bluuebunny/crossref_metadata_2025 huggingface dataset:
Porosity In The Microstructure Of Blended Cements Containing Fly Ash
Authors: Patel H. H. , Pratt P. L. , Parrott L. J.
Published: March 2011

The changes in porosity of OPC and an OPC-fly ash blended cement during hydration have been studied at water/solids ratios of 0.35, 0.47 and 0.59, cured for times of up to 1 year at 25°C. The porosity was measured indirectly by methanol exchange and methanol adsorption techniques and, directly, by quantitative image analysis using backscattered electron imaging in the scanning electron microscope. Measurements of porosity and of remaining anhydrous material by image analysis showed good correlation with indirect methods. Measurement of the diffusion of methanol and of the compressive strength were made in parallel with the determination of the porosity during hydration and attempts were made to relate the properties to the microstructure. For both binders the reduction of total porosity with increased reaction was small. The major change in pore structure was the subdivision of coarse pores by gel to form finer pores. Compressive strength and diffusion properties were dominated by the relative volume of coarse pores.
Evidence for Minimal Pozzolanic Reaction in a Fly Ash Cement during the Period of Major Strength Development
Authors: Diamond Sidney , Sheng Qizhong , Olek Jan
Published: March 2011

Strengths developed in fly ash concretes usually equal or exceed that of similar plain concrete after a few months, with much of the response usually attributed to “pozzolanic” reaction between ash and secondary calcium hydroxide (CH). The CH contents of pastes made with five different fly ashes were determined by DTA for periods up to six months. The CH contents found did not decrease notably over the period, and were substantially identical to that expected for plain cement pastes diluted with the same amount of inert material as the amount of fly ash used. Scanning electron microscope examination of the pastes showed only minimal evidence of reaction even up to 1 year of age, although many fly ash grains were in intimate contact with CH. Non-evaporable water contents of the fly ash pastes were substantially higher than expected at each age, suggesting that the fly ash promoted more complete cement hydration or that the hydration products formed bound substantially greater amounts of water than plain cement paste ordinarily does.
Early Stages of Oxygen Clustering and Its Influence on Electrical Behavior of Silicon
Authors: Oehrlein Gottlieb S. , Corbett James W.
Published: March 2011

Our knowledge of phenomena connected to the early stages of oxygen clusters, especially their electrical activity is reviewed. In addition to the well-known 450°C thermal donors, 'new oxygen donors', which occur in ca. 650°C annealing, have emerged in conjunction with low temperature processing for VLSI and are discussed. The existing models of thermal donors are reviewed. In a new model of thermal donor formation, thermal donors are viewed as metastable oxygen clusters which lower the compressive strain of the surrounding silicon matrix via bonding of 2p oxygen lone pair orbitals. It is shown how this bonding can result in shallow double donor states.
Transition Metal Impurities in Silicon
Authors: Weber Eicke R. , Wifhl Norbert
Published: March 2011

The properties of transition metals in silicon are reviewed, emphasizing those observations which allow conclusions to be drawn with respect to microscopic defect models. 3d metals diffuse interstitially into silicon and stay predominantly in these sites at high temperatures. 3d elements lighter than Co can be quenched into these interstitial sites, giving rise to well-established energy levels. First theoretic calculations for these ions yield promising results. Co, Ni and Cu vanish out of the interstitial solution during quenching; an appreciable fraction of Cu may form pairs. The understanding of 4d and 5d metals in silicon is much less advanced at present, even for the technologically important elements Au and Pt. Some observations indicate that for Au and Pt pair formation might as well be important.
Structural and Chemical Microanalysis of Oxygen-Bearing Precipitates in Silicon
Authors: Carpenter R.W. , Chan I. , Tsai H.L. , Varker C. , Demer L.J.
Published: March 2011

Precipitation in CZ-silicon during post-growth two-stage heat treatment has been examined using the methods of high resolution analytical electron microscopy. Electron transparent specimens prepared from these specimens, exhibited a low density of plate type precipitates on {100} planes. Microdiffraction experiments showed the precipitates to be consistently non-crystalline. Electron energy loss spectra showed that the precipitates contained oxygen, but carbon was not detected. It was found that carbon artifact absorption edges could be induced in spectra by specimen contamination in the microscope. The use of a low temperature stage eliminated this problem. Complementary characteristic x-ray microanalysis showed that metallic impurities had not segregated to these precipitates in this particular case, although this has been observed elsewhere.
Esr of Defects in III–V Compounds
Authors: Schneider Jürgen
Published: March 2011

A survey is given on deep defects in GaP, GaAs and InP identified by electron spin resonance (ESR). Defect structures to be discussed are (i) 3d transition metals, (ii) antisite defects and (iii) radiation induced centers. The relevance of such defects for the III–V materials technology will be illustrated by representative examples.
Dynamic Observation of Atomic-Level Events in Cadmium Telluride by High Resolution Tem
Authors: Yamashita T. , Sinclair R.
Published: March 2011

A conventional 120 keV high resolution TEM equipped with a TV camera has been used to make lattice resolution video recordings of cadmium telluride in the <110> orientation.The motion of dislocations and the migration of atomic species at the edge of the crystal have been studied. These processes are thought to be induced in the crystal by localized heating of the specimen by the electron beam. The observations are made on a TV monitor at a total magnification of 15 million times.
Electronic Properties of Grain Boundaries in GaAs: A Study of Oriented Bicrystals Prepared by Epitaxial Lateral Overgrowth
Authors: Salerno Jack P. , Mcclelland R. W. , Mavroides J. G. , Fan John C. C. , Witt A. F.
Published: March 2011

