Selective synthesis of DC carbon arc-generated carbon nanotube and layered-graphene and the associated mechanism

Abstract

Herein we report how an anode is eroded and the eroded mass is deposited on the cathode surface at different arc currents () in a DC carbon arc discharge using roughly oriented graphite (ROG) as electrodes. It was found that the nature of anode erosion critically depends on and has profound effects on the morphology of the as-synthesized cathode deposits (CDs), the conversion efficiency of the system to form the CDs and their compositions. By characterizing the as-synthesized CDs in their totality by transmission electron microscopy, Raman spectroscopy, and x-ray diffraction it was found that there exists a critical value of below which the arc remains constricted, and above which the arc becomes intense. It was further found that the system can selectively generate both carbon nanotubes (CNTs) and layered-graphene sheets (LGs) when the carbon arc runs in constricted and intense modes, respectively. By the suitable adjustment of it is possible to switchover between the aforementioned arc-modes. Based on the experimental results, a semi-empirical model encompassing the plausible effects of rapid and random movement of the anode spot on the used ROG anode surface was developed to provide new insights into the growth mechanism of arc-generated CNTs and LGs. The state-of-the-art presented in this paper could facilitate the carbon arc discharge route for the tailored synthesis of highly crystalline CNTs and LGs.