Silicon carbide (SiC) microtubes were synthesized and characterized via a vapor–solid (VS) reaction of carbon fiber (Csolid) and SiO(gas). The synthesis mechanisms were investigated. The precursor led complete conversion of [SiO(gas) + C(solid)] into [SiC(solid) + CO(gas)] through overall reaction under inert gas flow at and above 1350 °C. Carbon fibers with small surface area (0.7–2.0 m2 g−1) were gradually converted to SiC microtubes with large specific surface area (45–63 m2 g−1). Inner surface of SiC microtubes indicated a villus-like morphology, which consisted of submicron-sized SiC villi. The outer surface of the SiC microtubes was smooth. Inner surface morphology of SiC microtubes was dependent upon synthesizing temperature. Thickness of villus-like layer in SiC microtubes increased with increasing synthesizing temperature, showing 0.25 and 0.5 at 1350 and 1400 °C, respectively. Both VS and gas–liquid–solid (VLS) growth mechanisms were investigated in synthesis of SiC fiber as a reaction byproduct, and the reaction was governed by both growth mechanisms.

Liquidus temperatures (TL) were measured, and primary phases were determined for 50 (from an initial test matrix of 76) compositions within the Al2O3–B2O3–CaO–Na2O–SiO2 glass-forming system and its constituent ternary subsystems. Strong linear correlations have been found between composition and TL for melts within the same primary phase fields. The TL and primary phase data are being used to develop and refine a modified associate species model (ASM). The impacts of Fe2O3, Li2O, NiO, ZrO2, Cr2O3, ZnO, and MnO additions on the TL of two baseline glass compositions are reported. These data are intended as benchmarks for further expansion of the ASM or other silicate melt solution models of nuclear waste glasses.

Copper-tungsten films were deposited on Si and Al2O3 substrates by magnetron sputtering and then in situ annealed in vacuum chamber at different temperatures. X-ray diffraction (XRD), scanning electron microscopy (SEM), and the polarization phase shift technique were used to characterize the microstructure, surface morphology, and residual stress of Cu–W films. The results indicated that there are two successive but distinctive stages of phase transition with the change of annealing temperatures. The evolution of surface morphology of Cu–W thin films shows a significant effect on the distribution of in-plane stresses. A strategy of integrating discrete wavelet transform and fractal geometry concepts was developed to analyze the anisotropy of surface structure of Cu–W thin films. The correlation between the anisotropy of surface morphology and the stress distribution of thin films was constructed. It is found that the stress distribution of the thin films is sensitive to the variations of the anisotropy of the surface structure with annealing temperature. The variation in the uniformity of in-plane stress distribution with the evolution of surface structure of thin films is independent of the choice of substrate materials.

A thin-frame nano-network film of titania with backbone diameter of 20–30 nm was obtained from precursor templating of nano-porous polymer with nano-channels 50 nm in width. The nano-porous polymer templates were prepared by selective removal of the polyisoprene (PI) domain with ozone from the bicontinuous structure formed through blending a symmetric polystyrene-block-polyisoprene (PS-b-PI) copolymer with a PS homopolymer (h-PS). The titania network possessed the preferred anatase crystallinity for photocatalytic applications and a specific surface area of 53 m2/g, comparable to that of Degussa P25, a widely used commercial photocatalyst. Photocatalytic performance of the fractured titania network film was also comparable to that of Degussa P25 in both gas-phase NO oxidation and liquid phase methylene blue degradation. The much larger overall structure size of the fractured titania network film, however, offers advantages over the nano-particulate form of P25, namely, easy handling and rapid recycling from treated streams.

Nanopatterned sapphire substrates offer the potential for improved performance of devices based on III-V nitrides, e.g., light-emitting diodes and laser diodes. Due to the chemical stability and hardness of sapphire, however, surface patterning is a time-consuming and expensive process. Therefore, a novel method was utilized, whereby a surface coating of Al was deposited on a sapphire substrate and patterned into an array of square mesas using e-beam lithography. The lateral dimensions of each mesa were approximately 400 × 400 nm, and the average height was approximately 100 nm. The metallic film was subsequently subjected to an oxidation treatment at 450 °C for 24 h (a heat treatment which had previously been shown to minimize hillock formation). For the second heat treatment, which is necessary to induce migration of the sapphire interface and hence achieve solid state conversion, a range of temperatures (800–1350 °C) was explored. Results showed that for a heat-treatment time of 1 h, pattern retention was achieved for annealing temperatures less than or equal to 1250 °C. Successful epitaxial conversion of the patterned mesas to sapphire was confirmed using electron backscatter diffraction.

