1,721,030 research outputs found
Charge Carrier Mobility in Organic Mixed Ionic–Electronic Conductors by the Electrolyte-Gated van der Pauw Method
Full text linkOrganic mixed ionic–electronic conductors (OMIECs) combine electronic semiconductor functionality with ionic conductivity, biocompatibility, and electrochemical stability in water and are currently investigated as the active material in devices for bioelectronics, neuromorphic computing, as well as energy conversion and storage. Operation speed of such devices depends on fast electronic transport in OMIECs. However, due to contact resistance problems, reliable measurements of electronic mobility are difficult to achieve in this class of materials. To address the problem, the electrolyte-gated van der Pauw (EgVDP) method is introduced for the simple and accurate determination of the electrical characteristics of OMIEC thin films, independent of contact effects. The technique is applied to the most widespread OMIEC blend, poly(3,4-ethylenedioxythiophene) doped with poly(styrenesulfonic acid) (PEDOT:PSS). By comparing with organic electrochemical transistor (OECT) measurements, it is found that gate voltage dependent contact resistance effects lead to systematic errors in OECT based transport characterization. These observations confirm that a contact-independent technique is crucial for the proper characterization of OMIECs, and the EgVDP method reveals to be a simple, elegant, but effective technique for this scope
Going Beyond Counting First Authors in Author Co-citation Analysis
Full text linkThe present study examines one of the fundamental aspects of author co-citation analysis (ACA) - the way co-citation
counts are defined. Co-citation counting provides the data on which all subsequent statistical analyses and mappings
are based, and we compare ACA results based on two different types of co-citation counting - the traditional type that
only counts the first one among a cited work's authors on the one hand and a non-traditional type that takes into
account the first 5 authors of a cited work on the other hand. Results indicate that the picture produced through this non-traditional author co-citation counting contains more coherent author groups and is therefore considerably clearer. However, this picture represents fewer specialties in the research field being studied than that produced through the traditional first-author co-citation counting when the same number of top-ranked authors is selected and analyzed. Reasons for these effects are discussed
High-Endurance Long-Term Potentiation in Neuromorphic Organic Electrochemical Transistors by PEDOT:PSS Electrochemical Polymerization on the Gate Electrode
Full text linkThe brain exhibits extraordinary information processing capabilities thanks to neural networks that can operate in parallel with minimal energy consumption. Memory and learning require the creation of new neural networks through the long-term modification of the structure of the synapses, a phenomenon called long-term plasticity. Here, we use an organic electrochemical transistor to simulate long-term potentiation and depotentiation processes. Similarly to what happens in a synapse, the polymerization of the 3,4-ethylenedioxythiophene (EDOT) on the gate electrode modifies the structure of the device and boosts the ability of the gate potential to modify the conductivity of the channel. Operando AFM measurements were carried out to demonstrate the correlation between neuromorphic behavior and modification of the gate electrode. Long-term enhancement depends on both the number of pulses used and the gate potential, which generates long-term potentiation when a threshold of +0.7 V is overcome. Long-term depotentiation occurs by applying a +3.0 V potential and exploits the overoxidation of the deposited PEDOT:PSS. The induced states are stable for at least 2 months. The developed device shows very interesting characteristics in the field of neuromorphic electronics
Organic Electrochemical Transistors for Oxygen Sensing in Water with Battery Free, Near Field Communication Readout
No full textOrganic Electrochemical Transistors (OECTs) are investigated as electrochemical sensors due to their
amplification behaviour, stability in aqueous environments and compatibility with low-cost
processing on flexible plastic substrates. For widespread, sustainable application in sensor-networks,
OECTs must be compatible with wireless, battery free sensor readout schemes. Although OECTs
operate at low-voltages, high transistor channel currents and long response time-constants make the
integration with low-power electronics difficult. To address the issue, we investigate hydrogel based
OECTs for oxygen sensing in liquid and gas and their power consumption. To achieve stable,
interference-free O2 sensors with miniaturized OECTs we introduce a silicone based O2 permeable
membrane. Our results show how the membrane enables fast and stable sensor readout in
