Raman scattering in carbon nanotubes

Abstract

The vibrational properties of single-walled carbon nanotubes reflect the electron and phonon confinement as well as the cylindrical geometry of the tubes. Raman scattering is one of the prime techniques for studying the fundamental properties of carbon tubes and nanotube characterization. The most important phonon for sample characterization is the radial-breathing mode, an in-phase radial movement of all carbon atoms. In combination with resonant excitation it can be used to determine the nanotube microscopic structure. Metallic and semiconducting tubes can be distinguished from the high-energy Raman spectra. The high-energy phonons are remarkable because of their strong electron-phonon coupling, which leads to phonon anomalies in metallic tubes. A common characteristic of the Raman spectra in nanotubes and graphite is the appearance of Raman peaks that correspond to phonons from inside the Brillouin zone, the defect-induced modes. In this Chapter we first introduce the vibrational, electronic, and optical properties of carbon tubes and explain important concepts such as the nanotubes' family behavior. We then discuss the Raman-active phonons of carbon tubes. Besides the vibrational frequencies and symmetries Raman spectroscopy also allows optical (excitonic) transitions, electron-phonon coupling and phase transitions in single-walled carbon nanotubes to be studied. © Springer-Verlag Berlin/Heidelberg 2006.