A Research on the Thin Silver Film at Monolayer of Stearic Acid

Electrochemical reduction of silver ions at the interface of monolayer prepared from stearic acid resulted in the two-dimensional formation of silver film. The morphology of the deposits and their growth rate were studied at the surface of silver nitrate solution as a function of several physical and chemical parameters, namely, the pH of subphase, the surface pressure of the monolayer and the electric voltage were studied. The working electrode (0.33 mm diameter silver wire) just touched the solution surface, coating the surfactant monolayer and producing a small concave depression. The anode (0.33 mm diameter silver wire) was placed at the circumference of the Langmuir trough. A standard calomel electrode served as the reference electrode, via a luggin capillary whose tip was set near the cathode. The experiment was carried out under potentiostatic condition controlled by the TD 3690 potentiostat and the electrochemical system software. The silver film formed at the monolayer/solution interphase under different conditions was transferred to solid substrates by horizontal lifting in order to be investigated by SEM or TEM images. High concentration of silver ions localized at the monolayer interface, as opposed to those present in relatively low concentrations in the subphase, assured preferentially two-dimensional growth. In neutral or alkazid solutions, the silver film could be obtained under the surfactant monolayers. In contrast, the silver film could not be observed at the surface of the acid solution. The importance of the existence and the state of the negatively charged monolayer on the formation and structure of silver deposits are presented. Furthermore, the growth rate rises along with the increase of the electric voltage, making for the change in the shape of silver films from roundness to irregularity. It was found that silver ions, which nucleated heterogeneously firstly induced by monolayer at the surface of subphase, develop star-shaped particles from octahedral framework and become the pine-structured silver films gradually.