Increasing the Resolution of the Scanning Electrochemical Microscope Using a Chemical Lens: Application to Silver Deposition

Abstract

The introduction of a scavenger that reacted with the tip-generated species produced a significant focusing effect on the diffusion field. We investigated the basic principles of this new scanning electrochemical microscope operating mode, called a chemical lens. This focusing effect was demonstrated by silver deposition from solution, which enabled direct monitoring of the turnover at the sample's surface by measuring the current. In the electrolyte solution, silver cations were complexed by an excess of ammonia to avoid initial silver deposition at the gold substrate. Using this tip electrode, locally electrogenerated protons shifted the complex Formation equilibrium back to produce higher concentrations of free silver ions, which were subsequently discharged at the gold-covered sample electrode. The free silver cations in the outer parr of the diffusion field were recomplexed by the excess of ammonia, which as it acted as a scavenger, did not take part in the deposition. The resolution reached values as low as less than one-third of the active rip diameter. The introduction of a scavenger which itself does not take part in electrochemical reactions represents a general method for downscaling in microelectrochemistry. The improvement in resolution is not restricted to surface modifications but has been observed in surface analysis as well. (C) 1999 The Electrochemical Society. S0013-4651(98)11-089-3. All rights reserved