bluuebunny/crossref_metadata_2025 huggingface dataset:
HIGH RESOLUTION ELECTRON MICROSCOPE STUDY OF CdTe-Cd0.6Mn0.4 Te SUPERLATTICES
Authors: CHOI C. , OTSUKA N. , KOLODZIEJSKI L. A. , GUNSHOR-a R. L.
Published: March 2011

Structures of CdTe-Cd0.6Mn0.4Te superlattices which are caused by the lattice mismatch between suterlattice layers have been studied by high resolution electron microscopy (HREM). In thin-layer superlattices, the crystal lattice in each layeris elastically distorted, resulting in the change of the crystal symmetry from cubic to rhombohedral. The presence of the small rhombohedral distrotion has been confirmed through a phase contrast effect in HREM images. In a thick-layer superlattice, the lattice mismatch is accommodated by dissociated misfit dislocations. Burgers vectors of partial misfit dislocations have been identified from the shift of lattice fringes in HREM images.
PRESSURE—DEPENDENT MAGNETO—OPTIC MEASUREMENTS IN STRAINED—LAYER SUPERLATTICES AT LOW TEMPERATURES
Authors: JONES E. D. , SCHIRBER J. E. , FRITZ I. J. , GOURLEY P. L. , BIEFELD R. M. , DAWSON L. R. , DRUMMOND T. J.
Published: March 2011

Magneto—optic studies on InGaAs/GaAs and GaAs/GaPAs strained—layer superlattices are used to determine the in—plane light—hole valence—band effective masses. Also, hydrostatic pressure—dependent magneto—optic studies have been performed on these samples for magnetic fields up to 65 kG andpressures to 4 kbar in the temperature range of 1.6 - 4 K. The experimental pressure coefficients of the band—gap energy and the effective mass in the InGaAs/GaAsSLS structures were determined.
SEMICONDUCTOR QUANTUM-WELL HETEROSTRUCTURES
Authors: Chang L. L.
Published: March 2011

Activities in semiconductor heterostructures are reviewed, with focus on the fundamental physics aspects in the quantum regime and with emphasis on recent experimental observations. The GaAs-GaAlAs is used to illustrate the general electronic properties of interest, which are obtained through various measurement techniques. Other heterostructures, including III-V, II(IV)-VI, and IV materials, are covered to the extent that they exhibit new and specific features.
NOVEL MEASUREMENT OF THE BAND DISCONTINUITIES IN (Al,Ga)As HETEROJUNCTIONS
Authors: WILSON B. A. , DAWSON P. , TU C. W. , MILLER R. C.
Published: March 2011

A novel method has been used to obtain a direct and accurate measure of the valence-band discontinuity AlyGa1−yAs/AlAs heterojunctions in quantum-well structures. The technique takes advantage of the crossover occurring at a critical Al concentration above which the indirect X minimum in the AlAs becomes the lowest-energy conduction band in the system. Within these “staggered” band alignment structures, photoexcited electrons and holes are spatially separated, and recombination occurs across the interface. The resulting emission fixes the valence-band offset to within 1% without accurate knowledge of other system parameters, such as effective masses and exciton or dopant binding energies. These measurements represent the first direct optical confirmation of staggered band alignments in this technologically important material system.
STRUCTURAL CHARACTERIZATION OF HgTe/CdTe SUPERLATTICES
Authors: PAINE B. M. , VREELAND T. , CHEUNG J. T.
Published: March 2011

Superlattices of HgTe and CdTe, grown on (100) and (111) CdTe, have been characterized by He ion backscattering spectrometry and x-ray double crystal diffractometry. Backscattering spectrometry gave basic information about the depth-distribution of layers, i.e. the number of layers in the superlattice, the thickness of CdTe overlayer and the location of damage in the underlying CdTe. Symmetric and asymmetric rocking curves gave information about crystal quality and layer thicknesses. Average strains in the directions perpendicular and parallel to the layer interfaces were obtained directly from the rocking curves. Strains and thicknesses of the HgTe and CdTe layers, as well as variations from layer to layer, were found by fitting the symmetric rocking curves with theoretical calculations based on a kinematic model for the diffraction. A tilt of the atomic planes in the epitaxial layers, relative to those in the substrate, was observed by means of rocking curves recorded from the same diffracting planes, but with reversed incident and diffracted beam directions.
THE DEFECT STRUCTURE OF ION-IMPLANTED AlxGa1−xAs/GaAs SUPERLATFICES
Authors: COOMAN B.C. DE , CARTER C.B. , RALSTON J. , WICKS G.W. , EASTMAN L.F.
Published: March 2011

Cross-sectional transmission electron microscopy (XTEM) has been used to study the defect structure and intermixing of ion-implanted and annealed AlxGa1−xAs/GaAs superlattices. The results show clearly that the layer intermixing depends on mass and energy of the implanted species and the annealing conditions. The temperature and duration of annealing determines mainly the amount of residual damage. In addition it was observed that in all cases the point-defects agglomeration was influenced by the strain field present at the layer interfaces; extended defects nucleate preferentially in the GaAs layers.
MONTE CARLO STABILITY ANALYSIS OF STRAINED LAYER SUPERLATTICE INTERFACES
Authors: DODSON BRIAN W.
Published: March 2011

