UNDERPOTENTIAL DEPOSITION OF MERCURY ON AU(111) INVESTIGATED BY IN-SITU SCANNING-TUNNELING-MICROSCOPY

In situ scanning tunnelling microscopy was carried out for the underpo tential deposition (UPD) of mercury on Au(111) in sulphuric and perchl oric acid solutions. In a sulphuric acid solution, a ((2)((1) over bar )(2)(1)) structure is observed at potentials more positive than the fi rst UPD peak, which is assigned to be of the structure of adsorbed bis ulphate ions. After the formation of the first UPD adlayer in the sulp huric acid which is assigned to be of the structure of adsorbed bisulp hate ions. After the formation of the first UPD adlayer in the sulphur ic acid solution, two different structures of ((20)(33/2)) and ((1(1)( 4) over bar)(4)) are simultaneously produced on the same atomically fl at terrace. On the contrary, a single structure of ((02)(21)) is found in the perchloric acid solution. The different structures formed in t he different electrolytes indicate a large influence of the electrolyt e anions on the UPD structures, It is clearly shown that the bulk depo sition of mercury on Au(111) roughened the gold surface structure. The roughened surface is recovered as smooth after the stripping of Hg at 1.3 V vs. a reversible hydrogen electrode because of the surface diff usion of gold atoms.