Iodine adsorption on Ni(111): STM and DFT study
Iodine adsorption on the Ni(111) surface has been studied in ultra-high vacuum conditions with scanning tunneling microscopy (STM), Auger electron spectroscopy (AES), low-energy electron diffraction (LEED) and density functional theory (DFT) calculations. At the first stage of adsorption, iodine was found to form a simple commensurate v3×v3R30∘ structure at the coverage of 0.33 ML. According to DFT calculations, all iodine atoms in the v3×v3R30∘ structure occupy fcc hollow sites. Increase of the coverage in the range of (0.333 ML<θ <0.364 ML) results in the uniaxial compression of the iodine lattice and the formation of the high-order commensurate structure 11×3R30∘. The mechanism of compression involves the formation and the development of the striped super-heavy domain wall network. Further iodine dosing gives rise to nucleation and growth of flat 2D islands of surface nickel iodide. Atomic resolution STM images of iodide islands, in addition to atomic modulation, exhibit clear visible moiré-like superstructures with a period about 26Å. The origin of the moiré-patterns was explained by the incommensurability of lattices of the surface nickel iodide and underlying Ni(111).