<研究ノート>低エネルギー水素イオンを用いて水素化された二酸化チタンの水素分布と電子状態

Abstract

Hydrogenation of TiO₂ enhances its visible photoabsorption, leading to efficient photocatalytic activity. However, the role of hydrogen has not been fully understood. I introduce recent our studies on the hydrogenation of the rutile TiO₂ (110) surfaces and the anatase TiO2 (101) surfaces. On the rutile TiO₂ (110) surfaces, an ingap state (IGS) was formed at ~ 0.8 eV below the Fermi level, and the bands were downward bent by 0.5 eV with hydrogen irradiation. The H depth profile showed a maximum at about 1 nm, extending to ~ 30 nm with an average concentration of 5.6 at. %. On the anatase TiO₂ (101) surfaces, hydrogen irradiation induces an in-gap state 1-1.6 eV below the Fermi level and a downward band bending of 0.27 eV. The H depth profile at 300 K shows a surface peak with little concentration in a deeper region. At 200 K, on the other hand, the H depth profile shows a maximum at about 1 nm below the surface along with a broad distribution extending to 50 nm. These results show that H diffusion in anatase TiO₂ is much faster than in rutile TiO2