Effect of Catalyst Layer Thickness on Growth of Carbon Nanotube Film

The vertically aligned carbon nanotubes grown on Si substrates with Ni as catalyst were obtained by a technology of radio-frequency plasma enhanced chemical vapor deposition.The size of Ni particles and the surface morphology of carbon nanotubes were characterized by scanning electron microscopy.The effect of catalyst layer thickness on carbon nanotubes has been in depth investigated with the results that the density,size and distribution of Ni catalyst particles formed from catalyst layer of different thickness play a significant role in the surface morphology of carbon nanotubes.When the catalyst thickness is less than 5 nm by plasma etching,the density of catalyst particles are small and unevenly distributed,leading to a low yield and weak orientation of the prepared carbon nanotubes.And,if the thickness is beyond to 15 nm,the catalyst particles are prone to be larger and adhered together.In addition,the most of catalysts are wrapped by amorphous carbon during the process of growth,resulting in a low yield of the carbon nanotubes.However,when the thickness is approximate to 10 nm,the formed catalyst particles are distributed evenly and the density of the particles are large.The produced carbon nanotubes have a high purity and good orientation,compared with synthesized using 5 nm or 15 nm in thickness.