ISSN 1063-7842, Technical Physics, 2009, Vol. 54, No. 7, pp. 1034–1040. © Pleiades Publishing, Ltd., 2009. Original Russian Text © O.M. Artamonov, S.N. Samarin, J.F. Williams, 2009, published in Zhurnal Tekhnicheskoі Fiziki, 2009, Vol. 79, No. 7, pp. 108–114. 1034 INTRODUCTION One of the fundamental problems in solid-state physics concerns the approximation (either as a gas of weakly interacting particles of a liquid with a strong multiparticle interaction) that should be used for ana- lyzing the main properties of the electron subsystem [1]. It is generally accepted that the electron subsystem of normal metals can be described using the Fermi- liquid approximation [2]. At the same time, consider- able progress has been made using the approximation of weakly interacting Fermi gas in the description, for example, of heat capacity and electrical conductivity of metals [1]. The intensity of the multiparticle interaction (nat- urally, from the standpoint of the perturbation under investigation) can be estimated, in our opinion, from analysis of the electron–electron scattering. For a weakly interacting electron gas, electron–electron scattering can be described using the binary approxi- mation, in which the total momentum of two interact- ing particles is conserved. Binary scattering is the interaction of an impinging electron mainly with the field of an individual quasiparticle. An alternative is multiparticle scattering, in which an impinging elec- tron interacts with the total field of many quasiparti- cles. In the case of strong electron–electron interac- tion, scattering may occur in the region of superposi- tion of the fields produced by many charges. The binary scattering approximation in this case is inappli- cable since the momentum of the “probe” electron is lost in the “sea” of interacting particles. Consequently, the conservation of momentum during an individual interaction of particle and the extent to which the interaction can be treated as a binary interaction are important factors in determining the intensity of the interaction between quasiparticles. These questions are important, not only for deeper understanding of the fundamentals of solid-state physics, but also for developing many of its applica- tions. During the last decade, the injection of spin- polarized electrons from a magnet to a semiconductor and their extraction from the semiconductor to the magnet has been studied intensely [3, 4]. These pro- cesses are important for the development of semicon- ducting spintronics. Injection and extraction of “hot” electrons are considered in the ballistic approxima- tion, and the type of their scattering and momentum relaxation are of considerable interest. Binary and Multiparticle Electron–Electron Interaction on the Surface O. M. Artamonov a , S. N. Samarin a, b , and J. F. Williams b a St. Petersburg State University, St. Petersburg, 198504 Russia b School of Physics, University of Western Australia, WA 6009 Perth, Australia e-mail: arto@mail.nnz.ru Received June 25, 2008 Abstract—It is shown for the first time that electron–electron scattering of slow electrons with an energy of 10–50 eV at the surface of some metals is mainly an event of binary scattering of particles with conserved total momentum and energy, while analogous scattering at the surface of a semiconductor (n-Si) and an insulator (MgO) is a multiparticle event. A model is proposed, in which the electron subsystem of a solid is character- ized by short-range order. Each electron is at the center of a spherical cell and surrounded by nearest neigh- bors (electrons) with a coordination number of 12. The overlap of the fields of charges gives rise to a negative potential U c (r) ≈ U c , which is virtually constant along the coordinate and contains spherical cells with a cen- tral field U(r) of individual charges. The value of constant negative potential U c depends on the extent of elec- tron screening, which is high for metals and low for semiconductors and insulators. In metals, scattering gov- erned by the binary mechanism may take place (i.e., scattering of a primary electron in the central field of an electron of the metal); this is ensured by a relatively small value of constant potential U c . The electron sub- system of the metal behaves as a Fermi gas of weakly interacting quasiparticles. Electron screening in semi- conductors and insulators is insignificant, and constant negative potential U c is an order of magnitude higher than the analogous potential in metals. Slow primary electrons are scattered in the total field of many charges before they reach the central field of an individual electron. The electron subsystem of a semiconductor and an insulator in the excitation range studied here behaves as an ensemble of strongly interacting particles. PACS numbers: 79.20.Kz, 68.49.Jk, 72.10.-d, 71.10.Li DOI: 10.1134/S1063784209070184 SURFACE, ELECTRON AND ION EMISSION