Tower-Like ZnO Nanorod Bundles Grown on Freestanding Diamond Wafers for Electron Field Emission Improvement
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JMEPEG https://doi.org/10.1007/s11665-020-05059-3
Tower-Like ZnO Nanorod Bundles Grown on Freestanding Diamond Wafers for Electron Field Emission Improvement Yanyan Shen, Yubin Gong, Shengwang Yu, Yuxin Jia, Hongjun Hei, Jie Gao, and Huarong Gong (Submitted April 9, 2020; in revised form July 15, 2020) Tower-like ZnO nanorod (ZNR) bundles were grown on freestanding diamond (FSD) wafers by a lowtemperature hydrothermal method without any catalysts, and the corresponding electron field emission property was investigated. The structural characterizations disclosed that these tower-like bundles were composed of single crystalline ZNRs with hexagonal wurtzite structure. They grew perpendicularly to each crystal planes of the diamond grains. Different hydrothermal reaction times (e.g., 1.5, 3, 6, 8 h) were carried out to investigate the morphology features of ZNRs grown on the growth surface of FSD wafers. The ZNR bundles with a growth time of 6 h showed the highest crystallinity and aspect ratio. Such ZNR bundles/FSD hybrid exhibited a high emission current density of 0.2 mA at an applied field of 11.8 V/lm and a reduced turn-on field of 6.8 V/lm. The field enhancement factor b was calculated to be 4979 based on the FowlerNordheim theory. The geometry and structure of polycrystalline diamond were responsible for the formation of ZNR bundles and the high b-value. Keywords
electron field emission, growth evolution, hydrothermal method, ZNR bundles/FSD hybrids
1. Introduction Zinc oxide nanorods (ZNRs) are promising as an electronic material, because of its remarkable physical and chemical properties, such as large exciton binding energy of 60 meV and wide bandgap of 3.37 eV at room temperature. Especially, their high aspect ratio, chemical stability and negative electron affinity in various vacuum environments makes them an ideal potential electron field emitters (Ref 1-3). Although Si is widely used as a substrate to prepare ZNRs, its low hole-mobility makes the ZNRs prepared on Si substrates having larger diameter, lower crystallinity and crystal purity. Hence, the carrier mobility of ZNRs grown on Si will be reduced, as well as their electrical properties will be limited correspondingly. Moreover, Si cannot be used in severe environments (e.g., high temperature, high radiation flux, etc.). Therefore, it is necessary to develop alternative supporting substrates for the extensive applications of ZNRs.
Yanyan Shen and Jie Gao, National Key Laboratory of Science and Technology on Vacuum Electronics, School of Electronic Science and Engineering, University of Electronic Science and Technology of China, Chengdu, Peoples Republic of China; and Institute of New Carbon Materials, Taiyuan University of Technology, Taiyuan, Peoples Republic of China; Yubin Gong and Huarong Gong, National Key Laboratory of Science and Technology on Vacuum Electronics, School of Electronic Science and Engineering, University of Electronic Science and Technology of China, Chengdu, Peoples Republic of China; and Shengwang Yu, Yuxin Jia, and Hongjun He
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