Two-dimensional Electron Gas at Thiol/ZnO Interface

Abstract

Electronic modification of O-terminated ZnO(0001 _ ) and Znterminated ZnO(0001) by ethanethiol (C 2 H 5 SH) adsorption was investigated by angle-resolved photoelectron spectroscopy (ARPES) and X-ray photoelectron spectroscopy (XPS). Ethanethiol dissociates on both surfaces at room temperature to form C 2 H 5 S and H. The saturation coverage of ethanethiol is nearly three times larger on ZnO(0001) than on ZnO(0001 _ ). This suggests that Zn atoms exposed to the surface should act as adsorption and dissociation sites. Adsorption on the (0001 _ ) surface induces large downward band bending and accompanies a Zn 4s-derived metallic state at the center of the surface Brillouin zone. This proves that ethanethiol is a good electron donor on ZnO(0001 _ ). Contrastingly, ethanethiol on ZnO(0001) hardly affects the energetic position of the ZnO band so that surface metallization is not brought about.