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Showing papers in "MRS Proceedings in 1987"


Journal ArticleDOI
TL;DR: In this paper, a selective nucleation based crystal growth-technique over amorphous substrates is originated, which manipulates nucleation sites and periods and hence, controls the grain boundary location by modifing the substrate surface.
Abstract: A selective nucleation based crystal-growth-technique over amorphous substrates is originated. The method manipulates nucleation sites and periods and hence, controls the grain boundary location by modifing the substrate surface. In Si, small Si 3 N 4 nucleation sites are formed, 1–2 pm in diameter, 100 μm in period, over Sio 2 . One Si nucleus is formed exclusively in the small area of Si 3 N 4 by CVD. The highly faceted and periodically located nuclei grow over SiO 2 up to 100 μm in diameter before impingement. A MOS-FET fabricated inside the island operates comparably to the bulk Si control

155 citations


Journal ArticleDOI
TL;DR: In this paper, a new model for coal fly ash morphogenesis based on temperature-viscosity effects in the mineral precursor melts in the boiler flame is proposed and discussed in terms of phase relations in the CaO-SiO2-Al2O3 and FeO-Fe2O 3-A12O3−SiO 2 systems, modification of the aluminosilicate glasses by alkali and alkaline earth metal cations, and microheterogeneity involving glass devitrification and phase separation.
Abstract: Recent advances in the characterization of the glassy aluminosilicate phases in coal fly ashes are reviewed and discussed in terms of the development of new models describing their mechanism of formation, composition, structural relationships and chemical reactivity. Characterization techniques such as electron microscopy, x-ray diffraction, infrared and Raman spectroscopy, nuclear magnetic resonance and Mossbauer spectroscopies, thermal analysis, acid dissolution, silanation, and density fractionation have been used as experimental probes, and reveal a range of information relating to the glass phases from the macro, through the micro, to the nano-structural levels. Complex inter- and intra-particle heterogeneity in ash is observable not only in bulk chemical and mineralogical analyses but also at the molecular level in the constituent glasses. Remarkable relationships between ash particle size, density and glass composition have been observed and lead to a new proposed mechanism for ash morphogenesis based on temperature-viscosity effects in the mineral precursor melts in the boiler flame. A glass-ceramic model for fly ash particle structure is proposed and discussed in terms of phase relations in the CaO–SiO2–Al2O3 and FeO–Fe2O3–A12O3–SiO2 systems, modification of the aluminosilicate glasses by alkali and alkaline earth metal cations, and microheterogeneity involving glass devitrification and phase separation.

118 citations


Journal ArticleDOI
TL;DR: In this paper, a microstructural investigation of the interface between aggregate and concrete using backscattered electron (bse) imaging combined with quantitative image analysis was performed, and the results confirmed the applicability of the bse -image analysis technique, but indicate that the interfaces in specimens prepared in this manner may not be representative of aggregate paste interfaces in concrete.
Abstract: The effectiveness of condensed silica fume as a strength enhancing additive in concrete has been attributed to its ability to modify the interfacial zone between paste and aggregate. This paper describes a microstructural investigation of this interface using backscattered electron (bse) imaging combined with quantitative image analysis. Composite specimens were made in which a single piece of aggregate was embedded in cement paste. Granite, dolomite and garnet aggregates were used. After curing, the specimens were sectioned perpendicular to the surface of the aggregate particles and polished. The variation in porosity, amount of anhydrous material and calcium hydroxide (CH), with distance from the aggregate surface was measured. It was found that the porosity increases in the paste close to the interface, while the content of anhydrous grains decreases. No significant increase in CH content was found near the interface. The results confirm the applicability of the bse - image analysis technique, but indicate that the interfaces in specimens prepared in this manner may not be representative of aggregate paste interfaces in concrete.

96 citations


Journal ArticleDOI
TL;DR: In this article, a hand-held tool was developed for preparing TEM samples, which is 2.50″ in diameter and 3.0″ high and can be used for rough-cut samples.
Abstract: A grinding/polishing tool has been developed for preparing TEM samples. The hand-held tool is 2.50″ in diameter and 3.0″ high. Rough-cut samples, 300 to 600 microns thick, are routinely polished to 5 microns thick in four to six hours using this tool. As these 5 micron samples are so thin and uniform, a separate dimpling operation can be eliminated. Likewise, the time required to ion-mill the sample can be reduced to 0.5 to 2.0 hours – greatly reducing ion-milling artifacts and significantly increasing the area viewable by TEM. The process is equally effective for all classes of samples: Silicon devices, ceramics or metals – in either cross-section or planar views.

