Measurements of Bulk Concentration in the ppm-Region by Means of Surface Segregation: The System Sulphur-Nickel
During heat treatment of metals, surface segregation of solute atoms is quite frequently observed. Even impurities that are only present in minute concentrations can build up to large surface concentrations. This type of process is of great importance, especially in surface physics. The catalytic activity of the surface, the work function and other quantities strongly depend on the surface composition. One of the better known examples is the surface segregation of sulphur on otherwise “clean” nickel. Removal of the sulphur by chemical treatments or by ion bombardment is usually the first step in investigating nickel surfaces. Nevertheless, only very little information about the sulphur/nickel system can be found in the literature1,2. The main difficulty seems to be that there are no conventional methods able to determine reliably the bulk concentration of sulphur in nickel at the ppm-level. Our approach therefore will be to use the easily measurable surface concentration of sulphur to characterize the segregation behaviour.
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