bluuebunny/crossref_metadata_2025 huggingface dataset:
Kinetics of B2 and D03 Ordering: Theory
Authors: Anthony L. , Fultz B.
Published: March 2011

Monte-Carlo simulations (MCS) and the path probability method (PPM) were used to study disorder→order transformations in bcc alloys having the AB3 stoichiometry. Both methods used an explicit vacancy mechanism of ordering and an activated-state rate theory for the vacancy jumps. We studied the evolution of short-range order (SRO) as well as B2 and D03 long-range order (LRO) in alloys that began as random solid solutions. The growth rates of SRO and LRO were significantly higher for the PPM than for the MCS. We attribute this difference to improper handling of correlated vacancy motions in the PPM. The PPM also suffered from an artificial incubation time for the initiation of LRO. Both the MCS and the PPM showed that SRO has a tendency to develop in two stages. In the first stage there is a quick relaxation of the SRO by itself. In the second stage, which occurs with a longer time constant, the SRO and LRO grow simultaneously. Parametric plots of one order parameter against another, here termed “kinetic paths”, are discussed. A variety of different kinetic paths through the B2 and D03 order parameters can be predicted theoretically, depending on the choice of interatomic potentials. This range of calculated kinetic paths is broad enough to encompass our experimental results of SRO and LRO evolution in Fe3Al.
Photoemission Measurements from Nickel-Iron Alloys
Authors: Jordan R.G. , Hoyland M.A. , Johnson D.D. , Pinski F.J. , Staunton J.B.
Published: March 2011

We have studied the photoemission from the (110) faces of two disordered Ni-Fe alloys containing 25% and 50% Fe over the photon energy range 20 – 45 eV with the aim of investigating their electronic structure. We observe a number of features that disperse with photon energy and we indicate their possible origin with reference to the one-electron Bloch spectral densities calculated using the SCF-KKRCPA.
First-Principles Study of Phase Stability in Pd-Rh Alloys
Authors: Johnson D.D. , Turchi P.E.A. , Sluiter Marcel , Nicholson D.M. , Pinski F.J. , Stocks G.M.
Published: March 2011

We present a study of the mixing energies and the effective cluster interactions which form the configurational part of the internal energy of Pd-Rh substitutional alloys. We discuss the tendency towards phase-separation and more generally phase stability. The effects of a substitutional ternary addition on the tendencies toward order or phase-separation are also reported. The Korringa-Kohn-Rostoker Coherent-Potential Approximation (KKR-CPA) is used to investigate the electronic structure effects and energetics of the random alloy. Moreover, we use the Generalized Perturbation Method (GPM), using the KKR-CPA random alloy as a reference medium, to investigate the effective interactions which determine phase stability. We briefly comment on other factors which may give important contributions to the total free-energy of the alloy. We also contrast the GPM with the Connolly-Williams approach for calculating phase diagrams from first-principles. Finally, we explore the inadequacies of the frozen-potential and Harris approximations to the energetics of alloying.
The Effect of Scandium on the Phase Stability of Al3Nb AND Al3Zr
Authors: Nicholson D. M. , Schneibel J. H. , Shelton W. A. , Sterne P. , Temmerman W. M.
Published: March 2011

A series of Al-25 (Nb,Sc), at.%, and Al-25 (Zr,Sc), at.%, alloy buttons were arccast in argon and homogenized for 2 h in vacuum at temperatures ranging from 1473 to 1573K. X-ray powder-diffraction indicated that almost all the Nb in Al-25 Nb (DO22) had to be replaced by Sc in order to obtain the Ll2 structure. In the case of Al3Zr much less Sc was required - the single phase Ll2 composition is approximately Al16Zr8Sc.

Recent calculations [1,2] show that once the tetragonality is properly included the phase stability of the trialuminide transition-metal binary alloys can be understood in terms of their electronic density of states. The dominating feature is a deep minimum in the density of states just below the major transition metal d-band peak. The exact position of the minimum changes with structure type (i.e., Ll2, DO22, or DO23, and with c/a). The alignment of the Fermi energy with the minimum appears to determine the equilibrium structure. The results of linearized-muffin-tin-orbital [3] (LMTO) electronic structure calculations are compared to the rigid band model and checked against the experimentally determined phase boundaries.
Interaction between Lattice Dislocations and Grain Boundaries in Ordered Compounds: Theory and Experiment
Authors: Pestman B. J. , Hosson J. Th. M. De , Vitek V. , Tichelaar F.D. , Schapink F.W.
Published: March 2011

The interaction between a screw dislocation and symmetric [1 1 0] tilt boundaries under the influence of an applied shear stress was investigated by atomistic simulation. Many-body potentials representing Cu and Ni3Al were used for the description of the interatomic forces. A comparison will be made with in-situ observations in a transmission electron microscope of the interaction of screw dislocations with a coherent twin boundary.
First Principles Calculations of the Equilibrium Mechanical Properties of Simple Metals and Ordered Intermetallic Alloys
Authors: Mehl Michael J. , Osburn Jean E. , Papaconstantopoulos Dimitri A , Klein Barry M.
Published: March 2011

High-strength, light-weight intermetallic compounds which are ductile at high temperatures are of great technological interest. Purely experimental searches for improved intermetallic materials are time consuming and expensive. Theoretical studies can shorten the experimental work by focusing on candidate compounds which have several of the desired properties. Although current abinitio density functional calculations are not adequate to calculate material properties at high temperatures, it is possible to compute the equation of state and elastic moduli of ordered compounds with several atoms in a unit cell. Known correlations between equilibrium and high temperature properties can then be used to point the way for experiments.

