Momentum transfer broadening in Compton electron energy loss spectroscopy

Electron Compton scattering is a momentum resolved, electron energy loss spectroscopy (EELS) technique for measuring Jp_z, the electron momentum density for the solid projected along the scattering vector direction. For accurate Jp_z there should only be one momentum transfer vector. However, in practice the experimental conditions, i.e. specimen illumination and EELS detection, as well as multiple scattering within the specimen can cause momentum transfer broadening. The result is inaccurate Jp_z profiles. Here a numerical method that successfully removes the momentum spread of the electron beam and EELS spectrometer from measured Jp_z data is demonstrated. This novel data analysis procedure provides greater flexibility in the design of Compton EELS measurements, such as focussed electron probes for higher spatial resolution and larger EELS collection apertures for improved signal. Amongst multiple scattering artefacts, thermal diffuse scattering (TDS) is unavoidable. A simple model is proposed that estimates the maximum specimen thickness required to suppress TDS artefacts in Compton EELS. For intermediate and heavy atomic number, the maximum thickness is only a few nanometres. Therefore, Compton EELS is more suitable for materials with low average atomic number.