In previous research completed by Iski et al.¹, it was found that through specific electrochemical methods, a silver (Ag) monolayer could be formed on a Au(111) surface in both a chloride-free and chloride-rich solution. The electrochemical method used was under potential deposition (UPD) and reduced Ag⁺ to the surface. The previous study showed that, in a chloride-free environment, the Ag monolayer could be formed and atomically resolved; however, once removed from the cell, it could be completely destroyed via hydrogen flame annealing. Interestingly, in the presence of chloride, the same Ag monolayer was formed and was found to be extremely thermally stable after removal from the cell and was resistive to temperatures as high as 1,000 K. The atomic structure of these films can be studied with electrochemical scanning tunneling microscopy (EC-STM), which not only allows for atomic scale imaging of the surface layer within an electrochemical environment, but also facilitates the taking of cyclic voltammograms (CVs), which can be used to examine the redox behavior of the systems. Through this electrochemical manipulation, a newly hypothesized mechanism for the reduction of AgCl to the surface rather than bare Ag⁺ ions is proposed. Despite many studies on these types of surface layers², very few publications have directly studied their extreme thermal stability. Since it is known that the stability of bulk metal halide structures decreases as the halogen ion increases in size, an investigative study was performed following the same procedure, substituting chloride with bromide and iodide. As with the AgCl_x system, once AgBr_x was used to form the Ag monolayer, a new surface structure formed which was also thermally resistive to a hydrogen flame. Conversely, the surface formed by the AgI_x was not maintained and formed silver oxide insulating species after thermal treatment. CVs taken in the same region as those of the previous work show a definite surface modification by both AgBr_x and AgI_x before annealing which persists after the thermal treatment for the AgBr_x. Further electrochemical studies into these Ag monolayers formed in a halogenated environment are being conducted in an attempt to better understand the properties of these surfaces and the type of redox chemistry occurring at the relevant potentials. Using EC-STM, we plan to study the ways in which this remarkable stability is imparted to the single crystal surface under ambient conditions.

[1] Iski, E. V. et al. Electrochimica Acta 2011, 56 (3), 1652–1661.

[2] Michalitsch, R.; Laibinis, P. E. Angewandte Chemie International Edition 2001, 40 (5), 941–94.