THE UPD OF COPPER ON PT(100) - A 1ST QUANTITATIVE STRUCTURE DETERMINATION BY LEED

The adsorption of copper on platinum, obtained by electrochemical unde rpotential deposition (UPD), is a complex phenomenon. As observed by c yclic voltammetry, the underpotential is not limited to a narrow, well defined range of electrochemical potentials, but is spread out on a w ide range of potentials. On the Pt(100) surface, a lack of reversibili ty of adsorption and desorption occurs, and a gradual change in the vo ltammogram shape takes place under potential cycling. In this paper, w e describe a first ''ex situ'' low energy electron diffraction (LEED) structure investigation of that system, for a copper coverage of about 2/3 of a monolayer. The main result is that copper clusters in 2D isl ands with p(1 x 1) structure and a density of one Cu per Pt atom.