bluuebunny/crossref_metadata_2025 huggingface dataset:
The Chemistry and Packaging of Nanocomposite Confined Arrays
Authors: Stucky Galen D.
Published: March 2011

The 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

A 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

A 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

Nanometer-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

In 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.
Carbon Solvates: Redox Properties and Single Crystal X-Ray Structure
Authors: Gorun S. M. , Greaney M. A. , Cox D. M. , Sherwood R. , Day C. , Day V. , Upton R.
Published: March 2011

Carbon aggregates of various nuclearities have been recently the subject of renewed interest [1]. Despite an intense research, effort no molecular level characterization of C60 and related molecules has been reported yet [1,2]. Moreover, the chemical properties of these materials is virtually unknown. In this paper we report briefly the preparation, electrochemical and structural characterization of crystalline C60/70 solvates [3].
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

Newly 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.
First and Second Ionization Potentials, Reactions, and Surface Collisions of C60 and Related Clusters
Authors: McElvany Stephen W. , Ross Mark M. , Callahan John H.
Published: March 2011

The physical and chemical properties of large carbon clusters, Cn(n>40), have been studied extensively over the past six years. The spherical nature of these clusters has been debated and inferred from both experimental and theoretical studies until the recent isolation and subsequent spectroscopic identification of bulk C60 and C70. Although the n=60 and 70 cluster ions are anomalously abundant (“magic numbers”) in the mass spectra and are proposed to be highly symmetric species, the other “magic number” clusters have yet to be isolated.
Stm Topographical Images of C60
Authors: Wang Zhouhang , Zhang Ping , Moskovits M.
Published: March 2011

STM topographical images of C60 are reported. The images are consistent with a molecule approximately 9 Å in diameter possessing the now-famous soccer ball structure. With the molecule deposited on gold, its atomic structure is not resolved. On graphite the structure of the within the borders of the C60 molecule is dominated by that of the graphite forming a moiré-like pattern. Some evidence of atomic structure is seen in multilayers of C60 where some five- and six-membered rings are visible. These may, however, be features of fragments of the fullerene rather than whole molecules.
Quantum Molecular Dynamics of Solid C60
Authors: Zhang Q. , Yi Jae-Yel , Bernholc J.
Published: March 2011

We 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

We 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

The 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

Multilayer 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

X 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

The 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

A 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.
Reflection Electron Diffraction and Structural Behavior of Gaas / Gaas (111)B Grown Via Mbe
Authors: Rajkumar K. C. , Chen P. , Madhukar A.
Published: March 2011

Homoepitaxy on the {111} face of GaAs has been long known to give films with surfaces marred with macroscopic features. We have identified this problem to be tied to the surface phase regime. We have used Reflection High Energy Electron Diffraction (RHEED) to identify a phase regime wherein specular-surfaced GaAs films can be grown. We have found that it is possible to glean information regarding the macroscopic surface morphology by monitoring the variation in the RHEED specular spot intensity during growth. This has allowed in situ monitoring of the macroscopic surface morphology of a growing film in real time which has made it possible to grow specular-surfaced films reproducibly.
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

Strain 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

The 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

A 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

On 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

The 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

Helium 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

We 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

The 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.
Semiempirical Angular-Force Method for BCC Transition Metals
Authors: Carlsson A. E.
Published: March 2011

An angular-force method for bcc transition-metals is obtained by generating a functional form via a quantum-mechanical analysis, and subsequently fitting the parameters in this form to experimental and ab-initio theoretical inputs. The quantummechanical analysis uses a four-moment treatment of the electronic density of states (DOS) in a d-band tight-binding model. Calibration of the method gives excellent results for the bcc-fcc energy difference and the vacancy-formation energy in W. The method is used to treat relaxation and c(2 × 2) reconstruction on the W (100) surface. The relaxation energy is primarily due to two-body terms, while the reconstruction requires the angular terms. Agreement with ab-initio results is obtained for reasonable values of the parameters in the model. However, the energy difference between the reconstructed surface and the optimally relaxed surface is quite sensitive to the details of the implementation of the method.
Calculation of Defect Properties of NiTi and FeTi
Authors: Lutton Russell T. , Sabochick Michael J. , Lam Nghi Q.
Published: March 2011

