120 nm resolution and 55nm line width achieved in visible light STED-lithography

Abstract

Summary form only given. STED (stimulated emission depletion) nanoscopy[1, 2] has proven to provide even sub-10 nm resolution[3] in far field fluorescence microscopy and has found ample applications in biology or materials science. Similar to the development two-photon lithography[4] out of the concept of two-photon microscopy, it was proposed already in the very first reports on STED nanoscopy that the confined effective excitation volume can be used to spatially define chemical reactions on the nanometre scale.[1, 2] STED-inspired diffraction-unlimited lithography has been experimentally verified recently.[5-7]. In this presentation, we will address the question of minimal lateral structure size and minimal lateral resolution in STED-lithography. We show that single lines can be polymerized with a lateral width of only 55 nm and a full width at half maximum of 34 nm.[8] To the best of our knowledge, this is a new hitherto unreached limit in lithography using low energetic visible light photons. We further find that the resolution in STED-lithography can be pushed down to 120 nm. “Resolution” herewith refers to the minimal distance, at which two adjacent, yet separated lines can be written. The structures show good biocompatibility and allow for bio-functionalization with proteins, possibly down to a single protein level. The ability to place individual proteins into nano-confined spaces opens intriguing applications in bioscience, ranging from basic studies in biology to the development of localized, nanoscopic sensors. While STED-lithography cannot (yet) compete with electron beam, ion beam or UV lithography, there is justified hope that both, resolution and feature size can further be improved, similar to the progress in STED nanoscopy which started with a resolution above 100 nm[1] and has reached sub-10 nm resolution meanwhile.[3] Compared to UV and e-beam lithography, STED-DLW has two major advantages. First, it can be applied for three dimensional structuring. Second, photons of visible light contain much less energy per photon compared to UV photons or accelerated electrons or ions. Consequently, lithography on photosensitive substrates such as on polymers or even in living tissue might become in reach.