No full-text available
To read the full-text of this research,
you can request a copy directly from the authors.
X-ray resonant Raman scattering cross sections of Mn, Fe, Cu and Zn
Journal of Physics B Atomic Molecular and Optical Physics
Abstract
X-ray fluorescence spectra present singular characteristics produced by the different scattering processes. When atoms are irradiated with incident energy lower and close to an absorption edge, scattering peaks appear due to an inelastic process known as resonant Raman scattering. It constitutes an important contribution to the background of the fluorescent line. The resonant Raman scattering must be taken into account in the determination of low concentration contaminants, especially when the elements have proximate atomic numbers. The values of the mass attenuation coefficients experimentally obtained when materials are analysed with monochromatic x-ray beams under resonant conditions differ from the theoretical values (between 5% and 10%). This difference is due, in part, to the resonant Raman scattering. Monochromatic synchrotron radiation was used to study the Raman effect on pure samples of Mn, Fe, Cu and Zn. Energy scans were carried out in different ranges of energy near the absorption edge of the target element. As the Raman peak has a non-symmetric shape, theoretical models for the differential cross section, convoluted with the instrument function, were used to determine the RRS cross section as a function of the incident energy.
... It is worth mentioning that at incident photon energies in vicinity of the K-shell / Li / Mi sub-shell absorption edge energies for a given element, near-edge processes such as X-ray Absorption Fine Structure (XAFS) and the Resonant Raman Scattering (RRS) can contribute significantly to the mass attenuation coefficients. The XAFS occurs up to about 100-200 eV above the edge (Bianconi, 1988;Rehr, 2006), whereas the RRS at incident energies up to few tens of eV below the edge ( Sanchez, 2006;Karydas, 2002;Singh, 2004). It may be noted that the contribution of these near-edge processes have not been included in the existing theoretical tabulations (McMaster et al., 1970;Storm et al., 1970;Veigele, 1973;Berger et al., 2010;Chantler, 1995Chantler, , 2000Creagh et al., 1992) of the mass attenuation coefficients. ...
... At photon energies, E L1 < E≤14.0 keV, the measured values are higher than the two sets of theoretical values (Berger et al., 2010;Chantler, 1995) by 5-10%. It is worth noting that at photon energies just below an absorption edge (up to 25-30 eV) the resonant Raman scattering (RRS) dominates (Sanchez, 2006;Karydas, 2002;Singh, 2004) and is expected to enhance the attenuation of X-rays, whereas, at energies few eV above the edges the X-ray absorption fine structure (XAFS) creates strong modulations in the photoelectric absorption process. The near-edge structures (from around 20 eV below to 20 eV above the absorption edge) such as the white line emerged due to allowed transition to unoccupied states below the continuum, as well as the broadening of the edge due to the core level lifetime have the highest influence on the mass attenuation coefficient (more than a factor of two in case of white line), which is also evident from the L 3 edge jump ratio. ...
The absolute values of the mass attenuation coefficients have been measured at sixty two photon energies across the Li (i=1–3) sub-shell absorption edges of 66Dy covering the region 7.6–14.0 keV in order to investigate the influence of near-edge processes on the attenuation coefficients. The present measured attenuation coefficients are found to be higher by up to 10% than the theoretical values evaluated from the computer code XCOM (Berger et al., 2010) and the self-consistent Dirac-Hartree-Slater (DHS) model based values tabulated by Chantler (1995) over the energy region 7.6–14.0 keV, except at energies in vicinity (few eV) of the Li (i=1–3) sub-shell absorption edge energies where the measured values are significantly higher (up to 37%) than both the sets of theoretical values. Further, the Li (i=1–3) sub-shell photoionization cross sections, , deduced from the present measured mass attenuation coefficients are compared with the non-relativistic Hartree-Fock-Slater (HFS) model based values tabulated by Scofield (1973) and those evaluated from the theoretical total photoionization attenuation coefficients tabulated by Chantler (1995). The deduced (i=1–3) values are found to be in better agreement with those evaluated from the tabulations given by Chantler (1995) than the values given by Scofield (1973) over the energy region 7.8 – 14.0 keV included in this study. However, at photon energies up to few eV above the Li edges, the deduced (i=1–3) values are found to be significantly higher (up to 32%) than both the sets of theoretical values.
... doi:10.1016/j.nimb.2010.04.022 XAFS near-edge processes have received major impetus in recent years and are emerging as important probes of condensed matter systems [22][23][24][25][26][27]. The fine structures associated with the Auger RRS have also been investigated [28]. ...
... For small positive D i values, the finite Lorentzian energy profile of the incident X-rays can also cover the energy region in upper vicinity of the ionization threshold, where the photoionization process is expected to contribute significantly especially in case of the K shell, and the L 3 and M 4,5 subshells with large jump ratio. The band structure effects on RRS were studied by various investigators [25][26][27] using high resolution (<1 eV) photon beam from tuneable synchrotron source. Nakai et al. [27] measured the radiative emission spectra across the L 3 absorption threshold in 39 Y metal and its insulator compounds. ...
