Session R1 - Poster Session III.
POSTER session, Wednesday afternoon, March 05
Room Exhibit Hall 2/3, Austin Convention Center

[R1.001] Chemical Physics

[R1.002] On Planck

The production of Planckian shaped thermal emission spectra requires quantized energy levels. However, the nature of the physical species undergoing the transition between these energy levels has not yet been outlined. It is now stated that the transitions in Planckian Thermal Emission are performed by vibrating nuclei within the confines of an atomic lattice structure. It is impossible to obtain a Planckian shaped thermal emission profile if either the nuclei or the lattice is absent. Thus, gases are unable to produce Planckian shaped thermal emission spectra since they lack the structural constraint of an atomic lattice. Liquids possess fleeting lattices. As such, they can report Planckian shaped thermal emission spectra, but they report only an apparent temperature, not necessarily a real temperature. That is because their lattice are not sufficiently rigid. These observations are in fact the basis Kirchhoff’s law of thermal emission. If one desires to obtain a reliable temperature from a thermal emission profile the constraint set in Kirchhoff‘s law must be followed. Kirchhoff‘s graphite blackbodies acted by providing a nearly ideal rigid lattice. No lattice - no Planck.

[R1.003] Ensemble Dynamics with Quantum Forces

We present a new methodology for approximating the solutions of the time-dependent Schrödinger equation. Our approach is rooted in the de Broglie Bohm interpretation of the quantum theory in which the evolution of a quantum system is characterized by an ensemble of particle trajectories. The paths of these ``Bohmian'' particles are analogous to hydrodynamic trajectories and are determined by the presence of both classical and quantum forces in the system. The quantum force is due to the nonlocal interactions between particles and is related to the curvature of the quantum density. In the present study we invoke an expectation-maximization algorithm to approximate a functional form for the density of a finite ensemble of Bohmian particles. From this density information we then calculate a quantum force and propagate the system forward in time using a Verlet type integration. In what follows we will describe the details of this approach and present some numerical results.

[R1.004] Wavepacket Dynamics on Dynamically Adapting Grids: Application of the Equidistribution Principle

A moving grid approach to wavepacket dynamics is described that enables grid points to be used efficiently in regions where high resolution of the wavepacket is required. The grid movement is based on the principle of equidistribution and by using a grid smoothing technique the grid points trace a path that continuously adapt to reflect the dynamics of the wavepacket. The technique is robust and allows accurate computations to be obtained for long wavepacket propagation times. Results are presented for two systems: tunnelling dynamics in a double well potential and scattering of a wavepacket from a repulsive Eckart barrier.

[R1.005] Minimum Energy Structures of Ni, Au and NiAl Clusters: A Genetic Algorithm

The lowest energy structures of (Ni)_n, (Au)_n and (NiAl)_2n (with n up to 100) clusters were obtained through a genetic algorithm using the semi-empirical many-body Gupta potential to mimic the interatomic interaction. A variety of structure types are observed in all the three class of clusters, repeatedly appering the icosahedral structural motivs. Global minima are generally more difficult to find for bimetallic clusters than those for the pure element clusters.

Work supported by CONACyT-México under grant 35224-E.

[R1.006] Stability of Pyrimidine Nucleic Acid Bases with Respect to Intra- and Intermolecular Proton Transfer Reactions Induced by Excess Electrons

Chemically transformed nucleic acid bases are considered as sources of point mutations in genetic material. Our computational results and photoelectron spectra provide information about chemical transformations of pyrimidine bases induced by excess electrons. The isolated pyrimidine bases as well as their complexes with X (X= amino acid, carboxylic acid, or alcohol) have been studied with the B3LYP and MPW1K density functionals, as well as at the second order Moller-Plesset level of theory. The photoelectron spectra of some anionic complexes reveal broad features with maxima around 2 eV. These features cannot be associated with the anion of intact pyrimidine base solvated by X and indicate occurrence of chemical transformations. Our main findings are: (i) the excess electron attachment can induce a barrier-free proton transfer (BFPT) from X to the O8 atom of uracil or thymine, (ii) thymine in complexes with carboxylic acids is more resistant to BFPT than uracil, (iii) the instability of neutral rare tautomers of uracil or thymine can be significantly suppressed due to the interaction with zwitterionic amino acids.

[R1.007] Measurement of the lifetime and the electron transfer scavenging time of the p-state hydrated electron

Kinetics of the electron transfer scavenging reaction of the excited state hydrated electron in competition with non-reactive internal conversion is studied using femtosecond pump-probe spectroscopy. In pure water, transient absorption signal of the hydrated electron after optical excitation to the p-state has been assigned to internal conversion and solvation. In the presence of electron scavengers, however, the pump-probe data clearly exhibit a signature of the presence of an additional decay channel from the excited state due to electron transfer scavenging. Analysis of the pump-probe data with a multi-level kinetic model indicates that the time scale of scavenging upon optical excitation to the p-state is 300-400 fs. Based on spectral moment analysis on the non-equilibrium ground state hydrated electron, the scavenging after the optical excitation to the p-state occurs primarily from the p-state with insignificant contribution from the non-equilibrium ground state. This result suggests that the controversial lifetime of the p-state is several hundred femtoseconds rather than tens of femtoseconds.

[R1.008] First-Principles calculations of water adsorption at the defective anatase TiO2(101) surface

Water adsorption at TiO_2 surfaces is a crucial process in many applications of this material. The relative stability of the molecular vs. dissociated state has been recently clarified for rutile [1], where water dissociates exclusively at oxygen vacancies. An equally clear picture of water adsorption at the surface of anatase, which is more efficient in (photo)catalytic applications, is still lacking. Previous density functional calculations [2] have shown that the molecular state is always favored on the stoichiometric anatase (101) surface, irrespective of coverage. However, point defects, strongly affecting surface properties, can change this behavior [1]. We have studied the adsorption of water on a partially reduced anatase (101) surface by means of ab-initio molecular dynamics simulations. As in the rutile case, at the vacancy site dissociative adsorption, leading to formation of two bridging hydroxyls, is significantly more stable than the molecularly adsorbed state. The free energy barrier for dissociation has been determined to be \sim 440 K. [1] I.M. Brookes et~al., Phys. Rev. Lett. 87 (2001) 266103. [2] A. Vittadini et~al., Phys. Rev. Lett. 81 (1998) 2954.

[R1.009] Scattering of Methane by LiF(001)

A theory previously used to calculate the scattering spectra of acetylene from surfaces has been extended to treat the case of methane scattering from clean LiF(001). The theory uses a classical treatment of the exchange of rotational and translational energy between the molecule and the surface and the internal modes of the molecule are treated semiclassically. Results of calculations compare well with recent experimental measurements for the scattered angular distributions produced by well-defined incident beams, and also for the energy resolved spectra measured at fixed final angle. A number of predictive calculations are presented for quantities that could be measured in future experiments.

[R1.010] Photolysis and Radiolysis of Simple Ices

The Department of Physics and Astronomy at Northern Arizona University has recently completed the development of an ultra high vacuum analysis system to study the photolysis and radiolysis of ices. The investigation of these fundamental processes in ices have important applications in astrophysics, planetary astronomy and atmospheric physics. The system incorporates photoelectron spectroscopy, Fourier transform infrared spectroscopy and mass spectrometry as analytical techniques. The system also includes a closed cycle helium cryostat for the growth of the ice samples. Processing tools include x-ray and UV light sources and a low energy (up to several keV) ion source. The capabilities of this new system are described and XPS and FTIR results from several simple ices will be presented.

[R1.011] The Liquid Surface/Interface Spectrometer at ChemMatCARS Synchrotron Facility at the Advanced Photon Sources

In this poster we present experimental results obtained during the commissioning period of a new liquid surface x-ray spectrometer at the ChemMatCARS sector (Sector 15, undulator beamline, at the Advanced Photon Source, Argonne National Laboratory). The spectrometer was designed and developed for the investigation of interfacial phenomena and properties of a wide variety of liquid systems. These include studies of polarized liquid-liquid interfaces (Mark Schlossman, UIC), liquid metal-X interfaces (Stuart A Rice, U of Chicago, and Peter Pershan, Harvard, respectively), and Langmuir monolayers (Schlossman, UIC, and Ian Gentle, U of Queensland, Australia, respectively). These results demonstrate the initial capabilities and potential broad applications of this new instrument in the field of liquid surface/interface studies.

[R1.012] Anti-stokes photoluminescence of II-VI nanoparticles with different emitting states

Anti-stokes photoluminescence of II-VI nanoparticles with different emitting states

Birol Ozturk(a), Wei Chen(b), Yimg Wang(a), Nicholas Kotov (a) (a) Department of Chemistry, Oklahoma State University,Stillwater,OK 74078,USA (b) Nomadics Inc., 1024South Innovation Way, Stillwater, OK 74074, USA

Abstract

Anti-stokes photoluminescence (ASPL) in II-VI colloidal nanoparticles of CdTe and CdSe was studied in dispersions. The measurements showed that photoluminescence PL and ASPL were likely to originate from different although close-lying electronic states. Temperature dependence measurements between 10K and 300K showed that there is no thermal excitation step involved in ASPL emission. Emission intensity dependence on excitation intensity is linear which indicates deviation from the classical two-photon absorption mechanism. The ASPL excitation scheme involving a long-lived intermediate state is discussed.

[R1.013] Hot Electron Cooling Dynamics of Nanolithographcally Prepared Au Arrays

The relaxation dynamics of Au arrays prepared via nanosphere lithography were investigated1 using femtosecond pump-probe spectroscopy. The hot electron relaxation dynamics of arrays of truncated tetrahedra shaped 90 nm gold nanoparticles on glass, 50nm gold thin film, and gold nanodots in solution are compared. The initial relaxation (due to the electron-phonon relaxation) of the Au array is longer (2.9 ps) than the relaxation of the Au thin film (1.5 ps). The thin film system exhibited single component decay, while the nanodot solution displayed an additional longer decay due to the phonon-phonon relaxation or heat dissipation which is in the 80-100 ps range for the nanodots. The relaxation dynamics of the array particles are also investigated as a function of solvent interaction using toluene, pyridine, and water. The relaxation times show a dependence on the propensity and ability of the solvent molecules to interact with the particles. This is explained in the context of the differences in the relative rate of heat dissipation compared to the rate of electron-phonon relaxation in the different systems 1) S.Link, D.J Hathcock, B. Nikoobakht, M.A. El-Sayed, “Medium Effect on the Electron Cooling Dynamics in Gold Nanorods and Truncated Tetrahedra” Submitted to Advanced Materials

[R1.014] Probing the Mechanism of Excited-State Evolution in a Transition Metal Complex

Femtosecond electronic transient absorption spectroscopy is being used to explore excited-state relaxation in simple transition metal complexes. Cr(acac)_3 (where acac is acetylacetonate) presents a typical case, where the lowest-energy absorption feature does not correspond to the lowest-energy excited state of the molecule. Following ~100 fs excitation into this ^4T ligand-field state, we observe the formation of the lower energy ^2E state with a time constant of ~1 ps. These dynamics represent in principal a combination of vibrational relaxation on the ^4T potential energy surface, intersystem crossing to the ^2E, and vibrational relaxation once the ^2E is formed. Conventional photophysical models would hold that these decay processes are well-separated in time, with vibrational cooling being significantly faster than intersystem crossing. However, it is becoming increasingly clear that excited-state evolution in inorganic systems does not adhere to this picture. Results from variable-pump/ variable-probe wavelength measurements will be presented which are helping to differentiate these various processes in Cr(acac)_3 and other related Cr(III) systems.

