Amorphous hydrogenated silicon carbide (a–SiC: H) thin films (t < 1 μm) were grown from two different precursor gases, a methane/silane mixture and silacyclobutane (SiC3H8). Plasma enhanced chemical vapor deposition was used to deposit a–SiC: H thin films on silicon substrates at temperatures of 175 °C and 600 °C. These a–SiC: H films were characterized using the mechanical properties microprobe (nanoindenter) and by scratch testing. Data and mechanical properties information collected from these measurements have been correlated with film process conditions and materials characteristics. A simplified approach was used to calculate the average nanoindentation hardness from shallow indentations. Using this technique, results for a silicon wafer are in good agreement with that previously reported. Analysis of the substrate influence on the thin film nanoindentation data implies that the measured hardness is relatively unaffected by the substrate, while the measured elastic properties are somewhat influenced by the substrate. The a–SiC: H film hardness is shown to depend on the precursor gas and molecular bonding, while the elastic properties vary with precursor gas, composition, and density, as influenced by the plasma source deposition power. The MPM data and scratch test data show similar correlations to plasma source power, film structure, and film composition.

Despite the extremely low density and the hence low weight of aerogel materials, the applicability of these materials to reflective applications has had little attention due to the high porosities exhibited by the materials. This high porosity yields an intrinsically rough but uniform surface topology for aerogel of density in the low hundreds of milligrams per cubic centimeter and a fractal surface geometry for lower density aerogel (densities of the order of tens of milligrams per cubic centimeter). This paper presents new results of aerogel materials used as ultra-light substrates for reflective coatings by way of surface machining, polishing, and planarization prior to metallization, and the optical characterization thereof.

SnO2 hollow spherical particles have been prepared by pyrolysis of an aerosol produced by ultrahigh frequency of a SnCl2 precursor solution. The spheres obtained were found to be amorphous when the pyrolysis temperature is <500 °C, but they crystallize to cassiterite at temperatures higher than 600 °C. The spherical shape is kept when as-received samples are annealed at temperatures ranging between 500 and 1100°CC, but they are polycrystalline, the crystallite size being controlled as a function of the annealing temperature.

In this investigation buried Sb dopant profiles in single crystal silicon have been formed from evaporated layers using laser annealing. For irradiations carried out in air, severe oxidation of the surface layers inhibited epitaxy. Oxygen concentrations as high as 5 × 1017 atoms/cm2 (equivalent to about 105 nm SiO2) were measured. It was found that both the thin (less than 3 nm) Sb layer and the free volume in the a-Si, deposited by evaporation onto a cold substrate, need to be present for this degree of oxidation to take place. However, when silicon was evaporated onto a substrate heated to 350 °C, dense packing of the silicon atoms was obtained and even for irradiations in air good epitaxy (minimum yield of 7%) and no oxidation occurred. To form buried Sb profiles, laser energies only slightly higher than the threshold for epitaxy were used to prevent excessive spreading due to an increase in liquid state diffusion obtained at higher energies. Under these conditions the width of the buried Sb profile was typically about 120 nm, and up to 90% of the Sb atoms were found to occupy lattice sites.

Negative ion bombardment of an evolving thin film can cause changes in the film's surface due to resputtering of the already deposited material. Through the study of rf-sputtered perovskite (BaTiO3) thin films, we have found that surface micro-effects, i.e., changes in the surface morphology of the films at the μm-scale level, are dependent on the deposition conditions. Ripples, cones, ridges, and etch pits of various shapes and sizes were all observed on growing films. A transformation of the morphology of the top surface of the film as a function of both deposition time and location on the substrate has been observed. The type of surface morphology found at any point was found to be dependent on a number of factors, including deposition rates, flux and energy of bombarding ions, and the average angle of incidence of the bombarding ions. We have developed a qualitative model for the formation of these surface features, based on the resputtering yield as a function of the average angle of incidence of the bombarding ions. The model suggests that surface nonuniformities, often ripples, initiate the development of etch pits. Other mechanisms of the surface morphology development (such as clustering) are used to explain the formation of surface features other than etch pits.

