bluuebunny/crossref_metadata_2025_split huggingface dataset:
Does Σ Control Intergranular Cracking in Ni3Al?
Authors: Lin Hui , Pope David P. 
Published: March 2011

AbstractThe relation between intergranular fracture and grain boundary character was studied in Ni3Al using the electron backscattering pattern (EBSP) technique. Using specimens of small grain size, we are able to index the orientation of a large number of grains, thus improving the statistical quality of the data compared to previous results. Furthermore, we are able to characterize the boundary planes using the EBSP method because of the special specimen geometry used. It was found that Σ3 boundaries do have a substantially lower propensity for cracking as compared to other boundaries, but there is no correlation between grain boundary Σ value and the propensity for cracking for low Σ and low angle boundaries. These results are in general agreement with recent theoretical predictions of grain boundary structure.
On the Structure-Property Relationship of Rapidly Solidified High Temperature Application Aluminium Alloys
Authors: Chowdhury A.J.S. , Sheppard T. 
Published: March 2011

AbstractThe phases responsible for high temperature strength and ductility of Al-Fe based alloys, specifically Al-Fe-Mo alloys, have yet to be unambiguously identified. The phases appear to vary slightly under different experimental and processing conditions. This poses some queries concerning the reproducibility of mechanical properties of these alloys. In this paper an attempt is made to address these points and focus on the structure-property relationships of Al-Fe-Mo and Al-Fe-V rapidly solidified powder alloys.
Development of Microstructures with Improved Cryogenic Toughness Through Local Variations in Stress State: Aluminum-Lithium Alloys
Authors: Rao K. T. Venkateswara , Ritchie R. O. 
Published: March 2011

AbstractMicrostructurally-induced changes in the local stress state (triaxial constraint) and their effect on fracture-toughness behavior are examined at ambient and cryogenic temperatures in an Al-Li-Cu-Zr alloy, processed in the form of 12.7 mm-thick "naturally laminated" plate containing aligned-weak interfaces and 1.6 mm-thin unlaminated sheet. It is shown that marked improvements in long-transverse (L-T) toughness can be achieved in the plate material at cryogenic temperatures by promoting through-thickness delamination along these interfaces, which relaxes local constraint and promotes a fracture-mode transition from global plane strain to local plane stress. Conversely, in thin sheet material, the absence of such interface delamination leads to a reduction in toughness with decrease in temperature, consistent with the greater degree of crack-tip constraint.
Phase Stability in the Al(6−x)CuxZr2 System for 0 < × < 1.
Authors: Desch P. B. , Schwarz R. B. , Nash P. 
Published: March 2011

AbstractWe have determined the structures and thermal stability of AI(6-x) CuxZr2 (0≤ × ≤ 1) powders prepared by mechanically alloying elemental powder mixtures. In the as mechanically alloyed condition the structure is L12 for all ×. After heating to 750°C the alloy is single phase D023 for 0 < × < 0.2, is a two-phase mixture of D023 and L12 for 0.2 < × < 0.6, and remains in the Ll2 phase for 0.6 < × < 1. Al5CuZr2 is stable in the Ll2 structure up to 1300°C. The lattice parameter of the annealed L12 phase is Independent of ×.
On the Effects of Magnetic Bonding in Rare Earth Transition Metal Interxmetallics
Authors: Kumar R. , Bentley J. , Yelon W. B. 
Published: March 2011

AbstractNeutron diffraction experiments on rare-earth transition metal magnetic alloys Er2Fe14B and Er2Fe17 have been carried out at temperatures above and below the ordering temperature (Tc). An anomalously large magnetic moment is observed at the crystallographic j2 site in Er2Fe14 B which is the intersection point of the major ligand lines in the crystal structure. The interatomic Fe-Fe distances are in the range of strong ferromagnetic bonds (≥2.66 Å). The analogous f site in Er2Fe17 does not develop as large a magnetic moment. In addition, the same sites show strong preference for Fe atoms in the respective substituted compounds. Due to poor phase stability of Er2 (CoxFe1-x)14 B compounds, iron substitution has been studied in detail in Er2(CoxFe1-x)17 alloys for site specific order and lattice distortion effects. However, a nonlinear change in the c lattice parameter observed in the neutron diffraction results cannot be explained on the basis of site preference alone.The neutron refinement results indicate iron rich compositions in Er2(CoxFe1-x)17 materials, which is related to random substitution of Fe dumbbell pairs on the rare earth sites in the lattice. However, extensive electron microscopy (selected area electron diffraction and high resolution imaging) of Er2Fe17 and Er2 (Co .40Fe.60)17 failed to reveal any microscopic inhomogeneity. At this stage, the concept of direct negative exchange interaction between dumbbell Fe atom pairs at very short distances of −2.38 A is invoked and its effect is correlated with phase stability. We further suggest that the addition of boron in Er2Fe14B suppresses the substitution of dumbbell Fe pairs as a result of which Tc is raised significantly.
Quantum-Mechanical Origins Of complex Structures in Al-Transition Metal Compounds
Authors: Carlsson A. E. 
Published: March 2011

