The kinetics of MoSi2 pest, caused by oxidation in air, has been studied. Experimental results indicated that pest disintegration occurred at temperatures between 375 and 500 °C. The volumes of test samples increased with oxidation duration. Analysis of change in sample volume versus oxidation duration revealed that the pest disintegration consisted of two stages, namely nucleation (or incubation) and growth. The onset of the growth stage depended on the test temperature. More importantly, changes in sample volume were found to obey a linear relationship with time during the growth stage. Equations were formulated to demonstrate that the growth kinetics of pest disintegration was proportional to the rates of change in sample volume. The rates of volume change during MoSi2 pest were calculated to be 4.9 × 10−6, 2.8 × 10−5, 3.7 × 10−5, and 5.4 × 10−5 cm3/s at 375, 400, 425, and 450 °C, respectively; the growth kinetics increased with oxidation temperature. The activation energy for the growth stage of pest disintegration was determined to be 27.6 kcal/mole, which agrees well with the activation energy for the low-temperature oxidation of MoSi2.

Filament formation in V2O5 gel films leading to a two-terminal switching device has been observed. In a previous paper, we have identified the switching with a metal-insulator transition within a permanent, current-induced channel between the electrical contacts. Here, we describe the reversible formation of a filament inside the channel, and obtain a static solution of the heat transport equation for this device which indicates a large temperature variation within the filament, and further reveals the failure mechanism for the reversible switching. The principle of least entropy production has been used to analyze the filament growth, which results in a successful simulation of the “on” state I-V characteristic of the switching process, including its negative resistance region.

Diamond growth experiments were performed in a microwave plasma ball reactor on silicon wafers or on a molybdenum sheet provided with cones (stamped into the sheet with a punch). All substrates had been treated by scratching with diamond powder in advance. The gas mixture used was CH4/H2, sometimes with the addition of CO. Substrate temperatures ranged from 953 to 1428 K, pressures from 100 to 400 mbar, and microwave powers from 250 to 700 W. A strong preference of diamond growth was observed on the cones in the molybdenum substrates. This is interpreted as being caused by gas transport hindrance. The resulting deposition coefficient of the “active” species is about 0.1 under all conditions investigated. The deposition experiments on silicon substrates are numerically modeled in two steps. In the first step, temperature fields and electron density and energy distributions in pure hydrogen are calculated following the method described previously. The output of this first simulation step is taken as input data for the second step. The condition is applied that chemical reaction rates due to thermal or electronic activation and diffusional flows compensate each other at every point of the reactor. In this way stationary concentrations of the 13 species in 29 elementary reactions are computed and, from these, the expected deposition profile of diamond on the silicon substrate, assuming one of the carbon-containing species to be the “active” one. When the experimental deposition profiles are compared with the calculated ones, C2H as the “active” species gives the best match to all the experimental results. CH3 and C2H2 (and perhaps others) might contribute to the diamond growth to a limited extent only.

Cryptomelane-type manganic acid (CMA), H2Mn8O16 · 2.4H2O, with a theoretical cation exchange capacity of 2.70 meq/g, was prepared and its cation exchange properties were studied as a function of XM which is defined by the ratio of uptake in meq/g to the theoretical capacity. Plots of the corrected selectivity coefficients log KHM vs the fractional exchange M for alkali metal ions on a 2 × 2 type tunnel-structured manganic acid showed a gradual decrease in small XMM regions and a steep decrease in large XMM) were 0.92 for Li+, 0.74 for Na+ and K+, 0.67 for Rb+, and 0.44 for Cs+. These maximums have been attributed to steric limitation as well as a limit on the expansion of the crystal lattice. Some x-ray diffraction (XRD) data of alkali cation exchanged forms were in good agreement with the XRD data of synthetic alkali CMA phases as given in the cards by the Joint Committee on Powder Diffraction Standards (JCPDS). The lattice parameter a0 has been found to depend on the exchanged amounts and the nature of the cations involved, while the c0 value remained almost the same irrespective of the amount of exchange or the nature of the cations.

Copper silicide precipitation in Czochralski silicon influenced by the existence of a GexSi1−x heteroepitaxial layer has been studied. Samples with and without a 100 nm Ge0.016Si0.984 heteroepitaxial layer were annealed together for different periods of time at 1000 °C in air on copper containing iron plate and after copper plating of the backside, respectively. The absorption or emission of silicon self-interstitials (or vacancies) significantly influences the precipitation behavior of copper silicide. Undersaturation of silicon self-interstitials (or vacancy supersaturation) during oxidation of the heteroepitaxial layers is able to prevent the formation of copper silicide precipitate colonies in the surface region.

