Design Of Bi₂S₃ Gas Sensitive Material And Research On Sensor Performance

Semiconductor sensors have the advantages of high sensitivity,wide detection objects and long service life,and are in great demand in the fields of air pollution monitoring and artificial intelligence.At present,the development bottleneck lies in the high working temperature of metal oxides.Sulfide semiconductors,such as lead sulfide,have the potential to develop highly sensitive and low-power semiconductor gas sensors due to their room temperature sensitive characteristic.In this paper,lead-free and low-toxic bismuth sulfide is selected as the research object.Through controllable synthesis and theoretical calculation,the design theory and preparation method of high-performance sulfide gas sensitive materials are studied:Firstly,the effects of different crystal surfaces of bismuth sulfide in the process of synthesis and gas reaction were calculated and analyzed by means of density functional theory,and the simulation calculation was carried out for bismuth sulfide materials from the aspects of material synthesis and gas sensitive properties.Modeling and calculation of the adsorption effect of surfactant oleylamine on bismuth(130)and(211)crystal surfaces showed that oleylamine have stronger coating effect on(130)crystal surfaces than(211).Multiple adsorption models of bismuth sulfide on two crystal surfaces were established for nitrogen dioxide and water and oxygen in the air.The best adsorption model Bi Top-NO₂ was obtained through calculation and analysis,and differential charge density calculation and Bader charge analysis were further carried out.The results show that NO₂ molecule is dominant in the competitive adsorption with O₂,which can cause the electron transfer of bismuth sulfide to the surface,resulting in the change of electrical properties of the material,indicating the potential of bismuth sulfide material for the development of NO₂ gas sensor.In order to synthesize bismuth sulfide nanocrystals and verify the calculated results,orthorhombic bismuth sulfide nanocrystals were synthesized by solute thermal method.The crystal surface regulation experiment was carried out to change the volume of oleylamine,and the results showed that the exposure of(211)crystal surface increased with the increase of oleylamine volume within a certain range,which was consistent with the calculation results of density functional theory in Chapter 2.Further experiments were carried out on the synthesis of bismuth sulfide materials with different growth time.By analyzing the micromorphology and crystal surface exposure of bismuth sulfide materials at different growth stages,the results showed that the unstable bismuth sulfide amorphous particles first gathered at the gas-liquid interface during the growth process,so as to reduce the interface energy of the system.Then,due to the synergistic effect of bismuth sulfide anisotropy and activator,the crystal nucleus produced grows in a certain direction,obtaining the lowest energy configuration under the system,and generating the one-dimensional structure of bismuth sulfide.Finally,in order to further explore the gas sensitive characteristics of bismuth sulfide,bismuth sulfide gas sensors were prepared by using the synthesized bismuth sulfide material and the dynamic gas test was carried out.The results showed that the device remained stable(rate of response change<15%)and the gas response to 3 ppm NO₂ reached 35 during the40-day long continuous test at room temperature.The results in different relative humidity showed that the moisture resistance of the sensor increases with the increase of(211)grain surface of bismuth sulfide material.The gas sensitive mechanism and aging mechanism of bismuth sulfide gas sensitive material were analyzed and studied by in-situ"photo-electric-gas"characterization test.Nitrates were generated by reaction of NO₂ molecule and hydroxyl group on bismuth sulfide surface,sulfur atom,and oxygen adsorbed in crystal lattice or surface.The theoretical analysis of adsorption of different crystal planes showed that the adsorption capacity of bismuth sulfide(130)crystal plane and(211)crystal plane for NO₂increased gradually with the increase of H₂O molecules,and the enhanced effect of humidity on the competitive adsorption of NO₂ on(211)crystal plane was more significant.