Ordered Chlorine Layer Formation from a Supersaturation\nof Chloroform

The\nadsorption of ions on metallic surfaces is a powerful method\nto alter their electronic structure and thus tune their reactivity.\nA prominent example is chlorine on Ag(111). We investigate chlorine\ncreated by the room-temperature adsorption of chloroform on Ag(111)\nat supersaturation and the structures it forms from individual monomers\nto a full layer by using low-temperature scanning tunneling microscopy.\nThe data is supplemented by temperature-programmed desorption and\nX-ray photoelectron spectroscopy after low-temperature adsorption\nunder ultrahigh-vacuum conditions. Data interpretation is supported\nby density functional theory (DFT) calculations that account for dispersion\nforces. At low chlorine coverages, each chlorine locally alters the\nelectronic structure of the surface. The adsorbed chlorine-induced\nlocal environment modification thereby creates preferential adsorption\nsites for other chlorines in their vicinity, stabilizing extended\nchlorine structures on Ag(111). Oligomer formation leads to distance-dependent\ncooperative effects of the charge transfer and thus impacts the electronic\nstructure of the surface beyond the change by individual chlorines.\nAt intermediate chlorine coverage, chlorine forms meandering chains\nwith atoms adsorbed in alternating hcp and fcc hollow sites at distinct\nchlorine–chlorine distances. The one-dimensional structures\nconvert to an open network at intermediate coverages and a two-dimensional\nhexagonal superstructure at saturation coverage. The DFT calculations\nsuggest that the charge density extracted from the surface into the\nchlorines and the interaction between chlorine and silver atoms is\nimproved as chlorines are adjoined closer at intermediate and high\ncoverages.