Pascale Chenevier

Intrinsic current gain cutoff frequency of 30GHz with carbon nanotube transistors

High frequency capabilities of carbon nanotube field-effect transistors (CNTFETs) are investigated. Structures with a large number of single-walled carbon nanotubes were fabricated using dielecrophoresis to increase the density of nanotubes in the device channel. The authors obtained an intrinsic current gain cutoff frequency of 30GHz establishing state-of-the-art high frequency (hf) potentialities of CNTFETs. The device also showed a maximum stable gain above 10dB at 20GHz. Finally, the parameters of an equivalent circuit model of multitube CNTFET at 20GHz are determined, which open the route to the modeling of nanotubes-based hf electronics.

Mechanism of the coupling of diazonium to single-walled carbon nanotubes and its consequences.

On the tube: The coupling of diazonium ions onto single-walled carbon nanotubes is shown to proceed through a radical chain reaction by kinetic analysis of the absorption peak drop (see picture). Radical species are also revealed by ESR. Metallic (m) nanotubes play a special catalytic role in the functionalization of semiconducting (sc) nanotubes.Due to its simplicity and versatility, diazonium coupling is the most widely used method for carbon nanotube (CNT) functionalization to increase CNT processability and add new functionalities. Yet, its mechanism is so far mostly unknown. Herein, we use kinetic analysis to shed light on this complex mechanism. A free-radical chain reaction is revealed by absorption spectroscopy and ESR. Metallic CNTs are shown to play an unexpected catalytic role. The step determining the selectivity towards metallic CNTs is identified by a Hammett correlation. A mechanistic model is proposed that predicts reactivity and selectivity as a function of diazonium electrophilicity and metallic-to-semiconducting CNT ratio, thus opening perspectives of controlled high-yield functionalization and purification.

High hydrostatic pressure small-angle X-ray scattering cell for protein solution studies featuring diamond windows and disposable sample cells

A high-pressure cell for synchrotron small-angle X-ray scattering (SAXS) studies of protein solutions is described. The design was optimized for use at up to 400 MPa in liquid pressure and with 8−12 keV X-rays with particular emphasis on the ease of use. The high-pressure cell was fabricated from corrosion-resistant Inconel 725 (Special Metals Corporation, Huntington, WV, USA) and featured Poulter-type windows [Poulter (1932). Phys. Rev. 40, 861–871]. Flat natural diamonds, 500 µm thick, were recycled from diamond anvil cells and were shown to perform well as high-pressure SAXS windows. For a simple and effective method of sample isolation, disposable plastic sample cells with a defined path length and reproducible parasitic scattering were designed. These sample cells enable efficient use of synchrotron time. The cells facilitate rapid and easy sample changes, eliminate the need to clean the cell between sample changes, and reduce the sample volume to as low as 12 µl. The disposable cells can also be used separately from the high-pressure cell for SAXS measurements at ambient pressure and temporary storage of samples. The performance of the apparatus is demonstrated with T4 lysozyme.

Interaction of Cationic Colloids at the Surface of J774 Cells: A Kinetic Analysis

We have characterized the binding of multilamellar colloids to J774 cells. Cationic colloids were shown to bind much more efficiently than neutral ones. Particle uptake by cells was followed by flow cytometry and fluorescence microscopy. Analysis of the kinetics of uptake of cationic particles indicated that binding on the cell surface occurred with two characteristic times. Analysis of the dissociation properties allowed discriminating between several alternative models for adsorption and led us to propose a mechanism that involved two independent classes of binding sites on the cell surface. One class of sites appeared to be governed by a classic mass action law describing a binding equilibrium. The other sites were populated irreversibly by particles made of 10% cationic lipids. This was observed in the absence of endocytosis, under conditions where both the equilibrium and the irreversible binding occurred at the cell surface. We determined the rate constants for the different steps. We found that the reversible association occurred with a characteristic time of the order of tens of seconds, whereas the irreversible binding took a hundred times longer. The presence of serum proteins in the incubation medium did not drastically affect the final uptake of the particles. In contrast, the capture of the particles by cells significantly dropped when the fraction of positively charged lipids contained in the colloids was decreased from 10% to 5%. Finally, the results will be discussed within a comprehensive model where cationic particles find labile binding sites in the volume of the pericellular network (glycocalyx and extracellular matrix) and less-accessible irreversible binding sites at the cell membrane itself.

