Microelectronic Engineering 251 (2022) 111662 Available online 30 November 2021 0167-9317/© 2021 Elsevier B.V. All rights reserved. Hierarchical CuO nanostructured materials for acetaldehyde sensor application UmeshT. Nakate a , Yeon-Tae Yu b , Sungjune Park a, * a Department of Polymer-Nano science and Technology, Department of Nano Convergence Engineering, Jeonbuk National University, 567 Baekje-daero, Deokjin-gu, Jeonju-si, Jeollabuk-do, Republic of Korea b Division of Advanced Materials Engineering, Jeonbuk National University, 567 Baekje-daero, Jeonju-si, Jeollabuk-do, Republic of Korea A R T I C L E INFO Keywords: Acetaldehyde CuO Nanostructures Gas sensor High response ABSTRACT A nanocrystalline CuO with mixed morphologies (nanorods, nanoplates and nanoparticles) were prepared using simple room temperature wet chemical synthesis route. The nanostructured CuO material was characterized using FESEM, TEM, EDS, elemental mapping, UV–visible spectroscopy, and BET surface area techniques for various physicochemical characteristics. The gas sensor device was fabricated using CuO nano-powder and its acetaldehyde gas sensing properties was investigated. The CuO sensor showed excellent sensing response to- wards 20–100 ppm acetaldehyde. The acetaldehyde response of the CuO sensor was recorded at various oper- ating temperatures as well as concentrations. The responses of 418% and 115% were noted for 100 ppm and 20 ppm acetaldehyde concentration at 180 ◦ C respectively. The higher selectivity of the CuO sensor was observed towards acetaldehyde among various gases. The transient response of the sensor was observed to be consistent with concentrations. The dynamic repetitive response of the sensor was tested at 100 ppm acetaldehyde that revealed to be same. The sensor’s stability was tested and observed to be quite stable. A brief acetaldehyde sensing mechanism for CuO sensor was elucidated. The easy and large-scale formation of CuO nanostructures without growth controlling surfactants, and the good selectivity of the high response acetaldehyde sensor at relatively low operating temperatures may pave pathway for future gas sensor technology. 1. Introduction Volatile organic compounds (VOCs) are becoming serious concern as one of the major air pollutants in today’s modern world. The researchers actively develop metal oxides-based sensors to detect and monitor VOCs [1–5]. Acetaldehyde (CH 3 CHO) being one of the VOCs is potentially hazardous and toxic in nature that can readily transform in vapor phase at room temperature [6–7]. The acetaldehyde is extremely reactive that may react with DNA inducing mutagenesis and carcinogenesis [8]. Acetaldehyde after coming in contact with human may cause eye irri- tation, headache, protein denaturation, bronchitis, and dottiness etc [8]. Acetaldehyde in vapor phase is colourless, invisible, and has pungent odour [8]. The sources of acetaldehyde are ripened fruits, chemical in- dustries, laboratories, beverages, and vegetables etc. Acetaldehyde sensors using metal oxide have been studied. For example, Patil et al reported high response of acetaldehyde sensing at 200 ◦ C using CuO nanoparticles and Chava et al reported acetaldehyde sensing at 250 ◦ C using NiO [9,10]. Considering the potential threats of acetaldehyde towards health and environment monitoring, there is urgent need to develop high performance acetaldehyde gas sensor materials working at relatively low operating temperatures. Metal oxide nanomaterials such as SnO 2 , ZnO, WO 3 , TiO 2 , CuO, and NiO have been utilized for gas sensors applications due to their semi- conducting nature, defects, high surface area, reactivity towards gas, simplifed operation, and easy synthesis [11–16]. A CuO is known as p- type semiconductor having narrow bandgap of ~1.2–1.5 eV. CuO is a potential candidate for gas sensor application due to its high semi- conducting nature, thermal stability, excellent red-ox activity for vola- tile organic vapours, non-toxicity and abundant in nature [17]. The CuO nanostructures (nanowires/microwires) have been reported for gas sensing application [18–21]. Lupan et al reported improved hydrogen gas sensing using one-dimensional high aspect ratio CuO nanowires at 300 ◦ C [18]. Steinhauer has reported comprehensive review regarding CuO nanostructures for various gas sensor applications [19]. Apart from CuO, Lupan et al reported Cu 2 O phase with improved gas sensing properties [20]. The detail advantages of p-type semiconducting metal * Corresponding author. E-mail address: s.park@jbnu.ac.kr (S. Park). Contents lists available at ScienceDirect Microelectronic Engineering journal homepage: www.elsevier.com/locate/mee https://doi.org/10.1016/j.mee.2021.111662