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Scientific Report 1999/2000

The Institut für Mikrostrukturforschung (Institute for Microstructure Research) is working in a number of scientific fields. These were selected with an emphasis on modern-materials aspects, on the importance of an atomistic and microstructural understanding for materials performance and, if possible, on the possibility of an evolution of research into technical devices. The goal is an interdisciplinary research group working on a spectrum of scientific problems sufficiently wide to allow a flexible and rapid reaction to new scientific developments. In some of these fields the competence should span the whole range from materials preparation via basic physics investigations to technical devices. In others access to interesting materials and device problems is provided by qualified collaborations inside and outside the Jülich research centre. Besides this general-physics and technology part of the institute there is a second part of special competence. This is the structure research by means of modern transmission electron microscopy and scanning tunnelling microscopy. This work is carried out within the Centre for High-Resolution Electron Microscopy. It is operated by the institute and serves a wider community of users.

The research fields can be characterised as follows:

(1) Ceramic Superconductors: Here the emphasis is (a) on thin-film and heterostructures production, Josephson effects, and their application in magnetometer systems and spectroscopic techniques.

(2) Semiconductors: Here the emphasis is on III-V compounds. In collaboration with various research groups we are studying, mainly by transmission electron microscopy, the growth of thin films and heterostructures and problems related to the production and application of low-temperature GaAs. Another topic is the study of electronic states in compound semiconductors by scanning tunnelling microscopy employing a technique pioneered in our group. It permits, via the detection of the far-reaching Debye screening cloud at the surface, an investigation of charged doping or impurity atoms in the bulk of the samples.

(3) Metallic Alloys: These are at present quasicrystalline alloys and related normalcrystalline approximants. We are growing large single-quasicrystals for our own research but also for users world-wide, in particular for the participants in the DFG priority program on quasicrystals. Our own work on quasicrystals and approximants concentrates on phase-diagrams, plasticity and surface physics.

(4) Electroceramics: In the field of electroceramic materials we take advantage of our long-standing experience with respect to perovscitic materials both in preparation and in microstructure research by means of transmission electron microscopy. In collaboration with the Institut für Electrokeramische Materialien (Prof. Waser) we dedicate a large research capacity to the investigation of the structural aspects of the production and properties of electroceramic thin films.

(5) High-Resolution Electron Microscopy: Although in the beginning primarily considered as a tool for high-quality materials investigations the theoretical, methodical and technical aspects of atomic-resolution transmission electron microscopy have in recent years become one of the central fields of interest of our group. We have developed special competence in the theory of high-resolution electron microscopy. Advanced application packages for the exit wave-function reconstruction are installed and serviced by us world-wide. Since 1991 and 1997 we have in collaboration with EMBL Heidelberg and Technical University of Darmstadt developed the word's first aberration-corrected transmission electron microscope with record resolution, 1.3 Å at 200 kV. These developments are continued (see below).

The institute has at its disposal sputtering deposition machines, some of them with three-target facilities which were developed and built in the institute for the high-quality deposition of ceramic superconductor thin films and heterostructures. For device production local clean room, structuring and packaging facilities are available.

The institute operates together with the Institut für Streumethoden (Prof. Brückel) the laboratory for crystal-growth which was part of the former Institut für Materialentwicklung (Prof. Wenzl). This permits to maintain part of the outstanding expertise in the field of crystal growth for the benefit of the whole Department.

The institute operates the Jülich Centre for High-Resolution Electron Microscopy with two 400 kV JEOL machines of the type 4000 EX/FX, a JEOL 2000 EX, a PHILIPS CM20 FEG, the spherical-aberration corrected PHILIPS CM200 FEG and a JEOL 840A scanning microscope.

The priority in scanning tunnelling microscopy is on high-temperature investigations a field only rarely served by other competing groups. We have at our disposal two microscopes with in-situ cleaving facilities and ex-situ heating up to 750 °C. These instruments were designed and built inside the institute. An in-situ heating STM (Omicron) was installed and successfully tested end of 1999.

For the work on alloy plasticity a ZWICK mechanical testing system has been installed in 1998. The collaboration with the Max-Planck-Institut für Mikrostrukturphysik at Halle in this field is continued.

