Scanning electrochemical microscopy: theory and characterization of electrodes of finite conical geometry.

Finite conical electrodes, which are of particular interest as probes for imaging of surfaces using scanning electrochemical microscopy (SECM), in kinetic studies and in probing thin films were investigated. Theoretical SECM tip current-distance feedback (approach) curves for a finite conical electrode were calculated by numerical (finite element) analysis and compared to an earlier approximate model. The SECM curves obtained depended on the ratio of the base radius of the cone to the height of the cone and on the thickness of the insulating sheath. A new approach to fabricating conical tips of Pt in glass is described. These were used to obtain approach curves over both electrically conducting and insulating substrates. Comparison of experimental and simulated SECM approach curves provided a sensitive method of evaluating the size and shape of finite conical electrodes.