Preparation And Performance Study Of Semiconductor Gas Sensors Based On Two-dimensional Indium Selenide

The problem of environmental pollution in modern society is serious.Toxic and harmful gases are threatening human health and the entire ecosystem all the time.On the other hand,some gases are regarded as markers,and their concentration is related to the level of human health and food freshness.It can be seen that the development of effective gas detection methods is significant for environmental monitoring,medical health,food safety,etc.Large instruments such as gas chromatography can accurately detect relevant gases,but they are complex,time-consuming,expensive and not suitable for real-time analysis.In comparison,semiconductor gas sensors have been viewed as powerful gas detection tools due to their high response,low cost,small size and easy operation.In recent years,two-dimensional materials have been widely used to construct high-performance room-temperature semiconductor gas sensors.As a new member of two-dimensional materials,indium selenide（InSe）has exhibited ultra-high electron mobility,great optoelectronic properties,and excellent flexibility,which shows great potential in the field of optoelectronic devices.However,the current research based on InSe gas sensors was only at the stage of theoretical calculation.In this thesis,InSe was used as the research object.A series of InSe gas sensors were constructed,and the gas sensing properties of InSe were explored.The strategies of light excitation,surface modification and structural reconstruction were employed to effectively solve the problem of two-dimensional materials-based gas sensors such as low sensitivity,slow recovery speed and poor environmental stability.Besides,the gas sensing mechanisms of the prepared sensors were deeply discussed by combining with density functional theory and finite element analysis.The main research contents are as follows:Few-layer InSe nanosheets were prepared by a liquid phase exfoliation method,and then a photoexcited gas sensor based on InSe was constructed.It is found that the InSe sensor exhibited a wide photoresponse range,and the maximum photoresponse was observed under the illumination of 365 nm light source.The sensitivity of the prepared sensor for NO₂ detection was greatly improved under the UV light irradiation of ultraviolet light（190%）.In addition,the recovery behavior of the sensor was significantly improved,and the recovery time was 350 s.The theoretical limit of detection for NO₂ under illumination is 40 times lower than under dark conditions.Furthermore,the effects of O₂ and H₂O molecules on sensor performance were fully studied through experiments and density functional theory,and the prepared sensor can detect ppb-level NO₂ in human exhaled gas samples.The good sensing behavior of the sensor for NO₂ can be attributed to the excellent optoelectronic properties and good gas adsorption capacity of InSe.InSe can generate sufficient photogenerated electron-hole pairs under illumination,which not only improves the sensitivity to NO₂,but also significantly reduces the recovery time.On the basis of the above studies,the surface modification strategy was adopted.Au nanoparticles modified InSe nanosheets were successfully prepared by reducing chloroauric acid on the surface of InSe.The prepared materials were used to fabricate bifunctional gas sensors with enhanced sensitivity and practicability.The sensitivity of the sensor to NO₂ gas under red light irradiation was 1192%,which is about 10times higher than that under dark conditions.Besides,the response can also be recovered quickly with recovery time of 370 s.In contrast,the sensor exhibited higher sensitivity（11%）to NH₃ gas under darkness than under the light condition with recovery time of 340 s.The study showed that Au nanoparticles play an important role in enhancing the sensing performance,and a new strategy about carrier regulation with gold nanoparticles was proposed to explain the changes in the surface state of InSe under light modulation.Theoretical calculation results showed that the modification of gold nanoparticles can enhance the charge transfer of InSe to NO₂and NH₃,which is conducive to enhancement of sensor sensitivity.Finally,the dual-function sensor was successfully integrated into a wearable device,and the practical application ability in environmental detection was explored.The structural reforming strategy was introduced,and a large number of ultrathin InSe nanosheets were obtained by a electrochemical exfoliation method.The prepared nanosheets were then assembled into InSe nanoscrolls by heat treatment for constructing NO₂ gas sensors with improved response/recovery speed and stability.Compared with the InSe nanosheet-based sensor,the nanoscrolls devices exhibited higher response intensity（381%per ppm）and faster recovery speed（～200 s）for NO₂determination under 450 nm light irradiation with ligh intensity of 1.2 m W/cm².The excellent performance of the sensor was mainly attributed to the special tubular structure of the nanoscrolls.On the one hand,the tubular structure is conducive to full contact with gas molecules,thereby improving the sensitivity.On the other hand,this structure can generate light scattering effects to enhance light absorption,thus promoting sensing recovery.Furthermore,the sensor also exhibited excellent anti-oxidation ability.No obvious oxidation was observed after 2 months of storage in the air environment at room temperature,which can be attributed to the p-type doping and the protective effect of the carbon/oxygen functional groups on the surface of InSe.Finally,the sensor was further miniaturized and integrated into a portable wireless detection device,and its NO₂ detection ability in exhaust gas samples was explored.In summary,a series of InSe-based gas sensors were constructed in this study,and the corresponding gas sensing properties were studied.Reversible detection of NO₂ and NH₃ gases at room temperature was realized.This work provides a new strategy and theoretical support for the design of high-performance and room-temperature gas sensors.The prepared sensors have good application prospects and commercial values in some fields such as environmental monitoring and medical health.