Radiation tolerance of ultra-thin Formvar films

Mechanical behavior of free-standing polymer films with submicron thicknesses exposed to a radiation environment is poorly understood. Here, we study 110-nm-thin free-standing polyvinyl formal (Formvar) films irradiated at room temperature with 1-5 keV electrons or 3 MeV alpha particles. We measure mechanical properties and the elemental composition by spherical indentation and high-energy ion scattering, respectively. Results show that, with increasing radiation dose, the effective failure strain and film thickness decrease monotonically, while the dose dependence of the Young's modulus is non-monotonic. The failure strain and modulus scale with the average energy deposited in the film, while the film thickness exhibits a more complex behavior.