Abstract
ABSTRACT The role of epitaxial strain and chemical termination in selected interfaces of perovskite oxide heterostructures is under intensive investigation because of emerging novel electronic properties. SrTiO (STO) is one of the most used substrates for these compounds, and along its direction allows for two nonpolar chemical terminations: TiO2 and SrO. In this paper, we investigate the surface morphology and crystal structure of SrO epitaxial ultrathin films: from 1 to about 25 layers grown onto TiO-terminated STO substrates. X-ray diffraction and transmission electron microscopy analysis reveal that SrO grows along its direction with a 4% out-of-plane elongation. This large strain may underlay the mechanism of the formation of self-organized pattern of stripes that we observed in the initial growth. We found that the distance between the TiO plane and the first deposited SrO layer is nm, a value which is about 40% bigger than in the STO bulk. We demonstrate that a single SrO-deposited layer has a different morphology compared to an ideal atomically flat chemical termination.
Highlights
Multilayers of thin films of transition metal perovskite oxides are under intensive investigation due to emerging novel properties observed in selected interfaces
In the rest of this manuscript, we focus on the crystal quality of the different chemical terminations of STO, which is one of the most used substrates for the growth of perovskite oxide heterostructures
Several authors report on epitaxial growth of SrO thin films in the temperature range between 600 and 800°C [2,23,24,25,26,27]
Summary
Multilayers of thin films of transition metal perovskite oxides are under intensive investigation due to emerging novel properties observed in selected interfaces. It has been observed that, in case of mixed termination of STO, SrRuO3 selectively grows only on the TiO2 islands, i.e. the ruthenate reproduces the TiO2 pattern present on the surface [8,9] Another important example of a special interface phenomenon is the case of the LaAlO3/SrTiO3 (LAO/STO) epitaxial heterostructures, where two-dimensional electron gas (2DEG) forms unexpected at the interface of the two insulators [2,11,12]. This phenomenon has been observed only in case of TiO2-terminated STO substrate, and a debate about the role of polar discontinuity and strain-induced oxygen vacancies is still running [13,14,15,16]
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