Interaction of Slow Ions with a Solid Surface

Abstract

In order to develop our investigations into the interaction between atomic particles and solids, it is particularly important to understand the mechanism of this phenomenon. Many and various hypotheses have been advanced regarding the mechanism underlying the scattering of atomic particles by a solid surface. Thus, a number of research workers attempted to relate the direction of maximum intensity of the scattering of ions by solids with the angle of specular reflection. Later it was shown that the ions were scattered predominantly forward, and that any reflection at the specular angle or variation in the position of this angle with the energy of the incident ions (which had been considered as a proof of the diffraction of ion beams) were only apparent. Even in Gurney’s treatment [49] an attempt was made to explain the scattering of ions by a solid as being similar to elastic scattering in a gaseous medium. However, the limiting energy E of the scattered ions measured in this investigation was much lower than would follow from Eq. (1.9). This was due to the insufficiently clean conditions on the target surface. Agreement would also clearly not be achieved in the case of an ideally clean target, since, for the low energy range of the incident ions employed (20–60 eV) the atoms in the target could not be regarded as completely free owing to the bond forces between them. This would make the energy of the scattered ions greater than it should be according to Eq. (1.9). Much later, Arifov and Ayukhanov [219] and Eremeev [228] reliably established that only for incident energies E₀ of more than a few hundred eV would the ions be scattered from individual target atoms which could justifiably be regarded as free.