The interaction of a low-energy silicon beam with a silicon substrate has been simulated. The combined effects of vibrational lattice excitation and of covalent binding have been included for the first time by using a molecular dynamics technique and an empirical potential that accurately describes the covalent Si–Si interactions. A 10 eV silicon beam was directed normal to a silicon (111) substrate. Sticking ratio, penetration depth, substrate structure, and vibrational excitation of the substrate are quantitatively determined. The special features of such low-energy beam deposition relative to thermal deposition processes are discussed.

R. B. Fair et al. have analyzed original data on the effect of heavy, uniform background doping with As and B on the diffusivity of Sb in Si at 1000°–1200°C. Their analysis attributed a role to “electric fields” and led to the conclusion that, for n-type background doping, Sb diffusion is dominated by double-negatively charged vacancies with no contribution from V−. For p-type backgrounds they concluded that donor-acceptor pairing alone retards the diffusion. Here it is shown (1) that electric fields do not play a role in their experiments, (2) that the contribution of V− to Sb diffusion in an n-type background is not zero but is roughly equal to that of V= for n/ni = 10, and (3) that the retardation of Sb diffusion in p-type Si is due both to donor-acceptor pairing and, principally, to the elimination of the contributions of V− and V=.

The solidification behavior of Al–Mn alloy powders was studied as a function of cooling rate and manganese content. The phases present in the powders differed from those expecied at equilibrium due to competetive nucleation and growth kinetics. The equilibrium Al6Mn phase was absent due to its relatively sluggish nucleation kinetics, and in the more concentrated and rapidly cooled alloy powders, the metastable quasicrystalline phases were present. Nucleation temperatures measured in alloys cooled at 25°C/s are interpreted to represent formation of the icosahedral phase, which subsequently transforms to the decagonal phase and provides a lower bound estimate of 870°C for the melting point of the icosahedral phase in an Al-30 wt. % Mn alloy.

The expression used for electric field in the article being discussed is not appropriate for the experimental conditions, but there is a built-in electric field present that affects Sb diffusion. Thus the calculated values of D=i are reasonably within the experimental error of the data on which the calculations are based. Our conclusions that V− vacancies do not play an important role in Sb diffusion and that Sb–B pairs are responsible for retarded Sb diffusion in high-concentration B-doped Si are supported.

The steady-state erosion rate of electrodeposited amorphous Ni80P20 by angular alumina particles has been measured as a function of impingement angle from 15°–90°, particle velocity from 50–100 m/s, and average particle diameter from 40–390 μm. The erosion rate can be described by a power law in velocity and particle size. The erosion rates in Ni80P20 were compared to those measured for electrodeposited pure crystalline nickel. For all experimental conditions the erosion rate in the amorphous alloy exceeded that of nickel. The material removal in amorphous Ni80P20 is attributed to formation of plastic shear bands below the impact areas. For the most energetic particles the erosion leads to the formation of melt, which seems to be a consequence of the localized shear.

The crystallinity and morphology of thin, radio-frequency (rf) -sputtered MoS2 films deposited on 440C stainless steel substrates at both ambient (∼70°C) and high temperatures (245°C) were studied by scanning electron microscopy (SEM) and by x-ray diffraction (Read thin-film photography and 0−20 scans). Under SEM the films exhibited a “ridgelike” (or platelike) formation region for thicknesses between 0.18 and 1.0 μm MoS2. X-ray diffraction was shown to give more detailed and accurate information than electron defraction, previously used for elucidating the structure of sputtered lubricant films. Read thin-film x-ray diffraction photographs revealed patterns consistent with the presence of polycrystalline films and strong orientation of the MoS2 crystallites. Correlation of those patterns with 0−20 scans of the films indicated that the basal planes of the MoS2 crystallites [i.e., the (001) planes] were perpendicular to the substrate surface plane, and that various edge planes [i.e., the (h k 0) planes] in the individual crystallites were parallel to the surface plane, in agreement with previous observations of thinner films. Sliding wear caused the crystallites to orient with their basal planes parallel to the surface plane. The crystallite lattices in all films in this study were shown to exhibit compressive stress (∼ 3%–5% with respect to natural molybdenite) in the direction perpendicular to the (h k 0) planes, and the worn films were expanded (i.e., exhibited tensile stress) perpendicular to the (001) plane. In addition, the shapes of the x-ray diffraction peaks were strongly influenced by the presence of oxygen impurities and/or sulfur vacancies in the MoS2 lattice, indicating that x-ray diffraction may provide a simple quality-control test for the production of a film with optimum lubricating properties.

