By Knut Urban Stuttgart and Director of the Max Planck Stuttgart, Germany

I grew up in the early post-war period in by Knut Urban Stuttgart and Director of the Max Planck Stuttgart, Germany. This city is known for Institute for Metals Research, became its automobile industry and for its large interested in my results on the optical number of small and medium-sized apprenticeship in the field of electrical properties of plastically deformed industrial companies. engineering, which in the sixties, was the germanium at low temperatures and prerequisite for studying physics at the offered me a doctoral thesis. Seeger was My father was an electrical engineer and university. This was an important time for internationally recognized for his he ran a factory for small electric motors. me, because learning the skills of practical pioneering work in the field of crystal Over the decades, he set the main accents electrical engineering, including design defects, and he was one of the most of the company with a whole series of his and working in production with ordinary versatile solid state physicists of his time. own inventions. In my parental home workers not only helped me to acquire Accordingly, the fields dealt with in his there was a lot of thinking, reading and important professional knowledge, but institute and the experimental and discussing about science and technology. also strengthened my social skills. theoretical methods used were many and In addition to parental care, I owe to my Subsequently I enrolled at the Technical varied. father and my mother a critical, open, but University of Stuttgart to study physics. cooperative way of thinking. This was later Inspired by my work in the field of Seeger presented his doctoral students very beneficial to me, not least semiconductors at Bosch company with challenging topics and trusted that professionally. Still a young school boy, I already during my studies, I completed they would manage to be successful. The used the technical possibilities of the university with an experimental diploma cold water into which I had to jump company to build my first optical thesis in the field of semiconductors. Here according to his offer consisted of telescope together with my grandfather. I learned a lot about low temperatures, constructing an object stage for the new This instrument was followed by a about the optical properties of high-voltage electron microscope of the reflecting telescope, which could be used semiconductors and how these are Max Planck Institute. The challenge was for more serious observations. And a few influenced by crystal lattice defects. This that the stage should allow samples to be years later I was accepted as the youngest was my entry into solid state physics and cooled down to the temperature of liquid member of the Stuttgart observatory. especially into the physics of defects in helium (-269 °C) without impairing the That’s how I came to physics via crystals. resolving power of the microscope, in astronomy. order to study atomic lattice defects in A decisive factor for my entire further metals. This had been attempted by other After attending high school, I joined career was that Alfred Seeger, Professor groups for about a decade without any Siemens company for a shortened of Solid State Physics at the University of success. The vibrations of the boiling helium used for cooling and the instability a few years later. I earned my entry ticket devices; highly interesting topics for of the low temperature spoiled the optical into the club of quasicrystal scientists with advanced semiconductor technology. With resolving power. Seeger offered to me to a paper in which I combined cryo- and the oxide superconductors, two things do the design and construction of the high-temperature in-situ electron proved to be an advantage for us. We built system at the Fritz Haber Institute in microscopy to show for the first time that the facility for the deposition of Berlin under Ernst Ruska, who later won the quasicrystalline phase in alloys superconducting thin films and devices the Nobel Prize as the inventor of the developed by itself from the amorphous ourselves in order to realize our own electron microscope. Ruska, who was an state at elevated temperatures, whereas ideas, and we used our state-of-the art engineer through and through, was previously it was believed that the only electron microscopes to directly check the initially rather skeptical about the young access to the quasicrystalline phase would quality of the results of film deposition physicist. But my work in the Siemens and be by quenching from the melt. Some and to continuously improve them. We Bosch workshops had prepared me for years later, when I discovered by chance achieved international records in such a demanding job. And when I asked dislocations in one of our images, a kind Josephson-device and high-frequency Ruska for an interview a few months later, of lattice defect closely related to plastic performance, and our superconducting and approached him with a large bundle behavior in crystals, I became very microwave resonators flew on an of drawings under my arm, he was engaged with quasicrystal plasticity and international communication satellite impressed. From then on, he followed my then worked in this field for many years. mission. work with great interest, and he made all The discovery of dislocations was so the facilities of his institute available to exciting since it was against any Electron microscopy at that time was me. As it is not seldom the case, a expectation. Quasicrystals are based on more powerful than it had ever been newcomer who had six-dimensional lattice schemes and before, and we were proud of our new new and independent ideas could make understanding the topology of such instruments we were able to put into the breakthrough that had been denied to defects in these lattices turned out to be operation at the end of the eighties. Their others. rather difficult. Similarly complicated was resolution of about 2.4 Å at 200 kV and the formulation of a contrast theory for 1.7 Å at 300 kV was fantastic. On the other The helium-cooled object facility in the quantitative characterization of these hand, they still hadn’t reached atomic high-voltage electron microscope then defects in the electron microscope, which dimensions, which seemed to solid state served us for many years as a unique kept us busy for a long time. In addition, physicists, including me, at that time to be platform for experiments carried out the observation of dislocations indicated something like the Holy Grail. It was in-situ under direct high resolution that it might be possible to plastically therefore a great turn of events, that in observation. The microscope offered an deform quasicrystalline materials, which September 1989 during the ‘Drei- attractive advantage: at high electron are in general very brittle, and we were Ländertagung’ (the traditional quadrennial energy, atomic defects could be generated able to prove this at high temperatures by meeting of the electron microscopy by electron-atom displacements, and at performing in-situ experiments in the societies of Austria, Germany and low energy, their secondary reactions high-voltage electron microscope. Switzerland) at Salzburg, Austria, could be observed at any desired Maximilian Haider and Harald Rose told temperature. I myself was rewarded by a The eighties were exciting years for solid- me about a project that would decisively number of new observations. The most state physics and materials science. change our future professional life, and of important of these are certainly the Outstanding was the discovery of high- course that of electron microscopy in discovery of the radiation-induced temperature superconductivity in oxide general. Harald Rose had just completed a diffusion of atomic defects (brought about materials and the invention of scanning theoretical study of a new aberration- by electrondefect interaction) and the tunneling microscopy (STM). The corrected electron microscope objective proof of the spinodal ordering in alloys, a multifaceted interest in new solid-state lens which, according to a conservative sophisticated process based on special physics topics, which we learned from estimate, had a chance of being lattice symmetry properties, which had Alfred Seeger, and which he exemplified technically realized with the current state been theoretically treated and discussed to us, has never left me throughout my of the art of electronics technology. A few for years, but had never been professional life. And as someone who months later we agreed to submit a joint demonstrated experimentally. had just taken over a research institute at application to the Volkswagen Foundation. one of Germany’s national research The aim was to realize in Haider’s In the second half of the eighties I left the centers, which had reasonable financial laboratory at the European Molecular Max Planck Institute becoming a Professor resources for equipment and personnel, I Biology Laboratory at Heidelberg the new for Materials Science at the University of threw myself into setting up two more semi-aplanatic corrector lens, known Erlangen. A few years later I moved to working groups, one to set up STM and today as the ‘Rose corrector’, and to Research Center Jülich as Director of the one to study oxide superconductors. STM implement it into an appropriately Institute of Solid State Research. This had primarily been introduced as a modified commercial conventional position was combined with a Chair for surface physics technique. Following my transmission electron microscope (CTEM). Experimental Physics at RWTH Aachen interest in lattice defects, we built a novel Since in a CTEM one must also correct the University. In the meantime I had begun to STM, with which we were the first to study off-axial aberrations, this is the more take an interest in the new field of single dopant atoms in semiconductors, general case, which automatically includes quasicrystals, for the discovery of which their electric fields, their diffusion and the case of the correction of a scanning Dan Shechtman received the Nobel Prize their behavior in the pn-junctions of transmission electron microscope (STEM).

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