The nanopipes in undoped GaN epilayers grown on sapphire substrates were investigated by field emission high-resolution electron microscopy (HREM) and energy-dispersive x-ray spectrometry (EDS). In the HREM images, the cores of the nanopipes appeared disordered in the thin regions and more ordered in the thicker regions, indicating the amorphous layer on the surface has a significant influence on the visible image of the nanopipe in the thin regions. The EDS spectra showed that composition of the materials in nanopipes was mainly oxygen, carbon, and gallium elements. The results suggest that the nanopipes are related to impurities.

This communication reports the novel idea of using a magnetic field gradient to hold magnetic nanoparticles at desired densities in a fixed location (e.g., on an electrode surface), while metal atoms are deposited electrochemically in the interstices between them. Using it, nanocomposites consisting of γ–Fe2O3 nanoparticles (with a mean size of about 40 nm) in a copper metal matrix were reproducibly fabricated, with particle volume fractions ranging from 0.2% to 50%. These nanocomposites, ceramic magnetic particles in a conductive metal matrix, are expected to have unusual or enhanced mechanical, electrical, and magnetic properties.

The plastic deformation behavior of Knoop indentations made in a soft, porous titanium/aluminum multilayered thin film on a hard silicon substrate is studied through use of the focused-ion-beam milling and imaging technique. Pileup is observed for indentations with depths larger than 30% of the total film thickness. Analysis of the indentation cross sections shows that plastic deformation around the indentation is partly accommodated by the closing of the pores within the multilayers. This densification process reduces the amount of pileup formed below that predicted by finite element simulations. Experimental results show that the pileup is formed by an increase of the titanium layer thickness near the edges of the indentation. The thickness increase is largest near the film/substrate interface and decreases toward the surface of the multilayered film. The amount of normal compression near the center of the indenter is characterized, and it is demonstrated that the deformation becomes more nonuniform with increasing indentation depth.

We described previously the liquid phase synthesis and characterization of a nanostructured composite from an aqueous solution containing organic polymer and inorganic ions [J. Mater. Res. 7, 2599 (1992)]. The nanocomposite, termed an organoceramic, consisted of poly(vinyl alcohol) chains intercalated between the principal layers of a hydrated calcium aluminate ceramic. A key structural feature of the organoceramic is the polymer-induced expansion of the interlayer spacing by approximately 10 Å compared to the unmodified ceramic. In this paper, we describe the synthetic scheme that favors organoceramic formation and prove the existence of intercalated polymer by observation of reversible interlayer expansion and contraction in response to changes in ambient humidity. This property is unique to the organoceramic and is not observed in the unmodified calcium aluminate ceramic.

In this paper we provide a new mathematical model for front propagation with a nonlocal growth law in any space dimension. Such a problem arises in composite fabrication using the vapor infiltration process and in other physical problems involving transport and reaction. Our model, based on the level set equation coupled with a boundary value problem of the Laplace equation, is an Eulerian formulation, which allows robust treatment for topological changes such as merging and formation of pores without artificially tracking them. When applied to the fabrication of continuous filament ceramic matrix composites using chemical vapor infiltration, this model accurately predicts not only residual porosity but also the precise locations and shapes of all pores.

The maximum undercoolings of 304, 318, 308, and 296 K were achieved, respectively, in Fe-22, 26, 30, and 34 at.% Co alloys. The metastable bcc phase nucleated from melts when undercoolings exceeded critical ones. The critical undercoolings for the formation of metastable bcc phase from Fe-22, 26, 30, and 34 at.% Co melts were 104, 156, 204, and 248 K, respectively. The morphologies of as-obtained metastable bcc phase exhibited five typical patterns: dendrite cores with primary and second arms, well-developed second arms, and radiated, lath, and platelike structures. Based on the classical nucleation theory, the solidification behavior of the melts was analyzed with regard to the metastable phase formation when the melts were undercooled greater than critical undercoolings. The formation of various morphologies was also evaluated to consider the solidification behavior of the undercooled melts.

