bluuebunny/crossref_metadata_2025 huggingface dataset:
Structural and Electrical Characterization of CdSe Thin Films
Authors: Hatalis Miltiadis K. , Lin Fuyu , Westcott Michael R.
Published: March 2011

The structural and electrical properties of thin films of undoped and indium-doped cadmium selenide deposited on glass substrates have been investigated. The as-deposited films were found to be microcrystalline with grain size less than 10 nm. Grain growth occurred upon annealing. Enhanced grain growth was observed in the indium doped films. Transmission electron microscopy of in-situ annealed films revealed the formation of large single crystal areas having cubic structure with <111> as the dominant orientation. The resistivity and the effective electron mobility of polycrystalline cadmium selenide films were investigated as function of annealing conditions and device channel length. Reduction of the electrical resistivity and increase of the electron mobility was observed in devices with channel lengths less than 25μm.
Directional Deposition of Silicon Oxide by a Plasma Enhanced TEOS Process
Authors: Hsieh J. J. , Ibbotson D. E. , Mucha J. A. , Flamm D. L.
Published: March 2011

We have characterized the step coverage and film quality of (tetraethoxysilane) TEOS-based silicon oxides which are directionally deposited on horizontal surfaces of trench features under oxygen-lean conditions in a high frequency (14 MHz) discharge. The film thickness on the sidewalls depends most strongly on the O2 :TEOS feed ratio. Water uptake after ambient exposure was used as a measure of film quality and the amount of water absorbed in the film correlated well with changes in the refractive index and stress. Oxide quality on horizontal surfaces could be improved by decreasing the TEOS feed or increasing the discharge power, but the sidewall oxide quality could not be improved by these methods. Small NF3 additions to the discharge markedly improved sidewall quality, altered the angle between the sidewall and the bottom of trench features from 90° to ˜115° (tapered profile) and increased the deposition rate, while preserving the directionality of deposition.
Polyhydride Bonding Groups in PECVD Amorphous Si Thin Films.
Authors: Davidson B. N. , Parsons G. N. , Wang C. , Lucovsky G.
Published: March 2011

In glow discharge deposition (GD) of a-Si:H alloys, the concentration of electronically-active defects increases as the incorporation of bonded hydrogen in polymerized dihydride groups, (SiH2)n increases. Since the fraction of dihydride groups increases strongly with decreasing substrate temperature (Ts), the incorporation of these bonding groups can only effectively be reduced by restricting Ts to about 230°C or higher. We have found that a-Si:H films produced by remote Plasma Enhanced Chemical Vapor Deposition (remote PECVD) are qualitatively different than the GD films in the following ways: 1) the amount of bonded hydrogen for Ts > 100°C is less by about a factor of two; and 2) the fraction of polyhydride bonding is also significantly less than the monohydride fraction for Ts > 100°C. We develop a statistical model that provides a basis for translating any process-dependent representation of data for the polyhydride fraction into a universally-obeyed scaling relationship in which the independent variable is [H]. The agreement between the statistical model and the experimental data, replotted as a function of [H], supports our observation that the fraction of polyhydride bonding is not determined simply by Ts, but is a function of the particular reaction pathways in the deposition process chemistry.
Diamond Forming Discharges
Authors: Bachmann Peter K. , Lydtin Hans
Published: March 2011

Methods to prepare diamond thin films by means plasma chemical vapor deposition are reviewed. The various techniques available to date are compared with respect to their deposition rates, deposition area, quality and homogeneity of the material produced, and their specific advantages and drawbacks. The deposition rates of both thermally induced and plasma induced CVD methods correlate well with the gas temperature in the reaction zone supporting the hypothesis that the large quantities of diamond precursor species necessary for high deposition rates are formed in a hot spot of the deposition system.
In-Situ SubStrate Temperature Measurement During a-Sin Plasma CVD from N2 Rotational Temperature
Authors: Ishihara Shin-Ichiro , Otsuka Akira , Nagata Seiichi
Published: March 2011

Rotational temperature (Tr) of nitrogen molecule, equivalent to the gas temperature (Tg), was used for monitoring silicon nitride (SiN) surface temperature during rf glow discharge processing. SiN film characteristics such as deposition rate and etching rate for mixture of hydro-fluoric acid (HF) and ammonium fluoride : (NH4F) were dependent on Tr near the substrate. The Tr increased not only with substrate temperature setting (To) but also with gas mixing ratio of H2/(H2+N2) due to improvement of thermal conductance from heater to substrate in the process chamber.
ECR Plasma Deposition of Dielectrics for Optoelectronic Applications
Authors: Dzioba Steven
Published: March 2011

A UHV electron cyclotron resonance (ECR) plasma source has been used to deposit SiNx, SiOxNy and amorphous Si thin films on InP substrates for optoelectronic device applications. High quality dielectric films can be deposited at temperatures significantly lower than conventional techniques, namely less than 110°C. Selected applications pertinent to optoelectronic devices are used to establish the role of ion/electron fluxes in thin film properties.
Magnetoklasticity in Rare-Earth Kultiiayers and Films
Authors: Erwin R.W. , Rhyne J.J. , Borchers J. , Salamon M.B. , Du R. , Flynn C.P.
Published: March 2011

The magnetic structure has been measured with neutron scattering and SQUID magnetometry for a number of epitaxial multilayers and films of the magnetic rare-earths dysprosium and erbium grown with non-magnetic yttrium. In almost all cases the first order ferromagnetic phase transitions are suppressed, although the Néel temperatures are within 5% of the bulk values. The observed critical fields are explained by including epitaxial constraints with the bulk theory of magnetoelasticity.
Neutron Scattering Methods for Materials Science
Authors: Pynn Roger , Lujan Manuel
Published: March 2011

