Synergistic Effects of Au and SnO2 Nanoparticles Decorated on WS2 Nanosheets for Flexible, Room-Temperature CO Gas Sensing

Abstract

Two-dimensional (2D) materials such as graphene and graphene oxide are desirable for sensing applications owing to their high surface-to-volume ratio. Recently another class of 2D materials namely transition metal dichalcogenides (TMDs) with semiconducting properties have gained extensive attention for gas sensing studies due to their high surface area and excellent electronic and catalytic properties. TMDs form layered structures, where adjacent layers are held together by weak van der Waals forces. Accordingly, they can be easily exfoliated into individual 2D layers with high surface area which is a merit for sensing applications.WS2 is a promising 2D TMD for sensing applications thanks to high surface area and excellent electrical properties. However, for sufficient sensing applications its sensitivity needs to be improved more. A good strategy for that purpose is to functionalize with noble metal and metal oxide nanoparticles (NPs). NPs can make additional charge depletion zone in WS2 nanosheets, thereby amplifying their resistance modulation during interaction with gas molecules. Furthermore, NPs can provide a spillover effect; facilitating adsorption, dissociation, and transfer of target gases to WS2 nanosheets surface. This can lead to improved sensitivity towards a specific gas.In this study, WS2 nanosheets that are bare or decorated with Au, SnO2, or a combination of Au and SnO2 were realized on flexible polyamide substrates. The fabricated sensors were operated for CO gas sensing in applied-voltage-induced self-heating mode at room temperature (24 ºC). Not only optimal applied voltage was varied for the sensing of different gases, but also that the sensors behaved uniquely in response to CO gas. Therefore, the optimized applied voltage for the fabricated sensors and their room temperature sensing characteristics were investigated. Furthermore, we investigated that tilting, bending and stretching conditions to the optimized gas sensor. Also, we suggested that the enhanced response was related to the formation of Au-WS2 and Au-SnO2 Schottky junctions, n-SnO2-n-WS2 heterojunctions, and the catalytic performance of Au NPs towards CO gas. The results obtained in this study provide new avenues towards fabrication of flexible, low power gas sensors using metal chalcogenides.