ORCID Profile
0000-0003-3959-2595
Current Organisations
Istituto nazionale di astrofisica
,
Universiteit Utrecht
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Publisher: Wiley
Date: 17-06-2005
Publisher: American Chemical Society (ACS)
Date: 11-08-2017
Abstract: Janus nanoparticles (NPs) often referred to as nanosized analogs of molecular surfactants are hiphilic structures with potential applications in materials science, biomedicine, and catalysis, and their synthesis and self-assembly into complex architectures remain challenging. Here, we demonstrate the preparation of Janus heterodimers via asymmetric functionalization of Fe
Publisher: AIP Publishing
Date: 22-07-2002
DOI: 10.1063/1.1497197
Abstract: Spherical silica (SiO2), zinc sulfide (ZnS), and core-shell particles of these materials undergo substantial anisotropic plastic deformation under high-energy ion irradiation. In idual particles can be turned into oblate or prolate ellipsoids with exact control over the aspect ratio. In this letter, we report on the fabrication and optical characterization of thin three-dimensional photonic crystals of spherical particles, which have been anisotropically deformed into spheroidal oblates by means of ion irradiation. As a result of the collective deformation process, both the unit cell symmetry and the particle form factor have been changed leading to appreciable tunability in the optical properties of the photonic crystal.
Publisher: EDP Sciences
Date: 24-03-2023
DOI: 10.1051/0004-6361/202245542
Abstract: Context. The project called INvestigating Stellar Population In RElics ( INSPIRE ) is based on VLT/X-shooter data from the homonymous on-going ESO Large Program. It targets 52 ultra-compact massive galaxies at 0.1 z 0.5 with the goal of constraining their kinematics and stellar population properties in great detail and of analysing their relic nature. Aims. This is the second INSPIRE data release (DR2), comprising 21 new systems with observations completed before March 2022. For each system, we release four one-dimensional (1D) spectra to the ESO Science Archive, one spectrum for each arm of the X-Shooter spectrograph. They are at their original resolution. We also release a combined and smoothed spectrum with a full width at half maximum resolution of 2.51 Å. In this paper, we focus on the line-of-sight velocity distribution, measuring integrated stellar velocity dispersions from the spectra, and assessing their robustness and the associated uncertainties. Methods. For each of the 21 new systems, we systematically investigated the effect of the parameters and set-ups of the full spectral fitting on the stellar velocity dispersion ( σ ) measurements. In particular, we tested how σ changes when several parameters of the fit as well as the resolution and spectral coverage of the input spectra are varied. Results. We found that the effect that causes the largest systematic uncertainties on σ is the wavelength range used for the fit, especially for spectra with a lower signal-to-noise ratio ( S/N ≤ 30). When using blue wavelengths (UVB arm) one generally underestimates the velocity dispersion (by ~15 km s −1 ). The values obtained from the near-IR (NIR) arm present a larger scatter because the quality of the spectra is lower. We finally compared our results with those in literature, finding a very good agreement overall. Conclusions. Joining results obtained in DR1 with those presented here, INSPIRE contains 40 ultra-compact massive galaxies, corresponding to 75% of the whole survey. By plotting these systems in a stellar mass-velocity dispersion diagram, we identify at least four highly reliable relic candidates among the new systems. Their velocity dispersion is larger than that of normal-sized galaxies of similar stellar mass.
Publisher: Springer Science and Business Media LLC
Date: 08-06-2018
DOI: 10.1038/S41467-018-04644-4
Abstract: Self-assembly of nanoparticles (NPs) inside drying emulsion droplets provides a general strategy for hierarchical structuring of matter at different length scales. The local orientation of neighboring crystalline NPs can be crucial to optimize for instance the optical and electronic properties of the self-assembled superstructures. By integrating experiments and computer simulations, we demonstrate that the orientational correlations of cubic NPs inside drying emulsion droplets are significantly determined by their flat faces. We analyze the rich interplay of positional and orientational order as the particle shape changes from a sharp cube to a rounded cube. Sharp cubes strongly align to form simple-cubic superstructures whereas rounded cubes assemble into icosahedral clusters with additionally strong local orientational correlations. This demonstrates that the interplay between packing, confinement and shape can be utilized to develop new materials with novel properties.
Publisher: Wiley
Date: 17-12-2002
Publisher: American Chemical Society (ACS)
Date: 04-06-2002
DOI: 10.1021/CM0211599
Publisher: American Astronomical Society
Date: 05-02-2020
Publisher: American Chemical Society (ACS)
Date: 10-05-2005
DOI: 10.1021/NL050421K
Abstract: A method is presented to control the in-plane ordering, size, and interparticle distance of nanoparticles fabricated by evaporation through a mask of colloidal particles. The use of optical tweezers combined with critical point drying gives single-particle position control over the colloidal particles in the mask. This extends the geometry of the colloidal masks from (self-organized) hexagonal to any desired symmetry and spacing. Control over the mask's hole size is achieved by MeV ion irradiation, which causes the colloids to expand in the in-plane direction, thus shrinking the size of the holes. After modification of the mask, evaporation at different angles with respect to the mask gives additional control over structure and interparticle distance, allowing nanoparticles of different materials to be deposited next to each other. We demonstrate large arrays of metal nanoparticles with dimensions in the 15-30 nm range, with control over the interparticle distance and in-plane ordering.
