| 1. |
- Charrier, Dimitri S. H., et al.
(författare)
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Real versus measured surface potentials in scanning Kelvin probe microscopy
- 2008
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Ingår i: ACS Nano. - : American Chemical Society. - 1936-0851 .- 1936-086X. ; 2:4, s. 622-626
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Tidskriftsartikel (refereegranskat)abstract
- Noncontact potentiometry or scanning Kelvin probe microscopy (SKPM) is a widely used technique to study charge injection and transport in (in)organic devices by measuring a laterally resolved local potential. This technique suffers from the significant drawback that experimentally obtained curves do not generally reflect the true potential profile in the device due to nonlocal coupling between the probing tip and the device. In this work, we quantitatively explain the experimental SKPM response and by doing so directly link theoretical device models to real observables. In particular, the model quantitatively explains the effects of the tip-sample distance and the dependence on the orientation of the probing tip with respect to the device.
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| 2. |
- Chr Germs, Wijnand, et al.
(författare)
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High-efficiency dielectrophoretic ratchet
- 2012
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Ingår i: Physical Review E. Statistical, Nonlinear, and Soft Matter Physics. - : American Physical Society. - 1539-3755 .- 1550-2376. ; 86:4
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Tidskriftsartikel (refereegranskat)abstract
- Brownian ratchets enable the use of thermal motion in performing useful work. They typically employ spatial asymmetry to rectify nondirected external forces that drive the system out of equilibrium (cf. running marbles on a shaking washboard). The major application foreseen for Brownian ratchets is high-selectivity fractionation of particle or molecule distributions. Here, we investigate the functioning of an important model system, the on/off ratchet forwater-suspended particles, in which interdigitated finger electrodes can be switched on and off to create a time-dependent, spatially periodic but asymmetric potential. Surprisingly, we find that mainly dielectrophoretic rather than electrophoretic forces are responsible for the ratchet effect. This has major implications for the (a) symmetry of the ratchet potential and the settings needed for optimal performance. We demonstrate that by applying a potential offset the ratchet can be optimized such that its particle displacement efficiency reaches the theoretical upper limit corresponding to the electrode geometry and particle size. Efficient fractionation based on size selectivity is therefore not only possible for charged species, but also for uncharged ones, which greatly expands the applicability range of this type of Brownian ratchet.
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| 3. |
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| 4. |
- Roeling, Erik M., et al.
(författare)
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Organic electronic ratchets doing work
- 2011
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Ingår i: Nature Materials. - : Nature Publishing Group. - 1476-1122 .- 1476-4660. ; 10:1, s. 51-55
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Tidskriftsartikel (refereegranskat)abstract
- The possibility to extract work from periodic, undirected forces has intrigued scientists for over a century-in particular, the rectification of undirected motion of particles by ratchet potentials, which are periodic but asymmetric functions. Introduced by Smoluchowski and Feynman(1,2) to study the (dis)ability to generate motion from an equilibrium situation, ratchets operate out of equilibrium, where the second law of thermodynamics no longer applies. Although ratchet systems have been both identified in nature(3,4) and used in the laboratory for the directed motion of microscopic objects(5-9), electronic ratchets(10-13) have been of limited use, as they typically operate at cryogenic temperatures and generate subnanoampere currents and submillivolt voltages(10-14). Here, we present organic electronic ratchets that operate up to radio frequencies at room temperature and generate currents and voltages that are orders of magnitude larger. This enables their use as a d.c. power source. We integrated the ratchets into logic circuits, in which they act as the d.c. equivalent of the a. c. transformer, and generate enough power to drive the circuitry. Our findings show that electronic ratchets may be of actual use.
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| 5. |
- Roeling, Erik M., et al.
(författare)
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Scaling of characteristic frequencies of organic electronic ratchets
- 2012
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - : American Physical Society. - 1098-0121 .- 1550-235X. ; 85:4
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Tidskriftsartikel (refereegranskat)abstract
- The scaling of the characteristic frequencies of electronic ratchets operating in a flashing mode is investigated by measurements and numerical simulations. The ratchets are based on organic field effect transistors operated in accumulation mode. Oscillating potentials applied to asymmetrically spaced interdigitated finger electrodes embedded in the gate dielectric create a time-dependent, spatially asymmetric perturbation of the transistor channel potential. As a result, a net dc current can flow between source and drain despite zero source-drain bias. The frequency at current maximum is linearly dependent on the charge carrier density and the charge carrier mobility and inversely proportional to the squared length of the ratchet period, which can be related to the RC time of one asymmetric unit. Counterintuitively, it is independent of driving amplitude. Furthermore, the frequency at current maximum depends on the asymmetry of the ratchet potential, whereas the frequency of maximum charge pumping efficiency does not.
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| 6. |
- Roeling, Erik M., et al.
(författare)
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The performance of organic electronic ratchets
- 2012
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Ingår i: AIP Advances. - : American Institute of Physics (AIP): Open Access Journals / AIP Publishing LLC. - 2158-3226. ; 2:1
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Tidskriftsartikel (refereegranskat)abstract
- Organic electronic ratchets rectify time-correlated external driving forces, giving output powers that can drive electronic circuitry. In this work their performance characteristics are investigated using numerical modeling and measurements. It is shown how the characteristic parameters of the time-varying asymmetric potential like length scales and amplitude, as well as the density and mobility of the charge carriers in the device influence the performance characteristics. Various ratchet efficiencies and their relations are discussed. With all settings close to optimum, a ratchet with charge displacement and power efficiencies close to 50% and 7% respectively is obtained. Copyright 2012 Author(s). This article is distributed under a Creative Commons Attribution 3.0 Unported License. [doi:10.1063/1.3677934]
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