Session C1 - Poster Session I.
POSTER session, Monday afternoon, March 22
, Palais des Congres

[C1.001] Polymer Physics

This abstract not available.

[C1.002] Magnetism and nuclear magnetic resonance of smectite clays and their polymer nanocomposites

In an effort to understand the magnetic properties of polymer-clay nanocomposites and improve their nuclear magnetic resonance (NMR) spectroscopy, we have measured the “bulk” magnetization and magnetic susceptibility of three smectite clays (2:1 layered silicates), namely natural montmorillonite (MMT), synthetic mica-montmorillonite (SMMT), and natural hectorite (HCT), and correlated these data with the ^1H and ^29Si NMR signal intensities. As observed before, HCT provides much better NMR spectra than does MMT, even though its low-field magnetic susceptibility is larger than that of MMT. The reason is that the magnetization of HCT at ambient temperature is dominated by a contribution from ferromagnetic-like impurities, while MMT exhibits Langevin paramagnetism. Based on this insight, we have improved the HCT purification procedure, introducing magnetic separation and also avoiding centrifugation which enriches the sample with carbonates. This has increased the NMR signal intensity of HCT ~4-fold. The resulting improvement in the quality of ^1H-^29Si NMR spectra of HCT dispersed in a polymer matrix is demonstrated.

[C1.003] Lamellar Structure and Thermal Stability of isotactic Polypropylene Studied by Atomic Force Microscopy

Thin films of isotactic polypropylene were prepared with a spin-casting method at elevated temperatures. Different types of melt-crystallized ¦Á form isotactic polypropylene spherulites were obtained by annealing the thin films at different temperatures. The spherulitic morphologies were observed with polarized optical microscopy and atomic force microscopy. The detailed lamellar structures obtained by atomic force microscopy were correlated with the optical properties of different kinds of spherulites. Results suggest that the surface of flat-on lamellae is covered by a layer of nodular crystals. The melting behaviors of the nodular structures and the cross-hatched lamellar crystals of isotactic polypropylene were studied in real time at elevated temperatures using a high temperature atomic force microscopy. The results clearly showed that the nodular structures were not as perfectly stacked as the dominant flat-on and the cross-hatched lamellae. The morphological change started in the nodular structure regions during the heating process. It suggested that the nodular structures should be less stable than the flat-on and the cross-hatched lamellae.

[C1.004] Supramolecular complexes: lamellar structure and crystalline transformation

Interfacial reaction of highly-branched polyethyleneimine (PEI) with octadecnoic acid (OA) was performed to prepare a series of supramolecular complexes (PEI(OA)x, where x denotes the average numbers of OA per ethyleneimine repeat unit). The complexes at solid state have typical lamellar structure, and the interlamellar distance can be modulated by the OA content in the complexes. The long period values of the supramolecular complexes measured by SAXS were found to be dependent on the composition of the complexes, which are in good consistency with those measured by TEM. A model was proposed for the construction mode of the side alkyl chains (crystallization region) associated with the PEI backbone (amorphous region), in which the side alkyl chains were arranged to be ¡°end-to-end¡± packing for the x=1.03 complex, while an ¡°interdigitated structure¡± of the side alkyl chains was deduced for the x>1.03 and x<1.03 complexes. Temperature variable FT-IR combination investigation of the scissoring band and rocking band of methylene (¨CCH2) and stretching band of carbonyl group (C=O) indicated that the crystalline form of the crystallization region in the lamellae can be transformed from orthorhombic to hexagonal with increasing the temperature, and vice versa.

[C1.005] Lamellar Single Crystals of Poly(3-hydroxybutyrate) as Model Substrates for Enzymolysis: Origin of the Splintered Texture

The requirement for a model substrate to evaluate the manner of hydrolytic attack by depolymerases on crystalline poly(3-hydroxybutyrate), PHB, prompted the use of folded chain PHB single crystals as a model crystalline solid. Their nanodimentional thickness (5 nm), known crystal structure and lath shape with chain-folding parallel to the a axis of the unit cell are well understood. Recently Geil suggested that lath-shaped single crystals initially grow by apposition of chain-folded ribbons, one or only a few fold planes wide, which first form narrow laths and subsequently associate to form lamellae. Precursor laths have finger-like protrusions at the end indicating dominance of longitudinal growth. These observations relate to splintering when single crystals of PHB in aqueous suspension were exposed to PHB depolymerase enzymes. Our first interpretation of splintering proposed directional enzyme attack parallel to the a axis at tapered crystal edges. The presence of parallel oriented slits in the crystal suggests that longitudinal disregister between the precursor laths are also preferred locations of enzyme attack.

[C1.006] Depletion Bands in the Crystallization of Thin Isotactic Polystyrene Films

The morphologies of melt-crystallized isotactic polystyrene (iPS) thin films ranging from 100 to 300 nm were studied by optical microscopy, atomic force microscopy and transmission microscopy. The results show that banded hedritic structures composed of flat-on lamellae can be formed at a wide temperature range on different substrates. This kind of banding is not associated with changes in crystal orientation, but is likely associated with material depletion at the growth front. Because the specific volume deficit upon crystallization can be accommodated by voiding between lamellae or lamellar bundles, no bands are found whenever the film is composed of lamellae with their chain axes lying in the film plane. Taking into account that the formation of the bands appears to be caused by an inability of new melt to move to the growth surface as fast as that surface propagates, it is suggested that the diffusion length D/V is a controlling parameter in depletion band formation.

[C1.007] Crystallographic simulation of the crystalline phase of a nonracemic chiral main-chain liquid crystalline polyester

A nonracemic chiral main-chain liquid crystalline (LC) polyester has been synthesized using condensation reaction of an AB type monomer. In addition to multiple LC phases, a crystalline phase forms upon prolonged annealing in the SmC* or SmA* phase, or crystallizing from solution. Ribbon-like lamellar crystals with a monoclinic unit were found in both helical and flat forms. All the helical crystals possess the same handedness and the pitch length of helical crystals varies with growth condition. A force field crystallographic simulation was performed to probe the atomic structure of the crystalline phase and to understand the molecular origin of helical twisting. Simulation results suggest that the crystal structure belongs to space group P21/c. Each unit cell consists of four repeat units in two zigzag anti-parallel chains. The inter-chain interaction along the b-axis is significantly stronger than that along a-axis.

[C1.008] Tensile Deformation of Polyethylenes: Crystallinity Effects

The crystalline fraction of polyethylene can be reduced by increasing the cooling rate, the molecular weight or the fraction of comonomer. All three methods have been used in this study of tensile deformation which shows that true stress - true strain behavior depends systematically on morphology. The dependence of uniaxial yield stress on crystal thickness is well understood in terms of dislocation nucleation. Post yield flow is dominated by the strain hardening rate that is larger in polyethylenes of lower crystallinity. Noncrystalline polymer evidently reduces the plastic compliance while providing for elastic (reversible) strains. These observations are examined in terms of old and new theories for deformation of semicrystalline polymers.

[C1.009] Orientation Normal to the Surface in Semicrystalline Poly(lactic acid) Films

Dependence of poly (lactic acid) film morphology on thermal history was investigated. Polarized infrared spectrometry revealed that melted samples crystallized at high temperatures showed significantly large orientation in the thickness direction, while at low temperatures, mostly isotropy was observed. The difference in degree of orientation in the direction of the surface normal arises primarily from the large difference in nucleation rate. In contrast to lower temperature (fast nucleation) where spherical symmetry is preserved in the spherulites, higher temperature (slower nucleation) leads to formation of large spherulites to the extent that the spherulitic symmetry becomes pseudocylindrical (disc-like). The two different types of symmetry in the spherulites can explain the spectroscopic differences between the two thermally treated samples.

[C1.010] Heat capacity, magnetic susceptibility, EPR, and dc conductivity of some conducting polymers

Polyaniline doped with polystyrene-sulfonic-acid (PAN-PSSA), such that y =[sulfonate]/[aniline] = 1, exhibits a dc conductivity of 0.1 S/cm. On increasing the dopant concentration to y = 6, the conductivity drops by four orders of magnitude. Poly(3,4-ethylenedioxythiophene) doped with polystyrene-sulfonic-acid (PEDOT-PSSA) also exhibits a similar behavior on doping. The results of a study involving heat capacity, magnetic susceptibility, EPR, and dc conducting measurements will be reported.

[C1.011] Time-Resolved SANS Study of Polyethylene Crystallization from Solution

Using time-resolved small angle neutron scattering (TR-SANS), the crystallization kinetics of polyethylene from deuterated o-xylene solutions upon a temperature jump has been investigated. Based on a morphological model of coexisting lamellar stacks and coil chains in solution, experimental data are quantitatively analyzed to give the structure information such as the lamellar long period, the lamellar crystal thickness, the thickness of amorphous layers between lamellae, the degree of crystallinity, and the crystal growth rate at various degrees of undercooling. The viability of TR-SANS for studying polymer crystallization is demonstrated through the consistency between this measurement and well-established knowledge on polyethylene crystallization from xylene solutions. One unique feature of this experiment is that both the growth of lamellar crystals and the condensation of coil chains from solution are monitored simultaneously. The ratio of the crystal growth to the chain consumption rate decreases rapidly with decreasing degree of undercooling. The Avrami analysis suggests that the growth mechanism approaches 2D behavior at higher temperatures, which is consistent with the observation of the increasing ratio of the sharp-surface area to bulk crystal growth rate with temperature.

[C1.012] Morphological Studies and Thickness Effect on Crystalline P(VDF-TrFE) Copolymer

We report the results of a comparative study of the structure of random copolymer bulk and thin films of poly(vinylidene fluoride- trifluoroethylene) [P(VDF-TrFE)] in composition ratio 75 mol% VDF. All films were cast from dimethylacetamide solutions. Thin films were prepared either by doctor blading or by casting onto mobile (liquid) surfaces such as polyphosphoric acid or polyacrylic acid. Bulk films were crystallized isothermally from the melt on different substrates (glass, mica, or silicon) at temperatures within the paraelectric phase. Phase transformation to the ferroelectric phase occurred during cooling or during a second stage of isothermal crystallization. The crystalline morphology was characterized using atomic force microscopy in tapping mode. Lamellar bundles and larger scale domains are observed in bulk films. Fourier transform infrared spectroscopy confirms that the crystals formed are analogous to the beta phase of homopolymer PVDF. Structural evolution in crystals is compared with the data based on real-time simultaneous small- and wide-angle X-ray scattering and differential scanning calorimetry. Thin films with different thicknesses will also be studied using AFM, FTIR and dielectric spectroscopy measurements to compare structural information with that obtained on the bulk film.

[C1.013] Sub-micron Scroll/Tubular single crystals of Nylon 66

Through self-seeding solution crystallization, novel Nylon 66 single crystal scroll/tube morphologies have been observed. The diameter of the scroll/tube is ~ 350 nm with a ~ 10 nm thin wall. The thermodynamically more stable tubular/scroll single crystal form is presumably due to the asymmetric folding of Nylon 66. Furthermore, this imbalance of the folded basal surfaces can be turned on and off by controlling the self-seeding temperature: using the same crystallization temperature (174 degree C), self-seeding at 202 and 208 degree C leads to flat, regular single crystals while self-seeding at 206 degree C leads to nano scrolls and tubes, indicating that the chain folding was controlled by the self-seeding temperature, which in turn, affect the morphology formation. The present study also suggests that a variety of polymer structures can be designed to introduce the asymmetric folding and controlling the “degree of this structural imbalance” might also lead to sub-micron scrolls/tubes with different diameters. The similarity of the beta sheet structure of polyamide with that of polypeptide in their beta sheet structure might also suggest new polypeptide sequence design to produce designated tertiary structures.

[C1.014] Optical and X-ray scattering studies on a semicrystalline triblock copolymer

A triblock copolymer composed of semicrystalline blocks, poly(L-lactic acid-b-ethylene oxide-b-L-lactic acid), was synthesized, and its optical properties together with crystalline structures were studied. Above the melting point of poly(L-lactic acid) (PLLA), the triblock copolymer was in disordered state within the studied composition and molecular weight range, and it formed banded spherulites when crystallized. Its optical properties were measured with compensators in polarized optical microscope. The birefringence of the triblock copolymer spherulite resulted from the constructive addition of those of component blocks. The crystalline structure of the triblock copolymer, especially the lamellar orientation of each block was investigated with X-ray scattering. Samples for SAXS and WAXD were prepared via subsequent crystallization of poly(ethylene oxide) (PEO) after aligning PLLA lamella by applying shear above melting point of PEO. Detailed information about lamellar orientation depending on shear and crystallization condition will be discussed.

[C1.015] Double Reversible Melting of Isotactic Polystyrene

Quasi-isothermal temperature modulated differential scanning calorimetry (TMDSC) has been used to study the reversible crystallization and melting of isotactic polystyrene (iPS). IPS was cold crystallized at 140 °C or 170 °C until completion of crystallization, then heated from below the glass transition (Tg) to above the melting point (Tm) using step-wise temperature increase, with small amplitude temperature oscillation for 20 min. at each step. Reversible heat capacity measurements reveal existence of a small amount of locally reversible melting and crystallization. We observe two small reversible melting peaks for iPS samples cold crystallized either at the lower or at the higher temperature. The reversible melting peaks are located on the higher temperature side of two major endothermic peaks (Tm1 and Tm2) seen in regular (non-modulated) scanning calorimetry. In quasi-isothermal TMDSC, the portion of the crystallized chain with lower thermal stability melts first, and the molecules that are attached to these chains melt at the higher temperature end of the correspondent population. These portions demonstrate locally reversible melting and show a tiny reversible melting peak associated with the lower temperature endothermic peak (at Tm1). Molecules attached to the portion of chain with higher thermal stability (having higher melting temperature) show their reversible melting peak in association with the higher temperature endothermic peak (at Tm2).

[C1.016] Thermomechanical Properties of the Semicrystalline Interphase of Polyethylene

We present the first complete theoretical estimates for the thermal and elastic properties of the noncrystalline phase (the "interphase") of semicrystalline polyethylene obtained by Monte Carlo simulations, where polyethylene is represented by a realistic united atom force field, which includes torsional contributions. The interphase is modeled as a metastable disordered region constrained between two static crystalline layers and consists of bridge, loop and tail populations of varying lengths. Parallel tempering is used to simulate several isochoric/isothermal ensembles simultaneously and efficiently. Both energetic and entropic contributions to elastic moduli are calculated, the latter indirectly obtained through virial pressure calculations. The interphase region of real polyethylene, characterized by density, order and energy profiles, is compared to earlier work on freely rotating chains [Balijepalli and Rutledge, J. Chem. Phys. 1998, 6523]. The isochoric and isobaric heat capacities, Grueneisen coefficients, thermal expansion and elastic stiffness constants are reported. The interphase exhibits material properties comparable to that of the corresponding melt, with significant contributions of both enthalpic and entropic origins.

[C1.017] Crystal Structure of Hydrogenated, Atactic ROMP Polynorbornene.

Ring-opening metathesis polymerization (ROMP) of norbornene produces a polymer whose repeat unit contains a backbone cyclopentyl ring. The ``puckering'' of this ring leads to stereoisomerism, which is retained when the polymer is hydrogenated. Both classical heterogeneous and newer homogeneous ROMP catalysts produce an essentially atactic (Bernoullian) polymer, as confirmed by ^13C NMR; however, the hydrogenated polymer is highly (>70%) crystalline, with an equilibrium melting point of 156^oC. We have found that both m and r dyads crystallize into a common unit cell, where the backbone adopts a quasi-trans-zig-zag conformation; all the observed reflections in the fiber x-ray diffraction pattern can be indexed according to the C2/c space group (monoclinic-\beta ), with lattice parameters of a = 6.94 Åb = 9.60 Åc = 12.42 Åand \beta = 130.7^o at room temperature. The stereoirregularity of the polymer generates torsional distortions of the backbone which influence the intensities of the reflections; these distortions also cause a decrease in the c parameter with increasing temperature, and an abrupt loss of higher-order diffraction spots approximately 30^oC prior to melting.

[C1.018] Understanding the Complex Morphologies of Homogeneous Ethylene/α-Olefin Copolymers with Real-Time Small Angle Light Scattering

The melting behavior of homogeneous ethylene/\alpha -olefin copolymers with intermediate (6.4 mol % comonomer) to high branch content (18 mol % comonomer) has been studied by real-time small angle light scattering (SALS) under cross-polarized and parallel-polarized optical alignments. We show that the SALS melting measurements can be used to characterize the melting behavior usually measured by differential scanning calorimetry (DSC) as well as the spatial arrangement of crystals. The contrast variation (orientation and density fluctuations) during melting of different crystal populations measurable by SALS can be used to characterize the mixed morphologies (e.g., spherulitic/fringed-micellar crystals) typically observed for ethylene/\alpha -olefin copolymers with intermediate to low densities (\sim 0.87 < \quad \rho \quad < \quad \sim 0.91 g/cm^3). Thus, real time SALS provides a means for determining the characteristics (number, type and melting temperatures) of crystal populations and their spatial arrangement in one measurement. The complex morphologies of ethylene/\alpha -olefin copolymers can be described by the SALS model proposed and methods developed.

[C1.019] Capillary instabilities of thin nematic liquid crystalline polymer fibers embedded in a flexible polymer matrix

Capillary instabilities of both oriented and disoriented thermotropic liquid crystalline polymer (LCP) fibers (PSHQ-6,12) embedded in an immiscible flexible polymer matrix (PDMS) were investigated to determine the temperature dependence of dynamic interfacial tension. We have found that oriented (as-spun) LCP fibers feature several-fold larger interfacial tension values when compared with disoriented (previously “cleared”), but nematic, fibers at the same temperature. Despite this quantitative difference, both cases feature the same tendency: in the nematic phase, interfacial tension decreases monotonically with increasing temperature. On clearing to the isotropic phase, interfacial tension increases step-wise. Microscopic retardance imaging during the instability reveals differences in evolution of an early-time banded structure (and local retardance) between the crest and trough regions along the fiber. Additionally, direct observations of orientation at the LCP/isotropic interface reveal strong anchoring of the nematic director which aid in development of a quantitative model for this important system.

[C1.020] Surface Microstructure of Injection-Molded Thermotropic Liquid Crystalline Copolyesters

Near edge X-ray adsorption fine structure (NEXAFS) spectroscopy is being used to characterize anisotropy in injection-molded plaques fabricated from thermotropic liquid crystalline copolyester polymers (TLCPs). Skin orientation in TLCP moldings was previously measured by other researchers using WAXS of microtomed layers. An alternate and less intrusive means of determining surface orientation presents itself in the form of the synchrotron-based UV technique NEXAFS using the method of Stöhr and Samant.[1] NEXAFS is sensitive to the orientation of phenyl groups of the top 2 to 3 nm of a surface via the variation in intensity of the partial electron yield of Auger electrons of the 1s to \pi * transition of the C = C bonds within the C edge. Plaques were injection-molded under controlled conditions, and the orientation of the surface layers was determined. Good agreement was obtained between 2-D wide-angle X-ray scattering (in transmission) and NEXAFS results for situations where appropriate. Ref.: [1] J. Stöhr and M.G. Samant, J. Elec. Spectrosc. Relat. Phenom. 98-99, 189 (1999).

[C1.021] The relationship between photooxidation defects and quantum yield loss in a liquid crystalline oligofluorene

We have studied the photophysics of a liquid crystalline oligofluorene which emits blue light with a quantum efficiency of forty-nine percent.( Y. Geng, S. Culligan, A. Trajkovska, J. Wallace and S. Chen, Chem. Mater; 2003, 15, 542-549.) The fluorescent yield is reduced when the film has been exposed to ultra-violet light and air. The resulting photooxidation creates luminescent defects that have previously been observed in some polyfluorenes.( E. J. W. List, R. Guentner, P. Scanducci de Freitas, and U. Scherf, Adv Mater., 2002, 14, 374-378.) The defects decrease the overall fluorescent yield because they divert energy away from the blue-emitting chromophores and emit at longer wavelengths with low efficiency. In contrast with previous studies of photooxidized polyfluorenes, we observe two emission peaks associated with defects that have distinct intensity dependence and decay dynamics.

[C1.022] Understanding the Fundamental Mechanism Of Polymer-Substrate Adhesion Loss at a Critical Humidity Level By Combining Neutron Reflectivity and Adhesive Fracture Energy Measurements

Adhesion loss resulting from exposure to moisture is a fundamental problem in the adhesive industry. A class of adhesives that is particularly sensitive to moisture includes the epoxies. Given their extensive use in housing, composites, microelectronics, and automotive industry, the study of epoxy interfaces is of significant interest. Epoxies typically lose adhesion strength during moisture exposure above a critical relative humidity (RH) level, typically near 70%. The mechanism of adhesion loss at the critical RH is the subject of much speculation. The reduction in adhesion is caused by physical and chemical changes resulting from moisture absorption, but it is unclear whether the changes occur in the bulk adhesive or at the adhesive-substrate interface. To better understand this phenomenon, neutron reflectivity experiments combined with adhesive fracture mechanics are proposed. Using neutron reflectivity, the spatial distribution of water at the interface will be measured in a range of relative humidity levels above and below the critical level. These measurements will be correlated to adhesive fracture energies obtained by the shaft-loaded blister test, a newly developed adhesion test. Utilizing these two techniques in combination differentiates between the relative contributions of moisture content at the interface and the bulk to adhesion loss. Moreover, this study provides direct evidence for the fundamental mechanism of adhesion loss due to moisture.

[C1.023] Radical initiated polymerization in a bi-functional mixture by a computer simulation model

A computer simulation model is used to study the rate of reaction and concentration of bond growth in a mixture of bi-functional groups on a cubic lattice. The primary objective of this simulation is to understand the polymerization behavior of vegetable oil derived macromonomers (VOMMs) in solution: VOMM consists of a mixture of olefins (A) and acrylates (B). A set of interactions between particles (A,B) and solvent (S) sites are used to equilibrate their distribution at concentrations (p_A, p_B). Based on the interaction strength and their relative concentrations, polymerization in four systems (VOMMs) are examined. The total polymer concentration (p = p_A + p_B) is varied. Free radical initiated polymerization is implemented via reaction pathways, i.e., radicals move from one functional group to another forming covalent bonds on their trails. Decay of reaction rate depends on system and shows various patterns with power-law, exponential, and their combination. Relative ratios of acrylates to olefin and their proximity are found to affect the overall A-B bond concentration.

