bluuebunny/crossref_metadata_2025_split huggingface dataset:
Defect Mechanisms in Degradation of Long Wavelength (1.30–1.55 Micron) Laser Diodes
Authors: Chu S. N. G. 
Published: March 2011

ABSTRACTOptical degradation of long wavelength (1.30–1.55 micron) laser diodes during normal operation or accelerated aging test caused by lattice structural deterioration of the active region materials and mirror facet damage were investigated in detail. Extrinsic dislocation loops of 1/2<100>{010) types were observed in gradually degraded channeled-substrate-buried-heterostructure (CSBH) lasers. These dislocation loops, originated at the sidewall interfaces outside the active region, grew into the active region in the direction of minority carrier injection. A great enhancement of the loops' growth rate was observed after they entered the active region, indicating a nonradiative recombination enhanced defect reaction under the strong optical field. Furthermore, the <100> oriented extrinsic dislocation loops were confirmed to be dark-line-defects (DLDs). On the other hand, strong nonradiative recombination centers, created by mirror facet damage, or pre-existed internally inside the cavity, resulted localized melting on the {111} planes. The propagation of the localized melt-patch along the laser beam direction created a wormlike defect along the laser cavity, which degraded the laser device catastrophically. Various types of grown-in defects for CSBH and etched-mesa-buried-heterostructure (EMBH) laser devices are described and their effects on the device performance are demonstrated.
Properties of DX Centers in AlxGa1−xAs and Effects on Heterojunction Devices
Authors: Mooney P. M. 
Published: March 2011

ABSTRACTIn this paper the effects of DX levels on the properties of AlxGa1−xAs and certain heterojunction device structures are summarized. Studies of alloy effects, variations of the local atomic environment near the donor, are reviewed and microscopic models of the DX center are discussed in terms of these and other recent experimental results.
DX Centers and III-V Device Performance
Authors: Muñoz-Merino Elias 
Published: March 2011

ABSTRACTThe properties of deep donor states (DX's centers) in III-V alloys are reviewed in relation to their influence on the device characteristics and limitations. Because of the systematic research being performed on AlGaAs, most of the information presented refers to such material. The electron thermal emission and capture properties of the DX's are then related to the DC and noise characteristics in heterojunction transistors. The optical properties of DX centers indicate a clear difference between unipolar and bipolar device performance at low temperatures. The technical efforts to avoid DX centers will also be described.
Phase Stability in Binary Ti-Al
Authors: Anderson C.D. , Hofmeister W.H. , Bayuzick R.J. 
Published: March 2011

AbstractBinary Ti-Al samples containing from 46 to 54 at.% Al were solidified while undercooled by various amounts using electromagnetic levitation techniques. A detailed thermal history of these samples was obtained with sampling rates as high as 500 KHz during recalescence. This very high sampling rate was essential to resolve the thermal events. Primary α solidification was observed in samples containing from 51 to 54 at.% Al that were undercooled less than about 100 K at solidification. Primary β solidification was found for all undercoolings tested in samples containing less than 51 at.% Al and for undercoolings greater than about 100 K in samples containing 51 to 54 at.% Al. These first two observations are in agreement with results from Valencia et al. for Ti-45 at.% Al and Ti-50 at.% Al, respectively [4]. However, the third observation of β as the primary solidification structure at high undercooling and 54 at.% Al differs from Valencia's interpretation for Ti-55 at.% Al. The results in this study are consistent with the proposed McCullough Ti-Al phase diagram.
Amorphous Phase Formation in NiTi During Cold Rolling
Authors: Koike J. , Parkin D. M. , Nastasi M. 
Published: March 2011

AbstractThe intermetallic compound NiTi was cold rolled at room temperature. Amorphous bands were formed within the finely twined crystalline matrix after thickness reduction of 60%. Striking similarities were observed in microstructural morphology between amorphous bands and shear bands that are generally observed in heavily cold-rolled pure metals. We suggest from the present observations together with the reported results in other solid-state amorphization experiments that the amorphous bands are produced in the shear bands, and that amorphization is caused by mechanical instability against the shear stress.
Atom Probe Analysis of the Compositions of γ′ AND γ″ Intermetallic Phases in Nickel-Based Superalloy 718
Authors: Miller M. K. , Burke M. G. 
Published: March 2011

