Development and experimental evaluation of a simple system for scanning electrochemical microscopy

The development of a scanning electrochemical microscope (SECM) is described. The device was assembled from a commercially available open-loop piezoelectric micropositioning system and a digitally addressable bipotentiostat system. Software development had to be adapted to the special features of the micropositioning system and, along with minor hardware modifications, could eventually provide a partial closed-loop control. The user interface offers convenient access to the core routines, which are tightly time controlled by the clock of the analog-digital converter in order to achieve highly reproducible positioning and significant enhancement of the signal-to-noise ratio. The capabilities and limitations of the system are discussed using measurements of modified analytical electrodes and ultramicroelectrode arrays. A new approach is introduced for quantifying the spatial resolution, which simplifies its experimental determination. A general expression for the proposed resolution limit as a function of the tip radius and the tip-substrate distance was derived, which is based on experiments with different tip electrodes, substrates and mediator solutions. After investigating a set of microelectrodes with decreasing size, the parameter “smallest imageable object” was found to be less useful for comparing the ability of the instrument and the tip for high spatial resolution.