It is over four metres high, weighs tons and fills an entire room: the aberration-corrected low-voltage transmission electron microscope offers novel insights into the atomic-scale world of matter and is the first of its kind. This new development successfully concludes the seven-year-long SALVE-Projekt project.
SALVE stands for Sub-Ångström Low-Voltage Electron microscopy and is the name of a research initiative that was launched in 2009 at Ulm University with the purpose to develop a particularly material-friendly technology for electron-microscopic imaging with atomic-scale resolution.
Project partners are Heidelberg-based CEOS GmbH, which has been on board from the very beginning and specialises in the development and production of electron-optical aberration-correcting systems, and the American-Dutch company FEI, which joined the cooperation in 2014. FEI is one of the world’s leading manufacturers of platforms for transmission electron microscopy (TEM). Another founding partner was Zeiss AG, which dropped out of the project in 2014 for reasons of corporate strategy. The total costs of the development and construction of the device amount to around 10.6 million euros. The German Research Foundation (DFG) covers half of that with 5.3 million euros. The state of Baden-Württemberg (MWK) funds the project with roughly 3.8 million euros. The SALVE project was also supported by the Carl Zeiss Foundation, which funded the establishment of an endowed professorship for electron and ion microscopy as well as a senior visiting professorship at Ulm University.
With the conclusion of this project and through great efforts we have finally achieved our goal. The new SALVE microscope not just meets but exceeds all specifications! My team and I are very excited about all the completely new insights into the nanoworld of solid matter,' says project manager Professor Ute Kaiser, who heads the Electron Microscopy Group of Materials Science at Ulm University. The low-voltage transmission electron microscope operates within a voltage range from 20 kV - 80 kV, thus allowing the imaging of materials and biomolecules that are sensitive to electron radiation. This would not be possible with conventional TEM devices. Platform for the new development is the model TitanTM Themis TEM by FEI, one of the world's most powerful commercial TEM devices of this kind. 'In order to eliminate the colour aberrations that occur in addition to spherical aberrations when using low voltage, we developed a special correction system which compensates for both spherical and chromatic aberrations and improves the image quality significantly. This took us several years,' the co-founder of CEOS, Professor Maximilian Haider, elaborates. 'In the past we were able to set standards with spherical aberration-corrected microscopes in all voltage ranges. With the SALVE device we have now defined a new level of quality in terms of achievable resolution within low-voltage microscopy.'
Equipped with a so-called Cs/Cc-corrector, the SALVE microscope corrects both of the prevalent aberrations. In contrast, conventional aberration-corrected TEM models, which operate on medium or high voltage, are merely equipped with special correctors that eliminate the spherical aberrations.
The SALVE microscope not only affords high-resolution electron-microscopic imaging on an atomic level, but also facilitates spectroscopic analyses of molecular constellations, their electronic structures and bonding states. 'The fact that this project could be concluded in record time – with an even higher performance capacity than initially expected – is certainly also due to an outstanding teamwork between the project partners,' Bert Freitag, FEI's director of product marketing for Materials Science, states. 'The SALVE microscope allows us to finally examine electron radiation-sensitive samples that would be destroyed with higher voltages. This includes not only carbonic materials like graphene, which consists of a single atomic layer, but also particular biomolecules,' Professor Ute Kaiser explains. Her team research the emergence and avoidance of radiation damages in the context of this project. With conventional devices, which operate with voltages between 200 kV to 300 kV, the high amounts of energy cause atoms to be 'knocked out' in some materials. This makes imaging impossible.
The construction works for the new tram line made a new microscopy building necessary for Ulm University. The SALVE device will stay at CEOS in Heidelberg until the new building at Oberberghof is finished. The relocation is planned for September 2017. The new building, which will also become the home of another highly sensitive transmission electron microscope, is co-funded by the state of Baden-Württemberg, the city of Ulm and the university. The researchers from Ulm and their partners can already demonstrate, however, how promising a future low-voltage transmission electron microscopy has with this new technology at hand – both in the materials and the life sciences. The new technology thus affords imaging of temporal changes of atomic-scale processes, or the observation of individual atomic 'dislocations'. The accidental discovery of the world’s thinnest glass layer is one spectacular example. This gained the researchers at Ulm University an entry into the Guinness Book.
'We are very proud of contributing our piece to the history of microscopy with SALVE and thus continuing a tradition that is connected with the names of great German researchers and developers like Ernst Abbe and Carl Zeiss,' the research and development team states euphorically. One of the team members is Professor Harald Rose, senior professor at Ulm University and spiritual father of the electron-optical aberration correction. 'A project like SALVE would not have been possible without his pioneering theoretical groundwork,' Kaiser notes.
The successful acceptance of the new low-voltage transmission electron microscope was announced publicly at the latest SALVE advisory board meeting on 21 April in Heidelberg in the presence of the third-party funds providers DFG and the Ministry of Science, Research and the Arts (MWK).
Photos: Heiko Grandel
Text and media contact: Andrea Weber-Tuckermann