X-ray Emission Data Research Articles

RHESSI/GOESOBSERVATIONS OF THE NONFLARING SUN FROM 2002 TO 2006

In this work, we obtain the temperature (T) and emission measure (EM) for solar X-ray emission, using RHESSI and GOES data, at times for which there are no solar flares. Approximately 8700 time intervals during the RHESSI mission, from launch until 2006 August, are analyzed. We find that high-temperature emission, in the temperature range of 5-10 MK, is typically present during active times. When comparing temperature measurements, we find that RHESSI temperature measurements are consistently higher than GOES measurements, with smaller EM for RHESSI, but with values for the two instruments that are not necessarily well correlated.

Bulk electronic properties ofFeSi1−xGexinvestigated by high-resolution x-ray spectroscopies

We report an investigation of the bulk electronic properties of Fe in $\mathrm{Fe}{\mathrm{Si}}_{1\ensuremath{-}x}{\mathrm{Ge}}_{x}$ ($x=0$, 0.11, 0.19, and 0.44) measured by high-resolution x-ray absorption spectroscopy at the $\mathrm{Fe}\phantom{\rule{0.2em}{0ex}}K$ edge, $\mathrm{Fe}\phantom{\rule{0.2em}{0ex}}K\ensuremath{\beta}$ x-ray emission, and $1s3p$ resonant x-ray emission spectroscopies. The emission data clearly show an increase in the magnetic moment when $x$ increases from 0 to 0.44. This doping-induced spin transition is accompanied by the onset of the magnetic order at $x\ensuremath{\geqslant}0.2$. The $1s3p$ resonant x-ray emission data reveal that the $\mathrm{Fe}\phantom{\rule{0.2em}{0ex}}3d$ states exhibit a delocalized character, while no intermediate valence admixture takes place. This is at odd with the intermediate valence Kondo insulator model and rather supports the local density approximation band theory.

Electronic structure of transition metal fluorides and oxides determined by resonant X-ray absorption and X-ray emission spectroscopies

Experimental data for x-ray absorption at the transition metal L 2, 3 edge for FeF2 and CoF2 are presented. They are compared with the results of calculations that include the intra-atomic effects due to the ion atomic multiplet and also of the ligand field splitting of the 3d orbitals. Good overall agreement between experiment and theory is found. We also show resonant x-ray emission data for these compounds obtained at selected excitation energies and compare them with the results of the ligand field atomic multiplet calculation. Very good agreement between the experimental and the calculated energy splittings is found. We also found good agreement for the relative intensities of the emission peaks. This indicates that, as in the case of manganese compounds, the low energy loss peaks are due to decay into d-excited states of the ground configuration. A comparison of the emission spectra of LaMnO3, MnF2, FeF2, and CoF2 obtained at excitation energies at the top of the corresponding L 2 absorption peak is presented. This provides data for the projected d-density of states of d 4, d 5, d 6, and d 7 compounds, which are in good agreement with the results of ligand field atomic multiplet calculations.

Pressure effect on the electronic structure of iron in (Mg,Fe)(Si,Al)O3 perovskite: a combined synchrotron Mössbauer and X-ray emission spectroscopy study up to 100 GPa

We investigated the valence state and spin state of iron in an Al-bearing ferromagnesian silicate perovskite sample with the composition (Mg0.88Fe0.09) (Si0.94Al0.10)O3 between 1 bar and 100 GPa and at 300 K, using diamond cells and synchrotron Moss- bauer spectroscopy techniques. At pressures below 12 GPa, our Mossbauer spectra can be sufficiently fitted by a ''two-doublet'' model, which assumes one ferrous Fe 2+ -like site and one ferric Fe 3+ -like site with distinct hyperfine parameters. The simplest interpre- tation that is consistent with both the Mossbauer data and previous X-ray emission data on the same sample is that the Fe 2+ -like site is high-spin Fe 2+ , and the Fe 3+ -like site is high-spin Fe 3+ . At 12 GPa and higher pressures, a ''three-doublet'' model is necessary and sufficient to fit the Mossbauer spectra. This model assumes two Fe 2+ -like sites and one Fe 3+ -like site distinguished by their hyperfine parameters. Between

Understanding mixed valent materials: Effects of dynamical core-hole screening in high-pressure x-ray spectroscopy

Changes in the electronic structure of Yb, a material whose valence is modified under pressure, are observed with remarkable detail in x-ray absorption and emission data measured between ambient conditions and $20\phantom{\rule{0.3em}{0ex}}\mathrm{GPa}$. These changes are reproduced by a theory that essentially does not rely on experimental parameters, and includes dynamical core-hole screening. From the combined experimental and theoretical data we can firmly establish on a quantitative level how the valency of an intermediate valence material is modified by pressure. In metallic Yb it increases from 2 to $2.55\ifmmode\pm\else\textpm\fi{}0.05$ between 0 and $20\phantom{\rule{0.3em}{0ex}}\mathrm{GPa}$.

