Infrared optical properties of amorphous hydrogenated carbon nitride film

The microstructure and optical properties of nitrogen-doped hydrogenated carbon DLC:N films deposited by the rf plasma-enhanced chemical vapor deposition (PECVD) method were studied by atomic force microscopy (AFM), Raman, Fourier-transform infrared (FTIR) and infrared ellipsometric (IRE) spectrometry. The absorption intensities of the peaks CNH (1600 cm−1), CN (2200 cm−1) and NH (3250 cm−1) in the IR spectra increase with the N2/CH4 flux ratio. Raman spectra show that the shape of the D and G bands of DLC:N film varies slightly with the increase of N content, which means that the main structures of N-doped films are still diamond-like carbon (DLC). However, four Gaussian decomposition results show that the peak of the G band widens and shifts to the low wavenumber with increased nitrogen content in Raman spectra due to amorphous C3N4 structure being formed in the nitrogen-doped DLC film. AFM topographies and lateral force microscopy (LFM) images of DLC:N film confirm that the amorphous C3N4 exists as particles several tens of nanometers in size in the film. IRE spectral analysis results show that the refractive index of the film in the infrared region (2–14 μm) decreases slightly from 1.8 to 1.6 with increased nitrogen content.