A study of the Pd/highly oriented pyrolytic graphite electrodeposition system by in situ electrochemical scanning tunnelling microscopy

Instrumental effects on in situ electrochemical STM studies: An investigation of a current surge induced Pd deposit on HOPG

“…The currenttpotential characteristics of this anodic process are illustrated in Figure l c which exhibits a deposit dissolution peak at 4300 mV followed by commencement of an oxygen peak at -1,100 mV. These are consistent with previous results from conventional electrochemical studies (Tong et al, 1995). Figure Id is an STM image obtained from the region with Esub held at 1,000 mV and with EtiP raised to 1,190 mV.…”

“…The experimental conditions used were similar to those for our previous study (Tong et al, 1995). Thus, in situ images were obtained with a Digital Instruments Nanoscope I1 electrochemical STM using a tube scanner with a maximum range of 11.5 pm and operating in constant current mode.…”

“…Figure 5 is an AFM image obtained from the surface of one such sample for which there was an initial current surge of 69 FA and which was then subjected to five cathodic cyclic potential sweeps at 30 mV/s between 530 mV (OCP) and 380 mV. The electrochemical characteristics of the voltammetric curves were similar to those shown before (Tong et al, 1995): there was an increasing increment of the overall current as Esub was cycled and a minor depletion indicated by a diffusion limited current started to appear at the later cycles. It can be seen that the overall morphology of the final surface layer is similar to Such results clearly indicate that renucleation on uncovered HOPG and growth of Pd on top of the existing surge-induced deposit occurred during the subsequent cathodic sweeps.…”

“…The STM tip, whose potential Etip is controlled by a built-in bipotentiostat independently of the control of the substrate potential Esub, can be an active probe, applying a local perturbation to the substrate surface electrochemistry. Many in situ ECSTM studies of electrodeposition have shown that the tip can modify the local potential and diffusion fields at the substrate electrodes and thus shield the imaged region at the substrate surface from deposition (Bard and Fan, 1993;Hendricks et al, 1992;Nichols et al, 1991Nichols et al, , 1993Riddell et al, 1993;Tong et al, 1995). Another major concern in carrying out conventional electrochemical measurements is the response time to achieve potential control of the working electrode and imaging tip, which is determined by the design of both the potentiostat and the cell itself (Bard and Faulkner, 1980;Greef et al, 1985).…”

“…In a previous paper (Tong et al, 1995) we presented an ECSTM study of the early stages of palladium electrodeposition onto highly ordered pyrolytic graphite (HOPG), in which the electrochemical characteristics of the system and the nature of the surface defect sites at which the initial nucleation and growth occur were considered. In the present paper we describe further work on this system in which the effects of possible instrumental complications were investigated.…”