We have developed a procedure, based on conventional Monte Carlo methods, to investigate the limits of stability of a strained layer superlattice (SLS) system as a function of lattice mismatch and layer thickness. The method is demonstrated by the analysis of two-dimensional Lennard-Jones SLS systems, for which the regime of absolute SLS stability is mapped out. Extension of the technique to three-dimensional silicon-like model systems is discussed, and appropriate model potentials for stability analysis of the Si/SiGe system are introduced.
ORDER-DISORDER TRANSITIONS IN STRAINED SEMICONDUCTOR SYSTEMS
Authors: OURMAZD A. , BEAN J. C.
Published: March 2011

We describe the observation of a strain-induced order-disorder transition in the alloy layers of a GeSi/Si superlattice and discuss the possible implications of the transition for the opto-electronic properties of this important system.
MODULATION WAVELENGTH DEPENDENCE OF THE INTERDIFFUSION IN AMORPHOUS Si/Ge MULTILAYER FILMS
Authors: PROKES S.M. , SPAEPEN F.
Published: March 2011

Compositionally modulated amorphous Si/Ge thin films with repeat lengths (wavelengths) between 4.8 nm and 5.83 nm have been prepared using ion beam sputtering. The interdiffusion coefficient was determined from the decrease in the (000) x-ray satellite intensities with annealing, and was found to be relatively large, so that it could easily be measured without crystallization occurring. The effect of copper and oxygen impurities was found to be negligible. The dependence of the interdiffusivity on the modulation wavelength is similar to that of an ordering system. The temperature and wavelength dependence in the range T = 550-630 K is described by Dλ = 1.47×10−10 m.s−1 exp(-l.6 eV/kT)(l-21.8/λ2(nm)). It is suggested that diffusion is governed by the breaking of one bond near a pre-existing dangling bond.
Surface Studies of Silicon with a High Resolution Transmission Electron Microscope
Authors: Gibson J.M. , McDonald M.L. , Unterwald F.C. , Gossmann H.-J. , Bean J.C. , Tung R.T.
Published: March 2011

Using a specially modified ultra-high vacuum, ultra-high resolution transmission electron microscope, in-situ cleaned Si surfaces have been examined with near atomic resolution. By annealing the edges of a <110> thin Si specimen in-situ, it is found that low energy surfaces form. A surprising observation is that the {113} surface is stable and reconstructed by dimerization to a very low dangling bond density. It is also found that a 7×7 surface peridoicity can be preserved at a buried Si < 111 > / amorphous Si interface.
GROWTH AND STRUCTURE OF COMPOSITIONALLY MODULATED AMORPHOUS SUPERLATTICES
Authors: Persans P. D. , Abeles B. , Tiedje T. , Roxlo C.
Published: March 2011

We review recent measurements of the structure of amorphous solidsolid interfaces using compositionally modulated structures to increase the density of interfaces in thin film materials.
LIGHT-INDUCED EXCESS CONDUCTIVITY AND THE ROLE OF ARGON IN THE DEPOSITION OF DOPING-MODULATED AMORPHOUS SILICON SUPERLATTICES.
Authors: Su F.-C. , Levine S. , Vanier P. E. , Kampas F. J.
Published: March 2011

Amorphous semiconductor superlattice structures consisting of alternating n-type and p-type doped layers of hydrogenated amorphous silicon (a-Si:H) have been made by silane glow discharge in a single chamber system. These multilayered films show the novel phenomenon of light-induced excess conductivity (LEC) associated with a metastable state having a lifetime of order of days. This report shows that the LEC effect is quite dependent on the specific details of the deposition parameters, namely dilution of the silane with inert gas, substrate temperature and layer thickness. In order to investigate the origin of the LEC effect, argon dilution was used for specific regions of the structure. This experiment shows that the slow states are distributed throughout the layers, and are not concentrated at the interfaces.
X-RAY DIFFRACTION CHARACTERIZATION OF ELASTIC STRAIN IN COMPOSITION MODULATED LAYERED STRUCTURES
Authors: JANKOWSKI A. F. , STEINMEYER P. A.
Published: March 2011

X-ray diffraction techniques are utilized to characterize the biaxial state of stress in thermal vapor deposited, composition modulated layered structures. Thin film systems, as Au-Ni, Cu-Pd, Ag-Pd, Cu-Ni and Cu-NiFe, have manifested the ‘supermodulus effect’ as a mechanical property. The concept of interlayer coherency gives rise to the notion of accommodating misfit strains between the layers. In turn, such large elastic strains have been shown to cause large increases in the elastic moduli (the ‘supermodulus effect’) of noble metals. In the present work, pole figures are used to determine the texture and crystallographic orientations of these foils, and standard x-ray methods are then used to quantify this strain with lattice parameter measurements and diffraction peak profiles.
Epitaxy of Arsenic-Pressure-Controlled MBE-Grown GaAs Layers
Authors: Wang Y.H. , Liu W.C. , Chang C.Y. , Jean M.S. , Liao S.A.
Published: March 2011

Surface morphologies of the molecular beam epitaxy (MBE)-grown GaAs layers using the background-arsenic-pressure-control method were investigated. The growth parameters, such as substrate temperature, growth rate, epilayer thickness, As/Ga ratio, doping concentration, substrate type, etc., are related to the observed oval defect density. Protrusions and Ga-droplets caused oval defects during growth. The origin of the oval defects in our system is found to be the gallium oxide, not Ga "spitting" from the effusion cell.
Magnetic Resonance of Oxygen-Related Defects in Silicon
Authors: Michel J. , Niklas J. R. , Spaeth J.-M.
Published: March 2011

