bluuebunny/crossref_metadata_2025_split huggingface dataset:
Realization of Detailed Kinetic Models for the Growth of II-VI Compounds: Adopting DFT Calculations and Experimental Evidences
Authors: Cavallotti Carlo , Bertani Valeria , Masi Maurizio , Carrà Sergio 
Published: April 2011

AbstractThe kinetics of deposition of CdTe, ZnS and ZnSe films was studied. An overall microkinetically reversible kinetic scheme consisting of elementary reactions, comprehensive of gas phase and surface processes was developed. Kinetic constants of gas phase reactions were either found in the literature or determined through quantum chemistry methods. Kinetic constants of surface reactions were first guessed combining kinetic theory with quantum chemical calculations and then their values were refined to reproduce experimental data. The kinetics schemes so developed were tested through the simulation of deposition reactors. Measured growth rates and gas phase compositions were thus compared with those calculated. The major finding of this studies is that the growth of CdTe, ZnS and ZnSe can be represented adopting a surface kinetic scheme constituted essentially by the same fundamental steps.
Effect of Hydrogen Coverage on Silicon Thin Film Growth: Molecular Dynamics Investigation
Authors: Muramatsu Shinya , Shimada Masatoshi , Hirao Masahiko 
Published: April 2011

AbstractSilicon thin films grown by CVD processes take various structures depending on the reaction conditions. In the case of low-temperature CVD, hydrogen coverage on the silicon substrate affects the growth as well. In order to analyze the effect of hydrogen coverage on elementary surface reactions, we performed molecular dynamics simulations in which gasphase radicals, H and SiH3, fell onto a hydrogen-terminated silicon surface. We prepared monohydride and dihydride Si(100) surfaces and modified their hydrogen coverage in a certain area in the range from 0.5 to 2.0 monolayers so as to describe the growing surface. As a result of our simulation, H radicals mainly caused H adsorption and H abstraction reactions and altered the hydrogen coverage of the surface. While reactions of SiH3 radicals with monohydride or dihydride surfaces rarely occurred, these radicals reacted more frequently with the modified surfaces. These results indicate that the change in the local hydrogen coverage caused by H radicals may induce subsequent surface reactions
Effects of the Electronic Structure on the Stability of Metallic Superlattices. Semi-Emipirical Calculations of the Total Energy
Authors: Mazzone A. M 
Published: April 2011

AbstractIn this work the total energy of metallic superlattices is evaluated at semi-empirical level. The superlattice has an heterogenous composition and it has two shapes, i.e.(i) two facingA/B wires and (ii) a hut-shaped island of the element A deposited on a rigid B substrate. The elements A and B are Ag, Cu, Pd, Pt and Fe. The calculations show the existence of competing bonding contributions. In fact, a strong bond arises from charge exchanges at the A/B interface and from the bulk-like bonds of interior atoms. On the contrary, surface atoms are undercoordinated and reduce the strength of bonding. These contributions act on opposite sense on the large structures and the geometry dependence of the binding energy suggests a self-limited growth, rather than Ostwald ripening.
Nanoscale Electron-Beam Processes and Its Application to Nanodevices
Authors: Komuro Masanori 
Published: April 2011

AbstractIn this paper, electron beam (EB) lithography and direct processes are summarized for application to nanometer-scale electron devices such as single electron transistor. As decreasing line width in lithography, the delineated patterns has fluctuation of line width, which is so-called line-edge-roughness. It is kwon that such a roughness is caused by aggregates of resist molecules. Therefore to avoid the rougphness to make smooth line edge, we have to use rather low molecular weight resist materials. As one of such candidates, EB exposure characteristics of thermally oxidized SiO2 film are described. Although the sensitivity of the resist is about a few C/cm2 which is lower than conventional resists, it is possible to delineate fine line and space pattern with 15 nm pitch and 5 nm width. This technique is extended to make miniature metal/insulator/metal junctions using SiO2/Si bilayer resist system and the following metal liftoff process. Metal layer is directly deposited on SiO2 substrates in WF6 gas ambient simultaneously with EB irradiation. The resistivity of the deposited film is about 6×10/4 Ωcm depending on hydrocarbon contamination of the substrate itself. We can make the deposited lines with line-width of about 10 nm using 3 nm diameter of the incident EB. From current-voltage characteristics for single tunnel junctions with various tunnel resistances, the barrier height is estimated to be about 0.2 eV. This result indicates clearly the junction properties can be controlled at least with the accuracy of minimum deflection increment of the EB system used here. It is successfully observed that single-electron-transistor produced by EB-induced deposition exhibits Coulomb oscillation at temperature of 230 K.
Self-Organization of Steps and Domain Boundaries of 7×7 Reconstruction on Si(111)
Authors: Hibino H , Homma Y. , Ogino T. 
Published: April 2011

