Mechanism Study Of Metal Oxide Gas Sensor Based On Online Technology

With the development of science and technology,semiconductor gas sensors have been widely used in many fields such as safety production and environmental monitoring due to their fast,sensitive,and efficient characteristics.However,at present,the sensitive mechanism between semiconductor materials and target gases is not completely clear,especially the detection mechanism of inert gases.Therefore,this article mainly uses online technologies（online mass spectrometry,gas phase in situ TEM,etc.）to study the detection mechanism of metal oxide gas sensors.In this paper,an integrated micro-heating disk chip was fabricated using MEMS technology,and a Freon R134a gas sensor was fabricated.Using on-line mass spectrometry and off-line gas chromatography,the exhaust gas generated by gas flowing through the sensor was detected,revealing the sensitive mechanism of mesoporesγ-Al₂O₃ gas sensitive materials for catalytic cracking of R134a molecules.In this paper,an integrated hydrogen gas sensor based on hexagonal porous NiO nanoplate materials has also been prepared.By observing the lattice diffraction image changes of porous NiO under hydrogen atmosphere using gas phase in situ TEM technology,the sensitive mechanism of hydrogen reduction induced NiO has been revealed,and the research on the sensitive mechanism of hydrogen sensitive components has been improved.The specific results of various efforts are as follows:（1）A zinc oxide nanowire array（Zn O NWA）was grown on a MEMS micro heating plate by in-situ localized growth method and loaded with mesoporesγ-Al₂O₃ catalyst on its top was used to prepare a semiconductor gas sensor for the detection of Freon R134a.The sensor was fabricated using a low power consumption micro heating disk manufactured using a micro electro mechanical system（MEMS）process,and its operating power was only 22 m W.Using this sensor,a concentration of 1 ppm Freon R134a was detected.Flow of Freon R134a gas molecules through using online MS the free radicals generated by mesoporesγ-Al₂O₃ were detected,and the results showed that the gas molecules of Freon R134a were catalytically cracked to generate a variety of free radicals,which in turn generated electron transfer, causing changes in the resistance of zinc oxide materials,thereby achieving the detection of Freon R134a.The catalytic mechanism of mesoporesγ-Al₂O₃ on Freon R134a molecules is revealing.In addition,the reaction products were identified offline using gas chromatography mass spectrometry（GC-MS）,further verifying the gas sensitive mechanism of catalytic cracking.（2）Using Ni（OH）₂ as a precursor,porous NiO nanoplates with a size of about 150 nm were obtained through calcination.Temperature conditions were optimized for improving gas sensitivity through thermogravimetric analysis and performance testing results.The results show that the porous NiO obtained at a calcination temperature of 350℃has the optimal sensing performance,achieving the detection of 1 ppm H₂ concentration,and the sensor response has a good linearity in the range of 1-500 ppm concentration.In order to explore the sensitive mechanism,this article used gas phase in situ TEM technology to observe the changes in lattice diffraction patterns online.It was found that NiO was reduced to Ni under H₂ atmosphere,and Ni could be oxidized to NiO under air atmosphere again,demonstrating the reduction inducing principle of hydrogen on nickel oxide nanoplates.At the same time,this article further verified the products of the hydrogen sensitive process through XRD, verifying the above sensitive mechanism.The sensing mechanism clarified in this study enriches the mechanism of H₂ sensitivity of NiO nanoplates,and the research ideas and methods provided by this study can provide beneficial guidance for exploring the mechanism of metal oxide sensitivity.