Hydrogenated amorphous carbon thin films deposited by segmented hollow cathode

Full text: Diamond-like carbon (DLC) is a metastable form of amorphous carbon with attractive properties such as high hardness, low friction, chemical inertness and high wear resistance. From a physicochemical point of view, the fraction of sp³ and sp² sites, the nature and the energy of carbon bonds and the amount of hydrogen influence the morphology and properties of DLC thin films. As the sp³ content increases in a-C:H, the sp² site ordering changes from aromatic clusters at large sp² content. Moreover, the fraction of non-hydrogenated sp³ bonds influence the hardness of amorphous carbon. In this work, hydrogenated amorphous carbon (a-C:H) thin films were deposited using a simple, low cost and efficient pulsed DC plasma enhanced chemical vapor deposition technique provided by a segmented hollow cathode arrangement. The samples were characterized by Scanning Electron Microscopy, Energy Dispersive X-Ray Spectroscopy, Raman Spectroscopy, Nanoindentation measurements, Elastic Recoil Detection Analysis, and Glow Discharge Optical Emission Spectroscopy. a-C:H thin films are homogenous in terms of carbon and hydrogen contents along the film. According to Raman spectra, the thin film hardness depends linearly on both G peak position and I_D/I_G ratio. Moreover, the hardness depends on the working conditions such as power supply voltage and total working pressure. The sample with the highest hardness (14 GPa) was obtained by a voltage of 800 V and a pressure of 15 Pa. There are no significant changes on hardness when the proportion of methane is varied. Finally, a physical scattering model is proposed to estimate the mean ion energy of carbonaceous species arriving on a-C:H thin films as a function of processing parameters as pressure and voltage. This model allows to develop a relationship between the mean ion energy of carbonaceous species and the hardness of thin films and provides a simple and powerful tool to estimate the final hardness of a-C:H thin films, in particular those with properties of DLC, as a function of processing parameters. (author)