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Energy Dependence of Cu L2,3 Satellites using Synchrotron Excited X-rayEmission Spectroscopy
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.
... 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. ...
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.
... 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. ...
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 MC bonds in high-density MC slabs, and relatively weak MA 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. ...
Electron microprobe-based quantitative compositional measurement of first-row transition metals using their L X-ray lines is hampered by, among other effects, self-absorption. This effect, which occurs when a broad X-ray line is located close to a broad absorption edge, is not accounted for by matrix corrections. To assess the error due to neglecting self-absorption, we calculate the L X-ray intensity emitted from metallic Fe, Ni, Cu, and Zn targets, assuming a Lorentzian profile for the X-ray line and taking into account the energy dependence of the mass absorption coefficient near the absorption edge. We find that calculated X-ray intensities depart increasingly, for increasing electron beam energy, from those obtained assuming a narrow X-ray line and a single fixed absorption coefficient (conventional approach), with a maximum deviation of 15% for Ni and of 10% for Fe. In contrast, X-ray intensities calculated for metallic Zn and Cu do not differ significantly from those obtained using the conventional approach. The implications of these results for the analysis of transition-metal compounds by electron probe microanalysis as well as strategies to account for self-absorption effects are discussed.
... 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. ...
The electronic structure, chemical bonding and interface component in ZrN-AlN nanocomposites formed by phase separation during thin film deposition of metastable Zr1-xAlxN (x=0.0, 0.12, 0.26, 0.40) is investigated by resonant inelastic X-ray scattering/X-ray emission and X-ray absorption spectroscopy and compared to first-principles calculations including transitions between orbital angular momentum final states. The experimental spectra are compared with different interface-slab model systems using first-principle all electron full-potential calculations where the core states are treated fully relativistic. As shown in this work, the bulk sensitivity and element selectivity of X-ray spectroscopy enables to probe the symmetry and orbital directions at interfaces between cubic and hexagonal crystals. We show how the electronic structure develop from local octahedral bond symmetry of cubic ZrN that distorts for increasing Al content into more complex bonding. This results in three different kinds of bonding originating from semi-coherent interfaces with segregated ZrN and lamellar AlN nanocrystalline precipitates. An increasing chemical shift and charge transfer between the elements takes place with increasing Al content and affects the bond strength and increases resistivity.
... 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. ...
The electronic structure, chemical bonding, and interface component in ZrN-AlN nanocomposites formed by phase separation during thin film deposition of metastable Zr 1−x Al x N (x = 0.0, 0.12, 0.26, 0.40) are investigated by resonant inelastic x-ray scattering, x-ray emission, and x-ray absorption spectroscopy and compared to first principles calculations including transitions between orbital angular momentum final states. The experimental spectra are compared with different interface-slab model systems using first principles all-electron full-potential calculations where the core states are treated fully relativistically. As shown in this work, the bulk sensitivity and element selectivity of x-ray spectroscopy enables one to probe the symmetry and orbital directions at interfaces between cubic and hexagonal crystals. We show how the electronic structure develops from local octahedral bond symmetry of cubic ZrN that distorts for increasing Al content into more complex bonding. This results in three different kinds of bonding originating from semicoherent interfaces with segregated ZrN and lamellar AlN nanocrystalline precipitates. An increasing chemical shift and charge transfer between the elements takes place with increasing Al content and affects the bond strength and increases resistivity.
... Fig. 1 shows incident angle-and temperature-dependent X-ray absorption spectra of optimally doped YBCO at the Cu 2p absorption edge. In particular, we note the peculiar threshold shoulders that are absent in XAS spectra of pure Cu [15]. These shoulders are related to Zhang-Rice [3] plane-, and chain-excitations, respectively. ...
... Previous O K RIXS studies with E||ab suggested that O(2,3) with x = 6.94 have higher binding energy than those of O(1) and O(4) [34]. At 20 • incidence, the main O 2p peak is more localized at 526.2 eV emission energy, which is not enhanced by self-absorption effects [15] at 70 • incidence angle. Furthermore, an interesting feature resonating at the ZRB peak B is observed to be strongly enhanced in vertical polarization, i.e. -scattering, both for the 20 • -and the 70 •incidence angle. ...
