Article

Energy Dependence of Cu L2,3 Satellites using Synchrotron Excited X-rayEmission Spectroscopy

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Abstract

The L2,3 X-ray emission of Cu metal has been measured using monochromatic synchrotron radiation. The self-absorption effect in the spectra is shown to be very small in our experimental geometry. From the quantitative analysis of spectra recorded at different excitation energies, the L3/L2 emission intensity ratio and the partial Auger-width are extracted. High-energy satellite features on the L3 emission line are separated by a subtraction procedure. The satellite intensity is found to be slowly increasing for excitation energies between the L3, L2 and L1 core-level thresholds due to shake-up and shake-off transitions. As the excitation energy passes the L2 threshold, a step of rapidly increasing satellite intensity of the L3 emission is found due to additional Coster-Kronig processes.

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... For the Ti L 2,3 XES spectrum, E F is referenced to the L 3 emission line, while the L 2 line is observed at higher emission energy. Here, the L 3 /L 2 branching ratio depends on the L 2 → L 3 M Coster-Kronig decay changing the initial core-hole population from the statistical 2:1 ratio that is associated with the metallicity of the measured system [44]. For conducting systems, the L 3 /L 2 ratio is usually significantly higher than the statistical ratio 2:1. ...
... This is due to the Coster-Kronig process named after the physicists Dirk Coster and Ralph Kronig [48]. The Coster-Kronig decay from the 2p 1/2 core-level to the 2p 3/2 level that precedes the X-ray emission process, not only leads to a higher L 3 /L 2 branching ratio but also to a shorter lifetime and a larger Lorentzian width for the 2p 1/2 core state than for the 2p 3/2 state [44]. The trend in XES branching ratios (L 3 /L 2 or M 3 /M 2 ) in the transition-metal compounds is a signature of the degree of metallicity or ionicity in the systems [22,49]. ...
... As mentioned earlier, in a hexagonal lattice, there are five independent elastic constants, and the elastic anisotropy is described in terms of one compressional Δ P = C 33 /C 11 and two shear anisotropy ratios, Δ S1 = (C 11 + C 33 − 2C 13 )/4C 44 and Δ S2 = 2C 44 /(C 11 − C 12 ). Hence, the hexagonal lattice is isotropic if C 11 = C 33 , C 12 = C 12 and C 11 − C 12 = 2C 44 . For crystals with isotropic elastic properties Δ P = 1, Δ S1 = 1, and Δ S2 = 1, while values smaller or greater than unity provide a measure of the degree of elastic anisotropy. ...
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... For the Ti L 2,3 XES spectrum, E F is referenced to the L 3 emission line, while the L 2 line is observed at higher emission energy. Here, the L 3 /L 2 branching ratio depends on the L 2 → L 3 M Coster-Kronig decay changing the initial core-hole population from the statistical 2:1 ratio that is associated with the metallicity of the measured system [44]. For conducting systems, the L 3 /L 2 ratio is usually significantly higher than the statistical ratio 2:1. ...
... This is due to the Coster-Kronig process named after the physicists Dirk Coster and Ralph Kronig [48]. The Coster-Kronig decay from the 2p 1/2 core-level to the 2p 3/2 level that precedes the X-ray emission process, not only leads to a higher L 3 /L 2 branching ratio but also to a shorter lifetime and a larger Lorentzian width for the 2p 1/2 core state than for the 2p 3/2 state [44]. The trend in XES branching ratios (L 3 /L 2 or M 3 /M 2 ) in the transition-metal compounds is a signature of the degree of metallicity or ionicity in the systems [22,49]. ...
... As mentioned earlier, in a hexagonal lattice, there are five independent elastic constants, and the elastic anisotropy is described in terms of one compressional Δ P = C 33 /C 11 and two shear anisotropy ratios, Δ S1 = (C 11 + C 33 − 2C 13 )/4C 44 and Δ S2 = 2C 44 /(C 11 − C 12 ). Hence, the hexagonal lattice is isotropic if C 11 = C 33 , C 12 = C 12 and C 11 − C 12 = 2C 44 . For crystals with isotropic elastic properties Δ P = 1, Δ S1 = 1, and Δ S2 = 1, while values smaller or greater than unity provide a measure of the degree of elastic anisotropy. ...
