bluuebunny/crossref_metadata_2025_split huggingface dataset:
Nanocomposite Material, Liquid Crystal-Aerosil Particles: Dielectric and Photon Correlation Spectroscopy Investigations
Authors: Aliev F.M. , Sinha G.P. 
Published: April 2011

ABSTRACTNematic liquid crystal filled with Aerosil particles prospective inorganic-organic nanocom-posite material for optoelectronic application has been investigated by broadband dielectric spectroscopy (BDS) and photon correlation spectroscopy (PCS). The aerosil particles of diameter ≈ 10 nm in filled nematic liquid crystals form a network structure with linear size of LC domains about 250 nm and with random distribution of the director orientation of each domain. This material has a very developed liquid crystal-solid particle interface that makes the role of the surface layers of LC important in the determination of the properties of the material. BDS provides information on reorientational motion of polar molecules of liquid crystal while PCS probes dynamics of collective modes associated with director fluctuations. We found that the properties of 5CB are considerably affected by the network. Two bulk-like dielectric modes due to the rotation of molecules around short axes and the tumbling motion were observed in filled 5CB. Additionally, a low frequency relaxation process and dispersion of dielectric permittivity due to conductivity were observed. The treatment of the surface of filling particles has strongest influence on the properties of the slow process and it is less important for molecular modes. PCS experiment shows that two new relaxation processes appear in filled 5CB in addition to the director fluctuations process in bulk.
Fe-Al2O3 Nanocomposite: Synthesis and Magnetic Properties
Authors: Santos A. , Macedo W. A. A. , Ardisson J. D. , Viegas A. D. C. , Schmidt J. E. 
Published: April 2011

ABSTRACTWe have investigated the synthesis and the structural and magnetic properties of Fe nanoparticles embedded in Al2O3 matrix, a granular nanocomposite prepared by sol-gel processing. Samples with volumetric Fe content ranging from 20 to 62% were obtained starting from Al nitrate and Fe sulfate as precursors and the preparation method results initially in a mixture of Fe- and Al oxides. The conversion of Fe oxides into metallic Fe was done by calcination at 800°C followed of reduction at 600°C for 2 hours, in H2 atmosphere. Our results indicated the following phases in the amorphous alumina matrix, after reduction: α-Fe, the main phase, α- and γ-Fe2O3, Fe3O4 and some interstitial Fe2+ and substitutional Fe3+ atoms in the Al2O3 lattice. For the investigated system, Fe reduction rate was very sensitive to the sample porosity and, with the applied method, we have obtained reductions of the Fe atoms into metallic Fe ranging from 45 to 68%, preserving the mean diameter of the oa-Fe nanoparticles between 55 and 80 nm. VSM measurements at room temperature resulted in coercivity between 450 and 630 Oe and saturation magnetization between 40 and 110 emu/g. Magneto-transport measurements in samples with 25% metallic Fe (and 51% total Fe) reveal ΔR/R close to 2% at room temperature.
Thin Polytetrafluoroethylene Organosilane Nanocomposite Films Used as Ultra Low Dielectric Constant Materials in Microelectronics
Authors: Qu Shichun , Rosenmayer Tom , Xu Ping , Spevack Perry 
Published: April 2011

ABSTRACTReplacing the current on-chip dielectric materials such as silicon dioxide, which has a dielectric constant of approximately 4.0, with low dielectric constant materials can greatly improve the performance of high density VLSI device by reducing crosstalk and capacitive delay. Polytetrafluoroethylene (PTFE) has the lowest dielectric constant (k < 2.0) of any full density material, which makes it a promising candidate for this IC application. Pure PTFE thin films cast from PTFE nanoemulsion containing sub-20nm PTFE particles, though thermally stable, have some inherent sub-optimal properties. These include adhesion to other inorganic materials and mechanical strength at high processing temperatures. In order to improve these properties, we have developed a PTFE / silicon compound nanocomposite material. Initial tests have shown that this nanocomposite material has significantly improved high temperature mechanical properties and interfacial properties between the composite and inorganic materials such as silicon, silicon oxide, silicon nitride and some metals. The surface roughness of the thin film coatings is also reduced compared to pure PTFE thin film coatings. The coatings require no separate adhesion promoter to be applied to the substrate prior to deposition. Characterization work has been carried out with different techniques such as DMA, ToF-SIMS, XPS and AFM with hydrofluoric acid (HF) selective etching, in order to understand this novel nanocomposite and its surface and interfacial properties.
A Nano-Composite Poly(Methyl-Methacrylate) Bone Cement
Authors: Gomoll Andreas H. , Bellare Anuj , Fitz Wolfgang , Thornhill Thomas S. , Scott Richard D. , Jemian Peter R. , Long Gabrielle G. 
Published: April 2011