We present a study on the high-Tc superconductor (HTSC) YBa2Cu3O7-x (YBCO) using polarization-dependent X-ray absorption and resonant inelastic X-ray scattering. High-resolution measurements using synchrotron-radiation are compared with calculations using a quasi-atomic multiplet approach performed at the Cu 2p3/2-edge of YBCO. We use a multiplet approach within the single impurity Anderson model to reproduce and understand the character of the localized low-energy excitations in YBCO. We observe a distinct peak at about 0.5 eV in O K RIXS. This peak shows dependence on doping, incident energy, and momentum transfer that suggests that it has a different origin than the previously discussed cuprate bi-magnons. Therefore, we assign it to multi-magnon excitations between the Zhang Rice bands and/or the Upper Hubbard bands, respectively.
... 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]; ...
... Note that the M 3 /M 2 branching ratio is lower (0.8:1) for measurements with polarization along the c-axis than in the basal ab-plane (1:1). The trend in XES branching ratios in the transition-metal compounds is a signature of the degree of ionicity in the systems [40], due to the additional Coster-Kronig process [24,41]. The lower 3p 3/2 /3p 1/2 peak ratio along the c-axis is thus an indication of higher ionicity (resistivity) than in the basal ab-plane. ...
The anisotropy in the electronic structure of the inherently nanolaminated ternary phase CrGeC is investigated by bulk-sensitive and element selective soft x-ray absorption/emission spectroscopy. The angle-resolved absorption/emission measurements reveal differences between the in-plane and out-of-plane bonding at the (0001) interfaces of CrGeC. The Cr , C K, and Ge , emission spectra are interpreted with first-principles density-functional theory (DFT) including core-to-valence dipole transition matrix elements. For the Ge 4s states, the x-ray emission measurements reveal two orders of magnitude higher intensity at the Fermi level than DFT within the General Gradient Approximation (GGA) predicts. We provide direct evidence of anisotropy in the electronic structure and the orbital occupation that should affect the thermal expansion coefficient and transport properties. As shown in this work, hybridization and redistribution of intensity from the shallow 3d core levels to the 4s valence band explain the large Ge density of states at the Fermi level.
... 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: ...
... The base pressure was 6.7 × 10 −7 Pa during all the measurements. To minimize self-absorption effects [57], the angle of incidence was 20°from the surface plane during the emission measurements. The x-ray photons were detected parallel to the polarization vector of the incoming beam to minimize elastic (Rayleigh) scattering. ...
... The base pressure was 6.7 × 10 −7 Pa during all the measurements. To minimize self-absorption effects [57], the angle of incidence was 20°from the surface plane during the emission measurements. The x-ray photons were detected parallel to the polarization vector of the incoming beam to minimize elastic (Rayleigh) scattering. ...
The electronic structure of Sc1−xVxNy epitaxial films with different alloying concentrations of V are investigated
with respect to effects on thermoelectric properties. Band structure calculations on Sc0.75V0.25N
indicate that V 3d states lie in the band gap of the parent ScN compound in the vicinity of the Fermi level.
Thus, theoretically, the presence of light (dispersive) bands at the point with band multiplicity is expected
to lead to lower electrical resistivity, while flat (heavy) bands at X-W-K symmetry points are associated with
higher Seebeck coefficients than that of ScN. Hence, to probe the thermoelectric properties experimentally,
epitaxial Sc1−xVxNy thin film samples were deposited on MgO(001) substrates. All the samples showed N
substoichiometry and pseudocubic crystal structure. The N-vacancy-induced states were visible in the Sc 2p
x-ray absorption spectroscopy spectra. The reference ScN and Sc1−xVxNy samples up to x = 0.12 were n
type, exhibiting carrier concentration of 1021 cm−3, typical for degenerate semiconductors. For the highest V
alloying of x = 0.15, holes became the majority charge carriers, as indicated by the positive Seebeck coefficient.
The underlying electronic structure and bonding mechanisms in Sc1−xVxNy influence the electrical resistivity,
Seebeck coefficient, and Hall effect. Thus, this paper contributes to the fundamental understanding to correlate
defects and thermoelectric properties to the electronic structure in the Sc-N system with V alloying.
... All measurements were performed with a base pressure <6.7 × 10 −7 Pa. To minimize self-absorption effects [45], the angle of incidence was 20 • from the surface plane during the emission measurements. The x-ray photons were detected parallel to the polarization vector of the incoming beam to minimize elastic scattering. ...
