Browsing by Author "Chiarello, Gennaro"

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Complexity in astrophysical and laboratory plasmas
(2014-05-16) Servidio, Sergio; Carbone, Vincenzo; Primavera, Leonardo; Chiarello, Gennaro
Development of advanced systems for energy conversion based on innovative two- dimensional materials
(Università della Calabria, 2021-09-27) Zappia, Isabella; Critelli, Salvatore; Chiarello, Gennaro; Cupolillo, Anna
The even growing energy demand due to the demographic growth and the consequent economic expansion has led to the search for innovative technologies available for energy production and conversion from green and renewable sources such as solar energy. In this context, twodimensional (2D) materials, including either single- and few-layer flake forms, are constantly attracting more and more interest as potential advanced photo(electro)catalysts for redox reactions leading to green fuel production. Recently, layered semiconductors of group-III and group-IV, which can be exfoliated in their 2D form due to low cleavage energy (typically < 0.5 J m-2), have been theoretically predicted as water splitting photocatalysts for hydrogen production. For example, their large surface-to-volume ratio intrinsically guarantees that the charge carriers are directly photogenerated at the interface with the electrolyte, where redox reactions take place before they recombine. Moreover, their electronic structure can be tuned by controlling the number of layers, fulfilling the fundamental requirements for water splitting photocatalysts, i.e.: 1) conduction band minimum (CBM) energy (ECBM) > reduction potential of H+/H2 (E(H+/H2)); 2) valence band maximum (VBM) energy (EVBM) < reduction potential of O2/H2O (E(O2/H2O)). A requirement for large-scale applications is the development of low-cost, reliable industrial production processes. In this scenario, liquid-phase exfoliation (LPE) methods provide scalable production of 2D materials in form of liquid dispersions, enabling their processing in thin-film through low‐cost and industrially relevant deposition techniques. This thesis investigates, for the first time, the photoelectrochemical (PEC) activity of single-/fewlayer flakes of GaS, GaSe, and GeSe produced through ultrasound-assisted LPE in environmentally friendly solvents (e.g., 2-propanol) in aqueous media. Our results are consequently used to design proof-of-concept PEC water splitting photoelectrodes, as well as PEC-type photodetectors. Moreover, structural and electronic properties of PtTe2 have been investigated, being this material a potential catalyst for the hydrogen evolution reaction (HER) and other fuel-producing electrochemical reactions.
Diffusion and implantation of dopants in single-wall carbon nanotubes:a spectroscopic investigation of chemical and electronic properties
(2012-11-09) Giallombardo, Claudia; Papagno, Luigi; Chiarello, Gennaro
Raman measurements, performed on MWCNTs grown by arc discharge method in He atmosphere, have pointed out the occurrence of a band at 1780- 1860 cm–1, regardless of the use of a catalytic Ni-Cr alloy in the synthesis process [127]. This band has been attributed to the presence of carbon linear chains inside the innermost tube. The maximum Raman signal from the chain-related L bands is found inside a circular region, in correspondence with enhanced secondary electron emission, as evidenced by a strong white color in the SEM images. Furthermore, a temperature-dependent Raman study, up to about 1000K, has revealed for the first time a phase transition trend [128], which seems to be related to a strong, reversible reduction of the Peierls distortion at high temperatures.
Electronic and vibrational properties of ultrathin layers adsorbed on metal surfaces
(2011) Marino, Antonio Raimondo; Chiarello, Gennaro; Carbone, Vincenzo; Bartolino, Roberto
Innovative systems for energy harvesting and storage
(2014-12-01) Caputo, Marco; Chiarello, Gennaro; Goldoni, Andrea; Carbone, Vincenzo
Energy harvesting represent one of the most important problem in today's society: climate changes and geopolitical instabilities remember ourself everyday the needs to nd alternatives to hydrocarbon exploiting. During my PhD period I concentrated my e orts in elaborating new scienti c knowledge to be applied to innovative energy harvesting and storage systems. Most of my work has been focused on the organic energy harvesting systems, like photoelectrochemical cells, solid-state organic photovoltaic cell, and hybrid organic-inorganic perovskites. Electronic structure and interface dynamics of macromolecules (poprhyrins, phthalocyanines, phenacenes, and fullerenes) have been investigated by mean of synchrotron radiation-based experimental techniques. Alternative systems for dye sensitized solar cell to the commonly used Ru-dyes/TiO2 interface were investigated, with encouraging results in the case of Zn-tetra phenyl poprhyrine/ZnO, while K doped picene/C60 interface exhibited properties with possible applications in the eld of superconductivity. Interface e ect have been found to cause also in hybrid organic-inorganic perovskites interesting long-living excitonic states, whose tailoring can lead to high e ciency devices. Doping and morphology e ects have been investigated for polymers and molecular thin lms. It was shown that nanoimprinting treatments can improve the PEDOT:PSS conductibility and in the meanwhile control the work function, both key parameters in an organic photovoltaic device, instead simply crystal packing in octaethyl porphyrins has found to be responsible for heavy electronic modi cations in the frontier orbitals. E orts were also made in nding new systems for energy storage. Innovative electrodes for lithium batteries were chemically characterized, while a study on the oxidation dynamic of metallic alloy usable in advanced fuel cells revealed interesting segregation dynamics.
