bluuebunny/crossref_metadata_2025_split huggingface dataset:
Microstructure of YBa2Cu3O7-δ/Ag Bilayers Grown In Situ on Step-Edge SrTiO3 Substrates
Authors: Gong Z. H. , Grepstad J. K. , Andersen S. , Bardal A. 
Published: April 2011

AbstractThe microstructure of YBa2Cu3O7-δ(YBCO)/Ag bilayers sputter deposited in situ on step-edge SrTiO3 (STO) substrates, was carefully examined by transmission electron microscopy (TEM). Considerable variation in the YBCO film growth morphology is found near steps, including film protrusions beyond the step edges and film growth on slopes. Lattice images recorded near steps unveil a high density of crystalline defects in the film. An increased density of defects is also found near the substrate interface for film grown on etched STO surface. However, these defects are confined to the interface region and do not propagate beyond the scale of the STO surface roughness. Comparison of TEM lattice images of YBCO(100)/Ag and YBCO(001)/Ag junctions from the same specimen unveils a distinct difference in the interfacial microstructure of those two junctions. Whereas the former exhibits a sharp crystalline interface, the latter typically features a thin ( ∼ 20 Å ) interfacial layer of amorphous material. The YBCO film morphology and the high density of defects in the step edge region uncovered in this study suggest that manufacture of reproducible and uniform YBCO/Ag (Au)/YBCO (SNS) Josephson junctions using the step-edge technique, will prove a difficult task.
Microstructure of SrTiO3 Thin Films as Single Layer and Incorporated in Yba2Cu3O7-x/SrTiO3 Multilayers
Authors: Ryen L. , Olssoni E. , Madsen L. D. , Johnson C. N. L. , Wang X. , Jacobsen S. N. , Helmersson U. , Wernlund L.-D. , Rudner S. 
Published: April 2011

AbstractEpitaxial single layer (001) SrTiO3 films and an epitaxial Yba2Cu3O7-x/SrTiO3 multilayer were dc and rf sputtered on (110)rhombohedral LaAIO3 substrates. The microstructure of the films was characterised using transmission electron microscopy. The single layer SrTiO3 films exhibited different columnar morphologies. The column boundaries were due to the lattice mismatch between film and substrate. The boundaries were associated with interfacial dislocations at the film/substrate interface, where the dislocations relaxed the strain in the a, b plane. The columns consisted of individual subgrains. These subgrains were misoriented with respect to each other, with different in-plane orientations and different tilts of the (001) planes. The subgrain boundaries were antiphase or tilt boundaries.The individual layers of the Yba2Cu3O7-x/SrTiO3 multilayer were relatively uniform. A distortion of the SrTiO3 unit cell of 0.9% in the ‘001’ direction and a Sr/Ti ratio of 0.62±0.04 was observed, both in correspondence with the single layer SrTiO3 films. Areas with different tilt of the (001)-planes were also present, within each individual SrTiO3 layer.
Effects of Metal Buffer Layer on the Epitaxial Growth of YBa2Cu3O7-y. Superconducting Films by Dipping-Pyrolysis Process
Authors: Manabe T. , Yamaguchi I. , Nakamura S. , Kondo W. , Mizuta S. , Kumagai T. 
Published: April 2011

AbstractSuperconducting Yba2Cu3O7 -x(YBCO) films were prepared by dipping-pyrolysis process on SrTiO3 (001) or on MgO (001) substrates covered with a metal (Au or Ag) buffer layer, and the effects of these metal layers on the growth of YBCO films were investigated. Epitaxial growth of YBCO was found to be suppressed by the Au buffer layer, which crystallized to exhibit (111) orientation, after heat treatment at 700°C and higher. On the other hand, epitaxial YBCO films were obtained starting with Ag buffer layer by heat treatment at 700°C and higher, after which most of Ag was accumulated to particles. It was also found that the annealing temperature required for the epitaxial growth of YBCO films on MgO was lowered to 850°C by adopting the Ag buffer layer.
Magnetic and Structural Properties of MBE-grown Oxidic Multilayers
Authors: Bloemen P. J. H. , van der heijden P. A. A. , Wolf R. M. , de Stegge J. Aan , Kohlhepp J. T. , Reinders A. , Jungblut R. M. , van der Zaag P. J. , de Jonge W. J. M. 
Published: April 2011

