| 1. |
- Mantovani Nardes, Alexandre, et al.
(författare)
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Microscopic understanding of the anisotropic conductivity of PEDOT : PSS thin films
- 2007
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Ingår i: Advanced Materials. - : Wiley-VCH Verlag. - 0935-9648 .- 1521-4095. ; 19:9, s. 1196-
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Tidskriftsartikel (refereegranskat)abstract
- The amsotropic conductivity of thin films of poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) is correlated to the film morphology as obtained from scanning tunneling and atomic force microscopy images. The material was found to consist of layers of flattened PEDOT-rich particles that are separated by quasi-continuous PSS lamella (see figure).
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| 2. |
- Huijbregts, L. J., et al.
(författare)
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The optimal structure-conductivity relation in epoxy-phthalocyanine nanocomposites
- 2006
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Ingår i: Journal of Physical Chemistry B. - : American Chemical Society. - 1520-6106 .- 1520-5207. ; 110:46, s. 23115-23122
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Tidskriftsartikel (refereegranskat)abstract
- Phthalcon-11 (aquocyanophthalocyaninatocobalt (III)) forms semiconducting nanocrystals that can be dispersed in epoxy coatings to obtain a semiconducting material with a low percolation threshold. We investigated the structure-conductivity relation in this composite and the deviation from its optimal realization by combining two techniques. The real parts of the electrical conductivity of a Phthalcon-11/ epoxy coating and of Phthalcon-11 powder were measured by dielectric spectroscopy as a function of frequency and temperature. Conducting atomic force microscopy (C-AFM) was applied to quantify the conductivity through the coating locally along the surface. This combination gives an excellent tool to visualize the particle network. We found that a large fraction of the crystals is organized in conducting channels of fractal building blocks. In this picture, a low percolation threshold automatically leads to a conductivity that is much lower than that of the filler. Since the structure-conductivity relation for the found network is almost optimal, a drastic increase in the conductivity of the coating cannot be achieved by changing the particle network, but only by using a filler with a higher conductivity level.
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| 3. |
- Janssen, P., et al.
(författare)
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Tuning organic magnetoresistance in polymer-fullerene blends by controlling spin reaction pathways
- 2013
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Ingår i: Nature Communications. - : Nature Publishing Group: Nature Communications. - 2041-1723. ; 4
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Tidskriftsartikel (refereegranskat)abstract
- Harnessing the spin degree of freedom in semiconductors is generally a challenging, yet rewarding task. In recent years, the large effect of a small magnetic field on the current in organic semiconductors has puzzled the young field of organic spintronics. Although the microscopic interaction mechanisms between spin-carrying particles in organic materials are well understood nowadays, there is no consensus as to which pairs of spin-carrying particles are actually influencing the current in such a drastic manner. Here we demonstrate that the spin-based particle reactions can be tuned in a blend of organic materials, and microscopic mechanisms are identified using magnetoresistance lineshapes and voltage dependencies as fingerprints. We find that different mechanisms can dominate, depending on the exact materials choice, morphology and operating conditions. Our improved understanding will contribute to the future control of magnetic field effects in organic semiconductors.
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| 4. |
- Nardes, A. M., et al.
(författare)
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Conductivity, work function, and environmental stability of PEDOT : PSS thin films treated with sorbitol
- 2008
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Ingår i: Organic electronics. - : Elsevier. - 1566-1199 .- 1878-5530. ; 9:5, s. 727-734
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Tidskriftsartikel (refereegranskat)abstract
- The electrical properties of poly(3,4-ethylenedioxythiophene):poly(4-styrenesulfonate) (PEDOT:PSS) thin films deposited from aqueous dispersion using different concentrations of sorbitol have been studied in detail. Although it is well known that sorbitol enhances the conductivity of PEDOT:PSS thin films by three orders of magnitude, the origin and consequences of sorbitol treatment are only partly understood and subject of further study. By thermal annealing of spin coated PEDOT:PSS/sorbitol films and simultaneously monitoring the conductivity, we demonstrate that the strong increase in conductivity coincides with evaporation of sorbitol from the film. Hence, sorbitol is a processing additive rather than a (secondary) dopant. Scanning Kelvin probe microscopy reveals that sorbitol treatment causes a reduction of the work function from 5.1 eV to 4.8-4.9 eV. Sorbitol also influences the environmental stability of the films. While the conductivity of the pristine PEDOT:PSS films increases by about one order of magnitude at similar to 50% RH due to an ionic contribution to the overall conductivity, films prepared using sorbitol exhibit an increased environmental stability with an almost constant conductivity up to 45% RH and a slight decrease at 50% RH. The higher stability results from a reduced tendency to take up water from the air, which is attributed to a denser packing of the PEDOT:PSS after sorbitol treatment. (C) 2008 Elsevier B.V. All rights reserved.
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| 5. |
- Spijkman, M., et al.
