23 research outputs found

    Frequency Selectivity in Pulse Responses of Pt/Poly(3-Hexylthiophene-2,5-Diyl)/Polyethylene Oxide + Li<sup>+</sup>/Pt Hetero-Junction

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    <div><p>Pt/poly(3-hexylthiophene-2,5-diyl)/polyethylene oxide + Li<sup>+</sup>/Pt hetero junctions were fabricated, and their pulse responses were studied. The direct current characteristics were not symmetric in the sweeping range of ±2 V. Negative differential resistance appeared in the input range of 0 to 2 V because of de-doping (or reduction) in the side with the semiconductor layer. The device responded stably to a train of pulses with a fixed frequency. The inverse current after a pulse was related to the back-migrated ions. Importantly, the weight calculated based on the inverse current strength, was depressed during low-frequency stimulations but was potentiated during high-frequency stimulations when pulses were positive. Therefore, frequency selectivity was first observed in a semiconducting polymer/electrolyte hetero junction. Detailed analysis of the pulse response showed that the input frequency could modulate the timing of ion doping, de-doping, and re-doping at the semiconducting polymer/electrolyte interface, which then resulted in the frequency selectivity. Our study suggests that the simple redox process in semiconducting polymers can be modulated and used in signal handling or the simulation of bio-learning.</p></div

    Raman spectra for Pt/P3HT, Pt/PEO + Li<sup>+</sup>, and Pt/P3HT/PEO + Li<sup>+</sup>.

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    <p>Raman spectra for Pt/P3HT, Pt/PEO + Li<sup>+</sup>, and Pt/P3HT/PEO + Li<sup>+</sup>.</p

    Current variations in the final pulse response.

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    <p>The triangular pulse responses were used with three typical frequencies, i.e., 1, 40 and 142 Hz, which correspond to the baseline, depression and potentiation states in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0108316#pone-0108316-g004" target="_blank">Figure 4a</a>, respectively. The start times of the last pulse responses were normalized to 0. The scope of Y axis is –5 nA to 80 nA.</p

    Resistive Switching Induced by Metallic Filaments Formation through Poly(3,4-ethylene-dioxythiophene):Poly(styrenesulfonate)

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    We report the design and fabrication of Al/poly­(3,4-ethylene-dioxythiophene):poly­(styrenesulfonate) (PEDOT:PSS)/Cu resistive memory devices that utilize the Cu redox reaction and conformational features of PEDOT:PSS to achieve resistive switching. The top Cu electrode acts as the source of the redox ions that are injected through the PEDOT:PSS layer during the forming process. The Cu filament is confirmed directly using the cross-sectional images of transmission electron microscopy and energy-dispersive X-ray spectroscopy. The resultant resistive memory devices can operate over a small voltage range, i.e., the switching-on threshold voltage is less than 1.5 V and the absolute value of the switching-off threshold voltage is less than 1.0 V. The on/off current ratio is as large as 1 × 10<sup>4</sup> and the two different resistance states can be maintained over 10<sup>6</sup> s. Moreover, the devices present good thermal stability that the resistive switching can be observed even at temperature up to 160 °C, at which the oxidation of the Cu top electrode is the failure factor. Furthermore, the cause of failure for Al/PEDOT:PSS/Cu memory devices at higher temperature is confirmed to be the oxidation of Cu top electrode

    Ionic Species-Modulated Interfacial Polarization and Frequency Selectivity in Polymer Electrolyte/Semiconductor Heterojunctions

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    Microstructures and ionic species in Ca­(CF<sub>3</sub>SO<sub>3</sub>)<sub>2</sub> doped poly­(ethylene oxide)­(PEO-Ca<i>Tf</i><sub>2</sub>) are modulated by varying the ethylene oxide (EO)/Ca<sup>2+</sup> ratio. Increasing the salt concentrations, that is, reducing EO/Ca<sup>2+</sup>, can enhance the ratios of ion-pairs and aggregates but reduce the ratio of free ions, accompanied by reduced grain size and narrowed ion passages. Such microscopic variations influence the transportation properties of PEO-Ca<i>Tf</i><sub>2</sub>/poly­(3-hexylthiophene-2,5-diyl) (P3HT) heterojunctions in two aspects. First, the negative differential resistance (NDR) is under the bias loaded from PEO-Ca<i>Tf</i><sub>2</sub> to P3HT and shifts left to the region of low voltage with decreased EO/Ca<sup>2+</sup> because the interfacial polarization was weakened due to the reduced mobility of anions, confirmed by the fitted results of the facilitate time constant (τ<sub>F</sub>). Second, pulse responses were tested and the short-term synaptic plasticity was examined for the system. Evident frequency selectivity occurs for the heterojunctions with larger EO/Ca<sup>2+</sup>, but monotonous weight potentiation was only observed for the sample with an EO/Ca<sup>2+</sup> of 8:1. This is due to the reason that the reduced polarization does not induce effective doping. Our results demonstrate that the types of ionic species are able to modulate signal selectivity, which might be a part of the secrets of information handling the biological body

    Weight variations dependent on pulse frequency.