The institute was very successful in recent years in application of high-temperature superconductivity to communication systems. In particular the dielectric, and more recently the multipole dielectric filters designed in the institute received considerable attention world-wide. In 1998, as partner of BOSCH, we won the competition for a project "High-Temperature Superconductivity for the Communication Technology of the Future" which became one of the five priority programs of the German Federal Minister of Science and Technology. We also succeeded in obtaining funding for a project with the same title by the HGF-Strategiefonds. During the year 1999, in the course of a reorganisation of the Institut für Schicht- und Ionentechnik (ISI), Dr. Norbert Klein, who was responsible for our high-frequency superconductivity research, became head of the superconductivity group in ISI. In fact the very technology-oriented research of our group fits well into the mission of ISI. The free capacity, both with respect to personnel and funds, obtained in our institute by the shift of the whole high-frequency research group to ISI offers an excellent opportunity for development of new research competence.

Due to our unique position in this field we choose to direct our resources towards the development of Hilbert-transform spectroscopy. This technique provides an excellent and novel tool for spectroscopy in the frequency range of 10¹⁰ to 10¹³ Hertz. It is broad band and orders of magnitude faster than Fourier spectroscopy. Here we have an excellent collaboration with the Institute for Radioelectronics in Moscow. We succeeded in acquiring a BMBF-project for the development of a fast gas-spectrometer and a project with DESY, Hamburg. The latter is a consequence of our successful test of Hilbert-transform spectroscopy for the determination of the shape of electron bunches in the beam of the TESLA test facility in Hamburg. The goals are: Improving the sensitivity of the technique by development of even better Josephson junctions and constructing facilities for fast molecule spectroscopy in our own group.

Our dc-SQUIDs on the basis of ramp-type junction geometry continue their success both in performance and in their acceptance on the market. As a supplier of TRISTAN Company (USA, formerly Conductus) we deliver a larger number of SQUIDs and magnetometers per month. The new developments arising from the market demands are still meeting our scientific interests. Our dc-SQUIDs are also employed in a number of projects carried out together with ISI. Outstanding is the success of an investigation on stress-corroded steel rods in the concrete of highway-bridges in which cracks could be detected. This technique is under consideration for routine inspection of bridges on German highways.

The strategy for further developments in superconductivity will be to use our expertise in front technology in this field to develop applications which can also be used for our own research. Hilbert-transform spectroscopy has already been mentioned. SQUID-microscopy is another field. This project has been intensively followed in 1999 in a collaboration with ZEL (Prof. Halling) with the aim to built a SQUID-microscope prototype within this year 2000.

The successful project of the spherical-aberration corrected transmission electron microscope described above has triggered a priority program of the DFG. In the framework of this new program 3.8 Mio DM were granted in 1998 to our institute for the development, in collaboration with CEOS Company, Heidelberg, and ZEISS-LEO, Oberkochen, of the world's first Subangström-Instrument. Besides ultra-high resolution the 200 kV machine will contain a monochromator and an in-column energy filter of the Krahl-type. This will maintain the institute's position as a pioneer in advanced instrument development.

The institute is partner of PHILIPS Electron Optics with respect to theory and application of exit-wave function reconstruction in high-resolution electron microscopy. In this field our institute is respected as an international key institute. Recent developments, in particular in computer-controlled alignment, will be subject of further industry collaboration.

The quasicrystal group has currently three DFG funded projects. During 1999 we were lucky to find good scientists for the positions offered by DFG. This also concerns a young engineer, Carsten Thomas, who will be able to run a part of our crystal-growth facilities after the retirements expected for 2001. Great efforts went into a new PhD program with the Russian Academy of Sciences and other GUS state universities and universities in China. In the framework of this special program designed by the institute and the partners abroad the PhD students are working two years in Jülich on a grant supervised by the Jülich Doktorandenausschuß, but they will pass their examina in their home university.

We are happy that Mr. Werner Pieper joined our group in 1999 as an engineer. He will take over Jörg Hanssen's position after his retirement in early 2000. Mr. Hanssen was the technical father of our Electron Microscopy Centre from its very beginning in 1987 and he has rendered invaluable services to our group.

It is always difficult to select a few of the outstanding results and bring them to special attention here. This year the following results are mentioned: