Liquid-phase reactive infiltration is a rapid and net-shape method of synthesizing silicon carbide composites. We use reactive infiltration of carbon with Si–A1 and Si–Cu melts to prepare composites consisting of interpenetrating networks of β–SiC and a secondary phase assemblage containing ductile metal (A1–Si) or a metal silicide (Si–Cu). The mechanisms of phase formation have been characterized. It is shown that a rapid initial reaction upon infiltration forms a largely stationary SiC network, within which the secondary phase constitution evolves due to solute rejection and liquid phase diffusion processes. Both homogeneous composites and those with controlled composition gradients have been synthesized.

Local ordering around Te and Zn atoms of ZnO–TeO2 glass systems is investigated by Te K and Zn K EXAFS using synchrotron radiation. Tellurium K EXAFS results suggest the coordination states of tellurium atoms are changed from TeO4 trigonal bipyramids to TeO311 polyhedra or TeO3 trigonal pyramids with increasing of ZnO. Zinc K EXAFS results indicate that the Zn atom has the second oxygen shell which locates at the distance of 0.222–0.228 nm. The second harmonic intensity of the poled glass samples was also measured. The compositional dependence of the second harmonic intensity is explained in terms of the structural change of ZnO–TeO2 glass with the addition of ZnO.

Heteroepitaxial diamond has been successfully deposited on a Si(110) substrate by the microwave plasma chemical vapor deposition method. The pretreatment consisted of carburization and bias-enhanced nucleation steps. Cross-sectional transmission electron microscopy reveals that diamond can be in the cube-on-cube epitaxial relationship with the Si substrate. Various orientation relationships between diamond and Si substrates have also been observed, depending on the location where the plasma applied. Near the center of the plasma, twins were rarely observed in cube-on-cube epitaxial regions. Away from the center of the plasma ball, Σ3 twins are seen first, and then additional Σ9 and Σ27 twins occur near the edge of the plasma. In general, defect density in the epitaxial films is less than that observed in polycrystalline ones. No interlayer could be observed between diamond and silicon. In addition, 2H-type hexagonal diamond has also been found, and is in epitaxy with the Si substrate.

The magnetic softness of nanocrystalline materials prepared from amorphous precursors is attributed to the average of the local magnetocrystalline anisotropy of the individual crystallites. In the present paper we have studied the effective magnetic anisotropy of Fe-based nanocrystalline samples with different microstructures. These microstructures were produced by using different heating rates when crystallizing the precursor material by means of continuous heating treatments. From the results of our study of the magnetic properties of the samples, carried out from the measurement of the bias field dependence of the transverse susceptibility, it was possible to discern the occurrence of intergranular coupling and to evaluate the typical dimensions of the coupled units. Since these dimensions were larger than the characteristic length of the microstructure, we suggest that the enhancement of the soft properties is linked to the decrease of the microstructure-magnetization interactions originating in large units of coupled magnetic moments.

The microstructure of a muscovite mica exposed to a rare gas ion beam has been studied by transmission electron microscopy. The investigation of damage without implantation was carried out using argon and helium ions of sufficient energy to traverse the 100–150 nm mica specimens. For 340 keV Ar++ irradiation, amorphization of mica occurred at a fluence as low as 3.5 × 1014 ions · cm−2, which corresponds to 0.29 dpa. Muscovite can be amorphized using 80 keV helium ions, but this requires a much higher fluence and damage production of 4.6 × 10−6 ions · cm−2 and 0.60 dpa, respectively. Since helium irradiation results principally in ionization energy loss, it indicates that amorphization of muscovite results mainly from nuclear interactions. Complete amorphization of muscovite mica is found to take place for all ions at approximately the same amount of nuclear energy transfer to energetic primary knock-on atoms, assuming a recoil energy greater than 500 eV. This suggests that amorphization occurs directly in dense displacement cascades. A significant amount of helium, 100 ppm, can be implanted into muscovite mica without destroying the crystal structure.

In this study, porous Vycor tubes with 40 Å initial pore diameter were modified using low pressure chemical vapor deposition (LPCVD) of SiO2. Diethylsilane (DES) in conjunction with O2 or N2O were used as precursors to synthesize the SiO2 films. Both “single side” (reactants flowing on the same side of porous membrane) and “counterflow” (reactants flowing on both sides of porous membrane) reactant geometries have been investigated. The flow of H2, He, N2, Ar, and toluene (C7H8) was monitored in situ after each deposition period. Membranes modified by the “single side” reactants geometry exhibited good selectivities between small and large molecules. However, cracking in these membranes after prolonged deposition limited the maximum achievable selectivity values. Higher selectivities and better mechanical stability were achieved with membranes produced using the “counterflow” reactants geometry. Pore narrowing rate was observed to increase with oxidant flow (O2 or N2O). For membranes prepared using both oxidants, selectivities on the order of 1000: 1 were readily attained for H2 and He over N2, Ar, and C7H8. As compared to O2, the use of N2O caused improvements in both the pore narrowing rate and N2: C7H8 selectivity. Membranes prepared using the “counterflow” geometry showed no signs of degradation or cracking after thermal cycling.

