bluuebunny/crossref_metadata_2025_split huggingface dataset:
Nonlinear Optical Properties of Organic Photorefractive Polymers
Authors: Moerner W. E. , Walsh C. A. , Silence S. M. , Twieg R. J. , Matray T. J. , Scott J. C. , Lee V. Y. , Miller R. D. , Hache F. , Burland D. M. , Bjorklund G. C. 
Published: March 2011

ABSTRACTThis paper describes the photorefractive properties of a new and growing class of materials exhibiting the effect, doped nonlinear organic polymers. We show directly using a PMMA-based copolymer with a pendant nonlinear nitroaminotolane chromophore doped with a charge transport agent that the presence of photoconductivity and optical nonlinearity are only necessary, but not sufficient to guarantee that a given materials system will yield measurable photorefractive gratings, rather than gratings due to some other process such as photochromism. To prove photorefractivity unequivocally, direct measurement of the spatial phase shift between the intensity pattern and the index modulation is best, and we summarize a convenient way to do this using two-beam coupling and sample translation. In addition to the photorefractive epoxy materials such as bisA-NPDA:DEH reported earlier (Phys. Rev. Lett. 66, 1846 (1991); Proc. SPIE1560, 278 (1992)), a new PMMA-based copolymer with pendant p-nitroaniline chromophores doped with DEH also shows photorefractive grating formation, with writing speed 100 times higher than that for the epoxy material.
Photoconductivity of Photorefractive Polymers
Authors: Scott J. C. , Pautmeier L. Th. , Moerner W. E. , Walsh C. A. , Silence S. M. , Matray T. J. , Twieg R. J. 
Published: March 2011

ABSTRACTThe photorefractive effect has been recently observed by holographic grating formation in optically non-linear polymers molecularly doped with charge transport agents. Grating formation can be understood as a four-step process, the first three of which dictate the photoconductive response: charge generation, mobility and trapping. The fourth step is modulation of the refractive index by the resulting space-charge field, via the electro-optic effect. We present the results of photoconductivity experiments to determine charge generation efficiency, carrier mobility and the kinetics of recombination and trapping, focussing primarily on the epoxy polymer bisphenol-A-diglycidylether 4-nitro-1, 2-phenylenediaminc (bisA-NPDA) doped with the hole transport agent, diethylaminobenzaldehyde-diphenylhydrazone (DEH). The electric field dependence of the generation efficiency and mobility differ in detail from results on other molecularly doped polymers.
Photorefractive, Electro-Optical and Nonlinear Optical Properties of Conjugated Polymers
Authors: Peyghambarian N. , Tamura K. , Kippelen B. , Kawabe Y. , Jarka F. , Mazumdar S. , Guo D. D. , Hall H. K. , Padias A. B. 
Published: March 2011

ABSTRACTWe present experimental and theoretical results on electro-optical properties of some polymeric films. Specifically, we report on our measurements regarding a new, completely polymeric and potentially photorefractive material with a large electro-optic coefficient and photoconductivity. Furthermore, we summarize our investigations of electro-absorption in a DCH polydiacetylene where the important contributions of continuum threshold on the nonlinear and electro-optical properties of conjugated polymers are emphasized.
Introduction to the Theory of Space-Charge Grating Formation in Photoconducting Polymers
Authors: Schildkraut Jay S. 
Published: March 2011

ABSTRACTPhotoconducting electrooptic polymers are a new class of photorefractive material. Most applications of photorefractive materials require the formation of a space-charge grating. The formation of space-charge gratings in photorefractive semiconductors has been studied extensively. We consider the formation of photorefractive gratings in a polymer.
New Amorphous and Crystalline Complexes of Conjugated Aromatic Schiff Base Polymers
Authors: Yang Chen-Jen , Jenekhe Samson A. 
Published: March 2011

