Conversion of single-crystalline C-60 nanodisks and nanorods into graphitic nanostructures via hydrogen thermal annealing

Abstract

We have developed a process to convert C-60 nanostructures into graphitic nanostructures. Disk-shaped and wire-shaped C-60 nanostructures synthesized by the liquid-liquid interfacial precipitation method, the vapor-solid process, and solvent evaporation were successfully converted into graphitic structures by thermal annealing in hydrogen at 900 degrees C. Scanning electron and tunneling electron microscopic studies confirmed that the converted nanostructures were composed of multi-graphitic structures such as multi-walled carbon nanotubes, carbon nanofibers, and carbon onions. Fourier transform Raman spectroscopy and conductance measurements were carried out to further confirm the successful formation of graphitic layers. In the Raman spectra, the nanostructures converted from C-60 disks showed signature D, G, and G' bands of graphitic structures, while the Ag mode (1469 cm(-1)) of the original C-60 molecule disappeared. C-60 nanowire devices fabricated for the conductance measurements of the converted structures showed dramatically decreased resistance (R approximate to 100 k Omega) compared to the pristine C-60 wire (R > 100 M Omega). Further manipulation of the reaction environment, including the gas and the annealing temperature, may reveal a new way to attain diverse graphitic nanostructures economically.