Periodic lateral superlattice in bonded SrTiO3/SrTiO3 twisted perovskites

Abstract

Stacking of freestanding membranes enables the formation of interfaces beyond what can be obtained with classical heteroepitaxy. In particular, twisted interfaces provide unique physical properties not existent in the corresponding individual layers. An ideal twist grain boundary yields an in-plane screw-dislocation network, assuming sufficiently strong interactions across the interface, for example, via covalent or ionic bonding. Hereby, the distance between dislocation lines, that is the length scale of the Moiré pattern, is set by the twist angle between the adjacent crystalline surfaces and the lattice mismatch in case that different materials are placed together. The associated strain gradients of the periodic pattern are especially appealing for oxide-based perovskites due to the intricate connection between surface polarization and subtle structural deformations such as the oxygen octahedra tilt. Recently, freestanding oxide perovskites became available via the sacrificial layer approach, opening a pathway toward oxide-based Moiré materials. Here, we demonstrate efficient bonding of a freestanding SrTiO3 layer to a SrTiO3 single-crystal by initially conducting a wafer-bonding process at high temperature and only subsequently dissolving the sacrificial layer. We investigate the twisted SrTiO3/SrTiO3 interface with x-ray diffraction in grazing incidence geometry and observe clear signatures of a highly periodic lateral superlattice consistent with the formation of a screw-dislocation network. Our work demonstrates a robust route for the fabrication of twisted perovskites and their development into a functional material platform with designed strain gradients at the nanoscale.