Physical and chemical changes in polystyrene during electron irradiation using EELS in the TEM: contribution of the dielectric function.

We have performed electron energy-loss spectroscopy analysis of polystyrene in the analytical transmission electron microscope in order to evaluate the possibility of obtaining both chemical and dielectric information on the polymer at the submicrometre scale. Irradiation has also been studied, particularly the influence of the specimen temperature on the kinetics of degradation. The main results show that polystyrene is resistant to electron beam with a critical dose of about 104 C m-2 at 127 K. Spectra could be acquired with doses less than this critical dose. We were thus able to propose an identification of the different chemical bonds of carbon (including the C-H bond), in agreement with previous X-ray absorption near-edge structure experiments. The chemical changes in polystyrene due to severe irradiation damage are also visible in the carbon K-edge near-edge structure. At the same time, we calculated the dielectric function from the low-loss part of the spectra. Interestingly, this part of the spectrum is the most sensitive to irradiation, since great changes can be seen during exposure. Lastly, we propose a degradation process, in agreement with all these results.