Formation of icosahedron twins during initial stages of heteroepitaxial diamond nucleation and growth

Heteroepitaxy of diamond on single-crystalline iridium via bias enhanced nucleation remains the most successful, and simultaneously, the most unexplored crystallization process developed for fabrication of wafer-scale thin films and free-standing substrates. Unique conditions provided by nucleation and growth from ""soft-implanted"" carbon clusters cause the formation of three-dimensional crystallographic irregularities, which take the form of various polyhedrons, also known as multiply twinned particles (MTPs). It is shown here that the diamond MTPs retain a thermodynamically stable structure on the micrometer-scale and can be controllably reproduced using specific nucleation and growth conditions. Particular crystallization mechanisms leading to the formation of icosahedron twins and completed icosahedrons in thin diamond epilayers are discussed, and the experimental findings are supported by a phenomenological model based on thermodynamic and kinetic concepts.