[C1.024] A CONTACT MECHANICS METHOD FOR CHARACTERIZING THE ELASTIC PROPERTIES AND PERMEABILITY OF POLYMER GELS

When a gel in a saturated environment is suddenly brought into contact with an indenter, its mechanical response is influenced by the flow of liquid in its pores. The solvent in the gel cannot instantaneously respond by flowing out of the network, so the gel acts incompressibly. As a result, a pressure gradient forms in the liquid. Liquid flows out of the pores until the pressure drops to zero in the entire system, thereby allowing all stresses to be transferred to the network. Because of the flow of solvent in the gel, the force required to maintain a constant contact area will relax with time. Our work studies the feasibility of using an indentation test to measure this time dependent force, which is then used to determine the elastic modulus, Poisson’s ratio and the permeability, Dp, of the network. A theoretical framework based on two-dimensional Hertz contact problem of a rigid cylinder indenting on a linearly elastic, isotropic gel that is saturated in its own solvent is presented. This analysis is then compared to preliminary experimental results.

[C1.025] Study of PVA solutions and gels with Fluorescence Correlation Spectroscopy

Fluorescence Correlation Spectroscopy (FCS) is a noninvasive technique which is commonly used to study the dynamics of nanomolar concentrations of fluorophores in solution. We performed FCS experiments with rhodamine probes on aqueous poly (vinyl alcohol) (PVA) solutions of several concentrations (between 3% and 7% w/w) and chemically crosslinked PVA gels of different network densities (400 monomers per crosslink and 50 monomers per crosslink, with polymer concentrations between 3% and 6% w/w). Preliminary results indicate a monotonic increase in the characteristic diffusion time with increase in concentration of the PVA solutions. The gels exhibit a longer characteristic diffusion time than their respective solutions. We discuss these results in the context of what is known about the structure of PVA solutions and gels.

[C1.026] Broadband Dielectric Investigation of Hydrogen Bonded Poly(vinyl ether) Solutions

The relaxation dynamics of mixtures of poly(vinyl methyl ether)\textbf [PVME] with 4-ethylphenol and bis(4-hydroxyphenyl)-methane, and poly(vinyl ethyl ether) [PVEE] with 2,6-dihydroxy naphthalene [DHN], were investigated using dielectric relaxation spectroscopy. Time-temperature superposition was valid for all mixtures studied, and all of these solutions exhibit the same segmental relaxation time distribution as the neat polymers. This behavior is attributed to the strong intermolecular hydrogen bonding, increased mixing entropy, relatively small T_g contrast, absence of self-concentration effects, and reduced interchain cooperativity. The modification of the \alpha relaxation time of PVEE by DHN is in keeping with previous findings on binary glass-forming systems. PVME/toluene mixtures, however, exhibit a slightly broader segmental relaxation distribution due to the absence of hydrogen bonding. We also found that strong intermolecular associations are capable of slowing down the secondary relaxation of PVME.

[C1.027] Solvent Quality Based Gel Transitions in Triblock Copolymer Gels

Triblock copolymers with polystyrene end-blocks and a poly(ethylene-butylene) mid-block experience a shift in transitional temperatures when dissolved in various combinations of solvents. At high-temperatures the polymers are completely soluble. Upon cooling these solutions, they go through two transitions. The first transition occurs at the critical micelle temperature where the end-blocks begin to form physical aggregates, resulting in the formation of a viscoelastic solid. The second transition occurs at the glass transition temperature where the mid-block becomes glassy and an elastic solid is produced. In this work we explore the use of solvent mixtures to control the location of these two transition temperatures.

[C1.028] Exploring Fast Flow Behavior of Entangled Polymers

A variety of rheological measurements including oscillatory shear and steady shear in both controlled rate and controlled stress modes has been carried out to unravel the universal flow characteristics of different entangled polymers under the fast flow condition defined as applied shear rates reaching beyond the overall chain relaxation rate and/or applied stresses as high or higher than the dynamic plateau modulus. Flow birefringence and particle imaging velocimetry have been applied to detect any spatial variation of the shear rate across the sample under both controlled rate and controlled stress conditions. Our findings challenge the current theoretical knowledge (a) of the fast flow behavior of entangled polymers. (a) J. Bent et al, Science 301, 1691 (2003); R. Graham, A. Likhtman, T. McLeish and S. Milner, J. Rheol. 47, 1171 (2003).

[C1.029] Ultra-high Modulus Nano-Fluoroelastomers

The cross-linking densities, glass transition temperatures, and physical properties of fluoroelastomers filled with a nanometer-size particle have been determined as a function of filler concentration and co-solvent using both dry and wet filler incorporation methodologies. Addition of alcohol to the casting solvent such as methyl isobutyl ketone results in about a factor of 1.5-3 increase in elastic modulus for elastomer of the same filler concentration. It is discovered that a properly prepared nano-fluoroelastomer can exhibit as much as a two-order-of-magnitude increase in elastic modulus as the filler concentration increases from zero to 35 parts per hundred of rubber (phr) by weight while the glass transition temperature does not change substantially with filler concentration. The effect of cross-linking density on the elastic modulus for these materials will be discussed in this paper.

[C1.030] Supramolecular Thin Film Architectures of Oppositely Charged Polyphenylene Dendrimers by Layer-by-Layer Self-Assembly

Thin films of oppositely charged polyelectrolyte assemblies of L-lysine and carboxylic acid functionalized polyphenylene dendrimers were fabricated on 3-mercaptopropionic acid coated gold surfaces via electrostatic layer-by-layer self-assembly. The behavior of the film formation was monitored by surface plasmon resonance (SPR) spectroscopy. The permeability properties of the dendritic polyelectrolyte layers were investigated by electrochemical methods, i.e., cyclic voltammetry and ac impedance spectroscopy in the presence of [Fe(CN)6]3-/4- as the redox couple with respect to the thickness of the layers and the pH. A high interfacial charge-transfer resistance, originating from the electrostatic repulsion of the negatively charged redox couple from the negatively charged interface was observed. The interfacial charge-transfer resistance was also increased with increasing the number of layers.

[C1.031] Self-Consistent Field Calculations of Polyelectrolyte Systems

A self-consistent field theory is applied to inhomogeneous polyelectrolyte (PE) systems. We consider the smeared and the annealed charge distributions, corresponding to strongly and weakly dissociating polymers, respectively. The electrostatic interactions are described by the nonlinear Poisson-Boltzmann equation, where the dielectric constant of the system is treated as position-dependent to take into account the large dielectric difference between the hydrophobic polymer and the water-like solvent. We present results for several systems, including PE solutions, blends, block copolymers, brushes, as well as PE adsorption and multilayer formation on charged surfaces. We also present a general, efficient strategy of solving the self-consistent field equations using pseudo-spectral numerical schemes. This strategy is based on the saddle-point behavior and the random-phase approximation of the system, and allows large-scale, high-accuracy calculations without a priori knowledge about the symmetry of the inhomogeneous structure.

[C1.032] PBZO Based Proton Exchange Membrane (PEM) for High Temperature Fuel Cells

Most existing PEMs for fuel cells are limited to a temperature range below approximately 80 °C. Thus, an effort has been made to develop new polymer membranes which could be used in fuel cells at higher temperatures. Poly (p-phenylene benzobisoxazole) (PBZO) is a promising candidate for use as a structural membrane due to its good mechanical properties as well as chemical and thermal stability. Additionally, PBZO can be processed into thin membranes having a microporous structure, which can accommodate loading with an ion-conducting polymer (ICP) of sulfonated poly (ether sulfone). Our preliminary results demonstrate that the performance of the resulting PEM is comparable to that of the commercially available product. Aspects of the processing, morphology and properties will be presented.

[C1.033] Blend Miscibility of Polystyrene/Sulfonated Polystyrene Blends

A variety of recent findings suggest that the morphology and phase behavior in sulfonated polystyrene (SPS) systems require renewed research efforts. For example, while studying blends of polystyrene and SPS random copolymer, Beck Tan, et al. determined the Flory interaction parameter to be at least 5.6.[1] While such a high value is understandable given the chemical difference between these monomeric units, one ramification of this could be phase separation within a given sample of PS/SPS that naturally exhibits a distribution of sulfonation levels. The initial stage of our study is to focus on blends of PS/SPSx with different sulfonation levels using forward recoil spectrometry (FRES). This method provides depth profiles from bilayer samples that measure the coexistence compositions from which we construct blend phase diagrams. [1] Beck Tan, et al, ``Immiscibility in Polystyrene/Sulfonated Polystyrene Blends,'' Polymer 36 (10), 1969-1973 (1995).

[C1.034] Dynamically stabilized lateral patterns in changed blends

We investigate a thin film consisting of a symmetric melt blend of oppositely charged, yet thermodynamically incompatible polymers. In the absence of an externally applied electric field, microsegregation occurs in this system forming alternating layers of charged material resembling structures formed in layer-by-layer deposition of polyelectrolyte films. However, when subjected to an oscillating electric field aligned along the film normal, lateral striped microsegregation patterns are stabilized. In addition to a linear stability analysis, we present numerical simulation results on the development of the lateral ordering.

[C1.035] Influence of chain stiffness on the properties of polyelectrolyte solutions

Model systems for obtaining structural information on atomic-level interactions in polyelectrolyte solutions should incorporate primary features of the interactions of interest. For example, the effect of chain stiffness on polyelectrolyte conformation and counterion interactions can best be understood through the preparation of polyelectrolytes in which the same charge groups are attached to backbone structures of varying stiffness. For a ionizable group (sulfonate), the effect of chain stiffness can be elucidated through studies of poly(styrene sulfonate) (PSS) as a flexible example; poly(cyclohexadiene sulfonate) (PCHDS) as a ``semiflexible'' backbone structure. Small-angle neutron scattering (SANS) of PCHDS-h solutions have shown that the polyelectrolyte peak was observed to be much less pronounced and less dependent of polymer concentration compared to PSS. Finding peak position required working out an empirical procedure in order to subtract the contribution of excess scattering at small Qs. Preliminary data analysis shows that the peak position for solutions of PCHDS in D_2O scales with the polymer concentration (zero salt) with exponent \sim 0.1 to be compared with the scaling predictions of 0.5 for flexible chains.

[C1.036] Capillary electrophoresis of small ssDNA molecules

Recently, the electrophoretic separation of small ssDNA fragments (bellow 250 bases) has attracted a lot of attention because of applications related to Single Nucleotide Polymorphisms. In order to optimize these systems, we require a better understanding of DNA migration behavior in this size range. While the reptation model provides an excellent understanding of the dynamics of long DNA fragments in gel electrophoresis, the properties of small DNA fragments has not been studied extensively yet. At least three theoretical formulas have been proposed to explain the mobility of short ssDNA molecules in this regime. Specifically, the Ogston regime was introduced for small molecules having radii-of-gyration comparable to or smaller than the pore size of the sieving matrix. We introduce these three different formulas and discuss how their free parameters are related to actual physical parameters. We then test these formulas with new data obtained by capillary electrophoresis in our laboratory using poly(dimethylacrylamide) sieving matrices. Our results show that all three formulas provide decent fits, and that their fitting parameters are consistent with one another. This is the first step towards the development of a systematic approach to optimizing sequencing systems for this size range.

[C1.037] Complex Transformations between Bicontinuous Cubic and Cylinder Phases in a Polystyrene-block-Poly(ethylene oxide) Diblock Copolymer

Complex phase transformations between bicontinuous cubic and hexagonal cylinder (Hex) phases in a polystyrene-block-poly(ethylene oxide) (PS-b-PEO) diblock copolymer were investigated using small angle X-ray scattering (SAXS), transmission electron microscope (TEM), rheology, and polarized light microscope (PLM). The sample exhibited a typical double gyroid (G) phase, together with a minority plumbers nightmare (P) phase which was only \sim6 vol.% as calculated from the SAXS scattering intensities for each phase. These two bicontinuous cubic phases had the same unit cell dimensions. Under a large-amplitude reciprocating shear, the bicontinuous cubic sample transformed into a single-crystal Hex phase. Annealing this sample at 150 ^oC for 40 min, the Hex phase partially transformed into well-oriented G and P twin structures, as evidenced by two-dimensional synchrotron SAXS experiments. Epitaxial phase transformation relationships between the Hex/G and Hex/P phases were identified. The phase transformations were further confirmed by rheology study and PLM observations. The P phase was metastable with respect to the G phase, and it disappeared when the sample was heated above the order-disorder transition temperature and annealed at 150 ^oC. The mechanism of the Hex \rightarrow G transformation was investigated by TEM. Generally, in a hexagonal cell, three cylinders evolved into left-handed helices, while the other three formed right-handed helices. An intermediate five-fold junction was speculated to facilitate the phase transformation. The Hex -> G phase transformation was observed to follow a nucleation and growth mechanism, and the phase transition zone was less than one unit cell.

[C1.038] Electrophoretic collision of a DNA molecule with an insulating post

We study the dynamics of single DNA molecules driven by an electric field into a stationary obstacle. These collisions are broadly classified as ``hook'' and ``roll-off'' events. We show that obstacle-induced electric field gradients stretch impacting DNA and thus greatly influence the hooking probability. Consequently, in addition to collision geometry, determination of the hooking probability depends on the Deborah number (De) for 0.5

[C1.039] Thermo-mechanical properties of semicrystalline sPP-EPR diblock and sPP-EPR-sPP triblock copolymers

Polyolefin copolymers of diblock (poly)(syndio-)propylene-b-ethylene- propylene and triblock (poly)(syndio-)propylene-b-ethylene-propylene-(syndio-)propylene were synthesized using new living single site titanium catalyst. The phase diagram was established and interesting morphology was observed in the microphase-separated domains where both polypropylene (PP) and ethylene-polypropylene (EP) layers were semicrystalline. Crystallinity of the copolymers was determined and mechanical properties such as stress-strain and stress relaxation behaviors were examined to observe fracture stress and strain, Young modulus and mechanical hysteresis at different temperatures. It was found that molecular structures strongly affect the mechanical properties of the copolymers. Increasing molecular weight improves the ductility of the copolymers and increasing PP content increases Young modulus and the plastic strain after deformation. Higher ethylene content in EP block produces a higher fracture stress even in the weak diblock copolymers. We will discuss these interesting mechanical characteristics in terms of the semicrystalline microstructures of the copolymers.

[C1.040] Moiré Patterns of 2D Block Copolymer Arrays and Their Defects

Assessing the orientation and defect structure of large areas of 2D crystalline arrays of block copolymer spheres using scanning force microscopy (SFM) is very tedious, requiring many small area scans (2 by 2\mu m) to be pieced together. Moiré patterns from large area SFM scans offer an attractive alternative[1]. The technique does not require individual spheres to be resolved, and therefore permits scanning regions up to 50 by 50\mu m in size. The measured pitch and angle of the Moiré patterns follow theoretical predictions, and can be related back to the geometry of the underlying lattice. We demonstrate the use of this technique to determine the orientation as well as details of the defect structure of monolayers of poly(styrene-\emphb-2vinylpyridine) spherical domains confined laterally in hexagonal wells. In particular, the densities and Burger vectors of dislocations can be determined, provided that individual dislocations are separated by distances greater than the pitch of the Moiré pattern. [1]D. E. Angelescu et al., Appl. Phys. A, DOI 10.1007/s00339-002-2012-5.

[C1.041] Effect of Thermal History on Order of Confined 2D Layers of Block Copolymers

The order of a monolayer of spherical domain poly(styrene-\emphb-2 vinyl pyridine) block copolymer melt confined laterally in hexagonal wells is investigated as a function of thermal history. The wells range in size from 2 to 100\mum between parallel edges. All thermal treatments begin with a disordered film produced by spin casting. In one case the film is heated rapidly to a temperature T_A and held isothermally for a time t_REF to produce a 2D crystalline array of block copolymer spheres. The order for this case is compared with that after a brief heating to produce the 2D liquid, followed by cooling at a rate \textbfr through the hexatic intermediate phase to T_A and holding for t \leq t_REF. If \textbfr is sufficiently small (\ll 1^oC/min), 2D single crystals are obtained in 16\mum hexagons, whereas the direct annealing treatment yields 2D polycrystals in the same size wells. A possible explanation for the better order after cooling from the liquid is attributed to formation of an orientationally ordered hexatic phase near the edges of the well [1], which then templates the formation of a single grain orientation. [1] R.A. Segalman, A. Hexemer, E.J. Kramer, Phys. Rev. Lett. \textbf91 192101 (2003).

[C1.042] Block Copolymer Ordering in Swollen Films

To generate nano-structured materials from pure block copolymer materials in the size scale of 10 nm or less, segmental interactions must be very strong. Long-rang order on arrays generated from block copolymers mandates sufficient mobility to remove defects. Solvent casting films of block copolymers with strong segmental interactions fulfills both of these requirements. By controlling solvent evaporation rate, the orientation and long-range order of the block copolymer can be controlled. Block copolymer films of poly(ethylene-alt-propylene)-b-poly(lactic acid), which exhibit inter-domain spacings of 10 to 22 nm, are subject to various casting and solvent annealing conditions to achieve a desired orientation and order. Changing the solvent or evaporation conditions can achieve both parallel and normal orientation of the cylindrical microdomains with respect to the substrate. The films are examined by AFM and grazing incidence small angle x-ray scattering (GISAXS) to the structure of the copolymer morphology at the surface and throughout entire film.

[C1.043] Selective Metalization of Block Copolymer Films

Macromolecule-metal complexes are of interest to many applications, including photonic band gap materials. These materials typically have periodic structures approximately 100nm in length and a large refractive index contrast between their domains. Conversely, block copolymers characteristically have a small refractive index contrast between their domains. Thus, the refractive index contrast of block copolymers may be enhanced by selectively depositing metals or metal sulfides into one domain of the material. In this study, macromolecule-metal complexes were created using Polystyrene-b-Poly(2-vinylpyridine) block copolymer films as templates. Metalization of these films was accomplished through a ligand exchange reaction by means of supercritical carbon dioxide-soluble metal precursors. Next, either hydrogen or hydrogen sulfide gas reduced the metal precursor in the material to the metal or metal sulfide, respectively. This method allows for metallization of one domain without disruption of the ordered block copolymer template.

[C1.044] Separation of ABC triblock copolymer using HPLC

As-prepared ABC triblock copolymer does not reflect true behavior of triblock itself because it contains some of homopolymer and diblock copolymer formed in the process of synthesis. Temperature Gradient Interaction Chromatography (TGIC) is an HPLC technique changing the column temperature in a programmed manner to control the solute retention. In a typical chromatographic separation condition, the interaction of polymeric solutes with stationary phase increases with molecular weight. Therefore, in the interaction chromatography (IC) separation of polymeric materials, either the solvent gradient or the temperature gradient elution is employed to control the retention of polymeric solutes. The gradient elution is usually performed in the direction of reducing the interaction strength of polymeric solute and the polymers elute in the increasing order in molecular weight. We have examined about the optimal separation condition for ABC triblock copolymer using TGIC. All the block copolymer samples were synthesized by anionic polymerization and characterized by GPC. We employed TEM analysis of all the fractions we took as well as mother block copolymers that did not fractionate by HPLC to see the behavior of separated polymers. In this presentation, some recent results on the application of TGIC on ABC triblock copolymer are reported.

[C1.045] Thermally Cross-Linked Diblock Copolymer Templates

The ability to thermally set the morphology obtained from diblock copolymer microphase separation is important for potential applications such as data storage and nano-scale templating, in which the polymer may be exposed to higher temperatures. Copolymers containing thermally cross-linkable groups such as benzocyclobutene (BCB) or acrylonitrile can be annealed and subsequently heated to cross-link and thermally set the phase-separated morphology, eliminating the need for multi-step preparations such as UV irradiation or ion etching. Poly[(styrene-r-BCB)-b-lactic acid] (PSBCBLA) was synthesized by a combination of living free radical polymerization and ring-opening polymerization. The PSBCBLA was shown to maintain its cylindrical morphology in thin films (<100 nm) and bulk samples up to 250oC by AFM and SAXS; above the temperature at which the BCB groups will cross-link. The lactic acid cylinders were removed by washing with a weak base to give a nanoporous cross-linked template.

[C1.046] Defect trapping in ABC block copolymers

Equilibrium morphologies in molten ABC triblock terpolymers are much more difficult to attain than in AB diblocks. In practice, it is important to know whether and how synthesis conditions influence the morphology and properties of copolymer materials. It is also relevant to understand the mechanisms of defect formation and annihilation. Indeed, a potential use of copolymers in new applications such as lithography highly depends on the ability to produce regular structures with no or few defects. We show that even the simplest lamellar structures exhibit high sensitivity to preparation conditions and that strongly trapped structural defects inherent to ABC triblock architecture cannot be removed by long annealing. Annealing can induce a transition from a lamellar structure in which A and C blocks are mixed to a lamellar structure where A, B and C are segregated. We propose reorganization mechanisms that are at the origin of some characteristic defects.

[C1.047] Optimizing Graphoepitaxial Ordering in Cylindrical Diblock Copolymer Monolayer Films

Topographical surface patterns have been shown to induce epitaxial ordering in monolayers of sphere-forming diblock copolymers. Separately, the orientational correlation length in monolayers of cylinder-forming copolymers has been shown to be greatly enhanced by thermal annealing above the order-disorder transition temperature (ODT), followed by slow cooling through the ODT. Here, we combine these two approaches to produce monolayer films of cylindrical poly(styrene-b-2-vinylpyridine) (PS-PVP) with controlled cylinder orientation and very low defect density. The effects of the details of the thermal treatment (temperatures, soak times and cooling rates) are discussed, with an eye towards elucidating the mechanisms by which this ordering is produced.

