Microscopy and x-ray emission analysis have been performed on Y–Ba–Cu–O superconductors as a function of temperature using a scanning electron microscope equipped with a low-temperature stage. The samples exhibit a superconducting phase transition above liquid nitrogen temperature as determined by resistivity measurements and a demonstrated Meissner effect. Strong contrast changes in the micrographs due to the superconducting phase transition are found, which have been used to identify normal and superconducting regions of the sample. These samples are found to consist of particles with superconducting shells surrounding a nonsuperconducting core.

An Al-5 wt. % Co alloy has been rapidly solidified from the liquid state, resulting in the formation of a slightly supersaturated aluminum solid solution and the monoclinic Al9Co2 phase. High-resolution electron microscopy and electron diffraction have been extensively employed to characterize the as-solidified as well as the annealed foils. The high-resolution micrographs of the as-solidified solid solution showed the presence of clustering and D 1a - type ordering on an extremely small microscopic scale. Annealing at temperatures above 623 K resulted in the precipitation of Al9Co2 in the form of platelets arranged in a Widmanstätten pattern. Orientation relationships between the Al9Co2 platelets and the matrix have been established. Guinier-Preston zonelike platelets on close-packed {111} planes, however, have also been observed upon electron irradiation in the annealed alloys, presumably due to the enhanced diffusivity of cobalt atoms.

Aluminum films 1–6 kÅ thick deposited on Pt or Pd layers developed voids after annealing between 200 and 275°C. Void formation was also observed when the Pt layer was deposited above the Al film. The amount of Al surrounding the voids increased as the voids grew. The rate of void growth decreased as the thickness of the initial Al film increased. The driving force appears to be surface tension. The controlling mechanism is diffusion along the Al/Pt or Al/Pd interface made possible by compound formation there.

A scoping irradiation test was carried out to help define the performance of copper-base materials in potential fusion applications. Twenty-five different copper materials including oxide dispersion-stabilized and precipitation-hardened powder metallurgy alloys, as well as pure copper and solid solution-strengthened ingot alloys, were neutron irradiated to 13.5 dpa at 400°C in the Experimental Breeder Reactor II (EBR-II) fast reactor. Volumetric swelling and electrical conductivity data were measured for all irradiated materials, and four selected materials were characterized for mechanical property changes using a miniaturized disk bend test. A number of these copper alloys, especially those prepared by powder metallurgy techniques, showed low swelling (less than 0.3%), small changes in conductivity (less than ± 5%), and relatively small changes in yield strength with good post-irradiation ductility. Preliminary electron microscopy results show microstructural changes that are consistent with the results of the macroscopic studies. The pure copper materials showed significant changes in conductivity and high levels of swelling as a result of the neutron exposure. It is apparent that a variety of copper alloys can survive fast neutron exposures to at least 13.5 dpa at 400°C without unacceptable changes in density, conductivity, or yield strength. Further irradiation testing to much higher doses and experimental investigation of the effect of transmutation product gases are needed to fully define the response of available copper alloys to fusion reactor environments.

Single-phased films of α-Ti1−x Nx, ∊-Ti2Nx, or δ-TiNx with a homogeneous composition on more than 400 nm were produced by ion implantation at several different energies in the TiAl6V4 alloy. Secondary ion mass spectroscopy (SIMS) profiles and ionic images recorded within the tracks after incremented cycles of friction against a 35NCD16 steel ball in air have shown that a Ti–O–C–N film is progressively formed on the surface of α solid solutions, while more concentrated nitride films resist oxidation. The friction and abrasion resistances of ∊ or δ nitride films are initially improved for a time lasting for as long as their N content increases, but they are finally self-destroying. On the contrary, the hardening effect of N in an α-Ti matrix keeps a really severe amount of abrasion from occurring during running in of the implanted surface, without suppressing the building up of a lubricant oxide hardened by N.

A series of twelve Li1−x Ta1−3x Ti4xO3 solid solution ceramics was sintered following the low-temperature metal alkoxide routes. Measurements of dielectric constants, dielectric losses, and heat capacities as functions of temperature and frequency are presented. The Curie temperature (Tc) in comparison to LiTaO3 was reduced from 620°C to about 358°C in the Li0.91 Ta0.73 Ti0.36O3 ceramics. The heat capacity data showed no dependence on the bulk density or grain size. Also the mechanical properties of the undoped crystals appear to stay undisturbed. On the other hand, an apparently abnormal dependence of the Curie temperature on density was found. Heat capacity and dielectric loss decreased while the dielectric constant increased with the addition of Ti+4 doping in the LiTaO3 structure. Overall, a good detector performance might indeed be obtained from these ceramic materials if they can be poled reproducibly.