micrometric OECTs and reduces power consumption to be compatible with a commercial battery-free NFC chip readout. We also demonstrate stable O2 sensor operation in complex mixtures with
several competing redox analytes. Our result opens the opportunity for developing bio-compatible,
non-invasive and wireless OECTs sensors for wound healing monitoring or environmental monitoring
Organic Electrochemical Transistor to measure electrochemical potentials
No full textOrganic Electrochemical Transistors (OECTs) have been proposed as low cost chemical sensors for the detection of several analytes thanks to their remarkable features such as signal amplification, the use of an easy and cheap readout electronics, low supply voltage (usually < 1 V), low power operation (< 100 μW), bio-compatibility, and, moreover, they can be easily miniaturized and adapted to non-flat and/or flexible devices. An OECT is composed by a stripe of conductive polymer that works as a channel and by another electrode, usually a metal, that works as a gate. When the device is dipped in an electrolyte solution, the current flowing in the channel can be modulated through the gate voltage because it promotes electrochemical reactions that change the charge carrier concentration in the polymer and, consequently, its conductivity. Chemical sensors based on OECTs are usually obtained by exploiting as gate electrode a chemically modified electrode that acts as amperometric transducer. In such a way, the rate of electrochemical processes and thus of the gate action depends on the analyte concentration. In our previous work, we have demonstrated that the OECT transduction is generated by a variation of electrochemical potential of the channel, because the electrical conductivity of a conductive polymer is a function of its oxidation level. Consequently, OECTs could be also used as transducers for potentiometric sensing.
This contribution describes a strategy to exploit OECTs in the measurement of potentiometric signals with the final aim of obtaining sensors that cannot be fabricated with consolidated technology. In order to thoroughly investigate the potentiality of these devices, we fabricate transistors with different architectures wherein the channel is made of poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS) and the gate is an Ag/AgCl electrode. Since the Cl- concentration in the electrolyte rules the gate potential measured with respect to a reference electrode, it also controls the electrochemical potential of the channel and thus its conductivity. The current that flows in the channel linearly depends on the logarithm of Cl- concentration as expected from Nernst equation. Since the Ag/AgCl electrode can force the channel potential without the action of an external potential, the transistor can also operate when the gate and the source are short circuited in order to produce a two terminal device with the features of a transistor. The proposed approach is general and we have already fabricated similar devices for the detection of Br-, I- and S2-, based on AgBr, AgI and Ag2S gate electrodes, respectively. Moreover, we exploited such evidences to design new composite materials for the production of two terminal devices that maintain the amplification of a transistor. These evidences could pave the way to the production of both new materials and new sensors based on potentiometric transduction
Accurate determination of band tail properties in amorphous oxide semiconductors with Kelvin Probe Force Microscopy
No full textNeuromorphic organic electrochemical transistor with agarose hydrogel for high-endurance plasticity
No full textWith an increasing interest in information processing and the development of biocompatible technologies, the opportunities regarding neuromorphic structures have risen. Neural networks have the ability of storing information through irreversible chemical modifications, obtaining long-term plasticity. On the other hand, short-term plasticity, which is defined by the ability of temporarily store information, relates to an induced strengthening/weakening of the synaptic weight that is dissipated after a characteristic time constant.
Both the processes can be emulated by different structures as memristors, transistors or capacitors. Considering organic electrochemical transistors (OECT) as suitable components for these applications, our research group has recently developed a method that induces long-term plasticity involving direct electropolymerization of poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) on the gate electrode, thanks to a series of voltage pulses. [1]
Following the same direction, to enhance the compatibility with hardware electronics and durability of neuromorphic OECTs, the application of an agarose-based hydrogel as a solid electrolyte was investigated. The channel, connecting the source and drain electrodes, and the gate electrode are encapsulated in a hydrogel composed by agarose, EDOT and NaPSS. The hydrogel composition can be tuned to optimize the device performances, in terms of long-term plasticity emulation and transconductance.
