Search

Interest in the use of synchrotron radiation (SR) as a source of continuum in the extreme ultraviolet (EUV) spectral region was stimulated by the 1956 Physical Review article by Diran Tomboulian and Paul Hartman [1] of Cornell University. In their all-too-brief access to the Cornell 320 MeV electron synchrotron, they showed that SR should be an extremely useful intensity standard in the EUV. They also showed the continuum nature of SR by observing structure at the K-edge of Be at 112 eV.

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

We present results for X-ray absorption in the vicinity of the manganese L 23 edge of MnF 2 , MnO, metallic manganese and LaMnO 3 . We also present emission spectra that result when the 2 p hole produced in absorption is filled by decay from the 3 s and 3 d shells. The results are compared with Hartree–Fock calculations for Mn 2 + and Mn 3 + ions in a spherically symmetric environment. We found very good agreement between the MnF 2 absorption and emission spectra and the Mn 2 + calculated spectra. The absorption spectra for the other compounds are a superposition of Mn 2 + and Mn 3 + absorption. Effects due to the chemical environment are found for 3 s → 2 p X-ray emission. The energy losses measured for 3 d → 2 p emission indicate that both MnF 2 and MnO are Mn 2 + compounds, and that LaMnO 3 is a Mn 3 + compound.

X-ray emission and absorption spectroscopy (XES and XAS, respectively) are important and powerful techniques for determining the electronic properties of materials. Both are used to study magnetic circular dichroism (MCD) which is especially useful for analyzing the magnetic properties of materials. We present XAS and XES measurements and a MCD model study of two thin film layered samples containing SmCo layers in order to report on the applicability of soft x-ray spectroscopic techniques to determine the composition, layer thickness, and electronic structure of such materials. Using a transmission by fluorescence attenuation (TFA) technique we determined the composition and thickness of the SmCo layer to be consistent with the intended composition and thickness. We also confirmed the thickness of the other layers by comparing the XES from the thin film with that of a bulk sample. We showed by a model study that TFA could be used to obtain MCD, and thus the anisotropy of the sample, for film thicknesses b...

Non-resonant V L2,3 and OKα X-ray emission spectra of a new series of (Cu,V)Sr2Can−1CunOy (n=3–7) superconductors are presented. We have found that oxygen atoms surround V-atoms in the given compounds, form a (VO4)3− tetrahedrons and have a pentavalent state. This induces holes due to the substitution of divalent copper by pentavalent vanadium ions providing a hole-doping mechanism of superconductivity in this series of compounds. A spectral estimation of the oxygen concentration shows that the oxygen content under high-pressure/high-temperature synthesis conditions is not changed considerably from the start to the final product.

The results of X-ray fluorescence measurements of niobium metal and its oxides (NbO, NbO 2 and Nb 2 O 5 ) are presented. Non-resonant Nb M 4,5 and O Kα X-ray emission spectra (XES) have been measured at the Advanced Light Source (ALS, Berkeley). The experiments are compared with self-consistent band structure calculations of niobium metal and niobium oxides. We find the experimental spectra are consistent with band structure calculations of niobium metal and the oxides NbO 2 and Nb 2 O 5 . The difference between experimentally determined Nb M 4,5 XES of NbO and the calculated spectrum of Nb 1.0 O 1.0 is understood on the basis of vacancies. We have mimicked the natural structure of NbO, which contains vacancies amounting to 25% in both sublattices. The electronic DOS of Nb 0.75 O 75 is characterised by the formation of additional subbands connected with vacancy states. The calculated electronic structure based on this model is consistent with the XES measurements.

We present X-ray fluorescence measurements of biopolymer chitosan [C 6 H 11 NO 4 ] n and chitosan cross-linked with ethylene glycol diglycidyl ether (EGDE). Changes in the fine structure of resonantly excited O Kα X-ray emission spectra (XES) of unmodified chitosan are attributed to the excitation of non-equivalent oxygen sites belonging to –OH, –O– functional groups. The comparison of the nonresonant nitrogen Kα XES of unmodified chitosan cross-linked with EGDE does not show any differences, which excludes the model of chemical structure according to which EGDE is linked to chitosan via the amine group.

