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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.

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.

This paper is intended to illustrate two points. The first is the extensive growth of resonant Raman soft X-ray scattering due to the emergence of third-generation X-ray sources. With these sources, 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, as we show in our example of inelastic scattering at the 3d threshold of Nd2O3. 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. Second, it is very effective to use theory and experiment to characterize the electronic properties of materials. In particular we confirmed in-plane oxygen–ruthenium bonding in Sr2RuO4, the first copperless perovskite superconductor, by analyses using calculations, soft X-ray emission spectroscopy (SXE) and photoelectron spectroscopy (PES). Measurements of this type illustrate the importance of combining SXE and PES measurements with theoretical calculations.

The new results are presented of the experimental study of KNbO3 and KTaO3 by means of X-ray photoelectron spectroscopy, soft X-ray emission and X-ray fluorescence spectroscopy. In particular, Nb M(4,5) spectra have been measured over a range of near-threshold excitation energies 206.5 - 240.6 eV, and Ta N(3) spectra over 399.4 - 420.4 eV at the Advance Light Source in Berkeley. These spectra were found to be strongly dependent on the excitation energy. Moreover, the O K(alpha) X-ray emission spectra in both compounds as well as the valence-band photoelectron spectra are brought to the binding energy scale and discussed in combination. The trends in the spectra are explained on the basis of first-principles band-structure calculations, with the dipole transition matrix elements taken into account., Comment: presented at the '99 Williamsburg Conference on Ferroelectrics. 10 pages with 6 embedded postscript figures, uses elsart.cls

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.

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}

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.

We present synchrotron based soft x-ray emission (XES) measurements (Nb $L{\ensuremath{\beta}}_{2,15},$ Nb $L{\ensuremath{\gamma}}_{1},$ Nb ${M}_{3},$ Nb ${M}_{4,5},$ O K\ensuremath{\alpha}) and theoretical calculations of x-ray emission spectra of ${\mathrm{KNbO}}_{3}$. The obtained results are compared with x-ray photoemission spectroscopy valence-band measurements and band-structure calculations. The Nb ${M}_{4,5}$ emission spectra show strong dispersion and by tuning the exciting synchrotron radiation through the Nb 3d threshold ${(E}_{\mathrm{exc}}=206.5--240.6\mathrm{eV}),$ we identify contributions to the valence emission from the decay of both holes, ${3d}_{5/2}$ and ${3d}_{3/2}.$ It is also shown that it is generally possible to measure ${M}_{3}(4d5\stackrel{\ensuremath{\rightarrow}}{s}{3p}_{3/2})$ x-ray emission spectra of 4d metals in order to study the distribution of 4d valence-band states.

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.

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.

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}

X-ray absorption and emission spectra are used to characterize the effects of various treatment methods on explosive detonation nanodiamond (ND) products. Absorption spectra suggest strong near surface changes from treatment, while emission spectra show that the bulk structures remain relatively unchanged.

Soft x-ray emission near the 3d threshold of La is studied with synchrotron radiation. At excitation energies above the ${M}_{\mathrm{IV}}$ edge we observe Coster-Kronig enhanced fluorescence that refills the 3d hole via 5p and 4f electrons. We find a new delayed onset of the fluorescence as the 7.5-eV inelastic scattering evolves into 3d-4f emission about 8 eV above the absorption threshold, which we attribute to the energy required to produce a charge-transfer hole. The 16.3-eV Raman-scattering loss is due to a net transition of a 5p electron into a 4f orbit. The results are compared with our calculations.

Fluorescent soft X-ray carbon Ka 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 40 keV nitrogen or argon ions, at fluences ranging from 1 · 10 14 to 1 · 10 16 cm ˇ2 . The PCS films have been irradiated with 5 · 10 15 carbon ions cm ˇ2 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 fluence above 1 · 10 14 cm ˇ2 which we believe is due to the degradation of the PI into amorphous C:N:O. The width of the forbidden band as determined from the high-energy cut-oA of the C Ka X-ray excitation decreases with the ion fluence. The bonding configuration of free carbon precipitates embedded in amorphous SiC which are formed in PCS after irradiation with C ions or combined treatments (irradiation and subsequent annealing) is close to either to that in diamond-like films or in silicidated graphite, respectively. ” 1998 Elsevier Science B.V. All rights reserved.

