Browsing by Author "Chen, C. K."

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Anisotropic electronic structure in single crystalline orthorhombic TbMnO(3) thin films
(2010-02-01)
Wu, K. H.
;
Gou, I. C.
;
Luo, C. W.
;
Uen, T. M.
;
Lin, J. -Y.
We have deposited the c-axis-oriented orthorhombic TbMnO(3) (o-TMO) films with well-aligned in-plane orientations on NdGaO(3) (001) substrates by using pulsed laser deposition. The distinctive orientation alignments between the film and substrate allow the study of the X-ray absorption spectroscopy (XAS) with the electric field along three major crystallographic directions, respectively. Polarization-dependent XAS spectra show significant anisotropy in the electronic Structure of o-TMO. The correlation between the electronic structure, the bonding anisotropy, and the magnetoelectric effect in the multiferroic materials is revealed. (C) 2009 Elsevier B.V. All rights reserved.
Anisotropic electronic structure in single crystalline orthorhombic TbMnO3 thin films
(2010-02-01)
Wu, K. H.
;
Gou, I. C.
;
Luo, C. W.
;
Uen, T. M.
;
Lin, J. -Y.
We have deposited the c-axis-oriented orthorhombic TbMnO3 (o-TMO) films with well-aligned in-plane orientations on NdGaO3 (001) substrates by using pulsed laser deposition. The distinctive orientation alignments between the film and substrate allow the study of the X-ray absorption spectroscopy (XAS) with the electric field along three major crystallographic directions, respectively. Polarization-dependent XAS spectra show significant anisotropy in the electronic Structure of o-TMO. The correlation between the electronic structure, the bonding anisotropy, and the magnetoelectric effect in the multiferroic materials is revealed. (C) 2009 Elsevier B.V. All rights reserved.
Bonding anisotropy in multiferroic TbMnO(3) probed by polarization dependent x-ray absorption spectroscopy
(2009-01-26)
Chen, J. M.
;
Lee, J. M.
;
Chen, C. K.
;
Chou, T. L.
;
Lu, K. T.
O K- and Mn L(2,3)-edges x-ray absorption spectra of orthorhombic TbMnO(3) single crystals show strong polarization dependence, in contrast with results of previous experiments on orthorhombic LaMnO(3) and DyMnO(3) thin films that show nearly isotropic spectral structure. First-principles calculations reveal that TbMnO(3) exhibits a zigzag e(g) orbital ordering ground state. The highly distorted MnO(6) octahedron and orbital ordering in TbMnO(3) produce highly anisotropic Mn-O bonding within the ab plane, a frustration of the magnetic ordering, and the formation of complicated incommensurate magnetic structures.
Bonding anisotropy in multiferroic TbMnO3 probed by polarization dependent x-ray absorption spectroscopy
(2009-01-26)
Chen, J. M.
;
Lee, J. M.
;
Chen, C. K.
;
Chou, T. L.
;
Lu, K. T.
O K- and Mn L-2,L-3-edges x-ray absorption spectra of orthorhombic TbMnO3 single crystals show strong polarization dependence, in contrast with results of previous experiments on orthorhombic LaMnO3 and DyMnO3 thin films that show nearly isotropic spectral structure. First-principles calculations reveal that TbMnO3 exhibits a zigzag e(g) orbital ordering ground state. The highly distorted MnO6 octahedron and orbital ordering in TbMnO3 produce highly anisotropic Mn-O bonding within the ab plane, a frustration of the magnetic ordering, and the formation of complicated incommensurate magnetic structures.
Dissociation dynamics of positive-ion and negative-ion fragments of gaseous and condensed Si(CH3)(2)Cl-2 via Si 2p, Cl 2p, and Cl 1s core-level excitations
(2006-12-07)
Chen, J. M.
;
Lu, K. T.
;
Lee, J. M.
;
Chen, C. K.
;
Haw, S. C.
The state-selective positive-ion and negative-ion dissociation pathways of gaseous and condensed Si(CH3)(2)Cl-2 following Cl 2p, Cl 1s, and Si 2p core-level excitations have been characterized. The excitations to a specific antibonding state (15a(1)(*) state) of gaseous Si(CH3)(2)Cl-2 at the Cl 2p, Cl 1s, and Si 2p edges produce significant enhancement of fragment ions. This ion enhancement at specific core-excited states correlates closely with the ion kinetic energy distribution. The results deduced from ion kinetic energy distribution are consistent with results of quantum-chemical calculations on Si(CH3)(2)Cl-2 using the ADF package. The Cl- desorption yields for Si(CH3)(2)Cl-2/Si(100) at similar to 90 K are notably enhanced at the 15a(1)(*) resonance at both Cl 2p and Si 2p edges. The resonant enhancement of Cl- yield occurs through the formation of highly excited states of the adsorbed molecules. These results provide insight into the state-selective ionic fragmentation of molecules via core-level excitation. (c) 2006 American Institute of Physics.
