Iodine Adsorption on Ni(110): 2D-Phase Transitions and NiI2 Growth

Scanning tunneling microscopy, low-energy electron diffraction, Auger electron spectroscopy, and density functional theory calculations have been used to investigate I-2 adsorption on the Ni(110) surface. Dissociative adsorption takes place rapidly to form a c(2 X 2) layer at an iodine coverage of 0.5 ML. DFT calculations show that hollow sites are energetically preferable for iodine adsorption on the Ni(110) surface. Increase of iodine coverage above 0.5 ML leads to the commensurate-incommensurate phase transition via nucleation of loops of domain walls and to their subsequent ordering into the striped superstructure. At saturation, a striped domain-wall phase degenerates into the uniaxially compressed quasi-hexagonal phase. Further iodine dosing leads to the nucleation and growth of 2D nickel iodide islands.