Giovanni Mattei

University of Padova | UNIPD · Department of Physics and Astronomy "Galileo Galilei"

Chirality, an intrinsic property of certain entities in the universe, is characterized by the absence of mirror symmetry. Understanding chirality is crucial as it influences molecular interactions and properties. Circular dichroism (CD), measured using circularly polarized light, is a standard technique for probing chirality, but its sensitivity is...

The active modulation of optical response of quantum emitters at the nanoscale is of paramount importance to realize tunable light sources for nanophotonic devices. Herein, a thin film of phase‐change material (VO 2 ) is coupled to a 20 nm‐thick silica layer embedding Er ³⁺ ions, and it is demonstrated how the active tuning of the local density of...

We investigated infrared reflectivity of undoped and Tungsten (W) doped Vanadium dioxide (VO2) films at varying temperatures. Undoped VO2 exhibited a clear phase transition at 100°C, achieving near 0% reflectivity, or perfect light absorption. As W doping concentration increased, the phase-transition temperature decreased, maintaining the zero-refl...

Lattice plasmon lasers demonstrated to have many degrees of freedom useful to tailor the lasing properties, as the tuning of the morphological properties of the array or the coupling of proper emitters to band-edge states of the plasmonic crystal. Here, we present the results of the study of the lasing emission properties of a hexagonal array of al...

We have designed and realized all-dielectric lossless nanoantennas, in which a thin SiO2 layer doped with erbium ions is placed inside slotted silicon nanopillars arranged in a square array. The modal analysis has evi-denced that the slotted nanopillar array supports optical quasi-BIC resonances with ultra-high Q-factors (up to Q∼10⁹), able to boos...

Quantum technologies require advanced optical metamaterials whose properties can be tailored and controlled as desired. Hyperbolic metamaterials have great potential for applications in nonlinear nanophoton-ics, such as all-optical switching, optical limiting, mode-locking and optical sensing. In this work, we show how to obtain strong third-order...

Metamaterials are artificial media designed to display properies going beyond those of ordinary materials. Particularly interesting are ε-near-zero (ENZ) media with real part of the permittivity going to zero in a certain spectral range. Examples of ENZ metamaterials are metal dielectric multilayers, which allow to tune the position of the ENZ wave...

The transfer of photogenerated charges through interfaces in heterojunction photoanodes is a key process that controls the efficiency of solar water splitting. Considering Co3O4/SiOx/Si photoanodes prepared by physical vapor deposition as a representative case study, it is shown that defects normally present in the native SiOx layer dramatically af...

Plasmonic nanostructured materials made of nanohole arrays in metal are significant plasmonic devices exhibiting resonances and strong electromagnetic confinement in the visible and near-infrared range. As such, they have been proposed for use in many applications such as biosensing and communications. In this work, we introduce the asymmetry in na...

Developing intense, coherent and ultra-fast light sources with nanoscale dimensions is a crucial issue for many applications in nanophotonics. To date, plasmonic nanolasers represent one of the most promising nanophotonic devices capable of this remarkable feature. In the present work we report on the emission properties of two-dimensional Au hexag...

Plasmonic nanostructured materials made of nanohole arrays in metal are significant plasmonic devices exhibiting resonances and strong electromagnetic confinement in the visible and near-infrared range. As such, they have been proposed for use in many applications such as biosensing and communications. In this work, we introduce the asymmetry in na...

Scattering scanning near-field optical microscopes (s-SNOMs) based on pseudoheterodyne detection and operating at ambient conditions typically suffer from instabilities related to the variable optical path length of the interferometer arms. These cause strong oscillations in the measured optical amplitude and phase comparable with those of the sign...

In the quest for new and increasingly efficient photon sources, the engineering of the photonic environment at the subwavelength scale is fundamental for controlling the properties of quantum emitters. A high refractive index particle can be exploited to enhance the optical properties of nearby emitters without decreasing their quantum efficiency,...

Structural, optical, magnetic, and electrical properties of zinc oxide (henceforth, ZO) and iron doped zinc oxide (henceforth, ZOFe) films deposited by sputtering technique are described by means of Rutherford backscattering spectrometry, grazing incidence X-ray diffraction, scanning electron microscope (SEM), UV–Vis spectrometer, vibrating sample m...

