Surface roughening by anisotropic adatom kinetics in epitaxial growth of La0.67Ca0.33MnO3

The growth mechanisms and surface morphology of colossal magnetoresistance (CMR) La_0.67Ca_0.33MnO₃ films deposited by rf magnetron sputtering on SrTiO₃(0 0 1) substrates are investigated. The films are epitaxial, coherently strained and ferromagnetic. It is found that at early growth stages, in nanometric films, a layer-by-layer mechanism dominates, which results in step and terrace surface morphology. Upon further growth, the flat surface becomes unstable when large two-dimensional (2D) islands form. The Erlich-Schwoebel step-edge energy barrier induces an anisotropic adatom kinetics that favors 2D nucleation on top of the islands as it reduces downhill adatom current. As a result, there is an evolution with growth to mound-like structures of increasing height. Critical thickness for mound formation and average mound separation can be tuned by substrate miscut angle and growth temperature. These results provide a detailed understanding of the roughening process in manganites and are relevant for the controlled fabrication of CMR films, in particular for its use in epitaxial heterostructures.