bluuebunny/crossref_metadata_2025_split huggingface dataset:
Nanometer-Scale Composite Structures Formed by Simultaneous Oblique Sputter-Deposition of Two Materials from Different Directions
Authors: Motohiro Tomoyoshi , Takeda Yasuhiko , Watanabe Yoshihide , Noda Shoji 
Published: March 2011

ABSTRACTOblique depositlon(OD) provides an attractive anisotropic structure In nm-scale as a promising host structure to form anisotropic nm-scale composites(ANSC). Among a variety of possible methods to introduce a guest material Into the host structure of OD, we have attempted simultaneous oblique deposition of a guest and a host material from two different directions. The computer simulation for ballistic deposition, which had greatly contributed to the understanding of the morphology evolution in OD, has been carried out again here to design possible ANSC structures and to survey their variations. A typical ANSC structure obtained here is a composite of slender clusters of the guest and the host materials, which can be regarded as an anisotropic version of the well-known isotropic structures of the metal-insulator or semiconductor-insulator cermets for magneto-optical or nonlinear optical applications. This appears when the host and the guest materials are deposited from the directions of the same polar angle of 70° but from the reverse azimuthal directions. In accordance with this result, a specially designed sputtering apparatus has been constructed. Structures and optical anisotropy of the films of several composites' systems such as ZnTe-SiO2 and Cu-SiO2 formed by this apparatus have indicated that our attempt has hit the mark.
Magnetic Behavior of Nanocomposites Prepared in a Vitreous Alumina Gel
Authors: Shull R. D. , Ritter J. J. , Shapiro A. J. , Swartzendruber L. J. , Bennett L. H. 
Published: March 2011

ABSTRACTHomogeneous gelled composites of iron and vitreous alumina containing 10-40% Fe have been prepared by room temperature polymerization of aqueous aluminum alkoxide solutions containing ferric nitrate and nitric acid at low pH. Scanning electron microscopy, x-ray diffraction, and Mossbauer spectroscopy demonstrated that this bulk material is comprised of nanometer-sized regions of iron compounds embedded in a vitreous alumina gel matrix. Magnetization data showed that in the as-cured condition these nanocomposites are paramagnetic at room temperature and become either superparamagnetic or ferromagnetic on cooling to 10 K. The magnetic susceptibility increased with the Fe content and with decreasing temperature. Analysis of the temperature dependence of the magnetic susceptibility indicated the magnetic moment per Fe atom was 1.87 µB for the 10% Fe nanocomposite and that it increased linearly with composition to 1.96 µB for the 40% Fe material. Mössbauer effect data showed that subsequent treatment of these materials in a gaseous environment of hydrogen at elevated temperatures (T<400 C) changed the form of the iron in the magnetic regions. These results are compared to that observed for similar nanocomposites prepared using a silica gel matrix.
Microprobe Analysis of Nanophase Metal-Oxides using Inelastic Light Scattering
Authors: Parker J. C. , Siegel R. W. 
Published: March 2011

ABSTRACTNanophase TiO2 and ZnO were investigated with a Raman microprobe in order to determine the spatial variations in material composition, oxygen stoichiometry, and phase. Calibration of the oxygen stoichiometry of nanophase TiO2 was determined through a combination of Raman scattering and thermogravimetric analysis.
High-Resolution Electron Microscopy Study of Iron Nanocrystals Prepared by High-Energy Mechanical Crystallization
Authors: Trudeau M.L. , Van Neste A. , Schulz R. 
Published: March 2011

ABSTRACTRecently, there has been a growing interest on materials called “nanocrystalline solids”. These materials are made of crystals with sizes ranging typically from 1 to 10 nm. Several methods have been used to produce these solids. One of them is the high energy mechanical deformation (HEMD) process. Indeed, we have shown recently that some iron-based amorphous alloys crystallize completely into a nanocrystalline structure when they are subjected to HEMD. In this work, we present a TEM study of the nanocrystals formed by the mechanical crystallization of Fe66Co18si1B15 amorphous metallic ribbons.
The Chemistry and Packaging of Nanocomposite Confined Arrays
Authors: Stucky Galen D. 
Published: March 2011

