Applied Science and Convergence Technology 2014; 23(5): 201-210
Published online September 30, 2014
Copyright © The Korean Vacuum Society.
K. Takeyasua, K. Fukadaa, S. Oguraa, M. Matsumotob, and K. Fukutania*
aInstitute of Industrial Science, The University of Tokyo
bTokyo Gakugei University
Correspondence to:K. Fukutania*
The influence of electron irradiation and hydrogen adsorption on the electronic structure
of the SrTiO3 (001) surface was investigated by ultraviolet photoemission spectroscopy (UPS).
Upon electron irradiation of the surface, UPS revealed an electronic state within the band
gap (in-gap state: IGS) with the surface kept at 1×1. This is considered to originate from
oxygen vacancies at the topmost surface formed by electron-stimulated desorption of oxygen.
Electron irradiation also caused a downward shift of the valence band maximum indicating
downward band-bending and formation of a conductive layer on the surface. With oxygen
dosage on the electron-irradiated surface, on the other hand, the IGS intensity was decreased
along with upward band-bending, which points to disappearance of the conductive layer. The
results indicate that electron irradiation and oxygen dosage allow us to control the surface
electronic structure between semiconducting (nearly-vacancy free: NVF) and metallic (oxygen
de cient: OD) regimes by changing the density of the oxygen vacancy. When the NVF surface
was exposed to atomic hydrogen, in-gap states were induced along with downward band
bending. The hydrogen saturation coverage was evaluated to be 3.1±0.8×1014 cm−2 with
nuclear reaction analysis. From the IGS intensity and H coverage, we argue that H is positively
charged as H~0:3+ on the NVF surface. On the OD surface, on the other hand, the IGS intensity
due to oxygen vacancies was found to decrease to half the initial value with molecular
hydrogen dosage. H is expected to be negatively charged as H− on the OD surface by
occupying the oxygen vacancy site.
Keywords: Oxygen vacancy, SrTiO3, Hydrogen adsorption