Projects / Programmes
Studies of atoms, molecules and structures with photons and particles
January 1, 2004
- December 31, 2008
| Code |
Science |
Field |
Subfield |
| 1.02.00 |
Natural sciences and mathematics |
Physics |
|
| Code |
Science |
Field |
| P230 |
Natural sciences and mathematics |
Atomic and molecular physics |
Atomic physics, molecular physics, electron correlations, photoabsorption, fluorescence, Auger spectroscopy, time-of-flight spectroscopy, X-ray spectroscopy, Moessbauer spectroscopy, physics of surfaces, vibrationally excited hydrogen, He atom scattering, ion beam accelerator, ion beam analytical methods, EXAFS, XANES, PIXE, RBS, ERDA, electron scattering, ion microbeam.
Researchers (15)
Organisations (4)
Abstract
Research activity under the program is concentrating on two main aspects accessible by low energy excitation of various targets by photons and particles. The first regards a basic interaction of photons and particles with an atom. Its aim is to observe and explain correlation effects that go beyond the first order approximation where the atom is represented by a system of independent electrons moving in the average, local and static potential. We propose to study multielectron excitations of inner atomic shells by photon absorption and high resolution X-ray spectroscopy, providing information of both, the excitation distribution of the atom and branching of the relaxation decay paths. To test thoroughly the model predictions we are going to measure multidifferential scattering cross sections, for example, Auger electron - ion coincidence pairs after the electron beam excitation of the gas target. The research is devoted also to the study of vibrationaly excited hydrogen molecules, specifically to their interaction with the surface of materials which are relevant for the fusion research. The second main aspect of our research activity is to perform experiments under conditions of firm validity of the first basic approximations in order to study the structure in which the atoms are immersed. The atomic signal is often strongly modulated by the atom environment even in materials with medium and short-range order. We are going to study the structure by exciting the target with synchrotron radiation recording the X-ray and photoelectron diffraction patterns or by measuring the extended fine structure in the absorption cross section (EXAFS). The structure will be also studied by measuring the inner hyperfine magnetic and electric field of thin layers by means of Moessbauer spectroscopy and by observing the chemical shifts in the HRXRS. The surfaces in particular will be studied by scattering of the thermal beam of helium atoms. The ion beam excitation is going to be used for determination of elemental concentrations in various multilayered materials and samples by different ion beam techniques (RBS, PIXE, ERDA). Such nondestructive analysis will be performed, for example on the works of art, on the aerosol samples, in the geology and arheometry. Two-dimensional maps of elements can be measured with the ion beam microprobe reaching 1 um of lateral resolution. A particular attention will be devoted to the study of new materials like thin organic films on semiconductor or metal substrates and nanostructures. With more reliable data about the structure the golden dream of the material science is becoming true: the possibility of theoretical construction of new materials with the desired properties.
Significance for science
We have successfully performed the Auger electron – ion charge state experiment to study decay of Ar L3 hole(s) generated by 1 keV electron impact. We have reached 20-times better energy resolution than available before by introducing a new experimental concept to improve signal-to-noise ratio: 1 MHz pulsed electron impact excitation of the gas target. In coincidence experiments at Elettra and Bessy II synchrotron we have directly measured only few tens of ps long lifetimes of doubly excited helium atoms. This achievement demonstrates the possibility to measure reliably such a short lifetimes using a normal, multibunch operating mode of the synchrotron. We obtained attention for our theoretical analysis of VUV light scattered from helium in the strong homogeneous electric field; we have employed a complex rotation method which is interesting by itself since the method deals with nonhermitian operators. We have worked out theoretically a phenomenon of Young interference on a single atomic-size slit arrangement and proposed an experiment with He ions impinging onto hydrogen molecules. An independent group of French researches has recently preformed the experiment that fully confirmed our predictions and published their results in Phys. Rev. Lett. Recently we have collaborated with Hungarian researchers to measure for the first time the electron impact resonant Auger scattering in the vicinity of L3 edge of Ar. Besides important achievements in the basic science regarding study of multiply excited states of mono-atomic vapors the x-ray absorption group is active in the field of the structure research (EXAFS, XANES), where it focuses onto study of nanostructures and exotic aggregates of disordered compounds, quasi crystals and samples of importance for the environment protection research. We have studied resonant x-ray scattering (RIXS) with a home made high resolution crystal spectrometer, which is designed for the spectrometry of diluted and relatively large samples. Besides the gas targets at