Identifying Hydroxyls on the TiO₂ (110)−1 × 1 Surface with Scanning Tunneling Microscopy

We present the investigations of hydroxylated TiO 2 (110)−1 × 1 surfaces using scanning tunneling microscopy (STM). It is observed that in topographic images the protrusions of hydroxyls (OH) on TiO 2 (110) surfaces are dependent on the tip−sample distance in STM measurements at room temperature. In comparison with those of the fivefold coordinated Ti atoms and the oxygen vacancies, the relative apparent height of OHs becomes smaller and smaller with decreasing tip−sample distance by changing the imaging conditions. The OHs even become invisible in much shorter tip−sample distances. Reversibly, the OHs are almost completely recovered when the imaging conditions are restored. It suggests that the OHs may be identified by varying the imaging conditions in STM measurement.