ABSTRACTThe miniaturization of electronic and optic devices has revolutionized response times, energy loss and transport efficiency. An additional bonus is that as one approaches the nanosize regime the presence or absence of a few atoms and the geometrical disposition of each atom can significantly modify electronic and photonic properties. This control can be further supplemented by “packaging” assemblies of atoms or molecules into thin film or nanocomposite bulk materials to define surface states, cluster environment and geometry, intercluster interactions, and consequently, a wide tunable range of optical and charge carrier responses.The chemist is presented with an intriguing challenge. First the clusters must be unisized with identical geometries. Secondly, the atom or molecular assemblies should ideally have perfect periodicity in order to rigorously define optoelectronic densities and intercluster tunnelling. A third requirement is that the nanocomposite be processable, generally in the form of thin films or single crystals. Numerous approaches are being undertaken in achieve these goals, including molecular beam and atomic layer epitaxy, molecular sieve inclusion chemistry, molecular capping of inorganic clusters, porous glass and aerosol synthesis. This paper presents a brief review of the interface chemistry associated with nanophase confinement and packaging and some features of three dimensional surface confinement using molecular sieves and zeolites.
Synthesis of Sic Clusters in a Nonthermal Microwave Plasma
Authors: Singh A. K. , Kingon A. L. 
Published: March 2011

ABSTRACTA new technique has been developed to condense nanoparticles (clusters) of SiC and other nonoxide materials in a nonthermal microwave plasma. The experimental rationale and approach is described. It utilises silane and acetylene precursors in an Ar diluent, with the synthesis carried out in a microwave plasma at a pressure of ∼1 torr. The plasma conditions have been characterised, as have the effect of important parameters (gas ratios, flow rates and pressure) on the product nanoparticles. The resultant nanoparticles have been characterised ex-situ by TEM, Auger, and XPS spectroscopy. SiC particles collected are ∼5nm in size, with cubic, hexagonal and rhombohedral polytypes observed. Silicon nitride has been synthesised similarly by using silane and nitrogen as the precursor gases. Implications of the new technique are discussed.
A Novel Approach to Nanoscale Materials Synthesis Using Industrial Laser Processing of Organosilazane Liquid Precursors
Authors: Xiao Tongsan D. , Strutt Peter R. , Gonsalves Kenneth E. 
Published: March 2011

ABSTRACTA new approach has been developed for the synthesis of nanoscale ceramic powder materials from liquid organosilazane precursors. This technique, by exploiting fast kinetic chemical and physical reactions, makes it possible to synthesize significant quantities of material in a relatively short time. In the current approach aerosols of a silazane monomer, (CH3SiHNH)n, (n = 3 or 4), of mol. wt. 280–320, are injected into the beam of a cw industrial CO2laser to obtain nanoscale ceramic powders. Injection of the aerosol into the laser-beam results in a high-temperature plume. Rapid condensation of the molecular precursor species emerging from the laser plume results in the formation of preceramic polymer particles, with an average diameter of 62 nm. One attractive feature of this process is that 70 wt.% of the liquid precursor is converted into nanoscale powders. Another feature is that only a further 10 wt.% loss occurs during post thermal treatment to form the end-product.
Nanometer-Scale Iron Oxide Magnetic Particles: Synthesis and Magnetic Properties
Authors: Vassiliou John K. , Mehrotra Vivek , Russell Michael W. , Giannelis Emmanuel P. 
Published: March 2011

ABSTRACTNanometer-scale iron oxide magnetic particles have been formed in the porous network of a cross-linked polymer matrix by ion exchange and subsequent hydrolysis. The oxide particles are uniform, well-dispersed and spherical with a diameter ranging between 30 and 1200 Å depending on the synthesis conditions. The DC magnetic susceptibility, measured between 4 and 300 K, continuously increases with decreasing temperature and tends to saturate at low temperatures. Composites containing iron oxide particles with an average diameter of 80 Å exhibit superparamagnetism while those on the order of 1000 Å undergo an antiferromagnetic-type transition at 33 K. The magnetic susceptibility is critically dependent upon the particle size and the strength of the magnetic field.
C60 And C70: Here’s Looking at you
Authors: Cox D. M. , Behal S. , Creegan K. , Disko M. , Hsu C. S. , Kollin E. , Millar J. , Robbins J. , Robbins W. , Sherwood R. D. , Tindall P. , Fischer D. , Meitzner G. 
Published: March 2011