AbstractMultilayers composed of oxides including Fe3O4, CoxFe3−x, O4, CoO, NiO and MgO have been grown epitaxially by MBE on MgO(100) single crystal substrates. These structures can be grown with a high crystallinity in the form of flat layers having sharp interfaces. RHEED studies which commonly yielded sharp streaks accompanied by Kikuchi lines show that, for instance, growth of CoO on Fe3O4 changes the RHEED pattern from that consistent with a spinel structure to that of a rocksalt structure within about one and a half unit cell of CoO. STM studies on a 400 Å Fe3O4 layer displaying atomic resolution enabled us to identify the origin of the reconstruction that one commonly observes in the RHEED and LEED patterns for magnetite. Regarding important fundamental magnetic parameters, relevant thickness dependencies were mapped out using localized magneto-optical Kerr effect experiments performed on several samples that routinely included one or multiple wedge shaped layers. These studies revealed the existence of a region in the Fe3O4 layer near the interfaces which exhibits no net magnetic moment, strain driven perpendicular orientated magnetization for the CoO/Fe3O4(100) and CoO/CoxFe3−xO4(100) bilayer systems, and information on the thickness dependence of the magnetic interlayer coupling across an MgO spacer layer.
Growth and Stability of MgO/NiO Multilayered Films on Single Crystal NiO(100)
Authors: Imaduddin S. , Lad R. J. 
Published: April 2011

AbstractThe less than 1% lattice mismatch between MgO and NiO makes them ideal candidates for investigating the growth and stability of multilayered oxide films. Ultra-thin multilayers composed of alternating films of MgO and NiO were deposited onto a stoichiometric NiO(100) single crystal substrate at 250°C by evaporating Mg and Ni in 5×10−7 Torr of O2, respectively. The structure of these multilayers was determined using LEED. Reactivity and chemical composition studies of the MgO/NiO interfaces were carried out using XPS and UPS. The MgO/NiO multilayers grow epitaxially on NiO(100), as evidenced by LEED. XPS and UPS analysis indicates attenuation of the NiO or MgO peaks during growth which is consistent with discrete layering. Chemical analysis also reveals negligible intermixing of the MgO and NiO layers during deposition. Results pertaining to the thermal stability of the multilayers show that UHV annealing above 750°C results in significant diffusion of MgO into the NiO(100) substrate.
Localized-Itinerant Electron Transitions in the Orthomanganites
Authors: Goodenough John B. 
Published: April 2011

AbstractThe AMO3 perovskites containing transition-metal atoms M have an MO3 array with M-O-M bond angles 180°-φ in which the angle φ increases with the mismatch of the A-O and M-O equilibrium bond lengths. The tight-binding bandwidths for the π-bonding t and σ-bonding e orbitals of d-orbital parentage are Wπ < Wσ. In the orthomanganites Ln1−xAxMnO3 with A an alkaline earth, the octahedral-site high-spin Mn3+ ions have a d-electron configuration t3e1:5Eg that is orbitally twofold-degenerate, and the on-site electron-electron coulomb energy for adding a fifth d electron is Uσ ≈Wσ > Wπ. Consequently the equilibrium reaction t3e1 ≈ t3 σ*1 for a first-order transition from localized-e to itinerant-σ* electrons is shifted to the left as the bandwidth Wσ ≈ 12 εσλσ2 cos φ is narrowed by increasing φ, by perturbations of the periodic potential of the MO3 array, and/or by increasing spin-disorder scattering; it is shifted to the right by oxidation of the MnO3 array, by application of a magnetic field, and by pressure. Cross-over from polaronic-e to itinerant-σ* electrons at a ferromagnetic Curie temperature Tc or a charge-ordering temperature Tco < Tc can give a “colossal” negative magnetoresistance provided the Fermi energy εF lies below a mobility edge μc in the narrow σ* band of the ferromagnetic phase. Cooperative Jahn-Teller distortions that remove the orbital degeneracy of a localized 5Eg configuration also introduce unusual antiferromagnetic ordering of the manganese-atom spins.
Effect of Growth Conditions and Buffer Layers on the Metal-Insulator Transition in V2O3 Thin Films
Authors: Schuler H. , Weissmann G. , Renner C. , Six S. , Klimm S. , Simmet F. , Horn S. 
Published: April 2011

AbstractThin films of V2O3 with thickness from 20 to 450 nm were deposited on (0001) oriented sapphire substrates by reactive e-beam evaporation. LEED, x-ray diffraction and AFM studies show highly oriented grains with a lateral size of 50 to 800 nm, dependent on substrate temperature and deposition rate. The films were characterized by optical and infrared transmission, electrical resistance and Hall effect measurements. Films grown directly on the Al2O3-substrate show a very broad metal-insulator (MI) transition as a function of temperature. The width of the transition decreases with increasing film thickness. The insertion of Cr2O3 buffer layers decreases the transition width by a further factor of three. The electronic properties of the films can be drastically influenced by the growth conditions.
Domain Structure and Colossal Magnetoresistance of La1−xSrxCoO3 and La1−xCaxMnO3
Authors: Wang Z. L. , Zhang Jiming , Berta Y. 
Published: April 2011

