Near-Field Optical Imaging of a Porous Au Film: Influences of Topographic Artifacts and Surface Plasmons

Abstract

In this work, near-field scanning optical microscopy is employed to study a porous Au film and the direct observation of topographic artifacts and surface plasmon influences is revealed. Under tip illumination, topographic artifacts are found to be present in a reflection mode optical image but not in a transmission mode image. A simple algorithm is used for filtering the topographic artifacts and extracting a correct near-field optical image approximately. On the other hand, surface plasmon influences are present in both modes. By using three exciting wavelengths of 488, 647.1, and 520.8 nm, it is confirmed that a suitable wavelength should be chosen for avoiding the surface plasmon interference in a near-field optical investigation of morphological or material dielectric contrast. Finally, plasmonic or nonplasmonic regions on the porous Au film can be identified from the observed optical intensity variation in the optical images obtained at incident polarizations of 0 degrees, 90 degrees, and 45 degrees.