedom, including state populations and quantum coherences, expectation values of position and momentum variables and their dispersion of values, and the time evolution of the grid of points in the quasiclassical phase space. We also describe extensions of the formalism to study the electronic spectra of excited alkali atoms in rare gas clusters. Partial support from the NSF. ^1 D.~A.~Micha and B.~Thorndyke, IJQC 90, 759 (2002).

[K1.196] Expanding the range of agreement for perturbation theory energies in the anharmonic oscillator

A numerical comparison of the lowest levels of the anharmonic oscillator with a variety of perturbation approximations over a wide range of coupling constants has been carried out. Approximations derived from perturbation truncations similar to original ideas of Feenberg were compared with the exact energies. For the second and third order schemes the range of agreement was expanded over the Rayleigh Schrodinger range of agreement by a factor of 100. For some model Hamiltonians these approximations offer the possibility of perturbations in a strong coupling regime.

[K1.197] Charge Redistribution on Complex Formation.

Polarizable force fields require knowledge of the magnitudes and orientations of induced dipole moments since, as was first recognized by Debye, surrounding solvent molecules can distort the charge distribution of a dissolved solute molecule. In this report, I will describe recent high resolution laser experiments that provide one of the first measurements of the magnitude of this effect in the ground and electronically excited states of an isolated molecule and its water complex in the gas phase. Comparisons of our results with the predictions of a force field being developed by Ponder and co-workers will be provided.

[K1.198] T = 0 superconducting properties of a 2D plane of exchange-coupled chains

It is now recognized that hopping anisotropies may be beneficial to the formation of superconducting state. In two recent papers (Phys. Rev. B 63, 100506 (2001); Phys. Rev. B 66, 144507 (2002)) we have considered (using a two-dimensional t - J - U model) the case of extreme hopping anisotropy in which the hopping frequency in one direction, say t_y, is suppressed to zero, whereas the hopping in the perpendicular direction is left unchanged, allthewhile leaving the superexchange J isotropic and unchanged. We refer to the resulting system as exchanged-coupled chains. The earlier results included strongly enhanced two-electron bound state formation, as well as an enormous enhancement (as large as 10^3) of the superconducting T_c. Here, we have extended our work to calculate, within BCS theory, the anisotropic coherence lengths, and penetration depths at T = 0. It is found, in the direction perpendicular to the chains, the coherence length vanishes while the penetration depth diverges, thus signaling a highly unusual superconducting phase.

[K1.199] Surfaces and Interfaces

This abstract not available.

[K1.200] A study of CH_3 islanding on Cu(111) by STM and LEED

The formation of close-packed two-dimensional CH_3 islands on the Cu(111) surface was directly observed by STM. It was shown that chemisorbed CH_3 tend to aggregate into a (\sqrt3\times\sqrt3)-R30^0 structure at any coverage up to one saturation monolayer, consistent with LEED data. Higher resolution STM images revealed ''jagged''-shaped CH_3 islands with various sizes and a coexistence of ''liquid-like'' mobile CH_3 species and ''solid-like''islands. Upon annealing, an island melting transition occurred with a size-dependent melting temperature around \sim75-100 K. However, LEED patterns showed that a short-range (\sqrt3\times\sqrt3) CH_3 order seemed to retain to a much higher temperature \sim400 K. Such a tendency for CH_3 aggregation could explain the observed first-order reaction kinetics and simultaneous production of C_2+ alkanes, e.g., from C_2H_4 to C_4H_8, at the same temperature. Finally, several types of point defects inside a CH_3 island showed distinct bias-dependence contrasts, manifesting a rich structure-dependent electronic response in this simple hydrocarbon adlayer. This work is the first STM observation of island formation with hydrocarbon radicals (CH_3).

