Physik: DPG Tagungen - Sitzung O 28 - Nano-science.de

Physik: DPG Tagungen - Sitzung O 28 

http://www.dpg-tagungen.de/archive/2004/o_28.html 

Deutsche Physikalische Gesellschaft e. V. (DPG) 

WWW-Server für Frühjahrstagungen und E-Verhandlungen 

Programm und Abstracts der Sitzung O 28 

Postersitzung (Elektronische Struktur, Grenzfläche fest-flüssig, 

Halbleiteroberflächen und -grenzflächen, Magnetismus und Symposium 

SYXM, Methodisches, Nanostrukturen, Oberflächenreaktionen, Teilchen 

und Cluster, Zeitaufgelöste Spektroskopie) 

Mi 16:00-19:00 

Bereich C 

O 28.1 Poster Mi 16:00 Bereich C 

Bulk and surface sensitive photoemission on 1T-TiS 2 

•M. Garbrecht, O. Seifarth, M. Skibowski und L. Kipp 

Institut für Experimentelle und Angewandte Physik, Universität Kiel, D-24098 Kiel, Germany 

The bulk and surface sensitive electronic structure of the layered transition metal dichalcogenide 1T-TiS 2 is 

investigated by means of angle resolved photoemission spectroscopy with VUV and XUV photons. At photon 

energies around 50 eV where ARPES is extremely surface sensitive we observe a semiconducting band 

structure. This is contrasted by more bulk sensitive photoemission data obtained at 150 eV where a semimetallic 

behavior is found. The results are discussed in the context of recent band structure calculations performed 

within the density functional theory. The experiments have been performed with the ASPHERE spectrometer at 

the HASYLAB beamlines W3.2 and BW3. Work supported by the BMBF project no. 05 KS1 FKB and DFG 

Forschergruppe FOR 353 


Excited state UPS of C 60 

•Arne Rosenfeldt, Klaus Finsterbusch und Helmut Zacharias 

AG Zacharias, Physikalisches Institut, Westfälische Wilhelms-Universität 

A 200 layer C 60 film is prepard by growth on an annealed C 60 monolayer on Cu(111). This system is pumped 

with tunable 351 to 415 nm radiation of 100 ps pulse duration and probed with delayed 263, 211 and 150 nm 

photons. Using the time-of-flight technique photo-electrons are observed from LUMO+1, LUMO, and singlet 

exciton states. The excitation probability of these states as a function of photon energy is measured. A 

maximum is found for 

h ν = 3.16 eV ( λ ∼ 392 nm). Further, the electron dynamic is analyzed and will be discussed. 


Geometric and electronic structure of epitaxial PbS on HfS 2 

•J. Iwicki, A. Kamenz, O. Seifarth, S. Habouti, M. Kalläne und L. Kipp 


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Misfit layer compounds like (PbS)NbS 2 form a special class of layered heterostructures. Due to 4-fold 

symmetries of the PbS layers which contrast the 6-fold symmetry of the NbS 2 layers a misfit is constituted. Up 

to now, bulk crystals of misfit compounds could only be grown with metallic hexagonal layers like e.g. NbS 2 or 

TiS 2 . Here we show first steps of epitaxial growth of PbS on semiconducting HfS 2 with corresponding STM 

images and angle resolved photoemission spectra for different coverages of PbS on HfS 2 . The photoemission 

results are compared with data of clean HfS 2 and PbS bulk crystals. The experiments have been performed with 

the ASPHERE spectrometer at HASYLAB. 

Work supported by the BMBF proj. 05 KS1 FKB and DFG Forschergruppe FOR 353 


High energy conduction band states in layered materials 

•M. Marczynski, K. Rossnagel, M. Kalläne, E. E. Krasovskii, M. Skibowski, W. Schattke und L. Kipp 


Employing angle resolved photoemission in the constant initial state mode we investigate the conduction band 

states of layered materials up to about 100 eV above the Fermi level. The layered materials HfS 2 and TiTe 2 

serve as model systems showing distinct features even for higher conduction bands. The experimentally 

observed structures are discussed in the context of theoretical results obtained by ab initio calculations. In 

particular, photoemission final states are treated within ELAPW based scattering theory. 

The experiments have been performed at HASYLAB (BW3 beamline) and the Advanced Light Source (beamline 

7). 

Work supported by the BMBF project no. 05 KS1 FKB and DFG Forschergruppe FOR 353. 


Angle resolved measurement of the (1p) -1 photoemission cross section of CO adsorbed on Pt(111) 

•Sebastian Wegner, Grigorios Tsilimis, Jörg Kutzner und Helmut Zacharias 

Physikalisches Institut, Westfälische Wilhelms Universität Münster, Wilhelm-Klemm-Straße 10, D-48149 

Münster 

High order harmonic radiation is generated by focussing femtosecond Ti:sapphire pulses into a noble gas. The 

pulsed radiation is tunable in the range of 20-110 eV in steps of 3.1 eV. At an energy of 32.4 eV we measured 

the CO(1π) -1 photoemission of the c(4×2)-2CO/Pt(111) surface. In contrast to experiments on oriented 

molecules in the gas phase we observe emission parallel as well as perpendicular to the axes of the adsorbed 

CO. We fitted the angular distribution by Legendre polynomials P l (cosθ). It is best fitted by l = 3 and l = 4 

polynomials indicating a large contribution of d and f partial waves. 


Fermi-Surface-Mapping an Übergangsmetallen 

•M. Krause, S. Dreiner, M. Schürmann, U. Berges und C. Westphal 

Universität Dortmund, Experimentelle Physik I, 44221 Dortmund 

Die Kenntnis der elektronischen Struktur von Metallen ist grundlegend für das Verständnis vieler physikalischer 

Phänomene. Die elektronischen Zustände an der Fermikante bedingen z.B. die elektrische Leitfähigkeit, die 

Temperaturabhängigkeit des Ferromagnetismus, die Supraleitung und die Hochtemperatursupraleitung. Durch 

Aufnahme winkelaufgelöster Photoemissionsspektren über dem Halbraum der Probe mit HeI Strahlung wurden 

Schnitte durch die Fermiflächen gemessen. Zur Interpretation wurden Vergleichsrechnungen der 

Dichtefunktionaltheorie (LKKR) durchgeführt. 

Die Meßergebnisse für Cu, Ni, Pd und Rh werden gezeigt und mit den jeweiligen Rechnungen verglichen. Diese 

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Ergebnisse bilden die Grundlage für zukünftige Experimente. 


Surface state as local sensor for single magnetic impurities 

•Daniel Wegner, Andreas Bauer und Günter Kaindl 

Freie Universität Berlin, Institut für Experimentalphysik, Arnimallee 14, 14195 Berlin-Dahlem 

The (0001)-surface of Lu metal exhibits a highly localized surface state directly at the Fermi energy, E F [1]. It 

appears as a sharp peak in the tunnelling spectra measured by low-temperature scanning tunnelling 

spectroscopy (STS) at 10 K. We have used this surface-state peak as a sensor for single magnetic impurities of 

Gd and Ho atoms embedded in the film surface. Within a radius of about 15 Å around such an impurity, the 

surface-state appears as a double-peaked structure in the tunnelling spectra with a narrow dip in between; this 

dip is only a few meV wide and is located within less than 1 meV at E F . The results are discussed on the basis 

of the Kondo effect. 

This work was supported by the DFG, Sfb-290. 

[1] A. Bauer, A. Mühlig, D. Wegner, and G. Kaindl, Phys. Rev. B 65, 75421 (2002). 


Correlation of electronic transport and structural properties of Cs layers on Si(001) 

•Hong Liu, A.A. Shklyaev, V. Zielasek und H. Pfnür 

Universität Hannover, Institut für Festkörperphysik, Appelstr. 2, 30167 Hannover 

Combining LEED, EELS, and conductivity measurements we have studied the correlation of electronic transport 

with structural properties of Cs layers on Si(001). Depending on the substrate temperature T during Cs 

deposition we find three different growth regimes. Only for T < 160 K we observe the growth of a continuous 

metallic Cs film consisting of three-dimensional islands on top of the first 2 monolayers. Between 170 K and 

room temperature a pseudomorphic wetting layer forms with a saturation coverage of 1-1.5 ML. 

For Cs deposition at around 160 K we observe discontinuities of the surface conductivity at 0.5, 1, and 1.5 

monolayer coverage, respectively. Those at 0.5 and 1 ML can be associated with transitions of the surface 

reconstruction from 3 × 4 to 3 × 2 and 3 × 2 to 2 × 1, respectively. Based on EELS data, electrical phase 

transitions (metal - semiconductor - metal) in the submonolayer coverage range have been reported by others 

[1]. While according to EELS the wetting layer should be metallic, conductivity measurements show that the 

electrical transport in the layer is activated. Refined models of the surface structure will be presented. 

[1] Ki-Dong Lee and Jinwook Chung, Phys. Rev. B 55 (1997) 12906. 


STM-Simulation der Selbstassemblierung von Adenin auf Graphit in Abhängigkeit der Scanrichtung 

•Thomas Markert 1 , Thomas Markert 1 , Ferdinand Jamitzky 2 , Frank Trixler 3 , Axel Groß 1 , Wolfgang Heckl 3 , 

Ferdinand Jam itzky 2 , Frank Trixler 3 und Axel Groß 1 

1 Physik-Department, TU München, D-85747 Garching 

2 MPI für extraterrestrische Physik, D-85740 Garching 

3 Department für Geo- und Umweltwissenschaften, LMU München, D-80333 München 

STM-Bilder von Molekülnetzwerken, die über Wasserstoff-Brückenbindungen stabilisiert sind, zeigen i.a. eine 

deutliche Abhängigkeit von der Scanrichtung, da kleine Verschiebungen der Moleküle, die während des 

Scanvorgangs durch die Spitze verursacht werden, abhängig von der Orientierung der 

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Wasserstoff-Brückenbindungen sind. Bei gleicher Auslenkung sind die Rückstellkräfte parallel zur 

Wasserstoff-Brückenbindung größer als senkrecht zu ihr. Mit Hilfe von LDOS-Bildern, die aus 

DFT-Rechnungen erstellt wurden, wird am Beispiel der Selbstassemblierung von Adenin auf Graphit versucht 

die experimentell gewonnenen Bilder einer Drehserie zu simulieren. 


Elctronic structure of MgSO 4 crystals 

•V.V. Maslyuk 1,2 , C. Tegenkamp 1 , T. Bredow 3 und H. Pfnür 1 

1 Institut für Festkörperphysik, Appelstr.2 D-30167 Hannover, Germany 

2 Uzhhorod National University, Pidgirna St.2 88000 Uzhhorod, Ukraine 

3 Institut für Theoretische Chemie, Am Kleinen Felde 30 D-30167 Hannover, Germany 

Typically, the crystallographic structures of minerals are quite well investigated, but there is not much 

knowledge about their electronic structures. As one candidate of an insulator consisting chemically of more than 

two different elements, we investigated the crystallographic and electronic structure of MgSO 4 and kieserite 

(MgSO 4 ·H 2 O), respectively. Starting with kieserite with 36 atoms per unit cell, we determined the electronic 

structure by ab-initio calculations. Using CRYSTAL03 the lattice parameters were calculated within an accuracy 

better than 0.01 Å by choosing basis sets for magnesium and oxygen taken from MgO and for sulfur taken 

from CaSO 4 including also d-orbitals. In order to calculate the band gap of kieserite, the method of hybrid 

mixing of Hartree-Fock and DFT hamiltonians was used. The band gap at the Γ-point was detemined to be 7.4 

eV. To support the theoretical calculations, first photoelectron- and electron energy loss spectroscopy 

experiments have been performed. Thereby, bulk kieserite crystals have been used. Obviously, the effect of 

surface relaxation effects and defects are small, because the measured band gap agrees quite well with the 

theoretical findings. Nevertheless, our calculations will be further refined. 


Valence band photoemission spectroscopy of chemically disordered ultrathin Ni x Pd 1-x films on 

Cu 3 Au(100) 

•Frank Matthes 1 , Liu-Niu Tong 1 , Alexej Rzhevskii 2 und C.M. Schneider 2 

1 Leibniz Institut für Festkörper- und Werkstoffforschung Dresden, PF 27 01 16, D-01171 Dresden 

2 Institut für Elektronische Eigenschaften, Forschungszentrum Jülich, 52425 Jülich 

We have studied the valence band structure of ultrathin Ni x Pd 1-x alloys on a single crystalline Cu3Au(100) 

substrate. Ni and Pd are isoelectronic, but while Ni is ferromagnetic with an average exchange splitting of 0.3 

eV along the ∆ direction, Pd exhibits a higher spin orbit coupling (band splitting 0.3 eV). Via the alloy 

concentration one can conveniently vary the relative weight of these two spin-dependent interactions with 

profound effects for the electronic structure. We will present first results of our high-resolution photoemission 

measurements for 15 monolayer thick Ni x Pd 1-x films with different compositions. The measurements were 

performed along the ∆ direction for excitation energies from 16 eV to 40 eV. As a main spectral feature, we 

observed contributions from bands originating from 3d Ni and 4d Pd electrons near the Fermi energy. This 

feature only disperses weakly with the excitation energy. Starting with pure Ni films, we observed a broadening 

of the spectra while increasing the Pd concentration up to 30%. This may be caused by the chemically induced 

disorder. To distinguish the spin dependent contributions and thus arrive a more detailed interpretation of the 

photoemission data, we performed for three different Ni rich alloy compositions also spin-resolved 

photoemission experiments. 


Site-specific Valence-electronic Structure of SrTiO 3 by X-ray Standing Waves and XPS 

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•Sebastian Thiess 1 , Tien-Lin Lee 1 , Bruce C. C. Cowie 1 , Joe C. Woicik 2 und Jörg Zegenhagen 1 

1 ESRF, Grenoble, France 

2 NIST, Gaithersburg, USA 

We used the x-ray standing waves (XSW) technique and x-ray photoelectron spectroscopy (XPS) to determine 

the contribution of the constituent elements Sr, Ti and O of a SrTiO 3 (STO) crystal to the STO valence band, 

thus deriving their partial density of states. 

