Bethe ridge electron Compton spectroscopy

Compton spectroscopy measures J(p_z), the number density of occupied electronic states with momentum component p_z. In a transmission electron microscope (TEM) Compton spectroscopy is performed by acquiring a momentum resolved, dark-field electron energy loss spectrum (EELS). Here it is shown that the Bethe ridge in a single energy filtered diffraction pattern can provide identical J(p_z) information. The energy filtered TEM (EFTEM) approach is more dose efficient, since all (projected) momenta p_z are recorded in parallel. For weakly diffracting specimens, the J(p_z) profiles extracted using EFTEM are in reasonable agreement with dark-field EELS. Bragg diffraction and thermal diffuse scattering are known to introduce artefacts in Compton spectroscopy, and this is true for the EFTEM method as well. The artefacts can however be mitigated by analysing suitably thin specimens.