Berlin 2024 – scientific programme
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O: Fachverband Oberflächenphysik
O 24: Plasmonics and Nanooptics III: Light-Matter Interaction and Spectroscopy
O 24.1: Talk
Tuesday, March 19, 2024, 10:30–10:45, MA 042
Identification of weak molecular absorption on single-wavelength s-SNOM images — •Iris Niehues1,2, Lars Mester3, Edoardo Vincentini2, Daniel Wigger4, Martin Schnell2,5, and Rainer Hillenbrand2,5,6 — 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)]
Keywords: Near-field microscopy; s-SNOM; Phase contrast