669 research outputs found
Relaxation dynamics in covalently bonded organic monolayers on silicon
We study the dynamic electrical response of a silicon-molecular
monolayer-metal junctions and we observe two contributions in the admittance
spectroscopy data. These contributions are related to dipolar relaxation and
molecular organization in the monolayer in one hand, and the presence of
defects at the silicon/molecule interface in the other hand. We propose a small
signal equivalent circuit suitable for the simulations of these molecular
devices in commercial device simulators. Our results concern monolayers of
alkyl chains considered as a model system but can be extended to other
molecular monolayers. These results open door to a better control and
optimization of molecular devices.Comment: 1 pdf file including text, figures and tables. Phys. Rev. B, in pres
Cation Discrimination in Organic Electrochemical Transistors by Dual Frequency Sensing
In this work, we propose a strategy to sense quantitatively and specifically
cations, out of a single organic electrochemical transistor (OECT) device
exposed to an electrolyte. From the systematic study of six different chloride
salts over 12 different concentrations, we demonstrate that the impedance of
the OECT device is governed by either the channel dedoping at low frequency and
the electrolyte gate capacitive coupling at high frequency. Specific cationic
signatures, which originates from the different impact of the cations behavior
on the poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS)
polymer and their conductivity in water, allow their discrimination at the same
molar concentrations. Dynamic analysis of the device impedance at different
frequencies could allow the identification of specific ionic flows which could
be of a great use in bioelectronics to further interpret complex mechanisms in
biological media such as in the brain.Comment: Full text and supporting informatio
Learning policy constraints through dialogue
Publisher PD
An artificial spiking synapse made of molecules and nanoparticles
Molecule-based devices are envisioned to complement silicon devices by providing new functions or already existing functions at a simpler process level and at a lower cost by virtue of their self-organization capabilities, moreover, they are not bound to von Neuman architecture and this may open the way to other architectural paradigms. Here we demonstrate a device made of conjugated molecules and metal nanoparticles (NPs) which behaves as a spiking synapse suitable for integration in neural network architectures. We demonstrate that this device exhibits the main behavior of a biological synapse. These results open the way to rate coding utilization of the NOMFET in perceptron and Hopfield networks. We can also envision the NOMFET as a building block of neuroelectronics for interfacing neurons or neuronal logic devices made from patterned neuronal cultures with solid-state devices and circuits
Tunnel current in self-assembled monolayers of 3-mercaptopropyltrimethoxysilane
The current density-voltage (J-V) characteristics of self assembled
monolayers of 3-mercaptopropyltrimethoxysilane (MPTMS) chemisorbed on the
native oxide surface of p+-doped Si demonstrate the excellent tunnel dielectric
behavior of organic monolayers down to 3 carbon atoms. The J-V characteristics
of MPTMS SAMs on Si are found to be asymmetric, and the direction of
rectification has been found to depend upon the applied voltage range. At
voltages < 2.45V, the reverse bias current was found to be higher than forward
bias current; while at higher voltages this trend was reversed. This result is
in agreement with Simmons theory. The tunnel barrier heights for this short
chain (2.56 and 2.14 eV respectively at Au and Si interfaces) are in good
agreement with the ones for longer chains (>10 carbon atoms) if the chain is
chemisorbed at the electrodes. These results extend all previous experiments on
such molecular tunnel dielectrics down to 3 carbon atoms. This suggests that
these molecular monolayers, having good tunnel behavior (up to 2.5 eV) over a
large bias range, can be used as gate dielectric well below the limits of
Si-based dielectrics.Comment: Small, in pres
On n’enseigne pas la langue à l’école : là est le problème
International audienceNous nous intéressons à la problématique de la didactique de la langue dite « maternelle » en France. Notre perspective se situant au carrefour des préoccupations sociolinguistiques et didactiques, nous tenterons de défendre l’hypothèse selon laquelle l’absence de reconnaissance de la réalité de la langue dans les apprentissages peut être à l’origine des difficultés constatées à l’école primaire. A partir de données issues de l’enregistrement de séquences de classe et d’un corpus de manuels scolaires, nous tenterons de mettre en évidence l’absence de prise en compte de la variation de la langue dans les enseignements et montrerons en quoi cet état de fait est un frein au bon déroulement de l’enseignement. Il s’agit, en arrière plan, de penser un enseignement de la langue commune qui contribue à la cohésion sociale, à la reconnaissance de la communauté, sans entraver le développement de la construction identitaire des élèves en tant qu’elle est la manifestation de l’individualité de chacu
High Conductance Ratio in Molecular Optical Switching of Functionalized Nanoparticle Self-Assembled Nanodevices
Self-assembled functionalized nano particles are at the focus of a number of
potential applications, in particular for molecular scale electronics devices.
