Behavior of poly(methyl methacrylate) exposed to extreme ultraviolet laser radiation: A relationship between the high-energy photo-decomposition of the polymer and the mass spectra of emitted ions

This study investigates the fluence-dependent fragmentation of poly(methyl methacrylate) (PMMA) when irradiated with focused extreme ultraviolet (EUV) 26.4-eV photons, using an extreme ultraviolet laser ablation mass spectrometer (EUV LA-MS). Our findings reveal two critical fluence thresholds: the ablation threshold fluence (Fth=9 mJ center dot cm-2), after which the material begins to desorb and ionize nonthermally, and the transition fluence (Ftr=110 mJ center dot cm-2), where the interaction shifts to a thermal regime characterized by a nonlinear response in crater formation. The new nonlinear response function recovery (NoReFry) algorithm was used to reconstruct the dose-response curve, using detailed topographical data from atomic force microscopy scans of the ablated craters, enhancing estimation of beam fluence during the experiments. The mass spectra obtained during ablation showed distinct fragmentation pathways that evolve with fluence. Nonthermal conditions primarily produce small fragments, including short-chain ions and gaseous species, while the thermal regime allows for greater fragmentation complexity and the formation of higher molecular weight species. Using experimental data and Monte Carlo simulations, we compared the effects of nano- and femtosecond pulses on the ablation threshold of PMMA. Comprehensive analysis of the mass spectra highlights the dynamics of photoinduced processes, providing insight into the ablation and ionization mechanisms critical for applications in materials processing with EUV radiation.