Synthesis of aligned carbon nanofibers on electrochemically preroughened silicon

Aligned carbon nanofibers (CNFs) with a population density of about 3 × 10⁸ cm^-2 are synthesized on electrochemically roughened silicon using the bias-assisted chemical vapor deposition system. Isolated CNFs with much lower population density (∼3 × 10⁶ cm^-2) are formed on polished silicon wafer at the same growth conditions. The morphologies, microstructures, and components of the CNFs are accordingly characterized using scanning electron microscopy, Raman spectroscopy, transmission electron microscopy, and energy dispersive analysis of X-rays. On the basis of the surface barrier limited diffusion model, it is shown that electrochemical roughening of silicon surface can increase the population density of energetic carbon species that act as self-catalysts for the vertical growth of CNFs. The formation of CNFs with cone-shaped tips simultaneously involves the vertical growth and a continuous thinning of fiber tips by the bombarding of CH₄⁺ and H⁺ ions in CH₄/H₂ plasma.