Fast Timescale Effects of Photoinduced Surface Oxygen Vacancies on the Charge Carrier Dynamics of TiO₂

Defects determine the electronic properties of materials (e.g., metal oxide semiconductors) by altering charge carrier dynamics [1,2]. Experimental identification of such defect states under realistic conditions (e.g., ambient conditions) at governing time scales is particularly challenging due to low concentrations of surface oxygen vacancies (V_O) and their high reactivity. Here we present the effect of photoinduced surface V_O on fast charge carriers (e.g., electrons) via time-resolved atomic force microscopy (TR-AFM) measurements. We performed our TR-AFM measurements on gold-nanoparticle (Au-NP) deposited titanium dioxide (TiO₂), as it is widely used in industrial applications. Our measurements clearly show that the photoinduced surface V_O results in a slower movement of charge carriers at the Au-NP, TiO₂ interface. We believe that the slower movement of charge carriers is due to the increase in surface defects. Our results express the important effect of V_O on fast charge carriers, which underlines the need for further studies of defects under realistic conditions.

[1] Dagdeviren, O. E. et al., Nano Letters 20, 7530-7535, (2020).

[2] Dagdeviren, O. E. et al., Nano Letters 21, 8348-8354, (2021).