Abstract
The NO2 response in the range of 200 ppb to 1 ppm of a chemoresistive WS2-decorated rGO sensor has been investigated at operating temperatures of 25 °C and 50 °C in dry and humid air (40% RH) under dark and Purple Blue (PB) light conditions (λ = 430 nm). Few-layers WS2, exfoliated by ball milling and sonication technique, with average dimensions of 200 nm, have been mixed with rGO flakes (average dimension 700 nm) to yield WS2-decorated rGO, deposited on Si3N4 substrates, provided with platinum (30 μm gap distance) finger-type electrodes. TEM analysis showed the formation of homogeneous and well-dispersed WS2 flakes distributed over a thin, continuous and uniform underlying layer of interconnected rGO flakes. XPS and STEM revealed a partial oxidation of WS2 flakes leading to the formation of 18% amorphous WO3 over the WS2 flakes. PB-light irradiation and mild heating of the sensor at 50 °C substantially enhanced the baseline recovery yielding improved adsorption/desorption rates, with detection limit of 400 ppb NO2 and reproducible gas responses. Cross sensitivity tests with humid air interfering vapor highlighted a negligible influence of water vapor on the NO2 response. A charge carrier mechanism between WS2 and rGO is proposed and discussed to explain the overall NO2 and H2O response of the WS2–rGO hybrids.
Highlights
The intrinsic merits of Transition Metal Dichalcogenides (TMDs), including their high surface-tovolume ratio and semiconducting properties, have accelerated the development of a diverse range of applications of these materials as chemical sensors [1,2]
The aim of this paper is firstly to demonstrate the reliability of the decoration process leading to the deposition of thin films of well dispersed WS2 flakes over large-size, interconnected reduced Graphene Oxide (rGO) flakes, secondly, to demonstrate and discuss the influence of purple blue light (λ = 430 nm) to detect NO2 gas in air in the operating temperature range of 25 ◦ C to 50 ◦ C, and lastly, to investigate the influence of water vapor on the NO2 gas response
By a combined grinding and sonication technique, WS2 commercial powders into mono-to few-layer flakes of WS2, with an average dimension of 200 nm, which have been successfully dispersed with rGO flakes with average dimensions of 700 nm, to yield WS2 -decorated rGO as chemo-resistive NO2 thin film sensor
Summary
The intrinsic merits of Transition Metal Dichalcogenides (TMDs), including their high surface-tovolume ratio and semiconducting properties, have accelerated the development of a diverse range of applications of these materials as chemical sensors [1,2]. Among a large variety of gaseous species, NO2 , H2 and NH3 are the most investigated gases, considering their high chemical reactivity with mono- or few-layer MoS2 [3,4,5], WS2 [6,7], MoSe2 [8] and MoTe2 [9]. The increase of the operating temperature up to 150 ◦ C greatly improves adsorption/desorption rates and baseline recovery, but causes partial oxidation of TMDs into their metal oxide counterparts, as previously demonstrated for MoS2 and WS2 -layered materials [5,7,11]. It turns out that both low and high temperatures hinder the practical use of TMDs due to kinetic (i.e., slow recovery rates) and thermodynamical (i.e., spontaneous oxidation) reasons, Sensors 2019, 19, 2617; doi:10.3390/s19112617 www.mdpi.com/journal/sensors
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
