MODIFICATIONS OF SILICON SURFACES BY ENERGETIC ALKALI-METAL ION IRRADIATION

The irradiation of a solid surface with keV alkali-metal ions can lead to the formation of an adsorbed alkali-metal layer. Results obtained by bombarding silicon surfaces with Li+, Na+ and K+ ions are presented . The formation of the overlayer was monitored by ion-induced secondar y electron spectroscopy during the irradiation. The variation of the s ilicon and alkali-metal Auger yields, the surface work function and th e secondary electron emission coefficient were studied as a function o f the ion dose, the target temperature and for different ion beam para meters (energy, angle of incidence). The results show that the formati on of the alkali-metal overlayer comes from various interdependent mec hanisms: implantation, sputtering, diffusion, chemisorption and desorp tion. A model based on a diffusion-like equation allowed to account fo r the observed alkali-metal saturation coverage at the silicon surface .