Browsing by Author "Versace, Carlo C."

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Absorpitive losses mitigation in gain-plasmon hybrid systems as optical metamaterials
(2013-11-29) Rashed, Alireza Rahimi; Bartolino, Roberto; Versace, Carlo C.; Strangi, Giuseppe
In the past decade, plasmonic nanoparticles (NPs) have gained a lot of interest due to their exceptional and fascinating properties which have been accomplishing vital role in emerging science and technology towards multifunctional applications. The extensive current research efforts in nanoplasmonics trigger towards various opto-electronic and medical applications such as invisibility, perfect lens, increasing the efficiency of solar cells, designing and extra-sensitive single-particle detection of biomolecular recognition and in particular optical metamaterials. The negative real part and the low value of the imaginary part of dielectric permittivity are crucial for applications of nanoparticles as subunits of optical metamaterials. However, the performance of plasmonic nanostructures is significantly limited by the intrinsic and strong energy dissipation in metals, especially in the visible range. In fact, regardless of the challenges to synthesize plasmonic nanostructures, the path to use them as building blocks of optical metamaterial is crossing through the finding a solution to mitigate their optical losses. In this research thesis, it is demonstrated experimentally that the incorporation of gain material such as organic dye molecules and quantum dots in close proximity of enhanced local fields of various properly designed plasmonic systems makes it possible to induce resonant energy transfer processes from gain units to plasmonic nanoparticles, to accompanish loss compensation in optical metamaterials. Steady-state experiments and time resolved spectroscopy along with modification of Rayleigh scattering and optical transmission of a probe beam as a function of impinging energy are crucial evidences of mitigation of absorptive losses in different gain doped plasmonic systems The strategy that has been followed here towards mitigation of absorptive losses in optical metamaterials acts at different spatial scales from nano to macro (see Figure 1). The systems at nano-scale (10-100 nm) are based on dispersion of NPs, in particular, gain assisted (nanoparticle-dye dispersion), gain-functionalized core-shell gold NPs (encapsulated dye molecules into the shell) and dye grafted gold core multimeric nanostructures. The study of such nano-composites allows to recognize experimentally how the parameters such as the geometry and size of the metal nanostructures, inter-particle distance, overlap between emission spectrum of gain material and plasmon band of metal NPs, concentration and quantum yield of donor molecules are playing an important role to create more efficient nonradiative RET processes from donor molecules to acceptors. Figure 1 The followed spatial stages on this research study ranged from (a) nano-scale and (b) mesco scale towards (c) macro scale. The obtained results in nano-scale generate further motivations to move forward to study meso-scale (100-900 nm) plasmonic systems which include both dispersion (nanoshell composites) and bulk (periodic layers of gain materials and lossy metal elements) systems. The nanoshells which are consisted of dye doped dielectric core coated gold shell dispersed in ethanol solution are designed with an optimized ratio of core diameter and metallic shell thickness. The time resolved fluorescence spectroscopy results along with pump-probe experiments on nanoshells are convincing evidences for optical loss mitigation. Finally in third stage, the optical properties of gain-plasmon composites dispersed in PDMS host matrix as an example for bulk samples at the macroscopic scale (1 μm and beyond) have been investigated. The achieved results on this stage can help to design and fabricate such plasmonic structures that lead from fundamental physics towards practical applications. In this regard, the first four chapters provide the background concerning the main elements of this research work. The first chapter contains an introduction to the metamaterials. Second chapter describes the optical properties of plasmonic nanostructures. In third chapter, gain materials and the optical processes beyond these materials have been investigated. The fourth chapter deals with the optical properties of hybrid systems consisted of active materials and nano-plasmonic elements. After providing a brief introduction regarding the applied setups and instruments in this research study in chapter five, the last three chapters represent the acquired experimental results in each mentioned spatial scale. In chapter six, the optical properties of nano-scaled gain-plasmon systems in solution including gain-assisted, gainfunctionalized and dye grafted multimeric samples are investigated. Chapter seven explores the optical characteristics of dispersion of nanoshell sample as an example of the study in mesoscale. Finally, the thesis is completed with the study of the optical features of macro-scaled bulk samples based on core–shell type quantum dots and gold NPs dispersed in PDMS, and a short conclusion of this research study. This study emphasizes effective progress in materials science and paves the way towards further promising scientific research aimed to enable the wide range of electromagnetic properties of plasmonic metamaterials
Active plasmonics in soft matter doped with gold nanoparticles plasmonica attiva in materia soffice drogata con nanoparticelle d'oro
(2013-11-29) Cataldi, Ugo; Bartolino, Roberto; Caputo, Roberto; Versace, Carlo C.
