Electrochemical scanning tunneling microscopy.

The electrochemical scanning tunneling microscope was the first tool for the investigation of solid-liquid interfaces that allowed in situ real space imaging of electrode surfaces at the atomic level. Therefore it quickly became an important addition to the repertoire of methods for the determination of the local surface structure as well as the dynamics of reactions and processes taking place at surfaces in an electrolytic environment. In this short overview we present several examples to illustrate the powerful capabilities of the EC-STM, including the observation of clean metal surfaces as well as the adsorption of thin metal layers, specifically adsorbed anions and non-specifically adsorbed organic cations.

Redox activity and structural transition of heptyl viologen adlayers on Cu(100).

The redox behaviour and potential-dependent adsorption structure of heptyl viologen (1,1'-diheptyl-4,4'-bipyridinium dichloride, DHV(2+)) on a Cu(100) electrode was investigated in a chloride-containing electrolyte solution by cyclic voltammetry (CV) and in situ electrochemical scanning tunneling microscopy (EC-STM). The dicationic DHV molecules generate a few pairs of current waves in CV measurements which are ascribed to two typical one-electron transfer steps. STM images obtained in a KCl-containing electrolyte solution disclose a well-ordered c(2x2) chloride adlayer on a Cu(100) electrode surface.