In situ scanning tunneling microscopy in electrolyte solutions

Until recently, there had been only few in situ methods available for the structural determination of an electrode surface in solution at the atomic level. Now, several recent investigations have demonstrated scanning tunneling microscopy (STM) to be a powerful new technique for in situ characterization, with atomic resolution, of surfaces under potentiostatic control. The object of this review is to highlight some of the recent progress made, mainly, but not exclusively, in the author's laboratory, on in situ STM with atomic resolution. The review is focused on several selected topics, including structures of specifically adsorbed anions, underpotential deposition, adsorption of organic molecules, and electrochemical dissolution of metals and semiconductors. A combination of in situ STM and ex situ ultrahigh vacuum techniques has revealed detailed atomic structures of various adlayers, particularly iodine adlayers on Au, Ag, and Pc electrodes. It was recently demonstrated that aromatic molecules such as benzene adsorbed on Ph, Pt, and Cu can be clearly "seen" while the electrode is immersed in electrolytic solution. The atomic structures of semiconductor surfaces of Si, GaAs, and InP were successfully imaged in solution. Furthermore, it has been established that dynamic processes of electrochemical etching of metals and semiconductors can be followed by in situ STM. The work on semiconductors may well form the basis of development of a technology for preparing atomically flat substrate surfaces, which are expected to be required by the semiconductor industry of the next generation.