X-Ray studies on optical and structural properties of ZnO nanostructured thin films

Abstract X-ray absorption near-edge fine structure (XANES) studies have been carried out on nanostructured ZnO thin films prepared by atmospheric pressure chemical vapour deposition (APCVD). Films have been characterized by X-ray diffraction (XRD) and optical luminescence spectroscopy exciting with laser light (PL) or X-ray (XEOL). According to XRD measurements, all the APCVD samples reveal a highly (002) oriented crystalline structure. The samples have different thickness (less than 1 μm) and show significant shifts of the PL and XEOL bands in the visible region. Zn K-edge XANES spectra were recorded using synchrotron radiation at BM08 of ESRF (France), by detecting photoluminescence yield…

X-ray Absorption Study of Gallium Arsenide at the Ga and As K-edges

We present X-ray absorption study of gallium arsenide at the Ga and As K-edges. The analysis of the X-ray absorption fine structure was done in the framework of the multiple-scattering theory. Both XANES and EXAFS regions are considered. The calculated signals are in very good agreement with experimental data. It is shown that for both edges multiple-scattering contributions are negligible for wavevector values greater than 3 Å-1, and single-scattering analysis can be used without significant loss of accuracy in that region.

Local structure aroundEr3+inSiO2−HfO2glassy waveguides using EXAFS

${\mathrm{Er}}^{3+}$-doped $\mathrm{Si}{\mathrm{O}}_{2}\text{\ensuremath{-}}\mathrm{Hf}{\mathrm{O}}_{2}$ glassy waveguides with $\mathrm{Hf}{\mathrm{O}}_{2}$ concentrations ranging from $10\phantom{\rule{0.3em}{0ex}}\text{to}\phantom{\rule{0.3em}{0ex}}50\phantom{\rule{0.3em}{0ex}}\mathrm{mol}\phantom{\rule{0.2em}{0ex}}%$ were prepared using the sol-gel route and deposited on $v\text{\ensuremath{-}}\mathrm{Si}{\mathrm{O}}_{2}$ substrates using the dip-coating technique. The local environment around ${\mathrm{Er}}^{3+}$ ions was determined from Er ${L}_{3}$-edge extended x-ray-absorption fine-structure (EXAFS) measurements. The first coordination shell around ${\mathrm{Er}}^{3+}$ ions is comp…

Local structure and magnetization of ferromagnetic Cu-doped ZnO films: No magnetism at the dopant?

Abstract Relationship between magnetism and structure of Cu-doped ZnO was investigated at macroscopic and microscopic levels. Thin Zn1−xCuxO films (x = 0.02, 0.04, 0.07 and 0.10) were prepared by a pulsed laser deposition and characterized via superconducting quantum interference device (SQUID) magnetometry, high-resolution x-ray diffraction, and Cu K-edge and Zn K-edge x-ray absorption, x-ray linear dichroism and x-ray circular magnetic dichroism spectroscopy. Even though the samples exhibit room-temperature ferromagnetism with magnetization that increases with Cu concentration, we did not detect signatures of local magnetic moments associated with Cu atoms, as evidenced by the lack of any…

Short-range order around Er3+ in silica waveguides containing aluminium, titanium and hafnium

Er3+-doped silica waveguides, co-doped with aluminium, titanium, and hafnium oxides, were prepared using the sol-gel method and dip-coating processing. Here, we present a characterisation of the local environment around Er3+ ions, as determined from the Er L3-edge extended X-ray absorption fine structure (EXAFS) measurements performed at ESRF (France). The first coordination shell is composed of 5-6 oxygen atoms at distances ~2.32-2.35 A , slightly varying as a function of the modifier oxide. Er3+ nearest neighbors distance does not show a significant compositional dependence. On the contrary, outer shells analysis shows significant differences: Al2O3 doping (less than 2% mol) induces an or…

X-ray absorption spectroscopy of strongly disordered glasses: Local structure around Ag ions ing−Ag2O∙nB2O3

