Basics and Application of Diamond-Like Carbon Films

Carbon neutrality is widely considered to be one of the most important issues in the world in 2050.  Diamond-like carbon (DLC) films are expected to contribute to realizing the carbon neutrality because of its low friction coefficient against variety of materials. DLC have been widely applied in industries. In particular, there is a growing demand for their use as protective films for mechanical parts owing to their excellent wear resistance and low friction coefficient. DLC films have been deposited by various methods and many deviate from the DLC regions present in the ternary diagrams proposed for sp³ covalent carbon, sp² covalent carbon, and hydrogen. Consequently, redefining the DLC region on the ternary diagram is required especially from industrial point of view. Therefore, our research group have investigated the sp³ ratio, hydrogen content, and other properties of more than 70 types of amorphous carbon films and present the classification of amorphous carbon films, including DLC. Amorphous carbon films were widely found with nonuniform distribution on the ternary diagram. The number of carbon atoms in the sp³ covalent carbon without bonding with hydrogen and the logarithm of the hydrogen content were inversely proportional. Further, we elucidated the DLC regions on the ternary diagram, classified the amorphous carbon films, and summarized the characteristics and applications of each type of DLC.