The Austrian Scanning Transmission Electron Microscope –
The Story Behind
Aberration correction in electron microscopy
Being able to see and analyse materials at atomic resolution, has been a strong motivation for improving the electron microscope. However, the resolution of the conventional transmission electron microscope (TEM) was limited to around 0.2 nanometre, which is slightly larger than the diameter of atoms. This limitation comes from the spherical aberrations of the magnetic lenses, which lead to a blurring of images. Although this deteriorating effect was already recognised 80 years ago, it was only in the late 1990s that the first spherical aberration corrector improved the resolution of the TEM. The following development of commercial aberration-corrected TEMs was a revolution for microscopy research and helped to solve many open questions in physics, chemistry and materials and biological sciences.
The challenge in Austria
Immediately after their commercial introduction in 2005 aberration corrected TEMs became the standard in high resolution electron microscopy. However, due to the high costs there was no realistic chance to establish such an advanced instrument in Austria. Finally, the Association for Electron Microscopy and Fine Structure Research succeeded in 2011 via a complicated project mixture, which was supported by several funding organisations (FFG, ACR & BMWFW, Land Steiermark, WKO-STMK) and the TU Graz. This breakthrough allowed us to build one of the best aberration corrected microscopes in the world – delivered by FEI Company (Eindhoven, The Netherlands) – the Titan cubed 60–300 (Austrian Scanning Transmission Electron Microscope = ASTEM).
The operation of the ASTEM
In order to exploit all the benefits of the new instrument we had to improve the quality of our specimen preparation and to deal with theoretical modelling of the experimental results. Firstly, it was necessary to introduce a new method for low-energy ion milling (Nanomill, Fischione). Secondly, the atomically resolved STEM-images had to be interpreted with the help of advanced simulation tools such as QSTEM (Christian Koch, Berlin, Germany) or µSTEM (Lesley Allen, Melbourne, Australia); collaborations in the field of first principles calculations have been started (R.C. Picu, Troy, USA).
The impact of the ASTEM
With the ASTEM the institute has become the leading research institution in the field of advanced materials microscopy in Austria. The ASTEM plays a major role in the research of the FoE Advanced Materials Science of the TU Graz and increasingly also for the NAWI faculty of the University of Graz and TU Graz. Indeed, it developed into a national resource with intensive collaborations with the Universities of Graz, Leoben, Linz and Innsbruck. Its impact on research collaborations with Austrian companies is manifold, particularly for semiconductor, ceramic and metal industries. Finally, it enabled the access to the leading European research network on advanced electron microscopy (ESTEEM2, FP7).
The future of the ASTEM
The ASTEM is surely a stable platform for the next years to come, nevertheless upgrades and extensions are mandatory. Presently, we are working on projects for funding the introduction of new methods such as magnetic and electric imaging via differential phase contrast and radically improved detectors for imaging and spectroscopy (direct electron detection).