The energies and configurations of interstitials and vacancies in the B2 ordered compounds NiTi and FeTi were calculated using atomistic simulation. The stable configuration of a vacancy after the removal of an Ni atom was a vacant Ni site; similarly, the removal of an Fe atom in FeTi resulted in a vacant Fe site. Removal of a Ti atom in both compounds, however, resulted in a vacant Ni or Fe site and an adjacent antisite defect. The effective vacancy formation energies in NiTi and FeTi were calculated to be 1.48 and 1.07 eV, respectively. Interstitials in NiTi formed split <111> configurations consisting of a Ni-Ni dumbbell oriented in the <111> direction with one or two adjacent antisite defects. The Fe interstitial in FeTi had a similar configuration, except the dumbbell contained Fe atoms. The Ti interstitial in FeTi formed an <110> Fe-Fe dumbbell.
Calculation of Diffraction Patterns Associated with Electron Irradiation Induced Amorphization of CuTi.
Authors: Devanathan R. , Lam N. Q. , Sabochick M. J. , Okamoto P. , Meshii M.
Published: March 2011

A new approach that uses the multislice method in conjunction with molecular dynamics simulations to study electron irradiation induced amorphisation is presented. Diffraction patterns were calculated for CuTi and found to be more sensitive than the pair correlation function to the structural changes preceding amorphisation. The results from this approach and from a study of long range order are presented.
First-Principles Study of Soliton Hyperfine Interactions in Polyacetylene
Authors: White C. T. , Kutzler F. W. , Mintmire J. W. , Cook M. R.
Published: March 2011

All-trans-polyacetylene is considered the prototypical broad band gap quasi onedimensional organic semiconductor. Intrinsicsoliton defects have long been known to be important to the understanding of the observed properties of this system at low doping levels. Magnetic resonance techniques provide powerful experimental probes into the nature and environment of these neutral-radical defects. In an earlier work we showed that firstprinciples spin-polarized local density functional (LDF) methods reliably predict proton Fermi-contact coupling constants for planar, neutral, organic π-radicals. We have also used these methods to calculate the Fermi-contact proton coupling constants associated with the soliton defect in polyacetylene.Herein we compare the results of these earlier soliton calculations to results from recent electron-nuclear double-resonance (ENDOR) experiments. Our predicted ratio of the negative to positive spin densities is in good agreement with these ENDORstudies. The negative spin densities arise from spin-polarization effects which are found to cause the soliton level at midgap to be split by several tenths of an eV.
Alternative Length Scales for Polycrystalline Materials
Authors: Nichols C.S. , Cook R.F. , Clarke D.R. , Smith D.A.
Published: March 2011

It is well established from studies of bicrystals that the properties of a grain boundary depend on the atomic structure of the boundary. However, constitutive relations for the properties of polycrystalline materials do not currently take into account this boundary-toboundary variability. Instead, such relations depend on a single length scale, typically the average grain diameter. We extend the traditional viewpoint by proposing that boundaries may be divided into two distinct categories, depending on their misorientation angle. The relevant length scale in constitutive relations for polycrystals is then the average cluster size, where clusters consist of grains connected by boundaries in the same misorientation category. A brief discussion of this additional length scale and how it may be reflected in various constitutive relations for physical and mechanical properties of polycrystals is given.
Raman Studies of Fluorine-Intercalated Carbon Fibers
Authors: Rao A. M. , Fung A. W. P. , Dresselhaus M. S. , Dresselhaus G. , Endo M. , Nakajimat T.
Published: March 2011

We report Raman scattering measurements on fluorine-intercalated graphite fibers (CxF) for stoichiometries x =7.8, 4.5 and 2.9. Lorentzian fits to our Raman lineshapes indicate the presence of two lines around 1600 cm−1 and a broad line around 1355 cm−1 . The 1355 cm−1 line is the disorder-induced graphite line and the ratio of the integrated intensity of this line to that of the 1600 cm−1 doublet (R) provides a measure of the intercalationinduced disorder in the CjF fibers. Both TEM and Raman studies indicate the presence of unintercalated graphitic regions in the CxF fiber. The inverse relation between the average crystal planar domain size La, and the Raman intensity ratio R yields La. ,˜52Å for C7.8F fibers and La. , ˜40Å for C4.5,F and C2.9F fibers.
Vacancy Properties in Ordered NiGa And NiAl
Authors: Kim S.M.
Published: March 2011

