bluuebunny/crossref_metadata_2025 huggingface dataset:
Broad Bandwidth Study of the Topography of the Fracture Surface of Energetic Materials
Authors: Lanzerotti M. Yvonne D. , Pinto James J. , Wolfe Allan
Published: March 2011

The Z,X coordinates of the fracture surfaces of TNT have been measured witha stylus profilometer. The fracture surfaces of the material under study are obtained by accelerating prepared samples in anultracentrifuge. When the tensile or shear strength is exceeded a fracture surface is obtained. Usingdiamond and sapphire styli the topography of the fracture surface has been studied from a wavelength of 1.0 micron to nearly 1.0 centimeter. The powerspectra have been calculated from the data using a prolate spheroidal data window in the horizontal space domain prior to the employment of the fast Fourier transform algorithm. The power spectra are found to decrease with increasing spatial frequency. Peaks are observed in the low frequency region of the power spectra and indicate that much of the fracture is occurring atgrain boundaries.
Exploring Failure Mechanisms of Lubricated 52100 Steel Contacts in High Vacuum and Dry Air
Authors: Dugger Michael T. , Chung Yip-Wah
Published: March 2011

A vacuum chamber was designed for studying tribological properties of materials under pressures of 5xlO8 Torr to one atmosphere. The chamber is equipped with a pin-on-disk tribometer, in-situ Auger\X-ray photoelectron spectroscopies, a sputter-ion gun and a windowless solid-state X-ray detector. In this paper, we present results of a study using 52100 steel balls sliding on flat disks of the same material in vacuum and in dry air as a function of normal load. The contacts were lubricated with a synthetic hydrocarbon oil (poly-a-olefin). Failure is defined as the point at which the coefficient of friction increases rapidly above the steady state value.

As expected, failure occurs much sooner in vacuum than in dry air. Surface analysis (Auger and XPS) shows direct evidence of the occurrence of high temperature flashes on the surface, which allows the formation and maintenance of a thick oxide in the presence of an adequate supply of oxygen. In addition, a brown film is formed in the vicinity of the wear track for tests performed in dry air, while this film is absent in vacuum. The brown film appears to be a combination of iron oxide and oxidized hydrocarbon from XPS measurements. Results of these studies suggest that the maintenance of an oxide is associated with extended contact life in these studies.
Tribology in Slow Rolling Bearings
Authors: Kingsbury E.
Published: March 2011

Wear has been found in the Hertz tracks of fluid lubricated, high quality angular contact ball bearings which spin too slowly to generate an elastohydrodynamic lubricating film. Often a taper section or profile of the track shows a “W” or a “U” shaped groove. A mechanism is proposed to account for these shapes.

This wear has been detected by destructive long term life tests in expensive bearings. A bench test is described which gives accelerated results on easily rejuvenated plates. Connections between the ball on plate tester and any angular contact bearing are outlined.

Ball on plate tests using two perfluorinated and one synthetic hydrocarbon lubricant are interpreted in terms of a slow buildup of an electrically insulating, chemically derived film on the Hertz track. Details of the film buildup and its wear protection ability are specific to each lubricant.
Surface Modification for Tribology with Pvd Processes: Problems and Prospects
Authors: Ramalingam S.
Published: March 2011

The last two decades have seen substantial progress in the development of physical vapor deposition processes and in ion implantation technologies to modify the surface properties of engineering materials. Surface modification to engineer surfaces for tribological applications has become possible. Hard coatings are now in wide commercial use in tooling applications both to reduce wear and to extend the product life. However, the use of wear resistant coatings in engineered parts and components is yet to become significant. Some of the problems inhibiting wider use of surface modification in tribological applications are discussed in this paper. Recent developments in arc coating to overcome the discrete interface problem associated with low temperature PVD are described. It is shown that the creation of graded interfaces is now feasible. Results from a study involving the multi-layer deposition of titanium and nickel from a single, composite cathode are presented and discussed. It is shown that the prospects for increased use of surface modification to improve the characteristics of tribological components have been enhanced.
Energetics of Bcc-Fcc Lattice Deformation in Iron
Authors: Krasko Genrich L , Olson G. B.
Published: March 2011

The lattice deformation of the BCC-FCC martensitic transformation in iron can be described as a continuous change of the c/a parameter of the body-centered tetragonal (BCT) lattice from c/a=1 (BCC) to c/a=√2 (FCC). Along this deformation path, the total energy (as a function of volume), the enthalpy (as a function of pressure), the pressure-volume relations--both for nonmagnetic (NM) and ferromagnetic (FM) states--were calculated using the ab initio LMTO method. The ground-state magnetic properties: ferromagnetic contributions to the total energy and magnetic moments, were found by making use of the Stoner theory of itinerant ferromagnetism, rather than spin-polarized calculations. This circumvents the difficulties of using the traditional local spin-density approximation which failes to describe correctly the energetics of iron phases. The Stoner exchange parameter, I, was calculated from the linear response theory for each c/a as a function of volume. Then a constant enhancement factor, β, was introduced and the new Stoner parameter, βl, as used in all the calculations. The factor β was found by fitting the equilibrium atomic volume of the FM BCC phase to its experimental value. No other adjustments of any quantities were performed. The calculations revealed a somewhat unusual behavior of enthalpy along the deformation path. Instead of a double-well curve with a barrier maximum somewhere at 1 < c/a < √2, the enthalpy of the NM phase exhibits a monotonic decrease with c/a, the BCC modification being unstable with respect to the shear deformation. Moreover, up to a certain c/a (depending on pressure), the nonmagnetic BCT phase is also unstable with respect to spontaneous magnetization. Ferromagnetism stabilizes the BCT phases. However, the FM FCC phase is unstable with respect to shear deformation. The enthalpy curve along the deformation path then has a cusp corresponding to a first-order phase transition between ferromagnetic and nonmagnetic states accompanied by an appreciable volume discontinuity. The bulk modulus, the magnetic moments and the BCC-FCC enthalpy differences are in good agreement with the available experimental data.
Electron-Phonon Coupling Strength of Specific Phonons from First Principles Lapw Calculations
Authors: Krakauer H. , Cohen R. E. , Pickett W. E.
Published: March 2011

