Secondary-electron emission induced by in vacuo surface excitations near a polycrystalline Al surface

The double-differential spectrum of coincidences between backscattered electrons and secondary electrons (SEs) emitted from a polycrystalline Al surface bombarded with 100-eV electrons was measured. For energy losses of the scattered electron in between the work function of Al and the bulk plasmon energy, a sharp peak is observed in the SE spectra, corresponding to ejection of a single electron near the Fermi edge receiving the full energy loss and momentum of the primary electron. This process predominantly takes place when the primary electron suffers a surface energy loss in vacuum, and leads to SE ejection from the very surface. At energy losses just above the bulk plasmon energy, a sharp transition is observed, corresponding to a sudden increase in the depth of ejection. The latter is a direct consequence of the complementarity of surface and bulk plasmons, the so-called Begrenzungs effect.