Chiara Maurizio - Academia.edu (original) (raw)

Papers by Chiara Maurizio

Zenodo (CERN European Organization for Nuclear Research), Dec 14, 2022

This document resumes the activity of the Italian CRG beamline at ESRF (LISA project) during year... more This document resumes the activity of the Italian CRG beamline at ESRF (LISA project) during year 2020. The latest news from the beamline are presented as well as details on the technical activity, highlight experiments and publications. Italian beamline at ESRF, BM08 LISA project X-ray Absorption Spectroscopy Index 1. Foreword 2. News from the beamline 2.1 Beamline parameters with the EBS source … p. 5 Beam size … p. 5 Flux … p. 5 2.2 Quick-XAS … p. 6 2.3 Remote temperature control … p. 7 3. Scientific Highlights 3.1 Introducing Highly Redox-Active Atomic Centers into Insertion-Type Electrodes for Lithium-Ion Batteries … p. 8 3.2 Operando/In-situ X-ray absorption spectroscopy sheds light on composite phoelectrodes for photoelectrochemical water splitting … p. 10 3.3 Short-range chemical order and local lattice distortion in a compositionally complex alloy … p. 12 3.4 Amorphous intermixing of noble and magnetic metals in thin film-based nanostructures … p. 14 3.5 The fate of CdS Quantum Dots in A. Thaliana as revealed by EXAFS … p. 16

SSRN Electronic Journal, 2022

A new light is shed on the formation mechanism of Co 3 O 4 nanopetals on Si-based photoanodes by ... more A new light is shed on the formation mechanism of Co 3 O 4 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 to the public health. Using Au clusters as markers for the external surface of the as-deposited film, the results of complementary experiments indicate that the Co 3 O 4 petal formation during oxidizing annealing is related to the non-uniform Co out-diffusion and oxidation rather than to a local melting, as previously suggested. When grown on Si photoanodes under controlled conditions, Co 3 O 4 nanopetals are stable and exhibit high photoelectrocatalytic activity due to the increased active area with respect to the corresponding thin film. These nanostructures work efficiently for FNT sensing (sensitivity of 0.1 μA/(cm 2 μM)) through the direct coordination of the FNT nitro-groups on the Co(II) centers, that inhibit the Co(II) oxidation. Furthermore, we demonstrate that a low amount of this nanostructured film, polarized at a modest bias (1.45 V vs RHE) and under visible light illumination (100 mW/cm 2), can efficiently remove the pesticide in water with a time constant of 1 h without the need for catalyst recollection, and remains stable, thus making it suitable for environmental remediation applications.

Metal nanoclusters (NCs) embedded in insulating matrices have received in the last decade an incr... more Metal nanoclusters (NCs) embedded in insulating matrices have received in the last decade an increasing interest due to their optical, magnetic and catalytic properties when their size becomes comparable to or less than the electronic mean free path [1–8]. Metallic NCs embedded in glass can increase for instance the optical third-order susceptibility χ of the matrix by several orders of magnitude, making such systems interesting candidates to be used as optical switches [3, 9]. With respect to the monoelemental case, bimetallic nanoclusters have an additional way for controlling NCs properties, i.e., the composition. Of course, before the ”tunability” of the NCs properties can be used for actual devices, a careful control over alloy clusters synthesis and stability has to be achieved, in order to clarify which are the parameters (i.e., implantation conditions, subsequent thermal or laser annealings, ion irradiation, etc.) that can promote separation (via oxidation, for instance) ins...

This thesis develops in the framework of the Material Science for MagnetoPlasmonic purposes. Magn... more This thesis develops in the framework of the Material Science for MagnetoPlasmonic purposes. MagnetoPlasmonics is a recent and fast growing research _eld that aims at coupling the plasmonic properties typical of nanostructured noble metals (as, for instance, the local enhancement of electromagnetic _eld or the extraordinary optical transmission) with magnetic functionalities. Promising applications, just to mention a few, span from sensing to the realization of active optical circuits at a nanoscale level. MagnetoPlasmonic systems, so far mostly studied in the literature, are based on thin layers or nanostructures of noble metals coupled with ferromagnetic materials. Nevertheless, the requirement to increase the performances of such systems, and/or extend their functionalities, prompts the search for innovative compounds, which, displaying synergistic properties not otherwise achievable in phase segregated mixtures, can hold both plasmonic and magnetic features. The aim of the prese...