AbstractWe describe three different aspects of the self-organization of steps and domain boundaries of a 7×7 reconstruction on SI(111) surfaces. The first is the formation of a triangular-tiled pattern of “1×1’ and 7×7 domains during the phase transition. ‘1÷1’ and 7×7 domains have different surface stresses. The triangular-tiled pattern is stabilized through stress relaxation. The second is the step arrangement inside a hole, which was fabricated by a standard lithographic technique. The step arrangement in the hole depends on the temperature. Below the ‘1×1’-to-7×7 phase transition, the hole has a three-fold symmetry consisting of step-bunched and non-bunched regions. This is because the step arrangement on the vicinal Si(111) surfaces depends on the direction of the steps. The third aspect is the formation of a pattern of steps and domain boundaries induced by Si growth. During the step-flow growth on Si(111), steps preferentially protrude along the domain boundaries on the lower terrace. The resulting changes in step shape induce a unique rearrangement of the domain boundaries, the number of which decreases during growth. However, when a periodic pattern is formed in the initial stages, it remains stable during growth.
Triple Junction Engineering: the Distribution of Triple Junctions in Polycrystalline Gold Thin Films
Authors: Owusu-Boahen Kwame , King Alexander H. 
Published: April 2011

ABSTRACTWe have investigated compliance with the σ-product rule at triple junctions with a common [111] axis using computer simulations and in real thin films, using electron microscopy. Large discrepancies exist between the simulations, which assume randomly distributed misorientations, and the experiments. Although for both cases the rule fails at most triple junctions, the real material shows a much higher than expected occurrences of compliance. This result can be explained in two distinct ways: first, there might be a preference for triple junctions that obey the rule (implying a distinct influence of the triple junction itself). Alternatively, the misorientations in the real crystal might not be randomly distributed: if there is a preference for boundaries that have only small deviations from coincidence, there will be an increase in the compliance with the rule.
Local Potential at Atomically Abrupt Oxide Interfaces by Scanning Probe Microscopy
Authors: Kalinin Sergei V. , Bonnell Dawn A. 
Published: April 2011

ABSTRACTElectrostatic force microscopy and scanning surface potential microscopy are combined to quantify nanometer scale field variations in the vicinity of grain boundaries in donor doped σ15 SrTiO3 bicrystals. An analytical electrostatic model is used to develop a procedure for determining interface potential from measurements made above the surface. Grain boundary potentials and depletion widths determined by both techniques are in excellent agreement despite the fundamental difference in imaging mechanisms. The comparison confirms the analytical approach and illustrates use of scanning probes to image interface properties.
Measurements of the Adhesion Strength of Cu/Epoxy Interfaces
Authors: Lee H. Y. , Yu Jin 
Published: April 2011

ABSTRACTCopper-based leadframe sheets were oxidized in a black-oxide forming solution, molded with epoxy molding compound (EMC), and the interfacial fracture toughness was measured using sandwiched double cantilever beam (SDCB) and sandwiched Brazil-nut (SBN) specimens.Results showed that pebble-like Cu2O precipitates on the leadframe had almost no adhesion to EMC while the opposite was true of the acicular CuO precipitates. Thus, the fracture toughness of the leadframe/EMC interface was close to zero in the beginning but rapidly increased to ˜100 J/m2 as acicular CuO nucleated on the smooth-faceted Cu2O layer. Under the mixed Mode loading the fracture toughness increased parabolically with the phase angle (ψ) with minimum at ψ = 0°. For ψ < -340, interface crack kinked into EMC. Fractography analyses based on XRD, SEM and AES studies showed that the failure path along the leadframe/EMC interface varied significantly with the loading condition and the crack speed.
Observation of Localized Corrosion of Ni-Based Alloys Using Coupled Orientation Imaging Microscopy and Atomic Force Microscopy
Authors: Bedrossian Peter J. , Schwartz Adam J. , Kumar Mukul , King Wayne E. 
Published: April 2011

