We have performed x-ray diffraction experiments on MBE grown 〈111〉 and 〈001〉 oriented Co (3 Å)/Pt (18 Å) superlattices with the scattering vector Q covering a plane that includes a major component perpendicular and a minor component parallel to the plane of the sample. The superlattice diffraction peaks were found to have a large width parallel to the plane of the film, indicating that there is strong in-plane disorder. These broad peaks were integrated to evaluate more accurately the amount of interdiffusion at the interface, which was found to be similar in both films, contrary to what the conventional x-ray diffraction experiment suggests.

Diamond-like carbon with silicon (DLC-Si) coatings formed by plasma-assisted chemical vapor deposition showed low friction coefficients of the order of 0.01 against steel without a lubricant, not only in dry atmosphere but also in humid atmosphere, where conventional DLC coatings showed higher friction coefficients of 0.1–0.2. DLC-Si coatings with 1 μm thickness deposited on steel were slid against steel using a conventional ball-on-disk type of apparatus to compare with a low friction mechanism of DLC-Si in dry and humid atmospheres. Analyses of wear scars indicated that formation and/or transfer of graphite-like carbon including hydrogen that originated in a DLC-Si coating occurred in dry atmosphere, while oxidation of contained silicon with water vapor formed silica-sol by sliding in humid atmosphere. The latter, peculiar to DLC-Si, was considered to cause the low friction coefficient in humid atmosphere through adsorbed water on silica.

Three processing routes that generate uniaxial alignment but otherwise yield very different microstructure and critical current are compared. Fine grain size and c-axis alignment are obtained in magnetically aligned ceramics, pyrolyzed thick films, and in situ deposited thin films. The dense, well-aligned microstructure of the in situ process produces the highest zero field critical current Jc > 104 A/cm2 at 77 K. However, the critical current is suppressed in low magnetic field, suggesting that uniaxial alignment is not sufficient to avoid Josephson-type intergranular coupling. Above 1 T, the critical current of the aligned ceramic dominates in spite of its less ideal microstructure. The critical current in this high field region is one to two orders of magnitude greater than that of nonaligned material. This result implies the existence of a 3-d percolative network of strong links.

Superconducting materials in the Bi–(Pb)–Sr–Ca–Cu–O system have been synthesized by sol-gel processing from nitrates by complexation with citric acid. The gelation process and the microstructures of the gels obtained have been studied through titration and SEM observation. Their phase transformations and microstructure development, during heat treatment, have also been investigated. The critical temperature Tc of superconductors by this sol-gel processing can reach above 100 K.

The stability of chemical vapor deposition (CVD) source materials for high-Tc superconducting films was examined by 1H-NMR (nuclear magnetic resonance), 13C-NMR, IR (infrared) absorption, and TG-DTA (thermogravimetry and differential thermal analysis) measurements. Highly purified Ca(DPM)2 (DPM: dipyvaloylmethane: (CH3)3CCOCHCOC(CH3)3) and Sr(DPM)2, utilizing recrystallization and sublimation, easily decomposed at room temperature and changed their thermal properties when they were handled and stored in air or even in an Ar atmosphere without removing adsorbed species such as water. The stability increased by removing a trace of adsorbed species and storing in an Ar atmosphere at −30 °C. Bi(C6H5)3 and Y(DPM)3 showed higher chemical stability than Ca(DPM)2 and Sr(DPM)2.

Isotope diffusion and surface analysis has been used to investigate mass transport processes and oxide chemistry during oxidation of Ni3Al alloys in oxygen between 450 and 800 °C. In all cases, the oxide has an outer layer rich in NiO that grows by outward metal diffusion. Below 650 °C, an inner mixed oxide layer allows fast inward oxygen diffusion and growth. A porous inner layer of alumina forms at 700 °C that also allows oxide growth by oxygen in-diffusion. At 800 °C, the alumina becomes protective and halts the inner oxide growth mechanism. When macroalloyed with chromium, oxide chemistry is similar, but with an additional chromium oxide in the outer layer. There is an increased oxidation protection at temperatures ⋚600 °C that results from the inhibition of oxygen in-diffusion as an oxidation process. Above 700 °C, however, protective alumina formation is retarded and faster outward metal diffusion enhances the oxide growth rate when compared to Ni3Al.

We analyze the formation of VSi2 at the amorphous-vanadium-silicide/amorphous-Si interface by linear-heating and isothermal calorimetry, and cross-sectional transmission electron microscopy. We show evidence that indicates sporadic VSi2 nucleation with a steady-state nucleation rate after a transient period. The results are contrasted with those obtained for Al2Ni nucleating at the polycrystalline-Al/polycrystalline-Ni interface, where the kinetics appears to be controlled by growth of a fixed number of nuclei at quickly consumed preferred nucleation sites.

