Kinetics of two-dimensional phase transitions of sulfide and halide ions on Ag(111)

The kinetics of two-dimensional phase transitions of sulfide, iodide, bromi de, and chloride ions on Ag(111) was investigated at anionic concentrations ranging from 1 x 10(-4) to 1 x 10(-3) M by measuring the time dependence o f the charge following steps from a potential negative enough to exclude an ionic adsorption to a potential in the range of stability of either the fir st or the second, more compressed, ordered overlayer of the anions. The kin etic behavior is interpreted by a model that accounts for diffusion-control led random adsorption of the anions, followed by progressive polynucleation and growth. When stepping to the potential range of stability of the secon d overlayer, the kinetic behavior is accounted for by assuming that the pas sage from total desorption to the second overlayer occurs via the intermedi ate formation of the first one.