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Angular dependent resonant photoemission processes at the 2p thresholdsin nickel metal
Abstract
Angle-resolved valence-band resonant photoemission of nickel metal has been
measured close to the 2p core-level thresholds with synchrotron radiation. The
well-known 6-eV correlation satellite has an intensity enhancement of about two
orders of magnitude at resonance. The angular dependence of the photoemission
intensity has been studied as function of photon energy and provides
unambiguous evidence for interference effects all the way up to the resonance
maximum. The observation of different angular asymmetries, {\beta}, for the
valence band and the satellite is discussed in connection to the origin of the
resonant photoemission process and the character of the satellite.
... For x = 0.05, the double-peak structure has essentially vanished in comparison to at x = 0.16 due to the superposition of the strong fcc contribution. (iv) The 6 eV feature [19,31] above the main 2p 3/2 peak is prominent in Ni metal x = 0.0 that is associated with electron correlation effects and narrow-band phenomena [32]. The intensity of the 6 eV feature is very low in the Ni 1−x C x films in comparison to Ni metal even at x = 0.05 due to more delocalized bands. ...
... Moreover, the 6 eV feature in the Ni XAS spectra that signifies electron correlation effects and narrow-band phenomena in metallic Ni [19,31] is washed out in the Ni 1−x C x samples due to the Ni 3d-C 2p orbital overlap that changes the properties of Ni already at very low carbon content. Thus, the spectral profiles of the Ni 1−x C x samples exhibit carbide signatures and exclude metallic nickel. ...
... For x = 0.05, the double-peak structure has essentially vanished in comparison to at x = 0.16 due to the superposition of the strong fcc contribution. (iv) The 6 eV feature [19,31] above the main 2p 3/2 peak is prominent in Ni metal x = 0.0 that is associated with electron correlation effects and narrow-band phenomena [32]. The intensity of the 6 eV feature is very low in the Ni 1−x C x films in comparison to Ni metal even at x = 0.05 due to more delocalized bands. ...
... Moreover, the 6 eV feature in the Ni XAS spectra that signifies electron correlation effects and narrow-band phenomena in metallic Ni [19,31] is washed out in the Ni 1−x C x samples due to the Ni 3d-C 2p orbital overlap that changes the properties of Ni already at very low carbon content. Thus, the spectral profiles of the Ni 1−x C x samples exhibit carbide signatures and exclude metallic nickel. ...
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.
... Such spectroscopies probe respectively the radiative and non radiative autoionization decay of a core hole, and the signal can be strongly enhanced with respect to the non resonant mode. The element and orbital selectivity of core level resonant spectroscopies allows to access higher order multipoles which are left unexplored by MCD in X-ray absorption (XAS) [1][2][3][4][5][6], to distinguish and enhance specific electronic excitations and satellites [7,8], collective magnetic excitations [9], ultrafast and charge transfer dynamics [10][11][12] and to detect quadrupolar transitions towards localized empty states [13,14]. In particular, RPES has recently been applied to several correlated materials [15][16][17][18][19] and full two dimensional angular scans of resonantly emitted electrons in moderately correlated materials have also been carried out [20,21]. ...
... We again observe a region of deconstructive interference ( Fig.4(b)) and then a strong enhancement for the third photon energy (Fig.4(c)), which is different for the two spin channels. The massive enhancement of the signal observed here does not imply strong interference effects: an analysis of the different contributions in the amplitude reveals that, in our case, the enhancement is given essentially by the resonant excitation alone, as was also found in other cases [8]. ...
A first principles approach, based on the real space multiple scattering
Green's function method, is presented for spin- and angle-resolved resonant
photoemission from magnetic surfaces. It is applied to the Fe(010) valence band
photoemission excited with circularly polarized X-rays around the Fe L3
absorption edge. When the photon energy is swept through the Fe 2p-3d
resonance, the valence band spectra are strongly modified in terms of absolute
and relative peak intensities, degree of spin-polarization and light
polarization dependence. New peaks in the spin-polarized spectra are identified
as spin-flip transitions induced by exchange decay of spin-mixed core-holes. By
comparison with single atom and band structure data, it is shown that both
intra-atomic and multiple scattering effects strongly influence the spectra. We
show how the different features linked to states of different orbital symmetry
in the d band are differently enhanced by the resonant effect. The appearance
and origin of circular dichroism and spin polarization are analyzed for
different geometries of light incidence and electron emission direction,
providing guidelines for future experiments.
