Structure modelling of 3 and 9 coincident boundaries in CVD diamond thin films

Abstract

High-resolution electron microscopy (HREM) was used to investigate the structure of σ3 and σ9 coincident-site-lattice (CSL) boundaries in chemical vapour deposited (CVD) polycrystalline diamond thin films. In the incoherent σ3 boundaries, such as {112} S3, {111}/{115} S3, and {001}/{221}S3 boundaries, no rigid-body translation parallel to >111< direction was identified. The structural units in their atomic models consisted of symmetrical five and seven membered rings, which contained non-tetra-coordinated sites. The σ9 CSL boundary was always parallel to a {114} plane. Its structural units were composed of irregular five- and seven-membered rings, which also contained non-tetra-coordinated sites. Computer image simulations based on multislice calculations were performed using unrelaxed atomic models containing dangling bonds. The simulation results revealed that the models could describe the atomic structure of the boundaries quite well, except for the {112} S3 boundary, where a rigid-body translation perpendicular to the boundary plane is necessary to reproduce the experimental image. Although the reconstruction structure could not be observed along (110) axis directly, the possible influence of the non-tetra-coordinated sites on the boundary stability was discussed in relation to the electronic structure of the boundaries.