The goal of the proposed project is to understand the physico-chemical basis underlying the excellent tribological properties of silicon oxide-doped diamond-like carbon (SiOx-DLC) coatings. SiOx-DLCs are amorphous films supposedly consisting of two interpenetrating, interbonded networks, one being a hydrogenated amorphous carbon network and the other a silica glass network. They exhibit impressive thermal stability and oxidation resistance and excellent tribological behaviour even at elevated temperatures, high contact stresses and in humid environments, making them promising candidates for several engineering applications.The goal of the project will be achieved via a hierarchical methodological approach aimed to determine the structure and composition of SiOx-DLC followed by the investigation of its thermal stability and tribological properties. The project has a strong multidisciplinary character and requires the novel combination of advanced analytical techniques. A new methodology, based on one of the most important surface-analytical developments emerging in the last decade - elevated-pressure X-ray photoelectron spectroscopy - will be used, enabling the study of the surface chemistry of SiOx-DLC at its critical environmental conditions (partial pressures of water, molecular oxygen, or hydrogen). Furthermore, the research project involves the extensive application, for the first time, of in situ tribological tests methods to the study of carbon-based materials for understanding the fundamental mechanisms underlying the environment effect on the tribological performance of SiOx-DLC.Establishing a fundamental understanding of the interrelationships between composition, structure, tribological performance, and durability for this class of carbon-based films can lead to new strategies for designing improved solid lubricants that can meet the requirements of advanced industrial applications. This would have significant economic and industrial benefit to the EU.