[K1.201] Nanostructures of Self-Assembled Cyanuric acid through Hydrogen bond Networks on HOPG

Recent developments in nanostructured devices formed from the self-assembly of small molecular building blocks has influenced many groups to study small molecules that arrange into supramolecular aggregates in two-dimension on a surface. Supramolecular aggregates hold significant potential for the development of molecular devices. If the building blocks are biologically active molecules that form nanostructures on a surface, biocompatible materials and biosensors maybe realized. Cyclic amides, in particular cyanuric acid which is structurally similar to amino acids as well as DNA base pairs, are promising candidates to use to study the importance of noncovalent interactions in the assembly and stabilization of biological systems on a surface. The self-assembly of cyanuric acid into ordered nanostructures on a crystalline substrate, HOPG, has been investigated under UHV conditions by means of scanning tunneling microscopy and will be described.

[K1.202] Measurement of electron traps in molecular solids by photodetachment

Electrons can be trapped in molecular solids and dielectrics by three fundamental processes: intermolecular stabilization, resonance stabilization and dissociative electron attachment. Previous measurements on electron trapping within dielectrics and at their surfaces have determined the dependence of the trapping cross section on electron energy.

In this poster, we describe a new technique, which allows us to measure the nature of the electron traps. We probe traps created by injection of low-energy electrons into dielectric films and measure the electrons, which are photodetached by 1 - 3.5 eV photons. The investigation has been made for condensed films of n-hexane and carbon dioxide. We observed dissociative electron attachment to n-hexane for electrons of 10 eV and formation of H^- in correlation with charge and electron stimulated desorption experiments. We observed also three different types of interactions, with electrons of less that 5 eV, on CO_2 in correlation with clusters experiments.

[K1.203] Photochemical Processing of Simple Ices and Ice Mixtures

The investigation of simple ices and ice mixtures and the photochemical processes that can occur in these ices have important applications in atmospheric physics, astrophysics, and planetary astronomy. In this study, carbon dioxide ices and various mixtures are grown using a closed cycle helium cryostat. The ices are characterized using x-ray photoelectron spectroscopy (XPS) and Fourier transform infrared spectroscopy (FTIR), and the chemical changes are monitored while the solids are irradiated with x-rays for periods of up to six hours. A quadrapole mass spectrometer was also used to monitor the gas phase species evolving from the ice surface during the photoprocessing. The XPS and FTIR results are presented and correlated. It is noted that significant differences are observed, particularly for the time dependence of the evolution of the gas phase molecules, between ices grown at 77 K as compared to those grown at 20 K.

[K1.204] The correlation length amplitude for eight-arm star polystyrene in methylcyclohexane near the critical point

The turbidity of eight-arm star polystyrene in methylcyclohexane has been measured and used to determine the correlation length amplitude \xi_0 for different molecular weight polystyrene. The turbidity in this system was determined from the measured ratio of the transmitted to incident light intensities over three decades in reduced temperature. Using Ornstein-Zernike theory, we are able to fit the turbidity data and determine that \xi_0 increases systematically for this branched polystyrene in much the same way as a linear polystyrene of the same molecular weight. We acknowledge the support from NSF-REU grant DMR 0243811 and the donors of the American Chemical Society Petroleum Research Fund.

[K1.205] Two-dimensional dynamics of single actin filaments bound to fluid lipid membranes by processive motors

Biofunctionalization of solid surfaces by ultra-thin polymer films, supported membranes with reconstituted proteins or polymer/lipid composite films provides a powerful strategy to generate biointerfaces between inorganic and biological materials. In particular, the use of lipid coupled supramolecular protein assemblies as an interfacial matrix opens new fields for biophysical studies since they allow the assembly of more complex machineries such as chemomechanical actin/myosin systems on semiconductor devices or other solid surfaces. In the work presented here, we show data of actin dynamics in two-dimensional motility assays on fluid, solid-supported lipid membranes. Molecular motors (myosin V) were coupled to the membranes via monoclonal antibodies specific to a defined region of the myosin rod which does not interfere with the motor and/or ATPase activity. By using lipidated Fab fragments of these antibodies single double-headed motor molecules were anchored in the lipid membrane without intermolecular cross-linking. Thus, we were able to observe and analyze the two-dimensional dynamics of single actin filaments for long observation times, in the order of minutes, in the presence of either ADP (bound, but inactive motors) or ATP (active motors). A new method for analyzing images of such fluorescent labelled single filaments (up to 100 µm) is introduced.

