This abstract not available.
[R40.002] Mössbauer Studies of Melt-Spun Pr_2Fe_14B
J.C. Ho, X. Zhang (), H.H. Hamdeh (Wichita State University, Wichita, KS), W.C. Chang, H.W. Chang (), Y.S. Liou (National Chung-Cheng University, Chia-Yi, Taiwan)
Melt-spun ribbons of tetragonal Pr_2Fe_14B, like the isostructural Nd_2Fe_14B, exhibit favorable hard magnet characteristics. In practice, one invariably introduces a certain amount of soft magnetic phases such as \alpha-Fe for remanence enhancement. The nominal off-stoichiometric compositions lead to metallurgical complications, which are often not easily resolvable by standard phase identification techniques such as x-ray diffraction and thermal magnetic analysis. In contrast, ^57Fe-Mössbauer spectroscopy can be used to delineate individual Fe sites through their different hyperfine magnetic fields. This work yields Mössbauer parameters including hyperfine magnetic field, isomer shift, and quadrupole splitting values as obtained on a nearly stoichiometric Pr_2Fe_14B ribbon sample. They provide a basis in future analysis of similar data from multiphase but technically more relevant materials.
[R40.003] Cluster glass behavior of layered manganite above T_C
Kyunglim Lee, Ilryong Kim, Soonchil Lee (The Korean Physical Society)
It was reported that layered manganite
La_1.2Sr_1.8Mn_2O_7(327-phase) shows magnetic
phase transition at T_c=128K, and couple of more traces
of transitions over T_c, which are believed to be due to
intergrowth of (La,Sr)MnO_3(113-phase). Mn NMR spectrum
clearly shows two separate peaks coming from the 327-phase
and 113-phase. The signal intensity generated by the
327-phase does not vanish above T_c, meaning that the
ferromagnetic metallic clusters of 327-phase exists above
T_c. Most abnormal feature of this material is that La
NMR signal intensity decreases very slowly as the
temperature increases from below T_c to above T_c,
where the decay time is about 30 minute. Such anormalous
behaviors can be explained by the cluster glass model where
the interactions between the ferromagnetic clusters of the
113-phase mediated by the 327-phase are frustrated.
[R40.004] Studies on crystal structure and Magnetism of perovskite-like La_xPb_1-xMnO_3 system
Ming-Fomg Tai, Ting-Sheng Huang (Department of Physics, Chung Cheng University, Ming-Hsiung, Chia-Yi 621, Taiwan, R.O.C.), High Field Lab Team
Lattice structure, dc magnetism and ac susceptibility
measuremwnts have been investigated for
La_xPb_1-xMnO_3 system with x = 0.0 ~ 0.5 and
La_0.7Pb_0.3Mn_1-xCo_xO_3 with x = 0.0 ~
1.0. The structure of La_1-xPb_xMnO_3(x = 0.0 ~
0.5) is orthorhombic with lattice constant a \approx 5.47
Åb \approx 5.54 Åc \approx 7.78 ÅAc
and dc magnetic measurements are carried out as functions of
temperature (2 - 300 K), dc external field (H \le 12 T),
ac magnetic field (5 Oe), and ac frequency (50 - 20 kHz).
The effect of Pb^2+ substitution for La^3+ in
La_1-xPb_xMnO_3 system presents divalent and
induces mixed valence states of Mn^3+ and Mn^4+.
[R40.005] Pb-doping effects on crystal structure and spin-glass behavior in perovskite-like La_0.7(Ba_1-xPb_x)_0.3CoO_3 system
Ming-Fong Tai, Chiung-Hsiung Chen (Department of Physics, Chung Cheng University, Ming-Hsiung, Chia-Yi 621, Taiwan, R.O.C), High Field Lab Team
In this investigation, complex dielectric constants, ac
conductivity and ac/dc magnetic measurements for the
perovskite-like
La_0.7(Ba_1-xPb_x)_0.3CoO_3
polycrystalline system with x = 0.0 - 1.0. Various magnetic
measurements have indicat in Co ions exhibit various spin
state due to the Pb^2+ doping.
La_0.7(Ba_1-xPb_x)_0.3CoO_3 oxides has
cubic structure with a \approx 7.76 Åfor x = 0.0 -
0.1 and has orthorhombic structure with a \approx 5.46
Åb \approx 5.50 Åand c \approx 7.85 Åfor
x = 0.2-1.0 . Spin glass behavior was significantly observed
in all samples. The spin-glass transition temperature,
T_f, decreases with dc external magnetic field. The
effects of Pb doping on the crystal structure, magnetic
properties and electronic phase transition in this system
are detailly discussed in this report.
[R40.006] Observation of a Weak Ferrimagnetic Phase in Pr_1-xLa_xMnGe
Sunil Labroo (State University of New York at Oneonta), Naushad Ali, Shibaji Saha (Southern Illinois University at Carbondale), Dale Zych (State University of New York at Oswego)
A weak magnetic phase is observed in the Pr_1-xLa_xMnGe system by means of susceptibility measurements. This phase persists above the room temperature to about 330 K in the x=0.0 sample. Increase of La content does not seem to significantly affect the transition temperatures. Existence of a weak antiferromagnetic phase has been predicted in a prior neutron diffraction study^1, however, we observe only a partial cancellation of the moments, which suggests a ferrimagnetic-like phase. In this study we present a phenomenological model which shows a good agreement with the experimental data.
[1] Venturini et al., J. Magn. amp; Magn. Mater., Vol. 150, p.
197, 1995.
[R40.007] Magnetostructural Correlation in R_0.5Sr_1.5MnO_4 (R= La, Pr, and Nd)
Chang Seop Hong, Eun Ok Chi, Wan Seop Kim, Nam Hwi Hur (Center for CMR Materials, Korea Research Institute of Standards and Science, Yusong, P.O. Box 102, Taejon 305-600, KOREA)
The magnetic and structural properties in single crystals of
R_0.5Sr_1.5MnO_4 (R = La, Pr, and Nd; R-214) have
been studied using both the magnetization and neutron
diffraction measurements as a function of temperature.
Particularly, the structure and its correlation with the
magnetic properties have been investigated for Nd-214. An
antiferromagnetic ordering appears to develop at about 130 K
in the magnetization data, which coincides with the
superlattice peaks shown in the neutron powder diffraction
patterns below this temperature. The enhancement of the
magnetization below 21 K is likely to be associated with the
ordering of the Nd cations. With decreasing temperature, the
axial Mn-O(2) bond distance shortens abruptly at the
critical temperatures, accompanied by reducing the
Jahn-Teller distortion. This behavior is evident that the
magnetic ordering in Nd-214 is strongly correlated with the
structural transition. For comparison magnetic and
structural properties of La-214 and Pr-214 will also be
discussed.
[R40.008] Crystallographic, Magnetic Properties and Magnetosistance of Nd doped (La,K)MnO3
Yongquan Guo (Naushad Ali), Roger Wappling (Roland Mathieu, Per Nordblad, Peter Svedlindh)
ABSTRACT
The crystal structure, magnetic properties and colossal
magnetoresistance of Nd doped (La,K)MnO_3 have been
investigated by means of X-ray powder diffraction and
magnetic measurement. There are two kinds of structures have
been found in (La,Nd,K)MnO_3 samples. They are
rhombohedral and orthorhombic, respectively. The structural
transition from rhombohedral to orthorhombic occurs after Nd
dopant is more than 20 at%. The space groups are
Røverline 3C, with Z=6 for rhombohedral structure; and
Pbnm, with Z=4 for the orthorhombic structure, respectively.
The Nd doped samples are ferromagnetic, however, their Curie
temperatures decrease with Nd content significantly. The
sample without lanthanum exhibits antiferromagnetic behavior
at low temperature. The electronic transport measurement
shows that a transition from insulator to semiconductor
occurs for Nd rich samples at very low temperature, but the
resistivity transition temperature decreases with Nd
content. Two magnetic transitions are found for the Nd rich
samples, which is due to the competition between
ferromagnetic and antiferromagnetic coupling.
[R40.009] Colossal magnetoresistive properties of charge-disproportionate La_1-xNa_xMnO_3,x = 0.07-0.40
Sujoy Roy, Yongquan Guo, Naushad Ali (Dept. of Physics, Southern Illinois University, Carbondale, IL 62901)
We report the magnetoresistive properties of Na doped
La_1-xNa_xMnO_3, x = 0.05-0.40 which is a
charge-disproportionate manganite due to the inability of Mn
to acquire a formal valence of +5. X-ray diffraction results
confirm the formation of a single-phase compound with
rhombohedral structure in the R-3c space group and a
decreasing trend of the lattice parameter up to a Na content
of 20%. Transition temperatures of 278, 310 and 327K have
been found for x = 0.10, 0.20 and 0.30 although T_C
tends to saturate for compound with 20% or more sodium.
Unlike the conventional manganites the resistivity curves
show a metal-insulator transition temperature T_im at a
temperature slightly above T_C. The magnetoresistance is
53% for x = 0.10 compound and is obtained at a
temperature 20K below T_C. These results indicate the
effect of charge disproportionation on the double exchange
interaction that causes the holes to be accommodated
preferentially on the O 2p sites thereby affecting the
Mn-O-Mn bond distance. This work is supported by
CARS-University of Chicago.
[R40.010] Temperature Dependence of the Spin Wave Stiffness in LSMO CMR Manganite Thin Films
Edward Gillman (Jefferson Lab), Natalia Noginova, Rakhim Rakhimov (Norfolk State University)
We have measured the spin wave stiffness of LSMO CMR
maganite thin films as a function of temperature with
ferromagnetic resonance spectroscopy. Measurements taken
with the surface of the film perpendicular to the applied
magnetic field show satellites with respect to the primary
resonance peak. The satellites can be attributed to a spin
wave resonance in these films. The position of the satellite
peaks as a function of the applied magnetic field can be
used to determine the spin wave stiffness. Here we report on
measurements between 90K and 380K. These measurements will
be compared to other measurements of the spin wave stiffness
from neutron scattering and other ferromagnetic resonance
measurements.
[R40.011] Manganite oxide thin films deposited under low oxygen pressure
Shiu-jen Liu (Department of Electrophysics, National Chiao Tung University, Hsinchu, Taiwan), Jiunn-yuan Lin (Institute of Physics, National Chiao Tung University, Hsinchu, Taiwan), Yih-shuang Gou (Department of Electrophysics, National Chiao Tung University, Hsinchu, Taiwan)
Recently, there has been a surge of interest in the
tunneling magnetoresistive (TMR) junctions, which are based
on the spin-polarized tunneling. Due to being half-metallic,
the manganite oxides (La/sub 1-x/Ca/sub x/MnO/sub 3/)has
been considered as the potential materials to fabricate TMR
junctions. The spin polarization of tunneling electrons is
sensitive to the junction interface condition. Therefore, we
fabricate TMR junctions by Laser MBE to improve the
interface condition and employ reflective high-energy
electron diffraction (RHEED) to monitor the growth of the
interfaces. However, high vacuum is necessary for RHEED
operation. In this paper, we focus on the growth of La/sub
0.67/Ca/sub 0.33/MnO/sub 3/ thin films under low oxygen
pressure. The dependence of the transport, magnetic
properties, and morphology on the oxygen pressure will be
discussed. Furthermore, results of magnetoresistance
measurements will be shown.
[R40.012] Pinholes may Mimic Tunneling
David Rabson (Department of Physics, University of South Florida), B.J. Jönsson-Åkerman, A.H. Romero, R. Escudero, C. Leighton, S. Kim, I.K. Schuller (Department of Physics, Univ.\ of California, San Diego)
Interest in magnetic-tunnel junctions has prompted a re-examination of tunneling measurements through thin insulating films. In any study of metal-insulator-metal trilayers, one tries to eliminate the possibility of pinholes (small areas over which the thickness of the insulator goes to zero so that the upper and lower metals of the trilayer make direct contact). Recently, we presented experimental evidence that ferromagnet-insulator-normal trilayers that appear from current-voltage plots to be pinhole-free may nonetheless in some cases harbor pinholes.(B.J.\ Jönsson-Åkerman, R.\ Escudero, C.\ Leighton, S.\ Kim, I.K.\ Schuller, D.A.\ Rabson, Appl.\ Phys.\ Lett.\ \bf77), 1870 (2000) and B.J.\ Jönsson-Åkerman, invited talk at this meeting. Here, we show how pinholes may arise in a simple but realistic model of film deposition and that purely classical conduction through pinholes may mimic one aspect of tunneling, the exponential decay in current with insulating thickness.(D.A. Rabson, B.J.\ Jönsson-Åkerman, R.\ Escudero, C.\ Leighton, S.\ Kim, I.K.\ Schuller, J.\ Appl.\ Phys.), in press This work was supported in part by DARPA and ONR.
[R40.013] Spin-dependent transport between two ferromagnets separated by a nonmagnetic layer in the effective-mass approximation
Victor Los (Institute for Magnetism, Nat. Acad. Sci. , Ukraine), Vladislav Saltanov (National Kiev University, Ukraine)
A unified theory of a spin-dependent transport of electrons
through a thin metallic or insulating nonmagnetic layer
(spacer) sandwiched between two ferromagnets is developed in
the ballistic regime and current-perpendicular-to-plane
(CPP) geometry. The theory is based on the Landauer
formalism and the obtained transmission amplitude for the
electron Bloch waves travelling from one ferromagnet to
another through a nonmagnetic spacer. The influence of the
band structure on the magnetoresistance (MR) ratio was
studied in the effective-mass approximation. Dependence of
the MR ratio on the spin polarization, the depth of the
spacer potential well, the effective masses in different
layers and a spacer thickness was numerically obtained for
the case of a metallic spacer. Some of these results are
interpreted in terms of a semi-classical part of the MR
ratio. The parameters defining the MR ratio in the
effective-mass approximation are found. This work is
supported in part by the CRDF Award #UP2-2117 granted to the
joint project of the Institute for Magnetism (Ukraine) and
the Oak Ridge National Laboratory (USA).
[R40.014] Magnetic properties of nanoclusters embedded in a matrix
Renat Sabiryanov, You Qiang, Siataram Jaswal, David Sellmyer (116 Brace, Dept. Physics and Astronomy, University of Nebraska, Lincoln, NE68588-0111)
The technological demand to use smaller devices propelled
studies of the properties of nanoscale magnetic clusters
embedded in some medium. We present theoretical analysis of
the magnetic behavior of the monodispersed Co nanoclusters
embedded into Cu matrix. Co cluster embedded in Cu matrix,
prepared by using beam deposition technique, show that (i)
magnetizationof the Co clusters (M) is always much lower
than the magnetization of bulk Co, (ii) M increases with the
increase of the size of the co cluster (clusters between 300
atoms and 9000) were considered), (iii) magnetization of Co
clusters decreases with the increase of the volume
concentration of Co clusters at the same size of the single
cluster. In order to understand this behavior we performed
ab-initio calculations of the electronic structure and
magnetic properties of small Co clusters embedded in Cu
matrix using tight-binding linear-muffin-tin-orbitals and
recursion method. The calculation for single Co cluster
(1-321 atoms) show that the magnetic moments of inner atoms
in the Co cluster is close to the Co bulk value while 2-3
outer shells have reduced moment (up to 20magnetization of the cluster increase with the size of the
cluster as the surface effect but the total magnetic moment
is much closer to the bulk value than experimental data. We
found that interaction between clusters are very strong and
oscillate with the distance between two clusters causing
frustration in the system. We present model that takes the
interdiffusion at the interface into account. The Monte
Carlo simulations of the finite temperature magnetic
behavior of the system will be presented.
[R40.015] Magnetic Coupling in Fe3O4/Mn3O4 Superlattices
G. Chern, W.K. Shieh, M.T. Lin (Physics Department, National Chung-Cheng University, Chia-Yi, Taiwan, ROC), Lance Horng, T.C. Wu (Physics Department, Changhua University of Education, Changhua, Taiwan, ROC)
Recent magnetic response of Fe3O4/Mn3O4 superlattices has
shown antiparallel coupling between Fe3O4 and Mn3O4 at
interface[1]. As the thickness of constituent layers is < 8
nm, the interface effect dominates[1]. While extend the
study to a [Fe3O4(30 nm)/Mn3O4(30 nm)]x4 film, M-H curves
also show high field loops indicating that antiparallel
states still exist at the interface. An unexpected and
rather weak (or partial) compensation point is identified at
T\sim25 K and both remanence and coercive field again show
minima, but with limited values, at compensation. The
present results suggest that the interface effect of Fe3O4/
Mn3O4 decays within \sim10 nm and this length scale is believed
to be associated with the domain wall thickness at the
interface, which may originate from the competition between
exchange and Zeeman energies. [1] G. Chern, Lance Horng,
T.Y. Hou, M.Z. Lin, Appl. Phys. Lett. 76, 598 (2000)
[R40.016] Electronic and Magnetic Properties of 3d-single or Multilayers on Cu(001) Substrate
Zongxian Yang, Ruqian Wu (Department of Physics amp; Astronomy, California State University, Northridge, CA 91330-8268)
Electronic structures and magnetic properties of ultrathin Ni films (Ni_n, n=1,4) with Cu and Co coverlayers (Cu_2/Ni_4, Co/Cu_2/Ni_4) on the Cu(001) substrate are studied by using FLAPW method with GGA for the exchange correlation interactions. The equilibrium structures are determined through their atomic forces. It is found that the spin moments of interfacial Ni atoms are significantly weakened due to the proximity effect from Cu. The Co adlayer in Co/Cu_2/Ni_4/Cu(001) affect the Ni film very slightly due to the screening effects of the Cu layers. The average 3d-holes increases by about 10% from Ni_1/Cu(001) to Ni_4/Cu(001). In Cu_2/Ni_4/Cu(001), the Cu capping layers reduce the average number of 3d-holes of the Ni atoms by about 7.5% as compared to that in Ni_4/Cu(001). Results are compared to experimental data from recent measurements using magnetic circular dichroism.
[R40.017] Unidirectional Solidification of TbFe_2Alloy using Magnetic Field in Microgravity
Hideki Minagawa (HNIRI), Keiji Kamada (JSUP), Tomoya Konishi (NEDO), Takashi Tsurue, Hideaki Nagai, Yoshinori Nakata, Masataka Sasamori, Takeshi Okutani (HNIRI)
Unidirectional solidification experiments of TbFe_2 alloy using a static magnetic field in microgravity were performed in the Japan Microgravity Center (JAMIC). When the magnetic field strength was increased from 0 T to 4.5x10^-2 T during unidirectional solidification in microgravity, a [111] crystallographic alignment dominated, and the maximum magnetostriction constant increased from 1000 ppm to 4000 ppm. For unidirectional solidification in normal gravity, the maximum magnetostriction constant remained at 2000 ppm with increasing of magnetic field.
[R40.018] Broken-symmetry-adapted Green function Theory of Condensed Matter Systems: Towards a Vector-Spin-density-Functional Theory
Mogus Mochena (Florida A amp; M University), Attipat Rajagopal (Naval Research Laboratory)
The group theory framework developed by Fukutome for a
systematic analysis of the various broken symmetry types of
Hartree-Fock solutions exhibiting spin structures is here
extended to the general many-body context using spinor-Green
function formalism for describing magnetic systems.
Consequences of this theory are discussed for examining the
magnetism of itinerant electrons in nanometric systems of
current interest as well as bulk systems where a vector
spin-density form is required, by specializing our work to
spin-density-functional formalism. We also formulate the
linear response theory for such a system and compare and
contrast them with the recent results obtained for localized
electron systems. The various phenomenological treatments of
itinerant magnetic systems are here unified in this
group-theoretical description. We apply this theory to the
one-band Hubbard model to illustrate the usefulness of this
approach.
[R40.019] Classical ground states of a multiple-excahnge spin model on the triangular lattice
Kenn Kubo (Dept. Phys. Aoyama Gakuin Univ. Setagaya, Tokyo 157-8572 Japan), Tsutomu Momoi (Inst. Phys. Tsukuba Univ., Tsukuba, Ibaraki 305-8571 Japan)
We investigate a spin model on the triangular lattice with
multiple-exchange interactions, which is a model for the
nuclear magnetism of the solid ^3He layers adsorbed on
the graphite. The model contains the conventional Heisenberg
exchange terms as well as the four-spin exchange terms,
whose coupling constants are denoted by J and K. We
treat the spins as classical and searched for the ground
state spin structures varying J/K(K is fixed to be
positive). Previously reported intermediate phase[1] for -8
In some semimetals in a strong crossed electric and magnetic
fields the velocities of the charge carrier in Hall
direction may exceed the acoustic wave velocity. Nonlinear
magnetoresistance can be observed in nonequilibrium phonon
generation regime (Esaki effect). The acoustoelectric
instability have investigated in bismuth pure bulk crystals
in magnetic fields up to 15T in the temperature range of
1.6K to 22 K in the presence of a strong nonuniform electric
field distribution. It was found that acoustoelectric
nonlinearty is localized in high density current area.
Examination of these areas has revealed that these regions
exhibit the evidence of high temperatures gradient causing
by nonequilibrium phonon flux focusing. It was shown that
the phonon flux is normally a function of magnitude and
direction of external magnetic field. The effect of magnetic
field on acoustoelectric instability is studied in terms of
possible mechanism of nonequilibrium phonon stabilization.
Results will be discussed in relation to theoretical work
and recent measurements on related systems.
Fe-Au alloys are characterized by the complete solubility,
and form and exhibit an fcc - bcc structural transformation
near the Fe-rich side of the system. The magneto-optical
(MO) (equatorial Kerr effect) and optical properties of
Fe_1-xAu_x (0.10 \le x \le 0.93) alloy films
were investigated in the 0.5 - 5.0 eV energy range. The
x-ray diffraction study shows the structural bcc - fcc
transformation near 80 at. % Fe. The structural bcc - fcc
transformation leads to noticeable changes in the optical
properties of alloys: an absorption peak at 2.1 - 2.2 eV in
the optical conductivity spectra of Fe_1-xAu_x
alloys with the bcc-phase (which is originated from the Fe
peak at 2.4 eV) disappears in the fcc-phase. The shape and
intensity of the EKE spectra as well as the field dependence
of the MO response are also significantly changed. The
obtained results are explained in terms of the results of
the first-principles calculations on the electronic
structure and the optical properties of the Au-Fe alloys.