We have demonstrated the power of this approach by applying the linearized augmented plane wave (LAPW) method to calculate the equation of state and elastic moduli for several simple metals (Al, Ca, and Ir), binary cubic intermetallics (SbY, AlCo, AlNi, AlRu, and RuZr), and binary L1o intermetallics (AlTi and IrNb). Most of the calculated equilibrium lattice constants are within 3% of the experimentally observed lattice constants. Although the available experimental information about the elastic moduli is limited by the lack of single crystal data for most of these materials, we are in excellent agreement (within 10%) with the available experimental data, except for the shear modulus of IrNb. We also use known correlations between the elastic moduli and the melting temperature to predict melting temperatures of the intermetallics. In general the agreement there is good agreement between theory and experiment, indicating that we can qualitatively predict melting temperatures.
Extra Contribution of Tm Solutes to the Solute-Dislocation/Surface Interactions in Nickel
Authors: Shinoda T. , Masuda-Jindo K. , Suzuki Tomoo
Published: March 2011

The solute-dislocation (S-D) interaction energies for various kinds of transition-metal(TM) and B-subgroup solutes in nickel are calculated using a simple tight-binding electronic theory with lattice relaxations taken into account. As a result, the S-D interaction energy for TM solutes is almost identical with that for B-subgroup solutes when compared at an equal level of size-misfit strain( SMS) in Ni. This is neither more nor less than the answer from the classical elastic theory. However, in the solutions of the present calculation there are some points which can not be derived from the continuum elastic theory. Experiments show that Ni3Al is, differently from Ni, more strengthened by TM solutes than by B-subgroup ones. It is discussed that this may be due to the extra contribution of TM solutes to the S-D interaction energy in Ni3Al. As another possibility that TM solutes may contribute differently from B-subgroup ones to the macroscopic property of Ni, the (100) surface segregation of solute atoms in Ni is discussed.
The Dissociation of Sessile Superdislocations at a Coherent Twin Eoundary in Ordered CU3AU During Plastic Deformation
Authors: Tichelaar F.D. , Schapink F.W.
Published: March 2011

The glide behaviour of superdislocations at a coherent twin boundary in ordered Cu3Au was examined in a transmission electron microscope for the case when the superdislocations are sessile in the boundary. Possible schemes for dissociation of a superdislocation in the boundary were analysed geometrically. The leading superpartial of each superdislocation dissociated into a superpartial in the matrix and a residual Shockley partial in the boundary of glissile type. The trailing superpartial remained undissociated in the boundary. The superpartial in the matrix glided on a cube plane, and a ribbon of APB connected to the boundary was left in its trail. The cube slip occurs as a result of (i) a maximal resolved shear stress for the observed slip system and (ii) the geometric criteria for slip applied to all possible slip systems in the matrix. The Schmid factors for the slip systems in the matrix could be calculated by assuming a uniform tensile axis in the foil. The tensile axis was deduced from the observed slip systems in the twin.
Design of Li2 -Type Ni3 Si Intermetallics
Authors: Takasugi T. , Izumi O.
Published: March 2011

Based on the alloying method to improve the intergranular cohesion of LI2 alloys, it was shown that the Ni3 Si alloy was ductilized by the addition of Ti element and the control of stoicliometry. Metallographic and structural observations in the alloys along Ni3Si-Ni 3 Ti section were performed on optical microscopy, X-ray diffraction, TEM and ALCHEMI. It was shown that Ti element with a solubility of about 11 at.% substituted for the Si sites and the Ni3 (Si,Ti) alloys were highly ordered. The mechanical properties and fracture behavior of Ni3 (Si,Ti) polycrystals were investigated in terms of composition, the environmental effect, test temperature and the doping of B, C and Be. At ambient temperatures, higher ductility accompanied by a high portion of transgranular fractures was observed in the alloys with higher Ti and Ni contents, doped with B and C, and tested in vacuum. Hydrogen and oxygen from environment strongly affected the ductility and fracture of these alloys at ambient and elevated temperatures, respectively. The yield stress increased with increasing Ti content.
The Influence of Interstitial Alloying Elements on the Phase Stability and Fracture Toughness of V3Au
Authors: Kassem M. A. , Fahmy Y. , Koch C. C.
Published: March 2011

Additions of the interstitial elements oxygen and carbon to the A15 structure V3Au intermetallic compound resulted in the formation of the L'2 perovskite structure. The composition of the L'12 phase is about 17.5 at.% oxygen. Analysis of x-ray diffraction line intensities indicated that the interstitial stabilized phase was L'12 perovskite structure rather than the L12, Cu3Au structure type. The microhardness of the L'12 phase is about 20% lower than that of the A15 phase and its fracture toughness is 2 to 3.5 times greater. The mechanism for the improved fracture toughness in the L'12 phase is the subject of continued research.
Characterization of the Effect of Cr Additions to TiAl-Base Alloys
Authors: Huang Shyh-Chin , Hall Ernest L.
Published: March 2011

Ternary TiAl-base alloys containing Cr have been studied, using rapidsolidification processed materials. The mechanical behavior has been characterized and related to other results on microstructure, site occupancy, phase stability, and deformation mode. It was found that Cr additions enhance the plasticity of duplex γ+a2 alloys, but not single-phase alloys. The ductilization effect of Cr is partially due to its ability to occupy Al lattice sites and modify the Ti-Al bond. It is also partially due to its ability to promote twin formation, by modifying the Al partitioning and therefore the a2/γ volume ratio in transformed regions.
Alloy Phase Stability Requirements in Single Crystal Superalloys
Authors: Duhl David N.
Published: March 2011

Alloy phase stability is a critical parameter in the design and implementation of nickel-base superalloys. To achieve the high temperature properties required of single crystal superalloys for application in gas turbine machinery, these alloys must have a stable gamma plus gamma prime microstructure for long periods of time at elevated temperatures. Significant deviation from this stable two phase microstructure, due to the precipitation of other phases, results in the loss of critical alloy properties which can have a deleterious impact on engine performance.

