Photoinduced Surface Oxygen Vacancies and Effect of Methanol on the Charge Carrier Dynamics in TiO₂

The migration of holes in metal oxides such as TiO₂ plays a vital role in (photo)catalytic applications. The dynamics of charge carriers under operation conditions can be influenced by both methanol addition and photoinduced surface oxygen vacancies (PI-SOVs) [1]. Nevertheless, the existing knowledge of the effect of methanol as a function of PI-SOVs solely concentrates on the chemical reduction process. For this reason, the fundamental understanding of the time-dependent charge carrier-vacancy interactions with the presence of methanol is impaired. To overcome this challenge, we performed time-resolved atomic force microscopy measurements to quantitatively disclose the dynamics of charge carriers in a rutile-terminated, single-crystal TiO₂ (100) sample under the influence of methanol as a function of high-energy ultraviolet (UV) surface irradiation [2-4]. We have three major experimental findings: (I) The addition of methanol decreased the time constant, and hence, the mobility of the charge carriers. (II) The energy barrier within the system was decreased by UV irradiation; however, the presence of methanol did not alter the corresponding barrier. (III) The reversibility of the charge carrier dynamics was observed upon the termination of UV irradiation. Our analysis of methanol's role in hole mobility as a function of surface irradiation contributes to the understanding of surface interactions and charge carrier dynamics, offering valuable insights for (photo)catalytic applications.

[1] Orcun Dincer, Bugrahan Guner, and Omur E. Dagdeviren, APL Materials 12 (2) (2024).
[2] Bugrahan Guner, Simon Laflamme, and Omur E. Dagdeviren, Review of Scientific Instruments 94 (6) (2023).
[3] Bugrahan Guner and Omur E. Dagdeviren, ACS Applied Electronic Materials 4 (8), 4085 (2022).
[4] Bugrahan Guner, Orcun Dincer, and Omur E. Dagdeviren, ACS Applied Energy Materials 7 (6), 2292 (2024).

Funding information:
This work was supported by the Canada Economic Development Fund, Natural Sciences and Engineering Research Council of Canada, and Le Fonds de Recherche du Québec - Nature et Technologies.