Plenarvorträge - DPG-Tagungen

Oberflächenphysik Montag
se packed Pb regions, showing a moiré pattern, coexist with the surface
alloy phase.
We discuss the formation of these phases as well as the electronic properties
of this system, investigated by means of scanning tunnelling spectroscopy
(STS).
O 11.6 Mo 17:00 H44
Quantum well states and their influence on layer restructuring
in Pb/Cu(111) — •Hugo Dil 1 , JeongWon Kim 1 , Shubha Gokhale
2 und Karsten Horn 1 — 1 Fritz-Haber-Institut der MPG, 14195 Berlin
— 2 Indira Gandhi National Open University, New Delhi, India
Quantum well states in thin metal films, arising from one-dimensional
confinement of the conduction electrons, may have a profound influence
on their physical properties. Quantum well states may induce preferred
magic heights in thin film growth, and this has been observed several
systems. We have studied the electronic structure of Pb layers on
Cu(111) grown under different conditions, using angle-resolved photoelectron
spectroscopy. Our results for Pb films deposited at 100 K show
a series of well-resolved peaks in the s-p-derived valence band near the
Fermi level, the energy and intensity of which evolve in a complex manner
with Pb deposition. These data are analysed in terms of the phase
accumulation model, shown to account for quantum well states in a large
number of systems. Upon annealing, the layers undergo a restructuring,
and preferred layer height emerge as shown by their quantum well spectrum
signature. We interpret this process in terms of electronic energy
minimization.
O 11.7 Mo 17:15 H44
First Principles Study of Lead Surfaces — •Dengke Yu and
Matthias Scheffler — FHI der MPG, Berlin-Dahlem
Motivated by recent experimental work [1] and hitherto conflicting
theoretical results of various groups, we studied the surface energies
(and other properties) of Pb(111), Pb(100), and Pb(110) surfaces using
density-functional theory. All numerical parameters and approximations
are carefully checked, as for example the plane-wave cutoff, k-mesh
density, slab thickness, and non-linearity of the core-valence exchangecorrelation
interaction. Using local-density approximation the surface energies
(absolute and relative numbers) are found to be in excellent agreement
with recent experimental results. However, for the generalized gradient
approximation deviations from experimental results are significant.
All three surfaces are found to exhibit a pronounced first-layer contraction,
followed by a damped oscillatory multilayer relaxation. Our data are
consistent with previous low energy electron diffraction analysis. Based
on the calculated surface energies we predict a bilayer growth mode for
the thin film growth of Pb(100) and Pb(111) on a nonmetallic substrate.
For Pb(111) this has been indeed seen in recent experimental studies.[2]
[1] C. Bombis, A. Emundts, M. Nowicki, H. P. Bonzel, Surf. Sci. 511,83
(2002)
[2] M. Hupalo and M. C. Tringides, Phys. Rev. B, 65, 115406 (2002)
O 11.8 Mo 17:30 H44
Structure and dynamics of ultra-thin Ag films on Au(111) —
•Dunja Popović 1 , F. Forster 1 , V. Grigorian 2 , M. Springborg 2 ,
F. Reinert 1 , S. Hüfner 1 , H. Cercellier 3 , Y. Fagot-Revurat 3 ,
B. Kierren 3 , and D. Malterre 3 — 1 FR 7.2 Experimentalphysik, Universität
des Saarlandes, 66041 Saarbrücken — 2 FR 8.13 Physikalische
Chemie, Universität des Saarlandes, 66041 Saarbrücken — 3 Laboratoire
de Physique des Matériaux, Université Henri Poincaré, Nancy I - B.P.
239 F-54506 Vandœuvre-lès-Nancy
Epitaxial Ag ultra-thin films grown on Au(111) have been studied
by angle-resolved photoemission spectroscopy (ARPES). High resolution
measurements on Au(111) reveal the splitting of the dispersive surface
Shockley band in two spin-orbit contributions. Surface states corresponding
to completed Ag monolayers are analysed with respect to their band
minima and spin-orbit splitting and compared with the results of slablayer
band-structure calculations. Interdiffusion is found to play a significant
role in the formation of the first monolayer. Moreover, it has
been shown by ARPES that low deposition temperatures lead to poorly
defined surface states of the overlayer, whereas scanning-tunneling microscopy
revealed that post-annealed films grown at room temperature
show no sharp interface but an alloy formation.
