Maria Chiara SPADARO

Pubblicazioni

Maria Chiara SPADARO

 

38 pubblicazioni classificate nel seguente modo:

Nr. doc. Classificazioni
38 1 Contributo su Rivista
Anno
Risorse
2023
Unraveling Exchange Coupling in Ferrites Nano-Heterostructures
SMALL
Autore/i: Maltoni, P.; Barucca, G.; Rutkowski, B.; Spadaro, M. C.; Jonsson, P. E.; Varvaro, G.; Yaacoub, N.; De Toro, J. A.; Peddis, D.; Mathieu, R.
Classificazione: 1 Contributo su Rivista
Abstract: The magnetic coupling of a set of SrFe12O19/CoFe2O4 nanocomposites is investigated. Advanced electron microscopy evidences the structural coherence and texture at the interfaces of the nanostructures. The fraction of the lower anisotropy phase (CoFe2O4) is tuned to assess the limits that define magnetically exchange-coupled interfaces by performing magnetic remanence, first-order reversal curves (FORCs), and relaxation measurements. By combining these magnetometry techniques and the structural and morphological information from X-ray diffraction, electron microscopy, and Mössbauer spectrometry, the exchange intergranular interaction is evidenced, and the critical thickness within which coupled interfaces have a uniform reversal unraveled.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/325993 Collegamento a IRIS

2022
Sub-nanometer mapping of strain-induced band structure variations in planar nanowire core-shell heterostructures
NATURE COMMUNICATIONS
Autore/i: Marti-Sanchez, S.; Botifoll, M.; Oksenberg, E.; Koch, C.; Borja, C.; Spadaro, M. C.; Di Giulio, V.; Ramasse, Q.; Garcia de Abajo, F. J.; Joselevich, E.; Arbiol, J.
Classificazione: 1 Contributo su Rivista
Abstract: Strain relaxation mechanisms during epitaxial growth of core-shell nanostructures play a key role in determining their morphologies, crystal structure and properties. To unveil those mechanisms, we perform atomic-scale aberration-corrected scanning transmission electron microscopy studies on planar core-shell ZnSe@ZnTe nanowires on α-Al2O3 substrates. The core morphology affects the shell structure involving plane bending and the formation of low-angle polar boundaries. The origin of this phenomenon and its consequences on the electronic band structure are discussed. We further use monochromated valence electron energy-loss spectroscopy to obtain spatially resolved band-gap maps of the heterostructure with sub-nanometer spatial resolution. A decrease in band-gap energy at highly strained core-shell interfacial regions is found, along with a switch from direct to indirect band-gap. These findings represent an advance in the sub-nanometer-scale understanding of the interplay between structure and electronic properties associated with highly mismatched semiconductor heterostructures, especially with those related to the planar growth of heterostructured nanowire networks.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/308589 Collegamento a IRIS

2022
Author Correction: Sustainable oxygen evolution electrocatalysis in aqueous 1 M H2SO4 with earth abundant nanostructured Co3O4 (Nature Communications, (2022), 13, 1, (4341), 10.1038/s41467-022-32024-6)
NATURE COMMUNICATIONS
Autore/i: Yu, J.; Garces-Pineda, F. A.; Gonzalez-Cobos, J.; Pena-Diaz, M.; Rogero, C.; Gimenez, S.; Spadaro, M. C.; Arbiol, J.; Barja, S.; Galan-Mascaros, J. R.
Classificazione: 1 Contributo su Rivista
Abstract: The original version of this Article contained an error in Fig. 5, in which x-axis beneath panel c was incorrectly labelled. The correct version of Fig. 5 is: (Figure presented.).
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/308585 Collegamento a IRIS

2022
Direct Observation of the Chemical Transformations in BiVO4 Photoanodes upon Prolonged Light-Aging Treatments
SOLAR RRL
Autore/i: Arcas, R.; Cardenas-Morcoso, D.; Spadaro, M. C.; Garcia-Tecedor, M.; Mesa, C. A.; Arbiol, J.; Fabregat-Santiago, F.; Gimenez, S.; Mas-Marza, E.
Classificazione: 1 Contributo su Rivista
Abstract: Exposing BiVO4 photoanodes to light-aging treatments is known to produce a significant photocurrent enhancement. Until now, the interpretation given to this phenomenon is associated to the formation of oxygen vacancies and little is reported about chemical changes in the material. Herein, the chemical segregation of Bi species toward the surface upon light-aging treatment is demonstrated, which takes place with the concomitant formation of intra-bandgap states associated to the oxygen vacancies. It is further demonstrated that these intra-bandgap states are photoactive and generate photocurrent under infrared excitation. These results highlight the importance of understanding light-induced effects while employing multinary metal oxide photoelectrodes.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/308590 Collegamento a IRIS

2022
Sustainable oxygen evolution electrocatalysis in aqueous 1 M H2SO4 with earth abundant nanostructured Co3O4
NATURE COMMUNICATIONS
Autore/i: Yu, J.; Garces-Pineda, F. A.; Gonzalez-Cobos, J.; Pena-Diaz, M.; Rogero, C.; Gimenez, S.; Spadaro, M. C.; Arbiol, J.; Barja, S.; Galan-Mascaros, J. R.
Classificazione: 1 Contributo su Rivista
Abstract: Earth-abundant electrocatalysts for the oxygen evolution reaction (OER) able to work in acidic working conditions are elusive. While many first-row transition metal oxides are competitive in alkaline media, most of them just dissolve or become inactive at high proton concentrations where hydrogen evolution is preferred. Only noble-metal catalysts, such as IrO2, are fast and stable enough in acidic media. Herein, we report the excellent activity and long-term stability of Co3O4-based anodes in 1 M H2SO4 (pH 0.1) when processed in a partially hydrophobic carbon-based protecting matrix. These Co3O4@C composites reliably drive O2 evolution a 10 mA cm–2 current density for >40 h without appearance of performance fatigue, successfully passing benchmarking protocols without incorporating noble metals. Our strategy opens an alternative venue towards fast, energy efficient acid-media water oxidation electrodes.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/308586 Collegamento a IRIS

