bluuebunny/crossref_metadata_2025_split huggingface dataset:
Growth and Transport Properties of Tunneling Barriers in Hts Devices
Authors: Gerritsma G. J. , Verhoeven M. A. J. , Moerman R. , Blank D. H. A. , Rogalla H. 
Published: April 2011

AbstractIn this contribution we will discuss the charge transport of ramp-type HTS Josephson junctions with a Ga-doped PBCO barrier layer. It will be demonstrated that in these junctions charge transport takes place via tunneling processes. The Cooper pairs tunnel directly, at least for T ≤ Tc/2, whereas the quasiparticles tunnel indirectly via localized states. By substituting Cu-chain atoms with Ga-atoms the density of localized states appear to be reduced, resulting in an increase in IcRn-product. Another way to increase this product is a reduction in barrier thickness. Growth studies by AFM of PBCO barriers on ramps indicate that below about 10 nm barriers become increasingly less homogeneous, and below about 6 nm pin holes are very likely to occur. This sets a lower limit on the useful barrier thickness. Presently critical-current densities up to 104 A/cm2 at 40 K, and IlR,-products up to 10 mV at 4.2 K are easily obtained.
Nonlinear Dielectric Thin Films For Active and Electrically Tunable Microwave Devices
Authors: Findikoglu A. T. , Jia Q. X. , Reagor D. W. , Wu X. D. 
Published: April 2011

AbstractWe have prepared electrically tunable and active microwave devices incorporating (superconducting YBa2Cu3O7-x)/(nonlinear dielectric SrTiO3) or (normal metal Au)/(nonlinear dielectric Sr0.5Ba0.5TiO3) bilayers. The dielectric layer thickness for these samples varied between 0.5 μm and 2 μm. The top electrode layer for each sample was patterned into a coplanar waveguide device structure. We have configured these devices as voltage-tunable resonators, voltage-tunable phase shifters, voltage-tunable mixers, and voltage-tunable filters. Under dc voltage bias, these prototype devices have exhibited up to 30% resonant frequency modulation, about 1°/mm-GHz phase shift, more than 40 dB change in mixed microwave power, and finetunable symmetric filter profile with less than 2% bandwidth and more than 15% adaptive range.
Thermodynamic Stability of Binary Oxides in Contact with Silicon
Authors: Hubbard K. J. , Schloma D. G. 
Published: April 2011

AbstractUsing tabulated thermodynamic data, a comprehensive investigation of the thermodynamic stability of binary oxides in contact with silicon at 1000 K was conducted. Reactions between silicon and each binary oxide at 1000 K, including those involving ternary phases, were considered. Sufficient thermodynamic data exists to conclude that all binary oxides except the following are unstable in contact with silicon at 1000 K: Li20, the alkaline earth oxides (BeO, MgO, CaO, SrO, and BaO), the column IIIB oxides (Sc2O3, Y2O3, and Re2O3 where Re is a rare earth), ThO2, UO2, ZrO2, HfO2, and Al2O3. Of these remaining oxides, sufficient thermodynamic data exists to conclude that BeO, MgO, CaO, and ZrO2 are thermodynamically stable in contact with silicon at 1000 K. Our results are consistent with reported investigations of silicon/binary oxide interfaces and identify candidate materials for future investigations.
Oxide Superconductor Interfaces Studied by Spectroscopic Ellipsometry
Authors: Gibbons B. J. , Trolier-Mckinstry S. , Schlom D. G. , Eom C. B. 
Published: April 2011

AbstractIn the eight years since its discovery, numerous materials have been identified as being compatible with YBa2Cu3O7-δ (YBCO). Investigation of potentially compatible compounds requires a knowledge of both the chemistry and microstructure of the interface between the superconductor and the material. In this work, spectroscopic ellipsometry (SE) is being developed as a rapid and non-destructive characterization tool for investigating these interfaces. In addition, SE was used to determine reference optical data for common YBCO substrate materials. These include BaZrO3, 9.5 mol% Y2O3-ZrO2 (YSZ), NdGaO3 and LaSrGaO4.SE measurements of epitaxial YBCO on YSZ substrates have shown that it is possible to identify the formation of the known BaZrO3 reaction layer. The modeled thickness of the reaction layer, as well as the modeled thickness of the YBCO film, are as expected. SE measurements as a function of temperature for YBCO/SrTiO3 have also been obtained. The SE data shows dramatic changes from room temperature to high temperature. This is due to the strong dependence of the dielectric function of YBCO on the oxygen content of the film.
Oxygen Diffusion Coefficients for Sr2AlTaO6: Ramifications on Htsc Multilayer Processing
Authors: Tidrow S. C. , Lareau R. T. , King L. L. H. , Eckart D. W. , Tauber A. , Wilber W. D. , Pfeffer R. L. , Finnegan R. D. , Neal Matt 
Published: April 2011

