Research On Preparation And Sensing Performance Of Field-effect Transistor Gas Sensor Based On Two-dimensional Semiconductor Nanomaterials

In the last decade,China has been setting rather high priorities to prevent and combat gaseous pollutants in the atmospheric environment.Since the analysis and detection of gaseous pollutants is the prerequisite for treatments,the development of gas sensors is accelerating.In current practical application scenarios,gas detection is mainly carried out via colorimetric,luminescent photometric,solution conductivity,gas chromatography and photoionization detection methods,gas detection capabilities are limited by whose low sensitivity,complex operation,poor accuracy,long recovery time,slow response time and weak resistance to humidity.Nevertheless,researches on innovative gas sensing materials and devices are in urgent to optimize the performances of gas analysis,especially the rapid analysis as well as online monitoring of trace atmospheric pollutants.Field-effect transistor（FET）has come out to be the hotspots for gas/chemical detection owing to their high sensitivity,fast response,selectivity,and simple detecting processes.Serving as the core component within a FET sensor,the semiconducting channel material determines the detection performances.Two-dimensional（2D）semiconducting nanomaterials owns a unique mono-atomic layer structure and high specific surface area,providing an abundance of surface active sites for gas adsorption.Spontaneously,with the extremely high electron transfer efficiency and unique semiconducting electrical properties,2D semiconducting nanomaterials own great potential for gas sensing applications.This paper focuses on the sensing structure and gas-sensitive properties of advanced 2D semiconducting materials such as graphene,MoS₂,black phosphorous（BP）and titanium carbide（Ti₃C₂T_x）.In addition,the surface structure of 2D channel materials were innovatively modulated by means of surface functionalization,doping and hybridization to further improve gas selectivity and sensitivity.The sensing mechanisms was further investigated,providing fundamental sensing data and theoretical supports for the future developments of FET gas detection approaches.Our three major studies are as following.1.Preparation and comparison of FET gas sensors based on graphene,1T-phase MoS₂,2H-phase MoS₂,and BP nanomaterials.The intrinsic properties of these four 2D nanomaterials and the similarities and differences of their detection mechanisms for VOCs（Volatile organic compounds）gases were further investigated,and it was found that the sensing performance（sensitivity,response time and selectivity）of 1T/2H hybrid crystalline phase MoS₂ was better than that of BP,graphene and 2H crystalline phase MoS₂ gas sensors for low concentrations of formaldehyde gas,and showed a good performance in the same concentration of formaldehyde,ethanol,acetone,benzene and other VOCs with certain selectivity.It is attributed to the fact that 1T/2H hybrid crystalline phase MoS₂ has the strongest adsorption energy for formaldehyde gas and the electron migration efficiency is significantly better than the other three semiconducting nanomaterials.In addition,the detection of formaldehyde gas molecules using 1T/2H hybrid crystalline phase MoS₂ in simulated actual ambient relative humidity（RH,about 5%to 80%）was found to be more favorable for formaldehyde detection in high humidity environments,broadening the design methods of the sensor in practical application devices.2.Preparation of FET gas sensors based on polycrystalline phase transition metal sulfide nanomaterials.It was found that the MoS₂ nanomaterials loaded at the intercalated electrode area were subjected to high-temperature annealing in an Argon atmosphere,and the metal octahedral 1T crystalline phase with superconducting properties of MoS₂ prepared by the original lithium intercalation method would gradually and irreversibly transform into a semiconducting 2H crystalline phase with a direct band gap,and the annealing temperature range was set to be as 50～300℃.It was found that the ratio of the metal 1T crystalline phase to the semiconducting 2H crystalline phase was about 4:6 at annealing temperature of 100°C.At this time,the100℃-annealed 1T/2H-MoS₂ FET gas sensor exhibits the most superior performance for NO₂ detection,with a response sensitivity of up to 25%for NO₂at a concentration of 2 ppm at room temperature and a response time of less than 10 s.In addition,the sensor was able to detect NO₂ at a lowest detection limit（LOD）of 25 ppb.By comparison with the commercial gas sensors currently on the market,our sensor owns advantages of superior sensing performances and extremely low energy consumption（less than 1 m W,which is commonly between 800～14000 m W within the commercial sensors）.3.Preparation of FET gas sensors based on platinum single-atom modified transition metal carbides（MXene,based on titanium carbide Ti₃C₂T_x nanomaterial）.It was found that the gas sensor based on few-layer of Ti₃C₂T_x functionalized with Pt single atoms was significantly better than the Pt nanoparticles functionalized with few-layer of Ti₃C₂T_x and pristine Ti₃C₂T_x in detecting the hazardous gas triethylamine（TEA）molecules,proving that the Pt single atoms have specific catalytic cleavage performance for triethylamine.This experiment broadens the detection capability of gas sensors and the future application of single-atom materials.In this paper,four representative 2D nanomaterials are selected within the three experimental systems mentioned above,and surface functionalization methods such as crystalline structure adjustment and the introduction of single atoms are used to provide a new idea for the enhanced analysis of gaseous pollutants in the environment,especially the detection capability of FET gas sensors for lower concentrations of toxic and hazardous gases（including NO_x and VOCs）.