0000000000437614
AUTHOR
G. Buscarino
Structural relaxation of E_gamma centers in amorphous silica
We report experimental evidence of the existence of two variants of the E' gamma centers induced in silica by gamma rays at room temperature. The two variants are distinguishable by the fine features of their line shapes in paramagnetic resonance spectra. These features suggest that the two E' gamma differ for their topology. We find a thermally induced interconversion between the centers with an activation energy of about 34 meV. Hints are also found for the existence of a structural configuration of minimum energy and of a metastable state.
Metodologie da stampa a getto d'inchiostro per la fabbricazione di substrati SERS
Uno degli argomenti di maggiore interesse della Surface-enhanced Raman spectroscopy (SERS) è il controllo del posizionamento su superficie degli “hot spots” – le zone interstiziali fra aggregati di particelle metalliche che producono un aumento locale del segnale Raman. I substrati SERS consistono tipicamente in una matrice di hot-spots ad alta densità sui quali volumi macroscopici (>1 µL) di molecole di analita sono disperse. Questo approccio porta ad una alta invasività ed una distribuzione non uniforme dell’analita a causa dei flussi capillari. In questo lavoro, viene sviluppata una nuova piattaforma SERS realizzata da stampa a getto d’inchiostro2 in cui una miscela di un analita SERS…
Characterization of E'delta and triplet point defects in oxygen-deficient amorphous silicon dioxide
We report an experimental study by electron paramagnetic resonance (EPR) of gamma ray irradiation induced point defects in oxygen deficient amorphous SiO2 materials. We have found that three intrinsic (E'gamma, E'delta and triplet) and one extrinsic ([AlO4]0) paramagnetic centers are induced. All the paramagnetic defects but E'gamma center are found to reach a concentration limit value for doses above 10^3 kGy, suggesting a generation process from precursors. Isochronal thermal treatments of a sample irradiated at 10^3 kGy have shown that for T>500 K the concentrations of E'gamma and E'delta centers increase concomitantly to the decrease of [AlO4]0. This occurrence speaks for an hole tra…
Photoinduced charge separation in functional carbon-silver nanohybrids
In recent times, nanoscience is devoting growing interest to the easy assembly of well-established nanomaterials into hybrid nanostructures displaying new emerging features. Here, we study the photophysicochemical response of binary nanohybrids obtained by the spontaneous coupling of luminescent carbon dots to silver nanoparticles with controlled surface charge. Evidence of the successful coupling is obtained by steady-state and time resolved optical measurements and further confirmed by direct imaging. We demonstrate strong interactions within nanohybrids, which can be modelled in terms of a sub-picosecond electron transfer from photoexcited carbon dots to silver nanoparticles. Accordingly…
O2 trapping in silica nano-structures with high specific surfaces
We report an experimental investigation regarding the entrapping of O2 molecules inside various silica nano– structured systems having specific surfaces from 50 to 1000 m2/g. By recording Raman spectra and Near Infrared O2 emission we studied the O2 content per mass unit. Our data show that the internal voids of these nanostructured systems can trap O2 molecules diffusing from the surrounding air or from a pure O2 atmosphere, whereas the concentration of O2 that can be trapped in the silica near–surface layer is at least one order of magnitude lower. This low ability is consistently observed in non–porous and porous silica nanoparticles and in mesoporous silica systems. Furthermore, we obse…