Measurements of X-ray emission spectra of Cu L 2,3 , S Kβ 1,3 , S L 2,3 and Ir N 6,7 in CuIr 2 S 4 and CuIr 2 Se 4 have been performed. These measurements probe the partial Cu 3 d 4 s , S 3 p , S 3 s 3 d and Ir 5 d density of states, respectively, in the valence band. The excitation energy dependence of the Cu L 2,3 X-ray emission (XES) in CuIr 2 S 4 and CuIr 2 Se 4 has been measured using tunable synchrotron radiation. These measurements enabled us to obtain Cu L 3 XES free from overlapping Cu L 2 XES and high-energy satellites. These spectra reproduce the distribution of Cu 3 d -states in the valence band. X-ray emission spectra of constituents atoms of CuIr 2 S 4 and CuIr 2 Se, were adjusted to the binding energy scale using XPS binding energies of core levels and compared with band structure calculations and valence band spectra obtained by UPS and XPS. From these measurements one concludes that Cu 3 d -states are less mixed with Ir 5 d -states in CuIr 2 Se 4 and their contribution to the density of states at the Fermi level is smaller than that of CuIr 2 S 4 .

Soft X-ray emission studies for several early transition metal compounds, such as Sc, Ti and V compounds, have been studied. Raman scattering was found at the 2p→3d excitation in the transition metal compounds. The elementary excitation of the Raman spectrum is mainly elucidated by the d–d transition within the 3d bands, as well as the interband transition from the O 2p valence band to the conduction band, which consists mainly of transition metal 3d states. The charge transfer transition due to the localized electron picture is dominant in the soft X-ray spectra of Sc compounds. Raman scattering is a powerful tool in the study of the electronic structure of transition metal compounds.

Excitations within the $4f$ shell of ${\mathrm{Gd}}^{3+}$ in $({\mathrm{Y},\mathrm{G}\mathrm{d})}_{2}{\mathrm{O}}_{3}$ are observed by resonant elastic and inelastic soft x-ray scattering with synchrotron radiation. Inelastic scattering takes place when exciting ${4d}^{10}{4f}^{7}\ensuremath{\rightarrow}{4d}^{9}{4f}^{8}$ transitions and extends over an energy range of about 10 eV. The features can be assigned to the net transition from the ${}^{8}{S}_{7/2}$ ground state to the sextet multiplets of the ${4f}^{7}$ configuration in ${\mathrm{Gd}}^{3+},$ which have the same parity as the ground state. The inelastic scattering is maximal when the excitation energy is tuned to the ${4d}^{9}{4f}^{8}{(}^{6}D)$ intermediate state.

X-ray absorption spectra from iron donor impurities in mercury selenide have been analyzed in a concentration range where the Fermi energy of conduction electrons is close to the energy of the donor d level. At high impurity concentrations, the resulting spectrum corresponds to the completely filled donor state and coincides with the spectrum of a bivalent iron ion. A transition to an intermediate-filling state is observed with decreasing the concentration. The spectra are quantitatively analyzed in a model implying the existence of a mixture of ions that contain and do not contain a donor electron in a bound state. It has been found that such a model is significantly inconsistent with the experimental data. It has been shown that the concentration dependence of the x-ray spectra corresponds to the manifestation of the significant hybridization of localized and delocalized donor electron states in the conduction band.

Eu-doped Mg3GaN3 (I) and binary nitride Mg3N2 (II) are prepared by reaction of the corresponding metals with NaN3 in a sodium flux (welded Ta ampules, 760 °C, 2 d; cooling to 200 °C with a rate of 0.06 °C/min).

In this Letter using experimental and theoretical methods, we show that the solid solutions of group 14 nitrides having spinel structure ($\ensuremath{\gamma}\mathrm{\text{\ensuremath{-}}}{M}_{3}{\mathrm{N}}_{4}$ where $M=\mathrm{Si}$, Ge, Sn) exhibit mainly direct electronic band gaps with values that span the entire visible wavelength region, making these hard and thermally stable materials suitable for optoelectronic devices and, in particular, lighting applications. Using the simulated band structure, we also calculate the exciton binding energy. The combination of large exciton binding energies and the tunable electronic band gaps in the visible range makes these binary spinel nitrides and their solid solutions a new class of multifunctional materials with optoelectronic properties that can be engineered to suit the desired application.

