Low voltage and time constant organic synapse-transistor

We report on an artificial synapse, an organic synapse-transistor (synapstor) working at 1 volt and with a typical response time in the range 100-200 ms. This device (also called NOMFET, Nanoparticle Organic Memory Field Effect Transistor) combines a memory and a transistor effect in a single device. We demonstrate that short-term plasticity (STP), a typical synaptic behavior, is observed when stimulating the device with input spikes of 1 volt. Both significant facilitating and depressing behaviors of this artificial synapse are observed with a relative amplitude of about 50% and a dynamic response < 200 ms. From a series of in-situ experiments, i.e. measuring the current-voltage characteristic curves in-situ and in real time, during the growth of the pentacene over a network of gold nanoparticles, we elucidate these results by analyzing the relationship between the organic film morphology and the transport properties. This synapstor works at a low energy of about 2 nJ/spike. We discuss the implications of these results for the development of neuro-inspired computing architectures and interfacing with biological neurons.Comment: Full paper with supporting informatio

Nanostructuration par séparation de phase dans les monocouches binaires d'alkyltrichlorosilanes de grande longueur sur silicium

Au cours de ce travail, nous avons étudié la croissance de monocouches auto-assemblées d'alkyltrichlorosilanes de grande longueur ( 16, 18, 20 et 30 atomes de carbone dans la chaîne alkyle ) à diverses conditions de température et d'humidité relative ( HR ). Les analyses par AFM, ellipsométrie et les mesures d'angles de contact nous ont permis de proposer un modèle de comportement de ces molécules selon les conditions de dépôt. Il apparaît ainsi que les C30 à 20C et 40% HR croissent de manière similaire aux C16, C18 et C20 à 11C et 40% HR. De plus, nous avons pu voir que le coefficient de diffusion des molécules augmente avec l'humidité relative, et diminue avec la température. Une autre point important est que le temps caractéristique de croissance diminue lorsque le nombre d'atomes de carbone de la chaîne alkyle augmente, sauf pour les C30. L'étude du comportement des molécules seules était nécessaire à la compréhension des résultats obtenus pour les monocouches mixtes. Nous avons ainsi étudié la démixtion des C30 avec les C16, C18 et C20 en fonction des paramètres de dépôt. Outre la séparation de phase " classique " par îlots de C30 dans une phase de molécules courtes, nous avons, dans certains cas, observé une démixtion sous forme de " filaments " dendritiques de C30 dans une phase de molécules courtes, quel que soit le couple de molécules étudié. Les monocouches mixtes C30/C18 et C30/C20, présentent également des trous de molécules courtes dans une phase de C30, ce qui est possible car les deux molécules croissent par îlots. Ces études nous ont permis de montrer que, pour les monocouches présentant des îlots ou des trous, la composition des monocouches mixtes ( Rsam ) réalisées à basse humidité ( 20% HR ) reflète celle de la solution de silanisation ( Rsol ) et que pour les monocouches réalisées à haute humidité ( 40% HR ) Rsam est toujours inférieur à Rsol. En revanche, pour les monocouches présentant des filaments, quelles que soient les conditions, Rsam est indépendant de Rsol. En se basant sur le modèle de croissance DLA ( Agrégation Limitée par la Diffusion ), il apparaît que la croissance des monocouches à haute humidité est dictée principalement par le coefficient de diffusion des molécules sur la surface, tandis qu'à basse humidité c'est le taux de dépôt des molécules à partir de la solution qui prime. Afin de pouvoir utiliser ces structures pour la fabrication de composants nanométriques, des études complémentaires sont nécessaires. Il faut en effet notamment comprendre les mécanismes menant à la formation d'îlots, de filaments et de trous dans les monocouches afin de pouvoir contrôler efficacement la séparation de phaseDuring this work, we have studied the growth of long chain alkyltrichlorosilane self-assembled monolayers ( 16, 18, 20 and 30 carbon atoms chains ) at several temperature and relative humidity ( RH ) conditions. With AFM analysis, ellipsometry, and contact angle measurements, we could build a model of the behaviour of the molecules according to the deposition conditions. Thus we have shown that the C30 behaviour at 20C and 40% RH is similar to that of C16, C18 and C20 at 11C and 40% RH. We also saw that the molecules diffusion coefficient increased with relative humidity, and decreased with temperature. Another important result is that the growth characteristic time decreases when the number of carbon atoms increases in the alkyl chain except for C30. Studying the behaviour of those molecules was necessary in order to understand the results we obtained for binary monolayers. We have thus studied the demixtion between C30 and C16, C18, C20 according to the deposition parameters. In addition to the classical phase separation by islands of C30 in a surrounding phase of shorter molecules, we observed a demixtion involving dendritic filaments of C30 in a shorter molecules phase, regardless the couple of molecules studied. A third sort of phase separation also appears in the case of C30/C18 and C30/C20 : formation of holes of the shorter molecule in a surrounding phase of C30. We could obtain such a demixtion by working below the critical temperatures of the molecules. We have then seen, in the case of monolayers that phase separate by islands or holes, that the composition of binary monolayers ( Rsam ) realised at low humidity ( 20% RH ) was close to the one of the silanisation solution ( Rsol ) and concerning monolayers synthesized at high humidity ( 40% RH ) we note that Rsam is always lower than Rsol. On the other hand, concerning filaments we observed that, regardless the deposition conditions, Rsam does not depend on Rsol. Considering DLA ( Diffusion Limited Aggregation ) growth model, we found that at high humidity the monolayer growth is mainly driven by the diffusion coefficient, while at low humidity the deposition rate from solution is the leading parameter of the growth. In order to use those structures to build nanometric devices, some complementary studies are necessary. We must understand which mechanisms lead to the formation of islands, filaments and holes, in order to control efficiently the phase separationAIX-MARSEILLE1-BU Sci.St Charles (130552104) / SudocSudocFranceF

