Vacuum Properties of TiN/Stainless Steel for Extremely High Vacuum

Coating of titanium nitride TiN film on stainless steel by hollow cathode discharge method under the controlled conditions has been developed and could reduce outgassing rate at the extremely high vacuum due to the hydrogen barrier effect of TiN^1-3). This paper reports 1. further reduction of hydrogen permeation constant K of TiN film, 2. application of this technique to practical chamber preparation, and 3. reduction of outgassing rate of the resulting chamber. Hydrogen permeation constant of TiN films prepared by a laboratory equipment was decreased by improving the film structure to more dense and larger grains. The minimum hydrogen permeation constant K of TiN film at 500°C was 6 × 10^-13Pa^1/2·m²·s^-1. Considering the above result, the practical condition of manufactuaring equipment was adjusted to make large samples for new XHV chambers fabricated for standard pressure measurement by Electrotechnical Laboratory in Japan. The resulting outgassing rate of a TiN coated chamber was measured by switching between two pumping paths (SPP) method at room temperature. At the ultimate pressure the outgassing rates of the stainless steel chamber was 3 × 10^-12 Pa·m·s^-1 after the prebaking of (430°C × 100 h + 500°C × 100 h) and after TiN coating on the chamber it decreased to less than 1 × 10^-13 Pa·m·s^-1, the lowest value obtained for stainless steel.