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@PHDTHESIS{Romanyuk:51449,
author = {Romanyuk, Konstantin},
othercontributors = {Voigtländer, Bert},
title = {{I}nfluence of the step properties on submonolayer growth
of {G}e and {S}i at the {S}i(111) surface},
address = {Aachen},
publisher = {Publikationsserver der RWTH Aachen University},
reportid = {RWTH-CONV-113740},
pages = {167 S. : Ill., graph. Darst.},
year = {2009},
note = {Aachen, Techn. Hochsch., Diss., 2009},
abstract = {The present work describes an experimental investigation of
the influence of the step properties on the submonolayer
growth at the Si(111) surface. In particular the influence
of step properties on the morphology, shape and structural
stability of 2D Si/Ge nanostructures was explored.
Visualization, morphology and composition measurements of
the 2D SiGe nanostructures were carried out by scanning
tunneling microscopy (STM). The formation of Ge nanowire
arrays on highly ordered kink-free Si stepped surfaces is
demonstrated. The crystalline nanowires with minimal kink
densities were grown using Bi surfactant mediated epitaxy.
The nanowires extend over lengths larger than 1 µm have a
width of 4 nm. To achieve the desired growth conditions for
the formation of such nanowire arrays, a modified variant of
surfactant mediated epitaxy was explored. It was shown that
controlling the surfactant coverage at the surface and/or at
step edges modifies the growth properties of surface steps
in a decisive way. The surfactant coverage at step edges can
be associated with Bi passivation of the step edges. The
analysis of island size distributions showed that the step
edge passivation can be tuned independently by substrate
temperature and by Bi rate deposition. The measurements of
the island size distributions for Si and Ge in surfactant
mediated growth reveal different scaling functions for
different Bi deposition rates on Bi terminated Si(111)
surface. The scaling function changes also with temperature.
The main mechanism, which results in the difference of the
scaling functions can be revealed with data of Kinetic
Monte-Carlo simulations. According to the data of the Si
island size distributions at different growth temperatures
and different Bi deposition rates the change of SiGe island
shape and preferred step directions were attributed to the
change of the step edge passivation. It was shown that the
change of the step edge passivation is followed by a change
of the preferred steps direction resulting into different
islands shapes. The symmetry of the properties of the
different step directions can determine the symmetry of the
2D islands. The growth shape of reconstructed 2D islands
(nanostructures) on reconstructed surfaces can deviate from
the internal symmetry of the substrate and the island. An
analysis of the symmetry of the combined system of
reconstructed substrate and island can deduce predictions
for the island growth shape. It was found experimentally
that the shape of two-dimensional (2D) Si or Ge islands has
a lower symmetry than the threefold symmetry of the
underlying Si(111) substrate if Bi is used as a surfactant
during growth. Arrow-shaped or rhomb-shaped 2D islands were
observed by scanning tunneling microscopy. This symmetry
breaking was explained by a mutual shift between the surface
reconstructions present on the substrate and on the islands.
The mutual shift results into different step structure for
initially symmetry related step directions. Using the
kinematic Wulff construction the growth velocities of the
steps could be determined from the island shape if the
nucleation center had been located by a marker technique.
The structural stability of 2D SiGe nanostructures was
studied by scanning tunneling microscopy (STM). The
formation of pits with a diameter of 2–30 nm in one atomic
layer thick Ge stripes was observed. The unanticipated pit
formation occurs due to an energetically driven motion of
the Ge atoms out of the Ge stripe towards the Si terminated
step edge followed by an entropy driven GeSi intermixing at
the step edge. The pit formation can be also used for
nanostructuring. Using conditions at which pit formation is
enhanced the fabrication of freestanding GeSi stipes with
single digit nanometer width is possible. Continuous ~ 8 nm
wide freestanding GeSi wires have been fabricated by pit
coalescence.},
keywords = {Silicium (SWD) / Germanium (SWD) / Epitaxie (SWD) /
Oberfläche (SWD) / Wachstum (SWD) / Symmetrie (SWD)},
cin = {130000 / 132310},
ddc = {530},
cid = {$I:(DE-82)130000_20140620$ / $I:(DE-82)132310_20140620$},
typ = {PUB:(DE-HGF)11},
urn = {urn:nbn:de:hbz:82-opus-29840},
url = {https://publications.rwth-aachen.de/record/51449},
}
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