Hydrogen and Oxygen Bonding on Silicon Surfaces

Vibrational spectroscopy is an especially suited tool to investigate bonding configurations of chemisorbed species on solid surfaces. Here we employ high resolution electron energy loss spectroscopy to study the bonding structure of hydrogen, water and oxygen on Si(100) and Si(111) surfaces. Atomic hydrogen does not only saturate dangling bonds of Si surface atoms but also breaks Si−Si bonds to form SiH2 units which are thermally less stable than SiH units. Water chemisorbs dissociatively by forming SiOH and SiH complexes. At elevated temperatures the hydroxyl groups dissociate further and oxygen bonds in a bridge configuration between Si surface atoms. This energetically favourable bonding structure is also observed after oxygen adsorption at elevated temperatures. Only for low temperature adsorption and low oxygen coverage a peroxy radical with one oxygen atom bonding to one silicon surface atom occurs as a precursor state for bridge bonded oxygen.