2021
Nickel Iron Diselenide for Highly Efficient and Selective Electrocatalytic Conversion of Methanol to Formate
SMALL
Autore/i: Junshan, Li; Congcong, Xing; Yu, Zhang; Ting, Zhang; Spadaro, M; C, ; Qianbao, Wu; Yunan, Yi; Shenglan, He; Jordi, Llorca; Jordi, Arbiol; Andreu, Cabot; Chunhua, Cui
Classificazione: 1 Contributo su Rivista
Abstract: The electro-oxidation of methanol to formate is an interesting example of the potential use of renewable energies to add value to a biosourced chemical commodity. Additionally, methanol electro-oxidation can replace the sluggish oxygen evolution reaction when coupled to hydrogen evolution or to the electroreduction of other biomass-derived intermediates. But the cost-effective realization of these reaction schemes requires the development of efficient and low-cost electrocatalysts. Here, a noble metal-free catalyst, Ni1−xFexSe2 nanorods, with a high potential for an efficient and selective methanol conversion to formate is demonstrated. At its optimum composition, Ni0.75Fe0.25Se2, this diselenide is able to produce 0.47 mmol cm−2 h−1 of formate at 50 mA cm−2 with a Faradaic conversion efficiency of 99%. Additionally, this noble-metal-free catalyst is able to continuously work for over 50 000 s with a minimal loss of efficiency, delivering initial current densities above 50 mA cm−2 and 2.2 A mg−1 in a 1.0 m KOH electrolyte with 1.0 m methanol at 1.5 V versus reversible hydrogen electrode. This work demonstrates the highly efficient and selective methanol-to-formate conversion on Ni-based noble-metal-free catalysts, and more importantly it shows a very promising example to exploit the electrocatalytic conversion of biomass-derived chemicals.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/308953 Collegamento a IRIS

2021
Rotated domains in selective area epitaxy grown Zn3P2: Formation mechanism and functionality
NANOSCALE
Autore/i: Spadaro, M; C, ; S., Escobar Steinvall; Dzade, N. Y.; S., Martí-Sánchez; P., Torres-Vila; Stutz, E. Z.; M., Zamani; R., Paul; Leran, J. -B.; A., Fontcuberta i Morral; J., Arbiol
Classificazione: 1 Contributo su Rivista
Abstract: Zinc phosphide (Zn3P2) is an ideal absorber candidate for solar cells thanks to its direct bandgap, earth-abundance, and optoelectronic characteristics, albeit it has been insufficiently investigated due to limitations in the fabrication of high-quality material. It is possible to overcome these factors by obtaining the material as nanostructures, e.g. via the selective area epitaxy approach, enabling additional strain relaxation mechanisms and minimizing the interface area. We demonstrate that Zn3P2 nanowires grow mostly defect-free when growth is oriented along the [100] and [110] of the crystal, which is obtained in nanoscale openings along the [110] and [010] on InP(100). We detect the presence of two stable rotated crystal domains that coexist in the structure. They are due to a change in the growth facet, which originates either from the island formation and merging in the initial stages of growth or lateral overgrowth. These domains have been visualized through 3D atomic models and confirmed with image simulations of the atomic scale electron micrographs. Density functional theory simulations describe the rotated domains' formation mechanism and demonstrate their lattice-matched epitaxial relation. In addition, the energies of the shallow states predicted closely agree with transition energies observed by experimental studies and offer a potential origin for these defect transitions. Our study represents an important step forward in the understanding of Zn3P2 and thus for the realisation of solar cells to respond to the present call for sustainable photovoltaic technology.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/308941 Collegamento a IRIS

2021
Tailoring plasmonic resonances in Cu-Ag metal islands films
APPLIED SURFACE SCIENCE
Autore/i: Bubaš, M; Janicki, V; Mezzasalma, S A; Spadaro, M; C, ; Arbiol, J; Sancho-Parramon, J
Classificazione: 1 Contributo su Rivista
Abstract: The plasmonic response of Cu-Ag metal islands films is investigated. Films are obtained by subsequent electron beam deposition of Ag and Cu using different fabrication conditions: deposited mass thickness, substrate tem- perature and post-deposition annealing in vacuum. Optical properties of films are investigated by spectroscopic ellipsometry and correlated with the structural characterization results obtained by electron microscopy. It is observed that Ag enhances island growth and increases the percolation threshold of Cu films. The localized surface plasmon resonance of isolated particles shows signatures of both Cu and Ag. Moderate thermal annealing enhances island growth and favours Janus-like morphology, increasing the Ag contribution to the surface plasmon resonance. In case of percolated films, annealing-induced dewetting can lead to the appearance of large and irregular particles with a remarkable absorption peak in the near-infrared range. Composition and optical properties of the films can be further modified by Ag partial evaporation upon annealing at high temperatures. The variation of optical properties with aging is related to Cu oxidization and follows different trends depending on the sample morphology. Overall, it is shown that Cu-Ag island films are compelling systems for plasmonic applications, as their optical response can be widely and easily tuned by adjusting fabrication conditions.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/308922 Collegamento a IRIS

2021
NbSe2 Meets C2N: A 2D‐2D Heterostructure Catalysts as Multifunctional Polysulfide Mediator in Ultra‐Long‐Life Lithium–Sulfur Batteries
ADVANCED ENERGY MATERIALS
Autore/i: Dawei, Yang; Zhifu, Liang; Chaoqi, Zhang; Jordi Jacas, Biendicho; Marc, Botifoll; Spadaro, M; C, ; Qiulin, Chen; Mengyao, Li; Alberto, Ramon; Ahmad Ostovari, Moghaddam; Jordi, Llorca; Jiaao, Wang; Joan Ramon, Morante; Jordi, Arbiol; Shu‐lei, Chou; Andreu, Cabot
Classificazione: 1 Contributo su Rivista
Abstract: The shuttle effect and sluggish conversion kinetics of lithium polysulfides (LiPS) hamper the practical application of lithium–sulfur batteries (LSBs). Toward overcoming these limitations, herein an in situ grown C2N@NbSe2 heterostructure is presented with remarkable specific surface area, as a Li–S catalyst and LiPS absorber. Density functional theory (DFT) calculations and experimental results comprehensively demonstrate that C2N@NbSe2 is characterized by a suitable electronic structure and charge rearrangement that strongly accelerates the LiPS electrocatalytic conversion. In addition, heterostructured C2N@NbSe2 strongly interacts with LiPS species, confining them at the cathode. As a result, LSBs cathodes based on C2N@NbSe2/S exhibit a high initial capacity of 1545 mAh g−1 at 0.1 C. Even more excitingly, C2N@NbSe2/S cathodes are characterized by impressive cycling stability with only 0.012% capacity decay per cycle after 2000 cycles at 3 C. Even at a sulfur loading of 5.6 mg cm−2, a high areal capacity of 5.65 mAh cm−2 is delivered. These results demonstrate that C2N@NbSe2 heterostructures can act as multifunctional polysulfide mediators to chemically adsorb LiPS, accelerate Li-ion diffusion, chemically catalyze LiPS conversion, and lower the energy barrier for Li2S precipitation/decomposition, realizing the “adsorption-diffusion-conversion” of polysulfides.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/308936 Collegamento a IRIS