ABSTRACTNew soluble amorphous and crystalline complexes of conjugated aromatic Schiff base polymers with diarylphosphates have been prepared and their molecular and electronic structures and morphology characterized by FTIR spectra, electronic absorption spectra, differential scanning calorimetry and x-ray diffraction. The diphenyl phosphate (DPP) or di-m-cresyl phosphate (DCP) complexes of the conjugated polyimines have electronic structures and optical properties that are dramatically different from the pure polymers due to the formation of polyiminium ions on complexation. At diarylphosphate : imine ratio equal to 0.50, amorphous materials are obtained whereas highly crystalline complexes are obtained at the stoichiometric ratio. The potential of complexation in modulating and enhancing the thirdorder nonlinear optical properties of this class of polymers is demonstrated.
A Novel Poling Process for Polymeric Thin Films Exhibiting Second Harmonic Generation
Authors: Barry Stephen E. , Soane David S. 
Published: March 2011

ABSTRACTCarbon dioxide is used to induce glass transition in amorphous polymer films, allowing efficient alignment of chromophores with an applied electric field. The noncentrosymmetric films thus produced are capable of second harmonic generation (SHG). This method has advantages over previously investigated poling schemes, including poling at ambient temperatures and use of high glass transition temperature polymers. Several polymeric systems have been studied. The chromophrores were either dissolved in the polymer, attached as a side chain, or incorporated into the backbone of the polymer. The SHG of the films was observed as a function temperature. Of the systems studied, polyether sulfone retains SHG capability to the highest temperature. Two different systems had the greatest retention of SHG up to the glass htansition temperature. They were Poly((4-N-ethylene-N-ethylamino)- rz-cyanocinnamate), a polymer which has the chromophore incorporated in the backbone, and 4- (dimethylamino)-4'-(dimesitylboro)azobenzene, a host-guest system with a relatively large chromophore. These and other systems will be discussed.
Electrical Fatigue in Organic Layered Photoconductors
Authors: Pacansky J. , Waltman R. J. 
Published: March 2011

ABSTRACTThe relevance of photochemistry in the electrical fatigue of organic layered photoconductors is discussed. A hole transport molecule DEH undergoes a photocyclization reaction in the charge transport layer to an indazole derivative, causing residual surface charges to persist during light decay. A dye chlorodiane blue, in the presence of DEH, initiates photochemistry at the hole transport/carrier generation interface resulting in chemical consumption of the dye. An activation energy of 15 – 20 kcal/mol is reported for the dye bleaching reaction.
AZO Polymers for Reversible Optical Storage
Authors: Natansohn A. , Rochon P. , Gosselin J. , Xie S. 
Published: March 2011

ABSTRACTAmorphous high-Tg polymers films containing electron-donor-electronacceptor substituted azobenzene groups can be used as reversible optical storage materials. Optical information can be “written” on the film with a polarized argon laser beam and “read” with a low power HeNe laser. Erasing can be performed with a circularly polarized writing beam. A significant number of writing/erasing cycles can be performed on the same spot. Potential applications in optical memory, holographic storage, waveguides and second harmonic generation are discussed.
Photoinduced Charge Transfer Studies in Bolaamphiphile-Gramicidin-Porphyrin Membranes
Authors: Thompson David H. , Kim J.-M. 
Published: March 2011

ABSTRACTSynthetic ether-linked bolaform amphiphile vesicles and a novel gramicidin-porphyrin “diad” have been prepared. Photoinduced electron transfer properties of the diad were compared in bilayer (dihexadecylphosphate, DHP) and monolayer (2,2′-0-didecyl-1,1′-0-eicosamethylene-racdiglycero- 3,3′-diphosphoric acid, PS20) membrane vesicles with dithiothreitol sacrificial donor and methyl viologen electron acceptor present on both vesicle membrane surfaces. Although the rates of methyl viologen photoreduction varied depending on the mode of diad orientation within DHP bilayer membranes, photoreduction rates were not orientation-dependent in bolaform membrane vesicles containing the gramicidinporphyrin diad. The relevance of these results on vectorial electron transfer processes in closed membrane systems is briefly discussed.
Estimates of Binding Energies in Complex Crystal Structures
Authors: Jinlong Yang , Kelin Wang , Casula F. , Mula G. 
Published: March 2011

AbstractA parameter-free technique already proposed by the authors to estimate the binding energy of elementary crystals is here extended to more complex crystal structures. Test calculations are presented here for several families of semiconductors of technological interest, such as XAs (X = Al, Ga, In), InX (X = P, As, Sb) and MgX (X = 0, S, Se). The accuracy of our predictions turns out to be comparable with that of previous results obtained within the local density approximation. The computational advantages of the method will be also discussed.
An Atomistic Computer Simulation of Crack Extension in Cubic Silicon Carbide
Authors: Sawamura Akitaka , Watanabe Yoichi , Yamamoto Ryoichi 
Published: March 2011

