Chemically Tunable Apparent Effective Hole-Migration Barriers on TiO2(111)

Abstract

Charge migration in metal-oxide semiconductors is often described by thermally activated transport; however, reactive surfaces can reorganize carrier motion through facet- and stoichiometry-dependent defects and adsorbate interactions. Here, we use time-resolved atomic force microscopy to resolve hole-migration dynamics on rutile TiO2(111) under temperature variation, high-energy ultraviolet (UVC) irradiation, and alcohol exposure. Pristine TiO2(111) exhibits a negative apparent effective migration barrier, consistent with a mobility-controlled, defect-coupled regime rather than conventional thermally activated hopping. UVC irradiation modifies the apparent barrier, coherant with a reorganization of the carrier-migration landscape that may involve UVC-induced surface defects. Alcohol adsorption makes the response to UVC chemically selective: ethanol produces a comparatively small change in the apparent barrier, whereas methanol causes a pronounced shift toward more negative values under irradiation. Our measurements show that ethanol and methanol produce distinct modifications of hole-migration dynamics on TiO2(111). More broadly, these results demonstrate that TiO2 charge migration can be chemically tuned at the surface through facet selection, irradiation, and adsorbate chemistry.