High-resolution X-ray Emission Spectroscopy Research Articles

Evolution of charge and spin state of transition metals in the LaMn1−xCoxO3 perovskite series

Charge and spin state evolution of the transition metals in the LaMn1−xCoxO3 perovskite series was studied by means of high resolution x-ray absorption and emission spectroscopy. The gradual charge transfer from Mn to Co sites was observed upon increasing Co doping. The high spin of the Mn3+∕4+ and Co2+ ions is preserved in the entire solid solution. Co3+ ions reveal low spin state at low doping, while the gradual increase of the average Co3+ spin state is observed at higher cobalt concentrations. The results plausibly explain the observed magnetization anomalies.

Experiment investigation of La 1− xSr xMnO 3 by high-resolution X-Ray emission and spin-polarized X-ray absorption spectroscopy

Big changes in resistivity along with the changing of local structure in some oxide systems, such as high-temperature superconductors and colossal magnetoresistance system, strongly suggest the need of a systematic investigation of their local electronic and atomic structures. In this work we present the high-resolution X-ray emission spectra and the spin-polarized X-ray absorption near-edge spectroscopy (SPXANES) data at the Mn K-edge in the La 1− x Sr x MnO 3. This experiment is based on a high-resolution large-acceptance crystal analyzer based on Si (1 1 1) and optimized for X-ray fluorescence spectroscopy. With a spherical bent crystal monochromator, a Mn Kβ emission spectra with high resolution was obtained with a short collection time and SPXANES spectra of La 1− x Sr x MnO 3 at room temperature were also measured at high temperature.

Pressure-induced electron spin transition in the paramagnetic phase of the GdFe3(BO3)4 Heisenberg magnet

The HS → LS spin crossover effect (high-spin → low-spin transition) induced by high pressure in the range 45–53 GPa is observed in trivalent Fe3+ ions in the paramagnetic phase of a Gd57Fe3(BO3)4 gadolinium iron borate crystal. This effect is studied in high-pressure diamond-anvil cells by two experimental methods using synchrotron radiation: nuclear resonant forward scattering (NFS) and Fe K β high-resolution x-ray emission spectroscopy (XES). The manifestation of the crossover in the paramagnetic phase, which has no order parameter to distinguish between the HS and LS states, correlates with the optical-gap jump and with the insulator-semiconductor transition in the crystal. Based on a theoretical many-electron model, an explanation of this effect at high pressures is proposed.

High‐Resolution X‐Ray Emission Spectroscopy of Molybdenum Compounds.

High-resolution molybdenum K-edge X-ray emission spectroscopy (XES) was used to characterize the Kβ4 and Kβ‘ ‘ valence-to-core transition bands in the oxo-Mo compounds K2MoO4, MoO(S2CNEt2)2, and MoO2(S2CNEt2)2. The Kβ4 and Kβ‘ ‘ emission bands are attributed to transitions to the Mo 1s core hole from molecular orbitals possessing primarily molybdenum 4d and oxygen 2s character, respectively. This communication describes the first assignment of the Kβ‘ ‘ interatomic band in the emission spectra of molybdenum complexes. Additionally, the Kβ4 and Kβ‘ ‘ transitions are shown to be sensitive to the chemical and electronic environment of the metal, suggesting that high-resolution XES might be an effective method for elucidating the nature of the molybdenum centers in biological systems.

First-Order Isostructural Mott Transition in Highly Compressed MnO

We present evidence for an isostructural, first-order Mott transition in MnO at 105+/-5 GPa, based on high-resolution x-ray emission spectroscopy and angle-resolved x-ray diffraction data. The pressure-induced structural and spectral changes provide a coherent picture of MnO phase transitions from paramagnetic B1 to antiferromagnetic distorted B1 at 30 GPa, to paramagnetic B8 at 90 GPa, and to diamagnetic B8 at 105+/-5 GPa. The last is the Mott transition, accompanied by a significant loss of magnetic moment, an approximately 6.6% volume collapse and the insulator-metal transition as demonstrated by recent resistance measurements.

