Near-field scanning optical microscopy (NSOM) is a powerful tool for the characterization of the optical properties of nanoscale objects, although pervasive artifacts often create difficulties in image interpretation. A three dimensional scanning NSOM method that yields artifact-free, constant height mode (CHM) images is discussed. A set of λ = 488 nm, CHM images of a Au nanoparticle sample acquired at probe-sample separations varying from 7 ± 3 nm to 160 ± 3 nm are presented. Analysis of optical features due to scattering from a Au nanoparticle provides an experimental measure of the spatial resolution decay as the sample is moved from the near-field of the probe aperture toward the far-field. The spatial resolution decays slowly for probe-sample separations up to approximately 110 nm, beyond which it quickly approaches the far-field diffraction limit.
Citation: Journal of Applied Physics
Issue: No. 8
Pub Type: Journals
metal nanoparticles, near-field scanning optical microscopy, NSOM, optical microscopy