Properties of entanglement in a Spin Chain with impurities
(2012-11-09) Apollaro, Tony John George; Plastina, Francesco; Chiarello, Gennaro
In this thesis we have studied the e®ects on ground-state entanglement and quantum-state transfer caused by the presence of one and two diagonal impu- rities in a 1D ring-shaped spin-1 2 hamiltonian with XX ferromagnetic cou- pling placed in an otherwise homogeneous transverse magnetic ¯eld. We have restricted our attention to the one-excitation sector of the Hilbert space, where the hamiltonian becomes equivalent to a tight-binding model. In both cases, SchrÄodinger equation has been solved exactly via Green's operator formalism. In the one-impurity model the presence of the defect causes a ¯rst order quantum phase transition, where the new ground state of the system becomes localized around the impurity site. In this state bipartite entanglement is di®erent from zero for spins in a region contained within a localization length, which depends on the ratio of the magnetic inhomogeneity and the exchange coupling (®). We have also analyzed the transmission of quantum information along such a chain. We have found that the presence of the defect is responsible of various phenomena: 1.) information storage: if the state is encoded initially in the impurity, it doesn't di®use away and both ¯delity and concurrence retain its initial maximum value; 2.) mirror e®ect: if the state isn't encoded initially in the defect, entanglement waves get re°ected and transmitted at the impurity site by an amount depending on re°ection and transmission coe±cients, where, they too, involve the same ratio. In the two-impurity model, a similar quantum phase transition occurs, and ground-state entanglement becomes localized too, with the same func- tional relation for the localization length as in the one-impurity model. Nev- ertheless in this case two localization points arise in the spin ring. Quantum- state transfer, in the limit of ® >> 1, exhibits : 1.) bouncing e®ect: if the initial singlet state involves one of the impurities and the external spin, en- 72 tanglement bounces between the defects with Rabi oscillations of frequency given by the energy di®erence of the two localized eigenstates; 2.) entan- glement trapping: relying on the mirror e®ect of the two impurities, the entanglement waves remain con¯ned into the region delimited by the defects sites. From an experimental point of view, we have presented a model that permits to achieve quantum information tasks by systems realizable with present-day technology and requiring minimum control operations. Further studies (inclusion of dynamical properties of the impurities, characterization of the quantum phase transition from an q-information point of view, ex- tension to higher spatial dimensionality and/or other sectors of the Hilbert space, entanglement versus disorder, etc.) should be give more insight on the fundamental physics behind entanglement's theory as well as suggest some achievable experimental protocols for quantum information development.
Proprietà elettroniche e vibrazionali di strati sottili adsorbiti su substrati metallici
(2008) Politano, Antonio; Chiarello, Gennaro; Falcone, Giovanni
Understanding the adsorption, catalytic, and electronic properties of metal/metal interfaces is one of the foremost aims of surface science. In fact, through the tailoring of the characteristics of the substrate it should be possible to obtain more selective catalysts and more effective electronic devices. This thesis is focused on the vibrational and electronic properties of various metal/metal systems, studied by high-resolution electron energy loss spectroscopy. Firstly, alkali adsorption and their coadsorption with CO, O, and OH on transition-metal and noble-metal surfaces have been investigated. Vibrational measurements demonstrated that alkalis adsorb as neutral and polarized adatoms on metal surfaces. The adsorption of CO induces alkali ionization. Short-range effects dominate in alkali coadsorption systems. Alkali oxidation is more readily achieved upon CO adsorption or dissociation than by direct exposures to oxygen. The stabilization of subsurface O was obtained on alkali-doped Cu(111), while on alkali-modified transition-metal catalysts O adatoms remain in on-surface sites. In the latter case a softening of the O-substrate bond occurs. Moreover, we studied chemical reactions at clean and alkali-doped bimetallic surfaces obtained by depositing monolayers of silver on Ni(111) and Cu(111). Important information on the metal surfaces and interfaces could be provided also by the analysis of collective electronic excitations. Surface plasmon dispersion was investigated in metal/metal systems exhibiting electron quantum confinement. Screening effects are enhanced by the presence of quantum well states and a direct correlation between the free-electron density of states of the system, the chemical reactivity, and dynamical screening processes exists. Measurements have been performed on both flat thin films and films nanostructured in islands in order to shed light on the influence of the growth mode on the electronic response of the system. The knowledge gained herein has far-reaching implications to the general understanding of processes at metal/metal interfaces. Keywords: chemisorption, alkali metals, carbon monoxide, oxygen, metallic thin films, silver, bimetallic surfaces, electronic excitations, electron energy loss spectroscopy, surface chemical reactivity, charge transfers, electron confinement.
Rappresentazioni proiettive: applicazioni nella teoria quantistica
(2005) Filippelli, Gianluigi; Nisticò, Giuseppe; Giuliano, Domenico; Chiarello, Gennaro