ABSTRACTIn this paper we will describe the production, separation and characterization of the new all carbon molecules, C60 and C70. High performance liquid chromatography HPLC is used to obtain purified samples of C60 and C70, which are subsequently characterized by electron impact and chemical ionization mass spectrometry, IR and UV-visible absorption spectroscopy, NMR, ESR, scanning tunnelling microscopy, transmission electron microscopy and x-ray absorption fine structure measurements.
Possidle Isomers and Electronic Structure of C60H36
Authors: Dunlap B. I. , Brenner D. W. , Mowrey R. C. , Mintmire J. W. , Robertson D. H. , White C. T. 
Published: March 2011

ABSTRACTNewly developed empirical hydrocarbon potentials and self-consistent first-principles local density functional methods are used to investigate possible isomers and the electronic structure of C60H36. Within the high symmetry Th structure conjectured by the groups at Rice University there are two inequivalent sets of hydrogen atoms containing twelve and twenty-four atoms respectively. Binding each set either inside or outside of the C60 cage leads to four isomers of C60H36 with inequivalent strain energies. Although we find that placing twelve hydrogens inside the cage can lead to a metastable structure, our calculated total energies suggest that the isomer with all the hydrogens on the outside of the cage is the energetically most stable.
Quantum Molecular Dynamics of Solid C60
Authors: Zhang Q. , Yi Jae-Yel , Bernholc J. 
Published: March 2011

ABSTRACTWe report the first structure optimization and quantum molecular dynamics simulations for solid C60. The symmetry-unconstrained optimization results in nearly ideal buckminsterfullerene structure. This is due to the closed shell nature of C60 and the weakness of the intermolecular interactions in the solid. The lack of substantial intermolecular interactions allows for rotations at relatively low temperatures and these rotations are observed during simulations. Although the zero temperature structure consists of alternating single and double bonds, this distinction becomes blurred at moderate temperatures. However, computer generated movies show that the cage structure is preserved even at high temperatures, despite vibrational motion with substantial amplitude.
Production, Characterization, and Deposition of Carbon Clusters
Authors: Bae Y. K. , Lorents D. C. , Malhotra R. , Becker C. H. , Tse D. , Jusinski L. 
Published: March 2011

ABSTRACTWe have developed a new cluster ion source that can generate intense beams of metal and semiconductor clusters of a very wide-size range. With the source, we have observed intense beams of carbon clusters with mean cluster sizes of up to 4000 atoms/clusters. However, we have found that for generating small fullerenes, such as C60 and C70, the recently discovered technique by Kraetschmer et al. is much more efficient. By improving the technique, we have generated gram quantities of C60 and C70 and systematically investigated their thermal desorption properties. During the heating process, we have discovered that at high temperatures the bulk fullerenes, fullerite, transformed to another form of carbon, which still evaporates at temperatures above 700 C, but does not dissolve in benzene.
X-Ray Double-Crystal Diffraction Studies of Si+ Implantation in Si GaAs
Authors: Xia Guanqun , Chen Jingyi , Zhu Nanchang , Hu Suying 
Published: March 2011

ABSTRACTThe characteristics of Si+ implanted into SI GaAs and its annealing behavior have been studied by x-ray double-crystal diffraction method. Results show that there is much information on strain contained in the rocking curves. When implanting at low doses, most of the implanted Si+ is in interstitial positions in the GaAs, and this produces tensile strain. After annealing, most of the implanted Si+ can be activated and the strain can be relieved. But when implanting at large doses, the strain can not be completely relieved even after annealing at high temperature
Structural Characterization of Ru-B 4c Multilayers Fabricated By Magnetron Sputtering
Authors: Stearns D. G. , Rosen R. S. , Vernon S. P. 
Published: March 2011

ABSTRACTMultilayer structures composed of alternating, ultrathin layers of Ru and B4C have been fabricated using DC magnetron sputtering. These multilayers are potentially important as normal incidence x-ray reflectors at wavelengths above the boron K-absorption edge at 65Å. The detailed structure of the layers has been characterized using x-ray diffraction and high-resolution transmission electron microscopy. It is found that, under optimized deposition conditions, continuous layers can be grown that have smooth and abrupt interfaces. The normal incidence reflectivity at x-ray wavelengths of ∼70Å has been measured, and values as high as 20% have been obtained.
X-ray Characterisation of a V90S Sige MBE System
Authors: Powell Adrian , Kubiak Richard , Parker Evan , Bowen Keith , Polcarova Milena 
Published: March 2011

