bluuebunny/crossref_metadata_2025 huggingface dataset:
Interaction Between Lattice Dislocations and Grain Boundaries In Ordered Compounds
Authors: Pestman B.J. , De Hosson J. Th. M. , Vitek V. , Schapink F.W.
Published: March 2011

The interaction of 1/2<1 1 0> screw dislocations with symmetric [1 1 0] tilt boundaries was investigated by atomistic simulations using many-body potentials representing ordered compounds. The calculations were performed with and without an applied shear stress. The observations were: absorption into the grain boundary, attraction of a lattice Shockley partial dislocation towards the grain boundary and transmission through the grain boundary under the influence of a shear stress. It was found that the interaction in ordered compounds shows similarities to the interaction in fcc.
CVM Simulation of the Resistivity in L10 and L12 Co-Pt Intermetallic Compounds
Authors: Sanchez J.M. , Cadeville M.C. , Pierron-Bohnes V.
Published: March 2011

The contributions of the atomic and spin disorder to the resistivity of two intermetallic Co1−x Ptx (x=0.5 and 0.7) compounds have been previously determined from experimental studies and separated from the phonon contribution. Now, the atomic and magnetic contributions and their variation with temperature through the Curie and order-disorder transitions are analyzed using a statistical model. The components of the resistivity are described as sums of resistivities of individual tetrahedral clusters. The cluster probabilities are calculated in a magnetic (up and down spin model) CVM approximation, the parameters of which are those that reproduce the experimental Co-Pt phase diagram. The contribution of chemically (magnetically) ordered clusters to the resistivity due to the chemical (magnetic) disorder are taken equal to zero. It is the temperature dependence of all other cluster probabilities which determine the resistivity behavior. Although there are severe approximations in both the experimental analysis and the statistical model, the agreement between theory and experiment is very satisfactory, underscoring the strong interplay between chemical and magnetic order in such ferromagnetic compounds.
Effect of Aluminum Concentration And Boron Dopant on Environmental Embriitlement In Feal Aluminides
Authors: Liu C. T. , George E. P.
Published: March 2011

The room-temperature tensile properties of FeAl aluminides were determined as functionsof aluminum concentration (35 to 43 at. % Al), test environment, and surface (oil) coating. The two lower aluminum alloys containing 35 and 36.5% Al are prone to severe environmental embrittlement, while the two higher aluminum alloys with 40 and 43% Al are much less sensitive to change in test environment and surface coating. The reason for the different behavior is that the grain boundaries are intrinsically weak in the higher aluminum alloys, and these weak boundaries dominate the low ductility and brittle fracture behavior of the 40 and 43% Al alloys. When boron is added to the 40% Al alloy as a grain-boundary strengthener, the environmental effect becomes prominent. In this case, the tensile ductility of the boron-doped alloy, just like that of the lower aluminum alloys, can be dramatically improved by control of test environment (e.g. dry oxygen vs air). Strong segregation of boron to the grain boundaries, with a segregation factor of 43, was revealed by Auger analyses.
Deformation of Polysynthetically Twinned (PST) Crystals of TiAl in Tension and Compression at Room Temperature
Authors: Inui H. , Nakamura A. , Yamaguchi M.
Published: March 2011

Polysynthetically twinned (PST) crystals of TiAl have been grown and deformed in tension and compression at room temperature. A room temperature tensile elongation of 12.8% which is far larger than any other reported values of room temperature ductility was obtained for a specimen whose tensile axis is inclined at 51° to the lamellar boundaries. Deformation mechanisms of PST crystals of TiAl are discussed on the basis of the results of electron microscope observations of deformation structures.
Mechanism of Ductility Improvement In L12 Compounds by Interstitial Elements
Authors: Chaki T. K.
Published: March 2011

Interstitial boron atoms are known to increase room temperature ductility in Ni-rich Ni3Al and Ni3Si. Inerstitial carbon atoms increase ductility in Ni-rich Ni3Si, but not in Ni3Al. It is argued that grain boundary segregation of B or C is not the cause of the increase in ductility. Instead, strong Ni-B bonding and antisite Ni defects reduce the strength of directional Ni-Al bonding in ordered Ni3Al so that Ni and Al atoms can relax more easily to fill up the microcavities at the grain boundaries, thereby strengthening the boundaries. The reduced Ni-Al bonding will also enhance the ductility in the interior of the grains so that dislocations can be easily generated to shield the tips of the cracks at the grain boundary. In Ni3Si, strong Si-C bonds distort the directionality of Ni-Si bonding. Evidence for this model is presented. Estimates of the concentration of interstitial atoms to achieve maximum ductility are made and the estimate agrees well with the experimental value.
A Comparative Study on the Influence of Nb and Ti Additions to Different Processed Atomized Nial Powders.
Authors: Laag Rainhard , Kaysser Wolfgang A. , Petzow GÜnter
Published: March 2011

Prealloyed powders of NiAl, NiAl-5Ti, NiAl-5Nb and NiAl-5Ti-5Nb (at.%) were gas atomized with an average particle size of 90 μm and cooling rates of > 104 K/s. The powders were attritor milled under Ar atmosphere reducing the average particle size to 1.5 μm. Sintering CIP compacts developed microstructure and density distributions, which allowed subsequent containerless HIPing to near full density (>98.5%) and a final grain size < 8 μm. Alloying of NiAl with 5at.% Nb or Ti increased its hardness, Young's modulus, toughness and creep resistance. The room temperature fracture path changed from primarily intergranular (NiAl) to primarily transgranular (Nb, Ti alloyed), increasing the Klc, values from 3.8 to 14.4 and 15.3 MPa√m, respectively. For comparison, HIPed materials from the as-atomized powders were also tested.
Improvements in Strength and Ductility of Feal-ZrB2 By Rapid Solidification
Authors: Morris David G. , Morris Maria A.
Published: March 2011

Fe-35Al alloys containing various amounts of ZrB2 have been prepared by melt spinning and the microstructure and its stability examined. The mechanical properties are evaluated both on as cast materials as well as after high temperature heat treatments. The ZrB2 additions lead to a dramatic increase in hardness and strength. In addition, small amounts of ZrB2 lead to significant increases in ductility. Because the microstructure is fairly stable, these improvements in properties are maintained even after high temperature exposures.

