Physical and chemical approaches to tailor 2D coating/substrate adhesion - Experimental and theoretical insights

Two-dimensional materials have been extensively studied due to their superior electrical, thermal, optical and mechanical properties, while the latter creates an enormous potential in tribology, especially when utilized as solid lubricant coatings. However, their usage as solid lubricant coatings under applied conditions remains scarce and challenging due to a limited quality of the coatings/substrate interface and lack of adhesion, thus inducing excessive wear as well as increasing friction and compromising durability/reliability. To enhance the performance of 2D coatings and bridge the gap between lab-tests and applied conditions (real-world applications), it is crucial to improve their substrate adhesion, facilitating the transition from a potential to tangible usage of 2D materials in tribology. Therefore, our perspective aims at summarizing the primary factors influencing the coating/substrate interface and adhesion, which can be subdivided into physical and chemical approaches. After critically summarizing the existing state-of-the-art related to experimental approaches, the current understanding based on numerical simulations, from density functional theory to machine learning-assisted molecular dynamics, is holistically analysed to provides atomistic insights to predict and design adhesive 2D interfaces. Our article closes with a perspective outlook on how to further boost coating/substrate adhesion thus guiding research activities with the overall goal to take full advantage of the outstanding properties of 2D materials in solid lubrication enabling the reliable implementation of 2D coatings in demanding, real-world tribological environments.