| 1. |
- Dong, C. L., et al.
(författare)
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Electronic structure of nanostructured ZnO from x-ray absorption and emission spectroscopy and the local density approximation
- 2004
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 70:19
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Tidskriftsartikel (refereegranskat)abstract
- O 1s absorption spectroscopy (XAS) and O Kalpha emission spectroscopy (XES) were performed to study the electronic structure of nanostructured ZnO. The band gap is determined by the combined absorption-emission spectrum. Resonantly excited XES spectra showing an energy dependence in the spectral shape reveal the selected excitations to the different Zn 3d, 4s, and 4p states in hybridization with O 2p states. The partial density of state obtained from local density approximation (LDA) and LDA+U calculations are compared with the experimental results. The LDA+U approach is suitable to correct LDA self-interaction error of the cation d states. The atomic eigenstates of 3d in zinc and 2p in oxygen are energetically close, which induces the strong interaction between Zn 3d and O 2p states. This anomalous valence band cation-d-anion-p hybridization is verified by taking into account the strong localization of the Zn 3d states.
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| 2. |
- Persson, Clas, et al.
(författare)
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X-ray absorption and emission spectroscopy of ZnO nanoparticle and highly oriented ZnO microrod arrays
- 2006
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Ingår i: Microelectronics Journal. - : Elsevier BV. - 0026-2692. ; 37:8, s. 686-689
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Tidskriftsartikel (refereegranskat)abstract
- The electronic structures of ZnO nanoparticles and microrod arrays are studied by 0 Is X-ray absorption spectroscopy (XAS) and O K alpha X-ray emission spectroscopy (XES). We show that the present LDA +U-SIC calculation approach is suitable to correct the LDA self-interaction error of the cation d-states. The atomic eigenstates of 3d in zinc and 2p in oxygen are energetically close, which induces strong Zn-3d-O-2p hybridization. This anomalous valence band cation-d-anion-p hybridization is affected when the localization of the Zn 3d-states is taken into account. Experimentally, the XES spectra show energy dependence in the spectral shape revealing selected excitations to the Zn 3d, 4s and 4p states, hybridized with 0 2p states. Strong anisotropic effects are observed for the highly oriented ZnO rods, but not for the isotropic spherical nanoparticles. The nanostructured ZnO has primarily bulk XAS and XES properties.
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| 3. |
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| 4. |
- Kronawitter, C. X., et al.
(författare)
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Titanium incorporation into hematite photoelectrodes : theoretical considerations and experimental observations
- 2014
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Ingår i: Energy & Environmental Science. - : Royal Society of Chemistry (RSC). - 1754-5692 .- 1754-5706. ; 7:10, s. 3100-3121
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Tidskriftsartikel (refereegranskat)abstract
- A theoretical and experimental perspective on the role of titanium impurities in hematite (alpha-Fe2O3) nanostructured photoelectrodes for solar fuel synthesis devices is provided. Titanium incorporation is a known correlate to efficiency enhancement in alpha-Fe2O3 cc photoanodes for solar water oxidation; here the relevant literature and the latest advances are presented and various proposed mechanisms for enhancement are contrasted. Available experimental evidence suggests that Ti incorporation increases net electron carrier concentrations in electrodes, most likely to the extent that (synthesis-dependent) charge compensating cation vacancies are not present. However, electron conductivity increases alone cannot quantitatively account for the large associated photoelectrochemical performance enhancements. The magnitudes of the effects of Ti incorporation on electronic and magnetic properties appear to be highly synthesis-dependent, which has made difficult the development of consistent and general mechanisms explaining experimental and theoretical observations. In this context, we consider how the electronic structure correlates with Ti impurity incorporation in alpha-Fe2O3 a from the perspective of synchrotron-based soft X-ray absorption spectroscopy measurements. Measurements are performed on sets of electrodes fabricated by five relevant and unrelated chemical and physical techniques. The effects of titanium impurities are reflected in the electronic structure through several universally observed spectral characteristics, irrespective of the synthesis techniques. Absorption spectra at the oxygen K-edge show that Ti incorporation is associated with new oxygen 2p-hybridized states, overlapping with and distorting the known unoccupied Fe 3d-O 2xp band of alpha-Fe2O3. This is an indication of mixing of Ti s and d states in the conduction band of alpha-Fe2O3. cc A comparison of spectra obtained with electron and photon detection shows that the effects of Ti incorporation on the conduction band are more pronounced in the near-surface region. Titanium L-2,L-3-edge absorption spectra show that titanium is incorporated into alpha-Fe2O3 as Ti4+ by all fabrication methods, with no long-range titania order detected. Iron L-2,L-3-edge absorption spectra indicate that Ti incorporation is not associated with the formation, of any significant concentrations of Fe2+, an observation common to many prior studies on this material system.
