Misfit accommodation mechanism at the heterointerface between diamond and cubic boron nitride

Diamond and cubic boron nitride (c-BN) are the top two hardest materials on the Earth. Clarifying how the two seemingly incompressible materials can actually join represents one of the most challenging issues in materials science. Here we apply the temperature gradient method to grow the c-BN single crystals on diamond and report a successful epitaxial growth. By transmission electron microscopy, we reveal a novel misfit accommodation mechanism for a {111} diamond/c-BN heterointerface, that is, lattice misfit can be accommodated by continuous stacking fault networks, which are connected by periodically arranged hexagonal dislocation loops. The loops are found to comprise six 60° Shockley partial dislocations. Atomically, the carbon in diamond bonds directly to boron in c-BN at the interface, which electronically induces a two-dimensional electron gas and a quasi-1D electrical conductivity. Our findings point to the existence of a novel misfit accommodation mechanism associated with the superhard materials. Interfaces between two materials often show interesting properties. Here, the authors demonstrate that diamond and cubic boron nitride, the hardest materials known, can be grown on top of each other through a novel misfit accommodation mechanism, forming a two-dimensional electron gas at the interface.