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Metrology of Quantitative Surface Analysis by Electron Spectroscopies
(A. Jablonski, L. Zommer)


    The main field of interest is the theoretical basis of Auger electron spectroscopy (AES) and photoelectron spectroscopy (XPS). Current studies consist in introduction of new parameters describing the electron transport in formalism of both techniques, in developing of new methods for determination of these parameters, and edition of databases providing these parameters. In consequence, these studies are improving accuracy of quantitative analysis by above electron spectroscopies.
    The considered techniques, AES and XPS, make possible the identification of elements present in the surface region of a solid. The XPS spectrum recorded for the AuAgCuPd alloy, and an example of such analysis is shown below. It consists in identification of peaks visible in the spectrum. Qualitative analysis is presently a routine procedure providing information on elements present (or chemical compounds).
 Although the surface sensitive spectroscopies, AES and XPS, are developed since early 1970s, the quantitative analysis of surface still is a major scientific challenge. Derivation of such information of high accuracy from intensities of observed peaks is still a major scientific challenge.
     Research associated with quantification of electron spectroscopies is conducted in cooperation with National Institute of Standards and Technology (NIST) in USA. The databases containing parameters needed for quantitative surface analysis, edited within this cooperation, are currently recommended and distributed by NIST.
    Research is also devoted towards new parameters describing electron transport. Some of the parameters proposed in the past (the mean electron escape depth, the emission depth distribution function, and the effective attenuation length) have become the accepted international standards supported by the relevant organizations: ISO (International Standard Organization) and ASTM (American Society for Testing and Materials). Results of this research are very well cited in the literature.

Biomaterials, SERS active substrates, conductors for oxygen ions, physico-chemical investigation of the surface materials
(M.Pisarek, A.Roguska, M.Holdynski)

To date, studies of modified Ti surfaces for biomedical purposes have concentrated on observations of morphology and identifying their physicochemical properties. A promising approach to meet the above requirements it to create modern type of composite coatings on Ti substrate, namely Ca-P/Ag/TiO2 composite coatings, with well-defined microstructure, chemical and phase composition, controlled porosity and surface topography. Preliminary studies have shown that TiO2 nanotubes fabricated via anodization technique have ordered structure and their growth is perpendicular to Ti substrate. The specific surface morphology of TiO2 nanotubes facilitates the formation of calcium phosphate (Ca-P) layers under physiological conditions. Additional loading of the resulted coatings with Ag nanoparticles with diameter of 2 ? 50 nm using sputter deposition technique  is expected to provide antiseptic properties. Composite layers on Ti consisting of bioactive ceramic coating and Ag nanoparticles should have a positive impact on the osteoblasts activity and prevent bacterial adhesion to the implant surface. Moreover, nanoporous oxide layers (TiO2, Al2O3) decorated with nanoparticles of Ag, Au or Cu can be used as model substrates for SERS investigations. Such systems may be particularly active substrates capable of increasing the cross sections for Raman scattering of adsorbed organic molecules (e.g. pyridine) to a degree much higher than is possible on the electrochemically roughened surfaces of SERS active metals. SERS spectra of molecules adsorbed on the surface of new nano-structured materials will allow to understand electromagnetic (depending on the morphology) and chemical (the effect of CT (charge transfer) transition associated with a partial charge between adsorbate and adsorbent) effects. SERS investigation using substrates with variable nanoporous morphology and different sizes of metal nanoparticles, is of particular interest since the reduction in size of material through the nanoscale regime (< 100 nm) can lead to a new chemical n\and physical properties clearly different from the bulk counterparts of those materials.
Using simple methods of chemical synthesis of oxides based on rare-earth in aqueous solutions of organic acids, combined with heat treatment can lead to create a new generation of nanomaterials (oxygen ions conductors based on CeO2). These types of materials that can be used as solid electrolyte for intermediate-temperature solid oxide fuel cells (SOFC) or oxygen pumps, are showing a higher ionic conductivity in the temperature range 500oC - 700oC  than stabilized zirconia (YSZ) used so far. Low working temperature of electrolytes based on CeO2 and stability in a reducing atmosphere (in contrast to materials based on Bi2O3) can allow for their wider use.