Lattice site-specific electronic information - which is not available from standard XPS - is obtained by utilising 

the spatial intensity modulation of an x-ray standing wave (XSW) interference field, generated by the coherent 

superposition of an incident and a Bragg-reflected x-ray beam. By proper positioning the antinodes of the XSW 

within the STO unit cell, photoemission from specific lattice sites can be preferentially excited and their valence 

electronic contribution identified. 

XSW fields were generated by the STO(111) and STO(112) reflections at photon energies of 2.7 and 3.9 keV. 

XSW modulated, high-resolution core and valence-electron emission spectra were recorded from an in-situ 

UHV annealed STO single crystal at beamline ID32 at the ESRF. 


Mechanisms and capability of Steam Laser Cleaning 

•F. Lang 1 , M. Mosbacher 1 , S. Georgiou 2 und P. Leiderer 1 

1 University of Konstanz, Fach M676, 78457 Konstanz, Germany 

2 FORTH - IESL, P.O. Box 1527, 71110 Heraklion, Greece 

Steam Laser Cleaning is a powerful approach to remove submicron particles from surfaces. In the first step a 

liquid is applied onto the contaminated surface. Afterwards a laser pulse heats part of the fluid to a superheated 

state resulting in bubble nucleation and growth. Thereby strong forces are exerted on the contaminants, which 

are able to overcome the adhesion of the particles to the surface. 

Our measurements covering a broad range of particle sizes demonstrated the existence of a universal cleaning 

threshold for the laser fluence. In addition the influence of different liquid layer thicknesses was explored. 

Investigations of the surfaces after cleaning verified for the first time that damage free removal can be achieved, 

if the experimental parameters are chosen properly. Moreover fundamental studies of the bubble nucleation and 

growth in the superheated liquid were conducted to gain a more detailed understanding of the phase transition 

dynamics. 


In-situ Video-STM Untersuchung der Dynamik von Sulfidadsorbaten auf Cu(100)-Elektroden 

•Tunay Tansel und Olaf Magnussen 

Institut für Experimentelle und Angewandte Physik Christian-Albrechts-Universität Kiel 

Die Diffusion und Wechselwirkung von Adsorbaten an Elektrodenoberflächen ist von großer Bedeutung für das 

Verständnis der elektrochemischen Phasengrenze. Solche dynamischen Prozesse wurden hier am Beispiel von 

Sulfidadsorbaten (Bedeckungen 0,01 bis 0,03ML) auf Cu(100) in 0,01M HCl mittels elektrochemischer 

Hochgeschwindigkeits- Rastertunnelmikroskopie (Video-STM) direkt auf der atomaren Skala untersucht. Eine 

statistische Analyse der Diffusion isolierter S ad ergab Sprungfrequenzen im Bereich von ? 2·10 -1 Hz. An den 

Domänengrenzen c(2x2)-Phase ist die S ad Mobilität jedoch stark erhöht. Dies zeigt, dass die Gegenwart des 

c(2x2)-Cl Koadsorbatgitters die effektive Diffusionsbarriere von S ad deutlich vergrößert. Weiterhin weisen die 

Beobachtungen auf attraktive S ad -S ad Wechselwirkungen und eine erhöhte Mobilität von Clustern an mehreren, 

benachbarten S ad hin. 

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In-situ-Video-STM-Untersuchungen des (1x1) ? ''hex'' - Phasenüberganges an 

Au(100)-Elektrodenoberflächen 

•Klaus Krug 1 , Miguel Labayen 1 , Claudia Ramirez 2 , Wolfgang Schattke 2 und Olaf Magnussen 1 

1 Institut für Experimentelle und Angewandte Physik Christian-Albrechts-Universität zu Kiel 

2 Institut für Theoretische Physik und Astrophysik Christian-Albrechts-Universität zu Kiel 

Die Dynamik des elektrochemisch induzierten (1x1) ? ''hex'' Übergangs an Au(100)-Elektroden wurde in 0.01 M 

Na2SO4 + 1 mM HCl mittels in-situ Video-STM untersucht. Der Phasenübergang erfolgt über Nukleation und 

Wachstum elementarer Einheiten der Oberflächenrekonstruktion, 5 Atomreihen breiten, hexagonal geordneten 

Streifen in der obersten Atomlage. Wachstum, kollektive Bewegung und Wechselwirkung der Streifen konnten 

mit hoher Zeitauflösung als Funktion von Potential und Temperatur beobachtet werden. Diese Beobachtungen 

weisen unter anderem auf einen schnellen eindimensionalen Massentransport von Goldatomen entlang der 

Streifen hin, der sowohl über Verzerrungen im Streifen selbst als auch über Adatome auf dem Streifen erfolgen 

kann. Diese Interpretation wird durch Dichtefunktionalrechnungen gestützt. 


In-situ Video-STM-Untersuchungen der lateralen Bewegung von ''hex''-Streifen auf 

Au(100)-Elektrodenoberflächen 

•Christian Haak, Miguel Labayen und Olaf Magnussen 

Institut für experimentelle und Angewandte Physik, Christian-Albrechts-Universität, Leibnizstraß e 19, 24118 

Kiel 

Die Dynamik von fünf Atomreihen breiten, hexagonal geordneten Streifen auf Au(100)-Oberflächen wurde 

mittels Video-STM in 0.01 M Na 2 SO 4 + 1 mM HCl untersucht. Diese Streifen existieren transient während des 

potentialinduzierten Übergangs von der Au(100) (1×1) zur ''hex'' rekonstruierten Oberfläche und weisen eine 

überraschend hohe Mobilität senkrecht zur Streifenrichtung auf (Sprungraten von ca. 40 s -1 ). Die Bewegung 

dieser nanoskaligen Streifen wurde mit automatischen Bilderkennungsverfahren analysiert und statistisch 

ausgewertet. Dabei erhaltene Sprungverteilungsfunktionen weisen auf die Existenz zweier elementarer Prozesse 

hin (Sprünge um einen bzw. zwei Atomabstände), welche simultan ablaufen. Diese Sprünge können über die 

Bewegung versetzungsähnlicher Verzerrungen in den Streifen erklärt werden. 


Copper sulfidation at the solid/liquid interface 

•A. Spänig, T. Mangen, P. Broekmann und K. Wandelt 

Institut für Physikalische Chemie; Wegelerstr. 12; 53115 Bonn 

The initial stage of the sulfidation process of a Cu(100) electrode surface has been studied under 

electrochemical conditions by means of in-situ Scanning Tunneling Microscopy (STM). At negative electrode 

potential sulfide anions form a regular c(2 × 6) adsorbate layer which transforms irreversibly into 

two-dimensional copper sulfide phases at more positive potentials. Depending on the applied electrode potential 

different sulfide induced reconstruction phases could be generated which can be seen as precursor phases for 

the formation of bulk copper sulfide. The reconstruction process is accompanied by a massive mass transport 

out of the topmost copper layer pointing to a sulfide induced expansion of the topmost substrate layer. 


Katalytische und elektrochemische Oxidation von Ameisensäure auf einer Pd(111)-Elektrode 

•Katrin Brandt, Marco Steinhausen, Thomas Schmidt und Klaus Wandelt 

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Institut für Physikalische und Theoretische Chemie, Universität Bonn, 53115 Bonn 

Mit dem Ziel kleine, organische Moleküle als "Sonden" auf die Oberflächenreaktivität elektrokatalytisch aktiver, 

binärer Elektroden einzusetzen, werden potentielle organische Säuren zunächst auf den Oberflächen der 

einzelnen Metallkomponenten untersucht. 

Dazu wurde das Reaktionsverhalten von Ameisensäure (HCOOH) bei Kontakt mit einer Pd(111)-Elektrode im 

UHV mittels TDS, UPS und IRRAS sowie in Lösung mit IRRAS untersucht. 

Die spektroskopische Charakterisierung der chemisorbierten HCOOH im UHV zeigt die Desorption des intakten 

Moleküls aus der Multilage bei 160 K und in geringen Mengen aus der Monolage bei 186 K. In der Monolage 

überwiegt der Zerfall zu CO 2 und H 2 . Zahlreiche Intermediate des katalytischen Zerfalls können anhand ihrer 

IR-Absorptionsfrequenzen zwischen 1800 cm -1 und 1900 cm -1 nachgewiesen werden. 

In situ IR-Untersuchungen in reiner HCOOH zeigen sowohl die katalytische Freisetzung von CO 2 als auch die 

beschleunigte elektrochemische Oxidation ( > 0.4 V vs. NHE) der Säure. 


Ab-Initio-Investigation of Static and Magnetic Properties of Fe|GaAs(001) 

•Harald Dobler und Dieter Strauch 

Institut für Theoretische Physik, Universität Regensburg, 93040 Regensburg 

We determine the structure and magnetic properties of the (001)-surface of GaAs covered by iron. Encouraged 

by our former investigations of the system Fe|ZnSe, where we have obtained dramatic deviations from the ideal 

structure as well as sensitivity of the magnetic properties to structural changes, we consider another example 

for the compound semiconductor. Again, the lattice constant of GaAs and the doubled value of α-Fe agree very 

well. Nevertheless, we find significant variations of the ideal behavior. We present our results for one, two, 

three, and four monolayers of iron. Similar to the case of Fe|ZnSe the effects are most interesting for a single 

monolayer. Therefore, we show the structures and the profiles of the density of valence electrons and the 

magnetization in the direction perpendicular to the interface. 

The computations are carried out in the framework of spin polarized density functional theory implemented in 

the program package VASP [1,2]. Further, we use expansion in plane waves, ultrasoft pseudopotentials, and 

generalized gradient corrections (GGA). The relaxations of the structures are realized using a conjugate-gradient 

method. 

[1] G. Kresse and J. Hafner, Phys. Rev. B 47, 558 (1993) 

[2] G. Kresse and J. Furthmüller, Phys. Rev. B 54, 11169 (1996) 


Si(001) surface optical properties modified by organic functionalization and oxidation 

•Andreas Hermann, Frank Groth, Wolf G. Schmidt, Kaori Seino, Martin Preuss, Patrick H. Hahn und Friedhelm 

Bechstedt 

Institut für Festkörpertheorie und Theoretische Optik, Friedrich-Schiller-Universität, Max-Wien-Platz 1, 07743 

Jena, Germany 

Tremendous efforts have been devoted to investigate the optical properties of clean Si(001) surfaces. Their 

reflectance anisotropy spectra (RAS) are now well understood in terms of defects and transitions between 

surface states as well as surface-modified bulk wave functions [1]. Far less is known about the modifications 

of the surface optical response by chemical reactions. Inspired by recent experiments [2] we study numerically 

the influence of organic functionalization with phenanthrenequinone and layer-by-layer oxidation on the RAS 

spectrum of Si(001). The calculations are performed using the gradient-corrected density functional theory 

(DFT-GGA) in conjunction with non-normconserving ultrasoft pseudopotentials and a plane-wave basis. The 

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optical spectra are determined in the independent-particle approximation from all-electron wave functions 

obtained by the projector-augmented wave (PAW) method. 

[1] T. Yasuda et al., Phys. Rev. Lett. 74, 1995, 3431; R. Shioda, J. van der Weide, Phys. Rev. B 57, 1998, 

R6823; W.G. Schmidt, F. Bechstedt, J. Bernholc, Phys. Rev. B 2001, 63, 5322. 

[2] C.A. Hacker, R.J. Hamers, J. Phys. Chem. B 107, 2003, 7689; T. Yasuda et al., Phys. Rev. Lett. 87, 2001, 

037403. 


Rauheit und Schädigung einer GaAs-Oberfläche nach dem chemisch unterstützten Ionenstrahlätzen 

mit Cl 2 /Ar + 

•Jens Dienelt, Klaus Zimmer, Justus von Sonntag und Bernd Rauschenbach 

Leibniz-Institut für Oberflächenmodifizierung (IOM), Permoserstr. 15, 04318 Leipzig 

Die chemische und die physikalische Abtragskomponente während des chemisch unterstützten 

Ionenstrahlätzens (CAIBE) von GaAs mit Cl 2 /Ar + bewirkt sehr unterschiedliche Einflüsse auf die Rauheit und 

die Schädigung des oberflächennahen Bereiches. Die Charakteristik der Einzelprozesse spiegelt sich direkt in der 

Oberflächenrauheit wieder. Der starke chemische Ätzangriff von Chlorgas auf die GaAs-Oberfläche zeigt eine 

ausgeprägte Anisotropie der Ätzprofilentwicklung, wobei die {111}-Ebenen durch deren geringe Ätzrate den 

Abtragsprozess maß geblich beeinflussen. Neben der Temperatur oder dem Chlordruck hat demnach auch die 

Kristallorientierung einen großen Einfluss auf die Oberflächenrauheit. Beim reinen Zerstäubungsprozess ergeben 

sich aufgrund der Impuls- und Energieübertragung des gerichteten Ionenbeschusses die glattesten Oberflächen. 

Im Gegensatz zur geringen Oberflächenrauheit wird bei der Zerstäubung der oberflächennahe Bereich jedoch am 

stärksten geschädigt. Hierzu werden ortsaufgelöste Photolumineszenz-Untersuchungen an 

Mehrfach-Quantentrog-Strukturen aus Al 0,35 Ga 0,65 As/GaAs gezeigt, die unter Anwendung der 

Schrägschlifftechnik präpariert wurden. 


Structural, electronic and spin properties of In nanowires on Si(111) surface 

•Xóchitl López 1,2 , Anna Krivosheeva 1 , Friedhelm Bechstedt 1 , Jürgen Furtmüller 1 und Andrey Stekolnikov 1 

1 Institut für Festkörpertheorie und Theoretische Optik, FSU Jena, Max-Wien-Platz 1, 07743 Jena 

2 Instituto de Física, Universidad Autónoma de Puebla, Apartado Postal J-48, Puebla 72570, México 

In the last years the electronic and structural properties of the indium-induced (4×1), (4×2) and (8×2) surface 

reconstructions on Si(111) have been intensively studied due to the potential applications on novel 

optoelectronics devices. In this work the electronic structure calculations are performed using density 

functional theory in the generalized-gradient approximation and ultrasoft pseudopotentials. The atomic positions 

were taken from a previous calculations [1], which are consistent with experimental data. The electronic band 

structures with and without spin polarization are calculated and discussed with respect to the metallic/insulating 

character of the chains. Because the spin density distribution on these systems might be important for their 

electronic properties, we study the influence of the spin polarization on the atomic structure and electronic 

states of the In nanowires on Si(111). Several initial spin configurations are taken into account for all the 

surface reconstructions in order to observe a magnetic ordering. We acknowledge the partial financial support 

from CONACyT grants No.36651-E and 36764-E. [1] F. Bechstedt et al., Phys Rev B 68, 1934XX (2003). 


