Hydrogenated amorphous carbon films (a-C:H) and hydrogenated carbon films containing as much as 15 at.% nitrogen (a-CNx:H) were synthesised by a plasma-assisted chemical vapour deposition (PACVD) apparatus. By changing the gaseous precursor (CH4, C6H12, C6H6, C2H2) the hydrogen content of the films can be varied between 26 and 58 at.%; serious adhesion problems were found when the hydrogen percentage attains the highest value. Hydrogen-free layers were deposited by magnetron sputtering in Ar (a-C) and N-2 (a-CNx) : nitrogen fractions range from 8 to 28 at.% and increase when the substrate is closer to the graphite target during deposition. Film hardness was evaluated by nanoindentation in older to avoid inflation of the assessed value consequent to the elastic recovery, which results to be quite large in the examined layers. The hardness measurements show values up to similar to 30 GPa and point out that both nitrogenation of a-C:H films and deposition by magnetron of hydrogen-free a-C layers lead to softer materials (similar to 18 GPa). Main features of Raman spectra are broad 'G' and 'D' peaks, characteristic of DLC layers : correlation between parameters of these peaks is discussed.