Symmetric current oscillations at tip and substrate electrodes of scanning electrochemical microscope during silver deposition/stripping

Symmetric current oscillations at adjacent tip and substrate electrodes of the scanning electrochemical microscope during silver deposition and dissolution were described. Effects of the tip-substrate distance, the applied potential, the radius of the glass around the tip, diameters of the tip and substrate electrodes as well as the solution ionic strength (I) on the silver growth were examined and discussed. Electrochemical quartz crystal microbalance (EQCM) experiments were also conducted to examine the solution density-viscosity properties and the diffusion coefficients of Ag+ (D) in solutions of different ionic strength, and the obtained results are discussed according to the theoretical D−I relationship with the diffusion coefficient of Ag+ at infinite dilution and solvent factor. It is concluded that the lateral transport of silver ions via diffusion from the bulk solution to the thin-layer space enclosed by the substrate electrode and the tip remarkably affect the oscillations. An equivalent circuit is proposed to evaluate the resistance for the localized nanoscale silver contact between tip and substrate electrodes. When the tip was located far away from the substrate, instead, a current-time waveform at the tip similar to that at the dropping mercury electrode and periodic current pulses at the substrate electrode were observed.