Micro-schottky Junction Modulation Of SnO₂/rGO For Ultrasensitive NO₂ Sensing

Nitrogen dioxide(NO₂)is one of the most common air pollutants,and it is also a commonly used marker for diseases.The realization of ultra-low NO₂detection is a research hotspot.Therefore,the development of highly sensitive sensing materials and NO₂sensors is an urgent problem to be solved in the NO₂detection.The gas-sensing detection method based on metal oxide semiconductor materials has the advantages of simple structure,mature preparation process,good stability and low cost,which is widely used in the field of gas sensor detection.The detection process can be summarized as two processes:the first recepting stage,the active layer of the chemiresisitve gas sensing material interacts with the target gas molecules absorbed to perform charge transfer,which induces the charge carrier density change in the active layer of sensing materials.While in the second transducing stage,the charge transports through the sensing material to the electrodes to convey the charge carrier density change,which is transduced into detectable electrical variation signals.However,there is currently no clear attribution of the recepting stage and the transducing stage improvement strategy.At the same time,there are very few studies on the conduction process,and there is no research on the combination of recepting and transducing enhancement strategies for ultra-sensitive detection,so as to achieve the super sensitive detection.This work starts with the experimental design and construction of metal oxide semiconductor materials based on micro-Schottky junctions,which is committed to combining recepting enhancement strategies and transducing enhancement strategies to achieve ultra-sensitive NO₂detection.The main research content and results are divided into the following four parts:1.Construction of micro-Schottky junction of SnO₂/rGO nanoflower materialsUsing thermodynamic instability method and introducing graphene during the seed growth process,the micro-Schottky junction structure material with the surface superoxide complex defects(Sn⁴⁺-O₂^-·)by the form of coating was prepared.Based on Gibbs theory,the growth temperature was precisely controlled,and SnO₂/rGO-S nanoflowers and SnO₂/rGO-L nanoflowers with different sizes were further prepared.The control of SnO₂ nanoflowers by combined recepting and transducing enhancement strategies is realized.2.Research on the performance of the sensor based on the SnO₂/rGO nanoflowers to detect NO₂Through the gas-sensitive performance test,the sensor based on SnO₂/rGO-S nanoflowers has ultra-high sensitivity toward NO₂.The NO₂ responses to 10,20,50,100,200,500 ppt,1,2,5,10,and 20 ppb are 10.5,33.67,111.63,333.51,463.77,847.59,1585.3,2111.6,4058.85,8465.21 and 14176.17,respectively.Among them,the response reach to 10.5 at 10 ppt(NO₂),which is the lowest concentration detected at present.This sensor has good limit of the detection of 0.73 ppt by calculating at room temperature with fast alarm time and recovery time(1 s and6 s at 20 ppb).In addition,this sensor has the good characteristic of easy fabrication,good anti-interference characteristics and long-term stability.By comparing the performance of the sensor based on SnO₂/rGO-S nanoflowers and other NO₂ detection sensors at room temperature,it is further proved that the introduction of micro-Schottky junction structure has indeed improved the NO₂ sensing performance to a great extent.The limit of detection is the lowest detection limit at present,and experiments show that the micro-Schottky junction structure has great potential for ultra-sensitive detection.3.Research on the mechanism of the sensor based on the SnO₂/rGO nanoflowers to detect NO₂By the calculation of UPS and UV test,the work function of SnO₂ nanoflowers is 4.55 eV,electron affinity energy is 4.34 eV,the work function of rGO is 4.96 eV and the band gap width of SnO₂ nanoflowers is 3.64 eV.By the calculation and analysis of MS and EIS test,the carrier density of SnO₂ nanoflowers and SnO₂/rGO-S nanoflowers are 1.2578×10¹⁹ cm^-3 and 4.3013×10¹⁹ cm^-3 respectively,and the R_ct of SnO₂nanoflowers and SnO₂/rGO-S nanoflowers are2296?and 4399?,respectively.It shows that after constructing the micro-Schottky junction,the carrier density of SnO₂/rGO-S nanoflowers is increased,and the transducer of the material is enhanced.Furthermore,it proves that the micro-Schottky junction enhances the gas sensing performance by amplifying the sensing signal and enhancing the conduction.Therefore,compared with SnO₂ nanoflowers,the NO₂ detection sensitivity is further improved.In this work,through the combination of multiple material design strategies of performance enhancement,the design and construction of micro-Schottky junctions with the surface superoxide complex defects improves the sensor's recepting stage and transducing stage,and then improve the detection sensitivity,which provide a new idea to further improve the sensitivity of metal oxide materials.