Increasing the resolution of the scanning electrochemical microscope usinga chemical lens: Application to silver deposition

The introduction of a scavenger that reacted with the tip-generated species produced a significant focusing effect on the diffusion field. We investig ated the basic principles of this new scanning electrochemical microscope o perating mode, called a chemical lens. This focusing effect was demonstrate d by silver deposition from solution, which enabled direct monitoring of th e turnover at the sample's surface by measuring the current. In the electro lyte solution, silver cations were complexed by an excess of ammonia to avo id initial silver deposition at the gold substrate. Using this tip electrod e, locally electrogenerated protons shifted the complex Formation equilibri um back to produce higher concentrations of free silver ions, which were su bsequently discharged at the gold-covered sample electrode. The free silver cations in the outer parr of the diffusion field were recomplexed by the e xcess of ammonia, which as it acted as a scavenger, did not take part in th e deposition. The resolution reached values as low as less than one-third o f the active rip diameter. The introduction of a scavenger which itself doe s not take part in electrochemical reactions represents a general method fo r downscaling in microelectrochemistry. The improvement in resolution is no t restricted to surface modifications but has been observed in surface anal ysis as well. (C) 1999 The Electrochemical Society. S0013-4651(98)11-089-3. All rights reserved.