α-hexathienyl (α–6T) is a highly promising material for application in thin film transistor devices. Recently, record high mobilities, together with record high current on/off ratios, have been reported.1 Thus far, structural information on this exciting material is sketchy. The crystal structures of several such hexamers have been investigated, but only with powder samples, since the crystal growth has proven exceedingly difficult.2-5 Powder Rietveld refinements on these materials are severely hampered by the large number of overlapping reflections, preferred orientation, ambiguities in symmetry, etc. Here, we present a crystal structure of the high-temperature polymorph of α–6T (α–6T/HT), as determined from a single-crystal structure analysis. In this polymorph, the hexamer crystallizes in the smallest unit cell so far reported for this material, but the molecule is flat. Extended Hückel theory (EHT) band structure calculations show that α–6T/HT is an indirect gap semiconductor, with the conduction band minimum at Y and the valence band maximum at Γ. The conduction and valence bands both show a remarkable degree of dispersion along X and Y for a molecular crystal. The electronic band structure of this material is strikingly similar to that of the two-dimensional organic superconductors based on bis(ethylenedithio)tetrathiafulvalene (ET), such as κ−(ET)2 Cu(NCS)2.

This communication describes a technique used to pattern oxide thin layers using microcontact printing (μCP) and sol-gel deposition. The technique involves μCP of self-assembled monolayers (SAM's) of alkylsiloxane on various substrates (SiO2/Si, sapphire, ITO, and glass), followed by deposition of oxide thin layers from sol-gel precursors. Delamination of oxide layers from SAM-derivatized regions allows selective deposition of crystalline dielectric oxide layers on underivatized regions. To demonstrate the viability of this technique for integrated microelectronics and optics applications, patterned (Pb,La)TiO3 (PLT) and LiNbO3 layers were deposited on sapphire, silicon, and indium tin oxide (ITO) substrates. Use of lattice-matched substrates allows lithography-free deposition of patterned heteroepitaxial oxide layers. Strip waveguides of heteroepitaxial LiNbO3 with 4 μm lateral dimensions were fabricated on sapphire. Dielectric measurements for patterned PLT thin layers on ITO are also reported.

Molecular dynamics (MD) simulations of diffusion in a Σ5(310) [001] Al tilt grain boundary were performed using for the first time three different potentials based on the embedded atom method (EAM). The EAM potentials that produce more accurate melting temperatures also yield activation energies in better agreement with experimental data. Compared to pair potentials, the EAM potentials also give more accurate results.

Zircon, ZrSiO4, is a well-characterized, naturally occurring phase that is extremely durable. Zircon has been synthesized with Pu-concentrations up to 10 wt. % and radiation-damage effects studied to saturation doses of nearly 0.8 displacements per atom. We propose that zircon be used as a waste form for the disposal of the more than 100 metric tons of plutonium that will result from the dismantling of nuclear weapons. There are already several demonstrated processing technologies, of which hot pressing offers the most potential. This highly durable material, even under hydrothermal conditions, with its high waste loading and smaller volume allows deep, permanent disposal of the weapons plutonium in geologic environments in which the borosilicate waste-form glass would not be stable.

Single crystal fibers of A(B11/2B21/2)O3 perovskites type with compositions Sr(Al1/2Ta1/2)O3 (SAT) and Sr(Al1/2Nb1/2)O3 (SAN) were grown successfully for the first time, using a laser-heated pedestal growth (LHPG) technique. Their crystallographic structures were found to be simple cubic perovskite with lattice parameters a = 3.8952 Å (SAT) and a = 3.8995 Å (SAN) that are close lattice matches to the YBCO superconductors. No structural phase transitions or twins have been found, and the average coefficients of the thermal expansion match well with the YBCO superconductor materials. We report that SAT is one of the most promising substrates to date for the epitaxial growth of HTSC thin films suitable for microwave device applications as it has low dielectric constants (K ∼ 11–12, at 100 Hz–10 GHz and 300 K) and low dielectric loss (∼4 × 10−5 at 10 kHz and 80 K), together with lattice parameter matching, thermal expansion matching, and chemical compatibility with the high Tc superconductors (YBCO).

Diffusion in a regular solid solution was investigated. A thin plate of isotropic solid of constant surface molal fraction was considered. The regular solution is described by the parameter α. When α is positive, the attraction between unlike atoms is greater than the attraction between like atoms, and conversely. The depths of penetration and average molal fraction for a given period increase with increasing α. The separation of two curves for given α increase with increasing surface molal fraction. The diffusion coefficient is positive only if α is greater than −1/X(1 - X).

The Pb-based solder used in microelectronics industry is becoming an environmental issue. To understand the wetting behavior of solders with and without Pb, we have studied the surface morphology and wetting reaction of eutectic SnBi, eutectic SnPb, and pure Sn on Cu through the measurements of wetting angle change and wetting tip stability by SEM and EDX. The wetting angle remains constant after the initial spread, but the eutectic SnPb/Cu continues to react and forms a reaction band in front of the solder edge as well as intermetallic compounds at the interface. For eutectic SnBi/Cu, there is no reaction at the wetting tip, and the wetting angle does not change much; however, the interfacial reaction between eutectic SnBi and Cu forms intermetallic compounds at the solder joint; the wetting tip is not in a static equilibrium. A rough surface and edge was observed on the eutectic SnBi/Cu joint, but the eutectic SnPb/Cu has a smoother surface and edge.