ABSTRACTWe present a method for assessing the relative vulnerabilites of distinct classes of grain boundaries to localized corrosion. Orientation imaging microscopy provides a spatial map which identifies and classifies grain boundaries at a metal surface. Once the microstructure of a region of a sample surface has been characterized, a sample can be exposed to repeated cycles of exposure to a corrosive environment alternating with topographic measurement by an atomic force microscope in the same region in which the microstructure had been mapped. When this procedure is applied to Ni and Ni-based alloys, we observe enhanced attack at random grain boundaries relative to special boundaries and twins in a variety of environments.
Wet Etching Methods for Perovskite Substrates
Authors: Leca Victor , Rijnders Guus , Koster Gertjan , Blank Dave H. A. , Rogalla Horst 
Published: April 2011

AbstractIn oxide electronics substrates with atomically flat terraces are a request for growing high-quality epitaxial thin films. In this paper results on chemical etching of some substrates with perovskite, ABO3, structure (e.g., SrTiO3, LSAT - the (LaAlO3)0.3(Sr2AlTaO6)0.35 solid solution, and NdGaO3) are presented. In order to obtain high quality substrates, different etchants (NH4F + HF, HCl + NH4Cl, and HCl + HNO3) with various pH values have been studied. From Atomic Force Microscopy (AFM), in air, we conclude that, irrespective of the etchant that has been used, a substrate surface with a BOx terminated layer and atomically flat terraces without etch pits could be obtained. The pH-value and temperature of the etchant and the etching time, however, influence significantly the surface quality. Reflection high energy electron diffraction (RHEED) patterns confirmed the AFM results.
Authors: Norton D. P. , Budai J. D. , Chisholm M. F. 
Published: April 2011

AbstractWe describe the growth and properties of epitaxial (001) CeO2 on a (001) Ge surface using a hydrogen-assisted pulsed-laser deposition method. Hydrogen gas is introduced during film growth to eliminate the presence of the GeO2 from the semiconductor surface during the initial nucleation of the metal oxide film. The hydrogen partial pressure and substrate temperature are selected to be sufficiently high such that the germanium native oxides are thermodynamically unstable. The Gibbs free energy of CeO2 is larger in magnitude than that of the Ge native oxides, making it more favorable for the metal oxide to reside at the interface in comparison to the native Ge oxides. By satisfying these criteria, the metal oxide/semiconductor interface is shown to be atomically abrupt with no native oxide present. Preliminary structural and electrical properties are reported.
Mechanistic Studies of Wafer Bonding and Thin Silicon Film Exfoliation
Authors: Chabal Y.J. , Isaacs E. D. , Weldon M.K. 
Published: April 2011

AbstractIn this paper, we review and highlight the central role that infrared spectroscopy has played in elucidating the microscopic details of the bonding and exfoliation processes and we introduce a novel technique for imaging and measuring strain with submicron resolution. The mechanism for chemical bond formation between two interfaces is derived from monitoring the chemical evolution of interfacial species as a function of annealing. The mechanism for silicon shearing upon Himplantation/annealing is understood as an evolution of H-passivated point defects into H-stabilized internal surfaces, together with H2formation. The nucleation and propagation of microbubbles that form prior to exfoliation is imaged with x-rays and a detailed strain map in the vicinity of bubbles just prior to exfoliation can be made.
Growth of Large Diameter Silicon-Germanium Monocrystals
Authors: Deitch Richard H. , Jones Stephen H. , Digges Thomas G. 
Published: April 2011

AbstractSi-Ge monocrystals up to 50 mm diameter and up to 17 at% germanium were grown using a modified Czochralski technique. Pre-grown large diameter silicon seeds with various crystallographic orientations were used as templates for the alloy solidification to reduce cap crystallization time and insure monocrystallinity at desired diameters. Discussed are the influences that seed preparation, crystal growing parameters, and post-growth processing have on the material that was produced using this new technique.
Effects of Sapphire Substrate Configurations on MBE Growth of ZnO
Authors: Sakurai Keiichiro , Nakahara Ken , Tanabe Tetsuhiro , Fujita Shizuo , Fujita Shigeo 
Published: April 2011