A series of Cu/Pd superlattices with composition modulation wavelengths (Λ's) ranging from 1.6 to 3.5 nm and a strong [111] growth texture were prepared by electron beam evaporation. The elastic properties of the films were examined using the methods of uniaxial tension tests [a Young's modulus (1/s11), where sij is an elastic compliance] with the applied load parallel to the plane of the Cu/Pd interface and Brillouin scattering [a shear modulus (1/s44) with the shear waves parallel to the plane of the Cu/Pd interface]. Also, the films were characterized using both x-ray diffraction and high-resolution electron microscopy; this was done to assess the effect of the nanostructure on a possible “supermodulus effect.” The films are nanostructurally very similar to the superlattice films employed in previous studies at Northwestern in which a supermodulus effect was reported. But, contrary to previous studies, no anomalous behavior was observed for the measured elastic properties of the thin films. Therefore the present results negate the earlier results and cast a serious doubt on the existence of a supermodulus effect.

Due to the large positive heat of mixing associated with the Cu–Cr binary system, solid solutions exist only as nonequilibrium states. In this study, a series of metastable Cu–Cr alloys ranging in composition from 14.1 to 75.4% copper was fabricated by sputter deposition. Symmetric, asymmetric, and grazing incidence x-ray diffraction geometries were used to trace the phase transition from bcc to fcc crystal structures with increasing Cu fraction. It is shown that the transition takes place not by a two-phase region suggested by equilibrium thermodynamics, but rather through gradual disordering of the bcc lattice as copper atoms are substitutionally accommodated. At a critical saturation near 71% Cu, the bcc structure becomes unstable relative to the fcc and a phase transition occurs. The free energies of the kinetically constrained Cu–Cr system are modeled and the results are found to agree well with observed behavior.

The kinetics of the formation of intermetallics in the Cu–In bimetallic thin film couple have been studied from room temperature to 432 K by measuring the evolution of composite and contact electrical resistance with time and temperature. The resistivity measurements have been supplemented by x-ray diffraction (XRD), scanning electron microscopy (SEM), and transmission electron microscopy (TEM). Copper reacts with indium even at room temperature to form CuIn intermetallic and assuming a model of defect assisted diffusion into the grains, the activation energy averaged over five different samples is found to be 0.40 eV. The grain boundary diffusion is found to occur with an average activation energy of 0.55 eV. XRD confirms the growth of CuIn intermetallic and on annealing at higher temperature, for copper-rich films copper further reacts with CuIn to form Cu9In4. Further evidences of solid state reactions and grain boundary diffusion through Cu grain boundaries have been obtained from SEM study. TEM indicates the growth of the grain size on annealing and confirms the presence of the CuIn phase.

Elemental Fe and Sn powders in the ratio of 1:2 were ball-milled for various times at room temperature, and phase transformations in the powders were studied by 57Fe and 119Sn Mössbauer spectrometries, transmission electron microscopy, and x-ray diffractometry. Although Fe-Sn alloys are not obvious candidates for solid-state amorphization reactions, an amorphous phase formed after only a few hours of ball milling. Nanocrystalline intermetallic FeSn2 particles nucleated and grew within the amorphous phase, and FeSn2 became the major phase after 10–20 h of ball milling. These small particles were superparamagnetic, and were above the blocking temperature at room temperature.

Exoelectron emission from the surface of unexcited metallic glasses Fe78B13Si9 during heat treatment has been studied under ultra high vacuum condition. In the first heating cycle, exoelectrons are emitted from the as-cast ribbon in the temperature range from approximately 423 K to 773 K (150 °C to 500 °C), although the surface of the specimen is not excited by ionizing radiation, chemical processes, or mechanical treatments prior to measurements. In the second and subsequent heating cycles, however, there is no anomalous emission observed in the same temperature range. In order to elucidate the mechanism of emission, the surface of the specimen is observed by the atomic force microscope (AFM) before and after measurements. In the AFM image, many crystallites in the amorphous matrix can be found in the surface of the heated specimen. These experimental results show that exoelectrons are emitted in the same temperature range as the early stages of crystallization on the surface of metallic glasses. We hypothesize that the two effects are correlated.

Structural studies on kish graphite (KG) and highly oriented pyrolytic graphite (HOPG) were performed using the techniques of electron channeling pattern (ECP) and electron channeling micrograph (ECM) in the scanning electron microscope. In the KG specimens the ECP for the single crystal was observed for each specimen, while in the HOPG specimens those of polycrystalline graphites with parallel c-axes were observed. The crystal sizes along the a-axis in the HOPG specimens were evaluated by ECM's. The average crystal size was related to a parameter sensitive to their crystallinity, i.e., the ratio of the resistivity at room temperature to that at 4.2 K (residual resistivity ratio). A mapping of the a-axis orientation of HOPG specimens was carried out.

Diamond-hexagonal (dh) Ge has been produced by Vickers micro-indentation of a Ge single crystal and investigated by high resolution transmission electron microscopy (HREM). The results are consistent with the mechanisms that have been proposed earlier for the generation of dh Si. The hexagonal phase of these elemental semiconductors may be produced by two related mechanisms: (a) secondary twinning or (b) the intersection of two twins. The hexagonal germanium produced by both of these mechanisms has been observed and is presented in the present paper.

