Scanning Tunneling Microscopy Visualization of Polaron Charge Trapping by Hydroxyls on TiO 2 (110).

Using scanning tunneling microscopy (STM), we investigate the spatial distribution of the bridging hydroxyl (OH b ) bound excess electrons on the rutile TiO 2 (110) surface and its temperature dependence. By performing simultaneously recorded empty and filled state imaging on single OH b s at different temperatures in STM, we determine that the spatial distribution of the OH b bound excess electrons retains a symmetric four-lobe structure around the OH b at both 78 and 7 K. This indicates that OH b s are much weaker charge traps compared to bridging O vacancies (O b -vac). In addition, by sequentially removing the capping H of each OH b using voltage pulses, we find that the annihilation of each OH b is accompanied by the disappearance of some lobes in the filled state STM, thus verifying the direct correlation between OH b s and their excess electrons.