AbstractMBE growth of ZnO films for optical semiconductor devices was investigated on off-angled c-plane sapphire substrates. Twin crystal RHEED patterns and surface facetting observed with c-plane just-oriented substrates were suppressed by enlarging the offset angles from near-zero to 2.87 degrees. Though no significant changes were seen in optical characteristics, FWHM of XRC narrowed and surface morphology improved with larger offset angles, indicating that the offset angle is also a sensitive factor for ZnO film growth.
Faceting of Single-Crystal SrTiO3 During Wet Chemical Etching
Authors: Spalding G. C. , Murphy W. L. , Davidsmeier T. M. , Elenewski J. E. 
Published: April 2011

AbstractWe use an Atomic Force Microscope (AFM) to study changes in the surface of single-crystal SrTiO3 etched in HF-based solutions. Attention in this work has been focused upon observations of pyramidal pitting – both because of an interest in avoiding etch pits during substrate preparation prior to heteroepitaxial growth, and because of an interest in micromachining this highly polarizable material. We note that (110) SrTiO3 is surprisingly robust against the formation of pits, while pitting is significant on {100} surfaces. Particular etch rates have been measured, and we discuss anisotropies in the rates of dissolution. These data are combined to extract a macroscopic model describing processes relevant to the most extreme pitting, which we show to be associated with surface defects.
Optical Emission Related to Holes Confined in p-Type δ-Doped Layers in GaAs
Authors: Zhao Q.X. , Willander M. , Holtz P.O. , Lu W. , Dou H. F. , Shen S. C. , Li G. , Jagadish C. 
Published: April 2011

AbstractWe present an optical investigation of thin Zn-doped GaAs layers embedded in bulk GaAs, by means of stationary optical spectroscopy. The samples were grown by metalorganic vapor phase epitaxy (MOVPE) The concentration of doped Zn acceptors were aimed at 2×1020/cm3 in 4 nm wide doping regions. We observed a novel optical radiative transition (denoted as F-emission) appearing in photoluminescence (PL) spectra below the energy position of the transition between the free electrons and holes bound to acceptors in bulk GaAs. The F emission shows a strong dependence on excitation intensity and temperature. The energy position varies from 1.46 eV to 1.49 eV when the excitation density increases from about 40 mW/cm2 to 23 W/cm2. Our results indicate that this emission is related to the transition between spatially separated electrons and holes. The holes are located in the p-type Zn δ-doped region, while the electrons are located in the undoped GaAs region.
Analysis of the Crystallization Kinetics and Microstructure of Polycrystalline Sige Films by Optical Techniques
Authors: Olivares J. , Martín P. , Rodríguez A. , Sangrador J. , Martínez O. , Jiménez J. , Rodríguez T. 
Published: April 2011

AbstractIn this work, two optical techniques, Raman spectroscopy and ultraviolet reflectance, have been used to characterize the solid phase crystallization kinetics and the microstructure of SiGe films deposited by LPCVD on oxidized Si wafers. The results have been compared to those obtained by X-ray diffractometry. The Ge fraction of the films (x) was in the 0−0.38 interval. The samples were crystallized at temperatures ranging from 525 to 600 °C. The crystallization kinetics follows Avrami's model. Two different behaviours have been observed depending on the Ge fraction of the films and the crystallization temperature: a) Either the three experimental techniques yield similar results, or b) the crystallization process, as monitored by UV reflectance and Raman spectroscopy, exhibits a greater incubation time than the one obtained if X-ray diffractometry is used. The results are discussed in terms of the identification of the nucleation sites, taking into account the probe depth of the different techniques and the preferred orientations of the grains. These techniques have also been used to characterize the presence of defects, the overall crystallinity and the surface roughness of the fully crystallized films. The results are correlated to the grain morphology and grain size, obtained by means of transmission electron microscopy.
Optical Characterization of Individual Nanostructures by STM Light Emission
Authors: Ushioda S. 
Published: April 2011