Alloys with up to about 1%ZrB2 have the dispersoid particles arranged in an imperfect cellular microstructure after rapid solidification. The cell walls contain many fine particles and are efficient barriers against dislocation propagation. Strain occurs as dislocations escape through gaps in the imperfect cell walls at a stress level that is controlled by the size of these gaps. Ductility is improved since the deformation that results from such controlled strain progression through the material is much more uniform and large stress and strain concentrations are avoided.
Cracking in the Weld Heat-Affected Zone of COntinuously Cast Sheet and Ingot of Ni3Al
Authors: Li Huaxin , Chaki T.K.
Published: March 2011

Weldability is a key issue for successful applications of ductile Ni3Al in structural components. Here we report the results of an investigation of gas tungsten arc welding behaviors of continuously cast thin sheet and cast ingot of a Ni3Al alloy, known as IC-50, containing boron and zirconium. Cracking in heat-affected zone (HAZ) was prevalent in both types of specimens. Both in cast sheet and ingot, liquation cracking was observed to occur along the grain boundaries in HAZ. Microstructural studies showed that continuously cast thin sheet consisted of columnar grains along the thickness. Easy cracking along the boundaries of columnar grains made cast sheets more susceptible to hot cracking than ingots. The possibility of segregation of boron and zirconium, causing liquation cracking, will be discussed.
The Structure and Properties of a Ti-25Al-10Nb-3V-1mo Alloy
Authors: Wang Wego , Scanlon Marietta R. , Wells Martin G.H.
Published: March 2011

Six super α2 titanium aluminide pancakes were produced by rapid omnidirectional compaction of prealloyed Ti-25Al-l0Nb-3V-lMo (at%) [Ti- 14.1Al-19.5Nb-3.2V-2Mo (wt%)] powder. Various solution and aging heat treatments were investigated to yield the best combination of tensile and stress rupture properties. The β transus temperature was found to be about 1,090 °C (1,990 °F). The alloy was heat treated with four different schedules to develop various structure combinations of α2 and β, and followed by a series of microstructural analyses and mechanical property determinations. The highest ultimate tensile strength and yield strength attained at room temperature were 1,174.9 and 977.7 MPa (170.4 and 141.8 ksi), respectively, for a specimen heat treated at 1,140 °C (2,084 °F) for 1 hr and aged at 816 °C (1,500 °F) for 4 hr + air cooling. However, the elongation was less than 2%. Under the same heat treatment condition, the ultimate tensile strength and yield strength measured at 427 °C (800 °F) were 1,139.1 and 711.6 MPa (165.2 and 103.2 ksi), respectively, with an elongation of 6.7%. The alloy also showed good stress rupture resistance. Compared with a similar hot isostatically pressed material, the current alloy shows superior mechanical properties due to a finer microstructure.
Development of Surface Treatment Techniques to Improve Oxidation Resistance of Titanium Aluminide
Authors: Yoshihara Michiko , Tanaka Ryohei , Suzuki Tetuya , Shimizu Masayuki
Published: March 2011

The oxidation resistance of intermetallic compound TiAl was greatly improved in cyclic heating at 900°C by means of a new type of surface treatment, which is the heat treatment under a low partial pressure oxygen atmosphere. The treatment becomes more effective with increasing aluminum content in the specimen. It was presumed that the excellent oxidation resistance resulting from this method is due to preferential formation of a thin and tighit Al2 O3 surface layer, which is formed during the surface treatment at a temperature vicinity of 1000°C and air pressure of about 10−3 Pa. The oxidation resistance of Al2O3 film formed, however, was found to be insufficient at 950°C. A combined treatment consisting of the heat treatment under a low partial pressure oxygen atmosphere followed by a diffusion coating with aluminum showed an excellent resistance to cyclic oxidation even at 950°C.
Processing and Properties of Intermetallic Matrix Composites
Authors: Alman D.E. , Stoloff N.S.
Published: March 2011

This paper is concerned with the processing and mechanical properties of intermetallic-matrix composites. The effects of processing variables on fabrication of compounds including Ni3Al, NiAl, TiTaAl2, MoSi2 and their composites is described. A key concern is with processing effects on microstructure, selection of compatible ceramic reinforcing phases, and whisker alignment through injection molding.
In-Situ Derivative Cyclic Voltabsorptometric Studies On Poly-3-Methylthiophene
Authors: Hoier Sally N. , Ginley David S. , Park Su-Moom
Published: March 2011

