The lattice symmetry of strongly correlated oxide heterostructures determines their exotic physical properties by coupling the degrees of freedom between lattices and electrons, orbitals, and spin states. Systematic studies on VO 2 , a Mott insulator, have previously revealed that lattice distortion can be manipulated by the interfacial strain and electronic phase separation can emerge. However, typical epitaxial film-substrate interface strain provides a very limited range for exploring such interface-engineered phenomena. Herein, epitaxially grown VO 2 thin films on asymmetrically faceted m-plane sapphire substrates with the hill-and-valley type surfaces have been demonstrated. Interestingly, lattice symmetry breaking has been proven based on the large residual strain from the different faceted planes. By this lattice symmetry breaking, electronic phase separation and metal−insulator transition in the VO 2 films are modulated, and anisotropy in optical responses is exhibited. These results on asymmetrical interfacial engineering in oxide heterostructures open up new routes for novel functional materials design and functional electro/optic device nanofabrication.

Horizontal, single-dimensional, trianglelike poly(vinylidene fluoride-co-trifluoroethylene) (PVDF-TrFE) nanorods are prepared under lateral nanoconfinement induced by faceted m-plane sapphire surfaces. X-ray diffraction reciprocal space mappings reveal that the polymer contains polycrystalline ferroelectric β-phase PVDF. Depolarizing fields induce different polarizations in polymer nanorods along the out-of-plane and in-plane directions. The differences are characterized using vector piezoresponse force microscopy. The depolarizing fields in the lateral PVDF-TrFE nanorods are further discussed in theory. Our results suggest that a nanofaceted m-plane sapphire can be an alternative template to induce the depolarizing fields for future nanosacle devices.