Morphological instabilities attending the high growth rate of diamond films are examined. Pertinent literature on morphological instabilities and microstructure evolution in vapor deposited films is reviewed and theoretical treatments related to the case of diamond growth are discussed. Diamond films of various thicknesses have been synthesized utilizing the combustion flame synthesis technique involving diamond growth rates of ∼1 μm/min. Films of thicknesses under 20 μm are found to be dense and the surface smoothness of such films is governed by facets on the individual crystallites that make up the film. Increasing film thicknesses, at high growth rates, results in extremely rough surfaces, the trapping of voids and discontinuities, and the incorporation of non-diamond phases in the growing film. These characteristics are typical of morphological instabilities when surface diffusion and re-evaporation processes are absent and instability is promoted by the high rate arrival of the appropriate species from the flame ambient to the surface. Factors contributing to morphological instabilities include competitive shadowing and nutrient starvation and growth anisotropy of the different crystallographic faces on individual diamond crystals. It is shown that surface temperature and the presence of oxidizing species in the flame ambient contribute to anisotropic growth of diamond crystals and hence to morphological instabilities in diamond films. An approach to avoiding these instabilities is briefly discussed.

Spectrally resolved cathodoluminescence (CL) images and spatially resolved CL spectra were obtained from two specimens grown by hot-filament chemical vapor deposition. Each specimen consisted of a large number of unconnected diamond particles with cubo-octahedral and pseudo-fivefold twinned growth habits. The growth temperature was nominally 600 °C for one specimen and 750 °C for the other. In the 1.5–3.5 eV range, the spectra are composed of four defect and impurity related bands: there are three bands with zero-phonon lines at 1.68 eV, 2.156 eV, and 2.325 eV, and one broad band centered at 2.85 eV. A weak peak at 5.27 eV, due to exciton recombination, was also observed. Spectrally resolved images of the two most intense CL bands, at 2.156 eV and 2.85 eV, were obtained for several particles. In the low-temperature specimen, bright regions in images of the 2.156 eV band are correlated with {111} facets; bright regions in images of the 2.85 eV band are correlated in some cases with the central regions of {100} facets and in other cases with {111} facets. In the intermediate-temperature specimen, bright regions in the images of both bands are correlated with {100} facets. A model of competing recombination at different types of CL centers and nonradiative centers is proposed to facilitate the interpretation of the experimental results. For the low-temperature specimen, the model suggests that the 2.156 eV CL centers are located primarily in {111} growth sectors and the 2.85 eV CL centers are distributed relatively uniformly; images of the two dominant CL bands are predicted to have a complementary relationship in particles where there are few competing nonradiative centers. For the intermediate-temperature specimens, the model suggests that nonradiative recombination is dominant, and that the CL image contrast arises primarily from a nonuniform distribution of nonradiative centers.

Diamond-like (amorphous) carbon (DLC) films were prepared by dc magnetron sputtering and plasma enhanced chemical vapor deposition (PECVD) and diamond films were prepared by microwave plasma enhanced chemical vapor deposition (MPECVD). For the first time, chemical and mechanical characterization of the films from each category are carried out systematically and a comparison of the chemical and physical properties is provided. We find that DLC coatings produced by PECVD are superior in microhardness and modulus of elasticity to those produced by sputtering. PECVD films contain a larger fraction of sp3-bonding than the sputtered hydrogenated carbon films. Chemical and physical properties of the diamond films appear to be close to those of bulk diamond.

The optical absorption and photoluminescence of Eu2+ : Sm3+-doped CaS films have been investigated in this paper. The energy dependence of the refractive index and absorption coefficient of the film were obtained by analyzing transmission and reflection spectra of the thin film. The refractive index at low energies is very close to the bulk value for CaS (n = 2.03) and decreases with increasing energy in the range of 1.2 to 2.5 eV. The energy gap of CaS: Eu2+ : Sm3+ thin films is found to be a direct gap with value Eg = 4.48 eV. Photoluminescence studies on annealed CaS: Eu2+ : Sm3+ thin films showed a broad band at ∼1.92 eV identified with emission from Eu2+ ions, and a set of sharp lines corresponding to emission from Sm3+ ions. Most of the strong features presented in the room temperature spectra are found in good agreement with previous bulk studies of CaS: Eu2+ and CaS: Sm3+. The abnormal increase of the Sm3+ photoluminescence with increasing temperature is explained by the phonon-assisted energy transfer from Eu2+ ions to Sm3+ ions.

The evolution of the reaction between the binary graphitide KC8 and CoCl2 dissolved in anhydrous tetrahydrofuran (THF) has been investigated by in situ x-ray diffraction (XRD). During the reaction and whatever the host graphite (powder or HOPG), the first stage graphite intercalation compounds K(THF)2.5C24 and K(THF)1.7C24 are first formed and then transformed into higher stages. Finally the matrix is exfoliated and the phases identified are graphite, metallic cobalt, and KCl. Analyses by Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray (EDX) clearly show that the products are mainly located at the edge planes of the graphite, indicating that the electronic exchange occurs at the edge of the graphene layers. It is now clear that graphite-cobalt intercalation compounds cannot be obtained by this method.