Ultrathin layers of Ag deposited on 4H-SiC(0001) 

•Serguei Soubatch und Ulrich Starke 

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Max-Planck-Institut für Festkörperforschung, Heisenbergstraße 1, 70569 Stuttgart 

Despite the significance of SiC for high-temperature and high-power electronic devices based on 

metal/semiconductor interfaces, the initial stages of metal layer formation on SiC surfaces still remain 

insufficiently explored in comparison to well known metal/silicon heterointerfaces, such as Ag on Si. We 

investigated the deposition of Ag on 4H-SiC(0001) using quantitative low-energy electron diffraction (LEED). 

Ag layers of 0.2, 0.5 and 1 ML coverage were deposited on the clean (3×3) and (?3×?3)R30 ? SiC(0001) surface 

phases. The structural development after room temperature deposition as well as after annealing was studied. 

The (3×3) phase is only marginally influenced by Ag deposition at room temperature. Annealing leads to Ag 

diffusion and subsequent desorption without a significant phase transformation. In case of the (?3×?3)R30 ? 

phase considerable changes can be monitored in the LEED intensities spectra immediately after deposition. Here, 

structural changes are found during annealing also, possibly caused by Ag diffusion. In both cases the original 

surface phases reappear after Ag desorption. 


High temperature stable silicide contacts on the nanometer scale 

•G. Gardinowski, C. Tegenkamp, T. Block, S. Vagt, V. Zielasek und H. Pfnür 

Institut für Festkörperphysik, Universität Hannover, Appelstrasse 2, 30167 Hannover 

In order to characterize nanostructure electrically contacts are essential to build a bridge between the macrospic 

and the mesoscopic world. High temperature experiments with nanostructures on silicon substrates are 

particularly interesting, but require contacts which can withstand temperatures up to 1100 ? C without changes in 

their chemical composition and without interdiffusion at the contact area of the silicide and the silicon. Using 

electron beam lithography different silicide contacts on both Si(111) and Si(100) surfaces have been fabricated 

and tested. With regard to the specific formation temperatures for silicides, mainly Mo, Ta and Ti have been 

tested. All three silicides are stable up to at least 800 ? C. The metallic character of the silicides was tested by 

masurements of the conductivity. However, for higher temperatures the decomposition of MoSi 2 and TaSi 2 sets 

in leaving behind rough contact areas. Only the TiSi 2 silicide remains intact, as checked by µ-Auger 

spectroscopy. Furthermore, after optimization of the lithography parameters, TiSi 2 contact pads with separation 

lengths of 200 nm were fabricated successfully, i.e. after removing the native oxide from the silicon surface 

(with pads) by a high temperature annealing step, perfect silicon was found in between the contacts as seen by 

STM/SEM. The edges of the contacts are rather sharp and well-defined. The transition area was determined to 

be around 1nm. 


Direct evidence from FTIR for hydrogen incorporation into the MOCVD-grown P-rich reconstructed 

InP(100) surface 

•Tobias Letzig, H.J. Schimper, Thomas Hannappel und Frank Willig 

Hahn-Meitner-Institute, Glienicker Str. 100, 14109 Berlin, Germany 

Recently, the groups of Schmidt and Bechstedt have discussed several different surface reconstructions for 

InP(100). Three of those have been assigned to actually prepared surface reconstructions. In the case of 

MOCVD growth the P-rich (2x1/2x2) surface is postulated to contain hydrogen bonds that stabilize buckled P-P 

dimers. A P-rich surface with a different reconstruction is formed via MBE growth in the absence of hydrogen. 

The In-rich (2x4) reconstruction also does not contain any hydrogen atoms. We present here experimental 

support for the postulated hydrogen bonds on the surface of MOCVD grown P-rich (2x1/2x2) reconstructed 

InP(100) in the form of FTIR spectra that were measured in UHV. We made use of a patented contamination 

free transfer of the sample from the MOCVD reactor into a mobile UHV chamber. FTIR spectra will be 

presented for the as-grown surface and for the surface after further exposure to hydrogen and deuterium. 


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RMS-roughness of Si from nm to mesoscopic scale 

•Stefan Schröder, Herbert Pfnür und Martin Henzler 

Institut für Festkörperphysik, Appelstr.2 D-30167 Hannover,Germany 

The International Technology Roadmap for Semiconductors (ITRS) defines a decrease in surface roughness 

and an increase of the site planarity on a nm scale as two of the requirements for starting materials for industrial 

fabrication of next generations of silicon based micro- and nanodevices. The rms-roughness on different length 

scales is the principal property examined to verify the accomplishment of the goals set. We calculate Power 

Spectral Densities to examine the decay of rms-roughness on the length scales open to STM-measurements (nm 

to µ m) and light scattering methods (µ m to mm) on standard wafers after annealing in a hydrogen 

environment. The light scattering method allows the detection and counting of numbers of particles per area, as 

demanded by the ITRS, to make sure that improved flatness is not accompanied by an increase in 

defect-density. In further experiments profiles of etched steps are monitored to determine diffusion behaviour. 

We gratefully acknowledge financial support by Wacker Siltronic GmbH. 


Photoelektronenbeugung an der oxidierten 4H-SiC(0001) Oberfläche 

•M. Schürmann, S. Dreiner, U. Berges, M. Krause und C. Westphal 


SiC ist ein Halbleitermaterial mit großer Bandlücke. Aufgrund seiner Eigenschaften ist es hervorragend geeignet 

zur Herstellung von Halbleiterbauelementen, die bei hohen Temperaturen, mit hohen Strömen und hohen 

Frequenzen betrieben werden können. In diesem Zusammenhang gewinnt auch die Kenntnis über die Struktur 

an der SiO 2 /SiC-Grenzfläche an Bedeutung. In einer Photoelektronenbeugungsuntersuchung wurden 

Beugungsmuster an einer oxidierten 4H-SiC(0001) Oberfläche aufgenommen. Am U41-PGM Meßplatz bei 

BESSY II stand Synchrotonstrahlung mit hohem Photonenfluß und guter Energieauflösung zur Verfügung. 

Dadurch war es möglich die einzelnen, chemisch verschobenen Komponenten in den XPS-Spektren aufzulösen 

und unterschiedliche Beugungsmuster aufgrund der unterschiedlichen lokalen Umgebung der Emitter zu 

erhalten. Ein Vergleich mit Simulationsrechnungen gibt Aufschluß über ihren Ursprung und die atomare Struktur 

in der SiO 2 /SiC-Grenzfläche. 

O 28.28 Poster Mi 16:00 Bereich C 

Si2p-Photoemissionsspektroskopie an der SiO 2 /Si(100)-Grenzfläche 

•S. Dreiner, M. Schürmann, M. Krause, U. Berges und C. Westphal 


Die SiO 2 /Si Grenzfläche spielt eine wichtige Rolle in der modernen Halbleiterindustrie. Ein genaues Verständnis 

der Grenzschichtstruktur kann zur Verbesserung der Qualität von Halbleiterbauelementen beitragen. 

Die untersuchten SiO 2 /Si(100) Schichten mit einer Dicke von wenigen Ångström wurden durch thermische 

Oxidation erzeugt. Mit Synchrotronstrahlung (BESSY II, U41 PGM) wurden hochaufgelöste 

Si2p-Photoemissionsspektren über dem gesamten Halbraum bei einer Photonenenergie von hν = 180 eV 

aufgenommen. Diese Spektren ermöglichen durch Anpassungsroutinen die Trennung der Si-Oxidationszustände 

(Si 1+ , Si 2+ , Si 3+ , Si 4+ ) vom Volumensignal (Si B ). Dabei zeigt sich, dass zwei weitere Komponenten (Si α , Si β ) 

für eine verbesserte Anpassung nötig sind. Um den Ursprung dieser Komponenten zu ermitteln wird die 

Winkelabhängigkeit dieser Signale analysiert. Dazu werden die gemessenen Photoelektronenbeugungsmuster mit 

Vielfachstreusimulationen verglichen. 


Indium- und Indiumselenid-terminierte Si(111)-Oberflächen als neuartige Pufferschichten in der 

Heteroepitaxie 

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•Stefan Andres, Wolfram Calvet, Tilo Plake und Christian Pettenkofer 

Hahn-Meitner-Institut Berlin, Glienicker Strasse 100, 14109 Berlin 

Zur Passivierung von Silizium-Substraten für die Heteroepitaxie sind III-VI terminierte Oberflächen von grossem 

Interesse. Wir präsentieren erste Ergebnisse dünner In- bzw. InSe-Schichten auf Si(111). Die Präparation der 

Proben erfolgte mittels Molekularstrahlepitaxie (MBE) auf H-Si(111)1x1-, Si(111)7x7- und definiert 

nasschemisch oxidierten Si(111)-Substraten. Die Schichten wurden in situ mittels Photoelektronenspektroskopie 

(PES), niederenergetischer Elektronenbeugung (LEED) und Rastertunnelmikroskopie (STM) bezüglich ihrer 

Morphologie und elektronischen Struktur analysiert. Es wurde zunächst der Einfluss von elementarem Indium 

auf Si(111) untersucht. Im weiteren Prozess erfolgte durch sukzessives Koverdampfen von In und Se die 

Herstellung einer InSe-terminierten 1x1-Oberfläche. Es zeigt sich, dass InSe in einer sogenannten Halblage 

aufwächst, wobei die In-Atome direkt an die Si-Oberfläche gebunden sind. Eine Selenisierung der Si-Oberfläche 

findet nicht statt. Die Energetik der Grenzfläche wird bezüglich Bandversatz und Grenzflächendipolen bestimmt. 


Electrospray Deposition of Sensitive Analytes 

•Frank Stadler 1 , Sergei Koltsov 2 , Eugenio Lunedei 1 , Giovanni Costantini 1 und Klaus Kern 1 

1 Max-Planck-Institut für Festörperforschung, D-70569 Stuttgart 

2 Institute for Analytical Instrumentation, Russian Academy of Sciences, 19813 Saint Petersburg 

Electrospray ionization is well-known as a means to solve the volatilization and ionization problem of sensitive 

analytes such as large biomolecules [1]. Recently Ouyang et al. [2] reported that electrosprayed protein ions 

remain intact, after ionization, in vacuo transfer, mass-selection and soft landing. We present a novel 

electrospray deposition source, whose objective is the non-destructive deposition of large sensitive (e.g. organic 

and biological) analytes under UHV conditions. Aim of this project is to overcome the limitations of size and 

mass of the deposited sample material that are intrinsic to the organic molecular beam epitaxy techniques based 

on sublimation. Besides the explanation of the underlying working principle of this novel experimental setup, the 

relevant technological aspects will be discussed. In addition, AFM images of electrosprayed metal colloid- and 

protein-containing analyte solutions (deposited on highly oriented pyrolytic graphite) will be presented. 

[1] J. B. Fenn et al., Science, 246 (1989), 64-71 

[2] Z. Ouyang et al., Science, 301 (2003), 1351-1354 


VUV photon detector with improved resolution for inverse photoemission 

•R. Stiepel, R. Ostendorf, C. Benesch, H. Merz und H. Zacharias 

Physikalisches Institut, Universität Münster, D-48149 Münster, Germany 

We have significantly improved the energy resolution of a VUV isochromat spectrometer for inverse 

photoemission. The detector used is a Geiger-Müller counter with acetone as filling gas and a CaF 2 entrance 

window. With this detector we achieve an optical energy resolution of 330 meV (FWHM) at a mean energy of 

9.9 eV for the optical bandpass. With an additional gas absorption filter arranged between two CaF 2 windows at 

the entrance of the counting tube we enhance the resolution to 90 meV (FWHM) at a slightly decreased mean 

energy of 9.8 eV. The higher resolution decreases the counting rate to approximately 20%, but by filling or 

evacuating the gas chamber we can switch between the two modes high resolution and high counting rate 

within seconds. 


Konventionelle und positroneninduzierte Auger-Elektronenspektroskopie am System Kupfer-Gold 

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•Benno Straßer, Christoph Hugenschmidt und Klaus Schreckenbach 

Technische Universität München, Lichtenbergstraße 1, D-85748 Garching 

Bei positroneninduzierter Auger-Elektronenspektroskopie (PAES) erfolgt die Anregung der untersuchten Probe 

durch Annihilation von niederenergetischen Positronen mit Rumpfelektronen des Probenmaterials. Die Energie 

der eingestrahlten Positronen kann dabei so klein gewählt werden, dass sie keinen 

Sekundärelektronen-Untergrund im Energiebereich der Auger-Peaks erzeugen. PAES besitzt deshalb ein 

wesentlich besseres Signal-zu-Untergrund-Verhältnis als konventionelle AES und verfügt außerdem über eine 

höhere Oberflächensensitivität. 

Die an der Technischen Universität München bestehende PAES-Apparatur wurde mit einer Effusionszelle und 

einem Elektronenstrahlverdampfer zur Probenbeschichtung im Sub-Monolayer-Bereich erweitert. Daneben 

wurden eine Argonkanone zur in situ Probenreinigung, eine Probenheizung sowie einen Probenschleuse 

installiert. Die Beschichtungsanlage wurde an mit Gold bedampften, polykristallinen Kupferproben getestet und 

Vergleichsmessungen zur Oberflächensensitivität von elektronen- und positroneninduzierter AES durchgeführt. 


Focussing XUV photons with high contrast 

•J. Buck 1 , M. Kalläne 1 , S. Harm 1 , M. Skibowski 1 , R. L. Johnson 2 und L. Kipp 1 

1 Institut für Experimentelle und Angewandte Physik, Universität Kiel, D-24098 Kiel, Germany 

2 Institut für Experimentalphysik, Universität Hamburg, D-22761 Hamburg, Germany 

Photon sieves consisting of a large number of pinholes appropriately distributed over the Fresnel zones focus 

electromagnetic radiation [1]. As part of the program to develop photon sieves for VUV FEL radiation [2] we 

present first experimental results on the focussing properties of reflective photon sieves, which allow to 

enhance the image contrast efficiently. The experiments have been performed with visible light (hν = 1.96 eV) 

and XUV radiation (hν = 100 eV) supplied from the BW3 beamline at HASYLAB. 

