Microscopic Mechanism Of Metal Oxide Semiconductor Heterointerface Construction And Its Influence On Gas Sensing Performanc

The metallurgical production process involves many applications that require accurate gas detection,not only to analyze the composition of raw material gas in real-time,but also to monitor the concentration of volatile organic compounds,nitrogen oxides,and other polluting gases emitted.Metal oxide semiconductor（MOS）gas sensors are widely used in metallurgy,environment,agriculture,and other fields because of their advantages of high sensitivity,low cost,easy integration,etc.With the refinement of the metallurgical production process and the increasingly stringent environmental policies,higher requirements are put forward for the detection sensitivity and selectivity of MOS gas sensors,among which the design of material interface structure and regulation of interface binding state between material and device have become effective methods and research hotspots to improve the comprehensive performance of MOS gas-sensitive sensors.Although a large number of studies have found that the gas-sensitive performance of pure materials can be effectively improved by rationally constructing heterointerfaces,however,in the preparation process of composite materials,more attention is paid to the degree of binding between hetero components,and the formation of material heterointerfaces has large randomness,which brings significant challenges to the deep understanding of the gas sensitive enhancement mechanism brought by interface effects.This dissertation focuses on the controllable growth and heterointerface directional construction of MOS materials.The p-n hetero-type MOS/MOS directional heterointerface structure with different exposed crystal faces was constructed by hydrothermal method,the p-p homo-type MOS/MOS heterointerface was obtained by in-situ growth,and the MOS/MXene composite material with the two-dimensional conductive network was synthesized by electrostatic self-assembly.The materials’microstructure information such as micro morphology,phase composition,interface binding state,etc.were characterized.Taking the working temperature,response recovery characteristics,selectivity,and other indicators as the performance evaluation indicators of the sensor,the structure-activity relationship between the material interface state and gas sensing performance was studied.The enhancement mechanism of interface effect on gas sensing performance was discussed from the aspects of heterointerface band matching,carrier separation,and transport efficiency.The main research contents are as follows:The p-Co₃O₄/n-Fe₂O₃ordered heterointerface structure with exposed{100}crystal face was successfully prepared by hydrothermal method.The results show that Fe₂O₃/Co₃O₄composite material exhibits excellent comprehensive gas sensing performance for 100 ppm low concentration triethylamine（TEA）at 250℃,such as high response value（134.9）,fast response speed（28 s）,low working temperature（250℃）,etc.The gas sensing response of Fe₂O₃/Co₃O₄composite material is 5-6 times higher than that of pure Co₃O₄and pure Fe₂O₃.The reason for improving gas sensing performance can be attributed to the broader depletion layer formed by p-n heterointerface effect and a large number of Co²⁺adsorption active sites exposed by specific crystal faces,which synergistically promote gas adsorption and surface reaction.Based on the preparation of Co₃O₄with exposed{100}crystal face,n-Fe₂O₃/p-Co₃O₄chamfered cube heterointerface structure with simultaneously exposed{001}and{111}crystal faces were synthesized by using Na OH to inhibit the preferential growth of Co₃O₄crystal face.The results show that the binding state of the heterointerface structure of the prepared sample is similar to that of that described previously.The composite sample with exposed two kinds of crystal faces has a gas sensing response value of 318.7for 100 ppm TEA at 250℃,which is 1.65 times higher than that of the composite material with only{001}crystal face exposed.The main reason for the improvement of gas sensing performance is that the additional exposed{111}crystal face has a lower gas adsorption energy,which provides more high-activity Co²⁺ions on the surface by exposing more Co²⁺ions on the surface,not only promoting gas adsorption on the surface,but also forming more active sites for surface gas-solid reaction.The homo-heterointerface structure（p-Co₃O₄/p-Ni O）of the Co₃O₄nanowire array and Ni O nanosheet was in-situ grown on Pt-Al₂O₃electrode by hydrothermal heterogeneous epitaxial growth method.The results show that Co₃O₄/Ni O heterointerface structure has 3.4 times and 2.3 times higher gas sensing response for 100 ppm ethanol at250℃than pure Co₃O₄nanowire array and Ni O nanosheet,respectively.The improvement of gas sensing performance of composite material is partly due to the hole accumulation layer formed by band matching at p-p heterointerface and partly closely related to the unique“core-surface”coating structure of Co₃O₄/Ni O,in which the porous Ni O on the surface is conducive to gas diffusion and provides more active sites for surface reaction,while the Co₃O₄nanowires vertically nailed on the surface of Pt-Al₂O₃electrode provide a fast transport channel for the carrier transfer of surface reaction.The low-density foam structure of few-layer two-dimensional Ti₃C₂T_xand one-dimensional WO₃nanorod composite material（f-Ti₃C₂T_x/WO₃-NRs）was prepared by electrostatic self-assembly and bidirectional freeze-drying technology,and the influence of carrier separation efficiency based on interface effect on gas sensing performance was investigated.The results show that the gas sensing response of the composite material to 100 ppm NO₂at 200℃is 89.46,which is 5.3 times higher than that of pure WO₃-NRs.The gas sensing enhancement mechanism of heterointerface mainly comes from:the high-conductivity f-Ti₃C₂T_xwith two-dimensional network structure provides a convenient transfer channel for the free electrons excited in the conduction band of WO₃,which improves the separation efficiency of effective electron-hole pairs by promoting the long-range transport of carriers.This leads to more free electrons participating in the oxygen adsorption and gas-solid reaction process on the surface of WO₃-NRs.