Image contrast of dielectric specimens in transmission mode near‐field scanning optical microscopy: imaging properties and tip artefacts

Abstract

dimensions of the source are much smaller than the Near-field scanning optical microscopy (NSOM) is a scanned probe technique utilizing a subwavelength-sized light source for high-resolution imaging of surfaces. Although NSOM has the potential to exploit and extend the experimental utility of the modern light microscope, the interpretation of image contrast is not straightforward. In near-field microscopy the illumination intensity of the source (probe) is not a constant value, rather it is a function of the probe-sample electronic environment. A number of dielectric specimens have been studied by NSOM to elucidate the contrast role of specimen type, topography and crystallinity; a summary of metallic specimen observations is presented for comparative purposes. Near-field image contrast is found to be a result of lateral changes in optical density and edge scattering for specimens with little sample topography. For surfaces with considerable topography the contributions of topographic (Z) axis contrast to lateral ( X , Y ) changes in optical density have been characterized. Selected near-field probes have also been shown to exhibit a variety of unusual contrast artefacts. Thorough study of polarization contrast, optical edge (scattering) contrast. as well as molecular orientation in crystalline specimens. can be used to distinguish lateral contrast from topographic components. In a few cases Fourier filtering can be successfully applied to separate the topographic and lateral contrast components.

Probing the Mesoscopic Chemical and Physical Properties of Polymer-Dispersed Liquid Crystals

“…The dependence of the contrast on field strength and modulation frequency suggests, however, that it is not simply due to well-known near-field artifacts. [157,158] It is therefore believed that this feature arises from slight differences in the reorientation dynamics near the upper interface, resulting from spatial variations in the initial state of liquid crystal alignment.…”

Spectral inhomogeneities and spatially resolved dynamics in porphyrin J-aggregate studied in the near-field

“…This observation may be interpreted that the substance giving the assumed spectral component does not lie in the whole region of the sample, but quite localized in sparse regions. Since we obtained these images from spectral fitting rather than transmission intensity, artifacts due to coupling of topography to the SNOM images as a result of edge scattering may be minimized [14].…”

Polarization-Modulation Near-Field Scanning Optical Microscopy of Mesostructured Materials

“…As a topographic feature is crossed during the acquisition of an image, the distance between the NSOM probe aperture and the sample changes. 21 Tip/sample distance changes cause changes in the optical properties (i.e., from those of the sample showing apparent adherence to Beer's law. As noted in the text, the relationship is actually much more complicated than is suggested by this plot.…”