Surface morphology and in-plane-epitaxy of SmBa 2Cu 3O 7−δ films on SrTiO 3 (001) substrates studied by STM and grazing incidence x-ray diffraction

Abstract

The surface morphology and in-plane epitaxy of thin films of SmBa 2Cu 3O 7−δ (SmBCO) grown on SrTiO 3 (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 Å grow pseudomorphically on SrTiO 3 (001) surfaces, in comparison with a maximum of 130 Å for YBCO. This is probably due to a better lattice match of SmBCO ( ε a =1.2%, ε b =−0.5%) compared to YBCO ( ε a =2.0%, ε b =0.7%) with the SrTiO 3 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.