[K1.206] Brownian Dynamics Simulation of a Polymer Model for Artificial Molecular Motors

In this communication we report the results of numerical simulations for artificial biomimetic molecular motors. The theoretical models used in the simulations are based on generic ratchet models for the mechanisms that underlie force generation in actual biological motors. The expectation is, that when the motors are realized experimentally, they will be able to perform useful tasks. Two separate projects are envisaged: 1. An artificial molecular motor modeled by a single polyelectrolyte and based on the physics of a DNA molecule. 2. A model for a coupled motor consisting of many such polyelectrolytes attached to a larger object, e.g. a glass fiber. The driving force for the artificial motors is provided by a patterned assymetric electrode in flashing ratchet mode representing a Brownian motor. A Brownian dynamics algorithm is used and results for the kinetic behavior of the artificial motors will be presented.

[K1.207] Collisions and Reactions of Protic Gases with Surfactant-Coated Sulfuric Acid

The presence of surfactant molecules on sulfuric acid droplets in the atmosphere may alter the rates of heterogeneous reactions by impeding gas entry. We perform molecular beam experiments with deuterated sulfuric acid solutions (60-68 wt % D_2SO_4 at 213 K) with varying concentrations of surfactants including butanol, hexanol, and octanol. We direct a beam of a protic gas HX (X = Cl or Br) at a continuously renewed film of supercooled D_2SO_4/D_2O in vacuum and measure the fraction of thermalized HX that undergo HX\to DX exchange. Our results contradict the notion that surfactants impede gas transport. The presence of surface alcohol does not alter the rate of D_2O evaporation from the liquid surface. Our most striking result is that surface alcohol actually increases the HX\to DX exchange fraction, implying that HX dissociates more readily at the interface when alcohol is present. This enhancement may be caused by the dilution of the acid near the surface by segregated alcohol molecules, which provide additional OH groups for protonation by HX. We are now investigating other surfactants as well as other atmospheric gases.

[K1.208] Self-Diffusion of o-Terphenyl Near the Glass Transition Temperature

Isothermal annealing of deuterio and protio o-terphenyl layers on the order of 100 nm have been used to measure self-diffusion near the glass transition temperature (T_g). The deuterio and protio material is vapor-deposited as a glass in layers with an initially sharp interface. As the sample is annealed, a mass spectrometer records the amounts of deuterio and protio o-terphenyl that desorb from the surface of the sample, as desorption and diffusion occur on comparable time scales in o-terphenyl. Analysis of the mass spectrometric signals with respect to time allows the calculation of self-diffusion coefficients. Compared to the predictions of the Stokes-Einstein equation, we observe substantially enhanced translational diffusion ( > 2 decades), which is a hallmark of spatially heterogeneous dynamics. The order of deposition of deuterio and protio material, isotopic differences in desorption, and porosity of the films have been investigated to assess potential complications in data analysis.

[K1.209] Multiscale model of particle dynamics in nonequilibrium systems

Atomistic models and numerical simulation provide a better understanding of the dynamics of particles in nonequilibrium systems but a classical mesoscale model has the advantage that time and length scales are accessible far beyond atomistic simulation. A useful multiscale model is presented based on the distribution of atomic paths centered on the mean distance between collisions and on the mean diffusive step. The many possible paths determine the average evolution of a particle. Dynamics can be followed from the atomic to the hydrodynamic level. Two examples will be discussed: the flow of vapour atoms on condensation into a cluster and the passage of a gas within a rectangular nanopore.

