Estimates of the Efficiencies of Production and Detection of Electron-Excited Auger Emission

Abstract

The efficiency of production of electrons emitted by the Auger process from the surface of a solid irradiated with a beam of electrons in the energy region below 2 keV is estimated. It is shown that the probability of photon production is negligible and that to a first approximation the optimum primary energy required for the ionization of an inner atomic level is between 3 and 3.5 times the critical ionization potential of that level. Calculation of the Auger current is made for a chosen system, that of oxygen adsorbed on a copper surface, and is found to be about 2×10⁻¹¹ A in the group of oxygen peaks around 500 eV, for a complete monolayer, detected on a spherical screen of the size typically found in LEED display systems. Consideration of the two methods, the retarding field and the electrostatic deflection, that have been used for detection of Auger currents, leads to the conclusions that, in the retarding field analyzer, the current in the second derivative increases as the square of the amplitude of modulation up to an amplitude about one‐half that of the rms width of the Auger peak, and thereafter tends to a constant value, whereas in the electrostatic‐deflection analyzer, the current in the second derivative increases linearly with amplitude of modulation up to an amplitude about one‐third that of the rms width, passes through a maximum, and, beyond an amplitude about six times the rms width, decreases again as the inverse square root of the amplitude.