Thin LiNbO3 films were prepared from polymerized sol-gel precursor solutions having various concentrations and water:alkoxide ratios in an effort to investigate the effects of these and other processing variables on the resultant film properties and microstructure. Films deposted on silicon substrates were mostly amorphous when pyrolyzed at 435°C for 30 min. Randomly oriented polycrystalline films having distinctive microstnietures were produced using longer heating times or higher temperatures. All of the films exhibited low refractive indices due to porosity, which was attributed to the low level of hydrolysis water required to produce stable polymeric precursor solutions. When single-crystal LiNbO4 was used as the substrate, epitaxial growth of the film resulted. This ideal case establishes the feasibility of producing epitaxial films via sol-gel processing. All films were characterized by transmission electron microscopy (TEM) and thin-film x-ray diffraction patterns.

The electrical conductivity has been measured for the glasses in the system B2O3–Li2O–Li2X2(X = F, Cl, Br), where Li2O is replaced by Li2X2 with Li content kept constant. The conductivity decreases for F glasses and increases for Cl and Br glasses with increasing halide ion content, which is caused by the increase in the activation energy for F glasses and the decrease for Cl and Br glasses. The analysis of the activation energy in terms of the Anderson-Stuart model indicates that, with the increase in LiX, Δ Eb, (the electrostatic energy) increases for F glass, whereas ΔEs (the strain energy) and ΔEb decrease for Cl or Br glasses. The effects of F− and other halide ions are attributed to a stronger interaction between Li and F, and to expanded and weakened glass network due to accommodation of Br− and Cl− ions.

The electron-induced decomposition (EID) of SiO2 overlayers on various high surface area oxide substrates was studied using Auger electron analysis (AES). Bulk SiO2 was stable upon electron bombardment, but bulk Al2O3 decomposed readily to elemental Al when the primary electron beam energy was 2 keV and the beam current was 6–16 μA. On the other hand, SiO2 overlayers having an average thickness of about 10 Å on Al2O3 decomposed selectively under the same conditions. In contrast to Al2O3 substrates, SiO2 overlayers on TiO2, ZrO2, and MgO were quite stable to the same electron bombardment. Therefore it is concluded that Al2O3 accelerates the EID of SiO2 overlayers and the SiO2 overlayer suppresses EID of Al2O3 substrates.

Synthetic gray-blue diamonds were used as anvils in a diamond anvil cell to produce a pressure of 125 GPa (1.25 Mbar) in a gasketed sample. Pressure was measured by x-ray diffraction methods by using gold and iron as a calibrant and also by optical methods based on the shift of the fluorescence peaks of ruby with pressure. The future potential of synthetic diamonds for ultrapressure research is discussed.

This article is the first of a pair on a theory of chemically assisted fracture. It includes the Green's function analysis for a three-dimensional crack with a kink on it. Equations are developed for the activation energy for the motion and nucleation of such kinks using information to be found in the second article regarding the force laws appropriate for water attack of silica. The most general conclusion is that lattice trapping barriers to crack motion (including chemical effects) are associated with a narrow core region of the crack, which is in turn connected to the nature of the interatomic force laws of the material (including the modifications of these force laws induced by chemical reactions). Further, it is found that the force law must have a severely “snapping” characteristic in order to assure a narrow core, a feature not to be expected except under certain types of external chemical attack of the crack. Additional results are that the energy to nucleate a kink pair in silica under water attack is in the neighborhood of 2 eV and that the motion energy is of order 0.1 eV. Motion energies are expected to be considerably smaller than formation energies in general.

This article is this second of a pair on a theory of chemically assisted fracture. In it a simple bond orbital model of the force laws to be used in fracture is developed. In the bond orbital model, only a few of the atoms in the vicinity of the bond to be broken are considered and do not include interactions with the rest of the system, which is assumed to be Newtonian. Numerical accuracy is not required, but qualitative features of the force laws are believed to be valid. The silica bond is shown to rise quickly to a high peak, after which it develops a relatively long tail. When the bond is attacked by water, modeling by the same technique indicates that the bond has a “snapping” characteristic that is important in the theory developed in the first article. For bonds with smooth “back sides” the barriers to crack motion are shown to be low, but barriers are expected to be observable when the bond snaps. A tight binding treatment of a one-dimensional chain has been included in order to investigate the effect of including band effects in the force law. These effects are found to be small compared to the simple bond breaking of the bond orbital calculation.

Results of in situ optical (reflectance, Raman scattering) and 00l x-ray diffraction studies of hydrogen chemisorption in Grafoil-based stage 1 C8K intercalation compounds are presented. Upon hydrogen uptake, stage 2 KC8H2/3 was found to coexist with C8K forming first in the optical skin depth. The intensities of the 00l x-ray diffraction peaks show quantitatively that the reaction C8K + 1/2xH2 ⇉ (1 − 3/2x)C8K + 3/2xC8KH2/3 occurs for x>0.4 in the bulk. The effects of the surface morphology of Grafoil on the near-normal incidence reflectance was investigated and found to be described by an energy (E) dependent function S(E) = exp[−aEn], such that the corrected spectrum Rc = SR, where R is the Grafoil reflectance. In this manner, reflectance spectra of C8K-Grafoil and C8KH2/3-Grafoil were quantitatively analyzed to determine the free carrier contribution. The free carrier lifetimes were found to be a factor of 2 shorter in Grafoil-based hosts, compared to highly oriented pyrolytic graphite-based hosts. The optical results for C8KH2/3 indicate the H(ls) band is full (or very nearly full).