Chromium-based nitrides are used in hard, resilient coatings and show promise for thermoelectric applications due to their combination of structural, thermal, and electronic properties. Here, we investigate the electronic structures and chemical bonding correlated to the thermoelectric properties of epitaxially grown chromium-based multicomponent nitride Cr(Mo, V)N x thin films. The small amount of N vacancies causes Cr 3d and N 2p states to appear at the Fermi level and reduces the band gap in Cr 0.51 N 0.49. Incorporating holes by alloying of V in N-deficient CrN results in an enhanced thermoelectric power factor with marginal change in the charge transfer of Cr to N compared with Cr 0.51 N 0.49. Further alloying of Mo, isoelectronic to Cr, increases the density of states at the Fermi level due to hybridization of the (Cr, V) 3d and Mo 4d-N 2p states in Cr(Mo, V)N x. This hybridization and N off-stoichiometry result in more metal-like electrical resistivity and reduction in Seebeck coefficient. The N deficiency in Cr(Mo, V)N x also depicts a critical role in reduction of the charge transfer from metal to N site compared with Cr 0.51 N 0.49 and Cr 0.50 V 0.03 N 0.47. In this paper, we envisage ways for enhancing thermoelectric properties through electronic band engineering by alloying and competing effects of N vacancies.
... The measurements were performed with a base pressure lower than 5×10 −7 Pa. In order to enhance the π * contribution that is suppressed at normal incidence [35], the XANES spectra were measured at 20 • grazing incidence angle in total fluorescence yield (TFY) mode. The energy resolutions were 0.025 and 0.1 eV, at the B 1s and N 1s absorption edges, respectively. ...
The electronic structure of rhombohedral sp2 hybridized boron nitride (r-BN) is characterized by X-ray absorption near-edge structure spectroscopy. Measurements are performed at the boron and nitrogen K-edges (1s) and interpreted with first-principles density functional theory calculations, including final state effects by applying a core-hole. We show that it is possible to distinguish between different 2D planar polytypes such as rhombohedral, twinned rhombohedral, hexagonal and turbostratic BN by the difference in chemical shifts. In particular, the chemical shift at the B 1s-edge is shown to be significant for the turbostratic polytype. This implies that the band gap can be tuned by a superposition of different polytypes and stacking of lattice planes.
... 34 The measurements were performed with a base pressure lower than 5× 10 −7 Pa. To enhance the π* contribution that is suppressed at normal incidence, 35 the XANES spectra were measured at 20°grazing incidence angle in total fluorescence yield (TFY) mode. The energy resolutions were 0.025 and 0.1 eV at the B 1s and N 1s absorption edges, respectively. ...
The electronic structure of rhombohedral sp2-hybridized
boron nitride (r-BN) is characterized by X-ray absorption near-edge structure spectroscopy. Measurements are performed at the boron and nitrogen K-edges (1s) and interpreted with f irst-principles density functional theory calculations, including final state effects by applying a core hole. We show that it is possible to distinguish between different 2D planar polytypes such as rhombohedral, twinned rhombohedral, hexagonal, and turbostratic BN by the difference in chemical shifts. In
particular, the chemical shift at the B 1s-edge is shown to be significant for the turbostratic polytype. This implies that the band gap can be tuned by a superposition of different polytypes and stacking of lattice planes.
... All samples were measured in the same geometry with energy resolutions of 0.2 eV and 0.1 eV at the Fe 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 selfabsorption effects [15] with the program XANDA [16] in figures 6 and 7. ...
