Self-Bridged ZnO Nanowires through Simple Annealing Process and Its Humidity Sensing Properties
Authors: Park Subeen , Kwak Byungkwan , Lee Dongik , Lee Songjun , Yoo Bongyoung 
Published: February 2020

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.

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