Surface Characterization of Radio Frequency Water Plasma Treated and Annealed Polycrystalline Tin Oxide Thin Films

Angle-resolved X-ray photoelectron spectroscopy (AR-XPS) and electron energy loss spectroscopy (EELS) have been used to examine the consequences of the interaction of radio frequency water plasmas with polycrystalline tin oxide surfaces. Results from AR-XPS and EELS indicate that an extensive surface hydroxylation or “gel” layer (>10 Å) does not form on the tin oxide surface from exposure to atmosphere and/or water plasma treatment. Surface hydroxyl coverages determined by AR-XPS are a factor of 3 lower than those calculated from crystallographic models. Annealing of water plasma treated tin oxide films in ultrahigh vacuum results in the desorption of water, dehydroxylation of the surface, and creation of oxygen vacancies. AR-XPS data indicate a uniform concentration of oxygen vacancies over a sampling depth of approximately 15 Å. Water plasma treatment of oxygen-deficient tin oxide surfaces created by annealing in ultrahigh vacuum eliminates oxygen vacancies and restores Sn⁴⁺ valency in the surface region.