bluuebunny/crossref_metadata_2025_split huggingface dataset:
In-Situ Time-Resolved X-Ray Studies of Eutectic Crystallization in Amorphous Fe1−xBx and Co1−xZrx
Authors: Fischer Henry E. , Brauer S. , Sutton M. , Ström-Olsen J. , Zaluska A. , Stephenson G. B. , Koster Uwe 
Published: March 2011

ABSTRACTUsing a millisecond time-resolved x-ray scattering technique at the National Synchrotron Light Source, we have simultaneously obtained in situ both large-angle (LAXS) and small-angle (SAXS) diffraction patterns for isothermal crystallization of amorphous Fe1−xBx (0.16 < x < 0.21) and Co1−xZrx (0.08 < x < 0.11). The large-angle x-ray data are analyzed to determine which of the two crystalline products nucleate first in each compound, and also to assess the evidence for eutectic growth as shown by a time-independent ratio of volume fractions of these product phases. The small-angle data give the length scales of the eutectic structure as well as information about its time evolution. Combining our x-ray results with TEM studies, we examine the effects of changes in temperature and composition on the structural evolution of both the amorphous and crystalline phases.
Scanning Tunnelling Microscopy Investigation of Surface Morphology in the Growth of GaAs(001)
Authors: Heller E. J. , Lagally M. G. 
Published: March 2011

ABSTRACTThe surface morphology of MBE - grown GaAs(001) has been investigated using scanning tunnelling microscopy (STM) and reflection high - energy electron diffraction (RHEED). STM shows that the missing - dimer - row structure of the (2 × 4)/c(2 × 8) reconstruction consists of rows of clusters of two As dimers separated by rows of two missing dimers, in agreement with previous reports. Layers grown on nominally flat substrates display a multi - level system of terraces elongated along [110] suggesting that growth occurs primarily by sticking at B - type steps. For films grown under certain growth conditions, B - type steps on vicinal substrates exhibit a dendritic step morphology, which may be an example of a step flow growth instability consistent with limited Ga diffusion over steps.
Optical Second Harmonic Generation of Thiols Adsorbed on Gold
Authors: Buck M. , Eisert F. , Fischer J. , Grunze M. , Träger F. 
Published: March 2011

AbstractThe adsorption kinetics of self-assembling n-alkyl thiol films on poly cry stalline gold substrates was studied in situ by optical second harmonic generation (SHG). The relation between the SHG signal change and the thiol coverage was established by comparison with ex situ X-ray photoelectron spectroscopy measurements. We find that the temporal dependence of the adsorption is well described by Langmuir adsorption kinetics. The source of the SHG signal is found to be linearly related to the nonlinear susceptibility of the adsorbate-substrate interaction. Experiments with chain lengths ranging from 1 to 22 showed, that the saturation coverage for thiols longer than hexanethiol is equal.
Self-Assembled Monolayers as Models for Studying Protein Adsorption to Polymer Surfaces
Authors: Prime Kevin L. , Whttesides George M. 
Published: March 2011

ABSTRACTSelf-assembled monolayers (SAMs) of functionalized alkanethiolates on gold are a well-characterized system for studying the interfacial properties of organic materials. We have used SAMs as models for the surfaces of organic polymers and used mem to study the adsorption of proteins onto organic materials. We have formed SAMs from mixtures of alkanethiols in which one alkanethiol is hydrophobic and the other is terminated by a short (2 ≤ n ≤ 17) oligomer of poly(ethylene oxide). These “mixed” SAMs effectively resist the adsorption of fibrinogen from moderately concentrated (1 mg/mL) solutions. Protein adsorption begins when < 5% of the accessible area of the surface consists of hydrophobic groups. These findings suggest that real protein-resistant monolayers must present an almost defect-free surface of oligo(ethylene oxide) groups in order to eliminate adsorption.
Digital Electrochemical Etching of Compound Semiconductors
Authors: Lei Q. Paula , Stickney John L. 
Published: March 2011