AbstractThe energetic factors leading to the stability of complex structures in Al-rich transition-metal compounds are analyzed via ab-initio band-theoretic total-energy calculations comparing the Al12W and Cu3Au structures. For nearly half-filled d-bands, the Al12W structure is preferred by 1 eV per transition-metal atom or more. The preference for complex structures results from effects related to the shape of the d-projected electronic density of states, which are found to be more important than atomic-size effects, and are directly related to the complexity of the structure.
Investigations of CuInSe2 Thin Films and Contact
Authors: Raud S. , Vu Quat T. , Nicolet M-A. , Pollock G. A. , Mitchell K. W. , Leavitt J. A. , Ashbaugh M. D. , Mcintyre L. C. 
Published: March 2011

AbstractWe study the properties of CuInSe2 thin films grown on glass and on Mo substrates. The investigation is carried out with X-ray diffraction, RBS, XTEM and SEM.CuInSe2/Mo contact stability is investigated after annealing at 600°C. RBS reveals that this treatment induces an interdiffusion between the metal and the chalcopyrite. To clarify this reaction, we have investigated the individual thin-film couples upon annealing. RBS and X-ray diffraction reveal insignificant interaction between Mo/Cu and Mo/In, but Se reacts with Mo.
Computer Simulation Study of Thin Film Formation Process
Authors: Sasajima Yasushi , Ozawa Satoru , Yamamoto Ryoichi 
Published: March 2011

AbstractThe thin film formation process was studied by the molecular dynamics(MD) method and by the hybrid method which combined the MD method with the Monte Carlo(MC) simulation technique. The Morse potential was assumed as the atomic interaction model. The substrate temperature was changed to see its effect on the film structure. The MD simulation found that the reconstruction process of the deposited nuclei was essential to determine the metastable film structure and that the relaxed atomic arrangements were strongly dependent on the depth of the interaction potentials. The hybrid method simulated the high rate deposition process and confirmed the results of the MD simulation.
Magnetic Ordering of Tb Overlayers on Ni(111)
Authors: Lagraffe D. , Miller A. , Dowben P.A. , Onellion M. 
Published: March 2011

AbstractThe 5p3/2 to 5p1/2 shallow core level branching ratios in different photoemission geometries provide a measure of the magnetic ordering in rare earth overlayers as a result of final state effects in photoemission. This 5p level anisotropy can be used to probe magnetic ordering across the Tb Curie temperature as well as magnetic ordering induced by a ferromagnetic substrate in a paramagnetic overlayer. Results are shown for paramagnetic Tb overlayers on Ni(111). The Ginzberg-Landau theory can be used to accurately model terbium thin films for T>Tc.
Structural and Electronic Changes in the Growth of Mercury Overlayers on Cu(001): A Helium Beam Scattering, Leed and Arpes Study
Authors: Vidali G. , Li W. , Dowben P. A. , Karimi M. , Hutchings C.W. , Lin J. , Moses C. , Ila D. , Dalins I. 
Published: March 2011

AbstractWe used atom beam scattering (ABS), LEED and angle-resolved photo-electron spectroscopy (ARPES) to study bilayer films of Hg on Cu(001). In the surface temperature range of 180 to 330 K, the first Hg layer forms two ordered phases, a c(2×2) (with coverage=0.5 of Cu(001)) and a high density (partially commensurate) c(4×4) (coverage=0.62 ). ARPES data show that there is little or no dispersion of the 5d band of Hg. ABS data show that this layer is not flat, with in-registry Hg atoms lying about 0.15 below the not-in-registry Hg atoms. From ABS we find that the second layer forms a completely registered c(4times;4) phase. From ARPES we obtain that the second layer has an electronic structure, particularly the 5d levels, characteristic of bulk mercury.Preliminary results of calculations of the structure of the bilayer are given.
Scanning Tunneling Microscopy of Platinum Clusters on Hop-Graphite
Authors: Sattler Klaus , Mueller Ulrich , Xhie Jie , Venkateswaran Narayana , Raina Gargi 
Published: March 2011

