Program: K1 CEMS K1 CEMS K1.1. R. Gancedo (Madrid): On the Application of Mössbauer Spectroscopy to the Study of Surfaces K1.2. D. Hanzel (Ljubljana): Conversion Electron Mössbauer Spectroscopy Study of Langmuir-Blodgett Films K1.3. A. Kholmetskij (Minsk): Modification of Steel Surfaces After Plasma and Ion Beam Implantation Investigated by Means of CEMS K1.4. P. Schaaf (Göttingen): Surfaces, Interfaces, and Reactions Resolved by CEMS K1.5. M. Miglierini (Bratislava): CEMS Studies of Laser Treated Disordered Systems O1.1. M. Seberíni (Bratislava): CEMS Measurement of Surface Hardening of Toothed Wheels K1.1 On the Application of Mössbauer Spectroscopy to the Study of Surfaces J.R. Gancedo Instituto "Rocasolano", CSIC, Madrid, Spain Mössbauer spectroscopy is a very useful and well-known technique for the study of Fe containing materials. The majority of measurements with this spectroscopy are performed in the transmission mode, while for the study of surfaces the back-scattering mode is the preferred option. When the 57Co Mössbauer source radiation interacts with a surface radiation denominated "non resonant" is backscattered, related mainly with photoelectrical and Compton interactions. When the surface contains Fe, and providing that the source energy is properly modulated, besides the non-resonant radiation, a radiation, "resonant", consequence of the relaxation of the nuclear level of 14.4 keV of the excited 57Fe nuclei, is also present. This resonant radiation includes photons and electrons of well-defined energies, whose probability to leave the surface is related with their nature, energy and track within the solid. The relaxation process is rather complex and involves both nuclear and atomic relaxations. The 14.4 keV level can decay via to ways: A first one involves the fluorescent re-emission of a g-photon carrying the total nuclear transition energy. In the second one the nuclear level relaxes by ejecting one core electron, denominated conversion electron, whose kinetic energy is the energy of the nuclear level minus the binding energy of electron core level involved. For 57Fe this latter way is "10 times more probable than the fluorescent re-emission, K-shell electrons being those most probably involved. The hole left in the core shell is filled from upper levels which gives origin to a cascade of photons and Auger electrons, whose energies are related to the specific path followed in each particular event. Among the resonant photons, Fe Ka X-rays are the most abundant ones. Their range is several mm, too "deep " to be a useful probe in surface studies, but adequate for its use in surface coating studies. The resonant outcoming electrons are either mainly K conversion electrons (7.3 keV) or Auger electrons of energies lower than 7.3 KeV. The range of the electrons of 7.3 kev is "250 nm, suitable for surface studies. All the techniques related with the above described phenomena are encompassed within the CEMS (Conversion Electron Mössbauer Spectroscopy) family of techniques. In the most usual approach all the outcoming electrons are registered (ICEMS, Integral CEMS). This technique is experimentally very simple, since a detector sensitive only to electrons is required, living out the photons, a quite easy job considering the great difference in stopping power of matter for these two types of radiation. K1.2 Conversion Electron Mössbauer Spectroscopy Study of Langmuir-Blodgett Films D. Hanžel J. Stefan Institute, Ljubljana, Slovenia Langmuir-Blodgett films of iron stearate (23 and 27 monolayers) have been formed on silicon wafers and afterwards thermally treated in air at 260oC for 45 minutes. The resulting, very well defined oxide films exhibited very smooth and homogeneous surfaces. These oxide films have been investigated by ultra high vacuum low temperature conversion electron Mössbauer spectroscopy (CEMS). The oxide film, supposedly g-FeOOH, contains only 6 monolayers of iron corresponding to only three crystallographic unit cells (or 1.5 magnetic unit cells) and thus enables the study of non-equivalent sites in the oxide film due to surface and interface effects. The magnetic ordering temperature of the 27 layers sample corresponds almost to the bulk value, while the 23 layers sample orders at lower temperature. K1.3 Modification of Steel Surfaces After Plasma and Ion Beam Implantation Investigated by Means of CEMS A.L. Kholmetski1, V.V. Uglov1, V.M. Anishchik1, V.V. Astashinski1, V.M. Astashinski2, S.I. Ananin2, E.A. Kostyulevich2, A.M. Kuzmitski2, N.T. Kvasov3 