Intra- and intersite electronic excitations in multiferroic TbMnO(3) probed by resonant inelastic x-ray scattering
(2010-09-27)
Chen, J. M.
;
Lee, J. M.
;
Huang, S. W.
;
Lu, K. T.
;
Jeng, H. T.
Mn 3d valence states and elementary electronic excitations in single-crystalline TbMnO(3) were probed with resonant inelastic x-ray scattering (RIXS) (or resonant x-ray emission spectroscopy, RXES), polarized x-ray absorption spectra and ab initio electron-structure calculations. Polarized Mn K-edge x-ray absorption spectra of TbMnO(3) crystals exhibit a significant anisotropy along three crystallographic directions, particularly for the white-line region. The 1s3p-RXES spectra obtained at the Mn K edge reveal that the quadrupolar Raman regime is restricted predominantly to below the pre-edge peak whereas the fluorescence regime starts from the first pre-edge peak of 1s -> 3d transitions, indicating a relatively delocalized character of unoccupied Mn 3d states. The additional K beta emission profile at energy loss similar to 62 eV is attributed to the off-site dipole Mn 1s-Mn' 3d and/or Mn 1s-Tb 5d transitions, originating from hybridization between Mn 4p states and neighboring Mn' 3d/Tb 5d states. The off-site dipole transition makes a considerable contribution to the pre-edge region of Mn K-edge spectrum. Three prominent RIXS features at similar to 2.9, 7, and 11 eV were observed. Based on GGA+U calculations, the 7 eV region corresponds to transitions from O 2p states to unoccupied minority Mn 3d states, whereas the 11 eV band is ascribed to transitions from the O 2p band to the empty Tb 5d band. The broad 2.9 eV band is attributed to the coexistence of on-site Mn 3d-Mn 3d and off-site Mn 3d-Mn' 3d transitions.
Intra- and intersite electronic excitations in multiferroic TbMnO3 probed by resonant inelastic x-ray scattering
(2010-09-27)
Chen, J. M.
;
Lee, J. M.
;
Huang, S. W.
;
Lu, K. T.
;
Jeng, H. T.
Mn 3d valence states and elementary electronic excitations in single-crystalline TbMnO3 were probed with resonant inelastic x-ray scattering (RIXS) (or resonant x-ray emission spectroscopy, RXES), polarized x-ray absorption spectra and ab initio electron-structure calculations. Polarized Mn K-edge x-ray absorption spectra of TbMnO3 crystals exhibit a significant anisotropy along three crystallographic directions, particularly for the white-line region. The 1s3p-RXES spectra obtained at the Mn K edge reveal that the quadrupolar Raman regime is restricted predominantly to below the pre-edge peak whereas the fluorescence regime starts from the first pre-edge peak of 1s -> 3d transitions, indicating a relatively delocalized character of unoccupied Mn 3d states. The additional K beta emission profile at energy loss similar to 62 eV is attributed to the off-site dipole Mn 1s-Mn' 3d and/or Mn 1s-Tb 5d transitions, originating from hybridization between Mn 4p states and neighboring Mn' 3d/Tb 5d states. The off-site dipole transition makes a considerable contribution to the pre-edge region of Mn K-edge spectrum. Three prominent RIXS features at similar to 2.9, 7, and 11 eV were observed. Based on GGA+U calculations, the 7 eV region corresponds to transitions from O 2p states to unoccupied minority Mn 3d states, whereas the 11 eV band is ascribed to transitions from the O 2p band to the empty Tb 5d band. The broad 2.9 eV band is attributed to the coexistence of on-site Mn 3d-Mn 3d and off-site Mn 3d-Mn' 3d transitions.
Polarization-dependent x-ray absorption spectroscopy of hexagonal and orthorhombic TbMnO(3) thin films
(2010-01-01)
Wu, K. H.
;
Gou, I. C.
;
Luo, C. W.
;
Uen, T. M.
;
Lin, J-Y
Pure phase TbMnO(3) manganite thin films with hexagonal (h-TMO) and orthorhombic (o- TMO) crystal structures were prepared by pulsed laser deposition. The distinctive orientation alignments between film and substrate obtained here have allowed us to perform the x-ray absorption near edge spectroscopy (XANES) measurements with the electric field applied along the three major crystallographic directions. The XANES results, as expected, display significantly different spectral features for the h-TMO and o-TMO films. In addition, the XANES spectra also exhibit strong polarization dependence at O K and Mn L edges for both samples.