The evolution of radiation damage and of dopant profiles in Si samples subjected to self-annealing implantation with 160 keV As+ ions, under various transient heating conditions, depending on the beam current density, has been investigated. For temperatures in excess of 880 °C, the formation of voids is evidenced by Transmission Electron Microscopy observations. They are located in a layer extending from the surface over a depth of about 0.8 of the ion projected range, Rp (≃110 nm), while extended interstitial-type defects are observed in the region below. With increasing temperature (due to increasing beam power density and/or irradiation time), voids tend to anneal in the near surface region, while they survive and grow in a region about 40 nm thick, centered at a depth of about 50 nm, where an anomalous peak in the dopant profile is developed. The annealing of the extended interstitial-type defects at depths ≥Rp, which becomes appreciable for T ≥ 1050 °C, is coupled to a large enhancement of dopant diffusivity in the same region. It is argued that the local vacancy supersaturation, which leads to void formation, and the corresponding interstitial excess in the deeper region, which leads to extended defect formation, are a natural consequence of the collision kinetics of the displacement process, as suggested by Monte Carlo simulations reported in the literature. The evolution of damage and the anomalies in the redistribution of dopant, observed by increasing the temperature, are described as the result of the increase in the population of mobile point defects and of their influence on the mechanism of As diffusion in the different regions of the implanted layer.

It was found that the modulation wavelength and average composition of multilayers are related to the position, intensity, and diffraction order of x-ray modulation peaks for multilayers. The relation between the characteristics of the modulation peaks in different as-deposited multilayers and their interdiffusion capability is also discussed.

Diamond films were grown by microwave plasma assisted chemical vapor deposition using mixtures of 1% 13CH4 and 0.5% 12C2H2 in H2, and stable gaseous products were analyzed by mass spectrometry. The major gaseous products are methane and acetylene, and scrambling of the 13C label can be controlled at relatively high gas flow rates. At the highest flow rate studied a diamond film was grown with 77% 13C incorporation, while the methane in the reactor exhaust gas at this flow rate contained 83% 13C. By comparing gaseous 13C compositions with that of the films, the efficiency of diamond growth from methane (possibly via the methyl radical) is estimated to be about ten times higher than that for acetylene.

The fracture strength of polycrystalline diamond films deposited by filament assisted chemical vapor deposition in the thickness range of 3.5 to 160 μm is investigated. Using a burst pressure technique, the fracture strengths of circular diamond film specimens are calculated. An average fracture strength of 730 MPa for nine samples was computed. This value is in good agreement with published strengths of microwave plasma deposited diamond films, comparable to other high strength materials, and within an order of magnitude of the fracture strength of bulk natural diamond. The average fracture strength of the fine-grained substrate interface appears consistently higher than that of the coarse-grained diamond growth surface.

We describe two complementary studies of diamond growth by chemical vapor deposition. In the first, the early stages of growth of randomly distributed nuclei on silicon are studied by scanning tunneling microscopy. For growth times from 1 to 30 min nearly all crystallites are three dimensional, and increase in volume as t1.5. Although this result could be interpreted in terms of diffusion limited growth, the conditions for diamond CVD are more consistent with rate limited growth where the crystals are expected to gain volume as t3. This anomaly can be explained in terms of a two-species growth mechanism in which the rate constant for carbon addition is proportional to the diffusion limited flux of atomic hydrogen. Other mechanisms giving rise to the observed t1.5 dependence are also considered. The second study uses both scanning electron and tunneling microscopies to examine the morphology of a boron-doped film homoepitaxial to the {100} surface of natural type 2a diamond. In regions distant from gross defects, this film is very smooth. However, gross defects appear to initiate growth of new epitaxial layers at a rate much higher than in defect-free regions. This observation suggests that diamond growth is promoted by “enabling defects” and that without such defects nucleation of new layers is a slow process and permits layer-by-layer growth at a much lower rate.

Interface studies of CVD Si3N4 grown on (11$\overline 1$) SiC single crystal substrates have been made by transmission electron microscopy (TEM). It is found that there are two orientation relationships both of which involve the same (10$\overline 1$0)Si3N4//(11$\overline 1$)SiC planar relationship. However, the orientation relationships are not perfect and rotations of 2–6° are commonly seen between both directions and planes involved. High resolution electron microscopy (HREM) of the interfaces shows that the SiC and Si3N4 are continuous up to the interface and that no intermediate phases are formed. However, due to the small rotations, the HREM images are difficult to interpret directly in terms of atomic positions. Nevertheless, possible atomic models of the interface are proposed based upon the experimental findings. These models exploit the similarities between the [SiN4] and [SiC4] tetrahedra in Si3N4 and SiC, respectively. The observed orientation relationships appear to be due to matching of tetrahedra across the interface along with adequate lattice matches.