bluuebunny/crossref_metadata_2025 huggingface dataset:
Spatial Inhomogeneities of the Luminescence and Electrical Properties of Mbe Grown GaAs on Si
Authors: Reid G.A. , Nauka K. , Rosner S.J. , Koch S.M. , Harris J.S.
Published: March 2011

Spatial homogeneity of the luminescence and electrical properties of gallium arsenide films grown directly on silicon substrates (GaAs/Si) by molecular beam epitaxy (MBE) have been investigated with microscopic scanning photoluminescence (PL), cathodoluminescence (CL), electron beam induced current (EBIC), and scanning deep level transient spectroscopy (SDLTS). It was found that GaAs/Si exhibits a highly nonuniform lateral distribution of speckled appearance in CL and PL images. These centers are also responsible for short minority carrier lifetimes as determined by EBIC. The observed nonuniformities appear to be a fundamental material property which is not altered by post-growth annealing. Correlations between the luminescence and electrical inhomogeneities and structural defects will be discussed.
Strain in Graded Thickness GaAs/Si Heteroepitaxial Structures Grown with a Buffer Layer
Authors: Nemanich R.J. , Biegelsen D.K. , Street R.A. , Downs B. , Krusor B.S. , Yingling R. D.
Published: March 2011

The strain in MBE GaAs/Si heterostructures grown with a buffer layer are characterized by Raman scattering and luminescence. A graded thickness sample was produced by slowly moving a shutter in front of the sample during the growth. Raman scattering and luminescence measurements made as a function of distance could be related to the strain in the film as a function of film thickness. The measurements showed tensile strain for all thicknesses. The strain in the overlayer was accounted for by the difference in thermal expansion of GaAs and Si. The buffer layer showed the largest tensile strain, and it is proposed that this strain was due to the presence of vacancies.
Reduction of Strain in Epitaxial GaAs on CaF2/Si Substrates
Authors: Hashimoto Shin , Schowalter L.J. , Smith G.A. , Lee E.Y. , Gibson W.M. , Claxton P.A.
Published: March 2011

This paper reports on strains in epitaxial GaAs layers grown on CaF2/Si(001) and CaF2/Si(111) heteroepitaxial substrates investigated by MeV 4He+; ion channeling. The results indicate that the CaF2 buffer layers reduce strain in the GaAs.
Defects in Large-Misfit Heteroepitaxy
Authors: Eaglesham D.J. , Aindow M. , Pond R.C.
Published: March 2011

A Transmission Electron Microscopy (TEM) study is presented of GaAs on Si (100) and CdTe on GaAs (100), and the implications for defect nucleation mechanisms are discussed. MOCVD GaAs/Si is shown to grow by island nucleation followed by 3D growth. Single islands are free of inversion domain boundaries (or “APBs”) implying that a single domain is able to grow over a demi-step on the substrate surface during this 3D growth. Misfit dislocations are shown to be edge type during island growth, with 60° type being generated at island junctions. The predominant threading dislocations are found to have inclined a/2 <110> Burgers vectors. The implied mechanisms for the generation of both misfit and threading dislocations are discussed. In MOCVD CdTe/GaAs the microstructure is shown to have a number of qualitatively similar features; in addition, study of this much larger misfit system allows us to deduce a possible explanation for misorientation effects in these systems.
Heteroepitaxy of GaAs, GaP and InP on Si By Omvpe and Their Application to thin Film Solar Cells
Authors: Yamamoto Akio , Yamaguchi Safumi
Published: March 2011

Organometallic vapor phase epitaxial (OMVPE) growth of GaAs, GaP and InP on Si has been studied using the two-step growth method. Growth parameters for a heteroepitaxial film with a specular surface, a single-domain structure and high crystallinity are demonstrated and discussed. Residual strains in grown films are evaluated and analyzed by taking account of elastic lattice deformation due to lattice mismatch or thermally- induced strain accomodation by rearrangement of misfit dislocations. Thin film GaAs and InP solar cells are fabricated and their performances are discussed in relation to defect density in the films. For GaAs cells, an efficiency of 18 % (AM1.5, active area) is attained by reducing defect density to 2×106 >cm−2 . The defect density is ~. 5×107 cm−2 in the present InP films, and is needed to be less than 106 cm−2 to attain an efficiency of 18 %.
Low Pressure Mocvd Growth and Characterization of GaAs and InP on Silicon Substrates
Authors: Razeghi M. , Defour M. , Omnes F. , Nagle J. , Maurel P. , Acher O. , Huber A. , Mijuin D.
Published: March 2011

High quality GaAs and InP have been grown on silicon substrates, using low pressure metalorganic chemical vapor deposition technique. The growth temperature is 550ºC andthe growth rate 100 A/min.

