Coaxial nanowires as plasmon-mediated remote nanosensors.

This study reports on the plasmon-mediated remote Raman sensing promoted by specially designed coaxial nanowires. This unusual geometry for Raman study is based on the separation, by several micrometres, of the excitation laser spot, on one tip of the nanowire, and the Raman detection at the other tip. The very weak efficiency of Raman emission makes it challenging in a remote configuration. For the proof-of-concept, we designed coaxial nanowires consisting of a gold core to propagate surface plasmon polaritons and a Raman-emitting shell of poly(3,4-ethylene-dioxythiophene). The success of the fabrication was demonstrated by correlating, for the same single nanowire, a morphological analysis by electron microscopy and Raman spectroscopy analysis. Importantly for probing the remote-Raman effect, the original hard template-based process allows one to control the location of the polymer shell all along the nanowire, or only close to one or the two nanowire tips. Such all-in-one single nanowires could have applications in the remote detection of photo-degradable substances and for exploring 1D nanosources for integrated photonic and plasmonic systems.

Crystal structure and chemical bonding in the mixed anion compound BaSF.

BaSF was synthesised by a solid state reaction at high temperature and its crystal structure was determined thanks to X-ray diffraction on a single crystal. This transparent yellow fluorochalcogenide has an intergrowth structure built from the stacking of fluorite type layers and sulfur layers. In BaSF sulfur atoms form dimers with interatomic distances as short as 2.1074(10) Å. DFT calculations confirm that this compound is a band insulator with the Fermi level lying in between the antibonding π* and σ* molecular orbitals of the sulfur dimers. Reflectance measurements show that the optical band gap of BaSF is about 2.7 eV in good agreement with the value found from DFT calculations.

Carboxymethylcellulose/single walled carbon nanotube complexes.

In this work, Carboxymethylcellulose/single walled carbon nanotube hybrids are prepared. Our goal is to use the non-covalent association of an anionic polysaccharide and single walled carbon nanotubes to prepare a biocompatible complex which preserves the intrinsic properties of the nanotubes. The hybrids are characterized by Raman scattering, Emission spectroscopy and Atomic Force Microscopy. A comparison is made with sodium dodecyl benzene sulfonate dispersed nanotubes. We show that carboxymethylcellulose forms an apparently non-helicoidal superstructure with carbon nanotubes which leads to their individualization. Emission and Raman spectroscopies suggest that the interaction occurs preferentially with semiconducting nanotubes. Further sugar chemistry may open different functionalization opportunities that will contribute to the design of biosensors and open this field of applications.

Electropolymerization of N-ethylcarbazole on single walled carbon nanotubes-cyclic voltammetry, raman and FTIR studies.

The electrochemical polymerization of N-ethyl carbazole (EK) on carbon nanotubes (CNs) films immersed in a LiClO4/acetonitrile solution was studied by cyclic voltammetry. Cyclic voltammograms recorded on a blank Pt electrode were compared with those obtained when CNs films were deposited on a Pt plate. In the latter case, the oxidation maximum is not clearly observed. Using the Raman scattering studies, oligomers of poly(N-ethyl carbazole) (PEK) on CNs are shown to be formed. A covalent functionalization of CNs with the PEK oligomers is demonstrated by FTIR spectroscopy studies. The formation of new C-C covalent bonds between CNs and the benzene ring of PEK induces steric hindrance effects that are shown in FTIR spectra by the increase in the intensity of the absorption band at 1072 cm(-1) attributed to the vibration of C-H in plane deformation of aromatic ring. The influence of the monomer and the supporting electrolyte concentration as well as the sweep rate on the polymerization conditions in the case of the composites based on the PEK oligomers and CNs were also investigated.

Neutron spin-echo investigation of slow spin dynamics in kagomé-bilayer frustrated magnets as evidence for phonon assisted relaxation in SrCr9xGa12-9xO19.

A neutron spin-echo investigation of the low temperature spin dynamics in two well-characterized kagomé bilayer compounds SrCr9xGa12-9xO19 (x=0.95, SCGO) and Ba2Sn2ZnCr7xGa10-7xO22 (x=0.97, BSZCGO) reveals two novel features. One is the slowing down of the relaxation rate without critical behavior at Tg, where a macroscopic spin-glass-like freezing occurs. The second is, in SCGO at 4 K (approximately Tg)

Raman spectroscopy of single-wall boron nitride nanotubes.

Single-wall boron nitride nanotubes samples synthesized by laser vaporization of a hexagonal BN target under a nitrogen atmosphere are studied by UV and visible Raman spectroscopy. We show that resonant conditions are necessary for investigating phonon modes of BNNTs. Raman excitation in the UV (229 nm) provides preresonant conditions, allowing the identification of the A1 tangential mode at 1370 cm(-1). This is 5 cm(-1) higher than the E(2g) mode in bulk h-BN. Ab initio calculations show that the lower frequency of bulk h-BN with respect to large diameter nanotubes and the single sheet of h-BN is related to a softening of the sp2 bonds in the bulk due to interlayer interaction.