A superconductor ceramic oxide with the Y1Ba2Cu3O7−x phase and exhibiting a transition temperature at Tc ≍92K, was irradiated at room temperature with 1 MeV electrons. It was found that the irradiation produces a sharp drop in the Tc value from 92 K down to ∼40K. The irradiated sample suffered a change from metallike character to semiconductorlike behavior at T > Tc. It is also shown that after irradiation the twin boundaries on the material become irregular.

A sol-gel method of preparing fine-particle superconducting oxide YBa2Cu3O7−x was developed. Single-phase superconducting oxide YBa2Cu3O7−x formed at temperatures as low as 750°. The particle size obtained by this method was found to be ≤0.2μm. Pellets sintered from these sol-gel powders exhibited very sharp resistivity drops at Tc = 90 °C with a Δc of ∼3°K.

Powdered samples of the high-temperature superconductors A Ba2Cu3O7−δ (A = Gd,Y) were treated with fluorine gas (100 Torr) at room temperature and 400 °C for varying times (12–64 h). Magnetic shielding measurements on fluorinated products showed that the superconducting volume fraction in treated samples was greatly reduced or even completely eradicated. All samples were structurally characterized by x-ray powder diffraction. Two yttrium samples, one fluorinated at 25 °C and one at 400 °, were also examined by neutron powder diffraction. For samples treated at room temperature, no change in the structure or composition of the products was apparent by either technique. However, samples fluorinated at 400 °C are tetragonal, with a = 3.8641 (3), c = 11.704(1) Å, and bulk composition corresponding to the formula YBa2Cu3F3.5O4.5. Nuclear activation analysis, nuclear reaction analysis, and Auger spectroscopy were used to determine fluorine concentration and distribution in the fluorinated materials. For samples treated at room temperature, fluorine was found primarily within approximately 1 μm of the surface of the product particles. No evidence for a fluorinecontaining superconducting phase was found in any sample; fluorine was found to be detrimental to superconductivity in all cases. These results suggest that the 123 oxides are sensitive to surface effects.

Fluorination of YBa2Cu3O7−s at room temperature results in no change of the critical temperature but a drastic reduction of superconducting volume fraction as determined by magnetic flux exclusion measurements. Rietveld refinement of neutron powder diffraction data indicates that the bulk structure has not changed in any significant way despite the loss of superconductivity. In marked contrast, when the superconducting oxide is fluorinated at 400 °C, a structural transformation from orthorhombic to tetragonal symmetry occurs that is accompanied by essentially complete filling of eight of the nine perovskite anion sites and total loss of superconductivity above 7 K. Interpretation of neutron activation analysis and neutron diffraction results render the formula of the fluorinated product as YBa2Cu3F3.5O4.5, but fluoride ions in the unit cell were not distinguished from oxide ions.

Excimer laser-induced sputtering of YBa2Cu3O7−x targets has been investigated. Two aspects of this process are reported here: the spectral content of the emission and sputtering of the target. Postsputtering analysis of the sputtered area of the target shows a nonstoichiometric composition: rich in Cu but depleted of Ba and Y.

Changes in ac susceptibility of the high-Tc superconductor Y–Ba–Cu–O have been used to investigate the degradation of this material in the presence of high humidity. It is found that the fraction of YBa2Cu3O7 in a sample decreases exponentially with time when the sample is kept at 98% relative humidity and 20 °C. The time constant is approximately 22 days.

A structural phase transition study of Ba2YCu3O6+x (x = 0 to 1) has been conducted on a series of 13 quenched samples. These samples were prepared from an orthorhombic material by annealing at temperatures from 400 to 1000 °C in air, followed by rapid quenching. All quenchings were performed by using a liquid-nitrogen-cooled copper cold well with a continuous flow of cooled helium gas. Various measurements including x-ray diffraction, thermogravimetric analysis, Meissner effect, and scanning electron microscopy were carried out in order to correlate the nature of the phase transition with erystallographic data, superconductivity, and annealing temperature. The phase transition from Ba2YCu3,O7 to Ba2YCu3O6 appears to involve two orthorhombic regions: region A with a <b ≈ c/3 below approximately 600 °C and region B with cell parameters of a < b < c/3 from & 600 to 708–720 °C. The transformation from orthorhombic to tetragonal takes place in the temperature range of 708–720 °C. This transition appears to be a second-order, order-disorder type.

The nucleation and amorphization of radiation-induced (G) and radiation-enhanced (η) phases in a silicon- and titanium-modified austenitic stainless steel have been studied under nickel-ion irradiation. These silicon- and nickel-enriched phases form under high-temperature (950 K) irradiation as the result of radiation-induced segregation to radiation-produced interstitial dislocation loops. Availability of carbon promotes the formation of η phase relative to G phase. Under lower temperature (450 K) irradiation, G and η phases are amorphized without significant change in composition of metallic elements. Two carbide phases (MC, M23C6) remain crystalline for the same irradiation conditions. The amorphization of the silicides may result from (1) radiation damage increasing their free energy above that of the amorphous state or (2) direct formation of the amorphous phase in the damage cascade.

