Papers by Author: Naoto Koshizaki

Abstract: In this study, we present our recent work on microplasma synthesis in liquid (or liquid solution) and supercritical fluid (SCF) for carbon nanostructured materials. For microplasma synthesis in liquid (or liquid solution), we easily fabricated graphites, carbon nano-onions, carbon nanotubes (CNTs) and distinctive self-organized carbon nanostructures. On the other hand, for microplasma synthesis in supercritical CO2 (scCO2), carbon nanostructured materials, such as CNTs and carbon nanopolyhedrons, were synthesized with the arc plasma using sc CO2 as a processing medium and raw starting material. Additionally, we showed the film deposition of carbon nanostructured materials by using a dielectric barrier discharge under scCO2 environments.

Abstract: Amorphous/pseudoamorphous GaN was prepared by pulsed-laser ablation at room temperature without any heat treatment. The structure and chemical composition of the specimens were systematically investigated. Laser ablation at low Ar pressure (<50Pa) led to deposition of smooth Ga-rich films, which is independent with laser energy. Under same pressures, as laser energy increased, the film stoichiometry changed from Ga-rich to near stoichiometric composition. Varying background Ar pressure strongly affected the product structure showing little effect on the chemical composition. Under higher pressure than 100 Pa, fine nanoparticles with a size of 5 nm rather than films were deposited on substrate due to the increased collision by plume confining. The optical band-gap of the deposited a-GaN is 2.8 eV for thin films and 3.9 eV for nanoparticles.