Results of X-ray fluorescence measurements of MA 2 Ca n-1 Cu n O 2n + 3 compounds with [ M -12(n-1)n] type structures, ( C 0.8 N 0.2 Sr 2 CuO 5.3, [ Cu 0.25 (C,N) 0.75] Sr 2 CaCu 2 O y, Cu 0.5 V 0.5 Sr 2 CaCu 2 O 7.5, Cu 0.5 V 0.5 Sr 2 Ca 2 Cu 3 O 9.4, Cu 0.5 V 0.5 Sr 2( Ca 3.6 Sr 0.4) Cu 5 O 13.5 and Cu 0.5 V 0.5 Sr 2( Ca 4.7 Sr 0.3) Cu 6 O 15.3, are presented. The experiments show that C-atoms form a distorted CO 3 oxyacid group with a partial substitution of copper and nitrogen atoms in the M-sites. We conclude that the CO 32- group in (C,N) Sr 2 Ca n-1 Cu n O y and (Cu,C,N) Sr 2 Ca n-1 Cu n O y is substituted by the NO 2- which induces the creation of the hole carriers in these compounds. We have found that V-atoms in the given compounds form ( VO 4)3- tetrahedrons and have a pentavalent state.

We present X-ray photoelectron spectra and X-ray emission spectra of N,N′-bis(3-methylphenyl)-N,N′-diphenyl-1,1′-biphenyl-4,4′-diamine (TPD) films excited with synchrotron radiation. The measurements are compared with density-functional theory calculations performed for a TPD monomer and the electronic structure of this material is discussed in detail. The TPD films studied in this work were prepared by ionized and neutral cluster beam deposition (ICBD and NCBD, respectively) as well as by thermal evaporation. X-ray fluorescence measurements show that the ICBD technique provides the most promising way of preparing high quality TPD films with strong electroluminescence. C–N bonds in the TPD structure are destroyed under NCBD as well as under thermal evaporation.

The local atomic bonding structure of carbon nitride films synthesized by the reactive ionized cluster beam method using X-ray emission spectra (XES) was examined. An ionized cluster beam system was used to prepare the carbon nitride films. The composition of carbon nitride films was measured with Rutherford backscattering spectroscopy techniques and the N/C ratio was found to be approximately 0.25. The XES measurements of the carbon nitride films showed a predominant proportion of sp bonded carbon and nitrogen atoms.

We present results of X-ray fluorescence measurements (carbon Kα and Si L2,3) of methylhydroxylsiloxane and phenylmethylhydroxylsiloxane films. The films are converted into amorphous ceramics by irradiation with 500 keV C and 3 MeV Au ions. Changes in the composition (O/Si ratio) of some polysiloxane films are found when treated with ion irradiation. It is shown that ion irradiation induces a segregation of carbon atoms from methyl groups into diamond-like clusters whereas carbon atoms from phenyl groups maintain their sp2 configuration.

A short review of applications of soft x-ray emission spectroscopy for the study of electronic structure and chemical bonding of advanced materials is presented. It is shown that this technique is very efficient for characterizing different materials such as transition metal compounds, layered superconductors, conducting polymers, metal/polymer interfaces and ion-implanted insulators. Copyright © 2002 John Wiley & Sons, Ltd.

Results of X-ray fluorescence measurements of new oxycarbonitrate superconductors M Sr 2 Ca n −1 Cu n O y ( n =1 or 2 and M =Cu, C or N) are presented. The experiments show that C atoms form a distorted CO 3 oxyacid group with a partial substitution of copper and nitrogen atoms in the M sites. Based on the comparison of nitrogen Kα emission spectra and spectra of reference samples it is concluded that the CO 3 2− group in (C,N)Sr 2 Ca n −1 Cu n O y and (Cu,C,N)Sr 2 Ca n −1 Cu n O y is substituted by the NO 2 − instead of the NO 3 − group. This induces the creation of hole carriers in these compounds.

Results of X-ray fluorescent measurements of carbon–fluorine compounds are presented. We have measured carbon and fluorine K α X-ray emission spectra (2 p →1 s transition) of graphite fluorides ( CF ) n and ( C 2 F ) n . We found that carbon atoms are of the sp 3 type and covalently bound to fluorine. Our measurements show that results of band structure calculations based on chair-type structure of ( CF ) n are not confirmed by comparison of carbon and fluorine emission spectra in the binding energy scale. Therefore the crystal structure of graphite fluorides is still not solved and must be refined.

We present the results of soft x-ray emission measurements for undoped and protonated polyemeraldine. We show that the polaron-lattice band structure fully accounts for the observed x-ray transitions. A finite spectral intensity of C Kα and N Kα XES is observed at the Fermi level for protonated polyemeraldine, supporting the applicability of the polaronic-metal model for highly conducting polymers.

The results of X-ray fluorescence measurements of advanced organic materials (organic semiconductors, superconductors and molecular magnets) are presented. The electronic structure and chemical bonding of these materials is discussed basing on comparison of X-ray emission spectra with spectra of reference samples and our MO LCAO calculations.

