Mechanical properties of diamond/a-C nanocomposite films

Nanostructured amorphous carbon (na-C) is a hybrid form of carbon in which nanocrystallites are embedded in an a-C matrix. It has attracted considerable attention, because it offers the possibility to tailor the mechanical and electronic properties of a-C. We present here our studies of a particular form of na-C, containing diamond nanocrystals, using tight-binding molecular dynamics and empirical-potential Monte Carlo simulations. The calculations allow us to shed light into several properties of this material. We examine its structure, stability as a function of temperature and size of nanocrystals, stress state, and hardness. We find that the nanocrystals are stable only in dense, highly coordinated a-C matrices. The nanocomposite films possess negligible intrinsic stresses. The elastic moduli and yield stresses under tensile or shear load are consistently and considerably higher than those of pure a-C, making the nanocomposite diamond/a-C films suitable for ultra-hard mechanical coatings.