Photoluminescence, X-ray diffraction and electrochemical profiling verified the high quality of these layers. The use of superlattices as buffer layers, (GaAs/GaInP) in the case of GaAs/Si and (GalnAsP/InP) in the case of InP/Si, decreased the amount of misfit dislocations in the epitaxial layer. Carrier concentrations as low as 5.1015 cm-3 have been measured by electrochemical profiling.
Heteroepitaxy on Silicon by Molecular Beam Epitaxy
Authors: Schowalter Leo J.
Published: March 2011

In recent years extensive research has been conducted on growing heteroepitaxial layers of insulators, metals, and other semiconductors on silicon. This work promises to extend the use of Si (or, at least, Si substrates) far beyond present day devices into hybred semiconductor devices, optoelectronics, ballistic electron devices, and three-dimensional device structures. However, the “art” of heteroepitaxy is still poorly understood and much work remains to be done to realize most practical applications. Molecular beam epitaxy (MBE) represents an attractive technique for research and development of heteroepitaxy because of its relatively low growth temperatures, flexibility in working with different materials, and by providing a good environment for in-situ observation of the heteroepitaxial process. Using examples from recent heteroepitaxial work by molecular beam epitaxy in the areas of CaF2, NiSi2 and CoSi2, and GaAs on Si, this paper discusses how heteroepitaxial quality is affected by the relative surface free energies and strain (due to both lattice and thermal expansion coefficient mismatch). The goal is to produce better heteroepitaxial layers for device applications by an improved understanding of the process.
Epitaxial Growth of Inp on Si by Mocvd
Authors: Konushi F. , Seki A. , Kudo J. , Sato H. , Kakimoto S. , Fukushima T. , Kubota Y. , Koba M.
Published: March 2011

The heteroepitaxy of InP on Si substrates was investigated using MOCVD. A thin GaAs intermediate layer was used to alleviate the 8.4% lattice mismatch between InP and Si. With the use of this intermediate layer, four inch size, single domain InP epilayer with small residual stress was reproducibly grown on off-(100) oriented Si substrates. The etch pit density (EPD) of as-grown InP layer was 5x107~1x108 cm-2 . The post growth annealing of this epilayer at 800~850ºC in aPH3+H2 ambient reduced EPD to 1~2x107 cm-2
Heteroepitaxial Growth of Sic on Si - Highly Mismatched System -
Authors: Matsunami Hiroyuki
Published: March 2011

Single crystals of cubic(beta) SiC were heteroepitaxially grown on Si to ameliorate the large lattice mismatch of 20 %. The structure and the role of the carbonized layer used for crystal growth are discussed. Single crystals were successfully grown on Si(100) and(111). Antiphase domains on Si(100) were examined to obtain smooth surfaces. The use of Si(100) off-axis substrates oriented towards [011] allowed the successufulelimination of the antiphase domains. Anisotropy was found in the electrical properties of SiC on off-axis substrates. Possible applications are described.
Substrate Strain Measurements in Mbe Grown Silicon on Sapphire
Authors: Pellegrino Joseph , Qadri Syed , Richmond Eliezer , Twigg Mark , Vold Carl
Published: March 2011

An x-ray diffraction study is made of the effect of silicon film thickness on the peak broadening associated with the (024) sapphire Bragg reflection peak for MBE—grown SOS material. The predeposition treatment and growth parameters for the samples in the series were identical. The thicknesses ranged from 5500 to 40,000 angstroms and the growth rate was roughly I angstrom/second.

SOS films with silicon thicknesses below 5500A did not produce sapphire peak broadening when compared with the corresponding sapphire standard. With reference to standard sapphire reflection peaks, the 5500A film shows slight broadening while a I micron film broadened 14 seconds of arc when compared at FWHM with the sapphire standard. A possible explanation for this is that at overlayers less than 5500A, the film is not sufficiently massive to exert a uniform strain on the sapphire. At 5500A the film attains a critical thickness sufficient to strain the substrate and produce detectable broadening. For thickerfilms the strain would increase proportionally. Results from lattice parameter measurements on the silicon epilayer indicate that the perpendicular lattice parameter relaxes atgreater thicknesses but is still in tension when compared with bulk silicon. One would expect that the strain gradient suggested by these results would be greatest at the silicon/sapphire interface and that the defect concentration at the interface might beaffected by this strained condition.
Laser Probing of the Dynamics of Ga Interactions on Si(lO0)
Authors: Carleton Karen L. , Bourguignon Bernard , Smilgys Russell V. , Oostra Doeke J. , Leone Stephen R.
Published: March 2011

The kinetics of desorption and scattering of Ga atoms on Si(100) surfaces are probed by laser-induced fluorescence detection of the gas phase species and by Auger analysis of the surface composition. The kinetic parameters are correlated with the structures deduced by LEED and the coverages determined by Auger spectroscopy. The binding energy of Ga on Si(100) is found to be a function of coverage, starting out at 2.9 eV at low coverages and decreasing to 2.3 eV for coverages between 0.5 and 1 monolayer (ML). Ordered growth is always observed for coverages below 1 ML, but above one monolayer the growth of islands occurs on the wellordered monolayer. The onset of island formation is a strong function of temperature. A model is proposed for the structures and energetics involved in the growth of Ga on Si(100). The results are discussed in terms of the implications for epitaxial growth of GaAs on Si.
Low Temperature in Situ Cleaning of Si(100) Surfaces and Transmission Electron Microscopy of Subsequent Growth of Epitaxial Germanium
Authors: Rudder R.A. , Hattangady S.V. , Posthill J.B. , Markunas R.J.
Published: March 2011

A low temperature process for cleaning Si(100) surfaces has been developed. It involves a combination of a modified hot RCA wet chemistry treatment and an in situ hydrogen treatment for the removal of oxides and carbonaceous material from the Si surface. While this treatment is successful in producing reflection high energy electron diffraction patterns which show 1/2-order reconstruction lines, subsequent Ge heteroepitaxial growth at 300°C contains a high density of microtwins. Transmission electron microscopy reveals that most of the microtwins do not propagate to the wafer surface. Furthermore, the Ge/Si interface is not abrupt, and there are regions that do not appear crystalline. This suggests that some contamination is still present on the Si(100) surface after the in situ hydrogen treatments.
Photoemission Optogalvanic Spectroscopy: An in situ Plasma-Surface Diagnostic
Authors: Downey Stephen W. , Mitchell Annette , Gottscho Richard A.
Published: March 2011