Addition of asymmetry in plasmonic nanostructures can lead to chiro-optical phenomena, usually monitored as different absorption of left and right polarization, i.e. circular dichroism. Moreover, interesting features arise when the nanostructure changes the polarization state of the input beam. In this work, we perform extrinsic chirality character...

2D metasurfaces based on periodic nanoholes in metal have been proposed in various plasmonic platforms. Specifically, their resonant features have led to applications spanning in biosensing. Here we investigate additional degree of freedom in elliptical nanohole arrays with hexagonal geometry: chiro-optical effects. Namely, the in-plane asymmetry a...

In recent years the quest for novel materials possessing peculiar abilities of manipulating light at the nanoscale has been significantly boosted due to the strict demands of advanced nanophotonics and quantum technologies. In this framework radiative decay engineering of quantum emitters is of paramount importance for developing efficient single-p...

We are investigating the possibility of increase sensitivity in the detection of chiral molecules: by measuring, under circular polarized light, the luminesce of molecules when them are deposited on specific plasmonic asymmetric metasurfaces. Conclusion Despite the very small volume of molecules on the substrate, we camn measure the luminescence of...

A new light is shed on the formation mechanism of Co3O4 nanopetals on Si-based photoanodes by thermal oxidation of a deposited metallic film, and on their use for the rapid chemisorption, the photoelectrochemical detection and subsequent removal of harmful fenitrothion (FNT), a commonly used organophosphate pesticide which represents a serious risk...

Chirality, a lack of mirror symmetry, is present in nature at all scales; at the nanoscale, it governs the biochemical reactions of many molecules, influencing their pharmacology and toxicity. Chiral substances interact with left and right circularly polarized light differently, but this difference is very minor in natural materials. Specially engi...

We shed new light on the formation mechanism of Co3O4 nanopetals on Si-based photoanodes by thermal oxidation of a deposited metallic film, and on their use for the rapid chemisorption, the photoelectrochemical detection and subsequent removal of harmful fenitrothion (FNT), a commonly used organophosphate harmful pesticide.Using Au clusters as mark...

Metamaterials with properly engineered linear and nonlinear optical response are of great interest for many advanced applications in nanophotonics and quantum optics. In the present work, we perform a detailed spectral investigation of the third-order nonlinear optical properties (nonlinear refractive index and nonlinear absorption coefficient) of...

Nanoparticles CrxAl0.5–xCoFe1.5O4 (x=0.1, 0.25 and 0.4) spinel ferrites were synthesized by coprecipitation technique, aiming to study the relationship between cation distribution of the substitution of chromium and aluminum ions on the structure, morphology, magnetic properties, permeability, Curie temperature and AC loss. X-ray diffraction (XRD)...

This paper reports on the fabrication and characterization of a plasmonic/sol-gel sensor for the detection of aromatic molecules. The sol-gel film was engineered using polysilsesquioxanes groups to capture the analyte, through π-π interaction, and to concentrate it close to the plasmonic surface, where Raman amplification occurs. Xylene was chosen...

Measurements of difference in optical interactions between circularly polarized excitations of opposite handedness (circular dichroism) are highly important for both natural and artificial chiral structures. Here the photothermal deflection technique is proposed as a method to detect the optical chirality of a metasurface, analyzing the diffracted...

We demonstrate the angle, polarization and intensity tunability of the optical Kerr effect in gold/alumina metamaterials investigated by the z-scan technique. We propose a model to predict their effective nonlinear refractive index and absorption coefficient.

The mimicking of chiral effects at the nanoscale usually requires complex nanostructured systems fabricated by using highly sophisticated techniques. Here, we demonstrate that low-cost diffractive metasurfaces, fabricated by nanosphere lithography, can offer a remarkably rich chiral broadband response in the near-infrared range. We measure the spin...

Rare-earth ions sensitization is, nowadays, a relevant topic in modern technologies. Noble metal nanoclusters can effectively sensitize lanthanide photoluminecence (PL) via excitation energy transfer (EET). Recent experimental works reported how this process strongly depends on the nanoclusters size and composition, however, a comprehensive underst...

