Effect of catalytic metals of various elements on synthesis of graphite-capped, vertically aligned carbon nanotube arrays

Abstract

We investigate the effect of catalytic elements on the growth of graphite-capped, vertically aligned carbon nanotube (CNT) arrays (referred to as the “composite”) in terms of graphite precipitation and CNT growth followed by granulation of catalytic particles. The growth was carried out on Al2O3 (20 nm)/SiO2 (50 nm)/Si substrates covered with various thicknesses of catalytic layers of Fe or Co by thermal chemical vapor deposition at 670 °C using ethanol vapor as a carbon precursor. The structures of grown carbon films were evaluated by scanning electron microscopy (SEM) and dynamic force microscopy (DFM), and crystallinity was estimated by Raman spectroscopy. It is found that the catalyst element strongly affects the structure of the grown composite films. Iron catalyzes composite films in a wider and thicker region of catalyst film thickness (4.8–9.1 nm) than that of cobalt (3.9–4.2 nm). The difference is explained by the quality of graphite layers precipitated from catalytic particles: iron precipitates more defective graphite layers than cobalt through which the carbon supply is enhanced leading to the successive CNT growth.