The role of an electronic surface state in the stopping power of a swift charged particle in front of a metal

We study the stopping power and friction coefficient of a slow charged particle moving parallel to noble metal (111) surfaces. In the description of the surface electronic structure, information about a wide energy gap at the surface Brillouin zone, at the Fermi level, and the partly occupied s–pz surface state is introduced via the use of a model potential. The stopping power, S(b ,υ ), and friction coefficient, γ( b ,υ ), versus the projectile velocity υ and its distance from the surface b are investigated within linear response theory with self-consistent evaluation of the surface response function. The present calculations demonstrate the striking differences in the behavior of S(b ,υ )and γ( b ,υ )in comparison with those obtained from simpler models. In particular, for very low velocities, S(b ,υ )and γ( b ,υ )decay as b −3 at large b, mainly due to the electron–hole excitations within the surface state, instead of the ∼b −4 behavior expected from a jellium model. For velocities close to the surface state Fermi velocity, υ SS F , the energy losses with characteristic ∼b −2 decay are dominated by the excitation of the acoustic surface plasmons that can exist at some surfaces with partly occupied surface states. (Some figures in this article are in colour only in the electronic version)