AbstractWe have studied the rate of oxygen diffusion through Sr2AlTaO6 (SAT), a buffer and dielectric layer used in high critical temperature superconducting (HTSC) structures. An epitaxial bilayer film of SAT on YBa2Cu3O7-δ (YBCO) was deposited onto an (001) oriented single crystal LaAlO3 substrate using the pulsed laser deposition technique. The rate of oxygen diffusion through the bilayer was investigated over the temperature range 415 to 675 °C by post deposition annealing individual sections of the bilayer in 1/3 atm of 18O enriched molecular oxygen gas. Secondary ion mass spectroscopy was used to depth profile 18O and 16O in each sample. Oxygen diffusion coefficients for SAT at 418, 510, 570 and 673 °C were determined to be roughly (0.93, 6.31, 26.6 and 75.3) × 10−16 cm2 s−1, respectively. Since these diffusion rates can limit oxygen intake into underlying YBCO films, SAT may be an inappropriate choice as a dielectric candidate for use in an HTSC multilayer device technology and will at best require development of suitable post annealing schemes to oxygenate underlying YBCO layers.
Single Variant Orientational Growth of Yba2Cu3O7-x on Vicinal (011) SrTiO3 Substrates.
Authors: Vasiliev A. L. , Linehan D. S. , Kvam E. P. , Hou L. , McElfresh M. W. 
Published: April 2011

AbstractThe results of a transmission electron microscopic (TEM) and X-ray microanalysis (EDS) study of Yba2Cu3O7-x (YBCO) films grown on vicinal (011) SrTiO3 substrates are presented. The YBCO films tend to be single crystalline grown in single variant orientation with c-axis =;45° from the surface. Cracks, second phase precipitates (CuO and Y2O3), and a few small YBCO grains in other orientations were revealed in the films.
Surface Analysis of YBa2 Cu30 Thin Films with Rheed-Traxs
Authors: Ogota S. , Futaki N. , Liu Z. , Kanke Y. , Morishita T. 
Published: April 2011

AbstractTotal Reflection Angle X-Ray Spectroscopy with Reflection High Energy Electron Diffraction (RHEED-TRAXS) is a highly sensitive method for surface analysis. Yba2Cu3O7-x films of less than 1 unit cell average coverage can be detected by its characteristic x-rays. We grew YBCO films on MgO substrates by laser-ablation with two different kinds of surface morphology; one had few particles on a flat surface and the other had many long and narrow islands on the surface which we call linear islands. We measured the take-off angle dependence of TRAXS on these films. For the YBCO films with linear islands the intensities of YLα, BaLα and CuKα x-ray lines have shoulders at the critical angles given by a theoretical formula. For the YBCO films with smooth surfaces, only the BαLa intensity had a sharp peak at the critical angle. The result suggests that a BaO layer terminates YBCO films, or that a chemical reaction occurs at the surface and Ba compounds is produced.
Defects in YBa2Cu3O7−δ Thin Films and Their Influences on Tc
Authors: Ye Jinhua , Nakamura Keikichi 
Published: April 2011

AbstractCrystallographic defects introduced in the YBa2Cu3O7−δ thin films during depositions were studied using X-ray diffraction method, and their influences on superconducting properties were also investigated by examining Tc variation of the as-grown and post-annealed thin films. It was found that there exist several kinds of defects in the as-grown thin films, such as oxygen deficiency, cation disordering, and others like lattice dislocation, stacking faults, etc.. These defects could be relaxed by heat treatment at temperatures ranging from 400 to 900 °C, resulting in Tc enhancement more or less. Quantitative understandings of the relations among annealing temperature, structural relaxation, and Tc improvement has also been reached. The kinetics of the relaxation of the defects in the YBCO films was studied further using a high-temperature X-ray diffractometer. Interesting phenomena have been observed at around 400 °C due to abnormal desorption behavior of oxygen and at higher temperatures relating to cation ordering.
Investigation of Copper Ferrite, Cu0.5Fe2.5O4, as a High Saturation Magnetization Material
Authors: Sriram D. , Snyder R. L. 
Published: April 2011