[C1.048] CRYSTALLIZATION OF BISPHENOL-A POLYCARBONATE IN POLYCAPROLACTONE/POLYCARBONATE BLENDS

Blends of bisphenol-A polycarbonate (PC) and poly(e-caprolactone) have been reported to be miscible with an LCST phase diagram; however, their miscibility can change with aging time. In this work, we have been able to prepare miscible blends of PC and PCL by melt extrusion of thin sheets. The miscibility of the blends was demonstrated by the existence of a single Tg over the entire composition range, as determined by differential scanning calorimetry (DSC) and dynamic mechanical thermal analysis (DMTA). Furthermore, only the PCL component was able to crystallize during the air cooling process applied at the extruder exit, while the PC remained amorphous as indicated by wide angle x-ray scattering experiments (WAXS). When PC/PCL blends with PC contents lower than 60% are heated in the DSC at 10 or 20°C/min, a cold crystallization process of the PC can be clearly observed at temperatures higher than the Tg of the blend. The isothermal crystallization process of the PC component in such blends has been studied by DSC and the overall crystallization kinetics has been fitted to the well known Avrami equation. The Avrami index and the overall crystallization rate were found to be a function of composition, and the miscibility of the blend depended on the crystallization of the PC phase.

[C1.049] The Effect of Molecular Structure of Copolymers formed in-situ on Morphology at Reactive Polymer/Polymer Interface

We investigated the effect of molecular structure of copolymers formed in-situ on morphology and formation of microemulsion or micelles at (or near) the interface of reactive polymer/polymer layers. Thin films of poly(methyl methacrylate) with one carboxylic acid functional group (PMMA-COOH) and glycidyl methacrylate-terminated polystyrene (PS-GMA) which were synthesized by an anionic polymerization, were spin-coated sequentially onto silicone wafer. To have various molecular structures of copolymers formed in-situ, three PMMA-COOHs with different positions of -COOH in the PMMA main chain were anionically synthesized: middle, one-third, and the end of chain. Morphology at the interface between the films was observed by AFM after removing of PS by selective solvent rinsing as well cross-sectional TEM. We found that the Y-shape of copolymers induced more roughened interface than diblock copolymer. The formation of microemulsion or micelles was strongly related to the molecular structure of copolymers formed in-situ.

[C1.050] Piezo- and pyro-resistivity of carbon nanotube-elastomer nanocomposites

Demand for low-cost, integrated micro sensors, operable in a wide-range of extreme environments, is continually increasing. The combination of the unique mechanical characteristics and piezo- and pyro-resistivity of carbon nanotube-elastomer nanocomposites may enable novel bio-inspired sensors for flow field, pressure and temperature gradient evaluation. This property suite arises from the low volume fraction percolation of highly anisotrpic conductive tubes. The dependence of resistivity on tensile deformation and temperature sweeps of PDMS-multiwall carbon nanotube (MWNT; 0.1-10 wtnanocomposites are compared to polymer and MWNT alignment from in-situ x-ray diffraction to establish performance-morphology relationships and elucidate the conductivity mechanism and its relationship to a kinematic description of the morphology changes. Preliminary results indicate that conductivity behavior is dominated by a carrier hopping mechanism that is determined by concentration (distance) and alignment (tunneling) between anisotropic MWNTs. Findings from these experiments allow tailoring of piezo- and pyro-resistive properties and optimization of highly processible, mechanically robust nanocomposites with large piezoresistivity response and self-recovery characteristics if damaged.

[C1.051] A Bending angle of 180 of Single walled carbon nanotubes:Novel high resolution electron microscopy observations

Direct high resolution transmission electron microscopy images (HREM) showed the high flexibility of single walled carbon nanotubes (SWCNTs) without load. Bending angle of approximately 180º was shown in which no visible nanotube distortion was revealed. "Unbent" SWCNTs persisted in HREM image. Bending SWCNTs in 180º indicated an interesting network at the bottom of bent region. The new morphology image showing bent and unbent SWCNT bundles may provide interesting mechanical and electronic properties and structural characteristics.

[C1.052] Morphology and Phase Behavior of Polyhedral Oligomeric Silsesquioxane-Polybutadiene Random Copolymer Blends in Bulk and Thin Films

The morphology and phase behavior of Polyhedral Oligomeric Silsesquioxane-Polybutadiene (POSS-PBD) random copolymers and their blends were studied in bulk and thin films. The polybutadiene (PBD) forms the backbone of these random copolymers whereas the POSS units are randomly distributed along this backbone. In the bulk, these molecules self-assemble due to the crystalline aggregation of their POSS units and form randomly orientated lamellar sheets of POSS units in the PBD matrix. In this sense, the bulk morphology of these copolymers shows similarity to the lamellar morphology in block copolymers. Copolymers with varying volume fractions of POSS units and their blends either with a low molecular weight homopolybutadiene (hPBD) or POSS macromer are dissolved in a common solvent to prepare thin and bulk films. The features in bulk and thin films were studied using a comprehensive array of characterization methods. The bulk film results show that the domain spacing between POSS crystalline sheets increases with the addition of hPBD in the blends. The bulk film results are compared with the thin film results in order to understand the complete morphology and phase profile of the system.

[C1.053] Is Curing Behavior Dependent on Morphology in Reactive Polyurethanes

Reactive polyurethanes usually are formulated as ternary polymer blends whose components are often crystalline polyester, amorphous polyether, and acrylate with high glass transition temperature. Therefore, the morphology developed is highly dependent on the composition and thermal history. Ambient water vapor reacts with the isocyanate-terminated prepolymers, which leads to increase in molecular weight and mechanical properties achievable. Previously, there have been limited studies describing this reaction process. We have investigated the morphological and compositional effects on curing kinetics and chemical reactions induced by water vapor diffusion into prepolymer using time-resolved reflection-absorption infrared spectroscopy, optical microscopy, and atomic force microscopy. It was found that the curing kinetics is strongly related to the prepolymer composition, which affects the molecular mobility, hydrophilicity, phase separation, and crystallization. In addition, we found that the curing rate decreased significantly with the development of liquid/liquid phase separation.

[C1.054] Influence of prepolymer composition on polyurethane morphology

Polyurethane chemistry is one of the most studied subjects. Yet many aspects remain unexplained. Polyurethanes are synthesized by the reaction of diisocyanate with diol in the presence of nucleophilic catalysts. Polyurethane prepolymers are obtained by reacting the polyester diol / polyether diol with diisocyanate, with [NCO] / [OH] > 1, resulting in isocyanate-terminated polyester/polyether mixture. Prepolymers thus synthesized can be cured at a later stage to realize various morphologies and structures. Though the initial composition and the final morphology are known, little is known about the intermediate prepolymer mixture. Due to the different reactivity of primary and secondary hydroxyl groups in the polyester and polyether towards isocyanate, prepolymer has a non-random distribution in terms of composition as blends and copolymers. Our aim is to characterize the prepolymer by different techniques and study how the different prepolymer composition, with varying polyester and polyether ratio, affects the morphology and phase separation kinetics of the final product.

[C1.055] Theoretical study of copolymer/homopolymer blends of varying composition.

The polymer reference interaction site model (PRISM), a microscopic integral equation theory, is used to investigate a series of AB block copolymer/homopolymer blends. The copolymers in the blend vary in structure from diblocks to multiblocks with composition of the A blocks between 5030same degree of polymerization as the A block. Weak repulsion interactions are introduced between the A and B blocks and the homopolymer and B blocks. The effects of block size, degree of “blockiness”, and homopolymer concentration are explored numerically. Local structure and clustering are probed through a study of pair correlation functions and structure factors and comparisons made with experimental scattering data.

[C1.056] Structure and Nanomechanical Properties of Electrospun Polystyrene/Clay Fibers

Structure and nanomechanical properties of electrospun polystyrene /clay fibers were investigated by using Atomic Force Microscopy (AFM), Scanning Electron Microscopy (SEM) and Transmission Electron Microscopy (TEM). Polystyrene/clay nanocomposites with different clay concentrations (0, 1%, 4%, 8%) were dissolved in a mixing solvent with tetrahydrofuran and N, N-dimethylformamide and then electrospun to form fibers with diameters ranging from 200nm to 20um. The shear modulation force microscopy (SMFM) method was used to investigate the dependence of the relative modulus and glass transition temperature (Tg) of electrospun fibers as a function of fiber diameter and clay concentration. The surface morphology and clay distribution of the electrospun PS/clay fibers were also characterized by AFM, SEM and TEM. The result indicated that surface morphology of electrospun fibers changed from a typical porous structure (without clay) to a ridge like structure (with clay). Tg was found to increase by 8 degrees with the addition of 2% by volume of clay. Supported by NSF-MRSEC

[C1.057] P(VDF-TrFE) – Layered Silicate Nanocomposites: Dielectric Relaxation Studies

Dielectric relaxation spectroscopy (DRS) was used to investigate the effects of organically modified layered silicates (OMS) on the paraelectric and ferroelectric phase transitions in poly(vinylidene fluoride-co-trifluoroethylene) [P(VDF-TrFE)] /OMS nanocomposites. Nanocomposites comprising a 75/25 P(VDF-TrFE) random co-polymer with either Nanomer I.30TC or Lucentite STN OMS were prepared with compositions ranging from 2-25 wt.% OMS. Differential scanning calorimetry and wide-angle X-ray scattering results show that thermal transitions in the nanocomposites depend on OMS content. Nanocomposites with 2% OMS exhibited a crystal nucleating effect, which results in significant increase in the amount of ferroelectric crystals formed during cooling. For greater OMS additions (10-25%), the amounts of para- and ferroelectric crystals are reduced. Real-time DRS experiments show that the larger OMS additions depress the melt-to-paraelectric transition temperature, while an increase in the Curie temperature is observed for all compositions. The dipolar relaxation times associated with the crystal transitions are decreased by about three orders of magnitude in the nanocomposites, compared to unfilled copolymer.

[C1.058] Optical Properties of Flowing Carbon Nanotube Suspensions

We use depolarized shear light scattering, flow birefringence, flow dichroism, and optical microscopy to measure the optical properties of dilute and semi-dilute multi-walled carbon nanotube suspensions in highly elastic polymer melts under simple shear flow. Strong flow alignment of the tubes allows us to extract a measure of information about the real and imaginary pats of the polarizability along and normal to the nanotube axis, giving quantitative information about the optical anisotropy of individual tubes. We develop a first principles macroscopic theory of the optical anisotropy of flowing carbon nanotube suspensions which we apply to our measurements, and we compare our findings with results quoted in the literature.

[C1.059] Morphology Quantification Of Thermoset-Layered Silicate Nanocomposites Using Dielectric Spectroscopy

Advancing the current state of nanocomposite processing necessitates the establishment of techniques amenable to the real-time process monitoring of morphology development. In contrast to real and reciprocal space techniques, which are equipment, time and expertise intensive, adaptation of existing process-monitoring schemes based on dielectric sensing may provide rapid and facile measurement of the quantity of organic-inorganic interface, and thus the extent of layered silicate dispersion. Dielectric spectra of modified and unmodified montmorillonite, cured and uncured epoxy resin, and the corresponding nanocomposite are compared to deduce the unique, synergistic relaxations associated with the layered silicate-epoxy interface. Polarization of the mobile surfactant on the silicate surface, such as Maxwell/Wagner/Sillers, influences the complex dielectric function of the nanocomposites and provides a local probe of the interfacial environment. Correlations between temperature and frequency dependant changes in the dielectric spectra and characteristics of the morphology, such as degree of dispersion, intercalation and exfoliation, during process evolution are discussed.

[C1.060] Curing Kinetics and Gas Barrier Properties of Thermoset Polymer Nanocomposites

Polymer nanocomposites, especially polymer layered silicate nanocomposites, represent a rational alternative to conventionally filled polymers. Because of their nanometer scale dispersion, nanocomposites exhibit markedly improved many properties when compared with the conventional composites. In this study, we report the formation mechanism of thermoset polymer nanocomposites and their improvement in the gas barrier properties. Epoxy nanocomposites have been prepared by the reaction of alkylammonium exchanged smectite clays with diglycidyl ether of bisphenol A and m-phenylenediamine as the curing agent. Exfoliation of the clay layers in the polymer matrix is dependent on the accessibility of the epoxy and diamine monomers to the clay galleries and the relative rates of intra- and extra-gallery network formation. The curing rates of epoxy with different alkylammonium modified clay were monitored using FTIR and DSC. Moisture and oxygen barrier properties for epoxy nanocomposites were investigated for the samples prepared with different curing conditions.

[C1.061] Miscibility in Bisphenol-A Polycarbonate/ Poly(\epsilon -caprolactone)

Blends of bisphenol-A polycarbonate (PC) and poly(\epsilon-caprolactone) (PCL) have been studied by thermally stimulated depolarization currents (TSDC) in a wide temperature and composition range. The blends have been reported to be miscible for all compositions but they separate after thermal treatments or aging. In this work the blend samples were prepared by melt extrusion of thin sheets without any further treatment. WAXS studies of the extruded films showed that the PC component is amorphous over the entire composition range while the PCL crystallizes for composition richer than 40% in PCL. The TSDC experiments showed the existence of a single segmental mode at intermediate temperatures between the glass transition of the two homopolymers. However, there still exists a broad and weak TSDC peak located around the PCL glass transition temperature, T_g = 212 K, which indicates the existence of concentration fluctuations in these miscible blends. The effect of the blending on the low temperature modes of the PCL is also reported. The presence of PCL in low concentrations plasticizes the PC and allows its isothermal crystallization at temperatures above the glass transition temperature of the blend.

[C1.062] Electrodynamic and Optical Properties of Thin Films in Green's Function Approach

It is well known that the effective susceptibility of a nano-object (the linear response to the external field) allows describing the electrodynamic properties of the system. In this paper the effective susceptibility of the thin film was obtained in the framework of the approach based on formally exact solution of Lippmann-Schwinger equation [1] for the self-consistent field, developed in [2]. As a result the effective susceptibility with the self energy part is calculated. The self-energy is defined by the electrodynamic Green's function (photon propagator) of the medium in which the thin film is situated. The effective susceptibility allows calculating the reflection and transmission coefficients of the film using knowledge of linear response to the local field, which can be calculated within the standard microscopic theory.

[1] Greffet J-J, Carminati R 1997 Progr. Surf. Sci. 56 139. [2] S.Bozhevolnyi, V.Lozovski, Phys.Rev. B 61 (2000) 11139.

[C1.063] Magnetism and Magnetic Materials

This abstract not available.

[C1.064] Mossbauer Studies of GdFe2-xHfx Alloys

GdFe_2-xHf_x Alloys,where x=0, 0.05, 0.1, 0.15, 0.2, and 0.3, were prepared by arc-melting of pure elements of Gd, Fe, and Hf. The samples were investigated by x-ray diffraction and Fe^57 Mössbauer spectroscopy. We find that the alloy system GdFe_2-xHf_x have the cubic Cu_2Mg type structure. Mössbauer spectroscopic results show that all the samples studied are magnetically ordered at 78 K, and at room temperature. The spectra fitted with two magnetic components, which is consistent with the two magnetic sites in Rfe_2. The average magnetic hyperfine field is found to decrease with increasing the Hf concentration at 78 K and 300 K due to the replacement of Fe by nonmagnetic Hf. The above results indicate that Hf dissolves in the cubic lattice in this system resulting in the decrease of the hyperfine field with increasing the Hf concentration.

[C1.065] Grain Boundary Magnetoresistance in bi-axially Textured Manganite Thin Films

Enhanced low field magnetoresistance observed in polycrystalline CMR oxides has motivated research groups to study grain boundary magnetoresistance in polycrystalline thin films towards enhancing low field magnetoresistance. However, the irreproducibility of grain boundary properties is disadvantageous for device applications. Growth of films with a biaxial texture is expected to result in a high degree of reproducibility due to a controlled grain boundary angle in the plane of the film. This paper presents a study of colossal magnetoresistive properties in biaxially textured La_xCa _1-xMnO_3 and La_xSr_1-xMnO_3 films prepared using Ion Beam Assisted Pulsed Laser Deposition (IBPLD) technique. We prepared biaxially textured YSZ buffer layers by pulsed laser deposition, assisted by a 200 eV, 10 mA argon ion beam. The CMR films deposited on such YSZ layers have a controlled biaxial texture with reproducible CMR properties.

Acknowledgement: MR acknowledges support from the NSF MRI grant (DMR-011-6619) at Towson University.

[C1.066] Magnetoresistance of Nickel films with Striped Domains

We have studied magnetoresistance of thermally deposited Ni films with two different stripe domain orientations. The Ni films studied have a thicknesses ranging from 35 to 120 nm. Magnetoresistance measurements were made with both current parallel to the domain walls (CIW) and current perpendicular to the domain walls (CPW). The direction of the applied current was fixed relative to the sample geometry and the orientation of the striped domains was manipulated using in-plane field sweeps. We have studied how the CIW and CPW magnetoresistance varies with sample thickness and temperature. In particular, we have investigated why there is a higher resistance for current parallel to the domain walls compared to current perpendicular to the domain walls. This work was supported by the Parsons Foundation, the Office of Naval Research, and the Harvey Mudd College Faculty Research Committee.

References:

1) M. Viret \textitet al. Phys. Rev. B. 35, 8464 (1996).

2) P. Sparks, \textitet al, J. Appl. Phys. 93, 6608 (2003).

[C1.067] Nonuniform magnetization reversals in elliptical permalloy dots

Single domain state in magnetic thin film is extensively used in spintronic devices, and its magnetization can be reversed under an external field. It is therefore imperative to understand the magnetization reversals of the single domain thin films for the fundamental physics and applications. The micromagnetic simulations of the elliptical permalloy thin films are carried out by the integration of the Landau-Lifshitz-Gilbert equation. The hysteresis loops of elliptical elements are rectangular, which resemble those of ellipsoidal particles, but the switching fields for submicron elliptical thin films are reduced compared to those predicted from the Stoner-Wohlfarth model for the corresponding ellipsoids. The reduction of the switching fields comes from the incoherent magnetization reversal process. Before switching occurs, a magnetization deviation is nucleated. This deviation structure remains stable within a small field interval before reversal. The reversal happens eventually with several vortices nucleated and penetrating across the thin film. This deviation structure is also observed experimentally. We further investigate the relation between nucleation fields and lengths of elliptical thin films. The relation curve exhibits oscillation behavior and it gradually saturates as the length increases, and this agrees with the experimental data.

[C1.068] Variational Study of the t-U-J Model

Recently there are many suggestions of relaxing the constraint of no double occupancy in the theoretical study of the t-J model, for instance, the theory of gossamer superconductivity proposed by Laughlin (cond-mat/0209269). Noting that the constraint suppresses charge fluctuation, Daul et al (Phys. Rev. Lett. 84, 4188) suggested an extended Hamiltonian, the t-U-J model, may be more promising for the search of superconductivity. In this paper, we will present numerical results of the t-U-J model calculated by the variational Monte Carlo method and the improved power-Lanczos method. The wave function we employed is the one Laughlin proposed for the superconducting phase, which is just a generalized resonating-valence-bond (RVB) wave function. In the lightly doping region, a Jastrow correlated spin-density-wave is used to determine the anti-ferromagnetic phase. By studying the pairing correlation we determine the region with superconductive long-range-order. We will also explore the relation between the long-range d-wave pairing correlation and the momentum distribution at q=(\pi,0).

[C1.069] MAGNETIC QUANTUM PHASE TRANSITION IN YbFe2Ge2 HEAVY FERMION COMPOUND

The polycristalline heavy fermion (HF) YbFe2Ge2 compound shows a nonmagnetic ground state (P=0) and it is near the magnetic instability. We report electrical resistance measurements under pressure up to 18.6 GPa and low temperatures down to 0.1 K. Analysis of the resistance data as a function of pressure reveals a crossover from a Fermi liquid (FL) state to magnetic order (MO) state, so that the extrapolation of magnetic ordering temperature to zero, (Tm) \sim 0 K, we find the quantum critical point (QCP) close to Pc= 9.7 GPa.. The temperature dependence in power law of the resistance data as well as the values of anisotropic gap of magnons suggest that induced magnetic order is antiferromagnetic.

[C1.070] Magnetism of Ca_2-xNa_xCuO_2Cl_2 Probed by Muon Spin Relaxation

Insight into the pairing mechanism of high-T_c superconductors is being sought by studying the parent compounds which are generally undoped antiferromagnetic insulators. La_2CuO_4 is one of such superconducting parent compounds which have CuO_2 planes consisting of CuO_6 octahedra. La_2CuO_4 is orthorhombic below \sim 530 K, and the distortion associated with it brings about weak ferromagnetism of the Dzyalochinsky-Moriya type. Neither the covalently bonded apical oxygen atoms nor the orthorhombic distortion are common to other high-T_ c's, and they give rise to undesired complications. Simpler model systems, such as members of the series A_2CuO_2Cl_2 (A = Ca, Sr) are therefore being examined as model systems for undoped state of the single CuO_2 plane because all the oxygen atoms at the apices of the CuO_6 octahedra found in La_2CuO_4 are replaced by chlorine. In particular, Ca_2CuO_2Cl_2 can be hole-doped by substituting Ca with Na to exhibit superconductivity at relatively high temperatures (\sim 25 K). We have performed Zero Field \muSR measurements in Ca_2-xNa_xCuO_2Cl_2 in order to clarify the magnetic phase diagram compared with that in La_2CuO_4. In our preliminary results, we have observed static long range ordering in x \le 0.02 samples. Moreover, two components of muon spin precession signals were observed in Ca_2CuO_2Cl_2 below 260 K.

[C1.071] Direct time TDTF computation of the colossal magnetoresistance of a nanowire

We address the problem of the computation of the magnetoresistance of a nanowire connected to two electrodes modelized as bulk reservoirs of electrons. The nanowire is supposed to present a Neel wall between two domains. In order to treat cheaply the electron-electron interaction, we derive a version of the Time Dependent Thomas Fermi theory from well-established Time Dependent Density Functional theory. We solve numerically the resulting equations in direct time, getting the magnetoresistance as a function of domain wall width. We discuss and compare the results to those obtained by other groups.

[C1.072] Anisotropic Magnetoresistance of Fe_xCo_1-xS_2

We have investigated the magnetotransport properties of the spin polarized ferromagnetic alloy, Fe_xCo_1-xS_2, 0 \le x \le 0.3. Varying the alloy concentration is predicted to change the level of spin polarization and produce a half-metallic ferromagnet. The polycrystalline Fe_xCo_1-xS_2 samples were cut into relatively long rods with a nominally uniform cross section. The magnetotransport properties of each of these samples were studied, with particular attention paid to the Anisotropic MagnetoResistance (AMR). The measurements were made as function of the temperature (in the range of 300K to 2K), applied magnetic field magnitude (up to 8T), and the angle of the applied field with respect to the current. A model of AMR developed for elemental ferromagnets predicts a sensitivity to whether the majority carriers at the Fermi level are polarized up or down. The data will be discussed in terms of this model.

