Domain structure of epitaxial SrRuO3 thin films

Abstract

Growth of multidomains in epitaxial thin-film oxides is known to have a detrimental effect on some functional properties, and, thus, efforts are done to suppress them. It is commonly accepted that optimal properties of the metallic and ferromagnetic SrRu O3 (SRO) epitaxies can only be obtained if vicinal SrTi O3 (001) (STO) substrates are used. It is believed that this results from the suppression of multidomain structure in the SRO film. Here we revise this important issue. Nanometric films of SRO have been grown on STO(001) vicinal substrates with miscut (θV) angles in the ∼0.04°-4°range. Extensive structural analysis by x-ray-reciprocal space maps and μ -Raman spectroscopy indicates that single-domain, orthorhombic, SRO films are already obtained on the almost singular (θV ≈0.1°) substrate, and, thus, substrates with large miscut angles are not required to grow twin-free films. In spite of this, transport properties are found to be optimized for films grown on vicinal substrates (θV ≥2°). We claim that this is the result of the change of the growth mode and the resulting film morphology rather than the change of the domain structure. These findings drive the attention to the relevance of the growth mechanism at the initial stages of film growth, and we discuss its implications in other areas of oxide epitaxies. Moreover, we show that in clamped epitaxies on cubic substrates, in spite of isotropic biaxial substrate-induced strains, films may have an in-plane orthorhombic symmetry which results from the internal degree of freedom defined by rotations of the oxygen octahedrons. © 2005 The American Physical Society.