(a) Energy diagram of Auger neutralization: an ion with ionization energy E_i transfers its energy upon neutralization to the electronic system of the solid with the capture of an electron at energy E′. The solid is described by the Fermi well depth E_F and the work function Φ. E_0 is the sum of Fermi energy and work function. E_k is the kinetic energy of the SE outside the solid with respect to the vacuum level, and E_k with respect to the bottom of the Fermi well. (b) Energy distribution of emitted SE of a clean copper surface, in dependence of the kinetic electron energy E_k with respect to the bottom of the Fermi well. The Fermi well is indicated by the gray area with E_F=7 eV for Cu. The black solid line denotes the distribution Ni(Ek) of excited electrons inside the solid, the black dashed line the electron escape probability Pe(Ek),and the green solid line the distribution of escaped electrons N0(Ek) outside the solid,the so-called SE EEDF, electron energy distribution function of secondary electrons,according to the Hagstrum model. The energy distributions are given in units ofamount of electrons per ion per eV.