Reversible Resistance Modulation in Mesoscopic Silver Wires Induced by Exposure to Amine Vapor
By Murray, B. J.; Newberg, J. T.; Walter, E. C.; Li, Q.; Hemminger, J. C. & Penner, R. M.
Published in Analytical Chemistry
2005
Abstract
Ensembles of silver nanowires (AgNEs) with diameters ranging from 200 nm to 1.0 μm have been prepared by electrochemical step edge decoration. These AgNEs showed a rapid (<5 s), reversible increase in resistance upon exposure to the vapor of ammonia, trimethylamine, and pyridine. The amplitude of the resistance change was up to +3000% (ΔR/Ro)more than 2 orders of magnitude larger than can be explained based on boundary layer scattering effects. We experimentally probe the mechanism for this resistance modulation in the case of ammonia, and we propose a model to describe it. Conductive tip atomic force microscopy was used to probe individual sections of nanowires in AgNEs; these data revealed that the resistance change caused by NH3 exposure was concentrated within a minority (∼10%) of the 5-μm wire segments that were probednot uniformly distributed along each nanowire. All AgNEs showed a temperature dependence of their resistance, α, that was smaller than expected for silver metal. Highly sensitive AgNEs sometimes showed a negative α, characteristic of semiconductors, but negative α values were never observed for AgNEs with a low sensitivity to NH3. AgNEs did not respond to hydrocarbons, O2, H2O, N2, CO, or Ar, but a large (ΔR/Ro > |-50%|) irreversible decrease in resistance was seen upon exposures to acids including HCl, HNO3, and H2SO4. Based on these and other data, we propose a model in which oxidized constrictions in silver nanowires limit the conductivity of the wire and provide a means for “gatingâ€? conduction based on the protonation state of the oxide surface.