ACS Photonics, 2021

Rare-earth ions sensitization is, nowadays, a relevant topic in modern technologies. Noble metal ... more 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 understanding of this phenomenon is still lacking. Inspired by the current paradigm on the lanthanide−antenna complexes, where light is absorbed by the organic ligand, which then converts to a triplet and transfers the excitation to the lanthanide, we propose it also applies to sensitization by metal clusters. To prove this, we studied the optoelectronic features of several M N nanoclusters (M = Au, Ag, Au/Ag mix; N = 12, 20, and 58) at the Time Dependent Density Functional Theory (TDDFT) level, including, via simplified models, the silica matrix and its possible defects, and make considerations on the role these features can have on the EET toward Er 3+ ions. Our analysis suggests that PL enhancement is generally more effective when N = 12 and M = Ag or Au/Ag mix, while the worst cases are obtained when M = Au and N = 58. These findings are coherent with prior experimental data and with novel measures that are here presented for the first time. Notably, we recover that the matrix defects can actively take part in the EET and, in some cases, could be (counterintuitively) beneficial for the process efficiency. Globally, this theoretical framework gives a comprensive rationale that can guide the design of new effective rare-earth ion sensitizers based on metal clusters.

Surface and Coatings Technology, 2020

Abstract The stability upon air-annealing of uncapped Au-Co thin films is investigated. The analy... more Abstract 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, with nanocrystals which have a rod-like shape. Air annealing induces a progressive de-alloying which is complete at 500 °C, as shown by X-ray Absorption Spectroscopy and X-ray diffraction. The film, that is directly exposed to the oxidizing atmosphere, undergoes a de-wetting process, likely triggered by Au. X-ray nanoimaging mapping enlightens the presence of interpenetrating sub-μm Au and Co3O4 domains. This peculiar annealed nanostructured system can have interesting applications in the field of catalysis.

Thin Solid Films, 2019

Hierarchical transition metal oxide nanostructures are promising materials in the field of cataly... more 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 Co 3 O 4 , 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. Xray 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 Co 3 O 4 .

Journal of Luminescence, 2018

In this work, the optical properties of Er and Ag co-implanted silica slabs were investigated in ... more 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 layer, where luminescent Er ions can interact with Ag-related sensitizing species. The results evidenced that the sensitization process is effectively promoted in presence of Ag ultra-small structures, like fewatom aggregates or multimers, which can be already formed at the early stages of the metal clustering process. On the other hand, the precipitation of large, plasmonic clusters, occurring at high temperature post-Ag implantation annealing, produces a decrease of the fluorescence enhancement effect. Furthermore, it is suggested that the overall sensitization mechanism originates from an Ag-Er energy transfer that determines the possibility of a broadband photostimulation of the rare-earth ions, even by pumping in non-resonant excitation condition. Thanks to these features, the investigated Er and Ag co-implanted system can be considered for the realization of high-performing optical amplifiers in waveguide.

Surfaces, 2019

Cobalt oxide nanopetals were grown on silicon electrodes by heat-treating metallic cobalt films d... more 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 to the structure of its surface. The formation of Co3O4 nanopetals, induced by oxidizing annealing at 300 °C, considerably improves the performance of the material with respect to simple cobalt oxide films. Photocurrent measurements and electrochemical impedance are used to explain the behavior of the different structures and to highlight their potential application in water remediation technologies.

Applied Surface Science, 2018

Supported 3D hierarchical nanostructures of transition metal oxides exhibit enhanced photocatalyt... more 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 Co 3 O 4 hierarchical sea urchin-like nanostructured catalyst, starting from CoO -B layers deposited by Pulsed Laser Deposition (PLD). The particles deposited on the layer surface, that constitute the seeds for the urchin formation, have been investigated after separation from the underneath deposited layer, by X-ray diffraction, X-ray absorption spectroscopy and scanning electron microscopy. The comparison with PLD deposited layers without O and/or B indicates a crucial role of B for the urchin formation that (i) limits Co oxidation during the deposition process and (ii) induces a chemical reduction of Co, especially in the particle core, in the first step of air annealing (2 h, 500 • C). After 2 h heating Co oxidation proceeds and Co atoms outdiffuse from the Co fcc particle core likely through fast diffusion channel present in the shell and form Co 3 O 4 nano-needles. The growth of nano-needles from the layer beneath the particles is prevented by a faster Co oxidation and a minimum fraction of metallic Co. This investigation shows how diffusion mechanisms and chemical effects can be effectively coupled to obtain hierarchical structures of transition metal oxides.

