Kinematics of Desorption by Emerging High-Energy Electrons

Abstract

With certain systems the cross section for desorption of surface atoms by low-energy electrons is negligibly small. Desorption will not take place unless the electrons have sufficient energy to impart the required momentum by direct exchange. The present paper is relevant to such systems. Given a high-energy electron traversing a solid and emerging from the surface, there exists a finite probability that the electron will suffer a deflection in the Coulomb field of the nucleus of a surface atom and thereby impart sufficient momentum to the atom to result in its desorption. Assuming that a value for the binding energy is given, the paper sets forth the several considerations which must have a part in the computation of the desorption cross section as a function of electron energy. Calculated values are presented for the case of adsorbed thorium over a wide range of assumed binding energies and for electron energies up to 2 MeV. Results of the mechanical integrations are plotted in such a form that cross sections for other atomic species can be obtained by simple calculation.