COINCIDENT 2-ELECTRON EMISSION FROM SURFACES BY LOW-ENERGY ELECTRONS

The simultaneous ejection of two electrons from non-magnetic surfaces due to the collision of incident low-energy electrons with valence ele ctrons is treated in a relativistic distorted-wave Born approximation including exchange. The primary electron and the two emitted electrons are described by quasi-particle multiple scattering states. The valen ce electron is represented by linear combinations of Bloch waves match ed at the surface. Screened Coulomb interaction matrix elements betwee n these four states are evaluated. Numerical results for W(0 0 1) are presented and compared with one-dimensional bulk densities of states. Energy-integrated spectra and general features of the 2e-distribution are in good agreement with recent experimental data. (C) 1997 Elsevier Science Ltd.