bluuebunny/crossref_metadata_2025_split huggingface dataset:
In situ Pyrometric Interferometry For Molecular Beam Epitaxy of AlxGa1−xN on Si (111)
Authors: Nikishin S. A. , Francoeur S. , Temkin H. 
Published: April 2011

ABSTRACTWe apply pyrometric interferometery to control the growth of GaN, AlN, and AlxGa1−xN on Si (111) by molecular beam epitaxy. We show that the period of intensity oscillations in the temperature measured by the pyrometer is caused by optical interference in the growing nitride layer. The period of oscillations is inversely proportional to the growth rate. This effect is used for in-situ measurement of the growth rate of GaN, AlN, and AlxGa1−xN (for 0<×<1). We also show that pyrometric interferometery can be used for in-situ determination of the composition of the growing layer.
Two-dimensional electron gas scattering mechanisms in AlGaN/GaN heterostructures
Authors: Borovitskaya E. , Knap W. , Shur M. S. , Gaska R. , Frayssinet E. , Lorenzini P. , Grandjen N. , Baumont B. , Massies J. , Skierbiszewski C. , Prystawko P. , Leszczynski M. , Grzegory I. , Porowski S. 
Published: April 2011

ABSTRACTWe present the results of the experimental and theoretical studies of the low field mobility of two-dimensional electrons in the homoepitaxial AlGaN/GaN heterostructures and in the AlGaN/GaN heterostructures grown on SiC. We show that, at cryogenic temperatures, the temperature dependence of the mobility is primarily determined by the deformation potential scattering and that most of other important scattering mechanisms are temperature independent. We show also that two-dimensional (2D) and three-dimensional (3D) mobility models yield very close results. The analysis of the mobility dependence on the electron sheet density ns shows two possible explanations of the non monotonic mobility versus carrier density dependence: i) the alloy/interface scattering and ii) transfer of the 2D electrons into 3D states in GaN. We present experimental data suggesting that for high 2D gas densities in the investigated structure grown on SiC the 2D-3D transition should take place and might be responsible for the mobility decrease at high electron sheet densities.
Renaissance and Progress in Nitride Semiconductors - My Personal History of Nitride Research -
Authors: Akasaki Isamu 
Published: April 2011

ABSTRACTWide bandgap group-III nitride semiconductors are currently experiencing the most exciting development. High brightness blue and green light emitting diodes (LEDs) are commercialized, and UV and blue laser diodes (LDs), high-speed transistors (TRs) and UV photodetectors (PDs) with low dark current, which will be able to operate in harsh environments, have been demonstrated. In this paper, renaissance and progress in crystal growth and conductivity control of nitride semiconductors in the last quarter century are reviewed as the groundwork for all of those high-performance devices. My personal history of nitride research will be also introduced.
Dynamics of Ga Clusters on GaAs(001) Surface
Authors: Tsukamoto Shiro , Koguchi Nobuyuki 
Published: April 2011

AbstractDynamics of Ga clusters and GaAs epitaxial growth on a GaAs (001) surface were successfully observed by a system in which scanning tunneling microscopy (STM) and molecular beam epitaxy (MBE) were incorporated into one unit rather than in separate chambers. With the substrate temperature of 528°C, reflection high-energy diffraction (RHEED) patterns showed a (4×6) Ga-stabilized surface reconstruction and dynamics of steps and islands were clearly observed. The detaching and attaching of small Ga clusters might cause the change of steps and islands. It seems that the small Ga clusters migrated with the diameter of about 0.8 to 1.2 nm and around the steps and islands. These clusters could be observed only when they were detached from or attached to the steps and islands. Moreover, even under the substrate temperature of 440 oC and the As4 partial pressure of 2×10−6 torr, STM images were clearly observed. After 0.1 ML Ga was additionally supplied to the sample by migration enhanced epitaxy mode, step flow growth occurred, resulting in an additional GaAs layer grown on the B-step side. Moreover, the c(4×4) As-stabilized surface reconstruction was moderate. It seems that there is an equilibrium additional layer of As amorphous adatoms on the c(4x4) surface reconstructions.
Electromigration in Epitaxial Copper Lines
Authors: Goindi H.S. , Shin C.S. , Frederick M. , Shusterman Y. , Kim H. , Petrov I. , Ramanath G. 
Published: April 2011

