Relevance of the 3D to 2D growth mode transition for the transport properties of nanometric SrRuO3 films

Epitaxial SrRuO3 nanometric films were grown on SrTiO3(0 0 1) substrates by pulsed laser deposition. The films, at the early growth stages develop a pattern of one dimensional structures following the substrate steps along [1 0 0] direction and formed by three-dimensional (3D) islands. At a thickness of about 10 nm, these structures merge together, and thereafter the growth proceeds essentially by two-dimensional (2D) growth mode and the films become progressively smoother. This unusual 3D to 2D growth mode transition is responsible of an inhomogeneous microstructure, which has a strong impact on the electronic transport properties of the films. At the regions where the elongated structures merge together, structural disorder develops leading to a well oriented pattern of defective regions. On one hand, this results in the emergence of an in-plane resistivity anisotropy due to the different electronic properties of the island-merging boundaries. On the other hand, the microstructural disorder provokes a shortening of the electronic mean free path. As a result of this, the conductivity at low temperature becomes somewhat suppressed. These findings could be of relevance for technological applications of SrRuO3, and specifically for the electronic transport properties across magnetic tunnel junctions.