bluuebunny/crossref_metadata_2025_split huggingface dataset:
Nitrogen in Crystalline Si
Authors: Stein Herman J. 
Published: March 2011

ABSTRACTUse of N doping, N gas ambients and N implantation in Si processing has stimulated study of the incorporation and behaviour of N in Si. Studies of N-implanted Si and comparisons with melt-doped Si have shown that N pairing is the dominant mode for bonding of N into crystalline Si for a wide range of processing conditions. Studies have also shown that laser annealing quenches a small percentage of implanted N into a substitutional site. Nitrogen diffusion and aggregation have been shown to occur in N-implanted Si upon furnace annealing at temperatures >700°C and there is a simultaneous formation of shallow donors. Interactions between N and other impurities occur in both as-grown and ion-implanted Si. Additional studies are needed to describe more fully the electrical and structural consequences of N-N, Nimpurity and N-defect interactions in Si.
The Electronic Structure and Atomic Symmetry of The Oxygen Donor in Silicon
Authors: Stavola Michael , Lee Keon M. 
Published: March 2011

ABSTRACTThe infrared spectrum of oxygen donor complexes in silicon under uniaxial stress has been examined for the neutral and singly ionized charge states. Our results are consistent with an effective mass-like ground state wave function that is constructed from a single pair of conduction band valleys for both charge states. A thermal ionization experiment in which the stress split components of the ground state are monitored by the absorption of polarized light confirm this interpretation and provide correlation with DLTS and EPR results. Additional small splittings, due to deviations from effective mass theory, show that the electronic wave function of the oxygen donor is distorted by an extended “central cell” with C2v symmetry. Previously observed splittings of 1s → np± transitions for the singly ionized charge state at zero stress are interpreted in terms of the effect of the anisotropic oxygen donor structure upon excited state wave functions constructed from the single pair of conduction band valleys
Effect of Cerium Oxide Additions on the Densification Behaviour of Alumina Gels
Authors: Dwivedi Ratnesh , Adams Jane 
Published: March 2011

AbstractSintering behavior of gel-derived alumina containing 2.8 mol percent cerium oxide (Ce2 O3) was studied at 1400°C. The growth morphology of alpha alumina in cerium oxide-containing aluminas was found to be significantly different form that of pure gel-derived alumina. Alumina gel containing 2.8 mol % Ce2 O3 was found to densify to 81% of the theoretical density as compared to 65% for pure alumina gels. The powdered cerium oxide-containing gels, pressed into a pellet, could be sintered to 97% of the theoretical density at 1400°C as compared to 87% found for pure alumina gel powder processed in an identical manner.
Models for Electronic Conduction Across Ceramic Grain Boundaries
Authors: Burton L. C. 
Published: March 2011

AbstractElectronic current flow over grain boundary potential barriers for low resistance grains is first reviewed. It is then shown that if the resistance of the grains increases and/or grain size is reduced, the grains may be totally depleted of mobile charge. The grain boundary barrier is thus reduced to (D/2W)2 of its original large grain value, D being grain width and W the full space charge width. For high resistivity grains satisfying the relation D ≪ 2W, the conduction band becomes essentially flat. Phenomena formerly caused by grain boundary potential barriers (varistor and PTC effects seen in semiconducting ceramic) will be greatly reduced, or eliminated.Commercial COG and X7R MLC capacitors exhibit a transition from super-ohmic to ohmic behavior at high voltages, paralleling the behavior of the varistor. Two possible mechanisms that could account for this are varistor-like grain boundary behavior, or space charge limited diffusion current.
Defect Creation and Photoablation in Stoichiometric and Sub-Stoichiometric SiO2
Authors: Devine R. A. B. , Fiori C. 
Published: March 2011