Surface modification of emeraldine (EM) and nigraniline (NA) base films by argon plasma treatment was investigated by x-ray photoelectron spectroscopy (XPS). Argon plasma treatment, followed by atmospheric exposure, results in the oxidation of some carbon atoms, first to C–O species and then to C = O and COOH species for samples with extended plasma treatment time. Most important of all, Ar plasma treatment and the accompanied carbon oxidation readily cause a decrease in the intrinsic oxidation state ([=N— ]/[—NH—] ratio) of the aniline polymers.

Techniques from the field of materials science and engineering were utilized to examine the mechanical effects of dark pigment in exoskeleton material on the distal portion of stone crab, Menippe mercenaria, chelae. We made specimens from dark-and light-colored exoskeleton material to measure hardness and fracture toughness. The results from these tests showed the dark material to be much harder and tougher than light-colored material from the same crab chela. Scanning electron microscope photographs are presented to document the microstructure and level of porosity. We think that the structural difference in material properties is due to the lower level of porosity and phenolic tanning in dark material and that this tanning caused the dark color and filling of porosity. The exoskeleton structure is a laminated organic-inorganic structure which can serve as a model for self-healing structures.

Monocrystalline GaN(0001) thin films have been grown at 950 °C on high-temperature, ≈ 100 nm thick, monocrystalline AlN(0001) buffer layers predeposited at 1100 °C on α(6H)−SiC(0001)Si substrates via OMVPE in a cold-wall, vertical, pancake-style reactor. These films were free of low-angle grain boundaries and the associated oriented domain microstructure. The PL spectra of the GaN films deposited on both vicinal and on-axis substrates revealed strong bound excitonic emission with a FWHM value of 4 meV. The near band-edge emission from films on the vicinal substrates was shifted slightly to a lower energy, indicative of films containing residual tensile stresses. A peak attributed to free excitonic emission was also clearly observed in the on-axis spectrum. Undoped films were too resistive for accurate Hall-effect measurements. Controlled n-type, Si-doping in GaN was achieved for net carrier concentrations ranging from approximately 1 × 1017 cm−3 to 1 × 1020 cm−3. Mg-doped, p-type GaN was achieved with nA−nD ≈ 3 × 1017 cm−3, ρ ≈ 7 Ω · cm, and μ ≈ 3 cm2/V · s. Double-crystal x-ray rocking curve measurements for simultaneously deposited 1.4 μm GaN films revealed FWHM values of 58 and 151 arcsec for deposition on on-axis and off-axis 6H−SiC(0001)Si substrates, respectively. The corresponding FWHM values for the AlN buffer layers were approximately 200 and 400 arcsec, respectively.

High-purity tungsten was prepared by the self-propagating high-temperature synthesis (SHS) process from a mixture of CaO · WO3 and Mg. The complete reduction of CaO · WO3 required a 33% excess of magnesium over the stoichiometric molar ratio Mg/CaO · WO3 of 3: 1. The MgO and CaO in the product were leached with an HCl solution. The product tungsten had a purity of 99.980% which was higher than that of the reactants. The high purity results because the nontungsten reactants and products are volatilized by the high temperatures generated during the rapid exothermic SHS reaction and are dissolved during HCl leaching of the product.

Time-resolved spectroscopy of poly(ethylene) oxide (PEO) and poly(propylene) oxide (PPO) electrolytes containing different concentrations of Eu3+ and Nd3+ ions is reported. A description of the main luminescence features of the Nd3+ electrolytes is also presented. Lifetimes regarding the main transitions of the luminescence spectra (5D0 → 7F1,2 and 4D3/2 → 4I11/2 for Eu3+ and Nd3+, respectively) are determined and are presented as a function of temperature in the range of 13 to 310 K. The order of magnitude of the values obtained at room temperature (0.2–0.6 ms and ≈0.7 ms for Eu3+ and Nd3+, respectively) is a further indication of the technological potential of these new polymeric materials. For the Eu3+ ion the thermally activated quenching of the 5D0 → 7F2 luminescence is discussed in terms of the observed energy superposition between the 5D0,1 levels and the ligands-to-metal charge-transfer states.

An analytical model of hardness has been developed. Four major indentation tests, namely indentation by cones, wedges, spheres, and flat-ended, axisymmetric cylinders have been analyzed based on the model. Analytical relationships among hardness, yield stress, elastic modulus, Poisson's ratio, and indenter geometries have been found. These results enable hardness to be calculated in terms of uniaxial material properties and indenter geometries for a wide variety of elastic and plastic materials. These relationships can also be used for evaluating other mechanical properties through hardness measurements and for converting hardness from one type of hardness test into those of a different test. Comparison with experimental data and numerical calculations is excellent.

