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 †

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

Fermi level shift in carbon nanotubes by dye confinement

International audienceDye confinement into carbon nanotube significantly affects the electronic charge density distribution of the final hybrid system. Using the electron-phonon coupling sensitivity of the Raman G-band, we quantify experimentally how charge transfer from thiophene oligomers to single walled carbon nanotube is modulated by the diameter of the nano-container and its metallic or semiconducting character. This charge transfer is shown to restore the electron-phonon coupling into defected metallic nanotubes. For sub-nanometer diameter tube, an electron transfer optically activated is observed when the excitation energy matches the HOMO-LUMO transition of the confined oligothiophene. This electron doping accounts for an important enhancement of the photoluminescence intensity up to a factor of nearly six for optimal confinement configuration. This electron transfer shifts the Fermi level, acting on the photoluminescence efficiency. Therefore, thiophene oligomer encapsulation allows modulating the electronic structure and then the optical properties of the hybrid system