Influence of the Carbon Ion Implantation on the Adhesion and Properties of Amorphous Carbon Films on Germanium

Abstract

A method for the synthesis of amorphous hydrogenated (a-C:H) carbon films with high adhesion is proposed, based on the implantation of carbon ions into a monocrystalline germanium substrate. The flow of ionized carbon was created by an anode layer ion source in crossed electric and magnetic fields. Propane gas was introduced into the area with an increased electron concentration. The gas flow rate was ranged from 4.5 to 10 cm³/min. Ionized fragments of propane, including carbon, were accelerated by the electric field and deposited on the substrate. At the same time, ionized carbon penetrated into the surface layer of germanium, creating a interlayer that provides adhesion of the film. The substrate was sputtered by argon ions for several minutes. The synthesis of the coating includes two-stage deposition. At the first stage, the films were deposited by an ion beam with a mean energy of about 1.6 keV for 0.5 to 1 hour to obtain an adhesive interlayer. Then the mean energy of the beam was reduced to 0.3 keV and the deposition continued for 3.5 hours to maintain the hardness of the coatings. The coating growth rate was ranged from 0.3 to 1.3 Å/sec. Adhesion, the bond between the coating and the substrate, obtained is high: there is no detachment while scratching by the Berkovich diamond nanoindent with a load of up to 50 mn. The hardness is 20 GPa. The film thickness is 600 nm. Spectroscopic studies have shown that the maximum transmission of the germanium with a single side a-C:H coating is 67 % at a wavelength of 5 µm, and of the single crystal Ge is 51 %. The results of the current research can be applyed in the formation of protective antireflective coatings of optical systems, the creation of medical implants and mechanical devices.