AbstractWe report on recent studies of small platinum clusters supported on highly-oriented pyrolytic graphite, using a scanning tunneling microscope (STM). The clusters are generated by vapor deposition of single atoms with subsequent diffusion and growth processes occurring on large, flat and ordered substrates. Single adatoms, small clusters and larger islands are imaged with atomic resolution and their atomic structures are determined by direct observation. We find different isomeric structures for clusters of one size. Taking the substrate lattice as reference we determine bond lengths and angles for the clusters. We investigate the effect of the substrate on the adsorbed particles.
Epitaxial Grain Growth and Orientation Metastability in Heteroepitaxial Thin Films
Authors: Floro J. A. , Thompson C. V. 
Published: March 2011

AbstractConventional heteroepitaxial thin film growth may result in a film whose epitaxial orientation is metastable. One method of probing the relative energies of various film orientations is epitaxial grain growth. Epitaxial grain growth selects the orientation having lowest total free energy, including the free energy of both the film-substrate interface and the free surface of the film. Experimental examples of epitaxial grain growth in metal films on insulating substrates will be discussed.
Solid Phase Epitaxy of Strained Si1−xGex Alloys Formed by Highdose Ion Implantation into <001> Silicon
Authors: Howard D. J. , Paine D. C. , Stoffel N. G. 
Published: March 2011

AbstractIn this paper we propose a new method for the synthesis of Si1−xGex strained-layer alloys using high-dose ion implantation of 74Ge at 200 keV into a preamorphized <001> Si wafer followed by solid phase epitaxy (SPE). Cross-sectional TEM was performed on samples at various stages of regrowth which revealed the evolution of the amorphous/crystalline interface and the development of strain relieving defects during SPE. We report that stacking faults are kinetically favored during SPE of Si1−xGex but are energetically feasible only above a critical strain energy. We propose a model that is based on the well known Matthews and Blakeslee approach which predicts the onset of stacking faults during SPE of high-dose ion implant-synthesized Si1−xGex/Si.
On Geometric Models for Interphase Boundaries
Authors: Fecht Hans J. 
Published: March 2011

AbstractThe energy interphase boundaries can be described as a function of the lattice matching at the interface between two adjacent crystals, the chemical interaction and the interfacial entropy of the boundaries. Geometric models relating the energy of interphase boundaries (metal/metal and metal/non-metal) to their atomic structure can be based on the static distortion wave concept. This approach constitutes the physical basis for the lock-in model and the planar CSL-model proposed previously to describe the low energy configurations of such interfaces.
Structural and Elastic Properties of HF/ZR Multilayer Thin Films
Authors: Meng W. J. , Eesley G. L. , Svinarich K. , Meisner G. P. 
Published: March 2011

AbstractWe have investigated structural and elastic properties of Hf/Zr multilayer thin films by x-ray diffraction and transient piezoreflectance measurements. Similar structural and elastic behaviors have been observed in two series of samples grown at different deposition rates (1 – 10Å/sec). Our measurements suggest different (˜ 10%) effective elastic constants between multilayers with coherent and incoherent interfaces.
Molecular Dynamics Computer Simulation of the Rupture of the two - Dimensional Lennard - Jones Film
Authors: Maguire John F. , Leung Chun- Pok 
Published: March 2011

ABSTRACTWe have conducted a molecular dynamics computer simulation of the rupture of a small, two-dimensional film. The film was composed of two hundred atoms arranged on a close-packed triangular lattice and was thermally equilibrated at a reduced temperature of 0.05. Following equilibration, the rupture characteristics of the film were investigated under tensile loading, and the atomistic dynamical response was followed throughout the rupture process. An estimate of the internal stress field was made by performing a time average over the random forces. In tensile failure, the system undergoes an initial elastic deformation followed by plastic flow. The fundamental mechanisms of defect nucleation are briefly discussed.
Mechanisms and Kinetics of Misfit Dislocation Formation in Heteroepitaxial Thin Films
Authors: Nix W. D. , Noble D. B. , Turlo J. F. 
Published: March 2011

ABSTRACTThe mechanisms and kinetics of forming misfit dislocations in heteroepitaxial films are studied. The critical thickness for misfit dislocation formation can be found by considering the incremental extension of a misfit dislocation by the movement of a “threading” dislocation segment that extends from the film/substrate interface to the free surface of the film. This same mechanism allows one to examine the kinetics of dislocation motion and to illuminate the importance of dislocation nucleation and multiplication in strain relaxation. The effects of unstrained epitaxial capping layers on these processes are also considered. The major effects of such capping layers are to inhibit dislocation nucleation and multiplication. The effect of the capping layer on the velocity of the “threading” dislocation is shown to be small by comparison.A new substrate curvature technique for measuring the strain and studying the kinetics of strain relaxation in heteroepitaxial films is also briefly described.
The Low Temperature Phases of 3He
Authors: Richardson Robert C. 
Published: March 2011