The electronic properties of tilt boundaries with misorientation angles ranging from 0 to 30° in n-type GaAs bicrystal layers have been investigated. The current-voltage and capacitance-voltage characteristics are consistent with a double-depletion-region model. The height of the grain boundary potential barrier remains constant while the density of grain boundary states varies with misorientation angle. Deep level transient spectroscopy has revealed the presence of two bands of grain boundary states at approximately 0.65 and 0.9 eV below the conduction band. These states are attributed to bond reconstruction at the grain boundary.
Structural Studies of Metal-Semiconductor Interfaces with High-Resolution Electron Microscopy
Authors: Gibson J. M. , Tung R. T. , Poate J. M.
Published: March 2011

We have studied interface atomic structure in epitaxial cobalt and nickel disilicides on silicon using high-resolution transmission electron microscopy. By employing UHV techniques during deposition and reaction we have grown truly single-crystalline NiSi2 and CoSi2 films on (111) Si and in the former case on (100) Si. These films are shown to be continuous to below 10Å thickness. By close control over preparation conditions, afforded by UHV, we can greatly influence the nucleation and growth of these films to the extent, for example with NiSi2 on (111)Si, of yielding continuous single-crystal films with either of two orientations as desired. Whilst in the (111) NiSi2 on Si system the interfacial structure invariably appears to well-fit a model in which metal atoms nearest to the interface are 7-fold co-ordinated, for (111) CoSi2 on Si agreement is generally better with a model involving 5-fold co-ordination of these atoms. A misfit dislocation core is also imaged. Results are discussed in the light of silicide nucleation and growth. The structure and stability of the (100) NiSi2 on Si interface is also considered.
Formation of Titanium Silicide At Atmospheric Pressure
Authors: Revesz Peter , Gyimesi Jeno , Gyulai Jozsef
Published: March 2011

Two problems connected with the growth of Ti-silicide have been investigated. It is shown if a silicon dioxide step on a single crystal of silicon covered with titanium is annealed then, following vertical growth on the silicon part, lateral growth of Ti-silicide takes place over the oxide layer. We also studied the problems of Ti-silicide growthon samples implanted with high doses of Sb, As, P, Ar and O prior to Ti evaporation.
Comparison between Thermal and Laser Annealing in Ion-Implanted Silicon.
Authors: Blosse A. , Bourgoin J.C.
Published: March 2011

N-type, 1015 −1016 cm−3 doped, Fz, Silicon has been implanted with 1 to 4 × 1012 cm−2, 100 or 300 keV, As ions. The nature and concentration of the defects has been monitored using Deep Level transient Spectroscopy as a function of the thermal treatment (in the range 500–900°C) and of the energy of the pulse (15 ns) of a ruby (0.69,μm) laser (in the range 0.3 to 0.6 J cm−2). The defects resulting from annealing by the two treatments are found to be the same. Only, for energies higher than 0.5 J cm−2, the laser treatment introduced new defects (at Ec−0. 32 eV), presumably resulting from a quenching process. Thus a laser energy below the theshold for melting and epitaxial recrystallization is able to anneal the defects produced by implantation, demonstrating that the annealing process induced by the laser pulse is not a purely thermal process but probably involves an ionization enhanced mechanism.
Modelinig of Dopant Diffusion and Associated Effects in Silicon
Authors: Fair Richard B.
Published: March 2011

Research in the area of dopant diffusion in Si has focused on identifying the specific mechanisms and point defects involved. Recent approaches include observing the effects of diffusion and doping on oxygen precipitation, stacking fault growth or shrinkage, enhanced/retarded diffusion of one dopant in the presence of another. Very few of these studies have yielded unambiguous interpretations as a result of the indirect nature of the experiments. However, taken together we can infer the relative importance of vacancies versus Si selfinterstitials in the diffusion of each dopant species.
Interface Tribology Via Nonequilibrium Molecular Dynamics
Authors: Hoover W. G. , Hoover C. G. , Stowers I. F. , Siekhaus W.J.
Published: March 2011

By borrowing ideas from control theory, Nonequilibrium Molecular Dynamics incorporates temperature, stress, and heat flux directly into atomistic, time-reversible, deterministic equations of motion. We are applying this technique to studies of surface indentation, surface cutting, friction, ablation, and condensation. Here we describe simulations of the indentation and cutting processes using two-dimensional crystals composed of a few thousand particles.
Molecular Tribometry: Recent Results and Future Prospects
Authors: Alsten John Van , Granick Steve
Published: March 2011

The method of molecular tribometry is described. Ultrathin films of liquids are confined between parallel plates, usually of atomically smooth muscovite mica, such that the apparent area of contact equals the true area of contact. This paper consists of 5 sections. First, the phenomenon of solid lubrication by liquids is described. Second, the alternative viscous response of ultrathin liquid lubricants is described; the microviscosity is considerably enhanced over that of the isotropic liquid. Third, the critical shear strength is shown to have an extreme dependence on the normal pressure. Fourth, the materials requirements for molecular tribometry are discussed. Finally, a discussion is offered of the strengths and limitations of this new tool.
Structural Studies of Sputter-Deposited MoS2 Solid Lubricant Films
Authors: Hilton Michael R. , Fleischauer Paul D.
Published: March 2011