We have used ion-beam mixing to form Si nano-crystals in SiO2 and SiO2/Si multilayers, and applied photoluminescence and soft-X-ray emission spectroscopy to study the nanoparticles. Ion-beam mixing followed by heat treatment at 1100 °C for 2 h forms the Si nanocrystals. The ion-beam-mixed sample shows higher PL intensity than that of a Si-implanted SiO2 film. Photon and electron-excited Si L2,3 X-ray emission measurements were carried out to confirm the formation of Si nanocrystal in SiO2 matrix after ion-beam mixing and heat treatment. It is found that Si L2,3 X-ray emission spectra of ion-beam-mixed Si monolayers in heat-treated SiO2 films lead to noticeable changes in the spectroscopic fine structure.

We present resonant inelastic X-ray scattering calculations that realistically incorporate intermediate-state electron–core hole interactions and final-state electron–valence hole interactions. Intermediate-state interactions primarily affect the total fluorescence yield, whereas final-state interactions can change the relative strengths of spectral emission features. This is especially true in systems with strong valence–hole exciton effects. We also consider non-resonant excitation of core electrons. This work considers resonant scattering from B 1s electrons in cubic boron nitride (cBN) and hexagonal boron nitride (hBN) and non-resonant scattering from Mg and O 1s electrons in MgO, and compares theoretical results to experiment.

The electronic structures of the tungsten borides WB, W 2 B and W 2 B 5 were studied experimentally and theoretically. Using monochromatic synchrotron radiation as the excitation source, soft X-ray emission and absorption spectroscopic techniques were employed to probe the occupied and unoccupied states of the valence band, respectively. The linear muffin-tin orbital method was used to calculate the ground state electronic properties of these compounds. The experimental spectroscopic data and the calculated angular momentum- and site-projected densities of states yielded new useful information regarding bonding and hybridization in these materials.

Tunable synchrotron radiation was used to examine the boron K-valence emission from boron doped Ni 3 Al (500 parts per million boron). When compared with electronic structure calculations these measurements yield information regarding the local bonding environment of the doped boron atoms within the alloy structure. Our measurements appear to suggest that the boron atoms preferentially bond with the nickel atoms in this material. It seems that the boron atoms prefer to occupy octahedral interstitial sites surrounded by six nickel atoms. This suggests that the enhancement in ductility observed in this alloy is due to the interplanar metallic bonding provided by the doped boron atoms.

Inelastic scattering of 4d electrons near the 4d–4f thresholds of Gd 2 O 2 S and Tm 2 O 3 is studied with monochromatic synchrotron radiation excitation. The emission is dominated by inelastic scattering. We observe two energy loss mechanisms, which are 4f inner-shell excitations (4d 10 4f n →4d 9 4f n +1 →4d 10 4f n ) and 5p–4f excitations (4d 10 5p 6 4f n →4d 9 5p 6 4f n +1 →4d 10 5p 5 4f n +1 ). Our atomic calculations are in excellent agreement with the experimental emission spectra indicating strong localization and a low degree of correlation of the 4f electrons. Inelastic scattering can be used to elucidate the relative partial cross sections for the contributing transitions.

Resonant inelastic X-ray scattering (RIXS) has been observed in graphite and hexagonal boron nitride (hBN) above and below their K edges. Below the core threshold, inelastic-loss features are observed, which disperse linearly with excitation energy, but as the excitation goes above the core binding energy, nonlinear dispersive effects are observed in graphite but not in hBN. We show that these two effects, which have previously been thought of as separate processes, i.e. resonant X-ray Raman scattering (below threshold) and RIXS (above threshold), are in fact described by the same physics of coherent fluorescence. Very good agreement between experiment and simulated RIXS is achieved using a simple one-electron framework. The role core-excitons play in the RIXS process is examined in finer detail, by using narrow-band excitation. Our results indicate that core-hole effects play a minor role in the RIXS observed from graphite but are more pronounced in hBN.

We have performed Mn K-edge X-ray Absorption and Mn L-edge emission spectroscopies on LiMn2O4, its chemically delithiated and lithiated derivatives (λ-MnO2 and Li2Mn2O4, respectively), and two Mn3+ spinel model compounds. These experiments were undertaken to understand the associated changes in atomic and electronic structure occurring when LiMn2O4 is used in a rechargeable lithium cell. Subtle changes in the Mn K-edge X-ray absorption near edge structure (XANES) occur upon delithiation that are consistent with literature reports of the oxidation of Mn3+ to Mn4+, retention of the cubic phase, and contraction of the spinel lattice. Conversely, when LiMn2O4 is lithiated, the XANES changes dramatically due to the concurrent transformation from a cubic to a tetragonal spinel. The spectrum is different from XANES of tetragonal Mn3+ spinels possessing approximately the same degree of tetragonal distortion as Li2Mn2O4. This spectral difference is attributed to the inserted Li+ imparting an increased degree of co...

