Please activate JavaScript!
Please install Adobe Flash Player, click here for download
ePaper created 2013-08-02, 08:40:53 | version 1.25.20
2|2013 Research in Jülich 17 RESEARCH AT THE CENTRE | Electron Microscopy For example, many researchers are cur- rently working on what is referred to as spintronics. They no longer want to rely solely on the charge of electrons for in- formation processing, but also their an- gular momentum, also known as their spin. Using the spin, researchers are planning to make much more energy- efficient and faster computers a reality. As the spin of electrons is linked to a magnetic moment, electron holography could theoretically make visible the arrangement of spins inside nano- materials. AT THE LIMIT However, the method is currently reach- ing its limits. Despite its matchless reso- lution, it is not yet good enough for this purpose. So far, two field lines must be at least five nanometres apart in order for electron holography to show them as separate lines. In addition, the magnetic fields to be measured are very weak, particularly in particles with a diameter of less than 20 nanometres. This is the reason why another ques- tion of information technology currently remains unanswered: can data be stored securely in magnetic nanocrystallites consisting of only a few dozen atoms? The corresponding units in today’s com- puter hard disks are considerably larger, but with increasing miniaturization, this issue is becoming more and more ur- gent. With a view to practically relevant problems such as this, Dunin-Borkowski has been devoting himself to the task of making electron holography more sensi- tive and improving its resolution for many years. He came to ER-C, which is operat- ed jointly by Forschungszentrum Jülich and RWTH Aachen University under the umbrella of the Jülich Aachen Research Alliance (JARA), in 2011. What he found here are ideal conditions for breaking Any electron microscope can be used for the purpose of electron holography, provided that it has a field emission gun (FEG), a special source of electron emission. A bi- prism is also required as special equipment. This gold-plated quartz glass fibre is installed in place of one of the apertures of a conven- tional electron microscope. The electron beam from the field emission gun is bisected in the microscope. One half serves as a reference, the other is directed through the specimen. The biprism, to which an electrical potential is applied, then deflects the two elec- tron beams so that they overlap. This results in an interference pat- tern – the hologram. It contains in- formation on the magnetic fields in the specimen. How electron holography works Field emission gun (FEG) Reference beam Biprism Hologram Specimen new ground in his research: PICO at ER-C is one of only two microscopes of its kind in the world. They have special elements that are able to correct a lens error known as chromatic aberration. This al- lows PICO to image the arrangement of atoms inside crystals with unprecedented accuracy. Dunin-Borkowski hopes to repeat this success story with electron holography, using corrective lenses to improve this method, too. The European Research Council has faith in him. In late 2012, it provided Dunin-Borkowski with an Ad- vanced Grant, which is worth € 2.5 million in funding over a period of five years. :: Dr. Frank Frick Iron filings can make visible the field lines of a bar magnet about a centimetre in size. This magnet – an iron crystal in a carbon tube – has a diameter of 180 nanometres. Electron holography makes it possible to see the lines of force of a nanomagnet. Institute Ernst Ruska-Centrum Advanced Grant