ABSTRACTX ray techniques have enabled a fast characterisation of a new VG Semicon V90S MBE system for growth of Si and SiGe material. X-ray rocking curves have allowed characterization of SiGe layers to tolerances as tight as ± 0.1 At%. X-Y uniformity measurements demonstrated that layers are grown to ± 0.5 % over a 150 mm wafer. Information on the flux rate uniformity during growth can be obtained from analysis of superlattice structures. These enable calculation of “worst case” flux variation during a growth run. An empirical relationship has been found that enables the prediction of the degree of residual strain remaining in a buffer structure grown beyond the metastable critical thickness.
X-ray Diffraction from Surfaces and Interfaces:Atomic Structure and Morphology
Authors: Vlieg E. , Robinsson I. K. , Veen J. F Van Der 
Published: March 2011

ABSTRACTThe emergence of synchrotron radiation sources has greatly stimulated the use of X-ray scattering in surface science. The absence of multiple-scattering effects allows a straightforward data analysis. In addition to determining geometric structures, it is also possible with X-ray scattering to obtain information on various types of surface disorder. The large penetration depth enables the investigation of interfaces.
Microscopic Determination of Stress Distribution in GaAs Grown at Low Temperature on GaAs (100)
Authors: Liliental-Weber Zuzanna , Ishikawa A. , Teriauchi M. , Tanaka M. 
Published: March 2011

ABSTRACTA microscopic strain distribution across commensurate interfaces between GaAs layers grown on semi-insulating GaAs substrates was observed by means of convergent beam electron diffraction (CBED) and large angle convergent beam methods (LACBED). Strain relaxation at a specific distance from the interface was observed in these layers without formation of misfit dislocations. It was proposed that specific point defects distributed close to the interface can explain the asymmetric broadening of high-order Laue zone (HOLZ) lines in the CBED patterns.
X-Ray Characterization of Mbe-Grown InxGal-xSb/InAs Strained Layer Superlattices
Authors: Chow P. C. , Vigliante A. , Moss S. C. , Zborowski J. T. , Golding T. D. , Shih H. D. 
Published: March 2011

ABSTRACTStrain can play a critical role in determining the band structure and optical properties of semiconducting superlattices. Mailhiot and Smith [1] have predicted that strain, induced by mismatch, in InxGal-xSb/InAs makes the superlattice a candidate for infrared detectors. We present a preliminary analysis of the structure, in particular the strain in the layers, of an InxGal-xSb/InAs superlattice, which shows infrared absorption. Our ultimate objective is to relate the structural properties to the optical absorption and an extended (kinematical) diffraction treatment is presented for accomplishing this.
Rheed Study of Strain Relaxation in Epitaxial Cds and Sn Overlayers
Authors: Niles David W. , Höchst Hartmut 
Published: March 2011

ABSTRACTThe relaxation of strain in epitaxial overlayers is studied through an analysis of RHEED patterns. From the separation of the RHEED reflections, we determine the in-plane lattice constants for α-Sn/Cd0.8Zn0.2Te(100), CdS/GaAs(100), and CdS/CdTe(100) heterostructures. The discussion focuses on the critical thickness of the overlayers and the relaxation of the inplane lattice constant (a∥) of epitaxial films which exceed the critical thickness. Predictions based on Matthews and Blakeslee's mechanical equilibrium theory show reasonable agreement with our experimental findings, indicating that the metastability of the epitaxial overlayers does not cause a significant reduction in the critical film thickness.
In-Situ Strain Measurement Via X-Ray Diffraction
Authors: Thompson R. D. , Angilello. J. 
Published: March 2011

ABSTRACTA high speed x-ray diffraction system has been built around a Curved Position Sensitive Detector. This system has a hot/cold stage in a modified vacuum chamber to allow for control of the ambient gas mix while in-situ x-ray diffraction spectra are acquired. We have used this system to measure the strain in Al/Cr/SiO2 structures after abrupt changes in temperature. The good adhesion afforded by the Cr layer combined with the large difference in the thermal expansion coefficients of the Al (≃25×10−6/°K) and the quartz (≃0.5×10−6/°K) components make this an ideal sample for demonstrating the capabilities of this system. In-situ resistivity measurement provides an independent indication of the changes in the sample.
Structural Analysis of Adsorption Processes on Silicon by Rheed
Authors: Ichimiya Ayahiko 
Published: March 2011