ESRF we have made pilot RIXS measurements on solid samples containing Mo, W and S. Apart for the specific project this is important for the development of RIXS as a new powerful technique for structure studies. Synchrotron research of surfaces was focused onto thin layers of metallic and organic materials on semiconductor substrates, which are a prototype of nano, structured materials with new optical, transport and magnetic properties. The study of these complex systems with combination of different techniques was done at Elettra beamline ALOISA/HASPES. We deal with . The new spectrometer dealing with vibrationally excited hydrogen molecules was developed by our research program member and the operation is based on the principle of dissociative attachment of electrons.The work proceeds in the frame of Euroatom association and is partially funded by it due to the interest in the edge plasma, which occurs close to the walls of fusion reactors and where the role of vibrationally excited molecules is not yet fully understood. In the last period a proton microbeam was extensively used to reconstruct elemental distribution of quickly frozen biological samples. Other activities, which were further developed are the micromachining (production of micro sized objects by proton beam writing) and aerosol studies. In IBA development an important (and unexpected) achievement was the first successful set-up of con-focal PIXE method which allows a 3D element selective tomography by measuring x-ray yield of an object moving through the sensitive micro volume of the x-ray polycapillary.
Significance for the country
Our expertize with x-rays (EXAFS, XANES, RIXS, XPS) and ion beam methods (PIXE, RBS, ERDA, NRA) together with their micro- versions allows Slovenian laboratories (as well as those from abroad) working in the field of material research, geology, chemical synthesis, pharmacology, biology, vacuum technology, environmental research and cultural heritage preservation to approach modern analytical methods with synchrotron light and ion beams. So far our measurements are performed at synchrotron research centers HASYLAB, ESRF, ELETTRA, BESSYII and at the ion beam facility Mikroanalitical Center IJS in Ljubljana, where mostly our own instrumentation is used. We participated in the development of several technologically important materials, such as microporous catalysts, superconducting and ferroelectric ceramics, surfactants, thin layer and self-cleaning coatings and some pharmaceutical molecules. We are also active in solving the environmental problems due to pollution with heavy metals, pesticides and biological agents, and in preservation of the cultural heritage. A constant presence in the international research centers allows for a research work of enduring quality, the access to the foreign knowledge and indirectly, a generation of a positive image of Slovenia. A regular access to the synchrotron and ion accelerator beamtime is important also from the pedagogical point of view to demonstrate to students a wealth of experimental approaches which are developed to efficiently use the available resources. These techniques are also presented in a number of academic programs at the undergraduate or graduate level. The students can gain the knowledge of modern characterization techniques with synchrotron light and ion beams by direct involvement in our measurements and by the participation in data analysis. Equally, the program provides the opportunity for Slovene scientists to gain experience in the surface and material science and for the transfer of the high-technology know-how to the research and industrial labs. Our involvement with the fusion and free electron laser related research allows, in principle, the contact with the most advanced technologies for the construction of ITER and FEL sources. In the next phase these technologies will be commercialized and they offer the opportunity for the spin-off activities. We are actively collaborating in finding the solutions for the environment reconstruction due to the heavy metal and dust pollution and we are involved in the restavration project of important documents of the cultural heritage. Similar studies of the soil as performed for the Cornwall region (As pollution) we have started in Slovenia in Mežiška valley (Cd and Pb pollution). We will concentrate on studying the possibilities of toxic metal transfer into the food chain due to the accumulation in plants and on their bioavailability due to respirational and gastrointestinal uptake. An analysis of vineyard soils from southwest Slovenia and Friulia for contamination with Cu and Fe through intensive agricultural methods is under way; the results will be used in devising the efficient recovery measures. In collaboration with the National Library, historic documents are examined for the decomposition of the cellulose by the corrosive action of iron-gall inks. In the past we have successfully developed sampling and ion beam analysis techniques to determine elemental concentrations in aerosols. We reported the results at public workshops, working environments and in the research papers. A proton microbeam is used to generate high resolution elemental maps of frozen biological samples, for example to study the mechanisms of plant hyper accumulators of toxic metals.
Most important scientific results
Final report,
complete report on dLib.si
Most important socioeconomically and culturally relevant results
Final report,
complete report on dLib.si
