Early stages of the alkali-metal-promoted oxidation of silicon

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Abstract
We have studied the potassium- and cesium-promoted oxidation of Si(100)2×1 with photoelectron and Auger-electron spectroscopies in the range of submonolayer alkali-metal-atom coverages. The alkali-metal atoms efficiently promote the oxidation of silicon. Our results demonstrate that there are two oxygen species on the surface during the oxidation reaction: oxygen atoms which are bonded to potassium from the very beginning of the process and oxygen atoms bonded to silicon. These two oxygen species are detected in core level O 1s and in valence-band photoemission spectra. Oxygen is transferred from K to Si, and this process is thermally activated and its efficiency is increased by heating the substrate. To explain these results we propose a model based on the decrease of local work function produced by potassium, which reduces the activation barrier for oxygen dissociation. Oxygen reacts with potassium, forming a potassium oxide which efficiently transfers oxygen to silicon.