Ni_2MnGa alloy has been systematically investigated in
relation to its structure, premartensitic transition and
magnetic properties for years. However, little research was
focused on the physical properties. Study on the physical
properties can improve understanding of the phase
transformation and the characteristics of magnet-field
induced strain. Ni_2MnGa alloy was prepared in an
arc-furnace with a water-cooled copper hearth. The optical
properties, including n, k, optical conductivity
(\sigma)\epsilon_1 and \epsilon_2, were
investigated in an energy range of 0.5 - 4 eV, together with
the magneto-optical (equatorial Kerr effect: EKE) and
transport properties. The \sigma spectra were measured at
78 K, 293 K, 460 K and 600 K. All the spectra showed two
prominent peaks at about 1.75 eV and 3.1 eV. The EKE spectra
revealed the similar shape and peak positions as in the
optical-conductivity spectra. The high temperature phase
shows a higher temperature coefficient of resistivity than
the low temperature phase and a dramatic change in the
resistivity, accompanied by the phase transformation, is
also observed.
This abstract not available.
When two dielectric inclusions approach to each other in a composite medium,
significant mutual polarization effects must occur. These
effects are multipolar in nature and are difficult to treat
from first principles(J. D. Jackson, Classical Electrodynamics), 2nd edition, (Wiley, New York, 1975)..
In this work, we employ the discrete-dipole theory(B. T. Draine and P. J. Flatau, J. Opt. Soc. Am. A 11) 1491 (1994).
to account for the mutual polarization effects
by dividing the inclusions into many small subparts. We
begin the calculation at small inclusion sizes and large
separation, where the point-dipole limit being valid, and
proceed to larger inclusion sizes and small separation, for
which the mutual polarization effect becomes important.
Then, we apply the theory to determine the dipole moment of
each subpart self-consistently. In this way, each dipole
moment yields the local electric field, which in turn
polarizes the neighboring dipoles. We also begin the
calculation at small inclusion sizes and large separation,
where the point-dipole limit being valid, and proceed to
larger inclusion sizes and small separation. Our resluts
indicate that convergence is achieved with moderate
computational effects. The results produce valuable
information about the local electric field distribution,
which is relevant to optical absorption due to surface
phonon-polaritons of ionic microcrystals.
The processes of thermoluminescence (TL) of KBr:Eu2+ at 35 K
have been studied. In order to discriminate the origin of
activator center for TL response, we have selected a range
of excitation sources of UV light for filling crystal
electrons traps (named F centers). Contributions of 200-310
nm to the TL signal in the excitation stage have been
performed, and we found that TL has a maximum in its
intensity around 230 nm. This wavelength coincides with the
highest energy absorption band of Eu and thus, provides us
direct evidence about the Eu participation as luminescent
center. Additional bands from divalent europium precipitates
are included in TL signal and give us information about
mobility of F centers and their aggregate forms. In all TL
spectra the 90 K peak is involved as the dominant part. This
peak has been associated with a radiative recombination of
an F center with a hole trap center (H), and supports a
relaxation mechanism for TL at low temperatures. Finally, a
general TL process is discussed.
We have sintered an alkali halide KClXBr1-X:Eu2+ ceramics
phosphors. These KClXBr1-X:Eu2+ are considered as promising
selective ultraviolet dosimeter material and they exhibit
situable optical characteristics for using in digital
radiography and optical memory devices. In this work, the
thermoluminescence glow cuves were analized as a function of
composition x. We have found that for intermediate
compositions, around x = 0.6, a significant enhancement
respect to pure KBr and KCl ends of TL is achieved. This may
be interpreted as a result of increase of vacancies and
consequently the increase F centers. Finally, we discussed a
stimulation TL mechanism based in a phenomenological
recombination model.
We have prepared ferroelectric PZT thin films on silicon
substrates with aluminum - titanium layers as bottom
electrodes. This type of electrodes were used before and
promising results were obtained. However, in order to
optimize the ferroelectric properties of the deposited thin
films a complete characterization of the electrodes has been
undertaken. The Al and Ti layers were deposited by thermal
evaporation over Si (111) and (100) substrates. Then the
layer were annealed at seven different temperatures in the
300^oC to 600^oC range; the annealing was done in both
open and vacuum furnaces. Structure and surface
characteristics of the electrodes were determined by X-ray
diffraction analysis (XRD), scanning electron microscopy
(SEM) and Auger spectroscopy. The electrical properties of
the electrodes were also studied. In addition, the
structural and dielectric properties of the ferroelectric
thin films deposited on these electrodes have been
investigated.
Thanks are given to I. Gradilla and E. Aparicio for their
technical assistance. We gratefully acknowledge the
financial support from CONACYT and DGAPA-UNAM.
We suggest a greatly simplified model to describe the growth of
\beta-C_3N_4, p- C_3N_4 and
-(C_2N_2)_n- via magnetron sputtering. In the model the key
middle products in gas phase, CN and C_2N_2, are supposed
to be produced on the target surface. They move directly to
the substrate surface after being sputtered. Most possible chemical
reactions on the substrate surface have been selected by chemical
thermodynamics calculations. The growth
conditions of the three products
have been calculated. The results show that these three structures
should grow simultaneously if one wants to get diamond-like Carbon
Nitride. This conclusion may be consistent with the underlying
experimental results.
Ba_1-xSr_xTiO_3 films are know to exhibit strong
thickness dependent changes in electronic properties.
However, the details of the correlation between the
thickness and electronic properties has not been thoroughly
explored. We have performed systematic studies of the long
range structure of films by high resolution x-ray
diffraction. In concert with this, the local structure about
the Sr, Ti and Ba sites was also examined using x-ray
absorption measurements and computations. We compare
thickness and annealing dependent changes in the local and
long range structure of the films with changes in the
dielectric constant. The influence of strain is discussed.
This work is supported by NSF Career Grant DMR-9733862
We study the many quanta problem of an intramolecular
vibrational excitation interacting with optical phonons. In
the adiabatic limit we calculate numerically the ground
state for N vibrational quanta. We find strong red-shifts in
the overtone spectra and an increasing spatial localization
as the number of quanta increases. Through model parameter
fitting we achieve very good quantitative agreement with
experimental Resonant Raman scattering measurements in the
quasi one-dimensional charge transfer solid PtCl. Accurate
analytical expressions are also obtained.
Crystals of the piezoelectric material
0.68[Pb(Mg_1/3Nb_2/3)O_3]-0.32PbTiO_3 have
been studied by X-ray diffraction techniques over the
temperature range 25°C - 180°C. At this composition, the
material undergoes a rhombohedral(pseudo-cubic) - tetragonal
- cubic sequence of phase transitions in this temperature
regime. Structural analysis of the high temperature cubic
perovskite ABO_3 phase indicates a disorder of the
oxygen atoms in the space group Pm3m. Upon cooling, the
progression of the phase transitions is evident in the
broadening of the diffraction peaks. A superstructure is
observed in all phases, which corresponds to a doubling of
the lattice constants of the basic structures. Modeling of
the diffraction data indicates that the superstructure is
related to partial ordering of the oxygen atoms, rather than
ordering of the atoms occupying the A sites in the ABO_3
perovskite structure.
Work supported by ONR Grant N00014-99-1-15.
The compounds (Me_4P)_2ZnX_4 (X = Br, I) are
members of the \ beta -K_2SO_4 structure class which
undergoes phase transitions from the space group
P12_1/c1 to the parent Pmcn structure. This corresponds
to an antiferrodistortive transition of B_2g symmetry at
the zone center. The crystal structures of both compounds
have been determined as a function of temperature from
25-120°C. In the high temperature phase, the tetrahedral
cations and anions all lie on the crystallographic mirror
plane. Below the phase transition temperature, they show
displacement from the mirror plane as well as rotational
reorientation. The thermal evolution of these movements will
be presented.
The XNAES/ELNES spectra of yttrium aluminum garnet
(Y_3Al_5O_12) have been calculated using a
recently developed supercell method[1] which includes the
core-hole effect. The results are in excellent agreement
with the measured data and are significantly improved over
the previous calculation using the local density of
states[2]. The transition energies of the O-K, Al-K and Al-L
edges are accurately determined from the difference in the
total energies between the initial ground state calculation
and the final core-hole state calculation. The substantial
differences of the Al edges for Al at the octahedral site
and the tetrahedral site are discussed.
*Work supported by U.S. DOE.
[1] S.-D. Mo, and W.Y. Ching, Phys. Rev. B62, 7901(2000).
[2] M.A. Gulgun, W.Y.Ching, Y.-N. Xu and M. Ruhle, Philos.
Mag. B 79,921(1999).
We propose a mechanism for the formation of defects by
non-ionizing radiation in alkali halides doped with Eu2+
that is based on the creation of H and Fz centers similar to
the well-known model of creation of damage in pure alkali
halides by ionizing radiation. To gather information about
this mechanism we measured the afterglow luminescence (AG)
of several alkali halides doped with Eu, after UV
irradiation (380-205 nm), at low temperature (20 K). Our
measurements reveal that the AG has two components; one of
them decays during the first seconds after irradiation and
has complex excitation and emission spectra. The second one
remains for several minutes and its excitation and emission
spectra look similar to the ones obtained for the
thermoluminescence emission induced under the same
conditions. Furthermore, this slow component decays like
t^(-1/2), instead of t^(-1) as expected for a tunnelling
process. We demonstrate that this decay could be explained
by migration of H centers along dislocation lines.
We present measurements and analysis of the temperature
dependence of the luminescence lifetimes of Cr^3+ and
Mn^4+ in YAG. The measured temperature dependence of the
decay rates were modeled by considering radiative and
nonradiative processes. The temperature dependence of these
d^3 ions in YAG is very different owing to the need for
charge compensation to incorporate Mn into the YAG crystal.
We see no onset of nonradiative decay processes for the
Cr^3+ ions up to room temperature. However, we observe
an onset of non-radiative processes in the Mn^4+ decay
rate at temperatures above 200 K.
A Bohlin Rheometer fitted with a high temperature oven (-160
to 600C) and a solid-fixture device for applying torsion to
a bar shaped sample was used to measure the shear modulus of
polysilicon, silicon, 4H-SiC, 6H-SiC, and poly3C-SiC
samples. The samples had dimensions of about 5x1x50 mm. The
Young's modulus can be calculated from the measured shear
modulus values. Least-squares fits have been made to the
shear modulus, G', versus temperature data. From these
equations the Young's modulus values at 100, 200, 300 and
400C were calculated and used as input for simulations of
SiC microaccelerometers using Microcosm's Memcad software.
Many geographical locations share a common problem of high
environmental humidity. It is thus desirable to build houses
that can withstand strong water loading. In this work we
study the evolution of High Performance Concrete as a
function of hardening stage. The technique that we use is
based on the propagation of resonant audio frequency modes
of oscillation along the long axis of homemade HPC
cylindrical samples. An audio generator fed piezoelectric
(at one end of the rod) excites vibrations in the sample.
Off resonance these vibrations do not propagate away from
the piezoelectric site. On the other hand, when a resonance
is reached the vibration extends all over the bar. A second
piezoelectric is placed at the other extreme of the
cylinder. We measure three parameters: the resonant
frequency, speed of sound, and loss factor. To measure the
resonant frequency we connect the two piezos to an
oscilloscope in the x-y mode. At resonance the oscilloscope
displays an ellipse and the audio generator reports the
frequency. To measure the speed of sound, we excite the firs
piezo with a pulse and measure the delay time in the second
piezo. The loss factor can be extracted from the ratio of
the exciting pulse and the measured one. From these
parameters we calculate the Young modulus, the area moment
of inertia and the effective density of the HPC. These
quantities are measured twice a day during the 28-day
hardening time.
This abstract not available.
A theory of polar optical phonon limited transport is
developed in degenerate GaN-based heterostructures for which
the effective width of the triangular quantum well depends
on the electron density. A linearised Boltzmann equation
approach is used to produce a series of difference equations
for the effective momentum relaxation time. These are solved
using a ladder technique and the electron mobility is
calculated. Numerical solutions for the variations of the
effective momentum relaxation time with electron energy,
lattice temperature and electron density and the variations
of mobility with lattice temperature and electron density
are presented and discussed. We also investigate an
approximate solution where the results are analytical and
determine the regimes in which it provides a good
representation of the theory.
The most salient feature in the variation of the effective
momentum relaxation time with energy is the sharp change at
multiples of the optical phonon energy due to the onset of
emission at the optical phonon energy. If the electron
density is increased so that the Fermi energy is greater
than the optical phonon energy these discontinuities are
smoothed out. Another feature of our solution is the
existence of a minimum in the variation of the mobility with
electron density, which is due to increased scattering as
the Fermi energy passes through the optical phonon energy.
The 300 \mu m thick GaN films were grown on (0001)
sapphire substrates by hydride vapor phase epitaxy (HVPE)
and separated from the sapphire by UV laser processing.
Undoped and Si-doped freestanding GaN templates have been
characterized by micro-Raman spectroscopy. The free carrier
concentrations were determined by the longitudinal-optical
phonon-plasmon coupled modes. The cross sectional profile
obtained with micro-Raman line scanned from Ga to N face of
samples show that the free carrier concentration in the
Si-doped GaN sample is decreased with the depth up to the
center before it is increased. Although the A_1(LO) peak
position for the undoped GaN sample is not shifted, the
intensity of its phonon is found to be decreasing with the
increasing depth.
We report on recent progress in the investigation of
cathodoluminescence (CL) of GaN doped with Tb, the visible
photoluminescence (PL) and CL of GaN and Al_0.14Ga_0.86N /GaN
superlattice doped with Eu, and the CL from AlN doped with Eu and Tb.
The CL of GaN:Tb shows sharp emission lines corresponding to Tb^3+
ions transitions resolved in the spectral range from 350 nm to 750 nm,
and observed over the temperature range of 7 - 330 K. The luminescence
exhibits transitions which originate in the ^5D_3 and ^5D_4
levels and terminate in the ^7F manifolds. The depth resolved CL
spectra analysis show a luminescence surface dead layer thickness of
\sim20 nm. The decay times for ^5D_3-->^7F_5 (423.4nm)
and ^5D_4-->^7F_5 (551.6nm) transitions at 7 K are
\sim0.7 and \sim1.8 ms, with little change with temperature. The
visible PL and CL of GaN and Al_0.14Ga_0.86N/GaN superlattice
doped with Eu ions, show sharp characteristic emission lines
corresponding to Eu^3+ intra-4f^6-shell transitions.
The luminescence shows dominant ^5D_0-->^7F_1,2,3 and
weaker ^5D_0-->^7F_4,5,6 and ^5D_1-->^7F_1
transitions. The intensity of Eu emission from
Al_0.14Ga_0.86N/GaN superlattice annealed in N_2 is
\sim58% stronger than from Eu in the GaN epilayer. Strong CL was
observed from AlN thin single crystal films doped with Eu^3+ and
Tb^3+ ions. The space group symmetry of the wurtzite AlN is
C-P6_3mc and the Al cation occupies the site of point group symmetry
C_3v. We assume that those implanted RE ions in AlN occupy relaxed
substitutional Al-sites with hexagonal C_3v crystal symmetry.
Emission lines corresponding to Eu^3+ and Tb^3+ intra-4f^n-shell transitions are resolved in the spectral range from 300
to 900 nm. The CL kinetics for several transitions of Eu^3+
(^5D_0), Tb^3+ (^5D_3,4) were analyzed.
(Electronic mail: lozykows/@bobcat.ent.ohiou.edu)
A series of Al_1-xIn_xN films with 0 \le x \le 1 have been
grown by PSMBE on sapphire (0001) at 375^oC. RHEED and XRD
measurements confirm c-axis oriented epitaxial growth of these films.
Although the films do not show any alloy segregation, the degree of
crystalline mosaicity, compositional fluctuation and surface roughness
(AFM data), all increase with increasing x. The direct energy band gaps
of alloy films were determined using optical (UV-VIS) transmission and
reflection measurements. The observed bowing of the direct gap versus x
plot, when compared to the theoretical predictions, is less pronounced
than seen in earlier studies reported in literature. Ellipsometry data
on these samples are also analyzed to obtain film thickness and optical
constants as a function of composition. Resistivity and Hall effect
measurements show n-type electrical conductivity in these alloys with
carrier concentrations \sim10^19-10^20- cm^-3-at room
temperature for films with x > 0.5.
Work supported by NSF-IGERT-DGE-9870720
ZnO has hexagonal wurtzite structure and a band gap of about
3.3 eV at room temperature. Recently, the luminescence and
stimulated emission properties of ZnO films have received
attention for possible near-uv light emitting devices. Fu et
al have shown that ZnO films deposited by reactive DC
sputtering on [100] silicon substrates and then annealed
above 800 C exhibit 3.2-eV (band edge) cathodoluminescence
as well as defect-related bands at 2.4 and 2.9 eV.^1
Annealing and use of a Zn buffer layer improves the
crystallinity, c-axis orientation, and 3.2-eV luminescence
yield. We report photoluminescence excited by 4th harmonic
pulses from a Ti:sapphire laser and further characterization
of ZnO films grown by reactive DC sputtering at USTC and
WFU.
*Research at WFU supported by NSF grant DMR-9732023 and NATO
SfP-973686.
1. Zhuxi Fu, Bixia Lin, Guihong Liao, and Ziqin Wu, J.
Crystal Growth 193, 316 (1998).
We performed the thermodynemical analysis for the system
II-VI crystal-non-metal vapor pressure. For obtaining hole
conductivity in undoped ZnS crystal P=10000atm. sulfur vapor
pressure is required [1], for ZnS:Ag crystal the value of
this pressure is higher, unrealizable in the experiment. ZnS
crystals covered by silver protective layer are implanted by
30-50KeV energy Ag+ ion. Within a nerrow treatment
temperatures in sulfur saturated vapor atmosphere hole
conductivity is revealed in the samples, but they are of
very high resistivity. For improving the results, ZnS
crystals covered with silver protective layer are silver
doped by the mechanism of atoms recoil during S+ ion
implantation. The p-type ZnS crystals with lowest
resistivity are obtained after the treatment again within
some temperature interval, in argon atmosphere. The
electrical and luminescence properties of these crystals are
investigated.
References: 1. T.V. Butkhuzi, B.E. Tsekvava, N.P.Kekelidze,
E.G. Chikoidze. J. Phys .D:Appl.Phys. 32 (1999), 2683
Magnetic properties of single crystalline Ga1-xFexSe have
been measured. This material is in the new class of diluted
magnetic semiconductors (DMS) based on the III-VI
semiconductors. The magnetization versus field for an x =
0.05 sample deviates from the linear response seen
previously in Ga1-xMnxSe and Ga1-xMnxS and reaches a maximum
of 0.12 emu/g (<7% of the expected saturation value) at 1.8
K in 7 T. Ga1-xFexSe exhibits an anisotropy below 2 T from 5
to 400 K with the hard axis perpendicular to the GaSe
planes. Neither the broad peak observed from 119-195 K in
Ga1-xMnxSe nor the Curie-Weiss behavior observed above 75 K
in Ga1-xMnxS are observed in Ga1-xFexSe. The sharp cusp at
10.9 K in Ga1-xMnxS (characteristic of longer range
ordering) is also not observed in Ga1-xFexSe in temperatures
down to 1.8 K. In 0.1 T at temperatures between 50 and 400
K, the magnetization drops to a roughly constant 0.004
emu/g. Below 5 K, the magnetization approaches a constant
value of approximately 0.12 emu/g. The magnetic behavior of
Ga1-xFexSe is consistent with Van Vleck paramagnetism.
This abstract not available.
Using a direct Monte Carlo method we study the population dynamics of
cells, i.e., macrophages (N_M), helper T-cells (N_H), cytotoxic
cells (N_C), and antigens (N_V), with an HIV immune response model.
Cells interact with eact other with a set of rules based on known HIV
response. Cells can be mobile with a probability P_mob with a
local motility-bias and viruses can mutate with a probability P_mut.
Computer simulations are performed on cubic lattices with a number of
independent runs. Population of cellular elements with the Monte Carlo
time steps are monitored at a function of mutation at two extreme values
of mobility, P_mob = 0, 1. We find that,
in absence of mobility (P_mob = 0), the helper T-cells grow
nonmonotonically before reaching saturation while the viral population
grows monotonically to a constant value.
On the other hand, cellular mobility (P_mob=1)
enhances the viral growth and reduces the stimulative T-cell growth.
The relative magnitude of the steady-state density of helper cell and
viral infected cells determine the level of infection.
Viral population dominates over the helper T-Cells above a critical
mutation threshold (p_c) while helper T-Cells dominates below p_c.
Nature of transition depends on mobility.
We present a quantitative analysis of recent data on the
kinetics of ATP hydrolysis, which has presented a puzzle
regarding the load dependence of the Michaelis constant.
Within the framework of coarse grained two--state ratchet
models, our analysis not only explains the puzzling data,
but provides a modified Michaelis law, which could be useful
as a guide for future experiments.
The onset of pressure denaturation of globular proteins is
presumably triggered by a brakedown of intramolecular voids
which are penetrated by water. By contrast, the increasing
packing density with pressure enhances nonpolar interactions
and thus protein stability. The third component concerns the
hydration water which may destabilise the native structure
by stronger polar interactions. We have performed inelastic
neutron scattering experiments to monitor the evolution of
molecular motions of myoglobin and its hydration shell under
pressure up to 0.8 GPa. The correlation time of hydration
water shows the expected increase with pressure, an excess
increase is observed near the denaturation pressure of 0.4
GPa. By contrast the pressure effect on protein structural
fluctuations is more accurately characterised by a decrease
in amplitude and not by a significant slowing down. The
pressure dependence of the molecular amplitude shows a
sigmoid shape centered at the denaturation pressure. The
denaturation is irreversible, cycling the pressure results
in dynamic hysteresis effects. Thus water is interacting
more strongly with the denatured state than with the native
structure.
A recent theory for the long time dynamics of the flexible
chain molecule is applied for the neuron-transmitting
peptide met-enkephalin (Tyr-Gly-Gly-Phe-Met). The
mode-coupling theory (MCT) is successfully applied to the
flexible molecules such like linear and branched alkanes to
predict the global and local relaxation dynamics. In the
MCT, the effect of memory function that is neglected in the
generalized Rouse (GR) is systematically considered and the
time-correlation functions are expressed in terms of various
equilibrium averages. In this work the theory is applied to
a more complicated peptide chain and the dynamics are
compared with a number of simulation results including
molecular dynamics (MD) with explicit water and Brownian
dynamics (BD). The effect of various different friction
models is also employed to increase the accuracy and speed
of the theory.
