Study Of Gas Sensor Based On Graphene

Based on several unique and excellent properties of graphene,graphene has become a hot derection in many areas.Huge surface area,low electrical noise and so on makes graphene to be an important candidate of gas sensing materials.In this article,graphene grown by chemical vapor deposition(CVD)method,and graphene-based field effect transistor(GFET)gas sensors and surface acoustic wave(SAW)gas sensor have been carried out to study the gas sengding properties.In order to prearation of higher quality graphene(CVD),we focused on the temperature,the ratio of CH4/H2,the pressure and other factors which determine the quality of graphene,and found out that the graphene growth conform to the general crystal growth law,the nucleation rate and the growth rate have the classical growth relationship with temperature.We have suppressed the nucleation of graphene successfully,by using the method of oxidate copper before the growth of graphene,and succeeded in getting a millimeter single-crystal graphene finally.The gas sensor based on pristine graphene with conductance type was studied theoretically and experimentally.The time response of conductance measurements showed a quickly and largely increased conductivity when the sensor was exposed to ammonia gas produced by a bubble system of ammonia water.However,the desorption process in vacuum took more than 1 h which indicated that there was a larger number of transferred carriers and a strong adsorption force between ammonia and graphene.The desorption time could be greatly shortened down to about 2 min by adding the flow of water-vapor-enriched air at the beginning of the recovery stage which had been confirmed as a rapid and high-efficiency desorption process.Moreover,the optimum geometries,adsorption energies,and the charge transfer number of the composite systems were studied with first-principle calculations.With first principles calculation of the phenomenon,it is concluded that hydrogen atom in the whole process plays an important role,ammonia is mainly adsorbed on the surface of the graphite in the form of ammonium,water molecules away to join and help ammonium ions formed ammonia clusters in the desorption process that to make it easier to be desorbed from the graphene surface.We also prepared surface acoustic wave gas(SAW)sensor based on graphene oxide(GO)and built a SAW gas sensor test platform.We studied on the SAW gas sensor for the gas sensitive characteristics of CH4,and found that the device we prepared obtain a preliminary response to the methane,we can achieve the lowest concentration tested reached 4%.