4 research outputs found
Surface concentration dependent structures of iodine on Pd(110)
We use photoelectron spectroscopy, low energy electron diffraction, scanning tunneling microscopy, and density functional theory to investigate coverage dependent iodine structures on Pd(110). At 0.5 ML (monolayer), a c(2 × 2) structure is formed with iodine occupying the four-fold hollow site. At increasing coverage, the iodine layer compresses into a quasi-hexagonal structure at 2/3 ML, with iodine occupying both hollow and long bridge positions. There is a substantial difference in electronic structure between these two iodine sites, with a higher electron density on the bridge bonded iodine. In addition, numerous positively charged iodine near vacancies are found along the domain walls. These different electronic structures will have an impact on the chemical properties of these iodine atoms within the layer
Role of Defects in Surface Chemistry on Cu<sub>2</sub>O(111)
High-resolution photoemission spectroscopy
and scanning tunneling
microscopy (STM) have been used to investigate defects on Cu<sub>2</sub>O(111) and their interaction with water and sulfur dioxide (SO<sub>2</sub>). 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<sub>2</sub> surface chemistry. Multiply
coordinatively unsaturated oxygen anions (O<sub>MCUS</sub>) such as
oxygen anions adjacent to copper vacancies are believed to be adsorption
sites for both water and SO<sub>2</sub> 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<sub>2</sub> interacts with oxygen sites at the surface forming
SO<sub>3</sub> species. However, thermal treatment up to 280 K of
Cu<sub>2</sub>O(111)/SO<sub>2</sub> prepared at 150 K renders only
SO<sub>4</sub> on the surface