| Vacuum electronic devices(VEDs)are widely used in communication,medical diagnosis,aerospace and other fields,but there are still no effective methods to detect the inner vacuum of VEDs.In this thesis work,based on the carbon nanotube(CNT)micro pressure sensing technique developed in our lab,the sensing performances of various gases,including inert gases,were tested,which not only enriched the functions,but also broadened the application fields of this CNT sensor,including the leak detection capability.This thesis mainly consists of the following three aspects:(1)Firstly,carbon nanotubes were prepared by thermochemical vapor deposition combined with anodizing technique.The carbon nanotubes were characterized by SEM,and the results showed that the nanotubes were uniformly distributed under the conditions of 8 Torr growth pressure and 10 min growth time.The CNT samples under this growth conditions showed stable field emission performance.(2)The carbon nanotubes synthesized in this work were tested for sensing properties,mainly for argon,helium,oxygen and water gas.The results showthat the CNT sensor possesses clear sensing effects on inert gases,and the emission currents gradually increase with the raising the system pressure.The crystallinities of carbon nanotubes have no obvious impact on sensing properties of inert gases.The investigations of water vapor and oxygen provide information on the influence of sensing properties form the storage carbon nanotube samples in atmosphere.(3)The sensing mechanism of inert gases were analyzed theoretically from the first-principles investigation.The study shows that the physical adsorption of argon on the surface of carbon nanotubes creates a potential well in the adsorption position,which reduces the barrier width of electron tunneling and facilitates electron emission,and similar behavior was found for helium.The application test shows that the sensor works steadily and exhibits high accuracy. |
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