The Study Of Gas Sensor Based On Graphene-Metal Oxide

Graphene, a two-dimensional crystal of sp2 hybridized carbon atoms arranged in a honeycomb lattice with a unique series of unprecedented structure, thermal, mechanic and electrical properties. The excellent electrical properties and large specific surface ratio make it a good application prospect in the aspects of gas sensor. Metal oxide semiconductor was traditional gas sensing material. In recent years the large specific surface ratio structure, the heterogeneous structure and the different metal oxide composite material have been prepared to improve the gas sensitivity of metal oxide semiconductor. The study of combining the excellent electrical properties of graphene with the good sensitivity of metal oxide semiconductor will become a new research field of gas sensors.Graphene was prepared by the lower pressure chemical vapor deposition (LPCVD) method. Zinc oxide (ZnO) thin films with various thickness were fabricated by Atomic Layer Deposition (ALD) on graphene and their reponse to formaldehyde and NO2 has been investigated. It was found that 0.5 nm ZnO films modified graphene sensors response of 51.7% to lOppm formaldehyde at room temperature and the detection limit could reach 180 parts-per-billion (ppb). And with 3nm thickness ZnO, ZnO/graphene sensors response of 21.5%to 10ppm NO2 at 200℃ and the low detection limit of 200ppb could be obtained. Meanwhile, the phenomenon of ZnO/graphene sensors exhibited p to n conductance transition at elevated temperature was also investigated.Tin oxides and tin compound (SnOx-Sn) films were thermally evaporated onto the chemical vapor deposition (CVD) grown graphene films. The effects of SnOx-Sn film thickness, thermal evaporation rate, annealing time and temperature, and O2 flux on the SnOx-Sn modified graphene sensors response were investigated. With the optimal thickness of lnm, thermal evaporation rate of 0.1A/s, annealing time of 30min, annealing temperature of 300℃ and O2 flux of 5sccm, SnOx-Sn/graphene sensors response of 140% upon the exposure to 10 ppm of NO2 and the low detection limit of 200 ppb could be obtained. At the same time, the field emission scanning electron microscopy (FESEM), atomic force microscopy (AFM), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD) and Raman spectroscopy (Raman) were applied to characterize the surface morphology and composition of SnOx-Sn/graphene.