Micro-scale irradiation-induced effects of polyethylene film by 1 MeV proton beam writing

Ionizing irradiation is one of the most effective methods to chemically and physically modify polymers. Proton irradiation has offered applications in micro-nanoscience and engineering from 2D to 3D fabricated structures in resist polymers. On the other hand, irradiation-induced effects in non-resist polymers by focused proton irradiation are not well-understood. Linear low-density polyethylene (LLDPE) is a promising non-resist polymer with good thermal stability, chemical inertness, and biocompatibility. In this work, we applied 1 MeV proton beam writing (PBW) on thin LLDPE films with circular micropatterns and fluences between 50–5000 nC mm −2 . The morphological and chemical changes of irradiated LLDPE films were observed. The transition from a roughened surface to a crater-like structure was proton fluence dependent. The surface roughness was increased and saturated at fluences above 1200 nC mm −2 . Meanwhile, the depth of crater-like profiles starting from 1200 nC mm −2 was increased and could be described by a saturating exponential function. In addition, the focused proton-induced variations of chemical structures were determined spectroscopically. We furthermore demonstrated the successful replication of these microstructures in poly(dimethylsiloxane). These results suggest that PBW irradiation would be a promising method to chemically and morphologically modify polymer film properties with controllable designs and arrangements down to micro-scale precision.