Ge(011)-c(8x10) 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 x 10), as well as the desorption kinetics and pathways from hydrogen-adsorbed surf aces. For the TPD measurements, the samples were heated at 2 degrees C s(-1 ) after adsorbing atomic deuterium at 100 degrees C to coverages theta(D) r anging up to saturation. Low-energy electron diffraction (LEED) and STM sho w that saturation deuterium coverage results in a (1 x 1) structure with th e surface composed of randomly distributed adatom islands. TPD spectra exhi bit three second-order peaks corresponding to D-2 desorption from multideut erides, adatom monodeuterides and rest-atom monodeuterides. Desorption from the multideuteride phase (with an activation energy E-a of 1.61 eV) begins at 200 degrees C and, by 270 degrees C, only the D-adatom and D-rest-atom monodeuteride phases remain. D-2 begins to desorb from adatom sites (E-a = 1.76 eV) above 230 degrees C and from rest-atom sites (E-a = 1.83 eV) above 240 degrees C. From quantitative analyses of the TPD spectra, the adatom d ensity on the clean surface is greater than or equal to 0.47. This high ada tom density - similar to that of Si(111)-(7 x 7), Si(011)-(16 x 2) and Ge(l ll)-c(2 x 8), all of which contain adatoms and rest atoms as primary buildi ng blocks - appears to rule out previously proposed models for the Ge(011)- c(8 x 10) surface structure, for which the adatom density is 0.064. (C) 200 0 Elsevier Science B.V. All rights reserved.