Spectroscopic behavior of poly-3-methylthiophene (P3MT) has been studied employing derivative cyclic volt-absorptometric (DCVA) techniques. In the DCVA technique, the derivative absorption signal (dA/dt) is recorded as a function of the applied potential. The dA/dt signals, the spectroscopic analog of electrochemical currents in cyclic voltammetry, are capable of monitoring the potential dependency for the absorption band effectively discriminating against nonfaradaic signals. The DCVA studies on the P3MT system show that the neutral form of P3MT, absorbing at 490 nm (at less than 0.3 V vs. Ag), changes to the radical cation form, which absorbs at 760 nm. Initially, the formation of the radical cation goes through an isosbestic point, indicating that the conversion of the neutral to radical (polaron) form is chemically reversible. However, upon increasing the electrode potential, the rate of the radical formation at 760 nm starts to decrease, with the formation of another band at about 1250 nm, attributable to a quinoid (bipolaron) form. This trend begins above about 0.6 V, shifting to a more positive voltage as the thickness of the film grows. This observation indicates that the electrochemical conversion of the neutral to radical form, followed by the quinoid form, is a slow process controlled by the diffusion of counter ions through the film. In-situ conductivity measurements as a function of applied potentials support the observed spectroscopic behavior.
Fracture Energy and Critical Strength of High Molecular Weight Glassy Polymers
Authors: Mikos Antonios G. , Peppas Nikolaos A.
Published: March 2011

The fracture energy and the critical strength of glassy polymers with molecular weight larger than the critical value for the onset of chain entanglements are proportional to the number of chain segments entangled about a unit plane. A new molecular model is presented to calculate the crossing density of these chain segments when the segment length is a stochastic variable. The crossing density depends on the mesh size of the entanglement network and the number of entanglement network strands per unit volume. Theoretical predictions of the variation of the fracture energy and strength with the molecular weight are compared with experimental results for various glassy polymers.
Molecular Design of Stable Second Order Nonlinear Optical Polymers
Authors: Mandal Braja K. , Kumar Jayant , Tripathy Sukant
Published: March 2011

The temporal and thermal stability of second order nonlinear optical properties of polymers is an important issue in the development of poly meric electro-optic devices. This has been addressed by introducing interchain crosslinking. A number of crosslinked systems developed by photochemical reactions have been presented.
Optical and Electro-Optical Properties of a Photocross-Linkable Polymer
Authors: Rahman A. K. M. , Mandal B. K. , Zhu X. F. , Kumar J. , Tripathy S. K.
Published: March 2011

Planar waveguides from a photocross-linkable polymer have been fabricated on glass and Si0 2 on silicon using the spin coating process. The polymer has been cross-linked by exposure to UV radiation (λ = 254nm). Prism coupling technique has been used to couple a laser beam into the waveguide structure. The waveguiding parameters such as number of modes, loss, thickness, and index of refraction of the polymer have been determined before and after crosslinking. The refractive index of the polymer before cross-linking differs significantly from that after cross-linking. No anisotropy has been observed in the refractive indices for the uncross-linked or cross-linked samples. The refractive index and thickness of the polymer film before and after cross-linking have also been measured using an ellipsometer and found to be in very good agreement with those obtained by the prism coupling technique. Dye molecules with large second order hyperpolarizability were utilized as guests into the photocross-linkable polymer matrix for second order nonlinear optical applications. Electro-optic properties of this polymeric system are reported.
Carbon-13 Two Dimensional Chemical Shift Anisotropy Exchange Patterns in Blends of Polyphenylene Oxide and Polystyrene Near the Glass Transition
Authors: Inglefield P. T. , Jones A. A. , Wang P. , Zhang C.
Published: March 2011

Two dimensional solid state NMR exchange spectroscopy can be used to monitor slow motions on time scales comparable to dynamical mechanical spectroscopy. Polyphenylene oxide, carbon-13 labeled in a methyl position, was blended with polystyrene. The resulting compatible blends have single thermal glass transitions (Tg) at temperatures between those of the homopolymers. The chemical shift anisotropy line shape of the labeled methyl shows reorientational exchange at temperatures near the thermal glass transition. The 2D exchange pattern contains information on the rate and amplitude of the motion. The data indicate Brownian rotational angular diffusion of the phenylene oxide units with rates in the millisecond to second range. The motional description associated with the glass transition is contrasted with those appropriate to single component polymeric glasses. It is concluded that in the blend system the onset of motion occurs at a lower temperature relative to the DSC Tg than in the homopolymer and there is evidence for considerably more dynamic heterogeneity.
Residual Porosity and Relaxation in Polymeric Latex Films Studied by CO2 Diffusion
Authors: Balik C. M. , Said M. A.
Published: March 2011

Solubility and diffusivity measurements of CO2 have been used to measure amount of residual porosity (excess volume) and the kinetics of its removal in latex films cast from a terpolymer of butyl acrylate, vinyl acetate, and vinyl chloride. The pore volume fraction is very small, ranging from 0.5–0.05% for latex films aged from 62 hrs to 480 hrs, respectively. Long-term aging kinetics can be followed by sorbing to equilibrium at constant CO2 pressure and temperature, and following the weight loss as the sample relaxes and CO2 diffuses out. Relaxation data obtained at temperatures ranging from 25–50°C could be superimposed on a single master curve using the WLF equation. The implications these results have concerning the morphology of the residual porosity in latex films are discussed.
Free Volume Relaxation in Polycarbonate as a Function of Physical Aging
Authors: Heater Kenneth J. , Jones Phillip L.
Published: March 2011

Room temperature free volume relaxation of polycarbonate as a function of aging time at 393K has been evaluated via positron annihilation lifetime spectroscopy. Free volume response data were normalized and modeled using an expression of the Williams-Watts form. The process of physical aging is discussed in terms of the trends associated with the resultant characteristic relaxation time constants and distribution of relaxation times.
Effects of Complexation on the Glass Transition Temperature of Polymers
Authors: Roberts Michael F. , Jenekhe Samson A.
Published: March 2011

