SPECTROMICROSCOPY OF POLY(ETHYLENE-TEREPHTHALATE) - COMPARISON OF SPECTRA AND RADIATION-DAMAGE RATES IN X-RAY-ABSORPTION AND ELECTRON-ENERGY-LOSS

The C 1s and O 1s X-ray absorption spectra of poly(ethylene terephthal ate) (PET) have been recorded using transmission, fluorescence, and el ectron yield detection. The corresponding electron energy loss spectra (EELS) have been recorded in a scanning transmission electron microsc ope. These results are compared to the C 1s and O 1s spectra of gas ph ase 1,4-dimethyl terephthalate (the monomer of PET) recorded using EEL S. The comparison of monomer and polymer materials in different phases and with different techniques has aided the understanding of the rela tive strengths and limitations of each technique as well as assisting the spectral interpretation. Good agreement is found in the overall sh ape and the energies of the spectral features. Relatively minor differ ences in intensities can be understood in terms of the properties of t he individual spectroscopic techniques. The critical dose for radiatio n damage by 100 keV electrons incident on PET at 100 K is found to be (1.45 +/- 0.15) x 10(3) eV nm(-3). In contrast, the critical dose for radiation damage by 302 eV X-rays incident on PET at 300 K is (1.2 +/- 0.6) x 10(4) eV nm(-3). A figure of merit involving the product of cr itical energy dose and spectral efficiency (as expressed by the approp riate G value) is developed. This indicates that, for near-edge studie s involving a 20 eV spectral width, there is similar to 500-fold advan tage of X-ray absorption studies on room temperature PET relative to e lectron energy loss studies of cooled PET.