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Amorphous silicon carbide and silicon nitride thin films have attracted much attention in the last years because of their excellent physical and mechanical properties. Amorphous silicon-carbon-nitride (a-SiCN) belongs to a new class of ternary compound materials which show excellent mechanical properties, low friction coefficient, wide band gap, high refractive index and high chemical inertness. The physical properties depend, not only on the composition, but also on the chemical bonding and local atomic order of constituent elements in the films, which depend strongly on the deposition parameter. The objective of the present work is to link the structure of a-SiCN deposits to their optical properties. To carry out this study, a-SiCxNy thin films with various compositions were deposited by radiofrequency sputtering of a silicon-carbide target under different Ar:N2 atmospheres. The composition determined by Rutherford Backscattering Spectroscopy (RBS) is sensitive to the total pressure, the Ar:N2 flow ratio and the power used for deposition. Infrared spectroscopy (FTIR) was used to identify the chemical bonding configuration. Typical absorption spectra showed that a prominent band occurs in the 500-1600 cm-1 range. The decomposition of this band results in three parts: The band at about 720 cm−1 corresponds to Si–C asymmetric stretch vibration. The one at around 810 cm−1 is caused by Si–C–N bond and the last one which is located at around 1050 cm−1 corresponds to the C–N bond stretching vibration. The electron spin resonance (ESR) was used to identify the defects evolution. For that, the g-values and the line width peak to peak have been determined and discussed versus the composition. We show that these two parameters decrease when the nitrogen content increases in the deposits. The energy band gap Eg is a very useful parameter for characterizing amorphous semiconductors and can be determined from UV-vis spectroscopy measurements and using Tauc relation. It is clearly observed that the Eg values are both sensitive to the nitrogen content and the spin densities in the films. |