Iodine adsorption on the Ag(110) surface: Uniaxial compression and iodide growth

Adsorption of iodine on Ag(110) has been studied in ultra high vacuum with room temperature scanning tunneling microscopy (STM) and low energy electron diffraction (LEED) in combination with density functional theory (DFT) calculations. It was found that at low coverages iodine forms $c(2\times 2)$ structure. Further adsorption of iodine leads to compression of atoms in the troughs along $<110>$ direction and formation of domain walls separating $c(2\times 2)$ domains. As the coverage increases compression in the troughs causes domain walls to disappear and iodine atoms to form a distorted hexagonal structure. This structure is compressed with more iodine on the surface. With further exposure to iodine AgI islands are formed on the monolayer of iodine. The formation of islands begins at the edges of atomic steps and it was found that the top layers of islands also have distorted hexagonal structure. In this structure one of the directions of atomic rows coincide with the $<110>$ direction of the substrate. The other two directions of atomic rows are turned relatively to substrate causing a moire pattern on the surface of islands. The AgI growth occurs in the form of double layer honeycomb (DLHC) sandwich-like structure.