Plenarvorträge - DPG-Tagungen

Oberflächenphysik Dienstag
able to demonstrate an optical resolution of 30 nm.
[1] A. Naber et al., Phys. Rev. Lett. 89, 210801 (2002).
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Energy dissipation in non-contact AFM — •Domenique Weiner,
Andre Schirmeisen, and Harald Fuchs — Physikalisches Institut
and CeNTech, University of Muenster, Wilhelm-Klemm-Str. 10, 48149
Muenster, Germany
The atomic force microscope (AFM) driven in the non-contact mode
offers the possibility to measure long-range and short-range forces. Furthermore,
energy dissipation mechanisms can be studied which are up
to now not well-understood and are subject of current research [1]. One
important step towards a better understanding of the energy dissipation
is to study the temperature dependence of the effect [2].
We measure the damping signal on a Au (111) surface which is prepared
under ultra-high vacuum (UHV) conditions by sputtering and annealing.
The commercial silicon cantilevers are covered with a PtIr-layer
of about 30 nm thickness to ensure the measurement of a true metal contact.
We use an UHV-VT-AFM (Omicron) which is integrated in a two
chamber-apparatus. We investigate the frequency shift and the damping
simultaneously as a function of tip-sample separation for different sample
temperatures. Therefore we are able to gain quantitative values of
the dissipation which are compared to current dissipation models like
van der Waals friction [1], electrical dissipation [3] or dissipation induced
by inhomogeneous tip-sample electric fields [2].
[1] Volokitin, Persson, Phys. Rev. Lett. 91, 06101, 2003
[2] B. C. Stipe, H. J. Mamin, T. D. Stowe, T. W. Kenny, D. Rugar,
Phys. Rev. Lett. 87, 096801, 2001.
[3] W. Denk, D. W. Pohl, Appl. Phys. Lett., Vol. 59, No. 17, 1991
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Local interfacial dipoles of alkali chloride thin films on Au(111)
investigated with Kelvin probe force microscopy — •Ulrich
Zerweck, Christian Loppacher, Stefan Grafström, and
Lukas M. Eng — Institute of Applied Photophysics, University of
Technology, D-01062 Dresden
Interface dipole formation of alkali chloride thin films on Au(111) is
investigated under ultrahigh vacuum conditions at room temperature by
noncontact atomic force microscopy in combination with Kelvin-probe
force microscopy (KPFM). Sample preparation is carried out in-situ and
optimized in order to achieve a sub-monolayer coverage on Au(111) with
extended alkali chloride islands.
The local surface potential for LiCl, NaCl, KCl, and RbCl thin films
on Au(111) was determined by KPFM, with the bare Au(111) substrate
serving as a reference. We thus directly probe the local and absolute
change in the work function ∆Φ which is found to vary linearly as a
function of the radius of the alkali ion. Furthermore, good agreement
was obtained when checking our KPFM measurements with ultraviolet
photoemission spectroscopy on a larger scale.
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Scattering-type near-field microscopy for optical nanoanalytics
— •Rainer Hillenbrand — Nano-Photonics Group, Max-Planck Institut
für Biochemie, 82152 Martinsried
We present a scattering-type scanning near-field optical microscope
(s-SNOM) that allows optical imaging at 10nm spatial resolution [1] independent
of the wavelength. In our s-SNOMs the tip apex of an atomic
force microscope (AFM) is illuminated either by a HeNe laser at 633nm
or a CO2 laser at about 10um wavelength. Interferometric detection [2]
of the scattered light allows us to visualize the optical eigenfield patterns
of 91 diameter, plasmon resonant nanoparticles at 633nm wavelength
[3]. When operating the microscope at mid-infrared frequencies we find
a strongly resonant near-field coupling between tip and a SiC sample
due to local excitation of phonon polaritons in SiC [4]. Such phononenhanced
near-field interaction is not only sensitive to the local chemical
composition but also to the local crystal structure of the surface and
thus allows besides chemical imaging also mapping of crystal quality at
nanoscale resolution. Altogether, we envisage optical nanospectroscopy
and imaging of physical, chemical and biological nanocomposites.
