IFF
Scientific Report 2000/2001

Institute for Microstructure Research

General Overview

The Institut für Mikrostrukturforschung (Institute for Microstructure Research) is working in a number of fields. These were selected with an emphasis on modern-materials aspects, the importance of an atomistic and microstructural understanding for materials performance and the possibility to contribute to the development of technology. In some of these fields the competence spans 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. Besides this general-physics and technology part of the institute there is a second part of special competence. This is structure research by means of modern transmission electron microscopy and scanning tunnelling microscopy. This work is carried out within the Jülich Centre for High-Resolution Electron Microscopy. It is operated by the institute and serves a wider community of users.

1. Ceramic Superconductors: Here the emphasis is on thin-film and heterostructure production, Josephson effects, and their application in magnetometer systems and spectroscopic techniques.
2. Semiconductors: Here the emphasis is on structural investigations, mainly by transmission electron microscopy, of thin films and heterostructures. In collaboration with various research groups we are studying growth-related problems, like the relaxation mechanisms in SiGe films or the influence of doping on the microstructure in as-grown and annealed low-temperature grown GaAs films. Device relevant topics are addressed by studies on the interdiffusion in III-V heterostructures and by investigations of the microstructure of thin film solar cells of microcrystalline silicon. 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 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: The theoretical and technical aspects of atomic-resolution transmission electron microscopy have in recent years become one of the central fields of interest of our group. Computer program packages for the exit wave-function reconstruction developed in the institute are in use world-wide. In collaboration with EMBL Heidelberg and TU Darmstadt we 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 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) is used since early 2000. 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 operates together with the Institut für Streumethoden (Prof. Brückel) the IFF laboratory for crystal-growth.

The institute was very successful in recent years in application of high-temperature superconductivity to communication systems. In particular 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. During the year 1999, in the course of a reorganisation of our institute, the whole high-frequency research group was transferred to the Institut für Schicht- und Ionentechnik (ISI). The free capacity, both with respect to personnel and funds, offered to us an excellent opportunity for development of new research competence.

Due to our unique position in this field we chose to direct our resources towards the development of Hilbert-transform spectroscopy on the basis of the ac-Josephson effect. 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 (IRE) 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 market demands represent challenges to science and technology, and our work in this field will be continued as long as we can derive good science from these. 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 since 1999 in a collaboration (joint patents) with ZEL (Prof. Halling) with the aim to built a SQUID-microscope prototype. Current delays are due to loss in personell and difficulties with suppliers. First tests are expected during 2001. An industry company has been found which is interested in marketing the new instrument.

The successful project of the spherical-aberration corrected transmission electron microscope described above has triggered new activities in electron optics world wide. The novel technology is considered a quantum jump of great commercial impact. New generations of instruments are under construction or in the planning phase in Europe, Japan and the US. Together with other institutions, in particular the Max-Planck-Institut für Metallforschung, we have contributed to the installation of a priority program of the DFG. In the framework of this 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. Also in this field our institute is respected as an international leader. Recent developments, in particular in computer-controlled alignment, will be subject of further industry collaboration.

The quasicrystal group has currently three DFG funded projects and has submitted proposals for another four in the last phase of the DFG priority program. Great efforts went into new PhD programs 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 to three years in Jülich on a grant supervised by the Jülich Doktorandenausschuß, but they will pass their examina in their home university.

Outstanding results of the year 2000:

• In Hilbert-transform spectroscopy, a high dynamic power range of around 5 orders and broad spectral range of 2 orders have been realised by high-Tc grain-boundary Josephson junctions. A prototype of terahertz Hilbert-transform spectrum analyser integrated into a Stirling cooler has been developed and its application for the optimisation of single line operation of far-infrared optically-pumped gas laser has been demonstrated (in collaboration with IRE RAS, Moscow).
• The aberration corrected 200 keV transmission electron microscope has, after the curing of a large number of operation difficulties, at last reached stable high-quality operating conditions. The enormous, partially very frustrating efforts dedicated to the prototype in recent years are bearing ample fruit in the form of excellent high-resolution results.
• Studies of the structure of n-i-p microcrystalline solar cells revealed that the nucleation of the intrinsic absorber layer on the highly crystalline n-type contact layer determines the microstructure. The local epitaxy results in crystalline columns extending throughout the whole intrinsic layer, even if highly amorphous growth conditions are chosen.
• We have achieved a world record in high Tc SQUID sensitivity of 6 fTHz^-½ at 77 K. This was demonstrated together with our industrial partners, Tristan Inc. and STL, at exhibitions at HvH Symposium at PTB Berlin and at ASC2000 in the US.