Determination of bonding in diamond-like carbon by Raman spectroscopy

Raman spectroscopy is a very popular, non-destructive tool for the structural characterisation. of carbons. Raman scattering from carbons is always a resonant process, in which those configurations whose band gaps match the excitation energy are preferentially excited. Any mixture of sp(3), sp(2) and sp(1) carbon atoms always has a gap between 0 and 5.5 eV, and this energy range matches that of IR-vis-UV Raman spectrometers. The Raman spectra of carbons do not follow the vibration density of states, but consist of three basic features, the G and D peaks at approximately 1600 and 1350 cm(-1) and an extra T peak, for UV excitation, at similar to980-1060 cm(-1). We propose to rationalise the vast range of experimental data available in literature at any excitation wavelength by a simple model, which considers the main factors influencing the Raman spectra. The great advantages of multi-wavelength Raman spectroscopy will be clarified by a series of examples. In particular we show how it can be used to probe the structural changes induced by annealing and by nitrogen introduction. UV Raman spectroscopy also probes heteropolar or bonds in a complementary way to infrared spectroscopy. We demonstrate the direct detection of C-H vibrations in hydrogenated DLC samples, Si-H and Si-C vibrations in amorphous silicon and amorphous silicon-carbon alloys and the easier probe of CN sp bonds in amorphous carbon nitrides. (C) 2002 Elsevier Science B.V. All rights reserved.