Empirical methods based on the electron vacancy concept, commonly employed to predict and prevent the formation of undesirable topologically close packed (TCP) phases such as sigma or mu in polycrystalline nickelbase superalloys, are also used with single crystal superalloys. These undesirable phases result in the loss of alloy properties primarily as a result of the depletion of refractory strengthening elements from the superalloy matrix. The consequence of the formation of undesirable TCP phases on alloy properties and subsequent single crystal component behavior is reviewed.
Influence of Chromium and Molybdenum on the Structural Stability of a High Strength Damage Tolerant P/M Nickel Based Alloy for Turbine Disks
Authors: Marty Michel , Hug Gilles , Walder André
Published: March 2011

Aeronautical turbine disks are very critical parts in an aeroengine. Disk burst results in the loss of the engine and sometimes that of the aircraft. Their service lifetime being several thousand hours, it is necessary that the mechanical properties are not altered significantly during service.
Decomposition of Quasicrystalline Phase in a Rapidly Solidified Ai-Fe-V-Si Alloy
Authors: Park W. J. , Ahn S. , Kim N.J.
Published: March 2011

Decomposition of quasicrystalline phase formed in a rapidly solidified Al-Fe-V-Si alloy has been studied by TEM. The as-cast microstructure varies through the thickness of melt-spun ribbon; microeutectic precipitation of the bcc silicide near the wheel side, formation of globular quasicrystalline icosahedral phase with the microeutectic silicide phase at the middle of the ribbon, and the decomposition of quasicrystalline phase near the air side of the ribbon. During heating, as observed by annealing studies and by in-situ TEM studies, quasicrystalline phase decomposes into various phases such as aluminum, silicide and other unidentified phases. It has been shown that the preferential sites for the transformation are either at the center of quasicrystalline particles or at the quasicrystal/matrix interface, depending on the location of quasicrystalline particles.
Full Potential Lmto Study of Tial Alloy
Authors: Khowash Pradeep K. , Price David L. , Cooper Bernard R.
Published: March 2011

We have used a full potential all electron LMTO total energy calculation with a true interstitial to establish a baseline understanding of pure γ-TiAl. The c and a lattice parameters, Bulk modulus and the Young's modulus are calculated and found to be in excellent agreement with reported experimental values.
Magnetic and Chemical Ordering in the NiPt and the CoPt Systems
Authors: Sanchez J.M. , MorÁn-LÓpez J.L. , Cadeville M.C.
Published: March 2011

The interplay between atomic ordering and magnetism in the NiPt and the CoPt systems is investigated theoretically and experimentally. The complete equilibrium phase diagrams are calculated within the framework of statistical models and are compared with experimental data. Experimental results for the Curie temperature, magnetization and paramagnetic susceptibility in ordered and disordered states are satisfactorily reproduced by a Hamiltonian that contains chemical and short-range order dependent magnetic interactions.
Low Temperature Deposited High Quality ITO Films Prepared by E-Beam Evaporation
Authors: Chang C. S. , Wang J. C. , Kuo L. C.
Published: March 2011

An electron beam evaporation method has been used to prepare tin doped indium oxide (ITO) films with 95 wt.% In2O3 and 5 wt.% SnO2 in an oxygen atmosphere. It was found that the deposition rate and oxygen pressure strongly influence the film properties when the substrate temperature was lower than 200°C. In an optimal condition, highly transparent (transmittance ˜ 90% at wavelength 570 nm) and conductive (resistivity – 3×10−4Ω-cm) films of thickness around 2000 Å at substrate temperature as low as 180°C can be obtained.
Morphology of E-Beam Evaporated Cr Thin Films
Authors: Cheng Y. , Stearns M. B. , Smith David J.
Published: March 2011

Studies were made of the structural dependence on the growth rate and substrate temperature of Cr thin films prepared by e-beam evaporation. The d-spacings and the average size of the crystallites were determined from large angle x-ray scattering spectra. Detailed studies of the morphology were made by cross-sectional high resolution transmission electron microscopy.
Sxes Study of Transition Metal Silicide Films and their Contacts to Semiconductors
Authors: Watabe H. , Iwami M. , Hirai M. , Kusaka M. , Kubota M. , Nakamura H. , Kawai M. , Soezima H. , Akao F.
Published: March 2011

Spectra obtained by a new soft x-ray emission spectroscopy(SXES) apparatus again exhibited clear differences among Si-compounds and Si crystal. A non-destructive analysis of an annealed transition metal(TMSi:film)/Si(111) contact system was carried out using either the distinct differences of Si L2, 3 SXES spectra between TMSi's and Si single crystals or the fad that the soft x-ray production depth increases in a solid with the energy of the primary electron, Ep. It was shown that the apparatus was capable of exploring electronic and atomic structures of a multi-layered contact system grown on a Si(111) substrate.
Investigation into the Thin-Film Fabrication of Intermetallic NiTi
Authors: Jardine A. Peter , Zhang Hong , Wasielesky Lysa D.
Published: March 2011

