K-emission Spectra Research Articles

Chemical Bonding State Analysis with High Energy-resolution Carbon K-Emission Spectrum of Soft Materials Obtained by Soft X-ray Emission Spectrometer

Chemical Bonding State Analysis with High Energy-resolution Carbon K-Emission Spectrum of Soft Materials Obtained by Soft X-ray Emission Spectrometer

Chemical State Mapping of p/n-Controlled SrB6 Bulk Specimens by Soft X-ray Emission Electron Microscope

Elemental and chemical state maps of p/n-controlled SrB6 bulk specimens are presented by using a soft X-ray emission spectroscopy electron microscope. Those bulk specimens were obtained by sintering powder specimens, prepared by the molten-salt method with different compositions of initial materials. A Sr-map, a chemical shift map of B K-emission, and the spectra of characteristic regions of those materials were compared. It was observed that a local Sr deficiency caused a local hole-doped region, confirmed by a chemical shift in the B K-emission spectrum. n-type SrB6 was rather homogeneous. On the other hand, the p-type SrB6 bulk specimen was a mixture of two different p-type regions. This mixed nature originated, presumably, from an uneven Sr content of SrB6 particles prepared by the molten-salt method using a Sr-deficient starting material. A separation process of the two types of materials will realize a high-quality homogeneous p-type SrB6 bulk specimens.

Soft X-ray emission spectroscopy study of characteristic bonding states and its distribution of amorphous carbon-nitride (a-CNx) films.

Soft X-ray emission spectroscopy based on electron microscopy was applied to investigate bonding electron states of amorphous carbon nitride (a-CNx) films with different nitrogen contents of x. Carbon K-emission spectrum showed characteristic intensity distribution of not only sp2 bonding but also sp3 bonding. The a-CNx film with lager x, which has a larger macroscopic electric resistivity, shows a larger content of the carbon sp3: C-C bonding signal. Furthermore, the dependence of spectral intensity distribution on x suggests the presence of sp2: C-N and sp3: C-N bonding. Those results show that the relation between macroscopic electrical resistivity of a-CNx film and its nitrogen content is because of the decrease of sp2: C-C bonding and the formation of sp2: C-N and sp3: C-C and C-N bonding conformation induced by an introduction of nitrogen atoms. Spatial variation of a signal ratio of sp3/sp2 was visualized and was confirmed as a relation between sp3 boding amount and nitrogen content x.

Soft X-ray emission spectroscopy study of electronic structure of sodium borosilicide Na8B74.5Si17.5.

Chemical bonding state of sodium borosilicide Na8B74.5Si17.5, which is a new member of B12-cluster materials, is investigated by soft X-ray emission spectroscopy. The material is composed of B12 cluster network and characteristic silicon chains of [-Si-(Si-Si)3-Si-] connected by sp3 bonding, in which bonding distances and bonding angles are close to those in cubic Si crystal. B K-emission spectrum of the material showed a similar but a broader intensity distribution with those of B12 cluster materials of α-r-B, B4C and β-r-B. The broader intensity distribution can be due to a variation of B-B bond length in B12 cluster. The density of states (DOS) of silicon chains of [-Si-(Si-Si)3-Si-] was experimentally derived. It shows a similar energy width, and peak or shoulder structures in intensity distribution with those of L-emission spectrum of cubic Si. From comparisons between experimental spectra and corresponding calculated DOS, covalent bonding between Si chain and B12 cluster network is suggested. Those are discussed by using a theoretically calculated density of state of Na8B74.5Si17.5 by using WIEN2k code.

Electronic Structure of Rare-Earth Scandates from X-Ray Spectroscopy and First-Principles Calculations

Combined spectroscopic techniques were applied to the study of valence band, conduction band, and core levels (by X-ray emission, absorption, and X-ray photoelectron spectroscopy, correspondingly) of seven scandium / lanthanide (Pr to Dy) double oxides. A comparison of O K-emission and absorption spectra, brought to the same energy scale, permits to extract the band gap values by a method different from optical spectroscopy. The variation of band gap value over the row of scandates with different lanthanides is not monotonous. An inverse correlation is detected between the band gap value and the mean Sc-O bond length.