High-Resolution X-ray Emission Spectroscopy of Molybdenum Compounds

High-resolution molybdenum K-edge X-ray emission spectroscopy (XES) was used to characterize the K beta(4) and K beta' ' valence-to-core transition bands in the oxo-Mo compounds K(2)MoO(4), MoO(S(2)CNEt(2))(2), and MoO(2)(S(2)CNEt(2))(2). The K beta(4) and K beta' ' emission bands are attributed to transitions to the Mo 1s core hole from molecular orbitals possessing primarily molybdenum 4d and oxygen 2s character, respectively. This communication describes the first assignment of the K beta' ' interatomic band in the emission spectra of molybdenum complexes. Additionally, the K beta(4) and K beta' 'transitions are shown to be sensitive to the chemical and electronic environment of the metal, suggesting that high-resolution XES might be an effective method for elucidating the nature of the molybdenum centers in biological systems.

Direct observation of a neutralMnacceptor inGa1−xMnxAsby resonant x-ray emission spectroscopy

We have investigated the $\mathrm{Mn}$ acceptor state of III-V-based diluted magnetic semiconductor ${\mathrm{Ga}}_{1\ensuremath{-}x}{\mathrm{Mn}}_{x}\mathrm{As}$ by means of high-resolution resonant x-ray emission spectroscopy, across the $\mathrm{Mn}$ ${L}_{3}$ edge. We identify the coexistence of signals related to the neutral impurity ${A}^{0}$ and the ionized acceptor state ${A}^{\ensuremath{-}}$ in ${\mathrm{Ga}}_{1\ensuremath{-}x}{\mathrm{Mn}}_{x}\mathrm{As}$. This fact suggests that double-exchange-like interaction exists in the ferromagnetic coupling in addition to the free-carrier-induced interaction.

High-Resolution X-ray Emission and X-ray Absorption Spectroscopy

In this review, high-resolution X-ray emission and X-ray absorption spectroscopy will be discussed. The focus is on the 3d transition-metal systems. To understand high-resolution X-ray emission and reso-nant X-ray emission, it is first necessary to spend some time discussing the X-ray absorption process. Section II discusses 1s X-ray absorption, i.e., the K edges, and section III deals with 2p X-ray absorption, the L edges. X-ray emission is discussed in, respectively, the L edges. X-ray emission is discussed in, respec-tively, and section V on 2p3s and 2p3d X-ray emission. Section VI focuses on magnetic dichroism effects, and in section VII selective X-ray absorption experiments are discussed. To limit the scope of this review paper, many related topics (for example, EELS, XPS, and resonant photoemission, phonon-oriented inelastic X-ray scat-tering, and X-ray microscopy) will not be discussed. In addition, many aspects of X-ray absorption, such as reflection experiments, diffraction absorption fine structure, and related experiments, will remain untouched. EXAFS will be discussed very briefly, and its X-ray emission analogue EXEFS 69,71 will not be discussed.

Pressure-induced transformations in deep mantle and core minerals

AbstractRecent experimental and theoretical studies provide new insight into the variety of high-pressure transformations in minerals that comprise the Earth’s deep mantle and core. Representative examples of reconstructive, displacive, electronic and magnetic transformations studied by new diamond-anvil cell techniques are examined. Despite reports for various transitions in (Mg,Fe)SiO3-perovskite, the stability field of the orthorhombic phase expands relative to magnesiowüstite + SiO2 with increasing pressure and temperature. The partitioning of Fe and Mg between Mg-rich silicate perovskite magnesiowüstite depends strongly on pressure, temperature, bulk Fe/Mg ratio, and ferric iron content. The soft-mode transition in SiO2 from the rutile- to CaCl2-type structure, originally documented by X-ray powder diffraction, Raman scattering, and first-principles theory has been explored in detail by single crystal diffraction, and transitions to higher-pressure forms have been examined. The effect of H on the transformations of various nominally anhydrous phases and transitions in dense hydrous Mg-silicates are also examined. New studies of the phase diagram of FeO include the transition to rhombohedral and higher-pressure NiAs polymorphs, and provide prototypical examples of coupled structural, electronic, and magnetic transitions. High-spin/low-spin transitions in FeO have been examined by high-resolution X-ray emission spectroscopy to 150 GPa, and the results are compared with similar studies of Fe2O3 and FeS. Finally, laser-heating studies to above 150 GPa and 2500K show that (hcp) ε-Fe has a large P-T stability field. Radial XRD measurements carried out at room temperature to 220 GPa have constrained the elasticity, rheology and sound velocities of ε-Fe at core pressures.