The electron spin resonance (ESR) of a number of vacancy-oxygen complexes created in electron irradiated Si containing oxygen is briefly reviewed. In these centers the unpaired spin density is highly localised (50–70%) on two Si sites within the complex. The ESR spectra of several paramagnetic thermal donors (TD+) formed by annealing oxygen-rich Si at 450 °C for one to several hundred hours are reviewed as well as recent experiments under uniaxial stress from which for the ground state a 2 valley effective mass-like wavefunction was derived. Results of electron nuclear double resonance (ENDOR) experiments on the TD+ ESR line “NL8” are presented for the first time. They reveal that all TD's identified in IR-spectroscopy are superimposed in the NL8 ESR line and that upon growth of the TD the structure of the core and the symmetry of the TD's is not changed. The hyperfine interactions with up to 7 shells of Si nuclei of 5 TD+'s were determined. Their size and tensor orientations are consistent with the two-valley effective mass-like wavefunction. 4 TD's identified in ENDOR could be correlated with IR-bands from growth kinetics. Although the ENDOR experiments so far do not yet lead to a detailed TD model, the model possibilities are narrowed down considerably by these results. The core must consist of nuclei with very low magnetic abundancy. It is tentatively suggested, that the core contains an O2 molecule.
The Study of Oxygen Thermal Donors in Silicon by Photothermal Ionisation Spectroscopy
Authors: Griffin Jennifer A. , Navarro H , Genzel L
Published: March 2011

It is well known that Czochralski-grown silicon contains up to 2×1018 cm-3 oxygen atoms. When this silicon is annealed at 450°C a series of “thermal” donors are formed. In this work we present the results of a study of annealed Czcochralski-silicon samples by Photothermal Ionisation Spectroscopy and IR transmission measurements. All previously reported thermal donors, which occur in the spectral region above 330cm-1, and hove ionisation energies 53–69.3 meV, are observed by us. Also, our experimental results show the presence of at least three previously unreported thermally formed donor transition series below 330cm-1. Our results indicate that the ionisation energies of these new shallow thermal donors would be 36.3, 37.0 and 37.4 meV. Assignments are made by comparison of the energy differences between excited states to those predicted by the Effective Mass Theory.
Energy Levels and Capture Cross-Sections of Thermal Donors in Silicon
Authors: Henry A. , Pautrat J. L. , Magnea N. , Saminadayar K.
Published: March 2011

The electrical properties of thermal donors centers, generated after annealing CZ-silicon at 450° C are carefully evaluated. The energy levels are corrected for the Poole-Frenkel lowering are compared to the ionization energy of the dominant centers revealed by infrared absorption experiments. The capture cross sections are found to be ≈ 2 × 10-12 cm2 for TDI and ≈ 2 × 10-13 cm2 for TD2. Detailed examination of their temperature dependence reveals that they follow a common law σ α T-5.
A Unified Treatment of The Thermal Donor Hierarchies in Silicon and Germanium
Authors: Borenstein Jeffrey T. , Corbett James W.
Published: March 2011

The hierarchies of thermal donor binding energies produced by annealing oxygen-containing silicon or germanium at ca. 450°C are explained by using a generalized perturbation model which involves a standard repulsion parameter for the interaction between agglomerating oxygen atoms and the shallow donor electrons. This model is capable of fitting the ground state ladders for both charge states of the thermal donors in both Si and Ge, since differences between the two ladders can–ee explained entirely by the change in the electron-effective-mass and dielectric constant of the host.
Studies of Oxygen Thermal Donor Formation Under Stress
Authors: Wang Paul W. , Corbett James W.
Published: March 2011

Oxygen thermal donor formation under stress and following various pre-heat treatments was investigated by resistivity measurements. Thermal donor formation at 450°C, with and without bending stress, is monitored in p-type Cz-silicon following various heat-treatments. As has been shown by others, the thermal donor formation rate depends upon the pre-treatment of the samples. We find that the rate also depends on the stress, being faster, or slower, on the tensile side than on the compressed side depending on the pre-treatment.
Luminescence Properties of New Donors in CZ-Silicon
Authors: Vendage Ph. , Magnea N. , Saminadayar K.
Published: March 2011

We report the observation of a new shallow donor center detected in CZ Silicon annealed at 600°C, by EPR and luminescence experiments. The binding energy varies between 30 meV and 17 meV with the annealing time, showing the presence of several centers. The creation rate of these new defects is favoured in carbon rich material. This series of defects is probably one of the components of the New Donors.
Nucleation & Growth of Octahedral Oxide Particles in Silicon: Oxygen Ion Implantation
Authors: Carpenter R. W. , Vanderschaeve G. , Varkera C. J. , Wilson S. R.
Published: March 2011

Czochralski silicon was implanted with oxygen at 0.4 and 3.5MeV to obtain concentrations near 1020 oxygen/cm3 in the implanted region. Following implantation the wafers were aged at about 1000°C for 7 hours, and the resulting precipitates were examined by HREM. A high density of octahedral SiOx precipitates (∼1015/cm3) was the dominant morphology. Plate type precipitates and dislocations were also present at lower density. The data indicate octahedra grow from the plates.
Computer Modelling of the Temperature Distribution in the Silicon Single Crystals During Growth and the Thermal History of the Crystal
Authors: Anttila O. J. , Tilli M. V. , Lindroos V. K.
Published: March 2011