This article describes some of the neutron scattering techniques which can be used to probe structures of materials on length scales which range from less than 1 Å to 1 μm. The intent is to remove the veils of secrecy and mystery which have apparently prevented the wide application of these techniques to problems in materials science.
Neutron Depolarization by Flux Latrices in High-TC Materials
Authors: Pickart S. J. , Nunes A. C. , Crow M. L. , Fu Bo , McGuire T. R. , Shinde S. , Shivashankar S. A.
Published: March 2011

We have recently reported[l] neutron depolarization measurements on an YBa2Cu3O7−δ composition exhibiting a transition from a low temperature state which caused depolarization (P=0.76+−.02) to one at high temperatures (T=55K) where depolarization was absent. Since this temperature is well below the measured superconducting transition at 86K, we speculated that the transition was a dynamic one corresponding to flux lattice melting[2] or to formation of a glassy state[3]. We have now extended these depolarization measurements to two specimens of Bi2.2Sr1.7CaCu2O8+δ' prepared and characterized[4] at IBM, which showed superconducting transitions at 80K with weak tails extending to 110K. The two samples have critical current densities, as determined by the Bean expression[5], that differ by 50%.
In-Beam Small-Angle Scattering Studies of Phase Separation in Ni-Ti Single Crystals
Authors: Cerri Alberto , Schoenfeld Bernd , Kostorz Gernot , Wright Albert F.
Published: March 2011

Phase separation of quenched supersaturated Ni-(9.5-12.0)at.% Ti single crystals was followed by small-angle neutron scattering during in-beam aging at 773, 813 and 853 K. With the incident beam along <110>, scattering maxima in <100> directions were observed from the earliest stages of decomposition. While the results obtained at 773 K may be compatible with the general features of spinodal decomposition, a two-phase model with homogeneous precipitation in a depleted matrix is more appropriate at 813 and 853 K. Though scaling may be shown to hold, the aging kinetics is considerably slower than expected, which is related to a stabilizing effect of elastic coherency stresses.
Vibrational Spectra for Hydrogenated Amorphous Semiconductors
Authors: Kamitakahara W. A. , Biswas R. , Bouchard A. M. , Gompf F. , Suck J. B.
Published: March 2011

Hydrogen vibration spectra have been measured by neutron scattering for several amorphous semiconductor materials, including a-Ge:H and a-SiC:H samples containing about 10 at. % H. The data for a-Ge:H are compared in detail with the results of realistic computer simulations.
Comparison of Neutron Elastic and Inelastic Scattering from Fused Quartz, Cab-O-Sil and Aerogel
Authors: Root John H. , Buyers William J. L. , Page John H. , Schaefer Dale W. , Brinker C. J.
Published: March 2011

Neutron scattering experiments have been performed to study the structure and dynamics of three preparations of silica: a dense glass (fused quartz), a flame-hydrolyzed aggregate (Cab-O-Sil, grade M5) and a polymeric aerogel. The experiments were performed on the three materials at temperatures selected from 300, 77 and 4.2 K. Neutron inelastic scattering was measured at Q = 2.5, 2.9 and 4.0 Å−1.

The elastic scattering indicates a systematic decrease in positional correlations on progressing from fused quartz through Cab-O-Sil to aerogel. The inelastic scattering was analyzed with the Buchenau model [1] to obtain the sample, Q and temperature dependences of the density of states, g(v). In the aerogel g(v) increases with temperature at frequencies greater than 1.5 THz and is enhanced at Q = 2.5 Å−1. Thus a complete explanation of the inelastic scattering from aerogels must account for multiphonon processes, local antiphase motions and anharmonic effects.
Characterization of Molecular Network of Thermosets Using Neutron Scattering
Authors: Wu Wen-Li
Published: March 2011

Neutron scattering measurements were conducted to investigate the conformation of the molecular networks in epoxies. Emphasis was placed on the changes in the scattering intensity resulting from curing. Experimental results on homopolymerized epoxy as well as a theoretical interpretation of the results are presented.
Thermal Diffuse Scattering in Neutron Time-of-Flight Powder Patterns
Authors: Radler Michael J.
Published: March 2011

Inelastic scattering from lattice phonons contributes a significant fraction of the observed Bragg intensity in time of flight neutron powder patterns of transition metal monoxides at elevated temperatures. Ignoring this thermal diffuse scattering (TDS) leads to errors in the site occupations of defects present in these materials. The intensity from one phonon TDS has been calculated as a function of time-of-flight and used to correct the measured intensities. The effect of this correction on the results of Rietveld profile refinement is discussed.
Gas Phase Decomposition of an Organometallic Chemical Vapor Deposition Precursor to AIN:[AI(CH3)2NH2]3
Authors: Amato Carmela C. , Hudson John B. , Interrante Leonard V.
Published: March 2011

A novel technique for probing chemical vapor deposition reaction mechanisms is presented. A conventional hot-wall Pyrex reactor is coupled to a molecular beam apparatus. Preliminary results of the decomposition of an organometallic precursor to AIN, [AI(CH3)2NH2]3, indicate a decomposition temperature between 200 and 270°C. The mass spectrum of the precursor at 100°C provides evidence for the existence of a trimer-dimer equilibrium of the precursor at this temperature
Correlation Among Process Routes, Microstructures and Properties of Chemically Vapor Deposited Silicon Carbide
Authors: Davis Robert F.
Published: March 2011

“Silicon carbide” is a generic term for a host of different materials produced by several process routes which yield a variety of microstructures and associated property characteristics. The route of chemical vapor deposition (CVD) is used primarily to deposit SiC for wear- and corrosion- resistant coatings and for diffusion barriers to and from the underlying substrate. Presently this technique is also being used to deposit monocrystalline semiconductor thin films of SiC and to infiltrate various high temperature woven fabrics with this material. The following sections describe the results of thermodynamic calculations to define SiC CVD diagrams using various precursor gas mixtures, discuss various CVD techniques and detail the results of deformation, infiltration and thin film deposition studies that have been recently conducted on vapor deposited SiC.
Microstructural Characterization of Multiphase Coatings Produced By Chemical Vapor Deposition
Authors: Lowden R. A. , More K. L. , Besmann T. M. , James R. D.
Published: March 2011