AbstractThe ferrite of composition Cu0.5Fe2.5O4, prepared using a conventional solid-state processing route, was soaked at different temperatures between 1200°C and 1350°C, for an hour, in air. The samples were rapidly quenched into oil. Mössbauer, resistivity and x-ray lattice parameter data were obtained for the quenched phase. The maximum saturation magnetization value, obtained at 10K, was close to 5.0μB. The characterization of the sample showed Cu+1 to be partially disordered across both A and B sites of the spinel structure, with an excess occupancy of the A-site showing that under the proper conditions the ordered high 4πMs Cu+1 phase will be stable.
Study of the Verwey Transition of Fe3O4 Films and Fe3O4/MgO Multilayers Grown by Mbe
Authors: Veerdonk R. J. M. Van De , Gijs M. A. M. , Heijden P. A. A. Van Der , Wolf R. M. , Jonge W. J. M. De 
Published: April 2011

AbstractThin magnetite (Fe3O4) films and Fe3O4/MgO multilayers have been epitaxially grown by Molecular Beam Epitaxy (MBE) on MgO(100) and MgAl2O4(100) substrates. The epitaxial growth on MgO(100) substrates, with a slightly larger bulk lattice parameter than that of magnetite, resulted in an in-plane expansion of the magnetite lattice, accompanied by a perpendicular compression. For films grown on MgAl2O4(100), with a smaller lattice parameter, the substrate misfit is relaxed by the incorporation of misfit dislocations at the interface. It is shown that the substrates have a large effect on the magnetic and electronic properties of the films.The characteristic Verwey transition is shifted towards lower temperatures, broadened, and reduced in amplitude, more so for thinner films. This can not be quantitatively explained by substrate induced stress alone, but is more likely due to a rigid structural coupling between the magnetite film and the cubic lattice of the substrate. Hereby the orthorhombic deformation accompanying the Verwey transition may be supressed.When growing at reduced oxygen pressure, the length scale for the rigid coupling will be reduced by the introduction of vacancies. This leads to more bulk-like resistivity and Verwey transition characteristics, but also to deviations from stoichiometry, as suggested by magnetization and Ferromagnetic Resonance (FMR) experiments.
Molecular Beam Epitaxy of Single Crystal Colossal Magneto-Resistive Material
Authors: Eckstein J. N. , Bozovic I. , Rzchowski M. , O'donnell J. , Hinaus B. , Onellion M. 
Published: April 2011

AbstractWe have grown films of (LaSr)MnO3 (LSMO) and (LaCa)MnO3 (LCMO) using atomic layer-by-layer molecular beam epitaxy (ALL-MBE). Depending on growth conditions, substrate lattice constant and the exact cation stoichiometry, the films are either pseudomorphic or strain relaxed. The pseudomorphic films show atomically flat surfaces, with a unit cell terrace structure that is a replica of that observed on the slightly vicinal substrates, while the strain relaxed films show bumpy surfaces correlated with a dislocation network. All films show tetragonal structure and exhibit anisotropic magnetoresistance, with a low field response, (1/R)(dR/dH) as large as 5 T−1.
Dynamics of In Cluster Growth During InP(110) Surface Dissociation Studied by in-situ Reflection Electron Microscopy
Authors: Gajdardziska-Josifovska M. , Malay M. H. , Smith David J. 
Published: April 2011

AbstractAnnealing effects on InP (110) surfaces were observed in situ using a modified ultrahighvacuum transmission electron microscope equipped with a specimen heating holder. Reflection electron microscopy (REM) was used to record the dynamics of nucleation and growth of liquid In clusters at 650°C, following the desorption of P from the surface. These droplets showed no preference for nucleation at surface steps, and the steps appeared stationary throughout the annealing process. Two distinct types of In cluster growth rates and shape evolutions were detected. A model was developed to decouple height and length information in the REM images. Contact angle and volume above the InP(110) surface were calculated from the dynamic data. The change of contact angle with time provides evidence for sub-surface cluster etching.
Preparation of Ultrafine Supported Clusters for Electron Microscopy Studies
Authors: Singhal A. , Gibson J. Murray 
Published: April 2011

AbstractIn this paper, we discuss the sintering/fragmentation behavior of novel oganometallic rhenium compounds (candidates as catalyst materials) under high energy electron beam irradiation. The technique used was quantitative electron microscopy based on high angle annular dark field (HAADF) imaging in a scanning transmission electron microscope (STEM). Using this approach, we examine elastically-scattered electron intensity from graphite-supported rhenium clusters, and look for mass quantization. The emphasis in this article is not on the imaging technique, but on various sample preparation techniques, materials and synthesis issues of supports and of deposition of very small isolated clusters.
Hvem in situ Study of High-Temperature Deformation of Ceramic and Metallic Materials
Authors: Messerschmidt U. , Baither D. , Bartsch M. , Baufeld B. , Häuβler D. , Haushälter R. , Wollgarten M. 
Published: April 2011

