Plenarvorträge - DPG-Tagungen

Oberflächenphysik Donnerstag
keitszunahme optisch trennt. Demgegenüber erweist sich selbst die phasenoptimierte
Ellipsometrie als unempfindlicher. Die größere Empfindlichkeit
der BWA gegenüber Spurrauhigkeiten wird anhand von AFM
Messungen diskutiert.
O 40.2 Do 16:00 H45
On the origin of the STM induced Si(001)c(4×2) – p(2×2) phase
transition — •Kaori Seino, Wolf G. Schmidt, Frank Groth,
and Friedhelm Bechstedt — Institut für Festkörpertheorie und Theoretische
Optik, Friedrich-Schiller-Universität, Max-Wien-Platz 1, 07743
Jena, German
There has been a longstanding interest in the atomic and electronic
structure of the Si(001) surface, related to its industrial applications and
its model character for surface science. Recently the true atomic configuration
of the Si(001) surface at very low temperatures has again become
a very interesting subject. In particular the question whether the surface
ground state reconstructs c(4×2) or p(2×2) is controversially discussed.
A very recent STM study even demonstrates phase manipulation between
c(4 × 2) and p(2 × 2) at 4.2 K [1]. We study the energetics of
the Si(001) surface in an electric field using gradient-corrected densityfunctional
theory (DFT-GGA) and ultrasoft pseudopotentials. The influence
of the preparation conditions and experimental setup on the surface
reconstruction is discussed in detail.
[1] K. Sagisaka, D. Fujita, G. Kido, Phys. Rev. Lett. 91, 146103 (2003)
O 40.3 Do 16:15 H45
Initial and advanced stages of Si dissolution in alkaline media
using photoelectron spectroscopy — •Katarzyna Skorupska
1 , Mohammed Aggour 1 , Eder Goncalves 1 , Ralf Hunger 2 ,
Helmut Jungblut 1 , Michael Kanis 1 , Michael Lublow 1 , Elmar
Rüther 1 , Thomas Wilhelm 1 , and Hans-Joachim Lewerenz 1
— 1 Hahn-Meitner-Institut, Glienicker Str. 100, D-14109 Berlin — 2 TU
Darmstadt, Petersenstr. 23, D-64287 Darmstadt
Silicon dissolution in aqueous alkaline media is of ubiquitous importance
in micro- and nanostructuring. Never the less detailed surface analytical
investigations on the dissolution steps are lacking. The presented
study applies synchrotron radiation spectroscopy using a specifically designed
in-system electrochemistry vessel attached to the SoLiAS apparatus
at the U49/2 beamline at Bessy II. Initial and advanced oxide layers
are analysed in electrode potential-, current- and charge-controlled experiments.
Besides chemical surface changes also surface electronic effects
were monitored using ultraviolet photoelectron spectroscopy. The results
are compared with several recently proposed dissolution mechanisms.
O 40.4 Do 16:30 H45
In-Situ- and UHV-Investigation of MOCVD-Grown GaAsSb-
Interfaces — •Zadig Kollonitsch, Matthias Neges, Kristof
Möller, Frank Willig, and Thomas Hannappel — Hahn-Meitner-
Institut, SE4, Glienicker Strasse 100, D-14109 Berlin, Germany
The effect of antimony segregation at surfaces and interfaces complicates
the application of such layers in semiconductor devices. To improve
interface abruptness various protocols may be employed and investigated
at the atomic scale. Lattice matched GaAs0.51Sb0.49/InP(100)-layers were
grown by MOVPE at 770K. The surface and interface reconstruction
was monitored with reflectance anisotropy/difference (RAS/RDS) spectroscopy.
The RA-Spectrum of the As-rich GaAsSb(100) surface showed
different features compared to that of the Sb-rich surface. The in-situ
signals indicated that the surface was Sb-rich during growth and turned
preferably into an As-rich surface after growth. Contamination free
sample transfer into ultrahigh vacuum (UHV) allowed the correlation
of the in-situ signals with LEED and UV-photoelectron spectroscopy
(UPS). The LEED pattern of As-rich GaAsSb(100) showed a c(4 × 4)
reconstruction with bright spots, whereas the LEED pattern of Sb-rich
GaAsSb(100) showed a (1 × 3)-like reconstruction with weak spots. Possible
models for the surface reconstructions are discussed. Results are
presented for the growth of InP/GaAsSb heterojunctions on As- and Sbrich
GaAsSb(100) surfaces.