The relationship among electrical conductivity, optical properties, and carbon structure of ion-implanted polymers has been studied by optical transmission and Raman spectroscopy. The electrical conductivity, which depends not only on the ion dose but also on the dose rate in a complicated manner, was found to have a simple relation to the optical absorbance. By Raman spectroscopic analyses, the difference in the electrical conductivity was explained in terms of the difference in carbon structure.

Stick-slip process occurred during the scratch test of styrene-acrylonitrile copolymer. For the first time, a bamboo-like morphology of the scratch track corresponding to the stick-slip phenomenon was observed. A “joint” was formed during the stick stage and during slip a uniform “stem” was made. The period and amplitude of the stick-slip both increase with the vertical load and decrease with the driving speed. A theoretical model is constructed based on the stiffness of the system and the plastic deformation of polymer both in the vertical and horizontal directions. The model assumes no distinction between the coefficients of static and kinetic friction and gives quantitatively consistent results with experiments.

Optically clear monolithic (OCM) gels of mesoporous aluminosilicates (average pore diameter 3.6 nm) and alumina (6 nm) have been prepared by slow hydrolysis-polycondensation of alkoxides and converted into OCM mesoporous glasses by heating. In order to change the properties, different ways of modifying the pore size and structure are proposed. We show that addition of boron oxide reduces the average pore diameter. A higher effect can be obtained by addition of a surfactant. In this case the mesoporous matrix becomes microporous (d < 2 nm). Another way of modifying the pore structure consists of introducing nanoprecipitates inside the porosity by an impregnation process. Modifications of the porous structure are different in alumina and aluminosilicates.

Ion beam mixing, diffusion properties, and phase stability have been investigated in Cu/Al2O3 bilayer samples. Specimens were prepared by vapor deposition and irradiated with 150 keV Ar+ ions up to a fluence of 1.5 · 1017 Ar+/cm2. Sample temperature under irradiation was varied between 77 K and 673 K. The mixing behavior was studied by analyzing the concentration depth profiles, determined by Rutherford Backscattering Spectroscopy. It was found that mixing efficiencies of Cu, Al, and O scale with Ar+ fluence. Radiation enhanced diffusion (RED), observed above room temperature, is separated from ballistic mixing and high temperature diffusion. The migration enthalpy for interdiffusion in the RED region (between RT and 300 °C) was estimated to be approximately 0.3 eV. Sputtering yields depending on temperature gradient near to sample and phase stability versus ion dose and temperature are also discussed.

We review the device and materials science behind organic electroluminescent diodes made both using discrete evaporable molecules and spin-cast organic polymers. A great deal of progress has been made in improving the efficiencies and spectral properties of organic light-emitting diodes, and these are now adequate for many applications. More work is necessary to understand the stability and degradation of emissive and charge-transporting organics, but some systems have been shown to be stable for 104 hours at display brightness. Major challenges still face the community in terms of developing satisfactory systems design and processing techniques if organic electroluminescence is to realize either performance or economic advantages over technologies and significantly penetrate the display market. We present an analysis of the suitability of organic light-emitting diodes for various applications, and consider the materials and manufacturing obstacles that must be overcome.

The effects of Si additions on the behavior of high modulus carbon fiber reinforced aluminum matrix (CF/Al) composites during thermal exposure at 773 K for different times have been investigated. The composites were fabricated via hybridization with a small volume fraction of SiC particles using a pressure-casting process. The change of longitudinal tensile strength, the strength degradation of carbon fibers, and the microstructural observations on the interfaces of CF/pure Al composites and CF/Al-Si composites after thermal exposure undoubtedly indicate that the alloying element Si in an aluminum matrix can effectively prohibit the interfacial reactions at the fiber/aluminum interface and has positive effects on the characteristics of CF/Al composites.

The mechanical properties of many polymers are known to change as they absorb water. This fact has been used to monitor the absorption of water into the surface layers of an epoxy adhesive with a depth sensing indentation system. Two methods have been demonstrated. The sample can be immersed in water for a period of time and then removed and tested in air. Alternatively, the sample can be tested in in situ. In the second method the transport of water through the adhesive can clearly be seen in hardness/depth profiles. Hardness, elastic modulus, and creep strain of the adhesive change with time until a stable value is reached, which corresponds to full plasticization of the adhesive to the influence depth of the indenter. The initial mechanical properties of the epoxy are mostly recovered on drying.

Organic and polymeric materzials have seen a tremendous growth in research in the last five years as potential electroactive elements in thin-film-transistor (TFT) applications. These are driven by the increasing interest in flat-panel-display applications, for which organic and polymeric materials offer strong promise in terms of properties, processability, cost, and compatibility with eventual lightweight, flexible plastic displays. In this review we summarize the current status of our knowledge on the science of these organic and polymeric semiconducting materials. Most of these are based on linear thiophenes, especially a-hexathienyl, which has elicited by far the most attention. Mobility values in the 10−2–10−1 cm2/Vs and especially source-drain current on/off ratios of up to 106 make this a highly promising potential alternative to amorphous silicon. Other thienyl compounds are also discussed, as are polymeric analogues. A brief discussion of technological potential, limitations, and problems that need to be overcome is given at the end.