Resonant charge transfer at dielectric surfaces

Abstract

We report on the theoretical description of secondary electron emission due to resonant charge transfer occurring during the collision of metastable N₂(³Σ⁺ _u ) molecules with dielectric surfaces. The emission is described as a two step process consisting of electron capture to form an intermediate shape resonance N₂ ^-(²Π _g ) and subsequent electron emission by decay of this ion, either due to its natural life time or its interaction with the surface. The electron capture is modeled using the Keldysh Green’s function technique and the negative ion decay is described by a combination of the Keldysh technique and a rate equation approach. We find the resonant capture of electrons to be very efficient and the natural decay to be clearly dominating over the surface-induced decay. Secondary electron emission coefficients are calculated for Al₂O₃, MgO, SiO₂, and diamond at several kinetic energies of the projectile. With the exception of MgO the coefficients turn out to be of the order of 10^-1 over the whole range of kinetic energies. This rather large value is a direct consequence of the shape resonance acting as a relay state for electron emission.