Structural defects and sp2 localization in CVD diamond

Abstract

Transmission electron microscopy and energy loss near edge spectroscopy were used to characterize microstructural defects in polycrystalline CVD diamond films. Of particular interest here is the change in sp2 content catalyzed by structural defects such as twin boundaries, random grain boundaries, and dislocations. Changes in bonding configuration from sp3 to sp2 are known to have significant impact on many properties of interest in CVD diamond. I have shown here that coherent Σ = 3 twin boundaries do not lead to sp2 formation, while dislocations and random grain boundaries do. Another feature of interest here is the fivefold twining structure, which is typically found in CVD diamond. It comprises four Σ = 3 coherent twin boundaries, but topological constraint for filling the entire space induces the formation of low-angle grain boundaries and multiple stacking faults in one of the twin domains. I have shown that such defects are indeed present and primarily localized in one domain. The strain associated with these defects increases the localized sp2 content in the diamond.