AbstractVisible light is emitted when electrons (holes) are injected into a sample from the tip of the scanning tunneling microscope (STM). By analyzing the spectra of the emitted light, one can not only determine the surface geometry by usual STM imaging, but also learn the electronic and optical properties of specific individual nanostructures. This technique has been applied to investigate the electronic transitions of individual protrusions of porous Si and semiconductor quantum wells of AlGaAs/GaAs. The usefulness, limitations, and future expectations of this novel technique are discussed.
Quantum Confinement of Above-Band-Gap Transitions in Ge Quantum Dots
Authors: Teng C. W. , Muth J. F. , Kolbas R. M. , Hassan K. M. , Sharma A. K. , Kvit A. , Narayan J. 
Published: April 2011

AbstractA number of research efforts have been focused on self-assembled germanium quantum dots in which indirect optical transitions take place across the band gap. However, many questions regarding the confined electronic state transitions of Ge quantum dots still remain unanswered. In the present report, we have deposited ten alternating layers of crystalline Ge quantum dots embedded in an Al2O3 or an AIN matrix on sapphire substrates by pulsed laser deposition. The average dot sizes (73 Å to 260 Å) were controlled by the laser energy density, deposition time and substrate temperature. The spectral positions of both the E1 and the E2 transitions in the absorption spectra at room temperature and 77 K shift toward higher energy (ΔE1=1.19 eV, ΔE2 =0.57 eV) as the Ge dot size decreases (73 Å). Structural analysis using transmission electron microscopy and atomic force microscopy and the interpretation of optical absorption measurements in terms of quantum confinement of carriers in both transitions are presented.
Effects of Rapid Thermal Annealing on the Intersubband Energy Spacing of Self-Assembled InAs/Gaas Quantum Dots
Authors: Wang X. C. , Chua S. J. , Xu S. J. , Zhang Z. H. 
Published: April 2011

AbstractIn this paper, we showed the significant reduction of the energy spacing between ground state and excited state emissions from InAs/GaAs quantum dots due to interface interdiffusion induced by thermal treatment. In addition, the strong narrowing of the luminescence linewidth of the ground state and excited state emissions from the InAs dot layers for the annealed samples indicates an improvement of the size-distribution of the QDs. Large blue-shift of the energy positions of both emissions was also observed. High resolution X-Ray diffraction experiments give strong evidence of the interface atom interdiffusion in the annealed samples. This work shows ability to tune the wavelength for applications like infrared detectors and lasers based on intrasubband transitions of self-assembled QDs.
Hybridization in Electronic States and Optical Properties of Covalent Amorphous Semiconductors
Authors: Shinozuka Yuzo 
Published: April 2011

AbstractThe electronic structure and optical properties of covalent amorphous semiconductors are theoretically studied with special attention to the s-p hybridization in electronic states and the spatial correlation in their mixing. One-dimensional tight binding model is used in which the interatomic transfer energy of an electron between nearest neighbor atoms depends linearly on their interatomic distance. All the electronic states are numerically calculated for a 150-atom system and the ensemble average is taken over 10 samples. Following results have been obtained. As the degree of randomness increases, the degree of hybridization decreases and rearrangements in the covalent bonds take place. The width of the band gap decreases but the gap remains rather long compared to a case where the spatial correlation is neglected. There appears a characteristic peak in the optical absorption spectrum, which reflects central peaks in the partial (s- or p-) density of states in the valence and conduction bands and is related to an electron localization caused by the spatial correlation.
Development of Low Energy Cathodoluminescence System and its Application to the Study of ZnO Powders
Authors: Sekiguchi Takashi 
Published: April 2011

AbstractWe have developed a cathodoluminescence (CL) system with high spatial resolution using a thermal-field emission gun operating with low electron beam energies. Since the electron range is proportional to the 1.7th power of the electron beam energy, operation with a low energy electron beam strongly reduces the probe size of CL. Luminescence property of ZnO tetrapods was studied with this system. High spatial resolution better than 100 nm was achieved when it was operated with a beam energy less than 3 keV. The variation of CL spectra along one leg of tetrapod was recorded. The ratio of the ultraviolet emission to the visible luminescence at the center of tetrapod was different from those of the points along the arm, suggesting that the center of tetrapod is much defective compared with the arms. We also observed a decrease of CL intensity during observation. Possible degradation mechanisms were discussed.