Shock synthesis of nanocrystalline Si was accomplished for the first time using thermal spray in which Si powder is injected into a high-energy flame where the particles melt and accelerate to impact on the substrate. A stream of molten Si particles impacted onto Si wafers of two orientations (100) and (111). The shock wave generated by the sudden impact of the droplets propagated through the underlying Si layer, which experienced a phase transition to a high-pressure form of Si due to propagation of the shock wave. The metastable high-pressure form of Si then transformed to metastable Si-IX, Si-IV (hexagonal diamond-Si), R-8, and BC-8 phases as evidenced by transmission electron microscopy and x-ray diffraction studies. Back-transformed metastable Si grains, with a size range from 2 to 5 nm, were found to be dispersed within Si-I (cubic diamond-Si). The metastable phases formed mostly in deposits on the (100) substrate compared to those of the (111) substrate orientations. This behavior can be correlated with the anisotropic nature of the pressure-induced transformations of Si-I.

SiC (3C-SiC) was grown on the top Si layer of SIMOX (Si/SiO2/Si) by carbonization followed by chemical vapor deposition (CVD). Subsequently, GaN was deposited on the SiC by metalorganic (MO) CVD to produce a GaN/SiC/Si/SiO2/Si multilayer structure. This multilayer film was investigated by conventional transmission electron microscopy (TEM) and high-resolution (HR) TEM from cross-sectional view. The GaN layer was found to consist of predominately hexagonal gallium nitride (h-GaN), and a small fraction of cubic GaN (c-GaN) crystallites. The orientation relationship between most of the h-GaN grains and SiC (3C-SiC) was found to be (0001)Ga N||s(111)SiC; [1120]GaN||[110]SiC, while most of the c-GaN grains had an orientation relationship (001)GaN||(001)SiC; [110]GaN||[110]SiC with respect to 3C-SiC substrate. The hexagonal grains of GaN were found to grow as two variants. The defects in both h-GaN and c-GaN are also discussed.

In order to get detailed information of the core–rim interface of carbides in TiC–20 wt% Mo2C–20 wt% cermet, chemical analysis in the vicinity of the interface was carried out by energy dispersive x-ray spectroscopy equipped with a high-resolution transmission electron microscope (HRTEM) with a field-emission-type gun. It was found that the chemical composition discretely changed across the core–rim interface at a nanoscale level, whereas HRTEM observation revealed that the interface is highly coherent. The discrete change in molybdenum content at the interface may suggest the existence of a miscibility gap between TiC and MoC systems at the sintering temperature.

High-quality a-axis-oriented HgBa2CaCu2Ox superconducting thin films have been grown on (100) LaAlO3 substrates using a modified conventional method that contains a short annealing time of 5 min, rapid-quenching process, and an alternative encapsulated approach. We found that the preferred orientations of HgBa2CaCu2Ox thin films can be controlled by rapid quenching at specific temperatures: 800, 700, 600, and 500 °C. The films rapidly quenched in water from 700 °C during a cooling cycle showed predominantly a-axis orientation perpendicular to the film surface. Phase was confirmed by x-ray diffraction pole figures. The a-axis films exhibited a zero-resistance transition temperature >120 K, which is comparable to epitaxial c-axis-oriented films.

The magnetic properties of single-crystalline Tb2Fe17−xSix (x = 0, 1, 2, 3, and 3.3) have been investigated. The Si substitution constricted the lattices by 1.5% and caused the Th2Ni17 transfer to Th2Zn17. The Curie temperature increased from 413 to 526 K, and the spontaneous magnetic moment decreased from 82.6 to 46.4 emu/g with the increase of Si. The stronger anisotropy and coercivity were generated by Si occupying the Fe sublattices. A domain wall pinning-dominated mechanism was responsible for increasing the coercivity force from 0.01 T (x = 1) to about 0.36 T (x = 3.3) at 1.5 K.

The tendency of graphite-diamond transformation assisted by nonmetallic catalysts of carbonates, sulfates, or phosphorus under high pressure and high temperature has been investigated by calculating the activation energy and transformation probability of the carbon atoms over a potential barrier. It was found that the activation energy is highly sensitive to the catalyst chosen. The value of activation energy in the systems of graphite-carbonates, graphite-phosphorus, and graphite-sulfate are 130.71 × 103, 206.03 × 103, and 221 × 103 J/mol, respectively. If fd stands for the probability of the transformation from graphite to diamond, the probability sequence of graphite-diamond transformation in different systems was put forward: fd(gr.-carbonate) > fd(gr.-phosphorus). fd(gr.-sulfate).