Computer modelling of the silicon single crystal grown by the Czochralski method has been carried out in order to calculate the temperature isotherms as well as to evaluate the thermal history of the crystal. The aim of the present work is to find out to which extent the thermal history of the crystal can be altered without structural modifications of the single crystal furnace. Furthermore, another aim is to study the influence of external heaters, reflectors and cooling elements to the temperature isotherms as well as to the form of the solid-melt interface. The model developed so far takes into account the crystal diameter and the pull rate as well as the radiation from the heater, the crucible and the melt. Furthermore, the inclusive study of the cooling effect of the inert gas flow is under progress.
Quantitative Study of Metal Gettering in Silicon
Authors: Colas Etienne G. , Weber E. R. , Hahn S.
Published: March 2011

Intrinsic gettering of iron in silicon has been investigated with a novel quantitative approach. Concentrations of electrically active, interstitial iron were determined by Electron Pararnagnetic Resonnance before, and after, various annealing cycles, using Cz silicon with oxygen precipitates of different well defined morphologies. Significant differences in the gettering rate in as-grown Cz and Cz silicon with high temperature oxygen precipitates were found. High temperature treatments after metal gettering resulted in the re-emission of the transition metal atoms for both as-grown and high temperature precipitated Cz silicon. This allowed the conclusion that gettering took place via FeSi2 formation in these cases and did not involve any thermally more stable phases.
Chemical Origin of the Grain Boundary Carrier Recombination in Silicon Bicrystals
Authors: Battistella F. , Rocher A. , George A.
Published: March 2011

The minority carrier recombination related to grain boundaries is studied by the SEM/EBIC technique. The specimens investigated are silicon bicrystals obtained by the Czochralski pulling process. The specimens are heated for 2 hours at 750°C in a neutral atmosphere. Heterogeneous recombination of the grain boundaries is then observed.

X-Ray topography and Transmission Electron Microscopy (TEM) have been performed to determine the origin of the heterogeneous recombination. A direct relationship between the local recombination along the grain boundary and the precipitates localized at the interface has been established. The chemical origin of the precipitates is discussed.
Oxygen Effects on Plastic Flow During Growth of Dendritic Web Si
Authors: Spitznagel J. A. , Seidensticker R. G. , Lien S. Y. , Hopkins R. H.
Published: March 2011

The possible effects of oxygen on plastic flow of Si ribbons during growth by the, dendritic web process are described. Cooling rates preclude homogeneous nucleation and growth of detectable SiOx precipitates. Calculated resolved shear stresses on {111} <110> slip systems arising from thermoelastic strains exhibit periodic oscillations in sign and magnitude. The dwell times at elevated temperatures corresponding to zero or low stress periods accompanying such sign reversals are shown to be sufficiently long to permit decoration and locking of dislocations by oxygen atoms.
Yield Stress of Czochralski Silicon–The Effect Of Impurities and Oxygen Precipitate Morphology
Authors: Lawrence J. D. , Tsai H. L.
Published: March 2011

Quantitative measurements of the mechanical properties of Czochralski silicon were made. Samples were strained in tension to determine the yield characteristics (at 800°C) of silicon crystals which had been subjected to various heat treatments and which contained various concentrations of oxygen and carbon. The heat treatments included single step, two step (nucleation and growth) and three step (dissolution, nucleation and growth) annealing. Carbon concentration was found to affect both the rate of oxygen precipitation and the resulting precipitate morphology but did not have a direct effect on the yield stress of unprecipitated samples. There was a clear correlation between the amount of precipitated oxygen and the magnitude of the upper yield stress in samples with the same initial oxygen concentration. Precipitation caused a reduction in the upper yield stress for all precipitate morphologies, but the reduction was less severe (for a given amount of precipitation) where the precipitates were fine grains (<200Å) than where they were larger polyhedra or plates.
The Role of Carbon and Point Defects in Silicon
Authors: Gösele U.
Published: March 2011

An overview of the behavior of intrinsic point defects in silicon and their interaction with carbon is given for temperatures above about 500° C. The diffusive mechanism of carbon in silicon, which involves silicon self-interstitials, is treated in some detail and compared with the diffusion mechanism of oxygen. The solubility of interstitial carbon is estimated. Co-precipitation of carbon and self-interstitials or oxygen are dealt with in terms of simple volume considerations. It is proposed that the contradicting results on the influence of intrinsic point defect supersaturations on oxygen nucleation and precipitation may possibly be explained in the frame-work of opposite effects depending on the carbon concentration. Finally the influence of carbon on the incorporation and diffusion of gold in silicon is discussed.
Dlts-Studies on the “New Oxygen Donor” in Heat Treated and Hydrogenated CZ-Grown SI
Authors: Hölzlein Karlheinz , Pensl G. , Schulz M. , Johnson N. M.
Published: March 2011

Cz-grown Si samples containing a high concentration of oxygen are investigated after various processing steps by DLTS. Heat treatments ranging from 500°C–1000°C are performed to study the formation and annihilation of the “New Oxygen Donor” (ND) traps. Hydrogenation at low temperature leads to a reduction of the ND trap states. The experimental results confirm the “SiOx Interface Model” which assumes two differing types of interfacerelated states.
The Subsurface Hydrogen Barrier Layer in Plasma-Treated Silicon
Authors: Jaworowski A. E. , Wielunski L. S. , Bambakidis G.
Published: March 2011

