Carbon nitride films, deposited by reactive dc magnetron sputtering in Ar/N2 discharges, were studied with respect to composition, structure, and mechanical properties. CNx films, with 0x0.35, were grown onto Si 001 substrates at temperatures between 100 and 550 °C. The total pressure was kept constant at 3.0 mTorr with the N2 fraction varied from 0 to 1. As-deposited films were studied by Rutherford-backscattering spec- troscopy, x-ray photoelectron spectroscopy, electron-energy loss spectroscopy, Raman and Fourier transform infrared spectroscopy, and nanoindentation. Three characteristic film structures could be identified: For temperatures below 150 °C, an amorphous phase forms, the properties of which are essen- tially unaffected by the nitrogen concentration. For temperatures above 200 °C, a transition from a graphi- telike phase to a ‘‘fullerenelike’’ phase is observed when the nitrogen concentration increases from 5to 15 at. %. This fullerenelike phase exhibits high hardness values and extreme elasticity, as measured by nanoindentation. A ‘‘defected-graphite’’ model, where nitrogen atoms goes into substitutional graphite sites, is suggested for explaining this structural transformation. When a sufficient number of nitrogen atoms is incor- porated, formation of pentagons is promoted, leading to curving of the basal planes. This facilitates cross- linking between the planes and a distortion of the graphitic structure, and a strong three-dimensional covalently bonded network is formed.
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