Several sol-gel syntheses make use of “additives” in the sol-preparation step. These additives can react with metal alkoxides causing important structural changes. In order to demonstrate the nature of the reactions involved in the molecular modification process, a model system based on Ta(OC2H5)5, acetic acid and acetylacetone (as modifiers), was studied using FTIR spectroscopy. At room temperature, both modifiers react with the ethoxide to cause formation of new organotantalum precursors. The acetic acid modification was observed from the characteristic symmetric and asymmetric vibrations of the COO groups. The average difference in wave numbers (δv = vasymm – vsymm) between the two of 140 cm−1, observed for different ratios of ac/Ta, signifies a bridging nature of the acetate group. For ac/Ta ≥ 1, formation of ethyl acetate, probably as a result of the reaction between ethanol and excess acetic acid, was also observed using FTIR. Results of the acetylacetone modification showed the enol form of acetylacetone which has its v(C–O) and v(C–C) vibrations centered around 1625 cm−1, split into two bands at 1581 and 1518 cm−1, respectively, indicative of chelation of the acetylacetanate ligand to Ta. In the case of acetylacetone modification, the formation of ethanol was confirmed by FTIR analysis of the liquid fraction distilled at ∼80 °C.

The tribological properties of polycrystalline chemically vapor deposited (CVD) diamond films grown on silicon substrates and containing varying amounts of amorphous carbon impurities were investigated. Films were characterized by secondary electron microscopy (SEM) and atomic force microscopy (AFM) for surface morphology and roughness and by spatially resolved Raman spectroscopy for amorphous carbon (a-C) content. Friction measurements were performed with a Rockwell C hemispherical diamond tip in ultrahigh vacuum (UHV) and in ambient air. In vacuum, the friction coefficient rises monotonically from 0.6 in a region with substantial a-C to 0.85 in a region with pure diamond. Under ambient conditions, the friction coefficient is substantially lower than that in vacuum and deceases slightly (from ∼0.19 to ∼0.16) with the decreasing a-C content. Under both vacuum and ambient conditions, the friction coefficient was observed to be independent of load over the range of 0.1–0.5 N. The friction values are discussed in terms of adhesion between the diamond tip and the film. Qualitative scratch hardness measurements were performed in UHV by measuring the minimum load at which plastic deformation occurs for a single traversal of the tip. Scratch hardness is found to increase with increasing diamond content of the films. The wear mechanism of the pure diamond regions was evaluated by examining wear tracks with SEM and AFM. The wear tracks showed evidence of spalling, buckling, and grain pull-out indicative of a cohesive mode of failure (failure at grain boundaries). A decrease in surface roughness in the wear tracks indicates asperity wear. Adhesive failure at the Si substrate interface or of a phase transformation of the diamond film was not observed in this load regime.

Photoconductivity was measured on a series of carbon aerogels to investigate their electronic properties. Carbon aerogels are a special class of low-density microcellular foams, consisting of interconnected carbon particles (∼120 Å diameter) and narrow graphitic ribbons (∼25 Å width) intertwined within each particle. Both the dark- and photoconductivities show drastic changes in the temperature range 5–300 K, which are similar to those in a-Si and chalcogenide photoconductors. At high temperatures, the photoconductivity is dominated by the carrier recombination within each particle. The photoconductivity at low temperatures is dominated by the same carrier transport mechanism as that for the dark conductivity, which is based on hopping and tunneling transport. The activation energy values for transport and recombination identify the electronic structure of the particles among samples of different bulk density. The long decay time of the photoconductivity suggests a relaxation mechanism associated with the dangling bonds.

The competition between solid phase epitaxy and random nucleation in amorphous Si implanted with Cu and Ag has been studied. At low metal concentrations, solid phase epitaxy proceeds with slight deviations from the intrinsic rate, with the impurity segregated and evenly distributed in the amorphous layer. At an impurity concentration of 0.12 at.%, rapid nucleation occurs, transforming the remaining layer into polycrystalline Si. The nucleation rate is ≥108 the intrinsic homogeneous rate. The effects of the metals on epitaxy scale with the amount of metal–Si interaction. Nucleation appears to occur when the metal impurities exceed their absolute solubility limit and begin to phase separate.

Thin alumina films were prepared on stainless steel and glass surfaces by dip coating from an aluminum alkoxide solution. Multiple coatings from a low-viscosity solution were necessary for high quality and sufficient thickness of the films. To determine the bonding mechanism and strength, wavelength dispersive x-ray was used. Aluminum was found to diffuse into the substrate in both cases. The possible bonding mechanism is a combination of diffusion and the formation of chemical compound between the alumina and the substrates. The surface properties of stainless steel, such as microhardness, electric resistance, and corrosion resistance, were substantially improved when coated with alumina.