[K1.210] Nano-particle Enhanced Spectroscopies

This abstract not available.

[K1.211] Algorithm for Correlation of Metal Enhanced Fluorescence with NanoParticle Size and Spacing

Metal enhanced fluorescence with nano-particles has drawn a lot of interest in developing devices that can detect individual bio-molecules with fluorescence. We investigate the enhancement of fluorescence with silver particles deposited on silicon surface, which have range of sizes and spacings [1]. We report on the computer algorithm that allows us to correlate the fluorescence enhancement to the size and spacing distributions of the silver particles deposited on silicon surfaces. We apply a sequence of image processing methods to first define individual particles in the AFM images scanned from silicon surfaces deposited with silver nano-particles, and then use several mathematical algorithms to calculate and extract the statistic information of the particle size and distribution. This information allows us to determine the important factor that affects the fluorescence enhancement.

ľ Work supported by Laboratory for Physical Sciences. [1] T. Corrigan, et al. this session

[K1.212] All-optical constant force scanning-line laser tweezers.

Conventionally, optical tweezers are used to hold single molecules at constant extensions. However, many applications require that molecules be held under constant force conditions. This is traditionally achieved with an active feedback system which is cumbersome to build and operate and often too slow for true constant-force measurements. We present two all-optical alternatives based on a scanning-line optical trap. In these schemes, a laser beam is rapidly scanned along a line in the focal plane of the microscope objective, creating a 1-D optical potential. We can create a constant force on a trapped particle by a) modulating the beam intensity while scanning, which results in a constant lateral force; and b) using an asymmetric beam profile in the back focal plane of the microscope objective, which creates a lateral component in the scattering force. Our first scheme, can generate forces of up to 0.36 +/- 0.04pN, well suited for studies of the thermal fluctuations of DNA. The second scheme generates forces of up to 2.7 +/- 0.08pN, and combining the two takes the force up to 3.14 +/- 0.3pN, the range at which studies of molecular motors are carried out. We used these techniques with a fast position measurement to study the relaxation of DNA molecules against a constant external force with sub-millisecond time resolution and compared the results to predictions from the wormlike chain model.

[K1.213] An STM and TEM study of atomically-flat single-crystal gold nanoparticles on indium tin oxide.

We are investigating a novel substrate for use in single molecule electroluminescence experiments with the Scanning Tunneling Microscope (STM). These substrates are composed of flat gold nanoparticles supported on indium tin oxide (ITO). Because ITO is an optical frequency insulator and a DC conductor, the optical spectroscopy of the particles are behave like they are supported on glass, yet are electrically connected. We review the preparation of gold nanoparticles and optimization of the process for preparation of flat nanoparticles. Our TEM investigations show that flat nanoparticles can be prepared 100–500 nm across and range in geometry from triangular to hexagonal. These are typically 10 nm thick. The large flat surface is 111 its edges are in the <211> directions. We have also investigated the topography of the polycrystalline thin-film ITO surfaces using the STM. Polishing of the thin-films is possible, but did not improve the surface roughness. The ITO surface is smooth enough to support the gold nanoparticles.

[K1.214] Single-Molecule Protein Folding: A Study of the Surface-Mediated Conformational Dynamics of a Model Amphipathic Peptide

Most surface-active polypeptides, composed of 10-50 amino acids, are devoid of well-defined tertiary structure. The conformation of these proteins is greatly dependent upon their environment and may assume totally different characteristics in an aqueous environment, in a detergent micelle, or in an organic solvent. Most antimicrobial peptides are helix-forming and are activated upon interaction with a membrane-mimicking environment. We are seeking to physically characterize the mechanism of membrane-peptide interaction through studying a simple model peptide, MT-1. MT-1 was designed as a nonhomologous analogue of melittin, the principle component in bee venom. We are using single molecule spectroscopy to examine the induction of secondary structure upon interaction of MT-1 with various membrane-mimicking interfaces. Specifically, we monitor coil-to-helix transition through single molecule fluorescence resonance energy transfer (sm-FRET) to determine conformational distributions of folded and unfolded peptides at an interface. Studies with MT-1 will focus upon the biologically relevant issues of orientation, aggregation, and folding at surfaces using both ensemble and single molecule experiments.