A tabulation of characteristic X-ray energies across the periodic table are provided where those X-rays are expected to result in a significant fractional resonant Raman scattering (RRS) contribution to the X-ray attenuation from a particular shell/subshell of the same or another element. The tabulations can be considered as guideline so as to know what can be expected due to RRS in typical photon- and particle-induced X-ray emission spectrometry. The RRS contribution is not included in the available theoretical attenuation coefficients, which are generally used in estimation of the matrix corrections in routine quantitative elemental analysis based on various X-ray emission techniques. The radiative RRS peaks can also interfere with normal X-ray spectrum and influence the elemental analysis. The RRS cross-section depends upon the energy difference of the X-ray energy and the shell/subshell ionization threshold taken in the units of the shell/subshell energy width, density of available states near the Fermi level, and the band structure in case the element is in the solid form. Some aspects of the dependence of the RRS contribution on the chemical forms of the elements are also discussed.
... At 4.140 keV (2 eV below the L 3 edge energy) the µ ( / ) expt value is found to be higher by about a factor of 2 than both the theoretical sets of values, whereas, at 4.700 keV (7 eV below the L 1 edge energy) was found to be higher by 36% and 41%, respectively, than both the µ ( / ) XCOM and the µ ( / ) Chant values. It is noteworthy that at photon energies just below an absorption edge (up to 25 eV-30 eV) the resonant Raman scattering (RRS) dominates (Sanchez et al., 2006;Karydas et al., 2002;Singh et al., 2004) and is expected to enhance the attenuation of X-rays. The structure just above the L 3 edge and in particular the presence of the white line due to allowed transition to unoccupied states below the continuum, as well as the broadening of the edge due to the core level lifetime is expected to produce major influence on the mass attenuation coefficients. ...
In the present work, the X-ray mass attenuation coefficients have been measured for 51Sb (a medium-Z element) at forty energies across its Li (i = 1–3) sub-shell absorption edges covering an extended energy region within 4.0 keV–14.0 keV. The aim of this study is to experimentally determine the key X-ray fundamental parameters for 51Sb with improved accuracy by using tunable energy synchrotron radiation. From the present measured mass attenuation coefficients, the Li (i = 1–3) sub-shell photoionization cross sections (σLiP) have been deduced at twenty four energies across the Li (i = 1–3) edge-energies of 51Sb covering the region 4.150 keV–5.0 keV by using experimentally deduced Li (i = 1–3) edge jump ratios. Two theoretical datasets of X-ray mass attenuation coefficients and total photoionization cross sections were served to evaluate their consistency with the present experimental values and reveal possible discrepancies, in particular, across the Li (i = 1–3) edge-energies of 51Sb.
... When considering the incident photon energy distribution, a further ionization via an excitation of the remaining 1s electron can only occur through a TPA process which is less likely by a factor of 40 because of the larger energy difference to the ionization threshold compared to the ground state configuration of the scattering atom 36,41 . In general, the change of the valence state from 1+ to N+ and the associated increase of the ionization threshold by 10 eV to 160 eV implies that further core-level ionization events can be neglected until the scattering atom returns to ground state configuration (1s 2 2s 2 2p 6 3s 2 3p 6 3d 5 for Fe III) by electron capture processes. ...
Stochastic processes are highly relevant in research fields as different as neuroscience, economy, ecology, chemistry, and fundamental physics. However, due to their intrinsic unpredictability, stochastic mechanisms are very challenging for any kind of investigations and practical applications. Here we report the deliberate use of stochastic X-ray pulses in two-dimensional spectroscopy to the simultaneous mapping of unoccupied and occupied electronic states of atoms in a regime where the opacity and transparency properties of matter are subject to the incident intensity and photon energy. A readily transferable matrix formalism is presented to extract the electronic states from a dataset measured with the monitored input from a stochastic excitation source. The presented formalism enables investigations of the response of the electronic structure to irradiation with intense X-ray pulses while the time structure of the incident pulses is preserved. Free electron X-ray laser pulses, generated by self-amplified spontaneous emission, are stochastic in nature. Here the authors present a reconstruction method for 2D spectroscopy while preserving the intrinsic properties of the incident pulses and apply it to a study towards X-ray intensity induced effects.
... Finally, monochromatic synchrotron radiation was used to study the RRS effect on pure samples of Mn, Fe, Cu and Zn by Sánchez et al. [22] in 2006 at the LNLS facility (Campinas Brazil). Energy scans were carried out in different ranges of energy near the absorption edge of the target elements. ...
This work presents an overview of a novel spectroscopic tool: Energy Dispersive Inelastic X-ray Scattering
(EDIXS) spectroscopy. By the application of EDIXS, the local chemical environment of an element of interest can
be characterized in a variety of experimental conditions.
EDIXS makes use of core-level resonant inelastic X-ray scattering (RIXS), taking advantage of the benefits of
an energy dispersive detection system and multivariate methods for the data analysis. As result, the proposed
methodology presents a fast acquisition, energy-scanning free experiments, low self-absorption effects and an
objective interpretation of the data.
