Effects of Mercury
Electrodeposition on the
Surface Degradation of Microlithographically Fabricated
Melissa A. Nolan and Samuel P.
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.