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| 2. |
- Bergenti, I., et al.
(författare)
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Spin polarized La0.7Sr0.3MnO3 thin films on silicon
- 2007
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Ingår i: Journal of Magnetism and Magnetic Materials. - : Elsevier BV. - 0304-8853 .- 1873-4766. ; 312:2, s. 453-457
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Tidskriftsartikel (refereegranskat)abstract
- La0.7Sr0.3MnO3 polycrystalline manganite thin films were grown on silicon (Si) substrates covered by SiOx amorphous native oxide. Curie temperatures of about 325 K were achieved for 70-nm-thick films. Strong room temperature XMCD signal was detected indicating high spin polarization at the surface. Cross-sectional TEM images show sharp interface between SiOx and manganite without signature of chemical reaction at the interface. Unusual sharp splitting of the manganite film was observed: on the top of a transition layer characterized by low crystalline order, a magnetically robust layer is formed. © 2007 Elsevier B.V. All rights reserved.
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| 3. |
- Dannetun, Per, et al.
(författare)
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Proceedings of the International Conference on Science and Technology of Synthetic Metals The chemical and electronic structure of the interface between aluminum and conjugated polymers or molecules
- 1993
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Ingår i: Synthetic metals. - : Elsevier. - 0379-6779 .- 1879-3290. ; 55:1, s. 212-217
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Tidskriftsartikel (refereegranskat)abstract
- The interaction between aluminum and α-ω-diphenyltetradecaheptaenee (DP7), α-sexithienyl (6T), and poly(p-phenylenevinylene) (PPV), respectively have been studied using both X-ray Photoelectron Spectroscopy (XPS) and Ultraviolet Photoelectron Spectroscopy (UPS). The UPS valence band spectra, are interpreted with the help of quantum chemical calculations based upon Modified Neglect of Diatomic Overlap (MNDO), Valence Effective Hamitonian (VEH) and ab initio Hartree-Fock methods. DP7 is a model molecule for polyacetylene, while 6T is a model molecule (an oligomer) of polythiophene. The results indicate that aluminum reacts strongly with the surfaces of all of the materials studied. The π-electronic structure of each material was strongly modified. Furthermore, aluminum reacts preferentially with the polyene partof DP7, with the vinylene part of PPV, and with the α-carbons of the thiophene nits of 6T.
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| 4. |
- Dannetun, Per, et al.
(författare)
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The chemical and electronic structure of the interface between aluminum and polythiophene semiconductors
- 1993
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Ingår i: Journal of Chemical Physics. - : American Institute of Physics (AIP). - 0021-9606 .- 1089-7690. ; 99:1, s. 664-672
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Tidskriftsartikel (refereegranskat)abstract
- We have investigated the chemical nature and the electronic structure of the interface between a low work function metal,aluminum, and a conjugated polymersemiconductor, polythiophene. We have studied the initial stages of the interface formation by depositing the metal onto the surface of a polymer film. Charge transfer processes between the metal and the polymer are analyzed using core‐level x‐ray photoelectron spectroscopy (XPS); the evolution upon metallization of the valence electronic levels directly related to the polymerelectronic structure is followed with ultraviolet photoelectron spectroscopy (UPS). With these techniques, we investigate the deposition of aluminum on two polythiophene systems (i) the alkyl‐substituted poly‐3‐octylthiophene and (ii) the α‐sexithiophene oligomer. The experimental data are compared to the results of a recent quantum chemical study on model systems consisting of thiophene oligomers (up to sexithiophene) interacting with a few Al atoms. The interaction of polythiophene with Al atoms is found to modify dramatically the structure of the conjugated backbone, as strong carbon–aluminum bonds are formed in the α positions of the thiophene rings. A large charge transfer takes place from the Al atoms to the polymer chain, and the upper π levels of the polymer are strongly affected. The metallization is contrasted to the doping of conjugated polymers with alkali metals
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| 5. |
- Dediu, V., et al.