Chemical vapor deposition has been utilized to produce ternary, multiphase coatings of various compositions of silicon carbide (SiC) with Ti, Cr, and Mo. Thermodynamic calculations have been performed for a variety of experimental conditions in each system. Scanning, transmission and analytical electron microscopy, and X-ray diffraction techniques have been used to characterize the microstructures and to determine compositions.
Tungsten Carbide Erosion Resistant Coating for Aerospace Components
Authors: Garg D. , Dyer P. N.
Published: March 2011

An increasing problem faced by the aerospace industry is the erosive wear of engine components. Various PVD protection coatings have been used previously to combat this wear problem, but with limited success. This paper presents results obtained with a low-temperature CVD, erosion resistant, multilayer tungsten carbide coating system. The coating can be deposited at temperatures below 500°C on ferrous alloys used in the aerospace industry. The low temperature of deposition eliminates the problem of degradation of mechanical properties that occurs with normal high-temperature chemical vapor deposition processes. High-cycle fatigue strength and other mechanical property data are presented for coated stainless steel, as well as results on erosion and impact resistance at 90° impingement.
Effects of Deposition Conditions on The Microstructure and Properties of CVD SiC
Authors: Minford Eric , Stevens Robert E. , Magnotta Vincent L. , Dyer Paul N. , Watkins Thomas R. , Green David J.
Published: March 2011

As part of an ongoing program to develop high performance silicon carbide coatings for graphite, a research study into the effects of deposition conditions on residual stresses was initiated. A series of experiments was conceived and implemented to explore the microstructure and the elastic properties of the coatings and substrates as well as to directly measure the residual stress states. The results of these experiments are analyzed with respect to the effects of deposition temperature on the microstructure and properties of CVD SiC on graphite and how the observed differences affect the residual stresses in the coatings.
Bond Graphs For Cvd Processes
Authors: Kalidindi Surya R. , Desu Seshu B.
Published: March 2011

A unified approach to model the general CVD process, utilizing the versatility and flexibility of bond graph methods, is presented. The bond graph representations for important CVD sub-processes are derived. The application of these elements is illustrated through hypothetical examples of CVD processes. It is also shown that several different CVD processes can be handled by a single bond graph computer program.
Organometallic Chemical Vapor Deposition of Strontium Titanate thin Films
Authors: Feil W. A. , Wessels B. W. , Tonge L. M. , Marks T. J.
Published: March 2011

SrTiO3 thin films were deposited by low pressure organometallic chemical vapor deposition on silicon substrates using the volatile metal-organic precursors titanium isopropoxide and Sr(dipivaloylmethanate)2. Oxygen and water vapor were used as reactant gases and argon was used as a carrier gas. Growth rates ranging from 0.6–2.1 μm/hr were obtained at 650–800°C. Polycrystalline films were obtained at growth temperatures of 650–750°C, and amorphous films above 750°C. SrTiO3 films deposited on silicon substrates exhibited resistivities greater than 109 Ω-cm and dielectric constants up to 100.
Early Growth in the Chemical Vapor Deposition of Tin and TiC and Monitoring by Laser Scattering
Authors: Klein Max , Gallois Bernard
Published: March 2011

The early growth of chemically vapor deposited TiN and TiC coatings on pyrolytic graphite was studied in the kinetic- and mass transport-controlled regimes. While steady-state growth of these coatings results in columnar grains, such morphologies do not originate at the substrate/coating interface. Rather, TiC deposition begins on the substrate as fine grains less than 100 nm in diameter. Early TiN growth occurs in layers of 50 nm grains. In both cases, early fine-grained growth occurs at a lower rate than the linear, steady rate observed for columnar growth. A laser scattering technique has been developed as a tool for characterizing early growth through surface roughness. This noncontact method can be used as an in-situ diagnostic to detect changes in the surface of the growing deposit.
Xps Analysis of Y-Ba-Cu-O and Zr-O Thin Films and Interfaces with Silicon Substrates
Authors: Fenner D.B. , Viano A.M. , Connell G.A.N. , Boyce J.B. , Fork D.K. , Ponce F.A. , Tramontana J.C.
Published: March 2011

Thin films of Y1Ba2Cu3Ox,ZrO2, and yttria-stabilized zirconia (YSZ) have been deposited on Si(100) by the UV-laser ablation technique, and characterized by several techniques including x-ray photoemission spectroscopy (XPS) and cross-sectional transmission electron microscopy (XTEM). Si substrates were prepared by several techniques including thermal oxidation, and oxide etching and passivation by hydrogen termination. Certain of these YBCO films (= 250 nm thick) deposited on YSZ buffer layers have excellent superconducting properties. Other YBCO and zirconia films, deposited to 2-5 nm thickness and transferred under dry N2 into UHV, allowed XPS evaluation of the thermal and chemical stability of the interfaces and nearby regions. 2-nm films of YBCO on 15-nm films of SiO2/Si, deposited at 550–670 °C, showed Cu 2p core-level XPS lines similar to those of bulk YBCO (i.e., Cu II) but with two components due to reactions. The Si 2p line showed formation of silica on the YBCO surface at 670 °C and of silicate at 550 °C. XTEM lattice images showed that use of H-terminated Si produced superior interfaces with the zirconia films.
Phonon Anomaly at Tc In (Y/Er)Ba2Cu3O7–δ
Authors: Sharma Rajeshwar P. , Rehn L. E. , Baldo P. , Liu J. Z.
Published: March 2011