The effects of Lewis acid complexation on the glass transition temperature (Tg) of several polymers with strong intermolecular interactions was investigated. The decrease in the Tg due to GaCl3 complexation of aliphatic and aromatic polyamides was 40–600° C and 148° C, respectively, and was shown to originate from scission of the intermolecular hydrogen bonds. The reduction in the Tg due to GaCl3 complexation of rigid–chain polymers was greater that 325° C and can be explained by the mitigation of the otherwise strong van der Waals forces in the pristine polymers. Thus, the dominant effect of intermolecular interactions on the Tg of several polymers has been probed by Lewis acid complexation.
Effects of Aging on Polymerization Kinetics
Authors: Bowman Christopher N. , Peppas Nikolaos A.
Published: March 2011

A theoretical model was developed to describe the physical aging during photopolymerizations and crosslinking reactions of diacrylates and dimethacrylates. The model incorporates the strong coupling between the volume relaxation and the kinetics observed in these reactions. Model predictions are presented for the reaction kinetics, volume relaxation, radical concentration and maximum conversion as a function of light intensity and relaxation time of the polymer.
Structural Changes in Glassy Polycarbonate Due to Cyclic Loading
Authors: Liu Liang Bao , Yee Albert F. , Lewis John C. , Li Xiaowei , Gidley David W.
Published: March 2011

Glassy polycarbonate was subjected to cyclic stresses and the changes in its structure were studied by DSC, positronium annihilation lifetime spectroscopy (PALS), and small and medium angle X-ray scattering. Upon increased exposure to cyclic loading, the enthalpy overshoot near Tg increased in a manner similar to increasing physical aging. However, the “hole” size as revealed by PALS increased, unlike physical aging. SAXS reveals an increase in the short range order and the amplitude of density fluctuation. These results can be explained in a consistent manner. We conclude that mechanical loading does cause changes in the glassy structure.
Influence of Thermal History on the Glass Transition of Poly(Phenylene Sulfide)
Authors: Huo Pengtao , Cebe Peggy
Published: March 2011

PPS is increasingly interesting as a high performance polymer material. Recently, Cheng, et al. [1] reported observation of rigid amorphous phase (RAP) in the amorphous phase of semicrystalline PPS using differential scanning calorimetry. Using the heat of fusion from DSC to obtain the degree of crystallinity of the semicrystalline samples, a simple rule of mixtures was applied to calculate the change in heat capacity step. The heat capacity decreased much more than could be accounted for using the measured crystallinity. Thus, these authors assumed the existence of a rigid amorphous phase which did not become liquid-like at Tg. The ratio of heat capacity step at Tg of semicrystalline PPS to that of the purely amorphous polymer was used to find the fraction of amorphous chains that do become liquid-like at Tg. The amount of RAP was then obtained by assuming a three phase model.
The Volumetric Response of Polymeric Glasses to Complex Thermomechanical Histories: a Critical Evaluation of the Kahr Model
Authors: Greener J. , O'reilly J. M. , Ng K. C.
Published: March 2011

The KAHR model was used to predict the transient volumetric response of poly(vinyl acetate) (PVAc) and polystyrene (PS) glasses in various experiments involving controlled variations of temperature and pressure in the vicinity of the glass transition. The experiments considered include contraction following a quench from equilibrium, expansion after a temperature “jump,” and pressure-induced densification. The model parameters of PVAc were obtained by fitting experimental data via a 4-parameter Levenberg-Marquardt optimization. The optimized parameters were then used to predict the response of the material in three different experiments. The response of PS in a pressure densification experiment was also analyzed and compared with existing data. Generally, the predicted response of PVAc in the various temperature jump experiments is in excellent agreement with observation. The prediction of the response of PS in the pressure densification experiment is also in line with observation although the data for this case is limited and the results are still inconclusive.
Integrated MSM-FET Photoreceiver Fabricated on Mocvd Grown Hg1-xCdxTe
Authors: Leech Patrick W. , Gwynn Peter J. , Pain Geoffrey N. , Petkovic Novica R. , Thompson James , Jamieson David N.
Published: March 2011

We report on progress in the monolithic integration of a metal-semiconductor-metal (MSM) detector and transimpedence amplifier and of a photoconductive detector (PCD) with a metal-semiconductor field effect transistor (MESFET) in Hg1-xCdxTe. The layers of CdTe/n-type Hg1-xCdxTe were grown by MOCVD on semi-insulating GaAs substrates (2° misoriented 100). Fabrication of the devices was by an FET planar process; with a standard lift-off used to form Schottky metallization on both the interdigitated electrodes of the MSM detector (2μm width, 2μm spacing) and the gate of the MESFETs (5μm length, 100μm width). The MSM photodetectors exhibited breakdown voltages in the range 60 to 80V, a dark current of 1 Ona at 5V bias, and responsivities of > 1.0 A/W measured at 40V using CW 1.3um illumination. The integrated devices have been characterised by electrical and micro RBS techniques; the results were found to be strongly dependent on the stoichiometric x ratio of the Hg1-xCdxTe. This initial work demonstrates the suitability of Hg1-xCdxTe/GaAs structures in the fabrication of integrated optoelectronic circuits.
InAsSb Photodiodes Grown on InAs, GaAs and Si Substrates by Molecular Beam Epitaxy
Authors: Dobbelaere W. , Boeck J. De , Raedt W. De , Vanhellemont J. , Zou G. , Hove M. Van , Brijs B. , Mertens R. , Borghs G.
Published: March 2011