Optical properties of plasma-deposited amorphous hydrogenated carbon films were studied by spectroscopic ellipsometry. From the ellipsometry data, the real and imaginary parts, n and k, of the complex index of refraction of the film have been deduced for photon energies between 2.0 and 4.0 eV for as-grown as well as for thermally annealed films. Here n and k showed considerable variation with subsequent annealing, even under 400°C. A tentative explanation of the results is proposed.

Nanosecond resolution time-resolved visible (632.8 nm) and infrared (1152 nm) reflectivity measurements, together with structural and Z-contrast transmission electron microscope (TEM) imaging, have been used to study pulsed laser melting and subsequent solidification of thick (190–410 nm) amorphous (a) Si layers produced by ion implantation. Melting was initiated using a KrF (248 nm) excimer laser of relatively long [45 ns full width half maximum (FWHM)] pulse duration; the microstructural and time-resolved measurements cover the entire energy density (E1) range from the onset of melting (at ∼ 0.12J/cm2) up to the onset of epitaxial regrowth (at ∼ 1.1 J/cm2). At low E1 the infrared reflectivity measurements were used to determine the time of formation, the velocity, and the final depth of “explosively” propagating buried liquid layers in 410 nm thick a-Si specimens that had been uniformly implanted with Si, Ge, or Cu over their upper ∼ 300 nm. Measured velocities lie in the 8–14 m/s range, with generally higher velocities obtained for the Ge- and Cu-implanted “a-Si alloys.” The velocity measurements result in an upper limit of 17 (± 3) K on the undercooling versus velocity relationship for an undercooled solidfying liquid-crystalline Si interface. The Z-contrast scanning TEM measurements of the final buried layer depth were in excellent agreement with the optical measurements. The TEM study also shows that the “fine-grained polycrystalline Si” region produced by explosive crystallization of a-Si actually contains large numbers of disk-shaped Si flakes that can be seen only in plan view. These Si flakes have highly amorphous centers and laterally increasing crystallinity; they apparently grow primarily in the lateral direction. Flakes having this structure were found both at the surface, at low laser E1, and also deep beneath the surface, throughout the “fine-grained poly-Si” region formed by explosive crystallization, at higher E1. Our conclusion that this region is partially amorphous (the centers of flakes) differs from earlier results. The combined structural and optical measurements suggest that Si flakes nucleate at the undercooled liquid-amorphous interface and are the crystallization events that initiate explosive crystallization. Time-resolved reflectivity measurements reveal that the surface melt duration of the 410 nm thick a-Si specimens increases rapidly for 0.3E1 <0.6 J/cm2, but then remains nearly constant for E1 up to ∼ 1.0 J/cm2. For 0.3 < E1 < 0.6 J/cm2 the reflectivity exhibits a slowly decaying behavior as the near-surface pool of liquid Si fills up with growing large grains of Si. For higher E1, a flat-topped reflectivity signal is obtained and the microstructural and optical studies together show that the principal process occurring is increasingly deep melting followed by more uniform regrowth of large grains back to the surface. However, cross-section TEM shows that a thin layer of fine-grained poly-Si still is formed deep beneath the surface for E1<0.9 J/cm2, implying that explosive crystallization occurs (probably early in the laser pulse) even at these high E1 values. The onset of epitaxial regrowth at E1 = 1.1 J/cm2 is marked by a slight decrease in surface melt duration.

A phenomenological model is developed to treat defect properties and defect chemistry in melt-grown GaAs. Defects are characterized by their charge and their stoichiometric signature (local deviation from stoichiometry); no specific atomic structure is assumed for them. Good fits to existing data are obtained for the room-temperature concentrations of the midgap donor (EL2), an unknown double acceptor, electrons, and holes as functions of melt composition. In obtaining these fits the role and importance of the (unknown) GaAs solidus is emphasized and it is demonstrated that many popular models of EL2 are consistent with the data analyzed. The model is extended to account for the observed decrease of EL2 concentration with increasing boron or silicon doping concentration, and here again attention is clearly focused on certain unknown information concerning the crystal formation process. Fundamental parameters in the model whose values are estimated through fits to the data include (1) the equilibrium constant in the defect reaction between EL2 and the double acceptor, (2) the equilibrium constant in the defect reaction between EL2, BAs and BGa, (3) the fractions of boron and silicon taken up on Ga sites during the crystal formation process, and (4) the proportionality factor between the melt composition and the crystal composition.

Thin-film interactions have been increasingly important to various aspects of electronic technologies, including devices and packaging. Extensive outdiffusion and alloy formation, for example, can be detrimental to the yield and reliability of the parts fabricated. Understanding such interactions, and their dependence on various factors, continues to be a challenge to thin-film scientists. Several aspects related to thin-film interactions are described in this paper: a review of the ambient effects that provides an understanding of the basic reaction mechanisms at the interface; an illustration of concerns upon choosing a diffusion barrier layer, and reaction across such a layer; and the effect of undesired outdiffusion on the solder spread related to joining.