| In near-field scanning optical microscopy, a subwavelength aperture in an opaque material positioned less than a wavelength from the sample is used to confine the optical fields to a region smaller than the diffraction limit. In this work, a transmission mode near-field scanning optical microscope (NSOM) with polarization control capabilities was constructed and used to study the optical properties of novel oxides. The NSOM operates in air at room temperature and uses visible wavelengths for imaging.; By examining a simple sample consisting of two adjoining glasses of slightly different refractive index, anomalies in contrast arising from the use of point source illumination and finite numerical aperture collection optics were studied. Dependence of the image contrast on numerical aperture is then exploited in the study of a two dimensional photonic crystal. Crystalline materials studied include lanthanum aluminate (LaAlO{dollar}sb3),{dollar} in which the optical properties of twin domains, twin boundaries, and other defects were examined. Also studied were the fusion boundaries of strontium titanate (SrTiO{dollar}sb3){dollar} and sapphire (Al{dollar}rmsb2Osb3){dollar} bicrystal substrates. Dark circular defects from 0.1 to 1 {dollar}mu{dollar}m in diameter were identified along the fusion boundaries of SrTiO{dollar}sb3{dollar} bicrystals. These substrate defects have been shown to cause the grain boundary of a {dollar}rm YBasb2Cusb3Osb7{dollar} (YBCO) thin film grown on the bicrystal to wander up to 0.8 {dollar}mu{dollar}m. The correlation between these structural defects and the electrical characteristics of YBCO grain boundary junctions is investigated. Strain fields associated with these substrate defects are attributed to their influence on YBCO growth. A new polarization modulation technique was incorporated into the NSOM to map out the strain fields of the defects by measuring birefringence. Using this technique, features as small as 150 nm were imaged with a retardance sensitivity of {dollar}{lcub}sim{rcub}3times10sp{lcub}-3{rcub}{dollar} radians. |