(författare)
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Room-temperature spintronic effects in Alq3 -based hybrid devices
- 2008
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 78:11
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Tidskriftsartikel (refereegranskat)abstract
- We report on efficient spin polarized injection and transport in long (102 nm) channels of Alq3 organic semiconductor. We employ vertical spin valve devices with a direct interface between the bottom manganite electrode and Alq3, while the top-electrode geometry consists of an insulating tunnel barrier placed between the "soft" organic semiconductor and the top Co electrode. This solution reduces the ubiquitous problem of the so-called ill-defined layer caused by metal penetration, which extends into the organic layer up to distances of about 50-100 nm and prevents the realization of devices with well-defined geometry. For our devices the thickness is defined with an accuracy of about 2.5 nm, which is near the Alq3 molecular size. We demonstrate efficient spin injection at both interfaces in devices with 100- and 200-nm-thick channels. We solve one of the most controversial problems of organic spintronics: the temperature limitations for spin transport in Alq3 -based devices. We clarify this issue by achieving room-temperature spin valve operation through the improvement of spin injection properties of both ferromagnetic/ Alq3 interfaces. In addition, we discuss the nature of the inverse sign of the spin valve effect in such devices proposing a mechanism for spin transport. © 2008 The American Physical Society.
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| 6. |
- de Jong, Michel P, et al.
(författare)
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Electronic structure of La0.7Sr0.3MnO3 thin films for hybrid organic/inorganic spintronics applications
- 2003
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Ingår i: Journal of Applied Physics. - : AIP Publishing. - 0021-8979 .- 1089-7550. ; 94:11, s. 7292-7296
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Tidskriftsartikel (refereegranskat)abstract
- The electronic structure of the spin injecting La0.7Sr 0.3MnO3 (LSMO) thin film contacts was investigated using photoelectron spectroscopy. Clean LSMO surfaces were obtained by annealing at 450°C in vacuum, which additionally stabilized the oxygen content determined from the exchange splitting of the Mn(3s) x-ray photoelectron spectroscopy (XPS). The valence-band structure of the films showed features of metallic LSMO. The work-function measruements of clean, annealed films yield lower values due to oxygen depletion upon annealing.
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| 7. |
- de Jong, Michel P, et al.
(författare)
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Evidence for Mn2+ ions at surfaces of La0. 7Sr 0.3MnO3 thin films
- 2005
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 71:1
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Tidskriftsartikel (refereegranskat)abstract
- We present a detailed investigation of the valence of manganese sites at the surface of colossal magnetoresistance La0.7Sr 0.3MnO3 (LSMO) thin films by x-ray absorption spectroscopy (XAS). The XAS Mn L-edge spectra of epitaxial LSMO films usually show a peak or shoulder at 640 eV. Differences in the intensity of this feature are commonly attributed to slight changes in the Mn3+/Mn4+ ratio or the crystal field strength. By comparison of different XAS spectra of LSMO thin films with the known multiplet structure of Mn2+ in a cubic crystal field, we assign this 640-eV feature to Mn2+ ions. XAS with increased surface sensitivity, combined with photon energy-dependent photoelectron spectroscopy measurements of the Mn(3s) exchange splitting, show that the Mn2+ species are mainly located at the surface. The Mn2+ scenario indicates significant modification of the LSMO surface with respect to the bulk properties that should be taken into account in all the charge and spin tunneling and injection experiments. © 2005 The American Physical Society.
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| 8. |
- de Jong, Michel P, et al.
(författare)
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Valence electronic states related to Mn2+ at La0.7 Sr0.3 MnO3 surfaces characterized by resonant photoemission
- 2006
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 73:5
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Tidskriftsartikel (refereegranskat)abstract
- Nonferromagnetic Mn2+ ions can be readily formed at the surface of half metallic La0.7 Sr0.3 MnO3 manganite as demonstrated by deoxygenating surface treatments. The 3 d5 contribution of these Mn2+ ions to the valence-band electronic structure has been characterized using Mn(2p) to 3d resonant photoemission measurements. The Mn2+ related 3d electrons were found to be stabilized by about 2 eV with respect to the mixed-valence 3d states, indicating their strong localization. Active participation of Mn2+ states in both spin and charge conductivity processes is therefore excluded. A two-channel picture, including independent Mn3+ Mn4+ and Mn2+ channels, emerges from detailed data analysis. Reversible Mn2+ formation and straightforward oxygen annealing effects point to a direct bonding between Mn2+ and oxygen vacancies that are most probably created at preexisting structural defects. The t2g and eg states of the mixed valence Mn3+ Mn4+ ions remain unaffected as the Mn2+ content increases, indicating a robust Mn3+ Mn4+ channel independent of structural defects. © 2006 The American Physical Society.
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