The ability of heavy-ion beams to enhance the adhesion of thin metallic films to substrates has been studied as a function of projectile species. Measurements of the adhesion enhancement of a thin gold film to substrates of tantalum and silicon (with native oxides) have been made for beams of 12C, 16O, 28Si, 35Cl, and 58Ni at 2.85 MeV/nucleon. The threshold dose required to pass the Scotch tape peel test was found for the Au-Ta system to be D th (cm−2) = 1017 (dE / dx)−3±0.2 where dE/dx is the electronic stopping power (MeV mg−1 cm−2) of the ion in Au. For the Au-Si system, Dth = 6×1018 (dE/dx)−4.1±0.3. The steep dependence of D th on dE/dx found here is in contrast with an earlier measurement for the Au-Ta system by Tombrello et al. The adhesion enhancement was observed to decrease with time after the bombardment in a manner suggesting that diffusion of atoms through the gold film is important. The possible importance of small concentrations of extraneous atoms at the interface is discussed.

A Kikuchimap for the 6H polytype of α-SiC has been constructed for the standard triangle Selected, indexed diffraction spot patterns have also been produced and are included as companion information for the map.

The electron irradiation-induced, crystalline-to-amorphous transition was studied in the intermetallic compound Cu4Ti3 by high-resolution electron microscopy. Using highresolution maps from the crystalline region into the amorphized region, the amorphization process and the amorphous structure were examined. The extent of chemical order in crystalline regions just prior to amorphization was studied by simultaneously imaging superlattice and fundamental lattice fringe contrast. The chemical order continuously decreased in these regions but faint superlattice contrast was recognized as long as the crystalline feature remained on the image, supporting the theory that chemical disordering is the major driving force for amorphization. The amorphization process appears to be evolutionary, leading to a nanocrystalline type of amorphous structure. A model of the amorphization process is proposed based on the present results and those from previous studies.

The stability of ordered semiconductor alloys has been studied, using total energy pseudopotential calculations. The ordered alloys are found to be stabilized with respect to disordered alloys via reduction of the internal strain and by chemical interactions. The Si–C and Si–Ge systems are used as illustrations, finding that ordered Six Ge1−x should be a metastable alloy, in agreement with experimental observations.

The icosahedral phase has been produced by pulsed laser melting of thin films of Mn-implanted Al. With increasing laser intensity, we observe a mixture of icosahedral and fee phases followed by a single phase fee region. Grains as large as 1 μm in diameter have been observed in 0.1 μm thick films. Electron diffraction studies of individual icosahedral grains indicate that the rapid growth direction from the melt is along the threefold symmetry axis.

Many workers have recently conjectured that the underlying forces responsible for icosahedral clustering in crystals may also explain the origin of metallic glass formation. Critical examination of thermochemical structural diagrams and radial distribution functions of good metallic glasses shows that this assertion is unfounded.

Electrophotographic properties of chalcogenide materials are readily influenced by altering their composition and/or structure. Dark decay and cycle down of photoreceptors utilizing small particle generators are both directly proportional to average crystallite size (ACS). This paper describes a novel chemical method to control the ACS of Se, Te, and Sex Te1−x alloys. These chalcogenide materials are prepared as powders by the reduction or coreduction of SeIV and/or TeIV intermediates with hydrazine, in organic media. To control the ACS of precipitated chalcogens the reaction is carried out at the desired temperature. X-ray diffraction measurements are used to determine the ACS, homogeneity, and phase of these precipitated powders.

Electrohydrodynamic (EHD) atomization has been used to rapidly solidify micron and submicron size droplets of Al-14 at. % Mn to study nucleation behavior of icosahedral phase. Icosahedral grain size has been found to decrease continuously with decreasing droplet size. Based on this result, formation of the icosahedral phase is explained by homogeneous nucleation. Extremely low resistance to nucleation of icosahedral phase can be understood if possible topological similarities between liquid and icosahedral quasicrystal are considered. Formation of glass as configurationally frozen liquid in Al-Mn and similar alloy systems is questionable, implying that the reported Al-Mn glass probably has a microquasicrystalline structure.