[1] L. Kipp, M. Skibowski, R.L. Johnson, R. Berndt, R. Adelung, S. Harm and R. Seemann, Nature 414, 184 

(2001) 

[2] A free-elecron laser (FEL) delivering transversal coherent radiation in the vacuum ultraviolet regime with 

photon energies up to several 100 eV is currently under construction at the Hamburg Synchrotron Radiation 

Laboratory HASYLAB/DESY. Work supported by the BMBF proj. 05 KS1 FK1 


TOF-PEEM für zeitaufgelöste Mikrospektroskopie von Oberflächen basierend auf einer fs-Laser 

EUV-Lichtquelle 

•G. H. Fecher 1,2 , A. Oelsner 1 , G. Schönhense 1 , J. Kutzner 2 , G. Tsimilis 2 und H. Zacharias 2 

1 Johannes Gutenberg - Universität, 55099 Mainz 

2 Westfälische Wilhelms - Universität, 48149 Münster 

Die Kombination eines Photoemissions Elektronen Mikroskops (PEEM) mit einer Femtosekunden Laser 

gepumpten EUV Lichtquelle wird präsentiert. Das PEEM ist für simultane Bildaufnahme und Flugzeitanalyse 

(TOF) mit einem 3D (x,y,t) Detektor ausgestattet. Dies erlaubt neuartige Anwendungen in der 

Mikrospektroskopie von Oberflächen. 

Die Lichtpulse im extremen ultraviolett Bereich werden in Edelgasen durch ein 30fs Ti:Saphir Lasersystem 

generiert. Intensive IR Pulse erzeugen im Konversionsgas hohe Harmonische bis 120eV. Ein Toroidgitter wird 

zur Auswahl der Harmonischen eingesetzt. Al-Filter und Au-Spiegel beschränkten den Energiebereich auf 

15-72eV. Die herkömmliche Bildeinheit de PEEM wurde durch einen 3D-Delayline Detektor ersetzt. Dieser 

registriert die Elektronen in 2 räumlichen und einer zeitlichen Koordinate. Die rückwärtige Mikroskopsäule wird 

als Flugzeitstrecke betrieben. Die Zeitauflösung des Detektors beträgt 125ps. Erste Ergebisse zeigen, daß der 

12 of 32 07.06.2009 22:14



Bildkontrast empfindlich von der ausgewählten Energie der Elektronen abhängt. Die derzeitige Begrenzung der 

räumlichen (160nm) und zeitlichen Auflösung der Methode ist durch die Repetitionsrate (1kHz) des anregenden 

Lasers bedingt. 


Growth of Platin Nanowire Networks on Nafion 

•M. Elbahri, J. Franc, O.C. Aktas, R. Adelung und F. Faupel 

Lehrstuhl für Materialverbunde, Technische Fakultät der CAU Kiel 

The Nafion polymer, produced by the Dupont company, is still the most prominent membrane material for the 

commercial polymer electrolyte fuel cell (PMFC). Usually, the Nafion membrane is sandwiched by two catalytic 

layers, consisting of a metal-Nafion-carbon mixture in order to provide catalytic activity as well as electrical and 

proton conductivity. It turns out that most of the Platinum doesn't contribute to the catalytic efficiency, which 

increases the total cost for the PMFC-fuel cell. An alternative approach might be a catalytic layer formed by a 

Pt-nanowire network. We present here a strategy to deposit Pt in the form of a nanowire networks. Therefore 

we used sputter deposited Pt on a vacuum deposited amorphous carbon mask layer. We show different 

Pt-nanowire networks generated on the Nafion surface and discuss the mechanisms that tune the network 

parameters like nanowire dimensions and mesh width. 

The authors thank the Technologiestiftung Schleswig-Holstein for supporting the project. 


Imaging of optical near fields of nanostructures with fs laser pulses 

•Juliane Birk, Johannes Boneberg und Paul Leiderer 

Universität Konstanz, FB Physik, LS Leiderer, SFB 513, 78457 Konstanz 

The optical properties of nanostructures are a topic of interesting investigations. In analogy to the near fields 

around a Hertz dipole we expect near fields in the surrounding of all nanostructures. Up to now they were 

analysed with the scanning near field optical microscope (SNOM). We want to introduce an alternative method 

to image near fields with intensive short laser pulses. The intensity is adjusted to values where the substrate far 

from the particle is not affected. Nevertheless, the surface around and below the particle can be ablated, due to 

the local intensity enhancement in the optical near field. After the laser pulse the modified surface is imaged with 

atomic force microscopy (AFM) and thus the optical near fields of different nanostructures on several 

substrates, for example silicon, can be studied. A few examples of the near fields of various nanostructures are 

shown. 


Infrared-optical properties of Cu nanoparticles on CaF 2 (111) 

•Birgit Gehring, Andreas Priebe und Annemarie Pucci 

Kirchhoff-Institut für Physik, Im Neuenheimer Feld 227, D - 69120 Heidelberg 

Using IR spectroscopy the growth of Cu nanoparticles on UHV-cleaved CaF 2 (111) was investigated in situ. 

Relative transmission spectra informed about the dynamic conductivity of the nanoparticle film and about the 

influence of the substrate temperature on the percolation threshold. 

In the range from about 1000 cm -1 up to about 2500 cm -1 a relative transmission > 100 % was observed for Cu 

coverage below percolation, which corresponds to an anti-reflection effect. The magnitude of this effect 

depends on the growth temperature. 

For certain average Cu thicknesses we exposed CO at a sample temperature of about 100 K. The CO adsorption 

on different Cu facets was studied by IR transmission spectroscopy. The morphology of the nanoparticle layer 

13 of 32 07.06.2009 22:14



was verified with atomic force microscopy (AFM) ex situ. From the AFM pictures the particle density was 

estimated and the filling factor could be evaluated. 


Steering host-guest interactions at surfaces using tailor-made two-dimensional nanoporous 

coordination systems 

•Sebastian Stepanow 1 , Magalí Lingenfelder 1 , Alexandre Dmitriev 1 , Hannes Spillmann 1 , Erik Delvigne 2 , Nian 

Lin 1 , Xiaobin Deng 3 , Chengzhi Cai 3 , Johannes V. Barth 2 und Klaus Kern 1,2 

3 Department of Chemistry and Center for Materials Chemistry, University of Houston, Houston, TX 

77204-5003, USA 

1 Max-Planck-Institut für Festkörperforschung, Heisenbergstraße 1, D-70569 Stuttgart 

2 Institut de Physique des Nanostructures, Ecole Polytechnique Fédérale de Lausanne, CH-1015 Lausanne, 

Switzerland 

The so-called rational design principle, i.e., synthesis of materials with predictable structures and properties 

from appropriate organic molecular linkers connecting to metal nodes, has recently been explored to control 

pore size and functionality of open three-dimensional networks. Here we demonstrate the fabrication of 

surface-supported metal-organic coordination networks (MOCNs) comprising tailored pore sizes and chemical 

functionality by the modular assembly of polytopic organic carboxylate linker molecules and iron atoms on a 

Cu(100) surface under ultra-high vacuum conditions. The nanocavity arrays provided can be employed to host 

C 60 guest molecules. Temperature-controlled studies reveal at the single-molecule level how pore size and 

chemical functionality determine the host-guest interactions. 


Dynamic Mode Force Microscopy Studies of Individual Single Wall Nanotubes on HOPG 

•Timo Behnke 1 , Makoto Ashino 1 , Alexander Schwarz 1 , Roland Wiesendanger 1 , Keith A. Williams 2 und Cees 

Dekker 2 

1 Institute of Applied Physics, University of Hamburg, Jungiusstrasse 11, D-20355 Hamburg, Germany 

2 Department of Applied Physics and DIMES, Delft University of Technology, Lorentzweg 1, 2628 CJ Delft, 

The Netherlands 

The growing interest in single wall carbon nanotubes (SWNT) is related to their prospected applications of their 

unique possibilities in upcoming nanotechnology (1). To study structural properties of SWNTs down to the 

atomic scale dynamic mode force microscopy is well suited. 

In a first step, we developed a technique to prepare SWNTs on HOPG. Tapping Mode Imaging in ambient 

conditions showed a homogeneous SWNT distribution on atomically flat and well defined graphite (HOPG) with 

only negligible small amounts of contamination. Although most of SWNTs appeared as bundles or ropes, we 

found a sufficient density of individual SWNTs. In a second step, we took advantage of the increased resolution 

of dynamic mode force microscopy and spectroscopy in ultrahigh vacuum and used a home-built low noise and 

very stable low-temperature force microscope to resolve the atomic structure of individual tubes. 

[1] Baughman, Zakhidov, de Heer, Science 296, 787 (2002) 


Dynamik von selbstorganisierten Nanopartikeln auf Oberflächen 

•Anton plech 1 , Vassilios Kotaidis 1 , Samuel Gr'esillion 2 und Gero von Plessen 3 

1 Fachbereich Physik der Universität Konstanz, Universitätsstr. 10, 78457 Konstanz 

14 of 32 07.06.2009 22:14



2 ESPCI 10, rue Vauquelin, F-75005 Paris 

3 RWTH Aachen, I. Physikalisches Institut A, D-52074 Aachen 

Naßchemisch hergestellte Nanopartikel können über Selbstaggregationsverfahren auf Oberflächen abgelagert 

werden. Es werden so definiert Submonolagenbedeckungen erreicht. Diese Systeme erlauben das Studium der 

strukturellen Eigenschaften von quasifreien Partikeln, wie thermische Expansion oder strukturelle Dynamik. 

Es werden die strukturellen Relaxationen der Partikel auf die ultraschnelle Laseranregung der 

Plasmonenresonanz untersucht. Als Sonde dient ultraschnelle zeitaufgelöste Röntgenbeugung (Meßplatz ID09, 

ESRF, Frankreich). Neben der thermischen Anregung und Kühlung des Kristallgitters werden auch 

Nichtgleichgewichtsprozesse beobachtet und im Rahmen von Partikeleigenschwingungen gedeutet. 


Gold Nanoteilchen auf Al 2 O 3 /Nb(110): Eine STM Studie dynamischer Umladungeffekte bei 

Raumtemperatur 

•Christof Dietrich, Berndt Koslowski und Paul Ziemann 

Abt. Festkörperphysik, Universität Ulm 

Um ein System zu präparieren, das Coulomb-Blockade bei Raumtemperatur zeigt, wurden epitaktische 

Niob(110)-Filme auf Saphir(0001) durch dc-magnetron-Sputtern bei einer Substrattemperatur von 1200K 

hergestellt. Diese Metallschichten haben eine extrem glatte Oberfläche (RMS:2nm auf 500nm 2 ) und mit dem 

STM konnte atomare Auflösung erzielt werden. Auf diese Schichten wurde eine 1nm dicke Aluminiumschicht 

aufgedampft und anschließ end in einem Sauerstoffplasma oder in Sauerstoffatmosphäre oxidiert. Bei geeigneter 

Prozessführung kann auch ein epitaktisches Oxid hergestellt werden. Auf diese Tunnelbarriere wurden Gold 

Nanoteilchen mit Größ en von 1nm-15nm mittels einer mizellaren Technik aufgebracht. 

I-V-Spektroskopien auf den Teilchen zeigen eine klare Coulomb-Blockade, die sich sehr gut mit Hilfe der " 

orthodoxen" Theorie der Coulomb-Blockade anpassen lassen. Durch Präparation verschiedener Teilchengröß en 

konnten die Parameter der Coulomb-Blockade größ enabhängig bestimmt werden. Um die laterale Variation der 

Parameter der Coulomb-Blockade auf den Teilchen zu bestimmen, wurden zusätzlich I-V-Karten angefertigt. 

Demnach sind die Parameter stark von der Position auf dem Teichen abhängig. 


Kombination mizellarer und lithographischer Techniken - ein unkonventioneller 

Strukturierungsansatz 

•Oliver Dubbers 1 , S. Fricker 1 , A. Klimmer 1 , H.-G. Boyen 1 , A. Plettl 1 , P. Ziemann 1 , M. Ott 2 und M. Möller 2 

1 Abt. Festkörperphysik, Universität Ulm, D-89069 Ulm 

2 Abt. Organische Chemie 3, Universität Ulm, D-89069 Ulm 

Inverse P2VP-PS-Mizellen in Lösung können mit verschiedenen Metallsalzen beladen werden. 

Selbstorganisationsprozesse führen bei Abscheidung auf glatten Oberflächen zu einer hexagonalen Anordnung. 

Nach Entfernung des Polymers in einem H 2 - oder O 2 -Plasma erhält man schließlich Nanoteilchen, deren Größe 

und Abstand durch die Polymerkettenlängen bestimmt werden. Die Teilchen lassen sich auch noch nachträglich 

in einer HAuCl 4 /NH 2 OH-Lösung elektrodenfrei weiter vergrößern. Dieser mizellare Ansatz läßt sich mit 

lithographischen Methoden kombinieren. In lithographisch definierte Fenster von Lack- oder Metallmasken 

lassen sich Mizellen einfüllen und anschließend veraschen. Beim Lift-off der Maske werden die darauf liegenden 

Teilchen mit entfernt, so dass sich nur noch die Teilchen auf der Oberfläche befinden, die direkt auf dem 

Substrat aufgebracht wurden. Derart deponierte Nanoteilchen lassen sich beim anisotropen Plasmaätzen als 

Maske verwenden, um zum Beispiel Nanosäulen in Silizium und Titan herzustellen. 


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Nanostructures as a result of the thermal instability of metal thin films on insulators 

•Torsten Kolb, Dominik Enders, Annemarie Pucci und Gerhard Fahsold 

Kirchhoff-Institut für Physik, Universität Heidelberg, Im Neuenheimer Feld 227, D-69120 Heidelberg 

We investigate the possibility of structuring metal thin films on a nanoscale by exploiting their thermal instability. 