Thin-films of Ni and Ti were formed by sputter co-deposition of Ni and Ti onto amorphous SiO2 and single crystal NaCl and Sapphire substrates. Films were characterized as follows: a) The chemical composition of the films was analysed by EDAX b) The gross morphology was examined by Scanning Electron Microscopy. c) The crystal phases were indentified by X-ray diffraction and Electron diffraction. Intermetallic NiTi has been identified in samples annealed in vacuo at 850°C. Annealing at 500°C in vacuum produced chemical separation of the Ni and Ti. This effect may be due to a narrow solidus region for the existence of NiTi and inhomogeneities due to uneven deposition of the Ni and Ti.
Chemical Vapor Deposition of Copper From Metal-Organic Copper(I) Phosphine Complexes
Authors: Shin H.-K. , Hampden-Smith M.J. , Kodas T.T. , Duesler E.N. , Farr J.D. , Paffett M.
Published: March 2011

A series of new, molecular copper(I) compounds with the general formula (β-diketonate)Cu(PMe3) have been prepared which are specifically designed as precursors for the CVD of copper. These species have been designed such that the effects of systematic ligand variations on the CVD process can be examined. The series of derivatives where β-diketonate is one of hexafluoroacetylacetonate, 3, trifluoroacetylacetonate, 4, or acetylacetonate, 5, have been prepared in high yield and are described here. A solid state X-ray diffraction study of 3 reveals that it is monomeric. Cryoscopic molecular weight determination and gas phase FTIR spectroscopy are also consistent with a monomeric structure in liquid and gas phases. Hot-wall CVD of copper from these precursors has been examined under various conditions. Auger electron spectroscopy indicates that the films all exhibit some degree of carbon contamination, but little contamination by oxygen, fluorine or phosphorus.
Decagonal Al3Pd Phase Formation in Lateral and Conventional Thin Film Al/Pd Diffusion Couples.
Authors: Blanpain B. , Mayer J.W.
Published: March 2011

We show that the decagonal Al3Pd phase can be formed by solid state reaction in lateral and conventional thin film couples of Al and Pd. The metastable decagonal phase forms after the initial growth of the Al3Pd2 compound.
Epitaxy of Iron on Various Ruthenium Surfaces: Occurence of a New Fe Phase.
Authors: Piecuch Michel , Ravet Marie Françoise , Maurer Marc
Published: March 2011

We have deposited Fe on (0001) and (1122) Ru surfaces. The RHEED patterns of Fe layers on these two different surfaces show perfect 2 dimensionnal epitaxy. The symmetry of the RHEED patterns is clearly 6 fold in the case of the (0001) growth direction. The RHEED patterns in the case of Fe deposited on (1122) surface are the same as those obtained from the clean Ru surface. The structure of the Fe surface is then exactly pseudomorphous to the Ru surface in both cases. Superlattices of these new Fe atomic layers with Ru have been achieved. We have deduced from X-ray diffraction, the average interplanar spacing d and we have demonstrated the hexagonal close packed stacking sequence of the entire superlattice. Plots of d versus the average atomic composition are used to determine the value of Fe interplanar spacing as 2.075Å and 1.08Å for the (0001) and the (1122) plane respectively. We are then able to determine the average Fe atomic volume, 12.8Å3. We propose that Fe is in an expanded new metastable hexagonal phase.
Epitaxy of TiO2 Thin Film on Sapphire by MOCVD
Authors: Chang H. L. M. , You H. , Parker J. C. , Lam D. J.
Published: March 2011

Epitaxial TiO2 films have been successfully grown on sapphire substrate at temperatures from 400 to 800°C by thermally decomposing titanium isopropoxide in the presence of O2 in a cold wall low pressure MOCVD system. Rutile film was grown on sapphire (1120) at 800°C with (101) being the growth plane and 〈010〉 being parallel to sapphire 〈0001〉. Anatase film was grown on sapphire (0001) at 400°C with (112) being the growth plane and 〈112〉 being parallel to sapphire 〈1100〉. The film structure as a function of substrate surface orientation and growth temperature is discussed in detail.
X-Ray Double Crystal Diffraction Characterization of Epitaxial Magnetic Transiton Metal Difluorides
Authors: Lui M. , King A. R. , Jaccarino V. , Farrow R. F. C. , Parkins S. S. P.
Published: March 2011

Epitaxial films of a variety of magnetic transition metal difluoride films have been grown by molecular beam epitaxy techniques. The structural quality of these films have been characterized using X-ray double crystal rocking curve analysis. The observed rocking curve linewidths were compared to their intrinsic values as calculated by dynamical diffraction theory. The degree of crystalline perfection as judge by the rocking curves have been correlated with the amount of lattice mismatch between the various epitaxial films and substrates. In the well lattice match case (Δa/a < 0.2%) of epitaxial films of FeF2 and CoF2 grown on (001) ZnF2 substrates, the rocking curve line widths approached their intrinsic limit indicative of extremely high quality material. This work represents some of the best epitaxial magnetic insulating films grown to date.
Molecular Dynamics Study of (001) and (111) Thin Fcc Films
Authors: Streitz F.H. , Sieradzki K. , Cammarata R. C.
Published: March 2011

We report on the results of molecular dynamics simulations of thin unsupported fcc films ranging in thickness from 20 layers to a monolayer. The films were oriented with either (001) or (111) free surface normals. The atomic interactions were modelled using a standard Lennard-Jones potential and a short range analytic form of the embedded atom potential. The elastic moduli of the films were determined by measuring their response to very low levels of applied stress.