Thin films of carbon nitride have been prepared using triode ion plating. It has been observed that the compound formation occurs at ambient substrate temperature itself. Though the films are completely amorphous at temperatures below 900 °C. they are hard and transparent down to a wavelength of 200 nm. It has also been observed that the film transmission can be modulated using nitrogen ion flux and partial pressure. The IR transmission spectra clearly show the C-N stretch band around 2200 cm−1. Onset of crystallization, as evidenced from electron diffraction, occurs around 900 °C substrate temperature.

The Hg-Ba-Ca-Cu-O system phase diagram and the formation of HgBa2Can-1CunO2n+2+δ superconducting phases have been investigated by XRD (x-ray diffraction). The isothermal sections of the HgO-BaO-CuO system at 800 °C and the BaO-CaO-CuO system at 870 °C are presented. HgBa2Can-1CunO2n+2+δ superconducting phases are formed through the reactions of HgO with intermediate products Ba2CuO3 + BaCuO2 + CaO, BaCuO2 + CaO2, and BaCuO2 + Ca2CuO3 for n = 1, 2, and 3 phases, respectively.

Starting from a glassy precursor, Bi2Sr2Ca1−xDyxCu2O8−y (for x = 0.2) was recrystallized under a 0.6 T magnetic field. After splat quenching, the samples were heated and sintered at different temperatures T1, then slowly cooled. X-ray diffraction data, sometimes showing 00l peak splitting and electron scanning microscopy pictures, were collected. The results showed that the magnetic field could orient the grains and led to a magnetically textured growth process. Secondary phases formed in the system during this process were identified by EDX analysis. The optimum T1 for texturing was found to be between 930 °C and 950 °C.

YBa2Cu3O7−x (YBCO) and barrier layer films were deposited on single-crystal (Y2O3)0.09(ZrO2)0.91 substrates cut between 3.6 and 35.7°off-axis from the (001) planes. The barrier layers were (Y2O3)0.065(Y-ZrO2)0.935(Y-ZrO2), Y2O3, or multilayered structures of Y-ZrO2 and Y2O3. X-ray diffraction showed that the Y-ZrO2 and Y2O3 barrier layers generally grew epitaxially on the off-axis substrates, with the (001) barrier layer film planes being parallel to those of the substrate, and the (100) directions being parallel. YBCO films deposited on Y2O3 barrier layers also showed epitaxy with the YBCO (001) planes being nearly parallel to the substrate (001) planes, even for miscuts up to 35.7°. In contrast, the (001) planes of YBCO films deposited on Y-ZrO2 barrier layers were almost parallel to the substrate surface, not the (001) substrate planes. However, YBCO films on Y-ZrO2 films maintained particular in-plane epitaxial orientations with respect to the substrate. The YBCO full-width at half-maximum (FWHM) x-ray peaks were slightly narrower (0.8°) on Y2O3 barrier layers than on Y-ZrO2 layers (1.3°). The electrical resistivity versus temperature behavior of the YBCO/Y2O3 films was consistent with increased grain boundary scattering as the degree of substrate miscut increased, whereas YBCO/Y-ZrO2 films' resistivities showed less sensitivity to substrate miscut, consistent with the loss of epitaxy.

Thin films of Y-stabilized ZrO2 (YSZ) were deposited by RF diode sputtering on R-plane sapphire as a buffer layer for the deposition of YBa2Cu3O3 (YBCO). By increasing the partial pressure of oxygen in the sputter gas mixture from 20% to 50%, it was found that the substrate temperature required to obtain (100) oriented YSZ deposition could be lowered to 630 °C from 800 °C. This change is attributed to heating or mixing effects at the film surface, due to an increase in negative ion bombardment, which supplements the effects of external heating. Increases in the partial pressure of oxygen beyond 50% were found to be counterproductive. YBCO films, deposited on the YSZ buffer layers via magnetron sputtering, showed c-axis orientation and transition temperatures of 82 K. Orientation of both the YSZ and YBCO films was confirmed by x-ray diffraction and SEM characterization.

This paper describes a novel technology for a mercury-free metallic direct filling material, a substitute to dental amalgams. The consolidation relies both on cold-welding that takes place under moderate pressure between suitably surface-treated silver particles and on silver-tin intermetallic compound formation at ambient temperature. A dilute acid is used for removing the silver surface oxide layers, thereby promoting the cold-welding process. The condensability, namely the ability of a loose powder to undergo consolidation within a short time duration, at body temperature and under moderate pressure has been investigated for a variety of mixtures of silver, tin, and prealloyed silver-coated intermetallic powders. The resulting metallic composite material displays transverse rupture strength values higher than those of amalgams and somewhat lower values of compressive strength and Knoop hardness.