Etching processes of polytetrafluoroethylene surfaces exposed to He and He-O 2 atmospheric post-discharges

A comparative study of polytetrafluoroethylene (PTFE) surfaces treated by the post-discharge of He and He-O 2 plasmas at atmospheric pressure is presented. The characterization of treated PTFE surfaces and the species involved in the surface modification are related. In pure He plasmas, no significant change of the surface has been observed by X-ray photoelectron spectroscopy (XPS), dynamic water contact angles (dWCA) and atomic force microscopy (AFM), in spite of important mass losses recorded. According to these observations, a layer-by-layer physical etching without any preferential orientation is proposed, where the highly energetic helium metastables are the main species responsible for the scission of -(CF 2) n- chains. In He-O 2 plasmas, as the density of helium metastables decreases as a function of the oxygen flow rate, the treatment leads to fewer species ejected from the PTFE surfaces (in agreement with mass loss measurements and the detection of fluorinated species onto aluminum foil). However, the dWCA and AFM measurements show an increase in the hydrophobicity and the roughness of the surface. The observed alveolar structures are assumed to be caused by an anisotropic etching where the oxygen atoms etch mainly the amorphous phase. © 2012 American Chemical Society.SCOPUS: ar.jinfo:eu-repo/semantics/publishe

PTFE surface etching in the post-discharge of a scanning RF plasma torch: Evidence of ejected fluorinated species

The texturization of poly(tetrafluoroethylene) (PTFE) surfaces is achieved at atmospheric pressure by using the post-discharge of a radio-frequency plasma torch supplied in helium and oxygen gases. The surface properties are characterized by contact angle measurement, X-ray photoelectron spectroscopy and atomic force microscopy. We show that the plasma treatment increases the surface hydrophobicity (with water contact angles increasing from 115 to 155°) only by modifying the PTFE surface morphology and not the stoichiometry. Measurements of sample mass losses correlated to the ejection of CF 2 fragments from the PTFE surface evidenced an etching mechanism at atmospheric pressure. Poly(tetrafluoroethylene) (PTFE) surfaces have been texturized at atmospheric pressure by using the post-discharge of a radio-frequency plasma torch supplied in helium and oxygen gases. An etching mechanism of the surface has been highlighted by correlating the mass losses measurements to the ejection of CF 2 fragments from the PTFE surface and to an increase in the surface hydrophobicity. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.SCOPUS: ar.jFLWINinfo:eu-repo/semantics/publishe

Thermally induced coupling of poly(thiophene)-based block copolymers prepared by Grignard metathesis polymerization: a straightforward route toward highly regioregular multiblock conjugated copolymers

We report on a convenient and simple process to prepare highly regioregular poly(thiophene)-based multiblock copolymers by a novel thermally induced coupling reaction. Diblock copolymers of 3-hexylthiophene (3HT) and 2,5-dibromo-3-(2-(2-tetrahydropyranyl-2-oxy)ethyl)thiophene (THPET) end-capped by a nickel complex (Br-P3HT-b-PTHPET-Ni(dppp)Br) are first prepared using Ni(dppp)Cl2 as catalyst at 30 °C by Grignard metathesis polymerization (GRIM process). The coupling of these α-bromo, ω-Ni(dppp)Br telechelic diblock copolymers then occurs by heating the solution of the copolymer at 80 °C for a few hours without adding any additional reagent. Reactions are complete in only 10 min when heating the copolymer at 120 °C using microwaves. The deprotection of the alcohol groups of PTHPET blocks allows further modifications such as the incorporation of acrylates by esterification. AFM analysis on thin films shows the influence of the nature of side chains (protected alcohol or acrylate), the molecular weight, and the architecture (diblock or multiblock) of the copolymer on the supramolecular organization of the polythiophene chains

Electrografting onto ITO substrates of poly(thiophene)-based micelles decorated by acrylate groups.

We report on a simple process for the chemisorption of poly(thiophene)-based block copolymers onto ITO substrates. Two poly(thiophene) block copolymers functionalized by acrylates on the second block are prepared by the Grignard Metathesis (GRIM) process. The !rst block is composed of poly(3-hexylthiophene) (P3HT) and the second block is either a polythiophene bearing an acrylate group on each monomer unit (PAcET), or a polythiophene bearing both acrylate and poly(ethylene glycol) side chains (P(AcET-co-PEGET)). After characterizing their macromolecular parameters and optical properties, we investigate their ability to self-assemble into micelles in DMF solutions. This solvent is required for the electrografting procedure that is used for strongly anchoring the polymer to ITO. These micelles are expected to be formed by a P3HT core and a PAcET or P(AcET-co-PEGET) shell. When PEG side chains are present in the second block, the copolymer nicely self-assembles into micelles decorated by acrylates. Cathodic polarization of ITO induces chemisorption and polymerization of acrylate groups, leading to an adherent organized !lm of poly(thiophene)-based micelles. The optical absorption spectra show that the electrografted polymer chains have a degree of p-electron conjugation similar to that of crystalline P3HT !lms. In the absence of the PEG chains, the copolymer does not organize into micelles, due to the low stabilizing ability of the second block in DMF