398 research outputs found
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
The Cherenkov Telescope Array Performance in Divergent Mode
Two of the Key Science Projects of the Cherenkov Telescope Array (CTA)
consist in performing a deep survey of the Galactic and Extragalactic sky,
providing an unbiased view of the Universe at energies above tens of GeV. To
optimize the time spent to perform the Extragalactic survey, a so-called
"divergent mode" of the CTA was proposed as an alternative observation strategy
to the traditional parallel pointing in order to increase its instantaneous
field of view. The search for transient VHE sources would also benefit from an
extended field of view. In the divergent mode, each telescope points to a
position in the sky that is slightly offset, in the outward direction, from the
center of the field of view. In this contribution, we present the first
performance estimation from full Monte Carlo simulation of possible CTA
divergent mode setups
Conductance switching at the nanoscale of diarylethene derivatives self-assembled monolayers on LaSrMnO
We report on the phosphonic acid route for the grafting of functional
molecules, optical switch (dithienylethene diphosphonic acid, DDA), on
La0.7Sr0.3MnO3 (LSMO). Compact self-assembled monolayers (SAMs) of DDA are
formed on LSMO as studied by topographic atomic force microscopy (AFM),
ellipsometry, water contact angle and X-ray photoemission spectroscopy (XPS).
The conducting AFM measurements show that the electrical conductance of
LSMO/DDA is about 3 decades below that of the bare LSMO substrate. Moreover,
the presence of the DDA SAM suppresses the known conductance switching of the
LSMO substrate that is induced by mechanical and/or bias constraints during
C-AFM measurements. A partial light-induced conductance switching between the
open and closed forms of the DDA is observed for the LSMO/DDA/C-AFM tip
molecular junctions (closed/open conductance ratio of about 8). We show that,
in the case of long-time exposition to UV light, this feature can be masked by
a non-reversible decrease (a factor of about 15) of the conductance of the LSMO
electrode.Comment: Full paper with supporting informatio
Negative differential resistance and non-volatile memory in hybrid redox organic/nanoparticle devices
International audienc
Conductance statistics from a large array of sub-10 nm molecular junctions
Devices made of few molecules constitute the miniaturization limit that both
inorganic and organic-based electronics aspire to reach. However, integration
of millions of molecular junctions with less than 100 molecules each has been a
long technological challenge requiring well controlled nanometric electrodes.
Here we report molecular junctions fabricated on a large array of sub-10 nm
single crystal Au nanodots electrodes, a new approach that allows us to measure
the conductance of up to a million of junctions in a single conducting Atomic
Force Microscope (C-AFM) image. We observe two peaks of conductance for
alkylthiol molecules. Tunneling decay constant (beta) for alkanethiols, is in
the same range as previous studies. Energy position of molecular orbitals,
obtained by transient voltage spectroscopy, varies from peak to peak, in
correlation with conductance values.Comment: ACS Nano (in press
Clinical and genetic analysis of 29 Brazilian patients with Huntington’s disease-like phenotype
Huntington’s disease (HD) is a neurodegenerative disorder characterized by chorea,
behavioral disturbances and dementia, caused by a pathological expansion of the CAG
trinucleotide in the HTT gene. Several patients have been recognized with the typical HD
phenotype without the expected mutation. The objective of this study was to assess the
occurrence of diseases such as Huntington’s disease-like 2 (HDL2), spinocerebellar ataxia
(SCA) 1, SCA2, SCA3, SCA7, dentatorubral-pallidoluysian atrophy (DRPLA) and choreaacanthocytosis
(ChAc) among 29 Brazilian patients with a HD-like phenotype. In the group
analyzed, we found 3 patients with HDL2 and 2 patients with ChAc. The diagnosis was not
reached in 79.3% of the patients. HDL2 was the main cause of the HD-like phenotype in
the group analyzed, and is attributable to the African ancestry of this population. However,
the etiology of the disease remains undetermined in the majority of the HD negative
patients with HD-like phenotype.
Key words: Huntington’s disease, Huntington’s disease-like, chorea-acanthocytosis,
Huntington’s disease-like 2
Mutation update for the GPC3 gene involved in Simpson-Golabi-Behmel syndrome and review of the literature
Simpson-Golabi-Behmel syndrome (SGBS) is an X-linked multiple congenital anomalies and overgrowth syndrome caused by a defect in the glypican-3 gene (GPC3). Until now, GPC3 mutations have been reported in isolated cases or small series and the global genotypic spectrum of these mutations has never been delineated. In this study, we review the 57 previously described GPC3 mutations and significantly expand this mutational spectrum with the description of 29 novel mutations. Compiling our data and those of the literature, we provide an overview of 86 distinct GPC3 mutations identified in 120 unrelated families, ranging from single nucleotide variations to complex genomic rearrangements and dispersed throughout the entire coding region of GPC3. The vast majority of them are deletions or truncating mutations (frameshift, nonsense mutations) predicted to result in a loss-of-function. Missense mutations are rare and the two which were functionally characterized, impaired GPC3 function by preventing GPC3 cleavage and cell surface addressing respectively. This report by describing for the first time the wide mutational spectrum of GPC3 could help clinicians and geneticists in interpreting GPC3 variants identified incidentally by high-throughput sequencing technologies and also reinforces the need for functional validation of non-truncating mutations (missense, in frame mutations, duplications)
Kinetics of maternal immunity against rabies in fox cubs (Vulpes vulpes)
BACKGROUND: In previous experiments, it was demonstrated that maternal antibodies (maAb) against rabies in foxes (Vulpes vulpes) were transferred from the vixen to her offspring. However, data was lacking from cubs during the first three weeks post partum. Therefore, this complementary study was initiated. METHODS: Blood samples (n = 281) were collected from 64 cubs (3 to 43 days old) whelped by 19 rabies-immune captive-bred vixens. Sera was collected up to six times from each cub. The samples were analysed by a fluorescence focus inhibition technique (RFFIT), and antibody titres (nAb) were expressed in IU/ml. The obtained data was pooled with previous data sets. Subsequently, a total of 499 serum samples from 249 cubs whelped by 54 rabies-immune vixens were fitted to a non-linear regression model. RESULTS: The disappearance rate of maAb was independent of the vixens' nAb-titre. The maAb-titre of the cubs decreased exponentially with age and the half-life of the maAb was estimated to be 9.34 days. However, maAb of offspring whelped by vixens with high nAb-titres can be detected for longer by RFFIT than that of offspring whelped by vixens with relatively low nAb-titres. At a mean critical age of about 23 days post partum, maAb could no longer be distinguished from unspecific reactions in RFFIT depending on the amount of maAb transferred by the mother. CONCLUSIONS: The amount of maAb cubs receive is directly proportional to the titre of the vixen and decreases exponentially with age below detectable levels in seroneutralisation tests at a relatively early age
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