X-ray group follows the traditions based by Prof. Posejpal, Dr. Skulari, Prof. Dolejsek and Prof. Kochanovska, the scientific work of whom was always in some way connected to the development of X-ray diffraction methods on Charles University. The foundations of the present X-ray group were created by Doc. J. Sedivy in 1973, when the Department of Semiconductor Physics was founded at the reconstruction of former Department of Solid State Physics. Doc. Sedivy was the head of the department up to 1985. However, the structural research was performed in X-ray laboratory already before the 2nd World War. After the war, the leaders were Prof. Valouch and Prof. Kochanovska. Experimental facilities at the beginning of 70's consist of Mikrometa (Chirana) and Siemens generators and set of chambers for film methods. The only diffractometer was URS of Soviet production. Permanent staff consisted of two assistents, one technician and one laboratory worker. At present time - one professor, one associate professor, one prof. assistent, one research scientist, two research workers.
The former organization scheme directed the research to application of structure analysis to study of physical properties of metals and semiconductors, in general to materials science of polycrystalline compounds and it continues to these days. The first scientific project of the group was directed to the study of lattice vibrations in polycrystalline Ag, Cu, Mg, Mg -, Cd -, Ag-Cd-, Ag-Zn- alloys. In later years, the main attention was devoted to the materials of powder metallurgy - carbides and nitrides. These studies were extended also to other materials such as tellurium and CuCl single crystals and their anisotropic and antisymmetric characteristics of temperature vibrations. Studies of lattice vibrations were also connected with the investigations of rigidity of interatomic bonds which were later expanded to more direct analysis of binding characteristics by the study of the deformation electron density due to the bonds. Interatomic bonds were also investigated in semi-theoretical works dealing with the explanation of well-known empirical relations between physical quantities. It was possible to explain the relations from the first principle with the aid of the so-called potential wells of pair-atomic interactions.
Since 1985, the main research of the group has been directed to the study of thin films structure. In last years it was extended to the studies of multilayers. The main results achieved were in studies of influence of the picostructure (deviations of real thin film structure from equilibrium bulk structure in picoscale) on the thin film properties. This was studied on hard TiN coatings in collaboration with the group of J. Musil (Institute of Physics, Academy of Sciences of the Czech Republic). Strong anisotropy of of thin film picostructure was detected and described. The effect of texture on fine structural effects in powder and polycrystalline samples shown to be essential. This influences the registered intensity and we have to find suitable and precise correction procedure (in spite of the fact that we are not specialists in this field). This experience was also applied to strongly textured thin films. We have introduced the method called Joint Texture Refinement and partial multiplicity factors for the description of texture influence on intensities of reflections. General method for derivation of the so-called orientation factors determining X-ray line broadening anisotropy has been introduced. It is a contribution to the dislocation density determination methods. Multilayer structures (especially magnetic multilayers) are investigated in collaboration with the ROTAN laboratory (rotation anode) of the Institute of Physics (Academy of Sciences), in theoretical field the collaboration is with Prof. Holy (Masaryk University, Brno). Other field of interest is the study of diffusion processes. Some papers were directed to the study of interdiffusion in powder samples. At present time phase transformations and crystalline phases in carbides and nitrides of transition metals at reactive diffusion processes are investigated. These studies include cermets too. Attention was devoted also to the compounds with amazing structures and physical properties as for example high-temperature superconductors, intercalates, fullerenes, sollar cells (CdTe), cermets of carbon compounds, nanocrystalline materials obtained by severe plastic deformation (Ge, Cu, Ni, Si), thin coatings - metal, oxide, organic. In collaboration with the Faculty of Natural Sciences we studied also the dust particles taken from the air at different heights above the Earth surface.
At present time we contribute to the education system of the Faculty of
Mathematics and Physics, Charles University.
One topic of basic laboratory exercises (Physics IV) - determination of lattice
parameters, basic lecture for the course of solid state physics - Structure of
Solids and diffraction, demonstration of experimental methods and laboratory
work for several branches (solid state physics, biophysics, optoelectronics).
Special lectures - Diffraction methods, Crystallography, Real structure of the
matter studied by diffraction methods, Structure of surfaces and thin films,
Applied crystallography, Modern analytical methods, Matlab, PC for users -
physicists. Four teaching booklets adn one textbook Basics of Structure Analysis
appeared.
Other activities
X-ray group organized, in collaboration with the ICDD (International Centre for Diffraction Data), four Round Robin tests directed to the sensitivity of powder diffractometers, precise intensity measurements, precision and reproducibility of analysis by the Rietveld method, quantitative phase analysis. We have contributed to the International Tables for Crystallography (vol. C, 1992) by the chapter Radiations Used in Crystallography. The members of the group are active in the Czech and Slovak Crystallographic Association (CSCA), where we took part in the organization of four international conferences and many one days semianrs and traditional colloquium of the CSCA.
V. Valvoda