Boron carbide coating to improve the chemical stability of nm-thick graphite films

Abstract

Boron carbide is widely used as a coating material for wear resistance, neutron detection, and plasma facing in a tokamak nuclear reactor. We deposited boron carbide thin films on a Si substrate using magnetron sputtering at temperatures ranging from room temperature to 900 °C. When grown at temperatures higher than 700 °C, the boron carbide films showed significantly improved resistance to hydrogen plasma, comparable to that of highly oriented pyrolytic graphite. We investigated the origin of the improved hydrogen plasma resistance with X-ray diffraction, X-ray photoelectron spectroscopy, and high-resolution transmission electron microscopy. As the increase of deposited temperature, boron carbide films showed an amorphous phase and increase of B-C bond ratio. We annealed the boron carbide film deposited at room temperature for crystallization at 1,000 °C and 1,050 °C in an Ar atmosphere. The annealed boron carbide films still remained in the amorphous phase.