[K1.215] Time-resolved emission spectroscopy of CdSe quantum dots in polar and nonpolar solvents

Nanocrystal quantum dots (QD) offer the opportunity to study semiconductors in liquid environments. QD biological labels in water are often protected from emission quenching and surface oxidation. We wish to exploit these processes to construct novel “on/off” sensors based on energy and electron transfer. These systems offer the chance to probe the semiconductor surface-solvent interface. Time-correlated-single-photon-counting was used to measure the emission lifetimes of several QD-solvent systems. Typical lifetimes could be divided into fast single exponential (~100 ps) and slow stretched exponential (~10 ns) decays. CdSe and ZnS(CdSe) were prepared in non-polar solvents with high quantum yields. QD were solubilized in water with thiol-compounds, polymer/protein coats, and micelles/vesicles. Large changes in the emission profiles of the different systems were observed. Systems in water experienced a reduction in quantum yield and loss of the longtime emission decay. Surface oxidation lead to a recovery of the longtime decay which matched that of the ZnS-capped counterpart in non-polar solvents. Lifetimes of QD in the presence of energy/electron transfer donors/acceptors was measured to test the viability of constructing nanocrystal sensors that exploit these processes.

[K1.216] Quantum calculations of vibrational energies of H3O2(-) and H5O2(+) with new ab initio potentials

We have performed quantum mechanical studies of the vibrations of H3O2(-) and H5O2(+) in full dimensionality and with sufficient accuracy to resolve important features of the measured spectra. The computational procedure starts with extensive electronic structure calculations (several 10K configurations) at the CCSD(T) level of theory with augmented VTZ basis set using MOLPRO 2002. Then a global fit to the potential energy surface is constructed, based on a functional form that respects the spatial and permutational symmetries of the system. This PES fit is employed in a "Reaction Path Hamiltonian" MULTIMODE [1] calculation to obtain the vibrational spectrum. We provide comparisons with experimental data [2].

[1] MULTIMODE: A code to calculate rovibrational energies of polyatomic molecules, J. M. Bowman, S. Carter, and X.-C. Huang, Int. Rev. Phys. Chem. 22, 533 (2003).

[2] Quantum calculations of vibrational energies of H3O2(-) with a new ab initio potential reveal large tunneling splittings. Manuscript in preparation, Dec 2003.

[K1.217] Direct reduction of hydrogen peroxides into hydroxyl ions in peroxide-based fuel cells

The physics of catalytic electrochemical reduction of hydrogen peroxide (H2O2 + 2 e = 2 OH-) at the electrolyte/cathode interface of peroxide fuel cells is under study. This reaction is ideally suited for high efficiency fuel cell operation, but is nevertheless in competition with wasteful processes such as the direct decomposition of H2O2 to water and oxygen gas. The reaction kinetics of these competing processes are calculated with thermodynamic and electrochemical data of relevant materials, resulting in a qualitative guide to the selection of effective catalyst and cathode compositions. The experimental research includes cyclic voltammetry, used to probe the surface electrochemistry of the catalytic process, and to shed light on how a correct theoretical understanding is restricted experimentally. A fuel cell based on direct hydrogen peroxide cathode has the following distinct advantages: i) Very high volumetric power density (several times higher than conventional H2/O2 fuel cells) due to direct utilization of a liquid phase oxidant at the cathode; (ii) The potential for a very high efficiency (over 60%) because the use of H2O2 overcomes the oxygen over-potential problem (slow O2 reduction kinetics) inherent to a H2/O2 fuel cell designs, which require simultaneous transfer of four electrons; (iii) Safe, and long time stable storage of the energetic materials for fuel cells in special environment (space, underwater, etc.). The measurement on open cell voltage, short-circuit current density shows an improved performance compared to a typical H2/O2 fuel cell, indicating a higher efficiency at similar discharge conditions.