Some biological membrane and cells can perform
functions such as exchanging message, transferring energy
etc. These functions can be simulated by some
electric circuits. We have obtained a quantization
scheme for a RLC mesoscopic biologically equivalent circuit
and studied the fluctuation of the change and the generalized
current. The result suggests that the
quantum effects of both the biological electronic device and DNA
chip are important and can be taken into account.
The exchange of energy between structural and reactive
degrees of freedom is a basic feature of biomolecular
processes. We present a new method that allows to measure
the enthalpy and volume relaxation of light-induced
reactions.The method is based on a measurement of the
optical pathlength of the aqueous sample which changes with
temperature as a result of thermal expansion. By recording
the interference pattern produced by the sample and
reference path in a Michelson interferometer as a function
of time, we detect temperature changes with sub-millikelvin
resolution on a micro-second to second time scale. With this
method we studied the kinetics of ligand binding to
myoglobin and the P+Q- charge recombination reaction of
photosynthetic reaction centers. The enthalpic relaxation in
myoglobin follows the kinetics of ligand binding whereas the
charge recombination in Rb. sphaeroides involves a thermal
process which is not observed by optical detection. The
reaction volume of CO-binding to myoglobin is found to be
negative, while it is positive for oxygen binding.
We have investigated the photochemical destabilization of
large vesicles. Photofrin (QLT Inc.), a photosensitizer used
in photodynamic therapy of tumors, was added to a suspension
of vesicles wherein it intercalated into the bilayer
membrane of giant (20-40 \mum) vesicles. We irradiated the
samples with light at specific wavelengths. The light
excited the hematoporphyrin component of the Photofrin,
which in turn induced the excitation of oxygen gas molecules
from an unreactive triplet ground state to a highly reactive
singlet state. The reactive oxygen photooxidatively cleaved
hydrocarbon chains of the surrounding membrane. Using
optical microscopy, we have observed bilayer destabilization
and lysis resulting in loss of encapsulated contents when
these vesicles are irradiated with visible light (488-546
nm). We present the results of our experimental
investigations with regard to applications in drug delivery
schemes. This work is supported by NSF (DMR 99-71226) and
MRSEC (DMR 00-79909).
The human replication protein A (hRPA) is an essential
component of DNA replication and DNA repair multiprotein
complexes. hRPA consists of three subunits of 70, 32 and 14
kDA and binds specifically to single stranded DNA and to
damaged DNA. A molecular understanding of the interaction
between RPA and damaged DNA is still lacking. In the present
work, we use AFM TappingMode imaging under physiological
conditions to examine conformational changes related to the
complex formation of DNA and PRA. Double stranded DNA (530
bp) was exposed to UV to produce nonspecifically damaged
DNA. Complexes of damaged DNA with human RPA were imaged in
buffer solution on mica. The complexes were immobilized via
nickel ions. We observe a complicated structure of the
complex indicating that DNA wraps around the protein
molecule. This finding can be attributed to the numerous
binding sites on UV damaged DNA and more than a single
binding site on the protein.
We report on the first results from an AFM study of porcine
gastric mucin employing the tapping mode technique in
aqueous solution. This glycoprotein is responsible for
protecting the stomach epithelium from acid damage. Mucin
was imaged on a mica substrate at pH7, and at pH2. At the
higher pH we detected individual molecules in disordered
configuration, with characteristic lengths of 20-40 nm. At
the lower pH the mucin forms extended rod-like clusters
that, at high concentrations, are aligned into planar
arrays. Individual clusters are of order 50 nm long and 20
nm wide while the entire array is of order several hundred
nm both in length and width. The clustering behavior at low
pH is consistent with that previously detected in dynamic
light scattering experiments by Cao et. al. (Biophysical J.
76:120-1258 1999).
We have studied electrical transport properties of DNA
molecules trapped between two Au electrodes. The electrodes,
whose gaps were smaller than 20 nm, were fabricated by using
e-beam lithography and double angle evaporation techniques,
and the electrostatic trapping method was utilized to attach
DNA molecules to these electrodes. The measured
current-voltage characteristics through DNA molecules
exhibit nonlinear behaviors. At low bias voltage, small
currnet is measured, while the current rises sharply above a
threshold voltage. We have also measured the temperature
dependence of current-voltage curve. As the temperature
increases, the threshold voltage decreases and the
conductivity increases.
Electric Cell-substrate Impedance Sensing (ECIS) was used to
investigate changes in cell morphology and micromotion of
epithelial tissues in response to bacterial challenge. In
this study, HEp-2 laryngeal epithelial cells were grown on a
small gold electrode deposited at the bottom of a tissue
culture well. Following the addition of outer membrane (OM)
extract of Treponema denticola, the time-dependent and
frequency-dependent of impedances for electric current
flowing underneath and between cells were measured.
Movements of cells are revealed as fluctuations in the
time-dependent impedance and can be represented by
calculating the normalized variance. In addition, comparing
model calculations with frequency-dependent data, the
junctional resistivity of the cell layer and the average
cell-substrate distance can be determined. Our data indicate
that exposure of epithelial cells to various OM
concentrations leads to dose-dependent abrogation of
epithelial barrier functions and the reduction in
micromotion. These analytical applications of ECIS may serve
as a model for the exploration of cellular responses to
biological or chemical toxins in general.
Adhesion of cells for a variety of ligand-receptor pair have
been studies previously and in general, the ratio of cells
adhered at high and very low applied forces is used to
determine the strength of adhesion. There is then an
implicit assumption that the number of cells adhered
decreases monotonically with increasing force. However, in
recent experiments in which a wide range of normal force was
applied, cells were observed to respond unexpectedly to the
increase in the applied force. Mainly, the cell adhesion
profile with applied force is observed to have a maximum on
certain biomaterial surfaces. Although the response may be
due to a purely biochemical cascade of events, we explored
the effect of force-dependent Young's modulus and bending
coefficient on cell adhesion. We present the possibility of
many adhesion states, different from the usual two-state
models.
One of the oldest and most important dreams of the
scientific community is a microscope technology for
nondestructively observing the \emphin situ structure of
individual biomolecules. During the past decade,
\emphquantum microscopy has emerged as a powerful new
strategy for achieving molecular observation. At present,
the most advanced quantum microscope technology is magnetic
resonance force microscopy (MRFM), whose sensitivity has
doubled every six months since 1992, in reasonable accord
with ``Moore's Law''. Within a decade, if this Moore's Law
improvement continues, tabletop-scale quantum microscopes
will routinely observe thousands of atomic coordinates per
minute. This capability, if achieved, will revolutionize
structural biology as thoroughly as automated gene
sequencing has revolutionized genomics. This presentation
will review the new opportunities, enduring roles, and role
conflicts that quantum microscopy promises to create for the
physics community, the private sector, Defense, and the
general public.
The genomes of a number of microbial species have now been
completely sequenced. We have developed a program for the
statistical analysis of the appearance frequency and
location of short DNA segments within an entire microbial
genome. Using this program, the genomes of Methanococcus
jannischii (1.66 Mbase; 68radiodurans (3.28 Mbase; 66and compared to a randomly generated genomic pattern. The
random sequence shows the expected statistical frequency
distribution about the average that equals the genome size
divided by the total number of N size short segments (4N).
In contrast, the microbial genomes are radically skewed with
a large number of segments that rarely occur and a few that
are highly represented in the genome. The specific
distribution profile of the segments is strongly dependent
on the overall bias in the organism. The biased appearance
frequency allows us to develop a genome signature of each
microbial species.
In an effort to devise simple and robust systems that can
reproduce in synthetic membranes important features of
biological targeting and surface assembly, a versatile
system for targeting proteins to lipid membranes has been
developed.[1] This system utilizes metal-chelating
iminodiacetate lipids loaded with divalent metal ions (Cu+2
or Ni+2) to target adsorption of specific residues in
proteins. In the present work we use neutron reflection to
study the adsorption of myoglobin to monolayers containing
such lipids at the air-water interface. The metal-chelating
lipids were mixed with deuterated DPPC at a composition of
20subphase buffered with MOPS at a pH of 7.5, compressed to a
pressure of ~ 35-40 dyn/cm, and the reflectivity was
measured. Following this, a solution of CuCl2 or NiCl2 was
added to the subphase, and after mixing for ~1 hr the
reflectivity was again collected. Finally, a solution of
myoglobin was added to the subphase, and after mixing the
subphase for roughly ~ 1 hr the reflectivity was again
collected. The reflectivity revealed a greater adsorbed
amount of myoglobin in the case of the Cu+2 ions than for
Ni+2. In addition, the conformation of the adsorbed
myoglobin was quite different in the two cases, with the
adsorbed layer exhibiting a large dimension (~ 70 Å) in the
case of Cu+2 but a much smaller dimension (~ 20Å) for the
case of Ni+2.
[1] K. Ng, D. W. Pack, D. Sasaki, F. H. Arnold, Langmuir
1995, 11, 4048.
The internal structure and mechanical properties of
assemblies of \beta-keratin have been studied in its
natural forms and after dissolution and re-assembly. \beta
-keratin, the structural protein in feathers, is a fibrous
material containing small \beta sheet crystals, like silk.
But unlike silk or the mammalian \alpha-keratin it has
been little studied in recent years. We have found that
flight feather barbs (from domestic fowl, Gallo gallo) are
significantly stiffer and stronger than the central rachis
of similar feathers, while WAXD shows no significant
difference in crystalline structure or in crystalline
orientation. Feathers may be dissolved by a combination of a
reducing agent and a chaotropic agent. It is known that on
re-precipitation the natural crystal structure re-assembles,
and isotropic films have been made in this way ^2. Plane
strain deformation in a channel die can be used to produce
oriented re-constituted samples which allow direct
structural and mechanical comparison with naturally grown
samples.
^1 Work supported by NSF DMR 970 8062 and Cornell
University
^2 P. M. M. Schrooyen, P. J. Fijkstra, J. Feijen, Polym.
Prepr. (Am. Chem. Soc., Div. Polym. Chem.) 39, no. 2 p 160
(1998)
This abstract not available.
We present a simple method for obtaining the free energy of
dense liquid hydrogen by using the cusp theorem to take into
account the non-linear response of electrons. The cusp
condition is a rigorous requirement in hydrogen and it
originates with the singular nature of the bare Coulomb
interaction between electrons and protons. Our calculation
has shown that response determined with the cusp condition
enforced lowers the electron-proton coupling part of the
free energy at low densities, which leads to an increase of
the pressure (as compared with the standard linear response
approach). The method currently accounts for the non-linear
response around each proton but not between proton pairs,
and therefore it is appropriate for the study of states in
which molecules are fully dissociated but electron-proton
correlations remain strong. These conditions are expected to
be attained in some of recent shock-wave experiments, and
comparison is made between a calculated Hugoniot and the
corresponding experimental curve.
* Work supported by the National Science Foundation and the
Japan Society for the Promotion of Science.
An " In situ" deposition r.f. magnetron sputtering method
has been used to obtain thermoelectric Ce0.9CoFe3Sb12 thin
films on Al2O3, Si, MgO single crystals substrates at
substrate temperatures between 250 and 450ºC. Optical
Emission Spectroscopy (OES) allowed us to determined the
state of the chemical species present in the plasma during
the film deposition. A morphological analysis was carried
out using Atomic Force Microscopy (AFM), showing that the
surface morphology is formed by single grains in form of
oriented sticks in a well-defined direction. The composition
and the profile concentration of the films has been made
using Energy Dispersive X-Ray analysis, EDX. The q-2q scan
of a Ce0.9CoFe3Sb12 thin films grown on MgO show that grains
of the films grow preferentially in the (321) and (420)
orientations. The FWHM measured is 0.30º indicating very
strong alignment of the grains in the film. The resistivity
vs. temperature, between 20 and 350 K, for Ce0.9CoFe3Sb12
thin films, grown on single crystal substrates of sapphire
have similar linear behavior than measurements realized on
the same material in bulk. They show a decreasing of the
resistivity as substrate temperature increase, in the range
of Ts between 250 and 400ºC. The thermopower, at room
temperature, has values of 4.3 - 6.8 mV/K and 2.6 - 7.8
mV/K, for the samples grown on sapphire and silicon,
respectively. It means that thermopower values of
Ce0.9CoFe3Sb12 thin films are one order of magnitude lower
than values of the same material in bulk.
ABSTRACT
The crystal structures and magnetic properties of
EuMn_xGa_3-x (x=0.1-0.7) intermetallic compound have
been investigated by X-ray powder diffraction and magnetic
measurement. The space group is C mcm, with Z=4. The lattice
parameters are a=4.294(1)-4.287(1)Åb=18.50(3)-18.57(3)
Åand c=4.384(6)-4.372(9)ÅIn each unit cell, there
are four kinds of non-equivalent 4c crystal positions for
4Eu, 4Ga^I, 4(Ga^II,Mn) and 4Ga^III, respectively.
The EuMn_xGa_3-x(x\geq 0.28) intermetallic compounds
behave an antiferromagnetic coupling at low temperature.
However, for the samples with x=0.3, a magnetic transition
from paramegnetic to ferromagnetic occurs at 300 K in a low
applied field(H=40 Oe), this transition depends on the
filed, and it will be weaken until disappear with the
increase of filed. The saturation magnetic moment per
molecular is 7.25\mu_B for the samples with x=0.3.
It is well known the main role played by the diffusion
process to determine the physical behavior of materials
ranging from metals, semiconductors and isolators. The
knowledge of the physical laws controlling the diffusion
process allows to improve the search for new materials with
new or improved properties. Plastic deformation and
destruction of metals at high temperatures are just a few
examples where diffusion plays an important role. The
scarcicity of experimental information for the transport
properties in liquid metals makes interesting to simulate
liquid metals and calculate dynamical properties from
computer simulation. Using molecular dynamics computer
simulation, we calculated transport properties for liquid
metals modeling the interatomic interaction through a n-body
Gupta potential appropriate for transition and noble metals.
We analyze the behavior of the mean-square displacement and
the autocorrelation velocity function as a function of
temperature in the liquid state. The diffusion coefficient
is compared for those liquid metals where experimental
information is available, and with other theoretical
results.
We determine the statistical properties of wave functions in
disordered quantum systems by exact diagonalization of one-, two-
and quasi-one dimensional tight-binding Hamiltonians.(V.
Uski et al.), Phys.\ Rev.\ B 62, R7699 (2000) In the
quasi-one dimensional case we find that the tails of the
distribution of wave-function amplitudes are described by the
non-linear \sigma-model.(A. D. Mirlin, Phys. Rep. 326), 259 (2000). In two dimensions, the tails of the
distribution function are consistent with a recent prediction based
on a direct optimal fluctuation method.(I. E. Smolyarenko
and B. L. Altshuler, Phys. Rev. B 55), 10451 (1997).
We investigate the hydrodynamic response functions for
degenerate free-electron gases confined in low dimensional
systems (2D and 3D) when collisions are included.
Expressions for the complex stiffness parameter of the
nonlocal dielectric functions between high- and
low-frequency limits are obtained from the Boltzmann model
with the Mermin correction which guarantees local
conservation of particles.
The propagation of axially symmetrical electromagnetic waves
in an infinitely long cylindrical hole of circular cross
section and metallic walls is studied. For transverse
magnetic polarization we found that the hole can support
modes with surface character: the field intensity is maximum
at the metal-air interface.The calculations have been
performed employing the Drude model for the dielectric
constant of the metal. Absorption was neglected. For small
enough hole diameter, the structure of the dispersion curve
shows the occurrence of a self-interaction effect of the
surface wave. It is also interesting that the dispersion
curve crosses the air line-light. Thus the modes transform
from oscillatory type to surface type as the wave vector
increases. The dependence of the modes on the hole diameter
and the plasma frequency of the metal will be presented.
We have studied the reflection - and the transmission - of
longitudinal waves by a solid multilayer bounded by a fluid.
Thus, the reflected and the transmitted waves are also
longitudinal waves. Inside the multilayer the displacement
acquires an additional transverse component and the waves
are polarized within the saggital plane. We have found that
the transmission of acoustic energy is strongly dependent
not only on the number of layers in the multilayer but also
on the value of the elastic constant of the external medium.
Furthermore, knowing the band structure of the infinite
superlattice, one finds that the response of the finite
multilayer corresponds to the expected behavior only for
small contrast between the elastic parameters of the
bounding medium and those of the layers. For large contrast,
total reflectivity is obtained even within frequency regions
where the propagation is allowed in the infinite
superlattice. Results for a W/Al superlattice bounded by Hg,
water and air are presented.
Vanadium sesquioxide undergoes a phase transition at
155K~165K from an antiferromagnetic insulator to
paramagnetic metal with the crystal structure changing from
monoclinic(I2/a) to trigonal (R3C)) with a 1.4volume at elevated temperature. The metal-insulator
transition in V2O3 is generally believed to be driven by the
Mott-Hubbard (MH) mechanism. However, recent experiments
show there is still controversy with the metal-insulator
transition model. It should be emphasized that since the MH
mechanism depends on the distance between the first few
neighboring atoms and the corresponding overlap of their
wave functions, the measurements of the local structure may
help to determine whether this or some other mechanism
holds. In this paper, v2O3 Powder is detected by X-ray and
Neutron rays. The result shows that PDF patterns of
monoclinic phase and trigonal phase are similar, which means
the local structure of both phases do not change. The fact,
that local structures of both phases are similar, cannot be
explained by the pure orbital occupation of Mott-Hubbard
type of transition. Other mechanism, including electronic
and magnetic structure change may take an important role in
the transition
Mono- and bi-vacancy diffusion in aluminum bulk are investigated at a wide
range of temperature (300 K \sim 700 K) using the hyper molecular dynamics
(hyper-MD) method
with a well tested glue potential. The calculated diffusion
constants are well fitted by the Arrhenius law. For the
mono-vacancy diffusion, the calculated diffusion activation energy E_A
is 1.18 e V which is in good agreement with experiment data 1.28 e V.
While the obtained diffusion constants for the bi-vacancy by hyper-MD are
very close to that of conventional MD. We find that, for the bi-vacancy
diffusion, the two vacancies are close to each other during the diffusion,
which is consistent with the lower formation energy of the two nearest-neighbor
vacancies. Our results also demonstrate that the hyper MD method is efficient
to treat with the long time dynamical process such as the vacancy diffusion
in the real system.
Mass fraction of hydrogen contained within metal systems at
levels of 100 ppm can be determined by neutron incoherent
scattering (NIS), in addition to the standard technique of
prompt gamma activation analysis (PGAA). The NIS technique
takes advantage of the anomalously high incoherent
scattering cross section for hydrogen, potentially allowing
a more rapid detection of hydrogen than PGAA which uses the
much lower (by about 2 orders of magnitude) absorption cross
section. Previously we have shown [1,2] a linear
relationship between the scattered neutron intensity and the
hydrogen mass fraction within polypropylene films and
titanium alloys, employing neutron proportional counters
recording total scattered intensity at a given angle. The
present work attempts to resolve spatial distribution of
hydrogen in metals by acquiring an image of the scattered
neutrons using an imaging detector viewing through a
pinhole. Like transmission radiography, the image of the
scattered beams can be recorded in a quantitative manner
with position information. Unlike the transmission
radiography which relies on the removal process, the
"scatter-o-graphy" utilizes the strong scattering of
hydrogen, therefore enhances the contrast of the hydrogenous
matter to the matrix. By having the detector out of the
incident beam, better signal to noise can be expected. We
present preliminary results with discussions on spatial
resolution and detection limit of this new technique.
1. V.V. Kvardakov et al., J. Appl. Phys. 83, 3876-3879
(1998).
2. H.H. Chen-Mayer et al., Mat. Res. Soc. Symp. Proc. 513,
191-196 (1998).
This abstract not available.
Monte Carlo simulations are performed to study the interface growth in an
electrophoretic deposition of polymer chains. Effects of segmental dynamics,
i.e., kink-jump and reptation on conformation of chains and their density
profiles are examined. We consider a L_x \times L \times L lattice with
a large aspect ratio L_x/L with an impenetrable substrate/wall at x=L_x.
Polymer chains (of length L_c) are released from x=0 end in an electric
field E along x-direction. In addition to excluded volume, we consider a
nearest neighbor polymer-polymer repulsive interaction.
Kink-jump (slow) and reptation (fast) dynamics are considered to move chains
segments with a Metropolis algorithm.
Evolution of the density profile and conformations is studied
as a function of molecular weight (L_c), field (E), and temperature (T).
Growth of the interface width W \sim t^ \beta with the time step t and
scaling of the saturated width W_s = W as t \to \infty with these
parameters (L, L_c, E, T) are examined.
Segmental dynamics is found to be crucial in controlling the
interface growth - some of these observations, as reptation is added
to kink-jump dynamics, will be reported.
Computer simulations are performed to study the growth of polymer density,
conformational evolution, and interface growth in an electrophoretic
deposition model of polymer chains. We consider a discrete lattice of size
L_x \times L \times L with a large aspect ratio L_x/L.
An impenetrable substrate/wall is placed at one end of the sample
(x=L_x). Polymer chains of length L_c are released from the source
end (about 20% of longitudinal (x-direction) space near x=0).
A nearest neighbor polymer-polymer repulsive interaction is considered
along with the excluded volume effects. An electric field (E) couples
with the change in energy, positive and negative, as the chain nodes move
along (+x) and opposite (-x) to field direction. Metropolis algorithm
is used to move the chain nodes using kink-jump and crank-shaft dynamics.
Growth of density, interface width (W) and conformational profiles are
studied as a function of MC steps (t). We estimate the growth exponent
\beta, W \sim t^ \beta and roughness exponent \alpha, W_s \sim
L^\alpha, where W_s = W as t \to \infty. Longitudinal and
transverse components of the radius of gyration at the substrate,
bulk, and interface are analyzed in detail. Effects of temperature,
field, and molecular weight will be presented.
We present
movies of
pattern coarsening of block copolymer microdomains in thin
films. The system consists of a single layer of polystyrene
spheres or cylinders in a poly(ethylene-alt-propylene) matrix.
The modulus difference of the two blocks provides contrast for
time-lapse tapping mode atomic force microscopy. For cylindrical
microdomains, the orientational correlation function \xi has
been shown to grow with time t during annealing as t^1/4.
By presenting movies of the evolution of microdomain patterns we
show that such exponents can be understood in terms of
topological defect annihilations involving three or four
disclinations. Similar exponents have been measured for spherical
microdomains, suggesting similar coarsening mechanisms. However,
pattern coarsening in spherical microdomains produces grain
boundaries, largely absent in patterns of cylindrical
microdomains, suggesting alternative mechanisms of ordering.