Single crystals of α-alumina were implanted with 380 keV Fe+ and Cu+ ions at a dose of 2.6×10 17 cm−2. The specimens were annealed at 1073 K for 1 and 96 h and the chemical state of the metal ions was investigated using soft X-ray fluorescence spectroscopy. Fe L2,3 and Cu L2,3 X-ray emission spectra (XES) excited by synchrotron radiation were measured at the Advanced Light Source (ALS) Lawrence Berkeley National Laboratory. It is found that the Fe L2 to Fe L3 XES ratio of iron-implanted alumina dramatically increased after annealing at 1073 K for 96 h, which is attributed to the formation of Fe2O3. On the other hand, we have found that the chemical state of Cu ions is rather stable to post-annealing and close to that of metallic copper.

We present experimental evidence that the newly discovered multiatom resonant photoemission effect can be observed via secondary decay processes of the primary core hole: Auger electron emission, from Fe{sub 2}O{sub 3}, where the O KL{sub 23}L{sub 23} intensity is enhanced by 90% when h{nu} is tuned to the Fe L{sub 3} edge, and fluorescent x-ray emission, from MnO, where the O K{alpha} fluorescence intensity shows an enhancement of more than 100% at the Mn L{sub 3} edge when properly corrected for saturation and self-absorption effects. (c) 2000 The American Physical Society.

Rechargeable batteries using LiMn2O4 cathodes are commercially attractive, if the problem of excessive capacity fading can be overcome. The cycling properties of these systems can be improved by partial metal substitution for the Mn. To understand the correlation between electrode performance and composition, Mn, Co, and Ni L-edge XAS and XES spectra of a series of LiMn2-yMeyO4 samples (Me = Co, Ni, Li) were recorded. Cobalt is shown to substitute into the spinel system as Co(III) and nickel as Ni(II). A positive correlation between the cycling stability of the electrode and the covalency of the Mn is observed.

The electronic structure of spinel-type ${\mathrm{Cu}}_{1\ensuremath{-}x}{\mathrm{Ni}}_{x}{\mathrm{Rh}}_{2}{\mathrm{S}}_{4}$ $(x=0.0,$ 0.1, 0.3, 0.5, 1.0) and ${\mathrm{CuRh}}_{2}{\mathrm{Se}}_{4}$ compounds has been studied by means of x-ray photoelectron (XPS) and fluorescent spectroscopy. Cu ${L}_{3},$ Ni ${L}_{3},$ S ${L}_{2,3},$ and Se ${M}_{2,3}$ x-ray emission spectra (XES) were measured near thresholds at Beamline 8.0 of the Lawrence Berkeley Laboratory's Advanced Light Source. XES measurements of the constituent atoms of these compounds, reduced to the same binding energy scale, are found to be in excellent agreement with XPS valence bands. The calculated XES spectra which include dipole matrix elements show that the partial density of states reproduce experimental spectra quite well. States near the Fermi level ${(E}_{F})$ have strong Rh d and S(Se) p character in all compounds. In ${\mathrm{NiRh}}_{2}{\mathrm{S}}_{4}$ the Ni $3d$ states contribute strongly at ${E}_{F},$ whereas in both Cu compounds the Cu $3d$ bands are only $\ensuremath{\sim}1$ eV wide and centered $\ensuremath{\sim}2.5$ eV below ${E}_{F},$ leaving very little $3d$ character at ${E}_{F}.$ The density of states at the Fermi level is less in ${\mathrm{NiRh}}_{2}{\mathrm{S}}_{4}$ than in ${\mathrm{CuRh}}_{2}{\mathrm{S}}_{4}.$ This difference may contribute to the observed decrease, as a function of Ni concentration, in the superconducting transition temperature in ${\mathrm{Cu}}_{1\ensuremath{-}x}{\mathrm{Ni}}_{x}{\mathrm{Rh}}_{2}{\mathrm{S}}_{4}.$ The density of states of the ordered alloy ${\mathrm{Cu}}_{0.5}{\mathrm{Ni}}_{0.5}{\mathrm{Rh}}_{2}{\mathrm{S}}_{4}$ shows behavior that is more ``split-band''-like than ``rigid-band''-like.

The localization of Na impurities at the buried heterojunction of CdS/Cu(In,Ga)Se2 thin film solar cells has been studied by photoelectron spectroscopy and X-ray emission spectroscopy. This combination of a surface- and a bulk-sensitive technique allows to identify the localization of impurities at a buried interface in a non-destructive, semi-quantitative, and element-specific way. We compare samples with increasing CdS-overlayer thickness on (a) a CIGS film with nominal Na content and (b) a Na-rich CIGS film. The data clearly indicate a self-limitation of the Na content at this interface. The consequences are discussed in view of the possibility to tailor the electronic structure of the buried heterojunction by controlling the nominal Na content in the CIGS film.