Development of wavelength-dispersive soft X-ray emission spectrometers for transmission electron microscopes--an introduction of valence electron spectroscopy for transmission electron microscopy

Two types of wavelength-dispersive soft X-ray spectrometers, a high-dispersion type and a conventional one, for transmission electron microscopes were constructed. Those spectrometers were used to study the electronic states of valence electrons (bonding electrons). Both spectrometers extended the acceptable energy regions to higher than 2000 eV. The best energy resolution of 0.08 eV was obtained for an Al L-emission spectrum by using the high-dispersion type spectrometer. By using the spectrometer, C K-emission of carbon allotropes, Cu L-emission of Cu(1-x)Zn(x) alloys and Pt M-emission spectra were presented. The FWHM value of 12 eV was obtained for the Pt Malpha-emission peak. The performance of the conventional one was also presented for ZnS and a section specimen of a multilayer device. W-M and Si-K emissions were clearly resolved. Soft X-ray emission spectroscopy based on transmission electron microscopy (TEM) has an advantage for obtaining spectra from a single crystalline specimen with a defined crystal setting. As an example of anisotropic soft X-ray emission, C K-emission spectra of single crystalline graphite with different crystal settings were presented. From the spectra, density of states of pi- and sigma-bondings were separately derived. These results demonstrated a method to analyse the electronic states of valence electrons of materials in the nanometre scale based on TEM.

Soft X-ray emission spectroscopy study of the valence electron states of α-rhombohedral boron

High energy-resolution boron K-emission spectra of single-crystalline α-rhombohedral-boron (α-r-B) were measured with a newly developed soft X-ray emission spectroscopy (SXES) instrument attached to a conventional transmission electron microscope. The intensity profiles of the spectra, which correspond to the density of states of the valence bands with p-symmetry, were compared with those of amorphous boron (am-B), single-crystalline β-rhombohedral-boron (β-r-B) and B4C. A characteristic shoulder structure appears in the spectrum of α-r-B but not of am-B, β-r-B or B4C. This structure should be due to the inter-cluster three-center bonding states among B12 clusters in α-r-B.

Electron energy-loss and soft X-ray emission study of boron nanobelts

Electronic structure of individual boron nanobelts, which supposedly have α-tetragonal boron structure, was studied with electron energy-loss spectroscopy (EELS) and soft X-ray emission spectroscopy (SXES) in a transmission electron microscope. A boron K-shell excitation spectrum by EELS and boron K-emission spectra by SXES correspond to partial density of states of the conduction and the valence bands, respectively. Experimental results reveal that boron nanobelts are either a semimetal or narrow-gap semiconductor.

Soft-X-ray emission spectroscopy based on TEM—Toward a total electronic structure analysis

The construction and basic performances of wavelength-dispersive soft-X-ray emission spectroscopy (SXES) devices attached to a transmission electron microscope were presented. An energy resolution of 0.23 eV was obtained at the aluminum L-emission energy. A Cu L-emission spectrum obtained showed four L-emission lines of Lα, Lβ, Ll and Lη. Angle-resolved measurements of boron K-emission spectra of hexagonal-BN (h-BN) were presented. It clearly showed anisotropic emission intensity of the transition from π-bonding state to 1 s core hole. B K-emission spectra of h- and cubic-BNs showed a difference in energy positions of σ-bonding peaks. An electron energy-loss spectrum of B K-edge and a B K-emission spectrum of cubic-BN were compared with a result of a LDA band calculation. It showed that high symmetry points in the band diagram appeared as peak and/or shoulder structures in those spectra. Interband transitions appeared in the imaginary part of the dielectric function of cubic-BN experimentally obtained were assigned in the band diagram. These results demonstrated a method to analyze the entire electronic structure of materials in the nanoscale using high energy-resolution spectroscopy methods based on transmission electron microscopy.

Electronic structure analyses of BN network materials using high energy‐resolution spectroscopy methods based on transmission electron microscopy

Electronic structures of boron-nitride (BN) nanotubes and a BN cone-structure material were studied by using a high energy-resolution electron energy-loss spectroscopy (EELS) microscope. A trial of the whole electronic structure study of hexagonal BN (h-BN), which consists of flat BN honeycomb layers, was conducted by a combination of EELS and X-ray emission spectroscopy (XES) based on transmission electron microscopy (TEM) (TEM-EELS/XES). The pi and pi+sigma plasmon energies of BN nanotubes (BNT) were smaller than those of h-BN. The pi+sigma energy was explained by the surface plasmon excitation. The spectrum of a two-wall BNT of 2.7 nm in diameter showed a new spectral onset at 4 eV. The valence electron excitation spectra obtained from the tip region of the BN cone with an apex angle of 20 degrees showed similar intensity distribution with those of BNTs. The B K-shell electron excitation spectra obtained from the bottom edge region of the BN cone showed additional peak intensity when compared with those of h-BN and BNT. The B K-shell electron excitation spectra and B K-emission spectra of h-BN were compared with a result of a LDA band calculation. It showed that high symmetry points in the band diagram appear as peak and/or shoulder structures in the EELS and XES spectra. Interband transitions appeared in the imaginary part of the dielectric function of h-BN experimentally obtained were assigned in the band diagram. The analysis also presented that the LDA calculation estimated the bandgap energy smaller than the real material by an amount of 2 eV. Those results of TEM-EELS/XES analysis presented that high energy-resolution spectroscopy methods combined with TEM is a promising method to analyze whole electronic structures of nanometer scale materials.

