From sub-monolayer to multilayer––an in situ X-ray diffraction study of the growth of Pd films on Pt(1 1 1)

The structure of electrochemically deposited Pd thin films on the Pt(1 1 1) electrode surface has been studied by a combination of cyclic voltammetry (CV) and in situ synchrotron surface X-ray scattering. The films were examined at successively higher levels of thickness, ranging from the sub-monolayer regime to the n ML (n>2) regime. We found that on top of a pseudomorphic monolayer film, Pd forms three-dimensional islands which, in the n ML (n>2) regime are described using a half-Lorentzian distribution of layer occupation. These islands provide the large number of Pd step sites that give rise to the peak in the CV at 0.3 V. The deposition of Pd onto Pt(1 1 1), therefore, proceeds via a pseudomorphic Stranski–Krastanov growth mode.