The adhesive and overall mechanical properties of
nanostructured coatings made from latex particles or diblock
copolymer micelles have been characterized by a variety of
techniques. The micelles, based on diblock copolymers of
poly(methyl methacrylate) and poly(n-butyl acrylate),are
excellent models for the more complex latex particles.
Layers of micelles or latex particles were coated on
different substrates from solutions of various
concentrations. The adhesive response of these layers was
studied by a modification of the 'JKR' method of adhesion
testing. In addition,the surface structure was imaged using
atomic force microscopy. These data provide useful
information about the contributions of individual particles
to the overall adhesive response, and of the transition from
a layer of isolated particles to a continuous film.
We introduce a novel method of modifying the surface
properties of materials. This technique, called MAPA
(="mechanically assisted polymer assembly"), is based on: 1)
chemically attaching polymerization initiators to the
surface of an elastomeric network that has been previously
stretched by a certain length, \Deltax, and 2) growing
end-anchored macromolecules using surface initiated
("grafting from") atom transfer living radical
polymerization. After the polymerization, the strain is
removed from the substrate, which returns to its original
size causing the grafted macromolecules to stretch away from
the substrate and form a dense polymer brush. We demonstrate
the feasibility of the MAPA method by preparing high-density
polymer brushes of poly(acryl amide), PAAm. We show that, as
expected, the grafting density of the PAAm brushes can be
increased by increasing \Deltax. We demonstrate that
polymer brushes with extremely high grafting densities can
be successfully prepared by MAPA.
In lattice Monte Carlo simulations for a system with an
impenetrable wall, we usually assume that the wall sits on
one of the layers on the lattice points. We obtained monomer
density profiles of chain molecules near the wall for
different lengths and concentrations. Since the radius of
gyration Rg (correlation length in semidilute solutions) is
the only scale to measure the distance, the density reduced
by its bulk value should be a universal function of the
distance to the wall reduced by Rg and the exponent in their
relationship near the wall should be 5/3 for athermal chains
and 2 for theta chains. We found that placing the wall at
the lattice points does not yield a master plot and it
rather requires the wall be placed slightly behind the
lattice points, effectively increasing the distance by a
fraction of the lattice unit. The submerging depth is ca.
0.13 of the lattice unit in dilute solutions and 0.37 in
semidilute solutions for athermal chains and 0.5 at all
concentrations for theta chains.
Asymmetric diblock copolymers of poly(styrene) and
poly(methyl methacrylate), P(S-b-MMA), having cylindrical
domains of PMMA, provide a model system to produce
nanoporous thin films. Using either controlling interfacial
interaction or applying an external electric field, cylinder
domains can be oriented normal to the surface. Exposing the
film to deep UV radiation may degrade the PMMA and crosslink
the styrene matrix. After washing a porous film is obtained.
By changing the molecular weight, smooth porous films with
pore diameters ranging from 13 to 50nm are obtained where
the pores are closely hexagonal packed.
Controlled ordering of materials is key in utilizing
self-assembly processes for nanotechnological structures.
Self-assembly using specific molecular interactions provides
a route to controlled ordering from the molecular to the
macroscopic level. A polymer-mediated approach is utilized
to order gold nanoparticles into well-defined network
aggregates. The gold nanoparticles are functionalized with
recognition sites, whereas the polymer chains contain
complementary sites; randomly located along the chain. In
solution, the interactions between the functional groups on
the gold nanoparticles and those on the polymer cause an
aggregation of the particles. Well-defined gold particle
separation and aggregate sizes are observed. The former is
dictated by the length of the polymer and interaction
strengths, whereas the latter is governed by the solubility
limits of the aggregates. X-ray scattering studies as a
function of the particle size and interaction strengths will
be discussed.
Soft pressure-sensitive-adhesives are able to stick to a
surface by simple contact under light pressure. The feeling
of stickiness is due to their ability to form bridging
fibrils when they are subsequently removed from that
surface. Among other factors, the topography of the
adherent’s surface has an important influence in the details
of the observed debonding mechanisms. We investigated in a
systematic way the role played by a change in wavelength and
amplitude of the surface roughness, first with random
surfaces made by polishing, then with periodically rough
surfaces made by a lithographic technique. We observed that
the amplitude of surface roughness controls the stress level
at which failure is initiated and influences significantly
the propagation of cracks at the interface once they are
nucleated.
Experimental studies on the effects of physical
heterogeneity on polymer adsorption will be presented.
Planar substrates with different degrees of roughness were
prepared by thermal evaporation of gold onto glass slides
and mica templates followed by the stripping of mica
respectively. Chemical homogeneity of surfaces was achieved
by modification of the gold substrates with a self-assembled
monolayer of a long chain alkanethiol
(CH_3(CH_2)_11SH). Poly(ethylene oxide) (PEO)
adsorption was monitored by a surface plasmon resonance
technique with high time resolution. Experimental results
showed higher polymer adsorption amount and less distortion
of adsorbed polymer chains on rougher surfaces, which
corroborates previous theoretical predictions. Kinetic
studies also demonstrated that PEO adsorbed more readily on
the rougher surfaces. The reorganization of polymer chains
is found to be governed by a combination of parameters such
as polymer concentration and flow rate of polymer solution.
Ongoing work on adsorption on chemically heterogeneous
surfaces will also be discussed.
A recently reported method for photochemical attachment of
ultrathin polymer layers to solid surfaces ^2 is
extended to allow lateral patterning of these layers using
standard photolithographic equipment. Silane-modified
benzophenone molecules are synthesized and deposited as a
monolayer on a SiO _x surface. A polymer layer placed on
top of this monolayer is then bound to the photoreactive
benzophenone moieties by illumination with UV light, exposed
through a standard photomask. Non-bonded polymer is then
washed away, allowing a second polymer to be attached in
previously unoccupied areas by subsequent coating and
illumination steps. ^2 Prucker, O.; Naumann, C. A.;
Rühe, J.; Knoll, W.; Frank, C. W. J. Am. Chem. Soc. 1999,
121, 8766.
We report the first Monte Carlo simulations regarding the
morphology of asymmetric diblock copolymer thin films
confined between two hard surfaces, either homogeneous or
cross-patterned. In the bulk, the asymmetric diblock
copolymers form hexagonally packed cylinders consisting of
the minority component in a matrix of the majority
component. For thin films confined between two homogeneous
surfaces, we study systematically the dependence of the
morphology in the films on the surface-block interactions
and the film thickness. Cylinders either parallel or
perpendicular to the surfaces, as well as non-cylindrical
morphologies (including lamellae, spheres and perforated
lamellae), are all observed in simulations. A comprehensive
review of the literature indicates that our results are in
good agreement with experimental observations.
Nano-patterned substrates are then applied to induce
long-range ordered perpendicular cylinders that are
registered with the surface pattern. Our simulations show
that two conditions are essential for obtaining such
desirable structures: a lower cross-patterned surface
commensurate with perpendicular cylinders (having the same
dimensions and packing as in the bulk) and an upper neutral
or weakly preferential surface for the longer blocks.
We used dielectric measurement in the range 0.1 Hz to 1 MHz
to study the motions of molecules and ions in a conductive
polymer, polypropylene oxide with small quantities (on order
1%) added lithium ions (LiClO4), confined between two
insulating mica surfaces. In the dielectric loss spectrum,
we observed three peaks; they originated from the normal
mode of the polymer, segmental mode of the polymer, and ion
motions. With decreasing film thickness, the peak
frequencies corresponding to the normal mode and to the ion
motion shifted to lower frequencies, indicating retardation
due to confinement. On the contrary, the segmental mode was
not affected.
Electric fields provide an effective route to orient
microdomains in thin, diblock copolymer films either
parallel to or normal to the surface. In thin films of
poly(styrene-block-methylmethacrylate), a threshold electric
field strength Et was found, which for film thicknesses
greater than 10 microns, was independent of film thickness
and could be described by the difference in interfacial
energies of the blocks of the copolymer with the substrate.
Neutron reflectivity, small angle neutron and x-ray
scattering and off-specular scattering suggest that
interfacial fluctuations are amplified by the electric field
leading to an orientation of the cylinders along the field
lines. Time and temperature dependent studies on thin films
will be shown that elucidate the mechanism of alignment. In
addition, studies on thin films with the morphology oriented
normal to the surface using two orthogonal electric fields
in series will be presented.
Molecular dynamics simulations of the solid-vacuum
interfaces of more than a dozen polymer types have been
performed using the COMPASS force field (Molecular
Simulations, Inc.) A simple method for estimating the
enthalpy of adhesion for small molecule probes was
developed. The results for water, diiodomethane, and
ethylene glycol were compared to works of adhesion derived
from contact angle measurements. An extensive literature
search was performed to compile a table of average works of
adhesion, as measurements of this quantity can vary by as
much as 25diiodomethane and ethylene glycol are in excellent
qualitative agreement with experimental works of adhesion,
demonstrating that molecular dynamics simulations can
predict wetting trends. A similar comparsion for water
yields somewhat rougher agreement, probably because the
'parachute' method neglects probe-probe interactions and
does not allow the polymer to reorient in the presence of
probe molecules. Preliminary results from full molecular
dynamics simulations of polymer / water interfaces are
presented.
Traditionally, silicon rubbers (SRs) have been used as
insulators, coatings, and protection layers. Recently, novel
applications of SRs appeared, including those as flexible
supports for self-assembled monolayers (SAMs). In order to
form SAMs on SR surfaces, one has to generate surface
grafting groups on the originally hydrophobic SR surface. To
carry out this modification, several techniques can be
utilized, including oxygen plasma, corona treatment, various
forms of chemical treatment, etc. The extent to which the SR
surface gets altered depends crucially on the technique and
given experimental conditions. We investigate the effect of
ultraviolet (UV) radiation, and its combination with ozone
(UVO), on the modification of poly(dimethyl siloxane) (PDMS)
surfaces. Specifically, the effects of the UV light
wavelength and ambient conditions on the surface properties
of PDMS are studied using a palette of experimental probes,
including near-edge X-ray absorption fine structure, Fourier
transform infrared spectroscopy, X-ray reflectivity,
ellipsometry, and static contact angle. Using this database
of results, a new model describing the modification of PDMS
by UV and UVO is proposed.
A thermal probe is placed in contact with a polymer film and
the power loss from the probe is measured as a function of
the temperature at which it is held. We have made
assignments of the glass transition temperatures of various
polymer films by identifying the temperature at which there
is a change in the first derivative of the power loss from
the thermal probe. This method - local thermal analysis -
provides an alternative to the methods of determining T_g
based on changes in film thickness with temperature. The
glass transition temperatures of the films are found to
deviate considerably from the values in bulk, towards both
higher and lower values, and vary smoothly as a function of
the film thickness. We have also demonstrated experimentally
the linear dependence of the T_g on the interfacial energy
\gamma of the substrate surface. This is attributed to
changes in the mobility of the polymer chains at the
surfaces. In further experiments we have grafted the
polymers to the substrate and find that the deviations of
T_g from the bulk values are much higher than expected,
and these deviations manifest themselves at much higher film
thicknesses than expected. The results are again consistent
with the proposed mechanism of reduced surface mobility.
Finally, molecular simulations of thin polymer films are
consistent with these experimental results.
Morphlogy of thin films of asymmetric diblock copolymers on
passivated silicon surfaces was studied. The passivation was
achieved by eliminating native oxide layer of silicon wafers
with a buffered aqueous HF solution. Thin films of
asymmetric diblock copolymers of polystyrene and poly(methyl
methacrylate) show different domain orientation as a
function of film thickness on the passivated surfaces. By
controlling film thickness, a surface patterned with
perpendicular cylindrical domains was obtained. The surface
passivation provides a very simple, rapid route to produce a
nonpreferential surface to polystyrene and poly(methyl
methacrylate) diblock copolymers. Controlling the domain
orientation and lateral ordering on the surfaces will be
addressed.
Thin films of triblock copolymers of polystyrene,
polybutadiene, and poly methyl methacrylate, denoted
P(S-b-B-b-MMA), were investigated. Here, the nonfavorable
interactions between the S and MMA blocks are much weaker
than S-B and B-MMA interactions. The interfacial and surface
energies of the central block are much smaller than those of
either of the endblocks. This forces the central block to be
located at both the substrate and air interfaces, thereby
controlling the orientation of the microdomains. Variation
of block ratios and film thickness produced marked changes
in morphology as evidenced by atomic force microscopy.
We have undertaken a characterization in direct space of the
free surface of thin polymer films (polystyrene, poly methyl
methacrylate and poly(vinylpyridine)) by atomic force
microscopy (AFM) in contact and tapping mode. Films were
prepared by spin-coating and then annealed in a vacuum
furnace before being quenched in air at room temperature.
Power spectral densities (PSD) were computed from AFM images
obtained at room temperature at different magnifications.
The analysis shows that PSD's follow the theory of capillary
fluctuations, with the values of surface tension computed
from power spectral densities agreeing well with tabulated
values. In the poster, we present results obtained on
different systems where the nature of the polymer, the
thickness of the film and the polymer molar mass are
systematically varied.
Organization of polymers near heterogeneous surfaces
embodies a vast area of both practical and fundamental
interest. For example, these systems are relevant to such
applications as fiber-filled polymer composites and
adhesives. The interest in studying and utilizing these
phenomena is also catalyzed by numerous examples from
biology and biochemistry that constitute the structural and
functional foundations of life. In this work, we use Monte
Carlo (MC) simulation to investigate the effects of monomer
sequence distribution, polymer/surface interaction energy,
and the size of heterogeneous surface domains on the
copolymer adsorption at chemically heterogeneous substrates.
Based on the bond fluctuation model in conjunction with
configurational biased MC moves, our MC model is used to
uncover the ability of the adsorbing copolymer to recognize
the substrate chemical motifs and transcribe them into three
dimensions. A very good agreement between the MC results and
those obtained recently by 3D self-consistent field model is
found.
Helical polypeptides such as poly(g-benzyl-L-glutamate)
(PBLG) exhibit a large dipole moment along their molecular
axis and thereby allow for the preparation of a
macromolecular array of dipoles on a solid substrate. The
interplay among molecular parameters and solvent conditions
during the self-assembly of PBLG on a gold substrate will be
presented. SSPBLG was prepared by polymerization of the
N-carboxyanhydride using a disulfide-bearing amine
initiator. Surface plasmon resonance measurements indicate
rapid assembly of SSPBLG within the time scale of minutes.
An increase in length of the polypeptide leads to an
increase in the average tilt of the rod axis towards the
substrate, plausibly, due to larger dipolar interactions.
The time of assembly played a significant role as long times
of assembly led to a decrease in the surface coverage and an
increase in tilt angle. For the long polypeptide,
hydrophobic interactions with the substrate were found to
impede the assembly of SSPBLG with lower tilt. Ongoing work
on a photo-responsive PBLG system will also be presented.
The surface composition and structure of nanoscale
aggregates in ionomer thin films have been found to differ
from the bulk. Using Rutherford backscattering spectrometry,
surface segregation of counterions and acid groups is
observed in poly(styrene-co-methacrylic acid), P(S-co-MA)
and poly(ethylene-co-methacrylic acid), Surlyn®, neutralized
with several counterions. After annealing at 145°C, the
surfaces of P(S-co-MA) and Surlyn® are enriched with Cs and
Mg counterions, respectively. The effect of annealing
temperature and time will be presented for both systems.
Segregation is interpreted in terms of a combination of both
free counter ion diffusion and the motion of counter ions
associated with their acid groups. Using scanning force
microscopy, the surface topographies in both
poly(styrene-co-styrene sulfonic acid Zn) and P(S-co-MACs)
are investigated. For both systems, nanoscale dimples
associated with the ionic domains develop upon annealing.
Block copolymer thin films have tremendous potential for
applications in nanofabrication because they self-assemble
into ordered structures at the length scale of 5-50 nm. We
have developed techniques to orient the domains in
microphase-separated, symmetric diblock copolymer films such
that: 1) the domains are perpendicular to the substrate, 2)
the perfection of ordering of the domains extends over
macroscopic dimensions, and 3) the periodic structure of the
film is registered with features of the underlying
substrate. Organic imaging layers based on self-assembled
monolayers of alkylsiloxanes are patterned with regions of
different chemical functionality using advanced lithographic
tools. The surface chemistry of the imaging layer is modifed
by exposure to radiation in the presence of oxygen. The
imaging layers were designed such that unexposed regions are
wet by PS and exposed regions are wet by PMMA. The
chemically nanopatterned surfaces guide the self-assembly of
the block copolymer domains such that the surface pattern is
amplified throughout the thickness of the polymer film.
The controlled growth of organic thin layers consisting of
laterally separated areas of different composition, is a
great challenge for their application in the fields of
sensors and opto-electronics. As a first step towards this
goal we present STM studies on a two component system: PTCDA
and decanethiols (CH10) grown on Au(111) surfaces. PTCDA is
of great interest because of its organic semiconducting
behavior, whereas thiols are archetypical examples of
self-assembled growth. In a first series of experiments
PTCDA was deposited on the "striped" (low density, lying
down) phase of CH10 and it was found that the thiols are
displaced by the PTCDA molecules which form islands
surrounded by thiol domains of denser structure.
Interestingly, the PTCDA molecules order in a square pattern
different from that observed for PTCDA on bare Au. In a
second series of experiments, PTCDA was grown on the
initially prepared standing up phase of CH10. After
annealing the samples to 373 K, the thiol molecules are
partially desorbed and the PTCDA covers the Au surface in a
herring-bone phase comparable to that found for pure PTCDA
monolayers on Au(111). Adjacent to the PTCDA patches
"striped" CH10 domains were observed. Therefore the
structure of the PTCDA domains seems to depend on the way
they are prepared.
Dynamics of thermally induced phase separation and
morphology development in main-chain liquid crystalline
polymer (MCLCP) solutions have been investigated by
incorporating the combined free energy density with the
coupled time-dependent Ginzburg Landau (TDGL, Model C)
equations. The total free energy density for such a system
is described in terms of a simple addition of the free
energy densities for isotropic mixing, nematic ordering, and
chain stiffening. Numerical calculations have been performed
on a two-dimensional lattice in order to simulate various
thermal quench experiments into nematic-liquid coexistence
and unstable nematic regions. The competition of
liquid-liquid phase separation and nematic ordering in the
liquid crystalline polymer results in a variety of the
morphological patterns in the compositional order parameter
and the orientational order parameter fields.
Component miscibility plays a critical role in the physical
properties of polymer mixtures. Our inability to predict
blend miscibility has limited the applications of polymer
blends and their reuse by recycling.Here we present recent
efforts towards tuning the miscibility of polymer mixtures
based on a simple new model for the free energy of mixing of
compressible polymer blends. The model's ability to make
semi-quantitative predictions of phase diagrams for various
polymers pairs using only pure component properties is
discussed, along with our extension of the model to ternary
blends.
Muscovite mica is a 2:1 layered aluminosilicate, which has
outstanding corona and electric insulation properties. Each
2:1 layer consists of two tetrahedral silica sheets
sandwiching an octahedral alumina sheet and is about 1 nm
thick. These mica platelets are often used as filler in
polymer composites. However, they are poorly wetted by
hydrophopbic polymers due to their high energetic surfaces.
This leads to agglomeration of the filler particles and
deterioration of the composite mechanical properties. To
overcome this problem, the inorganic surface cations are
exchanged with organic ammonium ions. As a result, the mica
surface is covered by an organic (e.g. alkyl) monolayer,
which is ionically bonded to the surface. This ultrathin
layer represents an interphase between the two composite
phases and influences its properties. In this work, we study
the structure and the phase transitions of the organic
monolayer.
We report on the phase behavior of model rigid rod molecules
consisting of 11 beads that experience soft-core repulsion
of the form A/r^12. The system exhibits two mesogen phases,
nematic and smectic A. Both the isotropic-nematic and
nematic-smectic A transitions are weakly first order.
Kofke’s integration method for direct evaluation of phase
coexistence was used to obtain the first order coexistence
curves as a function of temperature and pressure. The
starting points for the Kofke’s integration method on the
coexistence curves were obtained by free energy calculations
using thermodynamic integration along reversible paths. The
influence of attractive interaction on the phase behavior is
also investigated. As intuitively expected, the attractive
potential stabilizes the ordered phase at the expense of
relatively disordered phase.
Phase segregated amorphous - side-chain liquid crystalline
block copolymers (SCLCBCs) have potential to serve in a
variety of self-supported electro-optic devices. Within
confined LC microdomains, mesogenic side-chains can form
ordered phases that respond to applied voltages. However,
applications of SCLCBCs are limited due to slow
electro-optic response times. In our earlier study, we
synthesized and characterized a series of SCLCBCs; the
amorphous block is polystyrene, and the LC block has a
methyl methacrylate backbone with biphenyl benzoate
mesogenic side-chains. Recent efforts have focused on
increasing electro-optic response times by introducing small
molecule LCs into the polymer LC domain. Here we report
experimental results of our investigation of binary
(LC/SCLCBC) blends. LC phases and glass transition
temperatures were determined using optical microscopy,
differential scanning calorimetry, and X-ray scattering.
Block copolymer microstructures were examined using electron
microscopy and small-angle X-ray scattering. Discussion will
focus on how the LC blend compositions affects glass
transition, LC phase stability, LC miscibility, and the
miscibility between the two blocks.
The role of polymer molecular weight on the phase behavior
of a small molecule liquid crystal,
4'-octyl-4-biphenylcarbonitrile (8CB), dispersed within a
poly(methylmethacrylate) (PMMA) matrix was determined using
optical microscopy, DSC, and wide angle light scattering.
The blends that were examined consisted of PMMA with Mw of
120,000, 340,000, and 996,000 g/mol and spanned the
concentration range of 20-100crystalline phase behavior of the blends was observed using
cross-polarized optical microscopy in conjunction with DSC,
while the isotropic two-phase to isotropic single phase
transitions were recorded using phase-contrast optical
microscopy as well as wide angle light scattering. Finally,
the solubility limit, b, of 8CB in the PMMA matrix along
with the relative amount of 8CB in the LC droplets, a, has
also been calculated from DSC measurements. These data will
be utilized to understand the coupling of polymer molecular
weight to the phase separation process that occurs in the
production of polymer dispersed liquid crystal devices by
polymerization induced phase separation.