AbstractLa1−xSrxCoO3 (LSCO) and La1−xCaxMnO3 (LCMO) are a class of magnetic oxides exhibiting the colossal magnetoresistance (CMR) effect. However, the CMR ratio of LSCO is much lower than that of LCMO. Microstructure studies were carried out to understand this difference. In La0.5Sr0.5CoO3 (LSCO), an ordered, anisotropic perovskite-type structure n-LSCO was observed. The ordered structure has a tetragonal cell with a La-Co-Sr-Co- [001] layered atom distribution along the c-axis. This new structure is intrinsic for the LSCO system and is a direct result of the lattice substitution between La and Sr. The entire film is composed of [001], [010] and [100] anisotropic domains with sizes on the order of 30–200 nm. The La0 7Ca0.3MnO3 (LCMO) film, however, does not exhibit a domain structure. It is concluded that the domain structure may have negative effect on the CMR ratio.
The Origin of Resonance Phenomena in Reflection High-Energy Electron Diffraction
Authors: Dudarev S. L. , Whelan M. J. 
Published: April 2011

AbstractResonance scattering of high-energy electrons is responsible for the appearance of bright features observed in reflection high-energy electron diffraction (RHEED) patterns and has found numerous applications in reflection electron microscopy and in RHEED studies of dynamics of molecular beam epitaxial growth of semiconductor crystals. In this paper we report on recent developments in theoretical understanding of the processes leading to resonance reflection of high-energy electrons from a crystal surface.
In-Situ Observation of Deformation Associated with R-Phase in NiTi Shape Memory Alloy
Authors: Gao Y. , Liu Y. Q. , Wu K. H. 
Published: April 2011

AbstractAn in-situ straining experiment was performed in a transmission electron microscope (TEM) on the polycrystalline Ti49Ni51 alloy with full R-phase at room temperature. The reorientation of Rphase variants to a single, favorable one was observed under small stress at the beginning of straining, corresponding to the deformation mode of the first yielding stage. During further straining, the observation showed that the reoriented R-phase undergoes a stress-induced martensite transformation, and this dynamic process was considered to contribute to the second stage deformation in the R-phase stress-strain curve. The orientation relationship between the R-phase and stress-induced martensite has been determined and the internal (001)M twins were found in the stressinduced martensite plates.
In-Situ Dynamic Transformation of Vanadyl Hydrogen Phosphate Hydrate, VOHPO4·1/2H2O, to Vanadyl Pyrophosphate Catalyst, (VO)2P2O7
Authors: Gai P. L. , Torardi C. C. 
Published: April 2011

AbstractWe report, for the first time, direct studies of the dynamic VOHPO4·1/2H2O precursor to (VO)2P2O7 catalyst transformation using recently developed in-situ environmental-cell, high-resolution, electron microscopy (in-situ ECELL-HREM) under controlled environments. Our observations provide fundamental evidence concerning the nature of the topotactic transformation and associated temperature regimes critical to the formation of active catalysts. The direct ECELL-HREM studies show that the structural transformation begins at ˜ 400°C, and a mixture of the precursor and pyrophosphate phases exists at ˜ 425°C. At 450°C, most of the conversion to VPO has taken place. These atomic-scale studies reveal no amorphous phases during the transformation, and that the atomic periodicity is maintained throughout. No other phases have so far been identified in the transformation. The direct studies are important in the development of selective catalysts.
Oxygen Related Defect Center Red Room Temperature Photoluminescence in as Made and Oxidized Porous Silicon
Authors: Prokes S. M. , Carlos W. E. 
Published: April 2011

AbstractSince bulk silicon does not emit light in the visible part of the spectrum, the discovery of strong visible luminescence from porous silicon has been quite surprising and has generated significant interest. This material differs from bulk silicon in that it consists of interconnected silicon nanostructures, having very large surface to volume ratios. The first emission mechanism proposed involved carrier recombination within quantum size silicon particles, but more recent work has shown that surface emission models are more likely. In this paper, an interfacial oxygen center luminescence model will be discussed, with supporting experimental data. A direct correlation between the presence of these centers and the red photoluminescence in both as-made and oxidized PoSi will also be presented.
Substrate Surface Dependence of the Microstructure of μc-Si,Ge:H Deposited by Reactive Magnetron Sputtering (RMS)
Authors: Cho S. M. , Christensen K. , Wolfe D. , Ying H. , Lee D. R. , Lucovsky G. , Maher D. M. 
Published: April 2011

