Nonlinear effects in low-energy ion sputtering of solids

Abstract

In this paper, we demonstrate that the sputtering of solids by ions of low (<30 keV) and even ultralow energies (<2 keV) is accompanied by nonlinear effects. These nonlinear effects are the result of heating a significant part of the cascades of collisions above the effective melting temperature of the material with the formation of local melts or “thermal spots” (a special case of the thermal spike regime). Nonlinear effects should primarily be observed in dense targets irradiated by heavy and cluster ions. In this paper, the question of the lifetime of such spots and their effect on the emission of secondary particles and the formation of specific surface topography is examined in detail. Another important assumption of the model is the existence of an intermediate ion sputtering regime, in that both linear cascades and thermal spots can exist simultaneously. A phenomenological model based on the effect of a rapid decrease in the cascade volume with a monotonic decrease in the energy of primary ions below 3 keV, which leads to the formation of thermal spots at ultralow energies (<2 keV), is also proposed. The suggested thermal spot model allows us to explain several experimental data that have not yet been explained in the framework of the traditional sputtering models. In particular, a simple explanation is given for the formation of pores in the surface layer during implantation and the formation of a relief on an ion-bombarded surface such as nanodots, pits (holes), and in the form of a foam-like surface. The small stationary concentration of cesium on the surface of the target sputtered by low-energy cesium ions is also explained.