In this review a first section providing an introduction to the evolution of RIXS and the development of the
EDIXS methodology is presented. After that, a theoretical frame from two different approaches is offered, pre-
senting several aspects of the RIXS spectrum features and letting glimpse the origin of the peak fine structure,
key issue of this technique. Next, an explanation of the different multivariate methods used for the data analysis
is provided. By the end, a set of experimental results obtained with EDIXS are revised, including several irra-
diation geometries and setups (as total reflection, grazing incidence and even confocal) for a variety of samples.
A brief summary with further discussions regarding the advantages of the presented methodology, including
future perspectives as its applicability to different X-ray sources, are giving closure to the paper.
... Many aspects of the RRS process have been discussed by Sparks and Ice (1997) and Manninen (1997) in detail. Most of the radiative RRS measurements have been performed using wavelength-dispersive detectors (Szlachetko et al., 2005(Szlachetko et al., , 2007Nakai et al., 2000) and synchrotron radiation (Sánchez et al., 2006). More information about the fine structure of radiative RRS (Nakai et al., 2000) can be obtained from high resolution Auger electron resonant Raman technique (Ichikawa et al., 1992;Baba et al., 1994). ...
The KL2,3 and L3M4,5 radiative resonant Raman scattering (RRS) cross sections have been measured for the quasimonochromatic Mn Kα1,2 X-rays (5.895 keV) in 24Cr (K-shell level width (ΓK) = 1.08 eV) and 59 Pr (L3-subshell level width (ΓL3) = 3.60 eV), respectively, using targets in metallic and various chemical forms. The incident Mn Kα1,2 X-ray energy is lower than the K-shell binding energy of 24Cr and L3-subshell binding energy of 59Pr by ~94 ΓK (Cr) and ~94 ΓL3 (Pr), respectively. The experimental measurements were performed with a low energy Ge detector (LEGe) and a radioactive ⁵⁵Fe annular source in conjunction with 24Cr absorber. The measured cross section values for the 24Cr and 59 Pr elements in their various oxidation states are found to be same within experimental errors. The measurements were further extended to investigate alignment of the intermediate L3-subshell (J = 3/2) virtual vacancy states in 59Pr through angular distribution measurements for RRS photon emission, which is found to be isotropic within experimental errors.
... This process was observed for first time in 1974 by Sparks [14], explained one year later by Bannet and Freund [15] and the main characteristics of its emission peaks described in 1976 by Eisemberger et al [16,17]. Several measurements were taken during the last decades for determining the RRS cross sections for several elements and even for some compounds [18][19][20][21][22][23][24]. Even so, this topic is far away from being completed, since several elements have not even been measured yet. ...
X-ray resonant Raman scattering was used, for the first time, in a confocal setup with the aim of determining different compounds of the same element in a copper-multilayer sample. This allowed us to resolve chemical environments with 3D-resolution using a detection system with low energy resolution. A stratified Cu-oxide-sample was studied in the Brazilian Synchrotron Light Laboratory (LNLS) using monochromatic radiation and an Energy Dispersive System (EDS) setup. The results are relevant since they allowed observing the presence of different oxide-layers, impossible to discriminate with conventional geometries of irradiation. They also permit the characterization of a compound present at a particular depth of the sample with micrometer resolution using a low-resolution system.
... From the fits we obtain a TPA cross-section value of 4.1 (+ /− 1.1) × 10 −55 cm 4 s. For the OPA process a value of 5.6(+ /− 0.6) × 10 −22 cm 2 is obtained, in agreement with other experimental data 35 . ...
X-ray techniques have evolved over decades to become highly refined tools for a broad range of investigations. Importantly, these approaches rely on X-ray measurements that depend linearly on the number of incident X-ray photons. The advent of X-ray free electron lasers (XFELs) is opening the ability to reach extremely high photon numbers within ultrashort X-ray pulse durations and is leading to a paradigm shift in our ability to explore nonlinear X-ray signals. However, the enormous increase in X-ray peak power is a double-edged sword with new and exciting methods being developed but at the same time well-established techniques proving unreliable. Consequently, accurate knowledge about the threshold for nonlinear X-ray signals is essential. Herein we report an X-ray spectroscopic study that reveals important details on the thresholds for nonlinear X-ray interactions. By varying both the incident X-ray intensity and photon energy, we establish the regimes at which the simplest nonlinear process, two-photon X-ray absorption (TPA), can be observed. From these measurements we can extract the probability of this process as a function of photon energy and confirm both the nature and sub-femtosecond lifetime of the virtual intermediate electronic state.
... Hanning window with a width of 0:5Å À1 . 13,22,23 The k 2 -weighted EXAFS as a function of photoelectron momentum and the magnitude of the FT of the isolated fine structure as a function of non-phase corrected radial distance is shown in Figs. 1(a) and 1(b), respectively, for the five different Ga concentrations. ...
