Ok Jong G, Lee Jae Yong, Baac Hyoung Won, Tawfick Sameh H, Guo L Jay, Hart A John
Department of Mechanical Engineering and ‡Department of Electrical Engineering and Computer Science, University of Michigan , Ann Arbor, Michigan 48109, United States.
ACS Appl Mater Interfaces. 2014 Jan 22;6(2):874-81. doi: 10.1021/am404131r. Epub 2013 Dec 27.
We investigate the rapid and anisotropic UV-induced photoconductive response of hybrid thin films comprising zinc oxide (ZnO) nanowires (NWs) directly grown on horizontally aligned (HA-) carbon nanotube (CNT) sheets. The films exhibit anisotropic photoconductivity; along the CNTs, conductivity is dominated by the CNTs and the photoconductive gain is lower, whereas perpendicular to the CNTs the photoconductive gain is higher because transport is influenced by ZnO nanoclusters bridging CNT-CNT contacts. Because of the distributed electrical contact provided by the large number of ZnO NWs on top of the HACNT film, this hybrid nanoarchitecture has a significantly greater photocurrent than reported for single ZnO NW-based devices at comparable UV illumination intensity. Moreover, the hybrid architecture where a thin basal film of ZnO ohmically contacts metallic CNTs enables rapid transport of photogenerated electrons from ZnO to CNTs, resulting in sub-second photoresponse upon pulsed illumination. The built-in potential generated across ZnO-CNT heterojunctions competes with the externally applied bias to control the photocurrent amplitude and direction. By tuning the anisotropic conductivity of the CNT network and the morphology of the ZnO or potentially other nanostructured coatings, this material architecture may be engineered in the future to realize high-performance optical and chemical sensors.
我们研究了由直接生长在水平排列（HA-）碳纳米管（CNT）片上的氧化锌（ZnO）纳米线（NWs）组成的混合薄膜的快速且各向异性的紫外光诱导光电导响应。这些薄膜表现出各向异性的光电导率；沿着碳纳米管方向，导电性主要由碳纳米管主导，光电导增益较低，而垂直于碳纳米管方向，光电导增益较高，这是因为传输受到桥接碳纳米管-碳纳米管接触的ZnO纳米团簇的影响。由于在HA-CNT薄膜顶部大量ZnO纳米线提供了分布式电接触，在可比的紫外光照强度下，这种混合纳米结构的光电流比基于单个ZnO纳米线的器件所报道的要大得多。此外，ZnO的薄基底膜与金属碳纳米管欧姆接触的混合结构能够使光生电子从ZnO快速传输到碳纳米管，从而在脉冲光照下产生亚秒级的光响应。ZnO-碳纳米管异质结上产生的内建电势与外部施加的偏压相互竞争，以控制光电流的幅度和方向。通过调整碳纳米管网络的各向异性导电性以及ZnO或潜在的其他纳米结构涂层的形态，这种材料结构未来可能经过设计以实现高性能的光学和化学传感器。
