Abstract
A key factor to the implementation of devices with vertically aligned carbon nanofibers (VACNFs) is fundamental understanding of how to control fluctuations in the growth direction of the fibers. It has previously been established that the electric field at the substrate is the primary factor in determining the orientation of fibers grown catalytically using plasma enhanced chemical vapor deposition (PECVD) process. However, the hypotheses for the mechanism that correlates the processes at the catalyst nanoparticle with the nanofiber growth direction with electric field still await validation. Synthesis of carbon nanofibers on insulating substrates by continuous direct current (DC) plasma in the vicinity of grid electrodes provide observations important in elucidation of the role of electric field in alignment. To perform these observations, VACNFs were synthesized on a fused silica substrates using direct current PECVD. To maintain continuous glow discharge above the substrate, a metal grid electrode layer (Cr) was deposited over silica with windows of exposed silica ranging in size from 200μm to 1mm. Observed trends in nanofiber alignment at the window-electrode interface suggests that the alignment is governed by the direction of the ion flux rather than the electric field at the substrate level. The proposed alignment mechanism is that ion sputtering of the carbon film on a catalyst particle defines the growth direction of the nanofibers. With this development, fiber growth direction can be better manipulated through changes in ionic flux direction, opening the possibility for growth of nanofibers on substrates with unique geometries.
