Coverage dependent structural changes during chlorine adsorption on Ag{110}

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Abstract
The adsorption of Cl2 on Ag{110} at room temperature has been studied using angle-resolved static mode secondary ion mass spectrometry (SIMS), Auger spectroscopy, and LEED. The system has been examined over a coverage range from near zero to the p(2×1) overlayer structure observed by LEED. This structure could be produced by exposing the Ag{110} crystal to 2.5 L of Cl2. The Cl LMM Auger spectra exhibited a distinct change in shape at about 1.0 L exposure which is attributed to a change in the electronic structure of the Ag–Cl bond. In addition, the SIMS Cl− secondary ion yield deviated at this exposure from the expected exponential dependence on work function predicted by theory. An analysis of the secondary Cl− ion kinetic energy distributions, and the polar and azimuthal angle distributions also suggests that the Cl atom is highly charged in the limit of zero coverage with an extended Ag–Cl bond length over that of bulk AgCl. As the coverage approaches the 1.0 L Cl2 exposure point, however, there is significant weakening of surface dipoles due to adlayer interactions. This depolarization appears to be sufficient to allow significant contraction of the Ag–Cl bond length, such that the Cl atom may actually fall into the valley of the {110} surface. A submonolayer Cs overlayer appears to stabilize the negatively charged Cl adatoms, inhibiting the changes observed on the undoped Ag{110} surface. It is suggested that adlayer interactions which influence the formation of ordered overlayer structures mask important electronic and structural features of adsorbates which may only be observed in the single atom limit.