An experimental technique of prestressing and quenching was employed in order to elucidate the nature of pinning points responsible for the anomalous yield strength of Ni3Al. The apparent number density of pinning points at room temperature was found to be unaffected by the prestressing and quenching from elevated temperatures. This result is consistent with the crossslip-pinning (CSP) model in that cross-slipped segments act as pinning points on the leading superpartial dislocations.

The role of interaction between slip dislocations and a Σ = 9 tilt boundary in localized microplastic deformation, cleavage, or intergranular fracture in the Li2 ordered structure has been analyzed by using the anisotropic elasticity theory of dislocations and fracture. Screw superpartials cross slip easily at the boundary onto the (1$\overline 1$1) and the (001) planes at low and high temperatures, respectively. Transmission of primary slip dislocations onto the conjugate slip system occurs with a certain degree of difficulty, which is eased by localized disordering. When the transmission is impeded, cleavage fracture on the ($\overline 1$11) plane is predicted to occur, not intergranular fracture, unless a symmetric double pileup occurs simultaneously. Absorption (or emission) of superpartials occurs only when the boundary region is disordered. Slip initiation from pre-existing sources near the boundary can occur under the local stress concentration. Implications of the present result on the inherent brittleness of grain boundaries in Ni3 Al and its improvement by boron segregation are discussed.

The structure of sputtered Mo/Fe superlattices of periodicities 9 to 30 Å grown at a substrate temperature of 300 K at various pressures and levels of low-energy ion bombardment have been studied using x-ray diffraction. The samples show the growth of an amorphous phase below 17 Å periodicity and a crystalline phase above 21 Å, with mixed phases in between. Limited ion bombardment reduces the coherency in the growth direction in the crystalline phase, while heavy bombardment sufficient to promote significant mixing acts to improve the coherency, but not to the level observed in films with no bombardment. The relative intensities of the average lattice spacing reflection and its most intense satellite give the composition profile change due to the ion mixing. Some ion bombardment of the iron layer markedly improves the reflectance for x-rays at both low and high angles near the Bragg peak due to the average lattice spacing.

Starting with corrosion-resistant amorphous Fe32Ni36Cr14P12B6 alloy material, rf sputter deposition has been successfully used to deposit amorphous thin films very similar in composition onto low-carbon (i.e., 1008) steel. The effects that varying sputter deposition parameters has on a film's corrosion resistance, microstructure, and chemical composition have been examined. Optical, scanning, and transmission electron microscopy, Auger depth profiling, and x-ray diffraction were used to characterize the microstructure and composition of the films, while the corrosion resistance was determined by anodic polarization in basic and acidic solutions. A ∼4000 Å thick amorphous film sputtered at ambient temperature onto a 0.05 μm polished 1008 steel substrate improved the corrosion resistance of the steel in a buffered borate solution by lowering the steel's critical current density by two orders of magnitude and by raising its corrosion potential by ∼0.4 V. Bias voltage sputtering was required to produce a film with properties that could withstand a sulfuric acid solution. For example, a film sputtered at – 70 V at ambient temperature onto a steel substrate passivated in sulfuric acid solution, whereas the steel was completely active in this solution without the sputtered film. Passive current densities in this case were ∼2x102μA/cm2. In both solutions the improved corrosion resistance was exhibited by films with lower oxygen content and a denser microstructure. Thus a direct correlation between corrosion resistance, microstructure, and composition is shown.

The hydrogen storage properties of a series of mechanically alloyed (MA) amorphous Ni1xZrx alloys are studied, using both gas phase and electrochemical techniques, and are compared to H storage of rapidly quenched (RQ) amorphous Ni1−xZrx. In the MA alloys, hydrogen resides in the Ni4−nZrn (n = 4,3,2) tetrahedral interstitial sites, with a maximum hydrogen-to-metal ratio of 1.9(4 n)xn(1 − x)4 − n. These features are identical to those of the RQ alloys and indicate that the topological and chemical order of the MA and RQ materials are essentially the same. However, the typical binding energy of hydrogen in a Ni4−nZrn site, En, is shifted in the MA alloys relative to the RQ alloys and the distribution of binding energies centered on En is significantly broader in the MA samples. Thus, the MA and RQ alloys are not identical and sample annealing does not alter this subtle distinction. The sensitivity of H storage to the presence of chemical order in binary alloys are analyzed theoretically and the data are found to be most consistent with little or no chemical order (random alloys).

Solid-state amorphization is reported to occur in aluminum-platinum thin films. A uniform amorphous alloy layer was observed at the interface between aluminum and platinum layers for electron beam evaporated samples in an as-deposited state. For a pure aluminum overlayer deposited on top of a coevaporated Al–Pt amorphous alloy, the aluminum dissolves into the amorphous phase leading to a fully amorphous sample. In this last case the amorphization is nonuniform upon low-temperature anneals (T < ≃2 200 °C) and gives rise to hole formation in the aluminum overlayer. Direct observations of this phenomenon during in situ annealing of the thin films in a transmission electron microscope were carried out.