The sensing mechanism of plasmonic nanohole arrays is investigated and a novel model is proposed to interpret their optical response over a wide dynamic range of concentrations (10-13-10-5 M), based on a double-Langmuir model. This model describes the signal response of the analyte binding as the sum of two independent contributions which are relat...

We study, both experimentally and theoretically, the modification of Er3+ photoluminescence properties in Si dielectric nanoslots. The ultrathin nanoslot (down to 5-nm thickness), filled with Er in SiO2, boosts the electric and magnetic local density of states via coherent near-field interaction. We report an experimental 20-fold enhancement of the...

Combining finite elements method electrodynamic simulations and cost-effective and scalable nanofabrication techniques, we carried out a systematic investigation and optimization of the sensing properties of non-interacting gold nanodisk arrays. Such plasmonic nanoarchitectures offer a very effective platform for fast and simple, label-free, optica...

In this work we present an approach to induce chiral effects in well-known plasmonic nanohole arrays with triangular unit cell. Arrays with circular nanoholes in metals can exhibit interesting light-matter interaction mechanisms such as surface plasmon polaritons and extraordinary optical transmission. Moving from circular to elliptical shape and t...

The stability upon air-annealing of uncapped Au-Co thin films is investigated. The analysis focuses on the modifications of the crystalline fraction of the films produced by physical vapor deposition. The film with the highest Au concentration exhibits the strongest diffraction signal, corresponding to a Au-rich fcc AuxCo1−x solid solution alloy, w...

Arrays of nanoholes in metal are important plasmonic devices, proposed for applications spanning from biosensing to communications. In this work, we show that in such arrays the symmetry can be broken by means of the elliptical shape of the nanoholes, combined with the in-plane tilt of the ellipse axes away from the array symmetry lines. The array...

Honeycomb plasmonic lattices are paradigmatic examples of non-Bravais lattices. We experimentally measure Surface Lattice Resonances in effectively free-standing honeycomb lattices composed of silver nanospheres. By combining numerical simulations with analytical methods, we analyze the dispersion relation and the near-field properties of these mod...

In nanostructures made of a mixture of bulk-immiscible metallic species, the alloy formation down to the atomic scale is a crucial and debated point. We report on the first experimental evidence of an amorphous metallic phase in Au-Co thin films and 2D array of nanostructures, that is constituted by a fine mixing of single-metal (sub)-nm domains, a...

Nanostructured materials with tunable nonlinear optical response are of great interest for different applications in nanophotonics. In this work we report the results of a comprehensive study on the nonlinear optical properties of two kinds of plasmonic metamaterials, i.e., honeycomb nanoprism arrays and multilayer hyperbolic metamaterials, which p...

A detailed structural investigation of the semiconductor-to-metal transition (SMT) in vanadium dioxide thin films deposited on sapphire substrates by pulsed laser deposition was performed by in-situ temperature-dependent X-ray diffraction (XRD) measurements. The structural results are correlated with those of infrared radiometry measurements in the...

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 C...

The capability to tune the linear and nonlinear optical response of plasmonic nanoarrays is of great interest for the realization of solid-state plasmonic nanodevices with application in many different fields in nanophotonics. In the present work we demonstrated the possibility to tailor, in a controlled way, the morphological properties of gold na...

Active, ultra-fast external control of the emission properties at the nanoscale is of great interest for chip-scale, tunable and efficient nanophotonics. Here we investigated the emission control of dipolar emitters coupled to a nanostructure made of an Au nanoantenna, and a thin vanadium dioxide (VO2) layer that changes from semiconductor to metal...

The second order nonlinear optical response of gold nanoprisms arrays is investigated by means of second harmonic generation (SHG) experiments and simulations. The polarization dependence of the nonlinear response exhibits a 6-fold symmetry, attributed to the local field enhancement through the excitation of the surface plasmon resonances in bow-ti...

Room temperature atmospheric plasma treatments are widely used to activate and control chemical functionalities at surfaces. Here, we investigated the effect of atmospheric pressure plasma jet (APPJ) treatments in reducing atmosphere (Ar/1‰ H2 mixture) on the photoluminescence (PL) properties of single crystal ZnO nanorods (NRs) grown through hydro...

