Depth-resolved characterization of mechanically weakened surface layers in vacuum ultraviolet-irradiated cycloolefin polymer films using micro slurry-jet erosion test and ToF-SIMS analysis

This study presents a depth-resolved characterization of cycloolefin polymer (COP) surfaces subjected to vacuum ultraviolet (VUV) irradiation using a combined approach of micro slurry-jet erosion (MSE) test and time-of-flight secondary ion mass spectrometry (ToF-SIMS) analysis. The MSE test reveals that VUV irradiation induces a mechanically weakened surface layer, with a maximum erosion rate—corresponding to the lowest mechanical strength—at the surface, which gradually decreases to the baseline of untreated COP within approximately 1200 nm. Simultaneously, ToF-SIMS analysis confirms the formation of an oxidized layer containing oxygen-related ions such as O−, OH−, and C2H2O2−. The depth profiles of O− and OH− closely align with the mechanically weakened region identified by the MSE test, indicating a strong correlation between chemical oxidation and mechanical weakening. These results are consistent with the interpretation that the weakened surface is associated with a combination of polymer chain scission and oxidative modification, which introduces polar functional groups. The integration of the MSE test and ToF-SIMS analysis offers a robust framework for optimizing surface modification while minimizing mechanical degradation and serves as a broadly applicable methodology for evaluating polymer surfaces in advanced technologies.