bluuebunny/crossref_metadata_2025_split huggingface dataset:
Investigating the Relationship Between Atomic Structure and Carrier Depletion at [001] tilt Grain Boundaries in Ybco
Authors: Browning N. D. , Buban J. P. 
Published: April 2011

AbstractRecent theoretical analyses [1] have suggested that the origin of the reduced Jc at grain boundaries in high-Tc superconductors may be band bending, which results in the depletion of mobile charge carriers at the boundaries. For this to occur in these p-type superconductors there must, by definition, be a high density of localized donor states in the boundary plane. Here we report a “structural unit” analysis of [0011 tilt grain boundaries in YBa2Cu 3O7-δ (YBCO) that indicates there may be a simple structural origin for such localized donor states.
Response of Semiconductors and Fullerenes to Ultrashort and Ultra-Intense Laser Pulses
Authors: Dumitrica Traian , Torralva Ben , Allen Roland E. 
Published: April 2011

ABSTRACTWe report new theoretical studies of the electronic and structural response of materials to fast intense laser pulses, with durations ∼ 10–100 feintoseconds and intensities up to ∼10 terawatts/cm2. The results provide still stronger evidence that GaAs undergoes a true nonthermal phase transition as the intensity is varied at constant pulse duration. For C60, there are also different regimes of behavior as a function of pulse intensity. At low intensity, various optically-active modes are observed. At high intensity, the breathing moode is by far the most dominant. At still higher intensities, there is photofragmentation, with the evolution of dinmers and other products. These results were all obtained in simulation-. using tight-binding electron-ion dyanamics (TED).
Predicting Nonlinear Optical Properties of Delocalized Charge States in Polyenylic Chromophores and Dendrimers
Authors: Dirk C. , Spangler C. , Madrigal L. , Elandaloussi E. H. 
Published: April 2011

ABSTRACTOver the past several years there has been continuing interest in the design of highly conjugated monomers, oligomers and polymers for a variety of photonics applications dependent on a nonlinear response to intense laser radiation. Materials design criteria for these various applications depend on accurate structure-property relationships, and while these relationships can best be determined experimentally, computational approaches that can accurately predict trends in series are extremely useful in establishing target molecules having the desired photonic properties. We have recently reviewed the relationship between incorporation of polaronic or bipolaronic charge states in oligomeric or polymeric conjugation sequences' and enhanced third-order optical nonlinearity, particularly for finite-length polyenes. In this presentation we will focus on how these charge states can be stabilized by electron-donating substituents in dithienylpolyenes, and in model dendrimers based on bis(diphenylamino)stilbene repeat units, and illustrate why these criteria are important for the design of new optical limiting chromophores.
Theoretical Investigation of the Second and Third Order Nonlinear Optical Properties of Some Fused Heterocyclic Aromatic Compounds
Authors: Bader Mamoun M. 
Published: April 2011

ABSTRACTWe report herein the results of coupled perturbed Hartree-Fock (CPHF) ab initio extended basis set calculations on the geometric structures, dipole moments, static first-order (α), second-order (β), and third-order polarizabilities (λ) of a series of fused heterocyclic aromatic compounds based on quinoline. The effects of the presence/absence of the heteroatom as well as the introduction of other substituents at various positions in the ring system on these molecular properties are described. The effect of the presence of N-oxide is also examined. Suggestions for the design of heterocyclic systems with enhanced polarizabilities are made.
Controlled Phase Formation by Using a Diffusion Barrier - The Fe-Si REACTION
Authors: Theron C.C. , Falepin A. , Degroote S. , Dekoster J. , Vantomme A. , Langouche G. , De Waal H.S. , Pretorius R. 
Published: April 2011

AbstractBy analogy to reactive deposition epitaxy and titanium interlayer mediated epitaxy experiments, an attempt has been made to constrain the supply of reactants to the reaction interface in the solid phase reaction between Fe and Si. The goal being to change the normal phase formation sequence by using a suitable diffusion barrier, so that β-FeSi2 forms directly. Both Fe-V and Fe-Zr diffusion barriers were used to constrain the supply of the two reactants during Fe-silicide formation. Measurements with these barriers, show first phase formation of β-FeSi2, but direct formation of 3-FeSi2 as first phase has not been observed. In the case of the Fe-V diffusion barrier it was shown that the use of the diffusion barrier resulted in smoother layers of β-FeSi2 than could be formed by direct reaction of Fe on Si. In the case of the Fe-Zr barrier it is found that the barrier fails structurally at high temperatures. While it does prohibit Fe diffusion at low annealing temperatures, significant Si diffusion occurs prior to ε-FeSi formation.
Effects of Ge on The Nucleation and Growth of Si1−xGex
Authors: Yamaguchi S. , Park S. K. , Sugii N. , Nakagawa K. , Miyao M. 
Published: April 2011