The device is prepared by drop casting the liquid gel precursor on the OECT, covering the channel and the gate electrode. Once the crosslinked network is physically formed, with the application of voltage pulses at the gate electrode between -0.5 and 1.3 V and of a fixed drain potential (Vd) of -0.3 V, the electropolymerization starts. Short-term plasticity was also investigated, observing an increase in characteristic time constant because of the presence of a porous 3D network, opposed to the previous aqueous solution.
Future perspectives involve the optimization of the composition, to increase the device transconductance, and the study of neuromorphic OECTs as control devices
Nanoparticle-Semiconducting Polymer Composites for a New, Intrinsically Amplified Chemical Sensors
No full textGreat research efforts are devoted to the development of portable and wearable sensors as they could have a broad impact on real life in different fields such as point-of-care medical applications and environmental monitoring due to the ubiquity of smart technologies and wireless communication networks,. The crucial bottleneck is the development of new smart materials capable to effectively convert the chemical information into an electrical signal. Amplified transduction of ionic or electrochemical signals is nowadays achieved in sensors that consist of three electrodes operating in a transistor configuration (see Figure 1A): Source and Drain electrodes which drive an electronic current through a semiconducting channel that is coupled to the gate electrode through an ionically conductive analyte solution.
In this contribution, we propose a nano-composite material based strategy to integrate the amplified electrochemical response and sensitivity of a three-terminal organic electrochemical transistor (OECT) into a simpler two terminal device, thus paving the way for a new generation of smart sensors. To do it, we design, synthesize and exploit a new composite material based on Ag/AgCl nanoparticles and PEDOT:PSS (poly(3,4-ethylenedioxythiophene) poly(styrene sulfonate)). The Ag/AgCl gate electrode, which is the transducer of the OECT, is embedded into the semiconducting polymer in the form of nanoparticles and, as a consequence, the sensor combines an intrinsically amplified response with a simple two terminal electrical connection. In order to demonstrate our strategy, we investigate the novel composite material by electrostatic force microscopy, scanning electron microscopy and electrochemical impedance spectroscopy and show that the spontaneous interaction between the NPs and Cl- ions present in the sample solution is directly coupled to the charge transfer process into the semiconductor, so inducing a fast modulation of the channel conductivity. Consequently, the current flowing in the channel is directly related to the logarithm of Cl- ions concentration. We show two application examples that demonstrate the efficacy and the robustness of our approach. The first regards a real-time, portable sensor for in-situ detection of salinity in water. The second is a textile sensor, obtained on a cotton yarn, for real-time sweat monitoring. The here presented sensors show an excellent reliability, as demonstrated by comparing the results obtained analyzing real-life samples with our sensors and with standard chemical analyses. Finally, our approach was successfully used to fabricate novel sensors for Br-, I- and S2-, demonstrating the widespread applicability of such devices
Variations on the Author
Full text link“Variations on the Author” discusses two of Eduardo Coutinho’s recent films (Um Dia na Vida, from 2010, and Últimas Conversas, posthumously released in 2015) and their contribution to the general question of documentary authorship. The director’s filmography is characterized by a consistent yet self-effacing form of authorial self-inscription: Coutinho often features as an interviewer that rather than express opinions propels discourses; an interviewer that is good at listening. This mode of self-inscription characterizes him as an author who is not expressive but who is nonetheless markedly present on the screen. In Um Dia na Vida, however, Coutinho is completely absent form the image, while Últimas Conversas, on the contrary, includes a confessional prologue that moves the director from the margins to the center of his films. This article examines the ways in which these works stand out in the filmography of a director who offers new insights into the notion of cinematic authorship
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