The relationship between the morphologies and crystal structures of sputter-deposited MoS2 films and their lubricating capabilities is discussed. In particular, aspects of plastic deformation processes are presented. Scanning elecron microscopy (top surface and cross sectional), transmission electron microscopy (lattice imaging and dark field), and x-ray diffraction techniques were used to characterize film structure. The asdeposited morphology, which can be described in terms of zone models, was found to influence the initial nature of the wear debris and the loadbearing capabilities of the films. In many cases a highly deformed region confined to the surface of the films was found. Applied stress was found to reorient crystallites and to induce crystallization, with the degree of both processes being related to the initial structure of the film. Criteria are presented for selecting the film type and preparation conditions to fit various applications.
Composition of Sputter Deposited MoS2 Films During Run-in in Vacuum
Authors: Ehni P.D. , Singer I.L.
Published: March 2011

Wear tests were performed under ultra high vacuum conditions in a ball-onflat configuration on magnetron sputtered and triode sputtered MoS2 films on 440C steel substrates. The issue of material loss versus deformation of the film was investigated using energy dispersive x-ray microanalyses for mass loss determinations and Michelson interferometry to measure the deformation of the tracks. Significant deformation without material loss was found in the first 10 passes. Surface composition of the tracks and the transfer film on the ball was determined by Auger electron spectroscopy. The S/Mo ratio wasfound to increase and the O/Mo ratio was found to decrease with increased sliding distance.
Microstructure and Wear Characterization of Selflubricating Al2O3 - MoS2 Composite Ceramic Coatings
Authors: Koshkarian K.A. , Kriven W.M.
Published: March 2011

Composite ceramic coatings of alumina (A1203) containing some molybdenum disulfide (MoS2) were electro-codeposited on to Al metal substrates by a combination of anodic sparks deposition of A1203 and electrophoresis of MoS2. The microstructures were characterized by XRD, XPS, SEM, EDS, SNMS,TEM, SAD and relative wear resistance measurements. The coatings consisted mostly ofa-A1203 with some γ and βpresent as well. The coatings were porous and microcracked. SEM showed them to consist of circular “splats” which had rapidly crystallized from the molten state in areas ofdielectric breakdown in the coating. In the TEM the microstructure was seento contain “sets” of parallel, elongated grains having a single crystallographic orientation. The grains were separated by dislocated, low angle grain boundaries or microcracks. The sets intersected at irregularly curved interfaces and were mechanically interlocked. Quantitative SNMS indicated that up to 26 wt% MoS2 was incorporated in coatings fabricated from 5g\1 solutions. SEM\EDS as well as TEM\SAD\EDS identified 1-3μm particles of MoS2 incorporated into the 5g\1 solution derived coatings. These coatings exhibited a 50% lower wear rate than pure alumina coatings deposited under the same conditions.
The Evaluation of Materials for Tribological Applications
Authors: Winer Ward O.
Published: March 2011

The goal of tribo-material development is to produce materials which can beused to construct tribo-elements for use in mechanical systems and which will perform in a predictable manner. Tribo-element performance is critical in determining mechanical system reliability. In addition, tribo-elements are among the most severely taxed mechanical system elements, and require a high level of geometric accuracy and stability. Because of the wide variety of operating variables and environments, there are no universal test procedures to determine the efficacy of materials for tribological applications. Tribo-material evaluation is complex, important, and not well understood.

This paper discusses the primary environmental operating variables for different tribo-elements, the rationale for their importance and will survey how they are normally included in tribo-material evaluation. The paper will also distinguish between tribomaterial evaluation for known well defined applications as compared with the evaluation of potential tribo-materials for which the relevant application is unknown. The objective of the material scientist, in either situation, is to select and use the evaluation program involving minimum time and cost consistent with generating results leading to design decisions with confidence.

The role and nature of the many available “bench tests” will be discussed as will be the role and sophistication of thorough tribo-system simulation.

As in many areas of materials development, it is appropriate for tribo-material development to paraphrase the well known adage; “the proof of the tribo-material is in the using.”
The Bonding of Fluorinated and Hydrogenated Ethers to Metal Surfaces: A Surface Science Approach to Tribology
Authors: Walczak M.M. , Leavitt P.K. , Thiel P.A.
Published: March 2011

We report a surface science study of fluorinated and hydrogenated ethers adsorbed at a metal surface. Fluorinated ethers bond less strongly to ruthenium surfaces than the hydrogenated analogs, both for atomically-smooth and atomically-rough surfaces. For the hydrogenated ethers, 0.03 to 0.17 monolayers undergo decomposition, while fluorinated ethers do not decompose significantly.
Molecular Contact Pressure in Tribology
Authors: J.M. Georges , J.L. Loubet , A. Tonck , Lyon Ecole Centrale De
Published: March 2011