The recently formulated theory of vacancy formation in CsCl-type ordered alloys has been applied to β-NiGa and β-NiAl. The observed Nisublattice vacancy concentrations in these compounds could be well described by the theory. For the first time it is also shown that structural vacancies most likely exist in Ga-rich NiGa and Al-rich NiAl at absolute zero temperature.
Hrem Investigation of the Structure of the σ5(310)/[001] Symmetric Tilt Grain Boundary In Nb.*
Authors: King Wayne E. , Campbell G. H. , Coombs A. , Mills M. J. , RüHle M.
Published: March 2011

Recent atomistic simulations using interatomic potentials for Nb developed employing the embedded atom method (EAM) and the model generalized pseudopotential theory (MGPT) have indicated a possible cusp at the Σ5(310) orientation in the energy vs tilt angle curves for<001> symmetric tilt grain boundaries. In addition, the most stable structure predicted using EAM exhibits shifts of one crystal relative to the other along the tilt axis and along the direction perpendicular to the tilt axis lying in the boundary plane. The structure predicted using the MGPT was mirror symmetric across the plane of the grain boundary. This boundary has been prepared for experimental study using the ultra high vacuum diffusion bonding method. A segment of this boundary has been studied using high resolution electron microscopy.
Impurity-Defect Complexes in Hydrogenated Amorphous Silicon
Authors: Yang Lin H. , Fong C. Y. , Nichols Carol S.
Published: March 2011

The two most outstanding features observed for dopants in hydrogenated amorphous silicon (a-Si:H) - a shift in the Fermi level accompanied by an increase in the defect density and an absence of degenerate doping - have previously been postulated to stem from the formation of substitutional dopant-dangling bond complexes. Using firstprinciples self-consistent pseudopotential calculations in conjunction with a supercell model for the amorphous network and the ability of network relaxation from the first-principles results, we have studied the electronic and structural properties of substitutional fourfoldcoordinated phosphorus and boron at the second neighbor position to a dangling bond defect. We demonstrate that such impurity-defect complexes can account for the general features observed experimentally in doped a-Si:H.
Spectroscopic Study of Hydrogen Induced Defect in a-Ge:H
Authors: Jin Shu , Ley Lothar
Published: March 2011

Total yield photoelectron spectroscopy has been used to study the electronic structure change of UHV evaporated a-Ge subjected to posthydrogenation and various annealing cycles. We identify in R.T. hydrogenated a-Ge:H a new hydrogen induced defect at about Ev + 0.45eV, which can be healed upon 300°C annealing. This new defect accounts for the defect density gradient of hydrogenated amorphous semiconductors, spanning the range from ∼ 1018 cm−3 at the growing surface to 1018−1015 cm−3 in the bulk, depending on growth condition and time. The origin of this new defect is discussed.
Diffraction Effects from [111] Twist Boundaries in Gold
Authors: Majid I. , Wang D. , Bristowe P. D
Published: March 2011

The structural characteristics of [111] twist boundaries in gold are investigated using a combination of x-ray diffraction and computer modeling techniques. Comparison of the measured scattering effects with those generated from EAM computer models reveals that the [111] boundary displacement field is weak, rotational in form and centered on ‘O’ lattice sites. Furthermore, the measured intensities of the strong ‘O’ lattice reflections decrease smoothly with increasing boundary angle up to 30°, as calculated from the model. The effect of double positioning on the diffraction pattern and the structural analysis is discussed.
Damage Freeze-In Phenomena as a Function of Dopant Implant Type In Germanium-Rich Regions in Silicon
Authors: Aronowitz Sheldon , Hart Courtney , Myers Sharon
Published: March 2011

End-of-range damage produced by n-type dopants is frozen-in if that damage is produced in germanium-rich regions in crystalline silicon. This is not the case with p-type dopants. High germanium doses were implanted into silicon; the wafers were annealed at 1000 C for 30 minutes under nitrogen. Phosphorus or boron then were implanted into the crystalline siliconfollowed by a 900 C, 30 minute neutral ambient anneal.

Explanation of the freeze-in phenomenon relies on results of semiempirical quantum chemical calculations that showed that group V dopants, whether interstitial or substitutional, as well as interstitial silicon, would be attracted to the vicinity of substitutional germanium sites in germaniumrich regions ofthe crystalline silicon. This general preferential diffusion behavior is not calculated to occur with the p-type dopants from group III. When substitutional, in fact, the group III impurities are predicted to be repelled from the germanium-rich regions.