AbstractCopper is becoming the metal of choice for interconnect applications in integrated circuits due to its lower electrical resistivity and higher electromigration (EM) resistance. The effects of grain size, preferred orientation, and interfacial layers, on electromigration in Cu lines are, however, not yet well understood. In this paper, we compare the EM characteristics of epitaxial Cu(111) lines with that of polycrystalline lines with a (111) texture. We also investigate the effects of Ta, TaN and TiN interfacial underlayers and Cu crystal quality on the EM response of epitaxial Cu(001) lines. EM tests were carried out on 2-μm-wide Cu lines at a constant current density between 0.02 and 3.5 MA/cm2 in an Ar ambient at 300 °C. Our results indicate that EM resistance of both (111) and (001) epitaxial lines have a higher mean time to failure (MTTF) than polycrystalline Cu lines. The presence of a TiN or TaN interfacial layer increases the MTTF in Cu(001) films, while a Ta underlayer degrades EM resistance. X-ray diffractograms indicating a smaller full-width-at-half-maximum of Cu(001) films on nitride underlayers suggest that lower defect densities in these Cu films is the likely reason for improved EM resistance. Both (111) and (100) orientations fail by formation of faceted voids.
The Effect of Pb on the Interface Structure of Fe/Cr(100) Metallic Multilayers
Authors: Kim Kyu-Young , Kamiko Masao , Oh Sang-Mun , Lu Guang-Hong , Yamamoto Ryoichi 
Published: April 2011

AbstractWe investigated the differences in the interface structures and magnetotransport properties between surfactant-mediated multilayers and normal ones. From the observations of RHEED and High-Resolution X-ray diffraction patterns, we confirmed that the surfaces of Fe/Cr(100) multilayers with Pb are flatter and the interfaces are sharper than one without Pb, which means that Pb operates as an effective surfactant. The magnetoresistance(MR) ratio of the multilayers prepared with Pb was larger than that of the multilayers prepared without Pb. The change of resistance with magnetic field was larger for the multilayers with a surfactant.
Surface structure and metal epitaxy: Ag/Cu(111)
Authors: Umezawa Kenji , Nakanishi Shigemitsu , Gibson Walter M. 
Published: April 2011

AbstractWe have investigated the growth of 3 ML (mono-layer) of Ag on Cu(111) for substrate temperatures from 170 through 640 K by using time of flight-impact collision ion scattering spectroscopy (TOF -ICISS). Two different types of epitaxial growth exist: Ag [112]//Cu[112](type-n) and Ag [112]//Cu[112] (type-r).The growth modes of the Ag thin films on Cu(111) surfaces depend strongly on the temperature during deposition with the Ag(111) planes having a preferred orientation of either type-n growth mode or type-r growth mode as a function of theCu substrate temperature. The experimental results concerning Ag/Cu(111) show many similarities to those in the previous study of Au/Ni(111). This would suggest that an observed oscillation in the growth mode, dependent on the substrate temperature during deposition may a general phenomenon on solid surfaces, in cases of large misfit since it has now been seen for both Au/Ni(111) and Ag/Cu(111) systems.
Molecular Orientation in The Peptide Self-Assembled Monolayers
Authors: Fujita Katsuhiko , Yokoyama Ryuichi , Tsutsui Tetsuo 
Published: April 2011

AbstractSelf-assembled monolayer (SAM) of peptides is investigated in terms of the correlation of their molecular orientation and the dipolar interactions. The used helical peptides containing a disulfide group on the terminal, which can form SAMs on a gold substrate, were synthesized. The molecular orientation was estimated from the reflection absorption IR intensity ratio of amide I and amide II bands which have transition moment almost parallel and perpendicular to the molecular axis, respectively. The adsorption behavior and layer thickness were determined by surface plasmon resonance.The molecular orientation depended on the dipolar interaction between the peptide molecules and between the peptide dipole and its image. The molecular direction against the substrate affects the orientation probably due to the interaction between the peptide dipole and Au-S polarization. This speculation is supported by the fact that the orientation difference by the molecular direction became smaller when the spacer from the helix body to the disulfide group is longer. The results indicate that the careful molecular design and optimal preparation condition of SAMs allow formation of well-organized and predetermined structure of nano-architecture even by use of large and complex molecules.
Mechanisms in embedded selective epitaxy and overgrowth of an integrated laser/modulator quantum well structure using MOMBE and MOVPE
Authors: Kröner Philipp , Baumeister Horst , Gessner Roland , Rieger Josef , Schier Michael , Veuhoff Eberhard , Marti Othmar , Heinecke Harald 
Published: April 2011