ABSTRACTPoly(methyl methacrylate) (PMMA) based orthopaedic bone cements contain 1-3 Pim size radiopacifier particles. Incomplete dispersion of these particles leads to the presence of 50-200 μm size agglomerates. These large defects are sites of high-stress concentration that reduce the fracture toughness of PMMA. In this study, the micrometer-sized radiopacifying particles of a commercial bone cement were replaced by nanosized fillers. Both, commercial and nanocomposite PMMA bone cements were characterized using ultra-small angle x-ray scattering and low voltage scanning electron microscopy; mechanical properties were evaluated using ASTM standard tensile testing. The results showed a substantial reduction of particle agglomerate size and a significant increase in tensile properties of the nanocomposite over that of the standard microcomposite bone cement.
Nanocomposites Based Upon Alumina and Zirconia Pillared Clays Loaded with Transition Metal Cations and Clusters of Precious Metals: Synthesis, Properties and Catalysis of NOx Selective Reduction by Hydrocarbons
Authors: Sadykov Vladislav A. , Bunina R. V. , Alikina G. M. , Doronin V. P. , Sorokina T. P. , Kochubei D. I. , Novgorodov B. N. , Paukshtis E. A. , Fenelonov V. B. , Derevyankin A. Yu. , Ivanova A. S. , Zaikovskii V. I. , Kuznetsova T. G. , Beloshapkin B. A. , Kolomiichuk V. N. , Plasova L. M. , Matyshak V. A. , Konin G A. , Rozovskii A. Ya. , Tretyakov V. F. , Burdeynaya T. N. , Davydova M. N. , Ross J. R. H. , Breen J. P. , Meunier F. C. 
Published: April 2011

ABSTRACTThermally stable alumina and zirconia pillared clays loaded with copper and cobalt cations and silver nanoparticles were synthesized. The structural and surface features of these nanosystems were studied and compared with those of bulk analogs -partially stabilized zirconias and γ-alumina loaded with the same active components. Specificity of the catalytic properties of nanocomposites in the reactions of nitrogen oxides reduction by propane, propylene and decane in the excess of oxygen appears to be determined both by the degree of interaction between pillars and active components and the type of reducing agent.
Characterization of Voids in Rutile Nanoparticles by Transmission Electron Microscopy
Authors: Turner S. 
Published: April 2011

ABSTRACTRutile nanoparticles containing voids or cavities have been characterized using transmission electron microscopy. The general morphology of the voids has been determined from images of nanoparticles in different orientations. In general, the longest dimension is along the c axis of rutile. Many of the voids show a prismatic morphology with dipyramid terminations. The prism consists of primarily four {110} faces with rounded or faceted comers between the primary faces. The pyramidal terminations can appear ovoid or faceted. A major facet plane of the pyramids is (101). A model consistent with the morphology of many voids in rutile nanoparticles is proposed.
Power of Mass Spectrometry for Analyzing Organometallic Molecules as Precursor of Nanomaterials
Authors: Strouse G.F. , Gaumet J.J. 
Published: April 2011

ABSTRACTA mass spectrometry method (Electrospray Mass Spectrometry [ESMS]) for analyzing organometallic precursors of nano-materials is described. We show that application of low-cone voltage ESMS is a useful technique for the rapid analysis of intact organometallic precursor molecules when both positive and negative ionic modes are analyzed. This method shows promise for extrapolation to analysis of the dynamics of growth in nano-scale materials.
Micro-Raman Study of Self-Assembled Nanostructures: (1−x)PZN:xPT Solid Solution
Authors: Gupta S. , Katiyar R. S. , Guo R. , Bhalla A. S. 
Published: April 2011