We investigate the amorphous structure, chemical bonding, and electrical properties of magnetron sputtered Fe 1−x C x (0.21 x 0.72) thin films. X-ray, electron diffraction and transmission electron microscopy show that the Fe 1−x C x films are amorphous nanocomposites, consisting of a two-phase domain structure with Fe-rich carbidic FeC y , and a carbon-rich matrix. Pair distribution function analysis indicates a close-range order similar to those of crystalline Fe 3 C carbides in all films with additional graphene-like structures at high carbon content (71.8 at% C). From x-ray photoelectron spectroscopy measurements, we find that the amorphous carbidic phase has a composition of 15–25 at% carbon that slightly increases with total carbon content. X-ray absorption spectra exhibit an increasing number of unoccupied 3d states and a decreasing number of C 2p states as a function of carbon content. These changes signify a systematic redistribution in orbital occupation due to charge-transfer effects at the domain-size-dependent carbide/matrix interfaces. The four-point probe resistivity of the Fe 1−x C x films increases exponentially with carbon content from ∼200 µµ cm (x = 0.21) to ∼1200 µµcm (x = 0.72), and is found to depend on the total carbon content rather than the composition of the carbide. Our findings open new possibilities for modifying the resistivity of amorphous thin film coatings based on transition metal carbides through the control of amorphous domain structures.
... 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. ...
... 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. ...
The crystal structure and chemical bonding of magnetron-sputtering deposited nickel carbide Ni 1−x C x (0.05 x 0.62) thin films have been investigated by high-resolution x-ray diffraction, transmission electron microscopy, x-ray photoelectron spectroscopy, Raman spectroscopy, and soft x-ray absorption spectroscopy. By using x-ray as well as electron diffraction, we found carbon-containing hcp-Ni (hcp-NiC y phase), instead of the expected rhombohedral-Ni 3 C. At low carbon content (4.9 at%), the thin film consists of hcp-NiC y nanocrystallites mixed with a smaller amount of fcc-NiC x . The average grain size is about 10–20 nm. With the increase of carbon content to 16.3 at%, the film contains single-phase hcp-NiC y nanocrystallites with expanded lattice parameters. With a further increase of carbon content to 38 at%, and 62 at%, the films transform to x-ray amorphous materials with hcp-NiC y and fcc-NiC x nanodomain structures in an amorphous carbon-rich matrix. Raman spectra of carbon indicate dominant sp 2 hybridization, consistent with photoelectron spectra that show a decreasing amount of C–Ni phase with increasing carbon content. The Ni 3d–C 2p hybridization in the hexagonal structure gives rise to the salient double-peak structure in Ni 2p soft x-ray absorption spectra at 16.3 at% that changes with carbon content. We also show that the resistivity is not only governed by the amount of carbon, but increases by more than a factor of two when the samples transform from crystalline to amorphous.
Following our discussion of XAS and its polarization dependence in the last two chapters we here continue with the discussion of two other important first order processes, namely x-ray emission spectroscopy (XES) and Thomson scattering, outlined in Sect. 9.5 and illustrated schematically in Fig. 9.4b, c. X-ray emission is the inverse of the x-ray absorption process, and both can be described within KHD theory by transitions between two states. The interaction Hamiltonian for the two processes is the same, given by in (9.22).
Chromium-based nitrides are used in hard, resilient coatings, and show promise for thermoelectric applications due to their combination of structural, thermal, and electronic properties. Here, we investigated the electronic structures and chemical bonding correlated to the thermoelectric properties of epitaxially grown chromium-based multicomponent nitride Cr(Mo,V)Nx thin films. Due to minuscule N vacancies, finite population of Cr 3d and N 2p states appear at the Fermi level and diminishes the band opening for Cr0.51N0.49. Incorporating holes by alloying V in N deficient CrN matrix results in enhanced thermoelectric power factor with marginal change in the charge transfer of Cr to N compared to Cr0.51N0.49. Further alloying Mo isoelectronic to Cr increases the density of states across the Fermi level due to hybridization of the (Cr, V) 3d and Mo 4d-N 2p states in Cr(Mo,V)Nx. The hybridization effect with reduced N 2p states off from stoichiometry drives the system towards metal like electrical resistivity and reduction in Seebeck coefficient compensating the overall power factor still comparable to Cr0.51N0.49. The N deficiency also depicts a critical role in reduction of the charge transfer from metal to N site. The present work envisages ways for enhancing thermoelectric properties through electronic band engineering by alloying and competing effects of N vacancies.