InAs and InAs0.85Sb0.15p-“i”-n structures were grown on InAs, GaAs and Si substrates by Molecular Beam Epitaxy. The structural quality of the layers is discussed using Transmission Electron Microscopy and Rutherford Back Scattering. The influence of the material quality on the 77 K current-voltage measurements is explained. The spectral response of the devices was measured demonstrating peak responsivities of 2.1 A/W at 3.5μm wavelength for InAs0.85Sb0.15 detectors with a 4.3 μm cut-off wavelength.
LPE Growth and Characterization of InAsSbP/In1-x GaxAs1-ySby /InAsSbP (X≥O,Y≥O) Heterostructures for Long Wavelength ( λ>3μm) Leds and Lasers.
Authors: Aydaraliev M. , Argunova T.S. , Zotova N.V. , Karandashov S.A. , Kutt R.N. , Matveev B.A. , Ruvimov S.S. , Sorokin L.M. , Stus' N.M. , Talalakin G.N. , Ioffe A.F.
Published: March 2011

The band gap of InAsSbP and InGaAsSb alloys enriched with InAs correspods to the spectral range 2.5 - 5 μm which make possible to manufacture LEDs and detectors for the second atmosphere window. Elevated hardness (see Fig.1a ) and small plasticity of the alloys results in an inversed plastic deformation process during LPE growth of InAsSbP (InGaAsSb) on InAs substrate.That is when growing graded( grad a ≈5*10−8 epilayers at elevated temperatures ( 680 - 720° C ) misfit dislocations are formed throughout the entire substrate thickness (C). Simultaneously with increasing dislocation density in InAs ( curves 1,3 ), the curvature of the structure increased within æ = 0.02-0.2 cm−1.
Low Pressure Mocvd Growth of InSb
Authors: Cunningham B.T. , Schneider R.P. , Biefeld R.M.
Published: March 2011

Low pressure (200 Torr) metalorganic chemical vapor deposition (MOCVD) of InSb has been examined through variation of the Column III (TMIn) and Column V (TMSb or TESb) precursor partial pressures. The use of lower growth pressure significantly enhanced the range of allowable Column III and Column V partial pressures in which specular morphology InSb could be obtained without the formation of In droplets or Sb crystals. In addition, a 70% improvement in the average hole mobility was obtained, compared to InSb grown in the same reactor at atmospheric pressure. SIMS analysis revealed that Si at the substrate/epitaxial layer interface is an important impurity that may contribute to degradation of the mobility. Substitution of TESb for TMSb did not result in any improvement in the purity of the InSb.
Undoped GaSb Growth by MOCVD
Authors: Su Yan Kuin , Juang Fuh Shyang
Published: March 2011

Undoped GaSb epilayers have been grown on (100) GaSb and S.I. GaAs substrates. The effects of growth temperatures and TMSb/TEGa mole fraction ratios on the epitaxial properties of surface morphology, growth rate, hole concentration and mobility (300K and 77K) have been studied. The lowest concentration 1.8x101 6 cm- 3 (77K) and the highest mdobility 1447 cm2/V.s (77K) can be obtained under V/III ratio of 6.64 at 550°C. Photoluminescence intensity was found to be a function of the V/III ratios. When V/III ratios increased or decreased beyond 6-8, the BE peaks disappeared and PL spectra became roughened.

To reduce the effects of large lattice-mismatch in highly strained GaSb/GaAs system (7% mismatch) on the electrical properties, a 10-period In0.3Ga0.7As/GaAs (60A/40A) strain layer superlattice (SLS) has been grown on GaAs substrates as a dislocation filter before the GaSb epitaxial growth. From the comparison of 77K Hall mobility of GaSb/GaAs as a function of growth temperature with that of GaSb/SLS/GaAs, it was clearly observed that the epilayers grown on SLS structures have higher mobility than those grown directly on GaAs substrates. From the TEM analysis, we observed that all dislocations propagated up to the GaSb epilayer surface in the GaSb/GaAs system but some of the dislocations bending before reaching the epilayer surface in the GaSb/SLS/GaAs system.
Properties of Pt/Ti Contacts to III-V Materials
Authors: Katz A. , Nakahara S. , Chu S. N. G. , Weir B. E. , Abemathy C. R. , Hobson W. S. , Pearton S. J. , Savin W.
Published: March 2011

Pt/Ti contact to variety of binary III-V and related ternary semiconductor materials were established. These contacts were formed by electron beam evaporation and subsequent rapid thermal processing in order to sinter the metal-semiconductor systems. The contacts to p-type InAs, GaAs, In0.53Ga0.43As, In0.52Al0.4As and Ga0.7Al0.3As were ohmic, as a result of heating at temperatures of 450°C or higher. The Pt/Ti contacts to InP and GaP displayed Schottky behavior as-deposited and preserved the rectifying nature through heat treatments, regardless of the processing conditions. The electrical properties and the microstructure evolution in these 7 systems is discussed in this paper.
Multiwafer Production of Long Wavelength Epitaxial Material
Authors: Heyen M. , Schmitz D. , Strauch G. , JÜrgensen H.
Published: March 2011

Low pressure MOVPE in a horizontal reactor has proven to be capable of yielding uniform InP, GalnAs and GaInAsP layers [1, 2]. However, the complexity of some devices as MQW lasers and HEMTs require even further improvement in thickness and compositional uniformity. This can be achieved by using the technique of sub-strate rotation to overcome gas phase depletion problems and geometry related non uniformities.
Traps in ZnS/Anodic Sulfide Film on Mercury Cadmium Telluride
Authors: Hikida S. , Kajihara N. , Miyamoto Y.
Published: March 2011

We studied the influence of visible light on the ZnS/anodic sulfide/HgCdTe interface.

