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
<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>.
<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.
<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)
We report the design and fabrication of Al/polyÂ(3,4-ethylene-dioxythiophene):polyÂ(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
Microstructures
and ionic species in CaÂ(CF<sub>3</sub>SO<sub>3</sub>)<sub>2</sub> doped
polyÂ(ethylene oxide)Â(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>/polyÂ(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 (Ï„<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.
<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.
<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
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 polyÂ(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
Pt/Ca<sup>2+</sup>–polyethylene oxide/polymer polyÂ[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> (Ï„<sub><i>F</i></sub> and Ï„<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
A (2,2,6,6-tetramethylpiperidin-1-yl)Âoxyl-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