Parallel EELS of polymers in a TEM: energy calibration of the carbon-K-edge

Abstract

Electron energy loss spectroscopy (EELS) measures the loss in energy of the primary electrons caused by inelastic scatter at the electron shell. The energy loss can be detected with magnetic spectrometers operating in parallel (PEELS) and with imaging magnetic/electrostatic Castaing or magnetic omega filters. To detect EEL-spectra of radiation sensitive polymers a PEEL-spectrometer is useful, because it allows a very fast detection of the spectrum. Dynamic measurements that show the changes in the PEEL spectra during irradiation, yield additional information.An important part of recording the spectrum at high energy resolution is the energy calibration. In parallel detection, the spectrum is displayed on a diode array with a finite number of diodes (1,024). So at high energy resolution (0.05 eV/ch) it is in general only possible to observe a narrow section of about 50 eV of the total spectrum. At higher energy losses that do not allow simultaneous measurement of the elastic peak, it is only possible to give a very approximate value in terms of eV units as the primary radiation energy can drift during the measurement. It is therefore impossible to compare spectra with one another as the absolute energy scale is not known. But, as the chemical shifts of interest have an order of magnitude ranging from fractions of an eV to several eV, it is essential to know the absolute energy scale.