Controlling Strain Relaxation by Interface Design in Highly Lattice-Mismatched Heterostructure

Strain engineering plays an important role in tuning the microstructure and properties of heterostructures. The key to implement the strain modulation to heterostructures is controlling the strain relaxation, which is generally realized by varying the thickness of thin films or changing substrates. Here, we show that interface polarity can tailor the behavior of strain relaxation in a hexagonal manganite film, whose strain state can be tuned to different extents. Using scanning transmission electron microscopy, a reconstructed atomic layer with elongated interlayer spacing and minor in-plane rotation is observed at the interface, suggesting that the bond hierarchy at interface transits from three-dimension to two-dimension, which accounts for the strain-free heteroepitaxy. Utilizing interface polarity to control the strain relaxation highlights a conceptually opt route to optimize the strain engineering and the realization of strain-free heteroepitaxy in such highly lattice-mismatched heterostructure also provides possibility to transform more bulklike functional oxides to low dimensionality.