bluuebunny/crossref_metadata_2025_split huggingface dataset:
Laser Deposition and Patterning of High-Temperature Superconductors
Authors: BÅuerle D. , Heitz J. , Ludorf W. , Schwab P. , Wang X.Z. 
Published: March 2011

ABSTRACTSuperconducting films of Y-Ba-Cu-O and Bi-Sr-Ca-Cu-O on (100) SrTiO3 and (100) MgO substrates have been fabricated by reactive excimer-laser sputtering from ceramic targets. Film patterning by laser-induced reduction/metallization, oxidation, and ablation has been investigated.
Ultrafast Imaging of Ultraviolet Laser Ablation and Etching of Polymethyl Methacrylate
Authors: Braren Bodil , Srinivasan R. , Casey Kelly G. , Yeh Mildred 
Published: March 2011

ABSTRACTAblation and etching of the surface of polymethyl methacrylate (=PMMA) by pulses of 248 nm laser radiation ∼20 ns full width at half maximum (FWHM) have been probed by pulses of visible laser radiation (596 nm; < 1 ns FWHM). The results were recorded photographically in real time with a set time delay between the 248 nm ablation pulse and the 596 nm probe pulse. Modification of the surface structure of the polymer at a fluence ∼ 3 J/cm2 is first visible at 12 ns and appears to be complete in ∼ 60 ns. The first manifestation of the ablation does not occur until the UV pulse is over and consists of a nearly transparent shock-wave that has an initial velocity of 6 ∼ 104 cm/sec. Solid material from the ablated zone begins to leave the surface at ∼150 - 200 ns and reaches a maximum in intensity at 6 µs, continuing for ∼ 20 µs. The average velocity of the solid material, which is probably a low molecular weight polymer of PMMA, is 1.5 ∼ 104 cm/sec. The conclusion to be drawn from the present work is that the signal measured by photoacoustic detectors does not coincide with the bulk of the material leaving the surface.
Time-Resolved Studies of Surface Melting During Laser-Induced Chemical Vapor Deposition with Laser Intensity Modulation
Authors: Comita Paul B. , Price Peter E. , Kodas Toivo T. 
Published: March 2011

ABSTRACTThermal laser-induced chemical vapor deposition of gold deposits has been studied using a modulated Ar+ laser. Deposition of gold from dimethylgold hexafluoroacetylacetonate is accompanied by surface melting of the deposit when laser source is modulated. Time-resolved reflectance measurements have been used to study the surface reflectance during growth with modulated and unmodulated laser source. The reflectance measurements indicated that surface melting does not occur under unmodulated cw irradiation at equivalent laser intensities. Variation in the modulation duty cycle indicates that there is a minimum laser-off cycle time length required for surface melting to be observed. Evidence is presented which suggests that surface melting is due to the heat released by the exothermic decomposition of reactant adsorbed during the time that the laser intensity is off.
An Interfacial Phase Transformation in CoSi2/Si(111)
Authors: Eaglesham D.J. , Tung R.T. , Headrick R.L. , Robinson I.K. , Schrey F. 
Published: March 2011

ABSTRACTA new type of phase transformation at the interface is described in CoSi2/Si(111) B (i.e. twinned) epilayers. Thin (25Å) CoSi2 films are codeposited at room temperature on Si (111) with a Si-rich surface layer, and subsequently annealed. Plan-view transmission electron microscopy (TEM) shows that these films have low symmetry, the interface being characterised by a shift “R” between (220) planes in CoSi2 and Si. X-ray diffraction from “R” films differs from otherwise identical films either grown without Si-rich surface layer, or not annealed, which have the conventional cubic structure (“C”); R-CoSi2 cannot be indexed on a single reciprocal lattice. Cross-section high-resolution TEM suggests the presence of a separate (non-cubic) layer ≈9Å thick at the interface in these films. Annealing of R-CoSi2in-situ in the TEM shows a reversible transformation R⇔C occuring at temperatures varying from 180°C to 150K, depending on layer stoichiometry. Rt⇔C is thus a quasi-equilibrium, diffusionless transformation. We propose that R-CoSi2 lowers interfacial free energy for certain stoichiometries, but that bulk constraints stop the entire layer from transforming.
Electronic Structure of Epitaxial SiO2/Si(100) Interfaces
Authors: Motooka T. 
Published: March 2011

