260 research outputs found
Hierarchical functionalisation of single-wall carbon nanotubes with DNA through positively charged pyrene
A simple and efficient method to link reversibly DNA to SWNTs via electrostatic interaction is reported. The DNA/nanotube hybrids are characterised by a combination of gel electrophoresis and AFM
New insights in the electronic transport in reduced graphene oxide using Scanning Electrochemical Microscopy
International audienceGraphene and graphene analogues such as GO or reduced-GO (r-GO) are attracting increasing attention from the scientific community. These materials have outstanding properties, so that many potential applications in the fields of electronics, sensors, catalysis and energy storage are being considered. GO combines several advantages such as availability in large quantity, low cost and easy processability. However, contrary to graphene, GO is electronically insulating and has to be reduced into a conductive material, r-GO. In a recent work we introduced a new localized functionalization method of GO deposited on a silicon oxide surface based on its reduction at the local scale thanks to scanning electrochemical microscopy (SECM): the reducer is generated at the microelectrode, that is moved close to the substrate. The recovery of electronic conductivity upon reduction enables the selective electrochemical functionalization of patterns. In the present work, we introduce a new method to evaluate at a local scale the conductivity of r-GO layers with SECM. In addition we show how images of individual and interconnected flakes directly reveal the signature of the contact resistance between flakes in a non-contact and substrate-independent way. Quantitative evaluation of the parameters is achieved with the support of numerical simulations to interpret the experimental results. Overall, these works illustrates the high potential and versatility of SECM to investigate and functionalize 2D materials
Signature of gate-tunable magnetism in graphene grafted with Pt-porphyrins
Inducing magnetism in graphene holds great promises, such as controlling the
exchange interaction with a gate electrode and generating exotic magnetic
phases. Coating graphene with magnetic molecules or atoms has so far mostly
lead to decreased graphene mobility. In the present work, we show that
Pt-porphyrins adsorbed on graphene lead to an enhanced mobility and to
gate-dependent magnetism. We report that porphyrins can be donor or acceptor,
depending on graphene s initial doping. The porphyrins transfer charge and
ionize around the charged impurities on graphene, decreasing the graphene
doping and increasing its mobility. In addition, ionized porphyrins carry a
magnetic moment. Using the sensitivity of mesoscopic transport to magnetism, in
particular the superconducting proximity effect and conductance fluctuations,
we explore the magnetic order induced in graphene by the interacting magnetic
moments of the ionized porphyrins. Among the signatures of magnetism, we find
two-terminal-magnetoresistance fluctuations with an odd component, a tell-tale
sign of time reversal symmetry breaking at zero field, that does not exist in
uncoated graphene sample. When graphene is connected to superconducting
electrodes, the induced magnetism leads to a gate-voltage-dependent suppression
of the supercurrent, modified magnetic interference patterns, and
gate-voltage-dependent magnetic hysteresis. The magnetic signatures are
greatest for long superconductor graphene superconductor junctions and for
samples with the highest initial doping, compatible with a greater number of
ionized and thus magnetic porphyrins. Our findings suggest that long-range
magnetism is induced through graphene by the ionized porphyrins magnetic
moment. This magnetic interaction is controlled by the density of carriers in
graphene, a tunability that could be exploited in spintronic applications
All solution-processed organic photocathodes with increased efficiency and stability via the tuning of the hole-extracting layer â€
International audiencePhotoelectrodes based on solution-processed organic semiconductors are emerging as low-cost alternatives to crystalline semiconductors and platinum. In this work, the performance and stability of P3HT:PCBM\MoS 3-based photocathodes are considerably improved by changing the hole-extracting layer (HEL). Oxides such as reduced graphene oxide, nickel oxide or molybdenum oxide are deposited via solution processes. With MoO x , a photocurrent density of 2 mA cm À2 during 1 h is obtained with the processing temperature lower than 150 C – thus compatible with flexible substrates. Furthermore, we show that the performances are directly correlated with the work function of the HEL material, and the comparison with solid-state solar cells shows that efficient HELs are not the same for the two types of devices
Total Angular Momentum Conservation During Tunnelling through Semiconductor Barriers
We have investigated the electrical transport through strained
p-Si/Si_{1-x}Ge_x double-barrier resonant tunnelling diodes. The confinement
shift for diodes with different well width, the shift due to a central
potential spike in a well, and magnetotunnelling spectroscopy demonstrate that
the first two resonances are due to tunnelling through heavy hole levels,
whereas there is no sign of tunnelling through the first light hole state. This
demonstrates for the first time the conservation of the total angular momentum
in valence band resonant tunnelling. It is also shown that conduction through
light hole states is possible in many structures due to tunnelling of carriers
from bulk emitter states.Comment: 4 pages, 4 figure
Chromophore Ordering by Confinement into Carbon Nanotubes
International audienceWe report an experimental study on the confinement of oligothiophene derivatives into single-walled carbon nanotubes over a large range of diameter (from 0.68 to 1.93 nm). We evidence by means of Raman spectroscopy and transmission electron microscopy that the supramolecular organizations of the confined oligothiophenes depend on the nanocontainer size. The Raman Radial Breathing Mode frequency is shown to be monitored by both the number of confined molecules into a nanotube section and the competition between oligothiophene/oligothiophene and oligothiophene/tube wall interactions. We finally propose simple Raman criteria to characterize oligothiophene supramolecular organization at the nanoscale
Autoimmune Pancreatitis Associated with High Levels of Chromogranin A, Serotonin and 5-Hydroxyindoleacetic Acid
We report a case of a male patient with autoimmune pancreatitis in whom biochemical examination revealed high plasma chromogranin A concentrations, histological demonstration of a small lymphocytic infiltrate and rapid decrease in size of the pancreatic mass following short-lasting therapy with methylprednisolone. To our knowledge, this is the first patient with autoimmune pancreatitis who had a simultaneous increase of serum chromogranin A levels, circulating and urinary serotonin concentrations and urine 5-hydroxyindoleacetic acid concentrations. This is one of the few cases of mass forming pancreatitis with small lymphocytic infiltrate found in a Caucasian patient and rapid decrease in size of the pancreatic mass following short-lasting therapy with methylprednisolone
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