Metallization effects of an adsorbed layer: An STM study at electrochemical interface

Abstract

The dependence of scanning tunneling microscopy (STM) tunnel current on the extent of coverage is considered for a metallic adlayer in an electrochemical environment. Apart from leading to a two-dimensional band formation in the monolayer regime, the metallization of an adsorbate layer results in a progressive desolvation of adspecies. As the associated energy change is a few

electron volts, it is shown that the effect of coverage variation is substantial on the current magnitude, ever if the potential difference between the electrode and the STM tip is kept constant. Next, the potential of a tip immersed in an electrolyte can be varied only in a narrow range. This, in general, makes it difficult to access the adsorbate electronic levels in an STM study. It is

demonstrated here that for a specific coverage range, it is possible to obtain the information regarding the adsorbate density of states. The formalism is finally applied to the STM studies of a copper layer chemisorbed on a gold electrode, and it is highlighted how the present study is relevant to the identification of the adsorbate at an electrode-electrolyte interface.