This paper is a part of a long-term study of the physics of boundary lubrication. In this regime, the shape and pressure of the film are controlled by two phenomena: first, the elastic or plastic deformation of the substrate, and second, the physical state of the film. Three physical states can be detected: the condensed solid, granular and colloidal states. A new piece of apparatus, allowing the continuous and simultaneous measurement of static and dynamic forces, displacement and current voltage between a sphere and a plane, is used to determine surface forces and rheological properties of the film. The viscous and elastoplastic behavior of the interface is given by a transfer function. The lubricant we studied was calcium dialkylbenzenesulfonate solution containing encapsulated calcium carbonate and dissolved in pure dodecane (volume fraction 5.10-). While a pure dodecane solution behaves like a Newtonian fluid, with its bulk viscosity, the colloidal solution shows an increase of the viscosity near the steel surfaces suggesting adsorption. After 8 hours, each steel surface is covered with a layer, which includes an almost complete “monolayer” of calcium carbonate particles, with some incomplete layers on top of it. During indentation of the layer the repulsive forces vary exponentially with the thickness of the layer. This result is consistent with two effects: the consolidation of the layer during the process and scaling factors such as the Hill number (a/D).
Universal Aspects of Brittle Fracture, Adhesion, and Atomic Force Microscopy
Authors: Banerjea Amitava , Smith John R. , Ferrante John
Published: March 2011

The universal relation between binding energy and interatomic separation was originally discovered for adhesion at bimetallic interfaces involving the simple metals Al, Zn, Mg, and Na. We show here that the same universal relation extends to adhesion at transition metal interfaces. Adhesive energies have been computed for the low index interfaces of Al, Ni, Cu, Ag, Fe, and W using the Equivalent Crystal Theory (ECT) and keeping the atoms in each semi-infinite slab fixed rigidly in their equilibrium positions. These adhesive energy curves can be scaled onto each other and onto the universal adhesion curve. We have also investigated the effect of tip shape on the adhesive forces in the Atomic Force Microscope (AFM) by computing energies and forces using the ECT. While the details of the energy-distance and force-distance curves are sensitive to tip shape, all of these curves can be scaled onto the universal adhesion curve. This means that although absolute magnitudes of adhesive forces in the AFM cannot be determined without knowing the geometry of the tip, the shape of the force-distance curve is universal, at least for distances changing normal to the substrate.
Nondestructive Evaluation for Materials Characterization
Authors: Green Robert E.
Published: March 2011

In recent years classical nondestructive testing techniques for detecting macroscopic defects have been augmented by more sophisticated nondestructive evaluation methods for characterizing the microstructure and associated physical and chemical properties of materials. This paper will briefly describe several such nondestructive evaluation methods developed in the Center for Nondestructive Evaluation (CNDE) at The Johns Hopkins University.
Gel Point Determination in Curing Polydimethylsiloxane Polymer Networks by Longitudinal Ultrasonic Waves
Authors: Shefer A. , Gorodetsky G. , Gottlieb M.
Published: March 2011

The formation of well characterized poly-dimethylsiloxane networks has been studied by means of an acoustic interferometer. The hydrosilation reaction used to form these networks was followed by infra red spectroscopy. The relative changes in velocity of the ultrasonic longitudinal waves propagating through the system are found to be very sensitive to gelation and to the density of crosslinks. Due to our simultaneous kinetic and ultrasonic studies it was possible to relate the changes in acoustic properties of the curing system directly to the cure state.
Laser-Ultrasonics for Materials Characterization
Authors: Monchalin J.-P. , Aussel J.-D. , Héon R. , Bussière J. F. , Bouchard P.
Published: March 2011

Several material properties and microstructural features can be determined or monitored by measuring ultrasonic velocity and/or ultrasonic attenuation. Conventional techniques which use piezoelectric transducers for generation and reception have several limitations, in particular in the case of materials at elevated temperature, of samples of complex shapes, and in regard to the detection bandwidth. These limitations are eliminated by laser-ultrasonics, a technique which uses lasers for generation and detection of ultrasound. Following a review of the various principles and methods used for generation and detection, we discuss the use of laserultrasonics for velocity and attenuation measurement. Examples of application to various materials are presented.
Ultrasonic Real-Time Monitoring of Slip Cast Cake Thickness
Authors: Jarman David , Gesing Adam J. , Farahbakhsh Bahram , Burger Gene , Huchins David , Mair H. D.
Published: March 2011

An ultrasonic method was developed for real-time monitoring of cake thickness during the casting of an alumina slip. The technique uses pulse-echo ultrasound to measure the time of flight and hence the thickness of the cast layer. Variations on the method are applicable to both production process control and to the fundamental studies of slip casting process kinetics.
Nondestructive Depth Profiling of a Diffuse Interface
Authors: Sinclair Anthony N. , Dickstein Phineas , Graf Michael A.
Published: March 2011

A numerical solution of the one-dimensional wave equation is used to find the characteristics of wave propagation in a non-homogeneous medium. The solution is used to determine the magnitude and phase of the reflection coefficient at a diffuse interface. The result is found to be strongly dependent on sonic frequency. Comparison is made between theoretical calculations and measurements of the reflection coefficient at a copper-to-nickel diffusion bond.
Neutron Diffraction Measurements of Strain and Texturre in Welded Zr 2.5 wt.Z Nb Tube
Authors: Holden T. M. , Hosbons R. R. , Root J. H. , Ibrahim E. F.
Published: March 2011

The axial and tangential components of residual strain have been measured through the region of an electron beam weld in Zr 2.5 wt.% Nb tube. Marked changes in grain orientation in the tube occur as far away as 10 mm from the weld-centre. In particular a large fraction of the grains which had an [0002] direction aligned tangentially in the original tube were reoriented with this direction aligned axially. These grains showed high (5 x 10-4) tensile strain. Compressive strains (-5 to - 10 x I0-4) were measured in the region 5 - 10 mm from the weld-centre in those grains with [1010] directioný aligned axially. The hoop straint vary from tensile (maximum 5 x 10-4) to compressive (maximum -5 x 10-4) as a function of distance from the weld centre.
Determination of Thermally and Mechanically Induced Internal Stresses in Metal-Matrix Composites by X-Ray Methods
Authors: Yazici Rahmi , Bagnoli K. E. , Bae Y.
Published: March 2011