Ion channeling in single crystals of (Y/Er)Ba2Cu3O7–δ reveal an abrupt change (~0.01Å) at the superconducting transition temperature (Tc) in displacements of the Cu and O atoms perpendicular to the [001] direction. This anomalous change in atomic displacements shifts directly with stoichiometry-induced changes in Tc. Blocking patterns indicate no large structural changes across Tc.
Magnetic Penetration Depth and Intragrain Critical Current Density in Grain-Aligned Tl2Ca2Ba2Cu3O10 Superconductor
Authors: Thompson J. R. , Christen D. K. , Deeds H.A. , Kim Y. C. , Brynestad J. , Sekijla S.T. , Budai J. , Ossandon J. G.
Published: March 2011

Magnetic studies were performed on the high temperature superconductor Tl2Ca2Ba2Cu3O10 (Tc = 123 K) in the form of a grain aligned composite. Investigations with the magnetic field applied parallel and perpendicular to the sample's cannon c-axes were analyzed to obtain the magnetic penetration depth as a function of temperature and the critical current density Jc(H,T).
Bulk Modulus of the YBaCuO Oxide Superconductor Obtained from Magnetic Measurements
Authors: Bokhimi
Published: March 2011

Starting from the fact that the YBa2Cu3O7-x oxide superconductor system has a constant magnetic susceptibility at high temperatures for each oxygen deficiency x, and assuming that the charge carriers have a free-electron-like behavior, the observed magnetic susceptibility of the samples at room temperature can be associated to the Pauli paramagnetismus and to the Landau diamagnetism of the charge carriers. This result allows one to calculate the charge carriers density from the magnetic susceptibility in the sample. If besides one assume that by applying an external pressure on the sample, there is a change of the volume of the unit cell, but not in the number of the charge carriers in it, then, it is possible to calculate the Bulk modulus of the YBaCuO system at room temperature starting from these magnetic measurements. The obtained results are of the same order of magnitude to those reported in the literature and obtained from thermodynamic and mechanical measurements.
Rf Surface Resistance Measurements in the Pb-Bi-Sr-Ca-Cu-O System
Authors: Lanagan M. T. , Bohn C. L. , Delayen J. R. , Einloth M. C. , Vogt R. N. , Balachandran U.
Published: March 2011

Wires were fabricated from the high-Tcsuperconductor Bi0.7Pb0.3SrCaCu1.8Ox(Pb-BSCCO) by an extrusion process. The specimens were sintered for periods up to 14 days, and density was found to decrease with longer sintering times. Rf surface resistance data revealed that the onset of superconductivity occurred at 105 K and that the transition was very broad.
Fabrication of High TC Superconducting Composite Structure
Authors: Chang J. , Song L.W. , Barone R. , Bush P. , Yang F. , Patel S. , Kao Y.H. , Shaw D.T.
Published: March 2011

The laser ablation technique was used to fabricate high Tc superconducting composite structures. The multilayered structures were fabricated in‐situ by changing the target during deposition. Thin MgO films and yttrium‐stabilized Zr02 films were used as buffer layers. The composite films were successfully fabricated on ZrO2(100) substrates. There is negligible interdiffusion occurring at the interfaces and the Jc at 77K is higher than 105A/cm2 for YBCO films in a triple layered structure.
Effect of Thermal Cycling and Mechanical Deformation on the Superconducting Properties of Ag/Yba2Cu3O7-X Wires
Authors: Ocampo M.A. , Orgaz E. , Akachi T.
Published: March 2011

Preforms made by filling silver tubes with YBa2Cu3O7‐x (YBCO) powder were drawn to obtain wires with diameters in the 0.25mm to 1.00mm range. Straight samples of these wires were sintered and oxygenated. The observed changes in Tc and Jc while the samples were thermaly cycled or mechanically deformed are reported.
Phase Equilibria in the System Tl-Ca-Ba-Cu-O. I. Stability of the 2122 Phase Under Conditions of Oxygen Annealing
Authors: Cook L. P. , Chiang C. K. , Wong-Ng W. , Swartzendruber L. J. , Bennett L. H.
Published: March 2011

Results are presented for 850°C oxygen annealing experiments (up to 62 hr) on the 2122 (Tl:Ca:Ba:Cu) oxide phase, with and without intermediate grinding. Samples were characterized by powder X-ray diffraction and a.c. magnetic susceptibility. The 2122 phase appears to be thermodynamically stable in oxygen under conditions of both extensive grinding, and, annealing of long duration. However, onset Tc's vary from 71 K to 109 K for apparently single-phase 2122 samples with nearly identical X-ray powder patterns, depending upon the heat treatment.
Oxygen Ordering in Yba2cu3oz at Low Temperature
Authors: Ceder G. , Asta M. , Fontaine D. de
Published: March 2011

A parameter‐free phase diagram is derived for oxygen ordering in the YBa2Cu3Oz compound. Four phase regions are found in which the following structures are stable: Tetragonal, Ortho I, Ortho II, and anti‐Ortho I. In addition, long‐period quasi‐one‐dimensional states of order can become stable at low temperature. A simple branching algorithm allows one to predict these additional structures and their diffraction patterns. Theoretical predictions are in excellent agreement with recent experimental findings. Implications for the existence of Tc plateaus are briefly discussed.
Non-Stoichiometry and Complex Defects in the Structure of R-Ba-Cu-O Single Crystals Determined by Neutron Diffraction
Authors: Schweiss P. , Galez Ph. , Collin G. , Marucco F.
Published: March 2011

The crystal structure of several RBa2Cu3-yO6+z (R=Y,Ho) crystals are investigated by neutron diffraction using an exact solution for the twinned orthorhombic samples. For an oxygen concentration >0.35 in the chains, the structure is orthorhombic due to an exclusive occupancy of the 0(4) site. A systematic and variable copper deficiency is observed on the Cu(l) site leading to a correlated defect on the chain oxygen O(4) and on the bridging oxygen O(l). Due to the presence of these defects, a transverse disorder is observed for the highest oxygen content with a residual occupancy of the forbidden O(5) site.
Superconductivity Above 77 K in the Cubic Ba2Ycu2Wo9-Y Oxide System
Authors: Bokhimi  , Garcia-Ruiz A.
Published: March 2011

