Well-aligned carbon nanotubes grown on a large-area Si substrate by thermal chemical-vapor deposition

We have grown vertically aligned carbon nanotubes (CNTs) on large areas of Co-Ni codeposited Si substrates by using thermal chemical vapor deposition with C₂H₂ gas. The CNTs grown by thermal chemical vapor deposition are multiwalled structures, and the wall surfaces of the nanotubes are covered with a defective graphite sheet or carbonaceous particles. The CNTs range from 50 to 120 nm in diameter and about 130 μm in length at 950 °C. The grown CNTs have a bamboo structure. As the particle size of the Co-Ni catalyst decreases, the diameter of the CNTs decreases, and the vertical alignment is significantly enhanced. Steric hindrance between nanotubes forces them to align vertically during the initial stage of the growth. The turn-on voltage is about 0.8 V/μm with a current density of 0.1 μA/cm², and the emission-current density is about 1.1 μA/cm² at 4.5 V/μm. The emission current reveals a Fowler-Nordheim mode.