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Preparation And Investigation Of Field Emission Properties Of Graphene/Zinc Oxides Composites

Posted on:2014-02-02Degree:MasterType:Thesis
Country:ChinaCandidate:L S GuoFull Text:PDF
GTID:2231330395998071Subject:Materials science
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Graphene has attracted vast interests in the field of solid-state physics, materials science andnano-electronics and other disciplines since it was discovered in2004as the first free-standing2D crystal. Graphene is constructed as a single atomic sheet of conjugated sp2carbon atoms,which is the thinnest two-dimensional material in the world.Owing to the unique networkstructure, Graphene shows unique and excellent electrical, mechanical and optical properties,which has a very wide range of applications in super capacitors, fuel cells,optoelectronic device,and field emission materials field.Graphene has unique electrical properties, good stability, high aspect ratio, a large specificsurface area and sharp edges, making it a good field emission material. Graphene can besynthesized by chemical vapor deposition, mechanical peeling and graphite oxide reductionmethod. However, the existing deposition methods lead to the sheets that have the planarmorphological features along the entire substrates, which limits the field enhancement.Grapheneprepared by plasma enhanced chemical vapor deposition (PECVD) grow vertically on thesubstrate surface, with many sharp edge improving the field emission performance of graphene.Zinc oxide is a wide band gap semiconductor (3.37eV), having a large exciton bindingenergy (60meV). One-dimensional nanostructures, such as nanowires, nanorods have a largespecific surface area, good thermo-chemical stability, relatively sharp top, which make it a goodcandidate material for field emission devices. In order to obtain a material having better fieldemission properties, graphene can be compounded with zinc oxide.Based on the above analysis, in order to improve the field emission properties of grapheneoxide and zinc oxide, in this paper, we prepared graphene on Si (100) substrate by PECVD, andthen the zinc oxide was synthesised on Si substrate coated with graphene using the hydrothermalmethod and magnetron sputtering method respectively. Hence we obtained the graphene/zincoxide composite materials with good field emission properties.Then we investigated theinfluence of the experimental parameters on the field emission properties of graphene/zinc oxidecomposites. The main contents and conclusions are as follows: 1. Graphene was synthesised on Si(100) substrate by PECVD for different deposition time of20min,30min and40min respectively. The obtained graphene was perpendicular to the Sisubstrate and among them, graphene for30min has sharp edges,the lowest turn-on field and thehighest field enhancement factor with4.94V/μm,2774respectively.2. Nano-zinc oxide was synthesised on Si substrate coated with graphene for30min byhydrothermal method and obtained graphene/zinc oxide composites with different morphologyby adjusting the concentrations of the reactants, the growth time and the reaction temperature.The results showed that when the concentration of the reactants was5mM, the growth time of4h and the reaction temperature of95°C,the graphene/zinc oxide composite materials had thebest field emission properties. The zinc oxide on graphene formed a hole-shaped continuousnanosheets, uneven surfaces, and relatively thin edge. The turn-on field of this compositematerial was1.24V/μm, below the pure graphene implying that the field emission properties ofgraphene/zinc oxide composite had been improved, compared to graphene,4.94V/μm.3. Zinc oxide was synthesised on Si substrate coated with graphene for30min by magnetronsputtering method and obtained graphene/zinc oxide composites with different morphology bycontrolling the deposition time, sputtering power, sputtering pressure, and the argon/oxygen flowratio. Then we studied the influence of preparation parameters on the field emission properties ofcomposites. The results showed that when the deposition time was20min, sputtering power of150W, sputtering pressure of2.5Pa, the argon-oxygen ratio of3:1, the graphene/zinc oxidecomposite had the best field emission properties.The zinc oxide nanoparticles aggregates ongraphene forming a ball island-shaped and rough surface.The turn-on field of this composite was5.15V/μm and the field enhancement factor was3441. The turn-on field of the compositematerial was higher than graphene, and in the same conditions, zinc oxide grown on the Si (100)substrate had no emission current due to equipment limitations, indicating that the turn-on fieldwas higher than9.1V/μm Therefore, the field emission properties of graphene/zinc oxidecomposite had been improved, compared to zinc oxide.
Keywords/Search Tags:graphene, PECVD, zinc oxide, hydrothermal method, magnetron sputtering, fieldemission
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