TEM studies show that any residual damage with boron as the implant and germanium present is low in density and within 20 nm of the silicon interface. This is contrary to studies involving phosphorus where damage is exclusively associated with the end-of-range of the phosphorus implant. Both sets of results are in accord with the theoretical considerations.
Electrical Properties Of S+Implantation in Si GaAs
Authors: Xia Guanqun , Guan Anmin , Geng Haiyang , Wang Weiyuan
Published: March 2011

The electrical properties of S+implanted in SI GaAs have been studied. The rapid diffusion and redistribution of S+implanted in GaAs after conventional thermal annealing (CTA) depends not on conventional diffusion of S+or VAs, but on the enhanced diffusion by ion implantation. By employing rapid thermal annealing (RTA) techniques enhanced diffusion can be restrained, redistribution of S+implantation can be decreased greatly and a thin active layer suitable for fabricating GaAs MESFET devices can be obtained.
Long Range Coulomb Effects on Hydrogen Debonding from Boron Acceptors in Silicon
Authors: Anderson R. A. , Seager C. H.
Published: March 2011

Previous work has demonstrated that B-H pairs in silicon thermally dissociate obeying simple first order kinetics if theyare located in a region depleted of majority carriers. B.H debonding in equilibrium, however, is a slower, more complex process. We have investigated the dissociation of B.H pairs under a variety of equilibrium and non-equilibrium conditionsand have demonstrated that the dissociation process is strongly influenced by the local concentration of majority and minority carriers. In particular, we show that injection of minority carriers can markedly accelerate the dissociation process. A model is proposed which suggests that hydrogen released from an acceptor, while initially positive, must always beneutralized before escape is possible. This picture correctly describes the time dependence of debonding in equilibrium, and it predicts the enhanced debonding in forward biassed diodes provided the characteristic time for H charge conversionislong.
Structural Properties of a-Ge1−xnx:H Alloys
Authors: Marques F. C. , Chambouleyron I.
Published: March 2011

Amorphous hydrogenated and unhydrogenated germanium-nitrogen alloys were prepared by rf glow discharge using a GeH4+NH3atmosphere and by rf sputtering using a Ge target with different gases (Ar, N2, NH3 , and mixtures). A difficulty in obtaining nonstoichiometric films was encountered for both methods. Films prepared by rf glow discharge tend to be either Gerich or close to stoichiometric composition, and films prepared by sputtering tend to have low nitrogen concentration. Thesamples prepared by glow discharge at 220°C do not contain the NH2 absorption band, which is usually present in filmsprepared by sputtering. The Urbach energy (determined by PDS), Tauc's gap, refractive index, dark conductivity and activation energy are also reported.
Temperature Dependent Recombination Lifetime in Silicon: Influence of Trap Level
Authors: Buczkowski Andrzej , Radzimski Zbigniew J. , Kirino Yoshi , Shimura Fumio , Rozgonyi George A.
Published: March 2011

This paper discusses the temperature dependence of recombination lifetime in a variety of silicon materials using energy level as a parameter. A theoretical approach based on the Shockley-Read-Hall theory for energy level calculations has been used. Various types of defects created by introducing impurities, dislocations and grain boundaries into silicon waferswere studied. Results are presented for Czochralski grown Si wafers intentionally contaminated with gold and chromium, EFG ribbon with varying concentration of oxygen, web ribbons with extended defects and contaminants, large grain polycrystalline material, and Si/Si-Ge/Si heterostructures with varying misfit and threading dislocation density.
Neutron Irradiated Uranium Silicides Studied by Neutron Diffraction and Rietveld Analysis
Authors: Birtcher R. C. , Mueller M. H. , Richardson J. W.
Published: March 2011

The irradiation behavior of high-density uranium silicides has been a matter of interest to the nuclear industry for use in high power or low enrichment applications. Transmission electron microscopy studies have found that heavy ion bombardment renders U3Si and U3Si2 amorphous at temperatures below about 250 C [1], and that U3Si becomes mechanically unstable suffering rapid growth by plastic flow [2,3]. In this present work, crystallographic changes preceding amorphization by fission fragment damage have been studied by high-resolution neutron diffraction as a function of damage produced by uranium fission at room temperature. Initially, both silicides had tetragonal crystal structures. Crystallographic and amorphous phases were studied simultaneously by combining conventional Rietveld refinement of the crystallographic phases with Fourier filtering analysis of the non-crystalline scattering component [4].
Analysis of Oxygen Gettering and Dislocation Locking in Silicon
Authors: Maroudas Dimitrios , Brown Robert A.
Published: March 2011

