ON TRANSITION FROM 2D TO 3D NUCLEATION IN THE ANODIC FILM FORMATION OF THIOUREA AT THE MERCURY ELECTROLYTE INTERPHASE/

The formation of anodic films of thiourea has been investigated by mea ns of current-time transients using the potential step technique. The transients can be theoretically well described with a transition from 2D to 3D nucleation (Stranski-Krastanov mechanism). Here, the formatio n of the first monolayer corresponds to a progressive 2D nucleation an d growth with constant rate. After completion of this layer, 3D nuclea tion with diffusion controlled growth proceeds. At the noncovered regi ons of the mercury surface and of the first monolayer an oxidation rea ction takes place leading to soluble products.