639 research outputs found
Toward a better understanding of the doping mechanism involved in Mo(tfd-COCF doped PBDTTT-c
In this study, we aim to improve our understanding of the doping mechanism
involved in the polymer PBDTTT-c doped with(Mo(tfd-COCF3)3. We follow the
evolution of the hole density with dopant concentration to highlight the limits
of organic semiconductor doping. To enable the use of doping to enhance the
performance of organic electronic devices, doping efficiency must be understood
and improved. We report here a study using complementary optical and electrical
characterization techniques, which sheds some light on the origin of this
limited doping efficiency at high dopant concentration. Two doping mechanisms
are considered, the direct charge transfer (DCT) and the charge transfer
complex (CTC). We discuss the validity of the model involved as well as its
impact on the doping efficiency.Comment: Accepted manuscript, J. Appl. Phy
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.
Negative Differential Resistance, Memory and Reconfigurable Logic Functions based on Monolayer Devices derived from Gold Nanoparticles Functionalized with Electro-polymerizable Thiophene-EDOT Units
We report on hybrid memristive devices made of a network of gold
nanoparticles (10 nm diameter) functionalized by tailored
3,4(ethylenedioxy)thiophene (TEDOT) molecules, deposited between two planar
electrodes with nanometer and micrometer gaps (100 nm to 10 um apart), and
electropolymerized in situ to form a monolayer film of conjugated polymer with
embedded gold nanoparticles (AuNPs). Electrical properties of these films
exhibit two interesting behaviors: (i) a NDR (negative differential resistance)
behavior with a peak/valley ratio up to 17, and (ii) a memory behavior with an
ON/OFF current ratio of about 1E3 to 1E4. A careful study of the switching
dynamics and programming voltage window is conducted demonstrating a
non-volatile memory. The data retention of the ON and OFF states is stable
(tested up to 24h), well controlled by the voltage and preserved when repeating
the switching cycles (800 in this study). We demonstrate reconfigurable Boolean
functions in multiterminal connected NP molecule devices.Comment: Full manuscript, figures and supporting information, J. Phys. Chem.
C, on line, asap (2017
Physical Study by Surface Characterizations of Sarin Sensor on the Basis of Chemically Functionalized Silicon Nanoribbon Field Effect Transistor
Surface characterizations of an organophosphorus (OP) gas detector based on
chemically functionalized silicon nanoribbon field-effect transistor (SiNR-FET)
were performed by Kelvin Probe Force Microscopy (KPFM) and ToF-SIMS, and
correlated with changes in the current-voltage characteristics of the devices.
KPFM measurements on FETs allow (i) to investigate the contact potential
difference (CPD) distribution of the polarized device as function of the gate
voltage and the exposure to OP traces and, (ii) to analyze the CPD hysteresis
associated to the presence of mobile ions on the surface. The CPD measured by
KPFM on the silicon nanoribbon was corrected due to side capacitance effects in
order to determine the real quantitative surface potential. Comparison with
macroscopic Kelvin probe (KP) experiments on larger surfaces was carried out.
These two approaches were quantitatively consistent. An important increase of
the CPD values (between + 399 mV and + 302 mV) was observed after the OP sensor
grafting, corresponding to a decrease of the work function, and a weaker
variation after exposure to OP (between - 14 mV and - 61 mV) was measured.
Molecular imaging by ToF-SIMS revealed OP presence after SiNR-FET exposure. The
OP molecules were essentially localized on the Si-NR confirming effectiveness
and selectivity of the OP sensor. A prototype was exposed to Sarin vapors and
succeeded in the detection of low vapor concentrations (40 ppm).Comment: Paper and supporting information, J. Phys. Chem. C, 201
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