Essay On Sputtering

When an ion impinges on a solid, it can transfer energy to the solid via collision with the atoms (“nuclear stopping”) or excitation of the electrons (“electronic stopping”). This can enable constituents of the solid to overcome their binding energy and propagate away from the surface. This process is called “sputtering.” Two different sputtering regimes are distinguished, depending on which the energy loss channel is prevalent. At low (keV) kinetic energies, the primary ion interacts with the solid primarily by (elastic) collisions, which initiates a collisional cascade. Recoils of this cascade can lead to the emission of secondary particles at the surface. In the following, this process is termed “collisional sputtering.” Part of the sputtered material is emitted in a charged state, and the resulting secondary ions are utilized in secondary ion mass spectrometry (SIMS) as an established surface analysis technique. In the high kinetic energy limit, collisions with the target nuclei become improbable. Consequently, the ion moves through the solid along a straight line while depositing energy mainly into the electronic subsystem. “Electronic sputtering” can occur, if a sufficient amount of this energy in transferred to the lattice, for example, by electron-phonon coupling.

Currently, direct observation of the dynamics of the sputtering process at the atomic scale is only possible in model

For that purpose, a pristine surface is first sputter-cleaned by kiloelectron-volt argon ion bombardment in order to remove the native oxide layer. Then, the oxygen surface coverage is varied in a systematic manner by dosing the surface with O2, and iys influence on the ionization probability is measured. The results are interpreted in terms of the particle emission mechanism under electronic