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By properly tuning the photon energy of a femtosecond laser pump, we disentangle, in carbon nanotube–Si (CNT/Si) heterojunctions, the fast relaxation dynamics occurring in CNT from the slow repopulation dynamics due to hole charge transfer at the junction. In this way we are able to track the transfer of the photogenerated holes from the Si depletion layer to the CNT layer, under the action of the built-in heterojunction potential. This also clarifies that CNT play an active role in the junction and do not act only as channels for charge collection and transport.

Photocurrent generation measured with an electrochemical cell on carbon nanotubes has been obtained mainly from single-walled nanostructures. In fact, multiwall carbon nanotubes (MWCNTs) were not expected to show analogous low-dimensional effects, due to their close similarity to metallic graphite. Recently we reported on the ability of MWCNTs to generate photocurrent in the visible and ultraviolet spectral range. In this paper we show a significant enhancement in the photocurrent generation when the walls of the MWCNTs were decorated with dispersed Cu nanoparticles. This result is of particular relevance for photovoltaic nanodevices and solar energy conversion applications.

We compare the local order in single-wall carbon nanotubes (SWCNTs) and highly oriented pyrolitic graphite (HOPG) by means of nanoscale transmission extended energy loss fine structure (EXELFS) measurements above the carbon K edge. The HOPG EXELFS spectra and their Fourier transform were compared to their synchrotron extended X-ray absorption fine structure (EXAFS) counterpart and discussed within a multiple scattering framework. By comparing the experimental EXELFS data to spectra calculated using a theoretical model based on a single scattering approach, we showed the fundamental importance of considering multiple paths (involving up to eight body scattering) to reproduce the fine details of EXELFS features. Simulating EXELFS spectra of SWCNTs by our theoretical model is shown to represent a measure of their chiralities. Finally, the shrinkage of the nearest-neighbor distance in the Fourier transform observed for SWCNTs (absent in graphite) is interpreted within a simple model invoking anharmonic effects.

The first example of deposition of Langmuir−Blodgett (LB) films of a manganese complex of corrole is described. Characterization of the morphological and molecular structure of these LB films has been carried out by means of different microscopic and spectroscopic methods. Depositions onto different substrates afford very uniform films of determined thickness; all the experiments carried out suggest that manganese corrolates in LB films are normally oriented to the substrate, with a face-to-face packing of the macrocycles, due to π−π interactions. The interactions of these LB films with different volatile organic compounds (VOCs) have been investigated using the quartz microbalance (QMB) technique.

The simultaneous analysis of nuclear relaxation behaviour of 119Sn-1H and 117Sn-1H dipolar vectors from the proton spinlattice relaxation rates of the relative satellite peaks may yield a very accurate calculation of correlation times. The dipolar interaction between the proton and the bound tin nucleus is differently observed on the 119Sn and 117Sn satellite resonances in the 1H partially relaxed spectra. Provided that the internuclear proton - tin distance is known, from the difference of the relaxation rate of the lH-118Sn signal with those measured from its satellite peaks, the correlation time can be calculated from the two independent set of data.

AbstractThe paramagnetic contributions to the spin-lattice relaxation rates of biotin 13C nuclei, induced by the presence in the water/DMSO solution of the TEMPOL nitroxide, have been analysed in the interaction with avidin. The paramagnetic relaxation data, obtained at different temperatures, indicate that the average solvent/spin-label exposure of biotin carbons is consistent with the conformational features previously observed for the complex in the crystal. The analysis of the paramagnetic perturbation profiles, derived from 13C spin lattice relaxation measurements, seems to be highly informative of the sterical aspects of interaction processes of large biopolymers with their ligands.

The use of stable free radicals such as aminoxyl spin-labels has been recently exploited for obtaining information on solution structures of peptides (1,2) and proteins (3,4) from multidimensional NMR spectra. In those reports, it has been suggested that an efficient spin-labelling of water and dimethylsulphoxide (DMSO) solvents may be achieved and the paramagnetic solvent yields relaxation effects on backbone proton nuclei which are directly driven by the molecular surface accessibility. Upon the addition of the paramagnetic probe, the observation of absence in chemical shifts changes and of nuclear relaxation effects which are fully rationalised in terms of the solution structure, support a dynamic model for the interaction between the chemical probe and the biomolecule where weak collisional adducts favour the dipolar coupling of the unpaired electron with the outer nuclei of the investigated molecule.