AbstractLateral integration of optoelectronic devices comprising strained multiple quantum well (MQW) structures can most successfully be accomplished by selective area epitaxy using metal organic molecular beam epitaxy (MOMBE). We optimized the growth parameters with respect to a planar butt coupling and sharp, flat MQW interfaces in an integrated MQW laser / MQW modulator structure. Defect generation in metal organic vapor phase epitaxy (MOVPE) overgrown cladding layers is analyzed and shown to contain information about the quality of the buried butt coupling. A ridge waveguide structure has successfully been fabricated from an optimized integrated laser / modulator structure.
Computational Study of Polymerization in Carbon Nanotubes
Authors: Stuart Steven J. , Dickson Brad M. , Sumpter Bobby G. , Noid Donald W. 
Published: April 2011

AbstractMolecular dynamics simulations of ethylene polymerization have been performed using a chemically realistic, reactive potential. These simulations have been performed in the bulk liquid and in the interior of both (10,10) and (7,7) nanotubes as a means of investigating the effects of nanoscale confinement on the polymerization reaction. The structure of the resulting polymer was found to be similar in the bulk and in the (10,10) tube at the elevated temperatures investigated, while only very small oligomers were formed in the (7,7) tube. The reaction rate was substantially reduced in the nanotubes, when compared to the bulk, primarily as a result of spatial interference due to reaction products. These simulations have implications for the possible use of nanotubes as synthetic reaction vessels, as well as for the general understanding of association reactions in confined spaces.
Flow, Diffusion, Dispersion, and Thermal Convection in Percolation Clusters: NMR Experiments and Numerical FEM/FVM Simulations
Authors: Kimmich Rainer , Klemm Andreas , Weber Markus , Seymour Joseph D. 
Published: April 2011

AbstractBased on computer-generated templates, percolation objects were fabricated. Random-site, semi-continuous swiss cheese, and semi-continuous inverse swiss-cheese percolation models above the percolation threshold were considered. The water-filled pore space was investigated by nuclear magnetic resonance (NMR) imaging and in the presence of a pressure gradient, by NMR velocity mapping. The percolation backbones were determined using velocity maps. The fractal dimension of the backbones turned out to be smaller by about 17 % than that of the complete cluster. As a further relation of interest, the volume-averaged velocity was calculated as a function of the probe volume radius. In a certain scaling window, the resulting dependence can be represented by a power law. The experimental results favorably compare to computer simulations with the finite-element method (FEM) or the finite-volume method (FVM). Thermal convection in percolation clusters of different porosities was studied using the NMR velocity mapping technique. The velocity distribution is related to the convection roll size distribution. The maximum velocity as a function of the porosity clearly visualizes a closed-loop percolation transition if the Rayleigh number conditions are appropriate. Percolation theory suggests a relationship between the anomalous diffusion exponent and the fractal dimension of the cluster,i.e.between a dynamic and a structural parameter. Interdiffusion between two compartments initially filled with H2O and D2O, respectively, was examined by proton imaging. The results confirm the theoretical expectation. Finally, advection driven dispersive transport was investigated in the large Péclet number limit. The superdiffusive transport anomaly was demonstrated and discussed in terms of the non-local advection-diffusion and the fractional diffusion theories.
Friction and the Continuum Limit – Where is the Boundary?
Authors: Zhu Yingxi , Granick Steve 
Published: April 2011

AbstractThe no-slip boundary condition, believed to describe macroscopic flow of low-viscosity fluids, overestimates hydrodynamic forces starting at lengths corresponding to hundreds of molecular dimensions when water or tetradecane is placed between smooth nonwetting surfaces whose spacing varies dynamically. When hydrodynamic pressures exceed 0.1-1 atmospheres (this occurs at spacings that depend on the rate of spacing change), flow becomes easier than expected. Therefore solid-liquid surface interactions influence not just molecularly-thin confined liquids but also flow at larger length scales. This points the way to strategies for energy-saving during fluid transport and may be relevant to filtration, colloidal dynamics, and microfluidic devices, and shows a hitherto-unappreciated dependence of slip on velocity.
Hydrocarbon Reactions in Carbon Nanotubes: Pyrolysis
Authors: Stuart Steven J. , Dickson Brad M. , Noid Donald W. , Sumpter Bobby G. 
Published: April 2011