The kinetics of the order-to-order transitions in a
styrene-isoprene (SI) diblock copolymer (11000-32000 g/mol)
dissolved in the styrene-selective solvent di-n-butyl
phthalate (DBP) has been studied using rheology. The
following sequence of phases was identified upon heating
near the copolymer volume fraction \phi=0.67: Lamellae (L)
\rightarrow Gyroid (G) \rightarrow Hexagonal Cylinder
(C) \rightarrow Disordered (D). Shear modulus measurements
on SI (11-32) in DBP were performed while cycling
temperature at different rates across the transition between
gyroid and cylinder microstructures. In the limit of high
heating and cooling rates, the apparent stability limit for
the G and C phase were determined to be 102 \pm 3 ^oC
and 65 \pm 3 ^oC, respectively. At low scanning rates,
the order-to-order transition temperature was determined as
79 \pm 3 ^oC. Furthermore, the cylinder phase was
quenched from 85 ^oC to various lower temperatures and the
kinetics of the C to G transition was studied. Following the
temperature quench, the shear modulus was observed to
increase with time in two distinctive steps. The details and
the interpretation for this two-stage transformation will be
discussed in the presentation.
We controlled DH(Degree of Hydrogenation) of C-9 resin. From
the upper critical solution temperature, a favorable
interaction between Polystyrene (PS) and HRs (Hydrogenated
Resin) was enhanced with increasing DH and an optimum value
of DH was approximately 0.7 in HR ,which gives the most
favorable interaction with Polybutadiene (PB). The adhesion,
viscoelastic properties, and the order-to-disorder
transition temperature were investigated for the mixture of
polydiene-based block copolymers/HRs with various DHs : (1)
polystyrene-block-polybutadiene-block-polystyrene (SBS)
copolymer ; and (2)
polystyrene-block-polyisoprene-block-polystyrene (SIS)
copolymer. We found that viscoelastic properties, such as
plateau modulus and glass transition, depend predominantly
on the miscibility between PS block and HRs as well as that
between PB (or PI) block and HRs, which in turn are strongly
affected by the DH in an HR. At lower values of DH, HRs are
associated with PS end block; thus tack properties become
negligible, although the plateau modulus increases greatly.
The tack properties depended remarkably on the miscibility
between HRs and elastomeric mid-block in the block
copolymers.
Depletion interactions in mixtures of polymers and spherical
particles have been of interest due to important
applications in the fields of colloid, materials, and
bio-molecular sciences. Pure entropic depletion interactions
induced between spherical colloids (or nano-particles) by
rod-like polymers and vice versa are investigated by
numerically solving the Polymer Reference Interaction Site
Model with the Percus-Yevick closure for hard-core
potentials. The density pair correlation functions and
collective structure factors have been obtained for model
mixtures at various particle densities and size ratios, from
which the inter-particle potential of mean force, the
liquid-liquid spinodal phase transition behavior, and some
dynamic properties can be examined. The predictions for the
phase transition boundaries and potentials of mean force are
compared with simulation results and other theoretical
approaches, and qualitative agreements are demonstrated.
Calculations that address the strong influence of
non-additive intermolecular repulsive interactions on
equilibrium behavior, and the modification of the colloidal
glass transition by rod additives will also be presented.
In previous studies of n-paraffins, it was observed that
there is no supercooling within the calorimeter on melt
crystallization up to at least C50H102. To find the limit in
chain length for the absence of supercooling, the study was
extended to polyethylene fractions (PE) and
poly(oxyethylene) (POE) of varying, low molar mass using
temperature-modulated, differential scanning calorimetry
(TMDSC) (Samples: PE560, PE1150 and PE2150, and POE1500,
POE1960 and POE3060, where the numerical identifier
specifies the molar mass). The analysis was by quasi-
isothermal temperature modulations of small amplitudes (0.05
K and 0.5 K). All crystals grow to extended-chain
macroconformations. The apparent reversing heat capacity on
melting and crystallization was measured for all samples,
and it was found that there is practically no supercooling
for melt crystallization up to PE1150. The higher molar mass
PE2150 and the POE oligomers, in contrast, show the typical
supercooling of polymers. The degree of supercooling of the
crystals is expressed as a function of chain length. The
data identify the critical chain length for secondary or
molecular nucleation as 10 nm. --- Supported by NSF,
Polymers Program, Grant DMR-9703692 and DOE at ORNL, managed
and operated by UT-Batelle, LLC, under Contract
DOE-AC05-00OR22725.
We examine the Landau free energy surface of a diblock
copolymer melt using self-consistent field theory. The
topography of its surface is found to exhibit a low-energy
pathway connecting the local minima associated with the
cylindrical (C) and spherical (S) morphologies. The pathway
corresponds to an epitaxial transition where the periodicity
of the two phases is matched with the cylinder axis oriented
in one of the [111] directions of the bcc spheres. The
energy barriers and stability limits are evaluated, and from
them we conclude that the C-S transition should normally
occur by a nucleation and growth mechanism. Based on the
generally small energy barriers, we suggest that fluctuation
effects are much stronger than previously anticipated.
Furthermore, we examine the way the morphology evolves
during a transition and discuss its signature in a
small-angle scattering experiment.
Discontinuous molecular dynamics simulation is used to study
the phase behavior of diblock copolymers - modeled as chains
of tangent hard spheres with square shoulder repulsions
between unlike species - as a function of chain length,
volume fraction (f) and interaction strength (\chi). The
location of the order-disorder transition for a symmetric
copolymer is close to the predictions of Fredrickson and
Helfand. Our simulation results for packing fractions of
0.35 - 0.45 and chain lengths 10-20 are summarized in phase
diagrams which display disordered, lamellae (L), cylindrical
(C), perforated lamellae (PL) phases in the \chi/f
plane. These phase diagrams are consistent with phase
diagrams from other simulation studies. Contrary to
theoretical predictions we observe the PL phase between the
C and L phases, and do not find ordered spheres for highly
asymmetric copolymers. We believe these results are due to
the short chain lengths considered. Using the peak values of
the structure factor, we can reconstruct the average 3-D
concentration profile. By including off-peak values of the
structure factor, we can reconstruct a density profile,
which includes the stable fluctuations in the system.
We apply a density functional theory to study the mutual
influence of the microphase segregation and the nematic
ordering of an AB diblock copolymer, which consisting of a
liquid crystalline polymer block and an isotropic one. Three
ordered morphologies are investigated: lamellae, hexagonal
packed cylinders, and bcc spheres. The phase diagram is
characterized by the Flory’s interaction parameter, the
molecular weight, the volume fraction of the liquid
crystalline block, and the Maier-Saupe parameter. We also
calculate the domain spacing and the interfacial width of
the ordered morphologies. The effect of topological defects
and the elastic energy on the phase behavior for rod-coil
type diblock copolymers is discussed.
We use a hybrid computer simulation method to study the effect of an
oscillating field on the mobility, conformation, and segregation of
polymer chains in a heterogeneous matrix.
The hybrid computational method involves discrete lattice simulation
to accelerate the sample preperation followed by an off-lattice
simulations to capture the details.
Polymer chains are represented by a bead-spring coarse-grained model
with a finitely extensible nonlinear elastic (FENE) covalent bond
potential between consecutive beads of the chain. A Lennard-Jones
(LJ) interaction is considered among non-bonded beads.
The external oscillating field E(t) consists of a sinisoidal
field of amplitude E_s with frequency f superposed on a steady biased
field E_b, i.e., E(t) = E_b + E_s Sin (2\pi ft). The field couples
with the change in energy with each movement of a bead along (positive)
or opposite (negative) the field (x-) direction.
We find that the mobility of the chains is enhanced at E_s > E_b,
consistent with recent experiments. As the chains mobility changes,
we observe interesting reponse in the radius of gyration (R_g),
their power-law motion, aggregation and segregation as a function
of field. Some of these results will be presented.
We have performed multi-nanosecond atomistic molecular
dynamics simulations of 1,2-dimethoxyethane (DME) and
1,2-dimethoxypropane (DMP) in aqueous solution in order to
determine the free energy, energy and entropy of solvation.
Using several types of biasing potential functions and
employing self-consistent multiple histogram method we were
able: (1) to compare the free energy, energy and entropy of
solvation for DME and DMP and ascribe the relative
differences in those properties to contributions from
different interactions (water-water and ether-water) in the
solution; (2) to determine the dependence of free energy,
energy and entropy as function of population of hydrophilic
conformers, extent of ether-water hydrogen bonding and
strength of ether-water electrostatic interactions. The
results of our simulations allow us to resolve the relative
importance of chemical structure, hydrogen bonding and
solvent-solute polar interactions for solvation of ethers in
aqueous solutions.
This work aims at testing the main assumption of the
standard Ogston model frequently used to predict the
electrophoretic mobility, or the diffusion coefficient, of
globular analytes. According to this model, the low-field
reduced mobility (\mu) and diffusion coefficient (D^*)
of an analyte are assumed to be equal to the fractional gel
volume (f) available to the particle. To test this
hypothesis, we developed a lattice model where \mu^*,
D^* and f can be calculated exactly. In order to avoid
lattice effects, we studied the continuum limit by
progressively decreasing the mesh size of the system until a
clear extrapolation could be obtained. Various types of gels
were examined, from simple periodic ones to more realistic
gels made of random tortuous fibers. All our data are
incompatible with the \mu^*=D^*=f assumption. We further
investigated the electrophoretic migration in dilute sieving
media made of non-conducting gel fibers; in the low-field
limit, the electrophoretic mobility is not affected by the
presence of curved field lines.
The heat capacity of the liquid-liquid mixture
perfluoroheptane and 2,2,4-trimethylpentane (also known as
iso-octane) has been measured for the first time near its
upper critical consolute point using an adiabatic
calorimeter. The theoretical expression for the heat
capacity near the critical point was applied to our combined
data runs. The critical exponent \alpha was determined to
be 0.106\pm0.026, which agreed with theoretical
predictions. When \alpha was fixed at its theoretical
value of 0.11, our value for the amplitude ratio A+/A- =
0.59\pm0.05 was consistent with experimental
determinations and theoretical predictions. However, the
two-scale-factor universality ratio X, now consistent among
experiments and theories with a value between 0.019-0.020,
was violated in this system when using the published value
for the correlation length. This work was supported by
NSF-DMR 9987850 and NASA grant NAG8-1433.
When a water-soluble polyelectrolyte is combined with an
oppositely-charged surfactant solution at a stoichiometric
charge ratio, self-assembly into highly-ordered,
water-insoluble structures occurs. We have prepared such
complexes with poly(sodium acrylate)-co-acrylamide, alginic
acid, and chitosan, combined with cationic and anionic
surfactants. The phases exhibited by these complexes in
aqueous solution are highly sensitive to such factors as
osmotic pressure, salt type, ionic strength, and
polyelectrolyte charge density. In this study, we have used
small angle X-ray scattering to examine osmotic
stress-induced structural phase transitions in these
complexes under these various environmental conditions. The
morphological consequences of combining polyelectrolytes
with swollen, emulsion-bound surfactant micelles were also
investigated. Results of this work, as well as the potential
to use these complexes as nanoporous, biocompatible
materials, will be discussed.
It was recently determined that L-3,4-dihydroxyphenylalanine
(DOPA) is primarily responsible for both the adhesion and
crosslinking that occurs in mussel adhesive proteins (MAPs).
In wet environments, MAPs form strong adhesive bonds to a
large variety of substrates, making DOPA-modified polymers
very interesting for adhesion studies. Polymer materials
modified from or modeled after DOPA have large potential as
biomedical adhesives and as adhesives in aqueous
environments.
The mechanical and adhesive properties of a DOPA-containing
hydrogel were tested using an axisymmetric adhesion test
modified from the method of Johnson, Kendall and Roberts. In
accordance with this technique, a rigid, hemispherical
indenter was brought into contact with hydrogel samples,
generating load and displacement data. In addition, images
were taken of the contact between the sample and indenter.
Using the collected data and images, the adhesive properties
of the material were calculated. Separate experiments were
conducted in conditions of varying humidity and aqueous
environments in order to determine any changes in the
adhesive behavior of the hydrogel. Data resulting from
experiments in each type of environment will be presented.
It has long been known that the reduced viscosity of
polyelectrolytes in low ionic strength solution presents a
peak as a function of concentration (Fuoss, R. M.,
and U. P. Strauss, J. Polym. Sci., 3, 246, 602 (1948)). Some
models seek to explain this in terms of interactions of the
polyelectrolyte molecules with other charges, generally
separated into the primary and secondary electroviscous
effects. Other theories explain the peak in terms of changes
in the conformation of the polyelectrolyte, induced by
increasing ionic strength (occasionally referred to as the
tertiary electroviscous effect). Using a novel
technique(Reed, W. F., private communication), we
present measurements of the viscosity of a very stiff
polyelectrolyte (xanthan, with a persistance length of about
1500 Å(Norwood, D. P., Mustapha Benmouna, and
Wayne. F. Reed, Macromolecules, 29, 4293-4304 (1996)) at
very low added salt. We measure reduced viscosity for
varying concentration but fixed ionic strength. In
conjunction with differential scanning calorimetry
measurements, we show that for this system, the
polyelectrolyte effect is due to almost exclusively to
electroviscous effects.
The effects of selected salt concentrations of LiClO4 on the
overall internal relaxation mode of high molecular weight
PEO in MeOH solutions were studied using the dynamic light
scattering technique of photon correlation spectroscopy.
Polymer sample and equipment preparation required in these
measurements to resolve the internal mode information of the
system will be described. Furthermore, the importance of the
sample molecular weight, polydispersity and that of the
laser output will be presented and discussed.
The structure and dynamic behavior of poly(ethylene oxide)
melts with and without lithium perchlorate were studied
using viscometry, static light scattering, and the dynamic
light scattering technique of photon correlation
spectroscopy. The results - interepreted in terms of a "wet
gel" model, i.e. in terms of an elastic PEO network immersed
in a viscous PEO fluid - will be presented and discussed.
Dendrimers possess hydrodynamic sizes in the few nanometer
range and well-defined chemical structures intermediate
between linear polymer and spherical colloid. By varying the
generation, size and structure can be adjusted over limited
ranges. Commercially available PPI dendrimers are soluble in
water and can be charged at their amine branches and termini
by protonation under acidic conditions. All of these
properties make dendrimers ideal candidates for testing of
theories for electrophoresis. Here, we present data for the
dependence of the free solution mobility on dendrimer
generation and ionic strength. Unlike linear polymers,
mobility changes with molecular weight. In fact, as the
generation varies, the mobility changes in the manner of a
spherical colloid of equivalent hydrodynamic radius, i.e.,
data for the dimensionless mobility collapses when plotted
against dimensionless size. Variation of mobility with
increasing dendrimer ionization is more complicated, as
might be expected for a solute of higher surface potential.
The structure and interaction of micelles formed by an amphiphilic
triblock copolymer P(EO)103-P(PO)39-P(EO)103 (F88) in aqueous
electrolyte solutions of several potassium salts has been investigated
using small angle neutron scattering as functions of temperature and
salt concentration. Modeling the SANS data from the copolymer solutions
using analytical expressions for the scattering intensity revealed the
remarkable effects of anion concentration and the temperature on the
self assembly of F88 into spherical and cylindrical aggregates and
subsequent phase separation. The critical micellization temperature
(CMT) of 5 wt. concentration and the CMT approaches ambient temperatures at particular
concentrations for certain salts. An increase in salt concentration
also shifts the temperature range in which the transition from
spherical to cylindrical micelles occurs to lower temperatures and
decreases the phase separation temperature of the copolymer from the
solution. These observations clearly indicate that the evolution of the
micellar structure and the phase separation are through gradual
dehydration of the copolymer chains with an increase in either the
temperature and/or the salt concentration.
Recent discoveries in polymer processing by CSP Technologies
have led to the production of molded polymer parts that
possess a significant capacity for moisture absorption. The
materials are manufactured by melt compounding three
components: a majority hydrophobic polymer (e.g. a
polyolefin), a minority hydrophilic polymer (e.g.
polyethylene glycol), and a particle (e.g. a zeolite) with
significant affinity and capacity for moisture. During melt
compounding, interconnected channels of the hydrophilic
polymer are formed that encapsulate chains of particles. The
channels are macroscopically percolating, as evidenced by
the high moisture uptake of the sample. Confocal
fluorescence microscopy is a powerful tool to study the
transport and diffusion of a fluorescent dye through the
hydrophilic channels as a function of time and particle
loading. Our study focuses on the critical particle loading
needed for percolation as function of particle type,
particle aspect ratio, and relative proportions of
hydrophobic and hydrophilic polymers. The results of this
study are expected to expand the applications base of this
fascinating three-component polymer processing technology.
The dynamics of the initial stages of polymer melt
intercalation into layered nanostructures have been studied
using coarse-grained molecular dynamics simulations. The
bead-spring model was used in representing both polymer
chains and the sheets comprising the layered nanostructure.
The initial condition of the simulation cell was comprised
of a stack of closely-packed sheets surrounded by polymer
melt. The influence of the sheet stiffness, sheet
dimensions, and the relative energies of polymer-sheet and
sheet-sheet interactions on intercalation behavior were
studied. The behavior for polymer chains above and below the
entanglement length, and the influence of pre-existing
galleries between sheets were also examined. It was found
that sheet stiffness plays a crucial role in determining the
ability of a layered nanostructure to intercalate.
Nanostructures comprised of flexible sheets intercalated
spontaneously. Stiff sheets did not intercalate but
manifested a sliding behavior, which occurred only when the
polymer-sheet interactions were very strong compared to the
sheet-sheet interactions. The process of filling larger
sheets with longer polymer chains was significantly
different behavior from small sheets and short chains. The
results will be discussed in the context of the
intercalation phenomenon occurring in aluminosilicates.
The time-dependent concentration and orientation behavior of
plate-like and spherical microparticles in solution has been
explored using computer simulations. These simulations are
based on the application of Langevin equations to previously
developed thermodynamic models for these systems. Among the
interesting phenomena captured by the model are the
formation of immobilized, disordered regions due to rapid
loss of solvent and the creation of compositional gradients
due to preferential immobilization of either plate-like or
spherical particles. The results have potential applications
for the development of materials with unique self-assembled
morphologies through solvent casting of nanocomposite films.
Relaxation modes and rates^1-3) of a polymer chain in a melt
are studied by Monte Carlo simulations of the bond fluctuation model,
where only the excluded volume interaction is taken into account.
Polymer chains of N monomers are located on
an L \times L \times L simple cubic lattice
with perodic boundary conditions,
where each monomer consists of 2^3 unit cells.
We choose L=128 and examine the cases of the volume fraction
\phi=0.5 for N=32,64,128 and 256 and
\phi=0.498 for N=48,96 and 192.
The relaxation modes and rates are estimated by
solving generalized eigenvalue problems for the equilibrium time correlation
matrices
C_i,j (t) = \frac13 \langle \barR_i (t) \cdot \barR_j (0) \rangle
of
the coarse-grained relative positions \barR_i (t) of
monomers of the polymer chain defined by
\barR_i = \frac1n \sum_k=1^n R_(i-1)n+k,
where R_k denotes
the relative position of the kth monomer.
For N \geq 100,
the behavior of the relaxation rates of a polymer chain
of N monomers is found to be consistent with
the prediction \lambda_p \propto p^2/N^3
by the reptation theory.
For N=128,192 and 256,
the slowest relaxation rate behaves as
\lambda_p=1 \propto N^-3.09.
Preliminary results for N=512 with L = 192
are also presented.
1) H.\ Takano and S.\ Miyashita: J.\ Phys.\ Soc.\ Jpn.\ 64 (1995) 3688.
2) S.\ Koseki, H.\ Hirao and H.\ Takano: J.\ Phys.\ Soc.\ Jpn.\ 66 (1997) 1631.
3) K.\ Hagita and H.\ Takano: J.\ Phys.\ Soc.\ Jpn.\ 68 (1999) 401.
The cure (polymerization and solidification) of thermoset
systems has been proposed also to involve phase separation
in cases where the reactants are strongly heterogeneous.
Vinyl ester (VE) resins are multi-component, thermosetting
systems that are suspected of undergoing such phase
separation during cure, and this work seeks to investigate
this possibility and how it might affect mechanical behavior
of the resulting solids. The autocatalytic equation is used
to describe the cure kinetics of these systems, and it is
found to work only at high levels of conversion. Mechanical
behavior, as studied by tensile and fracture toughness
tests, is correlated to initial cure conditions and the
presence or absence of initiator and accelerator species;
property optima have been established. No evidence was found
for a second phase formed during polymerization, explaining
why excellent physical properties are realized in these
materials.
Sometimes simple shear flow can induce phase separated
simple liquids into a single-phase state. In other cases,
shear flow can bring single-phase polymer solution into
phase separation. The cone-plate rheometer is the most
common technique to investigate this phenomena, in which the
system under study is sheared between the cone-plate
geometry. However, most of the available systems can only
apply moderate shear rate. The structures and rheological
properties under higher shear rates >104 s-1 have never been
investigated before. We have constructed an apparatus based
on the disc-drive configuration in which a thin film of
polymeric solution is sheared between optically transparent
disc and slider. Rheological properties can be probed using
the slider with strain gauges, and the structures can be
examined optically using a laser beam and a high performance
CCD camera. With this design, we may reach the strain rates
experienced by disc-drive lubricants, > 107 s-1 Initial
experiments with this apparatus are carried out with
semidilute PS solution and DOP.
A mechanical stretching apparatus for polymer fluids,
simulating the stretching that occurs in the electrospinning
process, was used to study the elongational relaxation of
polymer fluids. The elongational relaxation time was an
undetermined parameter in the computer model of the
electrospinning process (1). A column of fluid was created
by lifting a flat-faced cylindrical tip at a speed of
350mm/s for a distance of 21mm out of a pool of fluid. The
decrease of the column diameter as a function of time was
observed with a high-speed camera. Cylindrical liquid
columns were formed by poly(ethylene-oxide) with a molecular
weight of 400,000 g/mole in a concentration range from 2% to
10%. Surface tension and intermolecular forces dominate this
thinning process. The inertial and gravity forces are small
and can be neglected. The relaxation times were calculated
from the change of diameter with time (2). The relaxation
times for the solutions were in the range of ten to a
hundred milliseconds. The logarithm of these relaxation
times has a linear relation with polymer concentration. (1)
D. H. Reneker et al., J. Appl. Phys. 87, 9 (2000). (2) M.
Stelter et. al., J. Rheol. 44, 3 (2000).
