New Phenomenon in the Absorption of Oxygen on Silicon

Abstract

An ${\mathrm{O}}_{2}$ adsorption state on the Si(111) 2\ifmmode\times\else\texttimes\fi{}1 surface has been found which will remove surface states without producing a chemical shift of the Si $2p$ core level, suggesting a strongly covalent bond. This is accomplished by using an initial exposure pressure of ${10}^{\ensuremath{-}8}$ Torr. Exposures using an initial exposure pressure of ${10}^{\ensuremath{-}6}$ Torr also remove the surface states but produce a 2.0 eV Si $2p$ chemical shift indicating an ionic bond different from that of Si${\mathrm{O}}_{2}$ (shift of 3.8 eV).