Study of the influence of Ar on the formation of diamond-like bonds in films obtained from CH4+Ar, RF plasma deposition

The concentration of the sp3 bonds in the volume (ratio Φ=N3 sp3/(N3 sp3+N2 sp2+N1 sp1), where N1, N2 and N3 are the concentrations of sp1, sp2 and sp3 bonds, respectively), is the basic parameter which determines the `diamond-likeʹ properties of amorphous carbon (a:DLC) films. Electrical, morphological and mechanical properties, as a function of the partial pressure of Ar, of a:DLC films, were measured and their relation to Φ was shown. From Auger electron spectroscopy (AES) data it was shown that the presence of Ar leads to sputtering of the low adhesive carbon atoms from the deposited film, consequently, the a-a:DLC is much more adhesive and harder which make thickness (t) a function of Ar concentration. Ar atoms in the film were found to be less than 2%. Visible and UV Raman spectroscopy, FTIR and XPS, were used to determine the concentration of sp3 bonds, (Φ), which was maximum for Ar=30%. Studies of morphology of the a:DLC films have shown that the average height profile (AHP) obtained from AFM data show an abrupt change for Ar=30%. Results of electrical and mechanical (microhardness) measurements have shown a maximum value of resistivity (ρ=1.4×109 Ωcm) and microhardness (H=2700 kg/cm2) is obtained also for Ar=30%. Since the measurements of Φ is maximum at concentration Ar=30% and for AHP appears abrupt changes, for ρ and H maximum, we may assume that this behaviour of the physical parameter, is due to the diamond-like structure with maximum Φ. The results obtained in this paper also have practical importance since the sample deposited at 30% Ar exhibits 50% sp3 bonding or more, which is high enough to use this material where diamond-like properties are needed.