Phenomenology of the alpha-hydrogen desorption state on Si(110) surfaces

Adsorption of hydrogen on Si(1 1 0) surfaces was studied with thermal desor ption spectroscopy. Hydrogen desorption spectra measured after admission of H from a thermal atom source to clean Si(1 1 0) revealed in addition to th e mono- and dihydride peaks at 800 and 686 K, respectively, desorption from an a-state near 940 K. This state could be populated at Ar sputter/1060 K annealed surfaces only during admission of H between 300 and 800 K and afte r saturation of the monohydride state. The amount of H in the alpha -state was atmost 20% of that in the monohydride after sputtering at 800 K followe d by annealing. High temperatures and high ion energies (0.5-2 keV) during sputtering enhances its population during subsequent H admission. Without a nnealing, at a surface sputtered with 2 keV ions, the amount of hydrogen bo und in the a-state was as big as the amount of H in the monohydride. Anneal ing restored the normal mono/alpha population ratio. Using Ar evolution fro m sputtered surfaces as a monitor for rearrangement of surface atoms it was found that a-desorption coincides with the onset of Si atom mobility. From this it is concluded that the alpha -state is a defect related state below the surface plane. (C) 2001 Elsevier Science B.V. All rights reserved.