Structure changes of MPECVD-grown carbon nanosheets under high-temperature treatment

Vertically-aligned carbon nanosheets (CNSs), which were fabricated by microwave plasma-enhanced chemical vapor deposition in Ar and CH4 system, have been annealed at high temperatures in the range of 1200-3000 °C. The morphologies and microstructures of the treated CNSs were analyzed by scanning and transmission electron microscopes, and Raman spectroscopy. High temperature treatment process efficiently removed the amorphous carbon and some defects and improved the graphitization of the CNSs. The graphitized grains increase and the interlayer spacing decreases with increasing heat temperatures. Heat treatment of the CNSs at temperatures from 1500 to 2000 °C was found to achieve the edges consisting of many single-layer graphene sheets. Annealing at temperatures above 2100 °C, the edges of nanosheets consist of 2-5 layer graphene with many zigzag junctions. The mechanism of reconstruction for the edges in the CNSs ascribes possibly to the carbon atom vaporization at high temperatures.