Plenarvorträge - DPG-Tagungen

Oberflächenphysik Mittwoch
O 28.42 Mi 16:00 Bereich C
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 H2- oder O2-Plasma erhält
man schließlich Nanoteilchen, deren Größe und Abstand durch die Polymerkettenlängen
bestimmt werden. Die Teilchen lassen sich auch noch
nachträglich in einer HAuCl4/NH2OH-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.
O 28.43 Mi 16:00 Bereich C
Nanostructures as a result of the thermal instability of metal
thin films on insulators — •Torsten Kolb, Dominik Enders,
Annemarie Pucci, and 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, SiO2) 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 exsitu
by atomic force microscopy (AFM). The dependence of the resulting
morphology on annealing temperature and crystalline structure will be
demonstrated.
O 28.44 Mi 16:00 Bereich C
Metal-on-insulator nanostructures via surface color centers —
•Svend Vagt, Tammo Block, Volkmar Zielasek, and 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.
O 28.45 Mi 16:00 Bereich C
Pb on Si(557) - Steps towards a one-dimensional conductivity
— •Ziad Kallassy, Martin Henzler, Heinz-Lorenz Günter, and
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.
O 28.46 Mi 16:00 Bereich C
Dependency of the scattering of light by small planar particles
on the direction of incidence and polarization — •Manuel
Gonçalves and Othmar Marti — Department of Experimental
Physics, University of Ulm, D-89069 Ulm, Germany
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.
O 28.47 Mi 16:00 Bereich C
Self-imaging observed on colloid crystals and Fischer projection
patterns — •Manuel Gonçalves and 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
dT = ν 2d 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.
O 28.48 Mi 16:00 Bereich C
Plasma CVD-grown carbon nanotubes studied by field emission
— •Daniell Malsch 1 , Martin Sveningsson 2 , Eleanor Campbell
2 , and 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.