Verlag des Forschungszentrums Jülich
JUEL-3542
The Cu(110)-(2x1)0 striped phase is used as model substrate. The Cu(110) surface
reconstructs upon oxygen adsorption forming a striped phase with alternating
Cu(110)-(2 x 1)0 stripes and clean Cu(110)-areas. The Cu-O stripes of this self
assembled nanostructure are not only of the same width but also equally spaced.
Their period can be tuned through the oxygen coverage between 6 and 14 nm. In
addition, the striped phase is easy to prepare and as an equilibrium structure
it is thermally stable. Physisorption and desorption of thin films does not destroy
the structure of this phase. As a consequence, the Cu-O striped phase is suited
very well as model substrate to study the special physical and chemical properties
of nanostructured surfaces. Xenon (Xe), molecular nitrogen (N2) and
tetrafluormethan (CF4) are chosen as adorbates species because their structure
and dynamics on clean Cu(110) are well known from previous studies.
The main result of the studies is that the Cu-O striped phase can be used as a
template to produce a regularly patterned monolayer of an atomic or molecular
film with domain sizes reaching down to 2 nm. The driving force is the preferential
adsorption of the particles on the Cu-O stripes or the selective desorption of
the particles adsorbed on the clean Cu .
The selective adsorption which was observed for Xe atoms as well as for N2 and CF4
molcules is a consequence of the chemical heterogenity of the nanostructured
substrate. The binding energy of the particles on Cu-O stripes is higher than
on clean Cu which leads to the preferential adsorption on the stripes and
consequently a replication of the striped phase.
The quality and stability of the replicated nanostructure depends on the
selectivity of the driving forces, i.e., on the difference in the binding energies
on Cu and Cu-O. We find that the preferential adsorption or the chemical selectivity
persists even for stripe widths of only a few nanometer.
To what extend the physical properties of the nanostructured films - such as
the adsorption energy, the adsorption and desorption kinetics or the structural
ordering - are influenced by the small domain size, largely depends on the
adsorbed species. However there are also phenomena, which are common to all
three species, as for instance the existence of an indirect desorption channel
for atoms and molecules adsorbed on the Cu-O stripes.
Beside the physisorbed species, the growth of iron films on the Cu(110)-(2xl)O
striped phase was also studied. Up to 8 ML RHEED experiments show that Fe grows
in a layer by layer mode in fcc structure. The growth of the Fe film does not
seem to destroy the Cu-O striped phase. From the oscillations of the oberved
RHEED intensities with layer thickness a growth model of the deposited Fe film
is deduced: the Fe film is proposed to nucleate and grow in stripes at the step
edges originating from the height difference between the Cu-O and the Fe monolayer,
respectively.
Diercks, Verena Beate
Einfluß der Nanostrukturierung von Oberflächen auf das Wachstum dünner Filme
151 S., 1998
The physical and chemical properties of well defined nanostructured surfaces
are studied by means of thermal He atom scattering and thermal desorption
spectroscopy. The main issues are to what extend the long range ordered, complex
rare gas and molecular adlayers are influenced by the small domain size of the
substrate structure and how the elemantary processes involved in adsorption and
desorption depend on the size of the structures. By investigating the adsorption,
the atomic or molecular structure and the growth as well as the kinetics of
desorption of thin atomic and molecular films on a nanostructured model substrate
novel "finite-size" effects were found and could be characterized in a systematic
way.
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