Ge(011)-c(8×10) surface structure and hydrogen desorption pathways: A temperature-programmed desorption and scanning tunneling microscopy study

Temperature-programmed desorption (TPD) and scanning tunneling microscopy (STM) were used to probe the atomic arrangement on clean Ge(011)-c(8×10), as well as the desorption kinetics and pathways from hydrogen-adsorbed surfaces. For the TPD measurements, the samples were heated at 2 °C s^-1 after adsorbing atomic deuterium at 100 °C to coverages θ_D ranging up to saturation. Low-energy electron diffraction (LEED) and STM show that saturation deuterium coverage results in a (1×1) structure with the surface composed of randomly distributed adatom islands. TPD spectra exhibit three second-order peaks corresponding to D₂ desorption from multideuterides, adatom monodeuterides and rest-atom monodeuterides. Desorption from the multideuteride phase (with an activation energy E_a of 1.61 eV) begins at 200 °C and, by 270 °C, only the D-adatom and D-rest-atom monodeuteride phases remain. D₂ begins to desorb from adatom sites (E_a = 1.76 eV) above 230 °C and from rest-atom sites (E_a = 1.83 eV) above 240 °C. From quantitative analyses of the TPD spectra, the adatom density on the clean surface is ≥0.47. This high adatom density - similar to that of Si(111)-(7×7), Si(011)-(16×2) and Ge(111)-c(2×8), all of which contain adatoms and rest atoms as primary building blocks - appears to rule out previously proposed models for the Ge(011)-c(8×10) surface structure, for which the adatom density is 0.064.