X-ray surface diffraction studies of the restructuring and electrodeposition of Pb monolayers on Au(100) single crystals

Abstract

High-intensity synchrotron X-ray radiation has increased the feasibility of studying the electrochemical solid/liquid interface in situ. Recent work on the interfacial structure of Au single-crystal electrodes has shown the need to merge appropriate electrochemical cell designs to work on standard four-cycle diffractometers. In this report, an electrochemical-based methodology for use of in situ X-ray diffraction from the electrode/electrolyte interface is applied to electrodeposition of Pb on Au(100). The cell in this experiment, unlike traditional reflection cells, provides the necessary electrochemical control of the electrode surface, as determined by the cyclic voltammagram, in conjunction with the X-ray studies. Growth of the Pb monolayer begins with diffusion of Pb⁺² ions to the surface at potentials below the Au(00)–(5 × 20) p.z.c. Electrodeposition causes a lifting of the (5 × 20) reconstruction. Pb atoms are deposited on the (1 × 1) surface in a c(2 × 2) structure. Domain sizes are small due to constriction by Au islands formed when the (5 × 20) is lifted. Irreversible surface defects are observed at – 0.32 V vs. SCE. Potentials at which Pb on Pb deposition occurs result in a roughened surface and alloy formation.