[Work supported by the Parsons Foundation and the ONR]

[C1.073] Spin-polarized transport in semiconductor nanostructures.

We study spin polarization patterns in semiconductor nanostructures produced by stationary injected spin-polarized electrons using the Monte Carlo device simulation scheme. Spatial transport affects the spin polarization by means of a spin-orbit interaction. Effects of the applied electric field along the transport direction, temperature, non-parabolicity of conduction band and anisotropy of the spin-orbit interaction are considered. We compare the simulated results with the results obtained within the recently derived drift-diffusion model. The problem of spin injection through the Schottky barrier is considered. The developed approach can be a useful tool for spintronic device modeling.

[C1.074] First-principles calculation of the magnetoresistance in highly responsive Gd_5(Si_2Ge_2) compound.

Gd_5(Si_2Ge_2) compound undergoes unusual magneto-structural (MS) transformation at room temperature and exhibits a giant magnetocaloric, magnetostriction and magnetoresistance (MR) effects. In this work we apply LMTO LSDA+U method for description of 4f-Gd states. The dependence of the transport properties on the electronic structure was investigated. We have calculated the diffusive conductivity for low temperature orthorhombic and high temperature monoclinic structures. The giant magnetoresistance effect was reproduced qualitatively. The strong dependence of conductivity and MR effect on the direction of current was obtained. This result agrees with layered type of the compound and experiment. We discuss these results qualitatively and quantitatively using obtained electronic structure information and proposed in Ref.[1] mechanism of "bond breaking" through the MS transformation.

[1] W. Choe, V.K. Pecharsky, V.G. Young, Jr., A.O. Pecharsky, K.A. Gschneidner, Jr., and G.J. Miller. Phys. Rev. Lett. 84, 4617 (2000)

[C1.075] Geometrical Effect on Spin Current in Magnetic Nano-structures

Much attention has been focused on spin-dependent transport in magnetic nano-structures, where it is important to understand the spin accumulation and transport in order to inject the spin polarized electric current efficiently. In the recent experiments of spin injection and detection in ferromagnet/normal-metal/ferromagnet nano-structures of non-local geometry, spin accumulation has been observed at room temperature. Subsequently, the spin accumulation is efficiently improved with using tunneling contacts. A theoretical study of the spin accumulation signal has been made based on the one-dimensional model, and suggested that a large spin signals is obtained in nano-structures with highly resistive contacts. We study the spatial distribution of spin accumulation and spin current in the non-local geometry taking into account the finite size effect of the contact area by applying finite element method in two-dimension. The results show that, when the contacts are metallic, the current distribution in the contact area is inhomogeneous and influences the spin accumulation signal. We will present the detailed simulation results for the geometrical effect of junction shape on spin and charge current. This work was supported by NAREGI Nanoscience Project from MEXT.

[C1.076] Metal-insulator transition in Nd_0.49Sr_0.51MnO_3 films

Nd_1-xSr_xMnO_3 has attracted much attention due to the rich phase diagram. However metal-insulator (M-I) transition in thin films were not reported so far, because the charge ordered (CO) state existing at narrow range (0.49 \leq x \leq 0.51) is easily collapsed by the disorder arising from defects for polycrystalline films. In addition, pseudomorphic strain effect is crucial to the orbital ordering.

By fabricating fully and partially strained films having almost same thickness across the critical one, we have investigated the strain and disorder effect on the M-I transition in Nd_0.49Sr_0.51MnO_3 films, in which CE-type and A-type anti-ferromagnetic (AFM) state are intrinsically co-existed.^1 Temperature dependence of resistivity in epitaxial films was semiconducting due to C-type orbital ordering induced by the compressive strain, showing apparent change in resistivity at T_co of 160 K. As to polycrystalline films, we have realized distinct M-I (FM-AFM) transition with hysteresis under a magnetic field. Below T_co , we have observed spin-glass like behavior implying three phase co-existing state accompanied by the FM metallic state due to disorder. We will also discuss about the differences between spin-glass and magnetorelaxor properties in thin films. ^1 R. Kajimoto et al., Phys. Rev. B 60, 9506 (1999).

[C1.077] Antisite-defects vs grain boundaries competition in the magnetoresistance of the Sr_2FeMoO_6 double perovskite

It has been shown that the tunneling magnetoresistance (TMR) in the Sr_2FeMoO_6 compound can be readily improved by selected oxidation of the grain boundaries (gb's). However, the role of the antisite-defects (AS) which occur inside the grains is far from clear. AS appear due to the exchange of the crystallographic positions of Fe and Mo ions in the B site of the ordered perovskite, giving rise to a reduction in the saturation magnetization (M_S) due to antiferromagnetic Fe-Fe interactions. Here we present magnetotransport data on two samples with different concentrations of AS (w\sim 0.3 and 0.1). We performed several oxidation processes on these samples and studied the evolution of the magnetization and TMR. While M_S remained unchanged, the resistivity (\rho) was increased by more than 5 orders of magnitude after oxidation, showing the importance of the gb's. At the same time, at low \rho values the TMR is much higher in the less disordered sample (w\sim 0.1). On the contrary, when the gb's dominate in the transport properties both samples exhibit the same improved TMR values.

[C1.078] Temperature Dependence of the Spin-Dependent Mean Free Path in Backed Spin Valve Structures

Backed spin valves with the structure Si/30ÅRu/25ÅCu/80ÅIrMn /50ÅNiFe /30ÅCu /t_NiFe/t_Back have been used to make spin-dependent transport measurements in both magnetic and non-magnetic materials. An additional layer of a material, or back layer, on a spin valves, coupled with giant magnetoresistance (GMR) measurements, provides a mechanism for measuring the spin-dependent mean free path of the majority carriers in the back layer.[1] The NiFe filter layer for these samples was of thickness 20Åt_NiFe \quad < 100Åand the backing material used was either the magnetic layer CoFe (10Åt_CoFe \quad < 150Åor the non-magnetic layer Cu (10Åt_Cu \quad < 175ÅBy measuring the GMR of these structures as a function of temperature and we are able to determine the dependence of the spin-dependent mean free path on temperature over the range 5K to 380K.

[1] Gurney et al., Phys. Rev. Lett. \textbf71, 4023 (1993).

[Work supported by the Parsons Foundation, the Office of Naval Research, and the HMC Faculty Research Committee]

[C1.079] Perpendicular Ba-Ferrite Films by in situ Sputtering Process*

Barium ferrite films with perpendicular orientation are attractive candidates for ultrahigh density perpendicular magnetic recording and microwave device applications. Thick films with c-axis orientation are required for microwave applications. To obtain thick films multilayer deposition technique may be needed. Usually, after deposition, external annealing in air is required to crystallize the film. The external annealing process is difficult to incorporate with the multilayer procedure. We have developed an in situ sputtering procedure to obtain films with thickness in about 200-300 nm, which can be used as the basic component for future multilayer deposition. Barium ferrite films are first magnetron sputtered on bare silicon substrates in Ar + O2 atmosphere at substrate temperature of 550-600 C. After the deposition, the temperature of the substrate is immediately increased to about 860 C in Ar + O2 atmosphere without breaking the vacuum for ten minutes. With the in situ process c-axis orientated films with squareness of around 0.8 and coercivity value of about 4kOe are obtained.

[C1.080] Magnetic Anisotropy of Fe, Co and Ni Nanoribbons from First Principles

Coordination and quantization effects in magnets of reduced dimensions are of considerable scientific interest and important in areas such as magnetic data storage and spin electronics [1]. We use self-consistent relativistic LMTO-ASA calculations to study the magnetic anisotropy of free-standing Fe, Co and Ni wires. The calculations are performed for 1x1, 2x2 and 5x4 wires to study the effect of lateral dimension on the anisotropy. The calculated results are discussed in light of the recent experimental studies [2,3]. Due to crystal-field effects, there are qualitative differences between monatomic wires and more complicated structures. In the 2x2 and 5x4 ribbons, the absence of rotational symmetry yields a strong reduction of the orbital moment and an accompanying anisotropy change.

This work is supported by ONR, NRI, MRSEC, the W.M. Keck foundation, and CMRA.

References

[1] Jisang Hong and R.Q. Wu, Phys. Rev. B 67, 020406(R)(2003). [2] J. Shen et al., Phys. Rev. B 56, 2340 (1997). [3] P. Gambardella et al., Nature (London) 416, 302 (2002).

[C1.081] Effect of annealing and external stress on magnetic anisotropy and structure of rare-earth (TbFe amp; CoFe) iron alloy thin films

The magnetic properties of giant magnetostrictive TbFe and CoFe amorphous thin films on silicon substrate were investigated for potential application in magnetostrictive devices. RF magnetron sputtering was utilized for the film fabrication. Typical sample thicknesses ranged from 100-200nm under optimized fabrication parameters of 3 mTorr Ar pressure at an RF power of 150w. Post deposition annealing in forming gas was done in a temperature range from 250C to 450C in order to observe the in-plane anisotropy induced. The saturation magnetization had been optimized as high as 2T under 1000G field for CoFe and 0.625T under 500G field for TbFe. The strain bias was studied by mechanically introducing a small curvature into the silicon substrate and releasing after sputter deposition and thermal treatment of 400C. Based on the magnitude and shape of hysteresis loop for stressed vs non-stressed samples, both magnitude and direction of the magnetic anisotropy can be controlled by the magnitude of external stress introduced into these amorphous thin film. The surface and cross section were analyzed by SEM to study the effect of annealing temperature and external stress on the structure of both TbFe and CoFe samples.

[C1.082] Simultaneous measurements of magnetoresistance and magnetic force microscopy on elliptical permalloy element

In recent years, studies of magnetization reversal on patterned magnetic thin film have gained considerable attention. The best interest is not only focused on the fundamental understanding of the micromagnetism but also on one step further towards the potential applications, such as magnetoresistive random access memory and magnetic field sensors. In this presentation, bi-stable magnetic domain structures of permalloy ellipse at remnant state will be presented. Moreover, the magnetization reversal processes and magnetoresistance (MR) curves in ellipse with various remnant states will be also carried out using a novel technique for the simultaneous measurements of MR and MFM. Various permalloy ellipses were fabricated by using electron beam lithography through a lift-off technique. The images of magnetic domain configurations were acquired using magnetic force microscope equipped with a home-made electromagnet capable of applying an in-plane magnetic field up to 500 Oe. The MR curves and MFM images in ellipse with two stable remnant states were investigated simultaneously. As a result, changes of the magnetic domain structure were observed in the variation of magnetoresistance.

[C1.083] Investigation of Switching Fields of Magnetic Nanoparticles With Magnetic Force Microscopy

Magnetic quantum cellular automata (MQCA) has been proposed as an alternate paradigm for computing. This requires a thorough understanding of switching behavior of magnetic nanoparticles. Both experimental [1] and theoretical [2] investigations into MQCA rely on particle shape anisotropies as an intrinsic part of their architectures for input or control structures, while requiring other elements to be strictly uniform so that their switching behavior is consistent. We have patterned elliptical particles with and without characteristic edge flaws using electron beam lithography. Magnetic force microscopy with an in-situ magnetic field was then performed to produce an ensemble hysteresis loop. Particles with atypical switching fields were identified and further examined in a scanning electron microscope to search for any edge defects or characteristic edge roughness which could account for their atypical switching behavior.

[1] R. Cowburn et al, Science 287, 1466 (2000) [2] G. Csaba et al, Int. J. Circ. Theor. Appl. 31, 67 (2003)

[C1.084] Size effect on magnetoresistance of ring-shaped ferromagnetic elements

Generally, the geometry determines that which kind of magnetization configuration and switching mechanism may occur in the patterned magnetic thin films. Recently, many investigations have been carried out on microstructured elements with simple geometries such as squares, disks, rectangles, and rings. Among these various shapes of magnetic elements, the ring-shaped element has become a promising candidate for the magnetic random access memory or sensor devices. In addition, the application of such elements requires the simplest, fastest, and most reproducible switching mechanism. In order to explore the magnetization switching mechanism, some techniques, such as MOKE, VSM, and SHPM, have been vigorously adopted. Herein, the magnetization switching behavior of Permalloy ring elements as a function of ring diameter and film thickness by magnetoresistance measurement will be presented. The Permalloy ring elements, with diameters of 2-5 micrometers and thicknesses of 14 - 66 nm, were fabricated by electron beam lithography through a lift-off process. To conclude, the switching field for the transition from the vortex state to the onion state increases with decreasing diameter. Furthermore, as the film thickness is less/more than 53 nm the switching field increases/decreases with increasing film thickness.

[C1.085] FMR spectrum of a normally magnetized array of submicron circular magnetic dots

A dipole-exchange theory of spin wave dispersion in a normally magnetized infinite in-plane magnetic film is used to calculate a spectrum of standing spin wave modes in an array of circular submicron magnetic dots. In the case of a circular dot (having a shape of a thin disk) the finite in-plane size R of the dot brings two qualitatively new features into the spin wave dispersion equation. First of all, due to the finite radius of the disk only discrete values on the in-plane wave vector will be allowed. Secondly, due to the non-ellipsoidal shape of the dot, demagnetizing field inside the dot will be inhomogeneous, and the internal bias field will be a function of the radial coordinate r. It was assumed, that in the cylindrical geometry the dipolar eigen-modes m(r) of a thin disk-like dot will be described by the zeroth-order Bessel function, and will also satisfy the dipolar “pinning” condition at the dot edge: m(r=R)=0. Using these assumptions it was possible to find discrete values of the in-plane wave vector in the dot, to evaluate effective internal fields for spin wave modes having different values of this discrete wave vector, and to calculate the field positions of resonance peaks corresponding to different spin wave modes in the FMR experiment. Our theoretical results were compared with the results of the X-band FMR experiment performed in nickel and permalloy submicron dots. It was found, that our simple theory gives good quantitative description of the experiment in both materials.

[C1.086] Quantum fluctuations in low dimensional easy-plane spin models

A self-consistent harmonic approximation is used to treat the low temperature limit of the one and two-dimensional S=1 easy-plane magnets. For the one-dimensional model, the gap, caused by the presence of an external magnetic field, applied in the easy-plane, is calculated. The quantum phase transition, at T=O K, is studied using the path integral formalism. The effect of the strong quantum fluctuations is discussed. For the two-dimensional case, the Kosterlitz-Thouless (KT) transition temperature as a function of a single-ion anisotropy term is estimated. The line ends at a quantum critical point, where the KT temperature goes to zero.

[C1.087] Roughness Influence on Magnetisation Distribution in Magnetic Bilayers

In the presented work we investigate magnetisation distribution and its temperature dependence in the system of twomagnetic layers separated by nonmagnetic metallic f.c.c. spacer.We derive surface and interface roughness parameters using the discrete Gaussian model.Magnetisation of the system considered and its distribution is obtained by means of the Green function formalism in random phase approximation.The results obtained show that introduction of the interfacial and surface roughness leads to the change of the behaviour of the interlayer coupling parameter in relation to the spacer thickness and its orientation.

[C1.088] Quantum phase transition in spin-1/2 XX Heisenberg chain with three-spin interactions

The quantum phase transition in the spin-1/2 XX Heisenberg chain model with three-spin interactions is studied. Using the Jordan-Wigner transformation, density of states, thermodynamic quantities, and thermal and spin transports of the system are solved exactly. It is shown that the three-spin interaction influences the calculated quantities and leads to the characteristic features of the quantum phase transition. The effects of magnetic field on the magnetic moment and magnetic susceptibility are also discussed.

[C1.089] Far-Infrared Spectroscopy and Cluster Simulations of the Shastry-Sutherland Model for SrCu_2(BO_3)_2.

A two-dimensional spin gap system SrCu_2(BO_3)_2 is studied using far-infrared (FIR) spectroscopy in the frequency range from 3 to 100\,cm^-1 in magnetic fields at low temperature T=5K. A spin cluster simulation of the Shastry-Shuterland model is used to identify absorption lines in the FIR spectra. Our spin Hamiltonian consists of nearest- and next-nearest-neighbour exchange couplings and Dzyaloshinskii-Moriya interactions. We use exact diagonalisation of the spin Hamiltonian for clusters of up to ten spins. The Lanczos algorithm is used to solve the cluster eigenvalue problem for larger cluster sizes. The interaction constants are presented in accordance with our experimental results.

[C1.090] Phase separation in electron-doped La_0.7Ce_0.3MnO_3 thin films

The origins of colossal magnetoresistance in perovskite-type manganites have been widely investigated and the results have pointed to various possible mechanisms beyond the double-exchange effect. Recently, due to their rich phase diagram arisen from tight competitions between different order parameters, the intrinsic inhomogeneities have been proposed to explain the transport properties of hole-doped manganites. Previously, we used the scanning tunneling spectroscopic image technique to observe evidence of nanoscale phase separation in the hole-doped La_0.7Ca_0.3MnO_3 maganite at various temperatures and applied magnetic fields. In this report, we will present the results of the scanning tunneling spectra (STS) and spectroscopic images obtained in the electron-doped La_0.7Ce_0.3MnO_3 films. The results show that, similar to the hole-doped compounds, the phase separation starts to emerge in the vicinity of the transition temperature. The evolution of the separating phase as a function of temperature and applied magnetic field is clearly demonstrated in histogram of dI/dV distribution in STS.

[C1.091] Magnetic Order in Quasi-Two Dimensional Molecular Magnet Cu(pz)_2(ClO_4)_2.

Cu(pz)_2(ClO_4)_2 belongs to a family of pyrazine (pz) based molecular magnets found to produce two dimensional magnetic behavior with moderate exchange strengths (J = 10-20 K). Our characterization by susceptibility and isothermal magnetization studies indicate this system conforms to the 2D Heisenberg magnetic model at temperatures above 5 K. Using neutron diffraction we explore the magnetic ordering transition in Cu(pz)_2(ClO_4)_2 which occurs below 5 K. Our results show this systems exhibits antiferromagnetic order at T_N = 4.8 K, indicating the system is no longer in the 2D Heisenberg state. The details of this magnetic order, its relation to the 2D Heisenberg model, and perturbations which cause the ordering are discussed.

[C1.092] Specific Heat of GeCo_2O_4 and GeNi_2O_4: Frustrated Spinels

GeCo_2O_4 has a Kramers’ doublet ground state, with a first-order transition (accompanied by a structural modification) to an Ising antiferromagnet (AF) at T_N = 20.6 K. Below T_N the magnetic specific heat (C_m) can be fit to a gapped (38.6 K) AF spin-wave, which is probably associated with the tetragonal lattice distortion below T_N. The total magnetic entropy recovered is \sim70% of 2Rln2. GeNi_2O_4 has an S = 1 ground state with a split first-order transition to antiferromagnetism (T_N1 = 12.1 K and T_N2 = 11.5 K). Within the AF state, C_m can be fit to an expression which includes gapless and gapped excitations. Since GeNi_2O_4 remains cubic below T_N gapless AF spin waves are expected; gapped excitations could occur from splitting of the S = 1 ground state. The total magnetic entropy recovered is \sim57% of the expected 2Rln3. Spin clusters above T_N could account for the “missing” entropy in both cases.

[C1.093] Composition Dependence of Magnetism in Single Crystal Co/Ni Dichloride Dihydrate

This mixed magnet is composed of 3D Ising (Co system) and Heisenberg (Ni system) antiferromagnets ordering at 17.2 K and 7.3 K, respectively. Ferromagnetically coupled metal-dichloride-metal...chemical and structural chains occur in each component, with antiferromagnetic interchain interactions operating. Metamagnetic transitions in the pure Co and Ni systems occur near 31 and 19 kG, respectively. Mixed magnetic single crystals have been obtained and studied for Co-rich compositions. Strong anisotropy is apparent in the susceptibility vs temperature and in the magnetization vs field. The appearance of both the easy and hard axis susceptibilities and the easy and hard axis magnetizations evolve with composition. Metamagnetic transitions are evident, but appear at much lower fields than for either pure component. There is modest composition dependence in the apparent critical field. The temperature variation of easy axis hysteresis loop areas is analyzed to suggest an activation energy for domain wall motion which varies little with composition. *Supported by NSF-SSC-Grant No. DMR-0085662 and by an ACS-PRF grant.

[C1.094] Effects of uniaxial anisotropy on a quantum spin-glass model in three dimensions

The three-dimensional anisotropic Heisenberg spin-glass model is studied using a real-space renormalization-group procedure. The Hamiltonian of this model is: \cal H = - \sum_ J_ij \left[ (1-\Delta) (\sigma_i^x \sigma_j^x + \sigma_i^y \sigma_j^y) + \sigma_i^z \sigma_j^z \right], where \sigma_i^\alpha is the component \alpha of a spin-1/2 Pauli matrix on site i, 0 \leq \Delta \leq 1, and the sum is over all first-neighbor bonds on a cubic lattice. We consider two different initial probability distributions, Gaussian and uniform, with zero mean and width \barJ. The (kT/\barJ) \times \Delta phase diagram is obtained: no ferromagnetic phase is present. At high temperatures there is a paramagnetic phase; a spin-glass phase is found at low temperatures for \Delta_c < \Delta \leq 1, with \Delta_c \sim 0.6. For the isotropic Heisenberg model (\Delta=0), no spin-glass phase at finite temperatures is found. The transition temperature between the spin-glass and paramagnetic phase decreases with the anisotropy parameter \Delta, but goes to zero at \Delta = \Delta_c. The transition line between the paramagnetic phase and the spin-glass phase, for \Delta_c < \Delta < 1, belongs to the Ising spin-glass universality class.

[C1.095] Damping dependence of the relaxation time of the magnetization of single-domain ferromagnetic particles

It is shown that the Melnikov-Meshkov formalism [J. Chem. Phys. 85, 1018 (1986)] for bridging the very low damping (VLD) and intermediate-to-high damping (IHD) Kramers escape rates as a function of the dissipation parameter for mechanical particles as extended by Coffey at al. [Adv. Chem. Phys. 117, 483 (2001); Phys. Rev. E 63, 021102 (2001)] to the magnetization relaxation of single-domain ferromagnetic particles provides an excellent agreement with the results of numerical solution of the Landau-Lifshitz-Gilbert equation augmented by a random field term. The procedure is illustrated by considering superparamagnetic particles with various types of nonaxially symmetric potentials of the magnetocrystalline anisotropy (cubic, biaxial, etc.) so that both regimes of damping occur. Here, a universal asymptotic formula for the magnetization relaxation time predicted by the Melnikov-Meshkov approach is found to be in good agreement with numerical results for all values of the dissipation parameter including VLD, IHD, and crossover regimes. [The support of this work by EOARD (contract FA8655-03-01-3027) and INTAS (project 01-2341) is gratefully acknowledged.]

