Volatile organic compound sensing properties of MoO 3 eZnO coreeshell nanorods Wan In Lee a , Maryam Bonyani c , Jae Kyung Lee b , Chongmu Lee b, * , Seung-Bok Choi d a Department of Chemistry, Inha University, 253 Yonghyun-dong, Nam-gu, Incheon 402-751, Republic of Korea b Department of Materials Science and Engineering, Inha University, 253 Yonghyun-dong, Nam-gu, Incheon 402-751, Republic of Korea c Department of Materials Science and Engineering, Shiraz University, Shiraz 719646-84759, Iran d Department of Mechanical Engineering, Inha University, 253 Yonghyun-dong, Nam-gu, Incheon 402-751, Republic of Korea article info Article history: Received 27 July 2017 Received in revised form 16 November 2017 Accepted 24 November 2017 Available online xxx Keywords: MoO 3 nanorods Coreeshell Gas sensing Ethanol Heterojunction abstract MoO 3 eZnO coreeshell nanorods were synthesized by a simple two-step process. MoO 3 nanorods were synthesized by a hydrothermal method, which was followed by atomic layer deposition of a ZnO shell. The phase and crystallinity of the synthesized products were examined by X-ray diffraction, and the morphological features were studied by scanning electron microscopy. Gas sensing tests were performed on both pristine MoO 3 nanorods and MoO 3 eZnO coreeshell nanorods. Sensors containing the pristine MoO 3 nanorods and MoO 3 eZnO coreeshell nanorods showed responses (R a /R g where R a and R g are the electrical resistances of the sensors in air and the target gas, respectively) of 1.15 and 7.6, respectively, to 200 ppm ethanol at 350  C. Therefore, the response of the MoO 3 eZnO coreeshell nanorod sensors to ethanol gas was significantly better than that of pristine MoO 3 nanorods. The underlying mechanisms for the enhanced sensing performance are discussed in detail. © 2017 Elsevier B.V. All rights reserved. 1. Introduction Over the past decade, significant progress has been made in the use of 1D metal oxide nanostructures as gas sensors [1,2]. These sensors have higher sensitivity, better spatial resolution, and a more rapid response than thin or thick film gas sensors because of their high surface-to-volume ratios [3,4]. Despite their promising performance, further improvements in their sensitivity, selectivity, and operation temperature remain a challenge for realizing high- performance sensors [5]. The use of a heterogeneous interface be- tween oxide semiconductors is an effective strategy to enhance the sensitivity, stability, and response speed of gas sensors. Among various types of heterostructure nanocomposites, coreeshell nanocomposites, in which a core is coated with a shell, have attracted considerable interest recently because of their unique stability, high catalytic activity, controllable composition/structure, and potential applications in catalysis, optics, biotechnology, and gas sensors [6,7]. For gas sensing application, coreeshells have attracted great interest because the use of different combinations of n-type and p-type metal oxides, such as nen, nep, or pep, can lead to synergetic effects that ultimately enhance the gas sensing properties of the resultant sensor [8,9] (see Table 1). Despite numerous applications in catalysis, lithium batteries, and electrochromic display devices [10e12], molybdenum oxides are not very popular among metal oxides for gas sensing applications. Mo- lybdenum dioxide and trioxide are the most common and are more stable. Other oxides of molybdenum are metastable in nature, and surface instability is reported as one of the major issues with these oxides. Therefore, only the MoO 3 phase is recorded for gas sensing applications. It has a bandgap of 3.2 eV and exhibits an n-type elec- trical conductivity with a very high resistivity of 10 10 U cm in its natural form [13]. This very high resistivity makes it difficult to realize a gas sensor based on pristine MoO 3 and to integrate it with electronics. Although there are some reports of MoO 3 gas sensors [14,15], pristine MoO 3 does not show a high response to target gases, mainly because of the low mobility of its electrical carriers and its very high intrinsic resistivity. Therefore, researchers have tried to enhance the gas sensing properties of MoO 3 sensors using various strategies such as doping with metals [16] and forming composites with another metal oxide (Table 1)[17]. As ZnO is one of the most important gas sensors and has a lower electrical resistivity and high response to various gases, it seems that coreeshell structures with * Corresponding author. E-mail address: cmlee@inha.ac.kr (C. Lee). Contents lists available at ScienceDirect Current Applied Physics journal homepage: www.elsevier.com/locate/cap https://doi.org/10.1016/j.cap.2017.11.022 1567-1739/© 2017 Elsevier B.V. All rights reserved. Current Applied Physics xxx (2017) 1e8 Please cite this article in press as: W.I. Lee, et al., Volatile organic compound sensing properties of MoO 3 eZnO coreeshell nanorods, Current Applied Physics (2017), https://doi.org/10.1016/j.cap.2017.11.022