The electrical resistivity of fluorinated carbon black particles, CFx, is reported as a function of fluorine content, pressure, and temperature. Fluorination does not destroy the aggregate structure of carbon black, but does change its physical properties. The resistivity changes from 10−2 to 10+12 Ω cm as x increases from 0 to 1.2, with a very rapid change occurring in the range 0.08≤x≤0.27. Samples with x = 0 and x = 0.07 exhibit a pressure dependence described by p∝ P−s with s>0. Fully fluorinated samples (x = 1.2) have s≃0. Intermediate compositions have low-pressure regimes where the resistivity is independent of pressure, and high-pressure regimes with s>0. For all samples exhibiting pressure-dependent resistivity, s increases as x increases. For samples with low-fluorine content, the resisitivity increases with decreasing temperature. These observations are interpreted in terms of structure, especially surface structure.

The effect of implantation of low-solubility, metallic impurities into Si on the oxidation kineties in steam was studied. The list of impurities that were studied include Ti, Co, Ni, Fe, Yb, Pb, Sn, and Ag. Kinetic data from Pb+ -implanted Si is correlated with the impurity behavior during the oxidation. It will be shown that the oxidation rate is dependent both on the impurity segregation phenomena at the oxide/Si interface and on the nature of the ion-induced damage that is stable at the oxidation temperature. Also, it is shown that novel morphologies can develop in the Si substrate during oxidation. Transmission electron microscopy and Rutherford backscattering/channeling spectroscopy were used to characterize these structures. Mechanisms responsible for the morphological changes in the substrate during oxidation are discussed.

The ways in which iron may affect the reaction between silicon and nitrogen are summarized and considered both in terms of possible mechanisms of the nitridation process and also in terms of the phases produced by the reaction. Some new results are reported that indicate that, in addition to removing an oxide layer from the silicon, or forming an alloy with the silicon, iron can activate the gaseous nitrogen. Other impurities, such as hydrogen in the gas, may also modify the behavior of nitrogen.

A new rapid thermal annealing (RTA) procedure has been developed that eliminates the problem of crystallographic slip in 2 in, ion-implanted GaAs wafers. This annealing arrangement is easy to implement and is reliable. A precision machined graphite support structure and guard ring are used to insure uniform cooling across the entire wafer, thus eliminating slip line production. Characteristics of silicon ion implants have been determined using van der Pauw Hall, Polaron C–V profiling, and eddy current resistivity measurements. Characterization showed excellent dopant activation and uniformity can be achieved using this new technique. Low-temperature photoluminescence measurements were performed on samples annealed with and without graphite in the system, and no detectable difference in surface carbon contamination was found.

The solid-phase epitaxial regrowth of a III–V compound semiconductor by a two-stage reaction between a two-layer metallization and a compound semiconductor substrate is described. The regrowth process begins with a low-temperature reaction between a metal M (e.g. Ni, Pd, or Pt) and a compound semiconductor substrate, AB, to produce an intermediate M, AB or MB, phase. A subsequent reaction at a higher temperature between an overlayer of Si, Ge, Al, or In and the intermediate phase results in the decomposition of the intermediate phase and the epitaxial regrowth of a layer of the compound semiconductor. This regrowth mechanism is verified experimentally for the specific case of the Si/Ni/GaAs system. Rutherford backscattering spectrometry and transmission electron microscopy data show that the ternary phase Nix GaAs, formed during the initial stage of the reaction, decomposes toNiSi and GaAs by reaction with the Si overlayer. The incorporation of the overlayer element into the regrown semiconductor layer is proposed as a mechanism to explain the formation of Ohmic contacts in Si/Pd/n-GaAs, In/Pd/n-GaAs, In/Pt/n-GaAs, and similar two-layer metallization systems on n-GaAs.

A low-resistance nonspiking Ohmic contact to n-GaAs is formed via solid-state reactions utilizing the Si/Pd/GaAs system. Samples with Si to Pd atomic ratios greater than 0.65 result in specific contact resistivity of the order of 10−6 Ω cm2, whereas samples with atomic ratios less than 0.65 yield higher specific contact resistivities or rectifying contacts. Rutherford backscattering spectrometry, cross-sectional transmission electron microscopy, and electron diffraction patterns show that a Pd, Si layer is in contact with GaAs with excess Si on the surface after the Ohmic formation annealing. This observation contrasts with that on a previously studied Ge/Pd/GaAs contact where Ohmic behavior is detected after transport of Ge through PdGe to the interface with GaAs. Comparing the Ge/Pd/GaAs system with the present Si/Pd/GaAs system suggests that a low barrier heterojunction between Ge and GaAs is not the primary reason for Ohmic contact behavior. Low-temperature measurements suggest that Ohmic behavior results from tunneling current transport mechanisms. A regrowth mechanism involving the formation of an n+ GaAs surface layer is proposed to explain the Ohmic contact formation.