AbstractNucleation and growth properties of Si1-xGex (0≦x≦0.3) have been investigated by using ellipsometric spectroscopy. The incubation time and the crystallization time significantly decrease with increasing x; the estimated incubation time (and crystallization time) in Si0.7Ge0.3 is about 1/100 of that in Si. During the incubation time, the increase of the crystallinity has been observed which corresponds to the nucleation of crystal seeds. From the behavior of the crystallinity during the incubation and the crystallization time, we estimated the activation energy of the nucleation and the crystallization. Both energies monotonically decrease with increasing x. The saturated crystallinity after crystallization decreases with increasing x. It has been found that the effect of Ge reduces the crystallinity of Si1-xGex while significantly enhancing the crystallization.
Effects of Boron Doping on the Grain Growth Behaviour of γ/γ Nickel-Aluminium Alloy
Authors: Chiu Y.L. , Ngan A.H.W. 
Published: April 2011

AbstractEffects of 0.5 at. % boron doping on Ni85Al γ/γ superalloys were investigated for the first time, yielding a number of observations not previously observed in the literature. First, the grain growth kinetics of both the doped and undoped alloys were found to disobey the simple Nielsen law d = Ctn but instead follow an equation of the type d = C ln(t) + C0. The constants C and C0 were found to be respectively 10.2 and 23.2 for the boron-free alloy, and 6.2 and 14.2 for the boron-doped alloy, i.e., the grain growth rate was retarded significantly upon boron doping. Such a retarding effect is thought to be due to the formation of a boron-nickel cosegregated zone observed at the grain boundaries of the doped alloy; the width of the zone, in μm's, is two to three orders of magnitude larger than the boron induced disordered layer found in nickel rich Ni3Al compounds doped with boron. Other associated effects of the cosegregated zone include a sharp increase in toughness, much better slip transmission across grains and reduced workhardening rates. Another intriguing point is that the γ precipitates were found to segregate to the grain boundaries in the boron-free alloy after cold rolling, but no such segregation of γ precipitates has been observed in the boron-doped alloy. The different deformation microstructures and the retarded grain growth rates upon boron doping will be discussed.
Crystallization of Al-Gd-La-Ni Metallic Glasses
Authors: Croat T.K. , Gangopadhyay A.K. , Kelton K.F. 
Published: April 2011

AbstractThe crystallization kinetics of Al-Gd-La-Ni metallic glasses to nanostructured phases are analyzed using differential scanning calorimetry and transmission electron microscopy. In a narrow alloy composition range near Al88Gd6La2Ni4, TEM reveals an amorphous phase separation that occurs upon annealing at low temperatures prior to crystallization. Al-enriched regions, typically 40 nm in diameter, bounded by rare-earth rich regions, are visible. Upon crystallization, α-Al forms preferentially at the interface between these phase separated regions. The relevance of this crystallization sequence to previous work in Al-RE-TM glasses and to the evolution of nanoscale microstructures common in the crystallization of other metallic glasses are discussed.
Patterned ZnS Thin-Film Growth using KrCl Excimer Lamp on the Zn Nuclei
Authors: Toda M. , Lizuka H. , Murahara M. 
Published: April 2011

AbstractPatterned Zn nuclei were formed by exposure with a single shot of an ArF excimer laser through a patterned photo mask onto a Si substrate which adsorbed DMZ (dimethylezinc). A ZnS thin film was then grown only onto the patterned Zn nuclei by KrCl excimer lamp irradiation of the substrate which was sealed in the chamber along with DMZ and H2S.
Ion Irradiation Induced Crosslinking Effects on Mechanical Properties of Photoresist Films
Authors: Garcia I. T. S. , Samios D. , Zawislaka F. C. , Jornada J. A. H. Da , Foerster C. E. , Serbena F. C. , Lepienski C. M. 
Published: April 2011

