Low-temperature adsorption of oxygen on Si(111)

High resolution electron energy loss spectra and work function results are presented for the Si (111) surface held at 20 K during exposure to 0₂and subsequently annealed to 300 K. The data are consistent with the presence at 20 K of stable chemisorbed monatomic bridging, diatomic like nonbridging, physisorbed molecular, and metastable chemisorbed peroxy/superoxy oxygen on this surface. Upon warming the oxygen covered surface, the physisorbed oxygen evaporates at ≈ 35 K, the metastable superoxy oxygen converts to the peroxy oxygen above ≈ 60 K, the diatomic like nonbridging oxygen converts to the stable monatomic bridging oxygen above ≈ 60 K, and the metastable peroxy oxygen begins to convert to the stable monatomic bridging oxygen at ≈150 K.