Magnetism in FeO at Megabar Pressures from X-Ray Emission Spectroscopy

We report evidence for a preserved magnetic state in FeO up to 143 GPa at room temperature using high-resolution x-ray emission spectroscopy. This observation is based on the spectral line shape of the Fe Kb emission line. Up to the highest pressure, FeO remains a magnetic insulator. Combining our results with previous Mossbauer data, we present a new magnetic phase diagram of FeO. Features like a closed-loop P-T antiferromagnetic domain confirm that high-pressure investigations can reveal new physical properties and unexpected phenomena.

Density of states, hybridization, and band-gap evolution inAlxGa1−xNalloys

The electronic structure of the wurtzite ${\mathrm{Al}}_{x}{\mathrm{Ga}}_{1\ensuremath{-}x}\mathrm{N}$ alloy system has been studied for numerous values of Al concentration $x$ ranging from 0 (pure GaN) to 1 (pure AlN). The occupied and unoccupied partial density of states was measured for each alloy using synchrotron radiation excited soft x-ray absorption and emission spectroscopies. High-resolution x-ray emission spectroscopy allowed the motion of the elementally resolved bulk valence-band maximum to be measured as a function of Al concentration. Using this technique we estimate that the value of the band-gap bowing parameter for ${\mathrm{Al}}_{x}{\mathrm{Ga}}_{1\ensuremath{-}x}\mathrm{N}$ is zero. Furthermore, the x-ray emission spectra revealed resonantlike emission at approximately 19 eV below the GaN valence-band maximum. By measuring the intensity of this feature as a function of Ga content we prove conclusively that this emission arises from hybridization of N $2p$ and Ga $3d$ states. Finally, we find that the N $K$- and Al $K$-absorption spectra depend strongly on the photon angle of incidence with respect to the surface normal. We explain this in terms of orbital anisotropy in ${\mathrm{Al}}_{x}{\mathrm{Ga}}_{1\ensuremath{-}x}\mathrm{N}.$

Structural and electronic properties of low dielectric constant fluorinated amorphous carbon films

Fluorinated amorphous carbon (a-CFx) films were studied by high-resolution x-ray absorption, emission, and photoelectron spectroscopy. The composition and local bonding information were obtained and correlated with substrate temperature during deposition. The data suggest that the structure of the a-CFx is mostly of carbon rings connected by CF2 groups. The cross linking increases with substrate temperature.

Spectroscopic Studies of Low Dielectric Constant Fluorinated Amorphous Carbon Films for Ulsi Integrated Circuits

ABSTRACTPerformance of future generations of integrated circuits will be limited by the RC delay caused by on-chip interconnections. Overcoming this limitation requires the deployment of new high conductivity metals such as copper and low dielectric constant intermetal dielectrics (IMD). Fluorinated amorphous carbon (a-CFx) is a promising candidate for replacing SiO2 as the IMD. In this paper we investigated the structure and electronic properties of a-CFx thin films using high-resolution x-ray absorption, emission, and photoelectron spectroscopy. The composition and local bonding information were obtained and correlated with deposition conditions. The data suggest that the structure of the a-CFx is mostly of carbon rings and CF2 chains cross-linked with C atoms. The effects of growth temperature on the structure and the thermal stability of the film are discussed.

An Atom-Specific Look at the Surface Chemical Bond

High resolution x-ray emission spectroscopy is shown to reveal unprecedented details of the chemical bond formed between a molecule and a transition metal surface. An atom and symmetry projected view of the bonding orbitals is obtained. We find that all outer and inner valence orbitals of the molecule change due to the surface interaction. New types of molecular states are observed which are a direct signature of the surface chemical bond. [S0031-9007(97)02814-7] PACS numbers: 78.70.En, 73.20.Hb, 82.65.Pa It is generally assumed that the bonding of molecules to transition metals can be explained in terms of the interaction of the frontier orbitals, i.e., the highest occupied (HOMO) and lowest unoccupied (LUMO) orbitals of the free molecule with the metal d orbitals [1 ‐ 4]. This model of the surface chemical bond implicitly assumes that the intramolecular bond is stronger than the moleculesubstrate bond so that the molecule can be treated as a unit. In principle, however, it is more appropriate to use an atom-based, or linear combination of atomic orbitals (LCAO) type, description. Because conventional experimental techniques, in particular ultraviolet photoemission spectroscopy (UPS), do not allow an atom-based view of bonding effects, an LCAO-based look at the surface chemical bond has not been possible experimentally. Another complication has been the energetic overlap of the most important signatures of the surface chemical bond with the metal d states. The dominance of the d states in the electronic spectra has made it difficult to observe the direct signature of the surface chemical bond in all but a

