520 research outputs found
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
Tracking the origin and divergence of cholinesterases and neuroligins: the evolution of synaptic proteins
14. International Symposium on Cholinergic Mechanisms (ISCM), Hangzhou, 2013/05/05-9A cholinesterase activity can be found in all kingdoms of living organism, yet cholinesterases involved in cholinergic transmission appeared only recently in the animal phylum. Among various proteins homologous to cholinesterases, one finds neuroligins. These proteins, with an altered catalytic triad and no known hydrolytic activity, display well-identified cell adhesion properties. The availability of complete genomes of a few metazoans provides opportunities to evaluate when these two protein families emerged during evolution. In bilaterian animals, acetylcholinesterase co-localizes with proteins of cholinergic synapses while neuroligins co-localize and may interact with proteins of excitatory glutamatergic or inhibitory GABAergic/glycinergic synapses. To compare evolution of the cholinesterases and neuroligins with other proteins involved in the architecture and functioning of synapses, we devised a method to search for orthologs of these partners in genomes of model organisms representing distinct stages of metazoan evolution. Our data point to a progressive recruitment of synaptic components during evolution. This finding may shed light on the common or divergent developmental regulation events involved into the setting and maintenance of the cholinergic versus glutamatergic and GABAergic/glycinergic synapses
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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