The Effect Of Catalyst On The Growth Of Carbon Nanotubes And Related Study

Since their discovery in 1991, Carbon nanotubes have attracted considerable interest amongst scientists because of their unique physical properties, chemical properties, and electrical properties. With the over ten years development, the controlling of the carbon nanotubes'diameter and vertically aligned growing on big area have been achieved basically, but industrialized massively produce and the structure controlling,direction of growth of carbon nanatubes haven't been carried out. In this paper , catalyst Fe film that affect the growth of carbon nanotubes have been studied with crystal dynamics theory. And also the solid-liquid-interface growth mechanism have been proposed.First, using vacuum evaporation method , plated iron on the SiO2(80nm)/Si(100) surface as catalyst was studied. To obtain desired catalyst film, evaporating time, evaporating speed, vacuum pressure must be controlled . The relation of the thickness of catalyst film with evaporating time, evaporating speed and vacuum pressure are also discussed. Then, several gases(H2,H2+N2, NH3) were used to etch the catalyst Fe film. In the same test condition , NH3 etching can make catalysis grains even, the diameter also smaller, and it is helpful to grow the minor-diameter carbon nanotubes.Then, from the crystal dynamics theory, the effects of catalyst Fe on the growth of carbon nanotubes, such as iron crystal structure, temperature, carrier gas and so on have been studied. The effect of temperature on the lattice structure will affect directly the solubility and diffuse velocity of carbon in catalyst, indirectly affecting the yield of carbon nanotubes, about 900℃, the lattice structure of iron is Fcc and the solubility of carbon in Fcc is biger than others. The other element added in catalyst metal will also affect the activity of carbon. If the element doesn't trend to form carbide, which will put carbon atom aside to enhance carbon activity, the element may accelerate carbon to separate from the catalyst freely, and help to increase the output of carbon nanotubes, The reason why the activity of two or more catalyst metals is better than single catalyst metal is explained. The melting point temperature of catalyst grain will be decreased when the catalyst size is reduced, in the process of growing of carbon nanotubes, most catalyst occupy the condition which the solid liquid coexists. According to the radius of curvature and the electrical influence, there is the function relation between the reduced temperature of melting point and the diameter of grains. Finally, several kinds of main growth mechanism of carbon nanotubes, separating energy and crystal interface have been compared and discussed, The growth mechanism of solid-liquid-interface growth model of carbon nanotubes is also proposed. In the aspect of driving force of carbon diffusing, chemistry grads were put forward."The uphill diffuser"explained the phenomenon that the carbon atoms gather in the interface. Si can prevent carbon from diffusing from catalyst to the basis interior, which cause the carbon"the uphill diffuser"to increase the concentration in catalyst and to get saturation ahead, which favor the carbon to separate out.