STM and DFT Study of Chlorine Adsorption on the Ag(111)-p(4 x 4)-O Surface

Coadsorption of chlorine and oxygen on the Ag(111) surface has been studied with low-temperature scanning tunneling microscopy in combination with density functional theory calculations. Room-temperature adsorption of chlorine onto the Ag(111)-p(4 X 4)-O surface leads to the appearance of new bright objects located between protrusions of the 4 X 4 reconstruction. As chlorine adsorbs, objects form rosettes around corner holes. This configuration coincides with the configuration of the chlorine atoms in the Ag(111)-(3 X 3) Cl reconstruction structure. We conclude that the adsorption of chlorine on the Ag(111)-p(4 x 4)-O surface occurs dissociatively, with chlorine atoms displacing oxygen atoms from the 4-fold positions. Adsorption of chlorine at 77 K results in the formation of the mixed Cl-O species on the Ag-6 triangles of the p(4 X 4) reconstruction. Both scenarios of chlorine adsorption are unexpected and cannot be explained within a commonly accepted Ag-6 model of the p(4 X 4) reconstruction.