We demonstrate how a combination of photoelectron spectroscopy and x-ray emission spectroscopy can be utilized to derive semi-quantitative information about the localization of impurities at buried interfaces. In the case of the CdS/Cu(In,Ga)Se2 (CIGS) thin-film solar cell heterojunction, segregated Na, which stems from the soda-lime glass substrate or is deliberately added, plays an important role. We find that almost all Na atoms are located at the external CIGS surface or at the CdS/CIGS interface, and that the Na concentration in the bulk of the CIGS film is

Soft x-ray emission through the 4d-4f resonance of Dy{sub 2}O{sub 3} is studied with monochromatic photon excitation. The different soft x-ray emission processes are compared and it is found that inelastic scattering due to 4f inner-shell excitation and resonant elastic scattering are the strongest emission processes followed by inelastic scattering due to 5p-4f net transitions. The nonresonant emission occurring for excitation energies above the 4d-4f resonance is an extremely weak process. The measurements are in good agreement with our calculations. (c) 1999 The American Physical Society.

Fluorescent X-ray emission spectroscopy has been used for the first time to study the electronic structure of polyimide films (PMDA-ODA) prepared on Si-substrates by spin-coating and ionized cluster beam deposition (ICBD) methods. The observed C K α and O K α X-ray emission spectra that probe the C 2 p and O 2 p partial density of states in the valence band, respectively, were compared with X-ray photoelectron valence band spectra. Theoretical simulations of X-ray energies and intensities for polyimide were performed with molecular orbital (MO) calculations of the model monomer, containing 41 atoms, utilizing a semi-empirical Hydrogenic Atoms in Molecules, V. 3 (HAM/3) method. Calculated Al K α photoelectron spectra were obtained using Gaussian lineshape functions of an approximate linewidth (0.10 I k for the model molecule): I k = I ′ k − WD , as indicated for analysis of valence X-ray photoelectron spectra for 63 polymers from some of our previous work. Theoretical C K α and O K α X-ray emission and valence X-ray photoelectron spectra show good agreement with the experimental results, and were used to identify certain spectral features.

金沢大学ナノマテリアル研究所 / 金沢大学理工研究域数物科学系, Changes to the local and electronic structures of phenyltriethoxysilane ~PTES! films when irradiated at room temperature with gold ion concentrations of 531014 to 2.531015 cm22 and with carbon ion concentrations of 531015 cm22 were studied using x-ray emission and photoelectron spectroscopies. The fluorescent ultrasoft silicon LII,III and carbon Ka x-ray emission spectra of unirradiated and irradiated PTES films were measured at the Advanced Light Source, and the Center for Advanced Microstructures and Devices. It is found that the PTES polymers that are exposed to ion doses higher than 531014 cm22 convert to Si:O:C ceramics. Annealing the irradiated PTES polymer films at 1000 °C segregates the carbon atoms into sp2-like clusters.

The electronic structure of organic superconductors {kappa}-(ET){sub 2}Cu[N(CN){sub 2}]Br and {kappa}-(ET){sub 2}Cu(NCS){sub 2} has been studied in detail by means of soft x-ray fluorescence spectroscopy. Cu L{sub 3}, S L{sub 2,3}, C K{alpha}, and N K{alpha} x-ray emission spectra are measured near the corresponding thresholds with synchrotron radiation. The experimental information about site-selective and symmetry-restricted partial density of states in the valence band of both compounds is compared with first-principles band-structure calculations and ultraviolet photoemission spectra. It is found that copper is monovalent in both compounds indicating that the electron is transferred from (ET) dimer to Cu(NCS){sub 2} and Cu[N(CN){sub 2}]Br and is localized mainly on the Cu site. {copyright} {ital 1999} {ital The American Physical Society}

Resonant soft-x-ray emission spectroscopy was measured on ${\mathrm{La}}_{x}{\mathrm{Sr}}_{1\ensuremath{-}x}{\mathrm{TiO}}_{3}$ $(x=0,0.05,0.10)$ in the $\mathrm{Ti}2p$ energy region. At the Raman scattering of the ${e}_{g}$ resonance, the $d\ensuremath{-}d$ transition whose Raman shift has an energy value of about 2.3 eV corresponds to the crystal-field splitting. On the other hand, at the ${t}_{2g}$ resonance, the $d\ensuremath{-}d$ transition whose Raman shift is about 2.2 eV is thought to be the transition reflecting half intra-atomic Coulomb energy.