[C1.096] Superparamagnetic behavior in (Fe_3-xCo_x)O_4 films grown by metalorganic decomposition (MOD)

Cobalt substituted iron oxide films with nominal thickness 850 nm have been prepared by MOD. XRD and Raman studies indicate that the films have inverse spinel (Fe_3-xCo_x)O_4 structural phase. XRD line widths analysis show composite of ~10 nm crystalline size. The SQUID magnetic hysteresis measurements exhibit a ferromagnetic behavior at low temperatures with no significant magnetic anisotropy between the parallel and perpendicular orientations of the applied field. The coercivity (H_C) is large at 5 K (15 - 16 kOe) and drops to ~100 Oe at room temperature. The field cooled and zero-field cooled magnetic measurements also indicate a superparamagnetic behavior with a blocking temperature close to 300 K. Using H_C(0) value, the uniaxial magnetic anisotropy value is estimated to be 0.7 - 1.2 x 10^6 erg/cm^3 which is in agreement with the previously reported values for iron oxide composite particles. The optical absorption spectra show a semiconductor behavior with an energy band gap of ~1.6 eV. Further details of the magnetic and the electrical properties will be presented.

[C1.097] Magnetic Characterization of Iron Oxide Cross Linked Hydro gels

Magnetic hydro gels have potential applications in drug delivery, cells sorting, sensors, and actuating technologies. Iron oxide alginate nanocomposites were synthesized following the method of Kroll et al^1 by cross linking sodium alginate with Fe^2+ and Fe^3+ in methanol: water. The ion-cross linked alginate hydro gels are oxidized in an alkaline solution. The resulting hydro gel consists of iron oxide cross linked alginate. The alginate hydro gels are inert to the reaction conditions and therefore the reaction sequence can be repeated. The multiple loadings result in an increase in the amount of iron oxide and the size of the iron oxide nanoparticles in the cross linked hydro gels. The third and sixth loaded iron oxide alginate hydro gels were dried and characterized by X-ray diffraction (XRD), Transmission Electron Microscopy (TEM), and Superconducting Quantum Interference Device (SQUID) magnetometry. The XRD patterns have characteristic features of \gamma- Fe_2O_3 or Fe_3O_4 phases. The average particle size, calculated from the XRD peaks, for third loaded iron oxide alginate was 2 nm. The zero-field-cooled and field-cooled SQUID measurements show the iron oxide nanoparticles are superparamagnetic with blocking temperature (T_B) of approximately 35 K. Above the blocking temperature, the inverse susceptibility versus temperature relationship does not follow the Curie-Weiss law, indicating strong inter-particle interactions. The M vs. H data above the blocking temperature was fitted with a modified Langevin function to obtain additional information about the iron oxide particle size. Details of the relationship between coercive field and temperature as well as the particle size distribution obtained from XRD and TEM measurements will be presented. *Research supported by NSF grant # DGE\sim980720 **Supported by NSF REU grant # EEC-0097736

^1E. Kroll, F.M. Winnik, and R.F. Ziolo, Chem. Mater, 8, 1594 (1996).

[C1.098] Magnetoresistive properties of Ni nanowires on nanotube templates

Continuous Ni nanowires with diameter 15-25 nm have been fabricated by thermal-evaporation coating of carbon nanotube ropes suspended across a trench. The magnetoresistive response is studied as a function of angle between an applied magnetic field and the wire direction. The results can be described on the basis of anisotropic magnetoresistance and domain wall nucleation.

[C1.099] Patterned Hard-Magnetic Nanostructures with Perpendicular Anisotropy

Thin-film nanostructures, such as dots, antidots, rings, and wires, are scientifically interesting model systems with many present and future applications in technology. Much work has been done on soft-magnetic systems, such as Fe, Ni, and permalloy, but hard-magnetic structures with well-defined anisotropies are more difficult to produce, because they require c-axis alignment. Our structures are produced by focused ion beam (FIB) milling of L1_0-phase FePt. First, highly anisotropic FePt<001> films are prepared by sputtering on oxidized Si<001> wafers and then annealed at 600^\circC. A protective layer of Al is then deposited to protect the film during the patterning but later removed by chemical etching. Finally, the structures are patterned by FIB milling and studied by AFM, MFM, and MOKE. The method makes it possible to realize virtually any geometry, with some restrictions applying to features smaller than 100 nm. We present examples of patterned hard-magnetic nanostructures, comment on their magnetism, and discuss conceivable applications.---This work is supported by NSF-MRSEC, the W. M. Keck Foundation, and CMRA.

[C1.100] Fe3O4 nanostructures grown by electrodeposition

Magnetite (Fe_3O_4) is one of the most studied magnetic oxides because of its interesting electronic and magnetic properties as well as its potential applications as spin injector in magnetic multilayer devices. We successfully prepared nanostructured Fe_3O_4 by electrodeposition in track etched polycarbonates membranes. Material characterization will be presented.

[C1.101] Magnetic and transport properties Ti1-xCoxO2 samples synthesized by sol-gel method with various post annealing sequences

We studied the post annealing effect on the magnetic properties Ti_1-xCo_xO_2 powder samples synthesized by sol-gel method. The same precursor was annealed at 770 K for 5 hours in air and in the pressure of 10^-6 Torr. In the case of samples annealed in vacuum, enhanced ferromagnetism was observed at room temperature, while only paramagnetic behavior was observed in samples annealed in air. Moreover, the magnetization of the vacuum-annealed sample sharply decreased around 650 K while measured in air, but such a decrease in the magnetization was almost absent while measured in He gas up to 750 K. We attribute the enhanced magnetization in the vacuum-annealed sample to the oxygen deficiency which deters the formation of non-magnetic CoTiO_3 complexes. The formation of Co-rich clusters is another possible cause for the enhanced ferromagnetism, and the Co clusters were found in transmission electron microscopy for the samples of x = 0.1, but no Co cluster was observed for the samples of x < 0.05. The measurements of magneto-resistance and the Hall voltage did not exhibit any characteristic behaviors known to exit in the magnetic semiconductors.

[C1.102] Intermediate valence model for colossal magnetoresistance

Colossal magnetoresistance (CM) is today known to occur in two different kind of compounds: Doped manganites and three undoped compounds, namely the metallic Tl_2 Mn_2 O_7, the semiconductor FeCr_2S_4 and the semimetal EuB_6. The double exchange and cooperative Jahn Teller model used for the doped manganites cannot be applied to the undoped compounds. We use Hubbard operators to reformulate a previous model of Ventura and Alascio (Phys. Rev. B 56, 14533 (1997)), and we obtain approximate one-electron Green's Functions (GF) for this model, following a method introduced by Foglio and Figueira (Phys. Rev. B 60, 11361, (1999)). With these GF we calculate the physical properties of Tl_2Mn_2O_7, including DC and optical resistivity, both with and without applied magnetic fields and magnetoresistance. We obtain the magnetization using the molecular field method and employing the experimental critical temperature and saturation magnetization. The model gives good agreement with the experimental data for this compound. We are developing variations of the model to try and describe the other undoped CM compounds.

[C1.103] Antiparallel Interface Coupling and High Anisotropy Effect in Fe3O4/Mn3O4 Superlattices Grown on MgO(011)

High quality Fe3O4/Mn3O4 superlattices are grown on MgO(001) and (011), respectively. Obserations of magnetic compensation and spin-flop transition indicate antiparallel coupling between Fe3O4 and Mn3O4 at the interface. Only the magnetic response from the sample grown on (011) plane shows strong anisotropy effect that compensation and spin-flop transition only occur along the [001] direction (easy axis) but disappear along the [001] direction (hard axis). The hysteresis curves, obtained from the easy magnetic axis, show typical spin-flop type loops in that square loops are observed at high field regions but both magnetization and coercivity tend to vanish at H=0. The magnetic response at low external field is related to the magnetic layers at the center of each constituent layers which shows gradually increasing of magnetization and low hysteresis. However, spin-flop transition at high external field is related to the magnetic coupling at the interface of Fe3O4/Mn3O4, which shows abrupt increases of magnetization and large hysteresis. More importantly, the area of the hysteresis loop also varies as varying temperature, which provides quantitative estimates of the magnetic-interface thickness.

[C1.104] Polaronic Aspects and Phase Diagram of the 2D Ferromagnetic Kondo Model

The 2D ferromagnetic Kondo model with classical corespins is studied via unbiased MC simulations. A canonical algorithm for finite temperatures is developed. We show that with realistic parameters for the manganites and at low temperatures, the model does not show phase separation on a 2D lattice but, rather stabilizes individual ferromagnetic polarons. Within the ferromagnetic polaron picture, the pseudogap in the one-particle DOS can easily be explained. Further, we explore the influence of the AFM superexchange coupling J'. We find that larger J' stabilizes the polarons and leads to the ''flux phase'' around half filling of the lower Kondo band. We also find that lower temperatures further enhance polaronic behavior at realistic parameters J' > 0.01. Detailed phase diagrams for \beta=50 and \beta=80 are determined, in which a narrow window in parameter space exists for phase separation.

[C1.105] SPIN DYNAMICS AND RELAXATION IN MAGNETICALLY DILUTED MANGANITES: EPR AND NMR STUDIES

The EPR spectra of Mn ions, as well as the Ga NMR and nuclear spin relaxation have been studied in magnetically diluted LaMn_xGa_1-xO_3 single crystals. The evolution of the exchange coupling has been monitored in a wide range of Mn concentrations (0.02 < x < 1). The temperature stimulated exchange narrowing was found at x=0.1, evidencing for thermally activated internal motion. Effect of similar motion (with the activation energy of 50 meV) on the ^69Ga and ^71Ga nuclear spin-lattice relaxation was also found. Plausible mechanisms are suggested, such as Jahn-Teller orbital re-orientations and/or polaron hopping.

[C1.106] Magneto-Transports in CuCr_2Se_4-x:Br_x under Hydrostatic Pressure

Here we report the pressure dependence of Magneto-resistance (MR) and Anomalous Hall Effect (AHE) in the itinerant ferromagnet(FM) spinel CuCr_2Se_4-x:Br_x at liquid Helium temperature. By applying hydrostatic pressure up to 10kbar, the amplitude of the MR gets bigger, while the FM transition temperature gets lower. The reduction of Tc is interpreted(T. Kanomata et al, J. Phys. Soc. Jap, 52, 1387 (1983)) as the competition between Anti-ferromagnetic (AF) interaction (direct exchange) and FM interaction (super-exchange) of Cr^3+-Cr^3+. The Hall resistivity of x=0.25 sample decreases rapidly for small field, then forms a small dip around saturation magnetic field (\sim0.3 Tesla), followed by a small positive slope. The dip gets bigger and wider as pressure goes higher. At 6.6 kbar, the size of the dip is about 50% of the saturation value, and the width is about 1 Tesla. Since the saturation of the Hall resistivity comes from the saturation of the magnetic moment, the dip-behavior indicates a non-trivial microscopic spin texture because of the enhancement of AF interaction.

[C1.107] TOWARDS A SILICON BASED MAGNETIC TUNNEL TRANSISTOR OPERATING AT ROOM TEMPERATURE

The Magnetic Tunnel Transistor (MTT) is a three terminal spintronic device similar to the Spin-Valve Transistor, except that it uses a magnetic tunnel junction to inject hot electrons into a ferromagnetic base and semiconductor collector. The MTT shows magnetocurrent above 100% and the energy of the injected hot electrons is tunable, which should lead to a higher output current. We have prepared MTT’s with the configuration Si/Au/Co/Al2O3/NiFe with a naturally oxidized barrier, and set up a lithographic process using various dry and wet etching techniques that allows fabrication of MTT’s with area down to 5 \mum, enabling room temperature (RT) operation. The resistance of the tunnel injector is a few kØmega to a few MØmega with breakdown voltage above 1.5V. The barrier characteristics were studied using x-ray photoelectron spectroscopy (XPS) and cross-sectional Transmission Electron Microscopy (TEM). We will present a detailed study of material aspects and processing parameters in view of achieving RT operation of the device.

[C1.108] Mn dimers in GaMnAs

When Manganese (Mn) atoms substitute Gallium in GaAs, they adopt the ionization state 2++, and therefore introduce spin degrees of freedom carried by the spin-5/2 state of Manganese d-electrons. Furthermore, substitutional Mn in GaAs acts as an acceptor center, and dopes holes in the system. It is believed that the interaction between the Mn spin-5/2 and hole spins are responsible for ferromagnetism in GaMnAs. It is therefore crucial to study this interaction in full detail at the simplest nontrivial level of two Mn ions embedded in GaAs host. Using envelope wave function approach and a realistic valence band model we investigate the bound states of Mn dimers. We calculate the binding energy and anisotropy as a function of the distance between the Mn ions, and the spin orientation. We use this numerical framework as a test bench for constructing Hamiltonians for Mn-Mn and Mn-hole interactions.

[C1.109] Amplification and Relaxation of Electron Spin Polarization in Semiconductor Devices

Dynamics of electron spins in semiconductor nanostructures has become of central interest in recent years because of the promise of spintronic devices. In these devices, the information is encoded in the spin states of individual electrons. In order to construct efficient spintronic devices it is necessary to understand electron spin relaxation mechanisms and obtain advanced control over the electron spin polarization. We report our studies on electron spin relaxation due to interaction with nuclear spins and on propagation of spin-polarized electrons through a boundary between differently doped semiconductors.

[C1.110] Cobalt doping of a low-energy interface in anatase

About two years ago Co-doped TiO_2 anatase has been discovered to exhibit ferromagnetism at and above room temperature, i.e.\ to be a magnetically robust diluted magnetic semiconductor (DMS). Since then it has attracted considerable interest, but there is still controversy over the origin of the magnetism as well as the influencing factors. In this work a low-energy \Sigma5(113)[-110] grain boundary in anatase is studied by density-functional band-structure calculations employing norm-conserving pseudopotentials and plane waves. The interfacial structure in pure anatase exhibits close structural and electronic similarity to the pure bulk anatase crystal. Yet, the grain boundary acts as a sink for dopant atoms, such as Co. This result confirms the importance of the investigation of grain boundaries in the discussion of DMS properties. The influence of inner interfaces on the magnetic properties of Co-doped TiO_2 is subject to ongoing investigations, the results of which will be shown in the talk.

[C1.111] Measurement of the conduction band offset at CdCr2Se4/AlxGa1-xAs interface

The conduction band offset \Delta E_C at CdCr_2Se_4/GaAs and CdCr_2Se_4/Al_0.09Ga_0.91As interfaces is determined to high accuracy in the temperature range of 10 - 300 K by using both improved theoretical and experimental free carrier absorption-induced internal photoemission (FCA-IPE) method. Theoretical calculations show that below the band offset the line shape of the FCA-IPE curve can be described very well by an exponential function. Therefore, \Delta E_C can be determined directly in a semi-log plot of the FCA-IPE curve. The weak temperature dependence of \Delta E_C indicates a paramagnetic state rather than a ferromagnetic state of CdCr_2Se_4 at the interface. This can be caused by the formation of a mixed layer at the interface which destroys the magnetic order in this layer. The results may explain the low spin injection efficiency of CdCr_2Se_4/Al_xGa_1-xAs\textbf heterostructure.

[C1.112] Complex Materials I

This abstract not available.

[C1.113] Edge Spin Currents in a Confined 2DEG with Rashba Spin-Orbit Interactions.

A new effect in semiconductor spintronics known as Spin-Hall effect has been described [1,2] recently as an intrinsic phenomenon due to spin-orbit interactions. According to these arguments, an electric field generates transverse spin currents that do not contribute to dissipation. According to the Kubo formula, the spin-Hall conductivity \sigma_SH of a 2DEG with Rashba spin splitting turns out to be universal (in the ballistic regime) and equal to \sigma_SH=\frace8\pi [2]. In order to shed further light on the meaning of these theoretical results we have analyzed ballistic transport in finite systems by by diagonalizing the Rashba Hamiltonian with a confinement potential. The main result is that (for systems much wider than a Rashba length) spin currents localized near the edges are created by the confining potential. The relationship between these edge spin currents and the dissipationless spin Hall effect is similar to the relationship between charge edge currents and the ordinary Hall effect. The magnitude of the edge currents is studied as a function of the dparameters of the system, and its relation to the spin-Hall conductivity is established.

[1] S. Murakami et al. Science 301, 1348 (2003) [2] J. Sinova et al. cond-mat/0307663

[C1.114] Amphiphilic Polyelectrolytes Solubilize Carbon Nanotubes in Aqueous Dispersions

A convenient procedure for forming stable suspensions of SWNT's in water and water/DMF solutions is reported. The dispersion process is effective, simple, and universal. It can be applied to different types of single-walled carbon nanotubes (SWNT's) as well as multi walled carbon nanotubes (MWNT's). The stability of SWNT suspensions was achieved by adsorbing an amphiphilic cationic [poly (N-cetyl-4-vinylpyridinium bromide-co-N-ethyl-4-vinylpyridinium bromide-co- 4-vinylpyridine) (16/75/9)] polymer to carbon surface. The amphiphilic nature of the polymer plays a dual action in the functionalization and solubilization of the nanotubes. The hydrophobic alkyl pendent groups of the polymer bind strongly to the surface of the nanotubes, whereas the hydrophilic groups exposes the nanotubes to the solvent medium rendering them soluble in water. The frequency of the Raman radial breathing modes (RBM) and the carbon-carbon stretching mode (known as the G-band) of the nanotubes were seen to increase in the presence of the polymer. Some increase in the intensity of the Raman disorder band (the D-band) was also observed. Raman spectral observations indicate the strong binding of the copolymer to the nanotubes (wrapping) which causes the unbundling of the nanotubes, making them easier to disperse in aqueous solvents.

[C1.115] Electron Lifetime in Armchair Carbon Nanotubes

The inverse electron lifetime in armchair carbon nanotubes is studied by the screened exchange energy. It comes from the single-particle and collective excitations of different angular momenta (L's). The excited conduction electrons can decay by the L\neq\,0 plasmon modes except those in the lowest subband. The higher conduction subbands have more excitation channels or shorter electron lifetime. A simple relation between the inverse electron lifetime and the state energy is absent, mainly owing to the severe restrictions of the one-dimensional excitation spectra. The energy dependence quite differs from that of graphite. The femtosecond time-resolved optical measurements could be used to verify the predicted results.

[C1.116] Magnetic Moment of Armchair Carbon Tori

Magnetoband structures of armchair carbon tori are studied from the tight-binding model. They strongly depend on the agnitude and the direction of the magnetic field (\textbf B). There exist metal-semiconductor (MS) transition as \textbfB varies. They happen more frequently when \textbfB is relatively close to the toroid axis. The characteristics of band structure are directly reflected in magnetic properties. The magnetic moment exhibit special jump structures at T=0, mainly owing to the MS transition. Paramagnetism or diamagnetism is mainly determined by the toroid radius (R) and the angle \alpha) between the magnetic field and the toroid axis. Most of armchair carbon tori are paramagnetic for \alpha > 30\circ. The temperature dependence is strong at \alpha = 0\circ, but weak at \alpha=90\circ.

[C1.117] Magnetoelectronic Structures of Double-Walled Armchair Carbon Nanotubes

The magnetoelectronic structures of the double-walled armchair carbon nanotubes are calculated from the tight-binding model. They are strongly dependent on the geometric symmetry, the intertube interaction, the magnetic flux, and the Zeeman splitting. The intertube interaction leads to the drastic changes of the low energy states, such as energy dispersions, wave function, and Fermi level. The magnetic flux could change linear bands into parabolic bands, destroy state degeneracy, open an energy gap, and affect Fermi level. However, the magnetic flux and the intertube interaction compete with each other in the metallic or semiconducting behavior. The Zeeman splitting would suppress the metal-semiconductor transition, while the opposite is true for the magnetic flux.

[C1.118] The workfunction of carbon nanotube studies by first-principles calculation

Nanoscale materials such as carbon nanotubes (CNT's) have attracted great attention. CNT's show interesting material properties because their unique structures and stability. The field emission properties of these quasi-one-dimensional nanomaterials are of particular interest because of their large aspect ratio. Recently, a large area CNT-based filed emission display (FED) with full color has been demonstrated.The workfunction plays an important role in understanding the field emission properties of the carbon nanotubes. Up to now, theoretical works were only limited to the calculations on the workfunction of individual carbon nanotubes and nanotube bundles. The effects of tube lengths and tube-tube distance on the workfunction of the tube are not clear. To fill this gap, we present in this paper first-principles calculations of the workfunction for capped and H-terminated (3,3) and (5,0) tubes with various tube length and tube-tube distances. The effects of tube length, tube-tube distance, chirality, and structure of the tip were investigated.We found the workfunction of capped (3,3) and (5,0) tubes decreases linearly with the inverse of tube-tube distance and the workfunction of H-terminated (3,3) and (5,0) tube increases linearly with the inverse of tube-tube distance. The workfunctions for various tube length and tube-tube distance can be fitted by WF = A + B/Dx + C/L +D/(DxL), where Dx is the tube-tube distance and L is the tube length, where A is the workfunction for an isolated infinite tube.The value of A is given by 4.61eV for capped (3,3) tube, 4.63 for H-terminated (3,3) tube, 5.40eV for capped (5,0) tube, and 5.55 eV for H-terminated (5,0) tube respectively. These are consistent with the value calculated by an infinite isolated tube.

[C1.119] The Effects of Alkali Metals on the Radial and Tangential Raman Modes of Single Wall Carbon Nanotubes (SWCNTs)

We present a theoretical study of the Raman modes in SWCNTs, and in particular the effects of K, Rb, and Cs doping. It was previously shown that alkali-metal doping causes shifts of the RBM and G-bands (Bendiab, et al., Chem. Phys. Lett., 2001). Applying first principles density functional theory within the generalized gradient approximation, we report results of the Raman modes of pristine SWCNTs in crystalline-rope and isolated tube forms, and discuss changes for SWCNTs adsorbed with alkali atoms at various sites. For example, among the proposed models for Cs adsorption, we find intercalation to be the mechanism whereby the Raman modes are downshifted, which can be rationalized by the tube distortion, hence lowering its symmetry.

