Chemical changes in PMMA as a function of depth due to proton beam irradiation

Highlights: → Chemical changes were investigated as a function of depth in proton irradiated PMMA → The depth profile of numerous functional groups was determined along the depth → The degree of chemical modification strongly depends on the LET of protons → At low-fluences the zone of maximal modification is restricted to the Bragg peak → At higher fluences the zone of max. modification extends towards the sample surface. - Abstract: In this work we determined depth profiles of the chemical change in PMMA irradiated with 2 MeV protons by infrared spectroscopic and micro-Raman measurements. The measurements were carried out on 10 μm thin stacked foil samples using an infrared spectrometer in universal attenuated total reflectance (UATR) and transmission modes; while the thick samples were analyzed with a confocal micro-Raman spectrometer. The depth profiles of the changes formed due to the various delivered fluences were compared to each other. The measurements show the strong dependence of the degree of modification on the energy transfer from the decelerating protons. Depth profiles reveal that at the fluences applied in this work the entire irradiated volume suffered some chemical modifications. In case of low-fluence samples the zone of maximal modification is restricted only to the Bragg peak, but with increasing fluences the region of maximal modification extends towards the sample surface.