Research project SU/01 (Research action SU)
Coordinator: Prof. Y. BRUYNSERAEDE
1. Objectives:
The project tackles the major problems, both fundamental and applied in nature, of the physics of high-temperature superconductors. It is based on a collaboration between eight physics, materials engineering, and microelectronics laboratories. These laboratories have considerable expertise in superconductivity and microelectronic devices, including manufacture and characterisation of bulk and thin-film superconductors, and are devoting major experimental and theoretical efforts to aspects of superconductivity, surfaces and interfaces.
The experimental efforts in ceramic superconductors will include material preparation, structural characterisation and measurement of physical properties, their relationship to theory and the develoment of a number of applications.
Preparation work will include conventional bulk and thick-film methods. For thin-film methods, the project will focus on magnetron sputtering, laser ablation, and if necessary, molecular beam epitaxy.
Structural characterisation will involve many different techniques, including electron and X-ray diffraction, electron and scanning tunnelling microscopy, electron probe micro-analysis, Rutherford backscattering, and a variety of surface and interface analysis techniques such as Auger electron spectroscopy, X-ray and ultraviolet photoemission spectroscopy and high-resolution electron-energy loss spectroscopy.
Major efforts will be devoted to the experimental study of physical properties in order to elucidate the mechanism of superconductivity, especially flux pinning, in the novel oxide superconductors. The connection between superconductivity, stoichiometry, and microstructure will be explored in order to evaluate which structural features are operational.
As an input for theoretical studies, superconductive phenomenology will be explored by a wide variety of measurements including magnetic susceptibility, magnetotransport, infrared spectroscopy. This will make it possible to determine critical fields and currents, the superconducting energy gap, the internal field distribution, the anisotropies. The electronic structure will be explored, mainly by studies of photoemission and electron spectroscopy. Proximity effect studies will be performed mainly in thick-and thin-film configurations.
The development of superconducting devices in thick- and thin-film form will also require diagnostic techniques capable of characterising the influence of the environment (substrate, contacts, packaging, stress). The intrinsic stability of these devices will be studied.
The high-Tc superconducting thick and thin films will be used as functional elements in microelectronic devices. Applications based on Josephson and tunnel junctions will be developed; unconventional applications such as microstriplines, resonant circuits and fast switching devices will receive special attention.
Finally, theoretical investigations will link together the various experimental studies and concentrate on a wide variety of aspects of superconducting mechanisms. Studies include the use of modern computational techniques to investigate surface electronic properties, to simulate electron spectroscopy data and to interpret optical spectra of single- and multilayered materials.
2. Coordinated programme of research
A. Synthesis and processing of powder precursors for the preparation of high-temperature superconductors in the form of thick polycrystalline films and bulk materials:
1. sol-gel method based on the use of organic complexing agents;
2. freeze-drying ;
3. texturing including high temperature plastic deformation;
4. optimisation of sample processing.
B. Thick film preparation: screen printing.
C. Thin film preparation:
1. laser ablation ;
2. dc and rf magnetron sputtering from multiple sources.
D. Film patterning:
1. wet etching
2. dry etching.
E. Microstructural characterisation of the films, powders, and bulk samples:
1. Rutherford backscattering and transmission electron microscopy;
2. X-ray diffraction ;
3. scanning tunnelling microscopy and electron spectroscopy.
F. Study of the electrical and magnetic properties of the films:
1. critical parameters (Tc, Jc, Hc2): inductive and resistive measurements;
2. magnetic flux-line lattice: measurement of the ac susceptibility.
G. Reliability studies of the films:
1. interaction with the environment (substrate, ohmic contacts, stresses, etc);
2. intrinsic stability: dc resistance measurements.
H. Study of the interfaces, sandwiches and junctions :
1. superconductor/semiconductor interfaces;
2. superconductor/ insulator interfaces ;
3. superconductor/metal contacts and sandwiches;
4. Josephson junctions.
I. Development of prototypes of superconducting devices for microwave circuits:
1. coplanar waveguide transmission line resonator;
2. delay line ;
3. microstrip filters.
J. Basic research on superconducting materials:
1. electronic and vibrational structure characterisation by means of electron spectroscopies ;
2. modelling of interfaces and superconducting planes;
3. theoretical interpretation of spectroscopic data (electron and optical infrared spectra) ;
4. FIR paramagnetic resonance.