We present calculated electronic structures and x-ray emission and absorption spectroscopy measurements of five copper pnictides. The x-ray emission and absorption spectra, which probe the occupied and unoccupied states, respectively, provide an empirical justification of the calculated electronic structure. We therefore verify the prediction that the copper 3$d$ states are fully occupied and buried deep in the valence band, and the Fermi surface of these materials is characterized by $s$,$p$ states. We show that generally the calculated electronic structure is in excellent agreement with our measurements. We finally examine the Fermi surfaces of these pnictides, and suggest that copper antimonides may exhibit efficient Fermi surface nesting similar to iron pnictides.

In recent years much progress has been made in the field of spectromicroscopy, the combination of spectroscopy with lateral resolution. This method is applicated increasingly to problems in biology, material and surface science. Different technical approaches will be outlined and discussed with respect to their imaging and spectroscopic properties. The scanning soft x-ray microscope at HASYLAB has been equipped continuously with new operating modes and has now the capability to use photoelectrons, photodesorbed ions, luminescence, fluorescence, scattered and transmitted photons for imaging and spectroscopy. Examinations of artificial structures, of luminescent ceramics and crystals and of porous silicon will be presented.

The Hamburg soft X-ray scanning microscope at HASYLAB/DESY has been equipped with detectors for luminescence in the visible and X-ray fluorescence or backscattered radiation. The microscope is operating in the region from 20–1200 eV and uses an elliptical grazing incidence mirror to focus the soft X-rays on a spot of about 1 μm. By varying the energy of the incoming radiation, excitation spectra can be taken from small sample areas (microspectroscopy). Defect structures on polished luminescent ceramics were investigated. The influence of the Gd 4d→4f giant resonance on the luminescence signal is observed in the yield spectra and compared with our calculations.

The first attempt to combine luminescence spectroscopy with scanning soft x‐ray microscopy has been realized in our experiment. A new imaging luminescence spectrometer with a Schwarzschild objective was designed and built with a spectral resolution of 1.3 nm in the energy range of 1.6–6.5 eV for this purpose. Some luminescent ceramics have been investigated by using this spectrometer. A high contrast in luminescence micrographs is achieved due to the confocal arrangement of the Schwarzschild system and the microscope. The spectral and microstructural properties of these ceramics could be determined by means of luminescence microspectroscopy and spectromicroscopy.

We present soft x-ray spectroscopy measurements and electronic structure calculations of ZnTiO${}_{3}$, a ternary oxide that is related to wurtzite ZnO and rutile TiO${}_{2}$. The electronic structure of ZnTiO${}_{3}$ was calculated using a variety of exchange-correlation functionals, and we compare the predicted band gaps of this material obtained from each functional with estimates from our experimental data and optical gaps quoted from the literature. We find that the main hybridizations in the electronic structure of ZnTiO${}_{3}$ can be predicted from the electronic structures of the two binary oxides. We further find that ZnTiO${}_{3}$ has weaker O 2p-Zn 3d repulsion than in ZnO, resulting in a relatively lower valence band maximum and consequently a larger band gap. Although we find a significant core hole shift in the measured O $K$ XAS of ZnTiO${}_{3}$, we provide a simple empirical scheme for estimating the band gap that may prove to be applicable for any $d$${}^{10}$-$d$${}^{0}$ ternary oxide, and could be useful in finding a ternary oxide with a band gap tailored to a specific energy.

Observations of magnetism in semiconductors doped with nonmagnetic atoms (C, N, etc.) show promise for spintronics applications, but pose an interesting challenge for conventional theories of magnetism. In this work, the magnetic semiconductor carbon-doped In${}_{2}$O${}_{3}$ is studied using theoretical and experimental techniques. Density-functional theory calculations predict that ferromagnetism can exist near room temperatures when substitutional carbon atoms have a formally unpaired $2p$ electron that does not participate in bonding. The unpaired $2p$ electrons lead to an impurity band near the Fermi level and consequent enhanced density of states which accommodates a strong $p\ensuremath{-}p$ coupling between local magnetic moments. The unpaired electrons and ferromagnetic coupling are found to arise from a combination of interstitial and substitutional carbon atoms in close proximity. Finally, experimental measurements on samples with varying magnetic properties verify the importance of both strong C $2p$ character at the Fermi level and strong C $2sp$-In $4d$ hybridization for yielding room-temperature ferromagnetism. These results shed light on the interesting field of nonmagnetic dopants inducing ferromagnetism in semiconductors.