The electronic structure and chemical bonding of unirradiated and irradiated Poly-1,4-phenylene-ether-sulphone (PES) films have been studied with fluorescent X-ray emission spectroscopy. PES films have been irradiated with 150 keV Ar + ions at concentrations of 5 × 10 13 , 1 × 10 14 , 1 × 10 15 and 7.5 × 10 15 cm −2 . The electronic structure of PES has also been calculated with MO LCAO calculations using a deMon density functional theory (DFT) program and shows good agreement with the experimentally obtained X-ray fluorescence spectra (S L 2,3 , C Kα and O Kα). It is found that the C Kα X-ray emission spectra (XES) of irradiated PES films display marked changes at very high concentrations (1 × 10 15 − 7.5 × 10 15 cm −2 ), similar to the spectroscopic characteristics of amorphous carbon. According to our measurements, the low-energy shift of the S Kα 1,2 XES is observed for concentrations greater than 5 × 10 13 cm −2 which is related to the reduction of –SO 2 – to –S– following the transfer of an oxygen atom from the –SO 2 – functional group to the radical site.

The results of our theoretical and experimental study of electronic structure of poly(sulfur nitride) are presented. The S L2,3 (3s→2p transition) and N Kα (2p→1s transition) X-ray emission spectra (XES) of (SN)x single crystal are measured using synchrotron radiation. The experimental spectra are compared with the results of ab-initio TB-LMTO band structure calculations of 3D solid (SN)x and molecular (S2N2)2 crystals. It is found that the molecular (S2N2)2 is an insulator with a band gap about 2.7 eV whereas the solid (SN)x is metallic. According to the theoretical and experimental information, the S 3p states dominate the density of states (DOS) at the Fermi level and provide the metallic and superconducting properties of this compound.

Excitation-energy dependence of $\mathrm{Ti} {L}_{2,3}$ soft x-ray emission spectra (XES) of a ${\mathrm{TiO}}_{2}$ single crystal is measured near $\mathrm{Ti} 2p$ threshold using tuneable synchrotron radiation at excitation energies ${E}_{\mathrm{exc}}=458.2--476.9\mathrm{eV}.$ It is found that the emission spectra exhibit normal soft x-ray emission features, which do not change with excitation energy and inelastic and resonant x-ray emission features (RXES), which strongly depend on the excitation energy. We are using a band approach in order to discuss the excitation-energy dependence of $\mathrm{Ti} {L}_{2,3}\mathrm{RXES}$ of ${\mathrm{TiO}}_{2}.$ The RXES process is described as a convolution of occupied and unoccupied d states in the intermediate and final states. In this procedure the d states are limited to those which lie in the energy interval ${E}_{\mathrm{exc}}\ifmmode\pm\else\textpm\fi{}\ensuremath{\Delta}E$ taking into account the rule of k conservation. We calculate the curves of restricted joint density of states using the full potential linearized muffin-tin orbital method and the results are found to be in reasonable agreement with the experimental $\mathrm{Ti} {L}_{2,3},$ RXES of ${\mathrm{TiO}}_{2}$ measured at different excitation energies.

The results of measurements of X-ray photoelectron (XPS), X-ray emission (XES) and X-ray absorption spectra and LSDA band structure calculations of Pr0.5Sr0.5MnO3 are presented. The excitation energy dependence of Mn L2,3 and O Kα X-ray emission spectra of Pr0.5Sr0.5MnO3 is measured using tunable synchrotron radiation. Comparing XPS and XES measurements and the LSDA band structure calculations, one concludes that the Mn 3d states are localized near the top of the valence band. Some differences in the Mn 3d-distribution in the upper part of the XPS valence band and Mn L3 XES are due to spin selection rules.

Fluorescent soft X-ray carbon Kα and silicon L 2,3 emission spectra (XES) have been used to characterize the bonding of carbon atoms in polyimide (PI) and polycarbosilane (PCS) films. The PI films have been irradiated with either 40 keV nitrogen or argon ions, at concentrations ranging from 1×10 14 to 1×10 16 cm −2 . The PCS films have been irradiated with 5×10 15 carbon ions cm −2 of 500 keV and/or annealed at 1000°C. We find that the fine structure of the carbon XES of the PI films changes with implanted ion concentrations above 1×10 14 cm −2 which we believe is due to the degradation of the PI film into amorphous C:N:O. The bonding configuration of free carbon precipitates embedded in amorphous SiC which are formed in PCS films after irradiation with C ions or combined treatments (irradiation and subsequent annealing) is similar to that found in diamond-like films or in graphite-like films, respectively.