O 40.5 Do 16:45 H45
Importance of carrier dynamics and conservation of momentum
in atom-selective STM imaging of semiconductor surfaces
— •Philipp Ebert 1 , Nikos Jäger 1 , Eicke Weber 2 , and Knut Urban
1 — 1 Institut für Festkörperforschung, Forschungszentrum Jülich,
52425 Jülich — 2 University of California and Lawrence Berkeley National
Laboratory
Scanning tunneling microscopy and spectroscopy measurements on the
GaAs(110) surface with complementary theoretical calculations are performed
to clarify the effects involved in the tunneling of unpinned semiconductor
surfaces. We show that the flatband and tip-induced band
bending as well as equilibrium conditions are insufficient to describe the
effects involved. Instead, carrier dynamics and conservation of momentum
of the tunneling electrons need to be taken into account for a complete
description of the contributions of the valence or conduction band
states. The results allow us to understand the unique properties needed
to achieve the atom-selective imaging on semiconductor surfaces as well
as the determination of the band gap energy.
O 40.6 Do 17:00 H45
First-principles calculations for initial adsorption of manganese
on Si(001) — •Mahbube Hortaman, Hua Wu, Peter Kratzer,
and Matthias Scheffler — Fritz-Haber-Institut der MPG, Faradayweg
4-6, 14195, Berlin
Heterojunctions between a semiconductor and a ferromagnetic metal
have attracted attention in the context of spintronics. In this work, we
choose the Mn on Si(001) system as a possible candidate for the growth
of magnetic thin films, and investigated the adsorption behavior of Mn
(coverage θ < 0.5 monolayer) by first-principles total-energy calculations
using density functional theory and the FP-APW+lo method. For one
Mn atom in the Si(001)(2x2) unit cell, the sub-surface site is 0.9 eV lower
in energy than the on-surface position due to the strong Mn-Si covalent
bonding. Moreover, we find a pathway to the subsurface region that exhibits
a practically zero energy barrier. As seen from the potential-energy
surface of Mn in different adsorption geometries, the most stable site on
the surface is the hollow site where Mn is placed between two Si dimers
in the same row. Diffusion barriers both along and perpendicular to the
dimer row are about 0.7 eV, which indicates isotropic diffusion. For onsurface
Mn adatoms we find a strong tendency towards the formation of
Mn islands on the surface. The resulting structure resembles that of a
next Si layer. If the sub-surface site is reached by Mn adatoms before the
on-surface islands are formed, a mixed on-surface/sub-surface structure
will result. We discuss the above sketched results in a simple physical
picture and propose ideas how these different structures may be grown
experimentally.
O 40.7 Do 17:15 H45
Si addimer nanowires on SiC(001) surfaces — P. Krüger and
•J. Pollmann — Institut für Festkörpertheorie, Universität Münster,
Wilhelm-Klemm-Str. 10, 48149 Münster
In recent years it has been observed by scanning tunneling microscopy
that particular reconstructions of the SiC(001) surface show Si addimer
nanowires. Their occurrence depends crucially on preparation conditions.
To explain the physical origin of such nanowires we scrutinize current reconstruction
models of various SiC(001) surfaces. Analysing the energetics
of the c(4×2), 3×2, 5×2 and 7×2 reconstructions, as resulting from
our first-principles DFT-LDA calculations of the formation energy, we
find that the higher N×2 reconstructions can be formed by two basic
building blocks, the c(4×2) and the (3×2) unit. This finding allows us
to set up a simple model which extrapolates to all possible N×2 reconstructions.
First, the model reveals in excellent agreement with experiment
that neither a 4×2 nor a 6×2 reconstruction should occur. Second,
it predicts that all higher reconstructions with N ≥ 7 are possible. This
is in contrast to an earlier notion that only odd reconstructions (with N
odd) were to be expected. In fact, the more recent observations of the
above mentioned Si nanowires have been made at a SiC(001)-(8×2) surface.
This structure directly derives from our model as consisting of one
c(4×2) and two 3×2 units per 8×2 unit cell revealing the origin of the
experimentally observed Si addimer nanowires. In general, all kinds of
Si nanowire arrangements can be achieved depending sensitively on the
distribution of the two structural building blocks at the SiC(001) surface.
O 40.8 Do 17:30 H45
Einfluss photoinduzierter Effekte auf die Photoemissionsspektren
gesputterter ZnO-Schichten auf Si(111)-H — •Henning
Wolf, Ulrich Meier, Tilo Plake und Christian Pettenkofer
— Hahn-Meitner-Institut Berlin, Glienicker Strasse 100, 14109 Berlin
Durch Magnetronsputtern abgeschiedenes ZnO enthält H-Konzentrationen
bis zu 10 21 cm −3 im Volumenmaterial. Tempern in Sauerstoffatmosphäre
bei 400 ◦ C reduziert den Anteil des Wasserstoffs um etwa 2
Grössenordnungen. Bei der Untersuchung gesputterter ZnO-Schichten