Well-crystallized polycrystalline films of cubic BaTiO3 have been synthesized on Ti metal substrates by electrochemical, hydrothermal, and electrochemical-hydrothermal reaction of a Ti metal with a saturated solution of Ba(OH)2 in the temperature range 80 °C−200 °C. The films can be produced in the electrochemical process by the anodization of a Ti substrate in Ba(OH)2 solution at pH = 13 and current densities of the order of 10–50 mA/cm2. The films can also be synthesized by the hydrothermal reaction of Ba(OH)2 and a Ti substrate without electrical bias. A combination of these two techniques reduces the reaction time to 30–45 min. The films were found to have good adherence on the substrate and films of thickness up to 2 μm could be formed within a reaction time of 45 min. Capacitance measurements have yielded a dielectric constant of 300. The films prepared by the three different techniques have been compared for crystallinity and microstructure. The thickness of the films increased with temperature and time of reaction. The crystallinity decreased with extended time of reaction for a given temperature. It is likely that a reactive intermediate such as Ti(OH)4 (aq.) is formed in all the three cases which leads to the formation of crystalline BaTiO3.

Ultrafine (≍0.4 μm) strontium titanate powder was synthesized using strontium nitrate and potassium titanyl oxalate as precursors. An aqueous (0.1 M) potassium titanyl oxalate solution was added dropwise to a (0.1 M) strontium nitrate solution with continuous stirring at room temperature to precipitate strontium titanyl oxalate (STO). The precipitate, after careful washing with distilled water several times, was air-dried and calcined at 550 °C/6 h to obtain homogeneous, spherical, stoichiometric powder of SrTiO3 ≍0.4 μm in size. The calcined powder was characterized using different techniques such as XRD, DTA/TG/DTG, SEM, and IR.

On heating a gel of composition 33.5SnO2−66.5SiO2 (wt. %) up to 1050 °C, SnO2 crystallization occurred with different mechanisms according to thermal treatments. Thermal analysis, SAXS (Small Angle X-Ray Scattering), WAXS (Wide Angle X-Ray Scattering), and TEM (Transmission Electron Microscopy) results obtained for samples treated at different temperatures demonstrated that the SnO2 load is divided into two moieties, one composed of isolated SnO2 particles suitable for primary crystallization yielding crystallites with 4.0 nm of average size; the other, being dissolved in SiO2, remains in the amorphous SiO2/SnO2 solid solution up to the highest temperature. The presence of these two phases accounts for SnO2 surface segregation at the expense of the SnO2 concentration of neighboring outer layers and the independence of apparent density on temperature.

Boehmite compacts and boehmite gels (seeded and unseeded) were annealed at various temperatures in nitrogen and 1 atm water vapor to determine the influence of water vapor on boehmite transformation to new phases, changes in porosity, and morphology. Water vapor was found to accelerate the phase transformations markedly compared to dry N2 treatment. The catalyzing effect of water vapor may be due to its interactions on grain surfaces and generation of fast diffusion paths, resulting in nucleation and growth of new phases. This result shows that control of the furnace atmosphere is a useful variable in thermally activated processes.

The ultra-low load indentation response of ceramic single crystal surfaces (Al2O3, SiC, Si) has been studied with a software-controlled hardness tester (Nanoindenter) operating in the load range 2–60 mN. In all cases, scanning and transmission electron microscopy have been used to characterize the deformation structures associated with these very small-scale hardness impressions. Emphasis has been placed on correlating the deformation behavior observed for particular indentations with irregularities in recorded load-displacement curves. For carefully annealed sapphire, a threshold load (for a given indenter) was observed below which the only surface response was elastic flexure and beyond which dislocation loop nucleation occurred at, or near, the theoretical shear strength to create the indentation. This onset of plasticity was seen as a sudden displacement discontinuity in the load-displacement response. At higher loads, indentations appeared to be accommodated predominantly by dislocation activity, though microcracks were observed to form ät contact loads of only tens of milliNewtons. Possibly such cracks are the incipient slip-induced nuclei for the much larger, indentation-induced cracks usually apparent only on the surface at much higher loads and often used for estimating indentation toughness. By contrast, silicon did not show this behavior but exhibited unusually large amounts of depth recovery within indentations, resulting in a characteristic reverse thrust on the indenter during unloading. TEM studies of indentations in silicon revealed less evidence of obvious dislocation activity than in sapphire (particularly at the lowest loads used) but did show residual highly imperfect–and often amorphous–structures within the indentations, consistent with a densification transformation occurring at the very high hydrostatic stresses produced under the indenter. The reverse thrust is caused by the relaxation of densified material during unloading. Thus, it appears that the low-load hardness response of silicon is controlled by a pressure-sensitive phase transformation. Though SiC has been predicted to undergo a densification transformation similar to silicon, its load-displacement behavior was found to be similar to Al2O3 suggesting that, for these contact experiments at least, the critical resolved shear stress for dislocation nucleation is exceeded before the critical hydrostatic pressure for densification is reached. In all cases, residual, plastically formed indentations were measured to be smaller than the fully loaded indentation depths would suggest, confirming that a significant portion of the deformation is elastic surface flexure. However, there is some doubt as to whether silicon displays elastic-only deformation even at very small penetration depths. The use of microstructural studies to complement nanoindentation experiments is shown to be a key route not only to interpreting the recorded load-displacement responses, but also to examining the deformation mechanisms controlling the mechanical behavior of ceramics to surface contacts at these small spatial scales.