[K1.218] Magic number silicon dioxide-based clusters: Laser ablation-mass spectrometric and density functional theory studies

The magic number silica clusters [(SiO2)nO2H3] with n=4 and 8 have been observed in the XeCl excimer laser (308nm) ablation of various porous siliceous materials. The structural origin of the magic number clusters has been studied by the density functional theoretical calculation at the B3LYP/6-31G** level. The DFT results of the first magic number cluster predict that the first magic number cluster (SiO2)4O2H4 and its anion [(SiO2)4O2H3] will most probably take pseudotetrahedral cage-like structures. To study the structural properties of the second magic number cluster, geometries of the bare cluster (SiO2)8, the neutral complex cluster (SiO2)8O2H4, and the anionic cluster [(SiO2)8O2H3] are fully optimized at the B3LYP/6-31G** level. These calculations predict that the most stable states for the complex cluster (SiO2)8O2H4 and its anion [(SiO2)8O2H3] are cubic cage-like structures with an O atom inside the cage.

[K1.219] General Physics

This abstract not available.

[K1.220] Progress in physics through small advances without paradigm change: Development of Smoluchowski's coagulation theory into a generic model of growth in contemporary physics

The well known scenario of progress in science is Kuhn's idea of "scientific revolutions" and change of "paradigm" of research associated with it. While the "revolutions" in science have received much attention, the counterparts of these illustrious events have been more on aside. Progress in science - notion well known to all scientists and also admitted by Kuhn - is not only, and perhaps not even mainly, through revolutions but instead through small advances through research conducted within established views and methods, within the "normal paradigm" of science. In contemporary physics there are several examples of the advance and genuine progress of this kind, without paradigm changes. Particularly rich of these examples is the field of statistical physics, where in many cases, the ideas and approaches can be directly traced back to research programs in the end of 19^th century or in the beginning of 20^th century. Here we have chosen to tell the story of certain development starting from 1916 end still continuing. It is the theory of kinetics of growth through aggregation. It originated in 1917 from Smoluchowski's research on kinetics of coagulation, but nowadays it has acquired more or less a basic theory for generic properties of many growing and interacting systems.

[K1.221] Practical considerations in the construction of pulseshapers for ultrafast spectroscopy

Optical pulseshapers play an important role in ultrafast spectroscopic techniques, and are widely implemented in many labs. Most commonly, pulseshapers consist simply of a grating, lens, and mirror with an adjustable slit in the focal plane. Pulseshaping is accomplished by truncating part of the spectrum, often leading to unwanted temporal satellite peaks. A dramatic improvement can be made by replacing the mirror/slit with a mask consisting of an array of microlithographically etched metallic lines for amplitude shaping. Along with phase masks, pulses can be almost arbitrarily reshaped. Here we present a method to computationally design masks. An output pulse can be determined for a given mask by convoluting the beam distribution in the Fourier plane with the mask. By inverting the procedure, a discrete mask pattern can be determined for a desired reshaped pulse. We also discuss practical issues in the design of the pulseshapers. Advantages of spatial light modulators are discussed, and the spectral filtering technique is compared to a recent acoustooptic temporal pulseshaping technique.

[K1.222] Erbium Doped Fiber Laser Modeling

A key component to developing lasers for use in technological applications (e.g. fiber optic telecommunications) is a fundamental understanding of the underlying physics. A physical model that can be used to predict relevant laser characteristics (output power, output wavelength, pulse length, etc.) is a vital part of this understanding.

The main goal of this project is to model the lasing process in erbium doped optical fiber (edf). The model involves equations that govern the erbium ion population dynamics and optical power propagation in the fiber. A computer program is being written to solve these equations numerically. This model will be used to study novel erbium doped fiber laser designs. The preliminary results of this project are presented here.