and A.L. Danilyul3 1) Belarussian State University, Minsk, Belarus 2) Institute of Molecular and Atomic Physics, National Academy of Sciences of Belarus, Minsk 3) Belarussian State University of Informatics and Radioelectronics, Minsk, Belarus At present time the methods of high-current ion implantation (HCII), plasma-immersion implantation (PIII), and compression plasma flow (CPF) method attract a great attention due to their ability to create comparably thick modified surface layers (up to 500 mm). Many authors reported about enhancement of mechanical properties of steels after these kinds of treatment of surfaces. Using CEMS and XMS as the main methods of research, we aimed to find correlation between mechanical properties of modified surfaces and their structure. Mossbauer spectroscopy was used in combination with XRD and AES. HII and PIII were made with AISI M2 steel; the CPF was applied to Y8A carbon steel samples. High-current ion implantation used the ions of nitrogen, ions of boron, as well as B+N and N+B. We revealed a formation of thin surface layers with nitrides a"-Fe16N2, e-FexN and borides FeB, Fe2B, as well as a formation of a layer with a thickness up to 10 mm containing only nitrides. A presence of double-layer system with borides and nitrides essentially increases a microhardness of surface and decreases a friction coefficient. At the same time, analysis of mechanical properties of the surface of AISI M2 shows that the revealed phase transformations cannot completely explain the observed changes in microhardness and friction coefficient of the surface layers. This fact allows to propose a formation of cubic boron carbide, which greatly increases a microhardness of surface. Plasma-immersion implantation modifies a surface layer of AISI M2 with the thickness of few micrometers, and it leads to formation of S-phase (expanded austenite) in a surface layer of about 0.1 mm, that enhances mechanical properties of steel. The main attention in this work was given to comparably new CPF method. The flows were generated by a Magnetoplasma compressor (MPC) on Y8A carbon steel samples is carried out. The parameters of accelerators energy accumulator (W0 = 10 kJ, U0 = 4 kV) enable to obtain the maximum value of a discharge current (80 kA) at a discharge duration of 140 ms. Under these conditions a CPF 12 cm in length and 1 cm in diameter in the region of maximum compression is formed downstream of a tip of a discharge device of MPC. Charge particle concentration in CPF is 7×1017 cm-3, characteristic velocity of plasma formations is 4×106 cm/s. Mössbauer measurements of YA8 steel after CPF do not reveal a formation of any compounds of iron with nitrogen. In a thin surface layer 0.1 mm an intensive a®g transformation takes place, concentration of a-Fe decreased to about 40%. Under XMS measurements the concentration of a-Fe is essentially higher. In non-magnetic structure one can distinguish g-Fe and g-Fe(C) lines, the latter resulting from perlite-austenite transformation. The paper presents an analytical description of Mössbauer spectra taking into account fissioning effects, enabling to reveal the evolution of Mössbauer nuclei surroundings. K1.4 Surfaces, Interfaces, and Reactions Resolved by CEMS P. Schaaf, A. Müller, S. Wagner and E. Carpene Universität Göttingen, Zweites Physikalisches Institut, Göttingen, Germany Soon after the discovery of the Mössbauer effect and its use in materials research on atomic scales, Conversion Electron Mössbauer Spectroscopy (CEMS) was developed as an alternative measuring method, especially sensitive to surfaces. Now, CEMS is used in numerous investigations of problems on surfaces, in interfaces and thin films. Here, some newer developments will be presented concerning thin iron films deposited on single crystalline silicon by pulsed laser deposition (PLD), electron beam evaporation and an also effusion cell. Their surfaces, interfaces and their magnetic behavior are investigated by CEMS in the as-deposited state as well as after ion-beam and laser treatments [1,2]. The resulting changes and reactions can be accurately determined by that. This becomes even more sophisticated by sandwiching in some nanometer thick 57Fe marker layers [3]. Furthermore, special attention will be given to a new CEMS-based method for determining magnetic spin textures in thin iron films before and after ion irradiation. It is unambiguously proven by the CEMS results that ion irradiation can induce a perfect uni-axial spin texture in these iron films. The method and the results are explained and compared with magneto-optical Kerr effect (MOKE) measurements [4]. [1] M. Milosavljevic, S. Dhar, P. Schaaf, N. Bibić, Y-L. Huang, M. Seibt, and K.