Interfacial Engineering for Enhanced Adhesion of Diamond Coatings

Diamond coatings feature a variety of intriguing properties, such as high thermal conductivity, hardness, mechanical and chemical resistance, and tunable electrical conductivity. A variety of applications for this material have emerged. However, interfacial problems hinder the development of these applications. The adhesion of diamond coatings is of pivotal importance for the service life and performance of diamond coatings. Poor adhesion stems from several issues, for instance, a mismatch of thermal expansion coefficient (TEC) of the diamond and the substrate, poor nucleation of diamond, detrimental effects of elements in the substrates, poor bonding between the diamond coating and the substrate, and etching or degradation of the substrate during diamond deposition. The specific challenges depend on the substrate to be coated and the envisaged application. This review aims to introduce and explain the challenges encountered during thin diamond deposition on non-diamond substrates and delineates strategies to overcome issues related to poor adhesion and diamond film delamination. These strategies include pretreatment processes, such as changing the roughness of the substrate, interlayers, and advanced nucleation strategies, and methods during diamond film deposition, such as multilayer strategies. To complete the review, we provide a brief discussion of unanswered research questions.