Scanning Tunneling Microscopy Visualization of Polaron Charge Trapping by Hydroxyls on TiO₂(110)

Using scanning tunneling microscopy (STM), we investigate the spatial distribution of the bridging hydroxyl (OH_b) bound excess electrons on the rutile TiO₂(110) surface and its temperature dependence. By performing simultaneously recorded empty and filled state imaging on single OH_bs 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_bs 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_bs and their excess electrons.