AbstractAn atom probe field ion microscopy and transmission electron microscopy characterization has been performed on the intragranular precipitates that are formed in a niobium-modified nickel-base superalloy 718 after the various stages of a multistage heat treatment. Atom probe results indicate that there is a wide variation in the compositions of the DO22-ordered γ″, the Ll2-ordered γ′ precipitates and the γ matrix with heat treatment and with position in the microstructure.
Fracture Toughness and the Effects of Stress State on Fracture of Nickel Aluminides
Authors: Lewandowski John J. , Michal Gary M. , Locci Ivan , Rigney Joseph D. 
Published: March 2011

AbstractThe effects of stress state on the fracture behavior of Ni3Al, Ni3Al + B, and NiAl were determined using either notched, or fatigue-precracked bend bars tested to failure at room temperature, in addition to testing specimens in tension under superposed hydrostatic pressure. Although Ni3AI is observed to fail in a macroscopically brittle intergranular manner in tension tests conducted at room temperature, the fracture toughnesses (i.e. K IC presently obtained on Ni3Al exceeded 20 MPa1m and R-curve behavior was exhibited. In-situ monitoring of the fracture experiments was utilized to aid in interpreting the source(s) of the high toughness in Ni3Al, while SEM fractography was utilized to determine the operative fracture modes. The superposition of hydrostatic pressure during tensile testing of NiAl specimens was observed to produce increased ductility without changing the fracture mode.
Ground State Properties of the Ai-Ti System
Authors: Singh Prabhakar P. , Asta Mark , deFontaine Didier , Schilfgaarde Mark van 
Published: March 2011

AbstractGround state structural energies and lattice constants of Al-Ti system have been studied using the linear muffin-tin orbital (LMTO) method. In particular, we examine the effects of various approximations for the potential on the structural energies of low-symmetry compounds such as Al3Ti. In order to stabilize Al3Ti, in the atomic sphere approximation, the Muffin-Tin correction is essential although the resulting c/a is 10% too large. The lattice constants calculated with the full-potential LMTO method are in complete agreement with experiments, indicating the importance of non-sphericity of the potential for low-symmetry systems.
Ab Initio Calculation of the Cu-Pd One-Dimensional Long Period Superstructure Phase Diagram.
Authors: Ceder G. , Huang P. , Menon S. , Fontaine D. de , Nicholson D.M. , Stocks G.M. , Gyorffy B.L. 
Published: March 2011

AbstractThe FCC superstructure phase diagram for Cu-Pd is calculated by means of isotropic effective interactions derived from an ab initio KKR-CPA electronic structure calculation. We prove the existence of a region in which one-dimensional long period superstructures are stable. This region is composed of several single phase fields in which the modulation period is constant. The value of the modulation period is in close agreement with results from High Resolution Electron Microscopy. Adding oxygen to Cu-Pd is found to sharpen the antiphase boundaries. This experiment enables us to clarify the role of the Fermi surface in these alloys.
Electronic Structure and Phase Stability Properties of Ai-Li Alloys
Authors: Gonis Antonios , Turchi Patrice E.A. , Sluiter Marcel , Pinski Frank J. , Johnson Duane D. 
Published: March 2011

AbstractRecently, the phase diagram of AI-Li alloys was calculated with the use of the Connolly-Williams method. In an effort to test the validity and to supplement the results of that study, equilibrium lattice constants and effective cluster interactions have been obtained using the generalized perturbation method within the first-principles multiple-scattering formalism of the Korringa-Kohn-Rostoker coherent-potential approximation. The implication of these effective interactions to the phase stability of these alloys is discussed.
Characterization of Silicon and Indium Redistribution in InxGa1−xAs/n+-GaAs(100) Heteroepitaxial Layers Fabricated Using Pulsed Laser Melting
Authors: Chang Y. , Sigmon T.W. , Marshall A.F. , Weiner K.H. 
Published: March 2011

AbstractHeteroepitaxial InxGa1−xAs/GaAs structures have been formed by pulsed laser induced mixing of molecular beam deposited In films (˜200Å) on Si doped n+-GaAs (100) substrates. The Si dopant and deposited In are redistributed in a rapid melt-solidification process driven by a XeCl pulsed excimer laser. It is found, from high resolution cross-sectional transmission electron microscopy, that the epitaxial layers are crystalline and lattice matched to the substrate except for the misfit dislocations lying along the InxGa1−xAs/GaAs interface. These interfacial dislocations are used to identify the laser melted and unmelted regions. The dip and pile-up regions in the Si SIMS profiles are attributed to a segregation effect. Numerical simulation based on the liquid-solid interface velocity dependent segregation coefficient is used to investigate this effect and has approximated the trends in the measured characteristic In and Si profiles.
Boron Diffusion in Bulk Cobalt Disilicide
Authors: Gas P. , Zaring C. , Svensson B.G. , Östling M. , Whitlow H.J. , Barge T. 
Published: March 2011