The near-surface hydrogen profile was measured using the 15N hydrogen profiling technique in silicon. By depositing an adlayer of Al on the surface we were able to observe the separation of the near-surface hydrogen profile in silicon from the surface contamination layer. The hydrogen profiling of the near-surface region revealed the existence of a subsurface hydrogen layer which acts as a barrier to the transfer of hydrogen into the bulk. The observed subsurface layer is saturated with molecular hydrogen and its profile drops off sharply with increasing depth. The structure of this molecular hydrogen barrier and its thermal stability were studied.
Characterization of Dielectric Layers on Hydrogen Passivated Si Surfaces
Authors: Gregory J. A. , Dubé C. E. , Hanoka J. I. , Vayman Z. Y.
Published: March 2011

We have Investigated the layer formed on Si surfaces passivated by a Kaufman Ion source using mixtures of hydrogen and hydrocarbons. Chemical, optical, and electronic techniques were employed to characterize this layer and Its effect on passivation of defects in the Si. The evidence Indicates that the layer Is a dielectric and probably has the formula Six C(1-x) (H). It does not appear to Impede the passivation of polycrystalline Si, but it does affect the reflectivity of the Si material, and also the barrier height In Schottky junctions. We suggest that a similar layer may be formed during other hydrogen/hydrocarbon plasma treatments of SI.
Deep Level Generation-Annihilation in Nitrogen Doped FZ Crystals
Authors: Abe T. , Harada H. , Ozawa N. , Adomi K.
Published: March 2011

Nitrogen atoms exist in silicon as non-reactive nitrogen molecules. This is concluded from two I-R absorption experiments: one is the nitrogen isotope effects on N- N pairs and the other is silicon isotope shifts at 10 K. Intrinsic resistivities (over 20 K ohm-cm) are obtained by annealing at 1000°C, 1 min. in N2 in both p- and n-type nitrogen doped thin wafers. Resistivity increases are due to deep- level generations: 0.66 eV above the valence band for p-type and mainly 0.44 eV below the conduction band for n-type material. These deep levels are considered to be formed by nitrogen pairs and divacancies which are incorporated during growth. Since divacancies are easy to out diffuse to the wafers surface, the deep levels are also irreversibly removed. Diffusion coefficient of Si intersititialswici'ch are annihilated with divacancies in the lattice are calculated as 6×10−6cm2/s and 2×10−6cm2/s at 900°C and 1000°C respectively. Migration energy of Si interstitials is about 4.5 eV.
Off-Center N and O in Silicon
Authors: Hjalmarson Harold P. , Jennison Dwight R. , Binkley J. S.
Published: March 2011

The pseudo Jahn-Teller effect and chemical rebonding are both considered as mechanisms that drive substitutional atoms, such as N in Si, off-center. By use of an effective Hamiltonian technique, impurities forming very deep levels, such as Si:N, are found to be susceptible to off-center displacement by the pseudo Jahn-Teller effect. Using a Hartree-Fock technique, we find two classes of N displacements which depend on the relaxation of the nearest-neighbor Si atom “cage”. For outward relaxation of the four nearest neighbors, the N displaces by 0.05 Å in the [111] direction and retains sp3 bonding; this mechanism appears equivalent to the pseudo Jahn-Teller effect. For inward relaxation of the “cage” by 0.45 Å the N displaces by 0.75 Å in the [111] direction and forms a trigonal sp2 bond; this is a chemical rebonding mechanism. Additional cluster calculations suggest that inward relaxation of the “cage” is likely. Similar calculations for 0 revealed a <100> displacement of approximately 1.1Å.
Rheology and Component Interactions in Tape Casting Slurries
Authors: Morris John R , Cannon W Roger
Published: March 2011

Rheology and the component interactions which affect rheology were studied for a tape casting composition similar to commercial systems. Viscosity measurements at different shear rates were compared to measured tape properties to determine if high or low shear rate rheological behavior controls tape characteristics. Relative viscosity was measured to assess the contribution of each component to the stability of the dispersion.
Kinetics and Mechanisms of Creep in Hot Isostatically Pressed Niobium Carbide
Authors: Nixon Robert D. , Davis Robert F , Bentley James
Published: March 2011

Constant compressive stress creep experiments in the temperature and stress ranges of 1730K - 2100K and 16 MN/m2 - 70 MN/m2 on HIPed NbC0.74 have revealed stress exponents of 2.0 under stress levels of 16–54 MN/m2 at all temperatures investigated and 3.2 under stress levels of 54–70 MN/m2 at 1830K. The activation energy of steady state creep is approximately 230 kJ/mol in the temperature range of 1730K - 1930K under 48–54 MN/m and 470 kJ/mol in the temperature range of 1900K - 2100K under 64 MN/m2. TEM of the annealed but uncrept material reveals grown-in dislocation subboundaries. At 1730K and under 34–54 MN/m2, these subboundaries become single dislocations and dipoles. At 1830K and under 54–70 MN/m the subboundaries evolve into simple tilt boundaries which are occasionally knitted, indicating more glide activity at higher stresses. At 1930K and under 34–54 MN/m , hexagonal subboundaries form, but are not as well defined as in the annealed material. At 2100K and under 16–30 MN/m2, the subboundaries are well-defined hexagonal networks which become polygonized under higher stresses on 64 MN/m2. The experimental and TEM results indicate that at low temperatures (below 0.5 Tm = 2073K) and at all stresses, creep occurs by dislocation glide which is accompanied by subgrain and high angle boundary interaction. At high temperature (above 0.5 Tm), strain occurs by glide and subboundary movement; recovery occurs by climb in the subboundary.
The Defect Structure of Yttria Stabilized Zirconia
Authors: Catlow C.R.A. , Chadwick A.V. , Cormack A.N. , Greaves G.N. , Leslie M. , Moroney L.M.
Published: March 2011