Resonant inelastic X-ray scattering (RIXS) has been observed in many systems above and below their core threshold. Below threshold, inelastic-loss features are observed, which disperse linearly with excitation energy, but as the excitation increases above the core binding energy, nonlinear dispersive effects are observed. These two effects are described by the same physics of coherent fluorescence. Very good agreement between experiment and simulated RIXS is achieved using a simple one-electron framework. However, significant questions have arisen concerning core-hole effects and their influence on RIXS. In this work, the role core-excitons play in the RIXS process is examined in finer detail in graphite, by using narrow-band excitation, and through comparison between experiment and simulated spectra which include the core-hole effects explicitly in the modeling. Based on these findings, we conclude that core-hole effects play a minor but detectable role in the RIXS observed from graphite.

Inelastic scattering of 4d electrons near the 4d–4f threshold of Gd2O2S and Tb4O7 has been studied with monochromatic synchrotron radiation excitation. The emission in the vicinity of the 4d–4f threshold is dominated by inelastic and elastic scattering. The energy losses are due to 4f inner-shell excitations in which the d-electrons (initial state 4d104fn) are excited to the 4f level (intermediate state 4d94fn+1) and then refill the open d-shell (final state 4d104fn+1) leaving the 4f shell in an excited state. Our atomic calculations are in excellent agreement with the experimental emission spectra indicating strong localization of the 4f electrons.

The results of measurements of x-ray photoelectron (XPS), x-ray emission (XES), and x-ray absorption spectra and local spin-density approximation band structure (LSDA) calculations of ${\mathrm{Pr}}_{0.5}{\mathrm{Sr}}_{0.5}{\mathrm{MnO}}_{3}$ are presented. The excitation energy dependence of Mn ${L}_{2,3}$ and O $K\ensuremath{\alpha}$ x-ray emission spectra of ${\mathrm{Pr}}_{0.5}{\mathrm{Sr}}_{0.5}{\mathrm{MnO}}_{3}$ is measured using tunable synchrotron radiation. The XES measurements yielded no photon energy dependence for the O $K\ensuremath{\alpha}$ spectra, but the Mn ${L}_{2,3}$ spectra yielded inelastic scattering losses of 2 and 6 eV, corresponding to features in the structure of the occupied part of the valence band. Comparing XPS and XES measurements with LSDA band-structure calculations, one concludes that the electronic structure of the compound consists mainly of Mn $3d$ and O $2p$ states. States of $3d$ character localized at the Mn site predominate near the top of the valence band (VB). Some differences in the Mn $3d$ distribution in this part of the XPS valence band and Mn ${L}_{3}$ XES with d symmetry due to spin-selection rules that govern the Mn ${L}_{3}$ XES. In addition, the Mn $3d$ states distribution is hybridized with the O $2p$ part of the VB. Mn ${L}_{3}$ XES spectra were determined relative to the Fermi energy by assuming normal x-ray emission begins from the lowest level of the ${p}^{5}{d}^{n+1}L$ intermediate state (which is the Mn $2p$ ionizatation threshold). From the local spin-density approximation, the orbital character of the Mn $3d$ electrons can be assigned ${e}_{g}$ symmetry at the top of the valence band ${T}_{2g}$ in the central part of the VB, and equal contributions of ${e}_{g}$ and ${t}_{2g}$ states at the bottom of the valence band.

This paper is a summary of some of the recent activities of our soft X-ray spectroscopy collaboration. We are using soft X-ray emission spectroscopy to probe the electronic properties of matter, emphasizing atoms in the bulk and at interfaces. In particular we have used incoherent photon excitation to obtain a basic understanding of the electronic properties of a wide variety of materials including Sr2RuO4, a new superconductor. In this first copperless perovskite superconductor, we confirmed in-plane oxygen–ruthenium bonding by analysis using calculations and soft X-ray emission spectroscopy and photoelectron spectroscopy. In the case of the sulfides, the sulfur in FeCuS occupies a single site, and the sulfur in CuS forms dimers at two thirds of the sites. This behavior was confirmed by calculation and by measurement of soft X-ray emission spectra excited at different photon energies near the sulfur L2,3 absorption edge, and by core photoemission measurements. Measurements of this type illustrate the importance of combining SXE and PES measurements with theoretical calculations. The ubiquitous presence of Raman scattering near the 3d and 4d ionization thresholds has been used to elucidate the excitation process in a number of rare earth and transition metal compounds. Such scattering can produce dramatic changes in the emission spectrum that can further the basic understanding of the atomic excitation process in these compounds. Photon-in photon-out soft X-ray spectroscopy is adding a new dimension to soft X-ray spectroscopy by providing many opportunities for exciting research, especially at third generation synchrotron light sources.

