Characteristics and thermodynamics of carbon nanotubes synthesized via corona plasma deposition

Abstract

Summary form only given. Carbon nanotubes were synthesized via a cooperating technology of low-temperature plasma deposition and template-controlled growth at atmospheric pressure. The as-grown multiwall carbon nanotubes with outer diameter of about 40 nm were restrictedly synthesized in the channels of anodic aluminum oxide template from a methane/hydrogen gas mixture, whose molar ratio is 1/10, by AC corona plasma deposition. The innermost diameter of the carbon nanotubes is about 1.3 nm. Differing from the well-crystallized graphitic nanotubes synthesized via high-temperature DC arc plasma, the carbon nanotubes synthesized via low-temperature plasma deposition generally consist of carbon crystallites whose basal planes roughly arrange along the tubular axes. So there raise questions about the formation mechanism of the tubular structure and the innermost diameter of the nanotubes. Previous report in energetics predicted the smallest graphitic nanotube being 0.4 nm, and carbon nanotube with such size was indeed synthesized via DC arc plasma. But the energetics of crystalline carbon nanotube is complicated because there is considerable internal surface energy among the carbon crystallites. We calculated the Gibbs free energies of tubular crystallitic carbon nanotube and solid crystallitic nanowire. It was found that the carbon nanotubes consisting of crystallites with their basal planes arranging along the tubular axes have the lower Gibbs free energy, indicating a possible thermodynamic preference for their tubular structures