[1Da01-09] Surface Science(SS1) Physical Property

[1Da06] Electronic Structure and Conductivity Modifications of Rutile TiO₂(100) by Hydrogen Ion Irradiation

*Muhammad Irfandi¹, Takahiro Ozawa¹, GyeongCheol Lim², Mitsuhiko Maesato², Katsuyuki Fukutani^1,3 (1. Institute of Industrial Science, The University of Tokyo, 2. Division of Chemistry, Graduate School of Science, Kyoto University, 3. Advanced Science Research Center, Japan Atomic Energy Agency)

TiO₂ has promising applications in solar conversion and hydrogen storage. Hydrogen doping is reported to reduce the TiO₂ band gap to 1.54 eV. However, the interaction between hydrogen and TiO₂ requires further investigations in the aspects of electrical conductivity and electronic properties. The experimental investigation was conducted by means of simultaneous in-situ electrical conductivity and x-ray/ultraviolet photoelectron spectroscopy (XPS/UPS) in the ultrahigh vacuum environment. We employed hydrogen ion irradiation to achieve a high doping concentration of hydrogen in TiO₂(100). The results show that hydrogen ion irradiation at 295 K increases the TiO₂ conductivity and increases the formation of Ti³⁺ chemical state. The donated electron from hydrogen to TiO₂ induces an in-gap state (IGS) at 1 eV below Fermi level which acts as a small polaron center. In contrast, the hydrogen ion irradiation at 125 K decreases the TiO₂ conductivity but increases the Ti³⁺ chemical state. The low-temperature irradiation induces an in-gap state at 1.3 eV below Fermi level, which is suggested to be a non-conducting state.