AbstructAn atomistic computer simulation of mode I crack extension in cubic silicon carbide has been performed using a realistic many–body interatomic potential computed by Tersoff. The crack front is parallel to the [110] direction and the crack plane lies in the (111) plane. The stable crack tip configurations were calculated and the effective stress intensity factor and the effective crack tip position were evaluated in the relaxed atomic configuration by the least-square method. The crack was stable over a wide range of the stress intensity factors from 0. 6KG to 3. 4KG, where KG is the Griffith critical stress intensity factor. At 3.5KG an interatomic bond near the tip across the (001) plane ruptured and the crack advanced. When the crack is stable, the effective K is larger than the given K by nearly 0. 2KG to 0.4KG. Crack tip process was also simulated over a range of temperatures. At 1000K. secondary cracks were nucleated and grew like voids around the main crack, and thus the main crack was blunted.
Tight-Binding Lmto Approach to the Electronic Structure and Atomic Configuration in Extended Defects in Metals
Authors: ŠOB M. , Vitek V. , Oh Y. 
Published: March 2011

AbstractA new quantum-mechanical method capable of determining atomic configurations of extended defects has been developed. The Hamiltonian is constructed using the first-principles tight-binding linear muffin-tin orbital method in the atomic-sphere approximation. A semiempirical correction is employed to describe the effect of electrons in the interstitial region and the repulsive part of the total energy is described by a pair potential. The forces on atoms are calculated by differentiating the corresponding energy terms with respect to atomic positions. The equilibriun configuration is then found by minimizing the total energy. In this approach, the electronic and chemical aspects of defect structures can be accounted for more adequately than when using central-force pair or many-body potentials. In particular, the angular dependence of interatomic forces, which is important in transition metals with unfilled d-bands, is described correctly within the present quantum-mechanical treatment.
Cluster Molecular Dynamics on Massively Parallel Computers
Authors: Nelson K. M. , Smith S. T. , Wille L. T. 
Published: March 2011

AbstractWe report the results of computer simulations of phase transitions in noble-gas clusters. The calculations were performed on a MasPar MP-l massively parallel computer with 8,192 processing elements (PE's). We discuss the efficient implementation of molecular dynamics algorithms for small clusters on this type of architecture. The simulations are based on a classical Lennard-Jones pair potential and follow the temporal evolution of the system by numerically integrating Newton's equations of motion using the Gear algorithm. Because the number of particles is much smaller than the number of PE's, optimal partitioning of the processing element array is an essential and non-trivial task.
Dynamics of Silver Dimer Deposition on Platinum Surfaces
Authors: Blandin P. , Massobrio C. , Buttet J. 
Published: March 2011

AbstractWe present molecular dynamics results on the diffusion properties of Ag monomers and dimers on the (111) surface of Pt. In particular we focus on the behavior of dimers upon collision on the surface with impact energies of 0.5eV and 5eV. We found that the dimer has the largest probability of being found stable on the surface when the temperature is in the range 150K<T<300K, while at T=OK a metastable configuration featuring monomers and dimers is likely to form.
Monte Carlo Simulation of Gas Phase Particle Formation and Sintering
Authors: Akhtar M. Kamal , Pratsinis S. E. , Lipscomb G. G. 
Published: March 2011

AbstractA Monte Carlo model has been developed to describe the gas phase formation and sintering of nanoclusters. Sintering was incorporated into the model by modifying Kadanoff's algorithm [1] for random particle walks on the surface of the cluster. The effect of restructuring and sintering on cluster-cluster aggregation have been investigated via 2d simulations. In the initial stages the sintering process results in clusters which are compact on small length scales. As time progresses and the clusters become larger, the sintering process slows down and the fractal dimension of the clusters is decreased. The model shows the effect of time and temperature on the specific surface area and size distribution of clusters.
Modelling Growth Morphologies on Different Length Scales
Authors: Iwan J. , Alexander D. , Xiao R.-F. , Rosenberger F. 
Published: March 2011

