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VA: Fachverband Vakuumphysik und Vakuumtechnik

VA 2: Desorption mechanisms and vacuum generation

VA 2.1: Hauptvortrag

Montag, 26. März 2007, 11:15–12:00, H9

Outgassing behaviour, morphology and surface composition of vacuum fired stainless steel — •Manfred Leisch — Institute of Solid State Physics, Graz University of Technology, Graz, Austria

Stainless steel is one of the most used construction materials in vacuum technology. In order to reduce the outgassing of hydrogen from this material a high temperature treatment (vacuum firing) is a common used method especially in XHV applications. There is a considerable body of experimental studies on outgassing of hydrogen from stainless steel and basically two models have been presented: the diffusion limited model and the recombination limited model. Since the recombination process is strongly related to surface morphology and composition, surface characterization has been performed by atomic force microscopy (AFM), scanning tunneling microscopy (STM) and composition has been studied by atom probe depth profiling analysis. After vacuum firing a significant change in surface morphology is found by AFM and STM with respect to the original surface. The high temperature treatment leads to a complete reconstruction of the surface with wide closed packed terraces, atomic steps and facets formed by bunched steps. The atom probe depth profiling analysis results in a noticeable enrichment on Ni in the topmost layer, whereas Cr is found enriched in the second atomic layer. These experimental results are in a close relation to the recombination mechanism of hydrogen. The results will generally be discussion within the present picture of outgassing of stainless steel.

Supported by Zukunftsfonds des Landes Steiermark P 119