Towards sub-nanometer scale EELS analysis of polymers in the TEM

We have performed EELS analysis of poly(ethylene terephthalate) (PET) in the analytical TEM in order to evaluate the possibility to obtain chemical information on the polymer at both sub-micrometer and sub-nanometer scales (i.e, at 100 and 0.7 nm diameter probe). In the acquired spectra, we propose an identification to the different chemical bondings in agreement with XANES experiments and the characteristic signature of PET due to great irradiation damage. Main results confirm that PET is very sensitive to electrons when a large probe size is used, with a critical dose of about 10(3) C m(-2). At the opposite, a high dose rate in a sub-nanometer diameter electron beam is far less destructive and EELS spectra of non-degraded PET could be obtained even at 10(7) C m(-2). Irradiation damage was however thought to be the main limitation of the field-emission gun microscope, since high electron dose rate is produced. The radicals diffusion process reveals to be of prime importance as far as this surprising behaviour is concerned.