A kinetic model for the removal of sulfur from polycrystalline titanium surfaces exposed to oxygen
R. Reibel, S. Schneider, H. Cruguel, J. Lapeyre, R. J. Smith
Department of Physics, Montana State University, Bozeman, Montana 59717*


Recent studies using Auger Electron Spectroscopy (AES) on polycrystalline titanium surfaces led to the discovery of a temperature dependent phenomenon for the removal of sulfur using oxygen exposures.  It was seen that at temperatures greater than 200 C and pressures lower than 10^-7 Torr O2 the rate of sulfur removal from the surface was decreased significantly.  The decrease in this rate of sulfur removal can be linked to several factors including the temperature-enhanced diffusion of sulfur to the surface and the temperature-enhanced diffusion of oxygen into the bulk.  By varying the pressure of oxygen and the temperature of the substrate and by monitoring the surface with Auger Electron Spectroscopy we were able to identify the significant factors.  A kinetic model for the two surface species is discussed and fit to the experimental results.  This kinetic model includes physical parameters for such things as the activation energy for the sulfur diffusion to the surface as well as sticking coefficients for oxygen on the surface.  Through this model the relevant factors for the decrease in the rate of sulfur removal are examined.

*Work supported by NSF Grant No. DMR-9710092 and NASA EPSCoR Grant NCCW-0058

Surface Review and Letters, Vol 6, No 5 (1999) 775-780

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