Sub-Diffractional Optical Lithography Beyond Acrylates

Stimulated emission depletion (STED) broke the diffraction limit of resolution in fluorescence microscopy and it has been proposed that a STED-confined excitation volume should be equally applicable to spatially control chemical reactions on the nanometre scale.<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">1</sup> Meanwhile, this prediction has been experimentally realized using free radical polymerization of mostly (meth)acrylates.<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2-4</sup> Recent progress has been made in finding an optically depletable starter which shows only low autofluorescence in the visible spectrum, so that it can be used for biomedical applications without interfering with fluorescent tags.<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</sup> Using the STED-inspired concept of transient-state absorption depletion (TAD), three dimensional structures of 40 nm size in lateral and axial direction can be realized, which corresponds to 1/20 of the excitation wavelength.<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">5</sup>