ABSTRACTThe local densities of states (LDOS) of epitaxial SiO, layers on Si(100) surfaces have been calculated using the recursion method combined with the Harrison's universal tight-binding model. The interface states associated with strained epitaxial layers of β-cristobalite (√2×√2)R45° and tridymite (1010)<0001> || Si(100)<011> were examined. In the β-cristobalite layer, gap states due to the surface Si dangling bonds appeared while they were eliminated by H termination. In the tridymite layer, the interface states primarily composed of the surface Si back bonds appeared near the Si conduction band minimum. Comparing the calculated DOS with photoelectron spectra for initial oxidation processes of clean Si(100), it was found that the valence band spectrum from the initial oxide formed at ∼300°C resembled that of the β-cristobalite layer.
The Structure of Interfaces in Oxide Heterojunctions Formed by CVD
Authors: Tietz Lisa A. , Summerfelt Scott. R. , Carter C. Barry 
Published: March 2011

ABSTRACTWeak-beam imaging is used to characterize the interface structure of hematite (α-Fe2O3)/ sapphire (α-Al2O3) heterojunctions parallel to (0001). The heterojunctions were prepared by lowpressure chemical vapor deposition of hematite directly onto electron-transparent sapphire substrates. Bright-field imaging and selected-area diffraction show that the growth is epitactic. The 5.5% lattice misfit at the interface is found to be accommodated by one of two different hexagonal dislocation networks: (1) b = 1/3<1210> or (2) b = 1/3<1010>. The latter are associated with a “basal twin”-type orientation relationship of the hematite and the alumina.
A New Defect on the Reconstructed Si(100) Surface: An AB Initio Molecular-Dynamics Study
Authors: Ihara Sigeo , Ho Shi Lun , Uda Tsuyoshi , Hirao Masahiko 
Published: March 2011

ABSTRACTAn interstitial dimer, which is symmetric and recessed from the surface, is proposed as a new defect structure on reconstructed Si(100) surfaces. The structure of the interstitial dimer is studied using ab initio molecular-dynamics simulations, and shown to be stable. Possible arrangements of the new defects are discussed.
Imaging by Sliding Planes in Scanning Tunnelling Microscopy
Authors: Todd John D. , Pethica John B. 
Published: March 2011

ABSTRACTScanning tunnelling microscope images of layered materials in a non-uhv environment exhibit various anomalous phenomena, including enhanced corrugation heights, periodicity over large areas and a marked absence of point defects. We have modified a precision indentation device to allow STM rastering of a tip across a surface, while simultaneously monitoring mechanical contact. Images we have obtained from this apparatus on an HOPG sample exhibit atomic scale resolution with contact areas much larger than a single atom. Contrast in the image results from periodic conductance fluctuations as the layers of the sample undergo shear in the region of the tip. We provide a model for this process, which explains a variety of curious, and otherwise unrelated phenomena occurring during STM imaging of these materials.
STM of Gold on Graphite
Authors: Thomas P. A. , Lee W. H. , Masel R. I. 
Published: March 2011

ABSTRACTScanning Tunnelling Microscopy was used to examine the surface structure of gold films and supported gold particles. It was found that freshly evaporated gold films have a relatively smooth surface morphology. However, after 1 hr of annealing, a series of dendrites were clearly visible on the surface of the films. With additional annealing, the dendrites got larger, until the film broke into particles. STM images of annealed gold particles showed that annealed gold particles larger than 150 Å have a polyhederal shape and a smooth surface morphology. However, the surfaces of the particles smaller than 60 Å remained highly corrugated even after a long anneal. We believe that the difference in morphology of large and small particles may have some profound implications in supported metal catalysis.
μm-Scale Lateral Growth of Ga-Monolayers Observed In-Situ by Electron Microscopy
Authors: Osaka J. , Inoue N. 
Published: March 2011

ABSTRACTAn ultra high vacuum scanning electron microscope equipped to an MBE system is utilized to study a transient of a surface atomic structure during MBE growth of GaAs and AlGaAs by the alternate supply method. Lateral growth of a Ga-monolayer over microns is realized utilizing Ga droplets. This is confirmed by discriminating the Ga and As top layer by using the secondary electron intensity difference between the Ga and As top layer. The growth mechanism of the Ga monolayer is discussed based on the results.
Interfacial Stability and Interdiffusion Examined at the Atomic Level
Authors: Kim Y. , Ourmazd A. , Malik R.J. , Rentschler J.A. 
Published: March 2011

