Photoactivated Metal-Oxide Gas Sensing Nanomesh by Using Nanosphere Lithography

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Photoactivated Metal-Oxide Gas Sensing Nanomesh by Using Nanosphere Lithography Yu-Hsuan Ho1,2, Tsu-Hung Lin3, Yi-Wen Chen3, Wei-Cheng Tian1, Pei-Kuen Wei2, and Horn-Jiunn Sheen*3 1 Graduate Institute of Electronics Engineering, National Taiwan University, Taipei, Taiwan 2 Research Center for Applied Sciences, Academia Sinica, Taipei 115, Taiwan 3 Institute of Applied Mechanics, National Taiwan University, Taipei, Taiwan ABSTRACT A photoactivated ZnO nanomesh with precisely controlled dimensions and geometries is fabricated by using nanosphere lithography process. The nanomesh structures effectively increase the surface-to-volume ratio to improve the sensing response under the same testing gas. And the periodical nanostructures also increase the effective light path and lead to more efficient light activation for gas sensing. With the increase of the photoinduced oxygen ions by UV illumination, a distinguished sensing response is observed at room temperature. In the optimized case, the sensing response (ᇞR/R0) of the ZnO nanomesh at the butanol concentration of 500 ppm is 97.5%, which is 4.54 times higher than the unpatterned one. INTRODUCTION Gas sensors have been a focus of research in recent years for various applications, such as breath tests, environmental monitoring, indoor air quality, workplace health and safety, and homeland security. There have been numerous attempts to develop sensing devices with high sensitivity, stability, and rapid response1-4. There are four main basic concepts of gas sensors that have so far been reported including chemoresistive sensor5-8, capacitive sensor9, 10, micromachined cantilever11, 12 and microcalorimeter platform13. Among various types of sensing technologies, the chemoresistive gas sensor is one of the most promising methods due to its simple operation and high sensitivity. To provide sufficient reaction energy for oxidization, metal oxide gas detectors are typically operated above 100-200 °C to achieve a highly sensitive operation with a fast sensing response14. However, the necessity of high operation temperatures for conventional metal oxide gas-based detectors affects the potential usage of these devices, such as in those that require low energy consumption. Recently, several approaches have been proposed to reduce the operation temperature of detectors, such as using doped metal in metal oxide materials15, improving thermal isolation using MEMS technologies16, alternative nanosensing materials 17, and the incorporation of UV illumination during detection14, 18-20. Among these techniques, the application of UV illumination on metal oxide detectors is one of the most promising methods for achieving room temperature gas sensing. With this illumination, in which near-UV radiation is used in the heterogeneous photocatalysis21, 22, the metal oxide-based detector can significantly increase the bonding sites of the sensing materials at room temperature and increase the sensitivity of the detector. Some photocatalytic metal oxide, such as titanium oxide (TiO2) or zinc oxide