An obstacle to better design and control of plasma processes is our limited ability to monitor surface properties in situ. We describe a new plasma diagnostic technique, photoemission optogalvanic spectroscopy, which can be used to monitor surface contamination, etching rates, and end points. The experiment consists of irradiating a surface with a pulsed excimer or dye laser whose photon energy is above the substrate work function. Photoemission of electrons from the surface is detected by monitoring changes in the discharge current (optogalvanic effect). The technique is characterized by measuring signal strengths as a function of laser intensity, laser wavelength, and bias voltage in vacuum and in an Ar plasma. The technique is used to monitor contamination and etching end points in F-containing plasmas.
Particle Size Measurement in Optical Waveguide Manufacturing Torches Using Dynamic Light Scattering
Authors: Bautista J. R. , Potkay Eugene , Scatton Daria L.
Published: March 2011

The characterization of silica “sooting” torches used in optical waveguide manufacture by external flame-hydrolysis deposition processes such as Outside Vapor Deposition (OVD) and Vapor-phase Axial Deposition (VAD) prflents a formid.ble high temperature environment at > 2000°C in the presence of > 1012 particles/cm3 of silica. This paper describes the first application of Dynamic Light Scattering (DLS) to probe particle sizes in an actual lightguide burner following the “triple-flame” VAD design. DLS, also termed Photon Correlation Spectroscopy (PCS) or Diffusion Broadening Spectroscopy (DBS), was previously identified as a viable diagnostic tool for in-situ particle measurements in silica-sooting flames by W. L. Flower [1] and through an earlier collaboration between AT&T and the Sandia Combustion Research Facility. In applying DLS, however, our experience with the VAD torch reveals that a specialized experimental method will undoubtedly be required to deal with the inevitable presence of low frequency system instabilities in industrial systems.
Determination of Relative Number Densities and Quenching Rates of Sodium in an Atmospheric Flame by Asynchronous Optical Sampling
Authors: Fiechtner Gregory J. , Jiang Yanan , King Galen B. , Laurendeau Normand M. , Lytle Fred E.
Published: March 2011

Pump/probe methods are commonly employed to measure subnanosecond excited state processes in liquid and gas phase systems. Asynchronous Optical Sampling (ASOPS) is a newly-developed pump/probe method that will potentially allow the determination of number densities and relaxation rates in turbulent, high-pressure flames. In addition, ASOPS should yield a better signal-to-noise ratio than laser-induced fluorescence in practical combustion environments. The ASOPS method utilizes a coherent, signal-carrying beam and thus requires no more optical access than LDV measurements. The current ASOPS instrument consists of two dye lasers synchronously pumped by two frequency-doubled, mode-locked Nd:YAG lasers. The two lasers operate at slightly different repetition rates, causing a relative phase walk-out between the pump and probe beams. This strategy allows the mapping of subnanosecond excitation processes in a time scale on the order of milliseconds.
Spontaneous Raman Scattering for Gas Phase Diagnostics
Authors: Drake Michael C.
Published: March 2011

The use of spontaneous rotational and vibrational Raman scattering for nonperturbing measurements of temperature and gas phase concentrations in combustion and in materials processing is reviewed. Theory of Raman intensities is briefly discussed and examples of Raman scattering from metal halide vapors in high temperature furnaces, laminar flames, and turbulent flames are given to demonstrate its capabilities and limitations. At present spontaneous Raman scattering is the only method which can provide simultaneous nonperturbing measurements of temperature and many species concentrations with high spatial (≤ 0.1 mm3) and temporal (≤ 1μs) resolution. Rotational Raman scattering is generally preferred for low temperature measurements (≤ 1200 K), and vibrational Raman scattering is better for measurements of higher temperatures and of multiple-species concentrations. The disadvantages of Raman scattering stem for the weakness of the nonresonant Raman interaction which limits its sensitivity to major species concentrations, renders it vulnerable to interferences from other sources of visible radiation, and requires high powered lasers and sensitive detectors. Data from Raman scattering measurements, particularly when coupled with data from other laser diagnostic techniques and when compared to computer model calculations, have led to a better understanding of the complex interactions between fluid mechanics and chemical reactions which can govern the operation of turbulent combustors or chemical flow reactors.
Laser Probes and Numerical Modeling as Process Diagnostics in Chemical Vapor Deposition
Authors: Breiland William G. , Ho Pauline , Coltrin Michael E. , Kee Robert J. , Evans Greg H.
Published: March 2011

The chemical vapor deposition process consists of a chemicallyreacting flow in which the fluid mechanics and chemical kinetics are strongly coupled. Laser probes such as Raman spectroscopy and laserinduced fluorescence can be used to measure gas temperature fields and chemical species concentrations, but often the interpretation of such data is difficult because several interacting chemical and physical phenomena are occuring simultaneously. Detailed numerical modeling of the experinmental system under study provides valuable insights into these interactions and allows one to make useful comparisons between experiment and the model to gain a fundamental understanding of the CVD process. Examples of this approach are given for silicon deposition from silane and fluid mechanics diagnostics in a rotating disk CVD reactor.
Optical Diagnostics for Metallurgical Processes.
Authors: Williamson R. L. , Peebles H. C. , Hareland W. A. , Zanner F. J.
Published: March 2011

