The magnetic properties of nanocrystalline titanium carbide dispersed in a carbon matrix (TiCx/C) prepared by the non-hydrolytic sol-gel process have been studied by dc magnetization measurements. The superconducting phase of titanium carbide has been observed at low temperatures with the onset of the superconducting transition temperature Tc at about 3.5 K, superimposed on a ferromagnetic component. At T > Tc the magnetic response of TiCx/C is determined by the interplay of the ferromagnetic contribution with the paramagnetic/diamagnetic signal of the metallic system and the contribution of exchange coupled paramagnetic ions. Moreover, significant differences are observed in the magnetic response for samples of the same preparation batch, indicative of the magnetic/electronic inhomogeneity of nanocrystalline titanium carbide which is important for its practical applications.

Polarized micro-Raman spectroscopy was applied to investigate the phase composition and transformation from the amorphous to the crystalline state, size effects, and the crystallographic orientation and antenna polarization effects on self-organized anodic TiO2 nanotubes (NTs), The morphological characteristics of the NTs were tailored by electrochemical anodization in both aqueous (phosphate buffer) and organic (ethylene glycol) electrolytes as well as in perchlorate/chloride-containing electrolytes. Postgrowth thermal annealing was confirmed to reduce markedly the organic and inorganic species encapsulated in the as-grown arrays and drive the transformation of the amorphous titania to nanocrystalline anatase. Crystallite size and shape effects as well as oxygen nonstoichiometry were investigated through the variation of the low-frequency Eg anatase mode for the TiO2 NT arrays produced in different electrolyte media, and the results were compared with the predictions of the phonon confinement model for anatase nanoparticles. Polarized micro-Raman spectra identify partial orientation effects, indicating preferential (101) growth in the case of the shorter TiO2 NTs (length ≤ 1 μm), while a predominant random orientation of the anatase crystallites is found for the long tubes (length ≥ 10 μm). Polarized measurements on the cross section of free-standing NT membranes revealed significant enhancement of the Raman intensity when the polarization of the incident laser beam is parallel to the NT axis, indicating an "antenna" effect attributed to the enhanced light scattering along the cylindrical NT structure. Such an effect could result in optimum optical properties and selectively enhanced vectorial transport of electric carriers. © 2008 American Chemical Society.

Dye-sensitized solar cells (DSSCs) were prepared using TiO2 nanotubes, grown by controlled Ti anodic oxidation in non-aqueous media. Smooth, vertically oriented TiO2 nanotube arrays, presenting a high degree of self-organization and a length of 20 μm, have been grown using ethylene glycol electrolyte containing HF. As-grown nanotubes exhibit an amorphous structure, which transforms to the anatase TiO2 crystalline phase upon post-annealing in air at 450°C. Atomic force microscopy (AFM) revealed the porous morphology together with high roughness and fractality of the surface. The annealed tubes were sensitized by the standard N719 ruthenium dye and the adsorption was characterized using resonance micro-Raman spectroscopy and adsorption-desorption measurements. The sensitized tubes were further used as active photoelectrodes after incorporation in sandwich-type DSSCs using both liquid and solidified electrolytes. The efficiencies obtained under air mass (AM) 1.5 conditions, using a back-side illumination geometry, were very promising: 0.85% using a composite polymer redox electrolyte, while the efficiency was further increased up to 1.65% using a liquid electrolyte. © IOP Publishing Ltd.

The magnetic properties of γ-Fe 2O 3 nanoparticles embedded in a thermoplastic elastomer poly(ether-ester) copolymer by the in situ polycondensation reaction process have been investigated by means of magnetization and ferromagnetic resonance (FMR) measurements at low filler concentrations of 0.1 and 0.3 wt% with the magnetic additive introduced in the polymer matrix in powder and solution form. The magnetic behavior of the magnetopolymeric nanocomposites indicates significant interparticle interaction effects that depend mainly on the dispersion state of the magnetic nanoparticles as well as their concentration, consistent with the variation of the particle microstructure characterized by magnetic aggregates in the nanometer and micron scale for the solution and powder dispersions, respectively. The magnetization and FMR results at different filler concentrations and dispersions show a close correspondence to the relaxation processes of the copolymer, implying the coupling of polymeric and magnetic properties. Copyright © 2008 American Scientific Publishers All rights reserved.

Electron spin resonance (ESR) has been applied to study spin dynamics and charge transfer interactions in C60(Fe(C5H5)2)2. A low concentration of C60- spins is derived by ESR, suggesting the presence of weak charge transfer between C60 and ferrocene. The C60- ESR spectra display an appreciable anisotropy at T < 40 K reflecting molecular rotation freezing, while their low temperature variation (T < 10 K) implies development of antiferromagnetic spin-spin interactions. At high temperatures, the narrow ESR line of C120O- impurity spins inhibits observation of a C60- ESR. © 2008 Elsevier B.V. All rights reserved.