Diffusion, coalescence, and reconstruction of vacancy defects in graphene layers are investigated by tight-binding molecular dynamics (TBMD) simulations and by first principles total energy calculations. It is observed in the TBMD simulations that two single vacancies coalesce into a 5-8-5 double vacancy at the temperature of 3000 K, and it is further reconstructed into a new defect structure, the 555-777 defect, by the Stone-Wales type transformation at higher temperatures. First principles calculations confirm that the 555-777 defect is energetically much more stable than two separated single vacancies, and the energy of the 555-777 defect is also slightly lower than that of the 5-8-5 double vacancy. In TBMD simulation, it is also found that the four single vacancies reconstruct into two collective 555-777 defects which is the unit for the hexagonal haeckelite structure proposed by Terrones et al. [Phys. Rev. Lett. 84, 1716 (2000)].

The interface atomic structure was proposed to have a critical effect on the microstructure evolution during sintering of ceramic materials. In liquid-phase sintering, spherical grains show the normal grain growth behavior without exception, while angular grains often grow abnormally. The coarsening process of spherical grains with a disordered or rough interface atomic structure is diffusion-controlled, because there is little energy barrier for atomic attachments. On the other hand, kink-generating sources such as screw dislocations or two-dimensional (2-D) nuclei are required for angular grains having an ordered or singular interface structure. Coarsening of angular grains based on 2-D nucleation mechanism could explain the abnormal grain growth behavior. It was also proposed that densification process is closely related to the interface atomic structure. Enhanced densification by carefully chosen additives during solid state sintering was explained in terms of the grain boundary structural transition from an ordered to a disordered open structure.

A cauliflower structure is a granular film composed of spherical particles similar in size, each with numerous nanoscale nodules on its surface. The structure is produced during certain chemical vapour deposition (CVD) processes for diamond and silicon thin film growth. A classical account in terms of atomic unit deposition fails to explain the growth of such a cauliflower structure, as it requires a gas phase of much higher supersaturation than for onset of diffusion controlled growth. Another interesting and somewhat puzzling phenomenon encountered during a diamond CVD process is that while diamond is depositing on a graphite substrate, carbon atoms in the graphite itself are etched away into the vapour phase; that is, experience evaporation. Again, an elementary kinetic barrier mechanism fails to explain such CVD deposition of a less stable diamond phase combined with simultaneous evaporation of a stable graphite phase. In order to account for such puzzling CVD phenomena and others, a theory of charged clusters has been developed over the past decade as a new paradigm for thin film growth. The theory and its applications are reviewed in this work.

This paper proposes an optimal design method in an asymmetric wireless power transfer (WPT) system for a 150 watt LED TV. The WPT system has three self-resonators: a Tx resonator, an Rx resonator, and an intermediate resonator. The Tx and Rx resonators are perpendicular and offset, respectively, to the intermediate resonator in the geometry. For optimal design, the WPT system is analyzed using an equivalent circuit. In particular, a calculation method for mutual inductance in the system is expressed. The calculation results of mutual inductance are used to determine the optimal position of each self-resonator for maximizing the power transfer efficiency. For verification, a WPT system for a 150 watt, 47 inch LED TV is fabricated at 250 kHz. The WPT system exhibits wireless power transfer efficiency of 80%. 1

This paper presents wireless power transfer (WPT) characteristics according to load variation in multidevice WPT systems using capacitive impedance matching networks (IMNs). Two basis IMNs of using series-parallel (SP) capacitors and parallel-series (PS) capacitors are used. Four combinations of capacitive IMNs are considered, i.e., SP in a transmitting side and SP in a receiving (Rx) side (SP-SP), SP-PS, PS-SP, and PS-PS. The optimum capacitance values for each IMN are also derived by circuit analysis. For verification, three cases based on the number of Rx coils are considered, and the calculated results are compared with the simulated and measured results for each case. A WPT system for only a single device has identical power transfer efficiency for four combinations of the IMNs. Multidevice WPT systems with the PS IMN in Rx sides are found to transfer more power toward the Rx coil with lower load impedance according to the load variation. On the other hand, using the SP IMN in Rx sides is less sensitive to load variation than using the PS IMN. In addition, a WPT system using the PS-PS IMN combination is less responsive to the cross coupling between Rx coils than that using the SP-SP IMN combination.

