A new method of investigation of electron structure in metal surfaces with the aid of positron annihilation

Abstract

A method is given for the investigation of momentum distribution of γ‐quantum annihilation from the metal surfaces. The method uses the interaction between positronium atoms and surface atoms. Possible mechanisms of this interaction are discussed and the conditions under which the method may be applied are defined. The method was used for the investigation of the momentum distribution of photon annihilation from the surface of polycrystalline iron and aluminium, and single‐crystalline molybdenum. It is shown that this distribution is parabolic for Fe and Al and differs significantly from the conduction electron distribution in the bulk metal. For Mo crystals it was concluded that there are two states for electrons on the surface of the (100) plane. It is assumed that the experimental definition of the electrons density gradient on the metal–vacuum interface may serve as a criterion which allows to estimate some physical properties of metal and alloy surfaces. The possibilities of the new method are disccussed.

On the model of positron trapping by defects in metals

“…I n order to evaluate the annihilation parameter h, the data were used obtained for positron annihilation on aluiiiiniuin surface [6]; the values h = 0.067, h, = 0.053, and h, = 0.25 were obtained for nornialized areas under ADAPl) curves. These give at N 0.07 and ft = 0.12.…”