We have obtained a new family of oxide superconductors, which are characterized by a cubic structure with the space group Fm3m and transition temperatures to the superconducting state above 77 K. As prototype of this family, we have studied some properties of the Ba2YCu2WO9‐y system. We report details about the experimental conditions that are necessary in order to obtain the cubic structure and to change the charge carrier density. The samples show superconducting behavior around 90 K with only a small Meissner effect fraction. These results can be interpreted in terms of filamentary superconductivity, however, it is necessary to characterize the system further to give a correct interpretation of the results.
Preparation and Transition Temperature of Ca‐Substituted Yba2Cu4O8
Authors: Miyatake T. , Yamaguchi K. , Takata T. , Gotoh S. , Koshizuka N. , Tanaka S.
Published: March 2011

Samples of Y1‐xCaxBa2Cu4O8 are prepared by means of a new high pressure technique employing the oxygen‐HIP. We find that the transition temperature increases with Ca content, and that Tc=90K is realized at x=0.1. These data are explained by the hole concentration, i.e. average charge per [Cu‐O] site.
KEY‐WORDS: YBa2Cu4O8, Ca‐substitution, Transition temperature, Hole concentration
Seeding Induced Aligned Microstructures (S.I.A.M.) in Yba2Cu306+X
Authors: Zhang Lijie , Chan Helen M. , Harmer Martin P.
Published: March 2011

Annealing of YBa2Cu_Og (12 3) above the peritectic temperature, followed by slow cooling at 0.5 C/min, was found to produce a microstructure containing regions (d ‐ 200 microns) within which the grains were highly aligned. When these regions were used to “seed” 123 powder, an enhanced degree of texture was obtained, where the aligned regions were > 1mm in size.
Influence of Starting Material on Bi2sr2cacu2o8 Fibers Grown by the Float Zone Process
Authors: Moulton Linda V. , Brenner Joseph M. , Raymakers Robert J. , Peszkin Perla N. , Feigelson Robert S.
Published: March 2011

A miniaturized float zone technique using laser heating has been found to have potential for producing superconducting fibers of Bi2Sr2CaCu2O8 which can carry high currents. Growth stability and growth rate, however, need to be improved if this technique is to be useful for preparing long lengths of 30 μπι diameter high quality fibers for property evaluation and prototype devices. One of the first requirements toward achieving this goal is the preparation of dense, homogeneous starting material. Work on different strategies for starting material preparation are discussed.
Theory of the Normal State of Cuprate Superconductors
Authors: Anderson Philip W. , Ren Yong
Published: March 2011

We propose a framework for the theory of the "normal" metallic state of the CuO2 planes of high Tc superconductors. This state is closely analogous to the known state of the one-dimensional Hubbard model, with spin excitations which can be thought of as chargeless (Z = 0) Fermions occupying the interior of the conventional Fermi surface, and charged excitations which have zero energy near the spanning vectors 2kF of that Fermi surface. The electron spectrum is the composite spectrum of two of these excitations, and can be fitted to angle-resolved photoemission data. When we do so we can calculate or estimate many properties of the normal state in excellent agreement with experiment, and show that the pair susceptibility is anomalously large and temperature-dependent, explaining the high Tc and the specific heat behavior.
110K Superconducting Fibers of [Bi,Pb(Sb)]2Sr2Ca2Cu2O10 + x
Authors: Jincang Zhang , Aisheng He , Yujing Huo , Yusheng He
Published: March 2011

Superconducting fibers of [Bi,Pb(Sb)]2Sr2Ca2Cu3O10 + x high Tc superconducting materials have been prepared by means of the laser-heated pedestal growth method with Tc 0= 110K and Jc>103 A/cm2. Structure analysis showed that the a-b plane of the material prefers to align along the growth direction, though the post-growth heat treatment, which is still necessary at present stage, may destroy the texture structure in some extent.The existence of Pb is vital for stabilizing the 110K phase of the Bi-based fibers.
Superconductivity of Bi-Sr-Ca-Cu-O Prepared from CuO or Cu2O, and Doped with Ag Ions
Authors: Kato Teruo , Kazumata Yukio , Maeta Hiroshi
Published: March 2011

Superconductivity in Bi compounds is examined in samples prepared from CuO and Cu2O powders, and also in samples doped with Ag. In BiSrCaCuxO (x=2,3,4,5) prepared from CuO powder, Tc decreases with an increase of Cu content, while in samples prepared from Cu2O the opposite trend, an increase of Tc with Cu content, is observed. From Ag doping, BiSrCaCu2Oy+Agx (x=0, 1.0, 1.5, 2.0), the volume ratio of high to low Tc phase is found to be a maximum at a Ag content between 1.5 and 2.0. From these experiments, a strong correlation between the high Tc phase and Cu+ valence state is suggested.
Hyper- and Hypobaric Processing of T1-Ca-Ba-Cu-O Superconductors
Authors: Goretta K. C. , Routbort J. L. , Shi Donglu , Chen J. G. , Xu Ming , Hash M. C.
Published: March 2011

Tl-based superconductors of initial composition Tl:Ca:Ba:Cu equal to 2:2:2:3 and 1:3:1:3 were heated in oxygen at pressures of 104 to 6 x 105 Pa. The 2:2:2:3 composition formed primarily the 2-layer superconductor with zero resistance from 77 to 104 K. The 1:3:1:3 composition formed nearly phase pure 3-layer superconductor with a maximum zero resistance temperature of 120 K. Application of hyperbaric pressure influenced phase purities and transition temperatures slightly; phase purities decreased significantly with application of hypobaric pressures.
One-Step Synthesis and Densification of Bulk YBa2Cu4O8/Ni Composite Superconductors
Authors: Gélinas C. , Champagne B.
Published: March 2011

