Plenarvorträge - DPG-Tagungen

Oberflächenphysik Donnerstag
auf Si(111)-H mittels Photoelektronenspektroskopie (UPS/XPS) ist ein
Einfluss photoinduzierter Effekte auf die Intensität und energetische Lage
der Linien in den Spektren zu beobachten. Diese Veränderungen sind
nicht abängig von der Energie des anregenden Lichtes, jedoch von der
Intensität und der Bestrahlungsdauer. Wir diskutieren die Effekte anhand
von Diffusionsprozessen des Sauerstoffs aus dem Volumenmaterial
sowie des auf der Probenoberfläche und in den Korngrenzen in Form von
Hydroxid enthaltenen Wasserstoffs. Im Ergebnis stellen wir ein Modell
vor, das die Photolyse von Oberflächenhydroxid einerseits und von ZnO
bzw. Volumen-Zn(OH)x andererseits berücksichtigt.
O 40.9 Do 17:45 H45
Epitaxial Pr2O3 layers on Si (111) studied with LEED and surface
XRD — •Nicole Jeutter, Zarife Özer, and Wolfgang
Moritz — Section Crystallography, Department of Earth and Environmental
Sciences, University of Munich
Pr2O3 is one of the few oxides which are stable in contact with Si at
temperatures up to 1000 C. It has as high dielectric constant and a small
lattice mismatch (under 0.3 %) to the Si (111) substrate lattice. We have
grown Pr2O3 on the Si (111) surface by evaporation from a tungsten
crucible loaded with Pr6O11. Measurements with LEED and XRD show
that an epitaxial layer is formed at a substrate temperature of about
770 K with the (0001) plane of Pr2O3 parallel to the Si (111) surface.
Subsequent annealing up to 1030 K for less than 2 minutes leads to a
p(2x2) reconstruction of the Pr2O3 layer. Very weak reflections from a
( √ 3x √ 3) structure appear after slow cooling to room temperature. A
disordered (5x1) phase appears after desorption at temperatures above
1050 K. After further desorption the (7x7) structure of the Si (111) surface
is recovered. First x-ray measurements show the orientation relative
to the substrate. The interface consists of a Si-O-Pr bond with Pr above
the T4 site. No indication was found for an intermediate oxide layer. The
thickness of the layer was 0.6 nm, corresponding to one unit cell of Pr2O3.
O 40.10 Do 18:00 H45
Potential Energy Retention of Slow Highly Charged Ar-Ions in
Chemical Clean Silicon Surfaces — •Daniel Kost, Stefan Facsko,
and Wolfhard Möller — Institut für Ionenstrahlphysik und
Materialforschung, Forschungszentrum Rossendorf, 01028 Dresden
A UHV device with a base pressure of p < 10 −9 mbar was connected to
the ECR ion source of the Forschungszentrum Rossendorf for improved
calorimetric measurements of the retention of the potential energy of
highly charged ions. The chemical state of the target surface is controlled
by AES using LEED optics. With a clean silicon surface prepared
by sputtering using Ar + ions, the retained energy of Ar q+ (q = 1 up
to 9) ions was determined at kinetic energies between 60 eV ·q and 200
eV ·q. By extrapolation to zero kinetic energy, the retained fraction of
the potential energy is obtained, which is related to the full potential
energy given by the ionization potentials. The potential energy reten-
O 42 Hauptvortrag Hohage
tion coefficient results as 0.8 ± 0.2 and decreases weakly with increasing
charge state. This is about three times larger than earlier results with
contaminated copper surfaces.
O 40.11 Do 18:15 H45
Angle-resolved photoelectron spectroscopy of CuInSe2(001) —
•Ralf Hunger 1 , Wolfram Jaegermann 1 , Wolfram Calvet 2 ,
Carstan Lehmann 2 , Christian Pettenkofer 2 , Keiichiro Sakurai
3 , and Shigeru Niki 3 — 1 Surface Science Division, TU Darmstadt,
64287 Darmstadt — 2 Abt. Heterogrenzflächen, HMI, 14109 Berlin —
3 Thin Film Solar Cells Group, AIST, Tsukuba 805-8568, Japan
We have investigated the valence band structure of CuInSe2 by
angle-resolved photoelectron spectroscopy (ARPES). Heteroepitaxial
CuInSe2(001)/GaAs films were prepared by molecular beam epitaxy
which and covered by a protective selenium cap. In the UHV analysis
system, clean and ordered CuInSe2(001) surfaces were prepared by
thermal desorption of the Se cap layer. This surfaces exhibited a
(1 × 1)-LEED pattern and MgKα-ecited XPS proved the surface to be
free of oxygen and hydrocarbon contamination. ARPES experiments
were conducted at the TGM7 beamline at Bessy2 using a VG ADES500
analyser.
The final state bands were investigated by EDCs in normal emission
(ΓT direction in the tetragonal chalcopyrite lattice) using excitation energies
from hν = 9.6eV to hν = 40eV . A transition from the top of the
valence band (VBM) at Γ to a free-electron like final state band was observed
for hν = 11.3eV . Thereby, the inner potential V0 was determined
to −6.9eV and the VBM lies at 0.4 eV. Angular scans were performed
along the ΓX ([110]) and ΓM ([010]) directions with hν = 21.2eV . The
resulting experimental band structure will be presented and compared to
calculations by Jaffe&Zunger (PRB 28 (1983) p. 5822).
O 40.12 Do 18:30 H45
Oxide and Carbon contamination removal from semiconductor
surfaces using low-energy hydrogen ion beam etching —
•Nasser Razek, Axel Schindler, Dietmar Hirsch, and Bernd
Rauschenbach — Leibniz-Institut für Oberflächenmodifizierung e. V.,
Permoserstrasse 15, 04318 Leipzig, Germany
A new cleaning technology for semiconductor surfaces to remove oxide
layers and carbon contamination has been applied to GaAs and Ge
surfaces. The cleaning is performed at surface temperatures lower then
300 ◦ C using low energy bombardment of mass separated hydrogen (H + 2 )
ion beam of 300 eV ion energy and of about 4.5 µA cm −2 ion current
density from a broad beam ion source. In comparison to conventional
cleaning, this technique leads to surfaces which are free of contamination
and are characterized by an improved roughness. Surfaces have been
investigated by the X-ray photoelectron spectroscopy and atomic force
microscopy. This work focuses on the development of a room temperature
bonding technique for semiconductors of different chemical nature.
Zeit: Freitag 10:15–11:00 Raum: H36
Hauptvortrag O 42.1 Fr 10:15 H36
Reflectance Difference Spectroscopy : a powerful tool for surface
analysis — •Michael Hohage — Institute of Experimental Physics,
Johannes Kepler University Linz, A-4040 Linz, Austria
Reflectance Difference Spectroscopy (RDS) measures the in plane optical
anisotropy of a surface or a thin film by analysing the reflection of
linearly polarised light under normal incidence. Only recently, the scope
of this method has been extended to study anisotropic metal surfaces.
Since the bulk of cubic crystals is optically isotropic, the RDS signal
from such crystals arises exclusively from symmetry breaking surfaces
(e.g. Cu(110)) and interfaces. Indeed, RDS turned out to be a versatile
and surface sensitive in-situ tool to analyse the electronic structure
of anisotropic metal surfaces as well as to study growth and adsorption
on such surfaces. The RDS signal is extremely sensitive to surface state
transitions, surface modified bulk transitions and adsorbate specific transitions,
each located at characteristic transition energies. These different
and spectroscopically separable contributions can be utilised to monitor
adsorption and growth processes in real time as well as to identify surface
phase transitions simultaneously.