Static SIMS and XPS study of water plasma exposed tin oxide films

Static secondary ion mass spectrometry (SIMS) and X-ray photoelectron spectroscopy (XPS) were used to examine sputter-deposited tin oxide surfaces that were air-exposed, treated in a low-power water plasma, and annealed to 825 K in vacuum. The plasma reactor was appended directly to the surface analytical system, thus sample exposure to atmosphere was avoided. Water plasma treatment of the air-exposed films results in the removal of all XPS detectable carbon contamination while leaving the surface in hydrated and hydroxylated state. The static SIMS results coupled with XPS O(1s) data indicate that H^-, OH^-, H₂O⁺, and SnOH⁺ secondary ion intensities are sensitive to the concentration of surface hydroxyl groups and water. SnOH⁺ yields are shown to be enhanced by the presence of molecularly adsorbed water, suggesting that water is directly involved in the formation of SnOH⁺ species. Annealing of water plasma treated tin oxide films in vacuum results in the loss of molecularly adsorbed water and surface dehydroxylation. The secondary ion ratios of H^-/O^-, OH^-/ O^-, H₂O⁺/Sn⁺, and SnOH⁺/Sn⁺ can be used to monitor the thermally induced dehydration and dehydroxylation of the tin oxide surface. In addition, changes in the oxide surface the thermally induced dehydration and dehydroxylation of the tin oxide surface. In addition, changes in the tin oxide surface electronic structure are shown to strongly modulate both relative and absolute ion yields.