Beta–SiC specimens possessing 15% stacking fault density were annealed at various temperatures for various time periods under an Ar or a N2 atmosphere, and the mechanisms of stacking fault annihilation and grain growth were investigated. The values of the geometric factor in the Avrami–Erofeev equation indicated that the rate of stacking fault annihilation is controlled by the atomic diffusion process. On the other hand, the rate of grain growth was found to be limited by surface diffusivity. Coincidence in the values of activation energy for stacking fault annihilation and grain growth within experimental errors firmly suggested that the annihilation of stacking faults is an apparent phenomenon resulting from the microstructural development in which the grain growth is controlled by surface diffusivity. Incorporation of nitrogen during heating suppressed the surface diffusivity and, hence, the rate of stacking fault annihilation.

The time-differential perturbed angular correlation technique has been used to investigate the thermal behavior of a ZrO2−13.6 mole % MgO ceramic between room temperature and 1423 K. Two different quadrupole hyperfine interactions corresponding to a tetragonal structure have been found to result on cooling the ceramic from the single-phase cubic field. One of them agrees with that depicting the pure t-ZrO2 tetragonal phase and the other one has been interpreted as describing a high-MgO-content nontransformable t'–ZrO2 phase. As temperature increases, the latter gives rise to a similar but fluctuating interaction related to the oxygen vacancies mobility and which shows a thermal behavior analogous to that already reported for the stabilized cubic ZrO2. Above 1100 K these dynamic t'-sites transform into pure tetragonal ones which behave ordinarily, suffering the t → m phase transition when cooling to room temperature. Differences found between TDPAC results and information drawn from other techniques are discussed.

Thin films of GaN have been deposited at relatively low growth temperatures by remote plasma-enhanced chemical-vapor deposition (RPECVD), using a plasma excited NH3, and trimethylgallium (TMG), injected downstream from the plasma. The activation energy for GaN growth has been tentatively assigned to the dissociation of NH groups as the primary N-atom precursors in the surface reaction with adsorbed TMG, or TMG fragments. At high He flow rates, an abrupt increase in the growth rate is observed and corresponds to a change in the reaction mechanism attributed to the formation of atomic N. X-ray diffraction reveals an increased tendency to ordered growth in the 〈0001〉 direction with increasing growth temperature, He flow rate, and rf plasma power. Infrared spectra show the fundamental lattice mode of GaN at 530 cm−1 without evidence for vibrational modes of hydrocarbon groups.

We report the growth conditions necessary for highly oriented wurtzite GaN films on (111) GaAs, and single crystal GaN films on (111) GaAs using AlN buffer layers. The GaN films and AlN buffers are grown using rf reactive magnetron sputter deposition. Oriented basal plane wurtzite GaN is obtained on (111) GaAs at temperatures between 550 and 620 °C. However, using a high temperature 200 Å AlN buffer layer epitaxial GaN is produced. Crystal structure and quality are measured using x-ray diffraction (XRD), reflection electron diffraction (RED), and a scanning electron microscope (SEM). This is the first report of single crystal wurtzite GaN on (111) GaAs using AlN buffer layers by any growth technique. Simple AlN/GaN heterostructures grown by rf reactive sputter deposition on (111) GaAs are also demonstrated.

PbTiO3 thin films deposited on (001)MgO by the MOCVD technique have been characterized by x-ray diffraction and transmission electron microscopy (TEM). The PbTiO3 films grown at temperatures below Tc (~500 °C) are c-axis oriented polycrystals, while the PbTiO3 films grown at temperatures above Tc are single crystals with a bi-layer structure at room temperature. The top layers of the films near the free surface are c-axis oriented with the orientation relationship of (001)[100]PbTiO3||(001)[100]MgO. The bottom layers of the films near the substrate are a-axis oriented with the orientation relationship of The formation of the bi-layer microstructure of the PbTiO3 films will be discussed in terms of the effect of the cooling rate and the substrate on the phase transition of PbTiO3 from the cubic to the tetragonal phase. When the PbTiO3 films were grown with a large excess of the Pb precursor vapor in the vapor mixture, PbO and PbTiO3 coexisted in the films. Both PbO and PbTiO3 were grown epitaxially on (00l)MgO. The epitaxial orientation relationships were found to be (100) [001]PbO||(001) [100]MgO and (001)[100]PbTiO3||(001)[100]MgO. The 90° domains were observed in the PbTiO3 films deposited at temperatures above Tc. The domain walls are the ﹛101﹜ and ﹛011﹜ twin boundaries, which were formed during the phase transition from the cubic to the tetragonal phase.

