[en] Highlights: • 2D-ordered arrays of Co₃O₄ hierarchical nanostructures are fabricated by sputtering. • Each structural unit (nanodome or a nanotriangle) is decorated with thin Co₃O₄ petals. • The extent of Co oxidation depends on the kind of formed nanostructures. -- Abstract: Hierarchical transition metal oxide nanostructures are promising materials in the field of catalysis. Physical vapor deposition of a Co film on a mask of self-ordered nanospheres has been used to obtain a 2D-ordered array of Co metallic nanostructures. Then, oxidizing annealing in specific conditions resulted in the progressive oxidation of Co to Co₃O₄, with the concomitant growth of nanopetals out of the free surface of the deposited film. In this way hexagonal arrays of nanotriangles or of nanodomes decorated with nanopetals have been obtained. X-ray Absorption Spectroscopy shows that the extent of Co oxidation depends on nanostructuring, being the oxidation of nanotriangle and nanodome arrays more rapid than the one of a flat film produced in the same deposition. X-ray diffraction and Scanning Electron Microscopy show that for long annealing time the sample morphology is preserved, and the only crystalline phase is Co₃O₄.

[en] The nonlinear absorption of Au-Ag nanoplanets made by Ar irradiation of bimetallic nanoclusters in silica has been experimentally investigated by means of the single beam z-scan technique. The measurements have been performed in the picoseconds regime in order to isolate the fast electronic contribution to the third-order nonlinearity. The results reveal large nonlinear absorption properties of these systems, characterized by the concomitance of saturable and reverse saturable absorption. A phenomenological expression has been developed to fit the z-scan curves and to quantitatively determine the nonlinear optical parameters.

[en] In the present paper we combined ion implantation and nanosphere lithography to regularly dope, by a mask-assisted process, a SiO₂ substrate with rare earth ions (Er) by ion implantation and to fabricate by sputtering a plasmonic 2D periodic array of Au nanostructures on the silica surface spatially coupled to the implanted Er³⁺ ions. The aim of this work is to study how Er³⁺ emission at 1.5 μm can be affected by the interaction with a plasmonic nanostructure. In particular we have found a variation of the radiative lifetime of the Er³⁺ emission and a change from single exponential to bi-exponential of the luminescence intensity decay.

[en] Sequential ion implantation of Au and Fe ions has been performed in silica. Despite the fact that the two species are not miscible in the bulk, structural characterizations show that the nanoparticles produced are a Au-Fe alloy. The crystalline structure of the nanoparticles is fcc with a lattice parameter of 0.395 nm. The nanocomposite is ferromagnetic at 3 K, with a magnetic moment per Fe atom equal to 1.4μ _B and it shows a hysteresis loop with a coercive field of 24 mTorr. Due to alloying, the optical absorption spectrum does not exhibit the typical surface plasmon resonance of gold nanoparticles. The sample exhibits a change of its optical and structural properties when is annealed at 600 deg. C

[en] We report on the room temperature photoluminescence characterization in the visible and near-infrared range of Er–Au co-implanted silica systems as a function of the annealing temperature. Besides the characteristic Er"3"+ emission at 1540 nm, the samples exhibit luminescence bands in the wavelength region 600–1400 nm related to the formation of ultra-small Au_N aggregates with a number of atoms N less than 50 atoms. In particular, the correlation between such Au_N-related luminescence and the enhancement of the Er"3"+ emission was investigated and an anti-correlation between the Er"3"+ luminescence at 1540 nm and an Au_N-related band at 980 nm was revealed that represents a possible path for the energy-transfer from Au_N nanoclusters to Er"3"+ ions, giving rise to the Er"3"+ sensitized emission.

[en] The room temperature photoluminescence properties of ultra-small Au nanoclusters (made by 5–10 atoms) obtained by ion implantation in silica are presented. The results show a broad and intense luminescent emission in three different spectral regions around 750 nm, 980 nm and 1150 nm. The luminescence properties of the molecule-like Au clusters have been also correlated to the energy-transfer process to Er³⁺ ions in Au–Er co-implanted silica samples. A partial quenching of the 980 nm component is observed due to the Er³⁺ absorption level at 980 nm that acts as a de-excitation channel through which the photon energy is transferred from the Au nanoclusters to the Er ions, eventually producing the Er-related emission at 1.5 microns

[en] Multiple implantations of Au and Ag ions in pure silica and Er-doped silica matrices have been performed to promote the formation of small Au–Ag alloy clusters. Upon annealing in N₂ atmosphere at 600 °C the structural investigation based on X-ray absorption spectroscopy at Au L₃-edge detected for both cases the formation of Au–Ag alloy clusters, whose size is likely below 1 nm. The alloy composition is rich in Au; a minor part of Au atoms remains dispersed into the matrix and oxidized. In the Er-doped silica, the presence of these small alloy aggregates promotes a strong enhancement of the Er³⁺ luminescence at 1.54 μm, that is more marked with respect to similarly produced layers where only pure Au sub-nanometer clusters were present

[en] In this work we present in situ investigations on the increase of the hcp-to-fcc transition temperature for Co with respect to the bulk value (420 deg. C) when nanoclusters are considered. Starting from Co:SiO₂ composites obtained by ion implantation with average Co cluster size of about 5 nm, a transition temperature between 800 deg. C and 900 deg. C is found upon thermal annealing in vacuum by in situ transmission electron microscopy. Preliminary results on electron irradiation to promote the transition at lower temperatures are presented

[en] The radiation hardness of polysiloxane based scintillators has been measured by ion beam induced luminescence (IBIL). The light intensity as a function of the irradiation fluence with an He⁺ beam at 1.8 MeV (1.0 μA/cm²) has been measured on undoped polymers synthesized with different amounts of phenyl units and on polysiloxanes doped with two different dye molecules (BBOT and Lumogen Violet) sensitizing the scintillation yield.

[en] The structural evolution of cobalt nanoclusters synthesized in silica glass by ion implantation has been investigated upon thermal annealing. The samples were characterized by in-situ grazing incidence X-ray diffraction, exploiting a synchrotron radiation beam and following their evolution during thermal treatments in vacuo up to T = 800 deg. C. Before heating, the system is composed of hcp Co nanocrystals; we have not detected the transition from hcp to fcc structure that in the bulk phase occurs around 420 deg. C; nevertheless, the differences in the diffraction pattern recorded at T = 800 deg. C with respect to the corresponding one at room temperature suggest the presence of a second crystalline phase