Various metal thin films (Cu, Au, Fe) were deposited on different substrates (MgO, SiO 2 ) and subsequent 

annealing processes were applied for fractioning these films. For in-situ and online analysis of this fractioning 

we use infrared spectroscopy, which we perform during annealing in UHV. Measuring IR transmission enables 

investigation of both dynamics and energetics (critical temperatures) of the processes caused by the thermal 

instability of metal thin films. Their morphological properties were characterized ex-situ by atomic force 

microscopy (AFM). The dependence of the resulting morphology on annealing temperature and crystalline 

structure will be demonstrated. 


Metal-on-insulator nanostructures via surface color centers 

•Svend Vagt, Tammo Block, Volkmar Zielasek und Herbert Pfnür 

Institut für Festkörperphysik, Universität Hannover, Appelstr. 2, 30167 Hannover 

We present first experimental results obtained in a pursuit of a new type of electron beam nanolithography in 

UHV that is based on the generation of surface color center patterns on epitaxial insulator films and the selective 

nucleation of metal islands. Experiments were performed in a combined system of an SEM (1-25 keV, resol. 4 

nm) and a confocal variable temperature STM (80-900 K). Epitaxial NaCl layers on Ge(100) (up to 6 ML thick) 

were irradiated by the electron beam of the SEM under varying doses. EELS and scanning Auger microscopy 

showed the generation of color centers and Na clusters and colloids associated with electron-induced desorption 

of Cl in the irradiated areas. The NaCl films turned out to be extremely sensitive to a 3 keV electron beam and 

due to high surface mobility of Na metal clusters formed easily. After high e-beam exposure STM at 2 

monolayer thick NaCl layers revealed the formation of beam-induced line-shaped gaps in the film down to the 

substrate. Depending on the electron dose, a width down to 35 nm was observed, probably limited by 

secondary electrons. Deposition of Ag on the surface leads to metal aggregation in the center of the gaps, 

presently being investigated by STM and SEM. The underlying physical mechanisms as well as the potential use 

of this type of nanostructuring technique and possible refinements will be discussed. 


Pb on Si(557) - Steps towards a one-dimensional conductivity 

•Ziad Kallassy, Martin Henzler, Heinz-Lorenz Günter und Herbert Pfnür 

Institut für Festkörperphysik,Applestrasse 2,30167 Hannover 

The conductivity of ultrathin Pb films evaporated onto a highly stepped Si(557) surface was investigated by 

modified macroscopic 4-point measurements in UHV. After annealing 4 to 10 ML of Pb, evaporated at a sample 

temperature of 80K, to temperatures of 990K we obtained a strongly anisotropic conductivity at temperatures 

below 100K, with up to a factor of 20 higher conductance in the direction parallel to the step edges compared 

with the direction normal to them. While conductivity in this direction was found to be thermally activated and 

close to the conductivity of 1 ML of Pb on Si(111), it strongly decreases with increasing temperature in 

directions parallel to steps. The measurements will be correlated with LEED and STM results. 


Dependency of the scattering of light by small planar particles on the direction of incidence and 

polarization 

•Manuel Gonçalves und Othmar Marti 

Department of Experimental Physics, University of Ulm, D-89069 Ulm, Germany 

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The scattering of light by small particles has been intensively researched in the last decades. The well known 

dependencies of the scattering of light on the size, shape, material and environment of the particles reveals the 

complexity of the problem. Several publications have shown numerical simulations and experimental results 

demonstrating resonances and local field-enhancements on sub-wavelength particles. 

Particles of size comparable to the wavelength and of sub-wavelength size, of planar geometry i.e. where the 

thickness is much smaller than their linear dimensions, are of great interest in photonics. 

We have investigated planar particles of different shapes by confocal and SNOM microscopy. These particles 

show interesting dependencies on the direction of the incidence of light, on polarization and on the dielectric 

constant of the material. 

We have observed important differences in the scattering patterns for each material, and each relative orientation 

of the particles with the direction of incidence of the light. 


Self-imaging observed on colloid crystals and Fischer projection patterns 

•Manuel Gonçalves und Othmar Marti 

Department of Experimental Physics, University of Ulm, D-89069 Ulm, Germany 

The self-imaging phenomenon in optical systems is known since the Talbot effect was discovered in the 19th 

century. The Talbot effect is generated by the interference of the incoming light from a diffraction array of 

apertures of size a that takes place near the array (Fresnel zone). In general, a >> λ. 

Apertures separated by a distance d, when illuminated by a coherent and plane wave of wavelength λ produce 

self-images at distances d T = ν 2 d 2 / λ, for ν = 1, 2, ... [1],[2]. 

We have observed that arrays of colloidal crystals of polystyrene spheres with diameter of few µm produce 

self-images, at distances of several tenths of µm. The theoretical Talbot length is compared with the measured 

distances for self-images, for different illumination modes of coherent light. 

A discussion of the multiple scattering and diffraction of light by a regular array of colloidal particles is 

introduced and analyzed. 

[1] K. Patorski, in Prog. Opt. XXVII, Elsevier, 1989. 

[2] A. Lohmann and J. A. Thomas, Appl. Opt., 29 29, 4337-4340. 


Plasma CVD-grown carbon nanotubes studied by field emission 

•Daniell Malsch 1 , Martin Sveningsson 2 , Eleanor Campbell 2 und Juergen A. Schaefer 1 

1 Institut für Physik und Zentrum für Mikro- und Nanotechnologien, TU Ilmenau, P.O. Box 100565, 98684 

Ilmenau, Germany 

2 Department of Experimental Physics, Gothenburg University and Chalmers University of Technology, 41296 

Gothenburg, Sweden 

Films of carbon nanotubes show an excellent field emission behaviour that allows a wide range of application in 

field emitting devices. The influence of the different emission parameters has to be investigated in order to 

improve their performance. We study the field emission of vertically aligned PCVD-grown multiwall carbon 

nanotubes. A systematic influence of the tube length on the emission current, the light emission, and the surface 

temperature of the film is found. We also examine blackbody radiation from resistive heating during field 

emission. This leads, in agreement with light emission behaviour and long-time stability measurements, to a 

stepwise degradation of the carbon nanotube films. 

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Generation of metal nanodroplets and experiments on their velocity and landing 

•Anja Habenicht, Michael Olapinski, Johannes Boneberg und Paul Leiderer 

Universität Konstanz, FB Physik SFB 513, 78457 Konstanz 

An interesting observation can be made when gold nanostructures placed on a substrate are illuminated with an 

intensive short laser pulse: Just above the melting threshold all particles leave the surface. The reason for this 

effect is the wetting behaviour: Gold does not wet the glass substrate, thus the liquid nanostructures can reduce 

their surface energy by reforming to spheres. If this transformation is sufficiently fast the liquid spheres take 

off from the surface. The velocity of the flying nanodroplets can be determined by analyzing the time dependent 

scattering signal which arises when the droplets cross a sheet of light. This signal can be converted into a 

velocity dependent particle density. The particles cool down during the flight due to thermal radiation. By 

catching the nanodroplets on a further substrate at different distances, the droplets can be landed either in liquid 

or in solid state. First results of velocity measurements and the impact experiments are shown. 


Nanostructuring using colloid crystals and dry and wet etching techniques 

•Manuel Gonçalves 1 , Moritz Trautvetter 2 , Oliver Dubbers 2 , Sebastian Fricker 2 , Alfred Plettl 2 , Paul Ziemann 2 

und Othmar Marti 1 

1 Department of Experimental Physics, University of Ulm, D-89069 Ulm, Germany 

2 Department of Solid State Physics, University of Ulm, D-89069 Ulm, Germany 

Sub-wavelength structures produced using latex colloidal crystals have been intensively investigated in the last 

years, namely to produce photonic crystals. One of most known techniques to produce nanoparticles using 

monolayers of latex spheres as lithographic masks, has been developed by U. Ch. Fischer et al. in 1981 (Fischer 

projection patterns or FPP). This method, however, is restricted to few possible particle shapes. 

We have developed two techniques to extend the number the possible shapes and geometrical configurations, 

using colloidal crystals and FPPs combined with dry and wet etching techniques. 

Inverse projection pattens have been produced using the common FPPs combined with wet chemical etching. 

We have also developed a technique to produce sub-wavelength structures using monolayers of latex spheres 

etched by a plasma. The size and the separation of the particles can be controlled by the etching level and by 

selecting the size of the latex spheres. 

Several nanostructures using these techniques have been produced and characterized by scanning probe 

microscopy and scanning electron microscopy. The optical properties of some samples produced using metallic 

thin films are also presented. 


Application of imaging XPS for chemical analysis and mapping of magnetic domains 

•S. Schmidt 1 , M. Escher 2 , F. Forster 1 , D. Funnemann 3 , B. Krömker 3 , M. Merkel 2 , F. Reinert 1 und N. Weber 2 

2 Focus GmbH 

3 Omicron Nanotechnology GmbH 

1 Universität des Saarlandes, FR 7.2 Experimentalphysik, Postfach 151150, 66041 Saarbrücken 

We present first scientific applications of a new NanoESCA [1] spectrometer: we have used the good spatial 

resolution to investigate the chemical structure of plain and decorated grain boundaries in two reference 

materials Al 0.98 Sn 0.02 and Cu 0.98 Bi 0.02 [2]. The data measured at the high-intensity small-spot beamlines of 

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BESSY II also exhibit detailed information about the oxidation processes in such materials. In Al 0.98 Sn 0.02 we 

have detected small differences in the binding energy of the Al 2p XPS peak of 30-50 meV that could be related 

to different grain orientations. We also present data taken on the nanowire prototype system Cu/ZnSe 2 [3] 

where the Cu-nanowires are effectively protected against oxidation even during air-exposure. Using cicular 

polarization at the undulator we were able to map magnetic domains [4] in a Fe single crystal at the Fe 2p XPS 

core-level with high contrast. 

[1] D. Funnemann et al., Bessy Annual Report, 2002 

[2] S. Schmidt et al., Bessy Annual Report, 2002 

[3] R. Adelung et. al, Adv. Mater. 14, 15, p. 

[1056-1061, 2002 4] C. Schneider et al., Rep. Prog. Phys, 65, R1785-R1839, 2002 


Lead on hydrogen terminated Si(111): A comparison of two different deposition techniques 

•C. Rettig 1,2 , H. Hövel 1 , V. Chamard 1 , S. Warren 2 , T. H. Metzger 2 und J. Zegenhagen 2 

1 Universität Dortmund, Experimentelle Physik I, D-44221 Dortmund (Germany) 

2 European Synchrotron Radiation Facility (ESRF), B.P. 220, F-38043 Grenoble (France) 

We studied the epitaxy of electrochemically deposited Pb clusters on Si(111):H dependent on the applied 

overpotential. The former measurements [1] and the present investigations are carried out in-situ using Cyclic 

Voltammograms and Surface X-ray Diffraction (SXRD). The specular measurements show a predominant 

alignment of the Pb(111) plane parallel to the Si(111) plane. In the sample plane the Pb Clusters are aligned 

along the high symmetry direction of Si confirmed by Grazing Incidence Diffraction (GID). New results 

indicate a dependency of the Pb clusters alignment in the sample plane on the applied overpotential. Presently we 

extend our measurements to Ultra High Vacuum (UHV) environment with in-situ deposition of Pb on Si(111):H. 

This system is studied by Scanning Tunneling Microscopy/Spectroscopy (STM/STS), Low Energy Electron 

Diffraction (LEED) and Ultraviolet Photoelectron Spectroscopy (UPS). 

[1] J. C. Ziegler et al., Surf. Sci. 452, 150 (2000). 


Lifetime of particle plasmon excitation in Ag-Nanoparticles 

•Daniela Bayer, Alexander Mönnich, Jörg Lange, Michael Bauer und Martin Aeschlimann 

Dep. of Physics, University of Kaiserslautern 

The dynamics of photoexcited hot electrons are of special interest for a large variety of modern fields such as 

fs-photochemistry and (magneto)electronics. These specific applications depend critically on the inelastic 

lifetime T 1 of these hot electrons. Hence, the question arises if it would be possible to manipulate T 1 in a 

specific way. In this poster, we will demonstrate that the specific structuring of the material on a nanometer 

scale can govern the effective electron dynamics. Our interest is focused on localized collective oszillations of 

the electron gas in metal particles of nanometer size, the so-called particle plasmons. A. Liebsch predicts that 

under certain conditions the plasmon dephasing time at off-resonance excitation can be longer than on 

resonance due to the wavelength dependence of radiation damping. Making use of the Time-Resolved 

Two-Photon-Photoemission (TR-2PPE), our investigation concentrates on elliptically shaped silver 

nano-particles under resonant and off-resonant conditions. Experimental results confirming Liebschs theory will 

be shown. 


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Surface Plasmon Propagation In Metallic Nanostructures 

•Phillip Olk 1 , Jan Seidel 1 , Stefan Grafström 1 , Eng Lukas 1 , Fadi Baida 2 , Daniel Van Labeke 2 , Marcell Ott 3 und 

Lothar Bischoff 4 

1 Institut für Angewandte Photophysik, TU Dresden, 01062 Dresden 

2 Laboratoire d'Optique P.M. Duffieux, CentreNational de La Recherche Scientifique, Unité Mixte deRecherche 

6603, Université de Franche-Comté, F-25030Besançon Cedex, France 

3 Organic Chemistry III / Macromolecular Chemistry, Universität Ulm, 89081 Ulm 

4 Research Center Rossendorf, Institute of Ion BeamPhysics and Materials Research, 01314 Dresden 

Propagation of surface plasmons in metallic nanostructures and their interaction with defined surface features 

are presented. We use near-field optical methods in order to reveal various properties of such travelling surface 

waves, like optical transmission across barriers or coupling to free space electromagnetic waves. These 

characteristics are directly determined using an attenuated-total-reflection (ATR) excitation scheme together 

with dielectric fiber probes for near-field optical detection. We show results on plasmon propagation in 

self-assembled cluster films, discussing propagation lengths and resonance conditions. Furthermore, we present 

an experimental and theoretical analysis of plasmon mode coupling in continuous metallic films mediated by a 

single groove structure produced by focused ion beam (FIB) writing. 