Four types of structurally different, flat interfaces have been observed in ZnO-based varistor ceramics containing metal-oxides additives (Bi, Mn, and Ti) by bright-field and high-resolution imaging in a transmission electron microscope. Orientation relationships have been characterized by selected-area diffraction. The faceting of ZnO grains when in contact with β–Bi2O3 is discussed in relation to the anisotropic growth of the ZnO grains which leads to pronounced faceting parallel to (0001) planes.

Layered perovskites (Ruddlesden–Popper phases), (CaxSr1−x)n+1 TinO3n+1 with n = 3, ∞ and x ranging from 0 to 1, have been investigated by XPS and XAES. The structural transitions, identified in other studies, have been correlated with changes in the chemical environments of the constituent species. In particular, the tetragonal to orthorhombic transition at x = 0.65 ± 0.1 appears to generate nonequivalent cation environments for the alkaline earth species in (Ca, Sr)O12 coordination. Other binding and kinetic energy shifts can be correlated with changes in and distortions of unit cell volumes.

Porous hydroxyapatite ceramics with porosity up to 73% have been fabricated by microwave processing at 1150 to 1200 °C for 1 to 5 min. Various porosities in these ceramics have been obtained by using starting materials with different morphology, adjusting green density, changing sintering time and temperature, as well as optionally mixing ammonium carbonate in the hydroxyapatite powder during the consolidation process. Porosity, microstructure, and diametral tensile strength of the porous hydroxyapatite ceramics have been studied.

Models for nonthermal effects on ionic motion during microwave heating of crystalline solids are considered to explain the anomolous reductions of activation energy for diffusion and the overall faster kinetics noted in microwave sintering experiments and other microwave processing studies. We propose that radiation energy couples into low (microwave) frequency elastic lattice oscillations, generating a nonthermal phonon distribution that enhances ion mobility and thus diffusion rates. Viewed in this manner, it is argued that the effect of the microwaves would not be to reduce the activation energy, but rather to make the use of a Boltzmann thermal model inappropriate for the inference of activation energy from sintering-rate or tracer-diffusion data. A highly simplified linear oscillator lattice model is used to qualitatively explore coupling from microwave photons to lattice oscillations. The linear mechanism possibilities include resonant coupling to weak-bond surface and point defect modes, and nonresonant coupling to zero-frequency displacement modes. Nonlinear mechanisms such as inverse Brillouin scattering are suggested for resonant coupling of electromagnetic and elastic traveling waves in crystalline solids. The models suggest that nonthermal effects should be more pronounced in polycrystalline (rather than single crystal) forms, and at elevated bulk temperatures.

The formation of a polyester between citric acid (CA) and ethylene glycol (EG) was found to be a decisive factor for the foaming of resin intermediates in a Pechini-type powder process. This process was modified by changing the organic mass ratio of CA/EG which results in ceramic powders with different morphologies. The most porous resin intermediate (with or without chelated cations) was prepared using a polymeric gel made of equimolar citric acid and ethylene glycol. It was also found that a premixing of organic components, prior to adding constituent nitrate solutions, makes the whole process more controllable.

Nonagglomerated ceramic precursor for Sr-doped lanthanum chromite powder was prepared by a modified resin–intermediate process using equimolar citric acid, ethylene glycol, and metallic nitrates. Pure and well-crystallized submicron powders with a narrow particle-size distribution were calcined from an optimally pulverized resin at a temperature of 750 °C for 2 h in flowing air. The material cost for organics used in the investigated process was considerably lower than the original Pechini process.

The mass spectral fragment ion yields and total electron yields have been measured for the polymers poly(butene-1 sulfone) [PBS] and poly(1,4-phenylene ether sulfone) [PPES] around the sulfur 2p (LII) edge, using synchrotron radiation from the Canadian Synchrotron Radiation Facility [CSRF]. Ionization of the sulfur 2p orbitals of PBS produced a sharp decrease in the neutral yields of SO2 and 1-butene. Decreases in the SO2 and 1-butene neutral yield shapes “mirrored” the structure present in the total electron yield. Ionization of the sulfur 2p orbital does not appear to produce any enhanced cleavage of the C–S bonds in the polymer backbone. A G(olefin)/G(SO2) ratio of 0.96 ± 0.15 was determined at 21 °C from mass spectrometry, consistent with a depropagation reaction mechanism. PPES showed a much different behavior than PBS about the sulfur 2p edge, with no detectable yield of SO2.