Orientational Epitaxy of van der Waals Molecular Heterostructures

The shape of individual building blocks is an important parameter in bottom-up self-assembly of nanostructured materials. A simple shape change from sphere to spheroid can significantly affect the assembly process due to the modification to the orientational degrees of freedom. When a layer of spheres is placed upon a layer of spheroids, the strain at the interface can be minimized by the spheroid taking a special orientation. C₇₀ fullerenes represent the smallest spheroids, and their interaction with a sphere-like C₆₀ is investigated. We find that the orientation of the C₇₀ within a close-packed C₇₀ layer can be steered by contacting a layer of C₆₀. This orientational steering phenomenon is potentially useful for epitaxial growth of multilayer van der Waals molecular heterostructures.