| 1. |
- Roelofs, W. S. C., et al.
(författare)
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Fast ambipolar integrated circuits with poly(diketopyrrolopyrrole-terthiophene)
- 2011
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Ingår i: Applied Physics Letters. - : American Institute of Physics (AIP). - 0003-6951 .- 1077-3118. ; 98:20
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Tidskriftsartikel (refereegranskat)abstract
- Ambipolar integrated circuits were prepared with poly (diketopyrrolopyrrole-terthiophene) as the semiconductor. The field-effect mobility of around 0.02 cm(2)/V s for both electrons and holes allowed for fabrication of functional integrated complementary metal-oxide semiconductor (CMOS)-like inverters and ring oscillators. The oscillation frequency was found to have a near quadratic dependence on the supply bias. The maximum oscillation frequency was determined to be 42 kHz, which makes this ring oscillator the fastest CMOS-like organic circuit reported to date. (C) 2011 American Institute of Physics. [doi: 10.1063/1.3589986]
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| 2. |
- Germs, W. Chr., et al.
(författare)
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Charge transport in amorphous InGaZnO thin-film transistors
- 2012
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - : American Physical Society. - 1098-0121 .- 1550-235X. ; 86:15
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Tidskriftsartikel (refereegranskat)abstract
- We investigate the mechanism of charge transport in indium gallium zinc oxide (a-IGZO), an amorphous metal-oxide semiconductor. We measured the field-effect mobility and the Seebeck coefficient (S = Delta V/Delta T) of a-IGZO in thin-film transistors as a function of charge-carrier density for different temperatures. Using these transistors, we further employed a scanning Kelvin probe-based technique to determine the density of states of a-IGZO that is used as the basis for the modeling. After comparing two commonly used models, the band transport percolation model and a mobility edge model, we find that both cannot describe the full properties of the charge transport in the a-IGZO semiconductor. We, therefore, propose a model that extends the mobility edge model to allow for variable range hopping below the mobility edge. The extended mobility edge model gives a superior description of the experimental results. We show that the charge transport is dominated by variable range hopping below, rather than by bandlike transport above the mobility edge.
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| 3. |
- Fitie, Carel F. C., et al.
(författare)
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Polar Switching in Trialkylbenzene-1,3,5-tricarboxamides
- 2012
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Ingår i: Journal of Physical Chemistry B. - : American Chemical Society. - 1520-6106 .- 1520-5207. ; 116:13, s. 3928-3937
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Tidskriftsartikel (refereegranskat)abstract
- The hydrogen-bonded hexagonal columnar LC (Col(hd)) phases formed by benzene-1,3,5-tricarboxamide (BTA) derivatives can be aligned uniformly by an electric field and display switching behavior with a high remnant polarization. The polar switching in three symmetrically substituted BTAs with alkyl chains varying in length between 6 and 18 carbon atoms (C6, C10, and C18) was investigated by electro-optical switching experiments, dielectric relaxation spectroscopy (DRS), and solid-state NMR The goal was to characterize ferroelectric properties of BTA-based columnar LCs, which display a macroscopic axial dipole moment due to the head-to-tail stacking of hydrogen-bonded amides. The Col(hd) phase of all three BTAs can be aligned uniformly by a dc field similar to 30 V/mu m. Moreover, C10 and C18 display extrinsic polar switching characterized by a remnant polarization and coercive field of 1-2 mu C/cm(2) and 20-30 V/mu m, respectively. In the absence of an external field, the polarization is lost in 1-1000 s, depending on device details and temperature. DRS revealed a columnar glass transition in the low-temperature region of the LC phase related to collective vibrations in the hydrogen-bonded columns that freeze out below 41-54 degrees C. At higher temperatures, a relaxation process is present originating from the collective reorientation of amide groups along the column axis (inversion of the macrodipole). Matching activation energies suggest that the molecular mechanism underlying the polar switching and the R-processes is identical. These results illustrate that LC phases based on BTAs offer the unique possibility to integrate polarization with other functionalities in a single nanostructured material.
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| 4. |
- Roelofs, W. S. C., et al.
(författare)
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Accurate description of charge transport in organic field effect transistors using an experimentally extracted density of states
- 2012
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Ingår i: Physical Review B. Condensed Matter and Materials Physics. - : American Physical Society. - 1098-0121 .- 1550-235X. ; 85:8
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Tidskriftsartikel (refereegranskat)abstract
- The width and shape of the density of states (DOS) are key parameters to describe the charge transport of organic semiconductors. Here we extract the DOS using scanning Kelvin probe microscopy on a self-assembled monolayer field effect transistor (SAMFET). The semiconductor is only a single monolayer which has allowed extraction of the DOS over a wide energy range, pushing the methodology to its fundamental limit. The measured DOS consists of an exponential distribution of deep states with additional localized states on top. The charge transport has been calculated in a generic variable range-hopping model that allows any DOS as input. We show that with the experimentally extracted DOS an excellent agreement between measured and calculated transfer curves is obtained. This shows that detailed knowledge of the density of states is a prerequisite to consistently describe the transfer characteristics of organic field effect transistors.
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| 5. |
- Fitie, Carel F. C., et al.
(författare)
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Remnant Polarization in Thin Films from a Columnar Liquid Crystal
- 2010
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Ingår i: Journal of the American Chemical Society. - : American Chemical Society. - 0002-7863 .- 1520-5126. ; 132:20, s. 6892-
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Tidskriftsartikel (refereegranskat)abstract
- Ferroelectric switching is demonstrated in a hydrogen bonded columnar liquid crystalline (LC) material. Polar order induced in the LC phase can be frozen by crystallization of the alkyl chains in the periphery of the columns yielding thin films with remnant polarization and an unprecedented high surface potential as shown by scanning Kelvin probe microscopy.
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