Probing the sp~2 dependence of elastic moduli in ultrahard diamond films

摘要

The structural and elastic properties of diamond nanocomposites and ultrananocrystalline diamond films (UNCD) are investigated using both empirical potentials and tight-binding schemes. We find that both materials are extremely hard, but their superb diamondlike properties are limited by their sp~2 component. In diamond composites, the sp~2 atoms are found in the matrix and far from the interface with the inclusion, and they are responsible for the softening of the material. In UNCD, the sp~2 atoms are located in the grain boundaries. They offer relaxation mechanisms which relieve the strain but, on the other hand, impose deformations that lead to softening. The higher the sp~2 component the less rigid these materials are.