We measured flatband voltage of metal-insulator-semiconductor diodes with semitransparent electrodes at 77 K. In the dark (i.e., without visible light). The flatband voltage of an metal-insulator-semiconductor diode is 0 V. We scanned visible light from 400 to 800 nm and measured the flatband voltage using the photocapacitance measurement. After an initial positive shift, the flatband voltage moved negative by as the wavelength shortened. We studied the relationship between the flatband voltage shift and photon energy using Fowler plots. Results suggest one electron trap level 1.5 eV above the valence band and two hole trap levels 1.7 and 2.3 eV below the conduction band.

ZnS/anodic sulfide films on mercury cadmium telluride, studied using photoluminescence spectroscopy, showed broad photoluminescence peaks at 1.5, 1.7, and 2.3 eV, and the edge emission of the anodic sulfide.

These results suggest that photoionization of the electron trap and two hole traps in the ZnS/anodic sulfide film causes the flatband shift.
Local Phonon Heating and Recombination-Enhanced Defect Annealing
Authors: Abakumov V.N. , Pakhomov A.A. , Yassievich I.N.
Published: March 2011

A detailed study of local phonon heating due to multiphonon recombination process is presented. Nonequilibrium distribution of defects by vibration energy is calculated taking into account the dependence of capture and emission rates on the defect energy. It is shown that multiphonon generation and recombination of electron-hole pairs stimulate diffusion of defects in energy space. The results are used to calculate the rate of recombination-enhanced defect annealing.
NDT Applications of the 3D Radon Transform Algorithm for Cone Beam Reconstruction
Authors: Sire P. , Grangeat P. , Lemasson P. , Mélennec P. , Rizo P.
Published: March 2011

The paper describes our 3D X-ray CT algorithm “RADON” using attenuation measurements acquired with a bidimensional detector. Our inversion diagram uses the first derivative of the Radon transform synthesis then its inversion. The potentiality of that new method, particularly for the large aperture, prompted us to develop an optimized software offering convenience and high performances on a modem scientific computer. After a brief recall of the basic principle of X-ray imaging processing, we will introduce the theoretical developments resulting in the present inversion diagram. A general algorithm structure will be proposed afterwards. As a conclusion we will present the performances and the results obtained with ceramic rotors examination.
Preprocessing of Ion Microtomography Data for Improved Reconstruction Quality
Authors: Weirup David L. , Pontau Arthur E. , Antolak Arlyn J. , Morse Dan H. , Bench G. , Cholewa M. , Saint A. , Legge G.J.F.
Published: March 2011

In Ion Microtomography (IMT), material densities are determined from the energy lost by ions as they pass through a specimen. For fine-scale measurements with micron-size beams, mechanical stability and precision of motion can impact the quality of the reconstruction. We describe several preprocessing procedures used to minimize imperfect specimen manipulation, including adjustment of the center of mass motion in sinograms and correction for vertical translations. In addition, the amount of noise in the reconstruction is reduced by utilizing median (as opposed to mean) ion energy loss values for density determinations. Furthermore, particular portions of the sampled image can be enhanced with minimal degradation of spatial resolution by a judicial choice of spatial filter in the reconstruction algorithm. The benefits and limitations of these preprocessing techniques are discussed.
NMR Imaging of Solids Using Imaging Instrumentation Designed for Liquids
Authors: Cory D. G. , Gravina S. J.
Published: March 2011

The possibilities of acquiring NMR images of solids with conventional imaging apparatuses are explored. To this end a multiple-pulse line-narrowing sequence is introduced which averages both homonuclear dipolar couplings and time independent linear lz, interactions such as chemical shifts and susceplibility shifts. For imaging the multiple-pulse cycle is accompanied by an oscillating magnetic field gradient which phase encodes the spatial location o each spin. The period of the gradient oscillation is matched to the period of effective field toggling such that the multiple-pulse cycle does not average to zero the gradient induced spin evolution. A small radio frequency coil of 3.0 mm i.d. is used since then only modest radio frequency (RF) power is sufficient to generate a strong RF field, and the RF homogeneity is quite good over the sample volume. The resolution of the image is not spatially uniform, but near the center the resolution is better than 100 μm and the resolution at the edges of the image is degraded by only a factor of 3 to 5. Images of solids with acceptable resolution and sensitivity can be collected by this method- with minimal setup time and difficulties.
Comparative Imaging of Liquids in Rocks by NMR and Differential X Ray CT
Authors: Jeandey C. , Casagrande J.M. , Briguet A. , Ntoutoume T. , Guillot G.
Published: March 2011

We have applied NMR Imaging and X_Ray Computerized Tomography to the study of the structural properties of rocks. Samples from different porous rocks; sandstones, granites, limestones have been successively examined by both techniques. NMR images have been obtained on water saturated samples. The spatial distribution of liquid indicates the effective porosity. By constrast, X_Ray images display the mineral content of rocks. Standard tomographs do not have the required resolution to see pores smaller than 100 μm. We used water as a constrast agent to localize porosities by “differential” CT. Comparative results are shown.
The Study of Materials Using Wavelet Image Processing Techniques
Authors: Beltrán-Del-Rŕo L. , Gónez A. , José-Yacamán M.
Published: March 2011