We present results of EXAFS and computer simulation studies of the defect structure of yttria-stabilised zirconia. The results are analysed in terms of dopant-vacancy association models for this phase.
Structure of Dislocations and Interfaces in Non-Metallic Crystalline Materials
Authors: Carter C. B.
Published: March 2011

The present understanding of the structure of grain boundaries and phase boundaries in ceramic materials is briefly reviewed with a view to extracting general conclusions on the structure of such interfaces. Examples of experimental studies of grain boundaries in alpha-alumina, spinel and germanium are discussed together with illustrations of the wustite/spinel and sesquioxide/spinel interface. In the oxide systems discussed here, both the grain boundaries and phase boundaries can facet even in the case where the anion sublattice is effectively undisturbed, this observation emphasises the influence of the cations on the selection of the boundary plane.
The Structure of Surface Steps on Low-Index Planes of Oxides.
Authors: Susnitzky D.W. , Simpson Y. Kouh , De Cooman B.C. , Carter C.B.
Published: March 2011

Surface steps have been observed on low-index planes of alpha-alumina and spinel. The steps were produced by annealing both bulk and perforated thin foil single crystals. A comparative study of bright-field TEM and dark-field REM of the same crystals makes it possible to construct models for the surface structure. Many faceted steps can be observed on the (0001), {0112}, {1010} and {1120} surfaces of alpha-alumina and on the {100} surface of spinel. A detailed study of step faceting and step facet movement during reheating is presented.
Thermal Expansion Measurements by Photodetector Based Laser Beam Position Change Determination
Authors: Vikram C. S. , Agrawal D. K. , Roy R. , McKinstry H.A.
Published: March 2011

A new method for thermal expansion measurements is described. The technique is based on rotation of a laser beam reflected from a probe bar caused by uneven thermal expansions of sample and reference rods. At a distance, the reflected gaussian laser beam is observed with a small photodetector (much smaller than the beam cross-section). The measurement of minute beam position change thus results in related low thermal expansion measurement capability. Experimental arrangement and the sensitivity are described. Some results are also reported.
Synthesis of Metallo-Organic Compounds for Mod Powders and Films
Authors: Vest G.M. , Singaram S.
Published: March 2011

This paper gives the synthesis of several metallo-organic (MO) compounds. The MO compounds have been synthesized so that thermal decomposition produces fine metal oxide powders, or films ⋍0.1 to 0.3 μm thick without going through the powder stage. The Metallo-organic decomposition (MOD) process differs from the SOL-GEL process in that a gel is never formed, and the compound requirements are considerably different. Ferroelectric BaTiO3 and PbTiO3 powders were formed at 600°C and 450°C respectively, which are much lower temperatures than those required by conventional techniques. Defect free tetragonal PbTiO3 films have been formed 1 to 2 μm thick over an area of 1 cm × 1 cm at ⋍470°C, which is 20 to 30°C below its Curie Temperature.
Influence of Transition Metals on The Defect and Optical Properties of Yttrium Aluminum Garnet
Authors: Rotman S. R. , Tuller H. L.
Published: March 2011

The electrical and optical properties of single crystals of Ni, Ni + Zr, and Fe doped Y3Al5O12(YAG) were studied as a function of temperature, atmosphere and composition. The often dramatic changes in properties observed for these materials are interpreted in terms of the underlying defect structure of these materials. Defect formation and migration energies are derived as well as the position of energy states within the gap.
The Application of Transmission Electron Microscopy to the Study of Ti-Diffused Lithium Niobate
Authors: Twigg M. E. , Maher D. M. , Holmes R. J. , Nakahara S. , Sheng T. T.
Published: March 2011

Transmission electron microscope studies of Ti-doped, congruent lithium niobate (LiNbO3) have shown that extended structural faults are only present within the Ti diffused layer (i.e. the wave guiding region). Structural faults have not been observed in undoped control crystals of congruent and stoichiometric LiNbO3. Therefore, it appears that the introduction of Ti is responsible for the formation of these defects. The chemical driving forces which may be controlling the formation of structural faults are discussed.

Diffraction contrast experiments, which have been interpreted in terms of two-beam dynamical theory for a centrosymmetric crystal, indicate that the faults are tensile in nature (i.e. formed by removing a plane of atoms – so-called intrinsic faults) and have a displacement vector of the type c/12/001] when indexed in the hexagonal coordinate system. That is, the displacement vector is along the c-axis. The detailed crystallographic character of the fault planes is not clear; both (118) and (1 1 12) planes have been confirmed from trace analyses and therefore the fault has a shear component. Additional contrast experiments will be required in order to clarify this feature of structural faults in Ti-doped LiNbO3.

Since the extent of these structural faults is tens of microns, they are clearly potential scattering sites for photons. In this regard, a systematic understanding of their origin and thermal stability is crucial to integrated optical device technologies based on LiNbO3 and on the Ti-doped waveguide fabrication technique.
Dilute Aqueous Dispersions of Zro2 And Al2O3
Authors: De Liso Evelyn M. , Cannon W. Roger , Srinivasa Rao A.
Published: March 2011

Colloidal interactions in a heteroparticulate mixture of zirconia and alumina in water were studied for use in a transformation toughened alumina composite. The microelectrophoresis technique was used to measure the mobility of three zirconia powders and an alumina powder. The electro-phoretic mobility and particle size data were used to calculate total potential energy curves. The maximum height of the total potential energy barrier was used to predict the stability of a zirconia/alumina mixture. Theoretical predictions were compared to experimental results obtained from sedimentation and rheology measurements carried out as a function of pH of the dispersion. For a 5 v/o aqueous zirconia/alumina system stable dispersions were made at pH 3 and pH 5.
Glass Optical Guided-Wave Technology
Authors: Miyashita T.
Published: March 2011

