Performance of carbon as vacuum material and its degassing rate

An ideal surface with a low degassing rate must be low in attachment coefficient, activation energy for desorption, solubility, diffusion coefficient, and surface roughness coefficient. In the present work, carbon is selected as material that meet these requirements. In particular, it focuses on steel coated with carbon by the ECR plasma technique since pure carbon is not suitable as structural material. A permanent magnetic is employed to produce a resonant magnetic field, and the degassing rate is measured before and after the treatment. In addition, measurements are made of the activation energy for the desorption of water vapor from steel and carbon. Results demonstrate that a large steel surface can be coated satisfactorily with carbon by the ECR plasma technique using a permanent magnet. Steel surface and carbon film are exposed to steam, and the change in degassing rate is measured for 24 hours. The degassing rate is found to be largely decreased by the treatment. The ratio of the degassing rate of the carbon film to that of the steel is about 1/70 in 5 min and 1/5 in 60 min, respectively. The activation energy of desorption for graphite is significantly smaller than that for steel. (N.K.)