2021
Effects of solar irradiation on thermally driven CO2 methanation using Ni/CeO2–based catalyst
APPLIED CATALYSIS. B, ENVIRONMENTAL
Autore/i: V., Golovanova; Spadaro, M; C, ; J., Arbiol; V., Golovanov; T., Rantala; T., Andreu; J. R., Morante.
Classificazione: 1 Contributo su Rivista
Abstract: Utilization of the renewable energy sources is one of the main challenges in the state-of-the-art technologies for CO2 recycling. Here we have taken advantage of the solar light harvesting in the thermocatalytic approach to carbon dioxide methanation. The large-surface-area Ni/CeO2 catalyst produced by a scalable low-cost method was characterized and tested in the dark and under solar light irradiation conditions. Light-assisted CO2 conversion experiments as well as in-situ DRIFT spectrometry, performed at different illumination intensities, have revealed a dual effect of the incident photons on the catalytic properties of the two-component Ni/CeO2 catalyst. On the one hand, absorbed photons induce a localized surface plasmon resonance in the Ni nanoparticles followed by dissipation of the heat to the oxide matrix. On the other hand, the illumination activates the photocatalytic properties of the CeO2 support, which leads to an increase in the concentration of the intermediates being precursor for methane production. Analysis of the methane production at different temperatures and illumination conditions has shown that the methanation reaction in our case is controlled by a photothermally-activated process. The used approach has allowed us to increase the reaction rate up to 2.4 times and consequently to decrease the power consumption by 20 % under solar illumination, thus replacing the conventional thermal activation of the reaction with a green energy source.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/308943 Collegamento a IRIS

2021
Photodehydrogenation of Ethanol over Cu2O/TiO2 Heterostructures
NANOMATERIALS
Autore/i: C., Xing; Y., Zhang; Y., Liu; X., Wang; J., Li; Martínez-Alanis, P. R.; Spadaro, M; C, ; P., Guardia; J., Arbiol; J., Llorca; A., Cabot.
Classificazione: 1 Contributo su Rivista
Abstract: The photodehydrogenation of ethanol is a sustainable and potentially cost-effective strategy to produce hydrogen and acetaldehyde from renewable resources. The optimization of this process requires the use of highly active, stable and selective photocatalytic materials based on abundant elements and the proper adjustment of the reaction conditions, including temperature. In this work, Cu2O-TiO2 type-II heterojunctions with different Cu2O amounts are obtained by a one-pot hydrothermal method. The structural and chemical properties of the produced materials and their activity toward ethanol photodehydrogenation under UV and visible light illumination are evaluated. The Cu2O-TiO2 photocatalysts exhibit a high selectivity toward acetaldehyde production and up to tenfold higher hydrogen evolution rates compared to bare TiO2. We further discern here the influence of temperature and visible light absorption on the photocatalytic performance. Our results point toward the combination of energy sources in thermo-photocatalytic reactors as an efficient strategy for solar energy conversion.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/308932 Collegamento a IRIS

2021
Defect Engineering in Solution-Processed Polycrystalline SnSe Leads to High Thermoelectric Performance
ACS NANO
Autore/i: Y., Liu; M., Calcabrini; Y., Yu; S., Lee; C., Chang; J., David; T., Ghosh; Spadaro, M; C, ; Xie, ; O., Cojocaru-Mirédin; J., Arbiol; M., Ibáñez
Classificazione: 1 Contributo su Rivista
Abstract: SnSe has emerged as one of the most promising materials for thermoelectric energy conversion due to its extraordinary performance in its single-crystal form and its low-cost constituent elements. However, to achieve an economic impact, the polycrystalline counterpart needs to replicate the performance of the single crystal. Herein, we optimize the thermoelectric performance of polycrystalline SnSe produced by consolidating solution-processed and surface-engineered SnSe particles. In particular, the SnSe particles are coated with CdSe molecular complexes that crystallize during the sintering process, forming CdSe nanoparticles. The presence of CdSe nanoparticles inhibits SnSe grain growth during the consolidation step due to Zener pinning, yielding a material with a high density of grain boundaries. Moreover, the resulting SnSe–CdSe nanocomposites present a large number of defects at different length scales, which significantly reduce the thermal conductivity. The produced SnSe–CdSe nanocomposites exhibit thermoelectric figures of merit up to 2.2 at 786 K, which is among the highest reported for solution-processed SnSe.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/308944 Collegamento a IRIS

2021
Doping-mediated stabilization of copper vacancies to promote thermoelectric properties of Cu2− xS
NANO ENERGY
Autore/i: Yu, Zhang; Congcong, Xing; Yu, Liu; Spadaro, M; C, ; Xiang, Wang; Mengyao, Li; Ke, Xiao; Ting, Zhang; Pablo, Guardia; Khak Ho, Lim; Ahmad Ostovari, Moghaddam; Jordi, Llorca; Jordi, Arbiol; Maria, Ibáñez; Andreu, Cabot
Classificazione: 1 Contributo su Rivista
Abstract: Copper chalcogenides are outstanding thermoelectric materials for applications in the medium-high temperature range. Among different chalcogenides, while Cu2−xSe is characterized by higher thermoelectric figures of merit, Cu2−xS provides advantages in terms of low cost and element abundance. In the present work, we investigate the effect of different dopants to enhance the Cu2−xS performance and also its thermal stability. Among the tested options, Pb-doped Cu2−xS shows the highest improvement in stability against sulfur volatilization. Additionally, Pb incorporation allows tuning charge carrier concentration, which enables a significant improvement of the power factor. We demonstrate here that the introduction of an optimal additive amount of just 0.3% results in a threefold increase of the power factor in the middle-temperature range (500–800 K) and a record dimensionless thermoelectric figure of merit above 2 at 880 K.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/308929 Collegamento a IRIS

