Optical spectroscopy study of damage induced in 4H-SiC by swift heavy ion irradiation

Single crystals of 4H-SiC were irradiated with swift heavy ions (332 MeV Ti, 106 MeV Pb and 2.7 GeV U) in the electronic energy loss regime. The resulting damage was investigated with UV-visible optical absorption spectroscopy and micro-Raman spectroscopy. The evolution of the Raman data with fluence shows an accumulation of isolated point defects without amorphization of the material and a partial recrystallization of the structure, but only at the lowest fluence. Furthermore, the longitudinal optical phonon-plasmon coupling mode disappears upon irradiation, suggesting a strong perturbation of the electronic structure. This evolution is consistent with the optical bandgap decrease and the Urbach edge broadening that was also previously observed for the irradiation with 4 MeV Au ions.     

Positioning of strained islands by interaction with surface nanogrooves

When strained Stranski-Krastanow islands are used as "self-assembled quantum dots," a key goal is to control the island position. Here we show that nanoscale grooves can control the nucleation of epitaxial Ge islands on Si(001), and can drive lateral motion of existing islands onto the grooves, even when the grooves are very narrow and shallow compared to the islands. A position centered on the groove minimizes energy. We use as prototype grooves the trenches which form naturally around islands. During coarsening, the shrinking islands move laterally to sit directly astride that trench. In subsequent growth, we demonstrate that islands nucleate on the "empty trenches" which remain on the surface after complete dissolution of the original islands.     

Inclusive highP T π0 production from π± and protons at 200 GeV/c

We have measured the inclusive cross-section for π⁰ production at large transverse momentum by 200 GeV/c positive and negative hadron beams on Carbon targets (2.9<P _T <6 GeV/c; ?0.4<y ^*<1.2). We used the NA3 spectrometer at the CERNSPS.     

pH Switchable Water Dispersed Photocatalytic Nanoparticles

Photogeneration of Reactive Oxygen Species (ROS) finds applications in fields as different as nanomedicine, art preservation, air and water depollution and surface decontamination. Here we present photocatalytic nanoparticles (NP) that are active only at acidic pH while they do not show relevant ROS photo-generation at neutral pH. This dual responsivity (to light and pH) is achieved by stabilizing the surface of TiO₂ NP with a specific organic shell during the synthesis and it is peculiar of the achieved core shell-structure, as demonstrated by comparison with commercial photocatalytic TiO₂ NP. For the investigation of the photocatalytic activity, we developed two methods that allow real time detection of the process preventing any kind of artifact arising from post-treatments and delayed analysis. The reversibility of the pH response was also demonstrated as well as the selective photo-killing of cancer cells at acidic pH.     

Threshold energy of vectorial spatial solitary waves in non-linear quadratic crystals

Excitation and propagation of spatial solitary waves due to three-wave mixing in quadratic non-linear media lead to a rich variety of interesting phenomena some of which have already experimental evidence. Analytical and numerical modelling plays a key role in gaining insight in the experimental data, in completing the theoretical understanding of the process and in predicting new possible applications. In this context, we present an extensive analytical and numerical study on the multi-parameter family of vectorial spatial solitary waves in bulk quadratic crystals. We focus our attention particularly on the threshold energy necessary to drive solitary waves on available crystals exhibiting a second order non-linearity and in describing how this threshold depends on the crystal parameters.     

A computer simulation study of the formation of liquid crystal nanodroplets from a homogeneous solution

The aggregation of liquid crystal nanodroplets from a homogeneous solution is an important but not well understood step in the preparation of various advanced photonic materials. Here, the authors performed molecular dynamics computer simulations of the formation of liquid crystalline nanodroplets, starting from an isotropic and uniform binary solution of spherical Lennard-Jones (solvent) and elongated ellipsoidal Gay-Berne (solute) rigid particles in low (<10%) concentration. They studied the dynamics of demixing and the mesogen ordering process and characterized the resulting nanodroplets assessing the effect of temperature, composition, and specific solute-solvent interaction on the morphology, structure, and anisotropy. They find that the specific solute-solvent interaction, composition, and temperature can be adjusted to tune the nanodroplet growth and size.