IntroductionQuasi-ParticlesCollective ExcitationsExperimental Access to Quasi-Particle and Collective ExcitationsSummaryReferences
The present report adds to the ongoing research on Si/Ge nanostructures by discussing the results obtained utilizing unique features of Synchrotron radiation (SR). Based on the structural and electronic properties of this system investigated in our earlier work, we have synthesized [Si(5 nm)/Ge(5 nm)]×10 multilayers (MLS) and exposed it to a range of incident photon energies (utilizing synchrotron radiation) and at different incident angles for the photoemission spectroscopic measurements. It is shown how the interface features are enhanced simultaneously suppressing the signals from topmost atomic layers. Also the effect of incident angle variation is discussed, which gives a clear picture of interface electronic properties of Si/Ge system. Significant changes in Si 3p, Ge 4p and s band features are observed in the valence band density of states. The overall results present an interesting observation of thoroughly investigating the basic building bilayer stack of the multilayer structure by combining energy and/or angle variation with low energy sputter depth profiling.
The valence-band electronic structure of a decagonal Ni-rich Al-Co-Ni quasicrystal, Al72Co8Ni20, was investigated using soft X-ray photoelectron spectroscopy. In particular, the energy distributions of the transition metal 3d bands were determined from the Co and Ni 2p-3d resonance photoemission and compared with those calculated by the discrete variational X method for a model cluster based on a proposed Ni-rich Al-Co-Ni approximant, as well as the 3d band observed in the Co-rich Al-Co-Ni quasicrystal, Al72Co16Ni12. In the Ni-rich Al-Co-Ni, the transition metal 3d band exhibits a peak at a binding energy, EB, of 2.3 eV, which is higher than that of the Co-rich Al-Co-Ni. The observed Ni 3d band has a single-peaked distribution around EB 2.4 eV, in contrast to the calculated bimodal and wide-spread distribution for the proposed Ni-rich Al-Co-Ni model cluster, whereas the Co 3d band is located at EB 1.7 eV, consistent with the model calculation.
We have studied the Ni L edge x-ray absorption fine structure for thin Ni films evaporated on a Cu(001) substrate. The measurements have been carried out for films having coverages ranging from 0.07 monolayers (ML) up to 3.1 ML. The coverage has been calibrated using the ratio of the Ni L3 to Cu L3 edge jump heights and independently verified with titration experiments. We have found a clear evolution of the x-ray absorption fine structure at the Ni L3 edge with coverage. To interpret the measured spectra first-principles calculations have been performed modeling a two-dimensional growth. The calculations reproduced all features observed experimentally. From the comparison between experiment and theory we can conclude that submonolayer films contain a large number of small islands. Deposition of an amount of nickel corresponding to a single layer results in the formation of an almost perfect flat layer. Our studies show that L edge x-ray absorption spectroscopy can provide useful information on thin-film growth and morphology.
An interpretation of the spectral features in the Ni L3 x-ray absorption near-edge structure and x-ray magnetic circular dichroism signals is presented, based on both one-electron multiple-scattering and atomic-multiplet calculations. Neither of these approaches is fully satisfactory. Although most of the observed features are reproduced by one-electron calculations, the pronounced peak about 3 eV above the edge is not. Conversely, the peak at 6 eV and the smooth plateau just beyond are not reproduced by the multiplet calculations. The lack of the 3-eV feature is attributed to the neglect of many-body effects in the interaction between core hole and final-state dn configuration. The observed negative plateau between L3 and L2 edges is attributed to transitions to spin-polarized continuum εd states, and the 6-eV peak, to multiple scattering paths of intermediate range and disappears for Ni clusters smaller than 13 atoms. The necessity of both one-electron and atomic-multiplet calculations to explain all features in the data demonstrates the need for a combined approach.
The electronic structures of Ni3Al, Ni3Ga, Ni3In, and NiGa are studied by resonant photoemission spectroscopy (RESPES) and X-ray absorption near-edge spectra (XANES) at the Ni L2,3-edges. The RESPES spectra are explained with atomic multiplet model, and the XANES data are compared with those calculated with multiple-scattering theory. The number of 3d holes per Ni atom is calculated for Ni3Al, Ni3Ga, and Ni3In.
In order to test the presence of interatomic multi-atom resonant photoemission (MARPE) in 3d magnetic ultrathin films, 2p photoelectron emission of various ferromagnetic 3d metals was studied while the excitation energy was tuned around the L2,3 core level absorption edge of a different 3d metal. Both elements were in direct contact either as bilayer or as alloys to maximize this possible effect. Systems under study were Fe/Co, Fe/Ni, Fe30Ni70, Co, Co90Mn10, and Ni90Mn10, all grown as epitaxial films on Cu(001). No measurable change in intensity of the 2p photoemission intensities in normal emission for 45° incidence of more than 2.5–5% was found as a result of resonant excitation of neighboring atoms in any of these systems. We can thus exclude the presence of significant MARPE in these metallic systems in the present experimental geometry. This is further confirmed by the photon energy dependence of the linear magnetic dichroism in the Fe 2p photoemission of a Fe/Co film, which is not influenced by Co L2,3 edge resonant absorption.