AbstractThe principles for an electrochemical digital etching method for compound semiconductors are described and initial results reported. The method is designed to allow atomic level control over the etching process, resulting in the removal of a bilayer of the compound for each cycle. An atomic layer of one element is removed at one potential and then an atomic layer of the second element is removed at a second potential to complete one cycle. The results reported here are for the etching of CdTe. For CdTe, Te is stripped by reduction to Te2- while Cd is stripped by oxidation to Cd2+. Underpotentials are chosen so that only the top atomic layer of an element is removed. Potentials sufficient to strip the elemėnt from the bulk of the CdTe substrate are avoided. Application of the method should involve the use of a simple electrochemical cell, with solution convection. The substrate is placed in the cell and a square wave applied, where each cycle results in the dissolution of a bilayer of the compound. The two potentials of the square wave correspond to underpotential stripping potentials for Cd and Te respectively. Directions for the future development of this etching method are discussed.
Pinning of Misfit Dislocations in film Growth Studied by Grazing Incidence X-ray Scattering
Authors: Liang K. S. , Lee C. H. 
Published: March 2011

ABSTRACTUsing grazing incidence x-ray scattering, we have studied incommensurate structures of Pb adlayers on Cu(110) surface and epitaxial Al films grown on Si(111) surface. Similar diffuse scattering profiles were found in both cases, which can be fitted with a Gaussian-plus-Lorentzian lineshape. The results are attributed to a overlayer structure with pinned misfit dislocations at the interface.
Epitaxy Development in thin Superconducting YBa2Cu3O7 Films
Authors: Yen A. , Li L. , Klein J. D. , Nowak W. B. , Cogan S. F. 
Published: March 2011

ABSTRACTUltrathin superconducting YBa2Cu3O7, films were grown on (100) YSZ (yttria-stabilized-zirconia) substrates by off-axis if magnetron sputtering at a relatively high deposition rate. The structure, orientation, and morphology of the films were examined by x-ray diffraction, reflection high-energy electron diffraction (RHEED), and scanning electron microscopy. X-ray diffraction patterns of films deposited on YSZ substrates exhibited strong c-axis alignment with the YBa2Cu3O7 peaks sharpening as the film thickness was increased. The degree of epitaxy apparent in RHEED photographs was found to increase dramatically as the film thickness was increased from 12 nm to 108 nm. This behavior is attributed to a nucleation and growth process in which epitaxy develops as a result of a 3 stage progression from a random to an oriented film.The films were in-situ superconducting, exhibiting superconducting transition temperatures, Tc(0)'s, of 80 K for a 12 nm film and 88 K for a 280 nm film. However, the relatively low critical current densities (Jc < 1 × 106 A/cm2) at 77 K are probably due to a lack of in-plane epitaxy.
Low Temperature Silicon Epitaxy Grown by Electron-Beam Evaporation in an Ultra-High Vacuum System
Authors: Lin Yung-Jen , Yew Tri-Rung 
Published: March 2011

ABSTRACTThis paper presents the results of silicon epitaxial growth on silicon windows surrounded with oxide walls by electron-beam evaporation in an ultra-high vacuum system with a load-lock chamber. The wafer surface was in-situ cleaned in the growth chamber to remove native oxide by thermal desorption at about 840 °C and a base pressure of better than 2 × 10-9 Torr. The growth temperature was 200°C or higher. The pre-epitaxial silicon surface structure was inspected by reflection high energy electron diffraction (RHEED). The influence of the thermal desorption on the quality of the epi/substrate interface and epitaxial layers was studied. In addtion, the deposition parameters which control the epitaxial quality were investigated. The epitaxial films were characterized by cross-sectional trasmission electron microscopy (XTEM) and secondary ion mass spectroscopy (SIMS).
In-Situ Heavy as Doping in Si Selective Epitaxial Growth
Authors: Ohshita Y. , Kitajima H. 
Published: March 2011

ABSTRACTRole of in-situ heavy As doping in Si selective growth is studied using the SiH2Cl2/H2/HCl/AsH3 gas system. By increasing AsH3 flow rate, the growth rate decreases in proportion to In (AsH3 flow rate). This result is explained well using a Frumkin-Temkin adsorption model. The As concentrations in grown films depend on surface orientation. Moreover, the maximum As concentration is about ten times lower than the solubility limit at a given temperature. These results are able to be explained qualitatively, if equilibrium concentrations of impurities at the Si(100), the Si(111), and the bulk are assumed to be different from one another, and that the concentration at the surface is frozen in the grown film.
Growth Process of Si and GaAs in the Heterostructure GaAs/Si/GaAs(100).
Authors: Lopez M. , Takano Y. , Pak K. , Yonezu H. 
Published: March 2011