Polarization-dependent x-ray absorption spectroscopy of hexagonal and orthorhombic TbMnO3 thin films
(2010-01-01)
Wu, K. H.
;
Gou, I. C.
;
Luo, C. W.
;
Uen, T. M.
;
Lin, J-Y
Pure phase TbMnO3 manganite thin films with hexagonal (h-TMO) and orthorhombic (o- TMO) crystal structures were prepared by pulsed laser deposition. The distinctive orientation alignments between film and substrate obtained here have allowed us to perform the x-ray absorption near edge spectroscopy (XANES) measurements with the electric field applied along the three major crystallographic directions. The XANES results, as expected, display significantly different spectral features for the h-TMO and o-TMO films. In addition, the XANES spectra also exhibit strong polarization dependence at O K and Mn L edges for both samples.
Resonant x-ray emission spectroscopy of multiferroic TbMnO3
(2007-07-30)
Chen, J. M.
;
Chen, C. K.
;
Chou, T. L.
;
Jarrige, I.
;
Ishii, H.
The Mn 3d valence states in single-crystalline TbMnO3 were probed using x-ray absorption spectroscopy and resonant x-ray emission spectroscopy (RXES). The polarized Mn K-edge x-ray absorption spectra show a strong polarization dependence, particularly for the white line region, indicating the strong anisotropic Mn-O bonding within the ab plane in TbMnO3. The RXES data obtained at the Mn K edge clearly reveal that unoccupied Mn 3d states exhibit a relatively delocalized character, stemming from hybridization of the Mn 3d states with the neighboring Mn 4p orbitals. The authors demonstrated that resonant x-ray emission spectroscopy is able to characterize the degree of localization of the unoccupied states or hole carriers in manganites.
State-specific dissociation enhancement of ionic and excited neutral photofragments of gaseous CCl(4) and solid-state analogs following Cl 2p core-level excitation
(2008-05-07)
Lu, K. T.
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Chen, J. M.
;
Lee, J. M.
;
Chen, C. K.
;
Chou, T. L.
The state-selective dissociation pathways for ionic and excited neutral fragments of gaseous and condensed CCl(4) following Cl 2p core-level excitation have been characterized by combining photon-induced ionic dissociation, x-ray absorption, resonant photoemission and UV/visible dispersed fluorescence measurements. The Cl 2p -> 7a(1)* excitation of CCl(4) induces significant enhancement of the Cl(+) desorption yield in the condensed phase and the CCl(+) yields in the gaseous phase. Based on the resonant photoemission studies, excitations of Cl 2p electrons to valence orbitals and Rydberg states decay predominantly via the spectator Auger transitions. The transitions of Cl 2p electrons to the Rydberg state of gaseous CCl(4) lead to a noteworthy production of excited atomic neutral fragments (C*) and excited diatomic neutral fragments (CCl*). These results provide insight into the state-selective ionic and neutral fragmentation processes of molecules via core-level excitation.
Strong orbital polarization in orthorhombic DyMnO(3): A combined x-ray linear dichroism and ab initio electronic structure study
(2010-05-15)
Chen, J. M.
;
Hu, Z.
;
Jeng, H. T.
;
Chin, Y. Y.
;
Lee, J. M.
We present a combined experimental and theoretical study on the Mn 3d orbital occupation in orthorhombic DyMnO(3) single crystals. We have observed a very strong polarization dependence in the Mn L(2,3) x-ray absorption spectra, indicative for a distinct anisotropic orbital occupation. Ab initio electronic-structure calculations clearly infer the existence of a strong orbital polarization in the e(g) band with a staggered d(3x2-r2)/d(3y2-r2)-type ordering pattern in the ab plane. This finding is in excellent agreement with a quantitative analyis of the spectra using the atomic multiplet cluster approach.
Strong orbital polarization in orthorhombic DyMnO3: A combined x-ray linear dichroism and ab initio electronic structure study
(2010-05-15)
Chen, J. M.
;
Hu, Z.
;
Jeng, H. T.
;
Chin, Y. Y.
;
Lee, J. M.
We present a combined experimental and theoretical study on the Mn 3d orbital occupation in orthorhombic DyMnO3 single crystals. We have observed a very strong polarization dependence in the Mn L-2,L-3 x-ray absorption spectra, indicative for a distinct anisotropic orbital occupation. Ab initio electronic-structure calculations clearly infer the existence of a strong orbital polarization in the e(g) band with a staggered d(3x2-r2)/d(3y2-r2)-type ordering pattern in the ab plane. This finding is in excellent agreement with a quantitative analyis of the spectra using the atomic multiplet cluster approach.