Transition of carbon nanotubes growth mode on NH3 plasma-modified Ni films at different plasma powers

Catalytic Ni films on Si substrates were modified by NH3 plasma, and carbon nanotubes (CNTs) were then grown on the Ni films by plasma enhanced chemical vapor deposition. The effect of the NH3 modification power was investigated in relation to the growth of CNTs. As the modification power increased above 20 W, the structural phase of the Ni films evolved from pure Ni to Ni-silicide (Ni-Si) phase. This could be explained by the inter-diffusion of Ni and Si, due to the energetic ion bombardments, which resulted in the formation of Ni-Si layer on the Si substrate. In addition, the growth mode of as-grown CNTs changed from top-growth to base-growth mode after the formation of the Ni-Si phase. This indicated that the Ni-Si layer adhered to the Si substrate more strongly than the Ni layer and the formation of the Ni-Si layer led the change of the CNT growth mode.