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This is a critical review of MAX-phase carbides and nitrides from an electronic-structure and chemical bonding perspective. This large group of nanolaminated materials is of great scientific and technological interest and exhibits a combination of metallic and ceramic features. These properties are related to the special crystal structure and bonding characteristics with alternating strong M\ \C bonds in high-density MC slabs, and relatively weak M\ \A bonds between the slabs. Here, we review the trend and relationship between the chemical bonding, conductivity , elastic and magnetic properties of the MAX phases in comparison to the parent binary MX compounds with the underlying electronic structure probed by polarized X-ray spectroscopy. Spectroscopic studies constitute important tests of the results of state-of-the-art electronic structure density functional theory that is extensively discussed and are generally consistent. By replacing the elements on the M, A, or X-sites in the crystal structure, the corresponding changes in the conductivity, elasticity, magnetism and other material properties make it possible to tailor the characteristics of this class of materials by controlling the strengths of their chemical bonds.
... The first assumption is plausible because of the shallow depth of X-ray emission at 2 keV, which significantly minimizes self-absorption. On the other hand, satellite emission is known to be significantly attenuated only if the electron beam energy is lower than the ionization energy of the L 2 shell (Magnuson et al., 1997), which is 875.54 eV for Ni (Deslattes et al., 2003). Indeed, Magnuson et al. (1997) showed that the satellite contribution to the Cu La line may be measured by subtracting two spectra measured at 1088.5 and 932.5 eV (the ionization energy of the Cu L 2 shell is 952.2 eV). ...
... On the other hand, satellite emission is known to be significantly attenuated only if the electron beam energy is lower than the ionization energy of the L 2 shell (Magnuson et al., 1997), which is 875.54 eV for Ni (Deslattes et al., 2003). Indeed, Magnuson et al. (1997) showed that the satellite contribution to the Cu La line may be measured by subtracting two spectra measured at 1088.5 and 932.5 eV (the ionization energy of the Cu L 2 shell is 952.2 eV). The difference spectrum represents the satellite contribution, which is already present at 1088.5 eV excitation energy. ...
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... The XAS and XES spectra were measured at normal and 15 degrees incidence angle at 300 K and ∼ 1 . 10 -8 Torr at the undulator beamline I511-3 [26] at the MAX II ring of the MAX IV Laboratory, Lund University, Sweden). The XAS energy resolution at the N 1s edge of the beamline monochromator was 0.2. ...
... For x=0.12, this high-energy shift is negligibly small but the broadening is clearly noticeable in comparison to c-ZrN. For x=0. 26, the high-energy shift is 0.15 eV and for x=0.40, the shift is increased to 0.7 eV that resembles the peak position of w-AlN. ...
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... Self-absorption is known to affect the shape of the XES spectra on the high-energy flank of the main peak at the overlap with the XAS spectra. The observed XES intensity I, can be written as [24]; ...
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... The XAS and XES spectra were measured at normal and 15 degrees incidence angle at 300 K and ∼ 1 . 10 -8 Torr at the undulator beamline I511-3 [26] at the MAX II ring of the MAX IV Laboratory, Lund University, Sweden). The XAS energy resolution at the N 1s edge of the beamline monochromator was 0.2. ...
... For x=0.12, this high-energy shift is negligibly small but the broadening is clearly noticeable in comparison to c-ZrN. For x=0. 26, the high-energy shift is 0.15 eV and for x=0.40, the shift is increased to 0.7 eV that resembles the peak position of w-AlN. ...
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... This argument and the rule are analogous to those of Yablonskikh et al. [158] who discussed the ratio of L β emission intensity for excitation at the L 2 edge to L α emission intensity for excitation at the L 3 edge. To analyze in detail the L α /L β intensity ratio and the CK lifetime, we assume a simple model based on equation (1) of Magnuson et al. [159]. The contribution due to directly excited 2p 3/2 core holes and that due to CK derived core holes is summed incoherently. ...
... Following Magnu-son et al. [159], we use the approximation , so that: ...