The fabrication of bulk YBa2Cu307-x/metal composite superconductors is not easy because of the oxygen-temperature dependence of the YBa2Cu307-x phase (the socalled 123 phase). A loss of oxygen occurs during consolidation of these composites at high temperature and it is almost impossible to diffuse oxygen through the metallic envelope into the densified compound to restore the required oxygen content for superconductivity above 77K. To overcome this drawback, a one-step synthesis and consolidation process was used to produce YBa2Cu4O8/ nickel composites. The superconductive 124 phase has a more stable oxygen stoichiometry [1] and is synthesized under a high oxygen pressure at high temperature.
Ag/YBa2Cu3O7-x Powder Generation by Aerosol Decomposition
Authors: Kodas Toivo T. , Carim Altaf H. , Ott Kevin C.
Published: March 2011

YBa2Cu3O7-x (123) powders containing silver have been prepared by aerosol decomposition. Metal nitrate solution droplets were decomposed at temperatures above and below the melting point of the Ag-O eutectic. In both cases, the Ag was present as a separate grain attached to YBa2Cu3O7-x. Individual aerosol particles had dimensions of 50 – 1000 nm. Grain sizes of Ag and 123 crystallites within these particles were 10 to 100 nm. Larger 123 grain sizes could be obtained by varying the reactor operating conditions. The powders provide a source of material for generation of YBa2Cu3O7-x/Ag ceramics with smaller Ag and 123 grain sizes and more uniform composition than can be obtained by other methods.
The Evaporative Decomposition of Solutions Method (Eds) for the Production of Ultrafine Y1Ba2Cu3O7 from Nitrate and Mixed Anion Precursor Solutions
Authors: Lakis Rollin E. , Butler Sidney R.
Published: March 2011

Y1Ba2Cu3O7 has been prepared by the evaporative decomposition of solutions method. Nitrate and mixed anion solutions were atomized and decomposed at temperatures ranging from 300°C to 950°C. The resulting materials have been characterized using x-ray powder diffraction, Thermal Gravimetric Analysis (TGA), particle size analysis, Scanning Electron Microscopy (SEM), and Transmission Electron Microscopy (TEM). The powder consists of 0.3 micron agglomerated hollow spheres with a primary particle size of 0.06 micron. TGA and x-ray diffraction indicate the presence of barium nitrate and barium carbonate due to incomplete decomposition and/or product contamination by the process environment.
Metal-Organic Precursors to high Temperature Superconductors Using 2-(2-Ethoxyethoxy)Ethanol
Authors: Scozzafava Mary Rose , Rhine Wendell E. , Cima Michael J.
Published: March 2011

The copper(II) alkoxide, bis(2-(2-ethoxyethoxy)ethoxide)copper(II), was prepared and had a solubility in organic solvents greatly exceeding those of simple copper(II) alkoxides (>0.4 mol/L in toluene at room temperature). Copper 2-(2-ethoxyethoxy)ethoxide (2-(2-ethoxyethoxy)ethoxide = 2,2-EEE) toluene or toluene/THF solutions gelled upon exposure to moisture. These solutions were hydrolysed with 0.2, 1.0, 2.0, 4.0, and 20.0 equivalents of H2O and the resulting powders were characterized by IR spectroscopy and SEM.
Magnetic Alignment of Bi and T1 Cuprates Containing Rare Earth Elements (II)
Authors: Chen Feng , Markiewicz Robert S. , Giessen Bill C.
Published: March 2011

Continuing an earlier study, we report new data on the orientational effects of magnetic field alignment of some bismuth cuprates and 8 additional thallium cuprates. Strong parallel alignment is seen for Lu bismate and Nd, Sm and Ho thallate; strong normal alignment is seen for Tm; however, in contrast to bismates and 123 phase, Tl cuprates show little anisotropy among directions within the basal plane.
Structural Aspects of the Phase Separation in La2CuO4.032
Authors: Chailloutl C. , Bordetl P. , Chenavasl J. , Cheong S.W. , Fisk Z. , Mareziou M. , Morosin B. , Schirber J.E.
Published: March 2011

The average structure of superconducting La2CuO4.032 has been determined by single crystal neutron diffraction data. The excess oxygen is located between two adjacent LaO layers. Its presence distorts the apical‐oxygen sublattice in such a way that a short O‐O bond is formed (1.64Å). By scanning several hkl reflexions, we have confirmed that a phase separation occurs below room temperature. The peaks of the phases are in agreement with the unit cells proposed by Jorgensen et al. and Zolliker et al. However, Cmca seems to be the correct space group for both phases. La2CuO4+მ and the Ni counterpart are, thus, not isostructural.
Ybco Films and Buffer‐Layers Grown In‐Situ by Pulsed Laser Deposition
Authors: Connell G. A. N. , Fenner D. B. , Fork D. K. , Boyce J.B. , Ponce F.A. , Bridges F. , Geballe T.H.
Published: March 2011

YSZ [ (Y2O3)x (ZrO2)1‐x ] buffer‐layers for various compositions, x, and YBCO (Y1Ba2Cu3O7‐δ) films were grown on hydrogen‐terminated Si(100) substrates by laser ablation. The structural and electrical properties of the YBCO are found to depend strongly on x, and to be optimized near x=0.1.
Characterization of Ground State Neutral and Ion Transport During Laser Ablation of 1:2:3 Superconductors by Transient Optical Absorption Spectroscopy
Authors: Geohegan David B. , Mashburn Douglas N.
Published: March 2011