[R1.015] Preparation and characterization of Carbon-Polyvinylchloride composites

Composite materials have a big importance in many areas of science and technology because of their special properties. In this work, carbon-polyvinylchloride (C-PVC) composite was made by dispersing carbon powder in a PVC matrix. The physical and chemical properties of C-PVC composite allow us to use it as amperometric sensor of organic, inorganic substances or metallic compounds in a very low level of concentration. Morphological and structural characterization by SEM, EDS, AFM, TEM, and XR of C-PVC composite have shown that the composite works with a large effective surface area. Some physiological applications are discussed.

[R1.016] DSCF Study of Block Copolymers at Sheared Polymer Blend Interfaces

The dynamic self-consistent field (DSCF) theory, originally formulated for unentangled polymers, has been recently extended to entangled chains. The DSCF theory couples the time evolution of chain conformations, volume fractions and momenta, based on local conservation laws. A modification of the lattice random walk formalism of Scheutjens and Fleer is used to generate anisotropic chain conformations under flow. Here we present a DSCF study of the interfacial properties, such as velocity slip, interfacial viscosity and chain stretching, and explore how they are affected by the presence of block copolymer. We have studied both unentangled and entangled regimes and compared with experiments and other models when applicable.

[R1.017] The correlation length of an eight-arm polystyrene in methylcyclohexane near the critical point

The turbidity of eight-arm polystyrene in methylcyclohexane has been measured and used to determine the correlation length amplitude \xi_0. 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 = 0.604 \pm 0.010 nm for this branched polystyrene with a total molecular weight of 74,000. This value of \xi_0 is less than that reported in the literature for a linear polystyrene of the same molecular weight in methylcyclohexane. Support for this research was prvoided by NSF-REU 9987850 and NASA grant NAG8-1433.

[R1.018] Photophysics of Conjugated Polymers Aligned in a Nematic Liquid Crystal Host

It is of interest to develop new kinds of anisotropic optical materials. To this end, we have studied the orientation and the photophysics of a non-linear dye, N’,N’-Bis (2,6 dimethylphenyl)-3,4,9,10, perylenetetracarboxylic dimide (PERY), and a conjugated polymer, poly[2-(2’ethylhexyloxy)-5-methoxy-1,4-phenylenevinylene] (MEH-PPV), in a low molecular weight nematic liquid crystal matrix, 4-n-pentyl-4’-cyanobiphenyl (5CB). The dye was incorporated into the liquid crystal using the ‘guest-host’ method. A solvent-induced homogenous mixing (SIHM) technique was developed to embed the polymer into the liquid crystal matrix. Order parameters were obtained from polarized absorption and fluorescence spectra. The dynamics of intra- and interchain energy transfer in the aligned conjugated polymer samples will be reported.

[R1.019] Vibrational relaxation of photoexcited heme in Mb

Photoexcited heme shows a broad, red-shifted absorption spectrum. Relaxation of the "hot" photoproduct spectrum is well described using independent timescales for narrowing (400 fs) and blue shifting (0.4-4 ps) as the system returns to equilibrium. The vibrational relaxation pathway in Mb is explored by using samples with a modified local heme environment (e.g., His93->Gly mutation and protoporphyrin IX->porphine substitution). The His93->Gly mutation experiment demonstrates that the covalent bond between the iron and the proximal histidine has little effect on the overall vibrational relaxation of the "hot" heme. In contrast, the protoporphyrin IX->porphine substitution experiment demonstrates the importance of the van der Waals contacts between the heme and the protein/solvent matrix in cooling the locally hot heme.

[R1.020] Ultrafast Localization Dynamics and Evolution of the Spatial Extent of Solvated Electrons in D_2O/Cu(111)

Time- and angle-resolved two-photon photoelectron spectroscopy (2PPE) is used to investigate femtosecond dynamics of electron localization and solvation in ultrathin ice layers adsorbed on Cu(111). Electrons, optically excited in the metal, transfer into the conduction band of the ice layer giving rise to a feature e_CB in the angle-resolved 2PPE spectra. Electrons localize within the first 50 fs to form a state e_S at 2.9 eV above the Fermi level. The initially positive dispersion of the first moment of e_S and e_CB shows pronounced changes with time, which indicates a transition from a delocalized to a localized state. After 200 fs an apparent negative dispersion is observed for the localized state, which contains information about the momentum distribution of the localized state with width \Deltak. Model calculations, which describe the angle-resolved spectra, lead to the conclusion that \Deltak changes with the binding energy and is related to the spatial extent of the solvated electron, as will be discussed in detail.

[R1.021] Ultrafast Excited State Dynamics and Structures in Self-Assembled Molecular Aggregates of Helicenocyanines

A series of novel phthalocyanines – with and without Zn metallated cores – that have helicene groups substituted on the periphery were investigated. These compounds exhibit a tendency to self-assemble into molecular aggregates (likely dimers) even at very low concentrations (10^-7 M) in common organic solvents. This aggregation dramatically alters their optical properties compared to the monomer. New and/or reshaped absorption bands broaden coverage throughout the UV and visible regions. Emission measurements suggested an intramolecular coupling between the helicene groups and the Pc core. Transient absorption results indicated a fast (several hundred fs) process that may be related to a coherence effect in the excited state. X-ray techniques provided insight on the size distribution of the aggregates and the coordination of the Zn center. Work at ANL was supported by the US Dept of Energy, Office of Basic Energy Sciences, Division of Chemical Sciences, under contract W-31-109-Eng-38

[R1.022] Using pulsed X-ray diffraction to study protein dynamics with picosecond time resolution

With the advent of third-generation synchrotron sources, diffraction data useful for X-ray structure analysis can be acquired with exposure times shorter than 100 ps. An application of this time resolution is the study photochemical reactions that can be triggered in a crystalline sample by a laser flash. For this purpose, the ID09 beamline of the ESRF was equipped with a high-speed mechanical chopper to isolate single X-ray bursts from the pulse train of the synchrotron and a mode-locked laser that is phase-locked to the synchrotron, to obtain the necessary timing accuracy. We studied the oxygen storage protein myoglobin, with the aim of finding the escape pathway of the oxygen from its binding site, which is not obvious from the known X-ray structures. By using CO as a substitute for oxygen, we could take advantage of the photosensitivity of the Fe-CO bond to trigger the ligand release by a laser. The L29F mutant of myoglobin proved to be an interesting test case, because it shows ligand dynamics correlated with conformational changes of the protein on a time scale of 100 ps.

[R1.023] Superconductivity

[R1.024] New Robust Statistical Mechanics for High-Temperature Superconductors

The new statistical "complete boson-fermion model" (CBFM) of superconductivity [1] -in which both the BCS and BEC theories are contained as special cases- is used to calculate the superconductor transition temperatures T_C in both 2D and 3D systems. The model includes both two-electron and two-hole pairs in freely variable proportions, along with unpaired alectrons. For perfect electron/hole-pair symmetry and weak coupling one has BCS theory; for no hole-pairs and no unpaired electrons one gets the BEC T_C-formulae. Using the BCS model interaction for electron-phonon coupling and with no adjustable parameters the calculated T_C's compare well with experimental data, provided only that one departs moderately from perfect electron/hole-pair symmetry. These T_C's are also predicted in both 2D and 3D to be higher for hole- than for electron-superconductors, in agreement with general empirical trends.

[1] V.V. Tolmachev, Phys. Lett. A 266, 400 (2000); M. de Llano and V.V. Tolmachev, Physica A 317, 546 (2003)

[R1.025] Magnetotransport in NdNi_2B_2C and PrPt_2B_2C single crystals

Transport and magneto resistance measurements have been performed in NdNi_2B_2C and PrPt_2B_2C single crystals. In this study, we present susceptibility and resistivity measurements in the ab-plane and c direction from 2 K to 300 K. Magneto resistive behavior was studied from 0 to 8 Tesla. In NdNi_2B_2C, the magnetoresistance is negative below of the Neel temperature, T_N \sim 4 K, when H is parallel to the ab plane, and is positive with H\parallel c direction. Above T_N, the magnetoresistance shows positive values. At higher magnetic field and high temperature the contribution is positive, in both directions. PrPt_2B_2C shows no magnetic order at any temperature and is superconducting with T_c = 6 K. In this crystal we also determinate the upper critical fields H_c2.

A. Durán acknowledges a scholarship from IIM-UNAM. R. Escudero acknowledge financial support from CONACyT for grant G-0017; and UNAM-DGAPA, project No.IN-105597.

[R1.026] The Specific Heat of UGe_2: Effects of Pressure and Magnetic Field

At ambient pressure (P) UGe_2 undergoes transitions from paramagnetic, to ferromagnetic (FM), to coupled charge-density wave (CDW) spin-density wave (SDW) phases on cooling. Within a narrow range of P, and at temperatures (T) below \sim0.7 K (but depending on sample quality), superconductivity (SC) coexists with both the CDW-SDW and FM phases. The \gammaT term for the specific heat (C) increases with increasing P, most rapidly between \sim1 and \sim1.4 GPa, the region in which SC develops, then approaches a constant value at 1.8 GPa. The \gammaT term decreases in a magnetic field. In the CDW-SDW region of the phase diagram C includes an exponential term that represents the CDW-SDW and decreases in a magnetic field. The electronic entropy increases rapidly in a narrow interval of P in the vicinity of the CDW-SDW transition, which suggests that it might be broadened first order. A transition to SC is not observed to 0.35 K in the range of P where it is expected to occur, but there are upturns in C/T, absent at other P's, that suggest the onset of SC.

[R1.027] Anomalous Hole-Concentration Dependence of the Hall Coefficient of Oxygen-Intercalated La214 Superconductor

The Hall coefficient of La_2CuO_4+d was measured at room temperature and 77.4 K for d = 0.015 - 0.110. The behavior of the Hall number (p_H) defined as a quantity inversely proportional to the Hall coefficient as a function of the hole concentration p^+ was quite different from that of La_2-xSr_xCuO_4. The p_H at room temperature showed jumps at p^+ = 0.065 and 0.107 which accompanied an integral ratio change in p_H/p^+ such as 1.2 : 2.3 : 3.6, being close to 1:2:3. Above p^+ = 0.107, however, p_H decreased with increasing p^+, which indicates the localization of the holes. The anomalous changes were less distinctive at 77.4 K. The two anomalous points at room temperature are very close to the hole concentrations for the two-dimensional Wigner lattice formation of 4x4 (p^+ = 0.0625) and 3x3 (p^+ = 0.111), which was recently proposed from the optical reflectivity measurements of La_2-xSr_xCuO_4+d by Y.H. Kim and P.H. Hor [Modern Physics Letters B15, 497 (2001)]. Thanks are due to the Hokkaido Tokai University Shigeyoshi Matsumae Memorial Foundation, NSF (DMR9122043), ARPA (MDA972-90-J-1001), the Robert A. Welch Foundation (E1207), and the state of Texas.

[R1.028] Thermoelectric Properties of 123 superconductor with Europium rare earth at low temperatures

In this work we studied the thermoelectric properties in the superconductor 123 compound with rare earth Europium. We have measured a variety of its properties at low temperature, including thermoelectric power, electrical conductivity and thermal conductivity as a function of temperature and oxygen contents. We show the calculated curves of the thermoelectric figure of merit, resulting from those data.