[1] R. Hillenbrand, F. Keilmann, Appl. Phys. Lett. 80, 25 (2002)
[2] R. Hillenbrand, F. Keilmann, Phys. Rev. Lett. 85, 3029 (2000)
[3] R. Hillenbrand et.al., Appl. Phys. Lett. 83, 368 (2003)
[4] R. Hillenbrand, T. Taubner, F. Keilmann, Nature 418, 159 (2002)
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NanoSAM: Instrument characterisation at ultimate SAM resolution
— •Jörg Westermann, Ulrich Roll, and Georg Schäfer
— OMICRON NanoTechnology GmbH, 65232 Taunusstein
During the last few years, we have developed a new electron source
as an excitation source for UHV applications such as low voltage SEM,
SAM / small spot Auger, cathodoluminescense and others (BMBF FKZ
13N7486/7). Finally, we now report about the first results in small spot
Auger and Scanning Auger Microscopy utilising this source. We present
images and spectra demonstrating the ultimate lateral resolution and
energy resolution of the setup on various samples. These include gold
nanoparticles on HOPG, silver islands on silicon, and semiconductor heterostructures.
Furthermore, we compare the achieved results with theoretical
calculations and Monte Carlo simulations at different beam energies.
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An Ultra High Vacuum Scanning Tunneling Microscope system
operating at 300 mK and 14 T — •Focko Meier 1 , Jens
Wiebe 1 , Andre Wachowiak 2 , Daniel Haude 1 , Markus Morgenstern
1 , and Roland Wiesendanger 1 — 1 Institute of Applied
Physics, Hamburg University, Jungiusstr. 11, D-20355 Hamburg, Germany
— 2 University of California at Berkeley, Department of Physics,
366 Le Conte Hall, 7300 Berkeley, CA 94720-7300, USA
For scanning tunneling spectroscopy (STS) on low dimensional electron
systems, an ultra high vacuum (UHV) scanning tunneling microscope
(STM) operating at T=300 mK and in magnetic fields up to B=14
T has been built up.
The STM sitting in a bakeable UHV-insert within the 3 He-cryostat
can be operated continuously for about 30 hours witout any refill of the
cryogenic liquid. It achieves a z-noise level below 5 pm. Using superconducting
tips and samples first experimental STS results show that the
energy resolution reached is close to the predicted theoretical limit of 75
µ V. For exchanging tips and samples the insert with STM can be moved
to a UHV chamber. Further connected UHV chambers contain different
equipment for tip and sample preparation and characterisation, i.e.
a RT-STM , a LEED/Auger system, several evaporators and a variable
temperature system to detect the magnetooptical Kerr-effect (MOKE).
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SPM goes video rate and beyond — •M.J. Rost, T.H. Oosterkamp,
J.W.M. Frenken, and et al. — Kamerlingh Onnes Laboratory,
Leiden University, P.O. Box 9504, 2300 RA Leiden
The low imaging rates of conventional scanning probe microscopes
(SPMs) makes these instruments impractical for many applications. We
have developed a novel, flexible SPM control system that can be easily
connected to any SPM, which allows up to 50 Hz imaging rates with 256
x 256 pixels per image. Since fast scanning is impossible without fast
feedback electronics, we have also developed a low-noise STM-feedback
system with a total bandwidth of 600 kHz (including the preamp). We
present high-speed STM movies (images) with 25 Hz frame rate and tip
speeds up to 0.3 mm/s while keeping atomic step resolution on Cu(001),
obtained with a conventional STM. With a new, compact scanner we
have even reached 200 Hz frame rate on graphite while still obtaining
atomic resolution.
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Apertureless SNOM with vibrating AFM probes — •Ralf Vogelgesang,
Ruben Esteban, Alpan Bek, and Klaus Kern — MPI
für Festkörperforschung, 70569 Stuttgart
In the so called apertureless Scanning Near Field Optical Microscopy
(a-SNOM), strongly localized enhancement of the near fields at the apex
of a conical tip probe excited by external radiation is used to achieve
spatial resolution of optical surface properties in the range ∼ 10 nm at
infrared or visible frequencies.
We use Multiple Multipole (MMP) simulations to quantitatively understand
the interaction between the tip and substrate. We study the
variations due to changing tip sample distance in the near field and consequently
in the scattered far field, i.e., the measurable physical magnitude.
For a better understanding of the level of sophistication necessary,
different models are considered, ranging from a point dipole in the static
case to spheres or a conical tip with spherical apex including retardation.
In general two different regions are observed, slowly varying field
strengths for distances of several hundred nm or more and rapid increases
in field strengths for less than 10 nm. This strongly nonlinear dependence