Recent advances of glass materials and fabrication processes will be reviewed in the field of guided-wave technology. A variety of optical fibers and guided-wave devices are in development by using high-silica and non-silica glasses. Following the successful development of silica fiber, a new family of optical fibers is being investigated by using non-silica glasses such as fluoride and chalcogenide glasses, which operate at mid-infrared wavelength range and offer the potential of ultra-low loss. High-silica channel waveguides are fabricated by processing a SiO2TiO2 planer waveguide on a silicon substrate. These are applied to various guided wave optical circuits such as switch and wavelength-division multi/demultiplexer, which would be used for the construction of optical communication systems. The materials and processing techniques influencing optical guided-wave performance are described.
Effects of Irradiation on the Electrical Properties of Alpha-Quartz Crystals
Authors: Ling S. , Lim B. S. , Nowick A. S.
Published: March 2011

A study is made of irradiation effects on α-quartz crystals using the techniques of electrical conductivity and dielectric loss measurements. The initial radiation-induced conductivity (RIC) induced by X-ray irradiation over the temperature range from 94 to 250 K is found to have a nearly constant activation energy of 0.29 ± 0.02 eV. Since a large RIC still results from irradiation at temperatures too low for alkalis to be liberated, it is proposed that the RIC is due to holes (as small polarons) rather than to alkalis. The dielectric loss measurements in Na-swept quartz are used to follow the changes in the relaxation peaks due to the Al-Na defect as a function of radiation dose and annealing. At the same time a low-temperature “irradiation peak” is studied. Restoration of the main Al-Na peak during annealing occurs in two stages: one near 500 K and the other above 600 K. From the observed behavior of the irradiation peak in various crystals, it is concluded that this peak is probably due to alkali centers. Finally, a defect model interpreting the two annealing stages is presented.
Surface Modification of Sic by Ion Implantation
Authors: Wood Susan , Spitznagel J. A. , Choyke W. J. , Bradshaw J. , Greggi J. , Doyle N. J.
Published: March 2011

Predominantly 6H <0001> SiC single crystals have been implanted with nitrogen and aluminum at 300°K. The effects of implantation and post-implantation annealing at 573–1173°K have been characterized by Rutherford backscattering/channeling, microhardness measurements and transmission electron microscopy. Even at 1173°K, defect annealing was inhibited in amorphized regions. Progressive damage recovery as the anneal temperature was increased was otherwise generally observed. Fluences predicted by the critical damage energy of 2 × 1021 keV/cm3 did not quite produce amorphization to x = 0. In the as-implanted specimens, decreasing hardness was observed with increasing fluence. Significant surface softening (∼ 33% hardness reduction) was achieved at the highest aluminum fluence (5 × 1015 Al/cm2) and was stable at temperatures < 893°K.
R-Curve Behavior and The Mechanical Properties of Transformation-Toughened ZrO2-Containing Ceramics
Authors: Steinbrech R. W. , Heuer A.H.
Published: March 2011

Current understanding of R-curve behaviour and the strength-toughness relationship of transformation-toughened ZrO2-containing ceramics is reviewed. If the toughness increases with crack, extension along an R-curve, a maximum in strength versus toughness is observed, which is related to the crack instability criterion for R-curves. An analytical expression from a well-known “wake” theory of crack tip shielding due to McMeeking and Evans is used to compute R-curves and strength/toughness relations, which are compared with experiment.
Properties of Yttria Stabilized Tetragonal Zirconia Polycrystals
Authors: Matsumoto Roger L. K. , McEntire B. J.
Published: March 2011

The properties of yttria stabilized tetragonal zirconia polycrystalline ceramic fabricated from commercial powders are described. The fracture strength, fracture toughness, density, and low temperature aging effects, are studied for sintered and hot isostatically pressed ceramics. The role of alumina as an additive to the material and its influence on properties is also discussed.
X-Ray Photoelectron Spectroscopy of In-Situ Fractured Reaction Bonded Silicon Nitride
Authors: Donley M. S. , Stoebe T. G. , Thomas M. T.
Published: March 2011

The grain boundary chemistry of reaction bonded silicon nitride (RBSN) and the effects of iron species and content on this chemistry are investigated using X-ray photoelectron spectroscopy (XPS). Data are reported for semiconductor grade RBSN, Fe-doped semiconductor grade RBSN, and metallurgical grade RBSN specimens. Results indicate that the grain boundaries have an elemental composition of Si, N, O, and C, with important chemical differences depending on the purity of the starting material. In the RBSN made from metallurgical grade silicon, the grain boundaries have a distinct “oxide-like” layer, with a subregion of Si3N4. No distinct oxide layer was observed in the RBSN made from semiconductor-grade silicon, where the O appears to be uniformly incorporated into the Si3N4.
Processing and Properties of Reaction Bonded Silicon Nitride Made from Laser Synthesized Silicon Powders
Authors: Haggerty J. S. , Garvey G. , Lihrmann J-M. , Ritter J.E.
Published: March 2011

