Lithography Based on Memory Effects Resulting from Photoinduced Self-Assembly of Pyrene Dimers in Thin Polymer Films

Pulsed laser irradiation of pyrene in thin films through lithographic masks leads to blue fluorescent images characteristic of pyrene excimer emission. The images are stable at room temperature and are readily observable using fluorescence microscopy. For a constant energy dose, the images are stronger and better resolved at the shorter laser wavelengths and cannot be recorded with continuous wavelength (CW) light sources. Images are easier to obtain with high Tg films, while polymers with Tg below room temperature image only when the laser also causes polymer cross-linking. It is proposed that laser excitation generates excited singlet pyrene and simultaneously causes a temperature change that facilitates diffusion and thus excimer formation. Following excited state (monomer and excimer) decay, the polymer matrix cools down and prevents the separation of the pyrene pairs, that are preserved by the rigid polymer matrix. Some of the images can be thermally erased by annealing above Tg. The method may find applications in imaging and information storage.