[R1.029] Magnetic Exchange Interactions of Quaternary Intermetallic Superconductors

The magnetic exchange interaction constants J_ex^par for parallel to the c-axis (H//c) in quarternary intermetallic superconductors, RNi_2B_2C (R = rare earth elements), were estimated by substituting the anisotropic Weiss-temperatures (for magnetic field, H , parallel or perpendicular to c-axis), where J_ex^per(for H is perpendicular to c-axis) of R^+3 ions sublattice in RNi_2B_2C is assumed by that of Ho^+3 ions one. The magnetic susceptibility, \chi , showed the Curie-Weiss behavior at the high tempearture regions and two different Weiss-temperatures. From the high-temperature series expansion of \chi(T)¡¯s and the anisotropic Weiss temperatures, the magnetic exchange interaction constant J_ex^par of each R^+3 ions sublattice in RNi_2B_2C (R= Tm, Er, Ho, Dy, and Tb)were obtained. The magnetic ordering in these compounds at high temperature regions will be compared with the previous crystalline electric field effect results.

[R1.030] Temperature Dependence of the Raman Spectral Peaks for a Magnesium Diboride Superconductor

The recently discovered magnesium diboride (MgB2) polycrystalline superconductor has again stimulated the interest in conventional BCS superconductors that, as opposed to most high-temperature superconductors, can possess the high levels of critical current density so essential for magnetic field applications of superconducting materials. However, much remains to be learned about the structural mechanisms behind the magnesium diboride superconducting system. One of the most useful tools for an analysis of the structural features most involved in phonon-mediated superconductivity is the technique of Raman spectroscopy. In this study, we have collected the Raman spectra of a magnesium diboride polycrystalline superconductor over a large range of wavenumber shifts at temperatures ranging from 18K - 300K. We have observed the conventional gradual softening of the major Raman-active phonon mode with an increase in sample temperature. Immediately above and below the critical temperature (measured as around 38 K onset for our sample) we collected the spectra at a finer grid of temperatures in order to more accurately observe the specific phonon mode shifts as the sample passed through the superconducting transition. The Raman spectra were collected over multiple averaged scans with a GaAs PMT and a Triax 550 spectrometer equipped with a holographic Super-Notch Plus filter and were excited with 150 mW of 4880Å argon ion laser radiation at the sample surface. These spectra have provided us with further insight into the specific phonons responsible for the mediation of the Cooper pairing of the electrons on which BCS superconductors are inherently dependent.

[R1.031] Excitation-wavelength and temperature dependence of Raman-active phonons in the spin-ladder system Sr_14-xCaxCu_24O_41, \itx =0, 6, 9.

The so-called spin-ladder compound Sr_14-xCaxCu_24O_41 contains alternating layers of CuO-chains and quasi 1D two-legged CuO ladders. It support superconductivity at high pressure and heavy doping, but also temperature and doping dependent antiferromagnetism and lattice instabilities. The spin-ladder system may thus provide important information on the interplay between spin, electronic and lattice excitations in strongly correlated systems in general, including the conventional high-T_c cuprate superconductors. Here, we report on a Raman scattering study of undoped and moderately doped Sr_14-xCaxCu_24O_41. The chain-polarized Raman spectrum exhibits a complicated pattern of one- and two-phonon modes that renormalize below \sim200 K, signaling a lowering of the lattice symmetry possibly induced by charge ordering effects. Furthermore, the phonon spectrum is strongly dependent on excitation wavelength, demonstrating the resonant character of these modes. The resonance effect is qualitatively similar to what has been observed in the high-T_c superconductor Y123, indicating a common origin in electronic excitations localized to the CuO-chains.

[R1.032] Analysis of electronic structure of selected ruthenocuprates by electron energy loss spectroscopy

Te distortions and defects in the RuO_2 sublattice of RuSr_2RECu_2O_8 (RE=Gd, Eu)(Ru-1212)can affect not only the magnetic properties but also the inter-layer charge transfer in this compound.Microscopic origin of the differences, and relationship between microstructure and electronic structure of the superconducting and non-superconducting Ru-1212[1] are investigated by electron energy loss spectroscopy (EELS) in a transmission electron microscope. The EELS analysis of related SrRuO_3 revealed the correlation between changes of the Curie temperature and the electronic structure manifested as the Ru M- (L-) ionization edges and the O K-edge in EEL spectra, as well as changes in composition achieved by different annealing. In this study, interplay between the Ru M and L-edges and Cu L-edges and O K-edge will be discussed.

[1] P.W. Klamut et al. Physica C, vol 341-348, 455 (2000) This work is supported by NSF-DMR-0105398 and by the State of Illinois under HECA. Work at Argonne is supported by the US Department of Energy, Basic Energy Sciences-Materials Sciences, under contract #W-31-109-ENG-38.

[R1.033] Spectral Properties of Systems Near Metal-Insulator Transition: Coherence-Incoherence and Dimensional Crossover

We have studied single-particle excitations in ARPES in several layered systems (Sr_2RuO_4, NaCo_2O_4 and (Bi,Pb)_2M_3Co_2O_9 where M=Ba, Sr) that display a crossover in the c-axis transport, from insulating-like, at high temperatures, to metallic-like at low temperatures, while being metallic over the whole temperature range in the plane. We have found sharp, quasiparticle-like excitations in the low-temperature 3D-like phase, and their absence in the effectively 2D, high-temperature phase. Similarities with phenomena seen in high temperature superconductors will be discussed.

This work was supported by the DOE under contract number DE-AC02-98CH10886.

[R1.034] Gap anisotropy and defect induced local density of state modulation in YBa_2Cu_3O_7-\delta

Taking into account gap anisotropy and a weak and extended defect, we calculate the modulation of energy-dependent local density of states for cuprate superconductor YBa_2Cu_3O_7-\delta (YBCO). These are observable by scanning tunneling experiment. When there exists a sub-dominant s-wave component in addition to dominant d_x^2-y^2-wave gap, quasi-one-dimensional-like modulations are obtained which are most conspicuous at higher biases and easily understood by the local nesting effect for a Fermi liquid. If the proposed modulations are observed, it would lead to a unified picture among angle-resolved photoemission, inelastic neutron scattering, and scanning tunneling measurements that YBCO is a good ``Fermi liquid'' with a sub-dominant s-wave component in the superconducting gap.

[R1.035] Interaction of Ferromagnetism and Superconductivity in multilayers

We investicate the interaction of Ferromagnetism and Superconducttivity in multilayer system in two limits: First, when Nd \gg L we find spontaneous pancake vortices in each superconducting layer or Josephson vortices according to whether the magnetization m is perpendicular or parallel to the layers. Here N is the total number of layers, d is the interlayer spacing, and L is the linear size of layers. We then argue how this model can be applied to the superconducting weak ferromanet material. Secondly, when Nd \ll \Lambda we find width of the spontaneous stripe domain structure becomes much smaller compared with the bi-layer sysmtem. Here \Lambda=\lambda^2/d is the effective pentration depth and \lambda is the bulk London penetration depth in layers.

[R1.036] Magnetic resonance in RuCu1212: a mixed valency issue

99Ru Moessbauer (MES) experiments on Ru2Sr2GdCu2O8 (RuCu1212) have been performed by DeMarco et al.[1] The MES results are inconsistent with mixed valency, as suggested by NMR studies.[2] The MES hyperfine (hpf) field is ~58 T, indicating a high-spin Ru state (S=3/2) with a 5+ valency. The isomer shift indicates a 4.5+ Ru state. SrRuO3 MES results show a hpf field of ~33T and a 4+ valency with a low spin Ru state (S =1). In RuCu1212 MES, no such 4+ Ru state is observed. For RuCu1212, the linewidths of the sharp MES lines are close to the theoretical lower limit. If electron motion occurs for mixed valent Ru, this must be fast, otherwise line broadening should have been observed. However, fast electron hopping requires also hpf fields of roughly 45 T, which are not observed. NMR [2] shows a sharp 60-T subspectrum and a very broad 30-T subspectrum. The above MES data donot show a 30-T subspectrum. Thus, RuCu1212 powder magnetic resonance studies suggest that RuCu1212 contains another phase, likely to be associated with the 30-T NMR subspectrum. Such studies on aligned powder or single crystal RuCu1212 may prove otherwise. [1] DeMarco, Boekema et al, Am Phys Bull 45 (2000) 729, and DeMarco, Tallon et al, Phys Rev B65 (2002) 212506. [2] Tokunaga et al, Phys Rev Lett 86 (2001) 5767, and Kumagai et al, Phys Rev B63 (2001) 189509. Research is supported by NSF-REU, NHMFL and WiSE@SJSU.

[R1.037] Evolution of spin structure under magnetic field in Nd2CuO4

We use neutron diffraction to study magnetic field effect on magnetic ordering in the parent compound of electron doped cuprates superconductor Nd2CuO4. Previous work has mostly focused on effect of a magnetic field alinged within the CuO2 planes. In view of recent work on superconducting Nd1.85Ce0.15CuO4, we have decided to determine the effect of a c-axis aligned field on Nd2CuO4. In zero field, Nd2CuO4 exhibits noncollinear antiferromagnetic ordering below 270K (TN1) and two spin reorientation transitions at 70 (TN2) and 30 (TN3) K, respectively. When we applied magnetic field perpendicular to Cu plane, we confirmed that there is no change for the magnetic Bragg (1/2,1/2,0) and (1/2,3/2,0) below TN2. However, we observed slight enhancement of (1/2, 3/2, 0) at 100K (phase I) above H=4T. The significance of these results in relationship to the superconducting Nd1.85Ce0.15CuO4 will be discussed.

[R1.038] Entangled electron current through normal-superconductor interfaces

We study the tunneling current emitted from a BCS bulk superconductor into a bulk normal metal through an interface with a finite area, within the limit of vanishing temperature and voltage bias. We derive a local 3D tunneling Hamiltonian which accounts for the different hopping behavior at various electron energies. The equivalence between the pictures of two-electron emission and Andreev reflection is established. We analyze the radial dependence of the density current for different contact radii and barrier heights, and identify several transport regimes. We also calculate the current through two small orifices at a certain distance. Our prediction for the dependence of current on distance differs markedly from those based on calculations which implicitly assume energy independent hopping. Our formalism provides a method to compute transport properties through extended NS interfaces with arbitrary hole shape within the tunneling regime.

[R1.039] Magnesium diboride wire application to high power superconducting dc cables

In 1967, R. L. Garwin and J. Matisoo considered the possibility of constructing a 100 GW, 1000 km, dc superconducting transmission line based on the then newly discovered type II material, Nb_3Sn, refrigerated by liquid helium at 4.2 K.^1 Their paper is viewed by many as the seminal study on the practicality of superconductivity for use in electric transmission cables, and influenced the design of the high temperature superconducting cables now undergoing demonstration worldwide refrigerated by liquid nitrogen, although at much lower power capacities due to the high cost of high temperature superconducting wire. However, the recent discovery of the 39 K MgB_2 superconductor and its promise of cheap, high performance wire may enable the multi-gigawatt capacity transmission line Garwin-Matisoo envisioned. In this presentation, we will rescale their study for MgB_2 cooled by liquid hydrogen at 21 K, which will be used as an additional energy delivery agent as well as a cryogen.

