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MM: Fachverband Metall- und Materialphysik

MM 22: Topical Session TEM VI

MM 22.5: Vortrag

Mittwoch, 16. März 2011, 12:30–12:45, IFW B

Optimization of STEM Tomography Acquisition - A Comparison of Convergent Beam and Parallel Beam STEM Tomography — •Johannes Biskupek, Jens Leschner, Paul Walther, and Ute Kaiser — Central Facility of Electron Microscopy, Ulm University, Ulm, Germany

In this work two imaging modes available in state-of-the-art scanning transmission electron microscopes (STEM) are compared: conventional STEM with a convergent beam (nanoprobe) and STEM with a parallel beam (microprobe). The effect and influence of both modes with respect to their depth of field are investigated using standard gold cross grating TEM samples. It will be shown that microprobe posses a large depth of field (up to +/-30 micron), thus, all features are kept in focus even at high tilt without the necessity to apply specimen topology-dependent dynamic focus. A decrease of measured FWHM of gold beads at high tilt by a factor of three shows a gain in resolution by microprobe STEM and the advantage over conventional nanoprobe STEM imaging. Test tomograms are acquired, aligned, reconstructed, and evaluated using both modes. It is shown that STEM using the microprobe mode produces tomograms with fewer distortions and artifacts and allows resolving finer features. Microprobe STEM tomography is advantageous when semi thin TEM samples (ca. 500 nm thick) are imaged at relatively low magnification with a large field of view (more than 3 by 3 micron).

We acknowledge the DFG for financial support within the collaborative research centre SFB 569 and the project KA 1295-7/1.