ABSTRACTThe growth mode of Si on GaAs(100) substrates and that of GaAs on very thin (1/4 ∼ 3 ML) Si films grown pseudomorphically on GaAs was investigated by observing the behavior of the reflection-high energy electron diffraction (RHEED) specular spot intensity. From the presence of RHEED oscillations during the initial stage of the growth of Si on GaAs we infer a two-dimensional growth with nucleation on the terraces up to a thickness of 3 ML. During the posterior growth of GaAs on the pseudomorphic Si films, a tendency towards three dimensional growth was observed. This tendency increased with the Si interlayer thickness. The causes of the formation of these islands are discussed.
Morphology and Interface chemistry of the Initial Growth of GAN and ALN on α-SIC and Sapphire
Authors: Sitar Z. , Smith L. S. , Paisley M. J. , Davis R. F. 
Published: March 2011

ABSTRACTThe morphology and interface chemistry occurring during the initial stages of growth of GaN and A1N layers has been obtained. Films were grown using gas source MBE equipment containing an ECR plasma source to activate molecular nitrogen. The experiments consisted of sequential depositions of about one monolayer thick films and XPS analysis. Evidence for silicon nitride formation on the SiC surface was obtained from the studies of both the Si oxidation states and the substrate peak intensity dependence on film thickness. The growth of GaN on sapphire appeared to occur via the Stranski-Krastanov mode, while the growth on SiC showed characteristics of three-dimensional growth. AlN grew in a layer-by-layer mode on both substrates.
Orientation Dependent Epitaxial Growth of CeO2 Layers on Si Substrates
Authors: Inoue T. , Ohsuna T. , Yamamoto Y. , Sakurai Y. , Luo L. , Wu X. D. , Maggiore C. J. 
Published: March 2011

ABSTRACTCerium dioxide (CeO2) layers epitaxially grown on (100), (111) and (110) silicon substrates by electron beam evaporation in an ultra-high vacuum were investigated. CeO2 layers on Si (111) substrates were proved to be epitaxially grown at the substrate temperature above 200°C, and had considerably good crystalline quality. On the other hand, CeO2 layers grown on Si (100) at 800°C consisted of more than 98% volume fraction of (110) component. Cross-sectional high resolution transmission electron microscopy and selected area electron diffraction verified clearly the above crystallography orientation and that the <100> direction in the CeO2(110) plane was parallel with the <110> direction in the Si (100) plane. The cross-sectional lattice image confirmed the existence of ∼ 6 nm-thick intermediate amorphous layer between the CeO2 layer and the Si substrate.
Mechanism of Stress-Enhanced Solid-Phase Epitaxy
Authors: Chaki T. K. 
Published: March 2011

ABSTRACTEnhancement of solid-phase epitaxial growth (SPEG) due to hydrostatic pressures and bending stresses is explained by stress-enhanced mobility of point defects in the amorphous solid. The crystallization is by the adjustment of atomic positions in the vicinity of the crystallization/amorphous (c-a) interface due to self-diffusion in the amorphous phase, assisted by a free energy decrease equal to the difference in free energies between the amorphous and crystalline phases. Due to a mismatch in the bulk moduli between the amorphous and crystalline phases, the application of a hydrostatic pressure can develop tensile stresses in the amorphous layer near the c-a interface. Non-hydrostatic stresses in the amorphous layer enhance the mobility of point defects in the amorphous layer and, therefore, an enhancement of the SPEG rate. In the cases of both hydrostatic pressure and bending, the enhancement occurs in the tensile side, indicating that vacancy-like mechanism is predominant in SPEG.
The Universal Instability of the Separation Boundary Between a Non-Hydrostatically Stressed Elastic Crystal and its Melt
Authors: Grinfeld Michael A. 
Published: March 2011

ABSTRACTIn the absence of surface tension and external force fields, the equilibrium between a hydrostatically stressed crystal and its melt is neutral with respect to the perturbations associated with particle transfer from one region of the boundary into another. However, under the action of arbitrary small nonhydrostatic components of the stress field in the elastic crystal, the neutral equilibrium is transformed to an unstable equilibrium [1]. This instability is very general in nature; for example, for it to be seen the liquid media need only to be able to dissolve the solid phase or in some way to assist the transport of particles along the crystal's surface. In contrast, the surface tension, roughly speaking, stabilizes the shape of the interphase boundary but it cannot suppress the instability generated by the nonhydrostatic components of the stress field in the region of sufficiently long perturbations. Until now the basic instability mechanism discussed here seems to have escaped the attention of theorists. This mechanism allows one to look in a completely new way at a broad range of phenomena. We discuss tentative manifestations and role of this instability in low temperature physics, in materials science, in theory of crystal growth, and, in particular, in theory of epitaxy and of the Stranski-Krastanow pattern of growth of thin crystalline films.
Removable External Seeding for Solid phase Epitaxy of Amorphous Silicon on Glass Substrates
Authors: Doi Atsutoshi , Tsuda Takanori , Kumikawa Masa-ICHI , Nakamizo Yoshiyuki , Ueda Kazuyuki 
Published: March 2011