Many industrially important metallurgical processes are accompanied by the emission of light, the analysis of which often supplies useful information concerning the current state of the process while also providing insight into the details of specific process mechanisms. Optical diagnostic techniques are finding an increasingly wide range of application throughout the metallurgical community. This paper discusses the application of emission spectroscopy and imaging techniques to the analysis of such diverse processes as vacuum arc remelting, laser welding, and arc welding. A discussion of these techniques will be presented addressing such subjects as instrumentation, data analysis, the kind of information available and its potential impact on the selection of process parameters. Special attention will be given to discussing the difficulties encountered in applying these diagnostic technologies to “real life” processes in non-laboratory environments.
Aluminium-Transition Metal Thin-Film Reactions
Authors: Colgan E. G. , Mayer J. W.
Published: March 2011

A systematic study of Al/metal reactions has been performed. The thin-film interactions of Al with refractory metals (Ti, V, Ta, Cr, Mo, W and Co) and near-noble metals (Ni, Pd, and Pt) have been investigated. The initial aluminide phases to grow are the Al-rich phases: TiAl3, Val3, TaAl3, Cr2Al13, MoAl12, Wal12, Co2Al9, NiAl3, Pd2Al3, and Pt2Al3 at temperatures between 225 and 525°C. With the exceptions of Val3, Pd2Al3, and Pt2Al3. these are the most Al-rich phases on the phase diagrams. Marker experiments were performed and Al was the dominant diffusing species during the growth of these phases, TiAl3, Val3, Cr2Al3, MoAl12, Co2Al2, NiAl3, Pd2Al3, and Pt2AI3. Consistent with the faster Al diffusion, which provides a greater supply of Al to the growing interface, is the growth of the most Al-rich phase initially. For the exceptions to this rule, Val3, Pd2AI3, and Pt2 Al3, the complexity of the Al-rich V, Pd, and Pt end phases may have hindered nucleation, resulting in the growth of the observed phases. The subsequent phase formation was examined in the Ni-, Pd-, and Pt-Al systems. After initial phase formation consumed all the Al or metal, subsequent phases formed in accordance with the overall stoichiometry. The results of this study, along with a brief literature review, are presented and the generalized behavior of Al/transition metal reactions discussed.
Studies on the Adhesion of Au Films to GaAs
Authors: Bardin T. T. , Pronko J. G. , Senbetu L. , Kozak D. A.
Published: March 2011

The influence of a number of substrate conditions and interfacial contaminants on the adhesion strength of thin Au films (10 to 100 nm thick) to GaAs substrates was studied. The GaAs surfaces were prepared by cleaving on the <110> plane under controlled atmospheres and conditions prior to depositing the Au film. Adhesion strengths were measured using the pinpull test. The study included standard characterization techniques to examine the substrate surface and the Au-GaAs interfaces. A direct correlation was found between cases of poor adhesion and the presence of hydroxyl groups on the GaAs surface. The influence of post evaporative treatments to improve the adhesion of specific cases was also studied.
Growth Characteristics of Co-Cr Thin Films for Magnetic Recording
Authors: Demczyk B. G. , Laughlin D. E.
Published: March 2011

The growth characteristics of magnetron sputtered Co-22%Cr thin films on amorphous glass or carbon substrates have been investigated utilizing transmission electron microscopy,. X-ray diffraction, electrical resisivity and in-plane stress measurements. Results indicate that the initial deposit is “amorphous”, but that isolated islands of small crystallites form before the film reaches 5nm film thickness. By 10nm, well oriented grains with hcp c axis perpendicular to the film plane develop, and by 50nm, a twinned columnar microstructure is evident. As this occurs, the in-plane film stress becomes constant. Also, we have observed a distinct subgrain structure in the thinner films (10–50 nm), and this is reflected in the electrical resistivity. This cannot be accounted for by an “evolutionary selection” growth scenario, but must be related to the low surface mobility of adatoms at these low substrate deposition temperatures.
Interfacial Reactions Between Co and GaAs
Authors: Shiau F.-Y. , Zuo Y. , Zheng X.-Y. , Lin J.-C. , Chang Y. A.
Published: March 2011

Interfacial reactions between Co and GaAs have been studied using bulk diffusion couples of Co (∼0.5 mm thick)/GaAs and thin-film Co(∼-40 nm) on (001)GaAs as well as the epitaxial formation of CoAs and CoGa on (001)GaAs. In addition, phase diagram of Co-Ga-As at 600°C was determined. The thin-film results are rationalized in terms of the phase diagram and bulk diffusion data.
Modification of Copper Surfaces: Effect on Adhesion at the Copper Polyimide Interface
Authors: Parekh P. P. , Kembaiyan K. T. , Gonsalves K. E. , Bocarsly A. , Amos L.
Published: March 2011

Copper surfaces were derivatized resulting in the formation of Mx[Cu(II)(CN)Fe(II/III)(CN)5] at the interface. Polyimides were spin coated onto the modified metal surfaces and the degree of adhesion measured by the tape pull test. Effects of mechanical interlocking were evident in the case of modified copper samples, due to derivatization by ferricyanide. The chemical bonding and elemental analyses of the interfaces were studied by XPS and SEM.
Surface Characterization of Sputter Etched Polymer Films
Authors: Grant J. L. , Dunn D. S. , McClure D. J.
Published: March 2011