AbstractMolecular dynamics simulations have been used to study the pyrolysis of eicosane (C2042 both in the gas phase and when confined to the interior of a (7,7) carbon nanotube. A reactive bond-order potential was used to model the thermal decomposition of covalent bonds. The unimolecular dissociation is first-order in both cases. The decomposition kinetics demonstrate Arrhenius temperature dependence, with similar activation barriers in both geometries. The decomposition rate is slower by approximately 30% in the confined system. This rate decrease is observed to be a result of recombination reactions due to collisions with the nanotube wall.
Synthesis, Structure and Magnetic Properties of Monoclinic Nb12O29
Authors: Waldron J. E. L. , Green M. A. 
Published: April 2011

ABSTRACTThe synthesis, structure and magnetic properties of monoclinic Nb12O29 are described. The synthesis of a pure bulk sample is difficult due to the large number of other similar phases. It is achieved by rapid reduction of H-Nb2O5 with Nb metal. The compound is shown to undergo a charge ordering transition at low temperature which provokes long range magnetic order in an intriguing one dimensional arrangement.
Temperature Dependence of Magnetic Compton Profile in DyCo5
Authors: Miyagawa Hayato , Watanabe Yasuhiro , Koizumi Akihisa , Sakai Nobuhiko , Mizumaki Masaichiro , Sakurai Yoshiharu , Nakamura Tetsuya , Nanao Susumu 
Published: April 2011

ABSTRACTMagnetic Compton profiles (MCPs) of a DyCo5.4 single crystal were measured at 10 K, 200 K and 300 K. The temperature dependence of the spin moment, which is deduced from the areas under the normalized MCPs, is significantly different from that of the total magnetization measured by a superconducting quantum interference device (SQUID). This difference is due to the presence of a substantial amount of the orbital moment on a Dy site that does not contribute to the magnetic Compton scattering cross section. The analysis of the MCPs reveals that the absolute value of the spin moment increases with increasing temperature and that the spin magnetic moment of the conduction electrons has an opposite sign to the total spin magnetization in the covered range of temperature.
High Oxidation State Alkali-Metal Late-Transition-Metal Oxides
Authors: Currie David B. , Hector Andrew L. , Raekelboom Emmanuelle A. , Owen John R. , Weller Mark T. 
Published: April 2011

ABSTRACTLi2NaCu2O4 has been prepared by solid state reaction under high-pressure (250 Atm) oxygen. A structural study, using time-of-flight powder neutron diffraction on a sample made with 7Li, shows a material isostructural with Li3Cu2O4, with sodium occupying the octahedral and lithium the tetrahedral A-cation sites. A 7Li MAS-NMR study of Li3Cu2O4, Li2NaCu2O4 and Li2CuO2 has been used to confirm the Li/Na site ordering.
Effect of Strained Si-Si Bonds in Amorphous Silicon Incubation Layer on Microcrystalline Silicon Nucleation
Authors: Fujiwara Hiroyuki , Kondo Michio , Matsuda Akihisa 
Published: April 2011

ABSTRACTIn order to investigate microcrystalline silicon (μc-Si:H) nucleation from the hydrogenated amorphous silicon (a-Si:H) phase, we performed a H2-plasma treatment of a-Si:H layers deposited at different temperatures. In the H-treatment experiment, the formation process of an infrared peak at ∼1937 cm-1, assigned to SiHn (n=1∼2) complex, is studied, as the SiHn complex is proposed to be a precursor for the μc-Si:H nucleation. With increasing the a-Si:H deposition temperature, the total amount of the SiHn complex formed by the H treatment increased. Nucleation of μc-Si:H under high H2-dilution conditions showed a clear relationship with the SiHn complex formed by the H treatment. The SiHn complex formation process, in terms of strained Si-Si bond breaking by H, is discussed.
New experiments on the relationship between light-induced defects and photoconductivity degradation
Authors: Heck Stephan , Branz Howard M. 
Published: April 2011

