The Structure And Properties Of Amorphous Hydrogenated Carbon Films And Cr-containing Diamond-like Carbon Films

In the present work, the dependence of RF negative self-bias voltage on RF power and working pressure was systematically investigated by Oscilloscope with a high voltage probe at RF glow discharge in Ar, C₂H₂ and their mixture. It is found that the RF negative self-bias voltage, increasing with RF power and decreasing with working pressure, is a linear function of the square root of the RF power divided by the working pressure for all the gases used. Furthermore, the amorphous hydrogenated carbon films were deposited by RF-PECVD. According to the Raman spectra, the I_d/I_g ratio, increasing from 0.66 to 1.14 when the RF power increases from 500W to 700W, indicates that the sp² cluster size increases with the RF power. From the nano-indentation, the hardness and elastic modulus decrease from 10GPa and 135.5Gpa to 8Gpa and 106.6GPa respectively, as the RF power increases from 500W to 700W. All indicate that the higher RF power gives rise to a higher RF negative self-bias voltage and therefore a higher ion energy, which enhances the effect of ion bombardment and leads to a graphitization of a-C:H films and a reduction of the hydrogen content.The Cr-containing diamond-like carbon films (Cr-DLC) were also deposited by filtered cathodic vacuum arc technique. The surface morphology, composition, structure and properties of Cr-DLC film were investigated by SEM, EPMA, XRD, Raman spectra and nano-indentation. It is shown that the surface morphology of Cr-DLC film deposited at C₂H₂ flow rate of 15 sccm is smooth. Although there are a few particles, the size of them (about 1 μm) is much less than the size of particles on surface of films without filtering (large to about 100μm). When the C₂H₂ flow rate decrease from 30sccm to 10sccm, the content of Cr increases from 29.1 at.% to 49.3at.%, and the C/Cr increases from 1 to 2.5. The structure of Cr-DLC films is Cr-containing amorphous carbon films, and with increasing of C₂H₂ flow rate, the G site and the Id/Ig ratio decrease and more sp³C-H bond is formed. According to nano-indentation test, it can be seen that the hardness and elastic modulus of Cr-DLC films increase slowly with increase of Cr content at the beginning stage, and then sharply to 14Gpa and 198GPa respectively. It is suggested that when the Cr content increase, the Cr may transforms from metal Cr nano crystal to Cr carbide nano crystal, both them are surrounded by amorphous carbon matrix. And the formation of Cr carbide nano crystal leads to an increase in hardness and elastic modulus of Cr-DLC.