Group for the
characterization
of materials with X-ray
absorption spectroscopies

research interests

The group members are activated in the field of characterization of materials using X-ray absorption techniques using synchrotron radiation since 1990. The experiments are conducted in the European facilities BESSY, DESY, ESRF, ELETTRA , SLS with finacial support from European Community's programs. The groups has active collaborations with universities and research institutes in Greece and abroad.
The characterization techniques which are applied are the X-ray absorption fine structure (XAFS), the X-ray fluorescence (XRF) and the X-ray photoelectron (XPS) spectroscopies. The XRF and XPS spectroscopies provide quantitative information on the sample contet whereas XAFS spectroscopy provides information on the bonding enviroment of elements present in the sample, their oxidation state the materials symmetry and electroni structure. XAFS and XRF spectroscopies are also applied in combinations with XRF maping with micrometric spatial resolution providing information on the local composition and structure at the atomic scale.
The research activities of the group are summarized as follows:

Mobirise

silicon nitride

Determination of the bonding environment of N and the density of empty states. Effect of the O and H inclusion, ion implantation, annealing and growth method. Silicon nitride finds application in microelectronics

Mobirise

group III nitrides

Determination of the bonding environment around Ga, In, N in binary AlN, GaN, InN semiconcutors and their alloys. Effect of ion implantation, alloying and temperature. Group III nitrides are direct band gap semiconductors and find applications in the fabrication of light emitting devices as well as in high temperature/ high power microelectronics.

Mobirise

vitrified industrial wastes

Spatial distribution, bonding geometry and oxidation state of Fe, Pb, Cr which are present in toxic wastes from oil distilleries, tanneries etc. The bonding environment of these elements is crucial for their immobilization and inactivation in glass or glass-ceramic products which are prepared by means of vitrification.

Mobirise

toxic elements adsorbents

Oxidation state and adsorption type of As, Cr on Fe,Mn nanoporous (hydroxy)oxides etc. These elements are contained in natural waters and when they are present in certain oxidation states [e.g. As(III), Cr(VI)] they are toxic for the human organism. The investigation of their oxidation/reduction to less toxic species as well as the determination of the way they are trapped on the surface of the adsorbent are important because they determine the amount of the element that can be removed from the water.

Mobirise

magnetic nano-materials

Bonding environment and oxidation state of Fe, Mn in ferrite nanoparticles which find applications in biomedicine (magnetic hyperthermia, constrast media for MRI, drug delivery). The oxidation state of these elements and the tetrahedral or octahedral configuration determines their magnetic properties.

Mobirise

palaeontological findings

Bones, teeth, tusks up to 5 million years old which are fossilized in different depositional environments, exhibit different preservation state. The spatial distribution of various elements originating from the depositional environment (e.g. Fe, Mn) and their bonding environment are used in order to determine their role in the fossilization procedure. The donding environment of Ca is also studied in order to obtain information on the variations imposed by the fossilization on the bone apatite.

Mobirise

biominerals

Living organisms synthesize biomineral phases for support (e.g. bones) or protection (e.g. crustaceans). The concentration and bonding environment of various elements like Br (it was found bonded in the chromoprotein located at the epicurticle) and Sr (that substitutes for Ca). Information on the crystalline phase of the calcium caronate is also obtained (optimization of the mechanical properties - adaptation).

Mobirise

hard/soft tissues

Nails and hair contain small amounts of essential elements (Fe, Zn, Ca, P, K, Cl etc) as well S since they are contain keratin which is rich in cysteine. Lack or excess of these elements in often related with disorders or diseases. The effect of (lung and skin) diseases on the spatial distriution of these elements is studied. Soft (cancerous or adjucent healthy) tissues from companion animals are also studied.