Laser synthesized silicon powders have been used to make reaction bonded silicon nitride samples. Maximum hardness (11.3 GNm−2), fracture toughness (3.6 MNm−3/2), pore size (Hg porosimetry 50–300Å radius) and strength (∼460 MNm−2) values reflect the superior microstructures that are observed. With anaerobic anhydrous processing, these powders nitride to completion in less than 7 hours at 1400°C.
The Hardness Of Ion Implanted Ceramics
Authors: Oliver W. C. , McHargue C. J. , Farlow G. C. , White C. W.
Published: March 2011

It has been established that the wear behavior of ceramic materials can be modified through ion implantation. Studies have been done to characterize the effect of implantation on the structure and composition of ceramic surfaces. To understand how these changes affect the wear properties of the ceramic, other mechanical properties must be measured. To accomplish this, a commercially available ultra low load hardness tester has been used to characterize Al 2O3 with different implanted species and doses. The hardness of the base material is compared with the highly damaged crystalline state as well as the amorphous material.
Clean-Room and Co2-Laser Processing of Ultra High-Purity Al2O3
Authors: Morris P.A. , French R.H. , Coble R.L. , Tebbe F.N. , Chowdhry U.
Published: March 2011

Clean-room powder processing, furnace firing, and CO2-laser heating techniques to produce high-purity Al2O3 ceramics were applied to a new source of high-purity Al2O3 ( 〉13 ppm total and 〉8 ppm cation detected impurities). The chemical analyses of the material after each stage of processing and firing indicate that the procedures used in this work give no detectable contamination of the material. The microstructure of a CO2-laser ultra high-purity Al2O3 is illustrated. Densification is incomplete for this material. Calcination and deagglomeration were not optimized. Procedures, such as these are required to control the trace impurity contents in a fired ceramic material
Energy Changes During Crack Extension in Compression
Authors: El-Rahman M. , Shrive N. G.
Published: March 2011

Much is known about the tensile fracture, both brittle and ductile: theories are well developed. There is no equivalent theory for compressive failure. A generalized theorem has been developed based on the concept of cohesive strength and the fact that tensile stresses frequently develop around the surface of voids in a material subject to compression. The theory does not produce criteria on critical flaw size. The latter should result from an energy criterion. It is shown, however, that modelling compression cracks as zero width flaws results in no energy change as the crack extends: an anomalous result compared with experimental findings. Allowing compression cracks to have finite width results in strain energy reduction as the ‘crack’ gets larger. A three-dimensional ellipsoid has been used as a model of a compression ‘crack’. Strain energy reduction in the medium, due to the presence of the void, is shown to depend on both its shape and its size. Initial estimates of a compressive G - a compressive energy release rate as the ‘crack’ extends - also suggest a dependence on both size and shape of the cavity. The results indicate further investigation is warranted.
Strain Rate Effects on Concrete and Reinforcements, and their Contributions to Structures
Authors: Takeda Jin-ichi
Published: March 2011

This paper deals with the rate effects on concrete and reinforcements, especially unfavorable effects for the dynamic design of concrete or reinforced concrete structures. The rate effects on concrete are divided into two effects, the rate effect on stress-strain relations and that on fracture criteria of concrete which bringsabout occasionally the unfavorable and brittle fractures of concrete and reinforced concrete structures.

It is also described that the brittle fractures are usually caused by the rapid propagation of cracks generated in concrete under the high rate loadings, which can be said to be one of the rate effects on concrete.
Effects of Loading Rate on Cracking of Cement Paste in Compression
Authors: Darwin David , Attiogbe Emmanuel K.
Published: March 2011

Submicroscopic cracking within cement paste is studied for monotonic and short-term sustained loading. Loading times range from 1.25 minutes to 4 hours. Water cement ratios of 0.3 and 0.5 are used. Specimens are loaded to preselected strains and immediately unloaded. The specimens are then sliced with a diamond saw and viewed in a scanning electron microscope. Crack traces are cataloged based on length, width and orientation. The crack traces are converted to three dimensional crack distributions, which are in turn used to determine the degree of softening due to cracking. The results indicate that for loading to a fixed strain, slow loading results in less cracking than rapid loading. However, at the same stress-strength ratio, rapid loading results in fewer cracks. The results indicate that the role of submicroscopic cracking in the nonlinear behavior of cement paste increases with strain rate.
An Impact Damage Model of Concrete
Authors: Kobayashi A. S. , Hawkins N. M. , Du J. J.
Published: March 2011

Dynamic fracture of two impact loaded, plain concrete, three-point bend specimens was simulated using a dynamic finite element model. A three-segment fracture process zone, which was established in a previous static analysis, together with a tensile overload fracture criterion were used to propagate the crack from the tension side of the unnotched beams. Reasonable agreement between the measured and computed velocities at two points on one beam and estimated and computed average crack velocities was obtained.
Response of Confined Concrete to Cyclic Loading at Various Slow Strain Rates
Authors: Perry S. H. , Al-Shaikh A. H. , Cheong H. K.
Published: March 2011

Tests have been undertaken in the Imperial College concrete laboratories to study the effect of cyclic loading upon the compressive strength, the stress-strain relationship and the energy absorption and dissipation characteristics of concrete prisms at variable strain rates. Comparison is made with prisms loaded monotonically at similar strain rates. Prisms were confined by high-tensile steel bolts inserted horizontally in two orthogonal directions through pre-formed ducts, and the annular space between ducts and bolts was grouted with high strength epoxy resin. Both steel and concrete deformational response was measured. Significant enhancement of the strength and ductility of the concrete was obtained. Specimens displayed large energy absorption and dissipation capacity under cyclic loading. The validity of an envelope curve to describe cyclic behaviour is discussed.