Amorphous carbon nitride films irradiated with argon ions

Abstract

Hard, electrical-conductive and corrosion-resistant coatings can be obtained by energetic ion irradiation of amorphous carbonaceous materials such as organic polymers and hydrogenated amorphous carbon films. In this work, amorphous carbon nitride films (a-C:N) containing hydrogen and oxygen were deposited in glow discharges of C2H2, N2 and O2 mixtures and then irradiated with 150 keV Ar+ ions at fluences ranging from 1018 to 1020 m−2. The molecular structure and elemental composition of the as-deposited and irradiated films were studied using infrared reflectance spectrophotometry (IRS) and Rutherford backscattering spectroscopy (RBS). A significant change in the composition and structure of the films, produced by ion irradiation, was revealed by the IRS spectra. Increasing the ion fluence, Φ, the concentration of unsaturated CC bonds increased while that of N–H, C–H and CO bonds decreased. From the RBS data it was concluded that the O/C and N/C atomic ratios decreased with ion irradiation. Modifications of the electronic structure were manifested by changes in the optical gap, EG, and in the electrical conductivity, σ. Ultraviolet-visible spectroscopy was used to determine EG while σ was obtained using a two-point probe. While EG decreased, σ increased with increasing Φ. The dependence of EG and σ on the structural modifications is discussed. Comparison of the electrical conductivity measurements of this work with those reported for irradiated amorphous diamond like carbon (DLC) films revealed that even at high fluences – when the content of both the a-C:N and the DLC films are nearly 100% carbon – the electronic structures of these materials are different.