EFFECTS OF MERCURY ELECTRODEPOSITION ON THE SURFACE DEGRADATION OF MICROLITHOGRAPHICALLY FABRICATED IRIDIUM ULTRAMICROELECTRODES

The surface degradation of a microlithographically fabricated array of 10 mu m diameter iridium ultramicroelectrodes (UME) was investigated using atomic force microscopy (AFM), Auger scanning electron microscop y (SEM), and stripping voltammetry. Micrometer-size accumulations coul d be observed on the iridium surface after mercury was electrochemical ly deposited and stripped approximately five times in a perchloric aci d 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 dusters with Auger SEM identified them as mercury and a small amount of chloride. T he accumulations were determined to be mercurous chloride (Hg2Cl2) wit h the chloride contamination resulting both from leakage of the refere nce electrode and the decay of the perchloric acid. During subsequent depositions of mercury, chloride ions were eliminated by using a nitri c 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. (C) 1998 Elsevier Science S.A. All rights reserved.