Verlag des Forschungszentrums Jülich
JUEL-2572
Sander, Dirk
Adsorbat-induzierte Oberflächenspannungen
77 S., 1992
Abstract
A cantilever bending experiment has been set up to study adsorbate-induced surface
stress on silicon and nickel single crystal samples. The adsorbate-induced bending of
the substrate is detected using a very sensitive capacitance method. The resolution of
the stress measurements was ± 20 dyn/cm and ± 100 dyn/cm, on 0.3 mm thick Siand
Ni-samples, respectively.
Oxygen-induced surface stress on Sit l l l) and Si(1oo) has been investigated for
substrate temperatures ranging from 300 K to 700 K. As a result of the breaking of the
Si-Si bonds and the formation of 5i-0-5i bonds, both surfaces exhibit a measurable
stress. A linear stress vs, coverage dependence is found. The oxygen-induced surface
stress on silicon is independent of the adsorption temperature. A monolayer coverage
on 5i(11 I) causes a considerable compressive stress of -7000 ± 980 dyn/cm, wheras
the same oxygen coverage on Si(loo) induces a small tensile stress of 260 ± 40 dyn/em.
The experimental results are in decent agreement with a simple duster calculation
using a valence-bond model. Thus, the different stress behavior can be attributed to
differences in the local geometric structures of the o-Si(111) and the O-Si(loo) dusters.
Homoepitaxy on 5i( 100) has been studied to derive an experimental value for
the anisotropy of the surface stress tensor of the Si(loo)-lx2 surface. As it was not
possible to prepare a stable single domain lxz-reconsrructicn, no experimental value for
the anisotropic surface stress tensor can be given.
Surface stress induced by the adsorption of sulfur, oxygen and carbon on
Ni(IOO) has been determined. As a result of strong adsorbate-substrate interactions,
these strongly chemisorbed systems induce a consider-able compressive surface stress.
The c(2x2)-structures of sulfur, oxygen, and carbon cause a surface stress of
-6000 ± 920 dyn/cm, -75G'O ± 1050 dyn/cm, and -85C'O ± 1190 dyn/cm, respectively.
Tile experimental results are discussed with regard to Rayleig1:l wave dispersion
data obtained by electron energy loss spectroscopy. The magnitude of the oxygen- &"10
carbon-induced surface stress is in agreement with total-energy calculations by J.E.
Muller et al., whereas the stress induced by sulfur is surprisingly high. It is proposed
that for S/Ni(1oo) a considerable contribution to the adsorbate-induced surface stress
arises from a direct, repulsive adsorbate-adsorbate interaction. The results OIl C/Ni(100)
support the concept of surface stress as the driving force for surface reconstruction.
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