Effect of the carbon ion energy on the microstructure of ta-C/Cr multilayers

The effect of the carbon ion energy applied in a pulsed arc deposition process on the morphology of the interface between Cr layers and subsequently deposited tetrahedral bonded carbon (ta-C) coatings was investigated. The carbon ion energy was varied through the bias voltage between ~ 25 and 500 eV. Small-angle and wide-angle X-ray scattering (SAXS and WAXS), high resolution transmission electron microscopy (HRTEM) and electron energy loss spectroscopy (EELS) were used as the central experimental methods for microstructure analysis. In order to improve the scattering power of the ta-C/Cr interfaces for SAXS, the samples were prepared in the form of ta-C/Cr multilayers. SAXS revealed density and thickness of individual layers in the multilayer stack, and the roughness and morphology of the ta-C/Cr interfaces. The density of ta-C layers ranged between 2.72 and 3.15 g/cm3, which was related to the amount of sp3 bonds between 37% and 71%. The amount of the sp3 bonds calculated from the density of the ta-C layers agreed well with the amount of the sp3 bonds determined using EELS. HRTEM confirmed both the increase of the interface roughness with increasing carbon ion energy and the changes in the correlation of the interface corrugations observed by SAXS. Furthermore, HRTEM approved the crystallinity of Cr layers revealed by WAXS.