The electronic structure of several ternary oxides (Sn${}_{2}$TiO${}_{4}$, PbTiO${}_{3}$, Bi${}_{2}$Ti${}_{4}$O${}_{11}$, and Bi${}_{4}$Ti${}_{3}$O${}_{12}$) based on binary lone-pair oxides (SnO, PbO, and Bi${}_{2}$O${}_{3}$) and a $d$${}^{0}$ oxide (TiO${}_{2}$) is investigated using soft x-ray spectroscopy and electronic-structure calculations. We find that the valence band of these ternary oxides is bounded by bonding (at the bottom of the valence band) and antibonding (at the top of the valence band) O 2p lone-pair $ns$ (Sn $5s$, Pb $6s$, Bi $6s$) hybridized states, while the conduction band is dominated by unoccupied Ti $3d$ states. The existence of these two features is found to be independent of crystal structure or stoichiometry. The calculated hybridization in the bonding O $2p$ lone-pair $ns$ states is in reasonable agreement with the relative intensity of this feature in the measured x-ray emission spectra. The dominant influence on the conduction and the valence bands in the ternary oxides is due to different aspects of the electronic structure in the parent binary oxides, and we consequently find that the band gap of the ternary oxide is found to be a stoichiometric-weighed addition of the band gaps of the parent oxides.

The electronic structure of BaFe2As2 doped with Co, Ni, and Cu has been studied by a variety of experimental and theoretical methods, but a clear picture of the dopant 3d states has not yet emerged. Herein we provide experimental evidence of the distribution of Co, Ni, and Cu 3d states in the valence band. We conclude that the Co and Ni 3d states provide additional free carriers to the Fermi level, while the Cu 3d states are found at the bottom of the valence band in a localized 3d10 shell. These findings help shed light on why superconductivity can occur in BaFe2As2 doped with Co and Ni but not Cu., 18 pages, 8 figures

Oxide-based diluted magnetic semiconductors (DMSOs)have been studied extensively in the last years because of thepossibility of controlling both spin and charge of electronssimultaneously in future spintronic devices. Generally, oxidesemiconductors having a wide band gap are optically trans-parentforvisiblelightandthusimportantforthedevelopmentof spin-dependent optoelectronics. It is commonly acceptedthat doping a transition metal plays a key role in inducingferromagnetism (FM) in these DMS systems.

We demonstrate that the electronic structure of mesoporous silicon is affected by adsorption of nitro-based explosive molecules in a compound-selective manner. This selective response is demonstrated by probing the adsorption of two nitro-based molecular explosives (trinitrotoluene and cyclotrimethylenetrinitramine) and a nonexplosive nitro-based arematic molecule (nitrotoluene) on mesoporous silicon using soft X-ray spec- troscopy. The Si atoms strongly interact with adsorbed molecules to form Si-O and Si-N bonds, as evident from the large shifts in emission energy present in the Si L2,3 X-ray emission spectroscopy (XES) measurements. Furthermore, we find that the energy gap of mesoporous silicon changes depending on the adsorbant, as estimated from the Si L2,3 XES and 2p X-ray absorption spectroscopy (XAS) measurements. Our ab initio molecular dynamics calculations of model compounds suggest that these changes are due to spontaneous breaking of the nitro groups upon contacting surface Si atoms. This compound-selective change in electronic structure may provide a powerful tool for the detection and identification of trace quantities of airborne explosive molecules., 27 pages, 9 figures

Natural 12CaO$\ifmmode\cdot\else\textperiodcentered\fi{}$7Al${}_{2}$O${}_{3}$ (C12A7) is a wide band gap insulator, but conductivity can be realized by introducing oxygen deficiency. Currently, there are two competing models explaining conductivity in oxygen-deficient C12A7, one involving the electron transfer via a ``cage conduction band'' inside the nominal band gap, the other involving electron hopping along framework lattice sites. To help resolve this debate, we probe insulating and conducting C12A7 with x-ray emission, x-ray absorption, and x-ray photoemission spectroscopy, which provide a full picture of both the valence and conduction band edges in these materials. These measurements suggest the existence of a narrow conduction band between the main conduction and valence bands common in both conducting and insulating C12A7 and support the theory that free electrons in oxygen-deficient C12A7 occupy the low-energy states of this narrow band. Our measurements are corroborated with density functional theory calculations.

