Plenarvorträge - DPG-Tagungen

Oberflächenphysik Montag
Fachsitzungen
– Haupt-, Kurzvorträge und Posterbeiträge –
O 1 Hauptvortrag Hofmann
Zeit: Montag 09:30–10:15 Raum: H36
Hauptvortrag O 1.1 Mo 09:30 H36
Electron-phonon coupling and spin-orbit splitting in quasi twodimensional
metals: the surfaces of Bi — •Philip Hofmann — Institute
for Storage Ring Facilities, University of Aarhus, Ny Munkegade,
DK-8000 Aarhus C
Bi is a group V semimetal with a very low density of states at the
Fermi level. Several low-index surfaces of Bi support metallic surface
states which turn them into considerably better metals than the bulk.
Indeed, it is fair to view these surfaces as quasi two-dimensional met-
O 2 Hauptvortrag Nilius
als on an almost insulating substrate. We have studied the effect of the
electron-phonon coupling and the spin-orbit interaction on such systems.
For the former we find that the coupling strength depends strongly on
the binding energy of the states and it is therefore not possible to determine
the electron-phonon mass enhancement parameter λ from the
temperature-dependent width of surface states at higher binding energies.
For all Bi surfaces the spin-orbit splitting of the bands is very large
and dominates the two-dimensional dispersion. The consequences of this
on phenomena like screening or the formation of charge density waves
will be discussed.
Zeit: Montag 10:15–11:00 Raum: H36
Hauptvortrag O 2.1 Mo 10:15 H36
Tailoring electronic properties of atomic chains assembled in the
STM — •Niklas Nilius 1 , Thomas M. Wallis 2 , and Wilson Ho 2
— 1 Fritz-Haber-Institut der MPG, Berlin — 2 University of California,
Irvine, USA
The physical and chemical properties of ultra-small metal aggregates
sensitively depend on number and precise position of atoms in the structure.
Various applications in heterogeneous catalysis, optics and electronics
take advantage of this size-dependent behavior. However, preparation
and analysis of well-defined metal aggregates on surfaces are demanding
and interrelations between structural and electronic properties are not
well understood on the atomic level. In the present work, atom manipulation
techniques with an STM tip have been employed to construct
O 3 Nanostrukturen I
precise metal structures on a NiAl(110) surface. Single Au and Pd atoms
were assembled to atomic chains, whereby discrete adatom-resonances
develop into a series of quantum well states showing a parabolic dispersion.
Modifications of structural chain parameters, such as inter-atomic
distance, elemental composition and local impurities, decisively influence
the electronic properties of the atomic chains. Adsorption of a single
CO molecule on a Au chain interrupts the coupling between neighboring
chain atoms, breaking the chain into two independent electron systems.
A similar effect is observed upon introducing a single Pd atom into Au
chains. On the other side, the regular alternation of Pd and Au atoms
in alloy chains leads to properties in between those of pure Au and Pd
chains. The experiments demonstrate the possibility to manufacture and
characterize quantum systems with a well-defined electronic structure.
Zeit: Montag 11:15–13:15 Raum: H36
O 3.1 Mo 11:15 H36
Co nanostructures on Ag/v-Cu(111) — •Frank Ostendorf,
Andreas Bachmann, Georgi Rangelov, and Markus Donath
— Physikalisches Institut, Westfälische Wilhelms-Universität Münster,
Wilhelm-Klemm-Str. 10, 48149 Münster
Magnetic nanostructures play an important role in magnetic storage
technology. An important aim in this context is the customization of
the design parameters. The first step in preparing such nanostructures
is the controlled production of a suitable template. A new possibility to
produce regularly spaced nanostripes with controllable periodicity is the
deposition of Ag on vicinal Cu(111) surfaces [1]. Depending on the Ag
coverage, a rippled structure is formed in which Ag and Cu nanostripes
alternate with a periodicity between 10 and 30 nm. On the atomic scale,
the driving force for Ag-induced faceting is the lattice-matching between
the Ag overlayer and the faceted Cu substrate. The unique property of
this system is that the periodicity L of the nanostripes can be controlled
via the Ag coverage. Magnetic nanostructures can be produced by selective
deposition of magnetic material on the Ag or Cu facets of this
template. We report results of Co nanostripes with a thickness of a few
atomic layers, investigated by STM. The tunability of the spacing between
the stripes may lead to a detailed understanding of the magnetic
coupling between the nanostripes.
[1] A.R. Bachmann, F.Ostendorf and S. Speller, J. Phys.: Condens.
Matter, 15 (2003), 1-25
O 3.2 Mo 11:30 H36
Size-Effekt und Elektron-Phonon Kopplung in epitaktischen,
dünnen Gold-Filmen — •Gerd Kästle, Hans-Gerd Boyen,
Alexander Schröder, Alfred Plettl und Paul Ziemann — Abteilung
Festkörperphysik, Universität Ulm, 89069 Ulm
Epitaktische, glatte Goldfilme wurden auf Saphir mittels einer Niob
Keimschicht gewachsen. Die Temperaturabhängigkeit des Widerstand
wurde für Schichtdicken zwischen 2 und 50nm untersucht. Die Widerstandsmessungen
werden im Rahmen klassischer Size-Effekt Modelle analysiert.
Überraschenderweise beschreibt das ursprüngliche Model von
Fuchs-Sondheimer die Daten am besten und physikalisch konsistent -
auch für ultradünne Filme. Es zeigt sich allerdings, dass mit abnehmender
Schichtdicke die aus den Messungen abgeleitete Debye-Temperatur
stark reduziert ist. Im Gegensatz zu dicken Filmen wird in dünneren Filmen
die für den Transport relevante effektive Debye-Temperatur nicht
mehr durch die Debye-Temperatur von Bulk-Material sondern durch die
Debye-Temperatur der Oberfläche dominiert. Die Zunahme des Oberflächen-
zu Volumenverhältnisses führt somit zu einer Änderung der
Elektron-Phonon Kopplung im elektrischen Widerstand dünner Filme.
O 3.3 Mo 11:45 H36
Tip-substrate interactions: structure and electronic states —
•A.L. Klavsyuk 1 , V.S. Stepanyuk 2 , I. Mertig 2 , W. Hergert 1 , P.
Bruno 2 , and J. Kirschner 2 — 1 Fachbereich Physik, Martin-Luther-
Universität, Von-Seckendorff-Platz 1, 06120 Halle, Germany — 2 Max-
Planck-Institut für Mikrostrukturphysik, Weinberg 2, D-06120 Halle,
Germany
Atom resolved scanning tunneling microscopy images are known to de-