Optical absorption in the plume produced by excimer laser ablation of Y1Ba2Cu3O7‐x under film growth conditions has been observed for the first time and used to characterize the transport of ground state Y, Ba, and Cu neutrals as well as Y+ and Ba+ ions. Spatially and temporally resolved absorption measurements (0.6 mm, 20 ns resolution) indicate significant ground state number densities at times following the laser pulse that are up to an order of magnitude longer than the duration of fluorescence from excited states. Time‐of‐flight absorbance profiles result in velocity distributions that are broadened significantly toward lower velocities and reveal a low velocity component (<10 5 cm s_1) to the ablation process which is not observed using emission spectroscopy. Electric ion probe measurements of the time dependence of Y+ ions confirm the existence of the new, slow velocity component. Electron densities >1016 cm‐3 in the white plasma close to the pellet have been estimated using spectrally broadened emission lines. The effects of oxygen ambient pressures and the detection of YO, BaO, and CuO also are reported. This technique is applicable as an situ monitor of the kinetic energy of ablated species during low temperature deposition of epitaxial 1:2:3 superconducting thin films.
Pulsed Excimer Laser Deposition of YBaCuO and BisrCaCuO Compounds : Material Distribution and Stoichiometry
Authors: Fuchs Claude , Fogarassy Eric
Published: March 2011

We investigate, in this study, the laser evaporation processes for the deposition of YBaCuO and BiSrCaCuO compounds, using a pulsed ArF (193 nm) excimer laser. The deposition parameters, especially those which are relevant to the geometrical configuration and optical arrangement of the experimental set-up and laser irradiation conditions are examined in details.
A Study of the In Situ Epitaxial Growth of the 123 Ybco Films from a Stoichiometric Target by Rf Magnetron Sputtering
Authors: Meng R. L. , Wang Y. Q. , Sun Y. Y. , Gao Li , Hor P. H. , Chu C. W.
Published: March 2011

The synthesis parameters have been systematically examined for the in situ growth of high temperature superconducting Y‐Ba‐Cu‐0 thin films from a stoichiometric target by rf magnetron sputtering. By properly adjusting the deposition temperature, the total sputtering (O2+Ar)‐pressure and the O2‐partial pressure, we have reproducibly obtained 123 YBCO films with a zero resistivity temperature Tcz = 84 K and a transition width of 3 K°. The films so obtained have excellent surface morphology and a surface roughness better than ∼ 5 nm.
Highly Oriented Yba2Cu3O7-X Thin Films Prepared by Unbalanced Dc Magnetron Sputtering From a Single Stoichiometric Target
Authors: Savvides N. , Andrikidis C. , Hensley D.V. , Drivers R. , Macfarlane J-C , Tan N.X. , Bourdillon A.J.
Published: March 2011

Highly oriented films of YBa2Cu3O7‐x have been reproducibly prepared with the correct metal stoichiometry by dc magnetron sputtering from a single target of stoichiometric composition. To circumvent the resputtering effects, the magnetron used an unbalanced magnetic field configuration to direct the plasma away from the substrate. Typical films have sharp superconducting transitions with Tc up to 93 K and △TC(90%.‐10%.)=0.5 K, metallic resistivity above the transition with ρ300/ρ100=2‐4, and Jc>1.5xl06 A cm‐2 at 4.2 K. The temperature dependence of J,. obeys the flux creep model with activation energy U(0)=75 meV.
Growth and Characterization of La2-XSrXCuoY and Bi2-XSr2-ZCuoy Crystals
Authors: Osofsky M.S. , Cohn J.L. , Lechter W.L. , Skelton E.F. , Qadri S. B. , Hoff H.A. , Browning V.M.
Published: March 2011

In order to grow large single crystals of the La2‐xSrxCuOy and Bi2+xSr2‐zCuOy families of high Tc superconductors, we have studied the relationships between nominal Sr composition in the starting materials and the Sr compositions of the resulting products. We present growth, x‐ray, and composition data for these samples.
Properties of Thin Films of Yba2Cu3O7 Prepared by Coevaporation of Y, Cu and Baf2
Authors: Raistrick I. D. , Cooke D. W. , Beery J. G. , Garzon F. H. , Javadi H. , Maley M. P. , Rollett A. D. , Roy T. , Sinha D. N. , Wilde D. K.
Published: March 2011

The properties of thin films prepared by coevaporation of Y, Cu and Ba.F2, followed by post anneals in O2/H2O, are described. In particular, we emphasize what is known about. the relationship between the processing variables and the physical and chemical structure of the resulting films.
Y1Ba2Cu3O7‐x Films from Nitrate Solution using Rf Plasma Deposition
Authors: Shah A. , Haugan T. , Witanachchi S. , Patel S. , Shaw D. T.
Published: March 2011

A nitrate solution of Y, Ba and Cu was atomized and introduced into an inductively coupled argon ‐ oxygen plasma operated at 4.4 kW and 13.56 MHz under atmospheric pressure. As‐deposited superconducting films were grown on (100) YSZ substrates heated to 650°C. Critical temperatures of 85 K and critical current densities of 7.0 x 104 amp/cm2 at 77 K have been achieved. X‐ray diffraction shows the films to be oriented with the c‐axis perpendicular to the substrate surface. The effects of process parameters, solution composition, and aerosol concentration on the superconducting properties and microstructures will be discussed.
Processing and Characterisation of Single‐Phase Superconducting Thin Films in the Bi‐Sr‐Ca‐Cu‐O System from Chemical Precursors
Authors: Golden S. J. , Bloomer T. E. , Lange F. F. , Segadaes A. M. , Vaidya K. J. , Olson W. L.
Published: March 2011

Thin films in the Bi‐Sr‐Ca‐Cu‐O system have been synthesized from liquid ethyl hexanoate precursors by spin pyrolysis. An extensive solid solution range was determined for the two Cu‐layer phase through the study of c‐axis oriented, single‐phase thin films fabricated on single‐crystal MgO (100). Extensive cation non‐stoichiometry was observed in all cases. The variation of important thin film properties with composition within the solid solution range have been described.

