Scanning tunneling microscopy studies of the electrochemical reactivity of thiourea on Au(111) electrodes

In situ scanning tunneling microscopy (STM) is proposed as an option to investigate the electrochemical reactivity of nontrivial systems. For this purpose the controversial electro-oxidation and electro-reduction of thiourea at Au(111) surfaces under potential control and constant temperature are considered. Sequential STM imaging show thiourea adsorption in striped arrays that evolve to a hexagonal close-packed (hcp) structure when the electron surface charge density is decreased. The transient hcp structure is electro-oxidized to formamidine disulfide (FDS) that slowly yields adsorbed sulfur. These results show that STM is a powerful tool to understand the reactivity of adsorbed molecules at conducting surfaces, by sequential imaging at the molecular level.