The dynamics in the amorphous regions of semicrystalline
polymers exert important influences on mechanical properties
but have been difficult to characterize. New solid-state
nuclear magnetic resonance (NMR) techniques, PUREX
(pure-exchange) and CODEX (centerband-only detection of
exchange), enable studies of the molecular motions near the
glass transition (T_g) in the amorphous regions of
semicrystalline polymers. This is achieved by selectively
suppressing the dominant signals of the static segments in
the crystallites. We have applied both techniques to analyze
the geometry and time scale of the slow motions around
T_g in isotactic poly(1-butene) (iPB1), in
polypropylenes (iPP, sPP, aPP), and in fully amorphous
polyisobutylene (PIB) for reference. The apparent
activation energies for iPB1, sPP, and PIB were found
to be 90, 125, and 115 kJ/mol, respectively. In
iPB1, indications of slow motions in two distinct regions
were observed.
Using a Molecular Dynamics simulation we study the processes
by which a polymer film with nanoscaled filler particles
dewets a solid surface. We examine the effects of filler
size, polymer filler interaction and filler concentration on
the dynamics of the dewetting process. We also consider the
effect of fillers on the dewetting dynamics of a polymer
bilayer film. Our results indicate that the mobility of the
filler particles plays an important role in determining the
dynamics of the process
The Boson peak is a rather ubiquitous low frequency
excitation, in the energy range of approximately 1 meV to 10
meV, common to most glass forming materials. In this work we
use both inelastic neutron and low frequency Raman
scattering to characterize the Boson peak in a series of
polycarbonate copolymers. By combining these measurements
with complimentary positron annihilation lifetime
spectroscopy (PALS) studies, an intriguing correlation
between the Boson peak energy and the average size of the
PALS unoccupied volume cavities has been observed. The
inverse proportionality between the Boson peak energy and
volume of the PALS nanopore cavity is discussed in terms of
the acoustic modes for both our polycarbonate copolymers as
well as a wide range of glass forming materials.
Fluorescence anisotropy decay measurements of the dilute
solution local segmental dynamics of anthracene labelled
polyisoprene have been performed as a function of pressure.
Several solvents were utilised at 25^oC and 50^oC over a
pressure range of 0 to 2000 bar. The scaling of the dynamics
with solvent viscosity is presented as a function of
temperature at each fixed pressure and as a function of
pressure at each fixed temperature. Comparisons are made to
Kramers' theory which predicts \tau _c \alpha \eta.
Reference is also made to ongoing high pressure work of melt
samples.
We have investigated the surface morphology in thin films of
strongly-segregated polystyrene-poly(2-vinyl pyridine)
(PS-P2VP) block copolymer forming lamellar morphology by
using optical microscopy (OM) and atomic force microscopy
(AFM). When spun cast from NN-dimethylformamide (DMF)
solution onto a silicon wafer with a thin poly(allylamine
hydrochloride) (PAH) layer, the PS-P2VP copolymer forms
multilayered lamellae due to the strong affinity of the P2VP
blocks toward PAH substrate and the preferential attraction
of the PS blocks with free surface. Islands with a discrete
step height of t = 2.5 L_0 develop in thin films having
the thickness of 1.5 L_0 < t_0 < 2.0 L_0 (here,
L_0 is the domain periodicity) after a short-time
annealing at 180_oC. Further annealing, however, results
in the formation of fractal holes with step height of t =
0.5 L_0, showing abnormal coexistence of islands and
holes. The occurrence of fractal holes is much similar to
the one reported in strained block copolymer lamellar films,
and may be closely related to the high-shear spinning
process due to the slow evaporation of DMF and/or the strong
affinity of the P2VP blocks toward PAH substrate. At the
final stage of annealing, holes grow in both number and size
with gradual disruption of islands.
Sub-nanometer hole structures in polymers at the molecular
level are important for gas separation, membrane properties,
and coating applications. The change in these properties due
to gas exposure were studied by Differential Scanning
Calorimetry and Positron Annihilation Lifetime Spectroscopy.
Carbon dioxide, methane, nitrogen, oxygen and helium gas
treatments as a function of pressure and duration at room
temperature resulted in interesting changs in physical
properties. An increase in specific heat below Tg and a
decrease in Cp a this temperature will be discussed assuming
changes in sub-nanometer structures in glassy Polysulfones,
stable below Tg. The hole size and fraction increase and the
free-volume distribution broadens with the pressure in the
polysulfone-carbon dioxide system.
Although the structure of reactive polymers and its reaction
kinetics are crucial for understanding interfacial
properties, detailed studies are still lacking. In this
study, the effect of functionality of reactive polymers on
the reaction kinetics and the conformation of copolymers
formed at the interface due to reaction were studied using
the Monte Carlo simulation method. The copolymer coverage at
the interface, defined as the number of reacted groups in
the reactive polymers per interfacial area, for di-end
functional polymers is about twice higher than that for
mono-end functional polymers supporting the effectiveness of
multiple reaction sites in a polymer. We also found that the
limiting reactant controls the copolymer coverage. For
tri-functional polymers, which contain two endfunctional
groups and one additional functional group at the center of
the chain, the center functional groups are proven to be
much less preferred for the interfacial reaction. All the
simulation results obtained with reactive polymers
demonstrate that the functional group distribution in a
reactive polymer is also an important factor in controlling
the copolymer structure.
This abstract not available.
In recent year, the existence of anomalous incommensurate
satellite reflection above T_c was reported by the X-ray
and neutron scattering experiments.
This is explained to the coupling of a strain and order parameters
at structural phase transition. This distinct feature was interpreted as
the precursor effect which occurs in martensite transitions.
In our study, it was revealed that the intermediate phase is
limited in the range between 175^oC and
195^oC and high and low temperature
phases coexist. This region also showed the strong
bias-stress dependence and the abrupt jumpings of the
thermal expansion coefficient.
The additional small anomaly just above T_c was
suggested to be by the pinning effect of the microdomains.
The results of high resolution neutron diffraction(HANARO, KAERI)
very effectively revealed the region of intermediate
phase which was not clearly reported until now.
From this result, we could confirm the precursor effect in
nonmetallic material and obtain the insight into the mechanical
response of the ferroelastic phase transitions.
Many studies on molecular motors assume infinite protein sizes, simplifying
the analysis of the corresponding motion. We report the results of extensive
computer simulations on finite size systems, in which fluctuations in motor
force and/or velocity become significant. In particular, we study the motion
of the motor on a symmetric ratch et potential, which results in two symmetric
solutions in the direction of motion. Switching between these directions
sensitively depends on system size.
Direct oxide nanolithography1 on surfaces of semiconductors
is a very active area of nanotechnology because it provides
rapid prototyping of novel devices potentially useful for
space technologies. We recently demonstrated non-periodic
structures written on 110 Si surface and chemically etched
in KOH to produce lines 250 nm wide and 80 nm tall.
Non-periodic positioning of stripes allows encoding several
spatial frequencies in a waveguide structure created with an
AFM tip. The waveguide was designed to reject two specific
wavelengths from the spectrum and only permit one wavelength
to pass2.
Here we present results of the influence of AFM cantiliver
dynamics and shape of an atomic force microscope tip on the
anodization process of 100 p- and n- type silicon. There
is a correlation between the lateral size of the structures
written on silicon and the voltage applied to an AFM tip. It
is found there is an optimal voltage to write the structures
when cantiliver/tip parameters are optimized.
Nanolithography, although a very powerful tool, does not
allow writing structures at speeds common in traditional
optical holographic techniques, where 105 lines can be
written within 1-2 sec simultaneously. A novel concept,
which concatenates AFM direct-writing and holography will
also be discussed in this presentation.
References
1. Dagata, J.A.; Tseng, W.; Bennet, J; Evans, C.J.; Schneir,
J; Harary, H.H., Appl. Phys. Lett., 1990, 57, 2437; Snow,
E.S.; Campbell, P.M.; McMarr, P.J., Appl. Phys. Lett., 63,
3448, 1993. 2. Cohn, R. W.; Lyuksyutov, S. F.; Walsh, K. M.;
Crain, M. M. Opt. Rev. 6, 345, 1999.
Deposition of monolayers on solid surfaces is traditionally done using
Langmuir - Blogdett technique. However, the movement of barrier often
leads to pinhole defects. We have developed a method which consists of
slow ascent of monolayer constructed on the surface of subphase by slowly
raising the level of the subphase. This have been done without use of
pumps or motors which are likely to cause degradation of the monolayer.
The monolayer touches the solid surface which can be earlier processed to
have suitable functional groups anchored on the surface and gets
deposited. This process can be repeated to have muliple layers of the same
substance or appropriate other substances. Since the method is simple and
straight forward, it has multiple advantages. Namely, the subphase can be
aqueous as in LB techniche or any other organic solvent. This method has
been found to be particularly suitable for bio-materials such as enzymes
or cells and to have deposited layers in predetermined patterns. We have
used different troughs of different shapes ( rectangular, cylindrical,
inverted cone) and sizes. Details will be discussed in the presentation.
We report a new fabrication technique for realizing a high-density
penetrating metal probe array for interfacing the nervous system and
electronic devices, such as neural recording and stimulation apparatus. The
microelectrode array consists of multiple metal shanks projecting from a
silicon supporting bulk. One neural interface site is located at the tip of
each shank. The average distance between recording sites is 50 m. Each
shank is comprised of two distinct segments for realizing both mechanical
strength and tissue penetrating ability. A rear support segment is
6-mm-long, 40- m wide and 30- m thick. A front segment consists of a 250-
m-long and 6- m-thick tapered
tip, with the width at its widest point being 15 m. Electrical insulation
to the microelectrode body is achieved by conformal coating of a thin film
of Parylene-C. Exposed metal recording sites are defined by selectively
removing Parylene-C from the electrode tips using photolithography and
oxygen plasma etching. The electrical properties of the device were
characterized, and then its full functionality as an in vivo recording probe
was tested in ventral nerve cord ganglia of cockroaches.
A magnetotransport study of a two-dimensional electron-hole gas (2DEHG) in
GaSb-InAs-AlSb heterostructures with a GaSb cap layer of varying thickness
has been carried out. The 2DEHG densities, transport and magnetotransport
properties are expected to depend on the thickness of the GaSb cap layer
due to Fermi level pinning at the surface. Low-field magnetoresistance
data and the observation of Shubnikov-de-Haas oscillations confirm the
coexistence of a 2DEHG at the GaSb/InAs interface. The observed variation
of the magnetotransport properties of the 2DEHG with the thickness of the
cap layer is used to estimate the Fermi energy at the GaSb surface.
By arrangement of nanometer-sized symmetry-breaking elements into a
two-dimensional lattice, a new class of artificial functional material
is constructed. The nanomaterial is fabricated using electron beam
lithography and wet chemical etching on a high electron-mobility
InGaAs/InP quantum well structure. We show that the nanomaterial
exhibits intrinsic nonlinear electronic functionality and therefore
functions also as a two-dimensional ratchet. The distance between
neighboring elements is small enough to be comparable to the electron
mean free path at room temperature, and therefore operations of the
nanomaterial without using any cryogenic or other cooling have been
realized. Since it is a material, we show that individual devices can
be made by simply cutting pieces according to requirements for
different applications. We also demonstrate that these devices
operate at frequencies at least up to 50 GHz. Therefore, this novel
nanomaterial is expected to be used in real high-frequency
applications such as detection and second harmonic generation, etc.
Using the transfer matrix methods and rigorous results of the finite periodic
systems theory ( P. Pereyra, Phys.Rev. Lett., 80(1998)2677.),
a new approach for a high precision and simple calculation
of the band structure of real crystals is proposed. The well known valence
bands, fundamental gaps and conduction band of GaAs and AlAs are obtained free
of fitting parameters or experimental inputs. The calculated gap values coincide
with the experimental results within less than one percent.
A phenomenological theory to describe the electromagnetic properties of
granular superconductors, based on known bulk superconductors expressions
and conventional Josephson's junctions tunneling currents, is presented and
successfully used to fit distinct experimental results for the magnetic
susceptibility \chi as a function of the temperature and the applied
magnetic field of rather different samples.
An electron in the precense of magnetic and electric fields and a periodic
and anisotropic lattice is studied by means of the magnetic translations
and electric evolutions. We have calculated the electron spectrum as a
function of the magnetic field, the intensity and the direction of the
electric field and the anisotropy of the lattice. We show that the variation of
the electric and magnetic fields, and the modulation amplitudes of the periodic
potentical in the x and y direction may lead to transitions in the
electron transport.
Self-consistent diagrammatic methods have been shown to capture
the critical topological vortex fluctuations of a simple 2D
superconductor. We use generalizations of the Fluctuation
Exchange Approximation to study cases where the order gets
frustrated, leading to a transition with quantum critical
behaviour. First we investigate pair-breaking due to an external
magnetic field in a short-coherence length 2D superconductor.
Next we extend this framework to investigate frustrating order
in a strong-coupling scenario, namely the competition between
Neèl and spin-liquid states.
In this work we report the direct nano-wiring of carbon nanotube (CNT)
between micro-sized islands using conventional photolithography
technique necessary for the nanomachining and the molecular device
applications compatible with Si-based process. Most distinct feature in
this work is to use a
growth barrier of Nb metal or insulating layer on the top of the
catalytic metal to prevent the growth
of CNT from vertical direction to the substrate. As a result, CNTs of
either ¡°straight line¡\pm or a perfect
¡°Y shape¡\pm were selectively grown between lateral sides of the
catalytic metals or pre-defined electrodes without any trace of vertical
growth[Fig. 1]. The length of CNTs was 500-1000 nm and the diameter
thinner than about 20nm. These results clearly indicate that this method
would be one of the most feasible
fabrication techniques for the nanomachines or the electronic
applications with high integration level
[1, 2].
Acknowledgement
References
[1] C. Dekker, Phys. Today 52, 22 (1999)
[2] J. Kong, H. T. Soh, A. M. Cassell, C. F. Quate, and H. Dai, Nature
395, 878 (1998)
First-principles calculations of the electronic and magnetic properties
of the La_2CuO_4 and
Ba-doped La_2-xBa_xCuO_4 systems with
x \sim 0.125 are performed.
The cluster procedure is adopted, in which
the central atoms are treated with an all-electron basis and the remainder
of the lattice is approximated with point charges. Both the
Hartree-Fock (HF) and hybrid (combining both density functional
exchange-correlation and HF exchange)
methods are used in the calculations.
Three different lattice structures are used, which include the pure
La_2CuO_4
orthorhombic structure and the tilted LTO and LTT structures of
La_2-xBa_xCuO_4.
For the pure system, the calculated electronic field
gradient (EFG) is in agreement with experimental value and the magnetic
hyperfine field is 28% larger than the experimental
value(G. Q.
Zheng, et al., Physica C 208, 339 (1993)).
For the doped system, the hole-poor and hole-rich regions are considered
separately. For the hole-poor region, the EFG is in rather good agreement
with
the experimental results(H. Tou, et al., J. Phys. Soc. Jpn. 61,
1477, (1992))^,\!\!
(K. Kumagai, et al., J. Phys. Soc. Jpn. 60, 1448, (1991))^,\!\!
(A. W. Hunt, et al., Phys. Rev. Lett. 82, 4300, (1999))^,\!\!
(K. Yoshimura et al., Hyperfine Interactions 79, 867 (1993)) and
the
hyperfine field is 24% larger
than for experiment. For the hole-rich region, calculations assuming
different
spin states (0 or 1) are compared, and the the EFG results for the
spin 0 state are in agreement with experiments; the
corresponding results for the
spin 1 state are much smaller. Study of the local lattice relaxation
caused by Ba doping results in displacement of the nearest
apical oxygen away from Ba by about 0.29 Åwhich is
in the same direction as, but 70% larger
than, results from
XAFS measurements.(D. Haskel, et al., Phys. Rev. B. 61, 7055
(2000))
The solubility of polyoxyethylene in water is a result of the interactions
of ethylene oxide repeat units with water and the molecular conformations
due to intramolecular and intermolecular interactions of the ethylene oxide
units. The dynamics of low molecular weight oligomers of polyoxyethylene
were investigated by C-13 NMR relaxation studies. Several models for the
motions were applied to fit the data. Analysis of the relaxation data
using a model independent approach revealed a change in dynamics as a
function of carbon position in the oligomer and as a function of molecular
weight.
Molecular electronic junctions exhibiting negative
differential resistance show a marked substituent effect.
We propose a mechanism of electron transfer across such
a molecular junction based on resonant tunneling.
The model is supported with ab initio molecular
electronic structure calculations.
This model gives insight into how the electronic structure
affects electron transport, and offers an explaination for
the observed substituent effects.
We search for general patterns that explain the low field magnetoresistive
behaviour at low temperatures in the perovskite system
A_(1-x)A^\prime_xFeMoO_6, with A and A^\prime being isovalent or
aliovalent cation.
The observed linear dependence of the low field magnetoresistance with the
saturation
magnetization for the series is related to the anti-site disorder at the
Fe and Mo
sites. This fact is qualitatively explained in terms of a spin dependent
crossing of
intragranular barriers originated from the presence of antiferromagnetic
SrFeO_3
patches that naturally develop when anti-site disorder occurs in the double
perovskite.
It is concluded that anti-site disorder is at the very root of low field
magnetoresistance
although effects such as disorder distribution, connectivity or morphology
add their
contribution.
Optical and magneto-optical properties of YVO3 single crystals have been
studied in IR, visible, and UV regions.
Our measurements have revealed a large Kerr effect in this compound, comparable to those in
ferromagnets. This observation introduces a new class of materials:
insulating antiferromagnets with strong magneto-optical Kerr effect,
which can have advantages for practical applications. We look into the details of
electronic and crystal structure changes. YVO3 was found to undergo two structural
phase transitions. Initially the orthorhombic Pbnm symmetry is lowered
below a second order phase transition at 200 K and recovers below 74 K at
a first order phase transition. Two Mott-Hubbard (MH) bands dominate
the electronic spectrum in the visible range, followed by charge-transfer gap in UV.
Below the 200 K a transfer of the spectral weight to higher frequencies occurs and
a third MH band appears at 3 eV. We discuss the results on
the basis of spin and orbital ordering theory, proposed for YVO3.
Octafluorocyclobutane(c-C4F8) gas has been widely used in the
high-aspect-ratio, highly selective contact-hole etching process. However,
c-C4F8 gas is one of the PFC (perfluoro-compounds) gases that have a very
high global warming potential (GWP). We investigated perfluoro-2-butene
(linear-C4F8) as an alternative gas and studied the process performance
and
emission gases during oxide etching.
A parallel-plate dual-frequency etcher was used with the gas chemistries
c-C4F8/O2 /Ar or l-C4F8/O2 /Ar at a chamber pressure of 25 mTorr. The etch
rate and profile of contact holes were measured by SEM. The emission gases
were analyzed by a QMS and FTIR spectrometer.
Etching results show that, though the profiles of etched contact holes are
almost the same for both gas chemistries, the etch rate and nitride
selectivity of l-C4F8 based plasma were higher than those of c-C4F8 based
plasma. In the analysis of emission gases, it was found that, during
contact
hole etching, the decomposed c-C4F8 and linear-C4F8 gases were converted
into C2F4, CF4, CHF3 and C2F6 gases, and small amounts of C3F8, C4F6 and
C4F10 were also generated. Furthermore, some toxic gases such as CO, HF,
and
COF2 were also detected.
This work was performed under the auspices of MITI's Ramp;D program
supported
by NEDO.
Atomic force microscopy (AFM) is a technique that allows to image
surfaces with
atomic resolution. Recent progress in reducing the noise in this
technique has allowed
to detect internal structures in the previously hemispherical atom
images.
The imaging process in AFM is controlled by the forces that act
between a sharp tip and the surface. The short-range components of these
forces are
due to the formation of
chemical bonds during the imaging process.
Some types of chemical bonds, especially the covalent type,
display a strong angular dependence. This angular symmetry is
observable by AFM. Here, we present experimental results of images
of Si(111)-(7\times7), where a strong angular dependence of the forces
is present.
Comparison with simulations using the Stillinger-Weber potential for
mapping
the bonding forces shows excellent agreement with the data.
This work is supported by the Bundesministerium fuer Bildung,
Wissenschaft,
Forschung und Technologie (13N6918/1).
In this work, we report the optical properties are studies by optical absorption
in UV-Vis. region, photoluminescence under N_2 laser excitation at 12 K
and RT of
a novel quaternary crystal doped with Europium KCl:KBr:RbCl:RbBr, each component
in a 25 % molar fraction and 0.5% of Eu^++. Was determined from the optical
absorption and emission spectra the characteristic spectroscopy of the Europium
ion in this lattice. Was observed decay times of blue band emission is
independent of temperature and only one component decay is present in sample
quenched crystals. From the data obtained suggest the symmetry of surrounding
in quaternary crystal KCl_0.25KBr_0.25 RBCl_0.25RbBr_0.25
is similar to that sample
quenched of pure component crystal.
We report on the growth and optical defects characterisation of a novel family
of quaternary alkali halide crystals, produced by mixing four dielectrics salts.
This quaternary crystals implies the existence of four ternary crystals, one of
these recently studied and several binaries. The characterisation is done on two
different component concentrations. One of these component with Europium, an
impurity of high optical sensibility. We obtain lattice constants by X ray
diffractometry. The optical absorption spectra of irradiated crystals, shows one
single F band, Vegrad's generalised law, applied to the novel ternary system
recently studied, was extended to the quaternary crystal. Good agreement with
the experimental results was obtained.
q
Diamagnetic shift (DS) and Zeeman splitting (ZS) has been
investigated on GaAs-AlGaAs quantum wire (QWR) by
polarization dependent magneto-luminescence (PML) up to B=30 T at 4 K.
The g factor takes a drastic change at the field where cyclotron radius
becomes equal to QWR width, and the similar change observed in InGaAs-InP
QWR has been explained with valence band intermixing.[1]
The effective mass obtained from DS changes at the similar field.
Possible causes of the transition of ZS will be revealed.
[1] J. Hammersberg et al., Jpn. J. Appl. Phys. 36,1935 (1997)
Homogeneous semiconductors under spacially periodic external
magnetic fields exhibit spin-band splitting and displacements.
We study the influence of the geometrical parameters and the
spin-field interaction on the electronic transport properties.
We show that by varying the external magnetic field, one can
easily block the transmission of either the spin-up or the
spin-down electrons.
