Direct STM observation of surface modification and growth of AgCl islands on Ag(111) upon chlorination at room temperature

The results of STM, AES and TDS study of a Ag(lll) surface treated by molecular chlorine in UHV with doses up to 100000 L are presented. We obtained direct evidence of AgCl island formation on the surface upon chlorine adsorption at room temperature. The specific feature of the modified silver surface is AgCl islands surrounded by ditches with 50-150 Angstrom depth and untreated atomic plateaux. The atomic structure and chemical state of the surface area with no AgCl islands corresponds to saturated chlorine monolayer with a Ag(111)-(17 x 17)-Cl structure. A strong influence of AES primary electron beam on the morphology of the silver chloride film was observed by STM. A small (0.1 C cm(-2)) electron beam dose caused a tremendous modification of the AgCl island film forming 'giant' AgCl islands surrounded by a smooth surface covered by chemisorbed chlorine. This surface modification could be an origin of discrepancy in the interpretation of previous electron spectroscopy results. (C) 1999 Elsevier Science B.V. All rights reserved.