We investigated the surface potential of TiOâ single crystals using scanning probe microscopy (SPM) under different gas environment. The SPM tip-induced electrical stress resulted in reversal in the surface potential, V{sub surf}, polarity only in Hâ/Ar (ÎV{sub surf} = 0.30 eV) and not in Ar and Oâ. Quantitative measurement of the influence of ambient gas on the surface potential led us to develop a model where the adsorbed oxygen molecules and oxygen vacancies interact to change their relative concentration leading to different surface potential in TiOâ. These results will give us insights into ambient-dependent physical phenomena in oxide thin film nanostructures.