75 research outputs found
SILICATE NANOPARTICLES PRODUCED BY LABORATORY SIMULATED SPACE WEATHERING OF OLIVINE SINGLE CRYSTALS
No full textSilicate nanoparticles, otherwise
referred to as very small grains (VSGs) [1], occur in
the interstellar medium. These grains experience a
strong structural modification during their lifetime in
the diffuse interstellar medium, due to events such as
grain-grain collisions and irradiation. Grain
amorphization is one of the major effects, transforming
crystalline dust concentrated in star envelopes into
amorphous silicate grains populating the interstellar
medium [2]. Moreover, several studies have pointed
out that the main building blocks of these silicates are
O, Si, Fe, Mg, Al and Ca, all elements that are among
the principal constituents of the Earth’s surface [3],
thus leading to the name “astronomical silicates”.
However, the structure and chemical evolution
together with the origin of these grains are still poorly
understood and intensively debated [4,5].
The aim of this study is the simulation of space
weathering processes by liquid phase pulsed laser
ablation (LP-PLA) on olivine single crystals. We adopt
a multiple technique characterization, taking advantage
of optical spectroscopy analyses and high- resolution
transmission electron microscopy (HR-TEM), to shed
light on the structure and chemical evolution of the
ablated material
Astronomical silicate nanoparticle analogues produced by pulsed laser ablation on olivine single crystals
No full textSilicate nanoparticles, otherwise referred to as very small grains (VSGs) [1], occur in various
astrophysical environments. These grains experience substantial processing (e.g., amorphization)
during their lifetime in the diffuse interstellar medium due to events such as grain-grain collisions
and irradiation [2]. Moreover, several studies have pointed out that the main building blocks of
these silicates are O, Si, Fe, Mg, Al and Ca, all elements that are among the principal constituents of
the Earth’s surface [3], thus leading to the name “astronomical silicates”. However, the structure
and chemical evolution together with the origin of these grains are still poorly understood and
intensively debated [4,5].
The aim of this study is the simulation of space weathering processes on olivine single
crystals by liquid phase pulsed laser ablation (LP-PLA). The study of the resulting structure of both
the target and the ablated material together with their chemical evolution has been carried out by a
multiple technique characterization. In particular, spectroscopy and dynamic light scattering
measurements, analyses of the electrostatic properties and reactivity to acids and bases on the
obtained colloidal solutions of the ablated nanoproducts have been performed and coupled with highresolution transmission electron microscopy (HR-TEM).
Selected olivine target crystals (Fo87) from the São Miguel island (Azores) were analyzed
by Scanning Electron Microscopy (SEM) and Energy Dispersive X-ray spectroscopy (EDX). LP-PLA
experiments were performed with a Nd:YAG laser focused via a singlet lens onto the surface of the
target, which was fixed at the bottom of a polystyrene box filled with 4 ml of deionized water (type
1) to immerge it completely. Laser pulses of 5 ns and 100 mJ simulate the timeframe and energy
exchange occurring during grain-grain interstellar collisions [6] and they generate a plasma plume
at the crystal/liquid interface. The rapid cooling induced by the confining liquid layer brings about
the condensation of the chemical vapor it contains with production of a colloidal solution of
nanoparticles. These solutions were analyzed by dynamic light scattering techniques and optical
absorption spectroscopy in the range from 200 nm to 1100 nm (6.20 eV - 1.13 eV). Absorption
measurements on the colloidal solutions have been compared against reference colloidal solutions
dispersed in deionized water (i.e. mesoporous silica [SiO2] nanoparticles, brucite [Mg(OH)2]
nanoparticles, aluminum hydroxide [Al(OH)3] nanoparticles, chrysotile [Mg3Si2O5(OH)4] nanotubes,
and synthetic forsterite [Mg2SiO4] nanoparticles). Moreover, additional absorption analyses have
been carried out as a function of the addition of known aliquots of sulfuric acid and sodium
hydroxide solutions. TEM/EDS analyses were then performed on the ablated nanoparticles deposited
via electrophoresis on C-coated Cu grids and compositional variations of the ablated target were
determined by X-ray photo-emission spectroscopy analyses.
The size distribution of LP-PLA synthesized nanoparticles is typically multimodal due to
aggregation phenomena. Aggregation is consistent with the measured ζ-potential, which is negative
with a relatively low absolute value, within the range 30-50 mV. Nonetheless, a recurrent mode is
centered at about 2 nm (hydrodynamic diameter) and it is consistent with the measured size
distribution obtained by transmission electron microscopy analysis (average nanoparticles diameter
around 3-5 nm). Optical absorption measurements on the ejected material show a main band
around 215 nm. This feature is very similar to the “B2 band” reported in several studies on silica
glass [7] and ascribed to oxygen vacancies, but its nature is still far to be fully understood. We also
found that this feature at 215 nm is very common among both Si and Mg compounds (e.g., Sioxide, Mg-hydroxide, chrysotile). Moreover, additional absorption bands in the range 240-350nm are
observed suggesting the formation of new space weathering products as result of the ablation
process.
