| 1. |
- Aarnio, H, et al.
(författare)
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Recombination studies in a polyfluorene copolymer for photovoltaic applications
- 2005
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Ingår i: Synthetic Metals. - Elsevier B.V.. - 0379-6779. ; 155:2, s. 299-302
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Tidskriftsartikel (refereegranskat)abstract
- We present detailed continuous wave (cw) and transient photoinduced absorption (PA) measurements in thin films of a novel alternating polyfluorene copolymer, poly2,7-(9,9-dioctyl-fluorene)-alt-5,5-(4′,7′-di-2-thienyl-2′,1′,3-benzo-thiadiazole) (DiO-PFDTBT), and its blends with the soluble fullerene derivative 6,6-phenyl-C61-butyric acid methyl ester (PCBM) in weight ratios of 1:0, 4:1 and 1:4. We measure the frequency, intensity and temperature dependence of the PA signal in the frequency domain, and compare with the results obtained from the transient PA decay measurements in the time domain. In all blends, the PA spectrum shows a broad high energy PA band ranging from 1 eV to 2 eV as well as a low energy band peaking at 0.35 eV. We attribute the low energy band to the P1 transition of polarons and part of the high energy band to the correlated P2 transition of polarons. Both frequency and time domain measurements show that the high energy band has two decay components, a faster component in the microsecond time regime and a slower component in the millisecond time regime. The slow component is strongly dispersive, whereas the fast component is practically non-dispersive.
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| 2. |
- Abay, Simon, et al.
(författare)
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High Critical-Current Superconductor-InAs Nanowire-Superconductor Junctions
- 2012
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Ingår i: Nano letters. - 1530-6984. ; 12:11, s. 5622-5625
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Tidskriftsartikel (refereegranskat)abstract
- We report on the fabrication of InAs nanowires coupled to superconducting leads with high critical current and widely tunable conductance. We implemented a double lift off nanofabrication Method to get very short nanowire devices with Ohmic contacts. We observe very high critical. currents of up to 800 nA in a wire with a diameter of 80 nm. The current- voltage characteristics of longer and suspended nanowires display,either. Coulomb blockade or supercurrent depending on a local gate voltage, combining different regimes of transport in a single device.
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| 3. |
- Abrahmsen-Alami, S., et al.
(författare)
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New release cell for NMR microimaging of tablets Swelling and erosion of poly(ethylene oxide)
- 2007
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Ingår i: International Journal of Pharmaceutics. - 0378-5173. ; 342:1-2, s. 105-114
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Tidskriftsartikel (refereegranskat)abstract
- A small release cell, in the form of a rotating disc, has been constructed to fit into the MRI equipment. The present work show that both qualitative and quantitative information of the swelling and erosion behavior of hydrophilic extended release (ER) matrix tablets may be obtained using this release cell and non-invasive magnetic resonance imaging (MRI) studies at different time-points during matrix dissolution. The tablet size, core size and the gel layer thickness of ER matrix formulations based on poly(ethylene oxide) have been determined. The dimensional changes as a function of time were found to correspond well to observations made with texture analysis (TA) methodology. Most importantly, the results of the present study show that both the erosion (displacement of the gel-dissolution media interface) and the swelling (decrease of dry tablet core size) proceed with a faster rate in radial than in axial direction using the rotating disk set-up. This behavior was attributed to the higher shear forces experienced in the radial direction. The results also indicate that front synchronization (constant gel layer thickness) is associated with the formation of an almost constant polymer concentration profile through the gel layer at different time-points. (c) 2007 Elsevier B.V. All rights reserved.
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| 4. |
- Adebahr, Josefina, 1973-, et al.
(författare)
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Cation coordination in ion conducting gels based on PEO-grafted polymers
- 2000
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Ingår i: Solid State Ionics. - 0167-2738. ; 135:1-4, s. 149-154
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Tidskriftsartikel (refereegranskat)abstract
- Ionic conducting polymer gels prepared from PEG-grafted acrylates, ethylene carbonate (EC), dimethyl carbonate (DMC), and LiPF6 are studied by means of infrared and Raman spectroscopy. It is found that the presence of grafted PEO chains substantially changes the coordination of lithium cations from 'cation-solvent' to 'cation-polymer'. Spectroscopic studies show that Li+-PEO coordination is strongly favored in competition with the solvent molecules and dominates completely at ether oxygen to Li-cation ratios (O:Li) of 10:1 and 5:1. At an O:M of 4:1 a solvent-cation interaction arises, in agreement with previously reported MD calculations of a preferred coordination number of 5 in similar systems. The results suggest that the complex interactions which determine long time stability and ionic transport properties can be designed by functionalization of the polymer backbone in PMMA-based gel electrolytes.
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| 5. |
- Adebahr, J, et al.
