Carbon nanotube chemistry and assembly for electronic devices

Carbon nanotubes (CNTs) have exceptional physical properties that make them one of the most promising building blocks for future nanotechnologies. They may in particular play an important role in the development of innovative electronic devices in the fields of flexible electronics, ultra-high sensitivity sensors, high frequency electronics, opto-electronics, energy sources and nano-electromechanical systems (NEMS). Proofs of concept of several high performance devices already exist, usually at the single device level, but there remain many serious scientific issues to be solved before the viability of such routes can be evaluated. In particular, the main concern regards the controlled synthesis and positioning of nanotubes. In our opinion, truly innovative use of these nano-objects will come from: (i) the combination of some of their complementary physical properties, such as combining their electrical and mechanical properties; (ii) the combination of their properties with additional benefits coming from other molecules grafted on the nanotubes (this route being particularly relevant for gas- and bio-sensors, opto-electronic devices and energy sources); and (iii) the use of chemically- or bio-directed self-assembly processes to allow the efficient combination of several devices into functional arrays or circuits. In this article, we review our recent results concerning nanotube chemistry and assembly and their use to develop electronic devices. In particular, we present carbon nanotube field effect transistors and their chemical optimization, high frequency nanotube transistors, nanotube-based opto-electronic devices with memory capabilities and nanotube-based nano-electromechanical systems (NEMS). The impact of chemical functionalization on the electronic properties of CNTs is analyzed on the basis of theoretical calculations. To cite this article: V. Derycke et al., C. R. Physique 10 (2009).     

Large old trees influence patterns of delta13C and delta15N in forests

Large old trees are the dominant primary producers of native pine forest, but their influence on spatial patterns of soil properties and potential feedback to tree regeneration in their neighbourhood is poorly understood. We measured stable isotopes of carbon (delta(13)C) and nitrogen (delta(15)N) in soil and litter taken from three zones of influence (inner, middle and outer zone) around the trunk of freestanding old Scots pine (Pinus sylvestris L.) trees, to determine the trees' influence on below-ground properties. We also measured delta(15)N and delta(13)C in wood cores extracted from the old trees and from regenerating trees growing within their three zones of influence. We found a significant and positive gradient in soil delta(15)N from the inner zone, nearest to the tree centre, to the outer zone beyond the tree crown. This was probably caused by the higher input of (15)N-depleted litter below the tree crown. In contrast, the soil delta(13)C did not change along the gradient of tree influence. Distance-related trends, although weak, were visible in the wood delta(15)N and delta(13)C of regenerating trees. Moreover, the wood delta(15)N of small trees showed a weak negative relationship with soil N content in the relevant zone of influence. Our results indicate that large old trees control below-ground conditions in their immediate surroundings, and that stable isotopes might act as markers for the spatial and temporal extent of these below-ground effects.     

Prompt and delayed nonsteroidal anti-inflammatory drug-photoinduced DNA damage in peripheral blood mononuclear cells measured with the comet assays

Nonsteroidal anti-inflammatory drug (NSAID)-photoinduced DNA damage in human peripheral blood mononuclear cells measured using the alkaline comet assay is presented. Whereas Tiaprofenic Acid-photoinduced DNA damage was promptly induced (i.e. observed at relatively low radiation doses), Ketoprofen-photoinduced DNA damage was delayed. This prompt and delayed effect is observed with UVA (320-400 nm), UVB (290-320 nm) and solar-simulated radiation and is attributed to the different photochemical properties of NSAID. The results from these experiments, carried out in living cells, confirm the speculations of NSAID-photoinduced DNA damage brought up by the many experiments conducted in solution.     

Asymmetric Induction by Chiral Phosphorus

We report on the asymmetric induction by a chiral phosphorus atom contained in a 2-oxo-1,3,2-oxazaphosphorinane ring into an adjacent keto, alkane, or alkene function.     

Identification of Dihydrocarveol Stereoisomers and Their Acetates Using Carbon-13 NMR Spectroscopy

The Carbon-13 NMR spectra of dihydrocarveol and dihydrocarvyl acetate stereoisomers are characterized. The chemical shifts are assigned taking account the steric and electronic substituent effects, the lanthanide induced shifts and the proton-carbon correlation.     

Evaluation and optimization of solid adsorbents for the sampling of gaseous methylated mercury species

This study evaluates the suitability of commercially available adsorbents for the measurement of gaseous organic mercury species namely monomethylmercury (MMHg) and dimethylmercury (DMHg).     

Carbene‐Mediated Functionalization of the Anomeric C?H Bond of Carbohydrates: Scope and Limitations

Herein we investigate the scope and limitations of a new synthetic approach towards α‐ and β‐ketopyranosides relying on the functionalization of the anomeric C? H bond of carbohydrates by insertion of a metal carbene. A key bromoacetate grafted at the 2‐position is the cornerstone of a stereoselective glycosylation/diazotransfer/quaternarization sequence that makes possible the construction of a quaternary center with complete control of the stereochemistry. This sequence shows a good tolerance toward protecting groups commonly used in carbohydrate chemistry and gives rise to quaternary disaccharides with good efficiency. In the case of a disaccharide with a more restricted conformation, this functionalization process can be hampered by the steric demand next to the targeted anomeric position. In addition, the formation of transient orthoesters during the glycosylation step may also reduce the overall efficiency of the synthetic sequence.