ABSTRACTWe report experimental results that help settle apparent inconsistencies in earlier work on photoconductivity and light-induced defects in hydrogenated amorphous silicon (a-Si:H) and point toward a new understanding of this subject. After observing that light-induced photoconductivity degradation anneals out at much lower T than the light-induced increase in deep defect density, Han and Fritzsche[1] suggested that two kinds of defects are created during illumination of a-Si:H. In this view, one kind of defect degrades the photoconductivity and the other increases defect sub-bandgap optical absorption. However, the light-induced degradation model of Stutzmann et al.[2] assumes that photoconductivity is inversely proportional to the dangling-bond defect density. We observe two kinds of defects that are distinguished by their annealing activation energies, but because their densities remain in strictlinear proportionduring their creation, the two kinds of defects cannot be completely independent.In our measurements of photoconductivity and defect absorption (constant photocurrent method) during 25°C light soaking and during a series of isochronal anneals between 25 < T < 190°C, we find that the absorption measured with E ≤1.1 eV, first increases during annealing, then exhibits the usual absorption decrease found for deeper defects. The maximum in this absorption at E ≤1.1eV occurs simultaneously with a transition from fast to slow recovery of photoconductivity. The absorption for E ≤1.1eV showstwodistinct annealing activation energies: the signal rises with about 0.87 eV and falls with about 1.15 eV. The 0.87 eV activation energy roughly equals the activation energy for the dominant, fast, recovery of photoconductivity. The 1.15 eV activation energy roughly equals the single activation energy for annealing of the light-induced dangling bond absorption.
Contributions of D0 and non-D0 Gap States to the Kinetics of Light Induced Degradation of Amorphous Silicon under 1 sun Illumination
Authors: Pearce J. , Niu X. , Koval R. , Ganguly G. , Carlson D. , Collins R.W. , Wronski C.R. 
Published: April 2011

ABSTRACTLight induced changes to 1 sun degraded steady state (DSS) have been investigated on hydrogenated amorphous silicon (a-Si:H) p-i-n solar cells and corresponding films fabricated with and without hydrogen dilution of silane. Striking similarities are found for the degradation kinetics, between the electron mobility lifetime (μτ) products and the corresponding fill factors (FF). These correlations that exist for both intrinsic materials at temperatures between 25 and 100°C, are present for the DSS as well as in the kinetics, which exihibit distinctly different dependence on temperature. No such correlations are present between μτ, FF and densities of D0 defects, measured with subgap absorption α(E) at 1.2eV, and electron spin resonance (ESR). The creation of non-D0 defects is also clearly indicated by the temperature dependence of the kinetics and the changes in the shape of α(E) with the results suggesting the presence of more than one mechanism for the creation of light induced defects associated with the Staebler-Wronski effect (SWE).
Investigation of Light-Induced Defect Depth Profile in Hydrogenated Amorphous Silicon Films
Authors: Shimizu S. , Stradins P. , Kondo M. , Matsuda A. 
Published: April 2011

ABSTRACTWe report direct measurement of depth profile of light induced defects (LIDs) in hydrogenated amorphous silicon (a-Si:H) films. These depth profiles were measured by ESR measurements combined with layer-by-layer precise wet etching technique. We discuss those LIDs depth profiles in relation to the spatial depth distribution of photocarriers generation and recombination profiles, as well as the defect creation efficiency. In case of uniformly absorbed light, the light induced defects creation takes place uniformly in depth of the a-Si:H film. In case of nonuniformly absorbed light, the LIDs depth profile is spatially wider than photocarrier generation rate profile G(x), and depends on G(x) sublinearly. Moreover, the LID depth profile agrees well with the photocarrier direct recombination rate profile rather than the profile of total recombination rate or that through defects. The obtained results suggest that the LIDs creation takes place at local site where the photocarriers recombine directly.
Is interstitial hydrogen playing a role in the Staebler-Wronski effect ?
Authors: Longeaud C. , Roy D. 
Published: April 2011

ABSTRACTWe have studied the density of states (DOS) of many different series of a-Si:H samples prepared in radio-frequency powered deposition systems. Samples were obtained from decomposition of pure silane or of mixtures of silane with argon, helium or hydrogen. The DOS were investigated in the as-deposited, light-soaked and annealed states. For all the samples the light-soaking behaviour is almost the same: 2 min of light-soaking are enough to increase the deep states density and after full saturation both the deep states and the conduction band tail exhibit a large increase. The effect of the annealing process is sample dependent, the DOS being restored for some samples or almost insensitive to the annealing process in some cases. To explain all these results, we propose a mechanism of light-soaking/annealing in which interstitial H2 molecules and voids play a major role.