Functional nanostructured surfaces induced by laser on fullerene thin films

Abstract

We report a method to produce nanosecond pulsed laser induced periodic surface structures (LIPSS) on spin-coated [6,6]‑phenyl C71-butyric acid methyl ester (PC71BM) films exhibiting a photoinduced resist-free imprinting (PRI) property. LIPSS in PC71BM are resist free and can be solvent developed, under certain conditions, leaving the laser illuminated zone as an undissolved residue. LIPSS prepared with a wavelength of 532 nm selectively preserve the electrical conductivity on the LIPSS valleys. The heterogeneous conducting pattern consisting in conducting valleys and less conducting hills observed in the LIPSS has been interpreted as due to a reduction in the crystallinity of the hills provoked by the fast heating/cooling process induced by every laser pulse. On the basis of the experiments we propose that irradiated PC71BM films: i) suffer a fast heating/cooling process tending to reduce the overall crystallinity of the LIPSS and therefore decreasing the electrical conductivity of the hills while leaving a remnant conducting film underneath the hills, ii) during laser irradiation the sample suffers a heat treatment leading to the development of a buried phase with enhanced crystallinity, close to the silicon substrate, formed by larger crystals with enhanced electrical conductivity and iii) further solvent treatment reveals the buried phase which remains in the form of partially electrically conducting nanowires. These results point towards the potential use of the described technology for nanofabrication of organic electronic devices.