Characterization of nanostructures fabricated with two-beam DLW lithography using STED microscopy

The development of optical fabrication tools such as direct laser writing (DLW) lithography provides an unprecedented ability to rapidly generate arbitrary structures with control down to the nanoscale. Key to the further advance of these strategies is the development of simple and straightforward methods to monitor or characterize the fabricated structures. Here, we use a two-beam approach based on the reversible saturable optical fluorescence transition (RESOLFT) concept that enables the fabrication as well as the rapid characterization of nanometer-sized DLW lithography structures since both steps can be performed in the same experimental system. Our two-step approach uses two-beam DLW lithography based on the triplet state absorption (TSA) mechanism to polymerize a resist containing isopropyl thioxanthone (ITX) as the photoinitiator and Chromeo 488 carboxylic acid derivative as a fluorescent reporter, and then stimulated emission depletion (STED) microscopy to rapidly characterize the size and morphology of the polymerized structures after the development of the sample. Our results show photopolymerized lines with a linewidth of ~90 nm whose size was properly determined with STED microscopy.