ABSTRACTUsing chemical lattice imaging in combination with vector pattern recognition, we obtain quantitative profiles of the chemical change across single interfaces with atomic plane resolution. We thus study interdiffusiuon across single GaAs/AlGaAs interfaces as a function of temperature, depth of interface beneath the surface, and doping. Since our technique is sensitive to interdiffusion coefficients as small as 10−20 cm2/s, we can study atomic level changes at a single interface at the low temperatures used for many device processing steps (∼700C). Our results show interdiffusion, and hence the layer stability depend not only on temperature and doping, but also on the distance of the interface from the surface. The implications of these results for the stability of multilayered structures are discussed.
Atomistic Simulation Study of Interfaces in Nanophase Silicon
Authors: Lupo James A. , Sabochick Michael J. 
Published: March 2011

ABSTRACTNanophase silicon was investigated using atomistic simulation. The simulations employed a modified Stillinger-Weber potential appropriate for crystalline and amorphous silicon. Computer “samples” of nanophase material were formed by compressing together three grains of several hundred atoms each, using Fletcher-Powell minimization and external pressures of 0.5 to 13.5 GPa. Relative densities obtained in the samples ranged from 65% to 98% as compared to the perfect crystal. The nanophase materials maintained crystalline order up to the interfaces and no highly disordered interfaces were observed. Calculated bulk moduli exhibited a linear dependence with respect to density, with no significant dependence on structure. The calculated thermal expansion coefficients were up to twice as large as that in the perfect crystal and were structure dependent.
High-Resolution Electron Microscopy of Interfaces In Ain - Braze Metal Alloy Systems
Authors: Carim A. H. 
Published: March 2011

ABSTRACTThe microstructural aspects of active brazing of AIN with a Ag-Cu-Ti alloy have been investigated. A series of reaction product layers are formed. TiN is produced in contact with the polycrystalline, bulk AIN. High-resolution transmission electron microscopy and microdiffraction demonstrate that some of the TiN grains at the interface display specific orientation relationships with respect to the adjoining AIN crystallites. As has sometimes been observed in studies of epitaxy in other systems, these relationships are not necessarily those that provide the minimum geometrical mismatch between one or more sets of lattice planes. Farther from the substrate, an fl-type nitride phase with composition (Ti,Cu,Al)6N occurs as a reaction product. High-resolution images confirm the absence of amorphous or crystalline intervening phases at the TiN-ŋ interface and at ŋ grain boundaries.
Novel Compact and High-Resolution Ion Backscattering Analysis System,Chiribas
Authors: Kido Yoshiaki , Kawano Akira , Konomi Ichiro 
Published: March 2011

ABSTRACTThe design and performance of CHIRIBAS(Compact and High-Resolution Ion Backscattering Analysis System) are presented. The system consists of a 60 kV duoplasmatron and unique energy analysis systems connected to a microcomputer. The 5–60 keV H, He, and He+ beams are backscattered to 180° and their energies are analyzed by a time-of-flight technique or with an electrostatic deflector combined with a position sensitive microchannel plate. The probing depth and depth resolution are estimated to be up to 50 nm and better than 0.5 nm, respectively. The computer-simulated spectrum analysis allows rapid and accurate determination of surface and interface structures such as depth profiles of elemental compositions and lattice defects. CHIRIBAS also makes it possible to measure excited state populations using Stark ionization for 5–10 keV H neutralized at the exit surface and thus provides the possibility to determine the energy and spatial distributions of the valence electrons extending outward from the top surface. The present article includes the beam parameters achieved and the preliminary data on reactive-ion etched Si surfaces.
Spectroscopic Ellipsometry as a Non-Destructive Technique for Characterization of Atomic-Scale Interfaces
Authors: Stehle J.L. , Piel J.P. , Lecat J.H. , Pickering C. , Hammond L.C. 
Published: March 2011

ABSTRACTAnalysis of oxide interfaces with semi-conductor substrates, such as crystalline silicon, gallium arsenide, or indium phosphide is critical in processing and electrical performances. Interfaces can be characterized by spectroscopic ellipsometry (SE), which has a wide spectral range (1.3 to 5.3 eV ) allowing an optical penetration depth of 10 nm to a few microns.A multilayer stack can be characterized in terms of its layer thicknesses and composition. These physical parameters must be calculated through a mathematical model. Linear regression analysis is used to minimize the differences between the measured spectrum and the calculated model. If necessary, an interlayer can be introduced into the model to enhance the fit. This can be complemented by a new method involving calculation of apparent index values which amplifies interface sensivity allowing the thickness to be measured to better than 2 Angstroms. Examples will be given.
Numerical Model of Bond Strength Measurements
Authors: Nutt Gerald L. 
Published: March 2011

