Two charged states of hydrogen on the SrTiO3(001) surface

Abstract

The effects of hydrogen exposure on the electronic structure of two types of SrTiO3(001) surfaces, oxygen-deficient (OD) and nearly-vacancy-free (NVF) surfaces, were investigated with ultraviolet photoemission spectroscopy and nuclear reaction analysis. Upon molecular hydrogen exposure to the OD surface which reveals in-gap states at 1.3 eV below the Fermi level, the in-gap state intensity was reduced to half the initial value at a hydrogen coverage of 0.9 ± 0.7 × 10(14) cm(-2). On the NVF surface which has no in-gap state, on the other hand, atomic-hydrogen exposure induced in-gap states, and the hydrogen saturation coverage was evaluated to be 3.1 ± 0.8 × 10(14) cm(-2). We argue that H is positively charged as H(∼0.3 +) on the NVF surface by being coordinated to the O atom, whereas H is negatively charged as H(-) on the OD surface by occupying the oxygen vacancy site. The stability of H(-) at the oxygen vacancy site is discussed.

Electronic Structure of the SrTiO3(001) Surfaces: Effects of the Oxygen Vacancy and Hydrogen Adsorption

“…When the electron-irradiated surface was exposed Adapted with permission from [21]. to molecular oxygen, the IGS was found to decrease in intensity and eventually disappear at an oxygen exposure of ~2.5 L. This is because neutral oxygen is either dissociatively or molecularly adsorbed at the oxygen vacancy receiving electrons from the surface.…”

“…C nuclear reaction taken at room temperature for (a) the NVF SrTiO3(001) surface, (b) the NVF surface exposed to atomic H, and (c) the oxygen-de cient SrTiO3(001) surface exposed to H2. Adapted with permission from [21].…”

“…In the present article, we review our recent work on the electronic structure of the SrTiO3(001) surface investigated by ultraviolet photoemission spectroscopy (UPS) [20,21]. We first show that an in-gap state (IGS) appears within the band gap with electron irradi-ation, which is caused by oxygen vacancies.…”

Nuclear Dynamics and Electronic Effects of Hydrogen on Solid Surfaces

“…Simultaneously, the valence band maximum is lowered by 0.05 eV and the work function is lowered by 0.3 eV. With the atomic‐H exposure, furthermore, a small feature develops at − 10.5 eV due to the O−H bond implying that hydrogen is adsorbed on the oxygen atom ,,. As in case of the rutile TiO 2 (110) surface, these results indicate electron transfer from hydrogen to the surface.…”

“…As in case of the rutile TiO 2 (110) surface, these results indicate electron transfer from hydrogen to the surface. In contrast to TiO 2 (110), however, the conduction band minimum evaluated from the valence band maximum becomes lower than EF at a higher hydrogen dosage suggesting an insulator‐to‐metal transition of the surface ,,…”