X-ray reciprocal space imaging of a screw-dislocation network at a low-angle twist boundary in a SrTiO 3 membrane transfer-bonded to bulk SrTiO 3

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The transfer of oxide membranes provides a new dimension in material design that goes beyond the limitations of classical hetero-epitaxy. For example, the transfer of freestanding membranes offers the in-plane twist angle between film and substrate as a tuneable degree of freedom. An ideal twist boundary yields formation of an in-plane screw-dislocation network to reduce interfacial stress. Previously, periodic screw-dislocation networks have been demonstrated by wafer bonding of two crystals, where the twist boundary is embedded in the bulk and made accessible to detailed characterization mostly by destructive methods. Recent approaches exploited freestanding membranes to create twist boundaries with the interface located only nanometers beneath the surface, making it readily accessible by near-surface-sensitive techniques. In this work, both approaches were combined to transfer membranes on the mm²-scale via wafer bonding and subsequent release by etching the sacrificial layer. High-resolution synchrotron-based grazing incidence x-ray diffraction was performed to investigate the structure of the twisted SrTiO 3 / SrTiO 3 interface. In order to gain a better qualitative and quantitative understanding of the experimental results, we simulated the x-ray diffraction of twisted perovskites based on continuum elastic theory and kinematical scattering. Our measurements show that the measured diffraction patterns are consistent with the formation of a periodic screw-dislocation network, since the apparent superlattice reflections coincide with the obtained diffraction pattern from simulations. However, the intensity profile and appearance of specific symmetry-forbidden diffraction peaks in the experiments cannot be described by elastic displacements alone.