Applied Surface Science, 2018

Coupling a plasmonic metal with a magnetic one in thin films and nanostructures is very interesti... more 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) alloy material. In this framework, Au:Co bimetallic films have been produced via magnetron co-sputtering deposition. X-ray absorption spectroscopy (XAS) at both Au-and Co-edges clearly indicates the formation of a full-metallic layer composed for the major part of a binary Au x Co 1−x alloy, with x = 0.7-0.8. XAS and transmission electron microscopy analyses suggest the presence of a minor fraction of segregated metals. X-ray magnetic circular dichroism (XMCD) analysis at Au L 2,3 edges detected a net magnetic moment of Au atoms (= 0.06 B), significantly larger (≈3.5 times) that the one for Au-capped Co nanoclusters and comparable to the one for a Co-rich Au/Co multilayer, despite the 4 times larger concentration of Co with respect to the present case. This Au-Co magnetic coupling is favored by a high degree of mixing of the two metals in the alloy.

Materials, 2017

One fundamental requirement in the search for novel magnetic materials is the possibility of pred... more 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 natively oxidized Si substrates. They consist of a AuCo ferromagnetic alloy in which segregated ultrafine Co particles are dispersed (the fractions of Co in the AuCo alloy and of segregated Co increase with decreasing the Au:Co ratio). We have observed an unexpected hysteretic behavior characterized by in-plane anisotropy and crossed branches in the loops measured along the hard magnetization direction. To elucidate this phenomenon, micromagnetic calculations have been performed for a simplified system composed of two exchange-coupled phases: a AuCo matrix surrounding a Co cluster, which represents an aggregate of particles. The hysteretic features are qualitatively well reproduced provided that the two phases have almost orthogonal anisotropy axes. This requirement can be plausibly fulfilled assuming a dominant magnetoelastic character of the anisotropy in both phases. The achieved conclusions expand the fundamental knowledge on nanocomposite magnetic materials, offering general guidelines for tuning the hysteretic properties of future engineered systems.

RSC Advances, 2016

AuN quantum cluster sensitization of Er3+ photoemission in silica is boosted by H passivation of ... more AuN quantum cluster sensitization of Er3+ photoemission in silica is boosted by H passivation of Si dangling bonds around the clusters.

AIP Conference Proceedings, 2003

Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 2015

We report on the room temperature photoluminescence characterization in the visible and near-infr... more 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 energytransfer from Au N nanoclusters to Er 3+ ions, giving rise to the Er 3+ sensitized emission.

Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 2004

A superconducting transition edge sensor microcalorimeter was tested at the synchrotron radiation... more A superconducting transition edge sensor microcalorimeter was tested at the synchrotron radiation beam-line of the ESRF to collect the X-ray fluorescence spectrum of a Renaissance gold lustre on ceramic. The measured energy resolution of the detector in the range 6–9keV was 70eV, i.e. 3 times better than that of the usual solid state detector. The preliminary data collected demonstrate the

The Journal of Physical Chemistry C, 2015

A combined in situ X-ray diffraction (XRD) and Xray absorption spectroscopy (XAS) experiment was ... more A combined in situ X-ray diffraction (XRD) and Xray absorption spectroscopy (XAS) experiment was carried out to monitor hydrogen desorption from NbH 0.9 nanoclusters embedded into MgH 2. Just after the MgH 2 → Mg transition, a NbH x bcc nanophase is detected, whose lattice parameter measured by XRD is significantly longer than the one inferred from XAS. This difference is explained considering the broad niobium hydride cluster size distribution and in particular the fact that the XRD signal, differently from the XAS one, is dominated by larger NbH x crystalline structures. The results indicate that, during the hydride to metal phase transformation of the matrix, the NbH x cluster composition depends on the cluster size. It is shown for the first time for embedded nanoparticles that faster (and complete) Nb dehydrogenation is favored for small (1.5−4 nm) clusters with respect to larger (∼20 nm) ones. The role of the matrix and of the annealing atmosphere in the stability of the Nb-related nanophases is discussed.

