The dielectric function E = e1 - ieZ of the YBa&u,O, _ a high-TT, superconducting fdms
grown on (100) SrTiO, (c-axis oriented) and (110) SrTiO, (&oriented) substrate was
measured by spectroscopic polarization modulation ellipsometry (SPME) and changes
in film orientation were studied by comparing films of various thicknesses. The films deposited
on SrTiO, (100) substrates demonstrated an isotropic e1 that changed with film
thickness. It is observed that the decrease in the metallic dielectric behavior associated with
the increase in the thickness of the films grown on (100) SrTi03 substrates is mainly
due to a change in the orientation of the films. The films deposited on SrTiO, (110) showed
anisotropic dielectric behavior when the plane of polarization is parallel and
perpendicular to the c-axis of the film. These studies show that for this high-temperature
superconductor with anisotropic dielectric. behavior, SPME is a highly sensitive technique
capable of measuring small changes in the film orientation.