AbstractWe investigate the crosslinking process in ion irradiated AZ 1350J™ photoresist. The films were deposited on clean silicon wafers and irradiated with 380 keV He ions in the fluence range of 1013 to 1016 He.cm-2, corresponding to average deposited energy densities from 0.02 to 20 eV. Å-3.respectively. Nanoindentation, Raman spectroscopy as well as gel content and density measurements have been used to determine mechanical and structural properties of the irradiated films. The results show that the irradiation induces crosslinking of the polymeric chains but also produces carbonization of the films. For deposited energy densities up to 2 eV.Å-3. the crosslinking process is predominant and is mainly responsible for the increase of hardness and Young's modulus by respectively 5 and 2 times in relation to the values of the pristine film and for the gel content of 90%. For deposited energy densities larger than 2 eV.Å-3, the photoresist film is progressively transformed into an amorphous carbon layer as is shown by the Raman results, and also by the increase of the density at a deposited energy of 20 eV.Å-3.
Application of Cluster Ion Beam Smoothing to SiC and YBCO Surfaces
Authors: Fathy D. , Holland O. W. , Liu R. , Wosik J. , Chu W. K 
Published: April 2011

AbstractOptimization of the surface topography, especially in high-temperature superconductors (HTS) and silicon carbide is crucial for device processing. Surface smoothing in these materials was investigated using Gas Cluster Ion Beams (GCIB) capable of delivering cluster ions of ≥ 2000 Ar atoms with energies of up to 30keV. Examination of the surface topography after cluster-ion irradiation was done using cross-sectional transmission electron microscopy (TEM) and atomic force microscopy (AFM). The results indicate that typical as-deposited YBCO films on MgO substrates have an average roughness of the order of 40 nm, and interpeak distance between 300–600 nm. Application of GCIB to the surface planarization reduces the roughness to only 10 nm. Also power handling and microwave surface resistance of the YBCO film and its relationship to surface smoothness are reported. Similar observations using bulk SiC are discussed.
Ion Beam Induced Growth Structure of Fluorite Type Oxide Films for Biaxially Textured HYSC Coated Conductors
Authors: Iijima Y. , Kimura M. , Saitoh T. 
Published: April 2011

AbstractBiaxially aligned film growth by dual-ion-beam sputtering methods were studied for fluorite type (Zr0.85Y0.15O1.93(YSZ), Hf0.74Yb0.26O1.87, CeO2), pyrochlore type (Zr2Sm2O7), and rare-earth C type (Y2O3, Sm2O3) oxides on polycrystalline Ni-based alloy substrates. Cubetextured (all axes aligned with a <100> axis substrate normal) films were obtained for fluorite and pyrochlore ones by low energy (<300 eV) ion bombardment at low temperatures (< 300 °C). Besides, cube textured Y2O3 films were obtained in far narrower conditions with a quite low energy (150 eV)-ion bombardment at the temperature of 300 °C. The assisting ion energy dependence was discussed in connection with lattice energies for these oxide crystals.
Quantitative Rheed Analysis of Biaxially-Textured Polycrystalline MgO Films on Amorphous Substrates Grown by Ion Beam-Assisted Deposition
Authors: Brewer R. T. , Hartman J. W. , Atwater Harry A. 
Published: April 2011

AbstractWe have developed a computer simulation based on analytic calculation of reflection high energy electron diffraction (RHEED) patterns in the kinematic approximation for mosaic polycrystalline films for given values of electron beam incidence angle, polycrystalline texture, in-plane orientation distribution, and grain size. Although RHEED is most appropriately modeled using dynamical scattering theory, the computational efficiency of the kinematic approximation has enabled the development of a model suitable for real time measurement of crystallographic texture and in-plane orientation distributions for biaxially-textured films grown by ion beam-assisted deposition (IBAD). Using the simulation, we can quantitatively determine how RHEED spot shapes and relative intensities depend on the crystallographic texture and in-plane orientation distribution of polycrystalline films. RHEED patterns taken at 25 keV with incidence angle in the range 1–5 degrees from 10 nm thick, nominally [100]-textured MgO films grown on amorphous Si3N4 by IBAD were analyzed by comparing experimental RHEED phi rocking curves with those predicted by the simulation. For some films, an additional 200 nm thermally-grown MgO homoepitaxial layer was grown on top of the IBAD MgO layer. The model enables a quantitative correlation between biaxial texture and RHEED measurements. RHEED results are compared to X-ray rocking curve film analysis.
Specimen Current Imaging of Delamination in Ceramic Films on Metal Substrates in the SEM
Authors: Rangarajan S. , King A.H. 
Published: April 2011