We present an experimental lattice location study of Ga atoms in Ge after ion implantation at elevated temperature (250 degrees C). Using extended x-ray absorption fine structure (EXAFS) experiments and a dedicated sample preparation method, we have studied the lattice location of Ga atoms in Ge with a concentration ranging from 0.5 at. % down to 0.005 at. %. At Ga concentrations <= 0.05 at:%, all Ga dopants are substitutional directly after ion implantation, without the need for post-implantation thermal annealing. At higher Ga concentrations, a reduction in the EXAFS amplitude is observed, indicating that a fraction of the Ga atoms is located in a defective environment. The local strain induced by the Ga atoms in the Ge matrix is independent of the Ga concentration and extends only to the first nearest neighbor Ge shell, where a 1% contraction in bond length has been measured, in agreement with density functional theory calculations. (C) 2012 American Institute of Physics. [http://dx.doi.org/10.1063/1.4773185]
For incident x-ray energies below the core level ionization threshold, one-photon absorption (OPA) leads to off-resonant x-ray excitations that are mediated by a virtual intermediate electronic state. In the linear regime of x-ray interaction, this intermediate state may decay radiatively and the maximum energy of the emitted photon is given by the initial and final atomic state as well as the energy of the incident photon. In the nonlinear excitation regime, however, this intermediate state may be depleted by a second x-ray absorption process as described in the sequential two-photon absorption (TPA) mechanism. Since the same intermediate state is involved in the OPA and TPA processes, the cross-section values for OPA and TPA are interconnected. We report on the determination of cross-section values for off-resonant excitation conditions, and show how the data can be used for estimating the TPA cross section in the sequential absorption mechanism. The determined off-resonant cross sections for cobalt exhibit a Lorentz-like energy-dependent behavior allowing for an energy-dependent description of the OPA and TPA cross sections with semiempirical models. The dependence of TPA cross sections on atomic number is discussed and different scaling laws are investigated. The effect of the lifetimes of a virtual intermediate state is also studied in relation to the incidence x-ray energy.
Resonant inelastic X-ray scattering, also named X-ray resonant Raman scattering, was recently used to discriminate local chemical environments. By means of this novel technique, the speciation of samples could be attained in a variety of samples and experimental conditions. Until now, this discrimination methodology had been applied only to pure compounds, being the speciation possible by two different mathematical treatments. Nevertheless, the effectiveness/sensitivity of this technique has not been tested yet in samples containing mixtures of oxides of the same element. In this work, the first results of quantitative speciation of mixtures of manganese compounds, using resonant inelastic X-ray scattering/X-ray resonant Raman scattering spectroscopy, are presented. The results show that it is possible to discriminate and quantify oxide mixtures of the same element in slightly different proportions, allowing a quantitative speciation of compound mixtures in a variety of experimental conditions, presenting also several advantages over conventional spectroscopic techniques. Copyright
X-Ray fluorescence spectra present singular characteristics produced by the different scattering processes. When atoms are irradiated with incident energy lower and close to an absorption edge, scattering peaks appear due to an inelastic process known as resonant Raman scattering (RRS). In this process, the emitted photons have a continuous energy distribution with a high energy cut-off limit. This work presents results regarding the possibility of determining the oxidation state by resonant Raman scattering using an energy dispersive system. Pure samples of transition metals (Cu, Fe, Mn) and different oxides of them (CuO, Cu2O, Fe2O3, Mn2O3, MnO2) were irradiated with monochromatic synchrotron radiation below their absorption edges to inspect the RRS emissions. The spectra were analyzed with specific programs using non-conventional functions for data fitting and a FFT smoothing procedure was applied. After smoothing, the RRS residuals are studied in order to detect variation with respect to the theoretical curve. These variations are closely related with the chemical environments of the absorbing element and can provide relevant structural information of the sample. The changes existing in the RRS structure between pure elements and their oxides are clearly discriminated and suggest the possibility of structural characterization by means of resonant Raman scattering using an energy-dispersive system combined with synchrotron radiation.
We have shown that X-ray resonant Raman scattering (RRS) spectroscopy can be used to analyze arsenic species. This work is a pioneering work in the area and is important in the interpretation of results in the future. Nevertheless, the behavior of RRS residuals of compounds can be used to identify the oxidation state of the elements under study, offering a new possibility for chemical environment determination using RRS spectroscopy.
In this work we present theoretical calculations of the resonant Raman scattering contributions to the background of X-ray fluorescence spectra. The main goal of the paper is to obtain a simple and reliable procedure to calculate the influence of RRS in spectrochemical analysis by X-ray fluorescence including second order enhancement processes. In order to perform the calculations, the Shiraiwa and Fujino model was used to calculate the characteristic intensities of the different atomic processes involved. In the case of polychromatic excitation over a multi-element sample of proximate atomic numbers, the calculations show that the contribution of RRS is higher than Compton scattering but lower than coherent scattering, this last process being the most important source of background in the range of the fluorescent lines. The calculated effects of enhancements are rather low and have influence only on the lightest elements of the spectra. On the other hand, the resonant Raman scattering line interferes with fluorescent peaks in the case of monochromatic excitation when elements of proximate atomic numbers are analyzed (for example Al–Si). The model proposed here allows the analysis of the different sources of background, which contribute to a better understanding of the physical processes involved in the different techniques of XRF analysis. In addition, the calculations presented here can contribute significantly to a more precise quantification of traces and minor components.
