Photo induced NO 2 sensing properties of bismuth triiodide (BiI 3 ) nanoplates at room temperature Pham Tien Hung a , Vu Xuan Hien b , Phung Dinh Hoat a , Sangwook Lee a , Joon-Hyung Lee a , Jeong-Joo Kim a , Young-Woo Heo a,c, ⁎ a School of Materials Science and Engineering, Kyungpook National University (KNU), Daegu 41566, Republic of Korea b School of Engineering Physics, Hanoi University of Science and Technology (HUST), No. 01 Dai Co Viet street, Hanoi, Viet Nam c KNU Advanced Material Research Institute, Kyungpook National University, Daegu 41566, Republic of Korea abstract article info Article history: Received 9 April 2019 Received in revised form 7 June 2019 Accepted 1 July 2019 Available online xxxx Herein we report on the growth of layered BiI 3 nanoplates materials and their sensing properties of NO 2 under violet light illumination. The BiI 3 nanoplates were grown on a glass substrate using a chemical vapor deposition (CVD) system, with an average thickness of 30 nm and the lateral dimension of 150–170 nm. Their photo- induced sensing response for 20 ppm NO 2 and the response/recovery time are approximately ~11.2% and 18/ 36 s, respectively. The limit of detection (LOD) of NO 2 for the BiI 3 sensor is 25 ppb. A possible light-induced gas-sensing mechanism was proposed and investigated for the BiI 3 nanoplate. © 2019 Published by Elsevier Ltd on behalf of Acta Materialia Inc. Keywords: BiI 3 nanoplates Gas sensor Room temperature NO 2 Photo-induced Applications for detecting and monitoring toxic and greenhouse gases are important nowadays. In literature, various structures have been designed to detect toxic gases at operating temperature, such as zero-dimensional nanoparticles [1], one-demensional nanorods [2] or nanowires [3], two-dimensional (2D) nanoplates [4]. Among these mor- phologies, two-dimensional layered materials have attracted consider- able interest for fundamental materials science and potential new technologies [5–7]. The plate-like morphology could enhance the effec- tive surface area for gas adsorption/ desorption, which leads to superior gas–sensing performance [4,8]. Bismuth triiodide (BiI 3 ) belongs to a family of layered heavy–metal semiconductors with interesting aniso- tropic electronic and optical properties [9–11]. BiI 3 thin films have been investigated for hard radiation detection and for X-ray imaging due to the relatively wide band gap (1.67 eV) [12] and high mass den- sity [13–15]. BiI 3 has also been used as a nanoscale pressure sensor [16] and a photodetector [17]. However, there have been no attempts to use BiI 3 as a gas sensor. Thus, further investigation about the gas– sensing properties of this material is interesting. Nitrogen dioxide (NO 2 ), which is part of the group of important am- bient air pollutants, which is recognized as a bio-market of respiratory diseases that cause many respiratory diseases like airway inflammation, pulmonary edema, and even death [18–20]. Inside homes, hourly NO 2 peaks, typically arising in range between 0.4 and 1.5 ppm form gas- cooking [21]. Therefore, the detection of low concentrations of NO 2 is essential. In order to detect NO 2 , many researchers have reported on nanostructured metal-oxide-based NO 2 sensors [22–24]. These gas sen- sors usually operated within the temperature range of 100–300 °C to overcome the energy limits of chemisorptions and achiev high sensitiv- ity. However, the high operating temperature could lead to a risk of fire and explosion. Therefore, it is a significant challenge to achieve this sen- sitivity at room temperature. In order overcome this short coming, some techniques incorporate noble-like metals such as Au [25] and Pd [26] into modified nanomaterials; this has been confirmed to have potential to greatly en- hance the sensitivity and decrease the working temperature of tradi- tional gas sensors. But the high cost seriously limits their applications. Among these techniques, light irradiation attracted onto the surface of a material is the most studied and is a promising method to achieve room–temperature sensitivity [27–30]. This paper reports on the synthesis of BiI 3 nanoplates on a glass sub- strate via a facile chemical vapor deposition at 80 °C. The gas–sensing performance of the BiI 3 nanoplates under violet illumination at room temperature was characterized and discussed. By operating the fabri- cated gas sensors at room temperature under violet light illumination, the BiI 3 nanoplate were more selective towards NO 2 than to other gases. BiI 3 nanoplates were grown on a glass substrate with a Au electrode using a CVD system, as illustrated in Fig. S1 (Supplementary document). Scripta Materialia 172 (2019) 17–22 ⁎ Corresponding author at: School of materials Science and Engineering, Kyungpook National University, Kyungpook National University (KNU) E8-215, 80 Daehakro, Buk- gu, Daegu 41566, Republic of Korea. E-mail address: ywheo@knu.ac.kr (Y.-W. Heo). https://doi.org/10.1016/j.scriptamat.2019.07.001 1359-6462/© 2019 Published by Elsevier Ltd on behalf of Acta Materialia Inc. Contents lists available at ScienceDirect Scripta Materialia journal homepage: www.elsevier.com/locate/scriptamat