| Field emission is the basis for a variety of vacuum microelectronic devices, and carbon materials, especially carbon nanotube and graphite have excellent field emission properties . since 1991 the carbon nanotube was found by Iijima , because of its unique structural features (large diameter ratio, small radius of curvature, good thermal stability, good mechanical strength), showing a superior field emission characteristics, can be applied to field emission cathode and tunneling microscope tip, flat panel displays, microwave power amplifiers etc. .filamentary cathode can also be used to make new type of fluorescent lamps, compared to other light sources, such lamps have high brightness , simple structure, environmental protection, and low cost.In addition to carbon nanotubes, the diamond with the field emission properties was first discovered . Later, people found that the carbon fiber also has a certain field emission properties, largely because of its structure is similar to multi-walled carbon nanotubes, but with larger diameter, so the turn-on field and threshold field are bigger compared with carbon nanotubes ,But in general, it also showed good field emission characteristics. in 2004 a two-dimensional graphene structure was found, which is the basic structural unit of zero-dimensional fullerene ball,one-dimensional carbon nanotubes and three-dimensional graphite . the graphene plane was composed of basic unit of the hexagonal network structure, and formed by the sp2 hybrid. as it is the basis for the formation of other carbon materials, so the electronic transmission performance and the energy band structure are particularly important.This paper mainly focused on the field emission performance of carbon materials, starting from the crystal structure of graphene, the band structure and density distribution were simulated by Castep software to display the differences of one-dimensional carbon nanotubes, two–dimensional grapheme and three-dimensional graphite; at the same time, CVD method was adopted to deposit the carbon materials, a new morphology with combination of graphite and carbon nanotube field emitter was fabricated, field emission scanning electron microscope showing that this sheeted material has the edge with a prominent tip, transmission electron microscopy revealed that the prominent tip was formed by carbon nanotubes, so we named this material fractal graphite-carbon nanotubes, referred to as FGNT; the curve between voltage and current and current stability were tested by diode-structure, the result showed that the FGNT has a good field emission properties: low turn-on field and threshold field, large field enhancement factor, and stable emission current. Then the effects of test environment to the field emission properties was discussed: surface state of the FGNT do a great influence, the turn-on field and threshold field, and field emission current stability were mainly influenced by extruded tips ; the adsorbed gases and dangling bonds of carbon atoms combined to form new covalent bonds, affected the band structure and density of state of carbon nanotubes, surfaces of carbon nanotubes adsorbed with water vapor, hydrogen and oxygen conditions were simulated by the Castep software. The result show that When adsorbed with water vapor ,the density of states at the Fermi level increases, lower work function, is conducive to electron emission, adsorbed with oxygen, C-O bond was formed by carbon atoms and oxygen atoms on the surface of carbon nanotubes, increasing its work function, was disadvantaged to electron emission; when adsorbed with hydrogen , C-H bond was formed by carbon atoms and hydrogen atoms, the band structure and work function of carbon nanotubes has little change before and after adsorbed with hydrogen. and it has little effect on the field emission. identifying the factors, which help us to use and control these factors to improve field emission properties, and play a great significance to its application .
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