Yoshimitsu Tajima

Rechargeable lithium battery based on pyrolytic carbon as a negative electrode

Abstract We have developed a new type of rechargeable lithium battery composed of a pyrolytic carbon as negative electrode, a metal oxide as positive electrode, and a nonaqueous electrolytic solution. The main feature of this battery is the use of a new pyrolytic carbon, obtained by chemical vapor deposition of hydrocarbon, as a lithium intercalation electrode. The pyrolytic carbon has a layered structure whose interplanar spacing is larger than that of graphite. The size of the crystallites is extremely small. Lithium can be electrochemically intercalated into this carbon electrode in a nonaqueous electrolytic solution such as LiClO 4 in propylene carbonate at room temperature. The electrode shows good reversibility and its coulombic efficiency is greater than 99%. The battery has a long cycle life and endures deep discharge.

Effect of the junction interface properties on blue emission of SiC blue LEDs grown by step-controlled CVD

Abstract 6H-SiC blue LEDs were successively fabricated on off-axis (0001) substrates by step-controlled CVD at 1500°C using SiH 4 and C 3 H 8 . LEDs on the (0001)Si face showed dominantly a pure-blue 455 nm peak corresponding to the cathodoluminescence (CL) of the p-layer, while those on the (000 1 )C face showed mainly a purple-blue 425 nm peak corresponding to the CL of the n-layer. Considering the carrier concentrations of the LEDs, electrons are expected to be injected into the p-layer and to recombine with holes in the p-layer. The effect of a thin interface layer between the n-layer and the p-layer is supposed for the (000 1 )C face, but the effect disappeared by continuous electrical driving of the LEDs and the spectra became similar to those for the (0001)Si face. Atomic disorder of the SiC layer and/or doped impurities at the junction interface probably cause the interface layer.

Bulk Growth of Single-Crystal Cubic Silicon Carbide by Vacuum Sublimation Method

Bulk single crystals of cubic silicon carbide up to 4 mm in length have been obtained by means of the modified sublimation method. Growth temperature and pressure were examined in order to increase the growth rate. The temperatures of seed crystal and source material and the temperature gradient were 1750°C, 2250°C and 100°Ccm-1, respectively. The pressure was ~10-2 Pa. The growth rate obtained was 0.8 mmh-1, which is one order of magnitude larger than previously reported values. Raman spectroscopy, reflectoin high-energy electron diffraction analysis and molten KOH etching show that bulk crystals grown on 6H(0001) and 3C(111) seed crystals were 3C(111) single crystals. The crystal on the 6H(0001) showed no double positioning boundaries.