AbstractIt is demonstrated that microscopic point defects can be created in amorphous silica using pulsed ultraviolet irradiation (λ = 248 nm) at energy densities ∼ 100 times less than those normally estimated to lead to damage creation. Identification of the physical character of the defects has been made using electron spin resonance spectroscopy and electrical measurement techniques. Continued irradiation of the SiO2 is found to lead to photoablation. Results obtained for bulk dry SiO2, thermal SiO2 and vacuum deposited SiOx are presented. The important role of non-stoichiometry (defect structure) in the process of photoablation is clearly manifested by comparison of the results obtained for the different types of SiO2. Possible physical mechanisms involved are discussed.
Ion Beam, Rapid Thermal, and Laser Mixing Phenomena in Insulators
Authors: Narayan J. , Appleton B.R. 
Published: March 2011

AbstractWe have studied mixing of metal overlayers (Ni, Cr, Ti, W, Ta, Zr, Cu) on insulators (SiC, Si3N4, Al2O3, SiO2) after ion beam irradiation, rapid thermal annealing, and pulsed laser irradiation. The nature and amount of mixing varies from stoichiometric to continuous, to ballistic, to no mixing at all. For a given system, the amount of mixing was found to increase with increasing substrate temperature. The enhanced mixing with increasing substrate temperature is correlated with concomitant free energy associated with the reactions. Certain systems such as Cu on Al2O3 do not exhibit mixing, but rearrangement within a few atomic layers at the interface results in enhanced adhesion and no aggregation upon annealing at moderate temperatures.
Ion Implantation and Annealing of Crystalline Oxides
Authors: White C. W. , Sklad P. S. , Boatner L. A. , Farlow G. C. , McHargue C. J. , Sales B. C. , Aziz M. J. 
Published: March 2011

AbstractThe crystallization of amorphous surface layers produced by ion implantation of single-crystal α-Al2O3 and CaTiO3 are discussed. During annealing, amorphous A12O3 converts first to the α-phase. The crystallized γ then transforms to the a-phase by the motion of a well-defined planar interface. The temperature dependence of the velocity of the γ/α interface has been measured and is characterized by an activation energy of ∼3.6 eV. In CaTiO3, crystallization of the amorphous phase takes place by solid-phase epitaxy. The velocity of the amorphous/crystal interface is characterized by an activation energy of 1.3 eV.
Photoluminescence, Raman Scattering and Rbs/Channeling of Epitaxial Fluorides
Authors: Choyke W.J. , Bradshaw J.L. , Mascarenhas A. , Feng Z.C. , Sinharoy S. , Hoffman R.A. 
Published: March 2011

AbstractGrowth conditions are described for producing high quality crystalline films of CaF2 on (100) and (111) GaAs and LaF3, CeF3 and NdF3 on (111) Si. Rutherford backscattering/channeling, low temperature (<2K) photolumin-escence and Raman scattering are used as diagnostic techniques to probe the crystalline quality of the films and the stress/disorder induced at the film-substrate interface due to lattice mismatch.
The Formation and Annealing of Amorphous Layers of Al2O3
Authors: Farlow G. C. , Sklad P. S. , White C. W. , McHargue C. J. , Appleton B. R. 
Published: March 2011

AbstractThe critical dose for formation of an amorphous layer of Al2O3 by ion irradiation at 77 K has been determined. It is found to lie between 2 and 3 × 1015/cm2 if the sample is irradiated near the <0001> axis of the substrate and is found to lie in the neighborhood of 2 × 1016/cm2 if the irradiation is near the <1210> axis. The amorphous layers are found to recrystallize epitaxially if annealed at 1190 degrees C and to form a metastable microstructure upon annealing at 800 degrees C.
Problems Associated with Active Ion Distributions in Solid State Laser Materials
Authors: Powell Richard C. 
Published: March 2011

AbstractProblems associated with nonrandom distributions of active ions in solid state insulator laser materials are discussed. A12O3:Ti3+ and BeAl2O4:Cr3+ crystals are used to show typical examples of some of these problems. In addition some problems of this type observed in new materials with potential for solid state laser applications are discussed.
The Application of ß“-Alumina As A Solid State Laser Host
Authors: Barrie J. D. , Yang D. L. , Dunn B. , Stafsudd O. M. 
Published: March 2011

