Underpotential and bulk deposition of copper on Pd(111) in sulfuric acid solution studied by in situ scanning tunneling microscopy

The underpotential deposition (UPD) of Cu was investigated on a Pd(111) ele ctrode in a H2SO4 solution by using voltammetry and in situ scanning tunnel ing microscopy (STM). The UPD of Cu yielded a single current peak on Pd(111 ) in H2SO4 to form a (1 x 1) monolayer, The so-called (root 3 x root7) stru cture of sulfate/bisulfate was consistently observed at potentials negative and positive with respect to the UPD peak. Both the packing arrangement of (root3 x root7) and the internal structure of sulfate/bisulfate were image d by STM. Bulk deposition of Cu proceeded epitaxially. On the atomically fl at surface of the Cu layer, a Moire pattern was observed.