AbstractWe have investigated on the effect of different substrate surfaces in changing the microstructure of μc-SixGe1-x:H films prepared by reactive magnetron sputtering. Films were deposited on hydrogen terminated Si(111), Si(100) surfaces, and surfaces chemical and plasma oxides. The thin film microstructure was characterized by Fourier transform infrared spectroscopy (FTIR), high resolution transmission electron microscopy (HRTEM), X-ray diffraction (XRD), and Raman scattering.
Nonlinear Optical Properties of CuS Nanocrystals with Modified Surface
Authors: Yumashev K. V. , Mikhailov V. P. , Malyarevich A. M. , Prokoshin P. V. , Gurin V. S. , Artemyev M. V. 
Published: April 2011

AbstractNonlinear bleaching and induced absorption effects in CuS microcrystals with modified (after oxidation) surface have been studied. Relaxation times of these processes demonstrate two components - fast (˜ 80 ps) and slow (>>500 ps). Energy level scheme for explanation of these phenomena was proposed. Appearance of bleaching effect in CuS microcrystals due to surface oxidation makes them as perspective materials for saturable absorbers for pico- and femtosecond lasers.
ZnS/Si/ZnS Quantum Well Structures for Visible Light Emission
Authors: Bretschneider Eric , Davydov Albert , McCreary Clint , Wang Li , Anderson Timothy J. , Maruska H. Paul , Norris Peter E. , Goepfert Ian , Moustakas Theodore D. 
Published: April 2011

AbstractSilicon multiple quantum wells confined by ZnS barriers have been grown by MOCVD. Calculations indicate that well widths must be less than 15Å for visible light emission, basically independent of the band offsets. No near-infrared photoluminescence (except bulk Si band-edge emission) was observed from samples with 70Å or greater Si layers, using stimulation at 325 nm with a He-Cd laser; hole trapping in ZnS may play a role. However, we found evidence of yellow light emission from samples which possibly contain Si quantum dots embedded in ZnS.
Continuum Elastic Strain Effects at Semiconductor Interfaces
Authors: Pearsall T. P. 
Published: April 2011

AbstractHeteroepitaxy of semiconductor materials has introduced whole new classes of electronic and optical devices as well as new physical phenomena. Heteroepitaxy always introduces stress in some or all of the deposited material. The resulting strain changes the bandgap of the materials in which it occurs, and changes the conduction and valence band offsets relative to neighboring materials. In all instances studied so far, the effects of strain can be calculated accurately using continuum stressstrain relationships developed for homogeneous, bulk materials.
Desorption and Segregation of Indium and its Dependence on Surface As-coverage
Authors: Ekenstedt M. J. , Yamaguchi H. , Horikoshi Y. 
Published: April 2011

AbstractWe investigate the desorption and segregation rates of Indium atoms on fully strained InxGal-xAs surfaces and their dependence on the surface As-coverage. The results are obtained by measuring the desorption of As using reflection high energy electron diffraction. The desorption rate of As is sensitive to the interaction energies between the group III atoms and the As-atoms. A change in the surface Indium-fraction results in a corresponding change in the desorption behavior of the As-atoms. Information of the surface alloy concentration can thus be obtained. Using this technique we find that segregation and desorption of Indium atoms on strained InxGa1-xAs surfaces is reduced for As-covered 2x4 reconstructed surfaces. The desorption rate of Indium is found to increase with the proximity to an inverted InAs/InxGalxAs interface. In contrast, the normal interface consisting of an InxGal-xAs layer grown on InAs is not seen to influence the desorption rate. This results is attributed to growth related defects specific for the inverted interface.
Surface Effects in Silicon Doping with Boron During Proximity Rapid Thermal Diffusion
Authors: Mone S. , Zagozdzon-Wosik W. , Rastogi M. 
Published: April 2011

