Raman spectroscopy of CVD carbon thin films excited by near-infrared light

The interpretation of the Raman spectra of amorphous carbon thin films is still controversial. The concept of their decomposition into D and G peaks does not work in some cases, when presence of additional bands can be deduced from the shape of the spectra. One to investigate these extra component bands is to change the excitation wavelength. This results in the enhancement of the Raman scattering cross-section of the different structural units. Our investigations were aimed to detect the component bands become intense by using infrared excitation (785 nm) in the Raman spectra of amorphous carbon thin films prepared from benzene and methane in a wide range of deposition parameters. By comparing the visible and infrared excited Raman spectra it will be proven that the well-known G band of the a-C:H layers consists of two components, one of which exhibiting no dispersion. It will be also shown that he infrared excitation makes distinguishable Raman bands assigned to delocalized (pi) electronic structure due to resonant enhancement of the scattering.