A study on surface symmetry and interfacial enhancement of SrTiO3 by second harmonic generation

The symmetry of the surfaces of SrTiO₃ and slightly Nb-doped SrTiO₃ crystals was investigated by the optical reflected second harmonic generation technique. The good agreement between experimental and theoretical results of the second harmonic intensity dependence on the azimuth angle indicates that the SrTiO₃ (001) surface is with 4mm symmetry and the Nb-doped SrTiO₃ (111) surface with 3m symmetry. The measurements of the polarization dependent second harmonic intensity confirm that conclusion. The enhancement of the surface polarization in the structure of SrTiO₃ capped La_0.9Sr_0.1MnO₃ films compared with that in the La_0.9Sr_0.1MnO₃ films has been obtained.