LibCPIXE: A PIXE simulation open-source library for multilayered samples

Most particle induced X-ray emission (PIXE) data analysis codes are not focused on handling multilayered samples. We have developed an open-source library called “LibCPIXE”, for PIXE data analysis. It is written in standard C and implements functions for simulating X-ray yields of PIXE spectra taken from arbitrary samples, including multilayered targets. The library is designed to be fast, portable, modular and scalable, as well as to facilitate its incorporation into any existing program. In order to demonstrate the capabilities of the library, a program called CPIXE was developed and used to analyze various real samples involving both bulk and layered samples. Just as the library, the CPIXE source code is freely available under the General Public License. We demonstrate that it runs both under GNU/Linux systems as well as under MS Windows. There is in principle no limitation to port it to other platforms.

1,1,1,5,5,5-Hexafluoroacetylacetonate Copper(I) Poly(vinylsiloxane)s as Precursors for Copper Direct-write

Polymeric Cu(I) precursors which deposit metallic Cu films via thermally induced disproportionation have been investigated as inks for copper direct-write to address deposit haloing, a problem when monomeric CVD precursor are ink-jetted. Cu(hfac) was complexed to poly(methylvinylsiloxane) and poly(divinylsiloxane) and these novel precursor compounds were fully characterized by spectroscopic and thermal techniques and their ability to deposit Cu films was assessed. The polysiloxanes precursors did deposit metallic Cu films, which partitioned from the polysiloxane residues. Detailed particle induced X-ray emission (PIXE) and Rutherford backscattering spectrometry (RBS) data analysis provided valuable insight into the various stages of the deposition process. The mechanistic insight will be useful in the development of higher performing metal precursor inks.

A Test of External Compton Models for Gamma‐Ray Active Galactic Nuclei

There is clear evidence that the gamma-ray emission from active galactic nuclei (AGNs) can be attributed to inverse Compton scatterings in the relativistic blobs near the massive black holes. If the soft seed photons are from the regions outside the blobs, a linear relation between (vF(v,gamma)/vF(v,syn)u(*))(1/(1+alpha)) and the Doppler factor delta is expected, where vF(v,gamma) and vF(v,syn) are monochromatic gamma-ray and synchrotron fluxes, respectively, and u(*) is the energy density of soft seed photons. We estimate the soft photon energy density in the relativistic blobs contributed by the broadline regions (BLRs) in these gamma-ray AGNs using their broad-line emission data. The Doppler factors delta are derived from their radio core and X-ray emission data, based on the assumption that the X-ray emission is produced through synchrotron self-Compton (SSC) scatterings. We find two nearly linear correlations: (vF(v,gamma)/vF(opt)u(*))1/(1+alpha) proportional to delta(1.09) and (vF(v,gamma)/vF(IR)u(*))(1/(1+alpha)) proportional to delta(1.20), which are roughly consistent with the linear correlation predicted by the theoretical model for external Compton scatterings. Our results imply that the soft seed photons are predominantly from the BLRs in these gamma-ray AGNs.

Theoretical study of hydrogen adsorption on the GaN(0001) surface

Abstract Ab initio density functional theory, using the B3LYP hybrid functional with all-electron basis sets, has been applied to the adsorption of H on the (0 0 0 1) surface of wurtzite GaN. For bulk GaN, good agreement is obtained with photoemission and X-ray emission data for the valence band and for the Ga 3d and N 2s shallow core levels. A band gap of Eg = 4.14 eV is computed vs the experimental value (at 0 K) of 3.50 eV. A simple model, consisting of a (2 × 2) structure with 3/4-monolayer (ML) of adsorbed H, is found to yield a density of states in poor agreement with photoemission data for H adsorbed on surfaces prepared by ion bombardment and annealing. A new model, consisting of co-adsorbed Ga (1/4 ML) and H (1/2 ML), is proposed to account for these data.

Element distribution in mycorrhizal and nonmycorrhizal roots of the halophyte Aster tripolium determined by proton induced X-ray emission.