Here, we investigate chiral properties of polystyrene-based metasurfaces, fabricated by means of nanosphere lithography, and asymmetrically covered by a thin plasmonic layer (Au, Ag or Cr). We apply the low-cost, scattering-free photo-acoustic (PA) technique to directly characterize circular dichroism (CD) in absorption. Au-and Cr-hybridized sample...

We evaluate the performance of an adhesion buffer layer between ordered metal nanoparticle arrays and dielectric substrates on the particles' morphological manipulation by pulsed laser irradiation. The experiments are performed irradiating with only one nanosecond pulse at 355 nm, triangular nanoprism arrays fabricated by nanosphere lithography (po...

Nowadays, nanophotonics aims towards low-cost chip-scale devices that can tailor electromagnetic properties, one of which is the control of circular polarization at the nanoscale. Here, we demonstrate the chiral properties of metasurfaces produced by means of nanosphere lithography combined with tilted metal deposition. We apply the photo-acoustic...

Cobalt oxide nanopetals were grown on silicon electrodes by heat-treating metallic cobalt films deposited by DC magnetron sputtering. We show that cobalt oxide, with this peculiar nanostructure, is active towards the photo-electrochemical oxidation of water as well as of organic molecules, and that its electrochemical properties are directly linked...

Implantable devices need specific tailored surface morphologies and chemistries to interact with the living systems or to actively induce a biological response also by the release of drugs or proteins. These customised requirements foster technologies that can be implemented in additive manufacturing systems. Here we present a novel approach based...

F e doped ZnO (FeZO) thin films were deposited using magnetron co-sputtering (DC for Fe and RF for ZnO) on silica and silicon substrates. To better control the Fe-doping in the 1% atomic range, instead of reducing the DC power (which produced instabilities of the DC source), we performed the DC sputtering through a grid with different mesh size to...

The laser-induced plasmon heating of an ordered array of silver nanoparticles, under continuous illumination with an Ar laser, was probed by rare-earth fluorescence thermometry. The rise in temperature in the samples was monitored by measuring the temperature-sensitive photoluminescent emission of a europium complex (EuTTA) embedded in PMMA thin-fi...

We studied i) a set of three Co:Au continuous films, grown by sputtering co-deposition (~ 80 nm thick) and concentration ratio 2:1, 1:1 and 1:0 (i.e., a pure Co film was also included) and ii) a corresponding set of antidot arrays, produced by nanosphere lithography with the same hexagonal pattern (nominal lattice periodicity ~ 520 nm). The samples...

In this work, the optical properties of Er and Ag co-implanted silica slabs were investigated in order to shed light on the observed improvement of the rare-earth emission properties through a sensitization process activated by Ag implantation. A full ion implantation approach was adopted since it represents an effective way to create a thin doped...

The control of the spontaneous emission properties of quantum emitters with limited losses by near-field coupling with plasmons-supporting nanostructures is one of the keys for next-generation high-efficiency and high-coherence plasmonic devices. In the present work, gold nanohole arrays are demonstrated to be an effective plasmonic system for cont...

Coupling a plasmonic metal with a magnetic one in thin films and nanostructures is very interesting for the emerging field of magnetoplasmonics. In particular, coupling through alloying is a promising strategy to induce a magnetic moment on the plasmonic metal atoms, in a way that is intimately related to the local structure of the (metastable) all...

The capability to develop novel nanomaterials with properly tailored optical properties is of great interest for many nanophotonic applications. In the present work, 2D-ordered plasmonic nanoarrays with different morphologies, as nanoprism, nanoparticle, nanohole and semi-nanoshell arrays, are realized by nanosphere lithography, combining metal dep...

In this work we present the study of the ultra-fast dynamics of the nonlinear optical response of a honeycomb array of silver triangular nanoprisms, performed using a femtosecond pulsed laser tuned with the dipolar surface plasmon resonance of the nanoarray. Nonlinear absorption and refraction, and their time-dependence, were explored using the z-s...

Supported 3D hierarchical nanostructures of transition metal oxides exhibit enhanced photocatalytic performances and long-term stability under working conditions. The growth mechanisms crucially determine their intimate structure, that is a key element to optimize their properties. We report on the formation mechanism of supported Co3O4 hierarchica...

