A versatile plasma tool for the synthesis of carbon nanotubes and few-layer graphene sheets

A technique is reported for the study of the combined growth process of carbon nanotubes (CNTs) and few-layer graphene sheets (FLGS) by means of microwave plasma-enhanced chemical vapour deposition. The carbon radical concentration is identified as the most important parameter for determining the morphology of the as grown carbon nanostructures, either tubular CNTs or plain FLGS. During an experiment, each position on the samples is exposed to a specific carbon radical concentration. Samples, composed of nickel particles deposited on silicon oxide substrates, catalyze the growth of CNTs only if the carbon radical concentration is low. A rapid transformation of morphology from tubes to flakes can be observed when the carbon radical concentration increases. The flakes, formed at the highest carbon radical concentration, are identified as FLGS, only a few atomic graphene layers thick but up to several micrometers wide. A possible growth scheme, based on qualitative analysis by electron microscopy is presented. It is further shown that the growth of FLGS does not require a catalyst by using plain silicon and quartz substrates without nickel for the FLGS synthesis.status: publishe