The motion under an applied stress of dislocations in silicon crystals is slowed and stopped by the presence of oxygen inthe material. A model is presented that quantitatively describes the inhibition of dislocation motion by accounting for the oxygen gettering to dislocations caused by diffusion and stress-enhanced migration. Drag on the dislocation motion ismodelled using the elastic interactions between the interstitial oxygen and the dislocation and the energy needed to breakbonds formed between silicon and aggregated oxygen atoms within the dislocation core. The predictions of the model agree quantitatively with the experimental data of Imai and Sumino.
Electron Microscopy Study Of Mocvd-Grown Tio2Thin Films and Tio2/Al203 Interfaces
Authors: Gao Y. , Merkle K. L. , Chang H. L. M. , Zhang T. J. , Lam D. J.
Published: March 2011

TiO2 thin films grown on (1120) sapphire at 800°C by the MOCVD technique have been characterized by transmission electron microscopy. The TiO2 thin films are single crystalline and have the rutile structure. The epitaxial orientation relationship between the TiO2 thin films (R) and the substrate (S) has been foundto be: (101)[010]R║(1l20)[0001]s. Growth twins in the films are commonly observed with the twin plane{101} and twinning direction <011>. Detailed atomic structures of the twin boundaries and TiO2/α-Al203 interfaces have been investigated by highresolution electron microscopy (HREM).When the interfaces are viewed in the direction of [010]R/[000l]S, the interfaces are found to be structurally coherent in the direction of [1Ol]R/[1100]s,in which the lattice mismatch at the interfaces is about 0.5%.
Observation of Hexagonal AiGaAs Grown by OMCVD
Authors: Hwang D. M. , Ravi T. S. , Bhat R. , Simhony S. , Chen C. Y. , Kapon E.
Published: March 2011

Extended regions of hexagonal zinc sulfide (wurtzite) structure are found to exist in AlGaAs grown by low-pressure OMCVD at 750°C. The specimen was prepared on a (001) GaAs substrate patterned with [110]-orientedV-grooves, intended for a quantum wire laser structure. A high density of planar faults was observed to originate in theAl0.66Ga0.34As cladding layers near the inner corners of the V-grooves and propagate towards the surface along the {111} planes. Many of these faults are stacking faults and microtwins. However, there also exhibit extended regions of hexagonal structure, revealed in electron diffraction patterns and high resolution lattice images. The hexagonal phase shares the same close-packed layers with the cubic phase, i.e., (0001)hexagonal // {111}cubic. The mechanism for the formation of hexagonal structure in this specimen is not yet fully understood.
Interpretation of Alumina/Yttrium-Aluminum Garnet Orientation Relationships by Geometric Criteria
Authors: Hay R.S. , Matson L.E.
Published: March 2011

Geometric criteria for low interface energy and interface structure were tested for the cubic-rhombohedral system YAG/alumina. Orientation relationships near (111){110}a // (112){110}y and facets on (111)a(112)y were observed in both sol-gel derived composites and directionally solidified eutectic composites. The ΣYAG=12 near-CSL of 2{111}, {110}, {112} was inferred to be the preferred structural unit. Dislocations with b=1/3{111}a and b=1/2{110}a were observed and inferred to accomodate deviation from the structural unit, respectively. The {110}a,y direction met some of the criteria for an invariant line. Although the OR was explained by geometric criteria it would have been difficult to predict it with such criteria
Defect Dependence of Positron Lifetimes in Oxide Superconductors
Authors: Sterne P.A. , O'Brien J.C. , Howell R.H. , Kaisert J.H.
Published: March 2011

First principles calculations of the positron lifetimes are used to interpret experimental lifetime data for Ba1-xKxBiO3. The observed lifetimes are found to be very sensitive to the presence of defects in the sample. The temperature dependence of the lifetime and the change in lifetime with sample aging are both attributed to defects. The qualitative differences between metal vacancy defects and oxygen vacancy defects in metal oxides are also discussed.
Defect Chemistry of High Tc Superconductors
Authors: Fueki Kazuo , Idemoto Yasushi
Published: March 2011

The oxygen deficiency δ in YBa2Cu3O7−δ was determined as a function of oxygen partial pressure and temperature. It was found that all the δ−log Po2 data points fall on a single smooth curve (master curve) when the points for each temperature were shifted in parallel with each other in the direction of abscissa by a certain distance. A theoretical equation describing the δ−logP02 relation was derived on the basis of electroneutrality, mass action law and site conservation.The theoretical curve agreed well with the experimental hL.Lster curve.
Defects in Decomposed Yba2Cu4Ox(124) Superconductor after Rapid Annealing
Authors: Li Y. , Gao Y. , Merkle K. L. , Shi H. , Balachandran U.
Published: March 2011

