Hard three-dimensional sp~2 carbon-bonded phase formed by ion beam irradiation of fullerene, a-C and polymeric a-C:H films

摘要

The formation of new carbon amorphous phase through the ion irradiation of fullerene, a-C and polymeric a-C:H films is presented. The carbon films were subjected to N irradiation at 400 keV in the fluence range from 10~(13) to 3 x 10~(16) N cm~(-2). Modifications in the carbon structure, as function of the irradiation fluence, were investigated using the Rutherford backscattering spectrometry, nuclear reaction analysis, Fourier transform infrared, Raman spectroscopy, UV-VIS-NearIR spectrophotometry and nanoindentation techniques. After high fluence, the three carbon samples were transformed into very similar hard (≈14 GPa) and non-hydrogenated amorphous carbon layers with very low optical gaps (≈0.2 eV) and an unusual sp~2 rich-bonded atomic network. The mechanical properties of the irradiated films correlated with the bonding topologies of this new sp~2 carbon phase are analyzed in terms of the constraint-counting model. The results show that the unusual rigidity was achieved by the distortion of the sp~2 carbon bond angles, giving origin to a constrained three-dimensional sp~2 carbon bonded network.