AbstractThe lattice diffusion of boron in bulk cobalt disilicide has been studied at temperatures between 450 and 950°C. Two different diffusion sources, a deposited surface layer of boron and an implanted boron distribution, were used. The lattice diffusion coefficient has been deduced from the boron profiles measured by secondary ion mass spectrometry (SIMS); in the studied temperature range the coefficient varies between 6.2×10−17 and 3.0× 10−11 cm2/s with an activation energy of 2.0 eV. These values reveal a very rapid lattice diffusion and agree with results reported previously in the literature concerning redistribution of boron implanted in thin films of CoSi2, and it also emphasizes the important role played by interfaces during the boron redistribution.
Oxidation Kinetics of Metastable Electrodeposited and Sputtered Nickel Thin Films Via Thermogravimetric Analysis
Authors: Herrmann Ann C. , Brower D William E. , Lalvani Shashi 
Published: March 2011

AbstractThe effetzct of the amorphous state and the disordered sputtered state on the oxidation kinetics of nickel films was investigated by a comparison with annealed films and with pure nickel foil and powder. Specimens were exposed to oxygen in a thermogravimetric analyzer (TGA) in the temperature scan mode. An electrodeposited amorphous Ni-P alloy and sputtered pure nickel films were annealed in situ in argon and then oxidized in the same manner as the as deposited films. The as sputtered films oxidized faster at 500%C than pieces of the same film first annealed in argon. Conversely, the as deposited Ni-P film was more oxidation resistant below its crystallization temperature than the annealed Ni-P films.
Chemical Vapor Deposition of Binary Metal Germanides
Authors: Hampden-Smith M.J. , Garvey J. , Lei D. , Huffman J.C. 
Published: March 2011

AbstractA series of transition metal substituted germacyclopent-3-ene compounds containing transition metal-germanium bonds have been prepared with supporting ligands which are designed to be easily removed either thermally or photochemically. In solution, model thermal decomposition experiments show that either the geramanium or the transition metal substituents may be removed, depending on the nature of the metal. Preliminary hot-wall CVD experiments using manganese and cobalt derivatives result in films with small grain size.
On the Formation of Amorphous and Metastable PVD-Coatings
Authors: Knotek O. , Barimani A. , Löffler F. 
Published: March 2011

AbstractBy using differing target materials and admitting reactive atmospheres, thin protective coatings having an amorphous and/or metastable character such as sialon, (Ti, Al)N and (Ti, Zr)N are deposited. Phase formation, crystalline structure, morphology and mechanical properties of these films are investigated by X-ray analysis, transmisison electron microscope (TEM), scanning electron microscope, Auger electron spectroscopy (AES) and metallographic measurements. The thermal stability of the coating systems are examined and corrosion and wear test carried out.
Epitaxy of Ni on Si(111) by Ion Beam Assisted Deposition
Authors: Grabowski K. S. , Kant R. A. 
Published: March 2011

AbstractEpitaxial growth of Ni (111) on Si (111) has previously been obtained at room temperature by 25-keV-Ni ion beam assisted deposition, where both ion and vapor fluxes were incident at 45° to the specimen normal. This work explores the effect of a wider range of deposition conditions on epitaxial film quality. Nominally 300-nm-thick films were deposited at room temperature on Si (111) and other substrates. The substrates were sputter cleaned by the Ni ion beam immediately prior to deposition. Ion energies of 25 to 175 keV, relative ion to vapor fluxes R from 0 to 0.1, and vapor deposition rates of 0.05 to 0.5 nm/s were examined. Bragg-Brentano symmetric x-ray diffraction evaluated film quality while Ni (220) grazing-incidence x-ray diffraction rocking curves verified film epitaxy. Film quality changed gradually over these deposition parameters, with an optimum at 25 keV and an R of about 0.01. At higher energies and R values sputtering and radiation damage destroyed the film epitaxy
Structures of Silver/Chromium Metallic Superlattice
Authors: Kaneko Takeo , Kyuno Kentabo , Niikura Osamu , Hara Shigeki , Yamamoto Ryoichi 
Published: March 2011