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| 5. |
- Patthey, L, et al.
(författare)
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Adsorption of bi-isonicotinic acid on rutile TiO2(110)
- 1999
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Ingår i: JOURNAL OF CHEMICAL PHYSICS. - 0021-9606. ; 110:12, s. 5913-5918
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- Bi-isonicotinic acid (2,2'-bipyridine- 4,4'-dicarboxylic acid) is the ligand of several organometallic dyes, used in photoelectrochemical applications. Therefore the atomic scale understanding of the bonding of this molecule to rutile TiO2(110) should giv
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| 6. |
- Rensmo, Håkan, et al.
(författare)
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The electronic structure of the cis-bis(4,4'-dicarboxy-2,2'-bipyridine)-bis(isothiocyanato) ruthenium(II) complex and its ligand 2,2'-bipyridyl-4,4'-dicarboxylic acid studied with electron spectroscopy
- 1997
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Ingår i: CHEMICAL PHYSICS LETTERS. - : ELSEVIER SCIENCE BV. - 0009-2614. ; 274:1-3, s. 51-57
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- The electronic structure of the dye complex cis-bis(4,4'-dicarboxy-2,2'-bipyridine)-bis(isothiocyanato)ruthenium(II) as well as that of its ligand 2,2'-bipyridine-4,4'-dicarboxylic acid has been investigated with electron spectroscopy. Valence level spect
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| 7. |
- Beermann, Niclas, et al.
(författare)
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Photoelectrochemical studies of oriented nanorod thin films of hematite
- 2000
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Ingår i: JOURNAL OF THE ELECTROCHEMICAL SOCIETY. - : ELECTROCHEMICAL SOC INC. - 0013-4651. ; 147:7, s. 2456-2461
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Tidskriftsartikel (refereegranskat)abstract
- Thin films consisting of nanorods of hematite (alpha-Fe2O3) with controlled orientation onto transparent conductive glass substrates have been tested as photoelectrochemical cells. These films allow a more efficient transport and collection of photogenera
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| 8. |
- Guo, J. H., et al.
(författare)
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Polarization-dependent soft-x-ray absorption of a highly oriented ZnO microrod-array
- 2005
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Ingår i: Journal of Physics. - : IOP Publishing. - 0953-8984 .- 1361-648X. ; 17:1, s. 235-240
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Tidskriftsartikel (refereegranskat)abstract
- Polarization-dependent x-ray absorption measurements were performed on a crystalline ZnO three-dimensional array consisting of highly oriented microrods as well as on particulate thin film consisting of monodisperse spherical nanoparticles. Strong anisotropic effects have been observed for the highly oriented ZnO rods, unlike for the isotropic spherical ones. Full-potential calculations of orbital-resolved x-ray absorption of a ZnO wurtzite periodic crystal, including the Zn 3d as part of the valence states, shows a very good agreement with the experimental findings. Comprehensive fundamental knowledge of the electronic structure of ZnO is obtained by probing and demonstrating the orbital symmetry of oxygen and its contribution to the conduction band of this important II-VI semiconductor.
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| 9. |
- Guo, J. H., et al.
(författare)
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Polarization-dependent soft-x-ray absorption of highly oriented ZnO microrod arrays
- 2002
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Ingår i: Journal of Physics. - : IOP Publishing. - 0953-8984 .- 1361-648X. ; 14:28, s. 6969-6974
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Tidskriftsartikel (refereegranskat)abstract
- Polarization-dependent x-ray absorption measurements were performed on crystalline ZnO three-dimensional arrays consisting of highly oriented microrods as well as on particulate thin films consisting of monodisperse spherical nanoparticles. Strong anisotropic effects have been observed for the highly oriented ZnO rods, but not for the isotropic spherical nanoparticles. Full-potential calculations of the orbital-resolved x-ray absorption of a ZnO wurtzite periodic crystal, including Zn 3d among the valence states, show very good agreement with the experimental findings. Comprehensive fundamental knowledge of the electronic structure of ZnO is obtained by probing and demonstrating the orbital symmetry of oxygen and its contribution to the conduction band of this important II-VI semiconductor.
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| 10. |
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