ABSTRACTWe have reported bond strength measurements of metal/ceramic interfaces using shock waves to separate the bond by spallation[1,2]. The technique relies on the interpretation of the free surface velocity of the metal film as it is spalled from the substrate.We answer several questions relating to the details of the interaction of the shock with the interface. Specifically, we examine the role of sound speeds in the measurements. We also calculate the plastic strain in the the bond region and verify the theory relating to the jumpoff velocity of the scab to the bond strength.
Plan-View CBED Studies of Nio-Zro2(CaO) Interfaces
Authors: Dravid V.P. , Notis M.R. , Lyman C.E. , Revcolevschi A. 
Published: March 2011

ABSTRACTLow energy lamellar interfaces in the directionally solidified eutectic (DSE) NiO-ZrO2(CaO) have been investigated using transmission electron diffraction and imaging. The symmetry of this bicrystal and an aspect of interfacial relaxations in the form of symmetry lowering in-plane rigid body translation (RBT) have been explored by performing convergent beam electron diffraction (CBED) experiments of plan-view bicrystals. Edge-on interfaces have also been studied by conventional and high resolution transmission electron microscopy (CTEM and HRTEM respectively), and electron diffraction fine structure analysis. Despite certain experimental difficulties due to interfacial defects and strain, plan-view CBED patterns offered valuable information concerning bicrystal symmetry and indicated no symmetry lowering RBT in this bicrystal. The suitability of plan-view CBED is briefly discussed in view of its potential as a technique to determine bicrystal symmetry and RBT.
Bi4Ge3O12 (BGO) - A Scintillator Replacement for NaI(Tl)
Authors: Farukhi M. R. 
Published: March 2011

ABSTRACTScintillation performance of recent (2X) grown BGO is studied. Results indicate BGO to perform better than 8% 137Cs FWHM NaI(Tl) at energies 2.6 Mev and higher. Even the low energy performance of BGO is suitable for considering it in lieu of NaI(Tl) for many spectroscopic applications.
Materials Aspects of Germanium Radiation Detector Fabrication
Authors: Scott Hubbard G. 
Published: March 2011

ABSTRACTAn overview of the present status and future requirements of material for germanium radiation detectors is presented. Fabrication and storage problems for both lithium-drifted, doped germanium and high-purity germanium are compared to demonstrate the reasons for the recent complete dominance of the latter in commercially available radiation detectors. The effect of electrically active point and line defects on the resolution and operating characteristic of high-purity germanium radiation detectors is discussed. Emphasis is placed on deep impurities and dislocations. Present and future applications of high-purity germanium radiation detectors are reviewed.
Microdiffraction from Cleaved Si-Si1-xGex Multilayers
Authors: Pike W. T. 
Published: March 2011

AbstractUsing the nanometer probe available in the dedicated scanning transmission electron microscope (STEM) local structural information can be obtained from individual layers in [100] grown Si-Si1-xGex multilayer structures. Furthermore the small probe size enables cleaved specimens with their very large wedge angles to be analyzed in cross-section. Diffraction patterns are shown from multilayers of varying periodicity. Analysis of the patterns concentrates on the higher order Laue zone (holz) reflections in the high angle excess ring . The behaviour of the excess holz reflections indicates the transition from a strained layer superiattice to a dislocated structure as the thickness of the layers increases for a given composition.
Structural and Electronic Properties of GaAs/InGaAs/GaAs Heterostructures
Authors: Bonar J. M. , Hull R. , Malik R. J. , Ryan R. W. , Walker J. F. 
Published: March 2011

AbstractWe have made a study of GaAs/InGaAs/GaAs (001) strained layer heterostructures using Transmission Electron Microscopy (TEM) as a structural tool to determine the misfit dislocation structure and density as a function of Indium concentration. The average misfit dislocation spacing varies from > 10 µm for x < 0.3, to a few microns at x = 0.3, and drops to a few hundred Angstroms at x = 0.5. We did in-situ annealing experiments in order to study the strain relaxation process, measuring the temperature at which the structure begins to relax, and the dislocation velocities. Dislocation velocities are a few microns per second at the growth temperature of 450 ° C, and tens of microns per second at 690 ° C. In addition to interfacial dislocations in the usual <110> directions, in samples where x ≥ 0.4, we observed dislocations running in <100> directions. A study of the electrical characteristics of the material was made in parallel with the structural measurements: the mobility of the InGaAs layer was measured, the material was processed into Heterojunction Bipolar Transistors (HBT’s) and the gain was measured. The electrical characteristics initially improved with the addition of In, peaking at x = 0.1 and dropping sharply for higher x.
Effect of Annealing on Strained InGaAs/GaAs Quantum Wells
Authors: Koteles Emil S. , Elman B. , Melman P. , Armiento C.A. 
Published: March 2011