Electron-phonon matrix elements, phonon linewidths and mode coupling strengths are being calculated for La2-xMxCuO4 (M-divalent cation, for paramagnetic x-0.0 and for x-0.15 in a rigid band picture) from first principles local density calculations. The change in potential due to a particular phonon mode is calculated from the difference of self-consistent one-electron potentials, and appropriate Fermi surface averages are carried out for selected modes, allowing us to obtain the phonon linewidth due to the electron-phonon interaction, and the corresponding coupling strength λQ. Here we establish the numerical accuracy within the dual representation of the potential used in the Linearized Augmented Plane Wave (LAPW) method. Evaluations of phonon linewidths and mode coupling strengths are presented for Al and Nb and compared with previous information on these modes. We present preliminary results for the full matrix elements and coupling of the La2CuO4 oxygen planar X-point breathing mode, and compare with a simpler approximation.
Theory and Calculation of the Thermal Conductivity of Amorphous Si
Authors: Feldman Joseph L. , Allen Philip B.
Published: March 2011

Vibrations of amorphous Si are represented by three available 216 atom models and the forces of Stillinger and Weber. It is shown how the Kubo formula for thermal conductivity can be evaluated “exactly” assuming harmonic vibrations, making only finite system-size errors. The results are rather insensitive to the particular model for the coordinates of the atoms and support a “shunt resistor model” for the thermal conductivity which fits data for glasses very well.
Enhanced and Retarded Diffusion of Shallow Impurities in Silicon
Authors: Nichols C.S. , Walle C. G. Van De , Pantelides S.T.
Published: March 2011

We have carried out systematic state-of-the-art calculations using density-functional theory, norm-conserving pseudopotentials, and large supercells in order to investigate the diffusion mechanisms of B, P, As, and Sb in Si under both equilibrium and non-equilibrium concentrations of intrinsic point defects. In addition, we have developed a theory for the non-equilibrium concentrations of the relevant diffusing species from which expressions for the activation energies may be derived. In equilibrium, we find that vacancies and self-interstitials mediate the diffusion of B, P, and As with comparable activation energies, but we show from our non-equilibrium diffusion calculations that these impurities have a dominant interstitial component. Sb diffusion, on the other hand, is mediated primarily by vacancies. We also find that the direct exchange mechanism plays only a minor role in all cases.
Growth Kinetics of Grain-Boundary Induced Melting: A Molecular-Dynamics Study
Authors: Phillpot S. R. , Lutsko J. F. , Wolf D. , Yip S.
Published: March 2011

The growth kinetics of melting nucleated at a high-angle twist boundary in silicon are investigated using molecular dynamics. Melting is found to be a two-stage process. In the first stage order is lost within a single plane at the interface and the density of the solid increases to that of the liquid. In the second stage the atomic coordination changes and an isotropic liquid is formed.
High-Temperature Behavior of Grain Boundaries from Embedded Atom Method Molecular Dynamics Simulation
Authors: Lutsko J. F. , Wolf D. , Phillpot S. R.
Published: March 2011

The behavior of a metallic grain boundary at high temperatures is studied using an embedded atom potential. A recently developed molecular dynamics code is used which allows the simulation of an isolated grain boundary at temperatures as high as the bulk melting point. The stability of the boundary below the melting point is studied and compared with earlier investigations which have suggested the existence of a “premelting“ transition. It is found that the boundary migrates at high temperature but remains well defined up to the bulk melting point. In contrast to simulations of ideal crystals, it was not possible to superheat the grain boundary due to the nucleation of bulk melting at the boundary.
Electrostatic Models of Relaxation at Metal Surfaces
Authors: Marcus P. M. , Jiang P. , Jona F.
Published: March 2011

The physical basis for electrostatic models of relaxation at metal surfaces, including the meaning of the two parameters of the modified point-ion or α model, is discussed. The empirical α parameter is shown to produce agreement with experiment and to arise from the non-uniformity of the fixed background of electronic charge around the ions. An explicit non-uniform model of the background charge is defined which is shown to be equivalent to the successful α model and provides an example of a pure electrostatic model without empirical parameters.
The Self Energy Approach for Calculation of Quasiparticle Energies in Materials Systems
Authors: Hybertsen Mark S.
Published: March 2011

