The extraordinary stability imparted to silver monolayers by chloride

While single crystal surfaces facilitate the majority of surface studies, only a handful of these materials are stable under ambient conditions and at extreme temperatures. Therefore, there is a continued interest in the development of robust and ordered surfaces that can be studied under realistic conditions. Electrochemical scanning tunneling microscopy (EC-STM) revealed that in a chloride-free electrolyte, Ag forms an ordered monolayer on Au(1 1 1) with a structure that could be atomically resolved. However, upon removal from the cell, these chloride-free Ag monolayers were subject to degradation by air and high temperatures. Interestingly, if the Ag layer was formed in the presence of chloride, the resulting AgClx layer was stable both in air and at high temperatures. X-ray photoelectron spectroscopy was used to characterize the system and ambient-, low temperature-, and EC-STM revealed that even after exposure to extreme temperatures, the AgClx layer remained intact. Density functional theory (DFT) indicated that the equilibrium coverage of Cl on the Ag monolayer was ∼0.5 ML, and that the barrier for surface reorganization of the overlayer was low. It is proposed that this facile mobility of the overlayer imparts a protective property that allows the AgClx layer to withstand extreme temperatures and attack by oxygen.