AbstractIon exchanged ß“-aluminas display a number of interesting optical properties which suggest that the material is well suited for application as a solid state laser host. Small platelets of Nd3+ Ion exchanged β“-alumina exhibit laser action with gain coefficients many times greater than YAG. The versatility of the ion exchange process enables one to form a wide variety of compounds with different active ions and concentrations, thereby allowing the study of many different effects within a single host crystal.
Ion Induced Alterations of LiNbO3
Authors: Buchal C. H. , Appleton B. R. , Christie W. H. , Ashley P. R. 
Published: March 2011

AbstractAn attempt is made to fabricate positive-index waveguides by ion implantation of metal ions into crystals of LiNb03. The observed structural, chemical, and optical damage is summarized and possible solutions are discussed.
Voltage Dependent Plasticity in Mercury Cadmium Telluride
Authors: Pellegrino Joseph , Galligan J. M. 
Published: March 2011

AbstractThe effect of an applied, time varying voltage on the plastic behavior of (Hg,Cd)Te has been investigated. We observe that both positive and negative voltages suppress plasticity, with the negative voltage being more effective. The influence of this voltage polarity is strain dependent and provides information on the charge of the mobile dislocations. From these results we present a model of the strain dependence of the voltage dependent plasticity.
Point Defects and High-Temperature Deformation of NiO
Authors: Goretta K. C. , Routbort J. L. 
Published: March 2011

AbstractThe steady-state flow stress τs in nonstoichiometric NiO single crystals has been measured in the temperature range of 1428 to 1653 K with oxygen partial pressures p(O2) between 6 and 1×105 Pa. Strain rates were varied from 1×10−5 to 2×10−3 s−1. Transmission electron microscopy indicates that dislocation climb is the primary mechanism of recovery. Because dislocation climb is diffusion controlled, the data may be described at fixed temperature by = Aτns (O2)1/m, where n is the stress exponent and m is a parameter that is determined by the dominant atomic defects on each sublattice. At high temperatures and p(O2) > 2×104 Pa, n was found to be in agreement with dislocation-climb models; however, n increased at low p(O2) owing to effects of impurities. The values of m are consistent with control of climb rate by diffusion of singly charged oxygen vacancies for low p(O2) and by diffusion of neutral oxygen interstitials for high p(O2). At lower temperatures, the values of n are strongly affected by dislocation/impurity interactions for all p(O2).
Effects Of Excess Al2O3 And TiO2 On Microstructure And Properties Of Al2TiO2 Ceramics Prepared from CVD Powders
Authors: Hori Saburo , Yoshimura Masahiro , Sōmiya Shigeyuki 
Published: March 2011

AbstractThe effects of excess AI2O3 and TiO2 on microstructure, bending strength and thermal expansion of Al2TiO5 ceramics were studied by sintering various compositions of CVD Al2O3-TiO2 powders at 1310°C for 4 h. Excess Al2O3 resulted in much higher bending strength with slightly higher thermal expansion, while excess Ti02 resulted in slightly higher strength with lower thermal expansion. The excess AI2O3 and TiO2 were uniformly dispersed as particles on the Al2TiO5 grain boundaries, creating interlocked grains and dispersed microcracks. Excess TiO2 enhanced the material diffusion while AI2O3 did not, and appeared to develop more anisotropy of Al2TiO5 grains, resulting in lower expansion. It was proved that the overall properties of Al2TiO5 ceramics could be improved by dispersing excess Al2O3 or TiO2 uniformly onto the grain boundaries.
Phase Separation in Reduced LiNbO3
Authors: Chan H.M. , Zhuang Z. , Smyth D. M. 
Published: March 2011

AbstractLiNbO3 tolerates large amounts of disorder in the form of Li2O- deficiency, oxygen-deficiency, and substitutional impurities. These should all result in the formation of a self-consistent set of lattice defects, and there will thus be interactions between the different types of disorder. It is shown that reduction will result in an increase of the Li2O activity in LiNbO3 when it is kinetically hindered from exchanging Li2O with its surroundings. This is in fact the situation for exposure to reducing atmospheres for several hours near 1000°C. Available data on compositions and defect concentrations at 1050°C indicate that reduction should result in separation of a Li20-rich second phase for oxygen partial pressures below 10−17 about 10 atm. Evidence for such phase separation is described.
Crack Development in Cementitious Materials under Impact Loading
Authors: Mindess Sidney , Banthia Nemy P. , Ritter Andrew , Skalny Jan P. 
Published: March 2011

