The properties of free-standing diamond films after plasma high temperature treatment of the rapid heating

The plasma treatment of rapid heating was introduced for increasing fracture strength of free-standing diamond films. The effects of plasma high temperature annealing treatment on surface morphology, internal stress, vacancy defects, impurities and fracture strength of free-standing diamond films were investigated by scanning electron microscopy (SEM), Raman, positron annihilation technique (PAT) and mechanical property testing. It showed that the fracture strength of the diamond films increases up to 70% for lower fracture diamond films with treating temperature (1500–1600 °C). The graphitization in surface and interior of diamond films would be produced by high temperature treatment more than 1700 °C. Fracture strengths of diamond films could be enhanced after high temperature treatment and the main factor of that was compressive stress state in diamond films induced by graphitization. The impurity of N was segregated and integrated with vacancy cluster to become [N–V]0 and [N–V]−.

Research Highlights
► Plasma treatment increase fracture strength of free-standing diamond films.
► Strength increases up to 71.6% for the diamond films with lower strength.
► Graphitization in diamond films was produced at more than 1700 °C.
► Impurity of N integrated with vacancy as [N–V]0 and [N–V]¯.