Thematic focus and development of the Centre

Thematic focus and development of the Centre

The research activity of the Centre has an interdisciplinary approach and concerns the comprehensive characterisation of matter, particular the attention is put on detecting the heavy elements contents and the role and estimation of elements ionicity, which is crucial for estimation of the level of hazards. Over the past century the numerous techniques have been developed which investigate, on an atomic scale, the structure of the matter and which enable the physicists to describe with increasing precision the fundamental interactions. The techniques based on radiation and particles interaction with matter occupy a special place in these investigations. Beams of photon, electron, proton, light ion or atom and neutrons are of a special interest of the Centre.

A beam of well-defined and well-known energy and direction propagates through the matter under study and interacts with its basic constituents. Using several “radiation-probes”, different and complementary information can be gain.

To estimate the crystalline structure, ordering, texture, surface roughness, defects and phase composition of the bulk and layered samples formed by the new technologies and nature the Centre has applied the X-ray diffraction methods. Several diffractometers are at our disposal. The photo 1 shows the high-resolution diffractometer, Philips-MRD.

The new Philips-X’PERT System is just under installation and it will be in operation mode in March 2002.The self-made, single and double-crystal automated diffractometers (Photo 2) are used for characterisation of powders and flat single crystals. The self-made triple-crystal diffractometer is used for measurement of rocking curves that are the markers of crystal quality and the source of information about strain and chemical homogeneity of a sample. To solve the more detailed X-ray physics and structural problems the devices at the synchrotron radiation sources are used, after getting access to these large facilities. To get a beam-time a competition of scientific projects is announced each year. Starting from early nineties the scientists from the Center were awarded usually the several weeks of beam-time at the experimental stations of various synchrotrons, in dependence on, on the studied problems. Many research projects have been realising for several years in co-operation with the following European and American centers possessing the synchrotron radiation sources:

q HASYLAB at DESY, Hamburg, Germany,

q L.U.R.E. , Universite de Paris-Sud, Orsay, France,

q Advanced Light Source, Lawrence Berkeley Laboratory, Berkeley, USA,

q MAX-Lab, Lund University, Lund, Sweden,

q ESRF, Grenoble, France and

q ELETTRA, Trieste.

X-ray diffraction and imaging methods help to diagnose several diseases like osteoporosis and another bones illnesses. The investigation of crystal formed in human body (e.g. bile or kidney stones) help with recognising the morphology of the diseases. The Centre actively cooperates with medical clinics and participates in the programs aimed to estimate the correlations between pollutions of environment and content of heavy elements in bones, stones and tissues. As an example, there was proposed the new complete method for analysis of the microstructure of a trabecular bone in human bone bioptats. This method is based on the special X-ray high resolution imaging the structure and the mathematical method of its analysis by using the Fourier Transform of series obtained X-ray images of bone, the fractal dimension analysis and finally the discrimination analysis method. The correctness of the diagnoses was on the level of 98%. The method has been realised in collaboration with the Institute of Applied Optics - Warsaw, the Food and Nutrition Institute - Warsaw and the Ortopedic Hospital - Otwock. Two doctors theses were prepared on the base of this method.

The finest structure studies at the nano- and atomic scale are performed using the high-resolution electron transmission microscope JEM 2000 EX (JEOL) (Photo 3). The structure of thermally treated catalysts deposited on different substrates, structural changes in C₆₀/C₇₀: Me (Me=Fe, Ni, Pd, Hg) layers annealed under various conditions, self-assembled processes in multilayered semiconducting nanostructures, formation of semiconductor-metal ohmic contacts and many other problems were studied and solved bringing the technological feet-back. The quantitative high resolution transmission electron microscopy investigations of strain fields at atomic level and chemical composition of semiconductor heterostructures are currently under interest. The computer programs for processing, analysis and simulation of high-resolution images and electron diffraction patterns are developing and we do hope to intensify these fields of activity with the help of UE grants. The Electron Microscopy Group has already participated in the MULTIMETOX thematic network (see C9).

To study the chemical bonds and to estimate the level of formed bond ionicity, the perfection of formed phases, and variety of X-ray physics problems e.g. testing the limit of dipole electron approximation, the X-ray absorption and emission spectroscopy is applied. The shape of the spectra is a fingerprint of chemical compound and it is used in the Centre for solving the variety of problems in natural science and technology. To learn the base of the spectroscopy and to practice, the old RSM –500 emission spectrometer and electron probe microanalyser JXA-50A equipped with four-crystal spectrometers are used (Photo 4). The advanced studies are usually performed at the European and the USA synchrotron radiation sources.

To analyse the elements composition in variety of materials starting from these grown by new technology (semiconductors, papers, isolators, metals), through medical (bone, bile or kidney stones), archeological, biological, to environmental (sediments, dusts) the electron microprobe with scanning electron microscopy is used. To estimate the content of the elements at the level of at % we use the solid-state detector (EDS) and standard programs supplied by producer. To estimate the content of impurities the four-crystal spectrometers are applied with advanced analysis of data elaborated in the Laboratory.

