- Unoccupied electronic states in CaB6 studied by density functional theory and EELS measurements
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The electronic structure of CaB6 has recently attracted great interest because of the discovery that this compound is unexpectedly ferromagnetic and exhibits a surprisingly large thermoelectric effect. We have concentrated on studying the unoccupied electronic states by investigating the boron 1s core-level spectroscopy. Comparison of our data from electron energy-loss spectroscopy with that from x-ray absorption spectroscopy using the total electron yield mode reveals evidence for sample inhomogeneity. The ab initio band structural method has been successfully applied to simulate the overall features found in the boron 1s absorption spectrum. Correlation with the results of a ground state energy-band calculation allows the interpretation of the spectral features in terms of the density of states of the unoccupied conduction band, in particular the identification of a feature associated with hybridization of Ca d orbitals with B p orbitals. This interpretation is confirmed by comparison with similar calculations for related boride systems. However, simulation spectral data cannot be reconciled with high-resolution experimental data at the absorption threshold. The possibility of either the failure of the theoretical method employed to account for many-body effects and/or the need for improved experimental measurements is discussed.
- Gao, Shang-Peng,Jiang, Jun,Cao, Minghe,Zhu, Jing,Yuan, Jun
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p. 214419-1-214419-9
(2008/10/09)
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- Phonon structure of LaB6 by point-contact spectroscopy
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The differential resistance dV/dI versus voltage characteristics is studied for point-contacts between a LaB6-needle on one side and a LaB 6 (100)-cleavage surface on the other. A technique of automatic in situ cleaning is used to clean the sample surface. The spectra of pure metal point-contacts are contrary to that of the tunneling contacts interposed by the oxide layer, that is, the former is for the barrierless junction of enough clean surface and the latter is for the barrier-type junction of intentionally oxidized surface. The measurements of the second derivative d 2K/dI2 give the information on the phonon density of states of LaB6, adding new experimental results on the current neutron scattering experiment. The peaks of the phonon density of states of LaB6 are situated at 12, 24, 38 and 50 meV.
- Kunii, Satoru
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p. 361 - 366
(2008/10/08)
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- Studies of chemiluminescence in boron atom reactions with O2, SO2, N2O, NO2, and H2O2
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Chemiluminescence has been observed in the single collision reaction of boron atoms with O2, SO2, N2O, NO2, and H2O2.The experiments were performed in a beam-gas apparatus using photon counting to detect the optical signals.The electronically excited A2? state of BO was observed in all the reactions.In addition, the BO2(A2?u) state was observed in the reaction of boron with SO2.Cross sections for the production of electronically excited molecules were determined.These cross sections for the reactions with O2, SO2, N2O, NO2, and H2O2 are, respectively, 0.048, 0.0078, 0.01, 0.023, and 0.005 Angstroem2.In the reactions of boron with SO2 the branching ratio was obtained for the two observed chemiluminescent reaction channels.The vibrational distributions in the electronically excited state of BO were determined in the reactions where the spectra were adequately resolved.Some implications of the results are discussed.
- DeHaven, James,O'Connor, Michael T.,Davidovits, Paul
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p. 1746 - 1751
(2007/10/02)
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