EMERGENCE OF BASIC SITES ON A SI(111) SURFACE IN THE INITIAL-STAGE OFOXIDATION IN WATER

The surface oxidation of hydrogen-terminated Si(111) single crystals i n water has been studied by the adsorption of adenosinetriphosphate an d chlorine from their aqueous solutions. The radioactive tracer (P-32) method and Auger electron spectroscopy have revealed that these anion s are chemisorbed on the Si surface before the surface is fully oxidiz ed. The results indicate that the silicon surface is positively charge d in nearly neutral solutions, and is suggestive of the emergence of b asic sites in the initial oxidation stage. Structural change of the su rface-oxidized layer has been discussed in relation to the oxidation o f a clean silicon surface under low oxygen pressure in a vacuum.