^1R. L. Garwin and J. Matisoo, Proc. IEEE 55, 538 (1967).

[R1.040] Insulators and Dielectrics

[R1.041] Electrical Conductivity in Insulator

ABSTRACT

In insulating solid(Plastic Sheet)of 0.73mm thickness, the conduction process was ohmic at low D.C. electric feilds, but the feild strength increased the conductivity became feild dependent at high feilds and it exhibited some conductivity and the variation in conduction current was none-ohmic.The mechanism of electron transfer between two metallic electrodes separated by insulating material has received considerable attention. The electron transfer current was studied on 0.73mm plastic sheet and(I-V),(log I-log V),(log J-E^1/2)and (log o- 1/T) relations have been studied and the value of slope,electronic dielectric constant and activation energy for nature of conduction mechanism and process have been determined.The electrical conductivity measurements were carried out at room temperature (32.5 celcius)under high D.C. electric feilds of the order of 10^6 volt/meter.The sample of insulator(plastic sheet) was sandwiched between the aluminium electrodes of designed experimental cell,The effect of very high varying feilds at 32.5 celcius temperature,the electrical conduction has been proposed on the data obtained.The non-ohmic behavior in the sample seemed to start at an electric feild 3x10^6 volt/meter.In this case on data obtained it was concluded that "SCHOTTKY EMISSION MECHANISM" has been proposed. The activation energy was calculated by plotting(log o-1/T)characterstics at running temperature and it was found 0.325ev which is less than 1.0,It confirms predominance of Electronic Conduction. I=current in ampere V=volt T=temperature O=conductivity

[R1.042] In situ USAXS studies of nano-particle growth in a premixed flame.

Combustion of organo-metallic or halide vapors and aerosol liquid sprays can be controlled to produce enormous quantities of nano-structured powders. Such flame processes are common in the production of fumed silica, and pyrolytic titania on an industrial scale with primary particle sizes on the order of 10 nm. These nano-particles are typically connected through sintering bridges, ionic bonds or van der Waals forces into ramified, mass-fractal aggregates. The study of this promising technology for nano-particle production has been hindered by the kinetics of particle growth, typically on the order of milliseconds, at high temperature, 2000°C. Using synchrotron radiation and specialized scattering instrumentation capable of simultaneously measuring nano- to colloidal scales (1 nm to 1µm) we demonstrate the feasibility of in situ growth studies in these systems and were able to follow in situ the growth of silica nanoparticles, namely the evolution of primary and agglomerate particle diameter and mass fractal dimension df.

[R1.043] Dosimetric properties of new europium doped KBr phosphors

In this work, dosimetric properties of new sintered europium-doped KBr phosphors subjected to beta irradiation are investigated. The obtained results show that these phosphors exhibit promising thermoluminescence properties that made them a viable alternative to substitute the conventional alkali halides crystals of similar composition for dosimetric purposes, considering as important advantages the simplicity and economy of the fabrication. The thermoluminescence response shows a linear dose dependence up to order of some Grays, which is higher than the linearity presented by the crystals of similar composition. Also, the thermoluminiscence fading is stabilized faster than that of the crystals do.

[R1.044] NEGATIVE POISSON'S RATIO IN CRYSTALS WITH JAHN-TELLER PHASE TRANSITIONS

Microscopic theory of the negative Poisson's ratio in crystals with structural phase transitions is developed. Analysis is presented for the dielectric crystals undergoing structural phase transitions from the tetragonal to the orthorhombic phase. The dysprosium vanadate type crystals are considered as an example. In such a type of crystals the structural phase transition may be induced by the external uniaxial pressure applied along the tetragonal axis. The mechanism of the structural phase transition is based on tuning up the energy gap between the ground and excited Kramers' doublets of the dysprosium cation. As a result of the gap variation the electron correlation caused by the virtual phonon exchange may be reduced or enhanced and the critical temperature is decreased or increased correspondingly. The pressure along the tetragonal axis compresses (expands) the crystal along the z-axis, simultaneously inducing the compression (expansion) in one of the x,y-axes in the crystal plane. The connection between the Poisson's ratio and the microscopic parameters (the electron-strain interaction constants, the phonon exchange strenth) is found. The temperature dependence of the Poisson's ratio is calculated.

[R1.045] Quantized and Limited Distances Between Nuclear Particles in Atoms and Beams, Between Atoms in Molecules, in Nanostructures, in Bodies and Beams, Due to the Electron Positron Lattice (Epola) Structure of Space.

Each epola unit cube (edge 4.4 fm) expands when entered by a moving guest nuclear particle and contracts when left by it. Thus the involved epola particles vibrate with frequency proportional to the velocity (v << c) of the guest particle. These vibrations create electro-magnetic (EM) waves of de Broglie Wavelength (dBW), spreading in the epola with the speed of light. Their interference creates the Accompanying Wave (AW) of the motion, a wave-guide-like channel in the epola, pre-formed for the unresisted motion of the guest particle. Starting a motion requires pumping of "inertial" energy from the guest particle to the epola to create the AW; on stopping, the inertial (kinetic) energy is pumped back. Being a physical entity, the AW has a cross-section width able to resist the penetration into it of AW's of other moving guest particles, causing quantizations and limitations of distances between particles. For stability, an electron orbit length must contain an integral number of dBW's of the electron. Only then are the AW's of each circling of the electron identical to the AW's of all previous circlings. They thus create a rotating standing wave pattern with no centripetal acceleration of the electron, contained in one of the half-wave loops of the pattern. References: M.Simhony, Invitation to the Natural Physics of Matter, Space and Radiation, World Scientific, 1994 (292 pp.). ISBN 981-02-1649-1. Website: www.word1.co.il/physics

[R1.046] Electronic structure and poling characteristics of NaBiTiO3 system

The electron structure of the NaBiTiO3 system with ABO3 type perovskite structure was studied by using self-consult charge-discrete variation-X¦Á(SCC-DV-X¦Á)method, and the effect of A, B position substitute on poling characteristic was also analyzed. The results show that spontaneous polarization is existed in the NBT piezoceramics system, the piezoelectric properties are enhanced because of the displacement of the B position ions, the compound substituent of Ba, Sr and Mn ion can decrease coercive field, and increase the strength of spontaneous polarization, so the dielectric properties are improved.

[R1.047] First-principles analyses of the defect stability in Sn-doped indium oxide

First-principles calculation has been performed to investigate the stability of the defects in Sn-doped indium oxide (ITO). Stability of the defects was calculated as a function of chemical potentials of the constituent atoms of ITO and Fermi energy of electron, where we investigated several different defects beside the ones studied previously by the experimental techniques. As a result chemical potential region of oxygen to crystallize the In_2O_3 was found to be almost the same as that of SnO_2, which explains the physical reason why high efficient doping of Sn atom to In_2O_3 crystal can be realized without causing precipitation of SnO2-like complexes and solid elemental Sn. Moreover, different from a suggestion based on the previous experimental analysis, the strongly bound complex composed of the Sn atom which is surrounded by three nearest oxygen atoms at regular site and an interstitial oxygen atom at quasi-anion site was suggested to be most stable under the condition of high Fermi energy. Then, density of states analysis showed that this stable defect made impurity levels around top of valence band, which suggests that this defect is a origin of the carrier compensation for the ITO films with very low resisitivity.

[R1.048] Dosimetric characterization of chemical-vapor-deposited diamond film irradiated with UV and beta radiation

Diamond is an excellent prospect for clinical radiation dosimetry due to its tissue-equivalence properties and being chemically inert. The use of diamond in radiation dosimetry has been halted by the high market price; although recently the capability of growing high quality polycrystalline has renewed the interest in using diamond films as detectors and dosimeters. In the present work we have characterized the dosimetric properties of diamond films synthesized by using chemical vapor deposition. The thermoluminescence (TL) of UV and beta exposed samples shows a glow curve composed of at least four peaks; one located around 587 K presents excellent TL properties suitable for dosimetric applications with ionizing and non ionizing radiation. The TL excitation spectrum exhibits maximum TL efficiency at 220 nm. The samples show regions of linear as well as supralinear behavior as a function or irradiation dose. The linear dose dependence was found for up to sixteen minutes of UV irradiation and 300 Gy for beta irradiated samples. The activation energy and the frequency factor were determined and found in the range of 0.32 - 0.89 eV and 1.1x10^2 – 2x10^8s_-1, respectively. The observed TL performance is reasonable appropriate to justify further investigation of diamond films as radiation dosimeters.

[R1.049] Defects production in UV alkali halides doped with europium

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 (STE), which are formed by either the excitation of halogen ion or trapped electrons in V_K centers coming from prior halogen ion ionization. Radiative recombination of self-trapped exciton produces a characteristic excitonic luminescence and no radiative recombination causes Frenkel defects (F-H centers). In the present work we provide experimental evidence that indicates that same crystals when exposed to a non ionizing radiation, such as UV near to 230 nm, similar Frenkel defects are generated. This situation is remarkable since 230 nm photons (5.3 eV) cannot directly produce excitons because their energy is below of the creation excitons energy around 7.7 eV. Thermoluminescence and optically stimulated luminescence techniques were used for investigating comparatively the effects of both ionizing and no ionizing radiations. We found that for ionizing and non ionizing radiation the luminescence signal was composed by two bands; the main part of the luminescence response was a broad band centered at 420 nm, which is ascribed to the well known energy transition 4f^65d(t_2g)-4f^7(^8S_7/2) of Eu_2+ ion and other additional band near to 460 nm which it has perhaps an intrinsic origin. In addition, we addressed the participation of the F and F_Z centers in the TL and OSL processes. In this way, we found that TL signal are strongly correlated with F centers (470 K TL peak in KCl:Eu_2+) and F_Z centers (370 K TL peak). Furthermore, through a selective photostimulation process, we also obtained evidence that the F center is involved in the OSL process. The present results point the existence of a common mechanism for the formation of Frenkel defects under ionizing and no ionizing radiation, by means of a possible excitonic mechanism.

[R1.050] Comparative study of elastic constantd of \alpha-, \beta- and Cubic- silicon nitride

Silicon nitride is an important structural ceramic and dielectric insulator. Recently, the new high pressure cubic phase of silicon nitride in spinel structure has attracted a lot of attention.^[1] We have carried out a detailed ab-initio calculation of all independent elastic constants for all three phases of Si_3N_4 by using the Vienna Ab-initio Simulation Package (VASP) in both LDA and GGA approxmations. The results for \beta-Si_3N_4 are in reasonable agreement with a experimental measurement on single crystal samples.^[2] For cubic-Si_3N_4 , The three independent elastic constants are predicted to be C_11 = 504.16 GPa, C_12 = 176.66 GPa, C_44 = 326.65 GPa and a bulk modulus B = 286 GPa. This value is very close to the experimental value of 300 GPa.^[1] All these results will be compared with those obtained by using the OLCAO method based on localized orbital approach.^[3]

[1]. Wai-Yim Ching, Yong-Nian Xu, Jukian D. Gale, and Manfred Ruhle, J. Am. Ceram. Soc. 81, 3189 (1998) [2]. R. Vogelgesang, M. Grimsditch, and J. S. Wallace, Appl. Phys. Lett. 76, 8 (2000) [3]. W.Y.Ching, Lizhi Ouyang, and Julian D. Gale, Phys. Rev. B61, 13, (2000)

[R1.051] Temperature dependence of nuclear quadrupole coupling constant of ^7Li and ^93Nb in LiNbO_3^*

It is well established that the ferroelectricity of LiNbO_3 originates from the displacement of positive ions, lithium and niobium, relative to negative oxygen ions below T_c. The local structural environment of Li and Nb in the crystal is similar at room temperature. However, as the temperature increases they move opposite directions along the c-axis: Li ions move to the center of oxygen triangles while Nb move to the center of oxygen octahedra. The temperature dependence of the nuclear quadrupole coupling constant(QCC) of Li and Nb is quite different: the QCC of ^7Li increases while that of ^93Nb decreases as the temperature increases[1]. In order to understand this opposite tendency we calculated the electric field gradient(EFG) at the two sites due to the first and second nearest neighboring oxygen ions, by considering the effective charges. The calculated results turn out to be in good agreement with the temperature dependence of QCC for both cations in the crystal. \ * Supported by the National Research Laboratory Program(MOST). \ [1] H. J. Kim and S. H. Choh, J. Korean Phys. Soc. \b28, 513 (1995).

