Density gradient ultracentrifugation (DGU) becomes increasingly important for the sorting of nanomaterials according to the particles' density, hence structure and dimensions, which determine their unique properties, but the further development of this separation technique is hindered by the limited precision with which the densities could be characterized. In this work, we determine these densities by position-dependent 2D wavelength-dependent IR fluorescence-excitation and resonant Raman spectroscopy measured directly in the density gradient after ultracentrifugation. We apply this method to study the diameter and chirality-dependent sorting of empty and water-filled single-walled carbon nanotubes coated with two different surfactants, sodium cholate (SC) and sodium deoxycholate (DOC). The results elucidate the long standing contradiction that SC would provide better diameter sorting, while DOC is the most efficient surfactant to solubilise the nanotubes. A more predictable separation is obtained for empty DOC-coated nanotubes since their density is found to vary very smoothly with diameter. The accurate and chirality-dependent densities furthermore provide information on the surfactant coating, which is also important for other separation techniques, and allow to determine the mass percentage of water encapsulated inside the nanotubes.

We investigate the 1/3 monolayer α-Pb/Si(111) surface by scanning tunneling spectroscopy (STS) and fully relativistic first-principles calculations. We study both the high-temperature sqrt[3]×sqrt[3] and low-temperature 3×3 reconstructions and show that, in both phases, the spin-orbit interaction leads to an energy splitting as large as 25% of the valence-band bandwidth. Relativistic effects, electronic correlations, and Pb-substrate interaction cooperate to stabilize a correlated low-temperature paramagnetic phase with well-developed lower and upper Hubbard bands coexisting with 3×3 periodicity. By comparing the Fourier transform of STS conductance maps at the Fermi level with calculated quasiparticle interference from nonmagnetic impurities, we demonstrate the occurrence of two large hexagonal Fermi sheets with in-plane spin polarizations and opposite helicities.

Electrical conductivity and high dielectric constant are in principle self-excluding, which makes the terms insulator and dielectric usually synonymous. This is certainly true when the electrical carriers are electrons, but not necessarily in a material where ions are extremely mobile, electronic conduction is negligible and the charge transfer at the interface is immaterial. Here we demonstrate in a perovskite-derived structure containing five-coordinated Ti atoms, a colossal dielectric constant (up to 10 9 ) together with very high ionic conduction 10 −3 S.cm −1 at room temperature. Coupled investigations of I-V and dielectric constant behavior allow to demonstrate that, due to ion migration and accumulation, this material behaves like a giant dipole, exhibiting colossal electrical polarization (of the order of 0.1 C.cm −2 ). Therefore, it may be considered as a "ferro-ionet" and is extremely promising in terms of applications.