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O: Fachverband Oberflächenphysik

O 24: Plasmonics and Nanooptics III: Light-Matter Interaction and Spectroscopy

O 24.1: Vortrag

Dienstag, 19. März 2024, 10:30–10:45, MA 042

Identification of weak molecular absorption on single-wavelength s-SNOM images — •Iris Niehues^1,2, Lars Mester³, Edoardo Vincentini², Daniel Wigger⁴, Martin Schnell^2,5, and Rainer Hillenbrand^2,5,6 — ¹Institute of Physics, University of Münster, Germany — ²CIC nanoGUNE BRTA, Donostia-San Sebastián, Spain — ³attocubes systems AG, Munich-Haar, Germany — ⁴Department of Physics, University of Münster, Germany — ⁵IKERBASQUE, Basque Foundation for Science, Spain — ⁶Department of Electricity and Electronics, UpV/EHU, Donostia-San Sebastián, Spain

Scattering-type scanning near-field optical microscopy (s-SNOM) and nanoscale IR point spectroscopy (nano-FTIR) allow for nanoscale optical mapping of manifold material properties. Both techniques are based on elastic light scattering at an atomic force microscope tip that is illuminated with monochromatic or broadband laser illumination. For dielectric samples, the near-field amplitude and phase signals of the tip scattered field reveal the local reflectivity and absorption, respectively. Importantly, absorption in s-SNOM imaging corresponds to a positive phase contrast relative to a non-absorbing reference sample. Interestingly, a negative phase contrast (NPC) can be observed when imaging a non-absorbing material on a highly reflecting substrate. We explore the origin of the NPC using representative test samples and demonstrate straightforward simple correction methods that remove the NPC and that allow for the identification of weak absorption contrasts. [Opt. Express 31(4), 7012 – 7022 (2023)]