The purpose of manipulating isolated single-wall carbon nanotubes (SWNTs), rather than bundles, has led to an active research in the field of the functionalisation of such carbon compounds. Different ways exist today to obtain some new soluble macromolecules from SWNTs. Here we focus on the fluorination functionalisation. As the solubility properties depend essentially on the functionalisation degree, it is important to develop reliable and simple methods to quantify this degree. The C n F stoichiometry of three different fluorinated SWNTs samples are determined with the X-Ray Photoelectron Spectroscopy (XPS). Then the evolution of the Raman spectra with the fluorination degree of these samples is discussed. An atomic force microscopy (AFM) study highlights the good solvation properties of the most fluorinated sample with a majority of isolated nanotubes being observed. Then we take advantage of these good solvation properties, combined with the possibility of recovering the pristine non-fluorinated nanotubes, to carry out surface enhanced Raman spectroscopy (SERS) studies of well-dispersed SWNTs. These studies put in evidence the bundle effect, which is due to the agglomeration of SWNTs into bundles. This effect can be readily observed by Raman spectroscopy.
In 2001, Pickard and Mauri implemented the gauge including projected augmented wave (GIPAW) protocol for first-principles calculations of NMR parameters using periodic boundary conditions (chemical shift anisotropy and electric field gradient tensors). In this paper, three potentially interesting perspectives in connection with PAW/GIPAW in solid-state NMR and pure nuclear quadrupole resonance (NQR) are presented: (i) the calculation of J coupling tensors in inorganic solids; (ii) the calculation of the antisymmetric part of chemical shift tensors and (iii) the prediction of (14)N and (35)Cl pure NQR resonances including dynamics. We believe that these topics should open new insights in the combination of GIPAW, NMR/NQR crystallography, temperature effects and dynamics. Points (i), (ii) and (iii) will be illustrated by selected examples: (i) chemical shift tensors and heteronuclear (2)J(P-O-Si) coupling constants in the case of silicophosphates and calcium phosphates [Si(5)O(PO(4))(6), SiP(2)O(7) polymorphs and α-Ca(PO(3))(2)]; (ii) antisymmetric chemical shift tensors in cyclopropene derivatives, C(3)X(4) (X = H, Cl, F) and (iii) (14)N and (35)Cl NQR predictions in the case of RDX (C(3)H(6)N(6)O(6)), β-HMX (C(4)H(8)N(8)O(8)), α-NTO (C(2)H(2)N(4)O(3)) and AlOPCl(6). RDX, β-HMX and α-NTO are explosive compounds.
Semi-insulating GaAs materials, undoped or doped with concentration of chromium varying from 6×1015 to 4×1017 cm−3, have been studied using both Hall effect measurements and optical absorption measurements. It is definitively concluded that compensation comes from the presence of the deep donor EL2 in undoped materials, and from both this deep donor and the deep acceptor related to chromium in Cr-doped materials. Sets of curves are given which allow the determination of ND-NA, the concentration of shallow donors and acceptors, knowing the Hall mobility and the Cr concentration in a given sample. Such curves can be a working tool for assessing any piece of semi-insulating GaAs in a routine way.
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