[R1.052] Raman study of CaFe_2O_4

The polarized Raman spectra of single crystals of CaFe_2O_4 (space group Pnma, #62, Z=4) were studied between 15 and 523 K. Most of the Raman allowed modes (14 A_g + 7 B_1g + 14 B_2g + 7 B_3g) were identified and assigned to definite atomic vibrations in close comparison with results from lattice dynamics calculations and the Raman spectra of isostructural compounds. The temperature variation of the spectra is discussed.

[R1.053] Simultaneous EPR and optical spectroscopy of pure and Rh-doped barium calcium titanate crystals

The large electro-optic coefficients and high holographic sensitivity of barium calcium titanate (Ba0.77Ca0.23TiO3, BCT) make it promising candidate for various applications, since it has no drawback related to the phase transition at 280 K like barium titanate. The nominally pure and Rh doped BCT crystals were investigated with the help of optical absorption spectroscopy, light induced absorption change measurements and electron paramagnetic resonance (EPR) in the temperature range between 4.2 and 300 K. Analyzing angular dependencies of the EPR lines we succeed to identify low-symmetry and nearly cubic centers of iron trace impurity. Four other paramagnetic defects were found after illumination: Ti3+, Rh2+, O- and Pt3+. All these defects are participants of charge transfer processes. At the light energy E about 1.3 eV the holes abandon Ti4+ creating the paramagnetic electronic Ti3+. At E > 2.3 eV O2- ions capture the holes and create hole O- centers and simultaneously Ti3+ concentration increases. Nearly located non-controlled or intentionally introduced impurities (Sr, K, Na, Ca...) may serve as pins for the fixation of the electrons and holes. Additional correlated changes were found at E > 3.2 eV (band-band transition), when EPR lines of Rh2+, Pt3+ appear and intensities of Ti3+, O- and Fe3+ essentially increase. Models of defects involved in these light induced processes are proposed.

[R1.054] RAMAN SCATTERING STUDIES OF Pb_1-x Sr_x TiO_3 (x = 0 to 1.0) FILMS GROWN BY METALORGANIC DECOMPOSITION (MOD)

Pb_1-x Sr_x TiO_3 (x = 0 to 1.0) films of thickness \sim 4 \mu m have been prepared on Pt substrates by the metalorganic decomposition (MOD) technique. X-ray diffraction results show that the films are polycrystalline with a perovskite tetragonal phase at room temperature for x < 0.6 and a cubic phase for x > 0.6. Room temperature Raman spectra show a systematic variation of lattice vibrational modes with composition. The most notable changes in the Raman spectra with x are the coalescence of A_1(3TO) and E(3TO) modes into one at approximately x = 0.6, and a considerable softening of A_1 (2TO) mode. Temperature dependent Raman spectra of Pb_0.4Sr_0.6TiO_3 film (ferroelectric to paraelectric phase transition temperature \sim room temperature) show a reduction in the intensity of the characteristic phonon modes with an increase in temperature; however, the intensity of modes persist up to \sim150 ^\circC indicating a diffuse phase transition. For temperatures >150 ^\circC broad features remain that are characteristic of a disordered paraelectric cubic phase. The temperature dependence of dielectric permittivity shows a broad maximum, and the ferroelectric hysteresis loops persist up to \sim150 ^\circC in agreement with the Raman measurements.

[R1.055] NMR measurements in a hydrogen/helium slush at 4.2 K

Matrix isolation of various atoms in solid hydrogen presents both pure and applied research possibilities. When single atom properties are measured with NMR in the background of a quantum solid, insight into electronic interactions and quantum diffusion may be obtained. A cell has been constructed which, when filled with liquid helium, may have various gases injected into it. If this gas is a mixture of hydrogen and, say, boron, NMR may be performed on both the H and the B nuclei. Crystal or amorphous structures and atomic diffusion may be investigated. Design and construction of the apparatus will be presented. The first pulsed NMR data on H will be presented and interpreted.

[R1.056] Theory

[R1.057] A New Physics Simulation Machine

A new physics simulation language, byte code compiler and stack machine interpreter are described. This machine is capable of interactively solving research problems in quantum and classical mechanics, as well as simulating simple scenarios involving electromagnetic field production and the evolution of chaotic systems. On the educational side, the language is powerful enough to model most of the solutions of ‘introductory’ physics textbook problems. A near-term development goal of this project is to provide the capability to model molecular motors such as ATP synthase in the simulation machine.

[R1.058] Application of the Coupled-Cluster Method to the Single-Impurity Anderson Model

The Coupled-Cluster method (CCM) is applied to the well known single-impurity Anderson model wherein hybridization may occur between a localized \textitf-orbital and a filled Fermi-sea of conduction electrons. The basic ansatz of the CCM is to write the true wave function \Psi in terms of a ground-state function \Phi_0 as |\Psi\rangle=e^\tildeS|\Phi_0\rangle where the operators \tildeS describe the excitations of the system. For this particular system we choose |\Phi_0\rangle=f^_\sigma|0\rangle_f|F\rangle where |F\rangle denotes a filled sea of conduction electrons while |0\rangle_f is the unoccupied f-orbital. A simple expression for the ground-state energy is derived and comparisons are made with other methods.

[R1.059] Jahn-Teller Effect: A Plaquette Expansion Approach

A number of years ago Hollenberg et al.\ developed a closed form expression for the ground-state energy density for a general (extensive) many-body problem, written in terms of the Lanczos tridiagonal matrix form of the Hamiltonian. A plaquette expansion may be written for this matrix wherein the physics is encapsulated entirely through the connected moments of the Hamiltonian. We apply this method to study the ground-state energy of the linear E\bigotimes\epsilon Jahn-Teller effect.

[R1.060] Generalized Moments Expansions

For a number of years linked-cluster expansions have been a major part of techiques used for the investigation of quantum Hamiltonian systems. Such methods include the ``\textitt-expansion" of Horn and Weinstein [Phys. Rev. D \textbf30, 1256 (1984)] as well as the derivative expansions such as the Connected Moments Expansion (CMX) and the Alternate Moments Expansion (AMX). In this work we have derived a general expression for any moments expression of which both the CMX and AMX are particular cases.

[R1.061] Berry phase effects in a generalized Kronig-Penney model

Berry's phase (BP) has been shown to play an important role in a variety of seemingly dissimilar areas of physics: optics, molecular physics, nuclear resonance, etc. In solid-state physics, an understanding of the BP was crucial in developing a complete theory of electric polarization in dielectrics, and it has been shown that the semiclassical equations of motion for Bloch electrons should be modified by BP effects.(See e.g. R. Resta, J. Phys.: Condens. Matter 12, R107 (2000).) Why, then, is the BP not more widely known? We suggest that this is because there is a lack of simple model systems that exhibit BP effects. To address this, we have constructed a generalized Kronig-Penney model that produces BP effects. Model parameters are varied to show how the BP itself changes; in particular, in the limit where our non-symmetric model acquires inversion symmetry, the Berry phase is seen to go to expected values. We then illustrate how the existence of a BP can be seen in selected phenomena, for example the motion of electron wave packets.

[R1.062] Computational Themes

[R1.063] Quantum Molecular Dynamics with Non-Gaussian Wavepackets

The time-dependent variational principle provides a rigorous framework for developing approximate quantal equations of motion for many-body systems. To date, most calculations use Gaussian single-particle wavepackets. Such wavepackets represent the exact solution of both the free-particle and harmonic oscillator systems; these exact solutions do not represent the physical conditions of strong Coulomb interactions in warm dense matter. In the development of the equations of motion for self-similar exponential wavepackets, which are the exact solutions of the l=0 bound-state Coulomb system, we emphasize the importance of constraining the time-dependent variational principle with the continuity equation. We have compared Rutherford scattering trajectories with Gaussian and exponential wavepackets.

[R1.064] Three-Dimensional Simulation for Laser-Plasma Interactions; a Quasi-Static Approach

The interaction of a high intensity laser with ionizing gas and plasmas is of current interest for both Laser-Wakefield Acceleration and x-ray generation. Three-dimensional simulations of these interactions have been conducted using fully electromagnetic particle-in-cell calculations; however,long-interaction time simulations have been limited due to the computational cost. We discuss the quasi-static approximation, which allows simulations of longer interaction times, as well as the method used to implement this approximation using an object oriented structure. We also present preliminary results of a 3D simulation in the quasi-static approximation of a laser with a fluid plasma. We compare results of this three-dimensional simulation with WAKE [1], a two-dimensional quasi-static simulation, for effects which are predominantly 2D in nature, e.g., self-focusing. We also present preliminary results for instabilities which have a 3D structure, filamentation.

[1] T. M. Antonsen, Jr. and P. Mora, PRL 69(15), 2204, (1992)

[R1.065] Numerical Computation of Higher Order Derivatives to Arbitrary Precision

The numerical computation of higher order derivatives to arbitrary precision is shown to be related to the inverse of a Vandermonde-like matrix. The well-known formulas for lower derivatives and lower precision are obtained as special cases of the general formulation. This formulation is useful in problems requiring double, quad and infinite precision arithmetic.

[R1.066] Computational Methods incorporating symbolic Steps for solving the Poisson and Inhomogeneous Helmholtz Equations conforming to cylindrical Boundaries

It is a goal to solve the Helmholtz equation and the Poisson equation in a manner retaining insight of the functional structure. The conventional 2 or 3 dimensional integrals involved with solving such problems via Green's function often is prohibitive. It is often easier in terms of computational or analytical labors to use finite element or iterative schemes to solve such differential equations than to boldly integrate the source density with the Green's function in two or more dimensions. The purpose of this presentation is to demonstrate a method for solving such problems within the cylinder (where the source is confined) with a version of the element method and a computational method for solving such problems in the surrounding source-less region in analogy to long-range issues of electrostatics and long-range issues of diffusion. This outer region is modeled and/or calculated by using a finite difference scheme in a small intermediate region and with an appropriate term-by-term basis matching procedure in a suitable spherical boundary. This proximate spherical boundary serves to generate the homogeneous solution to either the Laplace or homogeneous Helmholtz equation with the appropriate spherical harmonic basis.