Wetting of α–Al2O3 single crystals with different crystallographic orientations, R(0112), A(1120), and C(0001), by molten Cu at 1423–1673 K was studied using an improved sessile drop method mainly in a reducing Ar–3%H2 atmosphere to determine the effect of the alumina surface orientation on the wettability and adhesion in this system. The contact angles were generally in the range of 110–117°, and the work of adhesion was between 0.7 and 0.8 J m−2, without a significant dependence on the alumina surface orientation. This result was explained by the possibly close bond strengths of Cu–O at the oxygen-terminated Cu/[R(0112)] and Cu/[A(1120)] α-alumina interfaces and Cu–Al at the Al-terminated (or Al-rich) Cu/[C(0001)] α-alumina interface under high-temperature and low oxygen partial pressure conditions. Additionally, the effects of alumina surface dissolution in the region around the triple junction and H2 in the atmosphere were examined. Some reasons for the controversy on the bonding nature at the Cu/α–Al2O3 interfaces, i.e., Cu–O or Cu–Al on earth, present in the literature were also addressed.

We report a unique morphology of diamond nanoplatelets synthesized by microwave plasma chemical vapor deposition on Ni coated polycrystalline diamond substrates. The diamond nanoplatelets were as thin as approximately 30 nm. Electron microscopy showed that the diamond nanoplatelets appear in a shape consisting of trapezoid and parallelogram tabular crystallites. Furthermore, the diamond nanoplatelets were single crystalline, as shown by electron diffraction. The edges of nanoplatelets were along the 〈110〉 direction with both the top and bottom tabular surfaces parallel to the {111} plane. Transmission electron microscopy revealed that the twinned planes are parallel to the platelet and side-face structure in ridge shape is bounded by {100} and {111} planes. Lateral growth of diamond nanoplatelet is believed to result from twin and ridge face structure. An oriented thin graphite layer was observed on some diamond nanoplatelets.

Growth of such non-superconducting whiskers [Sr2.24Ca0.4Al2Ox, (Ca0.8–0.85Sr0.15–0.1)2CuO3,CuO, or Bi2.44Sr2Ca1.3–2Cu6.9–9.95Al0.35–0.46Ox (Cu-rich whiskers)] formed during the growth of Bi-2212 superconducting whiskers from powder or glassy substrates, is discussed. These whiskers are likely to grow from the bottom end, and there is a tight relationship with the growth of the Bi-2212 whiskers. A general reaction-path model for the whisker growth in the BSCCO system, independent of the type of the catalytic impurity and substrate, is proposed. When whiskers are grown under magnetic fields, up to 10 T, changes in the whisker size, aspect ratio, and morphology are observed.

Pressureless sintered B4C relative densities as high as 96.7% were obtained by optimizing the soak temperature, and holding at that temperature for the minimum time required to reach terminal density. Although the relative densities of pressureless sintered specimens were lower than that of commercially produced hot-pressed B4C, their (Vickers) hardness values were comparable. For 4.45-cm-diameter, 1.35-cm-high disk-shaped specimens, pressureless sintered to at least 93.0% relative density, post-hot isostatic pressing resulted in vast increases in relative densities (e.g., 100.0%) and hardness values significantly greater than that of commercially produced hot-pressed B4C.

The structure and dielectric properties of Ca1−xYxTi1−xAlxO3 (CYTA) ceramics prepared by the mixed-oxide route have been investigated. CYTA forms a complete solid solution with an orthorhombic perovskite structure. Residual Y4Al2O9 and Y3Al5O12 resulting from incomplete reaction are observed for ⩾ 0.9. Scanning electron microscopy shows that CYTA ceramics exhibit uniform microstructures, with an average grain size that decreases from ∼200 μm at x = 0 to ∼10 μm at x = 1.0. Transmission electron microscopy of CYTA (x = 0.3) ceramics reveals the presence of ferroelastic domains, and electron-diffraction patterns are indexed on the Pnma space group, consistent with an a+b−b− octahedral tilted structure. The relative permittivity, ϵr, decreases continuously from 170 to 12, while the microwave quality factor, Q·fr, increases from 10,000 to 12,000 GHz, for x = 0 and 1, respectively. CYTA (x = 0.30) ceramics exhibit ϵr ∼ 38, Q·fr of ∼14,212 GHz, and a temperature coefficient of resonance frequency, τf, of −14 ppm/°C. Small additions of acceptor (0.3 wt% ZnO) or donor (1 wt% Nb2O5) dopants decrease Q·fr by ∼20–30%, respectively.

