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Li, Fenghong
Publications (10 of 15) Show all publications
Li, F., Zhan, Y., Lee, T.-H., Liu, X., Chikamatsu, A., Guo, T.-F., . . . Fahlman, M. (2011). Modified Surface Electronic and Magnetic Properties of La(0.6)Sr(0.4)MnO(3) Thin Films for Spintronics Applications. The Journal of Physical Chemistry C, 115(34), 16947-16953
Open this publication in new window or tab >>Modified Surface Electronic and Magnetic Properties of La(0.6)Sr(0.4)MnO(3) Thin Films for Spintronics Applications
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2011 (English)In: The Journal of Physical Chemistry C, ISSN 1932-7447, E-ISSN 1932-7455, Vol. 115, no 34, p. 16947-16953Article in journal (Refereed) Published
Abstract [en]

We present the surface electronic and magnetic properties of half-metal La(0.6)Sr(0.4)MnO(3) (LSMO) thin film modified by a simple cleaning procedure, the so-called SC1 (5 H(2)O, 1 NH(4)OH, I H(2)O(2)), at 85 degrees C for 10-40 min in ambient atmosphere. In this study, photoemission spectroscopy (XPS/UPS), X-ray absorption spectroscopy (XAS), and X-ray magnetic circular dichroism (XMCD) are used to characterize these properties of the manganites. Thanks to SC1 treatment, the work function of LSMO changes from 4.0-4.1 to 4.8-4.9 eV obtained from UPS measurements, while its surface roughness changes from 0.268 to 0.796 nm in AFM images. Combined 0 1s, Mn 2p, Sr 3d, La 4d, and Mn 3s core-level XPS spectroscopy investigations suggest that Mn and Sr contents decrease at the surface and the Mn value becomes 3.7 due to SC1 treament. Mn L-edge XAS spectra of LSMO thin film demonstrate that SC1 treatment results in a removal of Mn(2+) and an increase of the Mn(4+) concentration. OK-edge XAS spectra further prove an enhancement of hybridization between O 2p orbitals and e(g)down arrow, of Mn 3d induced by more Mn(4+). XMCD results show that SC1 treatment does not induce any drastic changes of magnetic properties of the LSMO thin film surface.

Place, publisher, year, edition, pages
American Chemical Society (ACS), 2011
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-70520 (URN)10.1021/jp112064y (DOI)000294146700028 ()
Note

Funding Agencies|Swedish Research Council||Knut and Alice Wallenberg Foundation||

Available from: 2011-09-12 Created: 2011-09-12 Last updated: 2017-12-08Bibliographically approved
Carlegrim, E., Zhan, Y., Li, F., Liu, X. & Fahlman, M. (2010). Characterization of the Ni/V(TCNE)x interface for hybrid spintronics applications. Organic electronics, 11(6), 1020-1024
Open this publication in new window or tab >>Characterization of the Ni/V(TCNE)x interface for hybrid spintronics applications
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2010 (English)In: Organic electronics, ISSN 1566-1199, E-ISSN 1878-5530, Vol. 11, no 6, p. 1020-1024Article in journal (Refereed) Published
Abstract [en]

Vanadium tetracyanoethylene, V(TCNE)x, is an organic-based magnet with properties suitable for spintronics applications, e.g. spin valves. In this paper we propose a new hybrid organic spin valve design where V(TCNE)x is used as a spin-transporting and spin-filtering layer sandwiched between two ferromagnetic (FM) metal contacts, i.e. FM/V(TCNE)x/FM. As the spin injection and detection of such a device occurs at the interfaces the quality of those are of crucial importance. Therefore, the Ni/V(TCNE)x interface has been investigated by X-ray photoelectron spectroscopy (XPS) and near edge X-ray absorption spectroscopy (NEXAFS) as well as compared with XPS results from a model system, Ni/TCNE. Ni chemically interact with both the vinyl and cyano groups but there is no evidence for significant diffusion of Ni into the V(TCNE)x film. As the chemical interaction affects the spin injection and detection negatively by modifying the lowest unoccupied molecular orbital (LUMO) and destroying the magnetic ordering network at the surface, these results indicate that there is need for a buffer layer between V(TCNE)x and Ni, and in extension most likely between V(TCNE)x and any FM contact.