Photothermal and photoacoustic techniques are utilized to explore the thermal properties of metal based metasurfaces. We experimentally evidence the role of the symmetry in the heat transport and its relation with the optical circular dichroism.

Plasmonic nanostructures have been the object of strong scientific interest in the last decade for their linear and nonlinear optical properties. The present work is focused on the capability to control and enhance the Er³⁺ emission efficiency in silica by near-field coupling with plasmonic and pre-plasmonic nanostructures. The results shows that m...

One fundamental requirement in the search for novel magnetic materials is the possibility of predicting and controlling their magnetic anisotropy and hence the overall hysteretic behavior. We have studied the magnetism of Au:Co films (~30 nm thick) with concentration ratios of 2:1, 1:1, and 1:2, grown by magnetron sputtering co-deposition on native...

Nanosphere lithography coupled to reactive ion etching has been used to synthesize hexagonal ordered arrays of Au-Ag bimetallic semi-nanoshells to be used as plasmonic biosensors. The degree of lateral interaction between adjacent semi-nanoshells can be controlled by tailoring the reactive ion etching time in order to boost the global plasmonic pro...

Ordered metallic nanoprism arrays have been proposed as novel and versatile systems for the observation of nonlinear effects such as nonlinear absorption. The study of the effect of the local field reinforcement on the fast optical third order nonlinear response around the Surface Plasmon Resonance is of great interest for many plasmonic applicatio...

The properties of dichroism in the nonlinear absorption response of silver nanoprism arrays are experimentally investigated by the z-scan technique. Open aperture z-scan measurements are performed with a picosecond laser at a low repetition rate to excite the third-order electronic component of the optical nonlinearity for different linear polariza...

Silver nanostructures are widely employed for Surface Enhanced Raman Scattering (SERS) characterizations owing to their excellent properties of field confinement in plasmonic resonances. However, the strong tendency to oxidation at room temperature of these substrates may represent a major limitation to their performances. In the present work, we i...

Los arreglos ordenados de nanopartículas metálicos han sido propuestos como fuentes novedosas y versátiles de efectos nolineales como lo es la absorción nolineal. Es de gran interés para aplicaciones nanofotónicas, estudiar los efectos sobre la respuesta nolineal de tercer orden originados debido el reforzamiento del campo eléctrico por la geometrí...

Inorganic-organic hybrid materials have shown excellent optoelectronic device performances from single-layer solution-processed thin films. Their electronic bands are coupled to the ionic interactions within the organic and inorganic moieties. Exactly these features also allow a sequential deposition route so as to implement thin films having inher...

One of the most promising Metallic Nanoparticle (MNP) geometries is the 2D ordered Plasmonic Nanoprism Array (PNPA), on which the plasmonic effects present in an array of thin triangular MNPs are used to provide greatly increased third order Nonlinear Optics (NLO) effects [1]. In this work, gold and silver 2D ordered PNPAs were fabricated using the...

The nonlinear absorption properties of Ag nanoprism arrays synthesized by nanosphere lithography have been investigated by z-scan measurements. A picoseconds and low repetition rate laser source has been used to excite the electronic component of the nonlinear optical response without inducing thermal effects on the samples. Spectral effects in the...

Finding effective strategies for improving the luminescence emission performance of Er³⁺ ions in silica is of paramount importance for the realization of efficient Er-based nanophotonic devices. To this aim, in the present work the sensitization mechanism of room temperature Er³⁺ luminescence by AuN quantum clusters, upon annealing in a reducing at...

The 22 Ne(p,γ) 23 Na reaction is included in the neon-sodium cycle of hydrogen burning. A number of narrow resonances in the Gamow window dominate the thermonuclear reaction rate. Several resonance strengths are only poorly known. As a result, the 22 Ne(p,γ) 23 Na thermonuclear reaction rate is the most uncertain rate of the cycle. Here, a new expe...

Ion implantation into silica is used to produce Au subnanometer metal clusters, whose size can be finely tuned from few-atom to about 1 nm by acting on the implantation fluence and post-implantation annealing conditions. The structural analyses rely basically on x-ray absorption spectroscopy that can investigate the metal site independently from lo...

Ion implantation is proposed to produce self-standing bent monocrystals. A Si sample 0.2mm thick was bent to a radius of curvature of 10.5m. The sample curvature was characterized by interferometric measurements; the crystalline quality of the bulk was tested by X-ray diffraction in transmission geometry through synchrotron light at ESRF (Grenoble,...

