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

TL;DR

This study investigates how the sp^2 carbon component affects the elastic moduli of ultrahard diamond films and nanocomposites, revealing that increased sp^2 content leads to material softening.

Contribution

It provides a detailed analysis of the sp^2 dependence of elastic properties in diamond-based materials using empirical and tight binding models.

Findings

Higher sp^2 content reduces material rigidity.

sp^2 atoms in the matrix and grain boundaries cause softening.

Strain relaxation mechanisms are associated with sp^2 regions.

Abstract

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.