Zenodo (CERN European Organization for Nuclear Research), Dec 14, 2022

This document resumes the activity of the Italian CRG beamline at ESRF (LISA project) during year... more This document resumes the activity of the Italian CRG beamline at ESRF (LISA project) during year 2020. The latest news from the beamline are presented as well as details on the technical activity, highlight experiments and publications. Italian beamline at ESRF, BM08 LISA project X-ray Absorption Spectroscopy Index 1. Foreword 2. News from the beamline 2.1 Beamline parameters with the EBS source … p. 5 Beam size … p. 5 Flux … p. 5 2.2 Quick-XAS … p. 6 2.3 Remote temperature control … p. 7 3. Scientific Highlights 3.1 Introducing Highly Redox-Active Atomic Centers into Insertion-Type Electrodes for Lithium-Ion Batteries … p. 8 3.2 Operando/In-situ X-ray absorption spectroscopy sheds light on composite phoelectrodes for photoelectrochemical water splitting … p. 10 3.3 Short-range chemical order and local lattice distortion in a compositionally complex alloy … p. 12 3.4 Amorphous intermixing of noble and magnetic metals in thin film-based nanostructures … p. 14 3.5 The fate of CdS Quantum Dots in A. Thaliana as revealed by EXAFS … p. 16

SSRN Electronic Journal, 2022

A new light is shed on the formation mechanism of Co 3 O 4 nanopetals on Si-based photoanodes by ... more A new light is shed on the formation mechanism of Co 3 O 4 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 to the public health. Using Au clusters as markers for the external surface of the as-deposited film, the results of complementary experiments indicate that the Co 3 O 4 petal formation during oxidizing annealing is related to the non-uniform Co out-diffusion and oxidation rather than to a local melting, as previously suggested. When grown on Si photoanodes under controlled conditions, Co 3 O 4 nanopetals are stable and exhibit high photoelectrocatalytic activity due to the increased active area with respect to the corresponding thin film. These nanostructures work efficiently for FNT sensing (sensitivity of 0.1 μA/(cm 2 μM)) through the direct coordination of the FNT nitro-groups on the Co(II) centers, that inhibit the Co(II) oxidation. Furthermore, we demonstrate that a low amount of this nanostructured film, polarized at a modest bias (1.45 V vs RHE) and under visible light illumination (100 mW/cm 2), can efficiently remove the pesticide in water with a time constant of 1 h without the need for catalyst recollection, and remains stable, thus making it suitable for environmental remediation applications.

Metal nanoclusters (NCs) embedded in insulating matrices have received in the last decade an incr... more Metal nanoclusters (NCs) embedded in insulating matrices have received in the last decade an increasing interest due to their optical, magnetic and catalytic properties when their size becomes comparable to or less than the electronic mean free path [1–8]. Metallic NCs embedded in glass can increase for instance the optical third-order susceptibility χ of the matrix by several orders of magnitude, making such systems interesting candidates to be used as optical switches [3, 9]. With respect to the monoelemental case, bimetallic nanoclusters have an additional way for controlling NCs properties, i.e., the composition. Of course, before the ”tunability” of the NCs properties can be used for actual devices, a careful control over alloy clusters synthesis and stability has to be achieved, in order to clarify which are the parameters (i.e., implantation conditions, subsequent thermal or laser annealings, ion irradiation, etc.) that can promote separation (via oxidation, for instance) ins...

This thesis develops in the framework of the Material Science for MagnetoPlasmonic purposes. Magn... more This thesis develops in the framework of the Material Science for MagnetoPlasmonic purposes. MagnetoPlasmonics is a recent and fast growing research _eld that aims at coupling the plasmonic properties typical of nanostructured noble metals (as, for instance, the local enhancement of electromagnetic _eld or the extraordinary optical transmission) with magnetic functionalities. Promising applications, just to mention a few, span from sensing to the realization of active optical circuits at a nanoscale level. MagnetoPlasmonic systems, so far mostly studied in the literature, are based on thin layers or nanostructures of noble metals coupled with ferromagnetic materials. Nevertheless, the requirement to increase the performances of such systems, and/or extend their functionalities, prompts the search for innovative compounds, which, displaying synergistic properties not otherwise achievable in phase segregated mixtures, can hold both plasmonic and magnetic features. The aim of the prese...