AbstractWe have demonstrated that shallow ion (75As+) implantation and rapid thermal annealing (RTA) of strained InGaAs/GaAs quantum well (QW) structures can modify the optical properties of these epitaxial semiconductor heterostructures in a spatially selective manner. After RTA, exciton QW energies, determined from peaks in the photoluminescence spectra, shifted significantly to higher values only in the implanted regions. The magnitudes of the shifts were dependent on QW widths, RTA temperatures, and implantation fluences. The shifts were interpreted as resulting from the modification of the shapes of the as-grown QWs from square (abrupt interfaces) to rounded (gradual interfaces) due to enhanced indium diffusion out of the well layers in irradiated areas as a consequence of the diffusion of vacancies generated near the surface by the implantation. The thermal processing had only a small effect on the strain present in the quantum well layers due to the difference in the lattice constant of the well and barrier layers.
A Tem study of Epitaxial FE/AG and MN/AG Superlattices
Authors: Nahm S. , Salamanca — Riba L. , Jonker B. T. , Prinz G. A. 
Published: March 2011

AbstractWe have studied the epitaxial growth and structural properities of single crystal Fe/Ag and Mn/Ag superlattices grown on (001) GaAs substrates using transmission electron microscopy. A buffer layer of Ag (001) was grown on a 5 monolayer Fe seed layer on the (001) GaAs substrate before the growth of the superlattice to obtain good quality films. For some samples an intermediate buffer layer of ZnSe was used, as well. Both Fe/Ag and Mn/Ag superlattices with a Ag buffer layer show very sharp interfaces. The densities of dislocations in the film and the buffer layer are the same suggesting that the dislocations originate at the film/substrate interface. We have observed evidence for a strain modulation of ≈ 8 Å in the Mn layer for thick (≈ 22 Å) Mn layers in the superlattice samples but not in samples with a thin Mn layer.
Columnar Epitaxy of CoSi2 on Si(111), Si(100), and Si(110)
Authors: Fathauer R.W. , Nieh C.W. , Xiao Q.F. , Hashimoto Shin 
Published: March 2011

AbstractEpitaxial columns of CoSi2 are produced when Si and Co are codeposited on heated Si substrates. These columns are surrounded by epitaxial Si with defect densities below the detection limit of transmission electron microscopy. This phenomenon has been studied as functions of substrate temperature, Si:Co ratio, deposition rate, thickness of the epitaxial layer, and substrate orientation. These data suggest that the distribution of columns is dictated by the nucleation of CoSi2 islands during the initial stages of the deposition.
The Mechanism of Epitaxial Si-Ge/Si Heterostructure Formation by Wet Oxidation of Amorphous Si-Ge Thin Films
Authors: Prokes S.M. , Rai A.K. , Carlos W.E. 
Published: March 2011

AbstractEpitaxial SiGe/Si heterostructures have been formed by wet oxidation from amorphous SiGe films deposited on Si(100). Amorphous SixGe1-x films were deposited at a vacuum of 10-7 Torr. The presence of an initial native oxide precluded solid phase epitaxy under standard annealing conditions, but epitaxy could be achieved by the use of wet oxidation. The samples were oxidized at 900°C for various times and examined in reflection electron diffraction, ellipsometry, cross-sectional and plan-view transmission electron diffraction, and electron spin resonance. The formation of the epitaxial layer and oxide has been examined, and an epitaxial growth model is suggested.
Heteroepitaxial Growth of Germanium Films by Supersonic Free Jet Chemical Beam Epitaxy
Authors: Eres Djula , Sharp J. W. , Lowndes D. H. 
Published: March 2011

AbstractA supersonic free jet operated in continuous wave and pulsed mode was used to grow Ge films on (100) GaAs and (100) Si substrates. The Ge-bearing source molecule digermane (Ge2H6) was seeded (at 5% concentration) in a helium carrier gas. A free jet expansion of this gas mixture was directed toward the heated substrate surface, where Ge film growth took place by surface-induced thermal decomposition of the ballistically impinging digermane molecules. The thickness distribution across the substrate surface was fitted by a cosmJ distribution. The values of m spanned the range 6–35. The upper limit on growth resulting from “background” gas scattered out of the jet was found to be less than 10% of the Ge film thickness for growth on (100) GaAs, and around 25% for growth on (100) Si.