Keyword
Organic-based molecular magnets; Spintronics; Interfaces; Photoelectron spectroscopy; Magnetic semiconductors
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-56259 (URN)10.1016/j.orgel.2010.03.001 (DOI)000277935200008 ()
Note

Original Publication: Elin Carlegrim, Yiqiang Zhan, Fenghong Li, Xianjie Liu and Mats Fahlman, Characterization of the Ni/V(TCNE)x interface for hybrid spintronics applications, 2010, Organic electronics, (11), 6, 1020-1024. http://dx.doi.org/10.1016/j.orgel.2010.03.001 Copyright: Elsevier Science B.V., Amsterdam. http://www.elsevier.com/

Available from: 2010-05-05 Created: 2010-05-05 Last updated: 2017-12-12
Zhan, Y., Holmström, E., Lizarraga, R., Eriksson, O., Liu, X., Li, F., . . . Fahlman, M. (2010). Efficient Spin Injection Through Exchange Coupling at Organic Semiconductor/Ferromagnet Heterojunctions. Advanced Materials, 22(14), 1626-1630
Open this publication in new window or tab >>Efficient Spin Injection Through Exchange Coupling at Organic Semiconductor/Ferromagnet Heterojunctions
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2010 (English)In: Advanced Materials, ISSN 0935-9648, E-ISSN 1521-4095, Vol. 22, no 14, p. 1626-1630Article in journal (Refereed) Published
Abstract [en]

The schematic visualization of the Alq(3) molecule on the Fe substrate with the optimized geometry at lowest total energy. When the Alq(3) molecule is relaxed on the surface, only two of the wings are lying down on the Fe surface, and the third wing remains perpendicular to the surface, showing a strong hybridization occurance.

Place, publisher, year, edition, pages
Wiley-VCH Verlagsgesellschaft, 2010
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-56460 (URN)10.1002/adma.200903556 (DOI)000277205900012 ()
Available from: 2010-05-17 Created: 2010-05-17 Last updated: 2017-12-12Bibliographically approved
Li, F., Graziosi, P., Tang, Q., Zhan, Y., Liu, X., Dediu, V. & Fahlman, M. (2010). Electronic structure and molecular orientation of pentacene thin films on ferromagnetic La0.7Sr0.3MnO3. Physical Review B. Condensed Matter and Materials Physics, 81(20), 205415-1-205415-6
Open this publication in new window or tab >>Electronic structure and molecular orientation of pentacene thin films on ferromagnetic La0.7Sr0.3MnO3
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2010 (English)In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 81, no 20, p. 205415-1-205415-6Article in journal (Refereed) Published
Abstract [en]

Pentacene thin films deposited on a ferromagnetic electrode, La0.7Sr0.3MnO3 (LSMO), have been studied using near-edge x-ray absorption fine structure (NEXAFS), ultraviolet photoemission spectroscopy (UPS), and atomic force microscopy (AFM). Here we present electronic structure and molecular orientation of pentacene thin film on LSMO. No evidence related to covalent bonding or significant charge transfer between pentacene and LSMO has been found in the NEXAFS or UPS results. UPS measurements suggest that the vertical ionization potential of pentacene on LSMO is 4.9 eV. Our results extracted from NEXAFS indicate that molecular long axis of pentacene stands on the LSMO substrate surface with a tilt angle of about 22 degrees +/- 2 degrees between the main molecular axis and the substrate surface normal. AFM images show the terracelike crystalline grain formed by stacking pentacene crystalline layers and a rough crystal-layer spacing of 14-15 angstrom. Findings deduced from UPS, NEXAFS, and AFM consistently demonstrate that pentacene stands on LSMO with a tilt angle.

Place, publisher, year, edition, pages
American Physical Society, 2010
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-57165 (URN)10.1103/PhysRevB.81.205415 (DOI)000278144500091 ()
Note

Original Publication: Fenghong Li, Patrizio Graziosi, Qun Tang, Yiqiang Zhan, Xianjie Liu, Valentin Dediu and Mats Fahlman, Electronic structure and molecular orientation of pentacene thin films on ferromagnetic La0.7Sr0.3MnO3, 2010, PHYSICAL REVIEW B, (81), 20, 205415. http://dx.doi.org/10.1103/PhysRevB.81.205415 Copyright: American Physical Society http://www.aps.org/

Available from: 2010-06-11 Created: 2010-06-11 Last updated: 2017-12-12Bibliographically approved
Chen, Y., Li, F. & Bo, Z. (2010). Facile Synthesis of 3,8-Dibromo-Substituted Phenanthridine Derivatives and Their Conjugated Polymers. MACROMOLECULES, 43(3), 1349-1355
Open this publication in new window or tab >>Facile Synthesis of 3,8-Dibromo-Substituted Phenanthridine Derivatives and Their Conjugated Polymers
2010 (English)In: MACROMOLECULES, ISSN 0024-9297, Vol. 43, no 3, p. 1349-1355Article in journal (Refereed) Published
Abstract [en]

We present an efficient and convenient synthesis of 3,8-dibromophenanthridine derivatives and their conjugated polymers and demonstrate that phenanthridine-containing conjugated polymers can be used as luminescent chemosensor materials. High molecular weight poly(phenanthridine-co-fluorene)s (P1, P2) and poly(phenanthridine-co-p-phenylene) (P3) were synthesized by palladium-catalyzed Suzuki-Miyaura-Schluter polycondensation (SMSPC). These phenanthridine-containing polymers are of high quantum yields in solution and show reversible optical response to protonation and deprotonation of the phenanthridine rings.