74 citations


Journal ArticleDOI
TL;DR: In this paper, the long term corrosion of two reference Belgian high-level waste glasses (SAN60 and SM58) was investigated in pure water using powdered glass at a high surface area to volume ratio and temperatures of 90 and 120°C.
Abstract: The long term corrosion of two reference Belgian high-level waste glasses (SAN60 and SM58) were investigated in pure water. The corrosion was studied using powdered glass at a high surface area to volume ratio and temperatures of 90 and 120°C. The experimental data at 90°C reveal a “final” leach rate which decreases with time. At 120°C this “final” state is transient and followed by an enhanced dissolution, which was correlated with extensive surface crystallization. Modelling using the PHREEQE and GLASSOL computer codes described the initial corrosion, but was unable to account for the enhanced dissolution at 120°C.

64 citations


Journal ArticleDOI
TL;DR: In this article, the final preparation methods described in this paper include electropolishing, ion beam thinning, ultramicrotomy and replication, and a guide to the choice of technique is presented.
Abstract: The aim of thin foil preparation is to produce a specimen for microscopy which is representative of a larger volume of material, and in which the detail can be seen and interpreted. It is in general necessary to undertake some initial preparation before the final thinning process. Both stages are described. The final preparation methods described in this paper include electropolishing, ion beam thinning, ultramicrotomy and replication. A guide to the choice of technique is presented.

58 citations


Journal ArticleDOI
TL;DR: In this article, the introduction rates of dominant defects have been determined for electron-irradiated, p-type silicon as a function of oxygen and boron concentration, and the identities of an electron trap and a hole trap have been clarified.
Abstract: Introduction rates of dominant defects have been determined for electron-irradiated, p-type silicon as a function of oxygen and boron concentration. Samples included those with oxygen content ranging from 8 × 1015 to 7 × 1017 cm−3. Initial results are described for samples with measured carbon content varying from 2 × 1015 to 6 × 1016 cm−3. Competing defect reactions involving the interstitial defects, Bi and Ci, and oxygen, boron, and carbon are observed. The identities of an electron trap (Bi-Oi) and a hole trap (Bi-Bs) have been clarified.

57 citations


Journal ArticleDOI
TL;DR: In this paper, the gas phase reactions taking place in the mixture of fragments (SiFn) resulting from plasma-induced dissociation and atomic hydrogens were widely investigated by a mass spectroscopy.
Abstract: Systematic studies have been made on preparation of Si thin films from SiF 4 under control over the flow of atomic hydrogens. The gas phase reactions taking place in the mixture of fragments (SiFn) resulting from plasma-induced dissociation and atomic hydrogens were widely investigated by a mass spectroscopy. Chemically active species,i.e., SiF 2 H and SiH 2 F were found as those related to the growth of films. The growth in the vicinity of substrates involves either endothermic or radical-enhanced reaction for the propagation of the three dimensional Si networks, accompaning release of terminators such as H and F. Accordingly, Si thin films with structures from amorphous to crystalline were obtained by controlling the flow of atomic hydrogen. A marked improvement in the hole-transport was established in the Si films containing hydrogen less than 5–6 at % due to the reduction in the tail states near the valence band.

54 citations


Journal ArticleDOI
TL;DR: In this paper, the crystal structures of several icosahedral boron-containing compounds have been refined using MoKα intensity data, and the results showed that the structures consist of icosahedric units bonded together with direct B-B bonds as well as other linkage units (B-C-B and As-As chains).
Abstract: The crystal structures of several icosahedral boron-containing compounds have been refined using MoKα intensity data. Preparation of crystals differs from previous procedures, with boron carbide grown from molten copper and boron arsenide by arsenic vapor transport. The structures consist of icosahedral units bonded together with direct B-B bonds as well as other linkage units (B-C-B and As-As chains).

