Pavlov's dog associative learning demonstrated on synaptic-like organic transistors

In this letter, we present an original demonstration of an associative learning neural network inspired by the famous Pavlov's dogs experiment. A single nanoparticle organic memory field effect transistor (NOMFET) is used to implement each synapse. We show how the physical properties of this dynamic memristive device can be used to perform low power write operations for the learning and implement short-term association using temporal coding and spike timing dependent plasticity based learning. An electronic circuit was built to validate the proposed learning scheme with packaged devices, with good reproducibility despite the complex synaptic-like dynamic of the NOMFET in pulse regime

Interface Dipole : Effects on Threshold Voltage and Mobility for both Amorphous and Poly-crystalline Organic Field Effect Transistors

We report a detailed comparison on the role of a self-assembled monolayer (SAM) of dipolar molecules on the threshold voltage and charge carrier mobility of organic field-effect transistor (OFET) made of both amorphous and polycrystalline organic semiconductors. We show that the same relationship between the threshold voltage and the dipole-induced charges in the SAM holds when both types of devices are fabricated on strictly identical base substrates. Charge carrier mobilities, almost constant for amorphous OFET, are not affected by the dipole in the SAMs, while for polycrystalline OFET (pentacene) the large variation of charge carrier mobilities is related to change in the organic film structure (mostly grain size).Comment: Full paper and supporting informatio

Electron transport through rectifying self-assembled monolayer diodes on silicon: Fermi level pinning at the molecule-metal interface

We report the synthesis and characterization of molecular rectifying diodes on silicon using sequential grafting of self-assembled monolayers of alkyl chains bearing a pi group at their outer end (Si/sigma-pi/metal junctions). We investigate the structure-performance relationships of these molecular devices and we examine to what extent the nature of the pi end-group (change in the energy position of their molecular orbitals) drives the properties of these molecular diodes. For all the pi-groups investigated here, we observe rectification behavior. These results extend our preliminary work using phenyl and thiophene groups (S. Lenfant et al., Nano Letters 3, 741 (2003)).The experimental current-voltage curves are analyzed with a simple analytical model, from which we extract the energy position of the molecular orbital of the pi-group in resonance with the Fermi energy of the electrodes. We report the experimental studies of the band lineup in these silicon/alkyl-pi conjugated molecule/metal junctions. We conclude that Fermi level pinning at the pi-group/metal interface is mainly responsible for the observed absence of dependence of the rectification effect on the nature of the pi-groups, even though they were chosen to have significant variations in their electronic molecular orbitalsComment: To be published in J. Phys. Chem.

Metal/organic/metal bistable memory devices

We report a bistable organic memory made of a single organic layer embedded between two electrodes, we compare to the organic/metal nanoparticle/organic tri-layers device [L.P. Ma, J. Liu, and Y. Yang, Appl. Phys. Lett. 80, 2997 (2002)]. We demonstrate that the two devices exhibit similar temperature-dependent behaviors, a thermally-activated behavior in their low conductive state (off-state) and a slightly "metallic" behavior in their high conductive state (on-state). This feature emphasizes a similar origin for the memory effect. Owing to their similar behavior, the one layer memory is advantageous in terms of fabrication cost and simplicity

A New Photomechanical Molecular Switch Based on a Linear {\pi}-Conjugated System

We report the electronic transport properties of a new photo-addressable molecular switch. The switching process relies on a new concept based on linear {\pi}-conjugated dynamic systems, in which the geometry and hence the electronic properties of an oligothiophene chain can be reversibly modified by the photochemical trans-cis isomerization of an azobenzene unit fixed in a lateral loop. Electron transport measurements through self-assembled monolayers on gold, contacted with eGaIn top contact, show switching with a conductance ratio up to 1E3. Ab initio calculations have been used to identify the most energetically stable conformations of the molecular switch, the corresponding calculated conductances qualitatively explain the trend observed in the photo-switching experiments.Comment: Full manuscript and supporting information, J. Phys. Chem. C,published on line (2017

Theory of electrical rectification in a molecular monolayer

The current-voltage characteristics in Langmuir-Blodgett monolayers of \gamma-hexadecylquinolinium tricyanoquinodimethanide (C16H33Q-3CNQ) sandwiched between Al or Au electrodes is calculated, combining ab initio and self-consistent tight binding techniques. The rectification current depends on the position of the LUMO and HOMO relative to the Fermi levels of the electrodes as in the Aviram-Ratner mechanism, but also on the profile of the electrostatic potential which is extremely sensitive to where the electroactive part of the molecule lies in the monolayer. This second effect can produce rectification in the direction opposite to the Aviram-Ratner prediction

A New Photomechanical Molecular Switch Based on a Linear {\pi}-Conjugated System

We report the electronic transport properties of a new photo-addressable molecular switch. The switching process relies on a new concept based on linear {\pi}-conjugated dynamic systems, in which the geometry and hence the electronic properties of an oligothiophene chain can be reversibly modified by the photochemical trans-cis isomerization of an azobenzene unit fixed in a lateral loop. Electron transport measurements through self-assembled monolayers on gold, contacted with eGaIn top contact, show switching with a conductance ratio up to 1E3. Ab initio calculations have been used to identify the most energetically stable conformations of the molecular switch, the corresponding calculated conductances qualitatively explain the trend observed in the photo-switching experiments.Comment: Full manuscript and supporting information, J. Phys. Chem. C,published on line (2017