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... All samples were measured in the same geometry with energy resolutions of 0.2 eV and 0.1 eV at the Ni 2p and C 1s absorption edges, respectively. The XAS spectra were normalized to the step before and after the absorption edges and corrected for background and self-absorption effects [17] with the program XANDA [18] in figures 6 and 7. ...
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The primary low-energy x-ray interactions within matter are photoabsorption and coherent scattering, which can be efficiently described for photon energies outside the threshold regions by using atomic scattering factors. These may be uniquely determined through quantum dispersion relations from photoabsorption data. With the available fittings of the photoabsorption cross sections and with a new compilation of such data for the region 30–300 eV, continuous sets of the photoabsorption cross sections from 30 to 10 000 eV have been determined for 94 elements. With these, for the region 100–2000 eV, atomic scattering factors which are independent of scattering angle and which include the relatively strong anomalous dispersion structures have been obtained. Methods are reviewed and currently important examples of the application of atomic scattering factors to the detailed characterization of selected x-ray mirror monochromators and of Bragg multilayer and crystal analyzers for low-energy x-ray analysis are presented.
Article
The 2p and 3p core level widths for the metals 22Ti-30Zn have been studied by photoelectron spectroscopy. The L2L3M45 Coster-Kronig rate is found to have a maximum for Co and Ni. The Coster-Kronig broadening seems to be a simple function of the kinetic energy of the emitted electron. Absolute 2p level widths have been determined which in general show much higher accuracy than previously reported values. The presently determined widths are found to agree well with theoretical predictions. The M2M3M45 super Coster-Kronig decay channel is open in Co but not in Ni.
Comparison of the high-resolution L2,3M4,5M4,5 Auger spectra and the L2,L3 XPS spectra of Zn and ZnO clearly shows a reduction in the L2L3M4,5 Coster-Kronig transition probability in the oxide. A simple calculation indeed shows this transition to be nearly at threshold for ZnO.
High resolution L3M4,5M4,5 Auger spectra of copper are compared with multiplet structure and transition rate calculations. The comparison reveals unexplained structure to lower energies which is attributed to Auger vacancy satellite lines.
Comparison of atomic and solid-state Auger spectra suggests that the relative intensities of various features in the M4,5N4,5N4,5 spectra of Xe and Cd are very similar in the solid and free atom, while in Zn Coster-Kronig transitions from the L2 level appear to be of some importance in the metal, though not allowed in the free atom. The conditions under which Coster-Kronig rates are enhanced in metals are discussed in terms of extra-atomic relaxation, and the large intensity ratio of L3M4,5M4,5/L2M4,5M4,5 processes in Co, Ni and Cu metals may then be readily understood.
High-resolution L2,3M4,5M4,5 Auger spectra of solid zinc are compared with vapour phase data. The comparison reveals extra structure on the low-energy side of the L3M4,5M4,5 group and a decrease in intensity of the L2M4,5M4,5 group in the solid. These features are attributed to the effects of L2L3M4,5 Koster-Kronig transitions. Solid-state effects are also observed in the intensity ratio of the 1G4:3F terms of the L3M4,5M4,5 group and in the region of the 1S0 term of the L2M4,5M4,5 group.
The L3-M4,5 X-ray spectra of Ni, Cu and Zn have been measured by recording the photoelectron spectra they excited from the C 1s level of graphite. The spectra are as well resolved as those obtained with crystal spectrometers and are accompanied by X-ray satellites. For Cu and Zn these satellites are sharp and are identified as L3M4,5-M4,5M4,5:1G4 and 3F transitions. For Ni the X-ray satellites probably arise from similar transitions but are broader due to the delocalised nature of M4,5M4,5 two-hole states.
Article
Das Rntgenspektrum zweiter Art wird von in ihren inneren Schalen zweifach ionisierten Atomen ausgesandt. Es wird die Intensitt dieses Spektrums relativ zu derjenigen des normalen Rntgenspektrums (Spektrum erster Art) theoretisch abgeschtzt und gezeigt, da die theoretischen Aussagen weitgehend von der Erfahrung gesttzt werden. Es werden neuere Meresultate bezglich der Linien zweiter Art mitgeteilt. Es gelingt, einen Teil dieser Linien theoretisch zu deuten und ihre Lage zu berechnen.