ABSTRACTA new method for obtaining a planar silicon film on glass substrates (SOG) with controlled crystal orientation has been introduced. This technique uses solid phase epitaxy (SPE) with external seed to fabricate the orientation-controlled SOG structure. Heat treatment of amorphous SOG substrate in contact with mesa striped Si seed crystal was performed at 540°C for 16 hours to form the SPE layer. The planar surface of the SOG structure is due to the most important feature of the present technique-the separation of the seed from the substrate after SPE.
Plasma Surface Interaction During the Growth of Semiconductor Thin Films Studied byin Situ Infrared Ellipsometry
Authors: Blayo N. , Drevillon B. 
Published: March 2011

ABSTRACTThe early stages of the growth of plasma deposited amorphous silicon (a-Si:H) and microcrystalline silicon (μc-Si) on glass substrates are investigated by in situ infrared phase modulated ellipsometry (IRPME) in the silicon-hydrogen stretching mode region. μc-Si are prepared by alternating SiH4 and H2 plasmas. New insights on the plasma-surface interactions during the growth of these films are given. During the deposition of the first 20 Å of a-Si:H, the hydrogen is incorporated as SiH2. During the further growth of a-Si:H the SiH2 bonds are located at the film surface inside a very thin hydrogen rich overlayer. During the deposition of the first 10–20 Å of μc-Si, the SiH2 bonds are predominantly removed by the H2 plasma, the material being amorphous. After this selective removal of the SiH2 groups, a transition from amorphous to microcrystalline growm is observed. A systematic hydrogen etching during the further growth of μc-Si is observed.
Structure of Grain Boundaries in L12 Alloys at Finite Temperatures: Effects of Deviations from Stoichiometry
Authors: Yan M. , Vitek V. , Ackland G. J. 
Published: March 2011

ABSTRACTAtomic structures of grain boundaries in Ni3Al and Cu3Au has been studied using a Monte Carlo relaxation technique and many body central force potentials to describe interatomic forces. The purpose of this work is to investigate the temperature dependence of the compositional order in the boundary region for both stoichiometric and non-stoichiometric alloys. In the former case the boundaries in Ni3Al remain ordered up to very high temperatures while boundaries in Ni3Al disorder at relatively low temperatures. In the non-stoichiometric case, the surplus of nickel in the bulk leads to segregation to grain boundaries and to a significant chemical disordering in the boundary region. The surplus of aluminum also leads to segregation but without disordering in the boundary region. Using these results we discuss the intrinsic brittleness of grain boundaries in Ni3Al as well as the effect of stoichiometry on the intergranular brittleness.
Reconstruction of a High-Angle Twist Grain Boundary by Grand-Canonical Simulated Quenching
Authors: Phillpot S. R. , Rickman J. M. 
Published: March 2011

ABSTRACTA formalism for obtaining the zero-temperature structure of mono-component solids by simulated quenching in the grand-canonical ensemble is outlined. The structure of a high-angle twist grain boundary on the (110) plane of an fee metal is investigated. The lowest energy structure is found to have a density approximately 20% higher than the structure obtained from canonical-ensemble energy-minimization.
Grain Boundary Transformations in Bi-Doped Copper
Authors: Urdaneta Elsie C. , Luzzi David E. , McMahon Charles J. 
Published: March 2011

ABSTRACTBismuth-induced grain boundary faceting in Cu-12 at ppm Bi polycrystals was studied using transmission electron microscopy (TEM). The population of faceted grain boundaries in samples aged at 600°C was observed to increase with heat treatment time from 15min to 24h; aging for 72h resulted in de-faceting, presumably due to loss of Bi from the specimen. The majority of completely faceted boundaries were found between grains with misorientation Σ=3. About 65% of the facets of these boundaries were found to lie parallel to crystal plane pairs of the type {111}1/{111]2- The significance of these findings in light of recent high resolution electron microscopy experiments is discussed.
The Determination of Interfacial Structure and Phase Transitions in Al/Cu and Al/Ni Interfaces by Means of Surface Extended X-Ray Absorption Fine Structure
Authors: Barrera E. V. , Heald S. M. 
Published: March 2011

