Scanning tunneling microscopy of electrode surfaces

• Main Author: Blackham, Ian George
• Published: University of Oxford 1992
• Subjects: 530.41; Solid-state physics
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.315726

A scanning tunneling microscope (STM) suitable for the in-situ study of electrode surfaces under electrochemical control has been developed. The system consists of commercially available software and feedback electronics, with a custom-built stage and electrochemical control. The stage incorporates an automatic coarse approach mechanism for ease of operation. Gold single crystal spheres (SCS) and gold on mica thin films have been studied as surfaces potentially suitable for samples in in-situ electrochemical STM experiments. Characteristic features of each surface have been identified. High resolution in-situ STM imaging of the electro-oxidation of a gold surface in a sulphuric acid electrolyte has been achieved. Surface rearrangement at potentials positive of the double layer region has been observed and correlated with cyclic voltammetry. As yet unexplained features resulting from biasing the surface at potentials negative of the double layer region are reported. In phosphate electrolyte, bulk surface oxide formation and the surface resulting from reduction of the oxide have been imaged. Some aspects of the direct electrochemistry of cytochrome c at 4,4' dithiodipyridine (SSBPY) modified gold electrodes have been investigated. In-situ FTIR showed the potential dependent orientation of adsorbed thiopyridine species, while ex-situ and in-situ STM studies showed a novel surface pitting process to be active. It is hypothesised the STM experiment itself induces the process to take place. Features attributable to cytochrome c molecules have been observed. Rearrangement of gold on mica surfaces, on exposure to certain aqueous solutions has been observed and the process is attributed to the interaction of the solutions with the original surface structure present.