Polycrystalline silicon carbide was deposited from methyltrichlorosilane in cold-walled and hot-walled reactors, on (100) SiC surface layers that were formed on (100) Si wafers. The initial stages of the process were studied by electron microscopy after relatively short deposition times. Submicron surface features nucleated with a specific crystallographic orientation with respect to the substrate, where h111j planes in th—SiC substrate coincided with h0001j planes in the a–SiC features. These a–SiC features occurred only at twins on h111j planes of the b–SiC substrate. This demonstrates that nucleation under these conditions is controlled by defects in the substrate. Surface contamination and the reactor configuration also had substantial effects on nucleation.

The solubility of Fe in CdSe crystal has been studied in detail in the past. Using powder diffraction and atomic absorption spectroscopy, it was concluded that the upper limit for the solubility of iron in CdSe is 12–15%, and the actual Fe concentration in a solid solution agrees with the nominal Fe concentration (calculated from the concentration of the reactants). In the present study this question is re-examined using techniques that probe the average properties of the solid solution, such as x-ray diffraction, and techniques that probe the local structure and composition of the solid solution on the micron scale, such as energy and wavelength x-ray dispersive microprobe analysis. It is shown that the solubility of Fe in the CdSe matrix is appreciably smaller than the nominal value, and that microsegregation is obtained at a much lower Fe concentration than previously concluded. The immiscibility of Fe in this matrix is consistent with the large deviation of the lattice constants from Vegard's law. It is attributed to the large strain exerted on the lattice upon substitution of Cd by the much smaller Fe ion.

Crystalline zinc ferrite particles of the general formulation ZnxFe3−xO4 (O ≤ x ≤ 1) were prepared by aging at elevated temperature solutions containing Zn(NO3)2, Fe(NO3)3, and triethanolamine in the presence and in the absence of hydrazine. The powders were characterized by x-ray diffraction and infrared analyses.

We have carried out Electron Spin Resonance (ESR) measurements on activated carbon fibers (ACF) with specific surface areas (SSA) of 3000 and 2000 m2/g. The ESR spectrum of ACF fibers in air is extremely broad (500 to 1000 Gauss), and the spin susceptibility decreases rapidly with decreasing specific surface area. Also measured was the ESR signal of the desorbed fibers in vacuum. As a result of desorption, the broad peak decreases slightly in intensity, and a narrow (≍65 Gauss at room temperature) peak appears. We report results on the temperature dependence of both peaks. The narrow peak is interpreted as due to spins associated with dangling bonds, whereas we attribute the broad peak to the conduction carrier spins which is broadened by the boundary scattering process (T1 contribution) and the dipolar broadening process (T2 contribution) associated with the dangling bond spins.

The oxidation of two α–Si3N4 powders has been studied using x-ray photoelectron spectroscopy (XPS) and Bremsstrahlung-excited Auger electron spectroscopy (AES). These two powders had comparable specific surface areas but were produced by different methods. The powders were oxidized by heating in air at temperatures between 850° and 1000 °C. The oxide thickness for each heating time and temperature was determined both from the relative O 1s and N 1s peak intensities and from the relative SiO2 and Si3N4 Si KLL peak intensities. In each case, the oxide thickness calculated from the XPS data was systematically higher than those determined from the AES data. This difference may be due to uncertainties in the data analysis procedures. The oxidation of each powder followed a linear rate law for these temperatures. On one of the powders, the XPS data showed evidence of oxynitride formation. Analysis with thermal decomposition mass spectroscopy also showed that much more hydrogen was evolved from this particular powder, particularly at temperatures >700 °C. These differences in bulk impurity levels are believed to be responsible for the differences in the activation energies for oxidation which were measured to be 104 ± 22 kJ/mol and 62 ± 4 kJ/mol for these two powders.

When an appropriate mixture of a low-softening borosilicate glass (BSG) and a high-softening high silica glass (HSG) is sintered at temperatures ranging from 800 to 1000 °C, a crystalline phase, identified as cristobalite by XRD, is known to precipitate out of the initial amorphous binary mixture of glasses as the sintering continues. The precipitation of cristobalite is found to originate in HSG, and is controlled by the transport of alkali ions (e.g., K+, Na+, and Li+) from BSG to HSG.1 In this paper, we report that when a small amount of alumina is present as a dopant in the above binary mixture of BSG and HSG, the cristobalite formation is completely prevented at the sintering temperatures investigated. The above result is attributed to a strong affinity between Al+3 from alumina and alkali ions from BSG, which diverts the diffusion of alkali ions from HSG to alumina, thus forming a K+ and Al+3-rich reaction layer adjacent to the alumina particles far too rapidly compared to that of cristobalite formation.