The salt aster (Aster tripolium L.) colonized by the arbuscular mycorrhizal fungus Glomus intraradices Sy167 and noncolonized control plants were grown in a greenhouse for nine months with regular fertilization by Hoagland nutrient solution supplemented with 2% NaCl. Mycorrhizal roots showed a high degree of mycorrhizal colonization of 60-70% and formed approximately 25% more dry weight and much less aerenchyma than the nonmycorrhizal controls. Cryosectioning essentially preserved the root cell structures and apparently did not cause significant ion movements within the roots during cuttings. The experimental conditions, however, did not allow to discriminate between fungal and plant structures within the roots. Quantification of proton-induced X-ray emission (PIXE) data revealed that in control roots, Na(+) was mainly concentrated in the outer epidermal and exodermal cells, whereas the Cl(-) concentration was about the same in all cells of the roots. Cross sections of roots colonized by the mycorrhizal fungus did not show this Na(+) gradient in the concentration from outside to inside but contained a much higher percentage of NaCl among the elements determined than the controls. PIXE images are also presented for the four other elements K, P, S, and Ca. Both in colonized and control roots, the concentration of potassium was high, probably for maintaining homoeostasis under salt stress. This is seemingly the first attempt to localize both Na(+) and Cl(-) in a plant tissue by a biophysical method and also demonstrates the usefulness of PIXE analysis for such kind of investigation.

A flexible and accurate quantification algorithm for electron probe X-ray microanalysis based on thin-film element yields

Quantitative analysis by means of electron probe X-ray microanalysis (EPXMA) of low Z materials such as silicate glasses can be hampered by the fact that ice or other contaminants build up on the Si(Li) detector beryllium window or (in the case of a windowless detector) on the Si(Li) crystal itself. These layers act as an additional absorber in front of the detector crystal, decreasing the detection efficiency at low energies (<5 keV). Since the layer thickness gradually changes with time, also the detector efficiency in the low energy region is not constant. Using the normal ZAF approach to quantification of EPXMA data is cumbersome in these conditions, because spectra from reference materials and from unknown samples must be acquired within a fairly short period of time in order to avoid the effect of the change in efficiency. To avoid this problem, an alternative approach to quantification of EPXMA data is proposed, following a philosophy often employed in quantitative analysis of X-ray fluorescence (XRF) and proton-induced X-ray emission (PIXE) data. This approach is based on the (experimental) determination of thin-film element yields, rather than starting from infinitely thick and single element calibration standards. These thin-film sensitivity coefficients can also be interpolated to allow quantification of elements for which no suitable standards are available. The change in detector efficiency can be monitored by collecting an X-ray spectrum of one multi-element glass standard. This information is used to adapt the previously determined thin-film sensitivity coefficients to the actual detector efficiency conditions valid on the day that the experiments were carried out. The main advantage of this method is that spectra collected from the standards and from the unknown samples should not be acquired within a short period of time. This new approach is evaluated for glass and metal matrices and is compared with a standard ZAF method.

Oscillatory Zoning in an Agate from Kazakhstan: Autocorrelation Functions and Fractal Statistics of Trace Element Distributions

The results of numerical treatment of proton-induced X-ray emission (PIXE) data for trace element (Fe, Sr, Zn) contents in agate from the environment surrounding the city of Pavlodar (Kazakhstan) are presented in this paper. In order to mathematically characterize the zoning pattern, fractal geometry, correlation, and Fourier analyses were used for investigation of trace element distributions. Autocorrelation calculations show that oscillations in Fe, Sr, and Zn along the profile have periodic components. It is shown that trace element distributions can be described in terms of fractal geometry. The measured Hurst exponents by methods of the width and the power spectrum are mostly in the range 0.14–0.28, indicating fractal scaling and antipersistent behavior of trace elements along the profile.

Ionoluminescence in CVD diamond and in cubic boron nitride

Using the new ion beam-induced luminescence (IBIL) apparatus in National Legnaro Laboratories, Italy, a series of measurements concerning both wide-area luminescence spectra and monochromatic luminescence maps with a space resolution of a few μm has been carried out on several CVD diamond and c-BN samples. Protons of 2 MeV with a penetration depth of approximately 25 μm have been used in order to investigate the materials in the bulk. These measurements have been correlated with particle-induced X-ray emission (PIXE) and EPR data. The measurements have been performed at increasing proton doses in order to also investigate the radiation hardness of luminescence peaks. The results indicate that ionoluminescence of CVD diamond is dominated by three bands at approximately 2, 2.4 and 2.9 eV, with the intermediate band being very radiation-hard, and the other two radiation-weak. The band at 2 eV is correlated with N content, and is particularly high in samples with poor electronic properties. IBIL in c-BN is also dominated by three bands, one at approximately 2 eV, and the other two at higher energies with respect to CVD diamond. All these three bands seem to be relatively radiation-hard with respect to CVD diamond, and to be related to defects induced by doping.

Thermal oxidation of V2S5/InP heterostructures in oxygen

X-ray emission and IR spectroscopy data are used to elucidate the mechanism of thermal oxidation of V2S5/InP structures in oxygen. The substrate-activator interaction is shown to have a significant effect on the oxidation mechanism and to improve the engineering performance of the structures.

