Amine Vapor Sensing with Silver Mesowires

Silver mesowires with diameters ranging from 150 to 950 nm and lengths of 100 μm or more were prepared by electrochemical step edge decoration. Upon exposure to ammonia (NH3) vapor, ensembles of these mesowires showed a resistance increase, ΔR/Ro, that was large (up to 10,000%), fast (<5 s), and reversible. The vapor of liquid amines, including pyridine and trimethylamine, produced a similar but slower (1 min) response. Hydrogen sulfide caused a large, irreversible resistance increase and carbon monoxide, dioxygen, hydrocarbons, argon, and water, caused no change in resistance for exposures of up to 10 seconds. Exposure to NH3 also induced unexpectedly large resistance increases for mesowires of copper and platinum but metal films showed a maximum ΔR/Ro of < 5%, just as reported previously. Atomic force microscopy analysis of individual silver wires suggests that the increased resistance induced by NH3 exposure was concentrated at a minority (<10%) of the interparticle boundaries present along the axes of...