We wish to exploit the high thermal conductivity, K(T), of Single Wall
Carbon Nanotubes (SWNTs) in augmenting the K(T) properties of a widely
employed industrial epoxy. The pristine epoxy possesses both thermal and
electrical conductivities several orders of magnitude smaller than that
of SWNTs, and epoxy samples which have had low weight percentages
(<1.0wt%) of SWNTs ultrasonically distributed have been produced,
yielding controllable enhancement of both K(T) and electrical
conductivity as determined by the weight percentage of SWNTs added.
Initial room temperature measurements as well as low temperature studies
will be presented.
We consider frustrated antiferromagnetic Heisenberg quantum spin systems
with regard to the Marshall-Peierls sign rule (MPSR). By using exact
diagonalization data we investigate the breakdown of the MPSR in dependence
on frustration for the one dimensional linear chain and the two dimensional
square lattice. We compare our findings for different spin quantum numbers
s=1/2, 1, 3/2 and 2. We calculate a critical value of frustration
J_2^crit where the MPSR is violated and extrapolate our findings to the
thermodynamic limit. For the linear chains we find different behavior for
integer and half-integer spin, namely a decrease of J_2^crit from s=1/2
to s=1, pointing to a stronger influence of frustration in case of s=1.
Nevertheless the calculation of the weight of the Ising-states violating the
MPSR shows that the MPSR holds approximately even for quite large
frustration and may be used for numerical techniques. For the square lattice
we find that a much stronger frustration is neccesary in order to break the
MPSR.
A density-functional theory of the isotropic-nematic phase transition in
both rigid and semiflexible hard-sphere chain fluids is described. The
theory is based on an exact analytical evaluation of the excluded volume
and second virial coefficient \( B_2 \) for rigid chain molecules, which
demonstrates that \( B_2 \) in these cases is equivalent to that of a
binary mixture of hard spheres and hard diatomic molecules. It is assumed
that the same binary-mixture representation applies to semiflexible
chains, while scaled particle theory is used to obtain the properties of
the fluid at arbitrary densities. The result s of the theory are in very
good agreement with Monte Carlo (MC) simulation data for rigid tangent
hard-sphere chains, but in lesser agreement with available MC studies of
rigid fused hard-sphere chains. We find that there is reasonable agreement
between the theory and MC data for semiflexible tangent chains, which
improves with increasing chain length. The behavior predicted by the
theory for semiflexible chains is contrasted with that given by the
Khokhlov and Semenov theory of nematic ordering of wormlike polymer
chains.
Our work deals with the research of optical and photoelectric properties
of titanium-doped CdTe crystals. The absorption, observing in the
crystal transparency region, is due to intracentral transitions from the
ground ^3A_2(^3F)-state to excited ^3T_1(^3P)- (1.15 eV)
and ^3T_1(^3F)- (0.65 eV) states. The photogalvanic current
(PGC) spectra show the absence of signal in the 0.65 eV region, and a
presence of a positive broad band (1.15 eV). The obtained results are
explained by the overlap of the excited ^3T_1(^3P) level of
Ti^2+ ions with the conduction band. The emergency of a new negative
PGC band in the \sim0.8 eV region after a prolonged (30 min.)
irradiation (h\nu=3D1.15 eV) of the crystal is due to a transition
from the valence band to the impurity level of Ti^3+ ions. It
should be noted that the energy structure of Ti^2+ and Ti^3+
ions in CdTe crystals is likely to one of V^2+ and V^3+ ions in
these crystals. At present, CdTe:V crystals are considered as the
photorefractive materials for the near infrared region. The optical
quality of CdTe:Ti crystals is better than CdTe:V. We believe that the
CdTe:Ti crystals may be considered as the promising photorefractive
materials.
Thin film technology for the development of high temperature superconducting
(HTS) coated conductors has been applied to thin film solid oxide fuel cells
(TFSOFC). Yttria stabilized zirconia (YSZ) epitaxially grown on atomically
ordered nickel foil substrates has been used as an electrolyte in the TFSOFC
design. Through the process of micro pore etching, the nickel substrate
became the TFSOFC porous anode capable of gas transport. A porous La-Sr-Co-O
cathode thin film was then deposited on the electrolyte. The new SOFC’s have
been operated at temperatures significantly lower than bulk SOFC’s
(\sim550^oC vs. \sim850^oC) and yielded a maximum output power
density of ~0.6W/cm^2. This new development allows for advances in SOFC
design and utilization through lowered working temperatures.
Energies and wave functions are calculated for d-wave quasiparticles
in the mixed state using the formalism of Franz and Te\usanovi\'c
for the lowest-lying energy levels. The accuracy of the plane wave
expansion is explored by comparing approximate to exact results for a
simplified one-dimensional problem, and the convergence of the plane
wave expansion to the two-dimensional case is studied. The results
are used to calculate the low energy tunneling density of states and
the low temperature specific heat, and these theoretical results are
compared to semiclassical treatments and to the available data.
Implications for the muon spin resonance measurements of vortex core
size and for the planar Cu spin-lattice relaxation due to electron
spin-flip scattering will also be discussed.
We investigate the pairing of two electrons mediated through an exciton,
using a non-perturbative method. The result confirms an attractive pairing
interaction between the electrons and suggests the formation of the Cooper
pair prior to the onset of phase coherence. The possible connection of such
a mechanism to high-T_c cuprate superconductors is discussed.
The 2D dielectric phases and phase transitions of adsorbed dipolar molecules
are modeled using a dilute spin-one Ising model. This model is studied in
the BEG approximation, using a mean-field approximation, where the
interaction parameters are related to system interaction energies using a
unique averaging procedure. The model is applied to halogenated methanes
physisorbed on MgO(100) and NaCl(100) using previous experimental and
theoretical studies to determine the interaction energies. We find
temperature-dependent antiferroeletric to ferroelectric dipole phase
transitions and order-disorder phase transitions can occur. Phase diagrams
are presented.
[R40.020] Acoustomagnetoelectric effect in bismuth in the presence of a strong current density gradients.
Peter Finkel (Rowan University, NJ), Sergei Bengus, Vitaliy Krasovitsky (Institute for Low Temperature Physics , Ukraine)
[R40.021] Magneto-optical and optical properties of Fe-Au disordered alloy films near the fcc-bcc structural transformation region
Y. P. Lee, Y. V. Kudryavtsev, X. S. Jin, Y. H. Hyun (Hanyang University, Seoul, Korea), R. Gontarz (Institute of Molecular Physics, Poznan, Poland), K. W. Kim (Sunmoon University, Asan, Korea)
[R40.022] Magneto-optical, optical and transport properties of Ni_2MnGa alloy
Y. Zhou, Y. V. Kudryavtsev, X. S. Jin, C. O. Kim, Y. P. Lee (Hanyang University, Seoul, Korea), J. Y. Rhee (Hoseo University, Asan, Korea)
[R40.023] Insulator and Dielectrics
[R40.024] Local-Field Distribution of Two Dielectric Inclusions at Small Separation
Yuet-lun Siu, Kin-wah Yu (Department of Physics, Chinese University of Hong Kong)
[R40.025] LOW TEMPERATURE THERMOLUMINESCENCE PROCESSES IN KBr:Eu2+
B. Castañeda, M. Pedroza-Montero (Programa de Posgrado en Física de Materiales, Centro de Investigación Científica y de Educación Superior de Ensenada, Baja California, México. P.O.Box 2681, 22800), R. Meléndrez, M. Barboza-Flores (Centro de Investigación en Física, Universidad de Sonora. P.O.Box 5-088, Hermosillo, Sonora, 83190 México.)
[R40.026] FABRICATION AND THERMOLUMINESCENCE CHARACTERIZATION OF NEW KClXBr1-X:Eu2+ PHOSPHORS CERAMICS WITH DOSIMETRIC APPLICATIONS
R. Bernal (Centro de Investigación en Física, Universidad de Sonora, P.O. Box 5-088, Hermosillo, Son., 83000, México.), M. Pedroza-Montero, B. Castañeda (Programa de Posgrado en Física de Materiales, Centro de Invest. Científica y de Educación Superior de Ensenada, P.O. Box 2681, Ensenada, Baja California, 22800 México.), M. Barboza-Flores (Centro de Investigación en Física, Universidad de Sonora, P.O. Box 5-088, Hermosillo, Son., 83000, México.), C. Cruz-Vázquez, K.R. Alday-Samaniego (Departamento de Investigación en Polímeros y Materiales de la Universidad de Sonora, P.O.Box 130, Hermosillo, Son., 83000, México.)
[R40.027] Al-Ti Electrodes for Ferroelectric Thin Films
Oscar Blanco (Posgrado en Física de Materiales, CICESE, México), Jesús Heiras (Centro de Ciencias de la Materia Condensada, UNAM, México)
[R40.028] A thermodynamic model of the growth of diamond-like Carbon = Nitride film
Xing-Jian Shi, Wen-Xiu Wang, Ying-Mei Wang, Da-Ren He (Dept. Phys., Yangzhou Univ., 225002, China), He-Bao Yao, Qing-Li He (Dept. Phys., Northwest Univ., 710069, China)
[R40.029] Influence of Strain on the Electronic Properties of BSTO Films
Q. Qian, T. A. Tyson (Department of Physics, New Jersey Institute of Technology), D. Bubb (Naval Research Laboratory), J. Bai (Oak Ridge National Laboratory)
[R40.030] A breather model for PtCl
George Kalosakas (T-CNLS, Los Alamos National Laboratory), Nikos Voulgarakis (Physics Dept., Univ. of Crete), Alan Bishop (T-Division, Los Alamos National Laboratory), George Tsironis (Physics Dept., Univ. of Crete)
[R40.031] A Single Crystal X-ray Diffraction Study of PMN-PT Single Crystals
Mingqin Zou (Material Science Program, Washington State University), Roger Willett (Department of Chemistry, Washington State University)
[R40.032] Single Crystal Structural Investigation of the Phase Transitions in (Me4P)2ZnBr4 and (Me4P)2ZnI4
Roger Willett (Department of Chemistry, Washington State University), Mingqin Zou (Material Science Program, Washington State University)
[R40.033] Ab-initio Calculation of XANES/ELNES Spectra of YAG (Y3Al5O12)
Yu Chen, Shangdi Mo, Wai-Yim Ching (University of Missouri-Kansas city, Kansas City, MO 64110)
[R40.034] Afterglow induced by UV radiation at low temperature in europium-doped alkali halides.
S. Àlvarez-García (Programa de Doctorado en Ciencias (Física). Universidad de Sonora. P.O. Box 5-088 Hermosillo, Son., 83190 México.), M. Barboza-Flores, T.M. Piters (CIFUS. Universidad de Sonora. P.O. Box 5-088 Hermosillo, Son., 83190 México)
[R40.035] Temperature Dependence of Radiative Decay Rates of Mn4+ and Cr3+ in YAG
Kurt Hoffman, Micheal Wimpee (Whitman College)
[R40.036] Dynamic Mechanical Measurements of SiC for Simulations of MEMS Devices
D.R. Wiff (Air Force Research Lab/ Materials amp; Manufacturing Directorate)
[R40.037] ELASTIC CHARACTERIZATION OF CONCRETE MATERIALS
Claudio Guerra-Vela, Abraham Ruiz (University of Puerto Rico), Fredy R. Zypman (Yeshiva University)
[R40.038] Wide Bandgap Semiconductors
[R40.039] Electron-Polar Optical Phonon Interactions and transport in degenerate GaN-based heterostructures
David Anderson, Mohamed Babiker, Colin Bennett (University of York), Nick Zahkleniuk (Marconi Caswell Technology), Brian Ridley (University of Essex)
[R40.040] Depth profile of carrier concentrations in bulk GaN crystals
S. S. PARK (Samsung Advanced Institute of Technology, P.O.Box 111, Suwon 440-600, Korea), I.-W. PARK, E. K. KOH (Korea Basic Science Institute, Seoul Branch, Seoul 136-701, Korea), S. H. CHOH (Department of Physics, Korea University, Seoul 136-701, Korea)
[R40.041] Luminescence Properties of GaN:Tb, GaN/AlGaN:Eu Superlattice, and AlN:Tb and Eu.
H.J. Lozykowski, W.M. Jadwisienczak (Ohio University), I.G. Brown (University of California Berkeley)
[R40.042] Optical properties of Epitaxial Al_1-xIn_xN Alloy Films Grown on Sapphire (0001) by Plasma Source Molecular Beam Epitaxy (PSMBE)
M.J. Lukitsch, Y.V. Danylyuk, C. Huang, L. Rimai, G.W. Auner, R. Naik (Wayne State U.), V.M. Naik (U. Michigan-Dearborn), W.H. Weber (Ford Motor Co.)
[R40.043] ZnO Film Luminescence*
GANG XIONG, JOHN WILKINSON, K. B. UCER, R. T. WILLIAMS (Department of Physics, Wake Forest University, Winston-Salem, NC 27109), BIXIA LIN, ZHUXI FU (Department of Physics, University of Science and Technology of China, Hefei 230026, People's Republic of China)
[R40.044] Silver doped p-type ZnS crystals
Ekaterine Chikoidze, Tamar Chelidze, Tamaz Butkhuzi, Nodar Kekelidze (Tbilisi State University, Semiconductive Materials Scirence Laboratory)
[R40.045] MAGNETIC MEASUREMENTS ON THE LAYERED III-VI DILUTED MAGNETIC SEMICONDUCTOR Ga1-xFexSe
T.M. Pekarek, C.L. Fuller, J.L. Garner (Univ. of N. Florida), B.C. Crooker (Fordham Univ.), A.K. Miotkowski, A.K. Ramdas (Purdue Univ.)
[R40.046] Biophysics
[R40.047] Effect of Mutation on Immune Response in an HIV Response Model via Population Dynamics of Cell - A Monte Carlo Approach
Ras Pandey (University of Southern Mississippi), Heather Ruskin, Rachel Mannion (Dublin City University)
[R40.048] Force Dependence of the Michaelis Constant in a Two--State Ratchet Model for Molecular Motors
Gianluca Lattanzi (International School for Advanced Studies (SISSA/ISAS), Istituto Nazionale Fisica della Materia (INFM)), Amos Maritan (International School for Advanced Studies (SISSA/ISAS), Istituto Nazionale Fisica della Materia (INFM), The Abdus Salam International Center for Theoretical Physics (ICTP))
[R40.049] Effect of Pressure Denaturation on Molecular Motions of Myoglobin
Martin Diehl, Hellmut Schober, Johannes Wiedersich, Wolfgang Doster (University of Munich, Germany)
[R40.050] On the Long Time Dynamics of Met-Enkephalin
Min-yi Shen, Karl Freed (Department of Chemistry and James Franck Institute, The University of Chicago)
[R40.051] Quantization of a RLC mesoscopic biologically equivalent circuit
Jiu-rong Han, Qiao Bi (Dept. Phys., Yangzhou Univ., 225002 China)
[R40.052] Time-resolved enthalpy measurements of light-induced reactions by optical interferometry
Harald Leyser, Wolfgang Doster (Technical University Munich, Physics Department E 13)
[R40.053] Light Induced Destabilization of Giant Vesicles
Daniel T. Chen, Keng-Hui Lin, Arjun G. Yodh (University of Pennsylvania)
[R40.054] AFM investigations of hRPA/DNA complexes
Maryna Lysetska, Georg Krausch (Universitaet Bayreuth - Physikalische Chemie II - 95440 Bayreuth - Germany), Daniel Boehringer, Thomas Hey, Gerhard Krauss (Universitaet Bayreuth - Laboratorium fuer Biochemie - 95440 Bayreuth - Germany)
[R40.055] Atomic force microscopy of gastric mucin
Bernard Chasan, Zhenning Hong, Rama Bansil (Boston University), Bradley Turner, K. Ramakrishnan Bhaskar, Nezam Afdhal (Beth Israel Deaconess Medical Center)
[R40.056] Electrical Transport Properties of DNA Molecules
J. O. Lee (Dept. of Physics, Chonbuk National Univ.), K.-H. Yoo, Jinhee Kim (Korea Research Institute of Standards and Science), J.-J. Kim (Dept. of Physics, Chonbuk National Univ.), S. K. Kim (Dept. of Chemistry, Yeongnam Univ.)
[R40.057] Electrical Impedance Analysis of Cellular Responses to Microbial Toxins
Chun-Min Lo (Department of Physics, Cleveland State University)
[R40.058] Mechanical response of cells: multi-state adhesion
Stella Park (MIT, Dept. of Mat. Sci. amp; Eng.), Darrell Irvine (Stanford Univ., Dept. of Medicine), Linda Griffith (MIT, Dept. of Chem. Eng.), Anne Mayes (MIT, Dept. of Mat. Sci. amp; Eng.)
[R40.059] Enduring Bioinformatic Roles for Quantum Microscopy
John A. Sidles (University of Washington), Joseph L. Garbini, William M. Dougherty, Shih-Hui Chao, Melissa M. MacBeth, UW MRFM Team
[R40.060] Computational Profiling of Microbial Genomes using Short Sequences
Dale Doering (Associated Western Universities, Inc.), Toyoko Tsukuda (Pacific Northwest National Laboratory)
[R40.061] Adsorption of myoglobin to metal-chelating lipid monolayers by neutron reflectivity
Michael Kent, Hyun Yim, Daryl Sasaki (Sandia National Labs.), Greg Smith (Los Alamos National Labs.)
[R40.062] Structure and properties of beta-keratin assemblies ^1
David Grubb, Anirban Mukherjee (Materials Science and Engineering, Cornell University)
[R40.063] Metals
[R40.064] Cusp Condition Constraints on the Thermodynamic Properties of Dense Liquid Hydrogen*
K. Nagao, N. W. Ashcroft (Cornell University)
[R40.065] Structural and Electrical Properties of Thermoelectric Thin Films of Ce0.9CoFe3Sb12
Lozano Giratá, Amalia Doris, Olmos Arnache, Luis Oscar, Muñoz Lopera, Wilson (Universidad de Antioquia), Castro, Fernando Luis, Pulido Prieto, Antonio Pedro (Universidad del Valle)
[R40.066] Crystallograpic and Magnetic Properties of EuMn_xGa_3-x
Yongquan Guo (Naushad Ali), Yuin Grin (Walter Schnelle)
[R40.067] Transport Properties in Liquid Metals by Computer Simulation
Efraín Urrutia-Bañuelos (Programa de Postgrado en Ciencias (Física), Universidad de Sonora), Alvaro Posada-Amarillas (Depto. de Investigación en Física, Universidad de Sonora, 0-588,83190 Hermosillo, Son., México)
[R40.068] An exact-diagonalization study of rare events in disordered conductors
Rudolf A. Roemer, Ville Uski, Michael Schreiber (Institut fuer Physik, Technische Universitaet Chemnitz), Bernhard Mehlig (Faculty of Physics, University of Freiburg)
[R40.069] Interpolation formalism for arbitrary frequencies in the hydrodynamic model for 1D and 2D degenerate free-electron gases
Marcelo del Castillo-Mussot, Gerardo J. Vazquez (Instituto de Fisica, UNAM, Mexico), Gregorio H. Cocoletzi (Instituto de Fisica, BUAP, Mexico)
[R40.070] Electromagnetic energy propagation in cylindrical holes of metallic walls
Sergey Sekerzh-Zenkovich (Departamento de Fisica, Universidad de Sonora, Mexico), Dimitry Sekerzh-Zenkovich (Moscow State University, Russia), Felipe Ramos-Mendieta (Centro de Investigacion en Fisica, Universidad de Sonora, Mexico)
[R40.071] Acoustical pseudo-gaps within allowed frequency bands in superlattices: finite multilayer - external medium mixed effect
Betsabe Manzanares-Martinez (Programa de Posgrado en Ciencias (Fisica), Universidad de Sonora, Mexico), Felipe Ramos-Mendieta (Centro de Investigacion en Fisica, Universidad de Sonora, Mexico.)
[R40.072] local structure study of V2O3 powder
Hao Chen, Wojtek Dmouski, Takeshi Egami (University of Pennsylvania)
[R40.073] Hyper molecular dynamics simulations of vacancy diffusion in Aluminum
X. M. Duan, D. Y. Sun (Institute of Solid State Physics, Academia Sinica, Hefei-230031, P.R. China), X. G. Gong (Department of Physics, Fudan University, Shanghai 200433, P.R. China)
[R40.074] Quantitative determination of hydrogen in titanium at hundred-ppm levels using an imaging detector
H. Heather Chen-Mayer, David F. R. Mildner, George P. Lamaze, Richard M. Lindstrom (National Institute of Standards of Technology)
[R40.075] Polymers II
[R40.076] Effect of Segmental Chain Dynamics on Interface Growth in Electrophoretic Deposition of Polymer Chains
Frank Bentrem (University of Southern Mississippi), Grace Foo (National University of Singapore), Ras B. Pandey (University of Southern Mississippi)
[R40.077] Density, Conformation, and Roughening at the Interface in Electrophoretic Deposition of Polymer Chains
Frank Bentrem, Ras B. Pandey (University of Southern Mississippi)
[R40.078] Mechanisms of Ordering of Block Copolymer Microdomains
Christopher Harrison, Matthew Trawick, P.M. Chaikin (Physics Department), John Sebastian, Richard A. Register (Chemical Engineering Department), Douglas H. Adamson (Princeton Materials Institute, Princeton University, Princeton NJ 08544), Harrison, Zhengdong Cheng (ExxonMobil Research and Engineering Company, 1545 Route 22 East, Annandale, NJ 08801-0998)
[R40.079] Investigation of the Mechanical and Surface Properties of Adhesive Films Made from Discrete Polymer Nanoparticles
Elizabeth F. Fabbroni, Kenneth R. Shull (Northwestern University, Dept. of Materials Science & Engineering)
[R40.080] Preparing high-density polymer brushes by mechanically assisted polymer assembly (MAPA)
Tao Wu, Kirill Efimenko, Jan Genzer (NC State University)
[R40.081] What is the distance to the wall in lattice Monte Carlo simulations?