ABSTRACTRelaxor ferroelectrics are one of the important classes of self-assembled nanostructure composite materials. Interesting features associated with the nanoregions give rise to the most interesting device related characteristics and unusual properties in these materials. Besides, they possess the largest property coefficients by themselves or when modified with lead titanate (PT). In this report, a detailed temperature dependent study has been carried out on (1-x)PZN-xPT relaxors with compositions x = 0.05 and 0.085 using polarized Raman scattering under optical and E-field variables and inferred the structure-property relations in order to obtain information to characterize the material for matching the application criteria. In addition, phase transitions associated with the relaxors have also been investigated to understand the polarization mechanism(s) for the unpoled and poled specimens.
Thermoelectric Properties of Bi2Te3-Sb2Te3 Compounds Prepared by Ma-Pulse Discharge Sintering Process
Authors: Park R.E. , Park Y.H. , Abe T. 
Published: April 2011

ABSTRACTThe Bi2Te3-Sb2Te3 compounds with the composition of useful thermoelectric cooling materials were prepared by mechanical alloying-pulse discharge sintering process. Effects of the process on the Seebeck coefficient, electrical resistivity and thermal conductivity were investigated. Temperature dependence of the Hall coefficient was also observed in the temperature range 80 - 325 K.The figure of merit, Z, was found to be about 4.0 × 10−1K−1 at room temperature in the 25%Bi2Te3-75%Sb2Te3 composition sintered at 618K using grain refined mechanically alloyed powders which had the size of under 32 μm. The value of Z was remarkably improved with a decrease of the thermal conductivity shown in the fine grain compacts fabricated by mechanical alloying-pulse discharge sintering process.
Thermally Driven Shape Instability of Multilayer Structures
Authors: Troche P. , Hoffmann J. , Herweg C. , Lang CH. , Freyhardt H.C. , Rudolph D. 
Published: April 2011

ABSTRACTThe thermally induced shape instability of Fe/Au, Fe/Ag, and Nb/Cu multilayer systems during heat treatments was investigated. The disintegration temperature of these systems decreases with decreasing single-layer thickness. Up to a critical thickness, the disintegration temperature is proportional to the reciprocal layer thickness. The driving force of this process is related to the interfacial stress and the local variation of the interface curvature. After heat treatment, spherically shaped Fe and Nb nanoparticles, located in chains perpendicular to the substrate, were observed and depicted by means of transmission electron microscopy (TEM) and X-ray microscopy (XRM).
Tight-Binding Molecular Dynamics of Ceramic Nanocrystals Using Pc-Based Parallel Machines
Authors: Tsuruta Kenji , Totsuji Hiroo , Totsuji Chieko 
Published: April 2011

ABSTRACTEvolution of atomic and electronic structures of silicon-carbide (SiC) nanocrystals during sintering is investigated by a tight-binding molecular dynamics (TBMD) method. An O(N) algorithm (the Fermi-operator expansion method) is employed for calculating electronic contributions in the energy and forces. Simulations are performed on our eight-node parallel PC cluster. In a sintering simulation of aligned (no tilt or twist) SiC nanocrystals at T = 1000K, we find that a neck is formed promptly without formation of defects. Analyses of local electronic density-of-states (DOS) and effective charges reveal that unsaturated bonds exist only in grain surfaces accompanying the gap states. In the case of tilted (<122>) nanocrystals, surface structures formed before sintering affect significantly the grainboundary formation.
Electrical Properties of Nanoscale Tisi2 Islands on Si
Authors: Oh Jaehwan , Ham Hoon , Laloli Peter , Nemanich R. J. 
Published: April 2011

AbstractNanoscale TiSi2 islands are formed by electon beam deposition of a few monolayers of titanium followed by in situ annealing at high temperatures (800–1000°C). The typical island sizes were ˜10 nm. Electrical characteristics of these islands were probed using UHV-STM. I-V spectroscopies on these islands show single electron tunneling effects such as Coulomb blockade and Coulomb staircase at room temperature.
Novel Strain-Relief Mechanisms For Ge/Si(100) Coherent Islands
Authors: Drucker Jeff , Chaparro Sergio , Zhang Yangting , Chandrasekhar D. , Mccartney M. R. , Smith David J. 
Published: April 2011