AbstractMicroscopic morphologies of monocomponent and binary solids growing from melts and vapors are simulated with a Monte Carlo model that accounts for bulk diffusion, interface attachment and detachment kinetics and surface diffusion. The interplay between transport and interface kinetics on morphologies and its effect on microstructures including lamellar spacing, tilted lamellar and oscillatory structures is investigated. An important aspect of these models is the length scale of the simulation.
Mathematical Model of the Bridgman-Stockbarger Method to Growth Semiconductor Single Crystals
Authors: Vega E. , Muiñiz G. , Rabago F. 
Published: March 2011

AbstractA two dimensional equation has been solved which represents the heat transfer equation for the growth of single crystals system called Bridgman- Stockbarger method. Two variations were analyzed with and without an insulation between heater and cooler. System without an insulation shows stability problems because it's directly affected by the boundary between the cooler and heater region, in this case we obtained a discontinuity in this point. System with an insulation shows higher stability.
Surface Sputtering of Ag{100} by KeV Particle Bombardment
Authors: Chang Che-Chen 
Published: March 2011

AbstractThe atoms emitted from the single-crystal surface due to keV particle bombardment have been characterized using molecular dynamics to simulate the energy dissipation process. The model system in the calculation utilizes a Ag(100) microcrystallite of about 2000 atoms which is bombarded by as many as 1600 incident Ar atoms of 2-keV energy. The surface order is found to be preserved to a certain extent during the bombardment of static particle beams. A preferred direction of ejection is observed for the lower-kinetic-energy atoms (< I eV) sputtered from the second surface layer. Most of these atoms which take off late in the collision cascade originate from positions on the surface within three to four lattice spacings from the point of impact. The ejecting atoms are confined by the top layer atoms which are still located close to their lattice points when the collision cascade subsides. In addition, the angular pattern of ejection changes slightly as the emission energy of detection is varied. We found that the angular pattern of ejection did not vary with the emission energy in the low energy regime, in which the surface structure may be better determined.
Effect of Structural Features on the Statistical Correlation of Dipole Moments on the End-to-End Distance of Polymer Chains
Authors: Galiatsatos Vassilios 
Published: March 2011

AbstractA recently developed computational methodology allows the quantitative study of the correlation between the end-to-end distance of a polymer chain and its dipole moment. This paper focuses on the further analysis of this correlation and aims in identifying the structural characteristics of the polymer chain that are responsible for the observed behavior of the correlation. We study chains in the independent rotation approximation with symmetric rotational potentials. We focus on two different orientations of the bond dipole moment vector : 010 and 001 (the bond length vector's orientation is [100]).
A Percolation Model for Elastic Softening in Intermetallic Compounds During Solid-State Amorphization
Authors: Massobrio Carlo , Pontikis Vassilis 
Published: March 2011

AbstractBy using isobaric-isothermal molecular dynamics and an n-body effective potential, we show that a dramatic elastic softening precedes the amorphization of NiZr2 occurring on chemically disordering the alloy. Above a critical level of chemical disorder, the shear elastic constant of the alloy increases suddenly up to a value comparable to the one of the amorphous solid obtained by quenching the liquid. This phenomenon occurs at the percolation threshold of the anelastically distorted regions surrounding the antisite defects. The percolation model describes satisfactorily experimental findings concerning the elastic softening and the loss of crystalline order in intermetallic compounds induced by irradiation or hydrogenation.
Entropy of Hydrophobic Hydration: A New Statistical Mechanical Formulation
Authors: Lazaridis Themis , Paulaitis Michael E. 
Published: March 2011

AbstractA statistical mechanical formulation is presented for the entropy of solution of simple molecules in water. The formulation is based on the Green-Wallace expansion for the entropy in terms of multiparticle correlation functions, which is derived here for rigid polyatomic fluids and for mixtures. With a factorization assumption for the solute-water correlation function we have been able to separate the translational and orientational contributions to the entropy of solution. This approach is applied to an infinitely dilute solution of methane in water. The required correlation functions are obtained by Monte Carlo simulation. The orientational contribution, which is due directly to the orientational asymmetry of water-water interactions, is found to be comparable to the translational contribution. We find that the large entropies and heat capacities of hydrophobic hydration can be accounted for by solute-water correlations alone and that large perturbations in water structure are not required to explain hydrophobic behavior.
A New Parametric Method for the Analysis of Ordering Configurations in Binary Alloys
Authors: Staley T.W. , Matyi R.J. 
Published: March 2011