In this study the progression of thermally and mechanically induced internal strains (stresses) in metal-matrix composites was investigated by X-ray methods. The materials studied were whisker-reinforced 2124 Al-SiC(w) and 6061 Al- SiC(w) composites. X-ray diffractometry was used to measure thermally induced stresses on samples cycled from ambient to 280°C. Significant variations in residual stress values were observed in the matrix depending on the location and direction of the measurements with respect to the whisker orientation. The determined stress states of the as-processed and the thermally cycled samples were evaluated with continuum models. The microstrains in composites induced during processing and tensile loading were also investigated by nondestructive means. Individual grains of the matrix were analyzed by rocking-curve measurements using a modified X-ray doublecrystal diffractometer. The relationship between the plastic deformation induced by applied loads and the progression of the microstrain/excess-dislocation values was determined.
X-Ray Diffraction for Nondestructive Characterization of Polycrystalline Materials
Authors: Ruud C. O. , Weedman S. D.
Published: March 2011

X-ray diffraction has long been the mainstay for materials characterization in the laboratory. This characterization includes the determination of phase composition, residual stress, microstrain, grain size, and crystallographic texture of polycrystalline metals, ceramics, and minerals. The analytical capabilities of XRD techniques have been expanded recently by the application of computer control to data collection and processing. These capabilities include the identification of irregularities in metals and ceramics that are caused by processing and fatigue damage, as well as the apriori prediction of processing anomolies. While the above applications have been largely restricted to the laboratory, the possibility for exploitation of the nondestructive nature of x-ray diffraction for inprocess evaluation of materials is now being realized. The availability of computer-controlled position-sensitive x-ray detectors can now provide rapid, non-contacting, in-process interrogation of materials. The examples of nondestructive characterization illustrated in this paper will be those that can be used for process control and/or damage assessment.
Acoustoelastic Determination of the Fourth Order ODF Coefficients and Application to R-Value Prediction
Authors: Daniel D. , Sakata K. , Jonas J. J. , Makarow I. , Bussiere J. F.
Published: March 2011

The fourth order orientation distribution function (ODF) coefficients of textured low carbon steel sheets were determined nondestructively from the anisotropy of the velocity of Lamb (So) and SHO plate waves measured using electromagnetic acoustic transducers (EMATs). The three coefficients (C411, C412, C413) are calculated from five velocity measurements made in three directions in the rolling plane of the sheet using the Hill approximation by an iterative numerical method. The coefficients were also determined from Young's modulus measurements based on a resonance technique and are compared to those obtained ultrasonically. The comparison with coefficients determined from X-ray diffraction pole figures permits adjustment of the C411 coefficient and then very good agreement is obtained. The plastic strain ratios (R-values) of the steel samples are predicted from the adjusted coefficients using a series expansion method based on the Taylor theory of crystal plasticity. These are compared with experimental measurements and again good agreement is displayed.
X-Ray Absorption Spectroscopic Studies of Catalytic Materials
Authors: Via G. H. , Sinfelt J. H. , Meitzner G. , Lytle F. W.
Published: March 2011

X-ray absorption spectra (XAS) contain information in the LIII near-edge region on filling of the absorber d-band, and in the extended fine-structure region on the physical environment of the absorber. We report here an evaluation of the effect on platinum LIII edges of preparation in clusters with a high fraction of Pt atoms at the surface. We also report the effects on platinum and rhenium LIII edges from addition of copper. These effects are surprisingly small.

We have also re-evaluated extended x-ray absorption fine-structure spectra (EXAFS) of platinum and rhenium in alumina-supported platinum-rhenium bimetallic catalysts. A novel feature of this new analysis was the requirement that interatomic distances, coordination numbers, and Debye-Waller type factors maintain certain physically necessary relationships among themselves. This procedure decreased the number of free variables and increased the amount of information returned by the analysis.
Time-Resolved X-Ray Absorption Spectroscopy: Strengths and Limitations
Authors: Fontaine A. , Dartyge E. , Itie J. P. , Jucha A. , Polian A. , Tolentino H. , Tourillon G.
Published: March 2011

X-ray Absorption Spectroscopy has proved to be a powerful tool to elucidate a huge number of questions in materials science. Great interest exists in time-resolved experiments achieved with extreme energy resolution and energy scale stability to take a full benefit of the strong correlation between the stereochemical environment of the absorbing atom and the exact shape and position of the absorption edge.