Here we report the hydrothermal synthesis of MoS2/Cu2O nanocomposites with tunable heterojunction for enhancing visible light photochemical activity and stability. The conduction and valence band positions of few-layers MoS2 have been tuned to optimize photo-induced charge separation efficiency by regulating the layer thickness of MoS2. The photochemical activity and stability of MoS2/Cu2O nanoparticles are demonstrated by visible light assisted degradation of methyl orange. Among all of the samples, the MoS2/Cu2O nanocomposite assembled with 6000 rpm centrifuged MoS2 has the highest degradation efficiency of 95.8 % after 3 h of visible light illumination, due to the high visible light absorption and optimized electron-hole separation by the tunable heterojunction design. The influence of MoS2 mass ratio was further investigated. At last, for better understanding of the enhanced photochemical activity, a novel charge separation mechanism is proposed based on the band alignment and build-in electric field between Cu2O and MoS2.
We report the design and performance of a 3-electrode device for real time in situ scanning transmission X-ray microscopy studies of electrochemical processes under both static (sealed, non-flow) conditions and with a continuous flow of electrolytes. The device was made using a combination of silicon microfabrication and 3D printing technologies. The performance is illustrated by results of a study of copper deposition and stripping at a gold working electrode. X-ray absorption spectromicroscopy at the Cu 2p edge was used to follow the evolution as a function of potential and time of the spatial distributions of Cu(0) and Cu(i) species electro-deposited from an aqueous solution of copper sulphate. The results are interpreted in terms of competing mechanisms for the reduction of Cu(ii).
Using monoenergetic X-ray photons from Indus-2 synchrotron Centre, the Coster-Kronig vacancy factor(κ) for L3 subshell X-rays of some lanthanide elements such as Gd, Tb, Ho and compounds such as Pr2O3, Pr2(CO3)3.8H2O, Nd2O3, Sm2O3, Sm2(CO3)3.2.85H2O, Sm2(SO4)3.8H2O, Gd2(CO3)3, Tb2O3, Dy2(SO4)3, Ho2O3 and HoF3 have been determined experimentally. By measuring Lα X-ray production cross-section, the L3 subshell fluorescence yield and theoretical values of the L3 subshell photoionization cross-section and level widths, the κ values have been determined. Comparison of the measured experimental κ values with theoretical values indicates that the influence of the chemical environment on κ values in the selected lanthanide targets is not noticeable.
The valence band electronic structure of GeSe single crystals has been investigated using angle resolved photoemission spectroscopy (ARPES) and x-ray photoelectron spectroscopy. The experimentally observed bands from ARPES, match qualitatively with our LDA-based band structure calculations along the Γ–Z, Γ–Y and Γ–T symmetry directions. The valence band maximum occurs nearly midway along the Γ–Z direction, at a binding energy of −0.5 eV, substantiating the indirect band gap of GeSe. Non-dispersive features associated with surface states and indirect transitions have been observed. The difference in hybridization of Se and Ge 4p orbitals leads to the variation of dispersion along the three symmetry directions. The predominance of the Se 4p z orbitals, evidenced from theoretical calculations, may be the cause for highly dispersive bands along the Γ–T direction. Detailed electronic structure analysis reveals the significance of the cation–anion 4p orbitals hybridization in the valence band dispersion of IV–VI semiconductors. This is the first comprehensive report of the electronic structure of a GeSe single crystal using ARPES in conjugation with theoretical band structure analysis.
The electronic structure of nanolaminate Ti2AlC and Ti2AlN thin films, so-called MAX-phases, were investigated by soft X-ray emission spectroscopy. These nanolaminated carbide and nitride compounds represent a class of layered materials with a combination of properties from both metals and ceramics. The bulk-sensitive soft X-ray emission technique is particularly useful for detecting detailed electronic structure information about internal monolayers and interfaces. The Ti-Al bonding is manifested by a pronounced peak in the Ti L-emission of Ti2AlC and Ti2AlN that is not present in the binary TiC system. The spectral shape of Al L-emission in the MAX-phase is strongly modified in comparison to metallic Al. By replacing or partly exchanging C with N, a change of the electron population can be achieved causing a change of covalent bonding between the laminated layers, which enables control of the material properties.
