The fate of the (reactive) primary ion: Sputtering and desorption

Accurate modeling of the enhancement of the ionization probabilities of secondary ions (positive and negative) by the presence of reactive species requires a precise determination of their concentration at the outermost surface and thus a fundamental understanding of their incorporation and release processes. In the present paper we discuss these processes for oxygen, cesium and cluster ion bombardment with a special emphasis on their importance at (very) low bombardment energies. At these energies the sputtering processes becomes very small and deposition instead of erosion is predicted while for some species such as oxygen and cesium, an additional process, i.e. desorption, becomes more important thereby enabling a stationary state without deposition. The desorption process is a property of the primary ion and element specific and can be predicted based on the sputter yields and heat of sublimation. For those species/conditions where desorption is not operational (such as for C60-beams), depth profiling at very low energies and with low sputter yields (<1) will not be possible and accumulation of the primary ion (thin film growth) is observed. The absence of deposition under oxygen, cesium and (SF5)n-bombardment and the positive impact of oxygen flooding on C60 bombardment can all be explained when the desorption mechanism is included in the balance equation.