The evaluation of the thermal stability of three different fully dense AlN materials in the temperature range of 600 °C to 1400 °C in air indicates the strong effect of the starting composition on the oxidation process. The oxidation resistance of pure AlN and Y2O3-doped AlN was found to be good up to ≍1350 °C. The kinetics are linear (1100 ≤ T ≤ 1400 °C) and the process is governed by a surface reaction that gives rise to the formation of a porous, nonprotective oxide scale, where Al2O3 and Y-aluminates (i.e., AlN–Y2O3) have been found as crystalline reaction products. For AlN-CaC2, higher oxidation rates indicate that the outward migration of Ca modifies the reaction mechanisms. Linear kinetics in the range 1100 ≤ T ≤ 1200 °C are followed by parabolic kinetics at higher temperatures (T > 1250 °C); with regard to the latter behavior, an activation energy of 160 kJ/mole could indicate the diffusion of oxygen through the oxidation scale as the rate-controlling mechanism.

Amorphous cobalt-boron alloy powders have been prepared by a high energetic ball mill at room temperature starting from different Co/B ratios. They were characterized by means of x-ray diffraction, scanning and transmission electron microscopy, and differential scanning calorimetry. Ball milling of Co–B mixtures induces solid-state amorphization which becomes faster with increasing boron content. After maximum amorphization ball milling leads to crystallization of t-Co2B in all the binary samples.

We have deposited hydrogen-free diamond-like amorphous carbon films by ArF (193 nm) pulsed laser ablation of graphite. The deposition process is performed with a laser power density of only 5 × 108 W/cm2 at room temperature without any auxiliary energy source incorporation. The resulting films possess remarkable physical, optical, and mechanical properties that are close to those of diamond and distinct from the graphite target used. The films have a mechanical hardness up to 38 GPa, an optical energy band gap of 2.6 eV, and excellent thermal stability. Analysis of electron energy loss spectroscopy reveals the domination of diamond-type tetrahedral bonding structure in the films with the sp3 bond fraction over 95%. Compared with other reported results of pulsed-laser-deposited diamond-like carbon films, our experimental results confirm that the laser wavelength or photon energy plays a crucial role in controlling the properties of the pulsed-laser-deposited diamond-like carbon films.

25 μm thick Upilex films (registered UBE trademark) were carbonized, then graphitized at various temperatures up to 2800 °C and studied by optical and electron microscopies. While the graphitizing behavior of Kapton films is similar to that of anthracites, Upilex graphitization is erratic from one film to the other. The thickness of the better graphitizing Upilex films decreases as the anisotropy increases. Their graphitization occurs at a relatively low temperature (2100 °C), because the oxygen is entirely labile (no cross-linking). Non-graphitizing films are obtained when oxygen remains stable as the heat-treatment temperature (HTT) increases. They stay optically isotropic and microporous without flattening, and even show a limited swelling instead of a thinning. This behavior is attributed to the random mobility of the imide part of the molecule when carbonization starts.

A two-step seeding process has been developed to lower the transformation temperature and modify the grain structure of ferroelectric lead zirconate titanate (PZT) thin films with high Zr/Ti ratio. Previous study has shown that nucleation is the rate-limiting step for the perovskite formation. Therefore, any process that enhances the kinetics of nucleation is likely to decrease the transformation temperature. In this process, a very thin (45 nm) seeding layer of PbTiO3, which has a low effective activation energy for perovskite formation, was used to provide nucleation sites needed for the low temperature perovskite formation. In this study, we have shown that the pyrochlore-to-perovskite phase transformation temperature of PbZrxTi1−xO3 films of high Zr/Ti ratio (e.g., x = 53/47) can be lowered by as much as 100 °C. The grain size of these films can also be substantially modified by this two-step approach.

The nanostructure and chemical distribution in semi-insulating polycrystalline oxygen-doped silicon (SIPOS) deposited on (001) Si and its isothermal transformation behavior at 900 °C were investigated by high resolution electron microscopy (HREM) and electron energy loss nanospectroscopy (EELS). The structure of the as-deposited film, which contained 15 at. % oxygen, was amorphous. No evidence for nanocrystalline second phases was found. It was similar in appearance to amorphous silicon. After annealing for 30 min at 900 °C in an inert environment (N2), a dispersion of small nanocrystals, identified as silicon by imaging, diffraction and EELS, formed in the amorphous SIPOS matrix, with a thin precipitate free zone (PFZ) adjacent to the Si substrate. The SIPOS matrix oxygen concentration increased to 36 at. % and the matrix remained amorphous after annealing. No other phases were observed in annealed specimens. Changes in Si–L near edge fine structure and low loss peaks in EELS spectra from SIPOS with increasing oxygen concentration indicated that it is a solid solution supersaturated with silicon. Microstructures indicated that the Si nanocrystals formed during a homogeneous precipitation reaction.

