UNDERPOTENTIAL DEPOSITION OF COPPER ON PD(100) - AN ELECTRON-SPECTROSCOPY STUDY

Underpotential deposition of Cu from an aqueous H2SO4 solution on a Pd(100) surface has been studied using low energy electron diffraction (LEED) and X-ray photoelectron spectroscopy (XPS). The first deposition stage is located at an underpotential of 270 mV and results in a c(2 x 2) Cu adlattice with THETA(Cu) = 0.5. The 2p3/2 binding energy of the electrodeposited Cu atoms is 0.7 eV lower than the corresponding value for bulk Cu. Completion of the monolayer (THETA(Cu) = 1.4) takes place at a potential about 250 mV more negative. At this point, a close-packed hexagonal Cu adlayer exists on the square Pd mesh. The electrodeposition beyond a monolayer proceeds as in the Stranski-Krastanov model. i.e. via a build up of three-dimensional clusters on top of the initial monolayer. The reasons for the structural differences between electrolytic deposition and vapour deposition, where pseudomorphic growth is observed, are discussed.