Surface morphology and in-plane-epitaxy of SmBa₂Cu₃O_7-δ films on SrTiO₃ (001) substrates studied by STM and grazing incidence x-ray diffraction

The surface morphology and in-plane epitaxy of thin films of SmBa(2)Cu3O(7-delta) (Sm-BCO) grown on SrTiO3 (001) substrates with various thicknesses have been investigated by scanning tunneling microscopy (STM) and grazing incidence x-ray diffraction (GIXRD). As revealed by GIXRD, SmBCO films as thick as 500 Angstrom grow pseudomorphically on SrTiO3 (001) surfaces, in comparison with a maximum of 130 Angstrom for YBCO. This is probably due to a better lattice match of SmBCO (epsilon(alpha) = 1.2%, epsilon(b)=-0.5%) compared to YBCO (epsilon(alpha)=2.0%, epsilon(b)=0.5%) with the SrTiO3 substrate. Three different types of surface morphology were observed by STM with increasing film thickness h: a) 2D growth for h<h(c1), b) columnar structures for h(c1) <h<h(c2), c) spiral growth for h>h(c2). With GIXRD, a density modulation is observed in the films with a thickness below h(c2). For thicker films above h(c2), introduction of screw dislocations leads to spiral growth.