(författare)
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Monolayer dual gate transistors with a single charge transport layer
- 2010
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Ingår i: Applied Physics Letters. - : American Institute of Physics (AIP). - 0003-6951 .- 1077-3118. ; 96:14
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Tidskriftsartikel (refereegranskat)abstract
- A dual gate transistor was fabricated using a self-assembled monolayer as the semiconductor. We show the possibility of processing a dielectric on top of the self-assembled monolayer without deteriorating the device performance. The two gates of the transistor accumulate charges in the monomolecular transport layer and artifacts caused by the semiconductor thickness are negated. We investigate the electrical transport in a dual gate self-assembled monolayer field-effect transistor and present a detailed analysis of the importance of the contact geometry in monolayer field-effect transistors.
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| 6. |
- Cox, M., et al.
(författare)
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Spectroscopic evidence for trap-dominated magnetic field effects in organic semiconductors
- 2014
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - : American Physical Society. - 1098-0121 .- 1550-235X. ; 90:15
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Tidskriftsartikel (refereegranskat)abstract
- Polaron traps are ubiquitous in organic semiconductors and recent evidence suggests they might be crucial for the large observed magnetic field effects (MFEs) in organic semiconductors. Here we measure MFEs in polymer thin-film devices with engineered, radiative trap sites in order to spectroscopically investigate the influence of the traps. Surprisingly, the luminescence at the trap sites and the polymer backbone is found to have an opposite response to a magnetic field. All our results are compatible with a mechanism in which spin mixing at the traps can create the large MFEs observed on the backbone. This scenario is quantitatively confirmed by numerical drift-diffusion modeling with magnetic-field-dependent exciton densities at the traps. These insights solve an outstanding controversy within the research field.
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| 7. |
- Cox, M., et al.
(författare)
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The influence of device physics on organic magnetoresistance
- 2013
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Ingår i: Synthetic metals. - : Elsevier. - 0379-6779 .- 1879-3290. ; 173, s. 10-15
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Tidskriftsartikel (refereegranskat)abstract
- In order to explain the surprisingly large, low field organic magnetoresistance (OMAR), several microscopic mechanisms have been proposed recently, but their effect on the polaron transport through a realistic device is relatively unknown. Here we study the effect of device physics on all proposed mechanisms, using a numerical drift-diffusion simulation method. We implement the local magnetic field dependent reactions via a magnetic field dependent recombination, mobility and triplet formation rate. Furthermore, a novel approach is used where we keep track of the subsequent particles formed from these reactions, including excitons and trions. We find that even in the most straightforward device structure sign changes can occur due to device physics. Especially the transition from a diffusion dominated to a drift dominated current near the built-in voltage plays a crucial role for understanding organic magnetoresistance. Finally, we conclude that the shape of the magnetocurrent as a function of voltage can be used as a fingerprint for the underlying dominant microscopic mechanism governing OMAR in a device. (c) 2012 Elsevier B.V. All rights reserved.
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| 8. |
- Kemerink, Martijn, et al.
(författare)
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Characteristics of a First-Generation X-Ray System
- 2011
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Ingår i: Radiology. - : Radiological Society of North America (RSNA). - 0033-8419 .- 1527-1315. ; 259:2, s. 534-539
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Tidskriftsartikel (refereegranskat)abstract
- Purpose: To compare the antiquated x-ray system of Hoffmans and van Kleef (circa 1896) with modern x-ray equipment in terms of radiation dose, x-ray beam properties, image quality, and electrical parameters. Materials and Methods: The antiquated x-ray system consisted of a Ruhmkorff inductor, battery, and Crookes tube. The radiation dose rate, x-ray beam properties, and electrical characteristics of this system were determined. A modern computed radiography plate was used to compare images of a hand specimen obtained by using the antiquated system with images obtained by using the modern system. Results: A peak voltage of 73 kV was obtained with an 8-V battery. With Crookes tube number 9, the half-value layer of the generated x-rays was 0.56 mm Al. Pinhole images showed that the x-rays originated from an extended area of the glass wall, causing image blurring. When measured on the skin of a hand specimen, the radiation dose of the antiquated system was about 10 times greater than that of the modern system for the same detector signal. The estimated skin dose was about 74 mGy for the antiquated system and 0.05 mGy for the modern system. The corresponding exposure times were 90 minutes and 21 msec. Conclusion: Radiation dose and exposure time of the antiquated system were greater than those of the modern system by about three and five orders of magnitude, respectively. Images of the hand specimen obtained with the antiquated system were severely blurred but were still awe inspiring, considering the simplicity of the system. (C)RSNA, 2011
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| 9. |
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| 10. |
- Kemerink, M., et al.
(författare)
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Temperature- and density-dependent channel potentials in high-mobility organic field-effect transistors
- 2009
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - : American Physical Society. - 1098-0121 .- 1550-235X. ; 80:11
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Tidskriftsartikel (refereegranskat)abstract
- The density-dependent charge-carrier mobility in high-mobility organic field-effect transistors is investigated by simultaneous measurements of the channel potential and the transfer characteristics. By working under ultrahigh-vacuum conditions extrinsic effects due to H(2)O traces could be eliminated. The shape of the channel potential is inconsistent with a density-independent mobility. We find that the variable range hopping model as derived by Vissenberg and Matters for an exponential density of states [Phys. Rev. B 57, 12964 (1998)] consistently describes the data.
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