AbstractIn ordering alloy systems, the overall long-range order parameter does not distinguish the degree to which the component structures are delocalized for different configurations of equal randomness. We define a new parameter, which is sensitive to such differences, by considering the short-range order parameters as a set of statistical moments for geometric variation in the crystal. A computer model has been developed which uses this parameter to analyze finite alloy systems for configurational preferences by a Monte Carlo method. Initial studies have established the parametric range as a function of LRO and nonstoichiometry. Qualitative results correspond well to predictions for ideal systems.
The Fast Multipole Method in Canonical Ensemble Dynamics on Massively Parallel Computers
Authors: Lustig Steven R. , Cristy J.J. , Pensak D.A. 
Published: March 2011

AbstractThe fast multipole method (FMM) is implemented in canonical ensemble particle simulations to compute non-bonded interactions efficiently with explicit error control. Multipole and local expansions have been derived to implement the FMM efficiently in Cartesian coordinates for soft-sphere (inverse power law), Lennard- Jones, Morse and Yukawa potential functions. Significant reductions in execution times have been achieved with respect to the direct method. For a given number, N, of particles the execution times of the direct method scale asO(N2). The FMM execution times scale asO(N) on sequential workstations and vector processors and asymptotically0(logN) on massively parallel computers. Connection Machine CM-2 and WAVETRACER-DTC parallel FMM implementations execute faster than the Cray-YMP vectorized FMM for ensemble sizes larger than 28k and 35k, respectively. For 256k particle ensembles the CM-2 parallel FMM is 12 times faster than the Cray-YMP vectorized direct method and 2.2 times faster than the vectorized FMM. For 256k particle ensembles the WAVETRACER-DTC parallel FMM is 33 times faster than the Cray-YMP vectorized direct method.
Cavities in He-Implanted Si: “Internal” Surface Science
Authors: Follstaedt D. M. , Myers S. M. , Stein H. J. 
Published: March 2011

ABSTRACTThe concept of using internal cavities in semiconductors for surface studies is presented. The microstructures of He-implanted (001) Si are characterized with [110] cross-section TEM, which shows that internal areas 5–7 times that of the specimen front surface are achieved with 1×1017 He/cm2 implanted at 30 keV and annealed at 700 or 800°C. Examples using internal cavities to determine surface bond strengths of other elements adsorbed on Si are indicated. Facets on the cavities are used to examine the equilibrium crystal shape of Si and to measure the ratios of the surface free energies of the observed planes. The {111} planes have the lowest energy, and those of {001} and {110} are 1.09(7) and 1.07(3) times higher, respectively. We also find cavities in He-implanted Ge after annealing that can be used for similar studies.
Influence of Electric Field on the Formation of Neutron, Electron and γ-Ray Radiation Defects in Silicon
Authors: Fengmei Wu , Yi Shi , Zhenzhou Wang , Qiji Lai , Lihua Zhao 
Published: March 2011

ABSTRACTThe influence of an electric field on the formation of radiation-induced defects in silicon irradiated respectively with γ-ray, electrons and neutrons has been investigated using the DLTS method. It is found that the application of an electric field across the p-n junction during irradiation can reduce the formation efficiency of A-centers, divacancies and E3(Ec-0.37 eV) defects, and that the concentration of radiation defects in the junction depletion region is lower than that in the quasineutral bulk. The formation characteristics of radiation defects in the depletion region could be related mainly to the transformation of the charge states of the defects caused by the electric field.
Photoluminescence of Silicon Nanostructures Formed by Ion Beam Implantation
Authors: Redman D. A. , Follstaedt D. M. , Guilinger T. , Kelly M. 
Published: March 2011

ABSTRACTA new method was used to fabricate nanometer-scale structures in Si for photoluminescence (PL) studies. He ions were implanted to form a dense subsurface layer of small cavities (1–8 nm diameters). The implanted specimens were either annealed in H or anodized with HF to evaluate the quantum confinement model for PL from porous Si. Incomplete passivation apparently prevented PL in the H-annealed specimens. Implantation combined with anodization produced a substantial blue shift relative to anodization alone, which is consistent with quantum confinement.