The anisotropy of the electronic structure of ternary nanolaminate V2GeC is investigated by bulk-sensitive soft x-ray emission spectroscopy. The measured polarization-dependent emission spectra of V L2,3, C K, Ge M1, and Ge M2,3 in V2GeC are compared with those from monocarbide VC and pure Ge. The experimental emission spectra are interpreted with calculated spectra using ab initio density-functional theory including dipole transition matrix elements. Different types of covalent chemical bond regions are revealed: V 3d-C 2p bonding at −3.8 eV, Ge 4p-C 2p bonding at −6 eV, and Ge 4p-C 2s interaction mediated via the V 3d orbitals at −11 eV below the Fermi level. We find that the anisotropic effects are high for the 4p valence states and the shallow 3d core levels of Ge, while relatively small anisotropy is detected for the V 3d states. The macroscopic properties of the V2GeC nanolaminate result from the chemical bonds with the anisotropic pattern as shown in this work.
The electronic structure and chemical bonding of the recently discovered inverse perovskite Sc3AlN, in comparison to those of ScN and Sc metal, have been investigated by bulk-sensitive soft-x-ray emission spectroscopy. The measured Sc L, N K, Al L1, and Al L2,3 emission spectra are compared with calculated spectra using first-principles density-functional theory including dipole transition-matrix elements. The main Sc 3d–N 2p and Sc 3d–Al 3p chemical bond regions are identified at −4 and −1.4 eV below the Fermi level, respectively. A strongly modified spectral shape of 3s states in the Al L2,3 emission from Sc3AlN in comparison to that for pure Al metal is found, which reflects the Sc 3d–Al 3p hybridization observed in the Al L1 emission. The differences between the electronic structures of Sc3AlN, ScN, and Sc metal are discussed in relation to the change in the conductivity and elastic properties.
This review focuses on the capabilities and potential of soft x-ray fluorescence spectroscopy for the study of the electronic
structure and chemical bonding of novel materials. The basic principle of x-ray fluorescence measurements using synchrotron
radiation and the corresponding instrumentation issues are outlined. Particular attention is given to x-ray spectroscopic
studies of the electronic structure and characterization of nanostructures, thin films, interfaces, adsorbates, half-metallic
ferromagnets, and impurities in alloys, superconductors, and semiconductors and the chemical bonding in biomaterials and liquids.
The microstructure, electronic structure and chemical bonding of chromium carbide thin films with different carbon contents have been investigated with high-resolution transmission electron microscopy, electron energy loss spectroscopy and soft x-ray absorption-emission spectroscopies. Most of the films can be described as amorphous nanocomposites with non-crystalline CrC(x) in an amorphous carbon matrix. At high carbon contents, graphene-like structures are formed in the amorphous carbon matrix. At 47 at.% carbon content, randomly oriented nanocrystallites are formed creating a complex microstructure of three components. The soft x-ray absorption-emission study shows additional peak structures exhibiting non-octahedral coordination and bonding.
The electronic structure and chemical bonding of wurtzite-GaN investigated by
N 1s soft x-ray absorption spectroscopy and N K, Ga M1, and Ga M2,3 emission
spectroscopy is compared to that of pure Ga. The measurements are interpreted
by calculated spectra using first-principles density-functional theory (DFT)
including dipole transition matrix elements and additional on-site Coulomb
interaction (WC-GGA+U). The Ga 4p - N 2p and Ga 4s - N 2p hybridization and
chemical bond regions are identified at the top of the valence band between
-1.0 and -2.0 and further down between -5.5 and -6.5 eV, respectively. In
addition, N 2s - N 2p - Ga 4s and N 2s - N 2p - Ga 3d hybridization regions
occur at the bottom of the valence band between -13 and -15 eV, and between
-17.0 and -18.0 eV, respectively. A band-like satellite feature is also found
around -10 eV in the Ga M1 and Ga M2,3 emission from GaN, but is absent in pure
Ga and the calculated ground state spectra. The difference between the
identified spectroscopic features of GaN and Ga are discussed in relation to
the various hybridization regions calculated within band-structure methods.
The frontier electronic structures of a series of organic dye molecules containing a triphenylamine moiety, a thiophene moiety and a cyanoacrylic acid moiety have been investigated by photoelectron spectroscopy (PES), X-ray absorption spectroscopy (XAS), X-ray emission spectroscopy (XES) and resonant photoelectron spectroscopy (RPES). The experimental results were compared to electronic structure calculations on the molecules, which are used to confirm and enrich the assignment of the spectra. The approach allows us to experimentally measure and interpret the basic valence energy level structure in the dye, including the highest occupied energy level and how it depends on the interaction between the different units. Based on N 1s X-ray absorption and emission spectra we also obtain insight into the structure of the excited states, the molecular orbital composition and dynamics. Together the results provide an experimentally determined energy level map useful in the design of these types of materials. Included are also results indicating femtosecond charge redistribution at the dye/TiO(2) interface.