The local structure around Ag ions in silver borate glasses $g\text{\ensuremath{-}}{\mathrm{Ag}}_{2}\mathrm{O}∙n{\mathrm{B}}_{2}{\mathrm{O}}_{3}$ $(n=2,4)$ was studied by x-ray absorption spectroscopy at the Ag $K$ edge for temperatures from $77\phantom{\rule{0.3em}{0ex}}\text{to}\phantom{\rule{0.3em}{0ex}}450\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. Extended x-ray absorption fine structure (EXAFS) analysis based on cumulant expansion or multishell Gaussian model fails for these systems. Therefore, the radial distribution functions (RDFs) around Ag ions were reconstructed using a method based on the direct inversion of the EXAFS expression. The RDFs consist of about eight atoms (oxygens and b…

Nanoscale x-ray absorption spectroscopy using XEOL-SNOM detection mode

The first results obtained with the prototype system at the synchrotron beamline ID03 at ESRF are presented and illustrate the possibility to detect an element-specific contrast and to perform nanoscale x-ray absorption spectroscopy experiments at the Zn K and W L 3 absorption edges in mixed zinc oxide-zinc tungstate thin films.

X-ray absorption spectroscopy study of local dynamics and thermal expansion in ReO3

The thermal expansion of polycrystalline ${\mathrm{ReO}}_{3}$ is studied in vacuum by x-ray diffraction from 300 to 600 K and by extended x-ray absorption fine structure (EXAFS) at the Re ${L}_{3}$ edge from 30 to 600 K. A detailed EXAFS analysis is presented up to the sixth coordination shell around Re. The crystal thermal expansion is weak throughout the explored range, negative below 100 K, positive from 150 to 500 K, and negative again above 500 K. The analysis of mean square relative displacements obtained by EXAFS and of mean square displacements available from x-ray and neutron diffraction measurements confirms the presence of significant static disorder in the investigated samples. …

Femtometer accuracy EXAFS measurements: Isotopic effect in the first, second and third coordination shells of germanium

The analysis of the EXAFS signals from 70Ge and 76Ge has evidenced the low-temperature effect of isotopic mass difference on the amplitude of relative atomic vibrations. This effect is reflected in the difference of the Debye-Waller factors of the first three coordination shells, and on the difference of nearest-neighbour average interatomic distances, evaluated with femtometer accuracy. The experimental results are in agreement with theoretical expectations.

Local Environment of Co2+ Ions in β″-Alumina Crystals

Isotopic Effect In Extended X-Ray-Absorption Fine Structure of Germanium

Extended x-ray absorption fine structure has been measured on two powdered samples of 70Ge and 76Ge as a function of temperature from 20 to 300 K. The effect of isotopic mass difference on the amplitude of relative atomic vibrations is neatly evidenced by the temperature dependence of the difference of Debye-Waller factors. The isotopic effect is also detected on the difference of nearest-neighbor average ineratomic distances, thanks to a resolution better than 10 fm. (DOI: 10.1103/PhysRevLett.100.055901)

XANES and EXAFS modelling of configurational disorder in silver borate glasses

The sensitivity of X-ray absorption spectroscopy (XAS) to the local structure around a selected atomic species (symmetry, distances and angles) is commonly exploited to quantitatively describe systems where all the configurations around the absorbing atoms may be approximated by the mean one. However, in many cases of disordered systems a simple description of the local structure with singleconfiguration models cannot be reconciled with experimental spectra. In this paper the necessity to analyse the XAS spectra by considering a multiplicity of atomic structural configurations is demonstrated in the case of silver borate glasses. The local coordination around Ag cations in (Ag2O.nB2O3) glas…

A high-temperature x-ray absorption spectroscopy study of

We present for the first time a high-temperature x-ray absorption spectroscopy study of at the edge. The analysis both of the XANES and of the EXAFS regions shows that, in , a progressive localization of the 5d states following the temperature rise is accompanied at T > 350 K by a distortion of the octahedra, which increases up to the decomposition temperature . The distortion leads to the lowering of the rhenium site symmetry from and is due to the electron - phonon coupling of the 5d electrons with the and phonons and to the Jahn - Teller effect caused by the rhenium electron which becomes localized at high temperature.