Structural Evolution of Annealed Graphitic Amorphous Carbon
Bulletin of the American Physical Society
We have used Raman scattering to investigate the effects of annealing on graphitic amorphous carbon (g-C). g-C is an amorphous phase of carbon primarily composed of sp^2 -planar-bonded carbon and no long-range order. g-C samples were annealed in 100^\circ C steps up to 1050^\circ C . Using 2.54 eV and 2.71 eV laser excitations, the Raman spectra show a clear progression from an amorphous phase to a nanocrystalline phase as the g-C is annealed to higher temperatures. The 1580 cm^-1 band emerges from the broad g-C spectrum and narrows, indicating ordering as the material slowly evolves toward graphite, but remains substantially broader than the 1581 cm^-1 E_2g^2 phonon of bulk graphite. Simultaneously, the 1350 cm^-1 (zone-edge) mode appears as structural order is gradually established. The Raman spectra were found to have a dependence on the excitation used: 2.41 eV excitation enhanced the 1350 cm^-1 band as compared to 1.92 , 2.54 , and 2.71 eV light. There is precedence for this type of enhancement in both graphite-like and diamond-like disordered materials, and the origin of this effect in our samples will be discussed.
T. Dallas, M. Holtz and JR Dennison, "Structural Evolution of Annealed Graphitic Amorphous Carbon," Bull. Am. Phys. Soc. 40(3), 538 (1995). APS Meeting, San Jose, CA, March 1995.