Katsuaki Suganuma

Boron Nitride Nanocage Clusters, Nanotubes, Nanohorns, Nanoparticles, and Nanocapsules

Various types of boron nitride (BN) nanostructured materials such as nanocage clusters, nanotubes, nanohorns, nanoparticles, and nanocapsules were synthesized by arc melting, thermal annealing, and chemical vapor deposition methods, which were characterized by high-resolution electron microscopy and molecular orbital calculations, and their properties were discussed. The BN clusters consisted of 4-, 6-, 8- and 10-membered BN rings satisfying the isolated tetragonal rule, which was optimized by molecular orbital calculations. Total energy calculation showed that some elements stabilize and expand the B36N36 structure. Bandgap energies of the B36N36 clusters were found to be reduced by introducing a metal atom inside the cluster, which indicates controllability of the energy gap. Chiralities of BN nanotubes with zigzag- and armchair-type structures were directly determined from high-resolution images, and structure models are proposed. Total energies of BN nanotubes with a zigzag-type structure were lower than those of armchair-type structure, and these results agreed well with the experimental data. Cup-stacked BN nanotubes and Fe-filled BN nanotubes were also produced, and the atomic structures, structural stability, and electronic property were investigated and discussed. BN nanohorns were synthesized, and multiwalled BN nanohorns would be stabilized by stacking of BN nanohorns. Formation and structures of multiply twinned nanoparticles with fivefold symmetry in chemical vapor-deposited BN were also investigated. A new process for Fe or Co nanoparticles coated with BN layers in large quantity was developed, and they exhibited a soft magnetic characteristic and good oxidation resistances. These unique structures would be suitable materials for nanoelectronics devices, magnetic recording media, and biological sensors with excellent protection against oxidation and wear. Possibility of hydrogen gas storage in BN clusters was also investigated by molecular orbital calculations, which indicated possibility of hydrogen storage of ~5 wt%. The new BN nanostructured materials would be expected as future nanocale devices.

Thermal conductivity of isotropic conductive adhesives composed of an epoxy-based binder

The thermal conductivity of a practical isotropic conductive adhesive (ICA) comprising of an epoxy-based binder containing flake-shaped and spherical Ag particles has been studied. The specimens exhibit anisotropy in their thermal conductivities. In addition, their thermal conductivities apparently depend on their thermal history during the curing and subsequent annealing processes, even if they are fully cured. Analysis using the Wiedemann-Franz rule indicates that their thermal conductivities increase with increasing contribution from electrical conduction. Curing and annealing conditions that induce a large shrinkage of the adhesive binder lead to decreased electrical resistivity and increased thermal conductivity, because the contacts between the filler particles are enhanced, therefore causing a decrease any interfacial resistances. In order to analyze the thermal conductivity of advanced conductive adhesives, a novel analytical method that includes a reasonable definition of the state of the percolation networks that are formed by the filler particles needs to be developed