Distinct behavior of localized and delocalized carriers in anatase TiO2 (001) during reaction with O2

• Published in: Physical review materials 2020-02, Vol.4 (2)
• Main Authors: Bigi, Chiara, Tang, Zhenkun, Pierantozzi, Gian Marco, Orgiani, Pasquale, Das, Pranab Kumar, Fujii, Jun, Vobornik, Ivana, Pincelli, Tommaso, Troglia, Alessandro, Lee, Tien-Lin, Ciancio, Regina, Drazic, Goran, Verdini, Alberto, Regoutz, Anna, King, Phil D. C., Biswas, Deepnarayan, Rossi, Giorgio, Panaccione, Giancarlo, Selloni, Annabella
• Format: Article
• Language: English
• Subjects: MATERIALS SCIENCE
• ISSN: 2475-9953; 2475-9953
• DOI: 10.1103/PhysRevMaterials.4.025801

Two-dimensional (2D) metallic states induced by oxygen vacancies $(V_{O}\text{s})$ at oxide surfaces and interfaces provide opportunities for the development of advanced applications, but the ability to control the behavior of these states is still limited. As such, we used angle resolved photoelectron spectroscopy combined with density-functional theory (DFT) to study the reactivity of $V_O$-induced states at the (001) surface of anatase TiO2, where both 2D metallic and deeper lying in-gap states (IGs) are observed. The 2D and IG states exhibit remarkably different evolutions when the surface is exposed to molecular O2: while IGs are almost completely quenched, the metallic states are only weakly affected. DFT calculations indeed show that the IGs originate from surface $V_{O}\text{s}$ and remain localized at the surface, where they can promptly react with O2. In contrast, the metallic states originate from subsurface vacancies whose migration to the surface for recombination with O2 is kinetically hindered on anatase TiO2 (001), thus making them much less sensitive to oxygen dosing.