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    <p>(a) Weight change calculated using triangular (black) and rectangular pulse (blue) described in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0108316#pone-0108316-g003" target="_blank">Figure 3a</a>. The value of <i>θ<sub>m</sub></i> indicates the threshold from depression to potentiation. (b) Weight variations obtained from the responses during negative pulse stimulations for Pt/P3HT/PEO + Li<sup>+</sup>/Pt (blue triangles) and the positive pulse stimulations for Pt/PEO + Li<sup>+</sup>/Pt (red cycles).</p

    Materials, device structure and DC properties.

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    <p>(a) Schematic diagram of device structure, ion migration and electric field distribution under bias. The label BE and TE refer to bottom electrode and top electrode, respectively. The larger ‘+’ and ‘–’ refer to Li<sup>+</sup> and CF<sub>3</sub>SO<sub>3</sub><sup>−</sup>, respectively, at the interface. E<sub>i</sub> is the internal electric field composed of Li<sup>+</sup> and CF<sub>3</sub>SO<sub>3</sub><sup>−</sup> pairs at the interface and E<sub>x</sub> is the external electric field. I–V curves were obtained by DC sweeping. The sweeping direction were (b) 0 → 2 → 0 V, (c) 0 →–2 → 0 V, and (d) 0 → 2 →–2 → 0 V, respectively. The sweeping rates are labelled in the figure.</p

    A Green Route to a Low Cost Anisotropic MoS<sub>2</sub>/Poly(Vinylidene Fluoride) Nanocomposite with Ultrahigh Electroactive Phase and Improved Electrical and Mechanical Properties

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    Environment issues due to growing energy consumption have motivated great research efforts on new materials for efficient energy storage and their low cost fabrication. This study reports an energy-efficient solution route for the fabrication of a unique high permittivity nanocomposite film consisting of molybdenum disulfide (MoS<sub>2</sub>) nanosheets spontaneously aligned in poly­(vinylidene fluoride) (PVDF) via super-2D-confinement and gravity sedimentation. A simple thermal lamination was further developed to get anisotropic films with controllable thickness. Interestingly, an ultrahigh fraction (∼86% as confirmed by synchrotron radiation XRD) of β-phase PVDF was directly obtained by only 3.4 vol % of orientated MoS<sub>2</sub> nanosheets due to possible crystallization disturbance and synergistically reinforced electrostatic interaction and super-2D-confinement. This reveals a greener route to the desirable electroactive phase PVDF, whose formation usually requires giant electrical field or mechanical stresses. Simulation of the permittivity perpendicular to the nanosheets (up to 146 @ 100 Hz with 19.8 vol % MoS<sub>2</sub>) also revealed anisotropy due to alignment. The permittivity and conductivity parallel to the nanosheets were much higher, showing anisotropic ratios of 3.96 and 6.14 (9.5 vol % MoS<sub>2</sub>), respectively. Furthermore, the nanocomposite with a suitable composition showed simultaneously increased tensile strength, elongation, and energy storage density, making it promising for multifunctional field applications. The results may also improve the understanding of polymer polymorph transition and provide hints on new green pathways for novel composites

    Diverse Synaptic Plasticity Induced by the Interplay of Ionic Polarization and Doping at Salt-Doped Electrolyte/Semiconducting Polymer Interface

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    Pt/Ca<sup>2+</sup>–polyethylene oxide/polymer poly­[3-hexylthiophene-2,5-diyl]/Pt devices were fabricated, and their pulse responses were studied. The discharging peak, represented by the postsynaptic current (PSC), first increases and then decreases with increasing input number in a pulse train. The weight of the PSC decreased for low-frequency stimulations but increased for high-frequency stimulations. However, the peak of the negative differential resistance during the charging process varied following the opposite trend. These behaviors suggested the ability for transferring the signal bidirectionally, confirming the equivalence between the ionic kinetics of our device and the transmitter kinetics of one kind of synapse. A facilitation (<i>F</i>)–depression (<i>D</i>) interplay model corresponding to the ionic polarization and doping interplay at the electrolyte/semiconducting polymer interface was adopted to successfully mimic the weight modification of the PSC. The simulation results showed that the observed synaptic plasticity was caused by the great disparity between the recovery time constants of <i>F</i> and <i>D</i> (τ<sub><i>F</i></sub> and τ<sub><i>D</i></sub>). Moreover, such an interplay could inspire the features of responses to post-tetanic stimulations. Our study suggested a means to realize synaptic computation

    Construction of β‑Oximino Phosphorodithioates via (2,2,6,6-Tetramethylpiperidin-1-yl)oxyl-Promoted Difunctionalization of Alkenes with <i>tert</i>-Butyl Nitrite, P<sub>4</sub>S<sub>10</sub>, and Alcohols

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    A (2,2,6,6-tetramethylpiperidin-1-yl)­oxyl-mediated difunctionalization of alkenes with tert-butyl nitrite, P4S10, and alcohols has been developed for the synthesis of β-oximino phosphorodithioates. The reaction goes through a radical pathway with the successive installation of phosphorodithioate and an oxime group. This four-component protocol offers a practical approach to constructing a variety of β-oximino phosphorodithioates in moderate to good yields with favorable functional group tolerance
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