Department of Photonics and Institute of Electro-Optical Engineering, National Chiao-Tung University , Hsinchu 30010, Taiwan, Republic of China.
ACS Appl Mater Interfaces. 2014 Jan 8;6(1):630-5. doi: 10.1021/am404717j. Epub 2013 Dec 10.
Metal nanowires (NWs) enable versatile applications in printed electronics and optoelectronics by serving as thin and flexible transparent electrodes. The performance of metal NWs as thin electrodes is highly correlated to the connectivity of NW meshes. The percolation threshold of metal NW films corresponds to the minimum density of NWs to form the transparent, yet conductive metal NW networks. Here, we determine the percolation threshold of silver NW (AgNW) networks by using morphological analysis and terahertz (THz) reflection spectroscopy. From the divergent behavior of carrier scattering time and the increase of carrier backscattering factor, the critical NW density at which crossover from Drude to non-Drude behavior of THz conductivity occurs can be unambiguously determined for AgNW thin films. Furthermore, the natural oxidation of AgNWs which causes the gradual reduction of the connectivity of the AgNW network is also realized by the THz spectroscopy. The selective oxidation of NW-to-NW junctions weakens the ohmic contact, and for AgNWs near a critical density, it can even lead to metal-insulator transition. The presented results offer invaluable information to accelerate the deployment of metal nanowires for next-generation electronics and optoelectronics on flexible substrates.
金属纳米线（NWs）作为薄而灵活的透明电极，在印刷电子学和光电子学中具有多种应用。金属 NW 作为薄电极的性能与 NW 网的连通性高度相关。金属 NW 薄膜的渗流阈值对应于形成透明但导电的金属 NW 网络所需的 NW 最小密度。在这里，我们通过形态分析和太赫兹（THz）反射光谱来确定银 NW（AgNW）网络的渗流阈值。从载流子散射时间的发散行为和载流子反向散射因子的增加，可以明确确定太赫兹电导率从 Drude 行为到非 Drude 行为转变时的临界 NW 密度。此外，THz 光谱还实现了 AgNW 自然氧化，导致 AgNW 网络的连通性逐渐降低。NW 到 NW 结的选择性氧化会削弱欧姆接触，对于接近临界密度的 AgNW，甚至会导致金属-绝缘体转变。所提出的结果为加速金属纳米线在柔性衬底上的下一代电子学和光电子学中的应用提供了宝贵的信息。