ABSTRACTIn the temperature range between 1 mK and 3 mK and in magnetic fields between 0 T and 1 T, there are four distinct phases of liquid 3He and three distinct phases of solid 3He. The liquid becomes a triplet superfluid and the solid becomes a nuclear antiferromagnet. Despite the great differences which exist between a superfluid and an antiferromagnet, there are remarkable similarities between phase diagrams of the two systems.
Effect of Concentration Gradient on Phase Stability
Authors: Tu K.N. , GöSele U. 
Published: March 2011

ABSTRACTA feature of thin film reaction that is different from the reaction in bulk samples is the tendency to form a single intermetallic compound rather than all of them which are allowed according to the equilibrium phase diagram. For example, in thin film silicide formation, Pd2Si has been found to form alone and to grow as a layer between Pd and Si. The silicide is stable over a wide temperature range of 100 to 700°C. The phenomenon of single intermetallic compound growth is not unique to silicide formation between transition metal films and silicon, but is also commonly observed in reactions between bimetallic thin films. The phenomenon indicates phase stability.
Phase Equilibria in the Ni–Rich Region of the Ni–Al–Zr System
Authors: Jayanth C.S. , Nash P. 
Published: March 2011

ABSTRACTAlloys from the Ni–rich corner of the Ni–Al–Zr system have potential for use in high temperature, high strength applications. Such applications require a detailed knowledge of the high temperature phase equilibria.In the case of the Ni–Al–Zr system no isothermal sections have been published although the existence of a monovariant eutectic valley between Ni3Al and Ni7Zr2 has been established. An experimental determination of the phase equilibria in this system is being carried out using quantitative electron microprobe analysis (JEOL JSM–U3), xray diffraction and optical metallography. Partial isothermal sections are being determined for 1373K (1100°C) and 1273K (1000°C) and the resulting phase equilibria compared to that in the Ni–Al–Hf system determined previously.
Semiconductor Epitaxy and Bandgap Engineering by Pulsed Laser Ablation
Authors: Cheung Jeff T. , Sankur H. 
Published: March 2011

IntroductionRecently, Pulsed Laser Ablation [1] has been receiving much attention as a viable thin film deposition technique due to its success in demonstrating excellent high Tc superconducting thin films, although the use of laser radiation as an external energy source to vaporize materials for vacuum deposition was first carried out more than twenty five years ago [2].Most of the early work was focused on dielectric films, a few sporadic reports on III-V compounds [3], some investigations on II-V compounds [4] and elemental semiconductors [5]. Since material qualities were inferior to those grown by Molecular Beam Epitaxy (MBE) at that time, this area of work was largely ignored. After further refinement, the quality of semiconductor films grown by Pulsed Laser Ablation is now comparable to those by MBE, most notably in HgCdTe, CdTe, their superlattices [6] as well as Ge epitaxy [7].
Thin Films of Uniform Thickness by Pulsed Laser Deposition
Authors: Erington K. B. , Ianno N. J. 
Published: March 2011

ABSTRACTIn order to enhance the utility of Pulsed Laser Deposition (PLD), a method to deposit uniform films has been devised. This method employs the deposition profile produced by PLD and the discrete nature of the process. We have simulated this process using experimentally determined deposition profiles and have used the results to design a system that produces films of uniform thickness to within a few percent across a substrate of 1 inch diameter and have obtained excellent agreement between theory and experiment.
Regularities of Laser-Stimulated Desorption from Oxide Semiconductors and Insulators
Authors: Moiseenko I. F. , Lisachenko A. A. 
Published: March 2011