We find that the embedded atom and Lennard-Jones results are in relative agreement for (001) films and qualitative disagreement for (111) oriented films. We relate these differences to the nature of the interatomic potential and the thermodynamic instability of the (001) surface.
Stability and Decomposition of IV-VI Semiconductor Films.
Authors: Salamanca–Riba L. , Nahm S. , Wuttig M.
Published: March 2011

Pb1−xEuxTe alloys with 0.41 ≤ x ≤ 0.51 have been observed to be unstable when grown at a temperature of 573K on BaF2 substrates. The alloys are stabilized when a buffer layer of PbTe is grown prior to the growth of the Pb1−xEuxTe alloy. In this work, we have observed tha the solid solution of Pb1−xEuxTe with x ≈ 0.5 can also be stabilized by increazing the growth temperature to 623K. Our results suggest that the critical temperature for decomposition is in the range 573–623K. We present a qualitative phase diagram for Pb1−xEuxTe alloy films.
Optimizing Process Parameters for the Growth of YBa2Cu3O7−δ thin-films
Authors: Norton M. Grant , Carter C. Barry , Moeckly Brian H. , Russek Stephen E. , Buhrman Robert A.
Published: March 2011

Laser deposition is widely used to fabricate thin-films of the YBa2Cu3O7−δ superconductor due to its ease of operation and its reproducibility. The films thus formed do not require post-deposition annealing to be superconducting. The processing route involves many variables which would be expected to exert an influence on the early stages of the film growth and thereby the final microstructure. The parameters which have been varied are the laser energy, laser pulse repetition rate and laser wavelength. The films have been examined using transmission electron microscopy (TEM) in order to determine the film orientation, composition and microstructure.
Preparation and Properties of Superconducting thin Films by Excimer Laser Ablation
Authors: Geusic Michael E. , Stewart Alan F. , Pederson Larry R. , Weber William J. , Marken Kenneth R. , Li Kin
Published: March 2011

Excimer laser ablation with an in situ heat treatment was used to prepare high quality superconducting YBa2Cu3O7−x thin films on (100)-SrTiO3 and (100)-LaAlO3 substrates. A pulsed excimer laser (XeCl; 308 nm) was used to ablate a rotating, bulk YBa2Cu3O7−x target at a laser energy density of 2–3 J/cm2. Based on four-probe dc resistance measurements, the films exhibited superconducting transition temperatures (Tc, midpoint) of 88 and 87K with 2K (90–10%) transition widths for SrTiO3 and LaAlO3, respectively. Transport critical current densities (Jc) measured at 77K were 2 × 106 and 1 × 106 A/cm2 in zero field for SrTiO3 and LaAlO3, respectively. X-ray diffraction (XRD) analysis showed the films to be highly oriented, with the c-axis perpendicular to the substrate surface.
Effects of Substrate Bias Voltages on Preparation of YBa2Cu3O7-δ Thin Films by Laser Ablation
Authors: Ohata K. , Izumi H. , Hase T. , Suzuki K. , Morishita T. , Tanaka S.
Published: March 2011

Superconducting films of YBa2Cu3O7-δ have been fabricated by pulsed laser deposition technique applying bias voltage to a substrate up to +/-500 V. It has been found that substrate bias voltages are effective for preparing the fidms with high Tc and high crystalline quality at lower substrate temperatures. Positive bias is more effective than negative one. Time resolved observation has been carried out in order to investigate the influence of biasing on the plume and revealed three kinds of light emission. The first is an ordinary plume with a velocity of 6×105 cm/s, which is independent of biasing. It suggests that most of the luminous particles in the plume are electrically neutral. The second is oxygen plasma with a short life time, which is triggered by laser pulse under the positive bias and triggered by arrival of the plume in 8 ps after the laser pulse under the negative bias. The third is an additional plume with a velocity of 3×105 cm/s. The oxygen plasma and additional plume have improved superconducting properties of films deposited with biasing to the substrate.
In Situ Growth of PbZrxTi1-xO3 Thin Films by Pulsed Laser Deposition
Authors: Chrisey D. B. , Horwitz J. S. , Grabowski K. S.
Published: March 2011

We have investigated the composition and structure of thin films of PbZrxTi1-xO3 (x-0.54) produced in situ by pulsed excimer laser deposition from a stoichiometric pressed oxide target. Thin films were deposited onto (100) MgO and SrTiO3 substrates as a function of substrate temperature between room temperature and 750 °C, and oxygen background pressures between vacuum and 300 mtorr. The deposited films were very smooth with particulates covering less than 0.5% of the surface. Elastic backscattering spectroscopy was used to determine the relative atomic fractions. In the deposited films, the Pb stoichiometry was found to be very sensitive to both the substrate temperature and the O2 background pressure. Above ∼600 °C, the Pb content dropped rapidly with increasing substrate temperature for a 50 mtorr 02 background. At 550 °C the Pb content was near-stoichiometric for O2 background pressures between 200 and 300 mtorr but dropped monotonically to ∼20% of the expected value for depositions in a vacuum (i.e., no O2 background). Over this entire range of pressures and temperatures the Ti/Zr stoichiometry ratio was relatively uneffected. The structure and orientation of the deposited films, as determined by x-ray diffraction, followed the Pb deficiency via the production of other phases and orientations. Crystallation of the deposited film was observed at temperatures as low as 400 °C for 200 mtorr O2 background. At 550 °C and 200 –300 mtorr, (100) oriented PbZrxTi1-xO3 was observed on SrTiO3 substrates.
Structural Implications for Optimizing A-Sige:H Alloys
Authors: Schubert M.B. , Eberhardt K. , Bauer G.H.
Published: March 2011

