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Mikroskopie und Tomographie Vortrag: Mi., 11:50–12:10 M-V3
SMART - an aberration corrected spectromicroscope for surface characterization
with high resolution
Th. Schmidt 1 , F. Maier 1 , U. Groh 1 , E. Umbach 1 , H. Marchetto 2 , P.
Lévesque 2 , T. Skàla 2 , H.-J. Freund 2 , R. Fink 3 , SMART Collaboration 4
1 Exp. Physik 2, Uni Würzburg – 2 Fritz-Haber-Institut, Berlin – 3 Phys. Chemie 2, Uni
Erlangen – 4 U Wü, FHI, U Erl., TU Darmstadt, TU Clausthal, Carl Zeiss NTS GmbH
With the availability of high flux beamlines at third-generation synchrotron radiation
sources spectromicroscopy has developed into one of the most promising techniques.
Combining high-brilliance synchrotron radiation with a parallel imaging LEEM (low
energy electron microscope) or PEEM (photoemission electron microscope) allows a
comprehensive characterization of surfaces, adsorbates, and ultrathin films. One of the
most challenging projects in this field is the SMART [1] (Spectro-Microscope with
Aberration correction for Resolution and Transmission enhancement), aiming at a lateral
resolution of 2 nm and an energy resolution of 100 meV which can only be achieved
by aberration correction and energy filtering. Regarding aberration correction pioneering
work has been done: the tetrode mirror [2] is the first and only working aberration
corrector which simultaneously compensates for both, the spherical and chromatic aberrations
of the electron lens system. The quality of our magnetic OMEGA filter - a
second-order aberration-corrected energy filter - is demonstrated by the absolute energy
resolution of 100 meV at a pass energy of 15 keV, yielding in an unusual resolving
power of 150.000. Utilizing different sources (linearly or circularly polarized x-rays,
UV-light, electron gun, etc.) the SMART excels as a versatile instrument with a variety
of contrast mechanisms by imaging photoemitted (XPEEM, UV-PEEM) and reflected
electrons (LEEM, MEM). Thus it enables the spatially resolved study of morphology,
chemical distribution, electronic state, molecular orientation, magnetization, work
function, structural properties, atomic steps, etc. Within seconds the instrument can be
switched from microscopy to two further methods [3]: (a) laterally resolved spectroscopy
from small object areas with the size of the lateral resolution (nano-XPS, nano-AES,
nano-NEXAFS, etc.) and (b) laterally resolved and energy filtered imaging of angular
distributions: nano-PED (Photoelectron diffraction), Fermi surface/valence band
mapping, LEED (low energy electron diffraction), etc. This variety of complementary
probing tools enables a comprehensive characterization of, e.g., deposited nano-objects,
nano-structured surfaces, and due to the possibility of real-time observation of processes
like crystal growth, chemical surface reactions, and surface phase transitions.
First experiments on the growth properties of organic thin films, their dependence on
the substrate, and the internal structure of microcrystallites of organic molecules show
the potential of the instrument and will be briefly presented in the talk.
Project funded by the BMBF, contract 05 KS4 WWB/4; [1] R. Fink et al., J. Electr.
Spectrosc. 84 (1997) 231; [2] D. Preikszas, H. Rose, J. Electr. Micr. 1 (1997) 1; [3] Th.
Schmidt et al., Surf. Rev. Lett. 9 (2002) 223.