Iwao Teraoka (Polytechnic University), Peter Cifra (Slovak Academy of Sciences), Yongmei Wang (North Carolina Aamp;T State University)
[R40.082] The Influence of molecular weight on nanoporous polymer films
Ting Xu, Ho-Cheol Kim, Jason DeRouchey (University of Mass., Amherst), Chevey Seney (Frontier Regional High School, S.Deerfield,MA), Cathy Levesque (Wilbraham Middle School, Wibraham, MA), Paul Martin (Boston Lation Academy, Boston, MA), Chris Stafford, Thomas Russell (University of Mass., Amherst)
[R40.083] Polymer mediated aggregation of Gold nanoparticles
Irene Tsai, Scott Kennedy (University of Mass. at Amherst-PSE), Andrew K. Boal, Faysal Ilhan, Vincent M. Rotello (University of Mass. at Amherst), Thomas P. Russell (University of Mass. at Amherst - PSE), Irene Y. Tsai, Scott Kennedy, Andrew K. Boal, Faysal Ilhan, Vincent M. Rotello, Thomas P. Russell
[R40.084] Effect of surface roughness on failure mechanisms of soft adhesive layers
Arnaud Chiche, Jacob Hooker, Costantino Creton (Laboratoire PCSM-ESPCI, France), Yong Chen (CNRS-L2M, Bagneux, France)
[R40.085] Effects of Heterogeneity on the Adsorption of Poly(ethylene oxide) at a Solid-Liquid Interface
Yu-Wen Huang, Vinay K. Gupta (University of Illinois at Urbana-Champaign, Department of Chemical Engineering)
[R40.086] Patterned Attachment of Ultrathin Polymer Layers to Solid Substrates
Matthew R. Hammond, Edward J. Kramer (UCSB)
[R40.087] Confined Asymmetric Diblock Copolymers
Qiang WANG, Paul NEALEY, Juan DE PABLO (Department of Chemical Engineering, University of Wisconsin - Madison)
[R40.088] Confinement-Induced Shifts in the Dielectric Response of a Conductive Polymer
Ken Kojio, Sangmin Jeon, Steve Granick (Department of Materials Science amp; Engineering, University of Illinois at Urbana-Champaign)
[R40.089] Alignment Mechanisms of Diblock Copolymers in Electric Fields
Jason DeRouchey, Thomas Thurn-Albrecht, Ting Xu (University of Massachusetts Amherst, MA), S.K. Satija (NIST, Gaithersburg, MD), Thomas Russell (University of Massachusetts Amherst, MA)
[R40.090] 'Parachute' Studies of Adsorption onto Polymer Surfaces: Comparison with Contact Angle Measurements
Neil Moe (Osmonics, Inc.)
[R40.091] UV/ozone induced modification of silicone rubber surfaces
Kirill Efimenko, Jan Genzer (North Carolina State University)
[R40.092] Thermal probe assignments of the glass transition temperature of ultrathin polymer films and the effects of thickness, interfacial energy and grafting
Ranjeet S. Tate, Tushar Jain, David S. Fryer, Paul F. Nealey, Juan J. de Pablo (Dept. of Chemical Engg., UW-Madison)
[R40.093] Surface Passivation: A Route to Nonpreferential Surfaces
Ho-Cheol Kim, Christopher M. Stafford, Thomas P. Russell (Polymer Science and Engineering Department, University of Massachusetts at Amherst)
[R40.094] Thin Film Morphologies of SBM Triblock Copolymers
K. Amanda Leach, Ho-Cheol Kim, Thomas P. Russell (Univ. of Massachusetts at Amherst - Polymer Science and Eng. Dept.), Ludwik Leibler, Francois Court (Elf Atochem)
[R40.095] Characterization by Atomic Force Microscopy of Capillary Wave Fluctuations at Free Polymer Surfaces.
Cecile Bollinne, Stephane Cuenot, Bernard Nysten, Alain M. Jonas (Department of Materials Science, Universite catholique de Louvain.)
[R40.096] Monte Carlo Simulations of Pattern Recognition of Copolymers near Heterogeneous Surfaces
James Semler, Jan Genzer (North Carolina State University)
[R40.097] Controlling Self-Assembly of Helical, Rod-Like Polypeptides on Solid Surfaces
Alveda J. Williams (University of Illinois at Urbana-Champaign, Department of Chemistry), Vinay K. Gupta (University of Illinois at Urbana-Champaign, Department of Chemical Engineering)
[R40.098] Surface Segregation and Nanostructure Formation in Ionomer Films
Russel Walters, Russell Composto (Materials Sci. & Eng and LRSM, Univ. of Pennsylvania), Joon-Seop Kim (Chosun University)
[R40.099] Guided self-assembly of symmetric diblock copolymer films on chemically nanopatterned substrates
R. D. Peters, X. M. Yang, P. F. Nealey (University of Wisconsin)
[R40.100] Growth routes of multicomponent thin organic films: the case of PTCDA and decanethiols deposited on gold.
Jens Pflaum, Giacinto Scoles, Antoine Kahn (Princeton Materials Institute, Princeton University, New Jersey 08544)
[R40.101] Dynamics of Thermally Induced Phase Separation in Main-Chain Liquid Crystalline Polymer Solutions
Do Kim, Thein Kyu (Institute of Polymer Engineering, The University of Akron, Akron OH 44325)
[R40.102] Polymer Mixtures by Molecular Design
Anne Mayes, Juan Gonzalez, Anne-Valerie Ruzette, You-Yeon Won (Department of Material Science and Engineering, MIT)
[R40.103] Phase Behavior of Alkane Monolayers Ionically Bonded to Mica
Rahmi Ozisik, Maged A. Osman, Ulrich W. Suter (Institute of Polymers, Swiss Federal Institute of Technology (ETH))
[R40.104] Molecular Dynamics Simulations of the Phase Behavior of a Soft-core Repulsion Liquid Crystal Model
Pu Tian, Grant Smith, Ramanathan Karthik (Department of Materials Science and Engineering and Department of Chemical and Fuels Engineering, University of Utah, Salt Lake City, Utah)
[R40.105] Liquid Crystal / Liquid Crystalline Diblock Copolymer Binary Blends
Mitchell Anthamatten, Andres A. Tamez, Paula T. Hammond (MIT, Dept. of Chemical Engineering)
[R40.106] Effect of Polymer Molecular Weight on the Phase Behavior of Polymer/Small Molecule Liquid Crystal Mixtures
Nathan Crawford, Mark Dadmun, Gary Lynn (University of Tennessee-Knoxville)
[R40.107] Kinetics of Order-to-Order Transitions in Block Copolymers
Chia-Ying Wang, Timothy P. Lodge (Department of Chemistry, University of Minnesota, Minneapolis, MN 55455)
[R40.108] The phase behavior and viscoelastic properties of block copolymers with hydrogenated aromatic hydrocarbon resins
Duyeol Ryu, Jin Kon Kim, WoonYong Jeong (Department of Chemical Engineering, Polymer Research Institute, Pohang University of Science and Technology, Pohang, Kyungbuk 790-784, Korea)
[R40.109] Depletion Phenomena in Suspensions of Rigid Rods and Colloids
Yeng-Long Chen, Kenneth Schweizer (University of Illinois at Urbana-Champaign)
[R40.110] Critical Chain Length for the Need of Supercooling of Extended-chain Crystals of Oligomers by Calorimetry
Jeongihm Pak, Marek Pyda, Bernhard Wunderlich (Department of Chemistry, The University of Tennessee, Knoxville, TN 37996-1600, and Chemical and Analytical Sciences Div., Oak Ridge National Lab., Oak Ridge, TN 37831-6197)
[R40.111] Cylinder-sphere epitaxial transitions in block copolymer melts
M.W. Matsen (University of Reading)
[R40.112] Computer Simulation of Copolymer Phase Behavior
Andrew Schultz, Carol Hall, Jan Genzer (NCSU)
[R40.113] Phase Behavior of Liquid-Crystalline/Isotropic Diblock Copolymer
Michael C.-Y. Huang (Dept. of Chemical Engineering, New Jersey Institute of Technology)
[R40.114] Effects of Oscillating Electrophoretic Field on Mobility, Conformation, and Segregation of Polymer Chains in a Porous Medium
Grace Foo (National University of Singapore), Ras Pandey (University of Southern Mississippi)
[R40.115] Solvation Thermodynamics of Ethers in Aqueous Solutions. A Molecular Dynamics Simulation Study
Yi Feng, Dmitry Bedrov, Grant Smith (Department of Materials Sci.amp; Eng., University of Utah)
[R40.116] On the Validity of the Ogston Obstruction Model for Diffusion and Electrophoresis in Gels
Jean-Francois Mercier, Gary W. Slater (University of Ottawa)
[R40.117] Heat Capacity of the Liquid-Liquid Mixture Perfluoroheptane and 2,2,4-Trimethylpentane Near the Critical Point
Emily R. Oby, D. T. Jacobs (Physics Department, The College of Wooster, Wooster, Ohio)
[R40.118] Phase Transitions in Nanostructured Polyelectrolyte-Surfactant Complexes
Michael Leonard, Helmut Strey (Department of Polymer Science and Engineering, University of Massachusetts at Amherst)
[R40.119] Adhesive and Elastic Properties of DOPA-Containing Hydrogels
Rebecca Webber, Ken Shull, Phillip Messersmith, Priti Madhav (Northwestern University)
[R40.120] Electroviscous effects of Xanthan in water
David Norwood, Tamara Pearson, Catherine diBenedetto (Southeastern Louisiana University)
[R40.121] The effects of LiClO4 on the overall internal relaxation mode of poly-ethylene oxide (PEO) in methanol solution
Gregory Piet, Jim Selser, Rainer Walkenhorst, Rene Walter (University of Nevada, Las Vegas)
[R40.122] Network viscoelastic behavior in poly(ethylene oxide) melts: effects of dissolved lithium perchlorate on the network structure and dynamic behavior
Rene Walter, Rainer Walkenhorst, Jim Selser, Malcolm Smith, Radoslav Bogoslovov, Greg Piet (Department of Physics, University of Nevada, Las Vegas)
[R40.123] Dendrimer Electrophoresis in Free Solution
David Hoagland, Cynthia Welch (Polymer Sci. amp; Eng., U. of Mass. Amherst)
[R40.124] PEO-PPO-PEO Block Copolymer Micelles in Aqueous Electrolyte Solutions: Effect of Anions and Temperature on the Micelle Structure and Interaction
Sathish Sukumaran (University of Cincinnati), Guomin Mao (Argonne National Laboratory), Gregory Beaucage (University of Cincinnati), Marie-Louise Saboungi, P Thiyagarajan (Argonne National Laboratory)
[R40.125] Stabilizing Co-continuous Morphologies in Polymer Blends with Particles
B.Y. Asoo, G.H. Fredrickson, E.J. Kramer (UCSB)
[R40.126] Intercalation of polymer melts in layered nanostructures: A coarse-grained molecular dynamics simulation study
B. L. Farmer, R. A. Vaia (Air Force Research Lab), R. K. Bharadwaj (Avery Research Center)
[R40.127] Dynamics of plate-like and spherical microparticles in evaporating solutions
Andrew Guenthner, Thein Kyu (The University of Akron, Department of Polymer Engineering)
[R40.128] Relaxation of a Polymer Chain in a Melt
Katsumi Hagita, Hiroshi Takano (Dept. of Phys., Fac. of Sci. amp; Tech., Keio Univ.)
[R40.129] Optimized Mechanical Behavior of Vinyl Ester Resins
Manisha Ganglani, John Torkelson, Stephen Carr (Northwestern Univ.)
[R40.130] An Optical Rheometer for Simultaneous Study of Structures and Rheological Properties of Polymer Solutions under High Shear Rates
Khaled S. Mriziq, James Dai, Mark D. Dadmun (University of Tennessee/Knoxville), Hank D. Cochran (Oak Ridge National Laboratory/Oak Ridge)
[R40.131] Elongational Relaxation of Polymer Fluids
D. H. Reneker (The University of Akron), A.L. Yarin (Technion-Israel Institute of Technology), Han Xu (The University of Akron)
[R40.132] Slow Dynamics at the Glass Transition in Semicrystalline Polymers Studied by Pure-Exchange ^13C NMR
Tito J. Bonagamba, Eduardo R. deAzevedo, Fabio Becker-Guedes (Instituto de Fisica de São Carlos, Univ. de São Paulo, Brasil), Klaus Schmidt-Rohr (Dept. of Chemistry, Iowa State Univ., Ames IA)
[R40.133] Dewetting Dyanmics in Filled Polymeric Systems
Luo Haobin, Dilip Gersappe (Dept of Materials Science, SUNY Stony Brook)
[R40.134] Positron Annihilation Lifetime Spectroscopy and the Boson Peak in Polycarbonate Copolymers
Christopher Soles (NIST Polymers Division), Robert Dimeo (NIST Center for Neutron Research), Alexander Kisliuk, Alexei Sokolov (University of Akron), Jianwei Liu, Albert Yee (University of Michigan), Wen-li Wu (NIST Polymers Division)
[R40.135] Pressure Dependance of the Segmental Dynamics of Anthracene-Labelled Polyisoprene in Dilute Solution
Benjamin Punchard, David Adolf (The University of Leeds)
[R40.136] Coexistence of Islands and Holes in Block Copolymer Thin Films
Seung-Heon Lee, Huiman Kang, Jinhan Cho, Yeon Sang Kim, Kookheon Char (School of Chemical Engineering, Seoul National University, Seoul 151-744, Korea)
[R40.137] Glass Transition in CO2 Treated Polysulfones by DSC and PAS
Y.C. Jean, J. P. Yuan, E.W. Hellmuth (University of Missouri-Kansas City)
[R40.138] Effect of Functionality of Reactive Polymers on Reaction Kinetics and Structure of Copolymers at Immiscible Polymer Interface
Yooseong Yang, Char Kookheon (School of Chemical Engineering, Seoul National University)
[R40.139] Post-deadline abstracts
[R40.140] The precursor effect and mechanical properties in Pb_3(PO_4)_2
Y.C. Cho, S.Y. Jeong (Dept. Physics, Pusan Nat'l Univ., Korea), C.R. Cho (COMTECS Research Lab., Korea), Y.N. Choi (KAERI, Korea)
[R40.141] Finite size effects in molecular motors
M. Cemal Yalabik, Sencer Taneri (Bilkent University)
[R40.143] Novel approach for silicon nanolithography.
R.M. Ralich, S.F. Lyuksyutov, R.D. Ramsier (University of Akron, Dept. of Physics)
[R40.144] Deposition of Multilayers Using Vertical Ascent of Monolayer
Ratna S. Phadke (UNV. Dept. Of Chemical Technology, UDCT. Nathalal Parikh Marg, Matunga, Mumbai India 400019)
[R40.145] A micromachined probe array for interfacing between electronics and neurons
Chenyang Xu (Micro Actuator, Sensor, and System Research Group (MASS), Microelectronics Laboratory, University of Illinois at Urbana-Champaign, Urbana, IL 61801)
[R40.146] Characteristics of a two-dimensional electron-hole gas in GaSb-InAs-AlSb heterostructures
P.A. Folkes (), J. Bruno, M. Taysing-Lara (Army Research Laboratory)
[R40.147] A nanostructured nonlinear electronic material that operates at room temperature and 50\ GHz
A.M. Song, P. Omling, L. Samuelson, W. Seifert, I. Shorubalko (Solid State Physics and Nanometer Structure Consortium, Lund University, 221 00 Lund, Sweden), H. Zirath (Department of Microwave Technology, Chalmers University of Technology, Sweden)
[R40.148] A new approach to calculate the band structures of real crystals
Pedro Pereyra (UAM-A, Area de Fisica Teorica y Materia Condensada, Mexico D.F.)
[R40.149] ac Susceptibility in Granular Superconductors: Theory and Experiment.
Jose Luis Cardoso, Andrzej Myszkowski, Pedro Pereyra, Alejandro Kunold (UAM-A, Area de Fisica Teorica y Materia Condensada, Mexico D.F.)
[R40.150] Boch Electrons in Magnetic and Electric Fields and an Anisotropic Lattice
Alejandro Kunold (UAM-A,Area de Fisica Teorica y Materia Condensada, Mexico D.F.), Manuel Torres (Instituto de Fisica, UNAM, Mexico)
[R40.151] Self-Consistent diagrammatics: frustrating order and quantum critical behaviour
Hongbo Zhao, Jan R. Engelbrecht, Ziqiang Wang (Department of Physics, Boston College)
[R40.152] Direct nano-wiring of carbon nanotube using growth barrier
Yun-Hi Lee, Yoon-Taek Jang, Byeong-Kwon Ju, Eun-Kyu Kim (Korea Institute of Science and Technology, Seoul, Korea), Dong-Ho Kim, Chang-Woo Lee (Department of Physics, Yeungnam University, Kyungsan, Korea), Jae-Eun Lee, Young-Soo Han, Sang-Soo Yoon, Jin-Koog Shin, Sung-Tae Kim (LG Electronics Institute of Technology, Seoul, Korea)
[R40.153] First-principles calculations of the local electronic and magnetic properties of Cu in La_2-xBa_xCuO_4
K. Nagamine (RIKEN, Wako-shi, Japan; KEK, Japan), H. Li (RIKRN, Wakoshi, Japan), T.M. Briere (KEK-MSL, Tsukuba, Japan), T.P. Das (SUNY Albany, Albany, NY)
[R40.154] Dynamics of Ethylene Oxide Oligomers in Water Investigated by NMR
J.H. Shibata, M.C. Kime (University of the South)
[R40.155] Resonant Tunneling and the Substituent Effect on Negative Differential Resistance in Molecular Electronics
Karl Sohlberg (Department of Chemistry, Drexel University), Nikita Matsunaga (Department of Chemistry, Long Island University)
[R40.156] Low field magnetoresistance in FeMo double perovskites
Mar Garcia-Hernandez, Jose Luis Martinez, Maria Jesus Martinez-Lope, Maria Teresa Casais, Jose Antonio Alonso (ICMM/CSIC, Spain)
[R40.157] Optical and Magneto-Optical Study of Orbital and Spin Ordering Transitions in YVO3
A.A. Tsvetkov, F.P. Mena, Y. Ren, I.S. Elfimov, D. van der Marel, G.A. Sawatzky (University of Groningen), A.A. Nogruho, A.A. Menovsky (University of Amsterdam)
[R40.158] Comparison of Process Performance and Emission Gases during Oxide Etch using Octafluoro-cyclobutane and Perfluoro-2-butene
Chang-Jin Kang, Yoshizo Miura, Hiroyuki Nakata, Akinori Kitamura, Makoto Sekine (Association of Super-Advanced Electronics Technologies (ASET), Environmentally Benign Etch Technology Lab (EEL), Totsuka-ku, Yokohama 244-0817, JAPAN)
[R40.159] Subatomic resolution with Atomic Force Microscopy - Experiments and Calculations
Franz J. Giessibl, Hartmut Bielefeldt, Jochen Mannhart (Institute of Physics, University of Augsburg, D 86135 Augsburg, Germany)
[R40.160] OPTICAL STUDY IN A NOVEL QUATERNARY CRYSTAL DOPED WITH EUROPIUM
E.R. Alvarez (Departamento de Fisica, Universidad de Sonora, Apartado Postal 1626, Hermosillo, Sonora, 83000, Mexico), R.M. Rodriguez, M.E. Atondo (Departamento de Investigacion en Fisica, Universidad de Sonora, Hermosillo, Sonora, Mexico), A. Cordero-Borboa (Instituto de Fisica, UNAM, Apartado Postal 20-364, 01000, Mexico, D.F.)
[R40.161] DEFECTS IN NEW MIXED IONIC CRISTALOGAPHIC FAMILY
R.M. Rodriguez , M.E. Atondo (Departamento de Investigacion en Fisica, Universidad de Sonora, Apartado Postal 5-88, Hermosillo, Sonora, 83190, Mexico), E.R. Alvarez (Departamento de Fisica, Universidad de Sonora, Apartado Postal 1626, Hermosillo, Sonora, 83000, Mexico), E. Camarillo, H.G. Riveros, G. Vazquez-Polo (Instituto de Fisica, UNAM, Apartado Postal 20-364, 01000, Mexico, D.F.)
[R40.162] Magnetic g factor and diamagnetic shift in narrow GaAs-AlGaAs quantum wire
Jong Chun Woo (Professor,School of physics,Seoul National University,Seoul,Korea), Do Hyun Kim, Min Gyu Sung, In Chun Moon (School of physics, Seoul National University, Seoul, Korea)
[R40.163] Transport and Spin Effects in Homogeneous Magnetic Superlattice
Jose Luis Cardoso, Pedro Pereyra, Alfonso Anzaldo-Meneses (Física Teórica y Materia Condensada, UAM-Azcapotzalco, Av. S. Pablo 180, C.P. 02200, México D. F., México)
[R40.164] Controllable Enhancement of the Thermal and Electrical Transport Properties of an Industrial Epoxy by the Addition of Low Weight Percentages of Single Wall Carbon Nanotubes
Michael Biercuk (Department of Physics and Astronomy, University of Pennsylvania), Marc Llaguno (Department of Physics and Astronomy and LRSM, University of Pennsylvania), Marko Radosavljevic (Department of Physics and Astronomy and LRSM, University of Pennslyvania), Alan T. Johnson (Department of Physics and Astronomy, University of Pennsylvania)
[R40.165] Marshall-Peierls sign rule in frustrated Heisenberg quantum antiferromagnets
Andreas Voigt (University of Georgia, Center for Simulational Physics, Dep. of Physics and Astronomy, Athens GA 30602), Johannes Richter (Otto-von-Guericke Universität Magdeburg, Institut für Theoretische Physik, D-39016 Magdeburg, Germany)
[R40.166] The nematic-isotropic phase transition in semiflexible fused hard-sphere chain fluids
K.M. Jaffer (McMaster University), S.B. Opps (University of Toronto), D.E. Sullivan, B.G. Nickel (University of Guelph), L. Mederos (CSIC)
[R40.167] Deep impurity centers in CdTe:Ti crystals
Yu.P. Gnatenko, I.O. Faryna, P.M. Bukivskij, P.A. Skubenko (Institute of Physics of NAS of Ukraine), R.V. Gamernyk (Lviv National University), P.I. Babij (Chernivtsi National University)
[R40.168] Advanced Oxide Thin Film Fabrication and its Application to Fuel Cells
X. Chen, N.J. Wu, L. Smith, A. Ignatiev (Space Vacuum Epitaxy Center, TCSUH and MRSEC, University of Houston, Houston, TX 77204-5507)
[R40.169] Dirac quasiparticles in the mixed state
Daniel Knapp, Catherine Kallin, A.J. Berlinsky (Department of Physics and Astronomy, McMaster University)
[R40.170] Non-perturbative approach to electron pairing mediated by excitons
N. Luo (Northwestern University)
[R40.171] Extended BEG model of halogenated methanes physisorbed on ionic crystals
Teresa Burns (Coastal Carolina University), Jason Kite, JR Dennison (Utah State University)
