The EEL Spectrum
The 1980s saw a large improvement in detection systems with the development of parallel position sensitive detectors based on photodiode or charge coupled diode or device (CCD) arrays. In 1962, Castaing and Henry developed a filter based on a magnetic prism, an electrostatic mirror electrode and an energy selecting slit. In a specimen of thickness less than the mean free path for inelastic scattering, by far the most intense feature is the zero loss peak (ZLP) at 0 Electron Volt (eV) energy loss which contains all the elastically and quasi-elastically scattered electron components. The energy of the plasmon peak is governed by the density of the valence electrons in the sample and the width by the rate of decay of the resonant mode. In a thicker specimen, there would be additional peaks at multiples of the plasmon energy, corresponding to the excitation of more than one plasmon by the incident electron.