ABSTRACTSurface extended x-ray absorption fine structure (SEXAFS) was used to investigate the interfacial conditions of Al/Cu and Al/Ni shallow buried interfaces. Previous studies using glancing angle extended x-ray absorption fine structure, x-ray reflectivity, photoemission, and SEXAFS produced conflicting results as to whether or not the interfaces between Al and Cu and Al and Ni were reacted upon room temperature deposition. In this study polycrystalline bilayers of Al/Cu and Al/Ni and trilayers of Al/Cu/Al and Al/Ni/Al were deposited on tantalum foil at room temperature in ultra high vacuum and analyzed to evaluate the reactivity of these systems on a nanometer scale. It became overwhelming apparent that the interfacial phase reactions were a function of the vacuum conditions. Samples deposited with the optimum vacuum conditions showed reaction products upon deposition at room temperature which were characterized by comparisons to standards and by least squares fitting to be CuAl2 and NiAl3 respectively. The results of this study showed that the reacted zone thicknesses were readily dependent on the deposition parameters. For both Al on Cu and Al on Ni as well as the metal on Al conditions 10A reaction zones were observed. These reaction zones were smaller than that observed for bilayers of Al on Cu (30Å) and Al on Ni (60Å) where deposition rates were much higher and samples were much thicker. The reaction species are evident by SEXAFS, where the previous photoemission studies only indicated that changes had occurred. Improved vacuum conditions as compared to the earlier experiments is primarily the reason reactions on deposition were seen in this study as compared to the earlier SEXAFS studies.
Surface Reconstruction of Platinum and Gold and the Embedded Atom Model
Authors: Haftel Michael I. 
Published: March 2011

ABSTRACTWe investigate the surface reconstructions of various faces of gold and platinum theoretically with a number of embedded atom potentials. We find that whereas all potentials examined predict equivalent bulk properties, only those with a relatively steep embedding function at surface electron densities predict the experimentally observed buckled quasihexagonal reconstruction for the (100) faces and surface energies in close agreement with experiment. Almost all embedded atom potentials considered predict the observed 2×1 missing row structure for the (110) faces, and some the observed missing row structure for the (311) face of platinum.
Thermodynamic and Kinetic Characteristics of Variations in Shapes of Ridges Formed on {100} Lithium Fluoride Surfaces
Authors: Bullard J. W. , Glaeser A. M. , Searcy Alan W. 
Published: March 2011

ABSTRACTChannels with widths in the range from 5 μm to 25 μm were formed in {100} surfaces of LiF single crystals by a photolithographic technique. Specimens annealed at or above 0.90 Tm, where Tm is the melting point, and then quenched showed die channels and the ridges between them develop rounded profiles. Evolution of these profiles was evaluated for the various channel widths and for interchannel ridge spacings of 5 to 100 μm in terms of: a) an accepted theoretical model for a surface diffusion controlled process, and b) a model which assumes that shape changes depend only on the relative energies of attachment of atoms in surface sites with various surface curvatures. Either model is consistent with the experimental observations to within the reproducibility in measurements.
Coarsening of a Population of Precipitates in a Soud
Authors: Lavine J. P. , Hawkins G. A. 
Published: March 2011

ABSTRACTCoarsening of a population of second-phase precipitates in a solid affects the physical properties of the solid. A numerical model of coarsening is introduced to treat both diffusion-controlled and interface reaction-controlled coarsening. The model is based on the escape probabilities of particles from precipitates. The experimental time dependences of precipitate coarsening are obtained.
Diffusion-Controlled Decohesion Using a Cu-Sn Alloy as a Model System
Authors: Bika Dafni , McMahon Charles J. 
Published: March 2011

ABSTRACTThis research deals with a mode of brittle intergranular fracture in which a surface-adsorbed embrittling element is driven into a grain boundary as a result of the application of a tensile stress across the boundary. A Cu-8%Sn alloy has been employed to explore this phenomenon, since tin is a surface-active element, and this alloy is known to suffer intergranular weakness at elevated temperatures. Intergranular cracking occurred by brittle, discontinuous crack advance at 265°C in vacuum with an average rate of 0.1μm/sec. This behavior is analogous to sulfur-induced stress-relief cracking in steels and several cases of liquid-metal embrittlement, suggesting that this phenomenon has a generic nature.