Heavy ion-surface interaction at low energy: scattering of 3–300 eV Cs +, Xe +, and Ar + from the Si surface

Abstract

In order to understand the nature of a hyperthermal collision between a heavy projectile and a light atom surface, Cs +, Xe +, and Ar + ion beams are scattered from Si surfaces for collision energies of 3–300 eV. The scattered ions are analyzed for their mass and kinetic energy. The kinetic energy of the scattered ions is much higher than expected from a classical binary collision model, for example, the ratio of scattered to incident ion energy ( E s E i ) is 0.64 for a Cs +Si(111) collision at an incident energy of 3 eV and a scattering angle of 90°. The E s E i for Cs + decreases sharply with increasing energy up to 50 eV. For Xe + and Ar + scattering from Si(100), even higher E s E i values are measured at low collision energy, but this is attributed to preferential neutralization of the slow noble gas ions on the surface and the resulting upshift in their ionic energy distribution. Molecular dynamics classical trajectory simulation of heavy projectile-light atom surface collisions reveals that the lattice atoms collectively respond during a hyperthermal collision, resulting in a drastic E s E i increase compared to the collision of a light projectile. An important parameter that determines the E s E i ratio is the time scale of the collision relative to the energy propagation inside a solid.