EUV induced ablation and surface modification of poly(vinylidene fluoride) irradiated in vacuum or gaseous environment

Extreme ultraviolet (EUV) is an ionizing radiation strongly absorbed in any kind of mater. In case of polymers absorption depth is of the order of 100 nm. Interaction of EUV photons with polymer chains results in chain scission and formation of low weight fractions. In this work interaction of intense EUV pulses with poly(vinylidene fluoride) (PVDF) was investigated. Mass spectroscopy was employed to investigate the ablation products indicating emission of numerous molecular species of C-containing fragments of the polymer chain. Chemical surface changes after irradiation were investigated using X-ray photoelectron spectroscopy (XPS). The XPS spectra obtained for PVDF, samples irradiated with low and high EUV fluence, indicate significant differences between chemical structures in near-surface layers. It was shown that irradiation with low fluence results in defluorination and thus carbon enrichment in near-surface layer. In contrary, irradiation with high fluence leads to intense material ablation and hardly modifies the chemical structure of the remaining material. Additionally chemical modification of the PVDF surface by EUV irradiation in a presence of ionized nitrogen was investigated. The nitrogen gas, injected into an interaction region, was ionized and excited by the EUV radiation from a laser-plasma source. An ionization degree and excited states of nitrogen were investigated using an EUV spectrometry and the corresponding spectra are presented. Chemical modification of the polymer after combined EUV and ionized nitrogen treatment was investigated using an X-ray photoelectron spectroscopy. Significant contribution of the nitrogen atoms in the polymer near-surface layer after the treatment was demonstrated.