The nanostructure of GaN and SiC nanowires produced by carbon nanotube confined reaction has been studied by means of high-resolution electron microscopy, microanalysis, and microdiffraction. The GaN nanowire is a single crystal with fewer defects and the SiC nanowire is a β–SiC crystal with heavy layer sequence faults. Considering experimental results, a possible reaction path for making GaN is suggested.

Highly (200)-oriented Pt films on SiO2/Si substrates were successfully prepared by a combination of a dc magnetron sputtering using Ar/O2 gas mixtures and subsequent controlled annealing. The intensity ratio of (200) to (111) planes (I200/I111) was over 200. The (200)-oriented Pt microcrystallites were less susceptible to amorphization due to their lower strain energy with oxygen incorporation than (111)-oriented ones. The controlled grain growth from the selected (200)-oriented seed microcrystallites during subsequent annealing provided a kinetic pathway where grain growth of the seed microcrystallites was predominant, while suppressing the nucleation of surface energy-driven, (111)-oriented seed microcrystallites and subsequent (111) preferred orientation.

Pb(Zn1/3Nb2/3)O3-based ceramics were thermally annealed at 700–900 °C for 4 h. Both the relative dielectric constant and dissipation factor in the vicinity of transition temperature were increased when the specimens were thermally annealed at 700–900 °C, but the diffusion factor was decreased. After thermal annealing, the maximum dielectric constant Km was increased from about 11,000 to 26,000. These phenomena can be related to the domain wall motion and the elimination of internal stress.

The roughness of metallic surfaces generated by machining depends on the intended intervention by the tool and the inadvertent consequences determined by the response of metals. The roughness generated in four different metals by grinding is studied using the power spectrum method. It was found that the level of power is determined by the intended intervention such as the depth of cut and, to some extent, by hardness because of its possible influence on micropileup geometry. The power gradient is, however, influenced by inadvertent damage which may be related to material properties such as thermal conductivity and adhesion.

Applying the scaling relationships developed recently for conical indentation in elastic–plastic solids with work-hardening, we examine the question of whether stress–strain relationships of such solids can be uniquely determined by matching the calculated loading and unloading curves with that measured experimentally. We show that there can be multiple stress–strain curves for a given set of loading and unloading curves. Consequently, stress–strain relationships may not be uniquely determined from loading and unloading curves alone using a conical or pyramidal indenter.

Subsolidus equilibria in air in the La2O3–Ga2O3–CeO2 system were studied with the aim of obtaining information on possible interactions between a LaGaO3-based solid electrolyte and CeO2 during preparation of the anode in solid oxide fuel cells. No ternary compound was found. The tie lines are between La4Ga2O9 and the end of the CeO2 solid solution range with composition La0.5Ce0.5O1.75 and between the LaGaO3 and CeO2 range of solid solutions.

The characteristics of a ferroelectric Pb(Zr0.52Ti0.48)O3 (PZT) capacitor on conductive BaRuO3 thin films deposited by pulsed laser deposition (PLD) were investigated. The BaRuO3 layer grown epitaxially on LaAlO3(100) substrates at a substrate temperature of 700 °C was found to have a resistivity around 145 μΩ cm at 300 K. The subsequently deposited PZT film showed a c-axis orientation perpendicular to the substrate, and the remnant polarization, ΔP (= P* – P^), and coercive field, EC, of the capacitor were 24.7 μC/cm2 and 52 kV/cm, respectively. Fatigue characteristics of the PZT on BaRuO3 electrodes are far better than those obtained with polycrystalline PZT with Pt structures and comparable to those on epitaxial Yba2Cu3O7−x electrodes. With the new metallic electrode, the PZT layer exhibits no serious degradation in fatigue endurance up to 1010 cycles.

It has been shown that sintering temperature can be lowered and the density, hardness, and toughness of MoSi2 raised by using nanophase MoSi2 and ZrO2 additives. A minimum hot-pressing temperature of 1350 °C is needed for complete densification without a significant increase in grain size.