Scanning electrochemical Microscopy with slightly recessed nanotips

Slightly recessed nanoelectrodes were prepared by controlled etching of nanometer-sized, flat Pt electrodes. By using high-frequency (e.g., 2 MHz) ac voltage, the layer of Pt as thin greater than or similar to 3 nm was removed to produce a cylindrical cavity inside the insulating glass sheath. The etched electrodes were characterized by combination of voltammetry and scanning electrochemical microscopy (SECM) to determine the radius and the effective depth of the recess. The theory was developed for current versus distance curves obtained with a recessed tip approaching either a conductive or an insulating substrate. Good agreement between the theoretical and experimental approach curves indicated that recessed nanotips are suitable for quantitative feedback mode SECM experiments.