Electronic structure of photochromic 2,4,6-triaryl-1-(spiro[2 H-1-benzopyran-2,2′-indoline]-6-yl)pyridinium salts

The nature of chemical bonding of nitrogen in spiro(benzopyran-indoline)pyridinium salts is investigated comparing the near edge X-ray absorption fine structure (NEXAFS) and X-ray emission spectra (XES) of nitrogen with that of reference compounds (thiourea, indoliumiodide and indoliumperchlorate). The X-ray absorption fine structure shows two π * peaks arising from 1 s −1 2pπ * excitations. Photoelectron spectra (XPS) and NEXAFS details point at two differently bound nitrogen atoms (>N and >N + ). Resonant N K-emission spectra reveal a strong dependence on the excitation energies.

The XPS spectra and the electron energy structure of tetragonal titanium cuprides and TiCu xNi 1− x alloys

The electron energy structure (EES) of the tetragonal intermetallic compounds TiCu, Ti 2Cu and several alloys TiCu x Ni 1− x with tetragonal and cubic lattices have been investigated both experimentally by X-ray photoelectron spectroscopy (XPS) and theoretically in the framework of the self-consistent cluster version of the multiple scattering theory. The theoretical shapes of the X-ray K-emission spectra of titanium in both compounds have also been calculated and compared with experiment. A satisfactory agreement of theory and experiment was found. The character of the chemical bonding in titanium cuprides and alloys is discussed.

Resonant inelastic x-ray scattering spectra of magnesium diboride

Using the tight-binding linear muffin-tin orbitals method, the soft x-ray fluorescence K-emission spectra of boron in MgB_2, excited close to the absorption edge, are estimated. In the calculations the angle of incidence between the direction of the incoming photon and the hexagonal axis of the specimen is 60 degrees and 75 degrees. Comparison with experiment is possible in the former case where good agreement is found. Furthermore, another resonant feature below the Fermi energy is predicted for the larger angle. This feature can be related to the excitations to the antibonding B pi-band in the neighbourhood of the L-H line in the Brillouin zone.

Resonant soft X-ray emission spectroscopy of doped and undoped vanadium oxides

Resonant soft X-ray emission (RSXE) spectra of NaV 2O 5, Mo x V 1− x O 2 and V 2O 3 have been recorded for a series of excitation energies at resonances of the V L- and O K-absorption band. Resonant excitation allows us, firstly, to separate V 3d and O 2p projected density-of-states of the valence band and, secondly, to study charge-neutral low-energy excitations due to resonant inelastic X-ray scattering (RIXS). We found that both the V L- and the O K-emission spectra clearly show components originating from O 2p- and V 3d-states, reflecting the high degree of hybridization of the valence band in all compounds. At threshold excitation we observed that NaV 2O 5 spectra are dominated by RIXS whereas Mo x V 1− x O 2 and V 2O 3 spectra show bandlike features, which may be due to differences in the correlation effects of the compounds. We compared the RSXE spectra with cluster model calculations, which gives a good account for NaV 2O 5 whereas the RSXE spectra of the other compounds show RIXS only at certain energies well above the threshold. In fact, we interpret the trend in the RSXE spectra of the Mo x V 1− x O 2 compound system as a successive filling of the (rigid) V 3d band with increasing Mo content.

Polarized x-ray emission and absorption spectra ofMgB2

The polarized K-emission and absorption spectra for ${\mathrm{MgB}}_{2}$ have been calculated using the tight-binding linear muffin-tin orbitals method. Within the dipole approximation a strong anisotropy is found. The core-hole effect has also been included in the calculation of the absorption spectra shifting the empty p-like states of Mg significantly towards lower energies in comparison with those of the ground state calculation. For the K-absorption spectrum of B the effect is much weaker in which the screening of the $1s$ core hole is much more efficient due to the higher density of states at the Fermi level in the ground state. The K-absorption process is predicted have a tendency to lower the critical temperature ${T}_{c}$ of the superconductivity.

