Raman Spectroscopy as a Characterization Tool for Carbon Materials

This chapter describes how the Raman spectroscopy can be applied to the characterization and study of the physical properties of carbon materials. The general characteristics of the Raman spectroscopy are compared with other spectroscopies. These include: the coherence length of periodicity for light scattering is relatively short-typically ~10 nm, and the Raman microprobe is capable of a high spatial resolution, typically 1 μm. One unique use of the Raman spectroscopy is the study of the disordering or defects in crystals-these giving rise to additional disorder-induced Raman modes because of the non-adherence to the strict selection rules. The phase transitions or changes in the structures caused by temperature, pressure or stress changes are extensively studied by Raman spectroscopy. Representative Raman spectra are presented for allotropic forms of carbon, including diamond, graphite, disordered carbons such as-glassy carbon, and the diamond-like carbon, C₆₀ and carbon nanotubes. The Raman spectroscopy studies the photo-induced structural changes in the C₆₀, the one-dimensional properties of carbon nanotubes in conjunction with their resonant behavior, the detection of the sp³-bonded carbons using the high energy ultra-violet (UV) excitation, the electron-phonon coupling in the superconducting K₃C₆₀, and the Raman imaging of diamond in a CVD-diamond film.