The X-ray microanalysis is non-destructive method. The more precise but destructive method of analysis of impurities applied in the Centre is the sophisticated secondary ion mass spectroscopy. Very modern and well equipped spectrometer CAMECA 6F SIMS is shared with the Institute of Technology (Photo 5). This technique is a powerful for detecting a very diluted elements as well in conductive and non-conducive samples and it is currently applied for the study of dopants in variety of semiconductors heterostructures and quantum dots structures. In the near future with the help of UE grants the Centre would like to expand the studies to the variety of geological, medical and environmental samples.

For studies of chemical compositions and chemical states of the elements the other advanced technique has been also applying in the Centre for many years. This is the ESCA (electron spectroscopy for chemical analysis). Starting from the post doctoral position of the senior of the Centre prof. J. Auleytner at the Siegban Laboratory in Uppsala, the several scientists still continue the collaboration with the Sweden and Finnish Laboratories equipped with the modern ESCA and Auger spectrometers. The photoelectron spectroscopy is used for elemental composition, chemical state, and band structure studies of crystal surface and this method, using synchrotron radiation, is generally acknowledged as the most useful tool for the band structure studies of crystals. Moreover, it is widely applied in the Centre for investigations of the phenomena occurring on the surface and in subsurface layers of solids. Together with another techniques, it is successfully used at realisation of several research projects of the Centre. The self made UHV set-up assembled in the Institute of Physics (Photo 6) enables us to carry out surface studies of solid samples. The clean surfaces of the samples, suitable for surface studies, can be prepared by cleavage under UHV conditions or by annealing in situ. The properties of clean surfaces or of those modified by deposition of small amount of metals can be investigated by means of low energy electron diffraction (LEED) and Auger electron spectroscopy. The set-up is still developed in order to increase the number of preparation and experimental techniques being at our disposal. In particular, assembling of a system for surface sensitive optical measurements is planed.

Finally, the neutron particles are also applied in the Centre to sample the matter owing to their very specific and unique properties. Neutron has no charge and has a spin of ½ which is the equivalent to same value of a magnetic moment and, consequently, is sensitive to the magnetic fields created by unpaired electrons present in the material under studying. In magnetic materials the matter-neutron interaction allows to study the magnetic order (magnetic structure, magnetic phase transitions) and the possible excitations in magnetic system, in technological materials as well in natural and biological samples. Selected neutron scattering techniques enable to detect even small contamination of the matter investigating the chosen magnetic or heavy elements, which is very important from the point of view of the environment pollution studies. In cooperation with the Laboratoire Le’on Brillouin (LLB) in the CE Saclay research center the scientists from the Centre carry out research programs covering different topics in the fields of condensed matter physics, magnetism and superconductivity, physical chemistry, biology and medicine as well as in material sciences (in particular, in the physical metallurgy).

The Institute of Physics of the Polish Academy of Sciences has a long history. It was founded in 1953. From the very beginning the Centre was integrated part of the Institute. In 1967 it was named the Department of X-ray Physics and Prof. Julian Auleytner was established as its leader. In 1973 the name of Department was changed into the Laboratory of X-ray and Electron Microscopy headed also by Prof. Auleytner. At that time the Laboratory was equipped with modern X-ray and electron analytical tools. During the past years a part of them was fully exploited, a part was renovated and the sources for new equipments were awarded. In 1994 Prof. Tadeusz Figielski took over the position of the head of Laboratory for 7 next years. Since 2000 Ass. Prof. Krystyna Lawniczak-Jablonska has been acting as the head of the Laboratory.

During about 30 year activity of the Laboratory 20 research workers were graduated the doctor degrees, and 6 of them qualified themselves as assistant professors. Currently 6 PhD students are preparing their theses at the Laboratory.

The Centre engages in its activity more than 1/10 part of the Institute of Physics. It employs 43 staff members among whom 36 are directly involved in the research activity. The personal roster is the following: 2 full professors, 5 associate professors, 19 researchers with the doctor’s degree, 4 assistance, 6 Ph.D. students (2 from Ukraine), and 7 technical staff.

The several former employees took the position of the permanent staff abroad. They are employed at the scientific institutions in the Federal Republic of Germany, the USA , Canada, Brazil, and Australia.

In summary, the research activities of the Centre concentrate on the developing of modern methods of characterisation of matter. These methods are applied with success to the variety of physical problems in technology of modern materials. The application to another natural materials (e.g. archaeological, geological, medical biological and environmental) has already started in the Centre. We do hope that with the help of UE grant it will be developed more intensively.

IN CONCLUSION, the research activities in the Centre attempt to bring together all important aspects of the modern methods of samples characterisation:

q conductive and non-conductive samples preparation and characterisation,

q experimental studies of interaction of beams with matter,

q theoretical investigation, including the basic aspects of interacting of beams with

matter,

q computer simulation of the interaction and comparison with the observation,

q estimation of the confidential limits of the evaluated characteristic parameters.