The influence of helium ion irradiation on amorphous hydrocarbon films

Amorphous hydrocarbon films were irradiated with 60–140 keV He ions at the dose ranging from 1.0 × 1015 to 1.0 × 1017 ions/cm2. The films about 1.4 μm thick were deposited on Si substrates and irradiated at room temperature. The surface and mechanical properties of as-deposited and He ion irradiated hydrocarbon films were analyzed by using atomic force microscopy (AFM), AFM-based nanoindentation and scratching tests. Their chemical compositions and structural properties were evaluated by FTIR and Raman measurements. Analysis showed that the He ion irradiation led to a decrease in their surface roughness and an increase in the nanohardness and scratching resistance. FTIR measurements indicated that the content of bonded H atoms in hydrocarbon samples was greatly decreased due to the He ion irradiation, and a dense and covalent three-dimensional network was formed in films. The Raman data confirmed the microstructural evolution of samples into a dense metastable structure containing a large fraction of sp2 C clusters.