The quasiparticle dynamics of electrons in a magnetically ordered state is
investigated by high-resolution angle-resolved photoemission of Ni(110) at 10
K. The self-energy is extracted for high binding energies reaching up to 500
meV, using a Gutzwiller calculation as a reference frame for correlated
quasiparticles. Significant deviations exist in the 300 meV range, as
identified on magnetic bulk bands for the first time. The discrepancy is
strikingly well described by a self-energy model assuming interactions with
spin excitations. Implications relating to different electron-electron
correlation regimes are discussed.
Unambiguous evidence for resonant photoemission in Ni is presented. Interference effects are identified at the 2p edges for the valence band and the 6 eV satellite. A rapid transition from a resonant Raman to an Auger-like regime shows that the core-excited states above threshold are not localized enough to significantly enhance the photoemission intensity, implying a large fraction of incoherent intensity. The results indicate that the appearance of interference effects does not require strong localization of the intermediate state.
We report on a resonant photoemission study of Ni metal and CuO at the LIII soft-X-ray absorption thresholds. The valence band spectra exhibit a strong enhancement of electron emission at resonance, which is shown to be mostly due to an incoherent superposition of a photoemission signal with a more intense signal from L3M4,5M4,5 Coster-Kronig decay of the core-ionized state. The resonant enhancement of the valence band photoemission satellite amounts to a factor of 12, far short of the recent claim of a giant resonance. Implications of these results with respect to the nature of the 3d states in these materials are briefly discussed.
We report on an angle-resolved resonant photoemission study of Co and Fe metal at the MIII absorption threshold. The intensity of the various spectral components was measured as a function of the electron emission angle relative to the E vector of the incident light. On MIII resonance, the main valence-band photoemission (PE) intensity of Co and Fe metal, located between EF and 3 eV, follows a cos2θ behavior, as is expected for a photoemission process. However, the intensity of the enhanced feature located at ≈5 eV is found to be almost independent of the emission angle, as expected for an incoherent Auger process. This clearly shows that the enhancement of the 5 eV PE signal is mainly caused by an incoherent Auger decay and not by a resonant PE process.
We report on comparative study of angle-resolved photoelectron spectra of Ni metal and CeGd at theM
III andN
IV,V soft-x-ray absorption threshold, respectively. OnM
III resonance, the valence-band photoemission (PE) intensity of Ni follows a cos2-behavior, while the intensity of the 6-eV satellite is independent of the angle of emission relative to the E-vector of the incoming beam. On the other hand, the 4f Ce PE signal behaves cos2 onN
IV,V resonance. This clearly shows that the resonant enhancement of the 6-eV PE satellite of Ni is mainly caused by an incoherent Auger decay and cannot be described as a resonant PE process.
We report the observation of a giant resonance in the Cu 2p resonant-photoemission spectra of CuO. The study allows the unambiguous identification of the local Cu 3d8 configuration in the valence-band photoemission spectrum, providing conclusive evidence for the charge-transfer nature of the insulating gap in the electronic structure of CuO. A comparison with 3p resonant-photoemission measurements is also presented to emphasize the strength of 2p resonant photoemission as a tool for studying the electronic structure of highly correlated 3d transition-metal systems.
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A strong resonance effect has been observed for the first time in photoemission: This happens on a metallic nickel (100) surface when the photon energy is close to that of the 3p energy level. The effect is interpreted as the autionization of an excited quasidiscrete atomic configuration into a continuum of excitations with two holes in the 3d shell.
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.
From an Auger study of dilute Ni alloys with electropositive metals it is concluded that multiplet splitting of the Ni configuration is important. It is shown that the () state is of sufficiently low energy to be strongly mixed in the Ni ground-state wave function whereas the other, mainly singlet, states are all well removed to higher energy. The relevance of multiplet splittings to polarity fluctuations and magnetism in transition metals and their alloys is discussed.
