Research Of Field Emission Cold Cathodes Based On Graphene Materials

Graphene, a two-dimensional material, has a hexagonal crystal lattice structure and little thickness at about 0.34 nm. It was found by Geim and Novoselov by exfoliation in 2004. With extraodinary properties, graphene has great potentials for application in nanocomposits, sensors, transpearent electrodes, supercapacitors and so on. The properties of graphene dosen’t change a lot when their layers less then 10. As a result, the meaning of graphene is extent to graphene structure whose layer less than 10.With high emission current, low power cost and cold emission property, field emission cold cathode has bright application potential in various vacuum electronics. Graphene is 2D material with very high aspect ratio, which makes the graphene as ideal emitters for high current emission and low operate electric field.The field emission researches are focused on reducing the operating electric field for plannar display and improving the field emission current for high current vacuum electronic devices. To meet the requirements above, the investigation in this thesis begins with preparation and analysis of graphene and graphene related structure, and then make graphene emitters to meet the requirement of various vacuum electronics. The researches are list as follow.1. Using chemical oxidation to make the gram scale graphene oxde and separate them at different scale.2. Exfoliating the graphene form carbon fiber colth to make excellent field emission property emitter with turn-on field at 0.4V/μm and threshold field at 0.7V/μm.3. Making graphene as low operating electric field emitter by electrophoretic and screen print for the plannar display.4. Growing graphene on the defect of carbon nanotubes with plasma enhanced chemical vipor deposition to investigate the growth mechanism of graphene. It was foud that the graphen is not only the basic element of carbon nanotubes, but also can make hybrid structure with carbon nanotubes. The graphene grew on the defect of carbon nanotubes and made epitaxial growth. With the high multistage field enhancement factor, this kind of graphene grown on carbon nanotubes has good field emission properties.5. Making flexible graphene paper with gaphene oxide. The graphene paper was used as edge emitter to make sheet electron beam and loop electron beam for specific requirement for vacuum electronic devices.6. Fabricating aligned field emitter array with flexible graphene paper. It was found that the maximum emission current of graphene emitter was 10 mA, with emission current density at about 5A/cm2. The emitter has high field emission stability and also has the application insight.The innovation in this thesis including preparation and purification the graphene and their related structures, making the graphene based emitters with inexpensive and industrial available methode to meet various vacuum electronics. The graphene emitters rang from very low operating field emitters for plannar display to very high emission current emitters for microwave electronics. Especially, the graphene emitters can also be elaborately controlled to make various sharps to meet the specific shapes electron beam requirement. The investigation in this thesis makes the graphene emitters have some potential for application in vacuum electronics.