Study on the surface topology of vacuum-fired stainless steel by scanning tunnelling microscopy

The surface of 304L stainless steel, after normal bakeout and vacuum firing, has been imaged in the scanning tunnelling microscope (STM). Probe tips with sharp apexes and well-known reproducible geometry which were previously characterized in the field ion microscope (FIM) were used. After bakeout the STM surface profiles show on chemical polished surfaces an average roughness of 3–5 nm and over 300–500 nm variations in height of 30–50 nm. After vacuum firing a significant change of the surface structure and topology is observed. Crystallites with almost (1 1 1) orientation show wide (1 1 1) terraces with monoatomic steps. On tilted crystallites again wide (1 1 1) terraces, intersected with bunched steps and facets forming nearly regularly pattern and corresponding in orientation almost to the (1 0 0) and (1 1 0) planes can be observed. From the general appearance of the surface after vacuum firing it can be concluded that the surface became less active with respect to gas surface interaction which supports the present understanding of outgassing of this material.