Analysis of the structure of multi-component carbon films by resonant Raman scattering

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Abstract
Diamond and carbonaceous films grown in a microwave assisted plasma reactor have been characterized by x-ray diffraction, scanning electron microscopy, and Raman spectroscopy. This study is mainly focused on the identification of the different carbonaceous compounds which can coexist with the diamond depending on the synthesis parameters. Selective etching reactions and the excitation wavelength dependence of Raman cross sections of the different carbon species reveal that the broad and poorly structured Raman spectra in the 1100–1700 cm−1 region contain six components that arise from three different carbonaceous species: (i) one species is graphitic and is identified from the components at about 1350 and 1590 cm−1 which are resonantly enhanced as compared to the other components when the excitation energy is lowered from 3 to 2 eV. (ii) The second species is associated with the two broad bands at 1350 and 1550 cm−1 and is attributed to amorphous diamond-like carbon (a-C:H); both bands are resonantly enhanced by excitation energies in the range from 2.41 to 3.53 eV. These bands do not shift with exciting energy. (iii) The third species is associated with a band centered at about 1470 cm−1 and a weak band at 1150 cm−1. This 1470 cm−1 band overlaps with the 1550 cm−1 band of the diamond-like component, resulting in an apparent frequency down-shift when the incident photon energy decreases below the resonant enhancement range of the 1550 cm−1 band. Possible models for the structure of the third species are discussed.