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. 2020 Jul 3;11:3359. doi: 10.1038/s41467-020-17034-6

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© The Author(s) 2020

Open Access This article is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons license, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons license and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this license, visit http://creativecommons.org/licenses/by/4.0/.

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Fig. 1 — a Illustration of the s-SNOM and nano-FTIR setup. A quantum cascade laser (QCL) is used for s-SNOM imaging. An infrared laser continuum based on difference frequency generation (DFG) is used for nano-FTIR spectroscopy. The light source is selected with a flip mirror (FM). A parabolic mirror (PM) is used for focussing the laser radiation onto the tip apex. After collection of the tip-scattered light with the PM, a Michelson interferometer comprising a beam splitter (BS) and moveable reference mirror (RM) is used for detection. b Simulated near-field distribution around a tip apex (30 nm radius) above a 10 nm-thick PS layer on PMMA. For simulation details see “Methods” section. c AFM mechanical phase image of a two-component rubber blend (SBR/PMMA) and d corresponding s-SNOM phase φ₃ image recorded at 1742 cm⁻¹, which maps the absorption of the C=O vibrational mode of PMMA. Scale bar: 200 nm. e Nano-FTIR phase φ₃ spectra of selected positions A–D. Vertical dashed line marks the imaging frequency.