ABSTRACT
In an electron energy loss spectrometry (EELS) experiment in a transmission
electron microscope (TEM), fast electrons (in general 80 to 300 keV) are used
as probe particles. Their kinetic energy corresponds to electron velocities of 50
to 80% of the light velocity. One would expect to see relativistic effects in the
experiment. Surprisingly, apart of the replacement of the electron’s rest mass by
the relativistic mass, the non-relativistic quantum mechanical expressions for the
scattering process hold in the majority of cases.1 The incoming electron is almost
exclusively considered as a plane wave. This fast electron may lose energy via
interactions with the sample. For instrumental reasons, the energy range accessible
is situated between 0 and at most 3000 to 4000 eV, with an energy resolution
of 0.1 to 0.2 eV on a monochromated TEM [Egerton (2009)] and 0.7-0.8 eV on
a conventional instrument with a field emission source. Phonon scattering is
not accessible via EELS since the energy loss is far too small and these events
are detected together with the very intense peak of the elastic scattering; they
are called quasi-elastic. Therefore the events accessible are only electron-electron
scattering events. Such events are referred to as inelastic as the internal energy
of the target is changed. Figure 1.1 shows a schematic diagram of the possible
scattering events together with an EELS spectrum.
