X-ray fluorescence study of organic-inorganic polymer conversion into ceramics induced by ion irradiation

金沢大学理学部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

Electronic structure of Li2 RuO3 studied by LDA and LDA+DMFT calculations and soft x-ray spectroscopy

The electronic structure of Li2RuO3 was investigated using x-ray emission and absorption spectroscopy and by theoretical calculations employing two approaches: the local density approximation (LDA) and a combination of LDA with the cluster extension of dynamical mean-field theory (LDA+DMFT). The evolution of the spectral properties with the strength of electronic correlations is analyzed. We show that for moderate values of on-site Coulomb repulsion U and intra-atomic Hund's rule exchange JH,Li2RuO3 is in an orbital-selective strongly correlated state in the sense that a part of the t2g manifold (i.e., xz/yz) behaves as local atomic orbitals susceptible to Hubbard correlations, while the remaining (xy) orbitals must be described as bond-centered molecular orbitals. Both theoretical approaches succeed in explaining the x-ray data, and a comparison of the theoretical and experimental spectra provides a reasonable estimate of the possible correlation strength (U) and Hund's coupling (JH) in Li2RuO3. © 2015 American Physical Society1771sciescopu

Electronic structure of thiophenes and phthalocyanines

金沢大学理学部The results of x-ray fluorescence measurements of thiophenes @regioregular poly ~3-hexylthiophene ~P3HT! and a,v-dihexylquaterthiophene ~DHa4T!# and phtalocyanines @copper phtalocyanine ~CuPc! and copper hexadecafluorophtalocyanine (F16CuPc)# are presented. Experimental carbon, nitrogen, fluorine Ka and sulphur, copper L2,3 x-ray emission spectra are compared with ultraviolet photoemission spectroscopy spectra and deMon density-functional theory calculations of model molecules. We find that the carbon Ka emission is almost identical for P3HT and DHa4T. This indicates that the electronic structure of the p system is not affected by the presence of the side group. The ratio of emission intensities of the Cu L2 to Cu L3 intensities is found to be smaller by a factor of 2 for CuPc and F16CuPc than it is for pure metal. This demonstrates the strong covalency in phalocyanines

Soft X-ray fluorescence study of the quasi-one dimensional Heisenberg antiferromagnet tetraphenylverdazyl

金沢大学理学部Soft-x-ray fluorescence measurements have been performed on a single crystal of the organic antiferromagnet 2,4,6-triphenylverdazyl. Resonant and nonresonant C Ka and N Ka (2p!1s transition! x-ray emission spectra ~XES! were measured and compared with x-ray photoelectron valence band spectra and deMon density-functional theory calculations. It is shown that intramolecular interactions are much stronger than intermolecular ones and give the main contribution to the formation of C 2p density of states. We present evidence of a delocalization of unpaired N 2p electrons over the verdazyl ring. The excitation energy dependence of C Ka and N Ka XES observed below the C 1s and N 1s thresholds, respectively, is discussed in terms of symmetry selective resonant inelastic x-ray scattering

Photoemission study of the metal-insulator transition in CuIr2S4

We have studied the electronic structure and its changes across the metal-insulator transition in the spinel-type compound CuIr2S4 using photoemission and inverse-photoemission spectroscopy. Photoemission spectra near the Fermi level show a gap opening of ~20 meV in the insulating phase, consistent with the transport activation energy. Core-level spectra indicate that the Cu ion is monovalent, and hence Ir is in the intermediate valence state of +3.5. Comparison between the spectra and band-structure calculation reveals that the Ir 5d density of states is strongly distorted, probably due to electron correlation in spite of the general belief of weak correlation in 5d-electron systems

Resonant inelastic x-ray scattering (RIXS) 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.Comment: 4 pages with 4 figure

Strength of correlations in pnictides and its assessment by theoretical calculations and spectroscopy experiments

LDA+DMFT (Local Density Approximation combined with Dynamical Mean-Field Theory) computation scheme has been used to calculate spectral properties of LaFeAsO -- the parent compound of the new high-T_c iron oxypnictides. The average Coulomb repulsion U=3-4 eV and Hund's exchange J=0.8 eV parameters for iron 3d electrons were calculated using the first principles constrained density functional theory scheme in the Wannier functions formalism. DMFT calculations using these parameters result in moderately correlated electronic structure with effective electron mass enhancement m^*~2 that is in agreement with the experimental X-ray and photoemission spectra. Conclusion of moderate correlations strength is confirmed by the observation that pnictides experimental spectra agree well with corresponding spectra for metallic iron while being very different with Mott insulator FeO spectra

Magnetic circular dichroism in X-ray fluorescence of Heusler alloys at threshold excitation

The results of fluorescence measurements of magnetic circular dichroism (MCD) in Mn L_2,L_3 X-ray emission and absorption for Heusler alloys NiMnSb and Co2MnSb are presented. Very intense resonance Mn L_3 emission is found at the Mn 2p_3/2 threshold and is attributed to a peculiarity of the threshold excitation in materials with the half-metallic character of the electronic structure. A theoretical model for the description of resonance scattering of polarized x-rays is suggested.Comment: 3 pages, 2 figures. Discussed at conferences, submitting process in progres

Electronic structure, charge transfer, and intrinsic luminescence of gadolinium oxide nanoparticles: Experiment and theory

The cubic (c) and monoclinic (m) polymorphs of Gd2O3 were studied using the combined analysis of several materials science techniques - X-ray diffraction (XRD), scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), and photoluminescence (PL) spectroscopy. Density functional theory (DFT) based calculations for the samples under study were performed as well. The cubic phase of gadolinium oxide (c-Gd2O3) synthesized using a precipitation method exhibits spheroidal-like nanoclusters with well-defined edges assembled from primary nanoparticles with an average size of 50 nm, whereas the monoclinic phase of gadolinium oxide (m-Gd2O3) deposited using explosive pyrolysis has a denser structure compared with natural gadolinia. This phase also has a structure composed of three-dimensional complex agglomerates without clear-edged boundaries that are ~21 nm in size plus a cubic phase admixture of only 2 at. % composed of primary edge-boundary nanoparticles ~15 nm in size. These atomic features appear in the electronic structure as different defects ([Gd...O-OH] and [Gd...O-O]) and have dissimilar contributions to the charge-transfer processes among the appropriate electronic states with ambiguous contributions in the Gd 5p - O 2s core-like levels in the valence band structures. The origin of [Gd...O-OH] defects found by XPS was well-supported by PL analysis. The electronic and atomic structures of the synthesized gadolinias calculated using DFT were compared and discussed on the basis of the well-known joint OKT-van der Laan model, and good agreement was established.Comment: 27 pages, 10 figures, accepted in Appl. Surf. Sc

Half-metallic antiferromagnets in thiospinels

We have theoretically designed the half-metallic (HM) antiferromagnets (AFMs) in thiospinel systems, $\rm Mn(CrV)S_{4}$ and $\rm Fe_{0.5}Cu_{0.5}(V_{0.5}Ti_{1.5})S_{4}$, based on the electronic structure studies in the local-spin-density approximation (LSDA). We have also explored electronic and magnetic properties of parent spinel compounds of the above systems; $\rm CuV_{2}S_{4}$ and $\rm CuTi_{2}S_{4}$ are found to be HM ferromagnets in their cubic spinel structures, while $\rm MnCr_{2}S_{4}$ is a ferrimagnetic insulator. We have discussed the feasibility of material synthesis of HM-AFM thiospinel systems.Comment: 4 pages, 5 figure