Optical anisotropy of Cs nanostructure formation on GaAs(110), InP(110) and InAs(110) 

•Karsten Fleischer 1,2 , Gianlorenzo Bussetti 2 , Claudio Goletti 2 , Pierro Chiaradia 2 und Wolfgang Richter 1,2 

2 Universitá ``Tor Vergata'', Dipartimento di Fisica, Via Ricerca Scientifica 1, 00133 Roma, Italy 

1 TU-Berlin, Institut für Festkörperphysik, Hardenbergstr. 36, 10623 Berlin, Germany 

We present reflectance anisotropy spectra (RAS) of Cs covered GaAs, InP and InAs cleaved (110) surfaces. In 

such systems Cs forms one dimensional wirelike structures at low coverages. For the first time we studied the 

formation of these wires in situ with optical and therefore nondestructive techniques. Wire formation is 

accompanied with characteristic minima in the RAS spectra between the E 0 + ∆ 0 and E 1 bulk critical point. 

With growing coverages (θ > 0.3 ML) and formation of the two dimensional closed Cs layer (θ ? 0.5 ML), 

changes in the Cs related minima occur. Different wire types and also the transition into the disordered Cs 

double layers at saturation coverage ( θ ? 1 ML) can be monitored optically. 


Methanol oxidation on clean and oxygen-covered copper surfaces 

•Sung Sakong und Axel Groß 

Physik-Department T30, Technische Universität München, 85747 Garching, Germany 

We have studied methanol oxidation steps over clean and oxygen-covered copper surfaces by density functional 

theory (DFT) calculations. The reaction pathways are determined by the nudged elastic band (NEB) method [1] 

which in particularly also yields the intermediate states and the reaction barriers. We find that on clean copper 

surfaces, methanol is only weakly bound. The decomposition into methoxy and hydrogen is activated. Upon 

heating, methanol rather desorbs than dissociates. The further decomposition of adsorbed methoxy into 

formaldehyde and hydrogen is hindered by large barriers ( ? 1.5eV). 

The surface intermediate states in the methanol oxidation are significantly stabilised by co-adsorbed oxygen. The 

DFT calculations show that on oxygen-covered Cu(110), methanol dissociates spontaneously because of the 

strong attraction between the methanol hydroxyl hydrogen and the surface oxygen. The reaction steps are 

analysed in terms of the underlying electronic structure. Our calculations confirm the importance of co-exposed 

oxygen in the methanol oxidation on copper surfaces found in experiments (see, e.g., [2]). 

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[1] G. Henkelman and H. Jónsson, J. Chem. Phys. 113, 9978 (2000). 

[2] Ch. Ammon et al., Surf. Sci. 507, 845 (2002). 


Electron Solvation during the Interaction of Na Atoms with Polar Molecules 

•A. Borodin 1 , O. Höfft 1 , U. Kahnert 1 , V. Kempter 1 , Y. Ferro 2 und A. Allouche 2 

1 Institut für Physik und Physikalische Technologien, TU Clausthal, Leibnizstr. 4, D-38678 Clausthal-Zellerfeld 

2 Physique des Interactions Ioniques et Moléculaires, CNRS-UMR6633 Campus Universitaire de Saint Jérôme, 

Marseille France 

The interaction of Na atoms with molecular films (H 2 O; CH 3 OH; NH 3 ) was studied with metastable impact 

electron spectroscopy (MIES) under UHV conditions. The films were grown at 90K, and exposed to Na. The 

spectral feature from 3sNa ionization occurs at an energetic position different from that found for metals or 

semiconductors. The results are compared with DFT calculations. Experiment and theory agree in the energetic 

positions of the main spectral features from the molecular and sodium ionization. The calculations suggest that 

the 3sNa emission observed experimentally originates from solvated 3s electrons which are located far from the 

Na-core and become stabilized by solvent molecules. The simultaneous emergence of emission from OH (or 

CH 3 O) and from solvated 3s electrons suggests that the delocalization and, consequently, the solvation play an 

important role in the Na-induced formation of CH 3 O and OH species from methanol and water, respectively. 


Spectral evidence for oxide free incorporation of oxygen into Ru(0001) 

•Raoul Blume 1 , Artur Böttcher 2 , Horst Conrad 3 und Horst Niehus 1 

1 Institut für Physik, HU-Berlin, Newtonstr. 15, 12489 Berlin 

2 Institut für Physikalische Chemie, Universität Karlsruhe, Kaiserstr. 12, 76131 Karlsruhe 

3 Fritz-Haber-Institut der Max-Planck-Gesellschaft, Faradayweg 4-6, 14195 Berlin 

The capability of a smooth and defected Ru(0001) surface towards the oxygen accumulation has been studied 

by the means of thermal desorption spectroscopy (TDS) and the high resolution scanning XPS (Elettra, 

Trieste). By applying a soft Ar + -sputtering procedure individual surface defects confined to the two outermost 

Ru layers were created. The oxidation procedure applied here assures an incorporation of oxygen atoms in the 

subsurface region up to 4 monolayer equivalents (MLE) without any traces of RuO 2 -domains (high-pressure 

and low-temperature surface oxidation). By measuring the temperature and exposure dependence of the oxygen 

incorporation and analyzing the corresponding evolution of the Ru 3d 5/2 band we found characteristic electronic 

signatures allowing to distinguish oxygen atoms occupying the Ru(I)-Ru(II) interlayer space and oxygen species 

associated with surface defects. This assignment is supported by mesoscopic-scale surface images as well as 

the quantitative O 2 -TD analysis. 


Investigation of Au electrodeposition processes on metal single crystal surfaces 

•Ahmed Ayyad, Jochim Stettner und Olaf Magnussen 

Institut für Experimentelle und Angewandte Physik, Christian-Albrechts-Universität Kiel, Leibnizstraße 19, 

24098 Kiel 

Metal electrodeposition processes have been a subject of substantial basic research during the last years, 

motivated by current technologies as well as future applications, such as the electrochemical formation of 

ultrathin layers and nanostructures. A major, largely unsettled question is how the electrode surface structure 

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and adsorbates, such as anions or organic additives, influence the growth process. We studied the homoepitaxial 

electrodeposition of Au on Au(111) electrode surfaces (deposition rates 0.05 to 0.23 ML/min.) by in-situ x-ray 

diffraction under real time conditions using a hanging-meniscus transmission cell (reduced cell resistance, 

unrestricted mass transport), where the Au(111) electrode surface is completely covered by an electrolyte 

droplet. Parallel to the X-ray measurements cyclic voltammograms were recorded, which confirm that the 

hanging-meniscus cell allows high quality electrochemical measurements combined with in-situ surface X-ray 

diffraction studies. The X-ray diffraction data and complementary in-situ ellipsometric measurements indicate 

that the deposition process is accompanied by substantial surface roughening. 


State selective detection of D 2 after femtosecond-laser induced desorption from Ru(001) 

•S. Wagner 1 , M. Rutkowski 2 , R. Dudek 3 , C. Frischkorn 1 , H. Zacharias 2 und M. Wolf 1 

3 Fritz-Haber-Institut der MPG, Berlin 

1 Freie Universtät, Berlin 

2 Westfälische Wilhems-Universität, Münster 

The energy transfer into different degrees of freedom in the fs-laser induced recombinative desorption of 

deuterium from Ru(001) has been investigated with (1+1')-REMPI and time-of-flight measurements. It has been 

shown that hot substrate electrons mediate this reaction within a few hundred femtoseconds [1]. The 

rovibrational distributions of the desorbing D 2 molecules are detected via various B 1 Σ u + ? X 1 Σ g + Lyman bands 

using tunable vacuum ultraviolet (VUV) laser radiation for the resonant excitation step [2]. Populations of the 

rotational quantum states in the vibrational ground and the first excited state are measured. The rotational energy 

of D 2 in the vibrational ground state (E rot /k B = 800?200 K) is much lower than the rotational energy in the 

excited state ( E rot /k B = 1500?300 K). Assuming a Boltzmann-like energy distribution, these results indicate a 

vibrational temperature of E vib /k B = 1200?150 K. The amount of energy coupled to the translation is E trans /k B = 

1700?300 K. Possible reasons for the incomplete thermalization will be discussed. 

[1] D. N. Denzler, C. Frischkorn, C. Hess, M. Wolf, and G. 

[Ertl, Phys. Rev. Lett., in press 2] D. Wetzig, M. Rutkowski, H. Zacharias, and A. Groß Phys. Rev. B 63, 

205412 (2001) 


Characterisation of Pd/Zn/ZnO real catalysts for methanol steam reforming 

•S. Pöllmann 1 , J. Pantförder 1 , A. Kölbl 2 , P. Pfeifer 2 , M. Fichtner 3 , D. Borgmann 1 , R. Denecke 1 und H.-P. 

Steinrück 1 

1 Physikalische Chemie II, Universität Erlangen, Egerlandstr. 3, 91058 Erlangen. 

2 FZ Karlsruhe GmbH, Institut für Mikroverfahrenstechnik -IMVT-, Postfach 3640, 76021 Karlsruhe. 

3 FZ Karlsruhe GmbH, Institut für Nanotechnologie -INT-, Postfach 3640, 76021 Karlsruhe. 

We studied the chemical composition and the temperature dependent behavior of Pd/Zn/ZnO catalysts that are 

used for methanol steam reforming. Real catalysts coated on microstructured foils have been used and their 

performance has been characterised in a high pressure flow apparatus under realistic reaction conditions. We 

investigated these samples by means of X-ray photoelectron spectroscopy (XPS) with Al Kα radiation. Utilizing 

a high pressure XPS system the experiments were performed in-situ and in the presence of methanol and water 

vapour in a pressure range up to 1 mbar, at different temperatures. These measurements allow to establish a 

correlation between the different activities for the methanol steam reforming and the chemical composition of 

the catalysts surface. Supported by the DFG (Schwerpunktsprogramm 1091, Ste 620/3-3, Fi 816/1-1,2) 

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Drei unterschiedliche Ursachen für beim maschinellen Geschirrspülen auftretende 

Glasoberflächenschäden 

•Chun Wang 1 , Klaus-Peter Martinek 2 , Edda Rädlein 3 und Georg Krausch 1 

1 Physikalische Chemie II, Universität Bayreuth 

2 Nachtmann GmbH 

3 IMA, Universität Bayreuth 

1. Glasstruktur: Nach einigen hundert Spülgängen ist die glatte "Glashaut" abgetragen und es bilden sich 

Kornmuster in der Größe von 30 nm. Bei mehr als tausend Spülgängen sind diese Körner verschwunden und 

Waffelmuster mit Löchern in der Größe bis zu einem µm haben sich gebildet. Damit erscheinen die Gläser 

getrübt. Dieses Phänomen kann mit der Theorie der Ionen-Kanäle im Glasnetzwerk von Greaves und mit 

unserem Vorschlag einer Glashaut gut erklärt werden. 

2. Feuerpolitur: An manchen Gläsern konnten bereits nach wenigen Spülzyklen wolkige Oberflächenschäden 

beobachtet werden. Die Schäden haben ihre Ursache im industriellen Prozess der Feuerpolitur. Die auf die 

Glasoberfläche treffende Flamme hat einen großen Temperaturgradienten. So treten je nach Position der Flamme 

unterschiedliche Muster der Phasentrennung in Erscheinung. 

3. Organische Komplexbildung durch Getränke: An der Innenseite einzelner, über lange Zeit verwendeter Gläser 

ist ein goldfarbiger Belag zu beobachten. Die Reaktionsschicht ist nicht dicht und das Glas unterhalb dieser 

Schicht zeigt eine weitere Korrosion. Die Schicht ist auf eine Komplexbildung von organischen Komponenten 

aus den Getränken mit dem Glas zurückzuführen. 


Deposition massenselektierter Metallclusterionen unter Verwendung einer Magnetronsputterquelle 

•Nils Bertram, Tim Fischer, Rainer Dietsche, Felix v.Gynz-Rekowski, Young Dok Kim und Gerd Ganteför 

Fachbereich Physik, Universität Konstanz, 78547 Konstanz. 

Das weiche Landen von massenselektierten Clusterionen erlaubt die Präparation von nanostrukturierten 

Oberflächen im extrem kleinen Größenbereich unterhalb von 3 nm und mit atomarer Präzision: die Zahl der 

Atome in der Nanostruktur ist exakt bekannt. Das Problem bei dieser Art von Experimenten ist die niedrige 

Intensität der üblichen Clusterionenquellen. Wir präsentieren erste Studien mit einer neu aufgebauten 

Magnetron-Sputterquelle (Haberland-Typ). Die deponierten Cluster werden mittels 

Elektron-Energieverlust-Spektroskopie untersucht. 


Katalytische Reaktionen massenselektierter Edelmetallcluster 

•T. M. Bernhardt, L. D. Socaciu, J. Hagen, D. Popolan, J. Le Roux, T. Gleitsmann, M. Vaida, B. Stegemann 

und L. Wöste 

Institut für Experimentalphysik, Freie Universität Berlin 

Kleine Gold- und Silbercluster mit bis zu 13 Atomen zeigen eine starke Größenabhängigkeit in ihrer chemischen 

Reaktivität. Für bestimmte Clustergrößen kann in der Gasphase die katalytische Konvertierung von 

Kohlenmonoxid zu Kohlendioxid nachgewiesen werden. Studien zur temperaturabhängigen Kinetik geben 

Aufschluß über den Reaktionsmechanismus. Strukturinformationen der Zwischenprodukte können aus 

theoretischen Berechnungen und laserspektroskopischen Untersuchungen gewonnen werden. Aus dem 

Vergleich zu auf definierten Oberflächen massenselektiv deponierten Clustern können Informationen über den 

Einfluß des Trägers auf die katalytische Aktivität gewonnen werden. Besondere Aufmerksamkeit gilt dem 

Einfluß der elektronischen Struktur der Cluster auf die Reaktivität und der Modifikation der elektronischen 

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Struktur durch den Kontakt mit verschiedenen Substraten. 


Einfluss der Brechzahl des dielektrischen Substrats auf die optischen Eigenschaften einzelner 

Goldnanopartikel 

•Katharina Schätzler, Benjamin Schmidt, Christian Dahmen und Gero von Plessen 

I. Physikalisches Institut (IA), RWTH Aachen 

In Berechnungen auf dem Gebiet der optischen Eigenschaften von Metallnanopartikeln wird die inhomogene 

dielektrische Umgebung des Partikels oft durch einfache Mittelwertbildung über die Umgebungsbrechzahlen 

berücksichtigt. In unserer Arbeit wird der Einfluss der Brechzahl des dielektrischen Substrats auf die optischen 

Eigenschaften sphärischer Goldnanopartikel mit Hilfe der Dunkelfeld-Mikroskopie sowie -Spektroskopie 

untersucht. Diese Methode macht es möglich, einzelne Nanopartikel zu spektroskopieren und so inhomogene 

Verbreiterungseffekte zu vermeiden. 


