Epitaxial Growth of (1 1 1)-Oriented Spinel CoCr$_2$O$_4$/Al$_2$O$_3$ Heterostructures

High quality (1 1 1)-oriented CoCr$_2$O$_4$/Al$_2$O$_3$ heterostructures were synthesized on the sapphire (0 0 0 1) single crystal substrates in a layer-by-layer mode. The structural properties are demonstrated by $in$-$situ$ reflection high energy electron diffraction, atomic force microscopy, X-ray reflectivity and X-ray diffraction. X-ray photoemission spectroscopy confirms that the films possess the proper chemical stoichiometry. This work offers a pathway to fabricating spinel type artificial quasi-two-dimensional frustrated lattices by means of geometrical engineering.