Vincent Huc

Covalent grafting onto self-adhesive surfaces based on aryldiazonium salt seed layers

The chemistry of aryldiazonium salts has been thoroughly used in recent years to graft in a very simple and robust way ultrathin polyphenylene-like films on a broad range of surfaces. We show here that the same chemistry can be used to obtain “self-adhesive surfaces”. This target was reached in a simple way by coating various surfaces with chemisorbed organic films containing active aryldiazonium salts. These “self-adhesive surfaces” are then put into contact with various species (molecules, polymers, nanoparticles, nanotubes, graphene flakes, etc.) that react either spontaneously or under activation with the immobilized aryldiazonium salts. Our self-adhesive surfaces were synthesized following a simple aqueous two-step protocol based on p-phenylenediamine diazotisation. The first diazotisation step results in the robust grafting of thin polyaminophenylene (PAP) layers onto the surface. The second diazotisation step changed the grafted PAP film into a “poly-aryldiazonium polymer” (PDP) film. The covalent grafting between those self-adhesive surfaces and the target species was achieved by direct contact or by immersion of the self-adhesive surfaces in solution. We present in this preliminary work the grafting of multi-wall carbon nanotubes (MWCNTs), flakes of highly oriented pyrolytic graphite (HOPG), various organic compounds and copper nanoparticles. We also tested these immobilized aryldiazonium salts as electropolymerization initiators for the grafting-to process.

Large and flat graphene flakes produced by epoxy bonding and reverse exfoliation of highly oriented pyrolytic graphite.

We present a fabrication method producing large and flat graphene flakes that have a few layers down to a single layer based on substrate bonding of a thick sample of highly oriented pyrolytic graphite (HOPG), followed by its controlled exfoliation down to the few to single graphene atomic layers. As the graphite underlayer is intimately bonded to the substrate during the exfoliation process, the obtained graphene flakes are remarkably large and flat and present very few folds and pleats. The high occurrence of single-layered graphene sheets being tens of microns wide in lateral dimensions is assessed by complementary probes including spatially resolved micro-Raman spectroscopy, atomic force microscopy and electrostatic force microscopy. This versatile method opens the way for deposition of graphene on any substrates, including flexible ones.

Ether-induced rate enhancement of Mo-catalyzed alkyne metathesis under mild conditions

A “user-friendly” catalyst system generated in situ in the absence of alkyne from Mo(CO)6, p-chlorophenol and a polyether over a bed of molecular sieves, is seen to achieve the metathesis of phenylpropyne at 50°C with a significant rate enhancement depending on the nature of the ether, with 1,2-diphenoxyethane exhibiting the highest efficiency.

Manipulation of cadmium selenide nanorods with an atomic force microscope

We have used an atomic force microscope (AFM) to manipulate and study ligand-capped cadmium selenide nanorods deposited on highly oriented pyrolitic graphite (HOPG). The AFM tip was used to manipulate (i.e., translate and rotate) the nanorods by applying a force perpendicular to the nanorod axis. The manipulation result was shown to depend on the point of impact of the AFM tip with the nanorod and whether the nanorod had been manipulated previously. Forces applied parallel to the nanorod axis, however, did not give rise to manipulation. These results are interpreted by considering the atomic-scale interactions of the HOPG substrate with the organic ligands surrounding the nanorods. The vertical deflection of the cantilever was recorded during manipulation and was combined with a model in order to estimate the value of the horizontal force between the tip and nanorod during manipulation. This horizontal force is estimated to be on the order of a few tens of nN.

A new approach to grafting a monolayer of oriented Mn12 nanomagnets on silicon

The functionalisation of a Si(100) silicon wafer allows for the oriented grafting of a monolayer of Mn12 nanomagnets using a two-step procedure.

Charge Transfer and Tunable Ambipolar Effect Induced by Assembly of Cu(II) Binuclear Complexes on Carbon Nanotube Field Effect Transistor Devices

Assembly of paramagnetic Cu(2) complexes with a Schiff base scaffold possessing extended electron delocalization together with a quasi-planar structure onto carbon nanotubes induces a diameter-selective charge transfer from the complex to the nanotubes leading to an interestingly large and tunable ambipolar effect. We used complementary techniques such as electron paramagnetic resonance, absorption spectroscopy, and photoluminescence to ensure the success of the assembly process and the integrity of the complex in the nanohybrid. We carried out density functional theory type calculations to rationalize the experimental results, evidencing the selective enhanced interaction of the metal complexes with one type of nanotube.

Grafting a Monolayer of Superparamagnetic Cyanide-Bridged Coordination Nanoparticles on Si(100)

The grafting of a monolayer of 6 nm superparamagnetic cyanide-bridged CsNiCr nanoparticles was achieved on a Ni(II)-functionalized Si(100) substrate; magnetic studies reveals that the grafted nanoparticles are nearly magnetically isolated within the monolayer.

Imaging and spectroscopy of individual CdSe nanocrystals on atomically resolved surfaces

Imaging and spectroscopy of individual CdSe nanocrystals have been performed with the scanning tunneling microscope (STM) on atomically resolved hydrogenated Si(100) surfaces. The CdSe nanocrystals have been deposited under vacuum onto the surface by using the pulse valve method. Two different types of CdSe nanocrystals, capped either with trioctylphosphine oxide ligands or with cadmium stearate ligands, have been studied to optimize their anchoring to the surface. The I(V) spectroscopy shows a characteristic resonant excitation spectrum through the unoccupied levels of the nanocrystals with no significant charging effect. This suggests that the nanocrystals are weakly coupled to the surface, thus requiring a stronger coupling with the STM tip to achieve a measurable tunnel current. These results demonstrate the importance of depositing nanocrystals on clean and atomically well-defined surfaces for reliable measurement of their properties.

Ultrahigh vacuum deposition of CdSe nanocrystals on surfaces by pulse injection

The fabrication of thin films of colloidal semiconductor nanocrystals is attracting much attention due to their exceptional optoelectronic properties. This requires the development of new methods for depositing nanocrystals under well-controlled conditions. Here, we report the use of the pulse injection method to deposit CdSe nanocrystals under ultrahigh vacuum (UHV) on clean and well-ordered surfaces. The deposition of nanocrystals has been tested by x-ray photoelectron spectroscopy (XPS) and near edge x-ray absorption fine structure spectroscopy. Special attention has been paid to the preparation of very pure solutions of CdSe nanocrystals using cadmium stearate, trioctylphosphine oxide (TOPO) and the TOP/Se adduct for the nanocrystals synthesis followed by dissolution in pentane. It has been found that CdSe nanocrystals adsorb with similar sticking coefficients on graphite, hydrogenated silicon (100) and hydrogenated diamond (100) surfaces. Furthermore, the XPS analysis has revealed that the surface of the CdSe nanocrystal is Cd rich, which has important consequences for the optical and chemical properties. This ability to deposit semiconductor nanocrystals under UHV conditions on clean and well-ordered surfaces opens up new perspectives for studying in a reliable manner all their chemical, electronic and optical properties.

Electrical-field-induced structural change and charge transfer of lanthanide–salophen complexes assembled on carbon nanotube field effect transistor devices

The application of a negative gate voltage on a carbon nanotube field effect transistor decorated by a binuclear Tb(III) complex leads to the generation of a negatively charged mononuclear one, presenting an electron density transfer to the nanotube and ambipolar behaviour.