Electron momentum spectroscopy of light and heavy targets

Electron momentum spectroscopy (EMS) measures the spectral function of electrons in matter directly, provided that multiple scattering effects are negligibly small. Even for the thinnest films this is not the case and one has to correct for multiple scattering effects in order to retrieve the spectral function. Both elastic and inelastic scattering effects affect the measurement. Elastic scattering is expected to increase greatly with increasing atomic number, much more so than inelastic scattering. For this reason EMS was thought to be of limited value for heavy targets. Here, we present data for carbon, silicon and gold and show that they are affected in different ways by multiple scattering. The gold sample has poor count rate, but in the spectra the multiple scattering effects appear rather minor. Carbon and silicon on the other hand have good count rates, but the spectra are strongly affected by multiple scattering. Monte Carlo simulations are used to try to understand these effects. Rather surprisingly the EMS spectra for heavy elements are of comparable quality to those of lighter elements.