[C1.120] Dynamic Properties of Polymer / Functionalized Carbon Nanotube Composites

We have investigated the influence of PMMA-functionalized multiwalled carbon nanotubes on the dynamic properties of polymer films. The dewetting of a polystyrene (PS) film (Mw=270K) from a poly(methyl metacrylate) (PMMA) film(Mw=60K) spun cast on a silicon substrate was studied at 175 ¡ÆC, a temperature above the glass transition temperatures of PS and PMMA. Using optical microscopy, the dewetting velocity was measured as a function of the concentration (0.02 to 0.2 wtunfunctionalized carbon nanotubes. The dependence of the dewetting velocity on concentration was the same regardless of functional group or whether the tubes were in the PS or PMMA films. The results showed that the dewetting velocity was suppressed by seven times at a concentration of 0.2 wtIn order to determine whether this is a pinning phenomena, or a rheological effect, we also measured the effect of the tubes on the tracer diffusion coefficient using neutron reflectivity and secondary ion mass spectrometry (SIMS). The results showed that no change even at the highest concentration. Hence we conclude that the suppressed dewetting is a dynamic effect where the tubes act physical obstacles. These results will be correlated to bulk rheological measurements.

[C1.121] Computational Studies of Mechanisms of Functionalization of Single Wall Carbon Nanotubes

Applications of single wall carbon nanotubes (SWCNTs) are still limited by the inability to carefully control the behavior of these materials. A number of selective chemical functionalization studies thus emerged, manipulating nanotubes of distinct electronic types, for example, regarding water soluble diazonium salts which exhibit highly chemoselective reactions with metallic vs. semiconducting tubes (Strano et al., Science, 2003). In order to gain insight into the proposed reaction mechanisms, we discuss density functional theory calculations of electronic structures for functionalized C(5,5) SWCNTs, with respect to the intermediates involved in the reaction, and details concerning the reaction paths.

[C1.122] PMMA/Multiwalled Carbon Nanotubes Nanocomposites Prepared by Melt Blending

PMMA/multiwalled carbon nanotubes (MCNTs) nanocomposites were prepared by melt blending in a twin-crew extruder. TEM images show that the MCNTs are well dispersed in polymer matrix without apparent damage, which results in a big improvement in mechanical properties and thermal stability. The DMA results indicate the incorporation of 0.1wt% MCNTs improves the storage modulus by 50% and increases the glass transition temperature 12 oC, which was also confirmed by DSC. The mechanical properties as a function MCNTs loading were further studied by using rheometer and DMA. These results could have important implication in polymer/carbon nanotubes processing and manufacturing.

Supported by NSF funded MRSEC at Stony Brook

[C1.123] Magnetoelectronic Properties of a graphite

Magnetoelectronic properties of graphite are studied by the tight-binding model. They strongly depend on the magnitude and the direction of the magnetic field, the dimensionality, and the stacking sequence. The magnetic field could effectively reduce the dimensionality of energy dispersions. It has a strong effect on the special structures of density of states and thus the optical absorption spectra.

[C1.124] Computational Study of Hydrogen in Nanodiamond

Both natural and polycrystalline chemical vapor deposition (CVD) diamonds are always contaminated with hydrogen. Various experimental techniques are used for the observation of hydrogen in diamonds, include infrared (IR) absorption electron paramagnetic resonance (EPR), muon spin rotation (\muSR) and optical measurements. Although several theoretical approaches have been used to predict the properties of H in bulk diamond, conclusive assignment of the hydrogen related-structure in the nanocrystalline diamond remains elusive. Thus computational methods, where processes can be modeled on an atomistic scale, are needed to explain this phenomena.

The purpose of our study is to understand the diffusion and bonding of hydrogen in carbon diamond and its effect on the diamond and amorphous diamond lattices. We have found that hydrogen atoms have a distinct, temperature dependent, set of energetically preferred locations in bulk and in amorphous diamond/diamond structures. Hydrogen atoms (and molecules) lead to the appearance of new electronic states, as compared to the pure carbon diamond structure.

[C1.125] Quantization and Low-Temperature Universality of Thermal Conductance of Single-Walled Carbon Nanotubes

Carbon nanotubes must be the best candidate for a ballistic phonon conductor as well as for a ballistic electron conductor, having a large experimentally estimated phonon-mean-free-path on the order of 1\mum. We study the thermal conductance of carbon nanotubes using the Landauer theory of heat transport. For semiconducting carbon nanotubes, thermal transport is dominated by phonons. The phonon-derived thermal conductance is quantized as a universal value of 4\pi^2k_B^2T/3h in the low-temperature limit, independent of their radii and chiralities. The low-temperature thermal conductance curves for tubes with different chiralities collapse onto a single curve once they are plotted against the temperature scaled by the gap of the lowest optical mode. For metallic carbon nanotubes, heat is carried by electrons as well as phonons, and an electronic contribution to thermal conductance is also quantized as the same universal value as that of phonon in the low temperature limit. The temperature range where the quantization is observable increases as the radius decreases, manifesting the nature of one-dimensional electron and phonon transport.

[C1.126] Partitioned Real-Space Density Functional Calculations: Principles and Applications

We have developed the partitioned real-space density functional (PRDF) method based on the density functional theory (DFT) to analyze nonequilibrium electronic states of nanometer-scale systems under bias voltage or in an electric field. This method consists of a very simple algorithm and can be straightforwardly applied to the analyses of nonequilibrium phenomena with no electron tunneling. The main procedure in the PRDF method is to divide the entire systems into subsystems and to calculate the electronic wave function for each subsystem using the self-consistent potential defined in the entire system. In this study, we apply the PRDF method to the investigation of the field evaporation from carbon nanotubes (CNT's) and capacitances of nanostructures and reveal field evaporation pathways from CNT's and the electronic states origin of electrochemical capacitances of nanostructures.

[C1.127] Sensitivity analyses of a H2 molecule in a SWNT

The unexpected high values for hydrogen storage capacity of single walled carbon nanotubes (SWNT) at room temperature has motivated a complete sensitivity analysis of potential energy of an H2 molecule as a function of its location inside the nanotube. Results of ab-initio calculations for SWNT’s are presented and compared with bibliography. Special attention is focused on the variation of inter nuclear distance for hydrogen atoms.

[C1.128] Energy decay pathways in C_60 with electron-phonon coupling coupling

Electron-phonon energy decay processes in C_60 are studied. Electrons are modeled using tight-binding, whereas phonons are simulated semi-classically. A vibrational self-consistent field algorithm is used. Decay pathways and rates are calculated for illustrative examples.

[C1.129] Opto-electric Transport Properties of Individual GaP Nanowires and Sensor Applications

We have fabricated field effect transistors (FET) with individual GaP nanowires. High quality single crystalline nanowires were grown by vapor deposition method, and gated-electrical transport measurement reveals that GaP nanowires exhibit n-type field effects with an on/off ratio more than105. Upon exposure to an UV-light source, abrupt increase of conductance observed at room temperature. Conductance enhancement of 106 occurred at 225 nm UV illumination, which is much larger than the gap energy of GaP (550 nm). This can be attributed to the oxygen chemisorption-desorption process at the nanowire surfaces. We will compare the calculated oxygen desorption energy with UV experiment. Since GaP nanowires offer both field effect and optical switching effect, they can be new class of electronic, opto-electric device elements. Sensor applications of GaP FETs will also be presented.

[C1.130] Nanotube and Nanowire Devices in the Space Radiation Environment

We report investigations of the radiation resilience of nanotube and nanowire simple circuits in simulated space environments. Earlier work by ourselves and other researchers indicates increased radiation resilience for nanoscale components. In the present experiments, we investigate two aspects: (1) size versus material dependence of the radiation resilience, through studies of carbon nanotubes, silicon nanowires and gallium nitride nanowires, and (2) contact formation and behavior of these three nanoscale components within simple inverter circuits.

[C1.131] Unique applications of Carbon nanotubes in medical imaging, bio-sensors and vaccine delivery

The dimensionality of a system has profound influence on its physical behavior. With advances in technology over the past few decades, it has become possible to fabricate and study reduced-dimensional systems, such as carbon nanotubes (CNTs). Carbon nanotubes are especially promising candidate for cold cathode field emitter because of their electrical properties, high aspect ratio, and small radius of curvature at the tips. Electron emission from the carbon nanotubes is investigated. As a result of this investigation, several prototype devices have been suggested that operate with low swing voltages with sufficient current densities for medical imaging. Physical characteristics that allow improved current stability and long lifetime operation for bio-sensors are presented. Carbon nanotubes offer tremendous applications in on-demand drug delivery. Research describing antigen-antibody interactions and immune responses using peptide-carbon nanotubes is presented. The aim of this brief overview is to illustrate the useful characteristics of carbon nanotubes and its possible biomedical applications.

[C1.132] Enhanced diffraction pattern from a Fibonacci chain

We study the diffraction patterns of a one-dimensional Fibonacci chain from quasiperiodic pulse trains. We find a single prominent peak when the dynamics of the incident wave matches the arrangement of the scatterers, that is, when the pulse train and the scatterers are in resonance. The maximum diffraction angle and the resonant pulse train determine the positions of the scatterers. These results may provide a methodology for quality control of Fibonacci multilayers, and may have further impact when extended to higher dimensions.

[C1.133] Energy landscape and rigidity

We show that there is a strong connection betwen the topography of the energy landscape, the topology of the phase space and the rigidity of a glass. By exploring these relationships, we are able to relate the number of mechanicals constraints and floppy modes with the statistics of the landscape, by providing an expression for the number of energy basins as a function of the rigidity. This allows to understand the jump in the specific heat during the glass transition of chalcogenide glasses. The relationship can be extended for entropy driven systems like hard-spheres, where jammed states and inherent structures are related with rigidity theory.

[C1.134] Undergraduate Education

This abstract not available.

[C1.135] “Web-book modules for teaching nanotechnology in introductory physics, chemistry, and engineering courses”

We have developed stand alone web-book modules for teaching an interdisciplinary sophomore-level course titled: “Frontiers of Nanotechnology and Nanomaterials.” This course is aimed at science and engineering students and is team-taught by a chemist, a mechanical engineer and a physicist. Our currently developed web-book modules include: Introduction to Nanotechnology; Scaling Laws; Quantum dots, wires, and wells; Characterization tools for nanomaterials; Magnetic nanomaterials and spintronics; Inorganic/organic nanocomposites; and Bionanomaterials. We believe that our modules could be used in other introductory courses on nanotechnology, as well as in traditional introductory science or engineering courses.

[C1.136] PR2EPS: Preparation, Recruitment, Retention and Excellence in the Physical Sciences

PR2EPS, is an NSF-DUE sponsored program at SUNY Oneonta designed to attract students to study physics, chemistry and related physical science disciplines at SUNY Oneonta. The program also seeks to increase the retention rate for all students in these disciplines by providing specialized skill-building and professional development courses, an evening tutoring center, and exposure to research and professional activities during the students first three-years of undergraduate study. A key focus of the project is drawing students from the five, primarily rural and agricultural, counties surrounding Oneonta, NY. Their first direct exposure to the program will be in recruiting visits to local high schools where promising candidates will be invited to participate in a weeklong summer camp designed to demonstrate to them that they possess the requisite skills and potential to succeed in these technically demanding disciplines. A description of the program, including the collaboration of faculty from the Departments of Physics amp; Astronomy, Chemistry amp; Biochemistry, Education and as well as the initial outcomes of the tutoring center and local outreach will be presented.

[C1.137] Scattering and Diffraction

This abstract not available.

[C1.138] X-ray microdiffraction study on domain structures and intermediate phases of Lead Phosphate

Lead Phosphate (Pb_3(PO_4)_2, PPO) is a ferroelastic material which has a monoclinic structure and three kinds of domains (3-orientation states in b-c plane) at room temperature. There are two kinds of domain walls (W_m , W_b wall) depending on the symmetries between neighboring domains. We carried out measurements of two dimensional mapping of X-ray microdiffraction for PPO at room temperature as well as higher temperatures. The mapping measurement was done for the sample area consisted of W_m-walls which have mirror symmetric characteristics at RT. Around 180\r C, mixed phases of monoclinic and rhombohedral structures were observed as domain size of a few microns, which is consistent with the intermediate phase assumed in previous works.^1)1) Yong Chan Jo et al. PRB \textbf66 184103

[C1.139] Superconductivity: Theory, Materials, Thermodynamics, and Transport

This abstract not available.

[C1.140] High Tc's from the Complete Boson-Fermion Model of Superconductivity

The new statistical ''complete boson-fermion model'' of superconductivity [1] is used to calculate the superconductor transition temperatures Tc in both 2D and 3D systems. The model considers both two-electron and two-hole pairs in freely variable proportions, along with unpaired electrons. For the weak coupling and perfect electron/hole-pair symmetry case, one gets the BCS results for Tc. When hole-pairs are not present and far away from perfect electron/hole-pair symmetry one gets the analytical Bose-Einstein condensation Tc values approximately. Using the Cooper/BCS model interaction for electron-phonon coupling, and with no adjustable parameters, the calculated Tc's compare well with experimental data, provided only that one departs moderately from perfect electron/hole-pair symmetry. These Tc's are also predicted in both 2D and 3D to be higher for hole- than for electron-superconductors, in agreement with general empirical trends.

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

[C1.141] Phase diagram of the two-dimensional extended Hubbard model

In order to explore how superconductivity arises when charge fluctuations and spin fluctuations coexist, we have obtained a phase diagram against the off-site repulsion V and charge density n for the extended, repulsive Hubbard model on the square lattice with the fluctuation exchange approximation. We have found the existence of (i) a quantum phase transition between d_xy and d_x^2-y^2 pairing symmetries, (ii) f-pairing phase in between the d_x^2-y^2 and CDW phases for intermediate 0.5

[C1.142] ^151Eu and ^57Fe Mössbauer study of EuFeO_3.

Samples of EuFeO_3 prepared by mechanical alloying starting from Europium oxide, Eu_2O_3 purity 99.9 Iron (III) oxide, Fe_2O_3 gamma 99+ combined in proportion to yield EuFeO_3. Samples were studied as a function of milling period using XRD and Mössbauer effect measurement. XRD showed that after 20 hours of milling Eu_2O_3 and FeO_3 with ball to powder mass ratio 4:1 the resulting compound is EuFeO_3. Results of magnetic and structural properties obtained after probing at both rare earth site and transition metal site using ^151Eu and ^57Fe Mössbauer effect measurements will be presented.

[C1.143] Effects of Heat Treatment Condition on the Structural, Electrical and Magnetic Properties of Pr(Ba1-xSrx)2Cu3O7-δ

Replace this text with your abstract.

-/abstract-

Structural, electrical and magnetic properties of polycrystalline samples of Pr(Ba_1-xSr_x)_2Cu_3O_7-\delta with x=0\sim 0.5 have been investigated. Samples were prepared under both in air (system A) and reducing atmosphere (system B). Their solid solubility limit for system B is higher than that for system A. The structure parameters were refined by the Rietveld analysis of X-ray powder diffraction data. The orthorhombic structure changed to the tetragonal at about x=0.3 in system B. whereas system A already showed the tetragonal structure for x=0. The electrical resistivity increased with x for the samples x\le 0.3 and decreased for x\ge 0.3 and the Neel temperature T_N(Pr) increased from 16.8K for x=0 to 21K for x=0.3 in system B. The electrical resistivity of system A is much higher than that of system B for x=0, however, it decreses with x. The variation of the hybridization between Pr 4f and O 2p in the CuO_2 planes is

[C1.144] Anisotropic Characterization of In-plane Aligned (100) Y_1-xCa_xBa_2Cu_3O_7-\delta Thin Films

Highly in-plane aligned (100) Y_1-xCa_xBa_2Cu_3O_7-\delta thin films have been deposited on (100) LaSrGaO_4 substrates by pulsed laser. Before the Y_1-xCa_xBa_2Cu_3O_7-\delta deposition, the (010) PrBa_2Cu_3O_7-\delta was grown as a template layer. The electric transport properties were measured by a standard four-probe method. The crystallinity of the films was analyzed by measuring the x-ray \theta -2\theta diffraction pattern and \phi scanning. The surface morphology of the films was examined by atomic force microscopy (AFM) and scanning electron microscopy (SEM). Furthermore, the electronic structure and ultrafast response of the (100) Y_1-xCa_xBa_2Cu_3O_7-\delta thin films have been investigated by the polarization-dependent x-ray absorption spectroscopy and femtosecond pump-probe technique, respectively. The anisotropic characterizations of these in-plane aligned (100) Y_1-xCa_xBa_2Cu_3O_7-\delta thin films are discussed.

[C1.145] Modification of superconducting properties of YBCO by high-intensity ultrasound

A novel sonochemical method of a controlled modification of the superconducting properties of YBCO granular superconductor is presented. Morphological and chemical changes induced by high-intensity ultrasound are analyzed and the consequences for the superconducting behavior are discussed. In particular, ultrasound-induced cavitation causes significant inter-grain fusion without affecting much the chemical composition and critical temperature of the material. Addition of volatile organometallics during the synthesis leads to in-situ production of flux pinning centers. However, annealing protocol should be further optimized to achieve maximal pinning efficiency.

[C1.146] Specific Heat of HfV_2: Effect of Magnetic Fields

Specific-heat (C) measurements on a single crystal of HfV_2 were made from 1 to 300 K in magnetic fields (H) along the [110] axis to 14 T. HfV_2 has a martensitic transition at T_M = 118 K and becomes superconducting (SC) at T_c \sim8 K. T_c is shifted and C varies following repeated cooling cycles from room temperature. This variation is probably related to an incomplete structural transition from cubic to orthorhombic at T_M. For zero field \DeltaC(T_c)/\gammaT_c = 2.07, is nearly independent of variations in T_c and C, which indicates strong coupling. The SC state C can be fitted with the alpha model for strong coupling using an energy gap \Delta(0)/k_BT_c = 2.1. In the normal state, the Sommerfeld constant (\gamma) depends on thermal history: for T_c = 8.0 K, \gamma_n = 42.1 mJ K^-2 mol^-1. When H > 0 the SC anomaly shifts to lower T. The mixed state \gamma is linear in H with a slope that is a function of thermal history. Extrapolating \gamma to \gamma_n yields an upper critical field H_c2 \sim30 T. From fits above T_c the Debye theta, characterizing the lattice C, is 177 K.

[C1.147] Two-dimensional nature and superconducting properties of the high-Tc cuprates TlBa2Ca3Cu4Oy

We have measured the temperature dependence of the reversible magnetization of the c-axis aligned TlBa2Ca3Cu4Oy with magnetic field H parallel to the c-axis. Using the high-field scaling law proposed by Ullah-Dorsey, we found that the magnetization shows two-dimensional scaling behavior in the critical region around Tc. This result supports an argument that the four-layered superconductor has a two-dimensional behavior. We also have obtained various thermodynamic parameters such as, the coherence length, the penetration depth, the critical field, and the Ginzburg-Landau parameter by using the Hao-Clem model. These parameters were compared to those of other four-layered compounds such as HgBa2Ca3Cu4O10+x and CuBa2Ca3Cu4O12-x.

[C1.148] Low-temperature specific heat of an extreme type-II superconductor at high magnetic fields

We present a detailed study of the quasiparticle contribution to the low-temperature specific heat of an extreme type-II superconductor at high magnetic fields. Within a T-matrix approximation for the self-energies in the mixed state of a homogeneous superconductor, the electronic specific heat is a linear function of temperature with a linear-T coefficient \gamma _s(H) being a nonlinear function of magnetic field H. In the range of magnetic fields H\agt(0.15-0.2)H_c2 where our theory is applicable, the calculated \gamma _s(H) closely resembles the experimental data for the borocarbide superconductor YNi_2B_2C.

[C1.149] Angle Dependent Magnetoresistance of the Layered Organic Superconductor \kappa-(ET)_2Cu(NCS)_2 : Simulation and Experiment

The angle-dependences of the magnetoresistance of two different isotopic substitutions (deuterated and undeuterated) of the layered organic superconductor \kappa-(ET)_2Cu(NCS)_2~are presented. These data are rich in features and it is instructive to compare them with simulations of the angle dependent magnetoresistance oscillations (AMRO) arising from the quasi-one-dimensional (Q1D) and quasi-two-dimensional (Q2D) Fermi surfaces. The simulations are accomplished using a Boltzman transport technique and agree well with the results of experiments. The success of the semi-classical simulations suggests that non-Fermi liquid effects are not required to explain the interlayer magneto-transport in this system.

[C1.150] The T-p phase diagram of Y1-xCaxBa2(Cu1-yZny)3O7-d from transport measurements: existence of the pseudogap below Tc0

The effects of planar hole content, p, and magnetic field on the resistivity, \rho (T), of high-quality c-axis oriented thin films and sintered Y_1-xCa_xBa_2(Cu_1-yZn_y)_3O_7-\delta samples were investigated over a wide range of Ca, Zn, and oxygen contents. Zn was used to suppress superconductivity which enabled us to extract the characteristic pseudogap temperature, T^\ast (p) below T_c0(p) [ \equiv T_c (x =0, y = 0)]. We have also located another characteristic temperature, T_scf, marking the onset of significant superconducting fluctuations above T_c, from the analysis of \rho (T,H,p) and \rho (T,p) data. This enabled us to identify T^\ast (p) near the optimum doping level where the values of T^\ast (p) and T_scf(p) are very close and hard to distinguish. We again found that T^\ast (p) depends only on the hole concentration, and not on the level of disorder associated with Zn or Ca substitutions. We conclude that (i) T^\ast (p) (and therefore, the pseudogap energy scale) persists below T_c0(p) on the overdoped side and does not merge with the T_c0(p) line and (ii) T^\ast (p) extrapolate to zero at the doping p = 0.19 \pm 0.01.

