| Abstract
| - Ensembles of silver nanowires (AgNEs) with diametersranging from 200 nm to 1.0 μm have been prepared byelectrochemical step edge decoration. These AgNEs showeda rapid (<5 s), reversible increase in resistance uponexposure to the vapor of ammonia, trimethylamine, andpyridine. The amplitude of the resistance change was upto +3000% (ΔR/Ro)more than 2 orders of magnitudelarger than can be explained based on boundary layerscattering effects. We experimentally probe the mechanism for this resistance modulation in the case of ammonia, and we propose a model to describe it. Conductivetip atomic force microscopy was used to probe individualsections of nanowires in AgNEs; these data revealed thatthe resistance change caused by NH3 exposure wasconcentrated within a minority (∼10%) of the 5-μm wiresegments that were probednot uniformly distributedalong each nanowire. All AgNEs showed a temperaturedependence of their resistance, α, that was smaller thanexpected for silver metal. Highly sensitive AgNEs sometimes showed a negative α, characteristic of semiconductors, but negative α values were never observed for AgNEswith a low sensitivity to NH3. AgNEs did not respond tohydrocarbons, O2, H2O, N2, CO, or Ar, but a large (ΔR/Ro> |−50%|) irreversible decrease in resistance was seenupon exposures to acids including HCl, HNO3, and H2SO4. Based on these and other data, we propose a modelin which oxidized constrictions in silver nanowires limitthe conductivity of the wire and provide a means for“gating” conduction based on the protonation state of theoxide surface.
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