Fast energy dispersive X-ray spectroscopy allows in-situ observations with data collected in a short time. Nowadays the main limitation concerns very low-concentration samples since It is no longer possible to use the dispersive geometry because detection of the signal via the decay channels is no more possible.
Reflection-Extended-X-Ray-Absorption-Fine-Structure Spectroscopy at the Carbon K-Edge
Authors: Long G. G. , Black D. R. , Tanaka D. K.
Published: March 2011

The carbon K-edge Reflection-Extended X-Ray Absorption Fine Structure (refl-EXAFS) spectra from graphite, diamond and glassy carbon have been investigated. There is good phase shift transferability between the two well-known bonding types in diamond and graphite, provided that appropriate inner potential corrections to the K-edge energy E. are made. The model spectra from diamond and graphite were used to investigate the nature of glassy carbon. It was found that, for the particular form of glassy carbon used in this study, the bonding more closely resembled sp3 than sp2. This result is preliminary pending our evaluation of the influence of surface oxygen.
Dispersive X-Ray Synchrotron Studies of Pt-C Multilayers
Authors: Rodricks B. , Lamelas F. , Medjahed D. , Passos W. Dos , Smither R. , Ziegler E. , Fontaine A. , Clarke R.
Published: March 2011

We demonstrate the simultaneous acquisition of high-resolution x-ray absorption spectra and scattering data, using a combination of energy-dispersive optics and a twodimensional CCD detector. Results are presented on the optical constants of Pt and on the reflectivity of a platinum-carbon multilayer at the LIII absorption edge of Pt.
X-Ray Microprobe for the Microcharacterization of Materials
Authors: Sparks C. J. , Ice G. E.
Published: March 2011

The unique properties of X rays offer many advantages over those of electrons and other charged particles for the microcharacterization of materials. X rays are more efficient in exciting characteristic X-ray fluorescence and produce higher fluorescent signal-to-background ratios than obtained with electrons. Detectable limits for X rays are a few parts per billion which are 10−3 to 10−5 lower than for electrons. Energy deposition in the sample from X rays is 10–3 to 10–4 less than for electrons for the same detectable concentration. High-brightness storage rings, especially in the 7 GeV class with undulators, will have sources as brilliant as the most advanced electron probes. The highly collimated X-ray beams from undulators simplify the X-ray optics required to produce submicron X-ray probes with fluxes comparable to electron sources. Such X-ray microprobes will also produce unprecedentedly low levels of detection in diffraction, EXAFS, Auger, and photoelectron spectroscopies for structural and chemical characterization and elemental identification. These major improvements in microcharacterization capabilities will have wide-ranging ramifications not only in materials science but also in physics, chemistry, geochemistry, biology, and medicine.
Soft X-Ray Absorption Microscopy of Surfaces with Synchrotron Radiation
Authors: Harp G. R. , Tonner B. P.
Published: March 2011

As a spectroscopic technique, x-ray absorption near-edge structure (XANES) of core-levels using synchrotron radiation is in wide-spread use for the determination of the molecular composition of solid surfaces. A common detection method measures the yield of secondary electrons, which is proportional to the x-ray absorption coefficient for sufficiently high photon energy. In the experiments reported here, we show how the secondary electrons emitted as a result of photoabsorption can be used to generate a magnified image of the sample surface, with fundamental spatial limits determined by the deBroglie wavelength of the emitted electrons. Contrast in the secondary electron spatial distribution contains both topographical and chemical information about the sample surface. The use of tunable synchrotron radiation enables us to separate these contributions to the microscopic image, and to spatially resolve surface chemical composition as reflected in micro-XANES spectra.
Epitaxial Layers of FCC FE on CU(001)
Authors: Willis R. F. , Morra R. , d'Almeida F. , Mankey G. , Kief M.
Published: March 2011

Metastable films of fcc Fe epitaxed to Cu(001) show unusual ferromagnetic properties(1). Changes in the lattice volume occur with film thickness in the 1 to 5 monolayer range, reflecting changes in the magnitude of the spin moments and the magnetic exchange coupling. The associated uniaxial strain is manifest in strong magnetic anisotropy, layer by layer lattice expansion, phonon softening, and surface layer atomic reconstructions. We present LEED results of a detailed structural investigation, neutron reflectance measurements of the spin moments, surface magneto-optic Kerr effect studies of the magnetic anisotropy, and angle resolved photoemission of the electronic states. The observed effects are due to the strain-related kinetic energy associated with the formation of the atomic spin moments, predicted by spin-density-functional calculations of bulk fcc Fe(2).
The Argonne Advanced Photon Source
Authors: Moncton David E.
Published: March 2011

Argonne National Laboratory is preparing to build a new synchrotron radiation source, the 7-GeV Advanced Photon Source (APS), that will provide the world's most brilliant x-ray beams for research. The APS will produce x-rays for materials research, condensed-matter physics, chemistry, and biological and medical studies by researchers from industry, universities, and national laboratories.
Bonding in Thin Epitaxial CoSi2 Films on Si(100)
Authors: Chambliss David D. , Rhodin T. N. , Rowe J. E. , Yalisove S. M.
Published: March 2011

Epitaxy of CoSi2 layers on Si crystal surfaces can be strongly influenced by growing appropriate template layers. The electronic structure of thin (∼7Å) epitaxial CoSi2 films on Si(100) has been studied with angle-resolved photoemission to investigate atomic bonding in the layers and at their boundaries. Most Co atoms in the layers are in a CoSi2-like environment, including those Co atoms near the free surface. Cobalt atoms at the Si-CoSi 2 interface seem to have fewer Si neighbors.
Valence Band Electronic Structure of Cleaved Iron Oxide Single Crystals Studied by Resonant Photoemission
Authors: Lad Robert J. , Henrich Victor E.
Published: March 2011