Interaction of high intensity picosecond laser pulses with large preformed plasmas

The interaction of short (1−2 ps) laser pulses with solid targets at irradiances of over 1016 Wcm−2, in the presence of a substantial prepulse has been investigated. High absorption of laser energy is found even at high angles of incidence, with evidence for a resonance absorption peak being found for S, P, and circular polarizations. It is considered that this may be a result of refraction and beam filamentation, which causes loss of distinct polarization. Measurements of hard X-ray emission (∼ 100 keV) confirm a resonance absorption type peak at 45−50°, again for all three cases. Typically, 5−15% of the incident light is back-reflected by stimulated Brillouin scatter, with spatially resolved spectra showing evidence of beam hot-spots at high intensity. The possibility that filamentation and refraction of the beam can explain the lack of polarization dependence in the absorption and hard X-ray emission data is discussed.

Low-Mass Pre-Main Sequence Stars and Their X-ray Emission

To investigate the formation and early evolution of stars, astronomers study the x-ray emission of T Tauri stars, which are young, solar-mass stars called pre–main sequence stars. Two Earth-orbiting x-ray satellites, the Röntgen X-ray Satellite (ROSAT) and the Advanced Satellite for Cosmology and Astrophysics (ASCA), have discovered x-ray emission from young protostars, called Class I objects. Many T Tauri stars were detected as x-ray sources by ROSAT. X-ray luminosity functions and correlations with other stellar parameters can be studied and used to investigate the x-ray emission mechanism. From the ROSAT data hundreds of T Tauri stars have been discovered, some of which are located outside regions of ongoing star formation. Stellar x-rays also irradiate circumstellar disks, regions where planets may form, so x-ray emission data from T Tauri stars may also be used to investigate the formation of planets.

Electron states in a nearly ideal random-network model of amorphous SiO2 glass.

A large continuous random-network model with 1296 atoms and periodic boundary conditions has been constructed for amorphous ${\mathrm{SiO}}_{2}$ glass. The atoms in this model are all fully coordinated with an overall small bond length and bond angle distortions. The calculated pair distribution function is in close agreement with the diffraction data. Based on this model, a first-principles calculation of the electron states is performed and the resulting wave functions are analyzed. Subtle differences in the density of states with the crystalline ${\mathrm{SiO}}_{2}$ are found. The calculated density of states are in good agreement with x-ray emission data and show the importance of Si 3d orbitals. The distributions of effective charges on Si and O atoms are studied in relation to the short-range order in the glass. It is found that O atoms with a Si-O-Si bridging angle of less than 120\ifmmode^\circ\else\textdegree\fi{} have smaller effective charges and can be identified as quasidefective centers that are responsible for the two-level tunneling at low temperature. It is also shown that localized states at the top of the band are induced by the elongation of the Si-O bond and those at the bottom of the band are related to atoms with shortened bonds. A mobility edge of 0.2 eV at the top of the valence band is obtained. A similar mobility edge for the conduction band cannot be located because of the much less localized nature of the states. \textcopyright{} 1996 The American Physical Society.

First-principles study of excitonic self-trapping in diamond.

We present a first-principles study of excitonic self-trapping in diamond. Our calculation provides evidence for self-trapping of the 1s core exciton and gives a coherent interpretation of recent experimental X-ray absorption and emission data. Self-trapping does not occur in the case of a single valence exciton. We predict, however, that self-trapping should occur in the case of a valence biexciton. This process is accompanied by a large local relaxation of the lattice which could be observed experimentally.

Intercalation of HTS by benzene; structure and magnetic properties

After intercalation of Bi-oxides by benzene in X-ray powder diffraction spectra a series of reflections corresponding to period of 4,9 nm appeared. The X-ray emission and ESR spectroscopy data indicated a charge redistribution on oxygen ions in BiO bilayers. We suppose that the benzene molecules were intercalated between BiO layers.

The X-ray emission spectra and electronic structure of the misfit layer compounds (BiS)1.08NbS2 and (PbS)1.14TaS2

The X-ray emission lines S K beta (3p to 1s) and S L2,3 (3s to 2p) have been measured for the misfit layer compounds (BiS)1.08NbS2 and (PbS)1.14TaS2 and the corresponding binary sulphides Bi2S3, NbS2, PbS and TaS2. The X-ray emission data are compared with X-ray photoelectron spectra and band structure calculations of isolated model layers. The experimental data show very clearly the character of the different valence band states, and partial density of states schemes are easily deduced from these data. A comparison with band structure calculations shows a good agreement with the measured spectra.