Photoplasticity in mercury cadmium telluride, Hg1-x Cdx Te with x = 0.3, has been studied as a function of light frequency and deformation temperature. We show that there is an easily measurable time delay accompanying irradiation of the crystal and the change in stress. This time delay is temperature dependent, suggesting a diffusion of charge carriers, introduced by the light, to the interior of the crystal. A simple analysis is given of the observed temperature dependence that is consistent with the experiments.

A model for the kinetic growth of oxygen-related thermal donors in Czochralski silicon at about 450°C is presented. The model, which is based on the work of Suezawa and Sumino, derives forward reaction rates for the electrically active species by comparing analytic expressions for the early-time annealing kinetics with the infrared electronic absorption data. The analytic expressions, which are independent of the chemical structure of each species, result from three assumptions: (1) the donor defects beyond the first donor species (TD-1) are chemically stable at the donor formation temperature, (2) the reactions for the TD-1 and those electrically inactive clusters smaller than TD-1 are in equilibrium, and (3) the oxygen interstitial concentration remains constant for short annealing times. The parametrized values of the rate constants indicate that the forward rates of reaction vary widely between species, with a sharp peak at the reaction which takes the first electrically active species to the second. If the rate constants are taken to be of the form K = 4πRD, where R is the capture radius for the given forward reaction and D represents the effective diffusion coefficient, then the variation between reaction constants may be associated with differences in capture radii between species, with the diffusion coefficient assumed to be the value determined by Stavola et al. [Appl. Phys. Lett. 42, 73 (1983)] for “as-provided” material, which has an activation energy of 1.95 eV. The model is successfully applied to the two available sets of infrared absorption data (the Oeder-Wagner and Suezawa-Sumino data) when differences in the annealing temperatures and initial oxygen concentrations are taken into account. The best-fit parameters found by fitting the analytic expressions are then applied to a set of chemical reaction equations which characterize the formation rates of specific oxygen aggregates. The use of such a set of coupled, nonlinear differential equations, which must be solved numerically, introduces free parameters for the oxygen clusters smaller than the first thermal donor. It is shown that the assignments of a thermal donor core containing two, three, four, or five oxygen atoms are all capable of fitting the experimental data. This result indicates that a best fit to the kinetic data cannot be used to argue for a specific thermal donor core. Finally, the authors discuss possible mechanisms for the enhanced values of the capture radii.

A simple, precise method for obtaining the average thickness of an amorphous layer formed by any surface treatment has been developed. The technique uses an x-ray diffractoeter to measure the reduction in the integrated intensity of several diffracted x-ray lines due to the near surface amorphous layer. The target material for generation of x rays is selected so that the emitted x rays are strongly absorbed by the specimen. This method permits thickness measurements down to ∼ 100 nm. It has been tested on a specimen of Fe80B20 on which an amorphous layer was produced by pulsed XeCl (308 nm) laser irradiation; the amorphous layer thickness was found to be 1.34 (∼0.1) um.

A Pd–U–Si metallic glass transforms upon annealing to a quasicrystalline phase of the same composition. Electron diffraction patterns of this material verify its icosahedral symmetry. Differential scanning calorimetry and transmission electron microscopy are used to obtain both the nucleation and growth kinetics of this glass-to-quasicrystal, first-order phase tranformation. The homogeneous nucleation rate of the quasicrystaUine phase in the metallic glass achieves a maximum at a temperture where its growth is still relatively slow.

Shape transitions and orientation alignment of elastically misfitting precipitates in the presence of an external stress field have been predicted using bifurcation and group theory and by performing actual energy calculations for elliptical cylinders under plane strain conditions. Under the assumption of system isotropy, the applied field acts to break or perturb the bifurcation. Both first- and second-order size-induced shape transitions are observed for elastically soft precipitates. Stress-induced shape transitions are shown to be either first-order or continuous for elastically soft precipitates. Only continuous stressinduced shape transitions are observed for hard precipitates.

The structure and thermal stability of rapidly solidified Al-Cr-Si, Al-Mn-Si, Al-Fe-Si, Al-Co-Si, and Al-Ni-Si alloys have been investigated using x-ray diffraction and thermal analysis measurements. Each series of alloys shows a region of stoichiometry that yields icosahedral symmetry and a region that yields an amorphous phase. Thermal and structural properties of these alloys are reported as a function of stoichiometry and quench rate.