A self energy approach directly taking into account the many-body nature of the electron-electron interaction is described which gives an excellent account of the quasiparticle band energies in semiconductors and insulators. The self energy approach provides a crucial link between structural models and spectroscopic probes of materials systems. Applications to bulk semiconductors, semiconductor surfaces and short period superlattices are described. A model for the screened Coulomb interaction can reduce the amount of computation required. Applicability of bulk self energy results to more complex systems, e.g. surfaces, is discussed.
Applications of Positron Annihilation to the Monitoring of Fatigue Damage and Creep in Technological Components
Authors: Allen A J , Coleman C F , Conchie S J , Smith F A
Published: March 2011

This paper reviews the use of positron annihilation methods for technological applications, particularly the use of positron annihilation gamma ray lineshape analysis for the non-destructive assessment of static deformation, machining processes, high cycle fatigue and creep in metal and alloy componen:s. The paper includes description of a transportable lineshape analysis system recently developed for field applications.
NDE Observations of Hydrogen Effects in 4340 Steel
Authors: Shim In-Ok , Byrne J. G.
Published: March 2011

Cathodic charging of hydrogen into 4340 steel produces drastic deterioration of mechanical properties such as the notch tensile strength, depending on current density, charging time, and the poison used as an inhibitor of hydrogen recombination and bubble formation at the specimen surface. Fusion of charged samples permitted hydrogen content to be measured and revealed a linear increase in the latter with charging current density. The change in the Doppler spectrum sharpness parameter Δ(P/W) deviates negatively with cathodic charging time but inversely with the charging current density (fugacity). Thus a low-fugacity hydrogen charging appears merely to screen existing positron trap sites, whereas a high-fugacity charge also creates new defect traps. This would result in a lesser net screeninig effect which would be seen as a smaller negative deviation in Δ(P/W) as observed. For cumulative charging, however, one finds oscillatory behavior in (P/W) as in earlier cumulative charging experiments with Ni. This behavior indicates that hydrogen screening of positron traps was followed by new positron trap site creation and that this sequence of events occurred repeatedly and in that order.
Assessment of Creep Damage by NDT
Authors: Willems Herbert H.
Published: March 2011

Residual lifetime analysis of power plant components requires information on the degree of degradation of the material. In case of hightemperature creep, material damage can be related to cavity formation or to the accumulated creep strain. At present, only metallographic replication technique is widely used for in-service inspection to detect creep cavitation. Other NDT-techniques like ultrasonic velocity and electrical resistivity, which have potential for detection of low pore concentrations, are being developed for practical application. The use of capacitive strain gages yields encouraging results for the long-time monitoring of creep deformation. Potential and limits of these NDT-techniques together with industrial needs for creep damage assessment are reviewed.
X-Ray Diffraction Determination of Metallurgical Damage in Turbo Blower Rotor Shafts
Authors: Porter John F. , Morehouse Dan O. , Brauss Mike , Hosbons Robert R. , Root John H. , Holden Thomas
Published: March 2011

Studies have been ongoing at Defence Research Establishment Atlantic on the evaluation of non-destructive techniques for residual stress determination in structures. These techniques have included neutron diffraction, x-ray diffraction and blind-hole drilling. In conjunction with these studies, the applicability of these procedures to aid in metallurgical and failure analysis investigations has been explored. The x-ray diffraction technique was applied to investigate the failure mechanism in several bent turbo blower rotor shafts. All examinations had to be non-destructive in nature as the shafts were considered repairable. It was determined that residual stress profiles existed in the distorted shafts which strongly indicated the presence of martensitic microstuctures. These microstructures are considered unacceptable for these shafts due to the potential for cracking or in-service residual stress relaxation which could lead to future shaft distortion.
Measurements of Strain Induced Resistivity by the Eddy-Current Decay Method
Authors: Theodore Hartwig K.
Published: March 2011

The eddy-current decay method developed by Bean for electrical resistivity measurements is well-suited for bulk metal characterization studies. The technique can be applied to investigations of low temperature plastic strain in pure aluminum.
Quantitative NDE Applied to Composites and Metals
Authors: Heyman Joseph S. , Winfree William P. , Parker F. Raymond , Heath D. Michele , Welch Christopher S.
Published: March 2011

This paper reviews recent advances at LaRC in quantitative measurement science applied to characterizing materials in a nondestructive environment. Recent demands on NDE have resulted in new thrusts to achieve measurements that represent material properties rather than indications or anomalies in a background measurement. Good physical models must be developed of the geometry, material properties, and the interaction of the probing energy with the material to interpret the results quantitatively.

In this paper are presented NDE models that were used to develop measurement technologies for characterizing the curing of a polymer system for composite materials. The procedure uses the changes in ultrasonic properties of the material to determine the glass transition temperature, the degree of cure, and the cure rate. A practical application of this technology is a closed feedback system for controlling autoclave processing of composite materials.