Attenuation of the characteristic K X-rays in the 48Cd, 50Sn, 52Te, 64Gd, 65Tb, 66Dy, 68Er, 74Ta, 75Re, 79Au, 82Pb and 83Bi elements have been measured with especial emphasis for the X-ray energies (Ein) in the region of respective K-shell/Li subshell (i=1, 2, 3) ionization threshold (BK/BLi). The characteristic X-rays were obtained from different fluorescent target elements excited by the X-rays and γ-rays emitted from the 55Fe and 241Am radioisotopes, respectively. The measurements were performed using an energy-dispersive detection set up involving a low-energy Ge detector. The measured attenuation coefficients for the X-rays with energies away from ionization thresholds of the attenuator element are found to be in good agreement with the available theoretical coefficients, which incorporate contributions of the photoionization, and the Rayleigh and Compton scattering processes. However, the measured attenuation coefficients are found to deviate significantly from the theoretical values for the X-rays with energies in vicinity of BK/Li. The observed alteration is attributed to the X-ray Absorption Fine Structure (XAFS) for negative BK/Li−Ein values, and the K-shell/Li subshell resonant Raman scattering (RRS) process for positive BK/Li−Ein values. Systematic of the K-shell/Li subshell RRS contribution to attenuation of the X-rays are discussed in terms of the respective oscillator density and fraction of electrons available in the K-shell/Li subshell Lorentzian profile of the attenuation element below Ein.
Both x-ray total reflection and x-ray Raman scattering techniques were combined to discriminate oxidation states in depth profiling studies using an energy dispersive system. This allowed, for the first time, to resolve oxidation state on surface nano-layers with a low resolution system. Samples of pure Cu and Fe oxidized in tap water and salty water respectively were studied in the Brazilian synchrotron facility using monochromatic radiation and an EDS setup. The measurements were carried out in total reflection geometry with incident energy lower and close to the K absorption edge of both elements. The results allowed observing the presence of very thin oxides, usually not observable with conventional geometries of irradiation. They also permit the identification of the oxidation state present in a particular depth of the sample with nanometric, or even sub-nanometric, resolution using a low-resolution system.
The Resonant inelastic X-ray scattering or resonant Raman scattering is an inelastic process of second order that becomes important when the energy of the excitation radiation is below but close to an absorption edge. In this process, the emitted photons have a continuous energy distribution with a high energy cut-off limit. In the last few years, experiments of resonant Raman scattering has become a very powerful technique to investigate excitations of electrons in solids. A qualitative study of the calcium local structure in the different layers of teeth was carried out. In order to perform the analysis, several measurements of tooth samples were achieved using monochromatic synchrotron radiation at the XRF station of the D09B-XRF beamline at the Brazilian synchrotron facility (LNLS, Campinas), below and close to the K absorption edge of Ca to inspect the resonant Raman scattering spectra. First of all, the spectra were analyzed with specific software to fit the experimental data. After that, the residuals were determined and a fast Fourier transform smoothing procedure was applied, taking into account the instrument functions of the detecting system. These oscillations present patterns that depend of the tooth layer, i.e. of the calcium state.
The Li- (i=1–3) subshell x-ray spectra for the 52Te, 53I, 55Cs, 56Ba, and 57La elements excited by Mn Kα (EKα2=5.888 keV and EKα1=5.899 keV) x rays have been investigated using the 55Fe radioisotope in conjunction with a Cr absorber. A low-energy Ge detector was used to measure the L x rays at an emission angle ψ=126°, where the second-order Legendre polynomial term P2 (cos ψ) associated with the angular distribution is annulled. In the case of the 56Ba and 57La elements, alignment of the L3-subshell vacancy states was investigated through angular distribution measurements of the emitted L3-subshell x rays. The Lα1,2 and Lβ2,15 x-ray groups are observed to be nearly isotropic, while the data for the pure Ll (L3-M1) x-ray emission are indicative of a small anisotropic trend, though within experimental error. The integral x-ray fluorescence cross sections are deduced and interpreted in terms of Li-subshell photoionization cross sections, fluorescence and Coster-Kronig yields, and x-ray emission rates. The L2-subshell x-ray cross sections for 57La measured using targets of lanthanum (III) fluoride and dilanthanum (III) trioxide are found to be unusually higher. The enhancement is observed due to the contribution of the L2-subshell radiative resonant Raman scattering (RRS) of Mn Kα x rays having energy around the L2-subshell binding energy of 57La in these compounds. Also, the observed enhancement of the L3-subshell x-ray cross sections in 57La is suggestive of intrashell vacancy transfer via L2-L3 Coster-Kronig RRS transitions. The L2-subshell total RRS cross sections in 57La have been deduced from the present measured attenuation coefficients for Mn Kα x rays in La2O3 and LaF3. The L2-subshell radiative and total RRS cross sections in 57La using LaF3 are higher by ∼30% than those using La2O3. The contribution of processes predicted in the framework of Mozouchi’s four-band model involving inner subshells along with the valence and conduction bands of these wide-band-gap insulator compounds is likely to account for the observed results. The L2-subshell radiative and L2-L3 Coster-Kronig yields and the ratio of the L2-M4 and L2-N4 radiative RRS intensities in both La compounds are found to be same and are consistent with values from photoexcited vacancy decay. The L2-subshell radiative RRS was also observed to be isotropic.
