Plenarvorträge - DPG-Tagungen

Oberflächenphysik Montag
sorbed on the copper substrate.
We present CdS-films prepared by starting up with a sulfide covered
copper surface as a template. Depending on the applied electrode potential
two different sulfide layers can be observed by STM, on top of a
Cu(111) surface exposed to a 10 mM S 2− electrolyte:
1. an incommensurate moiré pattern
2. a commensurate ( √ 7 × √ 7)R19.1 o adlayer
Cd deposition on the ( √ 7 × √ 7)R19.1 o phase at a potential of -375
mV with respect to the RHE results in the formation of a CdS-phase revealing
a complex dislocation network which also shows a √ 7 strukture
with respect to the Cu(111)-substrate. Subsequent termination with S 2−
leads to the loss, of this highly ordered dislocation network.
O 14.33 Mo 18:00 Bereich C
Growth and morphology of titanium dioxide on a Re(10-10)
surface — •Dirk Rosenthal and Klaus Christmann — FU Berlin,
Inst. f. Chemie
Titaniumdioxide films were prepared in UHV by co-adsorption of titanium
and oxygen on a Re(10-10) surface. The films were characterized
by means of LEED, XPS and LEIS. The oxygen partial pressure and
substrate temperature, rather than the titanium flux, are crucial parameters
that influence the resulting titaniumdioxide structure. Thin films
of a few monolayers prepared at 500K exhibit at least three different
LEED structures, one of which indicates an epitaxial phase. Preparation
at 700K on the other hand (after formation of several transient LEED
phases in the sub- and monolayer regime), leads to a (2x2) structure with
missing reflexes in (0, k ± 1/2) positions. The latter are characteristic of
a glide mirror plane in [1-210]-direction (parallel to the troughs of the
Re-surface). A prerequisite for this behavior is a non-primitive unit mesh.
XP-spectra of ultrathin titania films (around 1ML) suggest a stoichiometric
structure that could be attributed to TiO2. We present a structure
model to explain the (2x2) phase.
O 14.34 Mo 18:00 Bereich C
SPA-LEED- und Leitfähigkeitsuntersuchungen an dünnen epitaktischen
Silberfilmen auf Silizium — •Alexandra Goehlich
und Michael Horn-von Hoegen — Institut für Laser- und Plasmaphysik,
Universität Duisburg-Essen, 45117 Essen
Bei der weiterschreitenden Miniaturisierung von Halbleiterbauelementen
und der Entwicklung von Nanostrukturen gewinnt neben Streuphänomenen
im Volumen die Streuung von Leitungselektronen an Oberflächen
immer mehr an Bedeutung. Beispielhaft soll am Modellsystem quasi freitragender
dünnster epitaktischer Ag(111)-Filme auf Si(100) die Änderung
der elektrischen Leitfähigkeit in Abhängigkeit von der Oberflächenmorphologie
des Films studiert werden. Dazu werden bei 80K 20ML dicke
Ag-Filme deponiert. Nach Tempern bei 300K bildet sich ein glatter,
defektarmer Ag(111)-Film [1]. Sowohl die Rauigkeit des Films, die
durch weiteres Aufdampfen bei tieferen Temperaturen gezielt von einzelnen
Adatomen bis zu großen Inseln eingestellt werden kann, als auch die
Bedeckung mit verschiedenen Adsorbaten beeinflußt die elektronischen
Streuprozesse und wirkt sich damit auf die Leitfähigkeit des Films aus.
[1] M. Horn-von Hoegen, T. Schmidt, M. Henzler, G. Meyer, D. Winau
and K.H. Rieder, Phys. Rev. B, Brief Reports 52, 10764-10767 (1995)
O 14.35 Mo 18:00 Bereich C
Epitaxial Ag-films grown on silicon-on-insulator substrates
— •Marcin Czubanowski, Christoph Tegenkamp, and Herbert
Pfnür — Institut Für Festkörperphysik, Appelstr.2 D-30167
Hannover,Germany
Studies of the conductivity of ultrathin metallic films that are only a
few monolayers thick is physically interesting and technically challenging.
In order to make the system simple, the influence of the underlying
substrate should be reduced to a minimum. Therefore, we performed adsorption
experiments of Ag grown under ultra–high vacuum conditions
on silicon on insulator (SOI) substrates. The morphology and chemistry
of the surface was checked by means of LEED and Auger spectroscopy.
To obtain clean and smooth SOI(100) surfaces, the native oxide layer
was removed first by adsorption of Si forming volatile SiO. Because the
temperatures used for cleaning the surface are lower than 1050 K, the
buried oxide layers remain intact and the topmost SOI-film remains undamaged
[1]. For (100)–orientated silicon surfaces, Ag grows at low temperatures
layer–by–layer in (111)–orientation [2]. An important epitaxy
parameter is the growth temperature, which allows to control the defect
concentrations within the Ag–films. Best results with respect to large Ag
islands were obtained for substrate temperatures of 130 K. The conduc-
tivity measurements are done in–situ in a Van der Pauw geometry. First
conductivity measurements for different Ag coverages an adsorption temperatures
will be presented.