ABSTRACTFlexural specimens of hardened cement paste, fibre reinforced concrete, and conventionally reinforced concrete were tested in an instrumented dropweight impact machine, employing a 345 kg mass impact hammer dropped from a height of 500 mm. The crack development in the specimens was monitored using high speed motion picture photography, carried out at about 10,000 frames per second. It was found that, for all three specimens, some crack branching occurred. The cracks did not propagate in a continuous fashion; they appeared to arrest occasionally, and then began to grow again. However, it appeared as if the crack velocities reached a maximum value very soon after the impact occurred; they then decreased, and finally increased again just prior to failure. The average crack velocities were in the range of about 75 to 115 m/s.
Behaviour under Explosive Loading of Concrete Reinforced with Polymer Grids
Authors: Hobbs B. , Watson A. J. , Oldroyd P. N. 
Published: March 2011

ABSTRACTThe characteristic of a new form of high strength polymer grid are outlined and its possible uses as reinforcement in concrete subjected to dynamic loading are discussed. Details are given of a test programme in which concrete slabs reinforced with a range of grid types in various configurations have been subjected to explosive loading from contact charges of plastic explosive. A range of both transient and post-test measurements were taken. Results are presented showing how the various damage parameters measured vary with the position and number of polymer grids used in the slabs. The results of the transient measurements are used to suggest mechanisms for damage formation. It is concluded that these polymer grids are effective in restraining explosively generated damage in concrete slabs and that in many circumstances their light weight and their inherent resistance to normal corrosion processes may give them significant advantages over conventional steel reinforcement.
Strain Rate Effects on Tensile Properties of Fiber Reinforced Concrete
Authors: Nammur George G. , Naaman Antoine E. 
Published: March 2011

ABSTRACTHigh strain rates lead to substantial modifications in the stress-strain (or stress-displacement) response of fiber reinforced concrete in tension. These modifications include higher strength and corresponding strain, as well as smaller displacement at failure.The purpose of this paper is to investigate the behavior of fiber reinforced concrete under impact tensile loading, and to study the effect of strain rate on the post-cracking strength of the composite. The variation of the tensile strength of the matrix with the reinforcement parameters such as volume fraction Vfand aspect ratio |/φ of the fibers is also studied ip this paper. A special emphasis is placed on the stress-displacement relationship of steel fiber reinforced concrete in its post-cracking range. An empirical model of the stress- displacement relationship as a function of the strain rate is developed from experimental data from tensile tests on dogbone shape notched tensile prisms. The model highlights the effects of strain rate and fiber properties on the post-cracking strength of the composite, as well as the displacement at failure. The effect of strain rate on the post-cracking toughness of fiber reinforced concrete is also addressed. The literature on impact effects on concrete in tension (plain and fiber reinforced) is briefly reviewed in this paper, and so is the state of the art of testing techniques for strain rate effects.
Available Alkalis in Fly Ash
Authors: Lee Chau , Schlorholtz Scott , Demirel Turgut 
Published: March 2011

ABSTRACTThe available alkalis of six Iowa fly ashes, four Class C and two Class F, have been studied as outlined by the procedures listed in ASTM C 311. The purposes of the study were to: (1) assess the significance of the test when it is used to analyze different fly ashes; (2) to investigate the possibility of decreasing the time required to complete the test (it currently requires 28 days for curing). When cured for 28 days at 38 C, the available alkalis were found to be about 60% and 30% of the total equivalent alkalis (equivalent alkalis = %Na20 + 0.658 × %K20) for Class C and Class F fly ashes, respectively. However, more than 85% and more than 40% of the total equivalent alkalis for the Class C and Class F fly ashes, respectively, were mobilized after 5 to 6 months of curing at 38 C. It was concluded that the available alkali test described in ASTM C 311 tends to underestimate the amount of equivalent alkalis present in Class C fly ash-calcium hydroxide mixtures after long periods of time.
Fly Ash Cement: Production Methods, Materials Properties and Energy Savings
Authors: Stoltenberg-Hansson Erik 
Published: March 2011

