Effects of Mercury Electrodeposition on the
Surface Degradation of Microlithographically Fabricated
Iridium Ultramicroelectrodes
 

Melissa A. Nolan and Samuel P. Kounaves*
Department of Chemistry, Tufts University, Medford, MA 02155 U.S.A.

*Author to whom correspondence should be addressed (skounave[at]tufts.edu).

The surface degradation of a microlithographically fabricated array of 10 mm diameter iridium ultramicroelectrodes was investigated using atomic force microscopy (AFM), auger scanning electron microscopy (SEM), and stripping voltammetry.  Micron-size accumulations could be observed on the iridium surface after mercury was electrochemically deposited and stripped approximately five times in a perchloric acid media with a Ag/AgCl (3M NaCl) reference electrode.  AFM images of the accumulations revealed that they were pyramidal in shape and had a tendency to form in clusters.  Elemental analysis of the clusters with Auger SEM identified them as mercury and a small amount of chloride.  The accumulations were determined to be mercurous chloride (Hg₂Cl₂) with the chloride contamination resulting both from leakage of the reference electrode and the decay of the perchloric acid.  During subsequent depositions of mercury, chloride ions were eliminated by using a nitric acid media and a polyurethane solid state reference electrode.  With chloride eliminated, mercury could be electrodeposited and stripped at least ten times on the iridium UME array without any visible surface degradation.