National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-54063 (URN)10.1021/ma902375a (DOI)000274268400027 ()
Available from: 2010-02-22 Created: 2010-02-22 Last updated: 2015-05-27
Li, W., Qin, R., Zhou, Y., Andersson, M., Li, F., Zhang, C., . . . Zhang, F. (2010). Tailoring side chains of low band gap polymers for high efficiency polymer solar cells. Polymer, 51(14), 3031-3038
Open this publication in new window or tab >>Tailoring side chains of low band gap polymers for high efficiency polymer solar cells
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2010 (English)In: Polymer, ISSN 0032-3861, E-ISSN 1873-2291, Vol. 51, no 14, p. 3031-3038Article in journal (Refereed) Published
Abstract [en]

High efficiency organic solar cells (OSCs) require conjugated polymers with a low band gap, broad absorption in visible and IR region, high carrier mobility, and relatively high molecular weight as p-type donor materials. Flexible side chains on the rigid polymer backbone are crucial for the solubility of conjugated polymers. In this work, four polymers with the main chain structure of fluorene-thiophene-benzothiadiazole-thiophene and flexible side chains located on fluorene, thiophene, and benzothiadiazole moiety, respectively, have been synthesized by Suzuki-Miyaura-Schluter polycondensation. Photovoltaic device measurements with a device configuration of ITO/polymer:PC71BM blends/LiF/Al show that P1 carrying octyloxy chains on benzothiadiazole rings gives the best performance, with a power conversion efficiency of 3.1%.

Place, publisher, year, edition, pages
Elsevier Science B.V., Amsterdam., 2010
Keyword
Organic solar cell; Side chains; Low band gap
National Category
Engineering and Technology
Identifiers
urn:nbn:se:liu:diva-58286 (URN)10.1016/j.polymer.2010.05.015 (DOI)000279181400013 ()
Available from: 2010-08-10 Created: 2010-08-09 Last updated: 2017-12-12
Li, W., Du, C., Li, F., Zhou, Y., Fahlman, M., Bo, Z. & Zhang, F. (2009). Benzothiadiazole-Based Linear and Star Molecules: Design, Synthesis, and Their Application in Bulk Heterojunction Organic Solar Cells. CHEMISTRY OF MATERIALS, 21(21), 5327-5334
Open this publication in new window or tab >>Benzothiadiazole-Based Linear and Star Molecules: Design, Synthesis, and Their Application in Bulk Heterojunction Organic Solar Cells
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2009 (English)In: CHEMISTRY OF MATERIALS, ISSN 0897-4756, Vol. 21, no 21, p. 5327-5334Article in journal (Refereed) Published
Abstract [en]

Star molecules have many advantages, such as monodispersity, excellent solubility, and vast structures with different functional groups. A set of four-arm star molecules with benzothiadiazole as the core, oligothiophene its the arm, and triphenylamine its the end group and their linear counterparts were designed and synthesized Organic solar cells (OSCs) fabricated with these star molecules and [6,6]-phenyl C-71 butyric acid methyl ester (PC71BM) by spin-coating from solution demonstrate similar short circuit current density (J(sc)) and fill factor (FF) but larger open circuit voltage (V-oc) in comparison With solar cells fabricated with corresponding linear molecules and PC71BM A power conversion efficiency (PCE) of 18%, with J(sc) = 4.9 mA/cm(2), V-oc = 0 92 V, and FF = 0 41 was achieved with one of these star molecules

National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-51779 (URN)10.1021/cm902611b (DOI)
Available from: 2009-11-18 Created: 2009-11-17 Last updated: 2015-05-18
Liu, X., Zhan, Y., Braun, S., Li, F. & Fahlman, M. (2009). Interfacial electronic properties of pentacene tuned by a molecular monolayer of C-60. Physical Review B. Condensed Matter and Materials Physics, 80(11), 115401-1-115401-7
Open this publication in new window or tab >>Interfacial electronic properties of pentacene tuned by a molecular monolayer of C-60
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2009 (English)In: Physical Review B. Condensed Matter and Materials Physics, ISSN 1098-0121, E-ISSN 1550-235X, Vol. 80, no 11, p. 115401-1-115401-7Article in journal (Refereed) Published
Abstract [en]

Fine-tuning charge injection barriers between organic materials and electrodes is critical to optimize organic electronic device performance. Here we demonstrate that by modifying gold substrates with a monolayer of fullerene, significant decrease in the hole-injection barrier into pentacene films can be achieved. The insertion of the fullerene monolayer modifies the interfacial dipole and produces an interface where the pentacene molecules form a standing-up orientation with their long axis parallel to the surface normal. The latter effect lowers the vertical ionization energy of the pentacene molecules at the interface as compared to the pentacene-on-Au case, as well as improves the pi-pi overlap between the pentacene molecules that will likely enhance the transport properties in corresponding devices.

