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Synthesis And Field Electron Emission Properties Of Graphene Nanosheets And Their Composites

Posted on:2013-02-21Degree:MasterType:Thesis
Country:ChinaCandidate:Y H PeiFull Text:PDF
GTID:2231330371485405Subject:Materials Physics and Chemistry
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Graphene is isolated from graphite and could exist stably in2004by A K Geimand his co-workers. The excellent physical and chemical properties of graphene hasaroused the interest of scientists around the world. Recent years, both experimentalstudy and theoretical studies have made great progress. Graphene nanosheets haveexcellent conductivity and light transmission, large aspect ratio, high specific surfacearea, good stability and thermal conductivity, which could be used in the field ofphotonics, nanoscale devices, storage areas and the field of field emission.Various methods have been reported for the synthesis of graphene, whichincludes: micro-mechanical exfoliation, epitaxial growth, graphite oxide reductionand chemical vapor deposition method. Because of CVD method could synthesislarge-size thin film at lower temperatures and has more appropriate growth rate, it hasbeen widely used in large-scale industrial production of semiconductor thin filmmaterials.Graphene nanosheets has a large aspect ratio, good mechanical properties, goodstability and excellent electrical conductivity, which qualify it as an attractivecandidate for the used of field emission source. Furthermore, the presence of richedges may render graphene superior to CNTs for the tunneling of electrons and fieldemission properties. In this paper, we synthesized grahene and its composite materialsby RF-PECVD. We also studied the influence of catalyst thickness and the transitionlayer on their field emission properities.First of all, we prepared graphene nanosheets on Si(100) directly by rf-PECVDmethod. We researched the influence of growth time on the morphology and made abrief analysis of the growth mechanism. From the SEM and Raman spectroscopy,when the growth time is36min, the sample has more sharp edges, better crystallinityand higher degree of graphitization.Secondly´╝îwe studied the impact of Ni film thickness on the surface morphologymicro-structure, crystallinity and field emission properties of the carbon nanosheets.The surface morphology of the carbon nanosheets affected by the Ni film thickness strongly. With the increasing of Ni film thickness, the size of Ni nanoparticlesincreases which aggregated at high temperature. Increases to a certain extent, the largenanoparticles combined adjacent small nanoparticles becoming the island finally.Carbon nanosheets nucleated in the surface of Ni nanoparticles and Si substrate. Fromthe TEM characterization, the Ni nanoparticles were wrapped around by the graphitelayer. Graphene nanosheets nucleated at the breaking part and extension to formnamosheets. The graphene namosheets deposited on66nm Ni films desplay goodfields emission properties with the lowest turn-on field and largest field-enhancementfactor.And then, we studied the effect of Co film thickness on the morphology and fieldemission properties of carbon nanosheets. With the increase of the Co film thickness,the density of the carbon nanosheets increased, which has lower degree ofgraphitization. From the FN curve, it indeed enhanced field emission properties ofcarbon nanosheeets that the introduction of Co catalysts. The sample deposited on16.5nm Co film display the best field emission properties. In addition we discussedthe growth mechanism of carbon namosheets deposited on3nm Co film.Finally, we discuss the influence of Ti interlayers between Si substrate and Cothin film. Interesting is that we get the composite material of carbon nanotubes andnanosheets. The nanosheets distributed on the side wall or top of carbon namotubes.The Ti interlayer hinders the diffusion of Co into the silicon substrate and improve theperformance of Co catalytic, thus helps in the growth of carbon nanotubes. When theTi/Co film thickness were20nm/11nm, the composite of carbon nanotubes andnanosheets are vertically aligned on the flat substrate surface. Most of the carbonnanosheets distributed at the top of the carbon nanotubes, which increase the numberof emitters and enhance the field emission properties.
Keywords/Search Tags:PECVD, graphene nanosheets, catalyst, interlayer, field emission properties
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