Abstract
A study was carried out using photothermal deflection spectroscopy (PDS)-also known as the Mirage method-to detect underpotential deposition (UPD) of lead on silver. A laser beam for activation was first passed through a liquid electrolyte to be absorbed at the solid/liquid interface. The laser probe grazed the surface of the solid and was deflected by the gradient in the liquid, so that absorbed light heated the electrode surface causing a gradient in the refractive index of the liquid. Beam deflection was detected by a position sensitive detector as a photothermal deflection (PD) signal. The silver electrodes used were polycrystal, single crystal (111) and single crystal (100). For the (111) surface a very sharp UPD peak appeared in the current-potential curve and the corresponding PD signal also showed relatively abrupt changes. For the (100) surface, on the other hand the PD signal showed a two-step change and decay was relatively gentle.
UPD was also investigated by electrochemical scanning tunneling microscopy, yielding in situ STM images of the electrode surface in the solution. After UPD, the surface stepline of the STM images changed slightly and the height of the steps decreased. In addition corrugations appeared on the surface.