Inelastic x-ray scattering has been observed in the hexagonal forms of carbon (graphite) and boron nitride (hBN), both above and below their K edges. For excitation energies below the core threshold, inelastic-loss features are observed, which disperse linearly with excitation energy (Raman-like behavior). However, above the threshold, emission features that move in a nonlinear fashion are observed. We show that these two scattering regimes, which have previously been thought of as separate processes, viz., resonant x-ray Raman scattering (below threshold) and resonant inelastic x-ray scattering (above threshold), are described by the same theory for resonant fluorescence. Simulated spectra, with and without excitonic effects, are presented and compared with experiment. We conclude, based on this comparison, that excitonic effects influence these spectra in two ways. Primarily, the total fluorescence yields are enhanced or reduced simply because of changes in the absorption cross sections. Second, excitonic effects on emission features can be pronounced near some excitonic resonances, and these changes are more significant for excitation further above the K edges, which we attribute to the multiplicity of core-excited states being probed. Based on these findings, we conclude that core-hole effects do not necessarily undermine an interpretation of the scattering in terms of a one-electron (noninteracting) picture, and that resonant fluorescence spectroscopy may be successfully used to probe the band structure of solids.

Cu (40 nm)/Al/polyimide/Si was mixed with 80 keV Ar+ and N2+ from 5.0×1015 to 15×1015 ions/cm2. Ultrasoft x-ray emission valence spectra (XES) of Cu, C, N and O excited by electron and photon radiation were used for study of chemical reactions in Cu/Al/PI/Si and PI/Si systems induced by ion beam mixing in dependence of type of ions and dose. It is found that ion beam mixing changes the chemical state of Cu atoms with respect to that of pure metal. These changes depend on the dose of ion beam bombardment and type of ions and are attributed to a formation of CuAl2O4 interfacial layer, which can be responsible for enhanced interfacial adhesion strength. On the other hand, it is shown that the shape of C Kα, N Kα and O Kα XES of ion beam mixed polyimide layer (PI/Si) is modified with ion bombardment. This means that the ion-beam mixing process is able to break the bonding of constituent atoms of irradiated PI layers and can induce the formation of chemically bonded complexes linking atoms in the Cu, Al and PI...

Soft x-ray emission near the 3d-4f and 4d-4f thresholds of Nd{sub 2}O{sub 3} is studied with monochromatic synchrotron radiation excitation. At excitation energies above the M{sub IV} threshold, we observe Coster-Kronig enhanced fluorescence from the refill of the 3d hole via the 5p and 4f channel. Fluorescence occurs mainly due to transitions in which charge-transfer provides additional 4f electrons. Resonant inelastic scattering dominates the emission process and we observe two energy loss features at 2.3 and 21 eV, which are due to net transitions within the 4f shell (4f{sup 3}{r_arrow}4f{sup 3}) and 5p{sup 6}4f{sup 3}{r_arrow}5p{sup 5}4f{sup 4}, respectively. The emission spectra resulting from excitations at various energies through the 3d and 4d thresholds were compared and a number of differences were found. Our atomic calculations are in excellent agreement with the experimental results indicating strong localization and a low degree of correlation of the 4f electrons. {copyright} {ital 1999} {ital The American Physical Society}

Detailed experimental results and model caclulations for the evolution of the x-ray fluorescence in the vicinity of the {ital L} absorption edge of titanium in metallic Ti and TiO and insulating TiO{sub 2} and BaTiO{sub 3} are presented. Behavior characteristic of x-ray Raman scattering was found in all samples. We develop a model that describes the valence band emission below the L{sub 3} absorption threshold in terms of the calculated partial density of states and the Kramers-Heisenberg x-ray scattering formalism. Linear muffin-tin orbital band structure calculations were used for the projected density of states in the model. In the region below the L{sub 3} absorption edge very good agreement between experiment and the model was found for all compounds. We propose a mechanism for the energy shift of the emission spectra for TiO{sub 2} and BaTiO{sub 3}. An explanation of the Raman energy loss in terms of the excitation of a valence electron into localized states of {ital d} symmetry in the conduction band is also provided. {copyright} {ital 1999} {ital The American Physical Society}

Soft x-ray fluorescence spectroscopy has been used to examine the electronic structure of deeply buried silicide thin films that arise in Fe/Si multilayers. These systems exhibit antiferromagnetic (AF) coupling of the Fe layers, despite their lack of a noble metal spacer layer found in most GMR materials. Also, the degree of coupling is very dependent on preparation conditions, especially spacer layer thickness and growth temperature. The valence band spectra are quite different for films with different spacerlayer thickness yet are very similar for films grown at different growth temperatures. The latter result is surprising since AF coupling is strongly dependent on growth temperature. Combining near-edge x-ray absorption with the fluorescence data demonstrates that the local bonding structure in the silicide spacer layer in epitaxial films which exhibit AF coupling are metallic. These results indicate the equal roles of crystalline coherence and electronic structure in determining the magnetic properties of these systems.