The x-ray resonant Raman scattering (RRS) effect of polarized and unpolarized radiation in the vicinity of the 1s absorption threshold of low-Z elements such as magnesium, aluminum, and silicon is investigated. For the polarized and tunable exciting x-ray radiation the plane grating monochromator (PGM) beam line at the PTB laboratory in the BESSY II synchrotron radiation facility was employed, while unpolarized x-ray beams were induced by 1-MeV proton beam irradiation on various pure thick targets. For the latter case, a novel proton-induced x-ray fluorescence scattering chamber was designed and installed at the Tandem accelerator laboratory of the Institute of Nuclear Physics at N.C.S.R. “Demokritos.” The total RRS cross sections deduced from both independent excitation modes were found to be in a good agreement, within the experimental uncertainties. The predictions of the existing theory with respect to the dependence of the RRS to the incident beam polarization state is calculated and discussed with respect to the experimental results.
Monochromatic synchrotron radiation was used to study the Raman effect on pure samples of Mn, Fe, and Cu and on oxides such as Mn2O3, Fe2O3, CuO and Cu2O. Energy scannings were carried out for different ranges of energies near the absorption edge of the target element. Theoretical models for the energy distribution of the Raman scattered photons, convoluted with the instrument function, were used to determine the resonant Raman scattering (RRS) cross sections as a function of the incident energy. The results indicate that RRS cross sections for pure samples are similar to those for oxides for the same energy difference from the respective edge, showing that the Raman scattering takes place in the same way in both kinds of samples. Copyright © 2008 John Wiley & Sons, Ltd.
The near-edge processes, such as X-ray absorption fine structure (XAFS) and resonant Raman scattering (RRS), are not incorporated
in the available theoretical attenuation coefficients, which are known to be reliable at energies away from the shell/subshell
ionization thresholds of the attenuator element. Theoretical coefficients are generally used to estimate matrix corrections
in routine quantitative elemental analysis based on various X-ray emission techniques. A tabulation of characteristic X-ray
energies across the periodic table is provided where those X-rays are expected to alter the attenuation coefficients due to
XAFS from a particular shell/subshell of the attenuator element. The influence of XAFS to the attenuation coefficient depends
upon the atomic environment and the photoelectron wave vector, i.e., difference in energies of incident X-ray and the shell/subshell
ionization threshold of the attenuator element. Further, the XAFS at a shell/subshell will significantly alter the total attenuation
coefficient if the jump ratio at that shell/subshell is large, e.g., the K shell, L3 subshell and M5 subshell. The tabulations can be considered as guidelines so as to know what can be expected due to XAFS in typical photon-induced
X-ray emission spectrometry.
Keywords.X-ray absorption fine structure; resonant Raman scattering; characteristic X-ray; attenuation coefficient; X-ray emission-based
techniques.
A local structure study of ZnS nanocrystals, doped with very low concentrations of Cu, was carried out using the EXAFS technique to better understand how Cu substitutes into the host lattice and forms Cu luminescence centers. We show that a large fraction of the Cu have three nearest neighbor S atoms and the Cu-S bond is significantly shortened compared to Zn-S, by ∼0.08 Å. In addition, the second neighbor Cu-Cu peak is extremely small. We propose that Cu occupies an interior site next to a S(2-) vacancy, with the Cu displaced towards the remaining S(2-) and away from the vacancy; such a displacement immediately explains the lack of a significant Cu-Cu peak in the data. There is no evidence for interstitial Cu sites (Cu(i)), indicating that no more than 2% of the Cu are Cu(i.) This study provides new insights into the local structure of the Cu dopant in ZnS without the presence of CuS nanoprecipitates that are present at higher Cu doping levels.
When conducting EXAFS at the Cu
K
-edge for ZnS:Cu with very low Cu concentration (
The K-L and K-M resonant Raman scattering (RRS) cross-sections have been measured for the first time at the 59.536 keV photon energy in the 70Yb (BK=61.332 keV), 71Lu (BK=63.316 keV) and 72Hf (BK=65.345 keV) elements; BK being the K-shell binding energy. The K-L and K-M RRS measurements have been performed at the 59° and 133° angles, respectively, to avoid interference of the Compton-scatter peak. The Rayleigh and Compton scattering cross-sections for the 59.536 keV gamma-rays have also been measured at both the angles in the atomic region 1
A theory of the resonant x-ray Raman effect is presented and compared with recent experimental data of Sparks. Excellent agreement between theory and experiment is found for the integrated intensity of the scattering, the spectral density, and the output polarization. The potential importance of this newly discovered spectroscopic probe is discussed.
A theory of the resonant x-ray Raman effect is presented and compared
with recent experimental data of Sparks. Excellent agreement between
theory and experiment is found for the integrated intensity of the
scattering, the spectral density, and the output polarization. The
potential importance of this newly discovered spectroscopic probe is
discussed.
An overview is presented of the theory of X-ray Raman scattering as originally formulated by Kramers and Heisenberg and by Weisskopf and Wigner. Two particular aspects of the theory are described in some detail; the formation of band profiles and the role of symmetry. These aspects are discussed in connection with recent results for atomic and molecular scatterers obtained in radiative and nonradiative scattering experiments conducted with 2nd and rd generation synchrotron radiation sources.
