Monolayer attenuation length of low-energy electrons in Gd and Tb

Abstract

The electron attenuation length is a material property, which defines the probing depth of all electron spectroscopies. For kinetic energies below 50 eV, very few data exist in the literature, although this energy range is vital for electron spectroscopy using low-energy electrons, e.g., for studying the valence electronic band structure. Extremely short attenuation lengths are expected for the transition metals gadolinium and terbium. To determine the electron attenuation length in these materials, we conducted inverse-photoemission overlayer experiments with ultrathin Gd and Tb films on W(110). For 10-eV electrons, we find an attenuation length of about one monolayer in Gd and even less in Tb, i.e., two thirds (or more) of the electrons are stopped by only one monolayer. These results imply extremely short information depths for electron spectroscopies with low energies on the lanthanides Gd and Tb.