Detailed structural investigations have been performed on a-Si1−xGex:H in 0 ≤ × ≤ l namely Raman, X-ray Photoelectron, and Photothermal Deflection Spectroscopies, which reveal the silicon sub-matrix to be considerably more rigid than the germanium one. In Si-Ge dominated networks distinct deviations from an overall random distribution of Si and Ge atoms can be deduced from a semi-quantitative analysis of the Raman data.
Hydrogen Bonding in a-Si:H Prepared by Remote Hydrogen Plasma Deposition
Authors: Ready S. E. , Boyce J. B. , Johnson N. M. , Walker J. , Stevens K. S.
Published: March 2011

Nuclear magnetic resonance (NMR) has provided essential information on the local atomic bonding and microstructure of hydrogen in hydrogenated amorphous silicon (a-Si:H). Here we describe results from NMR and Raman spectroscopy on the hydrogen distribution and bonding in a-Si:H prepared by remote hydrogen plasma (RHP) deposition and contrast the results with those from a-Si:H prepared by conventional glow discharge (GD) deposition. The films prepared by the two techniques have similar H bonding except for the presence in the RHP sample of about 1 atomic % molecular hydrogen, a factor of ten higher than in GD material. For RHP samples prepared from a deuterium plasma rather than a hydrogen plasma, substantial differences in the hydrogen NMR spectra, hydrogen spin lattice relaxation time and Raman spectra are observed. The hydrogen which necessarily originates from the silane has a dramatically altered spectra.
Hydrogen Incorporation in A-Si:H: Temperature and Doping Type Dependence
Authors: Pruppers M.J.M. , Maessen K.M.H. , Habraken F.H.P.M. , Bezemer J. , Van Der Weg W.F.
Published: March 2011

Phosphorus, boron and compensation doped hydrogenated amorphous silicon films were deposited in a glow discharge at different substrate temperatures in the range 50–330°C. Gas phase doping levels were 1%. At the lower temperatures the hydrogen concentration in the B doped and compensated doped films is larger than in the P and undoped films. For higher deposition temperatures the H concentration of the B doped films appeared to be smaller than in the other materials. The difference in hydrogen content of the doped and undoped material, deposited at various temperatures, is considered as a function of the measured activation energy for conduction in these films. This difference varies in much the same way with the activation energy as the hydrogen content in films deposited at one substrate temperature, but with varying gas phase dopant levels. This represents strong evidence that, apart from the deposition temperature, the hydrogen concentration in glow discharge a-Si:H is determined by the position of the Fermi level.
Deep Levels and Hydrogen Evolution in Hydrogenated Amorphous Silicon
Authors: Zafar Sufi , Schiff E. A.
Published: March 2011

Two hydrogen-mediated models are applied to predicting the density of deep levels in hydrogenated amorphous silicon (a-Si:H) under variations in the material’s temperature and total hydrogen content. Both models depart from the assumption that hydrogen is bonded at two classes of sites, dangling bonds and weak bonds. The predictions of the two models for the temperature-dependence of the deep-level density are similar. The models differ in their treatment of the origins of the weak bonds; a model associating the weak bonds with the clustered phase of bonded hydrogen observed by nuclear magnetic resonance also appears to be in agreement with hydrogen evolution experiments.
Study of Bandgap Profiling Control on Photovoltaic Performance in the Three Stacked Amorphous Solar Cells
Authors: Nakata Y. , Sannomiya H. , Moriuchi S. , Yokota A. , Inoue Y. , Itoh M , Itoh H
Published: March 2011

A series of systematic experiments has been made on a bandgap profiling control using a-SiGe and a-SiC cells to clarify the cause for the improvement of the photovoltaic performance by the bandgap profiling in the photovoltaic active layer. It has been shown from the analysis that the most important contribution to the cell performance is an optimization of the ambipolar carrier collection by the bandgap profiling. On the basis of the results, an efficiency of 10.1% was obtained at the promising a-SiC/a-Si/ a-SiGe multi-bandgap stacked cell by the bandgap profiling.
Hopping of Electrons in Hybrid Band Tails of a-Si1-xGex:H
Authors: Nebel C. E. , Weller H. C. , Bauer G.H.
Published: March 2011

The thermalization of electrons in the medium temperature range (120K ≤ T ≤ 200K) is investigated by time-of-flight experiments on a-SiGe:H mim structures. The evaluation of the pre-transit current decay reveals a dual slope characteristic which reflects an initial hopping down (I ∼ t−1) followed by a thermally activated (I ∼ t−p 0 < p < 1) process. The transition time from hopping down to multiple trapping sensitively depends on temperature and alloy composition. The experimentally deduced features can be explained by the increased tail state density at the conduction band mobility edge of a-SiGe:H samples compared to a-Si:H.
Band Tails and Thermal Disorder in Doped and Undoped Hydrogenated Amorphous Silicon and Silicon-Germanium Alloys
Authors: Aljishi Samer , David Cohen J. , Jin Shu , Ley Lothar
Published: March 2011

The energy distribution and temperature dependence of the conduction and valence band tail density of states in a-Si:H and a-Si,Ge:H alloys is determined via total yield photoelectron spectroscopy. All films are observed to possess purely exponential conduction and valence band tail densities of states; however, the characteristic energy of the conduction band tail increases much more rapidly with temperature in the range of 300K to 550K than that of the valence band tail. This indicates that over that temperature range the conduction band tail is considerably more susceptible to thermal disorder than to structural disorder whereas the reverse holds for the valence band tail.
Cathodoluminescence of Diamond-Like and Hydrogenated Amorphous Silicon Carbide Materials
Authors: Alvarez F. , Koropecki R.R. , Fajardo F. , Fragnito H.L. , Santos P.V.
Published: March 2011

The room temperature cathodoluminescence (CL) of diamond-1ike materials produced by glow discharge is reported. The CL spectra of these samples (4 eV optical gap) display two bands located at 2.3 eV and 2.8 eV which are frequently found in natural and synthetic diamond. X-ray diffraction spectra (before electron bombardment) are identical to those obtained in natural powder diamond, confirming the existence of crystalline particles. The room temperature CL of phosphorous doped samples is also reported.