52 citations


Journal ArticleDOI
Alice E. White1, Kenneth Thomas Short1, Robert C. Dynes1, J. M. Gibson1, Robert Hull1 
TL;DR: In this article, the authors have focused on sub-stoichiometric implantation doses of oxygen, where it is easier to observe the coalescing layer and the resulting disilicide layers are of remarkably high quality: they are single crystals in registry with the silicon wafer and they have better residual resistivities than comparable UHV-reacted suicides.
Abstract: Ion implantation is widely used for doping semiconductors at low concentration, but, with the advent of a new generation of high current implanters, synthesizing new materials rather that simply doping them has become feasible. This technique has been successfully applied to fabricating silicon-on-insulator (SOI) structures with oxygen and nitrogen for several years. Since we are interested in understanding the mechanisms of formation of these layers, we have concentrated on sub-stoichiometric implantation doses of oxygen where it is easier to observe the coalescing layer. In order to determine whether this process of compound formation is more general, our studies were expanded to include implantation of the transition metals. Here, elevated substrate temperatures are necessary to minimize Si surface damage. The resulting disilicide layers are of remarkably high quality: they are single crystals in registry with the silicon wafer and they have better residual resistivities than comparable UHV-reacted suicides.

45 citations


Journal ArticleDOI
Don W. Shaw1
TL;DR: In this article, a realistic appraisal of the potential applications of epitaxial GaAs on Si with emphasis on the special demands imposed by each application and barriers that must be circumvented.
Abstract: Recent successes, such as the demonstration of a 1K SRAM, have established epitaxial GaAs on Si substrates as a promising technology rather than a device designer’s dream. For the first time we can seriously consider combining the individual electronic and optical properties of GaAs and Si within a single epitaxial structure. Applications for GaAs on Si range from those that simply utilize the Si as a low-cost, large-areapassive substrate with superior strength and thermal conductivity to the long-sought multifunction integrated circuits where Si and III–V components are integrated within a single monolithic chip. This paper will attempt to provide a realistic appraisal of the potential applications of epitaxial GaAs on Si with emphasis on the special demands imposed by each application and barriers that must be circumvented.

Journal ArticleDOI
TL;DR: The reversible introduction of atomic hydrogen into III-V semiconductors reduces the active concentrations of shallow donor and acceptor levels, as well as a variety of deep levels as mentioned in this paper.
Abstract: The reversible introduction of atomic hydrogen into III–V semiconductors reduces the active concentrations of shallow donor and acceptor levels, as well as a variety of deep levels. Dissociation of the hydrogen-containing complexes by thermal annealing can restore the original active concentrations, and aid in the characterization of the complexes involved. Hydrogen is in-diffused at temperatures typically in the 150 to 300°C range, most simply from an H2 plasma. In GaAs, the III–V compound which has been subjected to the most hydrogenation studies, carrier concentrations are reduced (by up to many orders of magnitude) in both n- and p-type material. Hydrogen diffusion depths are dependent on dopant concentration, but for similar doping levels, diffusion is always deeper into p-type GaAs. In addition, the type of plasma exposure strongly influences the depth of H diffusion, with low frequency, direct exposure producing the greatest penetration depth. A variety of deep level defects in bulk material (including EL2) and in MBE-grown layers can be passivated, and partial passivation of interface-related defects in GaAs-on-Si has been demonstrated. Reactivation kinetics are dependent on the nature of the dopant or defect, with the passivation of p-GaAs being less stable than that of n-GaAs. Recent infra-red absorption studies have confirmed the formation of a donor-hydrogen complex in n-GaAs, in contrast to an As-H complex in p-GaAs. In GaAIAs, acceptors, donors, and the DX center have been passivated. In some cases, the defect passivation has greater thermal stability than that of the shallow levels, a property of potential benefit. Recently demonstrated applications of hydrogenation include an MBE GaAs MESFET with a hydrogenated channel, and a GaAs/GaAIAs double heterostructure laser with current guiding provided by resistive hydrogenated regions.