Resonant raman scattering (RRS) can contribute considerably, under specific experimental conditions, to the attenuation of X-rays in matter. The experimental study of the RRS can lead to a better assessment of this contribution. In this work low energy proton induced vanadium Kα X-rays have been utilized in two different X-ray production geometries for RRS studies. The KL-RRS cross-sections for titanium and vanadium and the LM-RRS for cesium and barium are measured respectively, while the importance of the technique in the systematic measurement of X-ray interaction cross-sections in matter is also discussed.
In this Letter we report the first observation of inelastic x-ray scattering from an atom in which both Raman and Compton processes have been observed simultaneously. It has been observed that x-ray Raman and Compton scattering in the vicinity of a deep atomic level exhibit different behavior as a function of incident photon energy.
An inelastic resonance scattering of monochromatic Cu Kα x rays incident on various targets is observed when an absorption edge of the target is just above the energy of the incident x rays. This frequency-dependent and angular-independent inelastic scattering is interpreted with the x-ray scattering theory of anomalous dispersion. Conservation-of-intensity arguments allow a comparison of the observed inelastic intensity with the real part of the anomalous dispersion corrections to the coherent atomic scattering factors for x rays.
The available body of information on (a) fluorescence, Auger, and Coster-Kronig yields, (b) radiative and radiationless transition rates, (c) level widths, (d) x-ray and Auger line widths, (e) x-ray and Auger spectra, and (f) Coster-Kronig energies has been used to generate an internally consistent set of values of atomic radiative and radiationless yields for the K shell (5 ?Z?110) and the L subshells (12 ?Z?110). Values of fluorescence yields ωk, ω1, ω2, ω3, Coster-Kronig yields F1, F1.2, F1.3, F1.3, F2.3. Auger yields ak, a1, a2, a3, and effective fluorescence yields ν1 and ν2 are presented in tables and graphs. Estimates of uncertainties are given. Updated and expanded graphs of partial and total widths of K, L1, L2, and L3 levels are presented as well as a reference list of papers published since about 1972.
Partial cross sections for Ar K-L2L3(1D2)np, n=4 and 5 spectator Auger states excited by x-ray absorption across the K edge, were measured and compared with calculations based on the theory of radiationless resonant Raman scattering. Core relaxation and coherence among bound and continuum intermediate states produce shake-up, shake-down, and photoelectron-recapture effects in the cross sections. The width and position of the 4p spectator Auger peak are shown to be sensitive to resonance structure in the partial cross section via averaging over the x-ray bandwidth.
Synchrotron radiation is used to study resonant x-ray Raman scattering from copper metal. The study extends from above the K absorption edge resonance to 500 eV below it.
Absolute values for the differential cross section dσ/dΩdω of Cu Kα x rays inelastically scattered from the series of elements Ni-Ge are presented for the region 2.5-8 keV. These data display the resonance x-ray. Raman effect discovered by Sparks, and are also in very good qualitative agreement with a model H-atom calculation by Gavrila and Tugulea which predicts that at still lower energies the scattering cross section diverges.
Total reflection x-ray fluorescence using synchrotron radiation from the Stanford Synchrotron Radiation Laboratory has been used to study Al impurities on Si wafer surfaces. For primary excitation energies below the Si K absorption edge an inelastic resonance scattering due to resonant x-ray Raman scattering is observed. This scattering dominates the background behavior of the Al K fluorescence line, and consequently limits the achievable sensitivity for detection of Al surface contaminants. The energy and angle dependence of the resonant x-ray Raman scattering has been investigated to determine the experimental conditions for which the highest sensitivity for Al can be achieved. We find that for a precise determination of the achievable sensitivity, the specific shape of the continuous Raman background has to be taken into account. Our calculations demonstrate a minimum detection limit for Al of 6×109 atoms/cm2 for a 10 000 s count time. © 2000 American Institute of Physics.
The spectral distribution and integrated intensity of resonant Raman scattering was measured with tunable synchrotron radiation in the vicinity of the K edges of Cu and Zn and LIII edge of Ho. The assumption of a constant density of final states is adequate to describe the cross section more than 5-10 eV below the absorption edges. Despite the poor energy resolution afforded by a solid state detector the lifetime width of the inner-shell hole was determined to within a fraction of an electron volt. In the case of the L shell especially, the sub-shell widths can be measured individually in a straightforward low-resolution experiment. The result of 4.8+or-0.2 eV for the Ho 2p3/2 level is much closer to the predicted value of 4.0 eV than widths obtained from absorption edge spectroscopy.
The resonant Raman effect has been described as an inelastic scattering process occurring when the energy of the exciting x-ray beam approaches from below the energy of an absorption edge of a target element. It produces a scattered photon with a characteristic maximum energy and the emission of an inner-shell electron. A high monochromatic x-ray beam produced by protons was utilized for the measurement of the KL type of resonant Raman scattering (RRS) cross sections in V and Cr and of the LM ones in La and Ce. In the case of V and Cr targets, the fluorescence yields of the KL-RRS process were also extracted, while the fine-structure splitting in a LM-RRS spectrum was observed for the first time. The influence of RRS into different topics of x-ray spectrometry, like the quantitative x-ray flourescence analysis, the theoretical calculations of the mass attenuation coefficients or the shape of characteristic x-rays emitted from low Z thick targets, is also discussed.