AbstractWe investigated effects of surface preparation in doping silicon wafers using proximity rapid thermal diffusion (RTD). This process uses a spin-on-dopant (SOD) as an evaporating source for doping processed wafers. Various cleaning processes were used to study formation of the dopant glass on the silicon wafers during RTD. Doping was evaluated by sheet resistance measurements, dopant profiling using SIMS analyses, carrier distributions using spreading resistance profiling (SRP) or anodic oxidation, and was complemented by the composition analyses of the SOD deposited on the source wafers and of the dopant glass formed on the target wafers using Fourier Transform Infrared Spectroscopy (FTIR) in the transmission and reflection modes, respectively. It was found that the influence of the cleaning steps is much stronger in low temperature doping processes than at high temperatures. In addition, the temperature effect related to the wafer size was also an important factor in determining the doping efficiency in this RTDs.
Cathodoluminescence Study of Diffusion Length and surface Recombination Velocity in III-V Multiple Quantum Well Structures
Authors: Chao L.-L. , Freiler M. B. , Levy M. , Lin J.-L. , Cargill G. S. , Osgood R. M. , Mclane G. F. 
Published: April 2011

AbstractWe describe studies of luminescence and lateral transport properties of excited carriers in GaAs- AIGaAs multiple quantum well (MQW) structures by cathodoluminescence measurements in a scanning electron microscope. We examine the effect of in-plane, etch-defined feature size on MQW luminescence efficiency and variability, and determine the diffusion length and its temperature dependence from ˜ 8K to 250K. Our measurements also provide information about nonradiative surface recombination velocity at the side walls of etch-defined MQW structures.
Uniaxial Stress Applied To p-Type GaAs/AlGaAs Heterostructures: Influence on Heavy Hole Subbandsau
Authors: Hansen Ole P. , Olsen Janus S. , Kraak W. , Saffian B. , Minina N. , Savin A. 
Published: April 2011

AbstractQuantum Hall effect and Shubnikov-de Haas oscillations in a 2D hole gas at a p-GaAs/Al0.5Ga0 5As (001) interface show, that under in-plane (110) uniaxial compression a redistribution of carriers between the two spin-splitted subbands of the ground heavy hole state takes place. At the maximal compression of 2.5 kbar the carrier density of the most populated subband is decreased by 18%, while the total carrier density remains almost unchanged. A decrease of the spin-splitting under the uniaxial compression is proposed.
Ge-Related Interfacial Defects in Sige Alloy Structures
Authors: Macfarlane Patricia J. , Zvanut M. E. , Carlos W. E. , Twigg M. E. , Thompson P. E. 
Published: April 2011

AbstractThis paper reports etching results supporting the identification of the SG1 center as a germanium dangling bond defect at the interface between an oxide and crystalline SiGe. The presence of this defect is significant because, like an analogous center in Si-based systems, it may alter the operation of any microelectronic or micro-optical device which incorporates an interface between SiGe and an overlying oxide. The samples examined are oxygen implanted SiGe layers in which the SG1 center is believed to occur at the interface between oxide precipitates and SiGe. Because of the center's apparent relation to the oxide precipitates distributed through layers of the sample, a depth profile assists in confirming the interfacial nature of the defect. We obtain a depth profile by comparing electron paramagnetic resonance (EPR) spectra of samples etched to decreasing thickness. EPR spectra indicate that the SG1 center decreases with depth in a manner that when correlated to a cross sectional transmission electron micrograph confirms the association with SiO2 and supports its location at the SiGe/SiO2 precipitate interface.
Stress Evolution in Ultra Thin Sputtered Films
Authors: Su Quanmin , Cammarata R. C. , Wuttig Manfred 
Published: April 2011

AbstractThe stress and microstructure of growing thin films evolve with time if the deposition is interrupted or terminated. To establish the parameters which control both kinetic processes ultra thin Au, Cu and Al layers were sputter deposited on Si membranes and the stress evolution was monitored by a vibrating membrane technique. The related surface morphology was studied by scanning tunneling microscopy. Aging after each deposition causes stress evolution towards higher tension and the evolution of the stress with time follows an exponential law with a characteristic relaxation time of the order of tens of seconds. This time was found to depend strongly on the accumulated film thickness as well as the surface morphology. The intrinsic stress of the growing layer increases with the coverage of the film on substrate. Scanning Tunneling Microscopy (STM) shows that the film grows in a Volmer-Weber (VW) mode and the stress reaches a maximum as the film become continuous.
Crystalline Structure and Morphology of the Phases in MgO, TiO2 and ZrO2 Prepared by the Sol-Gel Technique
Authors: Bokhimi  , Boldu J. L. , Muñoz E. , Novaro O. , Lopez T. , Gomez R. 
Published: April 2011

AbstractThe temperature evolution of the crystalline structure of the nanophases found in sol-gel MgO, TiO2 and ZrO2 systems was analyzed by performing x-ray powder diffraction. The structure and concentration of each phase was determined by using the Rietveld technique. The effect of doping MgO and TiO2 systems with platinum was also studied.