A comprehensive investigation of antiphase domain boundaries (APB's) in GaAs-on-Si is presented. A comprehensive experimental approach, based on complementary electron microscopy (TEM and SEM) and chemical etch techniques, is developed and used in the study of the structural evolution of APB's on vicinal (001)Si substrates. The question of whether a GaAs selective nucleation or APB annihilation accounts for the absence of APB's in thick GaAs/Si films, grown on substrates misoriented from (001) toward (110), is addressed. APB's are revealed by two different TEM techniques to exist in the first interfacial layers of GaAs/Si even in samples considered to be “APB free”. The APB annihilation mechanism is illustrated in GaAs films grown on substrates misoriented toward (100), either directly, by cross-sectional TEM observations, or indirectly, by combined chemical etch/SEM experiments. In addition, the structural characteristics of APB's and their interaction with other extended crystal defects are clarified by XTEM and TEM observations. Finally, the influence of APB's on GaAs/Si surface morphology and their electrical activity are shown explicitly for the first time.

Highly oriented pyrolytic graphite has been implanted at room temperature with 165 keV C+-ions at doses from 6 × 1017 to 3 × 1019 ions/m2. Implantation-induced topographical changes of differing size scales were studied by optical, scanning electron, scanning tunneling, and atomic force microscopies. Defects with atomic resolution are seen for the lower dose implants. The formation of a vacancy line is revealed for the first time. At the higher doses a dendrite-like system of deep surface cracks is observed. This cracking develops as a result of the large basal plane contraction produced by irradiation which generates high shearing stresses between the implanted, damaged surface layer and the underlying material. Two independent systems of ridges have been characterized. One appears to follow a crystallographic direction while the other appears as a dense, intricate, generally curvilinear network with short ramifications. Additional experiments in which both the ion energy and dose rate have been varied indicate that ridge evolution progresses with increased energy and fluence, but is independent of dose rate. It is suggested that the ridge networks may form as a result of C transport by diffusion from the heavily damaged near-surface region or of a tectonic-plate-like motion or both. The geometric features of the ridge networks are related to the subsurface radiation damage as well.

Silicon is an attractive material for the construction of read/write head sliders in magnetic recording applications from the viewpoints of ease of miniaturization and low fabrication cost. In the present investigation we have studied the friction and wear behavior of single-crystal, polycrystalline, ion-implanted, thermally oxidized (wet and dry), and plasma-enhanced chemical vapor deposition (PECVD) oxide-coated silicon pins while sliding against lubricated and unlubricated thin-film disks. For comparison, tests have also been conducted with Al2O3–TiC and Mn–Zn ferrite pins which are currently used as slider materials. With single-crystal silicon the rise in the coefficient of friction with sliding cycles is faster compared to Al2O3–TiC and Mn–Zn ferrite pins. In each case, the rise in friction is associated with the burnishing of the disk surface and transfer of amorphous carbon and lubricant (in the case of lubricated disks) from the disk to the pin. Thermally oxidized (under dry oxygen conditions) single-crystal silicon and PECVD oxide-coated single-crystal silicon exhibit excellent tribological characteristics while sliding against lubricated disks, and we believe this is attributable to the chemical passivity of the oxide coating. In dry nitrogen, the coefficient of friction for single-crystal silicon sliding against lubricated disks behaves differently than in air, decreasing from an initial value of 0.2 to less than 0.05 within 5000 cycles of sliding. We believe that silicon/thin-film disk interface friction and wear is governed by the uniformity and tenacity of the amorphous carbon transfer film and oxygen-enhanced fracture of silicon.

A mathematical model was developed to elucidate the interaction between transport/reaction processes and the evolution of porosity in chemical vapor infiltration with microwave heating (MCVI). The analysis included a set of partial differential equations describing the spatiotemporal variation of gaseous species concentration, composite temperature, porosity, and stress. Maxwell's equations were used to determine the distribution of power dissipated inside the composite. The deposition of silicon carbide was selected as a model chemical system to explore the general features of MCVI. MCVI can provide a favorable temperature distribution in the composite yielding an inside-out deposition pattern, thereby preventing entrapment of accessible porosity. For this temperature profile, tensile stresses develop at the outer regions and compressive stresses are found in the composite core. For a given system there exists a minimum value of the coefficient for heat transfer from the composite surface, h, below which accessible porosity is trapped within the composite. Similarly, there exists a maximum value of the incident microwave energy flux, I0, above which accessible porosity is trapped within the composite. I0 and h can be optimized for a given preform to achieve complete densification with minimum processing time. Using the technique of pulsed-power, the processing time can be reduced even further without compromising density uniformity. Power dissipation profiles in the composite depend strongly on preform thickness, microwave frequency, and relative loss factor.