O 11.9 Mo 17:45 H44
Spin polarization of the L-gap surface states on Au(111) —
•Jürgen Henk, Arthur Ernst, and Patrick Bruno — MPI für
Mikrostrukturphysik, Halle (Saale), Germany
The electron spin polarization (ESP) of the L-gap surface states
on Au(111) is investigated theoretically by means of first-principles
electronic-structure and photoemission calculations. The surface states
show a large spin-orbit induced in-plane ESP which is perpendicular to
the in-plane wavevector, in close analogy to a two-dimensional electron
gas with Rashba spin-orbit interaction. The surface corrugation, i.e., the
in-plane asymmetry of the surface potential in the (1 ×1) unit cell, leads
to a small ESP component normal to the surface, being not reported so
far. The surface-states ESP can be probed qualitatively and quantitatively
by spin- and angle-resolved photoelectron spectroscopy, provided
that the initial-state ESP is retained in the photoemission process and
not obscured by spin-orbit induced polarization effects. Relativistic photoemission
calculations provide detailed information on what photoemission
set-ups allow to conclude from the photoelectron ESP on that of the
surface states.
O 11.10 Mo 18:00 H44
Interface states of rare gas covered noble metal surfaces —
•Frank Forster 1 , Dunja Popovic 1 , Stefan Schmidt 1 , Brigitte
Eltner 1 , Friedrich Reinert 1 , Stefan Hüfner 1 , Valeri Grigoryan
2 , and Michael Springborg 2 — 1 FR 7.2 Experimentalphysik,
Universität des Saarlandes, 66041 Saarbrücken — 2 FR 8.13 Physikalische
Chemie, Universität des Saarlandes, 66041 Saarbrücken
On the example of surfaces in (111)-direction of Cu, Ag and Au we
demonstrate that even one monolayer of physisorbed adsorbates like
Ar, Kr and Xe essentially influences the electronic structure of these
systems. Thus, angular resolved photoemission spectroscopy (ARPES)
(∆E = 3.5 meV, ∆Θ = 0.3 ◦ ) is not only able to measure subtle and
characteristic shifts of the binding energies of the L-gap Shockley states
of the substrates towards or even above the Fermi-level, but also — in the
case of Au(111) — an increase of the spin-orbit-splitting by about 30%.
Furthermore, we studied the influence of the surface reconstruction in
the case of the commensurate growth of one Xe layer on Cu(111) on the
bulk and surface states. Our results have been supported by slab-layercalculations
that also result in a detailed understanding of the electronic
processes in the adsorbate-substrate-interface.
O 11.11 Mo 18:15 H44
Surface state splitting in thin Mg films — •Frederik Schiller 1,2 ,
Vito Servedio 3 , and Clemens Laubschat 1 — 1 Institut für Festkörperphysik,
TU Dresden, D-01062 Dresden, Germany — 2 Donostia
International Physics Center, E-20018 Donostia/San Sebastian, Spain
— 3 Sezione INFM and Dip. di Fisica, Università “La Sapienza”, P. le
A. Moro 2, I-00185 Roma, Italy
Thin Mg films deposited onto a W(110) surface show a hexagonal closepacked
structure in (0001) direction. Photoemission spectra in normalemission
geometry reveal a surface state inside the Shockley-inverted
energy gap and quantum well oscillations on both sides of the gap.
We study the evolution of the surface and the quantum well states depending
on the emission direction and Mg thickness. For Mg films exceeding
12 ML, both, surface and quantum well states disperse parabolic-like
around the ¯Γ point of the surface Brillouin zone. In thinner films, however,
in off-normal geometry the surface state splits into several branches
with different effective masses. We ascribe this phenomenon to the lattice
mismatch between the Mg film and the underlying W substrate that may
lead (i) to distortions of the surface geometry and (ii) variations of the
confinement conditions at the Mg/W interface that reveal a periodicity
different from that of the Mg lattice.