An additional example is in the area of thermal NDE. Thermal diffusion models combined with controlled thermal input/measurement have been used to determine the thermal diffusivity of materials. These measurements are remote, require no contact with the material under test and thus have interesting promise for NDE applications.
Difficulties in Evaluating Aging in High Voltage Underground Cables From in Situ Measurements
Authors: Crine Jean-Pierre
Published: March 2011

The techniques used to evaluate HV cable aging during service are reviewed. It is concluded that none gives a satisfying evaluation of cable condition.
Application of Ultrasonic Techniques to Study the Properties of Silicone Elastomers in High Pressure Gas Media
Authors: Briscoe Brian J. , Zakaria Salman
Published: March 2011

Polymers absorb large quantities of gas under high pressure. This process is usually accompanied by a significant volumetric strain and also by changes in the mechanical properties of the sample. We will describe how these properties may be studied by using an ultrasonic technique. The sorption and volumetric changes are progressive in nature following the application of an incremental increase or decrease in ambient pneumatic stress. These techniques are also used to follow the time dependent changes in both the linear strain and the mechanical properties of the system. Data will be cited for a range of nitrogen gas pressures up to 27 MPa at 20°C for a virgin Poly-dimethylsiloxane (PDMS) elastomer and for its composite with glass filler to exemplify the experimental and analytical procedures. The final section of the paper shows how the same techniques may be used to monitor the inception and progressive development of internal cracks during certain ambient gas decompression profiles.

The information obtained provides a basis for better material selection and for the specification of the service life of particular materials in hostile environments.
The Role of NDE in Global Strategies for Materials Synthesis and Manufacturing
Authors: Thompson D. O. , Gray T. A.
Published: March 2011

During the past several years a number of design-centered “global” approaches have been offered that deal both with materials synthesis and with the manufacture of materials into finished products. Although the structure and constituent components of these approaches differ because of their different end purposes, they share major dependencies upon design, theoretical modeling, extensive computations, and confirming measurements using various NDE techniques. Materials-by-Design (MBD) is an example of these approaches that is focused on the synthesis of materials. As noted by Eberhard[l], a principal purpose of Materials-by-Design is to produce materials with prescribed macroscopic material properties by designing and controlling material structures at the atomic and molecular levels. At the other end of the spectrum, Unified Life Cycle Engineering (ULCE)[2] is an example of a “global” model for manufacturing. In this case, emphasis is placed upon the development of ways to predict the total set of important properties of a product–performance, quality, reliability, maintainability, and life cycle costs–at the designer's board. Taken together, these approaches offer the opportunity for designercontrolled materials with specified material properties to be fabricated into components of specified performance, quality, reliability, and cost. Even though this combination represents an idealistic vision which may never be perfectly realized, the potential payoff is so large that even imperfect realization may be worth a significant investment. Efforts in these directions can now be made because of the convergence of theoretical, instrumental, and computational techniques.
Microfocus Radiographic Characterization of Materials and Components for High Performance Applications
Authors: Cotter D J. , Koenigsberg W. D. , Dunn E. M. , Abdollahian M.
Published: March 2011

Results are presented from several studies where microfocus radiography has been applied to provide feedback necessary to improve reliability and performance of materials and components. Improving the reliability of advanced silicon nitride ceramics through the use of NDE was studied by exploring the relationship between process-related defects, radiography results, and fracture of test samples. Research in the areas of structural and electronic ceramic joining has been aided by monitoring the effects of process modifications with real-time microfocus radiography and computer- based image processing.

Microfocus projection radiography was used to nondestructively examine a large quantity of silicon nitride modulus of rupture test bars for internal defects. Failure stress prediction was attempted using a fracture mechanics model and quantitative NDE data, and compared to actual failure stress.

In-process NDE of silicon nitride ceramic to Incoloy 909 metal brazed test samples was performed. Correlation between NDE results, optical microscopy, and destructive mechanical strength levels of samples is discussed.

Microfocus x-ray imaging was used to monitor the process of bonding microwave power transistors to metallized BeO ceramic substrates. Nonuniform distribution of the eutectic bond was readily detectable, thereby providing feedback for process improvement. Comparison is made between x-ray, optical, and infrared images.
Ultrasonic Characterization of Thin Adhesive Bonds
Authors: Dickstein P. , Sinclairw A. N. , Segal E. , Segal Y.
Published: March 2011

A series of nondestructive and destructive tests were performed on samples of aluminumto-aluminum bonded plates. The specimens featured a range nominal thickness of the adhesive layer from 0.0 up to 0.5 mm. It was found that a commercial bondtester was inappropriate for assessing the thickness of the adhesive in this range. However, the frequency peak of an ultrasonic echo signal from the adhesive layer was a reliable indicator of bond thickness. It is proposed that nondestructive assessments of the bond thickness could serve as an indicator of the longterm resistance of the adhesive to water ingress and bond degradation.
Nondestructive Evaluation of Thin Film Microstructures by Picosecond Ultrasonics
Authors: Maris Humphrey J. , Grahn Holger T. , Tauc Jan
Published: March 2011

We describe a technique by which ultrasonic measurements can be made in the picosecond time domain. A light pulse (duration of the order of 0.1 psec) is absorbed at a surface, thereby setting up an elastic stress. This stress launches an elastic pulse into the interior. The propagation of this strain, including its reflection at interfaces within a microstructure, is monitored through measurements of the time-dependent changes of the optical reflectivity. These measurements are made using a time-delayed probe pulse. In these experiments the spatial length of the elastic pulses can be as short as 50 Å. We can therefore use this technique to perform a nondestructive ultrasonic evaluation of thin-film microstructures. We describe here results we have obtained which demonstrate the application of the method to the study of the mechanical properties of thin films, the geometry of microstructures, and the quality of bonding at interfaces.
Materials Properties Characterization in Fossil-Fuel Power Plants
Authors: Gehl S. M. , Viswanathan R. , Townsend R. D.
Published: March 2011

Significant changes in microstructure occur in many fossil plant components that operate for long times at elevated temperatures. Some examples include hydrogen damage in steam-generating boiler tubes, carbide coarsening in superheater tubes, creep cavitation in the heat-affected zones of thick-section weldments, and temper embrittlement in turbine rotors and disks. Quantitative estimates of the remaining useful lives of components affected by these damage mechanisms require that the degree of damage be determined and related to the life-limiting mechanisms.