AbstractAg/Cr metallic superlattices with bilayer thickness in the range of 17–136Å were prepared by metal-MBE method. X-ray diffraction measurements indicated that the thickness fluctuations of each layer were rather small. The lattice matching at the interface between Ag(100) and Cr(100) is almost perfect. But, the interplanar spacings of Ag(100) and Cr(100) changed as a function of bilayer thickness. Surface wave velocities have been measured using Brillouin spectroscopy. In contrast to Au/Cr superlattices which show a hardening, a plot of surface wave velocities as a function of the bilayer thickness in Ag/Cr superlattices showed a distinct dip.
Structures of Silver/Cobalt Metallic Superlattice and Changes Due to Annealing
Authors: Kingetsu T. , Sakai K. , Kaneko T. , Yamaguchi A. , Yamamoto R. 
Published: March 2011

AbstractAg/Co metallic superlattices were grown onto Ag buffer layers pre-deposited on sapphire or MgO substrates by ultrahigh vacuum alternate deposition technique. In-situ RHEED observations during superlattice growth and ex-situ XRD measurements revealed that structures of the superlattices were strongly affected by the condition of Ag buffer layer preparation. In case where the Ag buffer layers were single crystals with smooth (111) surfaces, Co layers were epitaxially grown on the buffer layers even in the presence of large lattice mismatch, and whole the superlattices were grown with an epitaxial relation. Interface smoothness was strongly related to the growth temperature. Spotty RHEED patterns of Co layers for a low growth temperature indicated that the Co layers had an FCC structure. Post-annealing of the samples, in some cases, destroyed a superlattice structure completely. From relations between magnetic anisotropy and Co-layer thickness obtained with VSM measurements, it was found that Ag/Co superlattice exhibited in-plane magnetic anisotropy down to a Co thickness of 4A and that the anisotropy was correlated with roughness of the interfaces.
Anomalous Small Angle X-Ray Scattering Studies of Metal-Germanium Alloys
Authors: Rice Marybeth , Wakatsuki Soichi , Bienenstock Arthur 
Published: March 2011

AbstractThe tunability of synchrotron radiation was used to perform anomalous small angle x-ray scattering (ASAXS) experiments on amorphous metal-germanium (a-Mx Ge1−x) alloys with the aim of detecting and characterizing compohitioK modulation and phase separation. Small angle x-ray scattering is sensitive to electron density fluctuations on a scale of tens to thousands of Angstroms. The combination of SAXS with the anomalous dispersion effect allows one to distinguish composition modulation from density fluctuations arising from voids and defects. Data gathered from a-FexGe1−x and a-WxGe1−x samples in the low metal concentration regime show nanometer scale composition modulation. In these samples the density of Ge atoms is uniform throughout the sample. The small angle x-ray scattering arises from fluctuations in the density of metal atoms.
Microstructure and Stability Comparison of Nanometer Period W/C, Wc/C, and Ru/C Multilayer Structures
Authors: Nguyen Tai D. , Gronsky Ronald , Kortright Jeffrey B. 
Published: March 2011

AbstractMultilayer structures of W/C, WC/C, and Ru/C, of various periods were prepared and studied by high-resolution transmission electron microscopy. Comparison of the phases in the layered structures is made for as-prepared and annealed samples. Both as-prepared and annealed WC/C multilayers are predominantly amorphous, while the phases in the W/C depend on the periods. The 2 nm period W/C multilayer remains amorphous after annealing, and the longer periods recrystallize to form W2C. The layered microstructures of W/C and WC/C are stable on annealing at all periods, while the amorphous Ru-rich layers in the 2 nm period Ru/C multilayer agglomerate upon annealing to form elemental hexagonal Ru crystallites. Larger period Ru/C multilayers show stable layered structures, and indicate hexagonal Ru in the Ru-rich layers. X-ray measurements show that the multilayer periods expand on annealing for all metal-carbon multilayers studied.
Superconductivity in Nonsymmetric Epitaxial YBa2Cu3O7−δ - PrBa2Cu3O7−δ Superlattices Grown by Pulsed Laser Ablation
Authors: Lowndes Douglas H. , Norton David P. , Budai J. D. , Pennycook S. J. , Christen D. K. , Sales B. C. , Feenstra R. 
Published: March 2011