(författare)
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Ion and solvent dynamics in gel electrolytes based on ethylene oxide grafted acrylate polymers
- 2002
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Ingår i: Journal of Physical Chemistry B. - 1089-5647. ; 106:47, s. 12119-12123
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Tidskriftsartikel (refereegranskat)abstract
- Multinuclear pulsed field gradient NMR measurements and theological viscosity measurements were performed on three series of polymer gel electrolytes. The gels were based on a lithium salt electrolyte swollen into a copolymer matrix comprising an acrylate backbone and ethylene oxide side chains. In each series the side chains differed in length and number, but the acrylate-to-ethylene oxide ratio was kept constant. It was found that the self-diffusion coefficient of the cations was much lower than that of the anions, and that it decreased rapidly when the side chains got longer. In contrast, the self-diffusion coefficient of the anions was found to be independent of chain length. In the gel electrolytes, the diffusion coefficients of the solvent molecules are relatively constant despite an increased viscosity with increasing length of the side chains. However, in saltfree gels made for comparison, the diffusion coefficients of the solvent molecules decreased with, increasing length of the side chains, which is consistent with an increased viscosity.
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| 6. |
- Adebahr, J, et al.
(författare)
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Lithium coordination and mobility in gel electrolytes based on an acrylate polymer with ethylene oxide side chains
- 2003
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Ingår i: Journal of Materials Chemistry. - 0959-9428. ; 13:4, s. 814-817
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Tidskriftsartikel (refereegranskat)abstract
- Multinuclear NMR has been used to investigate the structure and mobility of a series of polymer gel electrolytes. The co-polymers used as matrixes in the gels have acrylate backbones and side chains of ethylene oxide, where the length of the side chains has been varied, while the ratio of acrylate to ethylene oxide has been kept constant. The electrolyte is a mixture of lithium perchlorate and two solvents, ethylene carbonate and gamma butyrolactone. 13C spectra of the different gel electrolytes shows that both solvents interact with the salt, and that the strength of the interaction increases with decreasing length of the polymer side chains. It also appears that the lithium ions show no selectivity between the two types of solvent. Furthermore, the lithium chemical shift moves progressively upfield with increasing length of the side chains, showing a gradual change in interaction from lithium–solvent to lithium–(ethylene oxide).
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| 7. |
- Adell, Johan, 1980-, et al.
(författare)
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Electron spectroscopic studies of nanowires formed by (GaMn)As growth on GaAs(111)B
- 2011
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Ingår i: Solid State Communications. - 0038-1098. ; 151:11, s. 850-854
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Tidskriftsartikel (refereegranskat)abstract
- Valence band photoemission with photon energies around the Mn2p excitation threshold has been used to study the development of nanowires catalyzed by MnAs particles. A gradual change in the spectra with increasing nanowire length is observed, such that the resonant photoemission eventually dominates over the Auger decay channel. The change is ascribed to dilution of Mn, showing that Mn is transferred from the MnAs particles into the nanowires. (C) 2011 Elsevier Ltd. All rights reserved.
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| 8. |
- Adell, Johan, 1980-, et al.
(författare)
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Formation of epitaxial MnBi layers on (Ga,Mn)As
- 2009
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Ingår i: Physical Review B. - American Physical Society. - 1098-0121. ; 80:7, s. 075204
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Tidskriftsartikel (refereegranskat)abstract
- The initial growth of MnBi on MnAs-terminated (GaMn)As is studied by means of synchrotron-based photoelectron spectroscopy. From analysis of surface core-level shifts we conclude that a continued epitaxial MnBi layer is formed, in which the MnAs/MnBi interface occurs between As and Bi atomic planes. The well-defined 1×2 surface reconstruction of the MnAs surface is preserved for up to 2 ML of MnBi before clear surface degradation occurs. The MnBi layer appears to be free from intermixed As.
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| 9. |
- Adell, J., et al.
(författare)
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Thermal diffusion of Mn through GaAs overlayers on (Ga, Mn)As
- 2011
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Ingår i: Journal of Physics: Condensed Matter. - 0953-8984. ; 23:8
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Tidskriftsartikel (refereegranskat)abstract
- Thermally stimulated diffusion of Mn through thin layers of GaAs has been studied by x-ray photoemission. (Ga, Mn) As samples with 5 at% Mn were capped with 4, 6 and 8 monolayer (ML) GaAs, and Mn diffusing through the GaAs was trapped on the surface by means of amorphous As. It was found that the out-diffusion is completely suppressed for an 8 ML thick GaAs film. The short diffusion length is attributed to an electrostatic barrier formed at the (Ga, Mn) As/GaAs interface.
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| 10. |
- Adell, M, et al.
(författare)
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Photoemission studies of the annealing-induced modifications of Ga0.95Mn0.05As
- 2004
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Ingår i: Physical Review B. - American Physical Society. - 1098-0121. ; 70:12: 125204
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Tidskriftsartikel (refereegranskat)abstract
- Using angle resolved photoemission we have investigated annealing-induced changes in Ga1-xMnxAs with x=0.05. We find that the position of the Fermi energy is a function of annealing time and temperature. It is also established that the Curie temperature is strongly correlated to the separation between the Fermi level and the valence band maximum. Valence band photoemission shows that the Mn3d spectrum is modified by the annealing treatments.
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