The paper discusses recent progress in the development and field demonstration of nondestructive techniques for characterizing the damage types listed above. This research has produced several products that have achieved or are close to commercial status. The research has also helped to define some of the limitations related to access, sensitivity, and signal interpretation of the nondestructive techniques. The paper discusses how these limitations can often be mitigated by using several nondestructive techniques in concert to obtain a more complete picture of material condition or by removing small specimens for detailed laboratory analysis.
Occupation of Distorted Cu(1) Sites by Co and Fe in Y1Ba2Cu3O7−δ
Authors: Bridges F. , Boyce J. B. , Claeson T. , Geballe T. H. , Tarascon J. M.
Published: March 2011

Small perturbations of the structure and composition of the 90K superconductor Y1Ba2Cu3O7−δ (YBCO) have profound effects on its superconducting properties [1]. In an effort to understand the interaction between the structure of YBCO and its superconducting properties, we have made an extensive investigation of YBCO doped with Fe and Co, using x-ray absorption spectroscopy.
Some Industrial Applications of Grazing Incident Exafs Techniques
Authors: Dring I. S. , Oldman R. J. , Stocks A. , Walbridge D. J. , Falla N. , Roberts K. J. , Pizzini S.
Published: March 2011

An instrument to undertake grazing incident EXAFS has been developed. This is discussed along with some applications of its use on industrially important systems.
White Beam Synchrotron Topographic Studies of the Effects of Localized Stress Fields on the Kinetics of Single Crystal Solid State Reactions.
Authors: Dudley Michael
Published: March 2011

White Beam Synchrotron Topography has been used to determine the role of localized stress fields in the solid state polymerization of single crystals of the diacetylene PTS. Results indicate that the stress fields due to grown in dislocations can accelerate local reaction kinetics in thermally induced polymerization reactions, although no such effects were previously observable in photolytically or radiolytically induced reactions. Results are analyzed in an analogous fashion to the treatment of the nucleation of solid state phase transformations at dislocations. Good agreement was found between approximate theoretical treatments and experimental observation. The response of the monomer crystal to the inhomogeneous stresses generated as a result of inhomogeneous reaction and the implications regarding local reaction kinetics are discussed in detail.
In Situ Study of the Bonding of Impurities in Metal-Impurity-Metal Laminate Composites
Authors: Barrera E. V. , Heald S. M. , Marcus H. L.
Published: March 2011

The local structure of interface or near interface impurity elements has been observed by means of extended x-ray absorption fine structure spectroscopy (EXAFS). Multilayered samples were prepared using reactive ion sputtering, electron beam evaporation , and molecular beam deposition methods with vacuum conditions ranging from 10−5 to 10−9 Pa. The interface layers of titanium, gallium, and arsenic were deposited in partial to multiple atom layers alternating with 5 to 10 nm thick matrix layers of nickel, cobalt, or aluminum. Oxide phases, atoms in solution, and local ordering were identified. Ti oxides and silicon arsenide were used as standards for the EXAFS analysis. Auger electron spectroscopy complemented the EXAFS analysis.
X-Ray Scattering above 100KeV
Authors: Hastings J. B.
Published: March 2011

Conventional x-ray scattering studies have been limited to photon energies (wavelengths) in the 5 to 20 KeV (approx. 2A to 0..5A) regime. With these energies absorption lengths limit the volume of illumination to the first tens of microns of samples. If it were possible to use x-rays of very high energies, true bulk (tens of millimeters) samples could be studied. The availability, intensity and resolution possible with high energies will be discussed and their role in the expanding field of x-ray scattering presented. Preliminary studies at the Cornell High Energy Synchrotron Source (CHESS) will form the basis of these discussions.
Fluctuating Interfaces: a Series of Synchrotron X-Ray Scattering Studies of Interacting Stacked Membranes
Authors: Safinya C. R.
Published: March 2011

In this paper we concentrate on fluctuation phenomena encountered in interacting multilayered fluid membranes using synchrotron x-ray scattering as the primary tool. These systems consisting of surfactant or lipidic surfaces, are prototype models for understanding the statistical behavior of fluctuating surfaces embedded in three-dimensions. In elucidating the nature of fluid membranes we stress a unique intrinsic property: in contrast to usual surfaces with finite shear moduli, where surface tension plays a central role, the free energy of these essentially tensionless surfaces is governed by their geometrical shape and its fluctuations. We present data in a new regime of stability for very dilute and flexible membranes with interlayer separations of order hundreds of Angstroms. This is in contrast to most rigid membranes where the interlayer interactions are dominated by detailed microscopic interactions such as hydration and van der Waals. We show that the stability of these dilute lamellar phases is associated with violent out-of-plane fluctuations of the membranes giving rise to an effectively large long-range repulsive interaction theoretically elucidated by Helfrich. Because of its entropic origin, this interaction is universal and we present data for two different surfactant systems. Finally, we show that this new regime is distinct from the classical regime in which largely separated membrane sheets are stabilized because of their mutual electrostatic repulsion.
Convection Effects in Epitaxial Reactors: an Experimental and Theoretical Study
Authors: Chinoy P. B. , Agnello P. D. , Ghandhia S. K.
Published: March 2011