Y0.9Ba1.9La0.2Cu3Oy (La-YBCO) thin films were prepared by an off-axis magnetron sputtering method on MgO substrates with and without a BaZrO3 buffer layer. Insertion of BaZrO3 buffer layer was effective for obtaining La-YBCO films with pure c-axis orientation and in-plane alignment at low temperatures below 600 °C. We prepared La-YBCO thin films on BaZrO3-buffered MgO substrates using a temperature-gradient method, in which a template La-YBCO layer was first deposited at 600 °C, and then the temperature was continuously raised to 700 °C. By this method, La-YBCO thin films with improved crystallinity were successfully prepared. It was also proved that the insertion of the BaZrO3 buffer layer enables us to prepare high-quality La-YBCO films with high reproducibility.

The anodic films formed on AZ91D magnesium alloy after heat treatment were analyzed and their electrochemical properties were investigated. The results showed that the cooling rate had a significant influence on the microstructure evolution of the AZ91D magnesium alloy after solution heat treatment at 440 °C for 20 h in N2 atmosphere. A single-phase microstructure was observed when the alloy was quenched in water after solution heat treatment. However, a duplex structure consisting of both α and β phases was found if the solution-annealed alloy was cooled in air. The differences in microstructure of the heat treated AZ91D magnesium alloy gave rise to a significant change in the property of the anodic film formed in 3 M KOH + 0.21 M Na3PO4 + 0.6 M KF + 0.15 M Al(NO3)3 electrolyte. During the early stage of anodization, for the as-cast alloy, inhomogeneous anodic films were formed exhibiting relative rough surface appearances. A rather smooth anodic film was formed for the solution-annealed AZ91D magnesium alloy either followed by air cooling or water-quenched. The surface and cross section appearance was almost the same regardless of the prior heat treatment after anodizing for 20 min. The corrosion resistances of the various anodized AZ91D magnesium alloy were evaluated and compared by employing electrochemical impedance spectroscopy (EIS). The results demonstrate that the anodic film formed on the water-quenched AZ91D magnesium alloy had a slightly higher polarization resistance than that formed on the as-cast alloy. The highest polarization resistance of anodic film was found for that formed on annealed and air-cooled alloy. The presence of Al-rich β phase on the surface gave rise to the formation of a more protective anodic film which consisted of a great amount of Al2O3.

In a specially equipped transmission electron microscope (TEM), Ni particles were vapor deposited onto thin films of amorphous carbon (a-C), and subsequent reactions with the carbon support were observed at elevated temperatures. Particles deposited at temperatures around 370 °C developed a graphite shell at above 600 °C and subsequently spread and graphitized the substrate. This activity was enhanced by hydrogen. The speed of graphitization significantly increased during spreading of the metal, which is attributed to the concomitant increase of the length of the reaction front, as well as to a purifying effect of hydrogen. It is concluded that the driving force for spreading of the Ni is the interdiffusion and catalytic conversion of carbonto graphite at the reaction front. Particles deposited at 500 °C remained inactive at670 °C. This is probably due to the formation of a rather stable carbidic or graphitic interlayer during deposition.

We report the use of low-energy nitrogen ion beams to form ultra-thin (<2 nm) layers of AlNx to act as tunnel barriers in Nb/Al–AlNx/Nb Josephson junctions. We fabricated reproducible, high-quality devices with independent control of the ion energy and dose, enabling exploration of a wide parameter space. Critical current density Jc ranged from 550 to 9400 A/cm2 with subgap-to-normal resistance ratios from 50 to 12.6. The spatial variation of ion-current density was roughly correlated with Jc over a large-area on a Si substrate. The junctions were stable on annealing up to temperatures of at least 200 °C. This technique could be applied to form other metal nitrides at room temperature for device applications where a high degree of control is desired.

The Lithographie, Galvanoformung, Abformung (LIGA) technique is important for making metal-based high-aspect-ratio microscale structures (HARMS) and microdevices derived from metal-based HARMS. Recently, molding replication of HARMS made of Pb, Zn, and Al has been demonstrated, advancing LIGA technology from the state where only polymer-based HARMS could be replicated by molding. This demonstration offers a potential means for economical fabrication of a wide variety of metal-based microdevices. Micromolding of a metal requires heating the metal to be molded to a significant fraction of its melting temperature. At high temperatures, the strength of the mold insert itself will typically decrease. The insert strength thus places a limit on the range of materials that can be molded. In this paper, micromolding and tensile experiments on Pb were carried out. A simple mechanics model of the micromolding process was developed. This model relates the stresses on the insert during micromolding primarily to the yield strength of the molded metal and frictional tractions on the sides of the insert. Reasonable agreement was obtained between the Pb experiments and the model predictions. Ramifications for other material systems are discussed.

