Speaker
Description
Stimulated emission depletion (STED) broke the diffraction limit of resolution in fluorescence microscopy and it has been proposed that STED should be equally applicable to spatially control chemical reactions at the nanometre scale.1 Meanwhile, this prediction has been experimentally realized using free radical polymerization of mostly (meth)acrylates.2-4 Using transient-state absorption depletion (TAD) rather than STED, three dimensional structures of 40 nm size in lateral and axial direction can be realized, which corresponds to 1/20 of the excitation wavelength.5
However, this concept was restricted to free radical polymerization for a long time. Only recently, it has been transferred to optical nanolithography comprising cationic or oxidative polymerizations. For instance, we found a photosensitizer/initiator couple with which STED-inspired writing of sub-100 nm wide epoxide lines became possible.6, 7 Currently, we are exploring ways to optically interfere with the radical cation or the ketyl radicals of photo-initiators in order to prevent polymerization in the outer rim of the optical point spread function.
Besides, we also managed to write subdiffractional lines of -conjugated PEDOT (poly-3,4-ethylendioxythiophen), either by two photon, ultra-slow scanning or by applying TAD.8, 9 Besides, polypyrrole lines are also investigated. Such -conjugated structures are particularly intriguing because they hold promise for sub-diffractional organic electronic devices.
References
(1) Klar, T. A.; Hell, S. W. Subdiffraction resolution in far-field fluorescence microscopy. Optics Letters 1999, 24 (14), 954–956. DOI: 10.1364/OL.24.000954
(2) Li, L.; Gattass, R. R.; Gershgoren, E.; Hwang, H.; Fourkas, J. T. Achieving l/20 Resolution by One-Color Initiation and Deactivation of Polymerization. Science 2009, 324 (5929), 910–913. DOI: 10.1126/science.1168996
(3) Fischer, J.; Wegener, M. Three-dimensional direct laser writing inspired by stimulated-emission-depletion microscopy. Opt. Mat. Exp. 2011, 1 (4), 614–624. DOI: 10.1364/OME.1.000614
(4) Wollhofen, R.; Katzmann, J.; Hrelescu, C.; Jacak, J.; Klar, T. A. 120 nm resolution and 55 nm structure size in STED-lithography. Opt. Exp. 2013, 21 (9), 10831–10840. DOI: 10.1364/OE.21.010831
(5) Gvindzhiliia, G.; Sivun, D.; Naderer, C.; Jacak, J.; Klar, T. A. Low-Fluorescence Starter for Optical 3D Lithography of Sub-40 nm Structures. ACS Applied Optical Materials 2023, 1 (5), 945–951. DOI: 10.1021/acsaom.3c00031
(6) Islam, S.; Sangermano, M.; Klar, T. A. STED-Inspired Cationic Photoinhibition Lithography. Journal of Physical Chemistry C 2023, 127, 18736−18744. DOI: 10.1021/acs.jpcc.3c04394
(7) Islam, S.; Klar, T. A. Stimulated Emission Depletion Inspired Sub-100 nm Structuring of Epoxides Using 2‑Chlorothioxanthone as Photosensitizer. ACS Omega 2024, 9, 19203−19208. DOI: 10.1021/acsomega.4c00031
(8) Islam, S.; Gvindzhiliia, G.; Klar, T. A. STED-inspired optical lithography beyond acrylates. Proc. SPIE 12995: 3D Printed Optics and Additive Photonic Manufacturing IV 2024, 1299503. DOI: 10.1117/12.3022378
(9) Gvindzhiliia, G.; Angerer, C.; Schwaiger, C.; Sivun, D.; Jacak, J.; Hild, S.; Klar, T. A. Sub-diffraction multiphoton polymerization of PEDOT. submitted 2025.
We acknowledge financial support by the Austrian Science Fund (FWF) DOI: 10.55776/PAT3523723