[R1.067] Development of a Field-Aligned Integrated Conductivity Model Using the SAMI2 Open Source Code

The SAMI2 open source code is a middle and low latitude ionspheric model developed by the Naval Research Lab for the dual purposes of research and education. At the time of this writing the source code has no component for the integrated magnetic field-aligned conductivity. The dependence of human activities on conditions in the space environment, such as communications, has grown and will continue to do so. With this growth comes higher financial stakes, as changes in the space environment have greater economic impact. In order to minimize the adverse effects of these changes, predictive models are being developed. Among the geophysical parameters that affect communications is the conductivity in the ionosphere. As part of the commitment of Texas A amp; M Univeristy-Commerce to build a strong undergraduate research program, a team consisting of two students and a faculty mentor are developing a model of the integrated field-aligned conductivity using the SAMI2 code. The current status of the research and preliminary results are presented as well as a summary of future work.

[R1.068] WebTOP: Interactive 3D Web-based Simulations for Teaching Waves and Optics

WebTOP is 3D interactive computer graphics system designed to help students learn about waves and optics. It has been used to help teach undergraduate introductory physics and optics classes. It has sixteen modules that treat the following topics: waves, geometrical optics, reflection and refraction, polarization, interference, diffraction, lasers and scattering. WebTOP simulations have the following characteristics. First, they are three dimensional, i.e., they have navigation controls that allow the user to rotate the scene, pan it, or zoom into it. Secondly, they are interactive. The user can change the parameters either by typing the values into boxes, or by using the mouse cursor to move the corresponding widget in the scene. Thirdly, the simulations are animated, when animation is appropriate. Furthermore, the simulations include vcr-type controls that allow the user to record a session for later retrieval and viewing. Finally, these modules run inside a web browser. They can be run from our website, http://webtop.msstate.edu or be downloaded from this website and run locally. In addition to the simulations, each WebTOP module includes a short description of the theory used, and sets of recorded examples and suggested exercises. WebTOP is sponsored in part by the National Science Foundation (DUE 9950569).

[R1.069] Simple and unified derivation of conjugate gradient and variable metric minimization

Simple derivations of the most popular methods for finding the minimum of a function of many variables are presented in a unified manner at a level appropriate for an undergraduate computational physics course. In particular simple derivations of the conjugate directions method, the conjugate gradient method, and the variable metric method are described and some generalizations of these methods are also discussed.

[R1.070] Electronic Structure

[R1.071] A finite difference method for the solution of the coupled Schrödinger and Poisson equations for quantum dot systems

With the advent of recent advances in epitaxial crystal growth technology, such as molecular-beam epitaxy, which have enabled the fabrication of atomically sharp heterojunction interfaces, there has been a growing interest in spatially quantized systems. Of these systems, quantum dots (QD) have attracted much attention. Here we present a finite difference method for the solution of the coupled Schrödinger and Poisson equations for a number of QD systems. These systems consist of vertically aligned multiple QDs with varying numbers of electrons. The effect of the inter-dot separation on the energy levels of these QDs is investigated using this finite difference technique. The method has the advantages of being relatively fast and adaptable to any QD geometry. The method is outlined briefly and the results from these calculations are presented here, with the intention of using them as stepping stone to investigating more complex systems.

[R1.072] Variational anisotropic model of Wannier excitons compared with fractional-dimensional space approach

Binding energy of Wannier excitons in a quantum well of thickness L is studied using two models: a two-parameter trial wave function and a continous fractional-dimensional space with dimension alpha between 2 and 3. Since both models provide quantitative measures of the exciton spatial anisotropy as L changes, we give physical arguments for a plausible definition of alpha = alpha (L).

[R1.073] Tight-Binding model for Rubidium

The NRL tight-binding total energy method was applied to Rubidium, a material which is known as an utralsoft metal. We fit LAPW calculations of high symmetry structures onto a non-orthogonal tight-binding Hamiltonian. This Hamiltonian accurately reproduces the LAPW band structures, density of states and total energies as a function of volume. In addition, the tight-binding scheme determines various quantities that were not fitted, such as elastic constants and phonon frequencies in agreement with experimental values. We also explored the applicability of this model in performing molecular dynamics simulations and its extension to other alkali metals.

[R1.074] First-principles study of gradient corrections to the local density functional on the structural properties of ionic solids

We have studied the structural properties of ionic crystallie solids by means of first-principles total-energy calculations using the full-potential Linearized Augmented Plane Waves (LAPW) method. The calculations are based on the Density Functional Theory and we have used the Local Density Approximations (LDA) and the Generalized Gradient Approximation (GGA)for the exchange-correlation potential, in order to analyze the gradient effects. We present results for the lattice parameter and bulk modulus for ionic solids with NaCl structure. From a comparison of our results with experimental values, we find that LDA give errors of 3% and 25% for the lattice parameter and the bulk modulus, respectively. The inclusion of the GGA systematically improve these quantities, for the lattice parameter the errors are menor to 1% and about of 5% for the bulk modulus. The importance of gradient corrections in ab-initio calculation of ionic systems are emphasized.

[R1.075] Polymer Physics II

[R1.076] Infrared and Raman study of phase separation in binary n-alkane mixtures

The phenomenon of micro-phase separation occurs in certain solid solution of binary mixtures of n-alkane in room temperature. The blends of C36H74/C24D50 have been studied at different molar concentration ratios. The reflectance micro-infrared spectra and the Raman spectra have been obtained for the previously mixed, melted and quenched samples. The spectra changing in time show the proceeding process of phase separation. Similar polymers align themselves inside the micro-domains. The alignment results in a periodic intermolecular potential, often called the crystalline field, which induces line splitting, broadening and/or intensity changes. This has been clearly shown in the IR and Raman spectra taken from the various spots of the sample. Different band shapes in the region of 1400 cm-1 to 1500 cm-1 represent different contribution of amorphous and orthorhombic phases. The splitting and different band intensity at about 1090 cm-1 represent different mole fraction of the components in a certain small area of sample. This research is in early stages of development and only preliminary results will be presented.

[R1.077] Mass transport in thin polymer films during AFM-assisted nanolithography

An AFM-assisted nanolithography in thin polymer films is the subject of this presentation. We have developed the model describing three stages of the AFM-based nanolithography process in polymers: non-uniform electric field formation inside thin (20-50 nm) polymer film; polymer softening due to localized Joule heating a fraction of polymer film heated above the glass transition point; and mass transport of dielectric polymer liquid in the direction of electrically biased AFM tip.

The model is based on the numerical solution of three-dimensional non-uniform heat equation together with modified Navier-Stokes equation for uncompressible non-Newtonian polymer liquid in cylindrical coordinate system. The electric field in the polymer film is evaluated through the method of images. The pressure acting on the dielectric liquid is associated with a strong gradient of electric field induced by the AFM tip resulting in very fast (fractions of milliseconds) mass transport of polymer liquid and in formation of raised nanostructures (1-100 nm).

This approach suggests novel experimental lithography technique, which must be conceptually different from all lithography techniques (including thermo-mechanical writing - MILLIPEDE, AFM-assisted chemical modification in polymer resists, e-beam, ion-beam etc.) in polymer materials on nanoscale reported in the literature up to date.

[R1.078] In–situ Rheo-SAXS and Rheo-WAXD studies of Shear Induced Structures in Model Polyethylene Blend

The effect of chain length on shear-induced crystallization in model blend polyethylene melts was studied by in-situ rheo-SAXS (small-angle X-ray scattering) and -WAXD (wide-angle X-ray diffraction) techniques. Model polyethylene blend was prepared by solution blending of low molecular weight polydisperse PE (Mw = 50,000, MWD = 2) with 10wt161,000, MWD = 1). While shear-induced oriented crystalline structures were not observed in SAXS and WAXD of the single component low molecular weight polydisperse PE (shear rate = 60 1/s, shear duration = 5 s at 115ºC ), the blend showed oriented crystalline structures after shear and these structures were stable at temperature near the nominal melting point. SAXS and WAXD results clearly show that the high molecular weight species (or long chains) in the blend directly affect the formation and stability of the orientation-induced crystalline structures in polymer melts under flow. This study verifies that upon cessation of flow, the longer chain molecules remain oriented and can form stable precursors for nucleation; on the other hand the shorter chains relax and loose their orientation rapidly due to short relaxation time.

[R1.079] Structure of Secondary Crystals in Ethylene-Based Ionomers

A typical DSC thermogram of an ethylene-(meth)acrylic acid ionomer displays two melting endotherms: one near 100^oC reflecting the melting of primary ethylene crystals, and one at 40-60^oC which we have shown via simultaneous SAXS/WAXS/DSC to arise from the melting of interlamellar secondary crystals. Dynamic DSC (DDSC) confirms that the two peaks reflect a bimodal crystal thickness distribution, rather than a superposition of melting and recrystallization events. The melting temperature of these secondary crystals, estimated to be 2.5-3.5 nm thick, is sensitive to annealing history. DDSC also indicates that these secondary crystals melt irreversibly, as expected if each must be individually nucleated. The 2-D SAXS patterns of highly-oriented blown films of such ionomers show intense peaks, arising from the polyethylene lamellar crystallites, along the direction of principal orientation. Comparing the azimuthal variation in SAXS peak intensity at temperatures below and above the low-temperature endotherm reveals that the secondary crystallites are significantly oriented, but less so than the primary lamellae. Thus, the secondary interlamellar crystals also have a lamellar (anisotropic) habit, rather than resembling fringed micelles (isotropic).

[R1.080] Structural Studies of Ethylene-1-Octene and Ethylene-Norbornene Random Copolymers by NMR and WAXD

The properties of two series of melt-quenched, random ethylene copolymers (comonomer content < 15 moldiscussed. Changes in the crystallite properties with increasing comonomer content, including crystallite thickness reduction from ^13C T_1 NMR relaxation times and chain packing from the line widths of crystal NMR spectra, were found to be independent of comonomer type. Analyses of the non-crystalline regions revealed differences. Copolymers with norbornene showed a larger reduction in the peak position of the WAXD amorphous halo relative to copolymers with the same content of 1-octene. The NMR resonance of the amorphous CH_2 backbone units was broader in the copolymers with norbornene. Both observations are due to significant conformational differences in the non-crystalline chains with different comonomer type. Interestingly, the overall decrease in ^13C T_1 times of the amorphous CH_2 backbone units with increasing comonomer content was the same for both copolymer systems. Hence, in the range of comonomer content studied, the rates of fast motions for ethylene segments in the backbone are independent of comonomer type.

[R1.081] Morphology Evolution in Polytetrafluoroethylene as a Function of Melt Time and Temperature: Single- and Multi-molecule Folded Chain Single Crystals and Banded Structures

Examination of the evolution of the crystalline morphology of dispersed PTFE emulsion particles of various molecular weight resins as a function of time in the melt indicates that substantial molecular motion on the substrate occurs; large, angular particles, considerably larger than the original dispersion particles, form first for short melt times, followed by development of both planar folded chain single crystals and single molecule single crystals and banded structures with parallel double striations. The molecules in the single molecule single crystals and bands are parallel to the substrate, an individual double striation appearing to consist of a “double edge”, folded chain lamella, more or less normal to the substrate. In two “nano”-emulsion samples used (TE 5070 (DuPont) and 18749/26 (Ausimont)), comparison of measured molecular weight and particle morphology suggests chain folding in the as-polymerized single crystal particles.