Structural changes in amorphous silicon carbide samples (3.0 eV optical gap) associated with electron bombardnent are presented and elucidated by IR studies.
Analysis of the Amorphous Silicon Carbide/Crystalline Silicon Interface
Authors: Rahman M. M. , Harjono T. , Lui K. H. , Pagaduan F. E. , Inokawa H. , Yang C. Y. , Sugiarto Dian
Published: March 2011

The performance and reliability of silicon-based hetero-structure devices depend critically on their interfacial characteristics. Here we present high-resolution TEM (HRTEM) results for the a-SiC:H/c-Si (100) interface, substrate doping, and interface electrical characteristics derived from an Al/undoped a-SiC:H/p-Si metal-insulator-semiconductor (MIS) structure. The HRTEM study reveals an interface with a maximum asperity of three atomic planes. The substrate dopant profile for depths less than an extrinsic Debye length from the interface is computed from an iterative fit to the C-V data. A density of interface traps (Dit) of 1011 eV−1cm−2 at midgap is obtained.
Molecular Dynamics Simulations of the Structural, Vibrational and Electronic Properties of Amorphous Silicon
Authors: Biswas R. , Kwon I. , Soukoulis C. M.
Published: March 2011

Amorphous silicon models have been computer-generated by melt-quenching and film deposition molecular dynamics simulations, employing classical interatomic Si-potentials. The structural, vibrational and electronic properties of these models is described. Dangling-bond gap states are well localized whereas, floating bonds gap states are considerably less localized with wavefunction amplitudes on the neighbors of the five-coordinated atom. In contrast to melt-quenched models, the a-Si films displayed voids, a 15–28% lower density than c-Si, and no five- coordinated atoms. A-Si:H models with 5 and 22% hydrogen, and both monohydride and dihydride species, have also been developed.
Prospects of a-Sige:H Alloys for Solar Cell Application
Authors: Fortmann C.M.
Published: March 2011

The transport properties of intrinsic a-SiGe films are found to be limited by poor electron mobility. The relationship between electronic transport and composition (Si, Ge and H content) is established. The electron mobility decreases with increasing hydrogen content for a given Ge content. The relation between growth conditions and film composition is developed. Growth conditions that reduce the extent of gas phase polymerization as well as the flux of hydrogen radical to the growth surface yield the best electronic transport. The best a-SiGe:H alloys of 1.3 eV band gap are used to study the effects of band gap grading on solar cell performance. Solar cells analysis is used to determine both hole and electron transport. Cell designs that minimize performance loss due to poor electron mobility are considered.
A Comprehensive Defect Model for Amorphous Silicon
Authors: Hata N. , Larson E. , Liu J. Z. , Okada Y. , Park H. R. , Wagner S.
Published: March 2011

Based upon the thermal-equilibration theory and the annealing of defects introduced at the growing surface of amorphous silicon, the distribution of defect-states in energy and in space is calculated for a comprehensive set of deposition and post-deposition treatment parameters. We include the growth temperature, growth rate, illumination time, illumination intensity, annealing temperature, and annealing time. We compare the theoretical results with experimental data for the dark-conductivity-activation energy and for the fill factor of a solar cell. Agreement between the modelled and the experimental results reconfirms the validity of the assumptions made, and encourages further application of the model to analyses of a wide variety of amorphous silicon devices.
Observation of Quantized Ballistic Transport in Amorphous Silicon Memory Structures
Authors: Hajto J. , Rose M.J. , LeComber P.G. , Owen A.E. , Snell A.J.
Published: March 2011

We present experimental results showing that the ON state of amorphous silicon memory structures exhibits ballistic electron transport associated with a quantised resistance, h/2ie2, where i is the number of occupied one dimensional conducting channels (sub-bands) and the spin degeneracy is two (in the case when no magnetic field is applied). Conduction in the memory ON state is restricted to a narrow conducting channel through which the electrons can travel ballistically i.e. no collisions occur. As the applied voltage is increased, the width of the conducting channel is broadened. This results in additional conducting channels (sub-bands) passing through the Fermi energy and consequently the resistance drops by quantised values. In the presence of a magnetic field additional steps occur corresponding to the split levels at values of h/2(i + ½)e2. A particular feature of this quantised resistance is that the effect can be observed at relatively high temperatures effect can be observed at relatively high temperatures (from 4.2 K up to ∼190K).
A-Si:H Thin Film Transistors and Logic Circuits Fabricated in an Integrated Multichamber System
Authors: Kim S. S. , Wang C. , Parsons G. N. , Lucovsky G.
Published: March 2011

Hydrogenated amorphous silicon (a-Si:H) thin-film-transistors (TFT’s) and logic circuits have been fabricated using a simple 3-mask process. Inverted staggered TFT structures were prepared in a multichamber UHV-compatible system that provides: 1) sequential deposition of dielectrics, and intrinsic and doped a-Si:H by remote plasma-enhanced chemical-vapor deposition (Remote PECVD) in a single deposition chamber; 2) in-situ surface analysis by Auger Electron Spectroscopy (AES); and 3) dry etching of deposited thin films by Remote plasma-enhanced etching, Remote PEE. A field-effect electron mobility of 0.74 cm2/V-s, and a threshold voltage of 2.5 Volts have been measured at room temperature in the TFTs. The on/off current ratio of the TFT exceeds 106. The a-Si:H TFT logic circuits, 2-transistor inverters and addressable 6-transistor static memory cells, operate at a supply voltage of as low as 8 Volts. The experimental results indicate that high performance a-Si:H thin film devices can be fabricated by sequential Remote plasma processing in a multichamber integrated system.
Photoelectronic Properties of the Pipi... Multilayers and their Implications for the Operation of Solar Cells
Authors: Yang L. , Balberg I. , Skibo S.
Published: March 2011

