1. Department of Chemistry, University of Geneva, CH-1211 Geneva 4, Switzerland, Laboratoire d'Electrochimie et de Physico-chimie des Matériaux et des Interfaces, E.N.S.E.E.G., 38402 Saint Martin d'Hères, France, Institute of Microtechnology, University of Neuchâtel, 2007 Neuchâtel, Switzerland, and Institute of Physical Chemistry of Polish Academy of Sciences, 01-224 Warsaw, Poland