Here we perform experiments of self-assembly of 10 nm Au nano particles (NPs),
functionalized by a dense layer of azobenzene-bithiophene (AzBT) molecules,
with the aim of building a light-switchable device with memristive properties.
We fabricate planar nanodevices consisting of NP self-assembled network
(NPSANs) contacted by nanoelectrodes separated by interelectrode gaps ranging
from 30 to 100 nm. We demonstrate the light-induced reversible switching of the
electrical conductance in these AzBT NPSANs with a record on/off conductance
ratio up to 620, an average value of ca. 30 and with 85% of the devices having
a ratio above 10. Molecular dynamics simulation of the structure and dynamics
of the interface between molecular monolayers chemisorbed on the nano particle
surface are performed and compared to the experimental findings. The properties
of the contact interface are shown to be strongly correlated to the molecular
conformation which in the case of AzBT molecules, can reversibly switched
between a cis and a trans form by means of light irradiations of well-defined
wavelength. Molecular dynamics simulations provide a microscopic explanation
for the experimental observation of the reduction of the on/off current ratio
between the two isomers, compared to experiments performed on flat
self-assembled monolayers contacted by a conducting cAFM tip.Comment: pdf files : publication and supporting informatio
Molecular Signature of Polyoxometalates in Electron Transport of Silicon-based Molecular Junctions
Polyoxometalates (POMs) are unconventional electro-active molecules with a
great potential for applications in molecular memories, providing efficient
processing steps onto electrodes are available. The synthesis of the
organic-inorganic polyoxometalate hybrids
[PMO(Sn(CH)CC(CH)N)] (M = Mo,
W) endowed with a remote diazonium function is reported together with their
covalent immobilization onto hydrogenated n-Si(100) substrates. Electron
transport measurements through the resulting densely-packed monolayers
contacted with a mercury drop as a top electrode confirms their homogeneity.
Adjustment of the current-voltage curves with the Simmons equation gives a mean
tunnel energy barrier of 1.8 eV and 1.6 eV, for the Silicon-Molecules-Metal
(SMM) junctions based on the polyoxotungstates (M = W) and polyoxomolybdates (M
= Mo), respectively. This follows the trend observed in the electrochemical
properties of POMs in solution, the polyoxomolybdates being easier to reduce
than the polyoxotungstates, in agreement with lowest unoccupied molecular
orbitals (LUMOs) of lower energy. The molecular signature of the POMs is thus
clearly identifiable in the solid-state electrical properties and the unmatched
diversity of POM molecular and electronic structures should offer a great
modularity
My Way or the Highway: a More Naturalistic Model of Altruism Tested in an Iterative Prisoners' Dilemma
There are three prominent solutions to the Darwinian problem of altruism, kin selection, reciprocal altruism, and trait group selection. Only one, reciprocal altruism, most commonly implemented in game theory as a TIT FOR TAT strategy, is not based on the principle of conditional association. On the contrary, TIT FOR TAT implements conditional altruism in the context of unconditionally determined associates. Simulations based on Axelrod\'s famous tournament have led many to conclude that conditional altruism among unconditional partners lies at the core of much human and animal social behavior. But the results that have been used to support this conclusion are largely artifacts of the structure of the Axelrod tournament, which explicitly disallowed conditional association as a strategy. In this study, we modify the rules of the tournament to permit competition between conditional associates and conditional altruists. We provide evidence that when unconditional altruism is paired with conditional association, a strategy we called MOTH, it can out compete TIT FOR TAT under a wide range of conditions.Game Theory; Altruism; Prisoners' Dilemma; TIT FOR TAT; MOTH; Docking; Netlogo
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