ABSTRACTOn the basis of results of surface structure analyses by reflection high-energy electron diffraction(RHEED) with dynamical calculations, adsorption processes on Si(111) surface are discussed. On adsorption processes on Si(111)7×7 surface at room temperature, adatom bonds of the dimer-adatom-stacking-fault(DAS) structure are broken by adsorbed atoms and the structure changes into other 7×7 one called δ7×7. At the transition into the δ7×7 structure the dimer-stacking-fault(DSF) frame work is preserved. From rocking curve analyses during adsorption of Li and Si, back bonds of the adatoms of ])AS structure are cut off in the initial stage of the adsorption at about 0.2 monolayer coverage of the adsorbates. Metal adsorbed δ7×7 structures axe unstable and changes into structure by heating at about 300 °C with dissolution of the stacking fault layer into the normal stacking arrangement. During homoepitaxial growth of Si on Si(111)7×7 surface at about 300 °C, a new metastable surface structure is foundby RHEEDdynamical analysis. This structure is concluded as pyramidal cluster structure formed on the DSF frame work. It is discussed that formation of metastable structure promotes transition to from the 7×7, and promotes successive epitaxial growth accompanied with stacking fault dissolution at the DSF frame work.
X-Ray Diffraction From Buried GaAs/GaSb Interfaces
Authors: Bourret Alain , Fuoss P. H. , Rocher A. , Raisin C. 
Published: March 2011

ABSTRACTThe initial stage of epitactic growth of GaSb film on GaAs has been studied by X-ray diffraction. On each island the 8% misfit is accommodated by a periodic network composed of two perpendicular sets of Lomer dislocations. This network is already formed at 10Å nominal thickness. The relaxation of the e ilayer towards its bulk lattice parameter is almost complete so that a supercell is observed. The behaviour of the dislocation satellites is accurately explained by the presence of a periodic displacement field at and close to the interface. A quantitative fit with a simple elastic model is, however, insufficient to fit the data, implying that interdiffusion occurs close to the interface.
Surface Ordering and Kinetics From Atom Beam Diffraction
Authors: Hinch B. J. 
Published: March 2011

ABSTRACTHelium atom diffraction yields a wealth of information complementary to that obtainable from other experimental surface sensitive techniques. Atomic He scattering is extremely sensitive to surface defects. Also time of flight measurements enable energy transfer processes to be studied. An analysis of the energy broadening in quasi-elastic scattering can yield information on surface diffusion coefficients and may also be used to investigate diffusion mechanisms. The paper reviews how intensities of both coherent and incoherent scattering can be employed to study the kinetics of ordering at surfaces.
Phase Transitions Near Surfaces Studied By Grazing Incidence Diffraction of X-Rays
Authors: Mailander L. , Dosch H. , Peisl J. , Johnson R. L. 
Published: March 2011

ABSTRACTWe review two different experiments in order to demonstrate the power of grazing incidence diffraction of x-rays in studying phase transitions near surfaces and to show that it is well suited to get information on structural details even from subsurface layers: We have measured the near surface critical scattering at the continuous order disorder transition of an Fe3Al single crystal which provides information on modifications of critical behavior of a bulk transition near a surface. These modifications are detectable to a considerable depth due to the diverging range of correlations. We determined three different critical surface exponents which allow, for the first time, to confirm scaling laws for near surface critical behavior.- The experiment at a (100) surface of a discontinuous ordering Cu3Au single crystal shows that the surface is wetted by a disordered layer below the transition temperature. By means of the adjustable depth sensitivity of grazing incidence scattering we were able to demonstrate that the thickness of this layer increases logarithmically when approaching the transition temperature.
Molecular Dynamics Simulations of Steps at Crystal Surfaces.
Authors: Gilmer G. H. , Bakker A. F. 
Published: March 2011

ABSTRACTThe growth of semiconductor crystals by molecular beam epitaxy often involves the motion of distinct steps, which are the boundaries of incomplete atomic layers. We review some of the crystal growth mechanisms based on step generation and motion. Ising models have been widely used to study equilibrium faceting and crystal growth. We discuss more general models of steps which are based on molecular dynamics calculations of atomic motion and empirical interatomic potentials. These models include the possibility of surface and step reconstructions, and here we discuss their influence on the step energy and motion. We find that certain types of steps have a structure with drastically reduced energy compared to unreconstructed steps. We have also examined the effect of stress resulting from misfit in epitaxial systems. We find that 1% misfit can completely change the nature of a step, since its excess energy may change sign from negative to positive, or vice versa. Simulations of molecular beam epitaxy give direct information on the conditions under which step growth mechanisms play a role.