| Semiconductor gas sensors have low cost and simple manufacturing process,portable and large-scale preducts.Such outstanding advantages have become one of the hot research fields.In recent years,great progress in the research of oxide semiconductor gas sensing materials has made it possible to realize high performance gas sensors,and semiconductor devices based on metal oxide gas sensing materials have been commercialized for gas detections,such as Zn O,Sn O2 and Ti O2.However,semiconductor-type gas sensors based on oxide materials have also faced problems such as high operating temperature,poor selectivity,and high-power consumption.Therefore,developing new semiconductor gas sensitive materials which can work at low temperatures and are selective to certain gases should be the important research topics.Materials of two-dimensional transition metal dichalcogenide?TMDs?and chalcogenide nanosheet with similar structures are very suitable as new type of semiconductor gas-sensitive material due to their large specific surface area,narrower forbidden band width,and extremely low electronic noise.This thesis takes two-dimensional Sn S2,Sn S and Sn Se nanosheets as research objects,and studies their preparation methods,gas-sensing performance and gas-sensing mechanism.The main research contents are as follows:1.The preparation of tin chalcogenides nanosheet materialsThe methods for synthesizing tin chalcogenide nanosheet materials?Sn X?are mainly divided into two categories:bulk thinning method?physical method?and synthetic method?chemical method?.The chemical method is more suitable for preparing tin chalcogenide nanosheets due to whose higher yield and more uniform morphology of materials.In this paper,a high-temperature chemical bath method was used to prepare tin chalcogenide nanosheet gas-sensing materials.Two-dimensional Sn S2,Sn S and Sn Se nanosheet single crystal powders were prepared under different surfactants respectively,using octadecene?Ode?and oleylamine?OAm?as solvents,Sn Cl4·5H2O,S powder and Se powder as reactants.?1?Two-dimensional Sn S2 nanosheets were prepared using oleic acid?OAc?and OAm as surfactants.The experimental results show that the ratio between the surfactants OAc and OAm is the key factor controlling the morphology and size of the Sn S2 product.The growth mechanism is a synergy between the nucleation-growth model and the steric hindrance effect caused by the surfactant.When the volume ratio of OAc to OAm involved in the reaction is 1:1,the sythesized 2D Sn S2 nanosheets were hexagonal and uniform in size,and had a thickness of?6 nm and a diameter of?150 nm.The gas sensing performances of the 2D Sn S2 nanosheets were systematicaly studied as well in the later chapters.?2?Sn S nanosheets were prepared using OAm as a surfactant and deionized water as a reactant.The thickness is about 100 nm and diameter is about 5-20?m.The test results of X-ray diffraction pattern?XRD?,X-ray energy spectrum analyzer?EDS?and Fourier transform infrared spectrometer?FT-IR?show that the semi-crystalline Sn O2 produced during the hydrolysis of Sn Cl4·5H2O would react to S-OAm solution and produce Sn O,and then vulcanized to obtain Sn S.The degree of hydrolysis of Sn Cl4·5H2O can be controlled by the amount of deionized water,which in turn controls the composition of the product.?3?Sn Se nanosheets were prepared using 1,10-phenanthroline as surfactant,and OAm as surfactant and solvent.Scanning electron microscopy?SEM?measurements showed that the obtained Sn Se nanosheets was about 28 nm in thickness and 200 nm in diameter.2.The gas sensing performances and mechanisms of tin chalcogenides Sn X?X=S,Se?nanosheetsA series of gas-sensing performance tests and gas-sensing mechanism studies were carried out on the synthesized 2D Sn S2 nanosheets,Sn S nanosheets and Sn Se nanosheets.?1?The gas-sensing performance of 2D Sn S2 nanosheets were researched by measuring the resistance of the material and the frequency of the self-made wireless antenna.The 2D Sn S2 nanosheets in air have good selectivity and cyclicity to NO2 gas,and the signal[S=100%×?I0–Ig?/I0]strength is high.The best working temperature is 130°C,and the minimum detection concentration is less than 1 ppm.?2?The gas sensing performance of Sn S nanosheets was researched by measuring the resistance change.Sn S nanosheets can respond quickly to ethanol gas at 160°C in air.The minimum detection concentration limit is less than 1 ppm,the signal strength is high,and the response/response speed is fast?both less than 30 s?.In addition,the response signal[S=R0/Rg]strength of this material for ethanol gas is much greater than those for other common volatile organic compounds?such as methanol,acetone,etc.?,so it has high selectivity.?3?The gas-sensing performance of Sn Se nanosheets were researched under the conditions of 110°C heating excitation and 655 nm laser excitation at room temperature?RT?,respectively.Under thermal excitation conditions,Sn Se nanosheets have a good response to NO2 gas in the air,with high signal[S=100%×I0–Ig)/I0]strength and fast response?less than 20 s?.Under laser irradiation at room temperature,Sn Se nanosheets can also produce a clear response signal to NO2 gas in the air.The response signal is reversible and cyclic,but the response and recovery time are slow.In addition,gas-sensing mechanism of traditional zero-dimensional,one-dimensional and other structures oxide gas sensing materials has been deeply studied,but the mechanism of the emerging flaky chalcogenide gas-sensing materials such as various types of TMDs,black phosphorene and their analogue is far from enough.In order to study the gas-sensing mechanism of flaky chalcogenide materials,in-situ atmosphere Raman light?Raman?and photoluminescence spectroscopy?PL?were employed to test 2D Sn S2 materials and Sn Se nanosheets in specific gas,combined with the theoretical calculation results of the cooperative units,using the weakly chemisorption model to explain the gas-sensing mechanism.This has a certain guiding role in the study of the gas-sensing performance of flake sulfide materials. |
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