ABSTRACTA standard system for grinding of Portland clinker to cement and the different principles for producing fly ash cement is described. The quality is influenced by the grinding system selected. The preferred system for intergrinding of fly ash and clinker involves introduction of fly ash into the finishing compartment of the mill. Efforts made to relate cement quality to specifications are described. Much attention is put on the physical characteristics of the fly ash: bulk weight, specific weight, particle distribution, particle shape, degree of agglomeration and colour. Surface areas and pozzolanic activity matter, but the air void content, which is much affected by grinding, is more important. This observation is based on testing of fly ashes and fly ash cements from production and laboratory grindings. The testing includes compressive strength, specific gravity, laser granulometry and SEM. The results have led to the introduction of new analytical and control procedures. A review of fly ash quality factors of most importance for cement producers is given. The energy balance in the production of blended fly ash cement involves savings from reduced consumption of clinker, and expenditure on transport, handling of fly ash and extra grinding of clinker and fly ash; net savings may be considerable.
Trapping of Chloride Ions in Cement Pastes Containing Fly Ash
Authors: Roy D. M. , Malek R. I. A. , Rattanussorn M. , Grutzeck M. W. 
Published: March 2011

ABSTRACTChloride ions, when present at sufficient concentration in the concrete pore fluid, may be associated with corrosion of the reinforcing steel even in normally passivative environments. The effectiveness of fly ash containing pastes in trapping chloride ions was studied. A paste was prepared containing 30% low-calcium fly ash and 70% type I cement, with mixing water (50% by weight) containing 0.4% C1− with respect to the solid. Samples were cured at 25°C and 38°lC at 95% R.H. At designated times extending over a six-month period, the pore fluids were expressed from the hardened pastes using a squeezing cell designed for this purpose. Special precautions were taken to avoid carbonation of the fluids; contact with the atmosphere was minimized. The expressed fluids were analyzed by DC plasma emission spectrometry for cations and by automated selective ion exchange chromatography for anions. Other studies (XRD, thermal analysis) were carried out to identify the compounds formed and determine their mechanisms of formation. Investigations indicated that the mechanism of trapping chloride ion is partly chemical and partly physical through adsorption on the surface of fly ash particles (initially physical and subsequently chemical).
Danish Fly Ash Utilization
Authors: Jensen Svend Aage 
Published: March 2011

ABSTRACTSince 1976 the rate of utilization of fly ash from Danish power stations has increased from about zero to more than 75% of production. The main reason for this growth is the co-operation between the utilities and the fly ash consumers, i.e. predominantly the Danish and the Norwegian cement producers. This paper deals mainly with the precautions against separation, with storage and shipment of quality ash, and with the main principles of the co-operation between the producer and the consumer.
The Research-Technology Interface in the Fly Ash-Concrete Regime
Authors: Idorn G. M. 
Published: March 2011

ABSTRACTOpportunities for development of the use of fly ash in blends with Portland cement by improvement of the relevant research are discussed in view of the currently modest growth of the fly ash utilization, despite copious research activity during the past decade. Refined characterization is suggested of the decisive parameters of the chemistry, mineralogy and granulometry of both the components of the reacting, blended system, and also of the effects induced by chemical admixtures. Effective dispersion of the finest particle fractions in the fresh paste, and monitored integral hydration are indispensable successive precursors for the creation of a blended, hardened cement paste which acts as a “microconcrete”, having dense matrix consisting of fully hydrated, finest fractions of both source materials and coarser unhydrated particles representing “microaggregates”. Surface chemistry and energetics are emphasized as essential scientific regimes to apply for the explanatory research having as their aim substantial increases of the replacement ratios of fly ash to cement in concrete.The Materials Research Society (MRS) is a possible instrument for activity to encourage development of research planning and management methods, which are used in other fields of materials research, to strengthen research as an instrument for effective recovery of the chemical energy inherent in fly ash and for improvement of concrete durability.