[C1.151] Bolometric Technique for Measuring Microwave Surface Resistance of Superconducting Single Crystals

Over the past several years the experimental superconductivity group at UBC has developed a novel technique for measuring the surface resistance, R_s, of superconducting samples over a wide range of microwave frequencies. This technique uses non-resonant bolometric detection to measure the power absorbed by the sample over the entire microwave frequency range. By employing a power meter, consisting of a normal metal whose surface resistance is well understood, it is possible to extract R_s of the superconducting sample. To date this bolometric technique has predominately been used to measure R_s, and hence the real part of the conductivity \sigma_1, of YBa_2Cu_3O_6+x single crystals down to temperatures of 1.2~K. I am working towards adapting this method to be used on a dilution refrigerator, which can reach base temperatures below 50~mK. I will briefly describe the technique used to perform the measurements as well as present some preliminary surface resistance measurements on single crystals of Sr_2RuO_4.

[C1.152] Quasiparticle properties at microwave frequencies in the underdoped YBa2Cu3O7-δ thin films

Microstrip ring resonators with quality factor (Q) over 10^4 at temperature 5 K were fabricated using the double-side YBa_2Cu_3O_7-\delta (YBCO) films deposited on LaAlO_3 (LAO) substrates. By placing a narrow gap in the ring resonator, the original fundamental resonating mode (3.61 GHz) splits into two modes (1.80 GHz and 5.33 GHz) with distinct resonating frequencies. The samples allow us to determine the temperature and the frequency dependences of penetration depth and microwave conductivity for various underdoped-cuprates by using Drude formula and the modified two-fluid model. The natures of the order parameter of high-Tc superconductivity in the underdoped cases are shown to be of d-wave type in an exact manner. In particular, the Fermi-liquid correction factor \textit\alpha ^2 and the vertex correction factor \beta from the model, proposed by Wen and Lee, can be estimated that \textit\alpha ^2 is doping independent in the underdoped regime and \beta decreases as oxygen content is decreasing in our experiment data. All these results are independent of frequencies as well. The results reveal that the interaction between quasiparticles is insensitive dependence of the impurity concentrations due to oxygen deficiency on the CuO chain and the impurity potential for forward scattering approaches the same as back scattering with more oxygen deficiency.

[C1.153] Enhancement of low temperature Critical current density of MgB_2 thin films by Au coating

We measured the superconducting critical current densities (J_c) from the magnetization hysteresis (M-H) loop while depositing the gold on top of the MgB_2 thin film. The purpose of this experiment is whether the vortex avalanche phenomena which suppress the J_c for low temperature ( T < 15 K ) and low field (H \leq 1000 Oe) can be cured by gold deposition. This avalanche called flux noise has been headache for the application of the MgB_2 thin films. As increasing the thickness of Au film, fortunately, the flux noise in the M-H loop is suppressed and finally disappears when thickness of the gold becomes 2.55 ¥ìm. From this experiment, the obstacles of the application of MgB_2 thin film are completely overcome

[C1.154] Effects of Chemical Substitution on Properties of Bi-based High temperature Superconductors

One characteristic of the copper-oxide superconductors is the close relation between magnetism and superconductivity. In particular it has been found that transition metal substitutions for Cu in YBa_2Cu_3O_7 (YBCO) and its rare earth analogues, dramatically affect the transition temperature T_c. On the other hand substitutions of rare earth impurities metals for Y in YBCO were found to have little or no effect on T_c ^[( A. Kebede, PhD. Thesis, Temple University, 1990)^]. From the point of view of conventional, Bardeen, Cooper and Schreiffer (BCS) superconductivity this observations were unusual. In the case of Bi-based high Tc superconductors of the form Bi_2(SrCa)_2+n(Cu_1-x M_x)_1+n O_y, where M represents transition metals such as Zn and Ni as well as rare earth metals such as Gd., it is found out that both groups depress T_c in sharp contrast to what is observed in the YBCO system. This report describes some transport and magnetic properties of Bi_2Sr_2Ca_2(Cu_1-x Zn_x)_3O_y (Bi2223) and Bi_2Sr_2Ca2(Cu_1-x Zn_x)_3O_y (Bi2212) whiskers. Whiskers have advantages over polycrystalline sample as well as large bulk crystals in that they provide narrow transitions in resistance versus temperature as well as in magnetization versus temperature curves. In addition they are easy to grow and with very short oxygen annealing times. In this communication we present preliminary data on transport and magnetic properties of these superconducting whiskers.

[C1.155] Computational Nanoscience

This abstract not available.

[C1.156] Nanomechanical rotations in a single-C_59N aza-fullerene transistor.

The first one electron transistor based on C_60 was performed by researchers of the Lawrence Berkeley National Laboratory and of the University of California at Berkeley. They deposited a dilute toluene solution of C_60 onto a pair of connected gold electrodes fabricated using electron-beam lithography. The entire structure was on a SiO_2 insulating layer on top of a silicon wafer that serves as a gate electrode to modulate the electrostatic potential of C_60. The device showed a transistor behavior when bias and gate voltage were applied. According to the experiments, the device can give information of the nanomechanical vibrations of the C_60 molecule coupled to the gold atoms of the electrodes. In the present work we are simulating the C_59N aza-fullerene molecule between gold electrodes in order to study the possible changes in the transistor properties. The electronic and dipolar moment calculations are made using a hybrid density functional calculation B3-LYP. The rotational frequency was calculated from the dipolar moment- external electrical field coupling.

[C1.157] Local density of states for nanoscale graphene fragments

Graphene platelets (GPs) with dimensions in the nanometer range are of interest as substitutes for carbon nanotubules in composite materials. This is partly because these platelets can be produced more economically. We present a study of local DOS from very simple models of supported GPs with simple irregular selvedge and local imperfections. Characteristics appearing in the LDOS as calculated from the models are compared to STM data.

[C1.158] Structure and charge transport of Fullerene tunnel junctions

We have investigated the structure and charge transport properties of C_60 fullerene tunnel junctions. Using a non-orthogonal tight-binding model we calculated the structure of C_60 molecule on top of Au(111) surface. The equilibrium structure is then used as a basis for ab initio calculations of the properties of the gold-carbon complex, specifically the transport properties. These are compared with experimental STM data where possible.

[C1.159] Transmission resonance through the coupled quantum dots in Aharonov-Bohm rings

Stimulated by recent intriguing experiments with a quantum dot in an Aharonov-Bohm (AB) interferometer [1, 2], we investigate the total transmission probability of nanoscale AB rings with an embedded scattering center (single or double quantum dots) in one arm and a magnetic flux passing through its center. We find a peculiar quantum transport in this system such as a symmetric Breit-Wigner (BW) and an asymmetric Fano transmission resonance. In the AB ring with a quantum dot (QD) in one of the arms, we show the transition from BW to Fano resonance (or vice verse) occurs by tuning the magnetic AB flux threading through the AB ring, indicating the Fano asymmetric parameter is extended to a complex number whose argument has a magnetic flux dependence. On the other hand, this unique phenomenon of the Fano interference can also be observed in the AB ring with the coupled double-QDs by modulating the coupling parameters (a controllable height and width of the potential barrier) between the QDs for the fixed magnetic AB flux. In addition, the continuous AB phase of 2 pi periodicity between the adjacent Fano peaks is also studied.

[1] K. Kobayashi, H. Aikawa, S. Katsumoto, and Y. Iye, Rhys. Rev. Lett., 85, 256806 (2002). [2] U. F. Keyser, S. Borck, R. J. Haug, M. Bichler, G. Abstreiter, and W. Wegscheider, Semiconductor Science and Technology, 17, L22- L24 (2002).

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

[C1.160] Effects of Structural Relaxation on Conductance Oscillations in Atomic Chains

Many theoretical studies have been devoted to electrical properties of short atomic chains. One of the interesting features revealed by them is that the conductance of Na chains depends on the number of atoms being even or odd. This parity oscillation was suggested to be a universal feature of atomic chains. In contrast, a recent calculation reported that the conductance of Al chains would oscillate in a period of four atoms, instead of two. Since most of theoretical studies focusing on the parity oscillation assumed fixed atomic positions in the chains, we perform ab initio force calculation to consider relaxation effects on Na atomic chains between two electrodes using the boundary-matching scattering-state density functional method developed by our group. We have found that the oscillatory behavior of the conductance is much reduced after structural relaxation. From the current density distribution, it is seen that the reflection in the stable chain is much reduced than that in the initial geometry. Our results suggest that the conductance of relaxed Na chains may tend to be close to the ideal value of quantized conductance.

[C1.161] Ab Initio Study of Capacitance of Nanostructures

Capacitance is one of the important quantities that determine device operation. However, capacitance of nanostructures has been studied much less than their current-voltage characteristics. In this study, we have examined the quantum capacitance of a few nanostructures using an ab initio method developed by our group, which takes account of semi-infinite electrodes and applied bias voltages within the density functional theory. In the cases of two electrodes with a nanoscale gap and flat surfaces, the behavior of the calculated capacitance can be understood from two quantum effects, electron spill from electrodes and electron tunneling. When the effective distance including the correction for the first effect is smaller than about 5 a.u., the quantum capacitance is smaller than the classical one. The capacitance becomes maximum at about 2 a.u., though the precise value depends on systems. Further, we found that the quantum capacitance is sensitive to atomic structure of electrode surfaces including lateral arrangement of the two electrodes.

[C1.162] Heats of Segregation of BCC Binaries from Ab Initio and Quantum Approximate Calculations

We compare dilute-limit heats of segregation for selected BCC transition metal binaries computed using ab initio and quantum approximate energy methods. Ab initio calculations are carried out using the CASTEP plane-wave pseudopotential computer code, while quantum approximate results are computed using the Bozzolo-Ferrante-Smith (BFS) method with the most recent LMTO-based parameters. Quantum approximate segregation energies are computed with and without atomistic relaxation, while the ab initio calculations are performed without relaxation. Results are discussed within the context of a segregation model driven by strain and bond-breaking effects. We compare our results with full-potential quantum calculations and with available experimental results.

[C1.163] General Theory

This abstract not available.

[C1.164] Improved Atmospheric Refraction Correction Models in Satellite Laser Ranging (SLR)

The primary source of unmodeled error in space geodetic techniques such as VLBI, GPS and SLR is atmospheric refraction. SLR uses lasers (532 nm) to measure very precise ranges from ground tracking stations to spaceborne geodetic satellites with accuracies at the millimeter level. Improved refraction modeling is essential in reducing errors in SLR measurements that study variations in the Earth's gravitational field and vertical crustal motion as well as monitoring sea-level rise, post-glacial rebound and earthquake predictions. The Marini and Murray model developed in the 1970's has primarily been used for data analysis, but recent work by Mendes et al., 2002 provides significant improvement in modeling the elevation dependency of the zenith atmospheric delay. The elevation dependency is modeled by what are known as mapping functions. Improvements in modeling the zenith delay itself where achieved by computing the group refractivity using a procedure described by Ciddor [1996] and by including the non-hydrostatic (wet) zenith delay. Two color SLR can also be used to determine the zenith delay by measuring the dispersive delay of two laser pulses each at a different wavelength. By comparing the Mendes and Marini Murray models to this experimental technique, one is able to evaluate the accuracy of the two models. We have found errors between the two models when compared to two color SLR at the centimeter level, which increases significantly at 355 nm, indicating the need for an improvement of existing dispersion formulae.

[C1.165] About the calculation of the photon power

Owing to the pioneer works of Einstein and Planck at the beginning of the 20 century, we are able to calculate the energy of one photon today. With rapid growing meaning of the nanotechnologies and the development of the processes, which are based on the laser and solar power, the factor power will play a larger role in the future, however. The performance analysis and the determination of the efficiency makes a competent and safe control as well as the more economical use of complex plants and system processes possible. Usually the value of efficiency, which is important for technical and economic optimization is defined by the relationship between the supplied power and the won work. On which factors the power of the photon is dependent and how it changes quantitatively, is not clearly. From thermodynamics we know that the power can be determined by the temporal change of the energy. Hereby the following equation can be considered: P = \left| \fracdEdt \right| According to the world-famous formula of Planck and to the model of the photon, which was suggested in the applications [1, 2], the formula for the practical determination of the power of the light particle can be deduced. With the differentiation of the formula of Planck E = h \cdot f in the form \fracdEdt = h \cdot \fracdfdt as well as the use of the impulse equation [2, 3] with consideration of the rotation of the photon, the equation for the calculation of the power was derived. It resulted that the power can be represented in the following form: P = const \cdot f^2 The derivativing of this formula under appropriate boundary conditions will be entered more in detail during the meeting.

References 1. About the dualism of the light. S. Reissig, The 12th General Conference of the European Physical Society "Trends in Physics”, 2002 2. "About the nature of the photon. S. Reissig, www.efbr.de/de/publikationen/EFBR3. Bewegungsgleichung der Photonen. S. Reissig. www.efbr.de/de/publikationen/EFBR

[C1.166] THE PHOTON POWER AND STEFAN-BOLTZMANN RADIATION LAW

In [1], according to the world-famous formula of Planck and to the model of the photon, which was suggested in the applications [2, 3], the formula for the practical determination of the power of a light particle was derived: P = const \cdot f^2 = hf^2 (W). Of course, this theoretical result could be examined by an experiment. However, there is one possibility to test that formula on another way. The use of the relationship q = Q/A = \varepsilon P/A , the new formula for the photon power together with the estimation of the effective radiation area A leads to the following equation: q = const \cdot T^4 (W/m^2). This formula represents the well-known Stefan-Boltzmann radiation law, so that fact could be considered as a very proof confirmation of the derived equation of the photon power. The details of the theoretical procedure will be presented and discussed during the meeting. References 1. About the calculation of the photon power. S. Reissig, APS four corners meeting, Arizona, 2003 2. About the dualism of the light. S. Reissig, The 12th General Conference of the European Physical Society "Trends in Physics, Budapest, 2002 3. About the nature of the photon. S. Reissig, www.efbr.de/de/ publikationen/, 2003

[C1.167] Scale-Invariant Form of the Planck Law of Energy Distribution and its Connection to the Maxwell-Boltzmann Distribution

Scale-invariant form of the Planck law of energy distribution is introduced as \beginequation\labelE:first \frac\epsilon_\nuN_\nuV=\rho_\nud\nu=\frac8\pi m_\beta^2k \frac\nu^3d\nue^h\nu/kT-1 \endequation that at the chromodynamic scale \beta = \gamma for photon gas involves the gravitational mass of photon m_\gamma = (hk/c^3)^1/2. At a constant T, (1) describes the size spectrum of photon clusters of energy \epsilon_cj = N_\gamma jh\nu_\gamma j = N_\gamma j\epsilon_\gamma j where N_\gamma j is the number of photons in cluster j (energy level j) per unit volume and \epsilon_\gamma j is the energy of photon in cluster j. Similarly, at molecular-dynamic scale, Eq.(1) with m_\beta = M_\beta/N_o = M_\betam_\gammac^2 gives the spectrum of size of molecular clusters acting as composite bosons with energy \epsilon_cj = N_mjh\nu_mj = N_mj\epsilon_mj and matter wavelength and frequency given by h_\beta = p_\beta\lambda_\beta = h (de Broglie) and k_\beta = p_\beta\nu_\beta = k. Particles are suggested to oscillate in two directions (x^+, x^-) such that m_m < u^2 > = 2m_m < u^2_x^+ > = 3kT leading to calculated rms molecular speeds (1346, 336, 360, 300, 952, 287) m/s that are comparable with the observed velocity of sound (1286, 332, 337, 308, 972, 268) m/s for gases (H_2, O_2, N_2, Ar, He, CO_2) at s.t.p. as initially suspected by Newton.

[C1.168] Atonic Mechanics of H and He Spectra

We have created a new and simpler way to calculate atomic spectra than could be done with conventional quantum mechanics. Accordingly, we coin the term atonic mechanics. Spectra of hydrogen and helium are calculated. Atonic mechanics results are compared with NIST Atomic Spectra Database Levels Data He I taken from the NIST web site. Exact agreement is obtained, as we use an effective mass coefficient, m3, to account for three-body effects. The ground state (configuration 1s2 - term 1S) value of m3 is 0.9506109 where we expect three-body effects are strongest. The largest value of m3 is 1.0000868 (configuration 1s.5s - term 1S). As the outer electron energy further increases, m3 decreases monotonically to 0.9999242 where three-body effects diminish. This is for configuration 1s.15s - term 1S, the most energetic state that we considered. Although it is not done here, atonic mechanics may provide a way for modeling multi-body effects using atomic spectra.

[C1.169] Creating Voids by Annealing a-SiC:O:H Films Prepared by Plasma-enhanced Chemical Vapor Deposition

Hydrogenated amorphous silicon carbide (a-SiC:H) films were prepared by plasma-enhanced chemical vapor deposition from diethylsilane (C4H12Si) diluted in methane (CH4). The deposition conditions resulted in a highly unstable a-SiC:H film, which reacted with oxygen when exposed to air, forming Si-OH and H-OH bonds and Si-O networks as well. The Rutherford Back Scattering analysis shows 15incorporation. The Fourier transfom infra-red (FT-IR) measurement suggests the presence of a-SiC:O:H component and a-C:H moieties throughout the film. The films were then thermally annealed in vacuum at 450C to removed unstable C-H bonds and Si-OH and H-OH groups creating voids in the film. The removal of C-H, Si-OH and H-OH is evident from the FT-IR spectra. During the annealing process, the film also cross-links and formed a stable a-SiC:O:H film. After annealing, the dielectric constant of the films decreased from 4.2 to 2.1 suggesting the presence of voids/pores in the films.

[C1.170] Statistical Properties of Slowly Sheared Granular Materials

Slowly sheared granular materials occur in a broad range of phenomena, but the basic physics is still unclear. Flow often occurs in narrow shear bands of low density and large shear rate. Here, we describe recent results for both 3D and 2D shear experiments and for models of 2D Couette shear. The focus is on developing a statistical description, using the key feature of statistically steady states. In novel 3D experiments, a layer of material is subject to shearing from above, and from shaking from below. The latter feature allows an extra 'temperature'-like degree of freedom. In this system, we observe a transition to shear melting in the presence of vertical vibration, and we will present details of how this transition occurs. In the 2D experiments and simulations, we focus on the transfer of energy between kinetic and elastic modes. In the experiments, we show that elastic energy and elastic energy fluctuations can dominate those for kinetic modes. In the simulations, we pursue an extended granular temperature with both kinetic and elastic energy fluctuations. Interestingly, this extended temperature is in reasonable accord with temperature calculated from the fluctuation-dissipation relation.

[C1.171] Computational Plasma Physics

This abstract not available.

[C1.172] Hydrodynamic and Fokker-Planck simulations of electron transport in plasmas

Kinetic and hydrodynamic simulations of plasma dynamics are performed for different plasma regimes, with steep gradients. Temperatures ranged from 1 eV to 10 keV, densities from 10^14cm^-3 to 10^23cm^-3 and a variety of plasma materials were considered (Hydrogen, Beryllium, Carbon, Aluminum and Vanadium). The effect of laser heating of the plasma is analyzed, with laser pulse durations from 0.1 to 1 ns and intensities from 10^10 to 10^16 W/cm^2. The effect of the wave length (1.06, 0.53 and 0.35 \mu m) on absorption is also discussed. Limitations to usual hydrodynamic models such as nonlocal effects and non Maxwellian electron distribution function due to steep temperature gradients and strong laser heating are stressed and we show how our nonlocal model [1] can extend the hydrodynamic description to such regimes.

[1] F. Alouani Bibi and J.P. Matte, Phys. Rev. E \textbf66, 066414 (2002).

[C1.173] This abstract has been withdrawn

This abstract not available.

[C1.174] This abstract has been withdrawn

This abstract not available.

[C1.175] Multiscale Modeling

This abstract not available.

[C1.176] Direct Coupling of Discete and Continuum Diffusion

A framework to directly couple the discrete treatment of point defect diffusion, via the Kinetic Monte Carlo (KMC) method, with the continuum diffusion equation, via the finite element method (FEM), is presented. A domain decomposition approach is used to obtain solutions in the two different domains (KMC and FEM) and to connect the two simulations through the passing of information at the boundary. Information about the flux is supplied to the FEM problem from the KMC boundary whereas information about the concentration is supplied to the KMC problem from the FEM boundary. To avoid the time iterations required in a standard domain decomposition algorithm, which would be prohibitive for the KMC method, a modified domain decomposition algorithm is being developed whereby the system is evolved through suitably small timesteps. Preliminary results for several 2d diffusion problems are presented, with quantitative comparisons to full-scale KMC simulations.

[C1.177] Computational Fluid Dynamics

This abstract not available.

[C1.178] Numerical simulation of non-newtonian flows in journal bearings

We investigate the influence of rheological properties of inelastic and viscoelastic fluids in flows occurring in the annulus of eccentric cylinders, particularly in journal bearings. To compute these flows where vortex regions are encountered, the physical domain is split up into a finite number of sub-domains that are mapped into domains where open and closed streamlines are parallel and straight, by means of local mapping functions to be determined numerically. Such simplicity for the mapped streamlines makes it easy to handle time-dependent constitutive models in viscoelasticity. The results point out the role of shear-thinning properties and the influence of elasticity and underline the complex behavior of non-Newtonian fluids on the kinematics (velocities, vortex regions). The flow characteristics are notably highlighted by variations of the torque and the load on the inner cylinder versus the flow rate.

[C1.179] Electronic Structure

This abstract not available.

[C1.180] Pair State Analysis of the Hubbard Hamiltonian in One-Dimension

It can be shown that the exact energy E^\alpha of an N-electron system can be decomposed in the following manner: \begindisplaymath E^\alpha = \fracN(N - 1)2 \sum_a E_a^P \Gamma_aa^2\alpha \;\;\; \mbox\rmwhere \;\;\; \sum_a \Gamma_aa^2\alpha = 1. \enddisplaymath In this expression, E_a^P represents the a^th eigenvalue of the corresponding reduced two-particle Hamiltonian and \Gamma_aa^2\alpha denotes the expectation value of the two-particle density matrix evaluated in the pair state basis. We demonstrate this pair-state decomposition for the N_S-site one-dimensional Hubbard Hamiltonian evaluated using exact diagonalization and both fixed and periodic boundary conditions. Results are presented for various choices of N_S and N and for several values of the ratio of the Coulomb repulsion and electron hopping energies U/t.