ABSTRACTPulsed KrF (248 nm) excimer laser ablation has been used to grow nonsymmetric epitaxial YBCO/PrBCO superlattices containing 1-, 2-, 3-, 4-, and 8-unit-cell-thick YBCO layers, separated by N-cell-thick insulating PrBCO layers (N = 1–16). The 1×N and 2×N structures exhibit a rapid initial decrease of Tco with increasing PrBCO layer thickness, followed by saturation of Tco at a nonzero value, as the YBCO layers' separation is increased further. The limiting Tco values for 1-, 2-, 3-, 4-, and 8-cell-thick YBCO layers isolated in a PrBCO matrix are ∼19 K, ∼54 K, ∼71 K, ∼80 K, and ∼87 K, respectively. Single-cell-thick YBCO layers are found to be superconducting even when separated by ∼19 nm in a PrBCO matrix. These results are discussed in terms of possible Josephson and/or proximity effects coupling the YBCO layers, and the possibility that PrBCO modifies the electronic structure and depresses Tco in YBCO cells that are immediately adjacent to the PrBCO layers. Finally, high-temperature postannealing studies show that these superlattice structures are stable and that little diffusion occurs along the c-axis direction of compositional modulation.
Effect of Substrate on the Early Stages of the Growth of YBa2Cu3O7-δ Thin-Films
Authors: Norton M. Grant , Carter C. Barry 
Published: March 2011

ABSTRACTThe fabrication of high-quality thin-films often depends on the early stages of the growth process during which epitaxy is established. The substrate structure and orientation generally play a critical role at this stage through epitaxy and interaction or reaction. Many different materials are being used as substrates to support thin-films of the YBa2Cu3O7-δ superconductors. In this study the early stages of the growth of YBa2Cu3O7-δ thin-films have been investigated using transmission electron microscopy (TEM). Using pulsed-laser ablation, ultra-thin films were formed directly onto self-supporting, ion-thinned, single-crystal ceramic substrates. The substrates used were (001)-oriented MgO, (001)-oriented SrTiO3 and (001)-oriented LaAlO3.
High Rate Growth of YBa2Cu3O7-x Thin Films using Pulsed Excimer Laser Deposition
Authors: Muenchausen R. E. , Wu X. D. , Foltyn S. , Estler R. C. , Dye R. C. , Garcia A. R. , Nogar N. S. , England P. , Ramesh R. , Hwang D. M. , Ravi T. S. , Chang C. C. , Xi X. X. , Li Q. , Inam A. , Venkatesan T. 
Published: March 2011

ABSTRACTWe report here on the pulsed laser deposition of high quality, superconducting, 200 nm thick films of YBa2Cu3O7-x at rates approaching 15 nm/s. Film crystallinity and electrical properties were studied as a function of deposition rate from 0.1 to 14.5 nm/s. Though some degradation in the film crystallinity is observed by RBS channeling and X-ray rocking curve measurements, critical current densities (Jc = 4 × 106 A/cm2, 77 K, B = 0) are effectively unchanged in going to the higher deposition rates.
UV Tunable Laser Ablation of YBa2Cu3Ox+6: Changes in the Product Population and Kinetic Energy Distributions as a Function of the Laser Wavelength and Target Bulk Temperature
Authors: Wiedeman L. , Helvajian H. 
Published: March 2011

ABSTRACTWe have conducted two separate experiments in the UV laser ablation of a sintered Yba2Cu3Ox+6wafer. We have measured the photoejected population distributions using selected UV laser wavelengths (4.01, 4.17 and 4.35 eV) near the 4.1 eV optical transition in Yba2Cu3Ox+6 In addition, we have measured the change in the ejected species kinetic energy as a function of the target bulk temperature. All the experiments were conducted at laser fluences well below the plasma formation threshold, and near that for product formation. Our results show that the UV laser ablation, at threshold fluences, proceeds via a nonthermal electronic excitation mechanism.
Influence of Beam and Target Properties on the Excimer Laser Deposition of Yba2Cu3O7−x Thin Films
Authors: Foltyn S. R. , Muenchausen R. E. , Estler R. C. , Peterson E. , Hutchinson W. B. , Ott K. C. , Nogar N. S. , Hubbard K. M. , Dye R. C. , Wu X. D. 
Published: March 2011

ABSTRACTTarget modification by excimer laser exposure has been investigated. Under conditions typical in the fabrication of superconducting thin films, deposition rate decreases with exposure and significant physical and chemical modifications occur on the target surface. These modifications do not inhibit congruent evaporation.