The high-temperature oxidation of TiN, Ti0.9Al0.1N, and Ti0.6Al0.4N films which were deposited onto stainless steel substrates using an arc ion-plating apparatus was studied at temperatures ranging from 923 to 1173 K for 0.6 to 60 ks in air. The oxidation rate obtained from mass gain as a function of time was found to fit well to a parabolic time dependence. From their temperature dependence, the apparent activation energies of oxidation were determined. With increasing Al contents, the oxidation rate decreased, and the activation energies of oxidation reaction increased. Formed oxide layers were analyzed by XRD, SEM, and EPMA. With increased Al content in TiAlN films, the rate-determining step changes from oxygen ion diffusion in formed rutile to oxygen or aluminum ion diffusion in the formed Al2O3 layer.

Polycrystalline tungsten nitride thin films were grown by low pressure metallo-organic chemical vapor deposition (MOCVD) using (tBuN)2W(NHtBu)2 as the single-source precursor. Deposition of uniform thin films on glass and silicon substrates was carried out at temperatures 723–923 K in a cold-wall reactor, while the precursor was vaporized at 333–363 K. The growth rates were 2–10 nm/min depending on the condition employed. Bulk elemental composition of the thin films, studied by wavelength dispersive spectroscopy (WDS), is best described as WNx (x = 0.7–1.8). The N/W ratio decreased with increasing temperature of deposition. X-ray diffraction (XRD) studies showed that the films have cubic structures with the lattice parameter a = 0.414–0.418 nm. The lattice parameter decreased with decreasing N/W ratio. Stoichiometric WN thin films showed an average lattice parameter a of 0.4154 nm. X-ray photoelectron spectroscopy (XPS) showed that binding energies of the W4f7/2, W4f5/2, and N1s electrons were 33.0, 35.0, and 397.3 eV, respectively. Elemental distribution within the films, studied by secondary ion mass spectroscopy (SIMS) and Auger spectroscopy depth profilings, was uniform. The SIMS depth profiling also indicated that C and O concentrations were low in the film. Volatile products trapped at 77 K were analyzed by gas chromatography–mass spectroscopy (GC–MS) and nuclear magnetic resonance (NMR). Isobutylene, acetonitrile, hydrogen cyanide, and ammonia were detected in the condensable mixtures. Possible reaction pathways were proposed to speculate the origin of these molecules.

We have studied the influence of ion bombardment on the surfaces of MgO and Al2O3 single crystals. The two oxides were sputtered with low energy Ar+ ions, and x-ray photoelectron spectroscopy was used to analyze surface compositions and chemical interactions with metallic adsorbates. Expected changes in surface compositions have been calculated mathematically using first principle formulation from existing literature. The resulting effects on XPS spectra have been predicted based on concentration profile models and agree with experimental observations. Changes in surface oxygen activity were studied by evaporating Ni on these surfaces at an extremely slow rate and analyzing what fraction of the first monolayer was oxidized on adsorption. This fraction, used as a measure of surface oxygen activity, was substantially reduced in Al2O3 on sputtering, but remained practically unchanged for MgO. The amount of these changes matches reasonably well with calculated changes in surface oxygen fraction. Based on these results, the relation between ion bombardment and interfacial bonding has been discussed.

Stoichiometric β–SiC thin films with a high preferred orientation of (111) planes were successfully deposited on Si(100) substrates at a relatively low temperature of 1050 °C from the mixture of methyltrichlorosilane (CH3SiCl3 or MTS) and H2 in a hot wall LPCVD reactor. No etching of the Si substrate and smooth topography of the deposit were observed at high H2/MTS ratios and/or low deposition pressures. The presences of excess silicon, excess carbon, or incorporated hydrogen atoms in the films were not detected. Poor topography, degradation in preferred orientation, and etching of the Si substrate were observed at high values of deposition pressure, MTS concentration, and temperature. The etching on the Si substrate was due to the out-diffusion of Si atoms from the substrate and the presence of Cl-containing radicals resulting from the decomposition of MTS molecules while transporting to the Si substrates. A deposition mechanism was proposed to model the deposition of SiC in a hot wall reactor by using (1) gas phase decomposition of MTS molecules, (2) adsorption of the intermediates on the surface, and (3) reaction of the adsorbed intermediates to form SiC. The deposition rates were predicted very well for various deposition conditions in a hot wall LPCVD reactor.