The surface chemical changes induced in polystyrene, polypropylene and poly(ethylene terephthalate) (PET) by argon and oxygen rf sputter etching were studied by XPS and infrared reflection absorption spectroscopy (IRRAS). Thin (∼5nm) chemically modified surface layers were observed for all three materials. Polystyrene surfaces were oxidized by sputter etching in both oxygen and argon with differing chemical functionality resulting from etching in the different gases. Polypropylene surfaces, by contrast, were oxidized with similar chemical functionality resulting from etching in either gas. PET surfaces were oxidized slightly by oxygen sputter etching and reduced by argon sputter etching. For the model systems chosen, etch mechanisms are suggested based on trends in the chemical modification behavior.
Interfacial Adhesion: Theory and Experiment
Authors: Ferrante John , Bozzolo Guillermo H. , Finley Clarence W. , Banerjea Amitava
Published: March 2011

Adhesion, the binding of different materials at an interface, is of general interest to many branches of technology, e.g., micro-electronics, tribology, manufacturing, construction, etc. However, there is a lack of fundamental understanding of such diverse interfaces. In addition, experimental techniques generally have practical objectives, such as the achievement of sufficient strength to sustain mechanical or thermal effects and/or have the proper electronic properties. In addition, the theoretical description of binding at interfaces is quite limited, and a proper data base for such theoretical analysis does not exist.

This presentation will review both experimental and theoretical aspects of adhesion in nonpolymer materials. The objective will be to delineate the critical parameters needed, governing adhesion testing along with an outline of testing objectives. A distinction will be made between practical and fundamental objectives. Examples will be given where interfacial bonding may govern experimental consideration. The present status of theory will be presented along with some recommendations for future progress and needs.
The Role of Fracture Mechanics in Adhesion
Authors: Thouless M. D.
Published: March 2011

The problem of adhesion cannot be completely comprehended by consideration of interfacial properties alone. Other parameters such as geometry, applied and residual stresses, and the interfacial flaw population are equally important. The well-established field of fracture mechanics permits these aspects to be considered. One of the most important features of fracture mechanics is that it can provide a means of characterizing interfacial properties which does not depend upon the method of testing. It may also allow a predictive ability in determining failure and a rational explanation of what is known as “adhesive” or “cohesive” failure. These issues are addressed in conjunction with a discussion of the current limitations in the application of fracture mechanics to the topic of adhesion.
Enhancement of Thin-Film Adhesion by MeV-ION and keV Electron Bombardment
Authors: Tombrello T. A.
Published: March 2011

Since the discovery in 1981 that the electronic excitation produced by MeV ions can enhance thin film adhesion to a substrate, there have been many investigations to determine the origin of the effect and to apply it to problems of technological interest. As we approach the seventh anniversary of its discovery, I shall use this opportunity to review our progress toward these goals. In general, we have discovered that although the electronic excitation provided by the incident beam is responsible for the improvement in adhesion, it is certain that there are quite a number of separate effects involved. These have been shown to include: surface cracking of the substrate; the breakup of contaminant or oxide layers on the substrate by the beam; and the relaxation of surface strain in the substrate. The recent use of a variety of new techniques seems to offer the hope that we are beginning to make progress in untangling these phenomena.
Mechanical Behaviour of Eutectic Superalloys
Authors: McLean M.
Published: March 2011

The mechanical properties of in-situ composites intended for use as gas turbine materials are reviewed. Particular emphasis is placed on the current understanding of strengthening and fracture mechanisms of these materials. The need to modify current methods of data representation, that have been developed for more conventional materials, in order to improve property extrapolation and design procedures are highlighted.
Tensile Creep and Relaxation of the Lamellar Al-Al2Cu Composite. Experiments on the Tensile Stage of a High Voltage Transmission Electron Microscope (HV Tem)
Authors: Ignat M. , Caillard D.
Published: March 2011

Groundwater circulation is in the long term probably the most important mechanism for the transport of radionuclides from deep underground repositories to the biosphere. The fate of leached long-lived nuclides, such as the actinides, is of particular interest to repository safety analysis. Both experimental and theoretical studies should lead to a comprehensive description of their behaviour in the geosphere.
A Correlation Law for Steady State Creep and Stress Relaxation Tests on the Al-Al2Cu Composite
Authors: Ignat M. , Bonnet R. , Durand F.
Published: March 2011

Deformation by creep or by stress-relaxation involve similar thermally activated phenomena. In particular our microstructural observations on the Al-Al2Cu lamellar composite illustrated the importance of the interphase accommodation mechanisms, specially movements of linear defects at the phase boundaries.

Our experimental results have shown that the asymptotic stress measured in stress-relaxation tests takes the same value as the threshold stress limiting the steady state creep domain. From this finding we develop a simple Bingham rheological model in which a temperature dependent threshold stress is combined with a generalized Dorn viscosity law. The model correlates satisfactorily the results of both steady state creep tests and the results of stress-relaxation tests.

The calculated activation energy and stress exponent are compared with the values deduced from physical models of deformation accommodation through grain boundary sliding. The preexponential factor of the viscosity law is discussed with reference to its dependence on the dislocation substructure.
The Role of Solidification Rate on Fiber Distribution and Mechanical Properties of a Directionally Solidified Nickel Base-Tac Eutectic
Authors: Walter John L.
Published: March 2011

A nickel base-TaC eutectic alloy consisting of 53 wt % Ni, 11 W, 3 Re, 5 Co, 3 Mo, 2 Al, 21.67 Ta and 1.33 C was directionally solidified at rates from 0.32 to 3.8 cm/hr. Samples were taken from the regions of aligned TaC fibers and tested in tension at 1000°C and in stress-rupture. The fiber density increased from 1×106 fibers/cm2 at 0.32 cm/hr to 27×106 fibers/cm2 at 3.8 cm/hr. The stress-rupture life at 927°C and 275.6 MPa ranged from 4 hrs for samples solidified at 0.32 cm/hr to 4187 hrs for the sample solidified at 2.54 cm/hr at which time the test was terminated. Examination, by transmission electron microscopy, of the samples tested at 1000°C in tension, to just the beginning of fiber breakage, revealed a change in the mode of deformation of the nickel-base alloy matrix with increasing fiber density. It was also seen that the TaC fibers deformed by two mechanisms; by slip and by the formation of stacking faults.

