A common layer

Platinum chloride clusters self-assemble during the chlorine-induced corrosion of a platinum surface, which leads to the formation of a mixed Cl–PtCl₄ adsorbed layer

Credit: © 2009 ACS

Halogens are commonly used to initiate changes on platinum surfaces for the preparation of catalysts. They are also involved in electrode etching, a selective corrosion process used to prepare devices such as semiconductors — but the halogen–platinum interactions remain unclear.

Now, Erminald Bertel and co-workers from the University of Innsbruck, in collaboration with researchers in Vienna, have studied¹ these interactions by depositing bromine and chlorine on a platinum (110) surface under vacuum. Although bromine did not attack the surface, platinum atoms could be extracted by chlorine on heating, when sufficient coverage of the surface was reached. This led to the self-assembly of PtCl₄ clusters, and in turn the formation of a highly ordered, mixed Cl–PtCl₄ adsorbed layer. This structure, determined by scanning tunnelling spectroscopy and low-energy electron diffraction, was also indicated by density functional theory calculations.

A similar layer was obtained when the platinum corrosion was initiated by co-adsorption of chlorine with less reactive species. This layer is almost identical to that formed by depositing PtCl₄ units from an electrolyte solution on a gold surface (100) (ref. 2), despite the difference in processes and surfaces, suggesting that the layer is a transition state for the deposition and corrosion processes.