Role of Defects in Surface Chemistry on Cu₂O(111)

High-resolution photoemission spectroscopy and scanning tunneling microscopy (STM) have been used to investigate defects on Cu 2 O(111) and their interaction with water and sulfur dioxide (SO 2 ). Two types of point defects, i.e., oxygen and copper vacancies, are identified. Copper vacancies are believed to be the most important defects in both water and SO 2 surface chemistry. Multiply coordinatively unsaturated oxygen anions (O MCUS ) such as oxygen anions adjacent to copper vacancies are believed to be adsorption sites for both water and SO 2 reaction products. Water adsorption at 150 K results in both molecular and dissociated water. Molecular water leaves the surface at 180 K. At 300 K and even more at 150 K, SO 2 interacts with oxygen sites at the surface forming SO 3 species. However, thermal treatment up to 280 K of Cu 2 O(111)/SO 2 prepared at 150 K renders only SO 4 on the surface.