AbstractNovel strain-relief mechanisms for Ge/Si(100) coherent islands were identified. Ge/Si(100) islands were grown at temperatures, T, between 450 and 650°C for effective Ge coverages between 3.5 and 14.0 monolayers. The mean dome size increased and island dislocation was delayed as T increased. For T > 600°C, very large hut clusters populated a peak in island size distributions distinct from and between those of huts and domes. For T > 550°C, large dome clusters may form trenches at their base which extend well into the Si substrate. Increasing T reduced the island size for trench formation. Cross-sectional energy dispersive xray nanoanalysis confirmed that Si diffuses into the Ge clusters at T ≥ 550°C. Si interdiffusion was responsible for the increase in dome size and delay of dislocation with increasing T and the existence of very large hut clusters. AFM cross-sections indicate that there is a linear trench depth dependence on island size. A simple atomistic elastic model suggests that this experimentally observed self-limiting trench depth is kinetic rather than energetic in origin.
Atomic-Resolution Z-Contrast Imaging and its Application to Compositional Ordering and Segregation
Authors: Pennycook S. J. , Yan Y. , Norman A. , Zhang Y. , Al-Jassim M. , Mascarenhas A. , Ahrenkiel S. P. , Chisholm M. F. , Duscher G. , Pantelides S. T. 
Published: April 2011

AbstractIn the last ten years, the scanning transmission electron microscope (STEM) has become capable of forming electron probes of atomic dimensions making possible a new approach to high-resolution electron microscopy, Z-contrast imaging. Formed by mapping the intensity of high-angle scattered electrons as the probe is scanned across the specimen, the Z-contrast image represents a direct map of the specimen scattering power at atomic resolution. It is an incoherent image, and can be directly interpreted in terms of atomic columns. High angle scattering comes predominantly from the atomic nuclei, so the scattering cross section depends on atomic number (Z) squared. Z-contrast microscopy can therefore be used to study compositional ordering and segregation at the atomic scale. Here we present three examples of ordering: first, ferroelectric materials, second, III-V semiconductor alloys, and finally, cooperative segregation at a semiconductor grain boundary, where a combination of Z-contrast imaging with first principles theory provides a complete atomic-scale view of the sites and configurations of the segregant atoms.
X-ray Diffraction Study of Chalcopyrite ZnSnP2 Epitaxial Layers
Authors: Francoeur S. , Seryogin G. A. , Nikishin S. A. , Temkin H. 
Published: April 2011

AbstractWe apply the technique of x-ray diffraction to the determination of the crystallographic structure and the quantitative measurement of the order parameter of ZnSnP2 epitaxial layers. In bulk, ZnSnP2 it is possible to obtain highly ordered distribution of Zn and Sn atoms in the cation sublattice, but epitaxial growth often produces partially ordered layers. The ordered and disordered phases correspond to the chalcopyrite and sphalerite structures and their respective band gaps are 1.66 and 1.24 eV. Since ZnSnP2 is almost lattice-matched to GaAs. it is interesting candidate for optoelectronic applications.Samples used in this work were grown by gas source molecular beam epitaxy on GaAs substrates. Slight variations in growth conditions could be induced to produce partially ordered and disordered structures. Chalcopyrite ordering is determined by the observation of several characteristic reflections identifying the lower symmetry of this structure. For example, reflections from (101), (217) and (611) planes, strictly forbidden for sphalerite, were measured. The quantitative determination of the order parameter could be made by comparing intensities of a carefully chosen set of measured and calculated reflections. We show that while kinematic approximation can be used to model weak superstructure reflections, in the calculation of the strong, low-angle, fundamental reflections used for intensity normalization it is necessary to take into account extinction effects. Order parameters varying from 0 to 30% were obtained.
Reciprocal-Space and Real-Space Analyses of Compositional Modulation in InAs/AlAs Short-Period Superlattices
Authors: Follstaedt D. M. , Lee S. R. , Reno J. L. , Jones E. D. , Twesten R. D. , Norman A. G. , Ahrenkiel S. P. , Moutinho H. R. , Mascarenhas A. , Millunchick J. Mirecki 
Published: April 2011

AbstractThe microstructure of lateral composition modulation in InAs/AlAs superlattices grown by MBE on InP is examined. The use of x-ray diffraction, TEM, AFM, and STEM to characterize the modulations is discussed. Combining the information from these techniques gives increased insight into the phenomenon and how to manipulate it. Diffraction measures the intensity of modulation and its wavelength, and is used to identify growth conditions giving strong modulation. The TEM and STEM analyses indicate that local compositions are modulated by as much as 0.38 InAs mole fraction. Plan-view images show that modulated structures consists of short (≳0.2 μm) In-rich wires with a 2D organization in a (001) growth plane. However, growth on miscut substrates can produce a single modulation along the miscut direction with much longer wires (≲0.4 μm), as desired for potential applications. Photoluminescence studies demonstrate that the modulation has large effects on the bandgap energy of the superlattice.
Computer Simulations of the Self-Organized 3-D Islanding in Epitaxial Thin Film Systems
Authors: Zhang Y. W. 
Published: April 2011