Ohno’s preceding Comment [Phys. Rev. B52, 6127 (1995)] was based on experimental raw spectra of copper L x-ray emission. The Cu L x-ray emission spectra were, however, heavily smeared by the self-absorption effect, which was a source of contradiction. The electronic structure of divalent copper oxide was calculated placing one core hole and two 3d holes, with the result that the spectator 3d holes were delocalized in the adiabatic limit. This implies that the spectator 3d hole produced by the L1,2L3M4,5 Coster-Kronig transition preceding the L3-M x-ray emission will be mostly delocalized at the time of the L3-M x-ray emission, and thus the spectator satellite will be weaker than is expected for free atom. Ohno did not consider this delocalization, which was another source of contradiction.
In this paper we present conclusive experimental evidence that the Auger
satellite structure on the low-kinetic-energy side of the
L3M45M45 Auger spectra in Cu and Zn is
a direct result of the L2L3M45
Coster-Kronig transition preceding the Auger transition. The position of
the satellite structure is compared with numerical calculations of the
final state for the ionized atoms. The same Coster-Kronig process is
shown to be responsible for the anomalous intensity ratio of the
L2M45M45 to
L3M45M45 Auger spectra. From this
intensity ratio the Auger part of the L23 photoelectron
linewidths can be determined and is shown to be in reasonable agreement
with theoretical values.
The construction of a new electron energy analyzer for photoelectron spectroscopy is described. The analyzer is a full hemisphere with a mean radius of 200mm. The spectrometer incorporates highly stable voltage supplies and is equipped with a multidetection system. The electron lens can be operated in different modes, optimizing transmission, spatial resolution or angular resolution. An angular resolution of better than 0.2° can be obtained. UV excited Xe5p spectra recorded in the gas phase show that the energy resolution is better than 2.7 meV at 2eV analyzer pass energy.
The L and M XPS spectra of Cu (Z = 29) and the M and N spectra of Ag (Z = 47) are measured. The lineshift and the line-width of the L, M, and N core levels are analysed in a systematic way from the viewpoint of dynamic decay processes and fluctuations of a hole. The non-relativistic diagrammatic many-body calculations give much better agreement with the measured linewidths than the conventional methods because of a consistent treatment of correlation and localization effects.
Inner-shell ionization energies calculated from Koopmans' theorem are shown, by the sudden approximation, to relate to a weighted average energy for singly and multiply excited states in the photoelectron spectrum. This result is analogous to the Franck-Condon principle in molecular spectroscopy.
Semi‐empirical values of the natural widths of K, L1, L2, and L3 levels, Kα1 and Kα2 x‐ray lines, and KL1L1, KL1L2 and KL2L3 Auger lines for the elements 10?Z?110 are presented in tables and grapahs. Level width Γi (i=K, L1,L2, L3) is obtained from the relation Γi=ΓR,i/ωi, using the theoretical radiative rate ΓR,i from Scofield’s relativistic, relaxed Hartree‐Fock calculation and the fluorescence yield ωi from Krause’s evaluation. X‐ray and Auger lines widths are calculated as the sums of pertinent level widths. This tabulation of natural level and line widths is internally consistent, and is compatible with all relevant experimental and theoretical information. Present semi‐empirical widths, especially those of Kα1 and Kα2 x‐rays, are compared with measured widths. Uncertainties of semi‐empirical values are estimated.
In this paper we present conclusive experimental evidence that the Auger satellite structure on the low-kinetic-energy side of the L3M45M45 Auger spectra in Cu and Zn is a direct result of the L2L3M45 Coster-Kronig transition preceding the Auger transition. The position of the satellite structure is compared with numerical calculations of the final state for the ionized atoms. The same Coster-Kronig process is shown to be responsible for the anomalous intensity ratio of the L2M45M45 to L3M45M45 Auger spectra. From this intensity ratio the Auger part of the L23 photoelectron linewidths can be determined and is shown to be in reasonable agreement with theoretical values.
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.
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.
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.
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 5×1012 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.
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.
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.
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.
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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