Synchrotron radiation has been used to perform resonant photoemission measurements across the 3p→3d photoabsorption threshold from cleaved FexO (x ≃0.945), Fe3O4, and α-Fe2O3 single crystal surfaces. The resonant enhancement of the Fe 3d photoelectrons allows the Fe 3d-derived final states in the valence band to be distinguished from the overlapping O 2p states. Using well-characterized single crystals, the distributions of Fe 3d-derived states associated with the ferrous (Fe2+) and ferric (Fe3+) cations have been identified. The Fe 3d-derived states are found to extend about 18 eV below the Fermi level in each oxide, which can be attributed to a significant amount of hybridization between the Fe 3d and O 2p orbitals.
Photoemission Exafs from InP(110) and Al/InP(110)
Authors: Choudhary K. M. , Mangat P. S. , Kilday D. , Margaritondo G.
Published: March 2011

Photoemission EXAFS (PEXAFS) studies of InP(110), InP(110) + 1 Å Al and InP(110) + 3 Å Al are presented. In each case, photoemission from the P 2p core-level was monitored using a cylindrical mirror analyzer by a two-point CIS (constant-initial-state spectroscopy) method in 150–280 eV photon energy range. The data were analyzed by conventional Fourier analysis procedures using the theoretical phase function of McKale et al. plus absorber phase function of Teo and Lee. No diffraction effect other than EXAFS is observed. For the clean InP(110) surface, the PEXAFS results show relaxation (contraction) of the surface in excellent agreement with the LEED results. But a small contraction in the P-P bond length (surface unit mesh parameter, a0) has also been measured, which was not reported in the LEED studies. For the InP(110) surface covered with 1 Å Al, metal (cluster)-induced surface structural changes in the substrate are determined which include removal of relaxation of the surface unit mesh in combination with change in the P-In bond length within the surface unit mesh. At the 3 Å Al-coverage on the InP(110) surface, the interface resembles AlP.
Bond Selective Chemistry with Photon-Stimulated Desorption
Authors: Yarmoff J. A. , Joyce S. A.
Published: March 2011

Photon stimulated desorption of fluorine ions from silicon surfaces was studied via excitation of the Si 2p core level with synchrotron radiation. These results showed that the process is chemically selective in that the removal of a fluorine ion from a silicon species in a given oxidation state can be enhanced by tuning the photon energy to the excitation wavelength corresponding to a transition from the 2p core level of the bonding atom to the conduction band minimum. This process was studied as a possible means for the production of surfaces with selected compositions of species. The results of selective exposures of fluorinated surfaces to monochromatized radiation indicated that secondary desorption processes and the inherent chemistry of the surface reactions can override the effects of selective desorption. Other possibilities for selective surface reactions via core-level excitations are discussed.
Polarized X-Ray Absorption Studies of Oxide Superconductors
Authors: Alp E. Ercan , Mini S. M. , Ramanathan M. , Veal B. W. , Soderholm L. , Goodman G. L. , Dabrowski B. , Shenoy G. K. , Guo J. , Ellis D. E. , Bommanavar A. , Hyun O. B.
Published: March 2011

Polarized X-ray absorption studies have been carried out at the Cu K-edge to study the effect of Sr doping in La2CuO4 and oxygen doping in YBa2Cu3O6+x. These measurements help to elucidate the transitions giving rise to the absorption edges. We offer an explanation of the polarization shifts of features in terms of the results of our embedded cluster calculations of electronic structure.
Photoluminescence measurement of sidewall damage in etched InGaAsP/lnP and GaAs/AIGaAs microstructures
Authors: Grabbe P. , Scherer A. , Kash K. , Bhat R. , Harbison J. , Florez L. , Koza M.
Published: March 2011

We report the first investigation of the effect of dry etching parameters on the sidewall carrier recombination rate of GaAs/AIGaAs and lnPilnGaAsP microstructures. Surface recombination was measured as a function of ion voltage and etching time. The increase in recombination rate due to etching can be reversed by subsequent chemical removal of the immediate sidewall layer. By monitoring the recovery in recombination rate as a function of the amount of sidewall layer removed, the effective damage depth is inferred.
Comprehensive Investigation of Traps in GaAs/A1GaAs Heterostructures and Superlattices by DLTS
Authors: Papaioannou G. , Kiriakidis G. , Georgakilas A. , Christou A.
Published: March 2011

The electron traps of GaAs/AlGaAs heterostructures or superlattices (S.L.) have been investigated in a series of device structures which ranged from simple Schottky diodes to high electron mobility transistors. For the S.L. structure traps investigated, emission into the El miniband as well as A1GaAs trapping was considered. In simple heterostructures such as HEMTs, DLTS investigation of electron trapping from the 2DEG channel revealed a number of new traps, which were previously undetected with CTS (Current Transient Spectroscopy) investigations of the 2DEG. Interface traps in GaAs/AIGaAs heterojunctions were also investigated and distinguished from previously reported traps.
Molecular Beam Epitaxial Growth and Characterization of GaAs on Sapphire and Silicon-on-Sapphire Substrates
Authors: Humphreys T. P. , Miner C. J. , Parikh N. R. , Das K. , Summerville M. K. , Posthill J. B. , Nemanich R. J. , Sukow C. A.
Published: March 2011

