Adsorption of O and Cl on Tl/Si(111)––Suppressed spin polarization via bilayer formation

•Two dimensional spin polarized electronic states within the Tl/Pb adlayers on Si(111).•Adsorption of O(Cl) on Tl/Si(111) suppresses the spin polarization of surface states.•Formation of quasi-isolated O(Cl)-Tl bilayers due to O(Cl) adsorption on Tl/Si(111). Adsorption of O and Cl on Tl/Si(111) is studied using density functional theory. The surface of the Cl-Tl/Si(111) system was found to be metallic while that for O-Tl/Si(111), semiconducting. It is found, however, that the O/Tl and Cl/Tl interactions in Tl/Si(111) are very similar in nature and lead to the formation of the Tl-O and Tl-Cl bilayers weakly bonded to the Si(111)-1 × 1 substrate. The spin polarization of the Tl-induced gap states, originally present in Tl/Si(111), is also suppressed in both systems. [Display omitted]