Scientific measurements and industrial processes that require an ultra-clean environment are often performed in vacuum chambers. These are metal vessels where all of the air has been pumped out. Stainless steel is one of the most commonly used structural materials for vacuum equipment. If extremely high vacuum (XHV) is to be achieved, a reduction of the outgassing rates of the materials used in the construction of the vacuum system is essential. A high-temperature vacuum firing has become a widely accepted practice of reducing the amount of hydrogen dissolved in stainless steel. Evidence suggests that the hydrogen outgassing rate is limited by the surface recombination. It is well established that the rate of recombination depends strongly on the atomic structure of the surface. In this experiment a scanning tunneling microscope was used to determine the restructuring of the surface during vacuum firing.

A. Stupnik and M. Leisch, Study on the surface topology of vacuum-fired stainless steel by scanning tunnelling microscopy, Vol 81, pp. 748-751 (2007).