Alumina specimens with small amounts of CaO and TiO 2 were prepared and their microstructural evolution during sintering was investigated. Because of the appearance of a liquid phase during sintering, a duplex microstructure of a few abnormal grains and fine matrix grains was obtained when the CaO ؉ TiO 2 content was small (<0.04 wt%). When the CaO ؉ TiO 2 content was relatively high (>0.1 wt%), many grains grew and impinged upon each other. As a result, a rather uniform and homogeneous microstructure was observed.

The equilibrium shape of internal cavities in sapphire wasIn principle, there are two ways to form equilibrium shaped determined through the study of submicrometer internal crystals. ‡ One is to heat small crystals in a closed system at cavities in single crystals. Cavities formed from indentation high temperatures so that transport processes are rapid. This cracks during annealing at 1600؇C. Equilibrium could be technique is difficult because of the necessity of controlling the reached only for cavities that were smaller than 100 nm.external environment to prevent a volume change of the crystal Excessive times were required to achieve equilibrium for by evaporation, corrosion, or condensation. The second method cavities larger than 1 m. Five equilibrium facet planes is to use internal cavities, which are, in effect, "negative" cryswere observed to bound the cavities: the basal (C) {0001}, tals that, if lattice diffusion is very slow, are shapes of constant rhombohedral (R) {1012}, prismatic (A) {1210}, pyramivolume in contact with a fixed atmosphere. For the latter case, dal (P) {1123}, and structural rhombohedral (S) {1011}.the conditions of fixed volume in contact with its vapor are The surface energies for these planes relative to the surface easier to maintain than for the former case. The deviation of a energy of the basal plane were ␥ R ‫؍‬ 1.05, ␥ A ‫؍‬ 1.12, ␥ P ‫؍‬ crystal's shape from its Wulff shape at any time depends on the 1.06, ␥ S ‫؍‬ 1.07. These energies were compared with the starting shape and size of the crystal and the rates of kinetic most recent theoretical calculations of the surface energy processes that change its shape. If we want annealing times of sapphire. The comparison was not within experimental to be on the order of days, not years, crystals/cavities must be scatter for any of the surfaces, with the measured relative small, less and 1 m for many materials and annealing condisurface energies being lower than the calculated energies.tions, in order to minimize diffusion distances. The relationship Although the prismatic (M) {1010} planes are predicted between initial shape and size of the cavity and the kinetics of to be a low-energy surface, facets of this orientation were shape change has been discussed in Refs. 4 and 5 and is disnot observed.cussed in detail below. Internal cavities produced during sintering have been used to determine relative surface energies by Nelson et al. 6 for copper I. Introduction and aluminum and by Müller 7 for NaCl. Powell-Dogan and Heuer 8 noted the presence of facetted cavities in commercial A T EQUILIBRIUM, facetted crystals are bounded by flat, relagrades of vitreous bonded aluminum oxide and attempted to tively low energy crystallographic planes. For a given voldetermine the relative surface energies of the cavities using the ume, the total surface free energy of the crystal, ⌫, is given by result that ␥ i /ᐉ i ϭ constant. As a fivefold variation in relative the sum of the specific surface energies of the facets, weighted surface energy was obs...

SiC powder compacts were prepared with Al2O3, Y2O3, and CaO powders. By two‐step sintering, fully dense nanostructured SiC ceramics with a grain sizes of ∼40 nm were obtained. The grain size–density trajectories are compared with those of conventional sintering processes.