Place, publisher, year, edition, pages
College Park, MD, United States: American Physical Society, 2009
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-51266 (URN)10.1103/PhysRevB.80.115401 (DOI)000270383200113 ()
Available from: 2009-10-26 Created: 2009-10-26 Last updated: 2017-12-12Bibliographically approved
Zhou, Y., Li, F., Barrau, S., Tian, W., Inganäs, O. & Zhang, F. (2009). Inverted and transparent polymer solar cells prepared with vacuum-free processing. SOLAR ENERGY MATERIALS AND SOLAR CELLS, 93(4), 497-500
Open this publication in new window or tab >>Inverted and transparent polymer solar cells prepared with vacuum-free processing
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2009 (English)In: SOLAR ENERGY MATERIALS AND SOLAR CELLS, ISSN 0927-0248, Vol. 93, no 4, p. 497-500Article in journal (Refereed) Published
Abstract [en]

Inverted transparent polymer solar cells were fabricated by sequentially depositing several organic layers from fluids, on ITO/glass substrates. ITO was used as a cathode to collect electrons. The photovoltage of these diodes can be increased by up to 400 mV by inserting a buffer layer of polyethylene oxide between ITO and the active layers, which results in 4-fold enhancement of power conversion efficiency under the illumination of 100 mW/cm(2) simulated AM1.5 solar light. The enhancement of V., is consistent with the work function change between ITO and ITO/PEO measured by photoelectron spectroscopy. Solar cell production without vacuum processing may lower production costs.

Keyword
Inverted polymer solar cells, Vacuum-free processing, PEO, Open-circuit voltage
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-17695 (URN)10.1016/j.solmat.2008.11.002 (DOI)
Available from: 2009-04-16 Created: 2009-04-14 Last updated: 2015-06-01
Zhan, Y., Liu, X., Carlegrim, E., Li, F., Bergenti, I., Graziosi, P., . . . Fahlman, M. (2009). The role of aluminum oxide buffer layer in organic spin-valves performance. APPLIED PHYSICS LETTERS, 94(5), 053301
Open this publication in new window or tab >>The role of aluminum oxide buffer layer in organic spin-valves performance
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2009 (English)In: APPLIED PHYSICS LETTERS, ISSN 0003-6951, Vol. 94, no 5, p. 053301-Article in journal (Refereed) Published
Abstract [en]

The electronic structures of the 8-hydroxyquinoline-aluminum (Alq(3))/Al2O3/Co interfaces were studied by photoelectron spectroscopy. A strong interface dipole was observed, which leads to a reduction in the electron injection barrier. The x-ray photoelectron spectroscopy spectra further indicate that the Al2O3 buffer layer prevents the chemical interaction between Alq(3) molecules and Co atoms. X-ray magnetic circular dichroism results demonstrate that a Co layer deposited on an Al2O3 buffered Alq(3) layer shows better magnetic ordering in the interface region than directly deposited Co, which suggests a better performance of spin valves with such a buffer layer. This is consistent with the recent results from [Dediu , Phys. Rev. B 78, 115203 (2008)].

Keyword
alumina, buffer layers, charge injection, cobalt, electronic structure, ferromagnetic materials, magnetic circular dichroism, MIS structures, organic semiconductors, spin valves, X-ray photoelectron spectra
National Category
Natural Sciences
Identifiers
urn:nbn:se:liu:diva-16980 (URN)10.1063/1.3078274 (DOI)
Note

Original Publication:Yiqiang Zhan, Xianjie Liu, Elin Carlegrim, Fenghong Li, I Bergenti, P Graziosi, V Dediu and Mats Fahlman, The role of aluminum oxide buffer layer in organic spin-valves performance, 2009, APPLIED PHYSICS LETTERS, (94), 5, 053301.http://dx.doi.org/10.1063/1.3078274Copyright: American Institute of Physicshttp://www.aip.org/

Available from: 2009-03-06 Created: 2009-02-27 Last updated: 2015-05-18Bibliographically approved
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