-P. Lieb. "Growth of b-FeSi2 films via noble gas ion-beam mixing of Fe/Si bi-layers". J. Appl. Phys. 90 (2001) 4474-4484. [2] S. Wagner, E. Carpene, M. Weisheit, and P. Schaaf. "Formation of b-FeSi2 by Excimer Laser Irradiation of 57Fe/Si-bilayers". Appl. Surf. Sci. 186 (2002) 156-161. [3] P. Schaaf, M. Weisheit, and H.-U. Krebs. "Materials Surface Processing spied by Hyperfine Interactions". Acta Physica Polonica A 100 (2001) 699-706. [4] K.-P. Lieb, K. Zhang, G.A. Müller, P. Schaaf, M. Uhrmacher, W. Felsch, and M. Münzenberg. "Magnetic Textures in Thin Ion-Irradiated Ni and Fe Films". Acta Physica Polonica A100 (2001) 751-760. K1.5 CEMS Studies of Laser Treated Disordered Amorphous and Nanocrystalline Systems M. Miglierini1, K. Sedlačková1, E. Carpene2 and P. Schaaf2 1) Department of Nuclear Physics and Technology, Slovak University of Technology, Bratislava, Slovakia 2) Zweites Physikalisches Institute, Universität Göttingen, Göttingen, Germany Conversion electrons provide an information depth of about 150 nm for most iron rich alloys. Thus, surface effects can be effectively studied by means of Conversion Electron Mössbauer Spectroscopy (CEMS). We employ this technique as the principal method for the investigation of surface modifications induced by pulsed excimer laser irradiation. Such treatments proved to be an industrially promising technology when applied to steels under determined atmosphere - the so-called laser-nitriding [1]. The effects of laser beam on the structure of magnetic domains and, hence, on the microscopic behaviour of hyperfine fields in metallic glasses were also studied for a variety of systems with positive [2] and/or close-to-zero magnetostriction [3]. A rotation of the net magenetisation was observed by means of Mössbauer spectra in addition to surface crystallization initiated by laser treatment [4, 5]. This study reports on the magnetic microstructure of amorphous materials with Curie temperature close-to-room temperature exposed to laser treatment. Such systems do not show six-line Mössbauer patterns and represent an analytical challenge because of the line-intensity ratios, which are correlated to magnetic texture, cannot be used as a measure of laser-induced modifications. In addition, we have chosen such materials, which after suitable temperature annealing exhibit a nanocrystalline behaviour. This enables the effects of laser treatment on both the amorphous and the nanocrystalline disordered structures being investigated and discussed. Contribution of the grants SGA 1/8305/01 and DAAD 17/2002 is acknowledged. [1] P. Schaaf, Prog. Mater. Sci 47 (2202) 1-161 [2] U. Gonser and P. Schaaf, Fresenius J. Anal. Chem. 341 (1991) 131-5. [3] M. Sorescu, Phys. Rev. B 61 (2000) 14338-41. [4] G. Rixecker, P. Schaaf and U. Gonser, J. Phys. D: Appl. Phys. 26 (1993) 870-879. [5] M. Sorescu, J. Magn. Magn. Mater. 218 (2000) 211-20. O1.6 CEMS Measurement of Surface Hardening of Toothed Wheels M. Seberíni, J. Lipka and I. Tóth Department of Nuclear Physics and Technology, Slovak University of Technology, Bratislava, Slovakia Surface hardening is one of the final steps in production of toothed wheels. It is done by bombardment of the tooth surface in two steps: 1) by glass balls and 2) by steel balls. A search goes on after a reliable method, which could detect the quality and the intensity of the hardening process. Three samples in the form of steel plates were measured in common Mössbauer scattering geometry and by CEMS method. The samples were: 1) unprocessed, 2) shot for shorter process time and 3) shot for full process time. After CEMS measurement, the surface layer of the unprocessed sample was ground off and measured again in order to obtain a reference on bulk material. While little significant changes were found in the results of the common Mössbauer scattering measurement, the effect in the change of CEMS spectra is striking. A distinct paramagnetic component, with the area comparable to the spectrum of the basic material, appeared in the middle of the two spectra of the processed samples and, moreover, it seems to be sensitive to the time (or intensity) of bombardment of the material surface.