Investigation of Pt and Pd Modified WO 3 and ZnO Based Thin Film Sensors for Ethanol Sensing Subhashis Roy, Anup Dey, Bikram Biswas, and Subir Kumar Sarkar (Submitted April 20, 2017; in revised form November 1, 2017) Ethanol sensors based on different WO 3 and ZnO structures are studied in the present work. The XRD and SEM processes are used to characterize the sensing layerÕs surface morphology which reveals the presence of nanoparticle in sensing layer. Further reducing the nanoparticle diameter by the addition of palladium (Pd) and platinum (Pt) for both the sensors (ZnO and WO 3 ) gives good results on sensitivity, operating temperature, response time and recovery time. Nanoparticle diameter for undoped WO 3 , Pd-modified WO 3 and Pt-modified WO 3 based sensors is 11.8, 6 and 5.4 nm, whereas nanoparticle diameter for undoped, Pd- modified and Pt-modified ZnO based sensors is 20, 14 and 11 nm, respectively. Analysis of dynamic response of the sensors when exposed to different concentrations of ethanol vapour (from 500 to 10,000 ppm) and various temperatures indicate the improvement in sensitivity up to 77.2% for WO 3 and 74.6% for ZnO based sensors. Keywords microscopy, nanomaterials, nanoprocessing, Pd, Pt, semiconductors, WO 3 , ZnO 1. Introduction The widespread applications of volatile organic compound ethanol in domestic and industrial purposes include (1) space application—as fuel or fuel additives—(2) chemical indus- tries—as precursor or solvent to produce different organic compounds—and (3) alcohol beverage industries—as the prime component (Ref 1). Accurate and fast detection of ethanol with lower ppm value is an important issue in those industries to maintain the safety and security (Ref 2). The fabricated sensors must have very stable and repeatable features with fast response/recovery time and high sensitivity and high selectivity towards ethanol vapour. The operating temperature must be as low as possible, which results in low power consumption and better lifetime (Ref 2). In the literature, many types of ethanol detectors exist like chromatographs, mass spectrometers and specific ionization gas pressure sensors with limitations like large size, high cost, high response time, high operating temperature (Ref 3-6). Now ethanol sensor research is going on for smaller size, low cost, low power consumption, low operating temperature, faster response and portable monitoring. At present, there are many types of commercially available ethanol sensors such as electrochemical, semiconductor, ther- moelectric, metallic, optical and acoustic ones. The metal oxide technology-based semiconductor sensors are the best one among them with respect to attractive features (Ref 7-9). These types of sensors have already been established and used as promising materials to achieve highly sensitive VOC sensors (Ref 10). TiO 2 nanotube-based ethanol sensor was fabricated by Kwon et al. (Ref 11), where they found high sensitivity at operating temperature 250 °C in 1000 ppm ethanol, but the response time is quite very high 110 s. A new p-type TiO 2 - based senor with low humidity dependency, rapid recovery kinetics and high accuracy for ethanol vapour detection has been fabricated by Kim et al. (Ref 12). However, these types of sensors suffer from high operation temperature, causing safety hazards and cross-sensitivity to other combustible/reducing gases. Thus, in this work fabricating ethanol sensor with low power consumption, high sensitivity, low temperature opera- tion, fast response is the main focus. WO 3 and ZnO based metal oxide sensors are being fabricated. These two materials have some inherent advantages over other materials like CuO, Fe 2 O 3 In 2 O 3 (Ref 13-15): compatibility with Si technology, high sensitivity towards different gases (like NH 3 , CO) and volatile compounds like ethanol, acetone, having high specific surface area and novel electron transportation properties, smaller gain size. Further, the modification of sensing materials using noble metals (Ref 16-19) like palladium (Pd), platinum (Pt) has been carried out during fabrication process. The result shows promising outcome regarding sensor operating temperature, sensitivity, response time and recovery time at expanse of poor repeatability. 2. Gas Sensor Fabrication, Characterization and Experimental Setup 2.1 Fabrication The thin film of WO 3 and ZnO has been fabricated by sol– gel method using tungsten hexachloride and zinc acetate dehydrate as a precursor. Both the thin films were prepared by This article is an invited paper selected from presentations at ‘‘ICETINN-2017, International Conference on Emerging Trends in Nanoscience and Nanotechnology’’, held March 16-18, 2017, in Majitar, Sikkim, India, and has been expanded from the original presentation. Subhashis Roy, Anup Dey, Bikram Biswas, and Subir Kumar Sarkar, Department of Electronics and Telecommunication Engineering, Jadavpur University, Kolkata 700032, India. Contact e-mails: subhashisaec@gmail.com, anupetce@gmail.com, bikram94biswas@gmail.com, and sksarkar@etce.jdvu.ac.in. JMEPEG ÓASM International https://doi.org/10.1007/s11665-017-3105-9 1059-9495/$19.00 Journal of Materials Engineering and Performance