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O: Fachverband Oberflächenphysik

O 64: Plasmonics and nanooptics III

O 64.7: Vortrag

Donnerstag, 29. März 2012, 12:00–12:15, MA 005

Quantitative analysis and modeling of the near-field optical signals on vertically layered samples — •Benedikt Hauer, Andreas Engelhardt, and Thomas Taubner — I. Institute of Physics (IA), RWTH Aachen University, Sommerfeldstraße 14, 52074 Aachen, Germany

In scattering-type scanning near-field optical microscopy (s-SNOM) the evanescent electric fields at the apex of a sharp illuminated tip can be used to probe the dielectric properties of a sample with a sub-wavelength resolution given by the tip radius. The near-field coupling depends on both the three-dimensional composition of the sample and the tip’s material and geometry.

We present a quantitative and fully analytical theory to predict the s-SNOM signal strength of layered sample systems depending on the vertical tip–sample separation. The calculation is based on the well-established contrast model by Cvitković et al. [1] and coincides much better with experimental approach curves than a multilayer model in which the tip is approximated as a point dipole [2]. By varying the layer thickness and the imaging parameters we demonstrate the validity of our theory in the infrared spectral range. The findings are used to determine the optimum microscope settings in order to distinguish small differences in layer thickness or dielectric properties. Our work demonstrates the capability of s-SNOM to extract quantitative information on the vertical structure of a sample up to a depth of 100 nm.

[1] A. Cvitković et al., Optics Express 15, 8550 (2007)

[2] J. Aizpurua et al., Optics Express 16, 1529 (2008)