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 Cu₂O­(111) and their interaction with water and sulfur dioxide (SO₂). 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 SO₂ 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 SO₂ 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, SO₂ interacts with oxygen sites at the surface forming SO₃ species. However, thermal treatment up to 280 K of Cu₂O­(111)/SO₂ prepared at 150 K renders only SO₄ on the surface

The Surface Structure of Cu₂O(100)

Despite the industrial importance of copper oxides, the nature of the (100) surface of Cu₂O has remained poorly understood. The surface has previously been subject to several theoretical and experimental studies, but has until now not been investigated by atomically resolved microscopy or high-resolution photoelectron spectroscopy. Here we determine the atomic structure and electronic properties of Cu₂O­(100) by a combination of multiple experimental techniques and simulations within the framework of density functional theory (DFT). Low-energy electron diffraction (LEED) and scanning tunneling microscopy (STM) characterized the three ordered surface structures found. From DFT calculations, the structures are found to be energetically ordered as (3,0;1,1), c(2 × 2), and (1 × 1) under ultrahigh vacuum conditions. Increased oxygen pressures induce the formation of an oxygen terminated (1 × 1) surface structure. The most common termination of Cu₂O­(100) has previously been described by a (3√2 × √2)­R45° unit cell exhibiting a LEED pattern with several missing spots. Through atomically resolved STM, we show that this structure instead is described by the matrix (3,0;1,1). Both simulated STM images and calculated photoemission core level shifts compare favorably with the experimental results