Absence of midgap states due to excess electrons donated by adsorbed hydrogen on the anatase TiO(101) surface

Nagatsuka, Naoki*; Fukutani, Katsuyuki; 2 of others*

Hydrogen is involved in various important chemical processes on metal-oxide surfaces. Due to its electron-donating character, hydrogen tends to form polaronic states, where the electron is spatially separated from the proton, which exerts significant impact on the electronic properties of metal-oxide surfaces. By individually probing the proton with nuclear reaction analysis and the electron with ultraviolet photoelectron spectroscopy and in combination with density functional theory calculations, we clarify the electronic state of hydrogen on the anatase TiO(101) surface. Hydrogen is found to adsorb with a saturation coverage of 0.480.12 monolayers, donating an excess electron to the substrate without forming a midgap state, which is in contrast to the behavior of oxygen vacancies.