2020
Electrocatalytic behavior of PtCu clusters produced by nanoparticle beam deposition
JOURNAL OF PHYSICAL CHEMISTRY. C.
Autore/i: Spadaro, M; C, ; J. J. L., Humphrey; R., Cai; L., Martinez; S. J., Haigh; Y., Huttel; S. J., Spencer; A. J., Wain; R. E., Palmer.
Classificazione: 1 Contributo su Rivista
Abstract: State-of-the-art electrocatalysts for electrolyzer and fuel cell applications currently rely on platinum group metals, which are costly and subject to supply risks. In recent years, a vast collection of research has explored the possibility of reducing the Pt content in such catalysts by alloying with earth-abundant and cheap metals, enabling co-optimization of cost and activity. Here, using nanoparticle beam deposition, we explore the electrocatalytic performance of PtCu alloy clusters in the hydrogen evolution reaction (HER). Elemental compositions of the produced bimetallic clusters were shown by X-ray photoelectron spectroscopy (XPS) to range from 2 at. % to 38 at. % Pt, while high-angle annular dark field scanning transmission electron microscopy (HAADF-STEM) combined with energy dispersive X-ray (EDX) spectroscopy indicated that the predominant cluster morphologies could be characterized as either a fully mixed alloy or as a mixed core with a Cu-rich shell. In contrast with previous studies, a monotonic decrease in HER activity with increasing Cu content was observed over the composition range studied, with the current density measured at -0.3 V (vs reversible hydrogen electrode) scaling approximately linearly with Pt at. %. This trend opens up the possibility that PtCu could be used as a reference system for comparing the composition-dependent activity of other bimetallic catalysts.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/308938 Collegamento a IRIS

2020
Size control of Au nanoparticles from the scalable and solvent-free matrix assembly cluster source
JOURNAL OF NANOPARTICLE RESEARCH
Autore/i: Spadaro, M; C, ; L., Cao; W., Terry; R., Balog; F., Yin; R. E., Palmer.
Classificazione: 1 Contributo su Rivista
Abstract: Nanostructured gold is an intriguing system for heterogeneous catalysis at low temperature. Its activity is related to choice of support selection, particle-support interaction, and especially the particle size. Here, we investigate the possibility of controlling the size of Au clusters (nanoparticles) in the novel Matrix Assembly Cluster Source (MACS), a solvent-free nanoparticle source with potential for scale-up to the gram level. The novelty of the MACS is the idea of making clusters by sputtering a precondensed matrix of metal atoms embedded in a condensed non-reactive gas, e.g., Ar. This concept, introduced in 2016, has already proved deposition rates several orders of magnitude higher than conventional cluster beam routes. Such scale-up in the cluster production rate is crucial for industrial research on nanocatalysis under realistic reaction condition. Here, we report a systematic study of how Au metal loading in the matrix affects the size distribution of clusters generated. Furthermore, the obtained dependence of cluster size on deposition time provides clear confirmation of cluster formation inside the matrix by ion irradiation, rather than by aggregation of atoms on the TEM support after deposition.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/308933 Collegamento a IRIS

2020
Synergistic computational-experimental discovery of highly selective ptcu nanocluster catalysts for acetylene semihydrogenation
ACS CATALYSIS
Autore/i: O., Ayodele; R., Cai; J., Wang; Y., Ziouani; Z., Liang; Spadaro, M; C, ; K., Kovnir; J., Arbiol; J., Akkola; R. E., Palmer; Y. V., Kolen’Ko.
Classificazione: 1 Contributo su Rivista
Abstract: Semihydrogenation of acetylene (SHA) in an ethylene-rich stream is an important process for polymer industries. Presently, Pd-based catalysts have demonstrated good acetylene conversion (XC2H2), however, at the expense of ethylene selectivity (SC2H4). In this study, we have employed a systematic approach using density functional theory (DFT) to identify the best catalyst in a Cu–Pt system. The DFT results showed that with a 55 atom system at ∼1.1 Pt/Cu ratio for Pt28Cu27/Al2O3, the d-band center shifted −2.2 eV relative to the Fermi level leading to electron-saturated Pt, which allows only adsorption of ethylene via a π-bond, resulting in theoretical 99.7% SC2H4 at nearly complete XC2H2. Based on the DFT results, Pt–Cu/Al2O3 (PtCu) and Pt/Al2O3 (Pt) nanocatalysts were synthesized via cluster beam deposition (CBD), and their properties and activities were correlated with the computational predictions. For bimetallic PtCu, the electron microscopy results show the formation of alloys. The bimetallic PtCu catalyst closely mimics the DFT predictions in terms of both electronic structure, as confirmed by X-ray photoelectron spectroscopy, and catalytic activity. The alloying of Pt with Cu was responsible for the high C2H4 specific yield resulting from electron transfer between Cu and Pt, thus making PtCu a promising catalyst for SHA.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/308952 Collegamento a IRIS

2020
Optical and electronic properties of silver nanoparticles embedded in cerium oxide
THE JOURNAL OF CHEMICAL PHYSICS
Autore/i: Pelli Cresi, J. S.; Silvagni, E.; Bertoni, G.; Spadaro, M. C.; Benedetti, S.; Valeri, S.; D'Addato, S.; Luches, P.
Classificazione: 1 Contributo su Rivista
Abstract: Wide bandgap oxides can be sensitized to visible light by coupling them with plasmonic nanoparticles (NPs). We investigate the optical and electronic properties of composite materials made of Ag NPs embedded within cerium oxide layers of different thickness. The electronic properties of the materials are investigated by X-ray and ultraviolet photoemission spectroscopy, which demonstrates the occurrence of static charge transfers between the metal and the oxide and its dependence on the NP size. Ultraviolet-visible spectrophotometry measurements show that the materials have a strong absorption in the visible range induced by the excitation of localized surface plasmon resonances. The plasmonic absorption band can be modified in shape and intensity by changing the NP aspect ratio and density and the thickness of the cerium oxide film.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/308924 Collegamento a IRIS