It appears that tailoring the alloy composition to allow for higher solidification rates may be a more effective strengthener than alloying the matrix for high strength.
Thermal, Viscoplastic Analysis of Composite Laminates
Authors: Krempl E. , Lee K. D.
Published: March 2011

For the modeling of ply deformation behavior the orthotropic, thermal viscoplasticity theory based on overstress is used. It can represent creep, relaxation and rate sensitivity as well as monotonic and cyclic loadings. The theory is “unified” since creep and plasticity are not separately modeled. No yield surfaces and loading/unloading conditions are employed. The laminate theory for in-plane loading maintains the geometric assumptions of classical laminate theory. The elasticity law, however, is replaced by the thermal, orthotropic viscoplasticity law. Numerical experiments illustrate the predictions of the theory for an angle-ply and a cross-ply laminate subjected to a temperature increase, temperature hold and subsequent return to the original temperature. The ply and laminate stresses are calculated as a function of time for unconstrained and constrained conditions using postulated properties close to a real metal matrix composite. Redistribution of ply stresses and relaxation are found. In some cases, nearly permanent residual ply stresses are present after completion of the temperature cycle.
Fibers and Grids by Integrated Circuit Technology
Authors: Steinwall James E. , Johnson H. H.
Published: March 2011

Ceramic fibers and grids of controlled geometry and composition were fabricated by electron beam evaporation of Al2O3 onto substrates patterned by optical lithography. The fibers were 4 and 5μm wide by 1μm thick. In addition, mixed metal oxide films from 0 to 10at% Ti, Zr, or Cr were produced by coevaporation with Al2O3. The compositions of the films were determined by Rutherford Backscattering Spectroscopy. TEM and electron diffraction examination showed all the films to be amorphous in structure.

The Al2O3 fibers had tensile strengths between 143 and 168 ksi and the Al2O3 film had a microindentation hardness of 8.4 GPa. Films with ≈ 1at% additions of Zr, Ti, and Cr had hardnesses of 11.0, 9.7, and 8.8 GPa respectively. The hardness then decreased with higher Zr, Ti, and Cr concentrations
XD™ Titanium Aluminide Composites
Authors: Christodoulou L. , Parrish P. A. , Crowe C. R.
Published: March 2011

The advantages of reinforcing metals with ceramic particles to produce metal matrix composites are well known. The behavior of discontinuously reinforced intermetallic compounds, however, has not been extensively studied. Martin Marietta Laboratories has produced a new generation of discontinuously reinforced titanium aluminide composites using a proprietary casting process known as XD™ technology. These new materials possess enhanced properties at room and elevated temperatures and may be cast, extruded, or forged. The effects of matrix composition, reinforcing phase, and thermal mechanical processing on properties have been studied using optical and various electron microscopy and mechanical and physical property measurement techniques to characterize the alloys. To date, most work has been done on a two-phased lamellar Ti-45 a/o Al alloy reinforced with TiB2 ceramic having an equiaxed morphology. Data on temperature dependence of the dynamic Young's modulus, coefficient of thermal expansion, deformation and fracture behavior, and microstructure are presented.
Micromechanical Studies of Model Metal Matrix Composites
Authors: Wadley H. N. G. , Biancaniello F. S. , Clough R. B.
Published: March 2011

The fiber-matrix interface is believed to play a central role in the load-supporting and crack-growth resisting capabilities of fiber-reinforced high temperature composites. In metal matrix composites, this interface can be very complex: new phases may be present due to reactions between the matrix and reinforcement, compositional gradients due to interdiffusion occur, and the outer fiber surface is usually coated to avoid handling damage, improve fiber wetability, and/or control matrix reactivity. Attempts at measurements of fiber and interface strength from studies of actual composite samples are thwarted in part by the difficulty of determining the local distribution of stress and strain in these highly inhomogeneous materials. Furthermore, the inability to determine the point, during loading, where failure occurs in the interfacial zone also complicates the problem in these opaque materials. It is not surprising, therefore, that the fundamental relationships between the structure and properties of interfaces, on the one hand, and the load-supporting/crack-resisting properties of bulk metal matrix composities, on the other, have not been determined to date.
Hrem Characterisation of The Interface in A Sic Fibers/Ti Matrix Composite
Authors: Lancin M. , Bour J. S. , Thibault-Desseaux J.
Published: March 2011

The microstructure of the interfacial zone in a SCS6 filaments/Ti-6A1–4V matrix composite was determined using TEM and HREM. The interfacial zone (e ∼5 μm) consists of microstructurally distinct layers. The fiber/matrix interaction resulted in two layers respectively crystallized in grains of about 20 nm and 100 nm. The reaction zones are mainly made of brittle TiC. They are separated from the SiC reinforcement by five layers which form the coating of the SCS6 filament. These five layers may be described as SiC-C composites with either an equiaxe fine grain structure or a distorted lamellar structure. The structure of these layers can explain the toughning of the alloy by the SCS6 filaments despite of the brittle F/M reaction products formed during the processing.
Crack-Tip Shielding in Metal-Matrix Composites: Modelling Of Crack Bridging by Uncracked Ligaments
Authors: Shang Jian Ku , Ritchie R. O.
Published: March 2011

