X-RAY PHOTOELECTRON SPECTROSCOPIC STUDY OF SI(111) OXIDATION PROMOTEDBY POTASSIUM MULTILAYERS UNDER LOW O-2 PRESSURES

In the context of the alkali metal promotion of silicon oxidation, low pressure oxidation of potassium multilayers on cooled Si(111) has bee n investigated using XPS. Our measurements reveal that four potassium oxides (K2O, K2O2, KO2 and K2O3) are successively formed during increa sing O-2 exposure. Angular XPS analysis shows their relative depth dis tributions governed by the diffusion of oxygen atoms through the potas sium overlayer. We observe strong indications suggesting that the pota ssium overlayer is characterized by the Stranski-Krastanov (SK) growth mode on Si(111) at 150 K. Surprisingly, potassium islands seem to be leveled under low pressure of oxygen.