ACS Photonics, 2021

Rare-earth ions sensitization is, nowadays, a relevant topic in modern technologies. Noble metal ... more 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 understanding of this phenomenon is still lacking. Inspired by the current paradigm on the lanthanide−antenna complexes, where light is absorbed by the organic ligand, which then converts to a triplet and transfers the excitation to the lanthanide, we propose it also applies to sensitization by metal clusters. To prove this, we studied the optoelectronic features of several M N nanoclusters (M = Au, Ag, Au/Ag mix; N = 12, 20, and 58) at the Time Dependent Density Functional Theory (TDDFT) level, including, via simplified models, the silica matrix and its possible defects, and make considerations on the role these features can have on the EET toward Er 3+ ions. Our analysis suggests that PL enhancement is generally more effective when N = 12 and M = Ag or Au/Ag mix, while the worst cases are obtained when M = Au and N = 58. These findings are coherent with prior experimental data and with novel measures that are here presented for the first time. Notably, we recover that the matrix defects can actively take part in the EET and, in some cases, could be (counterintuitively) beneficial for the process efficiency. Globally, this theoretical framework gives a comprensive rationale that can guide the design of new effective rare-earth ion sensitizers based on metal clusters.

Surface and Coatings Technology, 2020

Abstract The stability upon air-annealing of uncapped Au-Co thin films is investigated. The analy... more Abstract 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, with nanocrystals which have a rod-like shape. Air annealing induces a progressive de-alloying which is complete at 500 °C, as shown by X-ray Absorption Spectroscopy and X-ray diffraction. The film, that is directly exposed to the oxidizing atmosphere, undergoes a de-wetting process, likely triggered by Au. X-ray nanoimaging mapping enlightens the presence of interpenetrating sub-μm Au and Co3O4 domains. This peculiar annealed nanostructured system can have interesting applications in the field of catalysis.

Thin Solid Films, 2019

Hierarchical transition metal oxide nanostructures are promising materials in the field of cataly... more 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 Co 3 O 4 , 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. Xray 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 Co 3 O 4 .

Journal of Luminescence, 2018

In this work, the optical properties of Er and Ag co-implanted silica slabs were investigated in ... more 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 layer, where luminescent Er ions can interact with Ag-related sensitizing species. The results evidenced that the sensitization process is effectively promoted in presence of Ag ultra-small structures, like fewatom aggregates or multimers, which can be already formed at the early stages of the metal clustering process. On the other hand, the precipitation of large, plasmonic clusters, occurring at high temperature post-Ag implantation annealing, produces a decrease of the fluorescence enhancement effect. Furthermore, it is suggested that the overall sensitization mechanism originates from an Ag-Er energy transfer that determines the possibility of a broadband photostimulation of the rare-earth ions, even by pumping in non-resonant excitation condition. Thanks to these features, the investigated Er and Ag co-implanted system can be considered for the realization of high-performing optical amplifiers in waveguide.

Surfaces, 2019

Cobalt oxide nanopetals were grown on silicon electrodes by heat-treating metallic cobalt films d... more 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 to the structure of its surface. The formation of Co3O4 nanopetals, induced by oxidizing annealing at 300 °C, considerably improves the performance of the material with respect to simple cobalt oxide films. Photocurrent measurements and electrochemical impedance are used to explain the behavior of the different structures and to highlight their potential application in water remediation technologies.

Applied Surface Science, 2018

Supported 3D hierarchical nanostructures of transition metal oxides exhibit enhanced photocatalyt... more 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 Co 3 O 4 hierarchical sea urchin-like nanostructured catalyst, starting from CoO -B layers deposited by Pulsed Laser Deposition (PLD). The particles deposited on the layer surface, that constitute the seeds for the urchin formation, have been investigated after separation from the underneath deposited layer, by X-ray diffraction, X-ray absorption spectroscopy and scanning electron microscopy. The comparison with PLD deposited layers without O and/or B indicates a crucial role of B for the urchin formation that (i) limits Co oxidation during the deposition process and (ii) induces a chemical reduction of Co, especially in the particle core, in the first step of air annealing (2 h, 500 • C). After 2 h heating Co oxidation proceeds and Co atoms outdiffuse from the Co fcc particle core likely through fast diffusion channel present in the shell and form Co 3 O 4 nano-needles. The growth of nano-needles from the layer beneath the particles is prevented by a faster Co oxidation and a minimum fraction of metallic Co. This investigation shows how diffusion mechanisms and chemical effects can be effectively coupled to obtain hierarchical structures of transition metal oxides.

