Silver Oxide Microwires:  Electrodeposition and Observation of Reversible Resistance Modulation upon Exposure to Ammonia Vapor

Wires composed of Ag x O (1 < x < 2) with diameters ranging from 0.7 to 1.1 μm were prepared by electrochemical step edge decoration on highly oriented pyrolytic graphite (HOPG) electrode surfaces. Ag x O microwires were obtained by the oxidative electrodeposition of Ag x O from a pH = 6 acetate-based plating solution. Step edge selectivity, coupled with the high nucleation density necessary for wire formation, required that the electrodeposition be carried out within a potential window of just 10 mV. The resulting microwires were characterized by scanning electron microscopy and electron diffraction, Raman spectroscopy, and X-ray photoelectron spectroscopy. Ag x O microwires were transferred from the HOPG surface to a glass surface, and electrical contacts were applied to ensembles of between 5 and 100 transferred microwires. The resistance of these microwire ensembles increased reversibly by up to 5000% upon exposure to NH3 vapor, whereas an irreversible decrease in the wire resistance was seen upon exposure to the vapors of strong acids. We propose that the mechanism responsible for this resistance modulation is identical to that proposed recently [Murray et al., Anal. Chem. 2005, 77, 5205] to account for resistance modulation by ammonia of electrodeposited silver metal nanowire ensembles.