We have studied the photoelectronic properties of pipi... multilayers made of a-SiC:H p-layers (∼ 100Å) alternating with a-Si:H i-layers (500Å to 4000Å). A large enhancement in d.c. coplanar photoconductivity (more than an order of magnitude) over that of bulk a-Si:H was observed with decreasing i-layer thickness of the multilayer. On the other hand, the ambipolar diffusion length was observed to decrease with decreasing i-layer thickness. These observations can be explained by the effect of charge separation due to the strong built-in electric field in the i-layer. The insertion of an ultrathin SiC layer at the p/i interface is shown to appreciably reduce the built-in field which may be directly related to the observed decrease in fill factor when such a buffer layer is used in a solar cell.
Full-Contact Type Linear Image Sensor by Amorphous Silicon
Authors: Hayase Masaki , Arita Hirotaka
Published: March 2011

A new type of the contact linear image sensor array using amorphous silicon photodiodes has been developed. The new device, namely “Full Contact” type, linear image sensor, has a pinhole of 60 µm in diameter at the center of the amorphous silicon photodiode pixel. With this structure, the focusing lens can be removed and the optical path can be reduced by about one half as compared with an ordinary facsimile scanner. Eventually the device becomes quite compact in volume and production process are rather simple, result in low cost. LED driven 1728 pixels for A4 size and 2048 pixels for B4 size devices with the resolution of 8 dots/mm have been developed so far. A series of technical data for the development of devices and their operational performance are presented and discussed.
Peak-To-Peak Voltage (Vp-p) on Rf Powered-Electrode and Sensitivity of Amorphous Silicon (A-Si) Photoreceptor
Authors: Yamazaki Toshinori , Kobayashi Nobuaki , Takahashi Satoshi , Nakanishi Tatsuo
Published: March 2011

It has been found that photosensitivity of amorphous silicon (a-Si) photoreceptor fabricated by g1ow-discharge decomposition of SiH4 – B2H6 – Ar has specific relation to peak-to-peak value of Rf (13.5 MHz) voltage (Vp - p) and DC bias voltage (Vdc) on the Rf powered-electrode. The lower the Vp - p value is depressed, the higher the photosensitivity is improved. Dependences of the Vp - p value on deposition parameters such as gas pressure, distance between Rf powered-e1ectrode and aluminum substrate, Rf electric power and dilution ratio of SiH4 to Ar seem to indicate correlation of Vp - p with electron energy and electron density in the plasma.

Furthermore, the Vp - p and Vdc values have been measured in plasma of He, Ne (rare-gases with no Ramsauer effect), Ar, Kr, Xe (rare-gases with Ramsauer effect), and H2, N2, CH4, SiH4 (molecular-gases): Specific behaviors in Vp - p and Vdc seem to have correlation with collision cross - sections of electrons (with the energy of 2 ∼ 10 eV) in these gases.
Thin-Film Amorphous Silicon Dynodes for Electron Multiplication
Authors: Tasker G.W. , Horton J.R. , Fijol J.J.
Published: March 2011

The design and fabrication of novel, thin-film continuous dynodes for a new generation of channel electron multipliers (CEMs) and microchannel plates (MCPs) are described. In particular, we demonstrate the feasibility of forming such dynodes by low pressure chemical vapor deposition (LPCVD) of amorphous Si films in capillary channels of macroscopic to microscopic dimensions. Finally, we discuss potential performance advantages of thin-film dynodes over conventional reduced lead silicate glass dynodes for CEMs and MCPs and implications for new applications.
Nucleation and Growth in Vicinity of Growing Surface in Making Microcrystalline Silicon
Authors: Nakata Masami , Namikawa Tatsuru , Shirai Hajime , Hanna Jun-ichi , Shimizu Isamu
Published: March 2011

A close study was conducted on microcrystalline Silicon (μc-Si) prepared by PE-CVD (Plasma Enhanced CVD) from SiF4 with the assistance of atomic hydrogen. The atomic hydrogen played a major role in either making precursors, SiFnHm (n+m=3), by gas phase reactions with the fragments, SiFn (≤3), or constructing Si-network in the vicinity of the growing surface. Proper conditions of nucleation were markedly different from those of growth with respect to parameters, flow of atomic hydrogen and substrate temperature.
New Doping Technique for Getting Highly Conductive p-Type Hydrogenated Amorphous Si and Sic Alloys
Authors: Takeuchi Y. , Nomoto K. , Ganguly G. , Matsuda A.
Published: March 2011

Highly conductive B-doped hydrogenated amorphous Si (a-Si:H) as well as amorphous SiC alloys (a-SiC:H) have been prepared from (SiH4) / (B2H6/SiH4) and (SiH4/CH4)/(B2H6/SiH4) plasmas, respectively by a novel surface-temperature-modulation method. Films produced by this technique exhibit a higher conductivity as compared to the conventionally prepared films, i.e., 7.0×l0−3scm−l for p-type a-Si:H with an optical gap of 1.7eV and 5.5×l0−5Scm−l for p-type a-SiC:H of optical gap 1.9eV.