A kinetic model for the removal of sulfur from polycrystalline titanium surfaces exposed to oxygen

Recent studies using Auger Electron Spectroscopy (AES) on polycrystalline t itanium surfaces led to the discovery of a temperature-dependent phenomenon for the removal of sulfur using oxygen exposures. It was seen that at temp eratures greater than 200 degrees C and pressures lower than 10(-7) Torr O- 2 the rate of sulfur removal from the surface was decreased significantly. The decrease in this rate of sulfur removal can be linked to several factor s, including the temperature-enhanced diffusion of sulfur to the surface an d the temperature-enhanced diffusion of oxygen into the bulk. By varying th e pressure of oxygen and the temperature of the substrate and by monitoring the surface with AES we were able to identify the significant factors. A k inetic model for the two surface species is discussed and fit to the experi mental results. This kinetic model includes physical parameters for such th ings as the activation energy for the sulfur diffusion to the surface as we ll as sticking coefficients for oxygen on the surface. Through this model t he relevant factors for the decrease in the rate of sulfur removal are exam ined.