Spin-polarized photoemission spectra have been measured on the ferromagnetic Ni(110) single crystal. Evidence for the Fano interference effect in the spin polarization of the 6-eV satellite of the valence band has been obtained. The results indicate that the interference effect between the direct 3d electron transition and the 3p core electron excitation followed by the MVV super-Coster-Kronig process to form the two-d-hole bound state is important to explain the behavior of the resonant 6-eV satellite. It is also found that the spin polarization is still large under an off-resonant condition, and this indicates that the direct 3d transition from the majority-spin state is effective to form the two-hole singlet bound state.
The angle-resolved resonant photoelectron spectra of Ni and Ce metals are reported. On MIII resonance, the intensity of the 6-eV satellite of Ni is found to be independent of the angle of emission relative to the -vector of the exciting light, while the valence-band photoemission (PE) intensity follows a cos2 behavior as expected for PE. In contrast to Ni, the enhanced Ce4f PE signal on NIV,V resonance also varies according to cos2. This shows that the resonant enhancement of the 6-eV Ni satellite is mainly due to a secondary Auger decay, whereas in case of the Ce4f signal it reflects resonant photoemission.
A comparative resonant photoemission (PE) study of Ni, Fe and Eu metal as well as Ce in CeGd is reported. It is shown that the resonant enhancement of the 6 eV satellite in the valence-band PE spectrum of Ni metal is almost completely due to an incoherent superposition of the valence-band PE spectrum with an intense Auger emission signal. On the other hand, the resonant enhancement of 4f signals from rare-earth systems turns out to be a true resonant PE phenomenon.
This book covers in a self-contained manner the properties of sources, elements of instrumentation and application to biological and medical research. The exception confirming the rule is EXAFS where it was felt that this topic at the border between inorganic chemistry and biochemistry was adequately covered in previous volumes and in several recently published textbooks. Each chapter provides an introduction for newcomers as well as a reference for more advanced researches. In conclusion this is a unique book providing a comprehensive overview of the use of S.-R. in biology and medicine.
This monograph largely confines itself to the study of photoabsorption processes involving individual, isolated molecules in the wavelength or photon energy range from the ionization thresholds of molecules (usually in the vacuum ultraviolet region) through the soft and hard x-ray region and beyond the K edge. It does not cover absorption processes in the liquid or solid phase. By molecule, it is meant diatomic or larger species. A synthesis of the field of photoionization mass spectrometry is also given. (SC)
The LMM Auger spectra of Cu, Zn, Ga, and Ge are presented and discussed. Transition probability calculations are described and with these a clear assignment of the peaks can be made. It is further shown that from the L3M45M45 Auger lines the term splittings and the effective on-site electron-electron interaction can be determined. The latter is shown to be strongly reduced from the free-atom value. This has important consequences for the description of the band structure using one-electron theories. The satellite structure for Cu and Zn in the L3M45M45 region of the spectrum is shown to be a result of strong Coster-Kronig processes involving the L2 and L3 core levels.
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.
High-resolution gold-valence-band photoemission spectra were obtained by the use of monochromatized Al Kα radiation and a single-crystal specimen. After background and scattering corrections were made, the results were compared directly with broadened theoretical density-of-states functions. The following conclusions were drawn: (i) Relativistic band-structure calculations are required to fit the spectrum. (ii) Both the Korringa-Kohn-Rostoker calculation of Connolly and Johnson and the relativistic-augmented-plane-wave calculation by Christensen and Seraphin give density-of-states results that (after broadening) follow the experimental curve closely. (iii) Of the theoretical functions available to date, those with full Slater exchange agree best with experiment (perhaps because of a cancellation of errors). Fractional (2/3 or 5/6) exchange gives d bands that are too wide. (iv) Eastman's 40.8-eV ultraviolet photoemission spectrum is similar to the x-ray spectrum, suggesting little dependence on photon energy above 40 eV. (v) Both (ii) and (iv) imply an absence of strong matrix-element modulation in the photoemission spectrum of gold.
The metallic renormalization of the LM45M45 Auger spectrum and in particular the L3M-MM45M45 Auger vacancy satellite spectrum is considered for Cu and Zn in terms of calculated one-, two-, and three-core-hole metallic shifts. Good agreement with experiment is obtained. Atomic calculations strongly support the interpretation given by Aksela and Sivonen for the recently observed satellite in Cu vapor, and furthermore it is shown that the same type of satellite has previously been observed, but not identified, in the spectrum from atomic Zn.
The present most sophisticated calculations for 2p photoionization in magnesium (RRPA and MBPT) still neglect important initial and final ionic state configuration interactions whose net effect can be described approximately by a spectroscopic factor and leads to an intensity borrowing model for the photo-process including main and satellite transitions. The validity of this model is checked by deriving from the spectrum of ejected electrons a numerical value for the spectroscopic factor and studying the angular distribution parameters for 2p photoelectrons and L3-M1M1 Auger electrons. As expected from the given model, the angular distribution parameters are found to be in excellent agreement with the binding-energy-adapted theoretical predictions from RRPA and MBPT.
