Murray B J, Newberg J T, Walter E C, Li Q, Hemminger J C, Penner R M
Department of Chemistry, University of California, Irvine, CA 92697-2025, USA.
Anal Chem. 2005 Aug 15;77(16):5205-14. doi: 10.1021/ac050636e.
Ensembles of silver nanowires (AgNEs) with diameters ranging from 200 nm to 1.0 microm 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% (DeltaR/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 NH(3) exposure was concentrated within a minority (approximately 10%) of the 5-microm wire segments that were probed--not uniformly distributed along each nanowire. All AgNEs showed a temperature dependence of their resistance, alpha, that was smaller than expected for silver metal. Highly sensitive AgNEs sometimes showed a negative alpha, characteristic of semiconductors, but negative alpha 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 (DeltaR/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 "gating" conduction based on the protonation state of the oxide surface.
通过电化学台阶边缘修饰制备了直径范围从200纳米到1.0微米的银纳米线集合体（AgNEs）。这些AgNEs在暴露于氨、三甲胺和吡啶的蒸汽时，电阻迅速（<5秒）、可逆地增加。电阻变化的幅度高达+3000%（ΔR/Ro）——比基于边界层散射效应所能解释的大2个数量级以上。我们通过实验探究了氨情况下这种电阻调制的机制，并提出了一个模型来描述它。使用导电尖端原子力显微镜探测AgNEs中纳米线的各个部分；这些数据表明，由NH₃暴露引起的电阻变化集中在所探测的5微米长的纳米线段中的少数部分（约10%）——并非沿每根纳米线均匀分布。所有AgNEs的电阻温度系数α都小于银金属的预期值。高灵敏度的AgNEs有时表现出半导体特有的负α值，但对NH₃低灵敏度的AgNEs从未观察到负α值。AgNEs对碳氢化合物、O₂、H₂O、N₂、CO或Ar没有响应，但在暴露于包括HCl、HNO₃和H₂SO₄在内的酸时，电阻出现了大的（ΔR/Ro > |-50%|）不可逆下降。基于这些及其他数据，我们提出了一个模型，其中银纳米线中的氧化收缩限制了线的导电性，并基于氧化物表面的质子化状态提供了一种“门控”传导的方式。