[R1.082] Observation of Double Glass Transition in Cold Crystallized Poly(phenylene sulfide)

The glass transition and crystallization of poly(phenylene sulfide), PPS, were studied using modulated differential scanning calorimetry (MDSC), density, and wide-angle X-ray scattering (WAXS). Amorphous samples were prepared through a rapid liquid Nitrogen quench from the melt and then were cold crystallized at 100C just above the glass-transition temperature of 88.5C. The glass transition was measured from the inflection point of the reversing heatflow curve of the MDSC. During crystallization Tg shifts from 90C to 100C by the time PPS achieves its ultimate crystallinity at a treatment time of 1500 minutes (25 hrs.). Tg also becomes broader as treatment time is increased, suggesting a broader distribution of the relaxation times. The degree of crystallinity measured by both density and WAXS increased with increasing isothermal crystallization time to an ultimate value of 0.185. When PPS is cold crystallized just above the Tg of an amorphous sample, two distinct relaxation processes are observed. Samples with treatment times below 25 hours had a Tg of 90C, while those treated for this time or longer had a Tg of 100C. A double glass transition was observed for sample treatment times between 660 and 1440 minutes. This is evidence of two distinct relaxation processes in the material. For treatment times less than 660 minutes there is only a single glass transition temperature corresponding to the first relaxation. As the isothermal treatment time was increased beyond 660 minutes a second Tg appears, signaling the onset of the second relaxation mechanism. This transition in the mode of relaxation was observed through examination of the reversing heatflow curve and in the Avrami fit of the density data.

[R1.083] Molecular relaxation process of isotactic polystyrene studied by real-time dielectric spectroscopy and small and wide angle X-ray scattering

The molecular relaxation processes of cold-crystallized isotactic polystyrene (iPS) have been investigated using real-time dielectric spectroscopy. Wide and small angle X-ray scattering studies were performed during, and subsequent to crystallization, to determine degree of crystallinity and lamellar thickness. The purpose of our study is to compare the restrictions imposed on molecular mobility by crystals in the vicinity of the alpha (glass transition) relaxation, for bulk films (reported here) and thin films of iPS. In separate experiments, dielectric and X-ray data were collected during isothermal crystallization at temperatures Tc = 140°C or 170°C for various times, followed by reheating. From dielectric loss tangent data we observe that the glass transition temperature, Tg shifts to lower frequency during crystallization, indicating the relaxation time increases as crystals constrain the amorphous phase. The frequency at which the alpha relaxation occurs shifts two orders of magnitude higher for Tc = 170°C compared to Tc = 140°C, indicating reduced relaxation time for higher crystallization temperatures. The dielectric data were well fitted to a Havriliak-Negami model, and the parameters describing the distribution of relaxation times and dielectric relaxation strength were obtained. The dielectric strength and symmetric broadening parameter both decrease, while the central relaxation time and asymmetric broadening parameter increase with crystallization time.

[R1.084] Characterization of Fiber and Bulk of Poly(trimethylene Terephthalate) by Quantitative Thermal Analysis

Quantitative thermal analyses fibers of poly(trimethylene terephthalate) (PTT) are presented based on the measured heat capacity by standard differential scanning calorimetry (DSC) and temperature modulated differential scanning calorimetry (TMDSC) and compared with earlier results for bulk PTT . The heat capacities of the solid and liquid states of semicrystalline PTT are reported from 5 K to 570 K. The low temperature heat capacity of solid PTT is linked to the vibrational spectrum, using the ATHAS method. The experimental heat capacities of liquid PTT can be expressed by: CpL(exp) = 211.6 + 0.434T J/(K mol). The semicrystalline fiber and bulk PTT are analyzed using the extrapolated vibrational heat capacity of the solid and the total heat capacity of the liquid as baselines. The glass transition temperature of amorphous PTT occurs at 310-315 K with a dCp of 94 J/(K mol). For 100is 30±2 kJ/mol. Using quasi-isothermal TMDSC, the apparent reversing and nonreversing heat capacities were determined from 220 to 540 K. Additional time-dependent, reversing contributions are linked to reorganization and recrystallization, while the major melting is irreversible. Truly reversible and time-dependent irreversible heat effects were separated. With these data one can compute crystallinity changes with temperature and the mobile amorphous fractions.

[R1.085] Effects of chain configuration on the crystallization behavior of poly(lactic acid)

Research interest in poly(lactic acid) stems not only from its environmentally appropriate synthesis and potential applications, but also from its complex crystalline forms. The building block, lactic acid, has two stereoisomers, L-type and D-type, which can form polymers of different regio-regularity. In addition, a blend of L- and D-homopolymers can form stereocomplex crystals with melting temperature much higher than homopolymer crystals. Based on the characteristic ratios measured, poly(lactic acid) chains are found to be inherently rigid. The D-L junctions have been characterized. The distribution of D- and L-block lengths has been analyzed. The configuration of the chains has a profound influence on the overall crystallization rate and crystalline perfection. Based on spectroscopic evidence, the molecular parameters governing the magnitude and specificity of interchain interactions in both homopolymer and copolymer stereocomplexes have been elucidated. Thus, the molecular origin of the thermal stability of stereocomplexes can be better understood.

[R1.086] X-ray Characterization of Row Crystallized Polymers

Polymer melt crystallization is strongly influenced by flows that orient some macromolecules that become fibrillar nuclei for subsequent epitaxial growth of folded chain lamellae. For polyethylene (PE) and poly(ethylene terephthalate) (PET), the resulting row structures have the additional feature that the ribbon-like epitaxial crystals twist coherently; the same sort of lamellar twisting gives rise to banded spherulites in quiescent crystallization. In oriented row crystallization, the crystallographic b axis is normal to the flow direction, while the average orientations of a and c axes are functions of the length of the twisted lamellae. A simple quantitative model with cylindrical symmetry accounts for the textures observed by wide-angle X-ray diffraction. The same model accounts for the small-angle X-ray pattern appearing to be well oriented, regardless of the length of the twisted lamellae and associated orientation of the c axis.

[R1.087] Crystallization Kinetics and Morphology of Thin Films of PEO/PMMA Blends

The morphology and crystal growth kinetics in thin films of PEO/PMMA blends were studied optical microscopy in the reflection mode. Samples (ca. 100 nm thick) were prepared by spin-casting a dilute dichloroethane solution onto a cleaned silicon wafer and subsequent drying under vacuum. Crystal growth rates were measured as a function of blend composition, crystallization temperature and film thickness. This presentation will specifically focus on studies of dendritic growth in 30/70 PEO/PMMA blends. Studies of the temperature dependence of the crystal growth rate and the morphology indicate that both are a complex function of the thermal history.

[R1.088] Lamellar Morphology of Metallocene Random Propylene Copolymers studied by Atomic Force Microscopy

Four sets of propylene based random copolymers with co-units of ethylene, 1-butene, 1-hexene and 1-octene, in a wide range of co-monomer contents up to 10 mol percent (including co-unit and other defects), were studied after both rapid and isothermal crystallization from the melt. Etched film surfaces were imaged so as to minimize catalyst and co-catalyst residues. As the concentration of the gamma polymorph increases with increasing comonomer content or increasing crystallization temperature, the thickness and lateral extension of the observed lamellae decreases rapidly. Spherulites are formed in copolymers with non-crystallizable units (1-hexene and 1-octene) up to 3 mol percent total defect content, and were observed right up to 7 mol percent total defect content in those with partially crystallizable co-monomers (ethylene and 1-butene). However, lamellae were observed in the surfaces of all copolymers analyzed, even in the most defective ones, highlighting the importance of the gamma polymorph in propagating lamellar crystallites in polypropylenes with a high concentration of defects. The morphology of equivalent microtomed bulk specimens will be comparatively discussed.

[R1.089] FTIR, DSC, WAXS and density study of cold crystallized isotactic polystyrene

The techniques of Fourier transform infrared (FTIR) spectroscopy, wide-angle X-ray scattering(WAXS), density measurement and differential scanning calorimetry (DSC) were used to study the cold crystallization behavior of isotactic polystyrene (iPS) films cold-crystallized at 140C and 170C for various times. It was observed from FTIR that the intensity of the peak at 981 cm-1 increases with crystallization time and this reflects the manner of crystallization. The degree of crystallinity was obtained from DSC by heat of fusion calculation, from WAXS by the crystal peak area after amorphous phase subtraction and from density measurement by two-phase model density calculation. Crystallinity determined by any method exhibits a correlation with the absorption peak intensity ratio I981cm-1/I1026cm-1 , obtained from FTIR. Such a correlation provides us a way to study the crystallization process for iPS thin films. The FTIR spectra of crystallized thin film was taken for films spin cast from solution on KBr disks. For the first time, crystallinity of iPS thin films was obtained by the reference to the correlation curves between the FTIR peak intensity ratio and crystallinity developed for bulk film.

[R1.090] Broadband Dielectric Investigation of Amorphous and Semi-Crystalline Polylactides

Molecular dynamics of poly (L-lactide) and several L-lactide/meso-lactide random copolymers were investigated in the frequency domain using broadband dielectric spectroscopy. The dielectric relaxation spectra of fully amorphous and crystalline samples reveal the influence of crystalline content and microstructure on chain motion in the amorphous phase. Differences in relaxation strength of the segmental processes were observed in these samples. While the strength of the crystalline samples increases with temperature, that of the amorphous samples changes only very little or in the opposite direction with temperature. This behavior will be discussed in the context of a rigid amorphous phase. As expected, mean segmental relaxation time is longer and its distribution is broader (at lower frequencies) in samples with higher crystallinity. Differences in the details of the relaxation processes as a function of the crystallinity and morphology will be discussed.

[R1.091] Breakup of Spiral and Concentric Ringed Spherulites in Polymer Crystallization

[R1.092] Controlling Crysallization Properties of Poly(ethylene oxide) Thin Film by Geometric Confinement

Semi-crystalline thin films of poly(ethylene oxide) were prepared by spin coating. Geometric confinement was implemented in different ways including: decreasing film thickness, nanopatterning the substrate, adding nano-particles. Morphology was measured by atomic force microscopy(AFM), melting temperature and lateral modulus were tested by shear modulus force microscopy(SMFM). The morphology was found to change from spherulite to shish-kebab, and then to finger patterns as the film thickness decreases from 200003 to 12003. The melting point was found to decrease gradually from 340K to around 320K. Both nanopatterning of the substrate and addition of functionalized nano-particles have the effect of inducing heterogeneous surface nucleation which resulted in a decrease of the spherulite size. The effects of increased nucleation sites on the melting point and hardness as a function of film thickness will be discussed.

[R1.093] Effect of fiber on shear-induced crystallization of i-PP in UHMWPE/i-PP and Aramid/i-PP fiber composites

Shear-induced crystallization of the isotactic polypropylene (i-PP) matrix in fiber composites containing ultra high molecular weight polyethylene (UHMWPE) fibers or Aramid fibers was studied by in-situ synchrotron small-angle X-ray scattering (SAXS) and wide-angle X-ray scattering (WAXS) techniques. The maximum fiber content was 10 wt composite and the shearing conditions included the application of step shear with rate = 60 1/s and duration time = 5 s at 145 ^oC. The development of lamellar structures (by SAXS) and crystal orientation (by WAXS) was strongly affected by the type of fiber present. It was found that Kebab structures were more likely to develop in the presence of UHMWPE fiber than Aramid fiber. In addition, the orientation of i-PP lamellae was greater in the UHMWPE composite than that in the Aramid composite, even though the crystallization rate was similar in both systems. As the UHMWPE phase was non-crystalline at the measurement temperature (145 ^oC), our results suggest that a high degree of molecular interactions between the oriented PE chains and the surrounding iPP chains makes the molten UHMWPE phase an effective nucleating agents for iPP crystallization under shear. The epitaxial effect of Aramid fiber on the crystallization of iPP was not a dominating factor under the shear conditions.