Soft x-ray emission spectrometer for undulator radiation

An experimental system for high-resolution soft x-ray emission spectroscopy was made. The experimental system is designed to be attached to the undulator beamlines. Spectrometer uses the Rowland circle geometry in which input slit, spherical grating, and multichannel detector lie on the focal circle. Three blazed holographic gratings are changeable in the vacuum. The Rowland circle radii of gratings are 5, 7, and 10 m and their line densities are 600, 1200, and 2400 lines/mm, respectively. The available photon energy is from 30 to 1200 eV. The resolution ΔE is achieved to 0.06 eV by 50 μ-input-slit width for hν=120 eV. Several experimental results measured by this system are presented.

Transmission electron microscopy analysis of a TiNx substoichiometric CVD coating

The TiNx □1−x substoichiometric chemical vapour deposited titanium nitride coatings have been studied in an early work by means of high-resolution X-ray emission spectroscopy. It was found that a strong vacancy-induced peak was present in the Ti K emission band. Its intensity can be correlated to the 1−x vacancy concentration deduced from nuclear reaction spectroscopy and X-ray diffraction. This relationship is linear if 0⩽1−x⩽0.3. If 1−x is higher than 0.3, an anomalous behaviour occurs which is expected to be due to microstructure change. For this purpose, transmission electronic studies of a TiN0.57 □0.43 layer have been developed. The most striking result of this work is the existence of many stacking faults. These defects are extrinsic ones and the stacking fault energy is about 3.5 mJ m−2. Their density seems to depend on their distance from the substrate-coating interface. Further investigations are needed to confirm this assumption.

Local electronic structure of Cu2O, CuO and YBa2Cu3O7??

Cu 3d and O 2p electronic states of Cu2O, CuO, and the highT c compound YBa2Cu3O7−δ have been probed by means of high resolution x-ray emission spectroscopy (XES). The CuLα and OKα XES bands are compared in detail with recently reported x-ray photoelectron and ultraviolet photoelectron spectroscopy (XPS and UPS) measurements and densities of states obtained by local density functional (LDF) theory. The XES data show that the hybridization between Cu 3d and O 2p states is completely modified in CuO and YBa2Cu3O7−δ, whered-d correlation energy is large, as compared to LDF predictions. Such is not the case for Cu2O where agreement between theory and experiment is good.

Structural characteristics of MgOP 2O 5 glasses

Previous investigators have believed that the “Phosphate Anomaly” in MgOP 2O 5 (MP) glass is due to an abrupt change in a coordination equilibrium between Mg and O ions, in which the oxygen coordination number (CN) of Mg 2+ is 6 ⇄ 4. However, we found recently that the CN of Mg is approximately 6 in MP glass with varying M/P ratio, by means of high-resolution X-ray emission spectroscopy. Thus, the density-anomaly in MP glass around M/P = 1 should not be interpreted by the change of the CN of Mg. Some speculative considerations on the structure and properties of MP glass are presented based on the results of our findings. Many facts reported by the researchers can be explained by assuming a voluminously mixing structure, in which phosphate anions in the glass of M/P = 1 mainly consist of long chain-type ions and partly of ring ions such as tetrametaphosphate. We have concluded that MP glass may have a different structure in comparison with other anomalous phosphate glasses, i.e. BeO- and ZnOP 2O 5 systems.

Multiplet splitting of manganese core p-levels in MnF2

High-resolution X-ray emission spectroscopy (XES) is used to measure splittings of core p-hole final states of Mn2+ ions in MnF2. It turns out that the Hartree-Fock free-ion approximation, including spin-orbit and crystal-field effects, is inadequate for a proper interpretation of the Mn K alpha 1,2 and K beta 1 structures. A comparison is made with the corresponding core p-level X-ray photoemission spectra (XPS). The observed 2p XES multiplet splitting is absent in the XPS in spite of narrower linewidths obtained by XPS. The K alpha 1 and K alpha 2 lines in MnF2 are broadened by 1.35 and 0.97 eV, respectively, while at least a 1.3 eV broadening of both 2p XPS levels is reported. The discrepancies between the XES and XPS may indicate importance of non-lifetime contributions to intrinsic XPS linewidths in MnF2.