High-resolution scanning optical microscopy of ferroelectric thin films

Two optical techniques are used to map the electric polarization in BaxSr1- xTiO3 (BST) thin films at room temperature. The first, confocal scanning op tical microscopy (CSOM), is a diffraction-limited technique with wide appli cability and ease of use. CSOM images taken at different static electric fi elds show reorientation of ferroelectric nanodomains. Local hysteresis loop s, obtained by cycling the applied electric field at one position on the sa mple, suggest a coexistence of both paraelectric and ferroelectric phases a t compositions x which exhibit paraelectric behavior in the bulk. Non-unifo rm strain is postulated to account for the apparent spatial variations of t he Curie temperature. The second technique, apertureless near-field Scannin g optical microscopy (ANSOM), is used to image polarization fluctuations wi th a spatial resolution of 30 Angstrom. ANSOM images of the same samples sh ow inhomogeneities in the ferroelectric polarization over the smallest scal es that can be observed, changes which are largely uncorrelated with topogr aphic features. The application of an in-plane static electric field causes domain reorientation and domain wall motion over distances as small as 40 Angstrom. These results demonstrate the utility of both CSOM and ANSOM in c haracterizing domain structure and dynamics in ferroelectric thin films.