Abstract
Carbon nitride films, deposited by reactive dc magnetron sputtering in discharges, were studied with respect to composition, structure, and mechanical properties. films, with were grown onto Si (001) substrates at temperatures between 100 and The total pressure was kept constant at 3.0 mTorr with the fraction varied from 0 to 1. As-deposited films were studied by Rutherford-backscattering spectroscopy, 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 an amorphous phase forms, the properties of which are essentially unaffected by the nitrogen concentration. For temperatures above a transition from a graphitelike phase to a “fullerenelike” phase is observed when the nitrogen concentration increases from ∼5 to ∼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 incorporated, 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.
- Received 16 June 1998
DOI:https://doi.org/10.1103/PhysRevB.59.5162
©1999 American Physical Society