The definition of a rigorous theoretical framework for the appropriate physico-chemical description of self-propagating high-temperature synthesis (SHS) processes represents the main goal of this work which is presented in two sequential articles. In this article, a novel mathematical model to simulate SHS processes is proposed. By adopting a heterogeneous approach for the description of mass transfer phenomena, the model is based on appropriate mass and energy conservation equations for each phase present during the system evolution. In particular, it takes microstructural evolution into account using suitable population balances and properly evaluating the differentdriving forces from the relevant phase diagram. The occurrence of phase transitionsis treated on the basis of the so-called enthalpy approach, while a conventional nucleation-and-growth mechanistic scenario is adopted to describe quantitatively the formation of reaction products. The proposed mathematical model may be applied to the case of combustion synthesis processes involving a low melting point reactant and a refractory one, as for the synthesis of transition metal carbides from pure metal and graphite. Thus, the model can be profitably used to gain a deeper insight into the microscopic elementary phenomena involved in combustion synthesis processes through a suitable combination of experimental and modeling investigations, as it may be seen in Part II of this work [J. Mater. Res. 20, 1269 (2005)].

The electrical properties of ultrathin amorphous Al2O3 films, grown by low temperature metal-organic chemical vapor deposition from aluminum(III) 2,4-pentanedionate and water as co-reactants, were examined for potential applications as gate dielectrics in emerging complementary metal-oxide semiconductor technologies. High-frequency capacitance–voltage and current–voltage techniques were used to evaluate Al2O3 films deposited on silicon oxynitride on n-type silicon (100) substrates, with thickness ranging from 2.5 to 6.5 nm, as a function of postdeposition annealing regimes. Dielectric constant values ranging from 11.0 to11.5 were obtained, depending on the annealing method used. Metal-insulator-semiconductor devices were demonstrated with net equivalent oxide thickness values of 1.3 nm. Significant charge traps were detected in the as-deposited films and were mostly passivated by the subsequent annealing treatment. The main charge injection mechanism in the dielectric layer was found to follow a Poole–Frenkel behavior, with post-annealed films exhibiting leakage current an order of magnitude lower than that of equivalent silicon oxide films.

We systematically introduced defects onto the body of multi-walled carbon nanotubes through an acid treatment, and the evolution of these defects was examined by Raman spectroscopy using different excitation wavelengths. The D and D′ modes are most prominent and responsive to defect formation caused by acid treatment and exhibit dispersive behavior upon changing the excitation wavelengths as expected from the double resonance Raman (DRR) mechanism. Several weaker Raman resonances including D″ and L1 (L2) + D′ modes were also observed at the lower excitation wavelengths (633 and 785 nm). In addition, specific structural defects including the typical pentagon-heptagon structure (Stone–Wales defects) were identified by Raman spectroscopy. In a closer analysis we also observed Haeckelite structures, specifically Ag mode response in R5,7 and O5,6,7.

An as-deposited Al–Cu–Fe–Cr film was annealed in flowing argon to study development of a quasicrystalline approximant microstructure. Sputter profile x-ray photoemission spectroscopy analysis showed oxygen incorporation reached approximately 70 at.% at the surface of the film, declined monotonically, and stabilized at ∼10 at.% at a depth of 160 nm. Synchrotron grazing incidence x-ray scattering was used to probe the structure of the coating at various penetration depths by altering the angle of the incident x-ray beam. An amorphous structure was observed near the termination surface, which coexisted with a compressively strained crystalline aluminum. These phases were the dominant microstructure to a depth of 110 nm. Below 150 nm, the film was primarily O1 decagonal approximant. Cross-section transmission electron microscopy elucidated a columnar growth morphology with associated porosity in the interstices between the columns. The resulting development of the Al–Cu–Fe–Cr decagonal approximant coatings from the precursor is reported.

Nanoparticulate materials are promising objects for studying the processes that triggermelting of solids. On a pyrolytic route, we successfully encapsulated 20–60 nm diameter Cu nanocrystals within multilayer graphitic carbon spheres. In situ electron microscope observations of the melting and displacement of the encapsulated Cu nanocrystals at temperatures up to 1175 K have provided clear evidence of the process of surface melting and its dependence on the quality of the metal/carbon interface. Detection of crystal defects inside the Cu particles during melting and vaporization has proved that the metal phase maintains its solid crystalline state in the particle center. Indications of the influence of surface anisotropy on the melting behavior were obtained. The carbon cages as a whole remained unchanged during the observations.