[R1.094] Study of the Reversibility in the Crystallization Behavior of Statistical Ethylene/Styrene Copolymers by Classical and Temperature Modulated Differential Scanning Calorimetry

The crystallization and melting behavior of statistical copolymers of ethylene and styrene (0 - 11 molwere studied using classical and temperature-modulated (TM) differential scanning calorimetry. The evolution of the reversible part of the excess heat capacity was measured during the slowest stage of primary crystallization and during secondary crystallization using TM-DSC in the quasi-isothermal mode. Evolution of the degree of crystallinity and the melting temperature(s) during primary and secondary crystallization was recorded with classical DSC. We will discuss the effect of crystallization temperature and copolymer composition on the primary and secondary crystallization behaviors and show correlations between the evolution of the excess heat capacity, the degree of crystallinity and the melting temperature(s). We will also show that TM-DSC experiments carried under quasi-isothermal conditions enable us to obtain information on the establishment of constraints during secondary crystallization, which can be linked to the evolution of the multiple melting behavior of these copolymers as a function of crystallization time. In turn, these studies shed some light on the relevance of the two existing models of reversible crystallization/melting for secondary crystallization processes by lamellar thickening or by secondary crystal formation.

[R1.095] Effect of complex flow kinematics on the molecular orientation distribution in injection molding of liquid crystalline copolyesters

Properties of liquid crystalline polymers (LCPs) depend critically on the molecular orientation distribution, which in turn can be dramatically influenced by flow fields during processing. Our group has previously applied in situ x-ray scattering to measure orientation distributions in steady, isothermal complex channel flows of LCPs. It was found that the complex orientation states arise from the competition of inhomogeneous shear and extension. Here we consider the extent to which these concepts translate to the more complex transient amp; nonisothermal case of injection molding, through ex situ studies of molecular orientation distributions in injection molded plaques. These studies employ a new, low-cost aromatic copolyester based on the mesogen dihydroxy-a-methylstilbene. We find strong similarities in the type of orientation states observed in both cases. Further, systematic changes in the relative importance of shear and extension through changes in the plaque thickness lead to changes in orientation distribution that would be anticipated from our evolving understanding of the effect of mixed shear amp; extensional flows on orientation. These results verify that idealized isothermal studies not only elucidate fundamental flow/orientation relations, but also serve as a useful intermediate step towards understanding true processing conditions.

[R1.096] The Phase Behavior of Liquid Crystalline Polymers Containing Sulfone Group in Side Chain

The phase behavior of side chain liquid crystalline polymers, (tetradecylsulfonyl) methyl-substituted polyoxyethylene (14SEO) and (octylsulfonylhexylthio) methyl-substituted polyoxyethylene (8S6EO), was studied by differential scanning calorimetry (DSC), polarized optical microscopy (POM), FT-IR, small and wide angle x-ray scattering (SAXS and WAXS) and rheology. POM showed that both 14SEO and 8S6EO had ordered smectic phases at room temperature. From SAXS measurements, it was found that the layer thickness of the smectic phase corresponds to twice the extended side chain length. Above the isotropization temperature (Ti), no scattering peaks were observed for 8S6EO, while broad scattering peaks were still persistent for 14SEO. It is believed that the broad peak after the Ti is related to the characteristic block copolymer-like correlation hole peak in the homogeneous state. On the basis of the SAXS results, rheological measurements were also performed in order to identify whether Ti of 14SEO was truly related to the order-disorder transition (ODT).

[R1.097] Geometric “Chirality” from “Umbrella” Molecules

A new series of liquid crystals with the unique combination of a discotic triphenylene core surrounded by six tails containing rod-like cyanobiphenyl as end groups were synthesized. The triphenylene core and cyanobiphenyl end groups are connected via different number of methylene units (n = 6 – 12). The phase behaviors and structural identifications of most of these molecules include a liquid crystal phase (N) and two crystalline phases. Under a direct current electric field, the cyanobiphenyl groups align along the electric field and there is a drastic change in the optical birefringence. Each individual molecule becomes “umbrella”-shaped, and the molecules stacked together to form columns. This anisotropic geometry generates a geometric “chirality” although the atomic structures of these molecules are achiral.

[R1.098] Supramolecular and Molecular Structures in Aromatic Polyimides Containing Cyanobiphenyl Side-Chains

A series of newly designed polyimides, which are composed of aromatic polyimide backbones and side chains containing 4-cyanobiphenyl mesogens, has been synthesized (abbreviated as BPDA-nCBBP, n represents the number of methylene units). Most of the crystal forms have been identified as triclinic lattices with large unit cells. The number of chains in those unit cells ranged from six to eight. The fact that large unit cells in these polymers include various numbers of chains leads to an important issue; how are the chains packed into these large unit cells. It has been found that a waved layer packing model with microphase separations between the main chains and the side chains can best fit our X-ray diffraction experimental results. This new concept of molecular packing may also provide explanations for some other unsolved experimental observations in polymer ordered structures.

[R1.099] Morphological Chirality and Crystal Twinning in Different Length Scales of a Chiral Liquid Crystalline Polyester

The chiral liquid crystalline polyester is synthesized from (R)-(-)-4'-ƒç-[2-(p-hydroxy-o-nitrophenyloxy)-1-propyloxy]-1-undecyloxy-4-biphenyl carboxylic acid via an A-B type condensation polymerization. The resulting polymer exhibits Chiral Smectic A, Chiral Smectic C and Twist Grain Boundary Smectic A phases, as indicated by DSC, WAXD and PLM. Helical morphologies exist in the latter two phases. By melt crystallization and solvent evaporation, flat single lamellar crystals have been obtained with a basic monoclinic unit cell with a=1.03nm, b=0.47nm, c=6.43nm and ƒ×=83„a by SAED and WAXD fiber pattern. SAED results also showed that two kinds of crystal twinnings existed in this polymer: micro-twinning within one single lamellar crystal and rotation-twinning between two lamellae. Morphological helical structures can also be obtained in the crystal form in this polymer. The helical lamellar crystals possess the same crystal structure as their flat counterparts and all helical crystals show a right-handed twist with pitch lengths on a micrometer size by TEM and AFM.

[R1.100] Physical aging in a polymer glass subjected to carbon dioxide pressure jumps

We report results from tensile creep tests performed on an epoxy resin in the presence of carbon dioxide at different pressures (Pco2) and at a constant temperature below the glass transition temperature Tg. Time – Pco2 superposition was applied to the data to account for the plasticization effect due to the interaction between the carbon dioxide molecules and the polymer. In addition, physical aging of the epoxy films was investigated using sequential creep tests after carbon dioxide pressure down-jumps at constant temperature and also after temperature down-jumps at constant carbon dioxide pressure. The isothermal pressure down-jump experiments showed physical aging responses similar to the isobaric temperature down-jump experiments. However, the aging rate for the CO2–jump was slightly lower than that for the T-jump and the retardation time for the Pco2-jump experiments was up to 6.3 times longer than for the T-jump conditions. The results are discussed in terms of classical physical aging and structural recovery frameworks and a speculation about the differences in the energy landscape resulting from Pco2-jump and T-jump experiments is also made.

[R1.101] Studies of Poly(vinyl chloride) Based Endotracheal Tubes From the Microscopic to Macroscopic Scale

The endotracheal tube (ET) is a polymeric conduit that forms a closed system of pulmonary ventilation that is most often used to allow delivery of air to critically ill patients via intubation. Currently used ETs cause a wide variety of clinical problems including laryngeal edema (inflammation), severe morbidity, and occasionally death. To investigate the origins of this behavior, mechanical, chemical, morphological, and biocompatibility characterization of injection-molded (Endotrol) tubes of poly(vinyl chloride) (PVC) containing ~35 wtplasticizer was conducted. Experiments included fourier-transform infrared spectroscopy, gel permeation chromatography, differential scanning calorimetry, accelerated solvent extraction, uniaxial tensile testing, high-resolution force spectroscopy, atomic force microscopy, and plasticizer leaching. We intend for these studies to form the basis for future ET materials selection and design.

[R1.102] Optical Spectroscopy and Modeling Studies of Poly(di-n-alkylsilanes)

The influence of thermal treatments on the photophysics in \sigma-conjugated poly(di-n-alkylsilanes) (i.e., butyl, hexyl, octyl, decyl and dodecyl) have been investigated. In situ measurements of both thin film absorption and photoluminescence reveal numerous distinct structural conformers. The exact distribution of these conformations is sensitive to both thermal quenching and subsequent heating. Molecular modeling studies of large oligomers and ab initio calculations of representative tetramers and hexamers are used to identify energetically favorable chain conformations. Zero-energy calculations identify deep local minima corresponding to simple 7/3, 9/4 and 15/7 helices. Models of repeating dyads identify a 14/6 helix and other candidate low energy structures. These results are compared to the experimental data.

[R1.103] Excitation Energies of Fluorene-Based Polymers and Oligomers- Ab Initio Approach

Organic light emitting polymers and oligomers are conjugated materials that are being considered for use in numerous optical devices e.g. light emitting diodes, flat panel displays etc. The key to commercialization of these product lies in producing stable blue light emitting polymers and oligomers. Fluorene-based polymers and their derivatives are possible candidates for blue light emitting materials.In this work, we investigate the geometrical, electronic and optical properties of fluorene-based \pi-conjugated monomers that include phenylene, thiophene and other units using computational quantum mechanical approach. The relaxed potential energy surface was generated for some systems using the Hartree-Fock method (HF/3-21G*). Fully optimized ground state structures were obtained using HF and various density functional theory (DFT) approaches (B3LYP/3-21G*, B3LYP/6-31G*, B3P86/6-31G*, B3PW91/6-31G*, MPW1PW91/6-31G*). The energies of the first 20 singlet-singlet transitions were then obtained by applying the corresponding time-dependent (TD) density functional theory (TD-B3LYP/6-31G*, TD-B3P86/6-31G*, TD-B3PW91/6-31G*, TD-MPW1PW91/6-31G*) to the previously optimized geometries. The results of calculations were compared with experimental values when possible. The main trends of these calculations will be presented and discussed.

[R1.104] Nanoimprinting of Photonic-Bandgap Devices in Ionically Self-Assembled Monolayers

Photonic Crystals (PCs) are a new class of materials providing new opportunities for the enhancement control of the propagation of light in waveguides and laser action in 2D distributed feedback structures. However, in order to possess nonzero even-order nonlinear optical susceptibilities, a material must lack a center of inversion at the macroscopic level. As a result several novel methods for creating noncentrosymmetric materials incorporating organic molecules with large molecular susceptibilities have been developed over the past decade. Using commercial ionic polymer dyes, ionically self-assembled monolayers (ISAMs) provide a new platform to produce such noncentrosymmetric arrangement of nonlinear optical chromophores Originally developed by Chou, nanoimprinting techniques provide a powerful alternative to e-beam lithography for definition of photonic structures in ISAM films. Here we report the nanoimprinting of photonic structures in such films.

[R1.105] A versatile fiber-coupled system design for Photon Correlation Spectroscopy and Fabry-Perot Interferometery