Applied Surface Science, 2018

Coupling a plasmonic metal with a magnetic one in thin films and nanostructures is very interesti... more 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) alloy material. In this framework, Au:Co bimetallic films have been produced via magnetron co-sputtering deposition. X-ray absorption spectroscopy (XAS) at both Au-and Co-edges clearly indicates the formation of a full-metallic layer composed for the major part of a binary Au x Co 1−x alloy, with x = 0.7-0.8. XAS and transmission electron microscopy analyses suggest the presence of a minor fraction of segregated metals. X-ray magnetic circular dichroism (XMCD) analysis at Au L 2,3 edges detected a net magnetic moment of Au atoms (= 0.06 B), significantly larger (≈3.5 times) that the one for Au-capped Co nanoclusters and comparable to the one for a Co-rich Au/Co multilayer, despite the 4 times larger concentration of Co with respect to the present case. This Au-Co magnetic coupling is favored by a high degree of mixing of the two metals in the alloy.

Materials, 2017

One fundamental requirement in the search for novel magnetic materials is the possibility of pred... more 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 natively oxidized Si substrates. They consist of a AuCo ferromagnetic alloy in which segregated ultrafine Co particles are dispersed (the fractions of Co in the AuCo alloy and of segregated Co increase with decreasing the Au:Co ratio). We have observed an unexpected hysteretic behavior characterized by in-plane anisotropy and crossed branches in the loops measured along the hard magnetization direction. To elucidate this phenomenon, micromagnetic calculations have been performed for a simplified system composed of two exchange-coupled phases: a AuCo matrix surrounding a Co cluster, which represents an aggregate of particles. The hysteretic features are qualitatively well reproduced provided that the two phases have almost orthogonal anisotropy axes. This requirement can be plausibly fulfilled assuming a dominant magnetoelastic character of the anisotropy in both phases. The achieved conclusions expand the fundamental knowledge on nanocomposite magnetic materials, offering general guidelines for tuning the hysteretic properties of future engineered systems.

RSC Advances, 2016

AuN quantum cluster sensitization of Er3+ photoemission in silica is boosted by H passivation of ... more AuN quantum cluster sensitization of Er3+ photoemission in silica is boosted by H passivation of Si dangling bonds around the clusters.

AIP Conference Proceedings, 2003

Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 2015

We report on the room temperature photoluminescence characterization in the visible and near-infr... more 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 energytransfer from Au N nanoclusters to Er 3+ ions, giving rise to the Er 3+ sensitized emission.

Nuclear Instruments and Methods in Physics Research Section A: Accelerators, Spectrometers, Detectors and Associated Equipment, 2004

A superconducting transition edge sensor microcalorimeter was tested at the synchrotron radiation... more A superconducting transition edge sensor microcalorimeter was tested at the synchrotron radiation beam-line of the ESRF to collect the X-ray fluorescence spectrum of a Renaissance gold lustre on ceramic. The measured energy resolution of the detector in the range 6–9keV was 70eV, i.e. 3 times better than that of the usual solid state detector. The preliminary data collected demonstrate the

The Journal of Physical Chemistry C, 2015

A combined in situ X-ray diffraction (XRD) and Xray absorption spectroscopy (XAS) experiment was ... more A combined in situ X-ray diffraction (XRD) and Xray absorption spectroscopy (XAS) experiment was carried out to monitor hydrogen desorption from NbH 0.9 nanoclusters embedded into MgH 2. Just after the MgH 2 → Mg transition, a NbH x bcc nanophase is detected, whose lattice parameter measured by XRD is significantly longer than the one inferred from XAS. This difference is explained considering the broad niobium hydride cluster size distribution and in particular the fact that the XRD signal, differently from the XAS one, is dominated by larger NbH x crystalline structures. The results indicate that, during the hydride to metal phase transformation of the matrix, the NbH x cluster composition depends on the cluster size. It is shown for the first time for embedded nanoparticles that faster (and complete) Nb dehydrogenation is favored for small (1.5−4 nm) clusters with respect to larger (∼20 nm) ones. The role of the matrix and of the annealing atmosphere in the stability of the Nb-related nanophases is discussed.