Optimized network of multi-walled carbon nanotubes for chemical sensing

This work reports the design of a resistive gas sensor based on 2D mats of multi-walled carbon nanotubes (MWCNTs) grown by aerosol-assisted chemical vapour deposition. The sensor sensitivity was optimized using chlorine as analyte by tuning both CNT network morphology and CNT electronic properties. Optimized devices, operating at room temperature, have been calibrated over a large range of concentration and are shown to be sensitive down to 27 ppb of chlorine. The as-grown MWCNT response is compared with responses of 2000 °C annealed CNTs, as well as of nitrogen-doped CNTs and CNTs functionalized with polyethyleneimine (PEI). Under chlorine exposure, the resistance decrease of as-grown and annealed CNTs is attributed to charge transfer from chlorine to CNTs and demonstrates their p-type semiconductor behaviour. XPS analysis of CNTs exposed to chlorine shows the presence of chloride species that confirms electron charge transfer from chlorine to CNTs. By contrast, the resistance of nitrogen-doped and PEI functionalized CNTs exposed to chlorine increases, in agreement with their n-type semiconductor nature. The best response is obtained using annealed CNTs and is attributed to their higher degree of crystallinity.

RGD-functionalized spherulites™ as targeted vectors captured by adherent cultured cells

Spherulites are multilamellar vesicles consisting of concentric shells that can encapsulate small organic molecules or macromolecules. We investigate the possibility of targeting neutral spherulites to adherent culture cells by functionalizing their surface with RGD-containing ligands. The strength and specificity of association of RGD spherulites with several cell lines (EAhy 926 endothelial cell line, human umbilical vein endothelial cell (HUVEC) and human osteoprogenitor (HOP) primary cells) was studied, and the molecular interaction of RGD spherulites with the EAhy 926 cell surface was investigated. We show that, after binding to cells, spherulites are internalized.

Grafting of synthetic mannose receptor-ligands onto onion vectors for human dendritic cells targetingElectronic supplementary information (ESI) available: full experimental details. See http://www.rsc.org/suppdata/cc/b2/b206980f/

A practical preparation of onion vesicles targeted to dendritic cells involves the grafting of mannose-mimetic clusters, bearing a hydrazino group, onto the surface of onion vesicles containing an aldehyde functionalized lipid.

Toward full carbon interconnects: High conductivity of individual carbon nanotube to carbon nanotube regrowth junctions

A versatile chemical vapor deposition (CVD) based method for the fabrication and electrical measurement of individual carbon nanotube junctions was developed. ferritin or Fe particles were grafted on multiwalled carbon nanotubes (MWNTs) and used as catalysts for the subsequent growth of secondary MWNT by CVD. Junctions were then individually connected. The conductivities of the MWNTs and of the junction were measured. Statistical data show that the conductance of the MWNT-MWNT junction is similar to that of MWNT. This result paves the way for the use of carbon nanotubes as electrical interconnects in electronic applications.

Conception and Realization of a Non-Cationic Non-Viral DNA Vector

Cationic non-viral DNA vectors are very successful in in vitro transfections but less efficient in in vivo tests. This seems mainly due to the cationic nature of the molecules used to complex DNA. In this article, we describe the design and the route towards the realization of a non-viral non-cationic vector. The strategy follows three steps: first, the incorporation of DNA to a lamellar phase; second, the making of multilamellar vesicles containing a high loading of DNA by shearing the lamellar phase and, finally, the grafting of peptides onto the surface of the vesicles to target a specific receptor on the cells. Throughout this process, we had to overcome many obstacles; this review describes the present state of our work and summarizes the remaining steps.

Directed assembly for carbon nanotube device fabrication

Chemically and biochemically-directed assembly of nanotubes (NT) for electronics is reviewed. Examples of new field-effect devices prepared this way either for high frequency (40GHz) operation or for applications to an optoelectronics multilevel memory are presented. A route towards (bio)molecular interconnects for NTs is outlined