High-resolution transmission-electron microscope characterization of onionlike carbon transformed from nanodiamond

Abstract

The onionlike carbon (OLC) was fabricated by annealing nanodiamond synthesized by detonation at the annealing temperatures from 500 to 1400 °C and at the pressure of approximate 2 Pa. A high-resolution transmission-electron microscope was used to characterize the microstructures of the OLC as-fabricated. The results showed that at the annealing temperature of 500 °C, nanodiamond began transforming into amorphous carbon. At the annealing temperature of 800 °C, nanodiamond was transformed into amorphous carbon completely. At the annealing temperature of 900 °C, OLC began appearing and the size of the OLC particles was smaller than 5 nm. At the annealing temperature of 1000–1200 °C, the OLC particle with larger size than 5 nm was fabricated. Moreover, the amorphous carbon untransformed and coexisted in the center of the OLC particle became fewer and fewer with the annealing temperature increase. At the annealing temperature of 1400 °C, all the amorphous carbon was transformed into the OLC. The OLC particles exhibited similarity to the original nanodiamond particles in shape. The formation process of the OLC included formation of amorphous carbon, formation of graphite fragment, connection of graphite fragment, connection and curvature of graphite sheets, and closure of graphite layers.