In this work the wavelet transform is used to process high- and medium resolution electron micrographs from small particles and their substrates. It is concluded that the edge sensitivity of the technique and its contrast enhancement capabilities are most useful in the processing of electron micrographs.
Neutron Tomography: A Survey and Some Recent Applications
Authors: Rodes E. A. , Morman J. A. , Mcclellan G. C.
Published: March 2011

A survey is given of recent developments in selected areas of neutron tomography, within the context of several applications Argonne is involved in, including high penetration of reactor-fuel bundles in thick containers (involving TREAT and NRAD facilities), dual-energy hydrogen imaging (performed at IPNS), dynamic coarse-resolution emission tomography of reactor fuel under test (a proposed modification to the TREAT hodoscope), and an associated-particle system that uses neutron flight-time to electronically collimate transmitted neutrons and to tomographically image nuclides identified by reaction gamma-rays.
NMR Imaging and the Electric Quadrupole Interaction in Solid Materials
Authors: Suits B. H.
Published: March 2011

Nuclei with a spin, 1 > 1/2, possess a nuclear quadrupole moment which can couple to the electric field gradients in a material. They can be static, leading to NMR frequency shifts, or dynamic, which can influence relaxation times. In either case, an NMR image can be made which is sensitized to changes in the electric quadrupole interaction to provide a sensitive measure of the macroscopic spatial dependence of the microscopic changes in the material. Several examples are presented. Special considerations need to be given in the case when the strength of the Zeeman interaction between the nucleus and the magnetic field and/or the rf field is small compared to the electric quadrupole interaction.
Schottky Barriers on Magnetron Sputtered a-Si:H: Depletion width Effects on Photocarrier Collection vs Bandgap and Light Soaking
Authors: Doyle James R. , Maley N. , Abelson John R.
Published: March 2011

We present a study of depletion width effects on the photocarrier collection efficiency in reactive magnetron sputtered a-Si:H films. Results are presented for as-deposited and light soaked 1.75 eV optical gap samples, and an as-deposited 1.60 eV gap film. The depletion width behavior with reverse bias is inferred from capacitance measurements. Comparison with photocurrent collection versus reverse bias voltage suggests that space charge effects can have an important role in the interpretation of collection efficiency on Schottky barriers.
Degradation Study of single a-Si:H Alloy Solar Cells
Authors: Pawlikiewicz Adam H. , Banerjee A. , Guha S.
Published: March 2011

The paper presents the experimental data of single a-Si:H cells degraded under high intensity illumination and compares them to the numerically calculated J-V characteristics of degraded a-Si:H solar cells. The cells were deposited at two different substrate temperatures. The current voltage characteristics were calculated using our simulation program which allows for accurate determination of cell response under monochromatic or global AM1.5 spectrum.

We have simulated the light-induced metastable defects (Staebler-Wronski degradation) by increasing the density of localized states. In order to test the validity of this approach we compared the calculated fill factors under AM1.5, blue and red illumination with the measured fill factors for the same light.

From the experimental data we observed mat at near room temperature (∼35°C) both cells reach saturation in degradation of fill factors under high intensity illumination. The saturation level corresponded to the minimum density of localized states (gmin) of 1.2×1017 cm-3eV-1 and is independent of the light intensity used in experiment.
The Dynamic Response of Htdrogenated Amorphous Silicon Imaging Pixels
Authors: Yorkston J. , Antonuk L. E. , Morton E. J. , Boudry J. , Huang V. , Kim C. W. , Longo M. J. , Street R. A.
Published: March 2011

The dynamic response of pixels from an a-Si:H imaging array are investigated and a model is developed to explain their observed behavior. Such arrays are under development for radiotherapy and diagnostic x-ray applications.
Correlation of Structure and Structural Changes with Photovoltaic Quality of a-Si:D,H and a-Ge:D,H Films
Authors: Norberg R. E. , Fedders P. A. , Bodart J. , Corey R. , Kim Y. W. , Paul W. , Turner W.
Published: March 2011

Deuteron magnetic resonance (DMR) resolves structures such as tightly bound D, weakly bound D, molecular HD and D2 in microvoids and trapped on nanovoid internal surfaces in plasma-deposited a-Si:D,H and a-Ge:D,H. The relative populations of these structures correlate with photovoltaic quality as characterized by photo response function ημτ in a series of deuterated a-Ge and a-Si films. It is found that photo-illumination produces DMR-detected changes in these populations. The changes, which are reversible upon a 150°C dark anneal, include a quadrupolar doublet from strained-bond configurations and a shift from metastable electronic species. The spin-lattice relaxation of most of the components follows an error-function behavior characteristic of magnetization transport under extreme inhomogeneity.
Correlation Between Structural and Photo Electrical Properties of a-Si1−xGex:H Alloy Films - New Interpretation Concerning the Preferential Attachment of Hydrogen
Authors: Schroeder B. , Leidner M. , Oechsner H.
Published: March 2011

a—Si1−xGex:H alloy films with 0 > × > 1 have been prepared by reactive co— sputtering (rf—magnetron) from separate targets. The preparation conditions which have been optimized for each composition x must be changed from a—Si:H—like (0 > × > 0.4) to a—Ge:H—like (× < 0.7) to obtain the best photoelectrical quality of the alloy material. The preferential attachment of hydrogen was quantitatively investigated by detailed ir—spectrometric studies. Its monotonic change with x is attributed to fundamental preferential attachment of hydrogen to silicon superimposed by a further preferential attachment to the respective minority alloy partner. The preferential attachment of hydrogen essentially influences the microstructure of the film and thus the material properties.
The Influence of the Bonding Structure on Disorder and Band-Tails in a-B:H
Authors: Bernhard N. , Eberhardt K. , Schubert M. B. , Bauer G. H.
Published: March 2011