Utilising the results from the thin film study together with data relating to liquid formation in mixtures of bulk material a working model describing the formation of the two‐layer phase has been formulated. The two‐layer phase is formed as the result of precipitation from a fugitive liquid at temperatures exceeding 730 *C.
A Study of Grain Boundaries in High TC Superconducting Yba2Cu3O7-x Thin Films Using High Resolution Analytical Stem
Authors: Shin D. H. , Silcox J. , Russek S. E. , Lathrop D. K. , Buhrman R. A.
Published: March 2011

Grain boundaries in thin films of high Tc YBa2Cu3O7-x superconductors have been investigated with high resolution scanning transmission electron microscope (STEM) imaging and nanoprobe energy dispersive x-ray (EDX) analysis. Atomic resolution images indicate that the grain boundaries are mostly clean, i.e., free of a boundary layer of different phase or of segregation, and are often coherent. EDX microanalysis with a 10 Å spatial resolution also indicates no composition deviation at the grain boundaries.
Structural Defects in Thin Films Of High TC Superconductors
Authors: Ramesh R. , Hwang D.M. , England P. , Ravi T.S. , Chen C.Y. , Inam A. , Dutta B. , Nazar L. , Venkatesan T.
Published: March 2011

In this short report, we describe some of the structural defects present in laser deposited Y‐Ba‐Cu‐O thin films. Many of the defects observed are polytypoidic variants, related to the layered structure of these cuprates. One possible model by which flux pinning can be achieved is presented.
Microstructural Evolution of Ba2Ycu3O7 Superconductor by Electron Irradiation in a Transmission Electron Microscope
Authors: ShiraiShi Kensuke , Itoh Hiroshi
Published: March 2011

Microstructural changes in a Ba2YCu3O7 pellet were continuously observed during electron irradiation in a transmission electron microscope operating at 200 kV. Twin lamellae of 2~10 nm in thickness with 1~50 nm spacings were seen parallel to the lattice image of (001) plane with 1.17 nm in lattice spacing. The tip of the twin was lenticular and the (001) lattice fringes were distorted around the tip. Upon intense electron beam illumination, the lamellae faded at the tip and the thickness gradually decreased which increased the spacing in the high density region. Defect clusters of about 10 nm in size were produced in the very early stage of electron illumination.
Critical Current Density of Narrow Superconducting Thin Films Fabricated by Laser Ablation Techniques
Authors: Song L. W. , Kao Y. H. , Ying Q. Y. , Zheng J. P. , Kwok H. S. , Zhu Y. Z. , Shaw D. T.
Published: March 2011

The variations of critical current density Jc of narrow Y‐Ba‐Cu‐O films as a function of temperature and magnetic field are investigated. Films with thickness of 150‐200 nm and width of 20‐100 urn were prepared by laser ablation and laser etching. For t (=T/TC) < 0.75, the temperature dependence of Jc shows a (1‐1) linear behavior, in sharp contrast to that of a Josephson junction. Near Tc, Jc varies with (1‐ t)n where n=3/2 or 2 depending on the morphology of films. The magnetic field dependence of Jc above a characteristic field value Hc’ can be described by a model based on flux creep.
Critical Current Density, Flux Creep, and Microstructure in A Bi-Sr-Ca-Cu-O System
Authors: Shi Donglu , Boley M. S. , Chen J. G. , Xu Ming , Fang M. M. , Welp U. , Vandervoort K. , Hong J. M.
Published: March 2011

We measured magnetization hysteresis and zero-field-cooled magnetic relaxation for liquid-quenched Bi-Sr-Ca-Cu-O samples at various temperatures. We found that there is a close correlation between the magnetic behavior and the microstructures of the samples. The magnetization hysteresis greatly increases in the samples with a large amount of crystal defects such as precipitates and stacking faults in the matrix of the material. We also found that the flux creep is reduced as a result of these microstructural changes.
Ir Laser-Induced Deposition of Silicon Thin Films
Authors: Gattuso T. R. , Meunier M. , Adler D. , Haggerty J. S.
Published: March 2011

The deposition of a-Si:H by means of CO2 laser-induced pyrolysis of silane gas is described. Deposition rates were found to increase with increasing silane flow rate, reactor pressure, laser power and substrate temperature. Spin density decreased and both optical gap, and hydrogen content increased with decreasing substrate temperature. Electrical conductivities are reported.
Submicrometer-Linewidth Laser Doping
Authors: Tsao J. Y. , Ehrlich D. J.
Published: March 2011

Dopant patterns of 250-nm linewidth have been written in silicon by localized heating with a cw laser beam, and then transferred into positive and negative surface-relief patterns by preferential etching. The tightly focused beam both generates free dopant atoms and simultaneously promotes solidstate diffusion into the substrate. Because of the nonlinear dependence of diffusion rates on temperature, the linewidths of the patterns are substantially narrower than those of both the temperature and the laser-beam profiles on tile surface. In addition, an enhancement is observed in diffusion rates under the strong thermal gradients associated with highly localized heating.
Laser-Pulsed Plasma Chemistry: Surface Oxidation of Niobium
Authors: Marks R.F. , Pollak R.A. , Avouris Ph.
Published: March 2011

Laser irradiation of a solid surface under an oxidizing ambient gas can activate localized, heterogeneous chemical reactions which modify the surface. Under suitable conditions, the laser initiates a reactive plasma near the gas/solid interface. This plasma mechanism is proposed as the basis for a new surface chemical technique which we denote laser-pulsed plasma chemistry (LPPC). LPPC experiments on niobium metal under one atmosphere of oxygen employed a pulsed CO2 laser and displayed single-pulse, self-limiting, oxide growth. Product oxide thickness increased with optical intensity. Surface layer thickness and chemical composition were determined for oxide layers between 1 nm and 5 nm thick using x-ray photoelectron spectroscopy (XPS or ESCA). Composition of these niobium oxide (Nb2O5−δ) surfaces was similar to the composition produced by RF plasma oxidation, but the valence defect, δ, for LPPC oxides was approximately two to five times lower. At high laser intensity (≥4 × 106 W/cm2), direct optical heating or plasma-mediated thermal coupling to the solid activates interdiffusion at the oxide/metal interface.