Synthesis and Optical Properties in UV-Visible Range of Carbon Nitride Thin Films

The carbon nitride (CN_x) coatings were synthesized by plasma enhanced chemical vapor deposition (PECVD).The influence of the substrate temperature (50~200℃) on the microstructures, electronic structures and optical properties of the CN_x coatings was investigated with scanning electron microscopy, energy dispersive spectroscopy and X-ray photoelectron spectroscopy.The results show that the substrate temperature had a major impact.For example, as the substrate temperature increased, while sp²C=C bond little changed and sp² C=N bond gradually decreased, the sp³ C-C and sp³ C-N bonds increased (28.6%~36.4% and 21.4%~33.4%, respectively), and the coating became increasingly compact; the reflectivity increased (8%~40%), accompanied by a decreasing absorbance (92%~60%) in 200~800 nm range; and the optical gap increased (2.5~3.57 e V), simply because of a decrease of sp²C=N bond.We suggest that controlling of the substrate temperature may adjust the optical band-gap of CN_x coatings in UV-visible range.