Growth of Metal-Free Carbon Nanotubes with an Amorphous Carbon Catalyst Layer

An amorphous carbon (a-C) thin film was used as a catalyst, layer to grow metal-free carbon nanotubes (CNTs). The a-C films were deposited with a closed-field unbalanced magnetron (CFUBM) sputtering method on Si substrates. The CNTs were prepared using a microwave plasma-enhanced chemical-vapor deposition (MPECVD) method with an a-C catalyst film coated onto a silicon substrate by using methane (CH4) and hydrogen (H-2) gas. The CNTs were grown at different temperatures (550 degrees C, 650 degrees C and 750 degrees C) with other conditions being held constant. Field emission scanning electron microscopy (FE-SEM) images showed growth trend of the CNTs against temperature. High-resolution transmission electron microscopy (HR-TEM) images showed the CNTs to be multi-walled. Energy dispersive spectroscopy (EDS) measurements confirmed that the CNTs consisted solely of carbon.