DYNAMIC AND STATIC STUDIES OF SI SURFACES UNDER ALKALI ION IRRADIATION

We investigate the change of the Si(111) surface under energetic alkal i ion bombardment by a combination of both ion-induced electron spectr oscopy and time of flight ion scattering spectroscopy (TOF ISS) techni ques. The analysis carried out in the dynamical regim showed that a st eady state is obtained, characterized by an alkali saturation at the S i surface. The saturation value depends on the sample temperature, the incidence angle, the nature and the energy of the alkali ion. In the case of K-Si system formed by bombarding Si sample with 4 keV K+ ions up to the saturation state, TOF ISS experiments allowed us to confirm K 'trapping' in the first atomic layers. Moreover the K depth profile and the K atom concentration at the surface were determined. The exper imental results were compared to a diffusion-like model taking into ac count the modification of the concentration profile of implanted atoms under the combined effects of implantation, sputtering, generalized d iffusion, chemisorption and desorption. Agreement between theoretical data and experimental results was found for K-Si combination concernin g the irradiation time needs to reach the steady state and the potassi um atom density in the first atomic layers.