Journal ArticleDOI
TL;DR: In this paper, the free energy of formation of the intermetallic layer is shown to be an important driving force for solder wetting, and the energy release during the incremental advance of a spreading solder droplet due to the interfacial energy imbalance and the formation of an intermetallic layer is calculated.
Abstract: The wetting of metal surfaces by molten solder is usually considered to be driven solely by an interfacial energy imbalance. The effect of chemical reactions on the wetting process is neglected, although the growth of an intermetallic layer in the wetted interface is commonly observed. In this work, the energy release during the incremental advance of a spreading solder droplet due to the interfacial energy imbalance and the formation of the intermetallic layer is calculated. The free energy of formation, ΔG, of the intermetallic layer is shown to be an important driving force for solder wetting. This approach to wetting has been applied to three systems, Cu-Sn, Cu-Sb and Cu-Cd. Liquid Sn, Sb and Cd react with solid Cu to form Cu6Sn5 (η), Cu2Sb (γ) and CuCd3 (e), respectively. The free energy of formation, ΔG, for these intermetallic compounds is unknown experimentally, but can be calculated from the phase diagrams and other solution data using classical thermodynamics. These thermochemical calculations yield ΔG(η) = 465-3.09T for Cu-Sn, ΔG(γ) = −2500+0.54T for Cu-Sb and ΔG(e) = −825+0.44T for Cu-Cd (cal/mole). These relations were evaluated at the respective melting temperatures and compared with the interfacial energy exchange. In all three cases the ΔG contribution was approximately two orders of magnitude larger than the interfacial energy exchange making it the dominant driving force for wetting kinetics.

Journal ArticleDOI
Brian G. Kushner, John A. Neff1
TL;DR: In this article, the authors discuss some of the most recent trends in nonlinear optical materials research from a device requirements perspective, including an overview of the results of the recent DARPA forum on optical materials and a discussion of future directions.
Abstract: Within the past several years, the development of advanced materials with large second and third order nonlinear (X2 and X3) effects has generated interest in developing devices to exploit these properties in military systems of the future. This interest has taken many forms, from the funding of basic research aimed at developing enhanced nonlinear optical effects in materials to the deployment of actual mil-spec devices. Two years ago, at this same forum, we delineated a series of materials performance requirements which, if achieved, would allow device developers to take maximum advantage of these nonlinear effects in such disciplines as optical computing, optoelectronic interconnects and sensor protection. In the interim, DoD requirements for advanced materials and devices have continued to accentuate the need for advanced nonlinear optical materials. This paper will discuss some of the most recent trends in nonlinear optical materials research from a device requirements perspective, including an overview of the results of the recent DARPA forum on nonlinear optical materials and a discussion of future directions. As in the previous paper, we will confine ourselves to three challenging areas: nonlinear optical materials for optical computing applications, materials for computer peripherals and internode communications, and materials for sensor protection.

Journal ArticleDOI
TL;DR: In this article, the active NLO unit is attached to the polymer backbone as a pendant side chain and poled in an external electric field at elevated temperatures resulting in second order susceptibilities larger than inorganic crystals.
Abstract: Although organic crystals may be used to experimentally verify the large nonlinearities and short response times of organics, such crystals are not acceptable for device applications due to significant fabrication difficulties. Further, the bulk material nonlinearity is a function of molecular orientation and symmetry which may not be controlled during the crystallization process. Nonlinear optical polymers have been synthesized at Hoechst Celanese for which the active NLO unit is attached to the polymer backbone as a pendant side chain. Control of orientation and symmetry of the unit is achieved by poling in an external electric field at elevated temperatures resulting in second order susceptibilities larger than inorganic crystals. The polymers have attractive secondary properties (i.e., optical transparency, high glass transition temperatures which are controlled by adjusting the side chain length and nature of the polymer backbone, low dielectric constants, and flat frequency respose). Further, single mode waveguides may be fabricated by spin coating. Deposition of electrodes on the waveguide permits application of an external field which changes the material’s index of refraction due to the linear electrooptical effect. Thus, a host of electrooptical waveguide devices may be constructed which operate at low voltages and very high frequencies.

Journal ArticleDOI
TL;DR: In this paper, the application of quantitative image analysis to the measurement of microstructural gradients in the interfacial zone in concrete is described and some preliminary results are presented and discussed.
Abstract: The application of quantitative image analysis to the measurement of microstructural gradients in the interfacial zone in concrete is described. Some preliminary results are presented and discussed.

