(303g) Single-Molecule Super-Resolution Microscopy in Nanostructured Polymer Thin Films

Super-resolution microscopy offers an exciting method to image nanostructures non-invasively, opening the possibility of direct in situ real-space observation at the nanoscale. In one form of these methods, sparse fractions of single fluorophores are switched into a bright state from a large population of dark molecules, and the locations of these molecules are determined by fitting their images to the expected point-spread function. Most previous studies have applied these techniques to important scientific problems in the biological community, but little work has explored their use in materials science, where important effects such as dye chemistry and fluorophore orientation introduce new demands.

We explore the capabilities of single-molecule super-resolution microscopy using lithographically patterned polymer thin films as model samples. Line and space patterns of varying pitch were written using electron-beam lithography, and the resulting super-resolution images were compared to the expected structures. Features as small as 20 nm half-pitch are clearly resolvable. From these results, we developed a theory that predicts the ultimate attainable resolution as a function of fluorophore localization precision, accuracy, and density. We then explore the effect of fluorophore orientation, which can alter the single-molecule point-spread function and reduce localization accuracy, but can also be used to report nanoscale chemical environment and dynamics in materials. This capability is demonstrated using polymer films that have been deformed by nanoimprint lithography, where mechanical stress is detected in areas as small as 15 nm through changes in the fluorophore orientation distribution.