Abstract3-D computer simulations were carried out to investigate the effects of surface energy anisotropy and initial surface roughness on the self-organization of 3-D islands in epitaxial thin film systems. Under the present scheme, the driving force for surface diffusion is the gradient of surface chemical potential, which includes strain energy and surface energy. The simulations demonstrate that the typical sequence of surface evolution is from an initial random surface to a rippled surface, then to irregular islands and then to self-organized islands. Whether the final islands are regular or not depends on both the form of surface energy anisotropy and initial surface roughness. However, the stability and shape transition of the epitaxially strained islands are associated with the form of surface energy anisotropy. The comparisons between the simulations and various experiments were also discussed.
Diffusion and Distribution of Photoacid Generators in thin Polymer Films
Authors: Lin Qinghuang , Angelopoulos Marie , Babich Katherina , Medeiros David , Sundararajan Narayan , Weibel Gina , Ober Christopher 
Published: April 2011

AbstractDistribution and diffusion of two fluorinated ionic photoacid generators (PAGs) in thin polymer films have been investigated by depth profiling of the intrinsic label elements of both the PAGs and a silicon containing carrier polymer with Rutherford Backscattering Spectrometry (RBS) and dynamic Secondary Ion Mass Spectroscopy (SIMS). Distribution and diffusion of the PAGs in a bilayer film stack, which consists of a thin silicon containing polymer film on top of a thick thermally cross-linked Novolak film on a silicon substrate, have been studied as a function of the Novolak cross-linking temperature. Deposition of the PAG containing polymer films on top of the cross-linked Novolak films by spin coating results in an interphase with enriched PAG. Subsequent annealing of the film stack causes expansion of the interphase and diffusion of the PAG into the underlying Novolak film when Novolak is cross-linked at lower temperatures. On the other hand, there is a uniform PAG distribution and no detectable diffusion of the PAG into Novolak when it is cross-linked at high temperatures. The variations in the PAG distribution and diffusion are attributed to the changes in the chemical and physical properties of Novolak during cross-linking.
Second Derivative Ballistic Electron Emission Spectroscopy in Au/(AlGa)As
Authors: Kozhevnikov M. , Narayanamurti V. , Smith D. L. , Chiu Yi-Jen 
Published: April 2011

AbstractOur current study focuses on an analysis of the ballistic electron emission microscopy (BEEM) spectra of Au/(AIGa)As heterostructures to estimate quantitatively the effect of the carrier scattering in the metal, at the metal-semiconductor (m-s) interface and in the semiconductor on the multivalley carrier transport. The second derivative (SD)-BEEM spectra, representing the heterostructure transmission coefficient, show explicit partitioning of the contribution of different transport channels (Γ, L and X conduction valleys). Our analysis of SD-BEEM spectra by the developed theoretical model indicates that about 85–92% of the BEEM electrons are scattered at the nonepitaxial Au/GaAs interface. We also show that initial electron distribution among the conduction bands of the semiconductor, specified by the m-s interface scattering, is modified by the further hot-electron transport inside the semiconductor.
Modeling of Structural and Elastic Properties of InxGa1–xN Alloys
Authors: Grosse Frank , Neugebauer Jörg 
Published: April 2011

AbstractInxGa1-xN alloys are investigated by combining density-functional theory (DFT) calculations and all extended valence force field model (VFF). Based on a large nuniber of ordered InxGa1-xN supercells we determined the accuracy of various valence force field models with respect to ab initio DFT calculations. To get the correct energy difference between the stable wurtzite and the inetastable zincblende phase the inclusion of the ion-ion-interaction within the VFF’ model was necessary. As a direct consequence the inequivalent bonds of the wurtzite structure including the non-ideal c/a ratio and internal u parameter are described correctly. The wurtzite phase is found to be stable against the zincblende phase for all concentrations. The calculated elastic constants and their dependency on In alloy composition enables the determination of the local concentration by simultaneous measurement of the local lattice constants a and c.