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Hydrogenation and hydrogen diffusion at the anatase TiO$$_{2}$$(101) surface

長塚 直樹*; Wilde, M.*; 福谷 克之

Nagatsuka, Naoki*; Wilde, M.*; Fukutani, Katsuyuki

Hydrogenation of TiO$$_{2}$$ enhances its visible photoabsorption, leading to efficient photocatalytic activity. However, the role of hydrogen has not been fully understood. The anatase TiO$$_{2}$$(101) surface treated by hydrogen ion irradiation at 500 eV was investigated by photoemission spectroscopy and nuclear reaction analysis. 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 an H amount of (2.9$$pm$$0.3)$$times$$10$$^{15}$$ cm$$^{-2}$$ 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 corresponding to an H amount of (6.1$$pm$$0.3)$$times$$10$$^{15}$$ cm$$^{-2}$$ along with a broad distribution extending to 50 nm at an average concentration of 0.8 at. %. These results show that H diffusion in anatase TiO$$_{2}$$ is much faster than in rutile TiO$$_{2}$$ [Y. Ohashi, J. Phys. Chem. C 123, 10319-10324 (2019)]. The H diffusion coefficient at 200 K is determined to be 2.7$$pm$$0.1$$times$$10$$^{-13}$$ m$$^{2}$$ s$$^{-1}$$.

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