2019
Highly efficient plasmon-mediated electron injection into cerium oxide from embedded silver nanoparticles
NANOSCALE
Autore/i: Pelli Cresi, J. S.; Spadaro, M. C.; D'Addato, S.; Valeri, S.; Benedetti, S.; Di Bona, A.; Catone, D.; Di Mario, L.; O'Keeffe, P.; Paladini, A.; Bertoni, G.; Luches, P.
Classificazione: 1 Contributo su Rivista
Abstract: The coupling with plasmonic metal nanoparticles (NPs) represents a promising opportunity to sensitize wide band gap oxides to visible light. The processes which come into play after the excitation of localized surface plasmon resonances (LSPRs) in the NPs largely determine the efficiency of the charge/ energy transfer from the metal NP to the oxide. We report a study of plasmon-mediated energy transfer from mass-selected silver NPs into the cerium oxide matrix in which they are embedded. Femtosecond transient absorption spectroscopy is used to probe the dynamics of charge carrier relaxation after the excitation of the LSPR of the silver nanoparticles and to evaluate the plasmon-mediated electron transfer efficiency from the silver nanoparticles to the cerium oxide. High injection efficiencies in the 6-16% range have been identified for excitation between 400 and 600 nm. These high values have been explained in terms of plasmon-mediated direct electron injection as well as indirect hot electron injection from the NPs to the oxide. The information obtained provides an important contribution towards a knowledge- driven design of efficient cerium oxide based nanostructured materials for solar to chemical energy conversion.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/308939 Collegamento a IRIS

2019
Angular dependence of nanoparticle generation in the matrix assembly cluster source
NANO RESEARCH
Autore/i: Spadaro, M; C, ; J., Zhao; W. D., Terry; J., Liu; F., Djurabekova; F., Yin; R. E., Palmer
Classificazione: 1 Contributo su Rivista
Abstract: The matrix assembly cluster source (MACS) represents a bridge between conventional instruments for cluster beam deposition (CBD) and the level of industrial production. The method is based on Ar+ ion sputtering of a pre-condensed Ar-M matrix (where M, is typically a metal such as Ag). Each Ar+ ion produces a collision cascade and thus the formation of metal clusters is in the matrix, which are then sputtered out. Here we present an experimental and computational investigation of the cluster emission process, specifically its dependence on the Ar+ ion angle of incidence and the cluster emission angle. We find the incidence angle strongly influences the emerging cluster flux, which is assigned to the spatial location of the deposited primary ion energy relative to the cluster into the matrix. We also found an approximately constant angle between the incident ion beam and the peak in the emitted cluster distribution, with value between 99° and 109°.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/308946 Collegamento a IRIS

2019
Insights into image contrast from dislocations in ADF-STEM
ULTRAMICROSCOPY
Autore/i: E., Oveisi; Spadaro, M; C, ; V., Grillo; E., Rotunno; C., Hébert
Classificazione: 1 Contributo su Rivista
Abstract: Competitive mechanisms contribute to image contrast from dislocations in annular dark-field scanning transmission electron microscopy (ADF-STEM). A clear theoretical understanding of the mechanisms underlying the ADF-STEM contrast is therefore essential for correct interpretation of dislocation images. This paper reports on a systematic study of the ADF-STEM contrast from dislocations in a GaN specimen, both experimentally and computationally. Systematic experimental ADF-STEM images of the edge-character dislocations reveal a number of characteristic contrast features that are shown to depend on both the angular detection range and specific position of the dislocation in the sample. A theoretical model based on electron channelling and Bloch-wave scattering theories, supported by numerical simulations based on Grillo's strain-channelling equation, is proposed to elucidate the physical origin of such complex contrast phenomena.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/308950 Collegamento a IRIS

2019
Physical Synthesis and Study of Ag@CaF 2 Core@Shell Nanoparticles: Morphology and Tuning of Optical Properties
PHYSICA STATUS SOLIDI B-BASIC RESEARCH
Autore/i: D'Addato, Sergio; Vikatakavi, Avinash; Spadaro, Maria Chiara; Valeri, Sergio; Pasquali, Luca
Classificazione: 1 Contributo su Rivista
Abstract: Pre-formed Ag nanoparticles (NPs) and Ag@CaF 2 core–shell NPs are physically synthesized using DC magnetron-based NP source and deposited on Si-SiO x wafers. The samples are prepared by co-depositing Ag nanoparticles and CaF 2 produced by an evaporation source, or by sequential deposition method, i.e., by depositing in a sequence a CaF 2 buffer layer, the Ag NPs generated by the NP source and a capping CaF 2 layer. The supported films are characterized by Scanning Electron Microscopy (SEM), X-ray Photoelectron Spectroscopy (XPS), and Surface Differential Reflectivity (SDR). SEM shows that Ag NPs deposited directly on Si-SiO x tend to diffuse and to agglomerate, affecting the size distribution of the nanostructures. The presence of a CaF 2 buffer layer between Ag and Si-SiO x limits this effect, while XPS reveals electrical charging, caused by the insulating nature of the CaF 2 continuous film. The surface plasmon resonance behavior for different samples is analyzed using SDR with p-polarized light. There is a clear evidence of a blue shift in the plasmon excitation due to the presence of CaF 2 on Si, which can represent a potential advantage for the technological applications in photovoltaics and optoelectronics.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/308951 Collegamento a IRIS

2019
Coordination Polymer to Atomically Thin, Holey, Metal-Oxide Nanosheets for Tuning Band Alignment
ADVANCED MATERIALS
Autore/i: S. S., Mofarah; E., Adabifiroozjaei; R., Pardehkhorram; M. H. N., Assadi; M., Hinterstein; Y., Yao; X., Liu; M. B., Ghasemian; K., Kalantar-Zadeh; R., Mehmood; S., Bhattacharyya; Spadaro, M; C, ; J., Arbiol; S., Lim; Y., Xu; T. S., Suzuki; H., Arandiyan; P., Koshy; C. C., Sorrell.
Classificazione: 1 Contributo su Rivista
Abstract: Holey 2D metal oxides have shown great promise as functional materials for energy storage and catalysts. Despite impressive performance, their processing is challenged by the requirement of templates plus capping agents or high temperatures; these materials also exhibit excessive thicknesses and low yields. The present work reports a metal-based coordination polymer (MCP) strategy to synthesize polycrystalline, holey, metal oxide (MO) nanosheets with thicknesses as low as two-unit cells. The process involves rapid exfoliation of bulk-layered, MCPs (Ce-, Ti-, Zr-based) into atomically thin MCPs at room temperature, followed by transformation into holey 2D MOs upon the removal of organic linkers in aqueous solution. Further, this work represents an extra step for decorating the holey nanosheets using precursors of transition metals to engineer their band alignments, establishing a route to optimize their photocatalysis. The work introduces a simple, high-yield, room-temperature, and template-free approach to synthesize ultrathin holey nanosheets with high-level functionalities.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/308949 Collegamento a IRIS

