Self-Bridged ZnO Nanowires through Simple Annealing Process and Its Humidity Sensing Properties

Abstract

One-dimensional (1D) nanomaterials, including nanowires, nanotubes, nanobelts, etc., are an important class of nanomaterials due to their uniquely anisotropic structures, which make them very promising as the functional materials for energy storage, photonics, catalysis, and nano-scale devices fabrication. Among which, 1D metal oxide nanomaterials are considered as some of the most fascinating functional materials and had been widely exploited [1-3]. On the other hand, humidity sensing based on metal oxides attracted a lot of attentions in meterology, health science, food science, and agriculture. In the past years, lots of detection method have been explored. Nowadays, capacitive, resistive detection methods are used. To improve the sensitivity, selectivity and stability at various condition, enormous efforts have been put on humidity sensor based on nanostructured materials. Therefore, it is of significance to develop the controlled synthesis of 1D metal oxide nanomaterials, considering the above-mentioned two aspects. ZnO nanowires demonstrate promising properties as sensing elements and widely used for UV sensing, humidity sensing, and gas sensing [4, 5]. Most work on growth of ZnO nanowires using vapor-liquid-solid (VLS) techniques and vapor-solid (VS) techniques. The synthesized nanowires are rearranged perpendicular to its substrate using “pick and place” technique. However, such a technique requires lots of time and efforts. Although enormous efforts have been put on massive production of ZnO nanowires, its directional growth between microelectrodes for the nano-device fabrication was still full of challenges [6]. In this study, ZnO nanowires were synthesized by controlled annealing process by which the interconnections between microelectrodes were made. Before annealing process, electrochemical deposition was carried out in the mixed electrolyte, containing 0.1 M ZnCl2and 1 M KCl. For verification of ZnO nanowires as a sensor material, scanning electron microscope (SEM), and X-ray diffraction (XRD) were carried out to characterized their morphology and microstructures, respectively. Also, electrical properties of ZnO nanowires were measured by semiconductor analyzer in the range from -1 V to 1 V. The characteristics of humidity sensor were confirmed with the variation of the current at 1 V based on relative humidity controlled with mass flow controller by combining dry gas and wet gas. REFERENCES [1] Qin Kuang, Changshi Lao, Zhong Lin Wang, Zhaoxiong Xie and Lansun Zheng, “High-Sensitivity humidity sensor based on a single SnO2nanowire,” J. AM. Chem. SOC. 2007, 129, 6070-6071. [2] Ming Zhuo, Yuejiao Chen, Jia Sun, Haiming Zhang, Di Guo, Haonan Zhang, Qiuhong Li, Qaihong Wang and Qing Wan, “Humidity sensing properties of a single Sb doped SnO2nanowire field effect transistor,” Sens. Actuators, B 2013, 189, 78-83. [3] Zhenyu Wang, Yan Xiao, Xiaobiao Cui, Pengfei Cheng, Biao Wang, Yuan Gao, Xiaowei Li, Tianlin Yang, Tong Zhang and Geyu Lu, “Humidity-Sensing properties of urchinlike CuO nanostructures modified by reduced graphene oxide,” ACS Appl. Mater. Interfaces 2014, 6, 3888-3895. [4] Sanghwa Yoon, Jae-Hong Lim and Bongyoung Yoo, “Oxygen re-adsorption of a single ZnO nanobridge by joule heating under ultraviolet illumination,” Appl. Phys. Express 2012, 5, 105003. [5] Nai-Feng Hsu and Tien-Kan Chung, “A rapid synthesis/growth process producing massive ZnO nanowires for humidity and gas sensing,” Appl. Phys. A 2014, 116, 1261-1269. [6] J.B.K. Law, C. B. Boothroyd and J. T. L. Thong, “Site-specific growth of ZnO nanowires from patterned Zn via compatible semiconductor processing,” J. Crystal growth 2008, 310, 2485-2492