AbstractA high-temperature straining stage was designed for the Halle HVEM. Electron bombardment is used to heat the specimen grips. At present the stage is operated at a maximum temperature of 1250 °C, but somewhat higher temperatures should also be possible. Details of the stage are described and results are presented on several materials. In yttria fully-stabilized (cubic) zirconia, the different slip behaviour on cube and octahedral planes is demonstrated at a specimen temperature of about 1150 °C. While the dislocations move very jerkily on the (primary) cube planes, their motion is more smooth on the octahedral planes suggesting the action of the Peierls mechanism. In t' zirconia, the switching of tetragonal domains was recorded during ferroelastic deformation. The same process was first observed for tetragonal precipitates in partially stabilized zirconia. In γ TiAl, at the temperature of the flow stress anomaly (about 650 °c), the so-called ordinary dislocations move in a viscous manner, in contrast to the room temperature behaviour, where glide seems to be controlled by localized obstacles. Over a wide temperature range in NiAl single crystals, moving dislocations show a discontinuous dependence of the curvature on the dislocation orientation, well agreeing with calculations of the line tension using anisotropic elasticity. Direct experimental proof of dislocation motion during plastic deformation of quasicrystals is first given for A1PdMn single quasicrystals. Dislocations smoothly move on planes orthogonal to threefold and fivefold directions.
1/60 Sec. Time-Resolved High-Resolution Electron Microscopy of Surface-Diffusion of Tungsten Atoms on MgO (001) Surfaces
Authors: Tanaka N. , Kimata H. , Kizuka T. 
Published: April 2011

AbstractSurface diffusion process of tungsten(W)-atoms on MgO (001) surfaces was studied by high-resolution electron microscopy (HREM) in the time resolution of 1/60 s. The W-atoms were prepared on single crystalline MgO (001) films at 300°C by vacuumdeposition of WO3 or W-metal. Analysis of the recorded images revealed individual jump-process of the W-atoms in the substrate temperature from R.T. to 400°C, and gave the barrier potential (Ed) and the pre-exponential factor (D0). The diffusion processes on terraces and along steps were also compared in viewpoint of the jump length.
In Situ High Voltage Electron Microscopy Observations of Deformation and Fracture in Multilayered Materials
Authors: Wall M. A. , Barbee T. W. , Weihs T. P. 
Published: April 2011

AbstractA novel, in situ transmission electron microcopy technique for the direct observation of deformation and fracture in multilayered materials oriented in cross-section is reviewed. Cross-sectional tensile specimens were prepared from thick, free-standing, Cu/Zr and Al/Ti multilayered foils. These tensile specimens contain a micro-gauge section, thus predetermining the location at which dislocation activity and crack nucleation and growth can be observed at high magnifications in the transmission electron microscope. The results from these experiments are unique and cannot be realized by any other technique. These observations will aid us in our understanding of the micromechanisms of deformation and fracture in multilayered materials.
Controlled Environment [Ecell] Tem for Dynamic In-Situ Reaction Studies with Hrem Lattice Imaging
Authors: Boyes E D , Gai P L , Hanna L G 
Published: April 2011

AbstractWith a controlled environment electron microscope it is possible to remove the effect of another atmosphere, such air, to which the sample may have become exposed; to study in considerable detail the continuous development of a series of microstructures in a dynamic process, to identify important intermediate phases and defects in them which may only be metastable under specific reaction conditions of atmosphere and temperature, and to establish whether they are the origin, or merely the consequence, of the reaction. In this paper we report the extensive modification of a high resolution transmission electron microscope (Philips CM30T HRTEM) to add facilities for dynamic in-situ gas-solid reaction studies in a controlled atmosphere of gas or vapor at pressures of 0–50mbar which replaces the regular high vacuum TEM environment. The new environmental cell (ECELL) capability is combined with the original 0.23nm TEM resolution, STEM (BF/ADF) imaging and chemical and crystallographic analyses. Regular specimen holders are used; including hot stages capable of temperatures >1000°C. The full TEM resolution has been demonstrated at temperatures above 700°C and with limited (mbar) amounts of gas flowing through the integral 4-aperture differentially pumped ECELL (and with the additional pumps for the system operating). The ECELL system can be used to preserve, or if necessary to recreate, a continuous chain of evidence in a chemical reaction process.
Mimicking the Real World and Exploring New Ones with In-Situ Electron Microscopy
Authors: Howie A. 
Published: April 2011