Epitaxial GaAs layers have been grown by molecular beam epitaxy on (1012) sapphire and silicon-on-sapphire substrates. The grown layers were characterized by optical and transmission electron microscopy; Rutherford backscattering/channeling of 2.1 MeV He+ ions; Raman spectroscopy; Hall mobility measurements; photoluminescence spectroscopy and current-voltage measurements from metal-semiconductor contacts. The extensive microstructural, electrical and optical analysis of the GaAs layers indicates that the films deposited on silicon-on-sapphire are superior to those grown directly on (1012) sapphire substrates.
Mechanisms of Self-Diffusion and of Doping-Enhancement of Superlattice Disordering in GaAs and AlAs Compounds
Authors: Tan T.Y. , Gösele U.
Published: March 2011

An understanding of the mechanisms of self-diffusion and of interdiffusion in the compound materials GaAs and AlAs may be arrived at byt noting the effects of (i) charge, (ii) As pressure, and (iii) point defect supersaturation, on the doping enhanced superlattice disordering phenomena. The Ga self-diffusion (and hence Ga-Al interdiffusion) is dominated by the triply-negatively-charged Ga (or Al) vacancy, , under intrinsic and n-doping conditions. Under p-doping, a positively charged Ga self-interstitial , with m not known, contributes to the Ga(AI) diffusion process. Less is known for the group V element diffusion, but the As vacancy (VAs) should be contributing under intrinsic and n-doping conditions while the As selfinterstitial (LAs) may be contributing under p-doping. The contribution of a defect pair may also be involved under p-doping.
Studies of In0.53Ga0.47As/InP Superlattice Mixing and Conversion
Authors: Schwarz S.A. , Mei P. , Hwang D.M. , Schwartz C.L. , Venkatesan T. , Palmstrøm C.J. , Stoffel N.G. , Bhat R.
Published: March 2011

Sealed ampoule Zn diffusions into an unstrained In0.53Ga0.47As/InP superlattice are observed to preferentially induce cation (In, Ga) interdiffusion. The extent of interdiffusion is monitored in these studies by SIMS (secondary ion mass spectrometry). In some cases, Zn entirely displaces In in the InP layers forming an In1−xGaxAs/Zn3P2 superlattice. Under still more stringent conditions, all In and Ga is replaced, resulting in a Zn3As2/Zn3P2 superlattice. These structures are capable of supporting considerable strain due to the absence of grown-in defects. TEM (transmission electron microscopy) micrographs of several samples reveal defect free highly strained layers with thicknesses exceeding the predicted critical values. A high dose Zn implant was examined in which mixing proceeded until the Zn concentration dropped below a threshold concentration of approximately 1020 cm−3 during the anneal. These results, in total, strongly support a kickout mechanism for Zn induced mixing. Si diffusion was observed, in one case, to induce comparable cation and anion interdiffusion, thereby reducing the layer bandgap disparity, as opposed to Zn which increases the difference in layer bandgaps. Almost no interdiffusion was induced by Si diffusion from MBE (molecular beam epitaxy) polycrystalline Si films, due either to the very high resultant Si concentrations or to the capping effect of the film. The data suggest that both anion and cation site defects play a role in the Si induced mixing process.
Doping Study of Se into AlGaAs Layers Grown by MBE, and their Application to HEMT Structures
Authors: Maed T. , Ishikawa T. , Kondo K.
Published: March 2011

We studied doping Se into AlGaAs layers using PbSe as a dopant source for molecular beam epitaxy (MBE). Good controllability and abruptness equivalent to that of Si-doping were obtained. Se-doping was successfully applied to HEMT structures with reduced DX center concentrations. The two dimensional electron gas (2DEG) characteristics of these structures were comparable to those of Si-doped structures.
On the Origin of the New Electron Traps Induced By Rapid Thermal Annealing in GaAs Using Capping Proximity Technique.
Authors: Marrakchi G. , Chaussemy G. , Laugier A. , Guillot. G.
Published: March 2011

Rapid Thermal Annealing (RTA) effects on generation or annihilation of deep levels in GaAs have been investigated by Deep Level Transient Spectroscopy (DLTS). Capping proximity technique using three annealing configurations are employed to anneal Liquid Encapsulated Czochralski (LEC) and Bridgman (B) substrates, or Vapor Phase Epitaxy (VPE) and Liquid Phase Epitaxy (LPE) layers. The RTA treatment is performed from 800 to 950°C for two annealing times ( 3 and 10s).

The DLTS data show that the evolution of the native defects depends on the GaAs growth method and also the annealing configuration. We observe the appearance of two new electron traps named RL1 and RL2 induced by the RTA process which depend on the kind of substrate: RL1 and RL2 are created in LEC material while only RL1 is detected in B material. A general comparison of our results with others reported in the literature show that these new electron traps are related to the change of stoichiometry at the GaAs surface and also depend on the existence of specific native defects in the starting GaAs material. It is proposed that the creation of RL1 is related to the EL6 native defect and discuss a possible physical origin for this level. We also propose that RL2 and EL5 originate from the same defect and suggest the divacancy VGaVAs as a possible origin for this trap.
Transient Thermal Analysis for Rapid Thermal Processing of GaAs
Authors: Yang F. K. , Pien S. J. , Kwor R.
Published: March 2011

A thermal analysis is performed to simulate the rapid heating process for ion implanted GaAs with consideration of the doping effect. The results are for cases with various concentrations and thicknesses of doping layer. Also studied are the heating processes for silicon dioxide capped GaAs. The effects of the thickness of the oxide layer are discussed. The magnitude of the temperature differences across the wafer is addressed. The present analysis considers xenon-arc lamps and tungsten-halogen lamps as the light sources.