Anomalous strain effect in heteroepitaxial SrRuO3 films on (111) SrTiO3 substrates

Abstract

We report comprehensive investigations into the structure of high-quality (111)-oriented SrRuO3 films on SrTiO3 substrates to elucidate the effect of (111) heteroepitaxial strain. We found that SrRuO3 film with a thickness of ∼ 40 nm is compressively strained in plane on the substrate with full coherency. Nevertheless, the out-of-plane spacing is almost the same as in the bulk, which is at odds with the conventional paradigm. By probing a series of half-order Bragg reflections using synchrotron-based x-ray diffraction combined with analyses of the scanning transmission electron microscopy images, we discovered that the heteroepitaxial strain is accommodated via significant suppression of the degree of c + octahedral tilting and the formation of three equivalent domain structures on the (111) SrTiO3 substrate. This anomalous effect sheds light on the understanding of an unconventional paradigm of film–substrate coupling for the (111) heteroepitaxial strain.