Metal oxide catalyst doped with nanoparticles.

(A. Jablonski, A. Bilinski, O. Chenyayeva, A. Kosinski, M. Krawczyk, W. Lisowski, K. Nikiforov, J. W. Sobczak)

AuCeMnMAThe subject of our studies are metal oxides doped with nanoparticles of other metals, which are used as supports for catalysts. The changes in the electron state of oxide-support  and doped metal-interactive chemical species induced by various preparation method, thermal processing and the impact of the selected reactive gases are examined using XPS, AES, SPM.
Ceria oxide doped by nanosize particles of gold and one of the metals: Co, Sn, Mn, Fe, is a model system of investigations. The method of preparation of such catalysts significantly affect the electron state of both oxide support and doped metals. An important prerequisite is to obtain highly dispersed nanoparticles of metals whose interaction with the  oxide support leads to the formation of catalytically active systems. Particularly important is Au doping. Unlike traditional metal supported catalysts, metallic gold nanoparticles are not active in the catalytic reaction and for the catalytic activity are responsible the nonmetallic, positively charged gold nanoparticles (described as Au+, which are strongly bound with CeO2. The presence of such nanoparticles on the catalyst surface shows the XPS spectrum of Au 4f , recorded on PHI 5000 VersaProbe spectrometer for Au/CeO2 sample doped with Mn.
Methods of preparation significantly affect the electron state of gold species supported on CeO2 support;  in addition to the desired states of Au+, also the negatively charged states of gold species Au- can be generated as a result of electron transfer from the ceria support, or as a result of the agglomeration the metallic Au crystallites may be formed, which do not generate the catalytic activity. In the model system Au-CeO2, the active site location of Au nanoparticles in ceria support is formed by oxygen vacancies, lattice sites with a deficit of oxygen, in which the cerium atoms are at a lower oxidation state (Ce+3) compared to the basic structure of the crystal lattice of CeO2 (Ce+4).
Model systems are also studied to determine the selected parameters of electron transport, particularly the mean free path by EPES. This parameter is very important in the practical quantitative analysis in XPS and AES spectroscopy. These studies are important for understanding the course of basic catalytic processes, selection of the optimal reaction conditions and the selection of the optimal catalyst support for the chosen reaction. Systems of metal nanoparticles on oxide supports are known as catalyst systems, with an exceptionally wide range of application in environmental processes: low-temperature gas combustion (removal of hydrocarbons, oxides of nitrogen) and low temperature water gas conversion reaction as a source of pure hydrogen for energy (fuel cells, clean motor fuel) and also photocatalytic removal of pollution from surface waters.

Cooperation

At present moment we have intense and fruitful cooperation with following laboratories and workgroups all around the globe:

-  Surfaces, Thin Films, Nanostructures Group,  Institute of Catalysis and Surface Chemistry PAS, Cracow (prof. Józef Korecki);
-  Surface and Microanalysis Science Division, National Institute of Standards and Technology, Gaithersburg, USA (dr C.J. Powell);
-  Surface physics/structure department, Research Institute for Technical Physics and Material Sciences, Hungarian Academy of Science (dr Miklos Menyhard);
-  Grup de física de les radiacions i llurs aplicacions a la física m?dica, Facultat de Fisica (ECM), Universitat de Barcelona, Barcelona, Spain (prof. F. Salvat);
-  LASMEA - LAboratoire des Sciences et Matériaux pour l?Electronique et d?Automatique- Universite Blaise Pascal, Clermont ?Ferrant, Francja (prof. Bernard Gruzza);
-  Department of Optical Crystals, Institute of Physics, Academy of Sciences of the Czech Republic, Praga (dr Josef Zemek);
-  Department of Scientific Bases for Synthesis and Selection of Heterogeneous Catalysts, Institute of Catalysis, Bulgarian Academy of Sciences, Sofia (prof. Dr Donka Andreeva).