2018
Low pressure bottom-up synthesis of metal@oxide and oxide nanoparticles: control of structure and functional properties
PHYSICA SCRIPTA
Autore/i: D’Addato, Sergio; Spadaro, Maria Chiara
Classificazione: 1 Contributo su Rivista
Abstract: Experimental activity on core@shell, metal@oxide, and oxide nanoparticles (NPs) grown with physical synthesis, and more specifically by low pressure gas aggregation sources (LPGAS) is reviewed, through a selection of examples encompassing some potential applications in nanotechnology. After an introduction to the applications of NPs, a brief description of the main characteristics of the growth process of clusters and NPs in LPGAS is given. Thereafter, some relevant case studies are reported: Formation of native oxide shells around the metal cores in core@shell NPs. Experimental efforts to obtain magnetic stabilization in magnetic core@shell NPs by controlling their structure and morphology. Recent advancements in NP source design and new techniques of co-deposition, with relevant results in the realization of NPs with a greater variety of functionalities. Recent results on reducible oxide NPs, with potentialities in nanocatalysis, energy storage, and other applications. Although this list is far from being exhaustive, the aim of the authors is to provide the reader a descriptive glimpse into the physics behind the growth and studies of low pressure gas-phase synthesized NPs, with their ever-growing potentialities for the rational design of new functional materials.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/308940 Collegamento a IRIS

2017
Investigation of Ni@CoO core-shell nanoparticle films synthesized by sequential layer deposition
APPLIED SURFACE SCIENCE
Autore/i: Spadaro, MARIA CHIARA; Luches, P.; Benedetti, Francesco; Valeri, Sergio; Turchini, S.; Bertoni, G.; Ferretti, A. M.; Capetti, E.; Ponti, A.; D'Addato, Sergio
Classificazione: 1 Contributo su Rivista
Abstract: Films of Ni@CoO core-shell nanoparticles (NP Ni core size d ≈ 11 nm) have been grown on Si/SiOx and lacey carbon supports, by a sequential layer deposition method: a first layer of CoO was evaporated on the substrate, followed by the deposition of a layer of pre-formed, mass-selected Ni NPs, and finally an overlayer of CoO was added. The Ni NPs were formed by a magnetron gas aggregation source, and mass selected with a quadrupole mass filter. The morphology of the films was investigated with Scanning Electron Microscopy and Scanning Transmission Electron Microscopy. The Ni NP cores have a shape compatible with McKay icosahedron, caused by multitwinning occurring during their growth in the source, and the Ni NP layer shows the typical random paving growth mode. After the deposition of the CoO overlayer, CoO islands are observed, gradually extending and tending to merge with each other, with the formation of shells that enclose the Ni NP cores. In situ X-ray Photoelectron Spectroscopy showed that a few Ni atomic layers localized at the core-shell interface are oxidized, hinting at the possibility of creating an intermediate NiO shell between Ni and CoO, depending on the deposition conditions. Finally, X-ray Magnetic Circular Dichroism at the Ni L2,3 absorption edge showed the presence of magnetization at room temperature even at remanence, revealing the possibility of magnetic stabilization of the NP film.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/308925 Collegamento a IRIS

2017
Steering the magnetic properties of Ni/NiO/CoO core-shell nanoparticle films: The role of core-shell interface versus interparticle interactions
PHYSICAL REVIEW MATERIALS
Autore/i: Ponti, Alessandro; Ferretti, Anna M.; Capetti, Elena; Spadaro, Maria Chiara; Bertoni, Giovanni; Grillo, Vincenzo; Luches, Paola; Valeri, Sergio; D’Addato, Sergio
Classificazione: 1 Contributo su Rivista
Abstract: Supported core-shell Ni/NiO/CoO nanoparticle (NP) films were obtained by deposition of preformed and mass-selected Ni NPs on a buffer layer of CoO, followed by a top CoO layer. The resulting NPs have core/shell morphology, with a McKay icosahedral Ni core and a partially crystalline CoO shell. X-ray photoelectron spectroscopy evidenced the presence of a thin NiO layer, which was shown to be between the Ni core and the CoO shell by elemental TEM mapping. CoO and NiO shells with different thickness values were obtained, allowing us to investigate the evolution of the magnetic properties of the NP assemblies as a function of the oxide shell thickness. Both exchange-coupling and magnetostatic interactions significantly contribute to the magnetic behavior of Ni/NiO/CoO NP films. After the Ni/NiO/CoO NPs are cooled in a weak magnetic field, they have blocking temperature higher than room temperature because of strong magnetostatic interactions, which support the formation of a spin-glass-like state below similar to 250 K. Exchange coupling dominates the magnetic behavior after the NPs are cooled in a strong magnetic field. The exchange bias (EB) is in the 0.17-2.35 kOe range and strongly depends on the CoO thickness (0.4-2.7 nm), showing the onset of the EB at the few-nanometer scale. The switching field distribution showed that the EB opposes the magnetization reversal from the direction along the cooling field but it does not significantly ease the opposite process. The EB depends on t(CoO) only for t(NiO) <= 0.5 nm, but when NiO is 0.7 nm thick it strongly interacts with CoO and a large increase of the EB and coercivity is observed.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/308930 Collegamento a IRIS

2017
Contraction, cation oxidation state and size effects in cerium oxide nanoparticles
NANOTECHNOLOGY
Autore/i: Cresi, Jacopo Stefano Pelli; Chiara Spadaro, Maria; D'Addato, Sergio; Valeri, Sergio; Amidani, Lucia; Boscherini, Federico; Bertoni, Giovanni; Deiana, Davide; Luches, Paola
Classificazione: 1 Contributo su Rivista
Abstract: An accurate description of the structural and chemical modifications of cerium oxide nanoparticles (NPs) is mandatory for understanding their functionality in applications. In this work we investigate the relation between local atomic structure, oxidation state, defectivity and size in cerium oxide NPs with variable diameter below 10 nm, using x-ray absorption fine structure analysis in the near and extended energy range. The NPs are prepared by physical methods under controlled conditions and analyzed in morphology and crystalline quality by high resolution transmission electron microscopy. We resolve here an important question on the local structure of cerium oxide NPs: we demonstrate a progressive contraction in the Ce-O interatomic distance with decreasing NP diameter and we relate the observed effect to the reduced dimensionality. The contraction is not significantly modified by inducing a 4%-6% higher Ce3+ concentration through thermal annealing in high vacuum. The consequences of the observed average cation-anion distance contraction on the properties of the NPs are discussed.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/308927 Collegamento a IRIS

