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Journal ArticleDOI

Optical anisotropy of aligned pentacene molecules on a rubbed polymer corresponding to the electrical anisotropy

01 Jan 2010-Current Applied Physics (North-Holland)-Vol. 10, Iss: 1, pp 64-67
TL;DR: In this paper, the optical anisotropic properties of a pentacene film on a rubbed polyvinylalcohol (PVA) layer were investigated and the electrical performances of the OFETs were correlated with the optical properties of the PVA layer.
About: This article is published in Current Applied Physics.The article was published on 2010-01-01. It has received 14 citations till now. The article focuses on the topics: Pentacene & Anisotropy.
Citations
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Journal ArticleDOI
TL;DR: In this article, a method of strain-aligning polymer films is introduced and applied to regioregular poly(3-hexylthiophene) (P3HT), showing several important features of charge transport.
Abstract: A novel method of strain-aligning polymer films is introduced and applied to regioregular poly(3-hexylthiophene) (P3HT), showing several important features of charge transport. The polymer backbone is shown to align in the direction of applied strain resulting in a large charge-mobility anisotropy, where the in-plane mobility increases in the applied strain direction and decreases in the perpendicular direction. In the aligned film, the hole mobility is successfully represented by a two-dimensional tensor, suggesting that charge transport parallel to the polymer backbone within a P3HT crystal is strongly favored over the other crystallographic directions. Hole mobility parallel to the backbone is shown to be high for a mixture of plane-on and edge-on packing configurations, as the strain alignment is found to induce a significant face-on orientation of the originally highly edge-on oriented crystalline regions of the film. This alignment approach can achieve an optical dichroic ratio of 4.8 and a charge-mobility anisotropy of 9, providing a simple and effective method to investigate charge-transport mechanisms in polymer semiconductors.

286 citations

Journal ArticleDOI
TL;DR: In this article, the properties of zinc oxide thin films on soda-lime glass substrate via dip-coating technique, using zinc acetate dehydrate and ethanol as raw materials, have been investigated using XRD, SEM and UV-Vis spectrophotometer.

26 citations

Journal ArticleDOI
TL;DR: In this article, the authors systematically studied how the mobility in a pentacene thin-film transistor (TFT) with an anisotropic polymeric insulator is decisively dependent on the deposition rate of Pentacene molecules.
Abstract: We systematically studied how the mobility in a pentacene thin-film transistor (TFT) with an anisotropic polymeric insulator is decisively dependent on the deposition rate of pentacene molecules. This occurs from the view point of both the morphological coverage and optical phase retardation. Until a value of 2 A/s, as the deposition rate increases, the alignment of pentacene molecules, examined by optical retardation improves due to the guaranteed diffusion process for more stable positioning and an improved packing density at an early stage. The corresponding mobility is found to be proportional to the deposition rate in this regime. For increased deposition rates above 2 A/s, due to the shortage of diffusion processing time, evaporating pentacene molecules damage the pre-deposited and pre-aligned pentacene molecules on the anisotropic insulator. Thus, the optical retardation starts to decrease definitely when the early stage packing density is saturated. The resultant mobility is found to be inversely proportional to the deposition rate. Based on the morphological, optical results and the corresponding mobility, we confirm that the deposition rate of an organic semiconductor has a critical effect on the structural orientation, the molecular growth, and the resultant mobility in organic TFTs.

14 citations


Cites background or methods from "Optical anisotropy of aligned penta..."

  • ...Recently, the alignment of pentacene molecules along the rubbed direction of polymers was reported [8,9,22]....

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  • ...In order to determine the optical anisotropy, which represents the degree of alignment capability, a photoelastic modulator (PEM) (Hinds, PEM-90) was used [22]....

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  • ...In order to generate the anisotropic property, a rubbing process for the PVA layer was conducted by a commercial rubbing machine with a cotton velvet material at a roller speed of 500 rpm [22]....

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  • ...In addition, the PEM method was recently introduced as a new technique to examine the aligning features of pentacene molecules [22]....

