Mechanism of formation of 〈110〉 oriented fivefold microcrystallites in diamond films

Abstract

We have investigated the formation of 〈110〉 oriented fivefold diamond microcrystallites on {001} silicon substrates using high-resolution transmission electron microscopy (HRTEM). The HRTEM micrographs clearly show that fivefold symmetry in diamond microcrystallites results from twinning in {111} planes, in agreement with electron diffraction data. The five 〈110〉 oriented microcrystallites that provide fivefold symmetry are enclosed by {111} planes. The angles between various planes in these microcrystallites can be directly measured in HRTEM micrographs. The angles between {111} planes are found to vary from 70.5° (ideal) to as much as 74° for some microcrystallites. The boundaries of microcrystallites contain coherent twins with only occasional presence of dislocations to accommodate the misfit. We propose a model for nucleation and formation of fivefold diamond microcrystallites. The proposed model, based upon the presence of a/2〈110〉{001} edge dislocations, is found to be consistent with HRTEM observations.