The g factor of conduction electrons in aluminium : calculation and application to spin resonance

We calculate the g factor at every point of the Fermi surface of aluminium by using a classical \'four orthogonalised plane waves scheme and by introducing the spinorbit potential as a perturbation. An important difficulty remains, linked to the choice of the wavefunction phase. Moreover we propose a phenomenological model based on the narrowing of the g distribution by two types of motion: a random one corresponding to the diffusion of electrons on the crystalline imperfections and a coherent one around the cyclotron orbits. A qualitative model accounts relatilely well for the spin resonance experimental data

Synthesis of conducting graphite-like nanometer wires via soluble precursors

Graphite - like conducting materials were encapsulated in the channels of new mesoporous MCM- 41 materials with typical channel diameters of 30-40 Ä. Acrylonitrile was introduced into the hosts via vapor transport, then polymerized with external radical initiators, K2S2O8 and HNaSOß. The polymers in the host cavities were further pyrolyzed at different temperatures under vacuum or nitrogen atmosphere. The properties of the polymer systems were studied while encapsulated or after dissolution of the host. The crystallinity of the hosts is intact after insertion of the polymer (even after pyrolysis at 800°C). The formation of conducting graphite - like materials inside the hosts was demonstrated with Raman and UV spectra. The nitrogen to carbon ratio of the pyrolyzed polymers depends on the pyrolysis temperature and the polymer environment. Most interestingly, the normalized AC absorption of pyrolyzed polyacrylonitrile in MCM-41 (at 800°C) is comparable to graphite

Spectroscopic evidence for large (>>1 µm) lithium-colloid creation in electron-irradiated Li2O single crystals

We have created lithium metal colloids by electron-irradiating single crystals of lithium oxide near 0°C. The striking feature is the observation of two kinds of colloids manifesting themselves as two EPR metallic lines, the narrow line corresponding to small metallic clusters (size < 1 µm) and the broad one associated with large metallic colloids visible by optical microscopy (~ 20 µm). The latter are also observed by NMR. A further indication for the presence of colloids of different types is the differing recovery behavior of the two EPR lines in an annealing treatment

Nucleation and growth of single wall carbon nanotubes

The nucleation and growth of single wall carbon nanotubes from a carbon-saturated catalytic particle surrounded by a single sheet of graphene is described qualitatively by using a very restricted number of elementary processes, namely Stone-Wales defects and carbon bi-interstitials. Energies of the different configurations are estimated by using a Tersoff energy minimization scheme. Such a description is compatible with a broad variety of size or helicity of the tubes. Several mechanisms of growth of the embryos are considered: one of them is made more favourable when the tubes embryos are arranged in an hexagonal network in the graphene plane. All the proposed mechanisms can be indefinitely repeated for the growth of the nanotubes.Comment: Solid state communications, in pres

Lithium colloids and color center creation in electron-irradiated Li2NH observed by electron-spin resonance

4 pagesInternational audienceWe have irradiated Li2NH powder with MeV electrons at room temperature and investigated the introduced defects with electron spin resonance. CESR indicates the presence of nanosize metallic Li colloids seen as a Lorentzian line with a g = 2.0023 and a line width DeltaH = 50 microT. A second, broader, signal (DeltaH = 3 to 4 mT) appears superimposed upon the Li line at low T (Curie-type behavior) which exhibits complex T-dependence with a break near 180 K for its g-value and DeltaH. We are suggesting for the latter a vacancy-type defect in the NH-sublattice, with freezing of its H-component below 180 K. When heated both the Li colloids and the color centers anneal around 100 C probably due to hydrogen evolution and subsequent chemical degradation

Nucleation and growth of single wall carbon nanotubes

Abstract The nucleation and growth of single wall carbon nanotubes from a carbon-saturated catalytic particle surrounded by a single sheet of graphene is described qualitatively by using a very restricted number of elementary processes, namely Stone-Wales defects and carbon bi-interstitials. Energies of the different configurations are estimated by using a Tersoff energy minimization scheme. Such a description is compatible with a broad variety of size or helicity of the tubes. Several mechanisms of growth of the embryos are considered: one of them is made more favourable when the tubes embryos are arranged in a hexagonal network in the graphene plane. All the proposed mechanisms can be indefinitely repeated for the growth of the nanotubes.

Thermal annealing study of swift heavy-ion irradiated zirconia

Sintered samples of monoclinic zirconia (alpha-ZrO2) have been irradiated at room temperature with 6.0-GeV Pb ions in the electronic slowing down regime. X-ray diffraction (XRD) and micro-Raman spectroscopy measurements showed unambiguously that a transition to the 'metastable' tetragonal phase (beta-ZrO2) occurred at a fluence of 6.5x10^12 cm-2 for a large electronic stopping power value (approx 32.5 MeV $\mu$m-1). At a lower fluence of 1.0x10^12 cm-2, no such phase transformation was detected. The back-transformation from beta- to alpha-ZrO2 induced by isothermal or isochronal thermal annealing was followed by XRD analysis. The back-transformation started at an onset temperature around 500 K and was completed by 973 K. Plots of the residual tetragonal phase fraction deduced from XRD measurements versus annealing temperature or time are analyzed with first- or second-order kinetic models. An activation energy close to 1 eV for the back-transformation process is derived either from isothermal annealing curves, using the so-called "cross-cut" method, or from the isochronal annealing curve, using a second-order kinetic law. Correlation with the thermal recovery of ion-induced paramagnetic centers monitored by EPR spectroscopy is discussed. Effects of crystallite size evolution and oxygen migration upon annealing are also addressed