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Research Of Gas Sensor And Photodetector Based On Ultra-thin Transition Metal Dichalcogenides

Posted on:2018-10-05Degree:MasterType:Thesis
Country:ChinaCandidate:H Y GuoFull Text:PDF
GTID:2348330512488884Subject:Optical Engineering
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Similar to graphene,two-dimensional?2D?transition metal dichalcogenides?TMDCs?have layered structure.In each layer,metal atoms were sandwiched by two layers of chalcogen atoms,and they were connected by covalent bonding.Meanwhile,adjacent layers of TMDCs were stacked together by weak van der Waals force,which makes it possible to obtain a single layer of TMDCs by many kinds of methods.2D TMDCs have extraordinary optical,electrical,and mechanical properties,so that they have potential applications in various sensors.As one of the TMDCs,monolayer tungsten disulfide?WS2?film has a direct band gap of 1.96 e V,which makes it an excellent material for photodetectors,especially for visible light photodetectors.In addition,2D WS2 has large surface-to-volume ratio,which is substantially important for gas sensors.Furthermore,because of the mechanical flexible property,2D WS2 can be used in flexible and stretchable devices by transferring it onto flexible substrates.Considering the crystallinity of materials will significantly influence the performance of many sensors,photodetectors and gas sensors based on high-crystalline and polycrystalline WS2 were fabricated,respectively.The main content of the thesis is as follows.Firstly,single-layer WS2 film with high crystalline was synthesized by chemical vapor deposition?CVD?method.Based on the as synthesized WS2 film,a photodetector was fabricated by directly depositing Ti/Au electrodes on it.By measuring the current with and without light illumination,the device was found to have photo-sensing performance.By transferring the WS2 film onto PDMS substrate,a flexible photodetector can be realized.Secondly,multi-layer WS2 film with polycrystalline property was synthesized by sulfurizing sputter-deposited W film on SiO2/Si substrate.Based on the as-synthesized WS2 film,a resistive type humidity sensor with high performance was fabricated.The sensor shows a room temperature water moisture sensing behavior with a sensitivity up to 2357?for 90% humidity?and fast response time of a few seconds.By comparing the response to different kinds of molecules,the selectivity of the WS2 sensor was also investigated.What's more,the humid-sensing mechanism was explained by comparing the difference of humid sensing performance between high-crystalline and polycrystalline WS2 film based sensors.Thirdly,by transferring the WS2 film and graphene interdigital electrodes?IDE?onto the pre-stretched PDMS substrate successively,a transparent,flexible and stretchable humidity sensor was fabricated.The device is transparent with more than 70% transmittance in visible regime.Besides,the sensor has similar sensing performance in bent and flat states.What's more,the sensor can withstand up to 40% tensile strain and still shows a repeatable humidity response.Considering the high sensing performance and flexible property,the WS2 flexible sensor may be used as e-skin as well as mask-free breath monitoring device.
Keywords/Search Tags:two-dimensional material, tungsten disulfide, photodetector, gas sensor, flexible and stretchable
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