Hydrogen concentrations and mass density obtained by X-ray and neutron reflectivity on hydrogenated amorphous carbon nitride thin films

In this work, specular reflectivity of neutrons and X-rays was used to determine the scattering-length density profile of nitrogen-doped amorphous carbon films (a-C:H:N) perpendicular to their surface. By the combination of these two techniques, we obtained not only the mass density, but also the concentration of hydrogen. This experimental approach was applied to study the influence of Ar plasma dilution on the properties of a-C:H:N films. The structure (Raman spectroscopy) and chemical structure (X-ray photoelectron spectroscopy) of two series of specimens, deposited with plasma decomposition of CH4/N-2 and CH4/N-2/Ar mixtures, were analysed and the results were correlated to the film hydrogen concentration. The differences observed suggest that as Ar is introduced in the gas mixture, a progressive graphitisation of the films is observed and the mass density decreases. The hydrogen content for films grown in N-2-rich plasma atmosphere is higher with respect to those obtained without nitrogen dilution; otherwise, Ar dilution promotes lower hydrogen incorporation. (C) 2002 Elsevier Science B.V. All-rights reserved. RI Valentini, Luca/D-5238-2011; Kenny, Jose/F-9372-2010