The main results regarding the synthesis of the graphite intercalation compounds containing a metallic alloy (constituted by an alkali metal and a heavy metal: mercury, thallium, or bismuth) are reported. The synthesis conditions are described: reaction temperatures, compositions of the reactive alloys, and reaction mechanisms. The differences of behavior of the various alloys with respect to the graphite are explained. The structure of the ternary phases is described, and their superconducting properties are reported.

Previous small-angle scattering measurements of the kinetics of changes of the surface area of pores in an annealed glasslike carbon have been reanalyzed in terms of the Lifschitz, Slyozov, and Wagner coarsening theory in which the surface area is used to obtain an average spherical pore size. When the data are corrected for the transient heat-up time to reach the annealing temperature, the reanalysis leads to an activation energy of 75 ± 7.2. kcal/mol, in agreement with recent results (75 ± 3.6 kcal/mol) obtained using direct measurements of changes in pore size as determined by the pore radius of gyration. The best value for the activation energy for vacancy migration in carbon is therefore estimated at 75 ± 3.2 kcal/mol.

Carbon fibers having various types of structures were prepared by spinning coal tar mesophase pitch, followed by thermosetting and heat treatment at high temperature. Two kinds of spinning—spinning with stirring the pitch above a capillary and without stirring—have been tried to form pitch fibers from coal tar mesophase pitch. Carbon fibers obtained from mesophase pitch and spun without stirring have a radial transverse structure where the graphite layers are arranged radially in the transverse cross section of the fibers. Carbon fibers made with a stirring system can have random, onion, and a novel “quasionion structure” by changing the spinning conditions. Carbon fibers spun with stirring are less graphitizable than those spun without stirring. No separation of the ten diffraction bands into 100 and 101 peaks and no appearance of a 112 peak were observed by x-ray diffraction when the fibers were heat treated at 2700°C, whereas carbon fibers spun without stirring show clear evidence of graphitization by heat treatment at 2700°C. Transverse magnetoresistance effects at 77 K, (Δρ/ρ)t have been measured to characterize the structure of the carbon fibers. The carbon fibers spun with stirring and heat treated at 2500°C generally exhibit a negative transverse magnetoresistance effect, whereas the carbon fibers spun without stirring exhibit a positive magnetoresistance. Good correlations are found among d002, Lc (002), transverse magnetoresistance, and resistivity at room temperature of carbon fibers spun under various conditions and heat treated at 2500°C. The tensile strengths (TS) of carbon fibers that are less graphitized are higher than those of carbon fibers with a higher degree of graphitization if tensile moduli (TM) are almost constant.

The results of an optical transmission study through ∼ 1000 Å thick flakes of graphite and the potassium graphite intercalation compounds KC8 and KC24 in the photon energy range of 1–5.5 eV are reported. Structure in the transmission spectra associated with the Drude minimum, the threshold for inter-π-band and the graphitic M-point absorption are observed. The transmission spectra are found to be consistent with the dielectric function ∊(ω) obtained from previous reflectance studies. The influence of the electronic absorption in the quasi-two-dimensional carbon π bands on the general form of the transmission spectra of graphite intercalation compounds is also shown.

Experimental results from x-ray scattering, Raman scattering, neutron scattering, and magnetic susceptibility measurements are presented to discuss hydration states and magnetic orderings in vermiculite intercalation compounds. In Na-vermiculite, the hydration transitions between 2- and I-water layer hydration states (WLHS), and 1- and 0-WLHS were studied as a function of temperature from 22–200°C. The transitions are of first order, exhibiting phase coexistence and large hysteresis. In Ni-vermiculite, de susceptibility measurements showed both magnetic-field directions and hydration dependencies. Also, ac susceptibility and small-angle neutron scattering experiments revealed evidence for magnetic phase transitions in a temperature range between 1.5 and 4 K.

Thermally stimulated luminescence (TSL) of x-ray-induced defects in R-Ba–Cu–O (R = Gd, Ho, and Eu) has been measured. In the interval 25–400°C, Ho- and Eu-doped samples exhibit similar TSL with peaks at 65, 135, and 185°C. The GdBa2Cu3Ox has, in addition to the three aforementioned peaks, a maximum at 310°C. All TSL peaks are attributed to recombination of F+s – and F−s center electrons with Vs-type holes, requiring typical thermal activation energies 0.5–1.0 eV. Spectral emission data support this conclusion. Irreversible quenching of TSL is found to occur in each sample. It is postulated that adsorbed oxygen molecules interact with radiation-induced F+s and Fs centers to produce O−2 and O2−2 molecular ions, respectively, thereby reducing the surface oxygen vacancy concentration and quenching the luminescence. In addition to activation energies, other TSL parameters are extracted from the data. It is suggested that surface TSL in these oxide superconductors is independent of rare-earth dopant.