AbstractPlasma spraying of yttria-stabilized zirconia on stainless steel substrates generates rapidly solidified thin film discs called splats. Constraint due to adhesion at their interface generates sufficient stresses during cooling from the splat melting to generate extensive cracking. Stress relief by cracking always accompanied by delamination of the thin films at the edges of cracked segments. It is shown here that images obtained in the SEM through amplification of the specimen current signal generate the right contrast for delineating regions of edge delamination in the cracked segments of a splat. Image analysis using this contrast provides a quantitative measure of the extent of delamination at the interface. Greater delamination in the splats formed on cooler substrates. Correlation also indicates complimentary nature of stress relief by delamination and cracking. A detailed analysis including data from solidification and cooling and cracking statistics will give a measure of the adhesion strength at the interface. This technique is a quick method for measuring delamination of microscopic degree in thin insulating films on conducting substrates.
Energy-Loss Filtered Imaging of Segregation-Induced Interface Broadening in SiGe/Si p-Channel MOSFET Device Structures
Authors: Norris D.J. , Cullis A.G. , Grasby T.J. , Parker E.H.C. 
Published: April 2011

AbstractSiGe/Si p-channel heteroepitaxial MOSFET test structures have been fabricated using solid-source molecular beam epitaxy. High-resolution transmission electron microscopy and energy-loss filtered imaging have been used to quantitatively determine the nanoscale Ge distributions across the SiGe alloy channel. The Ge profile at the edges of the alloy channel were found to be asymmetrical due to the effect of Ge segregation, with an exponential-like distribution directed toward the surface. The results agree well with the predictions of segregation theory and indicate that the concentration of Ge in the extended distribution lay in the range 10%-1% over a distance of several nanometers from the body of the channel. Secondary ion mass spectrometry measurements upon the same samples were insensitive to this short range extended Ge distribution.
Interface Structure and Zn Diffusion in the CdTe/ZnTe/Si System Grown by MBE
Authors: Tsen S.-C. Y. , Smith David J. , Crozier P. A. , Rujirawat S. , Brill G. , Sivananthan S. 
Published: April 2011

AbstractTwo CdTe/ZnTe/Si samples were grown on Si (211) and Si(111) substrates by molecular beam epitaxy for use as lattice-matched substrates for HgCdTe growth. An As precursor was used before growing ZnTe. In order to understand the interface structure, the Zn diffusion problem and any effect due to As passivation, high resolution bright-field images, dark-field images and energy-dispersive X-ray spectra were studied. Fourier-filtered images have revealed details of the atomic arrangements and the dislocation defects at the interface. Local lattice parameters such as (111) d-spacings at different distances from the interface were measured to determine the Zn concentration based on Vegard's law. The Zn concentration profiles were consistent with measurements from energy-dispersive X-ray spectroscopy. The As-passivated interface showed vacancy-type defects.
High-Resolution Scanning Electron Microscopy and Microanalysis of Supported Metal Catalysts
Authors: Liu Jingyue 
Published: April 2011

AbstractThe use of a high-brightness field emission gun and novel secondary electron detection systems makes it possible to acquire nanometer-resolution surface images of bulk materials, even at low electron beam voltages. The advantages of low-voltage SEM include enhanced surface sensitivity, reduced sample charging on non-conducting materials, and significantly reduced electron range and interaction volume. High-resolution images formed by collecting the backscattered electron signal can give information about the size and spatial distribution of metal nanoparticles in supported catalysts. Low-voltage XEDS can provide compositional information of bulk samples with enhanced surface sensitivity and significantly improved spatial resolution. High-resolution SEM techniques enhance our ability to detect and, subsequently, analyze the composition of nanoparticles in supported metal catalysts. Applications of high-resolution SEM imaging and microanalysis techniques to the study of industrial supported catalysts are discussed.
Atomic Scale Analysis of Cubic Zirconia Grain Boundaries
Authors: Dickey E.C. , Fan X. , Yong M. , Sinnott S.B. , Pennycook S.J. 
Published: April 2011

