Domain orientation in ultrathin (Ba,Sr)TiO3 films measured by optical second harmonic generation

The analysis of polarization diagrams for specular and scattered second harmonic generation (SHG) was used for the structural characterization of submicron domain structures of thin (Ba,Sr)TiO3 (BST) films. It is shown that the lack of separation of these two contributions may lead to completely wrong conclusions about the domain orientation in these films. SHG studies of the thickness dependence of domain fractions (including 180degrees domains) reveal the presence of ferroelectric domains in ultrathin BST films (6 nm), although no domain structure was observed by atomic force microscopy. Thus the presence of ferroelectric ordering was demonstrated in perovskite films with a thickness down to 6 nm. (C) 2003 American Institute of Physics.