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Journal ArticleDOI
TL;DR: In this article, the authors report on the enhancement of the field-effect mobility of solution-processed 6,13-bis(triisopropylsilylethynyl)-pentacene by unidirectional topography (UT) of an inkjet-printed polymer insulator.
Abstract: We report on the enhancement of the field-effect mobility of solution-processed 6,13-bis(triisopropylsilylethynyl)-pentacene (TIPS-pentacene) by unidirectional topography (UT) of an inkjet-printed polymer insulator. The UT leads to anisotropic spreading and drying of the TIPS-pentacene droplet and enables to spontaneously develop the ordered structures during the solvent evaporation. The mobility of the UT-dictated TIPS-pentacene film (0.202 ± 0.012 cm2/Vs) is found to increase by more than a factor of two compared to that of the isotropic case (0.090 ± 0.032 cm2/Vs). The structural arrangement of the TIPS-pentacene molecules in relation to the mobility enhancement is described within an anisotropic wetting formalism. Our UT-based approach to the mobility enhancement is easily applicable to different classes of soluble organic field-effect transistors by adjusting the geometrical parameters such as the height, the width, and the periodicity of the UT of an inkjet-printed insulator.

10 citations

References
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Journal ArticleDOI
TL;DR: In this paper, the contribution of van der Waals force to the azimuthal anchoring energy in a pentyl cyanobiphenyl (5CB)/PVCi system was investigated.
Abstract: The photopolymer material of poly(vinyl cinnamate) (PVCi) has been used to investigate the contribution of the anisotropic van der Waals force to the azimuthal anchoring energy in a pentyl cyanobiphenyl (5CB)/PVCi system. The optical anisotropy of a PVCi film is precisely controlled by varying the exposure time of linearly polarized UV light, and the azimuthal anchoring energy in the film is estimated by measuring the width of the Neel wall. The result shows that the azimuthal anchoring energy in the 5CB/PVCi system increases exponentially with increasing optical anisotropy, indicating the existence of additional contributions to the LC alignment.

74 citations

Journal ArticleDOI
TL;DR: In this paper, a thin polymethylmetacrylate (PMMA) buffer layer has been employed in order to fabricate high-quality pentacene thin-film transistors (TFTs), both in bottom contact and top contact configuration.
Abstract: A thin film of polymethylmetacrylate (PMMA) acting as a buffer layer has been employed in order to fabricate high-quality pentacene thin-film transistors (TFTs), both in bottom contact and top contact configuration. A PMMA buffer layer allows to reduce the interaction between a π-conjugated system of pentacene and the metal or dielectric substrate. We show that a thin PMMA buffer layer improves crystal quality along the metal contacts’ boundaries, while still allowing good ohmic contact. Pentacene TFTs, including a PMMA buffer layer, show very high field-effect mobility, μFE=0.65 and 1.4cm2∕Vs, for bottom and top contact configuration, respectively, and remarkable steep subthreshold region.

73 citations

Journal ArticleDOI
TL;DR: In this paper, an enhanced and anisotropic field-effect mobility of thin-film transistors based on pentacene was obtained on a substrate covered with a prerubbed, self-assembled monolayer (SAM) of n-alkyltrichlorosilane.
Abstract: Enhanced and anisotropic field-effect mobility of thin-film transistors based on pentacene was obtained on a substrate covered with a prerubbed, self-assembled monolayer (SAM) of n-alkyltrichlorosilane. The field-effect mobility along the rubbing direction increased by a factor of ∼15 on rubbed n-nonyltrichlorosilane-modified surface, whereas on n-octadecyltrichlorosilane-modified surface, an increase by a factor of 2–4 was observed. The structures of pentacene films deposited on the SAM/rubbed SAM were characterized by powder x-ray diffraction, atomic force microscopy, and carbon K-edge near edge x-ray fine structure spectroscopy. An in-plane alignment effect on the pentacene packing and film morphology is proposed.

58 citations

Journal ArticleDOI
TL;DR: In this article, the authors investigated preferentially oriented pentacene grains on rubbed polyimide (PI) layers under various conditions, such as substrate temperature and cumulative rubbing number.
Abstract: We investigated preferentially oriented pentacene grains on rubbed polyimide (PI) layers under various conditions, such as substrate temperature and cumulative rubbing number. In case of pentacene thin films deposited on rubbed PI at room temperature (RT), compared to unrubbed, the field-effect mobilities were improved by two- to threefold in contrast to the cases of elevated temperature. From the results of crystalline in-plane orientation and thin-film versus bulk-phase ratio, we proposed that pentacence crystalline orientation on a rubbed PI layer could be more favorable at RT, whereas the heating energy might weaken the interaction energy between pentacene molecules and aligned PI layer.

50 citations

Journal ArticleDOI
TL;DR: In this paper, an oriented growth of polycrystalline rubrene thin film on oriented pentacene buffer layer was investigated and the structure of successive layers was characterized by using grazing incidence X-ray diffraction (GIXD) and atomic force microscopy.

38 citations