Some recent studies on fluoropolymers that exhibit substantially increased barrier properties against the migration of moisture when compared to conventional fiber coating materials, and as a result may offer unique advantages for use in optical fiber applications, are reported. Moisture vapor permeability studies of cis-trans fluoropolyol polyacrylate indicate that it can offer up to an order of magnitude reduction in H2O permeability relative to commercially available UV curable acrylate coatings. Experimentally determined permeability coefficients were of the order of 10−12 g cm−2 s−1 cm/mm Hg and diffusion coefficients were of the order of 10−10 cm2 s−1. In addition to improved barrier properties, incorporation of fluorine into the polymer structure lowers the index of refraction of the polymer enabling a material to be tailored for use as a cladding in conjunction with silica glass. The index of refraction of cis-trans fluoropolyol polyacrylate was determined, using index matching oils, to be 1.437 (lower than the silica core) permitting its use as a cladding. Other material parameters relevant to fiber coatings have also been measured. The elastic modulus E of the material was determined to be 1010 dyn/cm2 with a slow drop to 108 dyn/cm2 at the glass transition temperature ∼45°C. In addition, an improved formulation of cis-trans fluoropolyol polyacrylate is presented that allowed in-line coating of the optical fiber in an oxygen environment.

Supercritical and compressed liquid CO2 extraction of thin solid organic films was studied using in situ capacitance monitoring. Parallel plate and fringe field capacitors were fabricated using organic films as principal dielectric media. Supercritical and compressed liquid CO2 extraction of these films at 100 bar and 30–45°C caused compositional and physical changes in the host polymer matrix that were correlated to capacitance history. As a result of these studies, film damage during extraction was attributed to explosive decompression of the CO2 solvent. In addition, a mechanism for supercritical fluid extraction of nonvolatile solutes from thin films, which is consistent with these capacitance measurements, is discussed.

Excimer laser-assisted etching of polysilicon at 193 nm was studied in the presence of CF3Br, CF2Cl2, and NF3. In the presence of 193 nm radiation, CF3Br showed some propensity to etch polysilicon, while CF2Cl2 did not show any appreciable etching. In the presence of NF3, maximum etch rates of 0.6 Å/pulse were obtained for pressures greater than 500 Torr and fluences exceeding 200 mJ/(cm2 pulse). The etch rate increased with both fluences and pressure to a limiting value of 0.6 Å/pulse. An adsorptive etch mechanism was proposed, where NF3 molecules diffuse to the surface, adsorb, and then react after absorbing laser radiation. Thermal effects enhance this process and appear to dominate at lower pressures (<400 Torr) and higher fluences. Etching caused by the gas phase formation of F atoms is minimal due to the low absorption cross section of NF3 at 193 nm. Etching of submicron profiles in polysilicon was also examined. Polysilicon samples masked by patterned SiO2 were exposed to NF3 and 193 nm ArF radiation. Subsequent scanning electron microscopy (SEM) analysis demonstrated directional etching with some surface roughening.

In order to quantitatively determine the residual stresses at the interfaces of laminate composite materials, a model involving exponential stress gradient in the substrate and no stress gradient in the film was derived. The measurements of residual strains at the Si/quartz interfaces using the Raman microprobe were compared to expected strains by the model. The model shows that a small volume of substrate near the interface about 2 times the film thickness was affected by the thermal mismatch of the two regions. Approximately 5–10 times higher residual strains were expected at the substrate-side interfaces compared to the measured results. This is explained by the experiments averaging along the probe thickness of about 10μm resolution. The recrystallization process of Si film by thermal annealing was also investigated using Raman spectroscopy.

The effects of high-dose iron implantation into high-purity fused silica have been investigated by conversion-electron Mössbauer spectroscopy, transmission electron microscopy, Rutherford backscattering, and optical spectroscopy. In addition to isolated Fe2+ ions, samples subjected to doses of 4⊠1016 and 6 ⊠ 1016 ions cm−2 were found to contain homogeneously dispersed, equidimensional, crystalline particles ⋍2 nm, similar to Fe3O4. Precipitated spherical particles of metallic α-Fe⋍4 nm were observed in samples receiving a dose of ⋍ 1017 ions cm−2; as the dose was raised to 2.5 ⊠ 1017 ions cm−2 the mean size of these particles reached ⋍ 30 nm. Annealing in air to 800°C resulted in the growth of acicular grains of α-Fe2O3 ⋍ 20–300 nm. The optical spectra of the implanted layers are compared with the predictions of small particle theory.