Band gap modulation of SrTiO upon CO adsorption.

Herein, CO chemisorption on SrTiO(001) surfaces is studied using ab initio calculations to establish new chemical sensing mechanisms. It was found that CO adsorption opens the band gap of the material. However, the mechanisms are different: the CO adsorption on the TiO-terminated surface neutralizes the surface states at the valence band (VB) maximum, whereas for the SrO-terminated surface it suppresses the conduction band (CB) minimum. For the TiO-terminated surface, the effect is explained by the passivation of dangling bonds, whereas for the SrO-terminated surface, the suppression is caused by surface relaxation. Modulation of the VB states implies a more direct change in charge distribution, and thus, the induced change in the band gap is more prominent at the TiO termination. Further, it has been shown that both CO adsorption energy and surface band gap are strongly dependent on CO coverage, suggesting that the observed effect can be utilized in sensing applications for a wide range of CO concentrations.