Publisher: AIP Publishing
Date: 15-06-2008
DOI: 10.1063/1.2939249
Abstract: Core-shell colloids composed of a dielectric core surrounded by a metal shell show geometric cavity resonances with optical properties that are distinctly different than those of the collective plasmon modes of the metal shell. We use finite-difference time domain calculations on silica colloids with a core diameter of 456nm, surrounded by a 38nm thick Au shell, to study the temporal evolution of the mode field intensity inside the cavity upon pulsed excitation. Calculations using Mie theory and the T-matrix method are used to analytically determine the dipolar cavity resonance spectrum, which is found superimposed on the broad collective dipolar plasmonic resonance modes. We characterize resonance wavelength and linewidth in terms of a geometric mode confined inside the cavity. Cavity linewidth can be controlled by metal shell thickness and quality factors Q& are observed. Due to the small cavity mode volume V=0.2(λ∕n)3, a Purcell factor as high as P=54 is calculated. Introducing shape anisotropy lifts the cavity mode degeneracy, yielding blue- and redshifted longitudinal and transverse resonant modes, respectively. The relatively large volume over which the field enhancement is observed in these spherical and anisotropic metal shell cavities, combined with cavity quality factors that are much higher than that of the collective plasmonic modes, makes them attractive for application in nanoscale light sources, sensors, or lasers.
Publisher: SPIE
Date: 28-08-2008
DOI: 10.1117/12.795389
Publisher: AIP Publishing
Date: 18-11-2003
DOI: 10.1063/1.1629793
Abstract: Contrary to earlier predictions, ion irradiation at energies as low as 300 keV causes dramatic anisotropic plastic deformation of silica glass. Spherical colloidal silica particles with diameters of 125, 305, and 1030 nm were irradiated with Xe ions at energies in the range 0.3–4.0 MeV at temperatures between 85 and 380 K. Irradiation-induced anisotropic plastic deformation changes the colloid shape from spherical into oblate ellipsoidal at a rate that strongly increases with ion energy. At a fixed fluence, the transverse diameter increases with electronic energy loss. Even at an energy as low as 300 keV large particle anisotropy was found (size aspect ratio of 1.43 at 1×1015 cm−2). The transverse plastic strain gradually decreases with increasing irradiation temperature: it decreases by a factor 4.5 between 85 and 380 K. The data are in agreement with a viscoelastic thermal spike model for anisotropic deformation.
Publisher: Wiley
Date: 03-02-2004
Publisher: American Chemical Society (ACS)
Date: 23-02-2008
DOI: 10.1021/JP710780J
Publisher: Elsevier BV
Date: 07-2004
Publisher: AIP Publishing
Date: 28-03-2002
DOI: 10.1063/1.1454190
Abstract: Optical waveguide lifiers based on polymer materials offer a low-cost alternative for inorganic waveguide lifiers. Due to the fact that their refractive index is similar to that of standard optical fibers, they can be easily coupled to existing fibers with low coupling losses. Doping the polymer with rare-earth ions that yield optical gain is not straightforward, as the rare-earth salts are poorly soluble in the polymer matrix. This review article focuses on two different approaches to dope a polymer waveguide with rare-earth ions. The first approach is based on organic cage-like complexes that encapsulate the rare-earth ion and are designed to provide coordination sites to bind the rare-earth ion and to shield it from the surrounding matrix. These complexes also offer the possibility of attaching a highly absorbing antenna group, which increases the pump efficiency significantly. The second approach to fabricate rare-earth doped polymer waveguides is obtained by combining the excellent properties of SiO2 as a host for rare-earth ions with the easy processing of polymers. This is done by doping polymers with Er-doped silica colloidal spheres.
Publisher: Springer Netherlands
Date: 2001
Publisher: Elsevier BV
Date: 2006
Publisher: The Optical Society
Date: 22-08-2008
DOI: 10.1364/OE.16.013831
Abstract: In an optical trap, micron-sized dielectric particles are held by a tightly focused laser beam. The optical force on the particle is composed of an attractive gradient force and a destabilizing scattering force. We hypothesized that using anti-reflection-coated microspheres would reduce scattering and lead to stronger trapping. We found that homogeneous silica and polystyrene microspheres had a sharp maximum trap stiffness at a diameter of around 800 nm--the trapping laser wavelength in water--and that a silica coating on a polystyrene microsphere was a substantial improvement for larger diameters. In addition, we noticed that homogeneous spheres of a correct size demonstrated anti-reflective properties. Our results quantitatively agreed with Mie scattering calculations and serve as a proof of principle. We used a DNA stretching experiment to confirm the large linear range in detection and force of the coated microspheres and performed a high-force motor protein assay. These measurements show that the surfaces of the coated microspheres are compatible with biophysical assays.
Publisher: AIP Publishing
Date: 19-02-2004
DOI: 10.1063/1.1640459
Abstract: Optically active erbium ions in the silica and silicon sections of a Si-infiltrated silica colloidal photonic crystal can be separately addressed. A face-centered cubic colloidal crystal composed of 860 nm silica colloids was made by self-assembly under controlled drying conditions. It was then infiltrated with Si using chemical vapor deposition at 550 °C. Next, the photonic crystal was doped with erbium ions by 2 MeV ion implantation. The erbium ions were activated by thermal anneals at 400 and 750 °C, and showed clear photoluminescence at 1.5 μm in both the Si and silica parts of the photonic crystal. By varying measurement temperature and excitation wavelength the erbium ions were selectively excited in Si and/or silica. In this way the local optical density of states in these photonic crystals can be selectively probed. The emission linewidth for Er3+ in crystalline Si is relatively narrow and fits well within the calculated photonic band gap. The long luminescence lifetime of Er in Si makes these photonic crystals an ideal geometry to measure effects of the optical density of states on spontaneous emission.
No related grants have been discovered for Paolo Saracco.