Journal ArticleDOI
TL;DR: In this article, a review of the results from the studies at the University of California at Berkeley on various factors influencing the microstructure of the transition zone in concrete is presented.
Abstract: This paper contains a review of the results from the studies at the University of California at Berkeley on various factors influencing the microstructure of the transition zone in concrete. Two types of aggregate, two different cement, and three mineral admixtures were investigated. Using cement paste-polished aggregate composite specimens cured up to three years, X-ray diffraction, scanning electron microscopy, and microhardness testing techniques were used for characterization of the transition zone. Compared to the transition zone between a quartz aggregate and an ASTM Type I portland cement, transition zones with smaller and less preferentially oriented crystals of calcium hydroxide were obtained when using a Type K expansive cement, or limestone aggregate, or mineral additives, such as condensed silica fume, granulated blast-furnace slag, and fly ash.

Journal ArticleDOI
TL;DR: In this paper, a broad surface characterization of pure Ti and Ti6A14V alloy surface oxides prepared by thermal oxidation by machining, or by electrochemical procedures (electropolishing and anodic oxidation).
Abstract: The biocompatibility of Ti and Ti alloys is closely associated with the passivating surface oxide which covers these materials. In this paper results are presented from a broad surface characterization of pure Ti and Ti6A14V alloy surface oxides prepared by thermal oxidation by machining, or by electrochemical procedures (electropolishing and anodic oxidation). The chemical composition of the surface oxide on both materials is mainly TiO2, as shown by XPS, AES, and SIMS analyses. Significant differences exist for both the thermal and anodic oxides, in that the alloying elements are present in the surface oxide of the alloy. TEM and STEM studies show that the microstructure of the anodic oxide films is rather heterogeneous with areas of different porosity which can be correlated with the grain structure of the bulk metals. Oxides on the alloy are even more heterogeneous than on Ti, due to the more complex (two-phase) microstructure of the bulk metal, and also differ in crystallinity. The differences in the surface oxide properties can be expected to lead to differences in the biological response to these two materials. With the alloy, one must consider the risk of Al and/or V dissolution into the biological system.

Journal ArticleDOI
TL;DR: In this paper, the strength of high strength silica fume concretes is attributed to the reduction in w/c ratio and the refinement of the pore structure, and it is suggested that the densification of the transition zone is the result of the effect of the silica Fume on the nature of the fresh concrete.
Abstract: The strength of high strength silica fume concretes is usually attributed to the reduction in w/c ratio and the refinement of the pore structure. A study of concretes and pastes, with and without silica fume, suggests that the contribution of the silica fume to strength is also the result of the densification of the transition zone. It is argued here that this influence is as important as the one due to the reduction in w/c ratio. It is suggested that the densification of the transition zone is the result of the effect of the silica fume on the nature of the fresh concrete.

Journal ArticleDOI
TL;DR: In this paper, a theoretical model has been developed to predict the pull-out force versus displacement relationship based on given fiber/matrix shear strength as an increasing function of the slippage distance.
Abstract: Experiments were conducted on specimens containing nylon or polypropylene monofilaments embedded in a precracked matrix During pull-out tests, it was generally observed that the pulling force continued to increase after one or both sides of the filament had begun to slip out, even though one or both of the embedded filament lengths were decreasing This indicated that the fiber/matrix shear stress increased with the fiber slippage distance Examination of the extracted filaments under a scanning electron microscope (SEM) revealed the increased shear resistance to be the result of fiber surface abrasion The severity of abrasion was observed to increase with the fiber slippage distance before complete pull-out A theoretical model has been developed to predict the pull-out force versus displacement relationship based on given fiber/matrix shear strength as an increasing function of the slippage distance The model gives good prediction in comparison with experimental results

Journal ArticleDOI
Gary L. Patton1, S. S. Iyer1, S. L. Delage1, E. Ganin1, R.C. Mcintosh1 
TL;DR: In this article, the authors studied the growth of strained SiGe alloy layers grown by Molecular Beam Epitaxy (MBE) and identified an initial fast growth regime for 800°C steam oxidations, where the growth rate was 2.5 times that of silicon.
Abstract: The oxidation of strained SiGe alloy layers grown by Molecular Beam Epitaxy (MBE) was studied. An initial fast growth regime was identified for 800°C steam oxidations, where the growth rate is 2.5 times that of silicon. The oxides formed on SiGe were found to be essentially Ge-free: Ge present in the material is rejected by the oxide, resulting in the formation of a Ge-rich epitaxial layer at the oxide/substrate interface.