The $^{22}$Ne(p,$\gamma$)$^{23}$Na reaction is included in the neon-sodium cycle of hydrogen burning. A number of narrow resonances in the Gamow window dominates the thermonuclear reaction rate. Several resonance strengths are only poorly known. As a result, the $^{22}$Ne(p,$\gamma$)$^{23}$Na thermonuclear reaction rate is the most uncertain rate o...

The nonlinear absorption properties of bidimensional arrays of Au-Ag bilayered nanoprisms have been investigated by z-scan measurements as a function of the bimetallic nanoprisms composition. A tunable ps laser system was used to excite the ultrafast, electronic nonlinear response matching the laser wavelength with the quadrupolar surface plasmon r...

The occurrence of a very efficient non-resonant energy transfer process form ultrasmall Au-Ag nanoalloy clusters and Er3+ ions is investigated in silica. The enhancement of the room temperature Er3+ emission efficiency by an order of magnitude is achieved by coupling the rare-earth ions to molecule-like (AuxAg1-x)N alloy nanoclusters with N = 10-15...

The very early steps of Au metal cluster formation in Er-doped silica have been investigated by high-energy resolution fluorescence-detected x-ray absorption spectroscopy (HERFD-XAS). A combined analysis of the near-edge and extended part of the experimental spectra show that Au cluster nucleation starts from few Au and O atoms covalently interconn...

X- and γ-ray detection is currently a hot topic for a wide scientific community, spanning from astrophysics to nuclear medicine. However, lack of optics capable of focusing photons of energies in the energy range 0.1-1 MeV leaves the photon detection to a direct-view approach, resulting in a limited efficiency and resolution. The main scope of the...

The variation of local density of states and/or excitation of surface plasmons in proximity of a metal surface can be used to control the emission rate of Er-doped materials for optical and optoelectronic devices. In the present work we studied the modification of the radiative lifetime of Er3+ ions incorporated in silica layers by magnetron co-spu...

To unveil the mechanisms of energy transfer between AuN nanostructures and Er3+ ions in silica is of paramount importance for the possible use of Au molecular clusters as sensitizing agents of the rare-earth luminescence in photonic devices. In the present work a phenomenological model was developed that allowed us to estimate the most important ph...

The sensitization mechanism of Er ions by sub-nanometric Au aggregates formed in silica by sequential ion implantation has been investigated by room temperature photoluminescence characterizations. Er–Au co-implanted samples with different Au and Er relative concentrations have been studied. The results allowed to point out a correlation between th...

Plasmonic sensors based on ordered arrays of nanoprisms are optimized in terms of their geometric parameters like size, height, aspect ratio for Au, Ag or Au0.5-Ag0.5 alloy to be used in the visible or near IR spectral range. The two figures of merit used for the optimization are the bulk and the surface sensitivity: the first is important for opti...

We present a synthetic strategy for the preparation of palladium-tin alloy and intermetallic nanoparticles. Complexes of palladium(II) and tin(IV) precursors in oleylamine were thermally decomposed in an organic solution in presence of reducing moieties, leading to the formation of monodispersed nanoparticles, with varying crystallographic structur...

High-performance intensity-interrogated magneto-optic surface plasmon resonance (MOSPR) sensors are designed by a multi-objective optimization approach. Designed devices show bulk refractive index sensitivity 1 order of magnitude larger than the current state of the art, while the design procedure allows to chose an appropriate trade-off between se...

A poly(methyl methacrylate) (PMMA) composite film containing 4 wt% of the strongly second order NLO active ionic material [(E)-N,N-dimethylamino-N’-methylstilbazonium][p-toluenesulfonate] (DAST) deposited on ITO substrate shows by a two step process (electric poling followed by controlled thermal annealing) a nonlinear optical coefficient d33 highe...

Sub-nanometric Au nanoclusters are known to act as very efficient sensitizers for the luminescent emission of Er(3+) ions in silica through a non-resonant broad-band energy-transfer mechanism. In the present work the energy-transfer process is investigated in detail by room temperature photoluminescence characterization of Er and Au co-implanted si...