Atomic subshell photoionization cross sections and asymmetry parameters are calculated with the Hartree-Fock-Slater one-electron central potential model (dipole approximation) for all elements Z = 1–103. The cross-section results are plotted for all subshells in the energy region 0–1500 eV, and cross sections and asymmetry parameters are tabulated for selected energies in the region 10.2–8047.8 eV. In addition, more detailed graphs are given for the 4d (Z = 39–71) and 5d (Z = 64–100) subshell cross sections in the vicinity of the Cooper minimum. These data should be particularly useful for work based on spectroscopic investigations of atomic subshells using synchrotron radiation and/or discrete line sources.
The interference of a discrete autoionized state with a continuum gives rise to characteristically asymmetric peaks in excitation spectra. The earlier qualitative interpretation of this phenomenon is extended and revised. A theoretical formula is fitted to the shape of the resonance of He observed in the inelastic scattering of electrons. The fitting determines the parameters of the resonance as follows: E=60.1 ev, \Gamma\sim ev, f\sim{}2 \mathrm{to} 4\ifmmode\times\else\texttimes\fi{}{10}^{-{}3}. The theory is extended to the interaction of one discrete level with two or more continua and of a set of discrete levels with one continuum. The theory can also give the position and intensity shifts produced in a Rydberg series of discrete levels by interaction with a level of another configuration. The connection with the nuclear theory of resonance scattering is indicated.
Three-hole satellites (3d7 final-state configuration) in the nickel valence-band photoelectron spectrum have been identified at 13 and 18 eV binding energy with use of synchrotron radiation from the MAX storage ring. The three-hole satellites show resonances at photon energies close to the threshold for excitation of 3p53d9 core-hole shake-up states. The 13-eV satellite also shows a resonance directly at the 3p threshold. This is interpreted as an interference between the direct three-hole ionization and a shake-up transition in the Auger decay of the 3p hole. This shake-up process is also identified directly in the M2,3M4,5M4,5 Auger spectrum.
The electronic state of ferromagnetic Ni and the expected magnetic circular dichroism (MCD) in Ni 2p→3d x-ray-absorption spectroscopy [2p (XAS)] are discussed from a viewpoint of 3d configuration interaction on the basis of the Anderson impurity model. The model includes multiplet effects arising from 3d-3d and 3d-2p electron interactions and a 3d interatomic exchange approximated by a molecular field acting on the 3d spin. By using commonly accepted values of the interaction strengths, it is shown that the ground state of a Ni atom in ferromagnetic Ni is expressed by a superposition of 3d10, 3d9, and 3d8 configurations with relative weights of 15%–20%, 60%–70%, and 15%–20%, respectively, and with an orbital-magnetic-moment contribution of ∼0.07μB to the total moment of 0.6μB. With these results, we can explain the recently observed MCD in Ni 2p XAS.
The observed enhancement in the 3d, 3p, and 3s photoemission structures at resonance with the 2p absorption edge of nickel is analyzed using a cluster calculation including multiplet structure. The result strongly supports the view of a localized electronic structure for nickel metal. It is found that the peak splitting in the 3s photoemission is due to d mixing, whereas the 3p photoemission shows the influence of both d mixing and electrostatic interaction.
By photoabsorption in the Ar 2p range of Ar multilayer condensates, distinct contributions of surface and bulk excitations can be distinguished in the characteristic core resonances detected by partial-electron-yield near-edge x-ray-absorption fine-structure spectra. Compared to the corresponding bulk/gas-phase features, the surface excitations are shifted by ~0.5 eV towards lower/higher photon energy. Deexcitation of core-to-bound 4s resonances in these condensates leads to distinct spectator-shifted Auger features (2h1e final states). Decay of the 3d,5s resonances, however, is dominated by normal Auger processes to 2h states; 2h1e features are weak. This differs from the behavior of free atoms; it can be understood by the lowering of the ionization threshold to below the 3d,5s resonances by screening in the condensate and by efficient ionization of the core excitonic states during core lifetime, i.e., within a few femtoseconds. Detailed analysis reveals differences for the decay spectra of the lowest resonance at the surface and in the bulk, and shows that the screening energies for the various 2h1e states differ from those of 1h states, as well as among each other. Evidence for the existence of weak participator decay channels (1h final states) at certain photon energies is also found.
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