A thorough investigation of plasma-CVD amorphous hydrogenated boron (a-B:H) has been conducted with the main emphasis on how in this amorphous semiconductor the variation of the coordination number in comparison to a-Si:H influences the structural disorder and density of states in the band tails. a-B:H was deposited from different concentrations of B2 H6 diluted in H2 by both DC- and RF-plasma-CVD. The influence of the change of substrate temperature, pressure, flow and deposition power on the structural, optical and electronic properties of the material was examined. Raman-scattering and IR-absorption reveal the clear non-crystallinity of the deposited films. Almost all samples show some photoconductivity with a σphoto/σdark ratio from 10-1 to 3×101. Although a strong influence of some of the deposition parameters on bandgap and refractive index, hydrogen content, dark and photoconductivity was observed, the density of states in the band tails as measured by PDS was relatively high, showing always a rather flat Urbach slope of about 180 – 220 meV. An explanation for this unexpected almost uniform huge Urbach slope might be that even in the amorphous state the behaviour of boron is still dominated by its electron deficiency character which leads to a certain amount of three centre bonds (as seen in IR-absorption) and results in comparison to amorphous hydrogenated silicon in even stronger constraints of the amorphous network and obviously in more potential fluctuations.
Transient Simulations of Amorphous Silicon Devices
Authors: Hack M. , Shaw J. G.
Published: March 2011

We have developed a numerical simulation program (MANIFEST) which calculates the time-dependent behaviour of one and two dimensional amorphous silicon devices. Our model solves the complete set of transport equations for both electrons and holes and fully includes the appropriate time dependent occupation functions for the traps in the band gap of the amorphous silicon. These traps are assumed to obey Shockiey-Read-Hall kinetics. We have simulated the transient behaviour of pin and nin diodes, both in the dark and under illumination, as well as the characteristics of thin film transistors. Our initial results are in good agreement with experimental data.
A New Device Model of Amorphous Silicon Thin-Film Transistor for Circuit Simulation
Authors: Choi Hong S. , Park Jin S. , Oh Chang H. , Joo In S. , Kim Yong S. , Han Min K. , Choi Yearn I. , Yun Jung G. , Park Won K. , Kim Woo Y.
Published: March 2011

We present a new analytical model of amorphous silicon thin-film transistor (a-Si TFT) suitable for circuit simulators such as SPICE. The effects of localized gap state distributions of a-Si as well as temperatures on the a-Si TFT performances have been fully considered in the presented model. The parameters used in SPICE, such as transconductance, channel-length modulation, and power factor of source-drain current, are evaluated from the measured current-voltage and capacitance-voltage characteristics by employing the proposed extraction method. It has been found out that the analytical model is in good agreement with experimental data at both room temperature and elevated temperature and successfully implemented in a widely used circuit simulator.
Reactive Ion Etched MO/CR Source-Drain Metallization for Amorphous Silicon Thin Film Transistors
Authors: Kwasnick R. F. , Possin G. E. , Saia R. J.
Published: March 2011

A novel two step reactive ion etch (RIE) process is described for the etching of bilayer Mo/Cr source-drain metallization on hydrogenated amorphous silicon (a-Si:H) inverted-staggered thin film transistors. The Cr acts as an etch stop during Mo etching, and is thin enough (∼3 0 nm) that only a small thickness of underlying a-Si is removed during the Cr etch. The resulting Mo/Cr profile is sloped, compared to the more vertical and somewhat uncontrolled slope that is achieved with Mo wet etch. Very similar transistor behavior was observed for both Mo wet etched and Mo/Cr reactive ion etched source-drain metallization. The major advantage of this process over wet etching of Mo source-drain is improved step coverage of subsequently deposited layers due to the less vertical sidewall slope.
Influence of the Gate Bias and Temperature on Positive Charge Generation in TFT Gate-Quality Amorphous Silicon Nitride Films
Authors: Kanicki Jerzy , Sankaran Mythili
Published: March 2011

We report on the illumination time dependence of the generation of positive charge in gate-quality nitrogen-rich amorphous silicon nitride films subjected to sub-bandgap illumination at different temperature in vacuum. The influence of film thickness and gate bias applied during illumination on the generation of positive charge is also described. We have found that a stretched-exponential function, which characterizes dispersive charge transport in silicon nitride, gives the best description of our experimental results.
Deposition and Characterization of Near “Intrinsic” μc-Si Films Deposited by Remote Plasma-Enhanced Chemical-Vapor Deposition - RPECVD
Authors: Williams M. J. , Wang C. , Lucovsky G.
Published: March 2011

Undoped films of μc-Si deposited by RPECVD are n-type with a room temperature dark conductivity of ∼6×10-4 S/cm and an activation energy of ∼0.3 eV. This is due to native donor-like defects. We report on the conductivity and photoconductivity of boron-doped μc-Si, with emphasis on low doping levels that are designed to compensate exactly these native donor-like defects. We describe the dark conductivity and the photoconductivity as functions of dark conductivity activation energy and the average boron concentration, and present a model for the photoconductivity based on band off sets between the crystalline and amorphous regions of the μc-Si.