Optische Eigenschaften kleiner Aggregate aus Goldnanopartikeln 

•Benjamin Schmidt, Katharina Schätzler, Christian Dahmen und Gero von Plessen 

I.Physikalisches Institut A, RWTH Aachen 

Liegen Edelmetall-Nanopartikel nah genug beieinander, um elektromagnetisch miteinander zu koppeln, bilden 

sich ausgedehnte Plasmonen-Moden aus. Hier untersuchen wir mit Dunkelfeldmikroskopie kleine Aggregate aus 

gekoppelten, kugelförmigen Goldnanopartikeln, insbesondere Partikelpaare. Um eine Korrelation der 

Aggregat-Topographie und der optischen Eigenschaften herzustellen und um inhomogene Verbreiterungseffekte 

zu vermeiden, wird polarisationsselektive Spektroskopie an einzelnen Aggregaten durchgeführt. Die nötigen 

topographischen Informationen werden aus elektronenmikroskopischen Aufnahmen gewonnen. Die 

experimentellen Ergebnisse werden mit Resultaten aus der Verallgemeinerten Mie-Theorie verglichen, und es 

wird der Versuch unternommen, die Beiträge bestimmter Moden zu den Spektren zu identifizieren. 


Homogeneous linewidth of gold nanoshells 

•S. Brogl, G. Raschke, A. Susha, A. L. Rogach, T. A. Klar und J. Feldmann 

Photonics and Optoelectronics Group, Physics Department and CeNS, University of Munich, Amalienstr. 54, 

D-80799 Munich, Germany 

Nanoshells composed of a few nanometer thin gold layer coated on Au 2 S nanoparticles show a pronounced 

resonance in their scattering spectra for visible light. Similar to solid noble metal nanoparticles the origin of the 

resonance is a collective oscillation of the conduction band electrons, which is known as the nanoparticle 

plasmon (NPP). The NPP resonance position of a gold nanoshell can be tuned over a large spectral range by 

varying the relative size of the nanoparticle core and the thickness of the gold shell. 

Experiments carried out on ensembles of nanoshells show a broad absorption linewidth (FWHM) of about 

600 meV. This is by far exceeding what is expected by Mie-theory calculations which yield a NPP resonance 

line width of less than 100 meV. We investigate this discrepancy by measuring the homogeneous scattering 

spectrum of a single gold nanoshell using dark field microscopy. The results show a homogeneous linewidth 

narrowed by 50% compared to ensemble measurements. This indicates that inhomogeneities e.g. distribution of 

shell thicknesses and/or core diameters are one important parameter for line broadening. 


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STM/STS on large silver clusters at germanium (001) 

•Karl-Ludwig Jonas, Armin Kleibert, Fanny Geisler, Ralf-Peter Methling, Joachim Bansmann, Viola von 

Oeynhausen und Karl Heinz Meiwes-Broer 

Fachbereich Physik, Universität Rostock, Universitätsplatz 3, D-18051 Rostock 

Cluster deposition is used to create metal-nanodots with a high aspect ratio. We present scanning tunneling 

spectroscopy (STS) measurements on isolated silver clusters at germanium (001). The clusters are generated 

using an arc cluster ion source (ACIS), mass selected and deposited under soft landing conditions (E kin /atom < 

0.5eV). Before performing STM experiments the cluster structure has been investigated using TEM, electron 

diffraction and EDX. Particle diameters between 5 and 14 nm have been used for the present studies. Scanning 

tunnelling microscopy images of large clusters always contain considerable tip folding at the steep cluster edges. 

Beside the accurately measured cluster height the imaging of particles of this height is therefore restricted to 

cluster facets at the top. Using STM and STS on deposited silver clusters structural and electronic properties 

are observed. In contrast to silver islands grown on germanium (001) the orientation of the crystal lattice is not 

fixed if cluster melting is neglected. However, some of the clusters show hexagonal facets at the top. STS is 

sensitive to occupied and unoccupied states near the Fermi level and reveals the existence of distinct states in 

the tunneling conductivity of the substrate as well as on the clusters. Thus, the richly structured density of 

states of the germanium (001) surface has been discovered and serves as STM/STS condition test. 


Application of the variable phase theory to the systems with quasistationary states. 

•Oleg Kidun 1 , Jamal Berakdar 1 und Natasha Fominykh 2 

1 Max-Planck Institut fuer Mikrostrukturphysik, Halle, Germany 

2 Institute of Physics, St. Petersburg State University, St. Petersburg, Russia 

We develop a method of investigation of the quasistationary (QS) states of different physical systems based on 

the variable phase approach [1-3]. We consider the modification of the physical properties of the QS states 

(energy position and resonance width) under the spatial transformation of the potential field as well as its 

asymptotical behavior. The role of the possible nonlocality of the potential in the observability of the QS states is 

also estimated. The realization of our approach in the studies of molecules and nanostructures is discussed. 

[1] F. Calogero, Variable Phase Approach in Potential Scattering, AP, NY (1967) 

[2] V. Babikov, Method of the Phase Functions in Quantum Mechanics, Nauka, Moscow (1969) 

[3] O. Kidun, N. Fominykh, J. Berakdar, J. Phys. A 35, 9413 (2001) 


Electron dynamics of buried interface states in Ar/Cu(100) probed by time-resolved two-photon 

photoemission 

•M. Rohleder, W. Berthold, K. Duncker, J. Güdde und U. Höfer 

Fachbereich Physik und Zentrum für Materialwissenschaften, Philipps-Universtät, D-35032 Marburg 

We demonstrate for the system Ar/Cu(100) how in favourable cases the dynamics of electronic states located at 

the interface between a metal and an insulator can be investigated by means of time-resolved two-photon 

photoemission (2PPE). The interface states of Ar/Cu are located above the vacuum level in the band gaps of 

both the Cu(100) surface and the Ar films which were as thick as 70 monolayers (ML). With increasing layer 

thickness the states evolve from quantum-well-like resonances into well-defined bound states which arise from 

the screened image-potential of the metal. Electrons excited into these states decay on timescales between 

100 fs and 250 fs by electron-hole pair excitation in the metal and - for thin Ar layers ( < 20-30 ML) - also by 

electron transfer through the insulating Ar layers into the vacuum. In comparison to the image-potential states of 

the clean surface, the interface states are modified by the potential inside the dielectric layers. Screening reduces 

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their binding energies with respect to the Ar conduction band and also results in longer lifetimes. The dispersion 

of the states is found to be parabolic near the band minimum with an effective mass of 0.5 m e . 


Zeit- und energieaufgelöste Untersuchungen des Transports optisch angeregter Elektronen in 

Metall-Isolator-Metall-Kontakten 

•Sven Schramm 1 , Johannes Schneider 1 , Walter Pfeiffer 1 und Detlef Diesing 2 

1 Physikalisches Institut Universität Würzburg, Experimentelle Physik 1, 97074 Würzburg 

2 Institut für Schichten und Grenzflächen, Forschungszentrum Jülich, 52425 Jülich 

Metall-Isolator-Metallkontakte (MIM) bestehen aus zwei Metallelektroden die durch eine dünne Oxidschicht 

getrennt sind (Ta-TaO-Ag, Al-Al 2 O 3 -Ag). Sie bilden ein Modellsystem zur Untersuchung des lichtinduzierten 

Elektronentransports durch die Oxid-Barriere. Aufgrund der starken Zunahme der Transmission der 

Tunnelbarriere für optisch angeregte Ladungsträger werden diese nach Anregung mit ultrakurzen Lichtimpulsen 

als kurzer Elektronenpuls in die Gegenelektrode injiziert. Aufgrund der inhomogenen Anregung kommt es zu 

einem resultierenden Photostrom. Ausgehend von den bislang durchgeführten Photostrommessungen [1] wird 

dieser Injektionsvorgang nun auch energieaufgelöst untersucht. Hierzu werden in der Rückelektrode des 

Kontaktes Elektronen mit einem ultrakurzen Lichtimpuls angeregt und dann durch zeitkorrelierte Photoemission 

in der Deckelektrode nachgewiesen. Der Nachweis des Injektionstromes hängt stark von den 

Anregungsbedingungen und den Barriereneigenschaften ab. 

[1] Thon et al., Appl.Phys. A 78 (2004) 189 


Time development of electronic excitations of CO on MgO(001) 

•N.-P. Wang 1 , M. Rohlfing 2 , P. Krüger 1 und J. Pollmann 1 

1 Institut für Festkörpertheorie, Universität Münster, Wilhelm-Klemm-Str. 10, 48149 Münster 

2 School of Engineering and Science, International University Bremen, P.O. Box 750761, 28725 Bremen 

Femtosecond laser excitation is a very useful tool for acquiring important knowledge about the short-time 

dynamics of surface excitations. In this context the fundamental question arises how fast an initially localized 

excitation, which is not an eigenstate of the surface system but rather defines the 'initial value' of the 

time-dependent Schrödinger equation, develops in space and time. Here the dependence of the time decay on the 

initial molecular excitation and the electronic spectrum of the substrate surface is of particular interest. We have 

studied therefore the dynamics of electronic excitations in a CO adlayer on MgO(001)-(1×1) from first 

principles. One-particle excitations of the ground state, described within DFT-LDA, are calculated employing 

the GW approximation. Two-particle excitations and their optical spectrum are obtained solving the 

Bethe-Salpeter equation including electron-hole interaction. The time evolution of the molecular excitation is then 

determined from the time-dependent Schrödinger equation. An initial CO exciton state is found to decay 

exponentially within two femto-seconds after coupling the adlayer to the substrate. This is due to a resonance 

with charge-transfer excitations between the substrate and the adlayer. Interestingly, the decay of the molecular 

exciton is an order of magnitude faster than the decay of single-particle states. 


Ultrafast energy relaxation and transport effects in photoexcited metals and metallic thin films 

•Panagiotis Loukakos, Martin Lisowski, Uwe Bovensiepen, Julia Stähler, Cornelius Gahl und Martin Wolf 

Fachbereich Physik, Freie Universität Berlin, Arnimallee 14, 14195 Berlin 

Time-resolved two-photon-photoemission spectroscopy is used to study the femtosecond dynamics of 

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photoexcited electrons in bulk Ru(001), Cu(111) and thin Cu(111) films epitaxially grown on Si(111)-7x7. After 

excitation with photon energies of 1.5-2.4 eV the time evolution of the non-equilibrium electron population in the 

vicinity of the Fermi level is probed by a time-delayed UV pulse. For Cu film thicknesses between 6 nm to 44 

nm we find that the electron relaxation rates increase monotonically with film thickness, which is attributed to 

electron transport out of the probe depth into the bulk. For the electron dynamics at the Ru(001) surface we 

observe an unexpectedly fast energy dissipation resulting in a decreased temperature at the surface with respect 

to predictions of the two-temperature model. We attribute this to the influence of the non-thermal electron 

distribution. With the aid of numerical calculations we propose an increased (ballistic) transport of 

non-thermalized electrons and a decreased electron-phonon coupling at the surface to account for the efficient 

energy dissipation into the bulk. 


Space Charge Effects during Ultrashort Laser Pulse Photoemission Electron Microscopy 

•D. Thien, M. Horn-von Hoegen, O. Heinz, P. Zhou, D. von der Linde und F.-J. Meyer zu Heringdorf 

Institut für Laser und Plasmaphysik, Universität Duisburg-Essen (Campus Essen), 45117 Essen 

Visualization of the dynamics of electronic states in mesoscopic structures requires the simultaneous application 

of 3 different tools: Ultrashort fs-laser pulses offer time resolution, spectroscopy allows separation of different 

excited electronic states and Photoemission Electron Microscopy (PEEM) provides the crucial possibility to 

study surface areas on the nanoscale. We are currently combining an amplified Ti:Sapphire laser system (40fs 

pulses at 1kHz repetition rate), and a PEEM with imaging energy filter (ELMITEC) into a novel pump-probe 

experiment. While our laser oscillator (20fs, 80MHz) typically images excited electronic states via 2 Photon 

Photoemission, the amplifier system provides a greatly improved intensity of more than 10 15 W/cm 2 and opens 

the door for frequency conversion and photoemission experiments with photon energies of more than 30eV. 

The intense ultrashort pulses confine a great number of photoemitted electrons into a small area resulting in 

coulomb interaction. Here we analyze these space-charge effects using frequency doubled laser pulses on 

patterned in-situ grown low-workfunction Cs-layers on Si and SiO 2 substrates. At high photon flux we observe 

that the edges of our Cs-pads appear blurred. Subsequent reduction of the laser peak power leads to sharper 

edges as are also observed when the 80MHz oscillator is used for illumination. 


Time-of-Flight Two-Photon Photoemission Spectromicroscopy of Noble metal cluster films with 

Femtosecond Laser Radiation. 

•M. Cinchetti, A. Gloskovskii, D. A. Valdaitsev, S. A. Nepijko und G. Schönhense 

Johannes Gutenberg-Universität, Institut für Physik, 55099 Mainz, Deutschland 

Time-of-Flight Two-Photon Photoemission Spectromicroscopy [1] was used to investigate the photoemission 

properties of some Nobel metal surfaces under femtosecond laser irradiation (photon energy 3.1 eV, pulse width 

< 200 fs, laser fluence 6.4 µJcm -2 ).In particular, we present the results of investigations of Cu surface 

inhomogeneities and Ag nanoparticle films deposited on a Si(111) substrate. The photoemission yield resulted to 

be enhanced in presence of surface inhomogeneities with dimensions in the nanometer range. The energy 

distribution curves obtained from regions characterized by a strongly enhanced photoemission yield are shown 

to have the same qualitative behaviour. They differ significantly from the energy distribution curves from the 

homogeneous and clean metal surfaces. The differences are explained in terms of (i) a reduction of surface 

potential barrier connected with the appearance of local fields between the nanoparticles and the substrate; (ii) 

the excitation of Localized Surface Plasmons in the nanoparticles and the consequent modification of the near 

field [2], that influences the photoemission. [1] M. Cinchetti, A. Oelsner, G. H. Fecher, H. J. Elmers, and 

G.Schönhense, Appl. Phys. Lett. 83, 1503 (2003). [2] V.M. Shalaev, C. Douketis, T. Haslett, T. Stuckless, and 

M. Moskovitis, Phys. Rev. B 53, 11193 (1996). 


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Time-Resolved Photoemission Electron Microscopy at nanostructured surfaces 

•Carsten Wiemann, Michael Bauer, Michael Munzinger, Daniela Bayer und Martin Aeschlimann 

TU Kaiserslautern 

TR-2PPE (Time-Resolved 2-Photon-Photoemission) is a well-established technique to investigate electron 

dynamics at surfaces on a femtosecond time-scale. A combination of TR-2PPE with a spatially resolving 

electron detection scheme such as Photoemission Electron Microscopy (PEEM) allows in addition to analyze the 

precise local origin of the emitted electrons. In this way a 'lifetime mapping' of heterogeneous samples is - in 

principle - possible. [O. Schmidt et al. Appl. Phys. B 74 (2002) 223-227] Recent time-resolved PEEM results on 

nanostructured surfaces demonstrating the capabilities and limits of this setup in extending time-resolved 

spectroscopy to the nanoscale will be presented. 