(1) M. Czubanowski et.al., submitted to APL. (2) Horn von Hoegen et.al.,
Surface Science vol.331-333 (1995) 575.
O 14.36 Mo 18:00 Bereich C
Influence of selenium and steps on the Si(111)-(1 × 1):GaSe
van der Waals — •Bengt Jaeckel, Rainer Fritsche, Andreas
Klein, and Wolfram Jaegermann — Darmstadt University of Technology,
Surface Science Division, Department of Materials Science, Petersenstr.
23, 64287 Darmstadt
Evaporation of GaSe onto heated Si(111) surfaces leads to the chemically
and electronically passivated Si(111):GaSe surface termination. Before
completion of the termination the Si(111) surface passes through
several Se-free Si:Ga surface terminations, which require considerable rearrangement
of the Si surface atoms. To suppress the intermediate Se-free
Si:Ga surface terminations, we have added additional Se during the formation
of the surface termination. However, the electronic passivation is
less good with additional Se, although the surface shows a clear Si(111)-
(1×1):GaSe structure in LEED and SXPS. UHV-STM studies have been
conducted to analyze the details of the surface termination process in dependence
on Se vapor pressure. The number and orientation of steps on
the Si(111)-surface is strongly modified by additional Se-flux.
O 14.37 Mo 18:00 Bereich C
Experimental and ab initio studies of ultrathin Ag films on
V(100) — •Marko Kralj 1,2 , Predrag Lazic 3 , Jörg Schneider 1 ,
Axel Rosenhahn 1 , Petar Pervan 2 , Milorad Milun 2 , Zeljko
Crljen 3 , Radovan Brako 3 , and Klaus Wandelt 1 — 1 Institut für
Physikalische Chemie, Bonn — 2 Institute of Physics, Zagreb — 3 Rudjer
Boskovic Institute, Zagreb
The growth and structure of ultrathin silver films (1-5 ML) deposited
on a reconstructed V(100)-(5x1) surface are studied by use of STM, AES,
and ARPES. To model the structure of the system we have also performed
first principles calculations.
It has been established that due to the annealing of deposited silver
uniform films are formed and that the vanadium reconstruction is completely
removed. As found from STM measurements and supported by ab
initio calculations in the in-plane direction silver follows the structure of
the V(100)-(1x1) lattice and is tetragonally distorted in the direction perpendicular
to the surface. The ab initio results predicted the adsorption
energies of individual silver layers and the work function of Ag/V(100)
in accordance with experiments.
O 14.38 Mo 18:00 Bereich C
Spot Profile Analysis-LEED and AFM Investigations of
Ge/CaF2/Si(111) Multilayers — •Eddy Patrick Rugeramigabo
1 , Carsten Deiter 1 , and Joachim Wollschläger 2 —
1 Institut für Festkörperphysik, Universität Hannover, D-30167 Hannover
— 2 Institut für Angewandte und Physikalische Chemie, Universität
Bremen, D-28359 Bremen
Nanoelectronic devices like resonant tunneling diodes offer very interesting
features and quantum effects. Therefore it is necessary to fabricate
high quality semiconductor insulator multilayers with few nanometer
thick films.
We have investigated the growth and crystallization of thin Ge films
(thickness 1-2 nm) deposited on CaF2 at several temperatures between
RT and by means of SPA-LEED (Spot Profile Analysis Low Energy Electron
Diffraction) and AFM.
O 14.39 Mo 18:00 Bereich C
Wachstumsstufen auf CaF2 (111) — •Michael Schick 1 , Heinz
Dabringhaus 2 und Klaus Wandelt 1 — 1 Inst. f. Phys. und Theor.
Chem. der Universität Bonn — 2 Mineral. - Petrol. Inst. der Universität
Bonn
Das Wachstum von CaF2(111) wurde mit Molekularstrahlmethoden
und AFM bei T = 1055 − 1099 K sowie Sättigungsverhältnissen S =
4 − 354 untersucht. Die Oberflächen sind charakterisiert durch Wachstumshügel
mit konzentrischen Anordnungen von Stufen (Höhe: eine Tripellage
F − -Ca 2+ -F − �=0.32 nm), die vorwiegend in -Richtungen
verlaufen, wobei der Typ I überwiegt. Die Abstände der Tripelstufen in
den Wachstumshügeln nimmt proportional zu 1/ ln(S) zu. Hieraus lässt
sich ein Wert für die Randenergie der Tripelstufen von ǫ = 0.7 nJ/m
bestimmen, der mit den theoretisch Werten 0.24 und 0.37 nJ/m für Typ