Multiple liver abscesses due to Yersinia enterocolitica reveal hereditary hemochromatosis

The transition energies corresponding to the transition array KMx→MxM2,3 (x = 1, 2, 3, 4, 5) have been calculated using Slater formulas for interaction between two holes in inner shells and HFS values of electrostatic Slater integrals. The initial and final state energies have been corrected for the adiabatic relaxation of atomic orbits, which take place due to creation of an inner vacancy. The value of this adiabatic relaxation energy for KM states has been calculated semi-empirically by comparing the KM13S1→L3M13P2 transition energies with the measured Kα1 line energies. For the final state, this value has been taken from available literature[21]. It is found that the satellite β10 in the K-emission spectra of Zn, Ga, Ge, Mo and Rh is emitted by the superposition of more than one transition of the array. Consideration of the relative transition probabilities shows that the major contribution to β10 comes from a K→M2,3 transition in the presence of a 3d spectator vacancy. It has been suggested that the satellite β′1 (7655.5 eV, Edamoto 1950) in the K-emission spectrum of cobalt, and the satellite β7 (8271.2 eV) in the K-spectrum of nickel should be reidentified as β10. It has been shown that the two lines β′1 (8268.0 eV) and β″1(8270.3 eV) observed[13] in the nickel Kβ spectrum are two components of the satellite β10, and it is hence suggested that these should be renamed β10(1) and β10(2) respectively. Similarly, the lines β″(1) (8909.3 eV) and β″(2)(8913.0 eV) in the CuKβ spectrum are proved to be two components of β10 and hence should be renamed β10(1) and β10(2) respectively.

Chemical bonding in carbon nitride films studied by X-ray spectroscopies

Carbon nitride films are deposited using dc magnetron sputtering in a N 2 discharge. The nature of chemical bonding of the films is investigated using X-ray photoelectron spectroscopy, near-edge X-ray absorption fine structure, and X-ray emission spectroscopy. X-Ray photoelectron spectroscopy spectra show that N1s binding states depend on substrate temperature, in which two pronounced peaks can be observed. The near edge X-ray absorption fine structure at C1s and N1s exhibits a similar absorption profile in the π* resonance region, but the σ* resonance is sharper in the N1s spectra. Resonant N K-emission spectra show a strong dependence on excitation photo energies. Compared XPS N1s spectra with recent theoretical calculations by Johansson and Stafstrom, two main nitrogen sites are assigned in which N bound to sp 3 hybridized C and sp 2 hybridized C, respectively. The correlation of X-ray photoelectron, X-ray absorption, and X-ray emission spectra for N in carbon nitride films is also discussed.

Spectroscopic study of CNx films grown by magnetron sputter deposition

Abstract The electronic structure of carbon nitride films has been studied using soft X-ray absorption and emission spectroscopy. Resonant N K-emission spectra show a strong dependence on excitation photon energies and the substrate temperatures, while C K-emission band appears insensitive to the different excitation photon energies and the substrate temperatures. Two nitrogen sites are assigned to N bonded to sp 3 -hybridized C and to N bonded to sp 2 -hybridized C.

Polarized dipole and quadrupole X-ray K-emission spectra of CuAu I alloy under isothermal compression

In this work we have investigated how the intensities of polarized electric dipole and quadrupole X-ray K-emission spectra of Cu and Au in CuAu I alloy change as a function of pressure. The effect of the axial ratio ( c/ a) on the intensities of spectra was also investigated. It is shown that the total intensity of the dipole spectra increases with increasing pressure whereas the quadrupole spectra show only minor dependence on pressure. Further, the change in c/a produces only a small effect on the spectral properties whereas the main effect comes through the change in volume.

Soft x-ray emission studies of the bulk electronic structure of AlN, GaN, and Al0.5Ga0.5N

The electronic structure of wurtzite GaN, Al0.5Ga0.5N, and AlN has been studied using synchrotron radiation excited soft x-ray emission spectroscopy. In particular, the elementally resolved partial densities of states has been measured and found to agree well with calculations. The shift in energy of the valence band maximum as x varies from 0 to 1 in AlxGa1−xN was measured by recording N K-emission spectra, and found to be linear. Furthermore, N K-emission spectra revealed resonantlike hybridization of N 2p and Ga 3d states at 19 eV below the GaN valence band maximum. The spectral intensity of this feature is proportional to Ga content.