Therefore, these results suggest that substantial chemical processing might be expected
during space weathering of “typical” interstellar grains into VSGs. Moreover, coupling these
experimental results with remote sensing datasets will provide fundamental information about the
origin and evolution of these silicate grains
Laboratory Simulation of Space Weathering on Silicate Surfaces in the Water Environment
No full textSilicate nanoparticles occur in various astrophysical environments where they experience
substantial processing due to events such as grain-grain collisions and irradiation. However, the
structure and chemical evolution together with the origin of these grains are still poorly understood
and intensively debated. For this purpose, we performed liquid-phase nanosecond pulsed laser ablation on olivine single crystals to (i) simulate space weathering in a water environment (e.g.,
hydrous or volatile-rich bodies) and (ii) study the chemical and structural evolution of both the
target surface and the ablated material. In particular, optical spectroscopy analyses have been
performed on the ablated material and correlated with high-resolution transmission electron
microscopy and diffraction; whereas, compositional variations of the ablated target surface were
determined by X-ray photoelectron spectroscopy. Our results show that the target material is
enriched in Fe and depleted in Mg after the ablation process, with the water environment triggering
the oxidation of Fe2+ into Fe3+ in a region confined at the solid-liquid interface and thus promoting
the formation of magnetite on the sample surface. On the other hand, in the ablated material we
find olivine crystalline fragments with shock features together with Mg-rich crystalline
nanoparticles. Notably, no metallic iron nanoparticles have been detected in the ablated material.
Our simulation of space weathering in water environment revealed structural and chemical
changes which are expected to give rise to distinctive features in the reflectance spectra when
compared to those from airless bodies of the inner Solar System
Lasing in one dimensional dye-doped random multilayer
No full textLasing action in a fully organic dye doped flexible 1D random multilayer photonic crystal is reported. The emission energy can be modulated by varying layers thicknesses to fit the dye characteristics, thus showing the potential interest of such cheap materials in active devices for optoelectronic applications
Ricerche biospeleologiche. VI Boldoria (Pseudoboldoria) belluccii nuova entità cavernicola d\u27Italia
No full textThe Author describes Boldoria (Pseudobaldoria) belluccii n. sp. collected in three caves of the side of the Lake Iseo belonging to the Bergamo district. This new species is related to Boldoria (Pseudoboldoria) gratiae Monguzzi, from which can be distinguished due to the particular characters of aedeagus and for other exoskeleton characteristics.Viene descritta la nuova entità Boldoria (Pseudoboldoria) belluccii n. sp. rinvenuta in tre grotte della sponda bergamasca del Lago d\u27Iseo (Lombardia). Simile a Boldoria (Pseudoboldoria) gratiae Monguzzi, si distingue sia per le peculiari caratteristiche dell\u27edeago, sia per altri caratteri esoscheletrici
Recent advances in the application triplet–triplet annihilation-based photon upconversion systems to solar technologies
No full text
Spectroscopic characterization of red perylimide/surfactant nanocomposites
No full textAbstract Novel photoluminescent materials formed by
some selected surfactants, metal derivatives of bis(2-ethylhexyl)
sulfosuccinate (M(AOT)n; M = Na?, Co2?, Er3
?
and Yb3?), bis(2-ethylhexyl) amine (BEEA), bis(2-ethylhexy1)
phosphoric acid (HDEHP) and a 1:1 BEEA/HDEHP
mixture, doped with the red perylimide (ROT-300) have
been prepared, and their optical properties have been tested
by absorption spectroscopy and steady state and timeresolved
fluorescence. Experimental results show spectral
shifts of the typical ROT-300 absorption and fluorescence
bands with respect to that in apolar solvent medium. Data
analysis leads consistently to attribute this feature mainly to
the freezing of the diffusive movement of the dye molecules
confined in the nanodomains of the surfactant liquid crystals,
whilst minor effects can be due to interaction with the surfactant
polar groups. Potentialities of these novel luminescent
nanostructured composites as dye lasers, optical
amplifiers and solar concentrators have been highlighted. In
particular, under optical pumping using a pulse laser,amplified spontaneous fluorescence emission of the ROT-
300/HDEHP system above an excitation energy threshold
value of about 725 mJ cm-2 was observed
Novel Er3+ Perfluorinated Complexes for Broadband Sensitized Near Infrared Emission
No full textThe synthesis and characterization of novel fluorinated Er3+ complexes emitting at the telecommunications wavelengths are presented. These new knowledge-based materials have been designed and optimized on the basis of an extensive photophysical investigation on the processes controlling the overall quantum yield, namely (i) the energy transfer process from the light harvesting conjugated antenna to the emitting ion and (ii) the nonradiative quenching of the lanthanide emission. The study of their photophysical properties has been used for the assessment of their application as active materials in a new generation of low-cost, optical communication amplifiers, based on solution-processed planar waveguides pumped by light emitting diodes (LEDs). Suitable ligands possessing a high-absorption cross-section (where commercially available LEDs operate), good energy level matching those of the ion, and high solubility in fluorinated polymers have been developed.
Design Principles of Hybrid Nanomaterials for Radiotherapy Enhanced by Photodynamic Therapy
No full textRadiation (RT) remains the most frequently used treatment against cancer. The main limitation of RT is its lack of specificity for cancer tissues and the limited maximum radiation dose that can be safely delivered without damaging the surrounding healthy tissues. A step forward in the development of better RT is achieved by coupling it with other treatments, such as photodynamic therapy (PDT). PDT is an anti-cancer therapy that relies on the light activation of non-toxic molecules—called photosensitizers—to generate ROS such as singlet oxygen. By conjugating photosensitizers to dense nanoscintillators in hybrid architectures, the PDT could be activated during RT, leading to cell death through an additional pathway with respect to the one activated by RT alone. Therefore, combining RT and PDT can lead to a synergistic enhancement of the overall efficacy of RT. However, the involvement of hybrids in combination with ionizing radiation is not trivial: the comprehension of the relationship among RT, scintillation emission of the nanoscintillator, and therapeutic effects of the locally excited photosensitizers is desirable to optimize the design of the hybrid nanoparticles for improved effects in radio-oncology. Here, we discuss the working principles of the PDT-activated RT methods, pointing out the guidelines for the development of effective coadjutants to be tested in clinics
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