Auger electron spectroscopy (AES) is based on the Auger total secondary electron energy distribution, and an ion gun to process, which involves the core-level ionization of an atom with provide depth profiling capability. subsequent deexcitation occurring by an outer-level electron de­ The high surface sensitivity of Auger spectroscopy which dictates caying to fill the core hole. The excess energy is transferred to the need for an ultrahigh-vacuum system is due to the limited and causes the ejection of another electron, which is by definition mean free path of electrons in the 0-3000 e V kinetic energy an Auger electron. The Auger electron transition, denoted by range. The Auger peaks decay exponentially with overlayer cov­ the electron levels involved, is independent of the excitation erage, which is consistent with an exponential dependence of source and leaves the atom with a constant kinetic energy. The escape probability on the depth of the parent atom. A compila­ kinetic energy is given by the differences in binding energies for tion of data from a variety of sources has been used to generate the three levels (for example, EK-E L, - EL ) minus a correction 2 an escape depth curve which falls in the range of 5-30 A in the term for the work function and electron wave function relaxation. energy range from 0 to 3000 eV. The observed escape depth does When the Auger transition occurs within a few angstroms of the not show a strong dependence on the matrix.