An experimental and theoretical study has been undertaken of the effects of natural and forced convection in horizontal epitaxial reactors. The epitaxial growth of GaAs was used as the experimental vehicle for this study. A mathematical model for mass, momentum and energy transfer in the reactor was developed. Excellent correlation between modeled and experimental results was demonstrated over a wide range of reactor pressures and susceptor geometries. Recirculation of hot gases, caused by natural convection, was found to result in a strong pressure dependence of growth rate at higher susceptor slopes. Low reactor pressures have been shown to be a more effective way to eliminate recirculation than high gas flow rates.
X-Ray Diffraction Analysis of Heteroepitaxial Cd1-yZnyTe on GaAs
Authors: Johnson S. M. , Ahlgren W. L. , Smith M. T. , Johnston B. C. , Sen S.
Published: March 2011

X-ray diffraction techniques were used to evaluate Cd1-yZnyTe grown on GaAs substrate orientations of {100}2°, {111}, {012}, and {123}. High-quality layers having compositions at or close to the CdTe and ZnTe binary end points can be grown on GaAs, but most of the ternary compositions have extremely broad rocking curves. Layers grown on {123} and {012} were found to have large tilts toward {111} about <121> that varied systematically with the lattice mismatch; this is consistent with the mismatch being accommodated by the formation of a low-angle tilt boundary at the interface. {111} layers were found to be twinned, and thus {100}2° and {123} appear to better suited for vapor-phase epitaxial growth (VPE). High-resolution x-ray diffractometer measurements showed that the lattice mismatch is almost entirely taken up by plastic deformation, and only a small tetragonal distortion was measured. CdTe was distorted more than ZnTe, and a greater distortion was measured for layers grown on {100}2° than on {111}, in agreement with estimates made using bulk elastic constants.
Atomic Abruptness and Smoothness at Heterointerfaces: Fact or Fiction?
Authors: Ourmazd A. , Kim Y.
Published: March 2011

It is now common to claim the fabrication of heterointerfaces, which are atomically flat over distances in the micron range. However, when chemical lattice imaging and digital pattern recognition are combined to examine quantitatively individual semiconductor heterointerfaces of the highest quality, substantial atomic scale roughness is observed. In this paper we review the application of chemical imaging and pattern recogntion techniques to the characterisation of heterointerfaces at near-atomic resolution, and discuss the possible ways the results can be combined with optical measurements to give an overall picture of interfacial roughness.
Defects Related to Mixing Behavior of Highly Silicon-Doped GaAs/AlAs Superlatitices
Authors: Theodore N. D. , Carter C. B. , Mei P. , Schwarz S. A. , Harbison J. P. , Venkatesan T.
Published: March 2011

The mixing of highly silicon-doped GaAs/AlAs superlattices as a result of annealing has been investigated by transmission electron microscopy and secondary ion mass spectrometry. As silicon doping-levels were raised in this study to 1019 cm−3 and 1020 cm−3 defects such as prismatic dislocation loops and Si-rich precipitates were observed to occur in the superlattices upon annealing. A correlation has been observed between the presence of particular defects and the inhibition of dopant-enhanced superlattice mixing.
Heteroepitaxial Growth of High Quality GaAs Films on Rapid-Thermal-anealing Processed CaF2/Si(511) Structures
Authors: Asano Tanemasa , Ishiwara Hiroshi , Furukawa Seijiro
Published: March 2011

Heteroepitaxial growth of CaF2 films on (511)Si and GaAs films on CaF2/Si(511) structures is investigated. CaF2 films and GaAs films are grown by vacuum evaporation and molecular beam epitaxy, respectively. Ion channeling measurements and replica transmission electron microscopy show that CaF2 films having good crystalline quality and surface steps can be formed by annealing at 900°C for 30 sec after the growth at 550° C. GaAs films having smooth surfaces and good crystalline quality can be grown on the annealed CaF2/Si(511) structures.
High Quality GaAs on Si and its Application to a Solar Cell
Authors: Ohmachi Yoshiro , Kadota Yoshiaki , Watanabe Yoshio , Okamoto Hiroshi
Published: March 2011

Epitaxial growth using thermal annealing and a strained layer superlattice is studied to obtain high-quality GaAs device layers on Si substrates. Crystalline quality of GaAs-on-Si is found to improve with thermal cyclic annealing at temperatures higher than the growth temperature and cooling down to 300°C. It is also found that the optimum InGaAs/GaAs strained layer superlattice buffer structure is one whose total thickness is several times the calculated critical thickness for the average In-mole fraction of the SLS buffer. Configurations and structures of dislocation reductions are ex-amined by TEM observations. A GaAs solar cell is successfully constructed and is found to show total area efficiencies of 18.3% under AM 0 and 20.0% under AM 1.5 conditions.
Plasma-Assisted Epitaxial Growth of GaAs on SI
Authors: Gao Qing Zhu , Hariu Takashi , Ono Shoichi
Published: March 2011

