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Preliminary Results from the First Monochromated and Aberration Corrected 200-kV Field-Emission Scanning Transmission Electron Microscope

Published online by Cambridge University Press:  11 October 2006

Thomas Walther  and
Heiko Stegmann
Thomas Walther
Affiliation:
Center of Advanced European Studies and Research (caesar), Electron Microscopy Group, Ludwig-Erhard-Allee 2, D-53175 Bonn, Germany
Heiko Stegmann
Affiliation:
Carl Zeiss Nano Technology Systems GmbH, Carl-Zeiss-Str. 56, D-73447 Oberkochen, Germany
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Abstract

Experimental results from the first monochromated and aberration-corrected scanning transmission electron microscope operated at 200 kV are described. The formation of an electron probe with a diameter of less than 0.2 nm at an energy width significantly under 0.3 eV and its planned application to the chemical analysis of nanometer-scale structures in materials science are described. Both energy and spatial resolution will benefit from this: The monochromator improves the energy resolution for studies of energy loss near edge structures. The Cs corrector allows formation of either a smaller probe for a given beam current or yields, at fixed probe size, an enhanced beam current density using a larger condenser aperture. We also point out another advantage of the combination of both components: Increasing the convergence angle by using larger condenser apertures in an aberration-corrected instrument will enlarge the undesirable chromatic focus spread. This in turn influences spatial resolution. The effect of polychromatic probe tails is proportional to the product of convergence angle, chromatic aberration constant, and energy spread. It can thus be compensated for in our new instrument by decreasing the energy width by the same factor as the beam convergence is increased to form a more intense probe. An alternative in future developments might be hardware correction of the chromatic aberration, which could eliminate the chromatic probe spread completely.

Keywords

scanning transmission electron microscopy (STEM)monochromatorspherical aberrationCs correctorchromatic focus spreadannular dark field (ADF) imagingelectron energy-loss spectroscopy (EELS)
Type
Research Article
Information
Microscopy and Microanalysis , Volume 12 , Issue 6: Special Issue: Frontiers of Electron Microscopy in Materials Science , December 2006 , pp. 498 - 505
Copyright
© 2006 Microscopy Society of America

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