Decomposition of 124 into 123 has been studied after rapid annealing at temperatures from 800°C to 1000°C. It was foundthat the superconducting transition temperature (Tc) depended on the annealing temperature and atmosphere. For decomposedsamples, fine-scale defects with strong strain contrast are observed in the 123 matrix. High-resolution electron microscopy studies show that the defects are parallel to the (001) planes of the 123 matrix. The length of the defects varies andranges from 5 nm to 50 nm in the direction parallel to the (001) planes. The defects have been interpreted to be copper oxides, which could be flux pinning centers in these materials.
Thermal Desorption Studies of Isotopically-Labeled Oxygen from La2Cuo4+δ
Authors: Shinn N. D. , Bartram M. E. , Schirber J. E. , Overmyer D. L. , Rogers J. W. , Fisk Z. , Cheong S.-W.
Published: March 2011

Isotopically-labeled oxygen enrichment and thermal desorption mass spectroscopy (TDMS) have been combined to study interstitial oxygen desorption from superconducting La2CuO4+δ(δ≤5 0.032). Single crystal samples of magnetic, insulating La2CuO4+δ were annealed at 860K under 1-3 kbar oxygen pressure for 12-100 hours to yield hole-doped, superconducting La2CuO4+δ samples with 35K <Tc <40K. Whereas no TDMS signals were observed for the insulator, rapid bursts (FWHM <0.5 sec) of molecular oxygen were observed above 350K while heating the superconductor at less than I K sec−1 in high vacuum. A kinetic model is proposed in which the interstitial oxygen diffuses to internal grain boundaries and defects during heating, thereby inducing stress in the lattice as it attempts to revert to the LaCuO4.00 crystal structure. This stress is relieved by lattice fracture at grain boundaries during the TDMS experiment, releasing the trapped oxygen from the sample as micro-cracks are formed. In addition, the facile oxygen exchange between interstitial and latticeoxygen sites has been discovered by TDMS and weight gain measurements from isotopically-enriched crystals, supporting thestructural model of Chaillout, et al. in which the interstitial oxygen atom dimerizes with a lattice oxygen ion.
High Resolution Double Crystal Diffractometry of High TcSuperconducting Epitaxial Gd-Ba-Cu-O Films
Authors: Dai D Y , Green G S , Tanner B K , Li H C , Yi H R , Wang R L
Published: March 2011

High-Tc superconducting epitaxial thin films of gadolinium barium copper oxide,grown in situ by dc-magnetron sputtering onto substrates of single crystal (001) orientated LaAIO3 , SrTiO3 and yttrium stabilisedZrO2 have been studied by high resolution double axis difffactometry, X-ray white beam-Laue topography and double crystal topography. Rocking curve halfwidths were found to vary from about 1000 to 3000 arc seconds, very good in thecontext of these complex materials. The topographs showed that the orientations of the small crystallites was randomly distributed across the sample.
Gamma Radiation Effects on Some Properties of YBCO
Authors: Luo L. , Zhang Y.H. , Hu S.H. , Liu W.H. , Chang G.L. , Hu W.X.
Published: March 2011

Radiation effects of polycrystalline YBCO bulk sample irradiated by 60Co γ-rays from a dose of 1x106 up to 7.5×l09 rad at room temperature on critical temperature and critical current were investigated. IR spectrum was also used to study the mechanism of the irradiation. A considerable dependence of these parameters upon irradiation dose was observed. No significant effects on critical temperature were found, but the critical current in zero magnetic field changed greatly. It shows a tendency to decrease with the increase of the irradiation dose except for a slight increase with the dose less than about 2×107 rad and no simple relations between critical currents and irradiation doses was found. A typical case is that the critical current is reduced to about 60% when the dose reaches 5×109 rad, but the dependence of critical currents on magnetic field shows that the critical currents are higher than that of the unirradiated one in the range of magnetic field higher than 100 Gauss and decrease more slowly in magnetic field compared with the unirradiated one. The results indicate that the defects produced by γ-ray irradiation are benefit to flux pinning in higher fields. IR spectra analysis reveals that the intensity of the peak responsible for the Cul-O1 chain vibration is decreased, indicating that the bond of the Cul-O1 may be partly broken through collision process of the Compton electron produced by the γ-ray. This effect probably gives rise to decrease of the critical currents.