A generalisation of the Kramers-Heisenberg formula is used to demonstrate the evolution of inelastic X-ray scattering into fluorescence across the K absorption edge. As an illustration the results of a recent synchrotron radiation study of the inelastic scattering in the vicinity of the Mn K absorption edge in KMnO4 by Briand et al. (1981) are analysed and found to be in qualitative agreement with the theory.
Formulas for the resonant cross section of X-rays are rederived emphasizing the similarity of the resonant Raman scattering (RRS) to the fluorescence, and are given in terms of the oscillator strengths and radiative widths. In both processes only a fraction results in radiation, and for the RRS this is termed the RRS yield, wRRS, in analogy with the fluorescence yield, wK. Measurements are made in the symmetrical reflection geometry from totally absorbing samples. The fluorescence yield is measured CuKα as exciting radiation for Ti, V, Cr, Mn, and Fe, the results being 0.237, 0.265, 0.291, 0.325, 0.356, respectively. The absolute cross section of the (1s, 2p) contribution to the RRS is measured for Cr, Mn, Fe, Ni, and Cu at energies 42 to 940 eV below the K absorption edge. The RRS yields are 0.404, 0.426, 0.422, 0.415 (0.460 in another measurement), and 0.473 (0.468), respectively. Also evidence is found for the existence of the (1s, 3p) contribution to the RRS.
Formeln für den Resonanzwirkungsquerschnitt von Röntgenstrahlen werden, mit Betonung der Gleichheit von resonanter Raman-Streuung (RRS) und Fluoreszenz, abgeleitet und mittels Oszillatorstärken und Strahlungsbreiten ausgedrückt. In beiden Prozessen resultiert nur ein Bruchteil in Strahlung. Für die RRS wird er die RRS-Ausbeute, wRRS, analog zur Fluoreszenzausbeute, wK, genannt. Die Messungen werden bei der symmetrischen Reflexion an voll ständig absorbierenden Proben ausgeführt. Die Fluoreszenzausbeute wird mit der CuKα-Primärstrahlung für Ti, V, Cr, Mn und Fe gemessen und es ergibt sich 0,237; 0,265; 0,291; 0,325; 0,3 56. Der absolute Wirkungsquerschnitt des (1s, 2p) Anteils an der RRS wird für Cr, Mn, Fe, Ni und Cu mit Energien von 42 bis 940 eV unterhalb der K-Absorptionskante gemessen. Die betreffenden RRS-Ausbeuten sind 0,404; 0,426; 0,422; 0,415 (0,460 mit einer anderen Messung) und 0,473 (0,468). Hinweise für die Existenz eines (1s, 3p)-Anteils an der RRS werden auch gefunden.
The dynamics in resonant inelastic scattering is reviewed. Simplifying pictures and basic conservation rules are used as starting point for the discussion, rather than a rigorous theoretical framework. It is emphasized that selectivity in terms of energy (and to some extent momentum and angular momentum) of the incoming photon has changed the perspective on core level spectroscopies during the last decade. Dynamics on the femtosecond timescale can be studied by comparing rates of competing processes and analysis of interference effects.
Near an absorption edge, x-ray emission cannot be treated separately from the absorption process itself; a scattering formalism must be used. Experimental data have been recorded showing x-ray emission from xenon following excitation by tunable synchrotron radiation below and above the L3 absorption edge. Complete data sets are presented for Xe Lalpha1,2 and Lbeta2,15 emission from 10 eV below to 40 eV above the L3 edge. In accord with the resonant-inelastic-scattering model, the observed x-ray emission evolves from resonant Raman scattering into characteristic fluorescence as the excitation energy is scanned from below to above the absorption edge.
Measurements of argon photoion yields obtained in coincidence with K-L2,3L2,3 Auger emission as a function of incident photon energy across the K-shell threshold are reported. These results are interpreted within the framework of lowest-order scattering theory, which describes the virtual creation and decay of 1s-hole states. Cross sections for the production of singly ionized spectator Auger states [2p2]np and the doubly ionized [2p2] states are calculated using nonrelativistic Hartree-Fock wave functions and their physical interpretation is discussed. When the behavior of the np spectator electron during and after the subsequent Auger cascade that fills the two core 2p holes is taken into account, excellent agreement with experiment is obtained. The mechanism for loss of the np electron in this cascade is shown to be a final Auger decay in which the np electron participates and np shake-off is found to be negligible.
The resonant enhancement of Raman scattering from nickel was studied with monochromatic synchrotron radiation at incident energies just below the K absorption edge. The intensities of the KL and KM contributions were recorded through the transition from resonant Raman scattering (RRS) to fluorescence and the yield was determined. The scattering cross section immediately below and above the fluorescence threshold reflected the density of states and followed the predictions of simple RRS calculations.