ABSTRACTThe time–of–flight method was used to study the laser stimulated desorption of atoms and molecules from the surfaces of Cr2O3, ZnO, TiO2, MgO, A12O3 under the influence of radiation of four harmonics of a pulsed neodymium laser. For the oxides studied, the kinetic energy distributions of desorbed oxygen molecules are characterized by the presence of two forms: “fast” with kinetic temperature Tk˜2500–3500 K, and “slow” with Tk˜350–550 K. The first one is typical for desorption excitation in the self-absorption region (hv > Eg), and the second one in the transparent region. “Fast” O2 desorption is accompanied by emission of single oxygen and metal atoms. Two non-thermal mechanisms of desorption are suggested, associated with the nature of the initial state of atoms and molecules on the surface and of the mechanism of the laser excitation of this states. The “slow” molecular oxygen desorption results from the excitation and subsequent neutralization of adsorbed molecular ions. The “fast” O2 emission is the result of recombination of oxygen atoms, after neutralization of the surface lattice ions by photoexcited carriers.
Fe Substituted, Laser Ablated YBa2Cu3O7 films using Off-Stoichiometric Targets
Authors: Bridges Frank , Truher J. , Fork D. K. , Boyce J. B. , Fenner D. B. , Connell G. A. N. , Geballe T. H. , Johnson S. , Liu L. 
Published: March 2011

ABSTRACTWe present data on thin films of YBa2Cu3O7 (YBCO) and YBa2(Cu1−xFex)3O7 prepared by laser ablation using a sequence of targets, including Cu-deficient YBa2Cu2.4O7, CuO, and (CuO)1−y(FeO)y. This technique achieves mixing on an atomic scale. We find that stochiometric films, made using a combination of the Cudeficient target and CuO, have a sharp transition (width < 1K) near 90K although the Cu-deficient material alone has a broad transition at a lower Tc. We have achieved substitution of Fe on the Cu sites, using a sequence of the three targets for a range of Fe concentrations. Tc decreases nearly linearly with concentration and Tc → 0 near 15% Fe. The Tc suppression for the films is slightly less than the corresponding value obtained for bulk samples.
Nd: Yag Laser Ablation of BaTiO3 Thin Films
Authors: Gibson Ursula J. , Ruffner J. A. , Mcnally J. J. , Peterson G. 
Published: March 2011

ABSTRACTWe have deposited thin films of barium titanate onto a variety of substrates, using picosecond and nanosecond pulsed Nd: YAG lasers. The films were deposited from a hot-pressed target onto substrates that were heated by either CO2 laser or conventional means, in a partial pressure of oxygen. Highly oriented films resulted from depositions onto MgO and LiF substrates held at temperatures greater than 600C.
Post-Deposition Patterning of Laser Deposited YBa2Cu3O7−δ Films
Authors: Dye R. C. , Foltyn S. , Martin J. A. , Nogar N. S. , Estler R. C. , Muenchausen R. E. , Mukherjree A. , Brueck S. R. J. , Carim A. H. 
Published: March 2011

ABSTRACTWe report here on two aspects of non-chemical, post-deposition processing of laser-deposited superconducting Yba2Cu3O7-δthin films. One patterning process consists of placing a contact mask over the film and removes the surrounding material by excimer laser ablation. Good edge definition for 30–100 μm etch features is obtained. However, some redeposition of material is observed. In separate patterning experiments, oxygen-deficient films were re-oxygenated by a direct-write laser heating method. This process produces very smooth edges between the superconducting patterns and the surrounding material.
Pulsed Laser Ablation as a Source of Energetic Reactants: Synthesis of Superconducting High to Thin Films
Authors: Lynds L. , Weinberger B. R. 
Published: March 2011

ABSTRACTPulsed KrF (248 nm) excimer laser ablation of targets can provide a source of atomic particles with energies in the range of 40 – 850 eV with beam-like characteristics. Optical intensities above about 109 W/cm2 lead mainly to single and multiply charged ground state positive atomic ions plus electrons with a pronounced angular energy dependence, the highest energies peaked in the direction normal to the target. A wide mass range of metallic and non-metallic targets were studied to determine the effects of atomic weights and other physical properties on the distribution of ion energies. Analysis of the energetics indicates that ablation mechanisms are non-equilibrium in nature. We have explored the use of very energetic (200–400 eV) Y, Ba and Cu ions to form very thin YBa2Cu3O7-x superconducting films grown on flat gold surfaces. SQUID magnetometry is used to study the temperature and field dependence of magnetization in these materials.
Growth of TiO2 Thin Films by Pulsed Laser Evaporation
Authors: Chen Ming Y. , Murray P. Terrence 
Published: March 2011

ABSTRACTThin films of TiO2 have been grown by pulsed laser evaporation. The films were analyzed by in-situ Auger and x-ray photoelectron spectroscopy as well as by ex-situ grazing incidence xray diffraction. Films grown at room temperature and at a pressure of 5×10minus; 3 Torr were oxygen deficient. Films grown at 500°C and higher were found to be stoichiometric TiO2.The effect of substrate temperature and evaporation conditions on film properties will be discussed.