硬脂酸单分子膜上电沉积Ag膜的研究

Research on the Thin Silver Film at Monolayer of Stearic Acid

通过电沉积方法 ,以气 /液界面上形成的硬脂酸单分子膜为模板诱导沉积金属银膜 .考察了镀液 pH值、单分子膜表面压及沉积电位对银膜形貌及结构的影响 .实验发现 ,酸性镀液的气 /液界面上形成的单分子膜不能诱导沉积银 ,而在中性和碱性镀液的气 /液界面上可以诱导银膜的生长 .当单分子膜处于液态或固态时 ,气 /液界面有银膜形成 ;液态单分子膜上的银膜生长速度较快 ,且银膜的结构一致 .随着电极电位的升高 ,银膜沉积的速度加快 ,呈环状向外生长的圆形银膜逐渐变得不规则 .将不同实验条件下的银膜转移出来 ,采用扫描电镜 (SEM )、透射电镜 (TEM )对银膜的结构与形貌进行了表征 .研究表明 ,银首先在单分子膜上异相成核 ,由八面体构型逐渐发展成星型 ,最终在气 /液界面形成具有松枝状微观结构的光亮银膜 .

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.