As part of an investigation into the micro-mechanisms of crack-tip shielding associated with the growth of fatigue cracks in metal-matrix composites, simple models are developed for the role of crack bridging in high-strength aluminum alloys reinforced with SiC particulate (AI/SiCp). Based on experimental observations of crack growth, crack-tip shielding and crack-path morphology in these alloys, the bridges are found to be associated with uncracked ligaments in the wake of the crack tip, and are modelled in terms of approaches based on a critical crack-opening displacement or critical tensile strain in the ligament.
Growth and Structure of Alumino-Silicate Polymers
Authors: Boilot J. P. , Pouxviel J. C. , Dauger A. , Wright A.
Published: March 2011

Gels have been prepared in the H2O, HOiPr, (BuO)2Al-O-Si(OEt)3 ternary phase diagram in a large range of oxide concentrations. The gelation time is governed by the initial water concentration, showing that the hydrolysis of Si-OR groups is the rate-determining process for the gelation.

The structure of clusters and the kinetics of aggregation have been studied by SANS. We observe mass-fractal particles characterized by a fractal dimension of 1.9, in agreement with the existence of a cluster-cluster aggregation mechanism during the gelation. The scattering curves exhibit a maximum intensity corresponding to interparticle correlations due to purely excluded-volume effects.
Correlations Between Processing Parameters, Ultrastructure, and Strength of Gel-Silica
Authors: West Jon K. , Nikles Randy , Latorre Guy
Published: March 2011

The effect of various processing parameters during the aging of sol-gel derived silica are evaluated. Improvement in the physical properties of the wet gel-silica are shown to be well correlated to their aging temperatures and time. Changes in the pore structure also show correlations with aging process parameters.
Sol-Gel Kinetics: 29Si NMR and a Statistical Reaction Model
Authors: Assitik Roger A. , Kay Bruce D.
Published: March 2011

The early time behavior of an acid catalyzed Si(OCH3),4 (TMOS) sol-gel was studied by high resolution 29Si nuclear magnetic resonance (NMR). Both the water producing and the alcohol producing condensation reactions were found to contribute significantly to the overall condensation rate. A general theoretical kinetic formalism which specifically treats the temporal evolution of the various chemical function groups about a specific silicon atom was developed. The experimentally observed functional group distribution was in agreement with the distribution predicted by a simplified statistical reaction model. The mathematical framework for the study of chemical speciation at the next-to-nearest functional group level was developed. This framework was used to assign several fine structure resonances, and to show that the formation of various dimeric species is also largely statistical in nature.
Preparation of Stoichiometric M'TiO3, Powders (M' = Ba, Sr, Ca) from Catecholate Complexes
Authors: Ali N. J. , Bultitude J. , Xue L. A. , Milne S. J.
Published: March 2011

Powders of BaTiO3, SrTiO3, and CaTiO3, were prepared from intermediate catecholate complexes, M'[Ti(C6H4O2], M' = Ba, Sr, Ca. Conversion to oxide was accomplished by heating at 600°C to produce stoichiometric powders of crystallite size, < 0.1 μm, with relatively weak agglomeration. Ultrasonic treatment of aqueous suspensions of the powders resulted in measured agglomerate sizes of less than 2–3 μm. Chemical and physical properties of the new powders are reported, together with information on sintering behaviour.
Light Scattering of SiO Monodisperse Microspheres Prepared by the Sol-Gel Route
Authors: Ziemath E. , Aegerter M. A. , Moreira J. , Figueiredo M. , Zarzycki J.
Published: March 2011

SiO microspheres have been prepared from TMOS/Methanol/water sols in basic condition (pH ≃ 12) by the Stöber method and studied by TEM static and dynamic light scattering techniques in order to determine the mean size Ṝ size distribution, hydrodynamic radius RH, radius of gyration RG and translational diffusion coefficient Dt; the ratio RH/RG was found less than 0.55 and the aggregates have a fractal geometry with df ∼ 2.3 ± 0.05. The results are compared to previous work on colloidal silica aggregates prepared by other techniques and discussed.
Dielectric Relaxation Analysis of Water Adsorption in Sol Gel Derived Silica Gel Monoliths
Authors: Wallace S. , Hench L. L.
Published: March 2011

The polarization mechanism of the low frequency dielectric relaxation (R1) observed in water adsorbed in porous silica gel is investigated using monolithic samples. It is attributed to electrode polarization involving proton hopping conduction. The influence of the thickness of the adsorbed water layer on the relaxation mechanism is discussed.
Low Temperature Direct Reactions Between Elemental Silicon and Liquid Ammonia or Amines for Ceramics and Chemical Intermediates
Authors: Pugar Eloise A. , Morgan Peter E.D.
Published: March 2011

Direct processes that may be used to manufacture high purity silicon nitride or silicon carbide are described. Elemental silicon has been found to react directly with liquid ammonia and amines at low temperature to yield compounds for both the ceramic and chemical industries. Silicon-amine direct reactions, previously thought not to occur, were investigated by using 29Si NMR, IR, UV, Raman, XRD, ICP, EDS and TGA methods to detect and characterize product formation. The [Si,N,H] and [Si,C,N,H] products transform to silicon nitride or silicon carbide respectively when heated above 1300°C.
The Synthesis of Boron-Containing Ceramics by Pyrolysis of Polymeric Lewis Base Adducts of Decaborane(14)
Authors: Seyferth Dietmar , Rees William Smith
Published: March 2011