Article
Soft x‐ray emission spectroscopy is a common tool for the study of the electronic structure of molecules and solids. However, the interpretation of spectra is sometimes made difficult by overlaying lines due to satellite transitions or close‐lying core holes. Also, irrelevant inner core transitions may accidentally fall in the wavelength region under study. These problems, which often arise for spectra excited with electrons or broadband photon sources can be removed by using monochromatized synchrotron radiation. In addition, one achieves other advantages as well, such as the ability to study resonant behavior. Another important aspect is the softness of this excitation agent, which allows chemically fragile compounds to be investigated. In this work we demonstrate the feasibility of using monochromatized synchrotron radiation to excite soft x‐ray spectra. We also show new results which have been accomplished as a result of the selectivity of the excitation. The work has been carried out using the Flipper I wiggler beamline at HASYLAB in Hamburg using a new grazing incidence instrument designed specifically for this experiment. The photon flux at the Flipper I station (typically 5×10<sup>1</sup><sup>2</sup> photons per second on the sample with a 1% bandpass) is enough to allow soft x‐ray fluorescence spectra to be recorded at relatively high resolution and within reasonable accumulation times (typically, the spectra presented in this work were recorded in 30 min). The spectrometer is based on a new concept which allows the instrument to be quite small, still covering a large wavelength range (10–250 Å). The basic idea involves the use of several fixed mounted gratings and a large two‐dimensional detector. The grating arrangement provides simple mounting within a limited space and, in particular, large spectral range. The detector can be moved in a three‐axis coordinate system in order to cover the- different Rowland curves defined by the different gratings. The arrangement permits the use of gratings with different radii, which further facilitate the achievement of optimum performance over a large range. Two‐dimensional detection is used to allow a large solid angle, without suffering from loss of resolution due to imaging errors. The detector is based on five 2‐in. MCPs with resistive anode read out. The sensitivity of the detector, which is normally very low for soft x rays, especially at grazing angles, is enhanced by CsI coating and by using an entrance electrode.
Article
A design of a small size grazing incidence instrument is presented, which offers large spectral range and high resolution without sacrificing luminosity. The instrument is particularly suited for use at synchrotron radiation sources since it can be conveniently attached to existing experiment chambers. The basic idea of the design is the use of fixed mounted gratings of diffent radii and groove densities and a big two-dimensional position sensitive detector mounted on a x−y angle table. The design is discussed in some detail and performance is presented.
Article
Kawai et al. [Phys. Rev. B 48, 8560 (1993)] concluded that for Cu compounds and high-Tc superconductors, there is a strong correlation between the L3 x-ray emission spectroscopy (XES) spectrum satellite intensity and the 2p3/2 x-ray photoelectron spectroscopy (XPS) spectrum satellite intensity. They interpreted the XES satellite to be mainly due to the transition from the initial core-hole charge-transfer (CT) shakeup state rather than due to the L2L3M4,5 Coster-Kronig (CK) decay preceding the L3M4,5-M4,5M4,5 spectator x-ray emission transition. One of the available experimental data shows that, despite a significant initial core-hole CT shakeup satellite intensity increase from metal Cu to high-Tc superconductors, the relative L3 XES satellite intensity does not change at all because of the relative CK satellite intensity decrease. The latter is due to the decrease of the CK decay energy from metal Cu to high-Tc superconductors.
Article
The L23 x-ray-emission spectra of Cu and Zn have been recorded using tunable-synchrotron-radiation-excited fluorescence spectroscopy. The satellite structure was studied in detail by varying the excitation energy from threshold to several hundred eV above. Strong satellites are observed which can unambiguously be associated with the decay of multiply excited states. This disproves recent claims of a breakdown of the sudden approximation in this regime.
Article
Results of an investigation of the discontinuity in the L2 level width and the L3-M45M45/L2-M45M45 Auger intensity ratio at Z=30. The afore-mentioned intensity ratio is found to undergo a sudden decrease at Z=30. Relative L2 and L3 level widths of Cu and Zn are derived from photoelectron spectra; while the L3 width increases from Cu to Zn, the L2 width of Cu is greater than that of Zn, contrary to the general trend. The above-mentioned discontinuity is traced to a discontinuity in the Coster-Kronig transition probability f sub 23 predicted in earlier calculations.
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