ABSTRACT This work presents an experimental study on the specific quantitative contributions of a... more ABSTRACT This work presents an experimental study on the specific quantitative contributions of antireflective and effective surface areas on the photocatalytic and antibacterial properties of rutile TiO2 nanospikes. They are studied when continuously distributed over the whole surface and when integrated into well-defined microstructures. The nanospikes were produced following MeV ion beam irradiation of bulk rutile TiO2 single crystals and subsequent chemical etching. The ion beam irradiation generated embedded isolated crystalline nanoparticles inside an etchable amorphous TiO2 layer, and nanospikes fixed to the not etchable TiO2 bulk substrate. The produced nanospikes are shown to resist towards aggressive chemical environments and act as an efficient UV antireflective surface. The photocatalytic activity experiments were performed under the ISO 10678:2010 protocol. The photonic and quantum efficiency are reported for the studied samples. The combined micro- and nanostructured surface triples the photonic efficiency compared to the initial flat surface. Results also revealed that the antireflective effect, due to the nanostructuring, is the dominating factor compared to the increase of surface area, for the observed photocatalytic response. The obtained results may be taken as a general strategy to design and precisely evaluate photoactive nanostructures.
ABSTRACT This work focuses on the study of photocatalytic and antibacterial activity of TiO2 nano... more ABSTRACT This work focuses on the study of photocatalytic and antibacterial activity of TiO2 nanoparticles synthesized by laser ablation in water. The nanoparticles have a log normal size distribution with a mean diameter of 34 nm and are composed by a mixture of small crystallites and disordered TiO2; they show good stability and are extremely pure. High photocatalytic (Methylene-Blue dye discoloration under UV illumination) and antibacterial (tested on Escherichia coli) activities comparable to that of commercial nanoparticles under the same experimental conditions were observed. Optical and structural properties were correlated to the photocatalytic and antibacterial activity, and compared to that of commercial TiO2 nanoparticles. An explanation of the high photo-activity yield is proposed taking into account the nanoparticles structure resulting from the peculiar synthesis procedure.
A complete study of the free and bound exciton photoluminescence (PL) line temperature behavior o... more A complete study of the free and bound exciton photoluminescence (PL) line temperature behavior on high-quality 4H-SiC epitaxial crystals is presented. At low temperatures (T<=60 K), in the PL spectra the lines related to both free exciton (FE) and nitrogen-bound exciton (N-BE) are visible. At higher temperatures are present exclusively FE emission lines; their intensity decreases as the sample temperature
Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 2009
The defects produced in 4H–SiC epitaxial layers by irradiation with a 200keV H+ ion beam in the f... more The defects produced in 4H–SiC epitaxial layers by irradiation with a 200keV H+ ion beam in the fluence range 6.5×1011–1.8×1013 ions/cm2 are investigated by Low Temperature Photoluminescence (LTPL–40K).The defects produced by ion beam irradiation induce the formation of some sharp lines called “alphabet lines” in the photoluminescence spectra in the 425–443nm range, due to the recombination of excitons at structural defects.From the LTPL lines intensity trend, as function of proton fluence, it is possible to single out two groups of peaks: the P1 lines (e, f, g) and the P2 lines (a, b, c, d) that exhibit different trends with the ion fluence. The P1 group normalized yield increases with ion fluence, reaches a maximum at 2.5×1012 ions/cm2 and then decreases. The P2 group normalized yield, instead, exhibits a formation threshold at low fluence, then increases until a maximum value at a fluence of 3.5×1012 ions/cm2 and decreases at higher fluence, reaching a value of 50% of the maximum yield.The behaviour of P1 and P2 lines, with ion fluence, indicates a production of point defects at low fluence, followed by a subsequent local rearrangement creating complex defects at high fluence.
ABSTRACT In this work we report a study on the determination of the shape of aggregated gold coll... more ABSTRACT In this work we report a study on the determination of the shape of aggregated gold colloids, obtained by adding pyridine to a solution of pure gold nanoparticles prepared by laser ablation in water studying their dynamic behavior. We have simultaneously measured the translational and rotational diffusion coefficients of dilute solutions of the as-prepared and aggregated gold nanoparticles by polarized and depolarized dynamic light scattering. An increase of the hydrodynamic radius from 26 to 135 nm and a decrease of the rotational diffusion coefficient of two order of magnitude are measured with increasing the pyridine concentration, both correlated to the aggregate formation. The dynamic properties of nanoaggregates have been interpreted by applying a model which allows a direct evaluation of translation and rotational diffusion coefficients of a chain of spherical particles by changing the number and the relative position of each nanoparticle in the aggregate. The comparison between experimental and calculated values indicates that an aggregation of less than ten isolated nanoparticles produces mainly rod-like chains, while aggregate morphology approaches the fractal-like configuration with increasing aggregation number.
ABSTRACT A polarized and depolarized dynamic light scattering analysis on gold nano-colloids prep... more ABSTRACT A polarized and depolarized dynamic light scattering analysis on gold nano-colloids prepared by laser ablation in water has been conducted. This technique allows a simultaneous measurement of the translational and rotational diffusivities and has been applied to characterize ‘as-prepared’ and aggregated colloids obtained either by “spontaneous” or with “controlled” procedure. A simple model was applied to obtain information on the size, shape and anisotropy properties of the nanoparticles directly in the liquid state. The ‘as-prepared’ Au nanoparticles (AuNPs) are spherical, while a prolate ellipsoidal shape can be attributed to the aggregated nanoparticles. Depolarized dynamic light scattering results a powerful technique to determine the size and shape of AuNPs directly in solution.