Thin AuGa2 films were grown by codeposition from separate Au and Ga evaporation sources on clean GaAs(001) substrates in ultrahigh vacuum, and were studied by Auger electron spectroscopy, electron energy-loss spectroscopy, low-energy electron diffraction, scanning electron microscopy, and x-ray diffractometry. The morphology and crystallinity of the AuGa2 were highly dependent upon the film deposition and annealing history. Films grown on room-temperature substrates were continuous, specular, and polycrystalline, but the dominant orientation was with the (001) planes of the crystallites parallel to the substrate surface. Annealing to temperatures between 300°and 480°C caused the film to break up and coalesce into rectangular crystallites, which were all oriented with (001) parallel to the surface. An anneal to 500°C, which is above the AuGa2 melting point, resulted in the formation of irregular polycrystalline islands of AuGa2 on the GaAs(001) substrate. No interface roughening or chemical reactions between the film and substrate or interface were observed for even the highest-temperature anneals.

Amorphous Al80Cr20 films were made by coevaporation and by room temperature ion irradiation of the coevaporated films. The amorphous phase was transformed into the quasicrystalline state through two routes: thermal and ion beam assisted anneal. The intensity of the quasicrystalline electron diffraction pattern increases continuously within the annealing temperature range from 547°to 607°C. The starting state of the films (as-deposited or ion-irradiated codeposited) had no effect on the thermal transformation to the quasicrystalline state. Ion irradiation of the amorphous phase at 200°C produces a more complete set of icosahedral diffraction lines. Icosahedral AlCr has the same reciprocal lattice spacings as icosahedral AlMn.

A new method of ceramic-to-metal welding has been developed using a pressurized combustion reaction to form Mo—TiB2—Mo and Mo—TiC—Mo couples. Mixtures of Ti powder with B or C between Mo disks were electrically ignited under 3 GPa pressure. The exothermic reaction of the powders resulted in the formation of TiB2 and TiC and reaction with Mo at the metal interface. Weld strengths of the Mo—TiB2—Mo and Mo—TiC—Mo couples were 20—40 MPa and ∼ 10 MPa, respectively.

Two currently proposed structural explanations for thermal embrittlement of Fe-based metallic glasses are discussed: embrittlement due to loss of excess free volume by annealing and embrittlement due to the formation of chemical heterogeneities due to phase separation in the amorphous alloy. It is shown that recent small-angle x-ray scattering results that were thought to be in disaccord with field-ion microscopy (FIM) atom-probe analyses indicating occurrence of phase separation are in fact in agreement with the latter. Then a new mechanism is presented, based on structural models and density measurements in Fe–B-type amorphous alloys, which results in loss of free volume during the occurrence of phase separation, thus integrating an important effect of phase separation in the free-volume models for plastic flow in amorphous alloys.

The equilibrium surface composition of a Cu-0.83 at. % Ag alloy has been studied over the range from 600°–400°C. Above 450°C the alloy consists of a single phase, whereas below that temperature the material separates into copper-rich and silver-rich phases. The kinetics of equilibration appear to be controlled by grain boundary diffusion, leading to more rapid equilibration than expected on the basis of lattice diffusion-controlled kinetics. In the single-phase regime, silver segregates to the surface with an average enthalpy of segregation of −24 kJ/mol and an entropy of segregation of 0.94 J/mol K, and displays a trend of increasing equilibrium silver surface concentration with decreasing temperature. Theoretical estimates of the enthalpy of segregation yield the somewhat more negative values of −60 and −47 kJ/mol, respectively. In the two-phase regime, the surface continues to be enriched in silver, but the silver surface concentration decreases with decreasing temperature as a result of the rapidly decreasing equilibrium solubility of silver in copper.

The influence of specific chemical dopants on the electrophotographic behavior of selenium and its alloys has been established in prior work. This communication describes a chemical procedure that has been found effective in removing electronically active impurities from amorphous selenium. The methodology involves converting contaminated selenium into a chemical intermediate that is separated by selective alcoholic dissolution and then reduced to high-purity selenium. The electrical characteristics of the amorphous films obtained by vacuum evaporation of the latter are determined directly from analysis of xerographic potentials.