Polymeric adducts, [B10H12L∼∼L]x, have been prepared by reaction of B10H14 with diphosphines and diamines. These show good promise as precursors whose pyrolysis can give either boron carbide (in the case of the diphosphine polymers) or boron carbonitride and boron nitride (in the case of the diamine polymers).
Aminoborane Polymers as Precursors of Ceramic Materials
Authors: Maya L.
Published: March 2011

A series of polymeric materials was prepared through the condensation of t ri ethyl borane or tris(dimethylamino)borane with polyfunctional amines. The amines examined and the ceramic yields of the corresponding condensation products after pyrolysis under vacuum at 800°C were as follows: Methylene dipyrazole – 52%, o-phenylenediamine – 85%, 3,3’ diaminobenzidine – 59% and diethylenetriamine – 12%. Volatile products evolved in the pyrolyses were identified and the solid residues characterized by chemical analyses and spectroscopie means.
Synthesis of Ain and AlN/SiC Ceramics from Polymeric Molecular Precursors
Authors: Paine Robert T. , Janik Jerzey FR. , Narula Chaitanya
Published: March 2011

Reactions of (Me3Si)3 AI·Et2O with NH3 in different stoichiometric ratios have been studied in search of useful precursors to AIN. Two molecular condensation-elimination compounds and an insoluble oligomer have been obtained from these reactions, and pyrolysis of the compounds leads to the convenient formation of AlN/SiC solid solutions.
Studies on Organoaluminum Precursors OP Aluminum Nitride Fibers
Authors: Thomas Baker R. , Bolt John D. , Rbddy Gade S. , Christopher Roe D. , Staley Ralph H. , Tebbe Pred N. , Vega Alexander J.
Published: March 2011

A melt-spinnable precursor of aluminum nitride fibers derived from triethylaluminum and ammonia contains AlNH, AlNH2 groups, and a small number of AlN units characteristic of aluminum nitride. The molecular weight of a spinnable composition is 070, corresponding to an average molecular weight of 13 organoaluminum groups. Ammonia, a curing agent for the fibers, accelerates elimination of ethane from the material, and decreases its solubility in toluene.
Sol-Gel Processed BaTiO3
Authors: Della Nelcy , Mohallem Santina , Aegerter Michel André
Published: March 2011

BaTiO. thin films deposited on pyrex supportsby dip-coating technique and powders have been prepared by the sol-gel route from sols containing a mixture of tetraisopropyl orthotitanate, iso propanol, barium acetate and glacial acetic acid. The thickness of the films is proportional to the first power of the withdrawal speed. Gelled sols have been dried hypercritically and by natural evaporation. Films and powders have been characterized by X-ray diffraction during their heat treatment. Tetragonal BaTiO structure is observed for T ≥ 600°C.
The Structures of Tantalum Pentoxide Film Formed by Reactive DC Magnetron Sputter-Deposition of Ta
Authors: Chang P.-H. , Bohlman J. G. , Liu H. Y. , Keenan J. A. , Shen B. W. , Chen I.-C.
Published: March 2011

Tantalum pentoxide (Ta2O5) films are candidates for application as storage capacitors in high density memory cells and as gate insulators in MOS devices because of their large dielectric constant. Thin Ta2O5 films deposited by reactive DC magnetron sputtering of a pure Ta target using an argon/oxygen mixture have been characterized using TEM, glancing angle X-ray diffraction and RBS. The films are amorphous in the as-deposited condition but crystallize after high temperature (> 600 °C) annealing. Numerous pores and significant grain boundary grooving were observed in the crystallized film. A high level (∼2 at. %) of argon was detected in both as-deposited and annealed films formed by Ar/O2 sputtering. The effects of sputtering and annealing conditions on the structure of the films were investigated.
Planarization of Metal Substrates for Solar Mirrors
Authors: Ashley Carol S. , Reed Scott T. , Roderick Mahoney A.
Published: March 2011

The planarizing ability of sol-gel films was investigated on several as-rolled stainless steel substrates. The smoothing effect afforded by the films was evaluated, using optical techniques, following deposition of silver over the planarized substrates. The specular reflectance of various substrates, initially ranging from 0.36 to 0.90, could be improved to final reflectance values of -0.93 with sol-gel processing. This process is being used to prepare prototype foil mirrors for evaluation in the next generation of solar concentrators.
In Situ NMR Study of Gel Pore Structure During Aging and Drying
Authors: Smith Douglas M. , Glaves Christopher L. , Davis Pamela J. , Jeffrey Brinker C.
Published: March 2011

Low field NMR spin-lattice relaxation measurements of pore fluid were used to study pore structure during aging and drying of two silica gels. The NMR method provides in situ information concerning pore size, size distribution and surface area which is impossible to obtain by other techniques. Surface areas measured for a sol-gel sample aged in a potassium hydroxide solution were compared to similar measurements made on an ethanol aged sample during drying. Surface area and pore size distributions of the corresponding final dried gels were measured by both NMR and nitrogen adsorption/condensation. The measurements for a given sample were in good agreement. The surface area of samples before drying were much higher than after drying and the base-aged sample had a higher initial surface area than the ethanol-aged sample although after drying, this trend was reversed.