Low‑damage thinning of polymer specimens for transmission electron microscopy by gas cluster ion beam irradiation

Focused ion beam (FIB) processing is widely used for preparing transmission electron microscopy (TEM) specimens of polymer materials. However, it often introduces damaged layers that hinder structural analysis. In this study, we demonstrate the effectiveness of gas cluster ion beam (GCIB) irradiation in reducing such damaged layers in polyethylene (PE) extracted from a PE/polyamide (PA) multilayer film, used here as a representative single-component polymer. GCIB treatment successfully removed the FIB-induced damaged layers and enabled access by ruthenium tetroxide (RuO4), which allowed clear visualization of the lamellar structure in PE. Electron tomography confirmed that GCIB not only eliminated damaged layers but also thinned the specimen. These findings suggest that GCIB is a promising technique for preparing ultra-thin, low-damage TEM specimens of polymer materials and can facilitate more accurate structural and chemical analyses.