AbstractRecent progress with in-situ observations by electron microscopy is briefly surveyed by referring to developments in instrumentation for reflection and low energy electron imaging as well as for high resolution transmission imaging and spectroscopy. New opportunities have been opened up by environmental microscopy. With increased levels of illumination intensity, the ever present question of beam-induced effects is of mounting concern particularly in studies of non-metallic materials.
Stress Distributions in Free Standing Quantum Well Dots and Wires
Authors: Gippius N. A. , Tikhodeev S. G. , Steffen R. , Koch T. , Forchel A. 
Published: April 2011

AbstractWe present a theoretical model for calculation of stress distributions in semiconductor nanostructures such as lattice-mismatched InGaAs/GaAs quantum well wires and dots. The model is based on a linear elastic deformation approximation, and assumes dislocation-free interfaces with an additional condition of continuous interatomic distance on the interfaces. The distributions of stress tensor components and the resulting effective potentials for electronhole pairs are calculated. The comparison of our model with the experimental data on the exciton spectra in free standing strained InGaAs/GaAs quantum well wires is also presented.
Three-Dimensional Epitaxy: Thermodynamic Stability Range of Coherent Germanium Nanocrystallites in Silicon Host
Authors: Balasubramanian S. , Ceder G. , Kolenbrander K. D. 
Published: April 2011

AbstractWe study the stability range for a coherent interface between Ge quantum dots and an epitaxial Si shell. The critical radius at which coherency is lost is evaluated as a function of Si shell thickness and Ge nanocrystallite radius by comparing the energy of the system in the coherent and incoherent state. We find that the system is coherent up to a Ge nanocrystallite radius of about 100 Å, irrespective of the Si shell thickness. Nanocrystallites of radii larger than 270 Å lose coherency by the generation of perfect dislocation loops. In nanocrystallites of intermediate radii ( between 100 Å and 270 Å), the coherency is lost by the introduction of partial dislocation loops enclosing a stacking fault. As the shell thickness decreases, the critical radius increases.
Photovoltaic and Electroluminescent Properties of Stainetched Porous Silicon Based Heterojunctions
Authors: Dimova-Malinovska D. , Tzolov M. , Kamenova M. , Tzenov N. , Sendova-Vassileva M. , Nesheva D. 
Published: April 2011

AbstractThe results of photoelectric properties and electroluminescent studies of structures ZnO/porous Si/p-type c-Si/Al and ZnO/porous Si/p-n c-Si junction/Al are presented. Porous Si is prepared by stain etching of c-Si covered with thin Al film. The transparent ZnO film allows light emission through the top surface of the device under forward electrical bias. Photocurrent is observed under reverse bias and a photovoltaic effect is measured on the p-n junction PS device. The model based on injection of minority carriers through a narrow energy barrier into the porous Si and the presence of the barrier at the interface porous Si/c-Si is suggested for describing the electrical, photoelectric and luminescent properties of the structures.
Micro Structural Investigation of Porous Silicon Depth Profile by Direct Surface Force Microscopy
Authors: Chang D. C. , Baranauskas V. , Doi I. , Prohaska T. 
Published: April 2011

AbstractWe propose a method for studies in deph profile of porous silicon (PS) using atomic force microscopy (AFM) to remove PS layers from the surface. The abrasion were made aplying forces between 10-11 to 10-13 N with the AFM liquid cell measuring method. These range of forces is enough to remove very thin PS layers of the surface at each scan the equipment makes. With this method we can make studies and see the PS diferences in depth profile made by different process or different manufacturing conditions.
Linear Polarization of Porous Si Photoluminescence
Authors: Gippius N. A. , Tikhodeev S. G. , Efros Al. L. , Rosen M. , Kovalev D. , Chorin M. Ben , Diener J. , Koch F. 
Published: April 2011

AbstractWe demonstrate experimentally that linear polarization of porous Si photoluminescence depends significantly on the excitation geometry and describe this effect within the framework of a dielectric model in which porous Si is considered as an aggregate of slightly deformed, elongated and flattened, dielectric elliptical Si nanocrystals with preferred orientation in the [100] direction. The theoretical best-fit analysis of the experimental data allows us to get certain information concerning the shapes and orientation of the ellipsoids.