Diamond-like carbon films prepared by facing-target sputtering

Diamond-like carbon films were prepared by a facing-target sputtering technique at different Ar pressures. The films were characterized using atomic force spectroscopy, Raman spectroscopy, ellipsometry and nanoindentation tests. All films are clean and exhibit smooth surface morphology, with RMS roughness of less than 0.2 nm over an area of 1 μm². The Raman spectra show a G-peak ranging from 1560 to 1565 cm^-1 and a D peak from 1395 to 1420 cm^-1. As the Ar pressure increased from 2 to 10 mtorr, the I_D/I_G intensity ratio increased monotonously from 1.1 to 2.4, and the G-peak width decreased from 199 to 145 cm^-1. The Tauc optical bandgap decreased from 2.1 to 1.7 eV, and the hardness decreased from 20 to 14 GPa with increasing Ar pressure. The variation in the parameters measured can be interpreted by the decrease in the sp³ fraction of carbon atoms with increasing Ar pressure.