ABSTRACT This work presents an experimental study on the specific quantitative contributions of a... more ABSTRACT This work presents an experimental study on the specific quantitative contributions of antireflective and effective surface areas on the photocatalytic and antibacterial properties of rutile TiO2 nanospikes. They are studied when continuously distributed over the whole surface and when integrated into well-defined microstructures. The nanospikes were produced following MeV ion beam irradiation of bulk rutile TiO2 single crystals and subsequent chemical etching. The ion beam irradiation generated embedded isolated crystalline nanoparticles inside an etchable amorphous TiO2 layer, and nanospikes fixed to the not etchable TiO2 bulk substrate. The produced nanospikes are shown to resist towards aggressive chemical environments and act as an efficient UV antireflective surface. The photocatalytic activity experiments were performed under the ISO 10678:2010 protocol. The photonic and quantum efficiency are reported for the studied samples. The combined micro- and nanostructured surface triples the photonic efficiency compared to the initial flat surface. Results also revealed that the antireflective effect, due to the nanostructuring, is the dominating factor compared to the increase of surface area, for the observed photocatalytic response. The obtained results may be taken as a general strategy to design and precisely evaluate photoactive nanostructures.
ABSTRACT This work focuses on the study of photocatalytic and antibacterial activity of TiO2 nano... more ABSTRACT This work focuses on the study of photocatalytic and antibacterial activity of TiO2 nanoparticles synthesized by laser ablation in water. The nanoparticles have a log normal size distribution with a mean diameter of 34 nm and are composed by a mixture of small crystallites and disordered TiO2; they show good stability and are extremely pure. High photocatalytic (Methylene-Blue dye discoloration under UV illumination) and antibacterial (tested on Escherichia coli) activities comparable to that of commercial nanoparticles under the same experimental conditions were observed. Optical and structural properties were correlated to the photocatalytic and antibacterial activity, and compared to that of commercial TiO2 nanoparticles. An explanation of the high photo-activity yield is proposed taking into account the nanoparticles structure resulting from the peculiar synthesis procedure.
A complete study of the free and bound exciton photoluminescence (PL) line temperature behavior o... more A complete study of the free and bound exciton photoluminescence (PL) line temperature behavior on high-quality 4H-SiC epitaxial crystals is presented. At low temperatures (T<=60 K), in the PL spectra the lines related to both free exciton (FE) and nitrogen-bound exciton (N-BE) are visible. At higher temperatures are present exclusively FE emission lines; their intensity decreases as the sample temperature
Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 2009
The defects produced in 4H–SiC epitaxial layers by irradiation with a 200keV H+ ion beam in the f... more The defects produced in 4H–SiC epitaxial layers by irradiation with a 200keV H+ ion beam in the fluence range 6.5×1011–1.8×1013 ions/cm2 are investigated by Low Temperature Photoluminescence (LTPL–40K).The defects produced by ion beam irradiation induce the formation of some sharp lines called “alphabet lines” in the photoluminescence spectra in the 425–443nm range, due to the recombination of excitons at structural defects.From the LTPL lines intensity trend, as function of proton fluence, it is possible to single out two groups of peaks: the P1 lines (e, f, g) and the P2 lines (a, b, c, d) that exhibit different trends with the ion fluence. The P1 group normalized yield increases with ion fluence, reaches a maximum at 2.5×1012 ions/cm2 and then decreases. The P2 group normalized yield, instead, exhibits a formation threshold at low fluence, then increases until a maximum value at a fluence of 3.5×1012 ions/cm2 and decreases at higher fluence, reaching a value of 50% of the maximum yield.The behaviour of P1 and P2 lines, with ion fluence, indicates a production of point defects at low fluence, followed by a subsequent local rearrangement creating complex defects at high fluence.
ABSTRACT In this work we report a study on the determination of the shape of aggregated gold coll... more ABSTRACT In this work we report a study on the determination of the shape of aggregated gold colloids, obtained by adding pyridine to a solution of pure gold nanoparticles prepared by laser ablation in water studying their dynamic behavior. We have simultaneously measured the translational and rotational diffusion coefficients of dilute solutions of the as-prepared and aggregated gold nanoparticles by polarized and depolarized dynamic light scattering. An increase of the hydrodynamic radius from 26 to 135 nm and a decrease of the rotational diffusion coefficient of two order of magnitude are measured with increasing the pyridine concentration, both correlated to the aggregate formation. The dynamic properties of nanoaggregates have been interpreted by applying a model which allows a direct evaluation of translation and rotational diffusion coefficients of a chain of spherical particles by changing the number and the relative position of each nanoparticle in the aggregate. The comparison between experimental and calculated values indicates that an aggregation of less than ten isolated nanoparticles produces mainly rod-like chains, while aggregate morphology approaches the fractal-like configuration with increasing aggregation number.
ABSTRACT A polarized and depolarized dynamic light scattering analysis on gold nano-colloids prep... more ABSTRACT A polarized and depolarized dynamic light scattering analysis on gold nano-colloids prepared by laser ablation in water has been conducted. This technique allows a simultaneous measurement of the translational and rotational diffusivities and has been applied to characterize ‘as-prepared’ and aggregated colloids obtained either by “spontaneous” or with “controlled” procedure. A simple model was applied to obtain information on the size, shape and anisotropy properties of the nanoparticles directly in the liquid state. The ‘as-prepared’ Au nanoparticles (AuNPs) are spherical, while a prolate ellipsoidal shape can be attributed to the aggregated nanoparticles. Depolarized dynamic light scattering results a powerful technique to determine the size and shape of AuNPs directly in solution.
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Papers by M. Zimbone