[K1.223] Experimental measurements and finite element models of High Displacement Piezoelectric Actuators.

Piezoelectric actuators have many applications including morphable wing technology and piezoelectric transformers. A Piezoelectric ceramic is a material that will move when a voltage is applied and conversely produces a charge when a pressure is applied. In our study, we examine THUNDER (Thin Layer Unimorph Ferroelectric Driver and Sensor) actuators (Thunder TM is a trademark of FACE International Corporation.) Thunder actuators are constructed by bonding thin PZT piezoelectric ceramics to metal sheets. We will present physical measurements of piezoelectric actuators, as well as measurements of the displacements due to applied voltages. In our studies we used a laser micrometer to measure the dimensional characteristics of four sizes of THUNDER actuators including TH-8R, TH-9R, TH-10R, and finally the TH-11R. We also developed computer models using a commercial fine element modeling package (FEM) known as ANSYS6.0®. This software enables us to construct our models controlling such attributes as exact dimensions of the three layers of the piezoelectric actuator, the material properties of each element, the type of load that is to be applied as well as the manner in which the layers are bonded together. The computer model compares favorably with the experimental results.

Acknowledgements: NASA Grant No. 0051-0078 Department of Defense (DoD) Control No.ISP02-EUG15

[K1.224] Geometry and Topology of Quamtum Dynamical Manifolds. Electroweak Many-body Systems.

E. Cartan's moving frame approach to differential geometry is used for describing the evolution of quasi-particle systems. Quantum dynamical manifold equations (QDMEs) are introduced and analyzed as a candidate geometrodynamical foundation for an ab initio, i.e., non effective field, theory of electroweak interactions. We show that so-called u(1)Xsu(2) color symmetric QDMEs can be interpreted along the lines of the Standard Model of elementary particle physics. A self-consistent calculation setup is presented where the Yang-Mills equations act as topological constraints on the conserved current for determining the gauge potentials. This approach allows computation of a Weinberg angle. The results also allow computing the Higgs-Anderson field and a mass renormalization without adjustable parameters. These results imply that there are different Higgs-Anderson fields for different symmetries. This approach is then generalized to a many-body theory. Initial results for the color algebra u(1)Xsu(2)Xsu(3) are reported.

[K1.225] Development of improved analysis of non-local electron parallel heat transport in divertor plasmas

Parallel electron heat transport in divertor plasmas is investigated. Our electron kinetic code "FPI" has been upgraded to take into account the hydrogen’s atomic physics, including 30 energy levels in the computation. This required important improvements in the numerical algorithms in order to run the code within a reasonable time and compute the effects of each inelastic process. Their effects on non-local transport and the large enhancement of the effective (i.e. including ionization via excited states) ionization rates in the cold plasma due to nonlocal transport will be presented. A non-local electron heat flow formula [1] has been adapted and implemented in the “UEDGE” code. Simulations using it were compared to runs made with the more traditional flux limited heat diffusion formula. Considerable differences were seen in the temperature profiles.

[1] F. Alouani Bibi and J.P. Matte, Phys. Rev. E 66, 066414 (2002)

[K1.226] Mossbauer Study of Uniaxial Anisotropy of Fe/Gd Multilayers

The presence of a uniaxial anisotrop (UA)is one of the fundamental requirements for materials of high density magneto-optic recording. For a better understanding of UA of the rare-earth transition-metal multilayers, a number of Fe/Gd samples were studied using Mossbauer spectroscopy. Multilayers of Fe/Gd, with single layer thickness of a few monolayers, were deposited by magnetron sputtering on polyester substrates at room temperature. The samples were characterized using x-ray, EDX, and SEM. Mossbauer measurements were made in the transmission mode using a cobalt-57 source. Two major magnetic structures and two non-magnetic structures were identified with Mossbauer measurement. The uniaxial anisotropy critically depends on the interface of Fe/Gd multilayers, and it shows a gradual increase as the Fe layer thickness decreases below a critical thickness. Details of the experimental findings, including the spin coupling at the interface, will be presented.