Low temperature cleaning process of Si surface and the subsequent epitaxial growth of GaAs on Si by Plasma-Assisted Epitaxy in hydrogen plasma are described. As the rf power applied to excite the plasma is increased, the temperature for both cleaning and epitaxial growth processes can be reduced. Then GaAs epitaxial layers were directly grown on Si at 440°C.
The Effects of Capless Face-to-Face Annealing Temperature and Time on the Properties of Silicon Implanted Gallium Arsenide
Authors: Paz Oded
Published: March 2011

Maintaining As overpressure during capless post-implantation annealing through the use of the face-to-face proximity configuration has proved to be a reproducible technique with less process parameters to control than the alternative techniques of capped or arsine annealing. An investigation of carrier mobility and dopant activation as a function of annealing temperature resulted in an optimum annealing temperature of 840 °C with activation improving for 9 min heat-up time as compared to a 14 min heat-up time. An increase in activation with anneal time during isothermal annealing was also observed. Dopant redistribution during annealing was modeled with an experimentally derived diffusion coefficient of 2×10−14 cm2/sec. This value is close to the diffusion coefficient published for capped annealing. Dopant redistribution in the near-surface (1000 Å) region was verified using SIMS. Based on presently available data there is no evidence for similar dopant redistribution during capless arsine annealing and this redistribution probably occurs whenever excess vacancy generation/redistribution is taking place, as during capped annealing and during proximity annealing.
Depth Oscillations of Planar Channeling Yields in InP and GaP for Lattice Location Applications.
Authors: Swanson M.L. , Parikh N.R. , Sandhu G.S. , Frey E.C. , Zhanc Z.H. , Chu W.K.
Published: March 2011

For compound semiconductors with the diamond structure, (111) planar channel walls contain different atomic species when viewed from different sides; thus under channeling conditions, the yields of ions backscattered from the different species oscillate with depth in opposite senses for ion beams directed towards the different channel sides. We have studied this effect for 2 MeV He ions in a (111) channel of InP crystals. The application of this channeling phenomenon to the determination of the lattice sites of solute atoms was demonstrated for implanted In and Sb atoms at different depths in GaP.
New Growth Chemistries and Techniques in Metal-Organic Vapor Phase Epitaxy
Authors: Kuech T. F.
Published: March 2011

The metal-organic vapor phase epitaxy (MOVPE) technique is perhaps themost versatile of the conventional III–V growth epitaxial systems. This versatility stems from the wide variety of chemical precursors available for the growth and doping of the films. Two examples of this versatility, carbon doping and selective epitaxy, are presented. Future progress within this technology will continue to be driven by the development of new chemistries.
Channeling of Shallow Si Implants Into GaAs as a Function of Tilt and Rotation Angles
Authors: Hovel Harold J. , McKoy T. E. , Mitcheli J. M. , Scilla G. , Moorea S. J. , Cardone F.
Published: March 2011

The effects of tilt and rotation angle on implant channeling are explored for Si implants into (100)-oriented GaAs substrates using Monte Carlo simulations, SIMS profiling, capacitance profiling, and Hall measurements. It is shown that the 7° tilt angle often used to prevent axial channeling is not large enough, and 11–13° angles are required to obtain the sharpest and most reproducible implant profiles. Rotation angles have a much smaller effect on the profiles as long as the beam incidence is kept away from the < 110 > direction.
Study of Layer Disordering in MeV Si Implanted GaAs/AlGaAs Superlattices.
Authors: Chen Samuel , Lee S.-Tong , Braunstein G. , Rajeswaran G.
Published: March 2011

Layer intermixing in MeV Si-implanted quantum well superlattices (SLs) has been studied by transmission electron microscopy, secondary ion mass spectrometry and Rutherford backscattering spectroscopy. Molecular beam epitaxially grown GaAs(200Å) - Al0. 5Ga0.5As(200Å) SLs were implanted with 1 MeV Si+ at doses between 3 × 1014 and 1 × 1016/cm2. The implanted SLs were either furnace annealed at 850°C for 3 hr or rapid thermally annealed at 1050°C for 10 sec, both under GaAs proximity capping conditions. Totally mixed regions were observed only for the SLs implanted with 1 × 1016 Si/cm2 and then furnace annealed at 850°C for 3 hr. For the same dose, the RTA annealed SLs only showed slight layer intermixing. At lower doses, no appreciable intermixing was detected in either furnace or RTA annealed samples. By contrast, under either annealing condition extensive intermixing has been demonstrated for lower energy (220 keV) implantation, but at doses almost two orders of magnitude lowerl XTEM showed that in all the annealed samples, a defect-free zone existed in the near-surface region, followed by a band of secondary defects, with the maximum density located at about 1 μm below the surface. In the disordered samples, the position of the intermixed layers correlated with the defect band maximum. Under both annealing conditions, Si concentration profiles only showed slight broadening, and they correlated with the distribution of secondary defects as well as with the depth of the intermixed layers. The effects of dynamic annealing and surface on the implantation energy dependence, i.e., MeV vs. keV, of layer intermixing are discussed.
Effects of Rapid Thermal Anneals on Boron Implanted GaAs
Authors: Bowman R. C. , Adams P. M. , Herman M. H. , Buttrill S. E.
Published: March 2011

