Chemisorbed halogen adlayers on Fe(110): Electronic band structure and surface geometry

A series of overlayer structures, starting with a c(3 × 1) geometry are formed during the dissociative chemisorption of chlorine, bromine, and iodine on Fe(110). These adlayers provide an opportunity to systematically examine the corresponding changes in electronic band structure as a function of coverage and adsorbate. At coverage levels greater than low-energy electron diffraction patterns obtained from the halogen-covered Fe(110) surface evolve continuously with coverage. The electronic band structure was examined as a function of coverage and adsorbate species via angle-resolved ultraviolet photoelectron spectroscopy. It is concluded that the electronic band structure measurements support an incommensurate structural model for halogen overlayer geometry on Fe(110) in which an overlayer lattice, that is in general incommensurate with the substrate, rotates and compresses with increases in coverage. An alternative interpretation of the diffraction results based on antiphase domain boundaries within the overlayer is not consistent with the photoemission data. The incommensurate model emphasizes adatom-adatom interactions over adatom-substrate interactions while the reverse is true for the antiphase boundary model.