Ca L2,3 edge XANES and Sr K edge EXAFS study of hydroxyapatite and fossil bone apatite

Upon burial, the organic and inorganic components of hard tissues such as bone, teeth, and tusks are subjected to various alterations as a result of interactions with the chemical milieu of soil, groundwater, and presence of microorganisms. In this study, simulation of the Ca L$_{2,3}$-edge X-ray absorption near edge structure (XANES) spectrum of hydroxyapatite, using the CTM4XAS code, reveals that the different symmetry of the two nonequivalent Ca$_{(1)}$ and Ca${(2)}$ sites in the unit cell gives rise to specific spectral features. Moreover, Ca L$_{2,3}$-edge XANES spectroscopy is applied in order to assess variations in fossil bone apatite crystallinity due to heavy bacterial alteration and catastrophic mineral dissolution, compared to well-preserved fossil apatite, fresh bone, and geologic apatite reference samples. Fossilization-induced chemical alterations are investigated by means of Ca L$_{2,3}$-edge XANES and scanning electron microscopy (SEM) and are related to histological evaluation using optical microscopy images. Finally, the variations in the bonding environment of Sr and its preference for substitution in the Ca$_{(1)}$ or Ca$_{(2)}$ sites upon increasing the Sr/Ca ratio is assessed by Sr K-edge extended X-ray absorption fine structure (EXAFS) spectroscopy

Characterization of fossil remains using XRF, XPS and XAFS spectroscopies

Synchrotron radiation micro-X-Ray Fluorescence (m-XRF), X-ray photoelectron (XPS) and X-ray Absorption Fine Structure (XAFS) spectroscopies are applied for the study of paleontological findings. More specifically the costal plate of a gigantic terrestrial turtle Titanochelon bacharidisi and a fossilized coprolite of the cave spotted hyena Crocuta crocuta spelaea are studied. Ca L2,3-edge NEXAFS and Ca 2p XPS are applied for the identification and quantification of apatite and Ca containing minerals. XRF mapping and XAFS are employed for the study of the spatial distribution and speciation of the minerals related to the deposition environment.Fil: Zougrou, I.M.. Aristotle University of Thessalonik; GreciaFil: Katsikini, M.. Aristotle University of Thessalonik; GreciaFil: Pinakidou, F.. Aristotle University of Thessalonik; GreciaFil: Brzhezinskaya, M.. No especifíca;Fil: Papadopoulou, L.. Aristotle University of Thessalonik; GreciaFil: Vlachos, Evangelos. Aristotle University of Thessalonik; Grecia. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Tsoukala, E.. Aristotle University of Thessalonik; GreciaFil: Paloura, E.C.. Aristotle University of Thessalonik; Greci

Study of the modification of the microstructure of GaN after high \u2013 dose Si implantation

Rare earth oxides are among the materials which are presently studied as possible replacements of amorphous silicon dioxide as gate insulators in nanometric Si devices; in fact, they generally exhibit high values of the dielectric constant (\u201chigh-k\u201d), a necessary requirement to obtain a high capacitance with layer thickness greater than the value below which tunnelling currents become unacceptably high. Lu2O3 is one of the rare earth oxides which may have the required properties in view of its quite high values of  and forbidden band gap. Since the envisaged dielectric layers are only a few nm thick a description and a physical understanding of the atomic and electronic structure of the interface are of great importance. In this paper, we report a study by synchrotron radiation photoemission and transmission electron microscopy of the growth of Lu2O3 on Si(001). We provide evidence of a rather complex structure in which all silicon suboxides and SiO2 are present at the same time, along with a silicate \u2013 like phase and Lu2O3 itself; moreover, both crystalline and amorphous portions are present. The valence band discontinuity is found to be 3.16 \ub1 0.16 eV. These findings are discussed in the context of available theoretical predictions of thermodynamic stability versus the formation of silicon oxide, silicates and silicides and of the band discontinuity problem

Oxidation of Cu3N thin films obtained from Cu annealed under NH3 O2 flow A Raman and N K edge NEXAFS study

Cu3N layers prepared by annealing, under NH3 O2 flow, of Cu sputtered on Si, fused SiO2, and soda lime glass were studied by Raman and N K edge Near Edge X ray Absorption Fine Structure NEXAFS spectroscopy. The annealing temperatures were ranging from 300 to 800 C. Benefiting from resonance effects on the Raman peak intensities when different excitation wavelengths are used, the contribution in the Raman signal of copper oxides, which provide peaks lying close to those of Cu3N, is more easily discriminated. The formation of Cu2O surface oxide is observed in almost all the samples even for annealing at low temperatures. CuO is generally formed at higher temperatures with the onset depending on the amount of O2 in the NH3 O2 mixture. However, high temperature is necessary to grow larger crystallites, as it is deduced from the decrease in the width of the high frequency Raman peak at ca. 650 cm amp; 8722;1 of Cu3N, in accordance with Scanning Electron Microscopy observations. The formation of CuO is accompanied by the creation of N2 trapped in the sample, which is directly detected by the NEXAFS measurements. N2 is most probably formed by the N atoms originating from the dissociation of the Cu N bond