Growth facets of SrIrO3 thin films and single crystals

The crystallographic orientation of SrIrO3 surfaces is decisive for the occurrence of topological surface states. We show from density functional theory computations that the (001) and (110) free surfaces have comparable energies, and correspondingly, we experimentally observe that single micro-crystals exhibit both facet orientations. These surfaces are found to relax over typically the length of one oxygen octahedron, defining a structural critical thickness for thin films. A reconstruction of the electronic density associated with tilts of the oxygen octahedra is observed. At the opposite, thin films have invariably been reported to grow along the (110) direction. We show that the interfacial energy associated with the oxygen octahedral distortion for epitaxy is likely at the origin of this specific feature, and propose leads to induce (001) SrIrO3 growth.