2016
Influence of defect distribution on the reducibility of CeO2-x nanoparticles
NANOTECHNOLOGY
Autore/i: Spadaro, MARIA CHIARA; Luches, Paola; Bertoni, Giovanni; Grillo, Vincenzo; Turner, Stuart; Van Tendeloo, Gustaaf; Valeri, Sergio; D'Addato, Sergio
Classificazione: 1 Contributo su Rivista
Abstract: Ceria nanoparticles (NPs) are fundamental in heterogeneous catalysis because of their ability to store or release oxygen depending on the ambient conditions. Their oxygen storage capacity is strictly related to the exposed planes, crystallinity, density and distribution of defects. In this work a study of ceria NPs produced with a ligand-free, physical synthesis method is presented. The NP films were grown by a magnetron sputtering based gas aggregation source and studied by high resolution- and scanning-transmission electron microscopy and x-ray photoelectron spectroscopy. In particular, the influence of the oxidation procedure on the NP reducibility has been investigated. The different reducibility has been correlated to the exposed planes, crystallinity and density and distribution of structural defects. The results obtained in this work represent a basis to obtain cerium oxide NP with desired oxygen transport properties.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/308942 Collegamento a IRIS

2016
Lepidocrocite-like TiO2 and TiO2 (110)–(1× 2) supported on W (100)
MATERIALS SCIENCE AND TECHNOLOGY
Autore/i: G. T., Harrison; Spadaro, M; C, ; C. L., Pang; D. C., Grinter; C. M., Yim; P., Luches; G., Thornton
Classificazione: 1 Contributo su Rivista
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/308935 Collegamento a IRIS

2015
Morphology, structural properties and reducibility of size-selected CeO2- x nanoparticle films
BEILSTEIN JOURNAL OF NANOTECHNOLOGY
Autore/i: Spadaro, MARIA CHIARA; D'Addato, Sergio; Gasperi, Gabriele; Benedetti, Francesco; Luches, Paola; Grillo, Vincenzo; Bertoni, Giovanni; Valeri, Sergio
Classificazione: 1 Contributo su Rivista
Abstract: Non-stoichiometric ceria nanoparticles (NPs) were obtained by a gas aggregation source with a magnetron and were mass-selected with a quadrupole mass filter. By varying magnetron power, Ar gas flow, and the length of the aggregation tube, NPs with an average diameter of 6, 9, and 14 nm were synthesized and deposited onto a substrate, thus obtaining NP films. The morphology of the films was studied with scanning electron microscopy, while high resolution transmission electron microscopy was used to gain a deeper insight into the atomic structure of individual NPs. By using X-ray photoelectron spectroscopy we analyzed the degree of reduction of the NPs of different diameters, before and after thermal treatments in vacuum (reduction cycle) and in O2 atmosphere (oxidation cycle) at different temperatures. From this analysis we inferred that the size is an important parameter only at intermediate temperatures. As a comparison, we evaluated the reducibility of an ultra-thin ceria film with the same surface to volume ratio as the 9 nm diameter NPs film, observing that NPs are more reducible than the ceria film.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/308934 Collegamento a IRIS

2015
Near-Field Optical Detection of Plasmon Resonance from Gold Nanoparticles: Theoretical and Experimental Evidence
PLASMONICS
Autore/i: Triolo, C.; Cacciola, A.; Saija, R.; Trusso, S.; Spadaro, M; Neri, F.; Ossi, P. M.; Patanè, S.
Classificazione: 1 Contributo su Rivista
Abstract: The study of plasmon-induced electromagnetic fields is a very interesting topic for basic research and photonic applications. The plasmon properties depend on many factors, such as composition, size, shape and arrangement of nanoparticles. In this paper, we propose an experimental and theoretical study on the optical properties of gold nanoparticles deposited by pulsed laser ablation and investigated by near-field optical microscopy (SNOM) in a transmission farfield collection scheme. The electromagnetic field properties have been simulated by an exact theoretical analysis based on the multipolar expansion of the fields and on T-matrix approach. The theoretical model almost accurately reproduces the experimental data and makes us confident that the used method is suitable to describe more complex system of metal nanoparticles.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/308947 Collegamento a IRIS

2015
On the role of the ablated mass on the propagation of a laser-generated plasma in an ambient gas
EUROPHYSICS LETTERS
Autore/i: Spadaro, M; C, ; Fazio, E; Neri, F; Trusso, S; Ossi, P M
Classificazione: 1 Contributo su Rivista
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/308948 Collegamento a IRIS

2015
Tunability of exchange bias in Ni@NiO core-shell nanoparticles obtained by sequential layer deposition
NANOTECHNOLOGY
Autore/i: Spadaro, MARIA CHIARA; D'Addato, Sergio; Luches, Paola; Valeri, Sergio; Grillo, Vincenzo; Rotunno, Enzo; Roldan, Manuel A; Pennycook, Stephen J; Ferretti, Anna Maria; Capetti, Elena; Ponti, Alessandro
Classificazione: 1 Contributo su Rivista
Abstract: Films of magnetic Ni@NiO core-shell nanoparticles (NPs, core diameter d ≅ 12 nm, nominal shell thickness variable between 0 and 6.5 nm) obtained with sequential layer deposition were investigated, to gain insight into the relationships between shell thickness/morphology, core-shell interface, and magnetic properties. Different values of NiO shell thickness ts could be obtained while keeping the Ni core size fixed, at variance with conventional oxidation procedures where the oxide shell is grown at the expense of the core. Chemical composition, morphology of the as-produced samples and structural features of the Ni/NiO interface were investigated with x-ray photoelectron spectroscopy and microscopy (scanning electron microscopy, transmission electron microscopy) techniques, and related with results from magnetic measurements obtained with a superconducting quantum interference device. The effect of the shell thickness on the magnetic properties could be studied. The exchange bias (EB) field Hbias is small and almost constant for ts up to 1.6 nm; then it rapidly grows, with no sign of saturation. This behavior is clearly related to the morphology of the top NiO layer, and is mostly due to the thickness dependence of the NiO anisotropy constant. The ability to tune the EB effect by varying the thickness of the last NiO layer represents a step towards the rational design and synthesis of core-shell NPs with desired magnetic properties.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/308928 Collegamento a IRIS