The magnetization direction of a cobalt-platinum film has been manipulated by magnetic-field-assisted ion-beam mixing. A uniaxial easy magnetization axis is induced along the oscillation direction of the incident beam of 80 keV Ar+ ions. The easy axis was then rotated by 60°, when the same ion irradiation process was carried out in the presence of an external magnetic field. Magnetic force microscopy measurements show that line shaped domain structures are created with their long axis along the induced magnetization directions. It is proposed that the creation of adjacent regions with orthogonal magnetization can play a crucial role in stabilizing the magnetostatic dipolar interaction between adjacent bits of magnetic data storage devices.

Herein we present a study of the electronic structure of lithium metagallate (LiGaO(2)), a material of interest in the field of optoelectronics. We use soft x-ray spectroscopy to probe the electronic structure of both the valence and conduction bands and compare our measurements to ab initio density functional theory calculations. We use several different exchange-correlation functionals, but find that no single theoretical approach used herein accurately quantifies both the band gap and the Ga 3d(10) states in LiGaO(2). We derive a band gap of 5.6 eV, and characterize electron hybridization in both the valence and conduction bands. Our study of the x-ray spectra may prove useful in analysing spectra from more complicated LiGaO(2) heterostructures.

The specific locations of the anions—nitrogen and oxygen—in the crystallographic sites are not known in the spinel-type gallium oxonitride. We report here on an indirect method for determining the specific location of the light elements N and O in a defect spinel-structured gallium oxonitride, Ga2.79O3.05N0.76. The locations of elements that are adjacent in the periodic table (�Z = ±1) are indistinguishable with conventional x-ray diffraction techniques. However, by examining the local electronic structure we show that the anions are spatially ordered such that R¯3m (no. 166) is the most appropriate defect-free space group. Finally, we determined the electronic band gap of Ga2.79O3.05N0.76 experimentally to be 2.95 ± 0.30, agreeing with our calculated value of 2.79 eV (direct) for Ga3O3N using a local density approximation functional including a semilocal potential modified from that of Becke and Johnson (the MBJLDA functional).

We have investigated the electronic structure and the Fermi surface of SnO using density functional theory (DFT) calculations within recently proposed exchange-correlation potential (PBE+mBJ) at ambient conditions and high pressures up to 19.3 GPa where superconductivity was observed. It was found that the Sn valence states 5s, 5p, and 5d are strongly hybridized with the O 2p-states, and that our DFT-calculations are in good agreement with O K-edge X-ray spectroscopy measurements for both occupied and empty states. It was demonstrated that the metallic states appearing under pressure in the semiconducting gap stem due to the transformation of the weakly hybridized O 2p-Sn 5sp subband corresponding to the lowest valence state of Sn in SnO. We discuss the nature of the electronic states involved in chemical bonding and formation of the hole and electron pockets with nesting as a possible way to superconductivity., 5 pages, 6 figures

The electronic structure of (Zn,Mn)O films with different Mn concentrations has been investigated by element-selective soft X-ray absorption and emission spectroscopy. The band gap narrowing of (Zn,Mn)O with increase of Mn concentration ( sp – d exchange interactions. According to analysis of the O K α and resonant Mn L 2,3 X-ray emission spectra, the splitting of Mn 3 d subbands is related to Mn-derived states. It indicates that ferromagnetic coupling in (Zn,Mn)O can be taken into account to be carrier-induced. The presence of antiferromagnetism in the heavier Mn-doped films can be explained in terms of the existence of MnO secondary phases.

The electronic structure of Co-doped anatase TiO(2) epitaxial thin films grown at different partial oxygen pressures is investigated using soft x-ray emission spectroscopy. The resonantly excited Co L(2,3) x-ray emission spectra of ferromagnetic Ti(0.96)Co(0.04)O(2) samples for the oxygen-deficient regime show that the ratio of integral intensities for Co L(2) and L(3) emission lines significantly decreases with respect to nonmagnetic samples in the oxygen-rich regime. This is due to L(2)L(3)M(4,5) Coster-Kronig transitions and suggests that ferromagnetic Ti(0.96)Co(0.04)O(2) samples have n-type charge carriers and Co-Co bonds between substitutional and interstitial Co atoms are present while Co-O bonds are dominant in nonmagnetic Ti(0.96)Co(0.04)O(2) samples in the oxygen-rich regime. Electronic structure calculations show that the presence of free charge carriers and Co segregation play a crucial role in strong ferromagnetism at room temperature in Co-doped TiO(2).