Effect of ion irradiation on the thermal stability of thin polymer films

We report on the stability of poly(methyl methacrylate) thin films in vacuum after exposure to moderate doses of 300 keV H+, 2 MeV H+, and 18 MeV Au7+ ions combined to thermal treatments. A small but steady increase in roughness of the films with increasing fluence was observed for bombardments at room temperature at a rate that varied strongly with dE/dx. For irradiations at 100 °C, the roughness also increased sharply at very low fluences, but it was followed by smoothing and stabilization of the surfaces at larger doses. In situ post-irradiation annealing of samples after a fixed irradiation dose caused evolution on the surface topography that was markedly different for the H+ and Au7+ beams. For samples bombarded with H+ and annealed at 100 °C, the radiation effect was to slow down the roughness increase, stabilizing its value at levels below those of the films not exposed to the beam. Irradiation with 18 MeV Au ions, on the contrary, destabilized the films, causing strong changes in surface morphology and roughness. Such differences in behavior are attributed to the type of damage introduced by each beam and to the synergistic effects of radiation-induced bond breaking and heating