Electron scattering at high momentum transfer

Energetic (multiple keV) electrons scattering at high momentum transfer (i.e. scatter over a large angle ($>20$°)) interact with a single particle, either a nucleus or a target electron. Energy transfer is then determined by the incoming energy, scattering angle and the mass and velocity of the scattering particle. When scattering from a target electron a large fraction of the incoming energy is transferred and scattered and ejected electrons can be detected in coincidence. The experiment is then known as electron momentum spectroscopy or (e,2e) spectroscopy and information about the electronic structure is obtained. When scattering from a nucleus the transferred energy is much smaller, and only the scattered electron can be detected. Then the experiment is known as electron Rutherford backscattering and one can measure the sample composition and vibrational properties. In this review we give examples of experimental results for both cases to illustrate the unique information that can be obtained by electron spectroscopy at high-momentum transfer, a less-frequently utilised experimental condition.