Investigations on the plasma enabled growth of vertical graphene sheets on CNT surface

Abstract

A theoretical model is developed to describe the plasma-assisted nucleation and growth kinetics of a vertical graphene (VG) sheet on a carbon nanotube (CNT) surface. The present model accounts the formalization of a charge separation region, i.e., plasma sheath between the bulk plasma and substrate surface in one-dimension along with the kinetics of all the plasma species (neutrals, positively charged species, and electrons), rate of charge accumulation on the graphene sheet surface, and growth of the VG sheet on the CNT surface owing to defect generation and various processes on the CNT surface. Using the model, we demonstrated that variations in the plasma enhanced chemical vapor deposition process control parameters such as the total gas pressure, input power, and substrate bias can be used for significant variation in the plasma composition and characteristics that in turn control the ion bombardment and generation of carbon species on the CNT surface and consequently tune the VG sheet growth characteristics such as height, thickness, and number density profiles of the VG sheet on the CNT surface. The results of the present study indicate that as the total gas pressure is lowered and the input power and substrate bias are enhanced, the number densities and height of the VG sheet on the CNT surface are increased; however, the thickness of the VG sheet is reduced. Some of our theoretical findings are in good agreement with the existing experimental results.