[K1.227] Molecular dynamics study of tethered polymers in shear flow: freely jointed and worm like chains.

The experimental study of the dynamics of single polymer molecules tethered to a solid surface in shear flow is now a reality due to videomicroscopy techniques. In order to better understand the observed dynamics in this system we use Molecular Dynamics computer simulations. We explicitly include solvent particles, giving us explicit hydrodynamic interactions. We examine the dynamical properties of a freely jointed chain in shear flow confined between two surfaces. The unstretched chain fraction increases like \dot\gamma^2/3 for strong shear rates \dot\gamma. In the region of large variance of the chain extension, we observe a cyclic motion (first experimentally seen by Doyle et al.). To complete the study, we also examine the nanoscopic regime by decreasing the distance between the surfaces to a few solvent particle diameters. Worm like chain are also studied using a similar approach.

[K1.228] Anomalous shift and attenuation of CO stretching vibrations in Ice/CO/Rh(111) by electron irradiation and heating

The adsorbed states of CO in Ice/CO/Rh(111) were studied by infrared reflection absorption spectroscopy (IRAS) and near-edge x-ray absorption fine structure (NEXAFS). The vibrational spectra show the anomalous shift and the intensity attenuation of CO stretching vibrations by electron irradiation with simultaneous heating. A possible change in the orientation of CO molecules on Rh(111) was examined using NEXAFS.

[K1.229] RECOMBINATION MECHANISMS IN UV LIGTH IRRADIATED KCl:Eu AND KBr:Eu

The defect production in alkali halide with doped divalent impurities and exposed to ionizing radiation can be explained by means of the creation of self-trapped excitons. It has been experimentally demonstrated that, when alkali halide crystals are exposed to non ionizing radiation such as UV (230 nm), Frenkel defects are generated. This is remarkable since 230 nm photons cannot directly produce excitons because their energy is below that of the excitons creation energy (7.7eV). We have investigated the recombination mechanisms with low energy UV light in alkali halides doped with Eu2+. TL and OSL techniques were used for studying comparatively the effects of both ionizing and non ionizing radiations associated to the creation of electron-hole pairs. We found that TL signals are strongly correlated with F centers and Fz centers. We also obtained evidence that the F center is involved in the OSL process. The results point to the existence of a common mechanism under ionizing and non ionizing radiation by means of a possible excitonic mechanism.

[K1.230] First-principles study of the high-spin to low-spin transition of iron in ferropericlase

Ferropericlase, (Mg, Fe)O, is widely believed to be a major phase in the lower mantle of the earth, coexisting with orthorhombic silicate perovskite, (Mg,Fe,Al)SiO3. Experiments on Mg/Fe partitioning at high pressures suggest that the FeO content in this ferropericlase phase lies in the range 10-20molthe earth¡¯s interior. Most recent experimental measurement of the spin state of iron in ferropericlase (Mg0.83Fe0.17)O at high pressure found a high-spin to low-spin transition, which is geophysically very important, occurring in the 60- to 70-gigapascal pressure range. In this study, the first-principles all-electron linearized augmented plane wave (LAPW) method within both GGA and LDA+U is employed to investigate this transition through total energy calculation for (Mg0.875Fe0.125)O. It is shown that the transition pressure (55Gpa) obtained from our calculations is in agreement with the experimental results. As well known, however, the insulating ground state can¡¯t be obtained within the GGA, which underestimates the local Coulomb repulsion. In order to correct it, LDA+U is considered in our calculations, and the insulating ground state under high pressure can be achieved even with small parameter U. Furthermore, the transition pressure can be obtained within LDA+U calculations.

Part K of program listing