2015
Influence of size, shape and core–shell interface on surface plasmon resonance in Ag and Ag@MgO nanoparticle films deposited on Si/SiOx
BEILSTEIN JOURNAL OF NANOTECHNOLOGY
Autore/i: D'Addato, Sergio; Pinotti, Daniele; Spadaro, MARIA CHIARA; Paolicelli, Guido; Grillo, Vincenzo; Valeri, Sergio; Pasquali, Luca; Bergamini, Luca; Corni, Stefano
Classificazione: 1 Contributo su Rivista
Abstract: Ag and Ag@MgO core-shell nanoparticles (NPs) with a diameter of d = 3-10 nm were obtained by physical synthesis methods and deposited on Si with its native ultrathin oxide layer SiOx (Si/SiOx). Scanning electron microscopy and transmission electron microscopy (TEM) images of bare Ag NPs revealed the presence of small NP aggregates caused by diffusion on the surface and agglomeration. Atomic resolution TEM gave evidence of the presence of crystalline multidomains in the NPs, which were due to aggregation and multitwinning occurring during NP growth in the nanocluster source. Co-deposition of Ag NPs and Mg atoms in an oxygen atmosphere gave rise to formation of a MgO shell matrix surrounding the Ag NPs. The behaviour of the surface plasmon resonance (SPR) excitation in surface differential reflectivity (SDR) spectra with p-polarised light was investigated for bare Ag and Ag@MgO NPs. It was shown that the presence of MgO around the Ag NPs caused a red shift of the plasmon excitation, and served preserve its existence after prolonged (five months) exposure to air, realizing the possibility of technological applications in plasmonic devices. The Ag NP and Ag@MgO NP film features in the SDR spectra could be reproduced by classical electrodynamics simulations by treating the NP-containing layer as an effective Maxwell Garnett medium. The simulations gave results in agreement with the experiments when accounting for the experimentally observed aggregation.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/308937 Collegamento a IRIS

2015
Structure and Morphology of Silver Nanoparticles on the (111) Surface of Cerium Oxide
JOURNAL OF PHYSICAL CHEMISTRY. C
Autore/i: Benedetti, Francesco; Luches, Paola; Spadaro, MARIA CHIARA; Gasperi, Gabriele; D'Addato, Sergio; Valeri, Sergio; Boscherini, Federico
Classificazione: 1 Contributo su Rivista
Abstract: The structure of Ag nanoparticles of different size, supported on the cerium oxide (111) surface, was investigated by X-ray absorption fine structure at the Ag K-edge. The results of the data analysis in the near and extended energy range are interpreted with the help of the results obtained by X-ray photoelectron spectroscopy and scanning tunneling microscopy measurements and allow to obtain a detailed atomic scale description of the model system investigated. The Ag nanoparticles have an average size of a few tens of angstroms, which increases with increasing deposited Ag amount. The nanoparticles show a slight tendency to nucleate at the step edges between different cerium oxide layers and they have a face centered cubic structure with an Ag-Ag interatomic distance contracted by 3-4% with respect to the bulk value. The interatomic distance contraction is mainly ascribed to dimensionality induced effects, while epitaxial effects have a minor role. The presence of Ag-O bonds at the interface between the nanoparticles and the supporting oxide is also detected. The Ag-O interatomic distance decreases with decreasing nanoparticle size.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/308926 Collegamento a IRIS

2015
Pyramid-Shaped Wurtzite CdSe Nanocrystals with Inverted Polarity
ACS NANO
Autore/i: S., Ghosh; R., Gaspari; G., Bertoni; Spadaro, M; C, ; M., Prato; S., Turner; G., van Tendeloo; A., Cavalli; L., Manna; R., Brescia
Classificazione: 1 Contributo su Rivista
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/308931 Collegamento a IRIS

2014
Controlled growth of Ni/NiO core–shell nanoparticles: Structure, morphology and tuning of magnetic properties
APPLIED SURFACE SCIENCE
Autore/i: D'Addato, Sergio; Spadaro, MARIA CHIARA; Luches, Paola; Grillo, V.; Frabboni, Stefano; Valeri, Sergio; Ferretti, A. M.; Capetti, E.; Ponti, A.
Classificazione: 1 Contributo su Rivista
Abstract: We performed a detailed study of Ni/NiO core–shell nanoparticles (NP) obtained with a gas aggregation source. The NP oxide shells were produced by oxidizing the NP with different procedures: deposition in oxygen atmosphere, post-annealing in air, sequential deposition of (a) first NiO layer, (b) Ni NP and (c) third NiO Layer. X-ray photoelectron spectroscopy from Ni 2p core-level gave information about the chemical state of Ni in the core and in the oxide shell, while scanning electron microscopy was used for investigation of the NP morphology. High quality scanning transmission electron microscopy in high angle annular dark field mode data demonstrated core–shell structure also for NiO/Ni NP/NiO samples. Fieldcooled/ zero-field-cooled magnetization curves and field-cooled isothermal hysteresis cycles at T = 5 K were recorded by a SQUID magnetometer. In this way, the relation between magnetic properties and oxide shell structure was assessed, showing the role played by the control of the formation of oxide on the exchange bias and interparticle magnetic interaction.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/308945 Collegamento a IRIS

2014
A brief tutorial for the STEM-CELL Software
MICROSCOPY AND MICROANALYSIS
Autore/i: Grillo, V.; Rotunno, E.; Campanini, M.; Spadaro, M; C, ; D'Addato, S.
Classificazione: 1 Contributo su Rivista
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/308923 Collegamento a IRIS

2014
On the influence of the mass ablated by a laser pulse on thin film morphology and optical properties
APPLIED PHYSICS. A, MATERIALS SCIENCE & PROCESSING
Autore/i: Spadaro, M; Fazio, E; Neri, F; Ossi, P M; Trusso, S
Classificazione: 1 Contributo su Rivista
Abstract: To know and to control experimental parameters that play a role in laser ablation is vital to define film properties. Among the others, laser fluence is commonly used. Yet, when plasma expansion dynamics takes place through an ambient gas, the relation between the ablated mass per pulse and gas mass is critical and till now it was poorly investigated. While the gas mass is fixed by the pressure in the deposition chamber, the ablated mass is not unequivocally determined by the laser fluence. For a given fluence value the ablated mass changes as a function of the irradiated target area. Here, we show that nanostructured silver thin films deposited keeping unaltered the laser fluence, while changing in a controlled way the irradiated area and hence the ablated mass per pulse, display markedly differentiated morphological and optical properties, as evidenced by electron microscopy and UV–Vis and Raman spectroscopies.
Scheda della pubblicazione: https://iris.univpm.it/handle/11566/308954 Collegamento a IRIS




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