[C1.181] The reduced density matrix method and the role of three-index representability conditions

The variational approach for electronic structure based on the two-body reduced density matrix is studied, incorporating two representability conditions beyond the previously used P, Q and G conditions. The additional conditions (called T1 and T2 here) are implicit in work of R. M. Erdahl and extend the well-known three-index diagonal conditions also known as the Weinhold-Wilson inequalities. Calculations of the ground state energy and the dipole moment are reported for 47 different systems, in each case using an STO-6G basis set and comparing with Hartree-Fock, SDCI, BD(T), CCSD(T) and full CI calculations [2]. It is found that the use of the T1 and T2 conditions gives a significant improvement over just the P, Q and G conditions, and provides in all cases that we have studied more accurate results than the other mentioned approximations.

[1] R. M. Erdahl, Int. J. Quantum Chem. 13, 697--718 (1978).

[2] Zhengji Zhao, Bastiaan J. Braams, Mituhiro Fukuda, Michael L. Overton and Jerome K. Percus: "The reduced density matrix method and the role of three-index representability conditions". Accepted for publication in Journal of Chemical Physics.

[C1.182] Classical and Quantum Molecular Dynamics

This abstract not available.

[C1.183] Computationally Designed Molecularly Imprinted Materials

Molecular dynamics simulations were carried out for different molecular systems in order to predict the binding affinities, binding energies, binding distances and the active site groups between the simulated molecular systems and different bio-ligands (theophylline and its derivatives), which have been designed and minimized using molecular simulation techniques. The first simulated molecular systems consisted of a ligand and functional monomer, such as methacrylic acid and its derivatives. For each pair of molecular systems, (10 monomers with a ligand and 10 monomers without a ligand) a total energy difference was calculated in order to estimate the binding energy between a ligand and the corresponding monomers. The analysis of the simulated functional monomers with ligands indicates that the functional group of monomers interacting with ligands tends to be either COOH or CH2=CH. The distances between the ligand and monomer, in the most stable cases as indicated above, are between 2.0-4.5 Å. The second simulated molecular systems consisted of a ligand and a polymer. The polymers were obtained from monomers that were simulated above. And similar to monomer study, for each pair of molecular systems, (polymer with a ligand and polymer without a ligand) a total energy difference was calculated in order to estimate the binding energy between ligand and the corresponding polymer. The binding distance between the active site of a polymer and a ligand will also be discussed.

[C1.184] Quantum Monte Carlo Method to Estimate the Exact Expectation Values of Non-differential Operators Using Approximate Wavefunctions

Our objective is to develop a Diffusion Monte Carlo (DMC) algorithm to estimate the exact expectation values of non-differential operators, such as polarizabilities and high-order hyperpolarizabilities, for isolated atoms and molecules: \langle \Phi_0|P_op| \Phi_0 \rangle.

The existing Ground State Distribution DMC (GSD DMC) algorithm which attempts this has a serious bias. On the other hand, the Pure DMC algorithm with minimal stochastic reconfiguration has a reduced bias, but the expectation values \langle \Phi_0|P_op| \Psi \rangle are contaminated by \Psi, an inputted, approximate wave function. We modified the latter algorithm to obtain the exact expectation values, while at the same time, eliminating the bias.

To compare the efficiency of GSD DMC and the modified Pure DMC algorithms we calculated simple properties of the H atom, such as various functions of coordinates and polarizabilities. Using two non-exact wavefunctions, one of moderate quality and the other very crude, in each case the results are within statistical error of the exact values.

[C1.185] Quantum Monte Carlo Study of Sulfur

We apply a recently developed quantum Monte Carlo (QMC) method (Shiwei Zhang, Henry Krakauer, Phys. Rev. Lett. 90). 136401 (2003). to calculate the atomization energy of sulfur molecule and the ionization energies of sulfur atom. The QMC method projects out the ground state by random walks in the space of Slater determinants, using auxiliary-fields to decouple the Coulomb interaction between electrons. A trial wave function |\Psi_T\rangle is used in the approximation to control the phase problem in QMC. We carry out Hartree-Fock (HF) and density functional theory (with the local density approximation (LDA)) calculations. The generated single Slater determinant wave functions are then used as |\Psi_T\rangle in QMC. The HF and LDA |\Psi_T\rangle's lead to atomization energies in agreement with each other and the experimental value.

[C1.186] Many Body

This abstract not available.

[C1.187] Can the eigenstates of a many-body Hamiltonian be represented exactly using a general two-body cluster expansion?

It has been conjectured that the exact ground-state wave function for an arbitrary two-body Hamiltonian in second-quantized, finite basis set, can be represented by a generalized coupled-cluster operator acting on an arbitrary initial trial function. In a way, the conjecture offered a solution to the infamous N-representability problem in quantum chemistry. However, we show that if the operator is required to be finite, the conjecture is false.

[C1.188] AC Conductance of a multi-probe conductor and the Generalized Fluctuations

We extend the work of Baranger and Stone^1 as well as Stone and Safer^2 by expressing the total current I_m through lead m in terms of the AC voltages V_n applied to the leads of a phase coherent multi-probe conductor in an arbitrary static magnetic field and an alternating electric field of frequency Ømega . Using linear response theory, we obtain the non-local response function \sigma (\vec x,\vec x'; Ømega ) in terms of the eigenfunctions of the unperturbed system as well as the retarded and advanced Green's functions. With the use of perturbation theory to perform impurity averaging, the conductance fluctuations (CF) in mesoscopic systems are evaluated at finite frequency. It is shown that the CF decrease monotonically as Ømega increases. Also, the frequency scale over which this decrease occurs is given in terms of the diffusion time for an electron to diffuse across the sample. We show that the universality of the CF at zero frequency is not preserved at finite frequency. We present numerical results for six leads attached to the faces of a 3D rectangular prism as well as four leads connected to a 2D sample. It is also shown that at finite frequency, the sample-to-sample CF have the same size as the fluctuations of a given sample as a function of frequency.

\beginenumerate \item H.U. Baranger and A.D. Stone, \textbfPhys. Rev. B, \textbf40, 8169 (1989) \item A.D. Stone andA. Safer, \textbfIBM Journal of Research and Development, \textbf32, 384 (1988) \endenumerate .

[C1.189] Phase Transitions and Strongly Correlated Electrons

This abstract not available.

[C1.190] The dHvA effect and transport properteis of Ce_xLa_1-xB_6

Ce_xLa_1-xB_6 exhibits a fascinating magnetic phase diagram as a function of x, magnetic field or temperature. We have studied the electronic properties via measurements of the dHvA effect and transport properties. At x=0.5, the dHvA signal has been successfully observed down to 10T and the effective mass is found to amount to 10m_0, indicating that a coherent heavy fermion state is formed. The effective mass increases with decreasing field and when the value of the effective mass is extrapolated to lower fields it appears to diverge around 2T. Correspondingly, the A coefficient of T^2 term in the resistivity increases with decreasing field and diverges at 1.1T. With decreasing the field further, the temperature dependence of resistivity starts to deviate from the T^2 dependence significantly, showing that the Fermi liquid ground state is no longer stable at lower fields. We will report these anomalous electronic properties including the Fermi surface topology at various x and discuss their origins.

[C1.191] Electrical and Thermal Transport in the Ruthenate Bi_3Ru_3O_11

Ruthenate Bi_3Ru_3O_11 consists of a three-dimentional network of edge-sharing and corner sharing RuO_6 octahedral. The interaction between nearly localized state centered on Ru-Ru bonds and delocalized state derived from Ru-O-Ru bonds is analogous to that between f electrons and s electrons in heavy-fermion system. In our polycrystalline sample, the resistivity, \rho, is metallic with residual resistivity ratio(RRR) around 13. Above 50K, the Hall resistivity, \rho_xy, is strictly linear in field, H. And the Hall coefficient changes sign at around 110K, indicating compensated electronic ground state. Below 50K, \rho_xy vs H rapidly acquires pronounced curvature. The field-dependent Hall coefficient, R_H(H), is linear in H at high field, and it deviates downwards for H < H_Z \equiv k_BT/g\mu_B. These features suggest that the field(H) changes the relative populations of electron and hole via Zeeman coupling to the spins of the conduction carriers. Below 25K, we also observed huge change in thermopower, S, with H. At 5K, S(H)/S(0) equals to 3 and 1.5 at 12 Tesla with H perpendicular and parallel, respectively, to the direction of temperature gradient. We suspect that band structure effect due to nontrivial Fermi surface in this system could be one possible mechanism.

[C1.192] Specific heat and materials analysis on U_1-xTh_xPt_3 for 0 \le x \le 0.05

UPt_3 exhibits anomalous, possibly time-fluctuating antiferromagnetic (AFM) order below 6K that is only detectable via neutron and x-ray scattering. Th substitution induces conventional AFM order with the same magnetic structure and an ordering temperature T_N \le 6 K. Recent \muSR studies on U_1-xTh_xPt_3 for 0 \le x \le 0.05 showed that the transition from the anomalous into conventional antiferromagnetic state was very broad (Graf et al., Phys. Rev. B 68,in press), indicative of a crossover behavior. X-ray diffraction and high-resolution transmission electron microscopy show no evidence for chemical or material inhomogeneity. Nonetheless, specific heat measurements corroborate the \muSR measurements and show signs of an increase near 6K for x \ge 0.01. This supports the conjecture that Th impurities slow down the fluctuating AFM, rendering them observable on the timescale of thermodynamic measurements.

[C1.193] Specific heat of U(Pt_1-xPd_x)_3 for 0 \le x \le 0.10

We have studied the specific heat of U(Pt_1-xPd_x)_3 for 0 \le x \le 0.10 to search for signs of a proposed antiferromagnetic (AFM) quantum critical point near x_c = 0.006 (de Visser et al., Phys. Rev. Lett. 85, 3005 (2000)). We find that C/T has a contribution which increases logarithmically with decreasing temperature at low temperatures, and the magnitude of this contribution increases monotonically with increasing Pd content over the entire range studied. Thus, we find no evidence for a QCP near x_c in the investigated temperature range; similar results were found from high precision cantilever magnetometry measurements. We discuss the possibility that the observation of a crossover from the anomalous time-fluctuating AFM present in pure UPt_3 to conventional AFM is dependent on the timescale of the measuring probe.

[C1.194] Renaormalization of the Anderson model: an alternative approach to heavy Fermion behavior

A recently developed projector-based renormalization method (PRM) for many-particle Hamiltonians is applied to the periodic Anderson model (PAM) with the aim to describe heavy Fermion behavior. In this method high-energetic excitation operators instead of high energetic states are eliminated. We arrive at an effective Hamiltonian for a quasi-free system which consists of two heavy-quasiparticle bands. In contrast to the usual slave boson mean-field (SB) treatment one of the bands describes a subsystem of renormalized but still correlated f electrons whereas the second band stands for renormalized conduction electrons. The resulting renormalization equations for the parameters of the Hamiltonian are valid for large as well as small degeneracy \nu_f of the angular momentum. An expansion in 1/\nu_f is avoided.

[C1.195] A Green's Function Calculation of the dHvA Effective Mass in a Heavy Fermion Superconductor

We calculate the de Haas-van Alphen effective mass for a heavy fermion material in the superconducting vortex state. We use the field theoretic method of Wasserman and Springford, which is capable of incorporating the many-body interactions responsible for heaviness and superconductivity in these materials. The thermodynamic grand potential is calculated from an imaginary energy Green's matrix. From the potential we obtain the effective mass as a function of magnetic field. This method makes explicit the many body effects contained in the measurements of a dHvA experiment.

[C1.196] Phase diagram and magnetic response in the doped two-leg extended Hubbard ladder

We investigate the ground-state properties and the temperature dependence of the spin susceptibility and the NMR relaxation rate in the doped two-leg Hubbard ladder with on-site and nearest-neighbor Coulomb repulsions, by using weak-coupling g-ology and the bosonization method. In the ground state, we have shown that, by increasing nearest-neighbor repulsions and/or decreasing the doping rate, the system exhibits a quantum phase transition where the dominant fluctuation of the singlet d-wave-like superconducting state changes into that of the coexisting state of charge-density-wave and p-density-wave. At finite temperatures, we have shown that, near the critical point, the spin susceptibility shows paramagnetic temperature dependence and the NMR relaxation rate exhibits anomalous power-law behavior at low temperature. The relevance to the experiments on Sr_14-xCa_xCu_24O_41 is also discussed.

[C1.197] Lorentz Microscopy Study in Cobaltites

The Pr_1-xSr_xCoO_3 (0.3¥leq x¥leq 0.5) series exhibit unusual magnetic behavior not found in other rare earth cobaltites. The dc magnetization exhibits an anomalous downward step in low fields (H< 0.01 T) at a temperature (T_A¥ symbol126120 K) much lower than the ferromagnetic transition (T_C~¥symbol126230 K). Lorentz electron microscopy was used to investigate this unusual magnetic behavior around T_A in Pr_0.5Sr_0.5CoO_3. The specimen is in a mag netic field-free environment. Ferromagnetic domain walls started to appear just below T_C. When further cooling down, the magnetic domain walls disappeared below 90 K. The magnetization patterns obtained by the so-called transport of intensity equatio n method indicate that ferromagnetic component decreases below 90 K. It is suggested that such behavior is possibly due to a temperature induced spin-state transition. We will discuss magnetic phase diagram of Pr_1-xSr_xCoO_3 (0.3¥leq x¥le q 0.5) and compare with other cobaltites.

[C1.198] Anion ordering effects on the quantum oscillations in Q1D Bechgaard salts

Among the Bechgaard salts, (TMTSF)_2ClO_4 exhibits unique features in the so-called rapid oscillations because the anion ordering along the b-axis at 24 K creates an additional pair of Fermi surface. While the oscillations in the metallic phase are due to the Stark interference effect, the existence of two oscillations with the same frequency but with opposite phase in the FISDW phases is explained by occurrence of the two different SDW nestings between two pairs of FS. The anion ordering can be suppressed by either pressure above 4 kbar or thermal quenching near 24 K. We investigated how hydrostatic pressure below and above 4 kbar affects on the rapid oscillations in magnetoresistance measurements up to 45 T on (TMTSF)_2ClO_4 with different cooling rate. While new oscillations appear above 5 kbar, the frequency of oscillations becomes double in thermally quenched state.

[C1.199] Temperature and Pressure dependence of the Raman modes in Barium Titanate Films

The integration of ferroelectric thin films with semiconductors substrates are of interest for electronics and optoelectronics due to their strong electro-optic coefficients and switchable polarization. We report here Raman studies on \sim 1 \mum thick barium titanate (BTO) films grown by pulsed laser deposition on GaAs and Si substrates with MgO and Pt buffer layers, respectively. Room temperature Raman spectra recorded on these films with the incident and scattered light polarized perpendicular to each other, show clearly a sharp peak at 308 cm^-1, in addition to the Raman peaks at 180, 520, and 715 cm^-1. The appearance of the E (TO+LO) mode at 308 cm^-1 confirms the presence of the tetragonal ferroelectric phase in these BTO films. We will report the high temperature (RT to 593 K) and high pressure (ambient to 4 GPa) dependence of the Raman modes in the BTO/MgO/GaAs film and compare the results to those from polycrystalline BTO powder. The work at U of M is supported by NSF grant ECS-0238108.

[C1.200] Insulating Phases of Spin-One Bosons in Optical Lattices

We consider insulating phases of cold spin-1 bosons with antiferromagnetic interactions, such as ^23Na, in optical lattices. We show that spin exchange interactions give rise to several distinct phases, which differ in their spin correlations. In two and three dimensional lattices, insulating phases with an odd number of particles per site are always nematic. For insulating states with an even number of particles per site, there is always a spin singlet phase, and there may also be a first order transition into the nematic phase. In a magnetic field all insulating states undergo a series of phase transitions between spin gapped phases with quantized magnetizations and phases with canted nematic order, in which magnetization can vary continuously. We discuss how such magnetization plateaus can be used to demonstrate a correlated nature of the insulating states in Stern-Gerlach type experiments.

[C1.201] Ternary polymer blends in bulk and thin films: a light scattering and AFM study

We have investigated and compared the behaviour of two ternary polymer blends: 1) polystyrene, poly(methyl methacrylate) and their block copolymer, and 2) polyoctylstyrene, poly(butyl methacrylate) and their block copolymer. The main goal was to investigate the formation of a bicontinuous microemulsion phase as a function of temperature and composition. Static and dynamic light scattering was used to study the correlation length of composition fluctuations in these blends. Thin films of these blends were cast from toluene solutions and investigated by atomic force microscopy. Under certain conditions, a regular structure has been produced representing the surface of a bicontinuous microemulsion with a characteristic dimension of about 200 nm. We acknowledge support of the Grant Agency of the Academy of Sciences of the Czech Republic (1050902).

[C1.202] Dynamics of Block Copolymer Adsorption

The adsorption of an A-B diblock copolymer to the interface between A and B homopolymers was studied, where A is saturated polybutadiene with 90% 1,2 addition and B is saturated polybutadiene with 64% 1,2 addition. A thin film of a blend of polymer A and the A-B diblock copolymer was placed on a thin film of pure polymer B to create a bilayer. Contrast between the polymers was achieved by deuterating one of the components, and the interfacial profile was measured with dynamic secondary ion mass spectroscopy. The adsorption was studied using various concentrations of the diblock copolymer and with different molecular weights of the three polymers. Dynamics for adsorption were observed in one of the systems studied, and more dynamic measurements are expected.

[C1.203] Localization of polaritons in disordered polar media

The main goal of this work is developing a simple theory of polariton propagation in disordered polar media. We have applied the generalized Born-Huang theory to find effective equations for polaritons in inhomogeneous media. In our approach we have considered dielectric functions and phonon-photon coupling parameter as local characteristics of media (random functions). It is shown that the problem of polariton localization may be formulated as the Anderson model with non-symmetric matrix, which describes the coupled phonon-photon modes. We have performed the exact diagonalization of the non-symmetric matrix for two-dimensional systems to find eigenfunctions and eigenvalues near the polaritonic gap. The density of states and some characteristics of localization have been calculated. The investigation of the density of states near the polariton "bottleneck" was shown that when the disorder in the medium is increased, the localized modes appear inside of the polaritonic gap, and then these states form tails inside of the gap. With the increasing of the magnitude of disorder the tails in the gap overlap and the collapse of the gap is occurred. As the strength of disorder is increased the localization is observed to be enhanced over broad energy ranges. To test localization we have investigated a generalized participation ratio, bathed on coupled phonon-photon eigenstates. In addition, the nearest-neighbor level statistics have been investigated. We found different behavior for the level statistics of the upper and lower polaritonic excitations: if the level distribution for the upper branch is a typical Wigner function, then the level distribution for the lower branch has a long tail for the large nearest-neighbor energy intervals. We found a link between this behavior and the peck of density states near the edge of the lower polaritonic band.

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

[C1.203] Localization of polaritons in disordered polar media

The main goal of this work is developing a simple theory of polariton propagation in disordered polar media. We have applied the generalized Born-Huang theory to find effective equations for polaritons in inhomogeneous media. In our approach we have considered dielectric functions and phonon-photon coupling parameter as local characteristics of media (random functions). It is shown that the problem of polariton localization may be formulated as the Anderson model with non-symmetric matrix, which describes the coupled phonon-photon modes. We have performed the exact diagonalization of the non-symmetric matrix for two-dimensional systems to find eigenfunctions and eigenvalues near the polaritonic gap. The density of states and some characteristics of localization have been calculated. The investigation of the density of states near the polariton "bottleneck" was shown that when the disorder in the medium is increased, the localized modes appear inside of the polaritonic gap, and then these states form tails inside of the gap. With the increasing of the magnitude of disorder the tails in the gap overlap and the collapse of the gap is occurred. As the strength of disorder is increased the localization is observed to be enhanced over broad energy ranges. To test localization we have investigated a generalized participation ratio, bathed on coupled phonon-photon eigenstates. In addition, the nearest-neighbor level statistics have been investigated. We found different behavior for the level statistics of the upper and lower polaritonic excitations: if the level distribution for the upper branch is a typical Wigner function, then the level distribution for the lower branch has a long tail for the large nearest-neighbor energy intervals. We found a link between this behavior and the peck of density states near the edge of the lower polaritonic band.

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

[C1.205] Deterministic transport of single ions in a linear Paul trap

Several recent proposed entanglement schemes for ions do not require the ions to be in specific motional states, removing the need for precise temperature control of the ions in the traps. However, all such schemes are limited to two-ion interactions. Quantum computers relying on such schemes would therefore need to be modular, and would require some or all of the ions involved in large-scale computations to be transported from place to place. In ultra-high vacuum conditions, ions can be cooled and stored in linear Paul traps for hours or even days at a time without losing their qubit state. The challenge is to move these ions deterministically without introducing any unknown phase shifts in their internal states. Schemes for ion transport involving laser-mediated forces are not considered favorable because of the likelihood of disrupting the internal state of the ions. We have developed a model for the transport of ions using quasi-static offset fields in a linear Paul trap. The time scale for this transport is limited by the secular frequency of the Paul trap. Issues related to the uncertainty in phase of the ion will be examined.

[C1.206] Optimization of Luminescent Solar Concentrators Using a Triple Dye System

A possible alternative to the expensive photovoltaic cell (PVC) is the Luminescent Solar Concentrator (LSC). A LSC is a flat, translucent plate that absorbs sunlight through embedded, highly fluorescent chromophores. About 74 percent of the fluorescence is concentrated via total internal reflection at the edges of the LSC where PVCs convert it to electricity. Cost savings are realized through the reduced area of PVC material. A typical LSC employs a single organic dye, limiting the amount of light absorbed. A multiple dye LSC absorbs more light resulting in greater optical efficiency. We report on the performance of LSCs made with one, two, or three dyes in a 20 micron thick polymer layer on a glass substrate. By varying the relative concentrations of the dyes contained within the film, fluorescence resonance energy transfer between the dyes was optimized. The triple dye LSC showed a 36 percent increase in power over that of our best single dye LSC.

[C1.207] Properties of Fe-Zr-O films.

In this communication the transport and magnetic properties of Fe-Zr-O, high resistive soft magnetic thin films, deposited on alumina (Al_2O_3) substrate and ZZT (Zr-Ti-Sn) substrate by PVD (magnetron sputtering) will be presented. The samples were characterized using x-ray diffraction (XRD) and Scanning Electron Micorscopy (SEM). In the SEM granules with size as large as 10\mu are seen. The normalized resistance shows semiconducting behavior near high temperatures, followed by a broad maximum near 50K. This broad maximum is attributed with feromagentic order of the Fe atoms.

Part C of program listing