Several conditions for hydroxyapatite ceramic preparation were used: sintering at 1150 °C in air or under H2O vapor flow, quenched in water at room temperature after sintering, or slow cooling inside the furnace. Depending on specific combinations of these preparation conditions, in the resulting ceramics significant differences are observed in the phase composition and dielectric properties, ranging from capacitive to a semiconducting response. Comparison between the experimental x-ray diffraction patterns and those calculated by the Rietveld method show that during sintering in air, approximately 40% of hydroxyapatite is transformed to tricalcium phosphate. The XRD analysis shows that this transformation could be possible using the following process: Ca10(PO4)6(OH)2 = 2Ca3(PO4)2 + Ca2P2O7 + 2CaO + H2O.

Thin films (4–1000 Å) of Co were deposited onto n-type 6H-SiC(0001) wafers by UHV electron beam evaporation. The chemistry, microstructure, and electrical properties were determined using x-ray photoelectron spectroscopy, high resolution transmission electron microscopy, and I-V and C-V measurements, respectively. The as-deposited contacts exhibited excellent rectifying behavior with low ideality factors and leakage currents of n < 1.06 and 2.0 × 10−8 A/cm2 at −10 V, respectively. During annealing at 1000 °C for 2 min, significant reaction occurred resulting in the formation of CoSi and graphite. These annealed contacts exhibited ohmic-like character, which is believed to be due to defects created in the interface region.

A composite microstructure consisting of small α-Al2O3 particles dispersed in a β-NiAl coating matrix was synthesized by chemical vapor deposition (CVD). White the surface of a pure Ni substrate was being reacted with AlCl3 and H2 to form β-NiAl at a temperature of 1050 °C, the partial pressure of CO2 in the reactor was controlled via pulsing to nucleate and disperse 50 to 500 nm α-Al2O3 particles in the β-NiAl matrix. The relative amount of the α-Al2O3 phase increased with coating thickness as the rate of the β-NiAl formation decreased with time. These experimental observations suggest that the synthesis of a graded composite microstructure by the CVD method is feasible.

The first use of continuous vapor grown carbon fiber (VGCF) as reinforcement in aluminum metal matrix composite (Al MMC) is reported. Al MMC represents a new material for thermal management in high-power, high-density electronic devices. Due to the ultrahigh thermal conductivity of VGCF, 1950 W/m-K at room temperature, VGCF-reinforced Al MMC exhibits excellent thermal conductivity that cannot be achieved by using any other carbon fiber as reinforcement. An unprecedented high thermal conductivity of 642 W/m-K for Al MMC was obtained by using 36.5% of VGCF.

MgO films and YBa2Cu3O7−δ/MgO multilayer films were developed with the pulsed organometallic beam epitaxy (POMBE) growth technique, and grain boundary junctions were fabricated from the films to demonstrate the utility of the multilayers. High-quality MgO films were grown on LaAlO3 substrates by POMBE using a Mg(dpm)2 precursor. MgO crystallinity, as assessed by x-ray diffraction rocking curves, improved with the use of CuOx or YBa2Cu3O7−δ buffer layers. YBa2Cu3O7−δ films grown on the MgO layer by POMBE exhibited a Tc0 of 83 K and a Jc (12 K) exceeding 106 A/cm2 for applied magnetic fields up to 3 × 104 G. Grain boundary junctions were formed by growing YBa2Cu3O7−δ on MgO films that had been pretreated with a simple sputtering technique. This sputtering induces a controlled, 45°grain boundary in subsequently deposited YBa2Cu3O7−δ films. The resulting boundary showed weak-link current-voltage behavior and an IcRn product of 52 μV at 10 K, demonstrating that sputter-induced grain boundary junctions are compatible with multilayer technology.

A rapid, pressureless infiltration technique for fabricating SiC-reinforced Al-Si composites is described. The infiltration can be performed by simply dipping a ceramic preform into a molten alloy in an open air environment. This method makes it possible to produce composites that contain a high volume fraction (80%) of a variety of ceramic reinforcements, including particulates and fibers. This technique has potential for low-cost and versatile production of SiC-Al-Si composites for many industrial applications, such as automobile components and electronic packaging.

YBa2Cu3C7−x (Y123) single crystals have been grown by the modified pulling method (Solute Rich Liquid Crystal Pulling method, SRL-CP). For further superconductor device application, it is important to establish a technique that enables us to produce larger Y123 single crystals consistently. We have investigated the relationship among the crystal size, the crystal rotation rate, the flow pattern in the melt, and the temperature at the crystal growth interface experimentally. Increase of the crystal diameter and/or the crystal rotation rate increased the strength of the forced convection in the melt, and as a result, the temperature at the crystal growth interface increased. This resulted in a reduction of the crystal growth rate. On the other hand, the forced convection should be kept high enough to prevent floating particles attaching to the growing crystal. Therefore, in order to grow a larger single crystal, it was necessary to control the crystal rotation rate according to the change of the crystal diameter with time. We succeeded in crystal pulling along the c-axis of a relatively large Y123 single crystal which was 17 mm × 17 mm and 8 mm in length.