Journal ArticleDOI
TL;DR: A number of different types of interfacial bonding occur in concrete, including: bonding between various phases (including anhydrous cement) in the hydrated cement paste (hcp) system, bonding between cement and aggregates, and bonding between concrete and steel reinforcing bars or prestressing cables as discussed by the authors.
Abstract: A number of different types of interfacial bonding occur in concrete, including: i) bonding between various phases (including anhydrous cement) in the hydrated cement paste (hcp) system ii) bonding between cement and aggregates iii) bonding between cement or mortar and the fibres in fibre-reinforced concrete; and iv) bonding between concrete and steel reinforcing bars or prestressing cables. The importance of these types of bonds with respect to the mechanical behaviour of concrete is discussed. It is concluded that in some systems, the mechanical properties are governed primarily by the interfacial bond; in other systems, however, this bond has only a secondary effect.

Journal ArticleDOI
TL;DR: In this paper, hydrogen injection with B acceptor neutralization in Si etched in HNOs and HF acid mixtures has been confirmed by isotopic substitution and secondary ion mass spectrometry [SIMS] profiling.
Abstract: Hydrogen injection with B acceptor neutralization in p-type Si etched in HNOs and HF acid mixtures has been confirmed by isotopic [D] substitution and secondary ion mass spectrometry [SIMS] profiling. Quantitative measurements of the near-surface Injected hydrogen were made following field-aided, in-bulk transport [H + drift] in reverse-bias annealed Schottky diodes from etched, B-doped Si. Chemical-etch injection is found to be self limiting with neutralization observed over a depth which is characteristic of the base material acceptor concentration and in the range 6–8 extrinsic Debye lengths, indicating that holes are essential in the injection mechanism. An effective diffusivity for hydrogen in etched p-Si of ∼ 2 × 10 −9 cm 2 s −1 was measured [300 K], considerably higher than previously reported.

Journal ArticleDOI
TL;DR: An amorphous silicon TFT particularly suited for the full color liquid crystal display driver has been developed and reported in this paper, where various fundamental factors involved in the a-Si TFT, such as the effects of structure, materials and the method of fabrications were reviewed and investigated in terms of the field effect mobility, the threshold voltage and the reliabilities.
Abstract: An amorphous silicon TFT particularly suited for the full color liquid crystal display driver has been developed and reported here. Various fundamental factors involved in the a-Si TFT, such as the effects of structure, materials, and the method of fabrications were reviewed and investigated in terms of the field effect mobility, the threshold voltage and the reliabilities. An inverted-staggered TFT structure was employed for the purpose wherein the interface states between two layers was successfully lowered by employing the successive deposition procedures of SiNx gate insulator on the a-Si layer. Proper ohmic contacts and the blocking of hole injections were accomplished by forming a n+ layer between the a-Si layer and the source/drain metal electrodes which consists of a double layer of Al/MoSi2 in order to prevent the aluminum diffusion into the a-Si layer during the 300°C heat treatment at the succeeding fabrication processes. The degradation of display images due to the high intensity backlights was minimized by employing a light shielding layer and by making the thickness of a-Si layer 200 A against the direct sunlight of up to 100,000 luxes. Stable actual performances of TFT for more than 4000 hours at 80 °C were confirmed. The development of a color LCD TV driven by this TFT is also reported.

Journal ArticleDOI
Wu Keru1, Zhou Jianhua1
TL;DR: In this article, the influence of the matrix-aggregate bond on the strength and brittleness of concrete is studied, in terms of energy dissipation and crack propagation during failure of concrete.
Abstract: In this paper, the influence of the matrix-aggregate bond on the strength and brittleness of concrete is studied. Six different matrixaggregate interfaces are used to evaluate the interfacial bond capability. The results obtained on the strength and brittleness index of concrete show that strengthening and toughening of concrete can be obtained simultaneously, if the interfacial bonds are changes so that they conform to a rational distribution according to aggregate size. These results are discussed in terms of the energy dissipation and crack propagation during failure of concrete.

