H. Kim et al., Ge(011)-c(8x10) surface structure and hydrogen desorption pathways: a temperature-programmed desorption and scanning tunneling microscopy study, SURF SCI, 457(3), 2000, pp. 337-344
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.