AbstractThe core structures of two symmetric tilt [001” grain boundaries in yttria- stabilized cubic zirconia are determined by Z-contrast imaging microscopy. In particular, near-σ=13 (510) and σ=5 (310) boundaries are studied. Both grain boundaries are found to be composed of periodic arrays of basic grain-boundary structural units, whose atomic structures are determined from the Z-contrast images. While both grain boundaries maintain mirror symmetry across the boundary plane, the 36° boundary is found to have a more compact structural unit than the 24° boundary. Partially filled cation columns in the 24° boundary are believed to prevent cation crowding in the boundary core. The derived grain boundary structural models are the first developed for ionic crystals having the fluorite structure
Electronic Effects on Grain Boundary Structure in Bcc Metals
Authors: Campbell Geoffrey H. , King Wayne E. , Belak James , Moriarty John A. , Foiles Stephen M. 
Published: April 2011

AbstractThe dominant factor in determining the atomic structure of grain boundaries is the crystal structure of the material, e.g. FCC vs. BCC. However, for a given crystal structure, the structure of grain boundaries can be influenced by electronic effects unique to the element comprising the crystal. Understanding and modeling the influence of electronic structure on defect structures is a key ingredient for successful atomistic simulations of materials with more complicated crystal structures than FCC. We have found that grain boundary structure is a critical test for interatomic potentials. To that end, we have fabricated the nominally identical Σ5 (310)/[001] symmetric tilt grain boundary in three different BCC metals (Nb, Mo, and Ta) by diffusion bonding precisely oriented single crystals. The structure of these boundaries have been determined by high resolution transmission electron microscopy. The boundaries have been found to have different atomic structures. The structures of these boundaries have been modeled with atomistic simulations using inter-atomic potentials incorporating angularly dependent d–state interactions, as obtained from Model Generalized Pseudopotential Theory. We report here new experimental and theoretical results for Ta
Effects of ‘As Deposited’ and Alloying Temperatures on the Distribution of Cu in 0.5%Cu-Al Films
Authors: Smith P. L. , Gazda J. 
Published: April 2011

AbstractThe Al-0.5wt%Cu alloys in Ti-TiN/Al/Ti-TiN metal interconnects were investigated using blanket and patterned films deposited on SiO2. Distribution of Cu and Ti within the Al films was determined using Resistivity (Rs), X-ray Diffraction (XRD), Rutherford Backscatter Spectroscopy (RBS), and Secondary Ion Mass Spectroscopy (SIMS). The location of Cu, Ti, Al and their intermetallics were studied in a CM300 field emission gun (FEG) TEM using Energy Filtered Transmission Electron Microscopy (EFTEM) with a Gatan Imaging Filter (GIF). No significant differences were observed with Rs or XRD textural analysis. Elemental distribution analysis from RBS and SIMS revealed relatively higher concentrations Cu at the Al/Ti-TiN barrier interface. This was attributed to sputtering bias during the start of the Al deposition and the subsequent snow plowing of Cu during the growth of the TiAl3 intermetallic. TEM imaging and elemental analysis showed that Cu is completely dissolved into solution at deposition temperatures ≥ 300°C. At temperatures ≤ 250°C some (Al2Cu) precipitates were observed on grain boundaries. Continued thermal cycling does not effectively change the elemental distribution. Therefore, it can be concluded that the solid solubility of 0.5wt%Cu in Al was not reached at these low temperatures or during the subsequent thermal cycling
Deposition and Annealing Studies of Diamond-Like Carbon Grown by Molecular Beam Deposition
Authors: Goetzberger Oliver , Kojima Nobuaki , Khan Aurangzeb , Yamaguchi Masafumi 
Published: April 2011

ABSTRACTStudies on the electrical conductivity of molecular beam deposited carbon films after annealing of the carbon films have been carried out. Detailed temperature dependence of conductivity on the as-deposited and on annealed samples has been investigated. The results were interpreted in terms of a model which includes a variable range hopping and strongly scattering metallic components. A correlation between annealing behavior of the electrical conductivity and the results of x-ray photoelectron spectroscopy and Raman spectroscopy is presented.