Journal ArticleDOI
TL;DR: In this article, the authors have made MINDO/3 calculations on a 47 silicon atom molecular cluster to model the diffusion of oxygen in silicon crystal, and they conclude that the diffusion constant for (O2) is eight orders of magnitude greater than that of (O1).
Abstract: We have made MINDO/3 calculations on a 47 silicon atom molecular cluster to model the diffusion of oxygen in silicon crystal. For interstitial oxygen (O1), we compute an activation energy for diffusion of 2.49 ev. We compute a binding energy of 0.1 ev. when two isolated interstitial oxygen atoms bond to a common silicon atom of the lattice. This complex (O2) is computed to move through the lattice with an activation energy of 1.36 ev. The diffusion path is through a four-member ring intermediate structure. We conclude that the diffusion constant for (O2) is eight orders of magnitude greater than that of (O1).

Journal ArticleDOI
TL;DR: In this paper, the performance advantages of thin-film SOI compared to bulk structures for the sub-micron scaling of MOS transistors are discussed, including short-channel threshold voltage stability, improved sub-threshold slope, increased saturation current, and reduced hot electron effects.
Abstract: In this paper the various performance advantages of SOI and SOS structures for submicron ULSI circuits will be described. In addition to the traditional speed and radiation-hardness advantages, there are several significant advantages of thin-film SOI compared to bulk structures for the submicron scaling of MOS transistors. These advantages include short-channel threshold voltage stability, improved sub-threshold slope, increased saturation current, and reduced hot electron effects. Both theory and data from several groups will be presented to illustrate these effects. Since these advantages all fall in areas that are critical limits to device engineering and scaling in the submicron regime, the motivation for using SOI should be even stronger as devices are scaled to smaller dimensions in the future. Consideration of SOI or SOS on the ULSI scale will require a technology capable of low defect films with a film thickness of 1000 A or less, however. The prospects for minority carrier devices such as bipolar transistors for BI-MOS will also be discussed. Both device structure (lateral vs. vertical) and material quality are issues that must be addressed.

Journal ArticleDOI
TL;DR: In this paper, it was shown that the superconducting grains have an epitaxial orientation with respect to the substrate and that the current densities on SrTiO3 and cubic zirconia substrates are as high as 106 A/cm2 at 81 K and routinely above 105 A/ cm2 at 77 K.
Abstract: High quality films of Ba2YCu3O7 have been made by coevaporation of Y, Cu, and BaF2 and subsequent annealing in oxygen. Addition of water vapor to the annealing gas at high temperatures has been found to greatly reduce the annealing time and, thus the substrate interaction. Transition temperatures (zero resistance) between 89–92 K are routinely obtained on SrTiO3 and cubic zirconia substrates. Critical current densities on SrTiO3 are as high as 106 A/cm2 at 81 K and routinely above 105 A/cm2 at 77 K. Transmission electron microscopy shows that on SrTiO3 the superconducting grains have an epitaxial orientation with respect to the substrate. Persistent current measurements in thin film rings demonstrate the absence of residual resistance in the superconducting state.

Journal ArticleDOI
TL;DR: A brief summary of the use of x-ray powder diffraction for studying the mineralogy of fly ash is presented in this article, where low-, intermediate-and high-calcium fly ashes are discussed and illustrated by results from XRD characterization of U.S. National Bureau of Standards fly ash Standard Reference Materials.
Abstract: A brief summary of the use of x-ray powder diffraction for studying the mineralogy of fly ash is presented. Mineralogies of low-, intermediate- and high-calcium fly ashes are discussed and illustrated by results from XRD characterization of U.S. National Bureau of Standards fly ash Standard Reference Materials.

Journal ArticleDOI
Frederick F. Morehead1
TL;DR: In this paper, a more complete analysis by numerical integration of the effective diffusion equation with fewer assumptions yields a higher minimum value, 6x10-6 cm2s-1 at 1100 °C.
Abstract: Values of the diffusivity of silicon self-interstitials have been previously inferred from analyses of the in-diffusion of Au in undislocated Si, e.g., 2x10-7 cm2 s-1 at 1100 °C. A more complete analysis by numerical integration of the effective diffusion equation with fewer assumptions yields a higher minimum value, 6x10-6 cm2s-1 at 1100 °C. Recently published experiments showing no measurable difference in the oxidation-reduced diffusion of Sb in Si at 10 and 40 microns are consistent with this high value.