DETECTION OF INTERNAL ELECTRIC-FIELDS IN BATIO3 THIN-FILMS BY OPTICAL2ND-HARMONIC GENERATION

We have studied optical second harmonic generation (SHG) in some BaTiO 3 thin films where, in each film, the SHG is unrelated to the crystall ographic texturing of the film. We compared the mean value of the SHG coefficient averaged through the depth of the film to the values in si milar to 15 nm thick regions at the film-air and film-substrate interf aces, and we studied the temperature dependence of the SHG. The SHG co efficients were strong functions of depth in the film. We suggest that the observed SHG is due to internal electric fields from asymmetric d istributions of oxygen vacancies in the films, such as those observed in numerous recent studies of imprinting in ferroelectric oxide thin f ilm capacitors. As such, SHG provides a new means of studying imprinti ng. The technique provides depth resolution and does not require elect rodes.