Electrochemistry of Cd at (root 3x root 3)R30 degrees-S/Au(111): Kinetics of structural changes in CdS monolayers

Atomic layers of Cd can be adsorbed onto the (root 3 x root 3)R30 degrees-S/Au(111) surface at underpotential. We have investigated the kinetics of Cd monolayer formation and dissolution at this surface using cyclic voltammetry and chronoamperometry. Scan rate dependent cyclic voltammetry experiments reveal that the peak current in the Cd UPD wave is not a linear function of the scan rate, v, but scales as v(2/3). Similar behavior is observed when the Cd monolayer is stripped from the surface. These results are characteristic of monolayer formation and dissolution by a nucleation and two-dimensional growth mechanism. Chronoamperometry experiments reveal that both the deposition and stripping of Cd involve two steps: an initial Langmuir-type adsorption-desorption process accompanied by nucleation and two-dimensional growth. CdS monolayer growth kinetics are strongly influenced by the chemisorption of Cd on the S-modified Au(111) substrate, which both increases its rate of adsorption and decreases the rate of lattice growth. The kinetics of monolayer dissolution are characterized by a very large random desorption component which is attributed to formation of CdS.