Phenomenology of the α-hydrogen desorption state on Si(1 1 0) surfaces

Adsorption of hydrogen on Si(1 1 0) surfaces was studied with thermal desorption spectroscopy. Hydrogen desorption spectra measured after admission of H from a thermal atom source to clean Si(1 1 0) revealed in addition to the mono- and dihydride peaks at 800 and 686 K, respectively, desorption from an α-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 after saturation of the monohydride state. The amount of H in the α-state was atmost 20% of that in the monohydride after sputtering at 800 K followed by annealing. High temperatures and high ion energies (0.5–2 keV) during sputtering enhances its population during subsequent H admission. Without annealing, at a surface sputtered with 2 keV ions, the amount of hydrogen bound in the α-state was as big as the amount of H in the monohydride. Annealing restored the normal mono/α population ratio. Using Ar evolution from sputtered surfaces as a monitor for rearrangement of surface atoms it was found that α-desorption coincides with the onset of Si atom mobility. From this it is concluded that the α-state is a defect related state below the surface plane.