Surface Recombination Dynamics of SiO2/Si(100) - A Combined Laser and Synchro Radiation Study 

•David Bröcker 1 , Tatjana Gießel 1 und Wolf Widdra 2 

1 Max-Born-Institut, Max-Born-Strasse 2a, 12489 Berlin 

2 Martin-Lutter-Universtität Halle-Wittenberg, Fachbereich Physik, Fachgruppe Experimentelle Physik III 

The charge carrier dynamics at the silicon surface has been studies by probing the surface photovoltage. Upon 

excitation of electron hole pairs in the surface-near region by picosecond laser pulses, the dynamics of the 

charge carrier recombination has been determined by time-resolved Si 2p core level photoemission. We 

compared several sample preparations, the clean Si(100) surface, the hydrogen monohydride, and thin oxide 

layers. The decay process could be described by a model based on thermionic emission. The influence of the 

laser fluence and the temperature on the decay process has been studied in detail. 


X-ray longitudinal Kerr rotation and ellipticity spectra measured at the 2p edges of Fe, Co, and Ni 

•Sergio Valencia 1 , Hans-Christoph Mertins 1 , Peter M. Oppeneer 2 , Dirk Abramsohn 1 , Andreas Gaupp 1 und 

Wolfgang Gudat 1 

1 BESSY, Berlin 

2 IFW Dresden 

The first measurements of the X-ray longitudinal magneto-optical Kerr effect (L-MOKE) at the 2p absorption 

edges of amorphous Fe, Co, and Ni films are reported. The L-MOKE rotation and ellipticity spectra are 

recorded by a complete polarization analysis of the X-rays reflected from the ferromagnetic surface. At the 

edges large Kerr rotations of up to ?24 ? are detected, which are more than two orders of magnitude larger than 

those in the visible energy range. Using a numerical simulation package based on the magneto-optical refractive 

indices, the spectral contributions stemming from magneto-optically active atomic transitions could be seperated 

from layer interference effects. Both theoretically and experimentally it is shown that at grazing incidence the 

longitudinal Kerr rotation and Kerr ellipticity are proportional to the transversal MOKE and the XMCD reflection 

spectrum, respectively. 


Magnetische Röntgenstreuung an lateralen Strukturen 

•Arndt Remhof, Johannes Grabis, Alexei Nefedov, Erik Verduijn und Hartmut Zabel 

Experimentalphysik/Festkörperphysik, Ruhr-Univeristät Bochum, 44780 Bochum 

Nano- und Mikrostrukturierung von dünnen magnetischen Systemen ermöglicht das 

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Ummagnetisierungsverhalten, d. h. die Hystereseschleife, gezielt zu verändern. Wir haben ein quadratisches 

Muster aus Co/CoO Inseln mittels Elektronenstrahl-Lithographie hergestellt. Die Inseln haben einen 

Durchmesser von 1mm und eine Periode von 2,5 mm. Die magnetische Hysterese wurde mit Bragg-MOKE und 

mit resonanter magnetischer Röntgenstreuung (XRMS) an der Co L 2,3 bei verschiedener Ordnung der 

Interferenz bestimmt. Bragg-MOKE liefert eine Fourieranalyse des Magnetisierungsprofils während des 

Ummagnetisierungsprozesses. Analog dazu liefern auch Hysteresen, die mit XRMS an verschiedenen Ordnungen 

von Bragg-Reflexen gemessen werden, eine Fourieranalyse der Ummagnetisierung. Im Vergleich zu 

Bragg-MOKE zeichnet sich XRMS durch Elementspezifität und durch höhere Eindringtiefen aus. Wir 

präsentieren erste Ergebnisse, die mit Bragg-MOKE und XRMS an strukturierten Co/CoO Proben gewonnen 

wurden, und vergleichen die Ergebnisse. 

Gefördert durch SFB 491. 


Faraday rotation spectrum at shallow core levels: 3p edges of Fe, Co, and Ni 

•Sergio Valencia 1 , Hans-Christoph Mertins 2 , Peter M. Oppeneer 3 , Dirk Abramsohn 1 , Andreas Gaupp 1 , Claus M. 

Schneider 4 und Wolfgang Gudat 1 

2 FH Münster 


4 IFF, FZ Jülich 

1 BESSY, Berlin 

We report measurements of the Faraday effect at the 3p edges of thin Fe, Co, and Ni films. The Faraday 

rotation and ellipticity are determined by a complete polarization analysis of the synchrotron radiation transmitted 

across the samples. Surprisingly, the rotation constants k attain large values comparable to those observed at the 

2p edges. Maximal rotation constants of 2.2 ·10 5 , 1.5 ·10 5 , and 0.8 ·10 5 deg/mm are found for Fe, Co, and Ni, 

respectively. While at the 2p edges the spin-orbit splitting of the 2p levels is considered to be mainly responsible 

for the magneto-optical effects, the unexpected similarity underlines the role of the exchange-splitting of the 3p 

core levels in the extreme ultra-violet region (EUV). A full set of optical and magneto-optical constants, which 

were determined from the measured rotation and ellipticity, are presented for the three elements in the energy 

range of the 3p edges. 


Anomalous ferromagnetism of monatomic Co wire at the Pt(111) surface step edge 

•Peter M. Oppeneer 1 , Alexander B. Shick 2 und Frantiek Máca 2 


2 Inst. of Physics, ASCR, Prague 

We report a first-principles investigation of the anomalous ferromagnetism of a quasi-one-dimensional Co chain 

decorating the Pt(111) step edge. Our calculations demonstrate that the symmetry breaking at the Pt step leads 

to an easy magnetization axis at an anomalous angle of ∼ 20 ? towards the Pt step, in semi-quantitative agreement 

with the experimentally observed peculiar easy axis at an angle of ∼ 40 ? [P. Gambardella et al., Nature 416, 301 

(2002)]. The computed hard magnetization axis direction also corresponds well to the experimentally observed 

hard axis. A (T = 0) magnetocrystalline anisotropy energy of 3 meV/Co is calculated in good agreement with the 

experimental value of ∼ 2 meV/Co at T = 45 K. On account of the symmetry breaking the Co spin and orbital 

moments become noncollinear, even in the case of a collinear ferromagnetic spin arrangement. We also 

performed LSDA+U calculations, with which a significant enhancement of the Co orbital magnetic moment is 

achieved already when modest electron correlations (small U) are taken into account. 


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Transverse magneto-optical Kerr effect at the 3p edges of Fe and Co 

•Armin Kleibert 1 , Sergio Valencia 2 , Hans-Christoph Mertins 2 und Joachim Bansmann 1 

1 Universität Rostock, Fachbereich Physik, Universitätsplatz 3, 18051 Rostock 

2 BESSY GmbH, Albert-Einstein-Str. 15, 12489 Berlin, Germany 

Soft x-ray based experimental techniques are powerful and very sensitive methods to investigate the magnetism 

of systems with low dimensions like ultrathin films or clusters, respectively. In particular, the magneto-optical 

Kerr-effect (MOKE) at the 2p edges of Fe, Co, and Ni has attracted much attention. In the transverse geometry 

(T-MOKE) huge intensity changes in the resonantly enhanced reflectivity upon reversal of the magnetization 

direction have been found. While effects near the 2p core levels were extensively studied in the last years, only a 

few experiments were reported concerning the vicinity of the 3p threshold. 

In this contribution, we present angular dependent measurements of the T-MOKE in the energy range of the 3p 

edges of thin Fe and Co films, respectively, revealing surprisingly large asymmetries up to 40% near the 

Brewster angle. From these reflectivity measurements it is possible to obtain information about the energy 

dependent refractive indices and magneto-optical Voigt constants. In order to simulate the measured reflectivity 

including the influence of capping layers we applied a multilayer formalism describing magneto-optics. A good 

agreement of calculation and experiment was achieved using tabulated values of the index of refraction and 

independently obtained Voigt constants. 


Resonant X-Ray scattering from TbBaCo 2 O 5.5 

•N.V. Kasper 1 , P. Wochner 1 , G. Carbone 1 , A. Vigliante 2 , D. Mannix 3 und G. Jakob 4 

4 Institut für Physik, Universität Mainz, Mainz, Germany 

1 Max-Planck-Institut für Metallforschung, Stuttgart, Germany 

2 Bruker AXS, Karlsruhe, Germany 

3 European Synchrotron Radiation Facility, Grenoble, France 

Resonant X-ray scattering at the Co K-edge from epitaxial films and single crystals of TbBaCo 2 O 5.5 cobaltite 

with perovskite structure has been studied in insulating and metallic states. Polarization, energy and azimuthal 

dependences of the intensity of (016), (116), and (310) Bragg peaks were measured. Strong oscillations of the 

resonantly scattered intensity were observed both in σ' and π' channels. The scattered signal changes very 

weakly during the metal-insulator phase transition. 

The azimuthal oscillations of the scattered signal are attributed to the tensor character of the anomalous 

scattering factor of Co. Using this concept we have developed a model, describing very well the measured 

azimuthal oscillations. On the basis of the obtained experimental results and literature data it is argued that this 

anisotropy of the anomalous scattering factor of Co is caused mainly by distortions of the local surrounding of 

cobalt ions and not by anisotropies due to ordering of electronic orbitals of Co. 


X-ray magneto-optical sum rules in small Co clusters 

•Kai Fauth 1,2 , Markus Heßler 1,2 und Gisela Schütz 2 

1 Physikalisches Institut der Universität Würzburg, Am Hubland, 97074 Würzburg 

2 MPI für Metallforschung, Heisenbergstraße 3, 70569 Stuttgart 

The so-called spin and orbital sum rules [1,2] in x-ray magnetic circular dichroism (XMCD) spectroscopy are 

often believed to apply with reasonable accuracy in the case of the late 3d transition metals and their 

compounds, if the magnetic dipole term T z can be neglected. Strong deviations can occur due to symmetry 

breaking such as given at surfaces, causing the magnetic dipole term to contribute significantly to the spin sum 

30 of 32 07.06.2009 22:14



rule, while not contributing to the magnetization. Much less is known in the case of small clusters. We have 

derived magnetic moments of superparamagnetic Co 55 clusters from XMCD at various applied magnetic fields. 

We find that the moments thus obtained from the magnetization curve and those determined separately from the 

sum rules agree to within 10%. This result sets an upper limit for the importance of T z in these clusters. 

[1] B. T. Thole et al. , Phys. Rev. Lett. 68, 1943 (1992) 

[2] P. Carra et al. , Phys. Rev. Lett. 70, 694 (1993) 


X-ray resonant magnetic scattering of Fe/Cr superlattices 

•Alexei Nefedov, Johannes Grabis, Andre Bergmann, Florin Radu und Hartmut Zabel 

Institut für Experimentalphysik/Festkörperphysik, Ruhr-Universität Bochum, D-44780 Bochum, Germany 

We have studied the magnetic and structural properties of an antiferromagnetically (AF) coupled Fe/Cr(001) 

superlattice by soft X-ray resonant magnetic scattering. Strong magnetic Bragg peaks are observed at the half 

order positions in reciprocal space parallel to the [001] growth direction and in between the structural Bragg 

reflections from the superlattice periodicity. The magnetic hysteresis loops measured at the structural Bragg 

peak and at the half-order peak clearly demonstrate the AF coupling of the Fe/Cr multilayer. Transverse scans 

and off-specular reflectivity measurements confirm an AF domain structure of the superlattice in remanence 

with large perpendicular correlation. In addition, the transverse scan of the half-order Bragg peak exhibits a 

Lorentzian line shape at zero field, which diminishes in higher fields, indicative for a remanent multidomain state 

which approaches a single domain state towards saturation. 

This work was supported by the German Federal Ministry of Education and Research (BMBF) under Contract 

No.03ZAE7BO. 


Inducing spin crossover in metallo-supramolecular polyelectrolytes through an amphiphilic phase 

transition 

•Yves Bodenthin 1 , U. Pietsch 1 , D. Kurth 2 und H. Möhwald 2 

1 University of Potsdam, Institute of Physics, Am Neuen Palais 10, 14469 Potsdam, Germany 

2 MPI-KG Golm, Am Mühlenberg 1, 14476 Potsdam-Golm 

In the last years resonant magnetic X-ray reflectivity experiments (XMCD) become important for the 

investigation of molecular magnetism in thin films. 

In the present work we report a novel approach to affect spin crossover by introducing mechanical strain 

through an amphiphilic phase transition in a metallo-supramolecular polyelectrolyte-amphiphile complex (PAC). 

The investigated system consists of thin layers deposited in Y-conformation on a silicon substrate by means of 

Langmuir-Blodgett technique. 

It was observed by EXAFS, x-ray reflectivity and in-plane diffraction experiments that the structural phase 

transition in the amphiphilic mesophase is responsible for the distortion of the coordination geometry of the 

tightly coupled transition metal centres. Consequently, the energetic separation of the subsets of the iron 

d-orbitals changes and gives rise to spin crossover. Using temperature resolved SQUID and XMCD 

measurements we observe a diamagnetic to paramagnetic phase transition above room temperature which is 

connected to a structural phase transition between two liquid crystalline phases. 

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