We have shown that titanium nitride ͑TiN͒ coating by activated reactive evaporation using the hollow cathode discharge method is a good surface treatment for stainless steel used in extremely high vacuum ͑XHV͒ applications. The TiN film blocks hydrogen diffusion because it has a much lower hydrogen permeation coefficient than stainless steel. By varying the coating and film parameters ͑e.g., thickness, composition, and substrate bias voltage V b ͒ the barrier effects on hydrogen permeation of the TiN films were evaluated using small membrane samples. The parameters were varied to optimize the properties of the TiN coating for vacuum materials. The structure of the TiN films was analyzed by an x-ray diffractometry and transmission electron microscopy to clarify the dependence of the barrier effect on the film structure. Stoichiometric TiN films with few defects were shown to have high barrier effects. To demonstrate the use of TiN coatings for XHV applications, the outgassing rates of a stainless steel chamber with and without a TiN film were measured by a modified throughput type apparatus that had a bakeable cryopump for obtaining XHV. The outgassing rates for the chambers were measured using a method which completely eliminated the outgassing contribution of the vacuum gauges. The nitrogen equivalent outgassing rates of the stainless steel chamber with and without a TiN film were 7ϫ10 Ϫ12 and 9.7ϫ10 Ϫ10 Pa m s Ϫ1 , respectively.

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