Raman scattering, double-crystal x-ray diffraction, and electron beam electroreflectance have been used to assess the damage produced in undoped (100)-GaAs by boron ion implants and the influence of post-implant anneals. Both conventional furnace and rapid thermal annealing treatments were found to remove much of the lattice strain created by the implants. However, considerable disorder also remains after these anneals.
Disordering of Si-Implanted GaAs-AlGaAs Superlattices by Rapid Thermal Annealing
Authors: Lee S.-Tong , Braunstein G. , Fellinger P. , Rajeswaran G.
Published: March 2011

We have studied the disordering phenomenon in GaAs-AlGaAs superlattices induced by Si implantation followed by rapid thermal annealing. Layer intermixing has been detected in superlattices implanted with 220 keV Si+ at doses ≥ 1×l015 cm−2 and annealed at 1050°C for 10 s. The amount of intermixing saturates with time after 10 s annealing, whence the lattice damage caused by the implantation is predominantly annealed out. The transient disordering is attributed to defect-induced layer intermixing occurring during the annealing of the implantation damage. Concurrent with the disordering, Si diffusion is observed to be minimal, which indicates that layer intermixing due to Si diffusion and other impurity effects lags behind that due to defects in the time scales of the present experiment.
Electrical Damage Introduced in GaAs by Reactive Ion Etching using CH4/H2 mixture
Authors: Collot P. , Gaonach C. , Proust N.
Published: March 2011

Electrical characterizations (I–V,C–V) of TiPtAu/n-type GaAs Schottky diodes were performed in order to investigate the electrical damage introduced by CH4JH2 RIE. The effective barrier height measured according to the thermionic conduction model decreases from 0.79 eV to 0.53 eV after RIE carried out at 1.3 W/cm2.

Recovery of the control I–V characteristics requires a wet chemical removal of 50 nm of the dry etched surface.

Doping profiles, derived from conventional C–V analysis at 80 K and 300 K, show a decrease in free carrier concentration within 500 nm from the surface. Hall measurementsbetween 4 K and 300 K show an increase in carrier mobility after RIE. These effects are essentially attributable to chemical neutralization of the silicon dopants by hydrogen. Thermal annealing at 360°C leads to an almost complete recovery of the electrical activity and of the control Schottky barrier height.
The Effect of Ar Sputtering on the Disordering of AlGaAs/GaAs Multiple Quantum Wells
Authors: Shieh C. , Colvard C. , Mantz J. , Alavi K. , Engelmann R.
Published: March 2011

The effect of Ar sputtering, in combination with different dielectric cappings, on the disordering of AlGaAs/GaAs multiple quantum wells was studied. It was found that the combination of Ar sputter etch and SiO2 capping provided the strongest enhancement in disordering. This effect generates enough change in refractive index to produce an index guided laser.
A Comparative Study of Thin-Film and Bulk Reaction Kinetics and Diffusion Path: the Ir/GaAs System
Authors: Schulz Kevin J. , Chang Y. Austin
Published: March 2011

Control of the structure and chemistry at the interfaces of compound semiconductors is essential for the commercial use of these materials in electronic and optical technologies. This can only be achieved when the governing thermodynamics and kinetics of interfacial reactions are understood. Based primarily on the experience of metal/Si interactions, however, a prevailing belief was born that thin-film reactions follow a separate set of thermodynamic and kinetic “rules” which are different from bulk reactions. The intent of our work has been to not only characterize metal/GaAs contact reactions but also to rationalize these reactions with equilibrium phase diagrams and bulk metal/GaAs diffusion couple experiments. Through this approach, a better understanding of thin-film and bulk differences has been obtained.

The Ir/GaAs system is used as an example. Phase formation and reaction kinetics were studied for 30 nm Ir films on (100) GaAs using TEM, XTEM, and AEM. Bulk diffusion between 0.25 mm thick Ir foil and (100) GaAs wafers was studied with SEM and electron probe microanalysis (EPMA). The diffusion paths and kinetics were the same for thin-film and bulk. The phase sequence Ir/IrGa/IrAs2/GaAs formed for all diffusion couples. Reaction kinetics were parabolic with an activation energy of 3.0 eV for both thin-film and bulk, and the data was colinear in an Arrhenius plot. Reacted layer morphology in both cases was layered. The effects of grain size, crystallographic texturing, and the relative diffusivities of the components on the reaction mechanisms in bulk versus thin-film reactions are considered.
Cobalt-Germanium Contacts to n-Type GaAs Electrical and Metallurgical Aspects
Authors: Genut M. , Eizenberg M.
Published: March 2011

The correlation between the microstructure and phase formation, and the electrical properties for the Co/GaAs, Co/Ge/GaAs and Ge/Co/GaAs systems have been studied. The microstructural analysis was carried out by transmission electron microscopy, and the component redistribution was determined by Auger electron spectroscopy. The electrical properties (Schottky barrier height and contact resistivity) were studied by means of current-voltage and capacitance-voltage measurements.