The main objective of this study is active plasmonics. The work has been focussed on the design, characterization and theoretical interpretation of novel systems. Top-down and bottom-up, self-assembling, approaches have been utilized to realize devices where spherical gold nanoparticles have been periodically and randomly arranged. Two main paths have been followed to achieve this goal. In the first one, by utilizing a rigid periodic structure as a host platform for soft-matter (cholesteric liquid crystals) mixed with plasmonic nano-entities, was possible to obtain a chirally-organized tuneable plasmonic system. The tunability of the obtained device has been induced by applying temperature changes or external electric fields. In the second one, the surface of an elastomeric platform has been randomly covered by gold-nanoparticles. Controlled nano-chemistry processes have been successively applied to the nanoparticles (immobilized on the surface) to locally increase their size. The elastic properties of the template together with the increased size of particles have allowed a systematic study of the coupling between near-fields of the spherical nanostructures. Colloidal nano-chemistry technics have been utilized both to synthetize spherical gold nano-particles and to increase their sizes. Spectroscopic analysis has been used to analyse the response of obtained structures under electrical, thermodynamical and mechanical stimuli. SEM and TEM imaging have been exploited to study the morphology of devices, the shape of nano-structures and to measure their sizes. Moreover, from SEM images, through the use of a MatLab code written to the purpose, it has been possible to extract fundamental parameters used to perform a theoretical analysis of experimental results
Advanced numerical models for highly frustrated liquid crystalline phases
(2014-11-03) de Jesus, Caldera Teresita; Bartolino, Roberto; Versace, Carlo C.; Barberi, Riccardo; Lombardo, Giuseppe
Novel molecular materials for photo/electro conversion based on Palladium and Iridium organometallic complex
(2013-11-28) Ionescu, Andreea; Bartolino, Roberto; Versace, Carlo C.; Ghedini, Mauro; Godbert, Mauro
Questo lavoro di ricerca è dedicato allo sviluppo di nuovi materiali molecolari basati su complessi ciclometallati di Pd(II) e di Ir(III) per la foto/elettro conversione. Negli ultimi quindici anni, al fine di ottenere dispositivi più flessibili, più leggeri e più facilmente processabili, sono stati studiati principalmente materiali a base organica. Tali materiali presentano però, proprio a causa della loro natura organica, molteplici svantaggi, tra i quali scarsa qualità delle interfacce formate, limitata stabilità chimico-fisica in fase di funzionamento del dispositivo, difficile trasporto di carica, scarso assorbimento nel visibile e basse efficienze di luminescenza. Al fine di migliorare le prestazioni finali dei dispositivi elettro-ottici, è stata introdotta una nuova classe di materiali che utilizza come specie attive i composti organometallici. Nell’ambito di questo lavoro di tesi, sono stati sintetizzati nuovi complessi organometallici di Pd(II) e Ir(III) e ne sono state studiate le proprietà chimico-fisiche alla base dello sviluppo di materiali efficienti per la foto/elettro conversione. La prima parte del lavoro di tesi ha riguardato la preparazione di complessi per la conversione dell’energia solare. In particolare sono stati sintetizzati e caratterizzati nuovi complessi fotoconduttori ciclopalladati di Rosso Nilo, contenenti basi di Schiff opportunamente funzionalizzate come leganti ancillari. Inizialmente si è scelto di utilizzare il colorante Rosso Nilo come legante ciclometallante per le sue ottime proprietà di assorbitore di luce visibile. Il suo utilizzo ha inoltre comportato, nei complessi ottenuti, anche la separazione fisica su scala molecolare degli orbitali di frontiera HOMO e LUMO. In particolare i due orbitali risultano essere prevalentemente localizzati su due diversi frammenti molecolari. Tale separazione induce un efficiente processo di fotogenerazione che è alla base delle ottime proprietà di fotoconduzione osservate per questa classe di composti in un ampio intervallo di lunghezze d’onda. Per finalizzare l’utilizzo di complessi ciclopalladati di Rosso Nilo a specifiche applicazioni optoelettroniche, sono stati introdotti opportuni gruppi funzionali sia sul legante ciclometallante che sul legante ancillare In particolare i nuovi gruppi funzionali hanno permesso di : i) indurre proprietà mesomorfiche caratterizzate da un ampio grado di ordine in un grande intervallo di temperature e di ottenere così una nuova classe di metallomesogeni fotoconduttori; ii) aumentare la solubilità dei complessi preparati rendendo possibile il loro utilizzo unitamente al PC61BM, nella costruzione di celle solari ad eterogiunzione dispersa; iii) preparare, tramite il processo di elettropolimerizzazione, film sottili fotoconduttori di elevata qualità su elettrodi modificati; iv) poter ancorare i complessi sintetizzati a substrati di TiO2 e costruire celle solari di tipo Dye Sensitized (DSSCs). La seconda parte del lavoro di tesi, ha invece riguardato, la sintesi e la caratterizzazione fotofisica ed elettrochimica di complessi di Ir(III) per lo sviluppo di dispositivi elettroluminescenti. Sebbene esista in letteratura un elevato numero di esempi di complessi cationici di Ir(III) solamente pochi complessi anionici di Ir(III) sono stati descritti finora. Inoltre, i pochi esempi riportati, contengono leganti ancillari monodentati che rendono tali complessi chimicamente instabili all’interno di dispositivi elettroluminescenti. Al fine di ampliare la classe di composti anionici di Ir(III) esistenti e di migliorane la stabilità chimica, sono stati sintetizzati nuovi complessi anionici aventi leganti ancillari bidentati di tipo catecolato e orotato. E’ stata inoltre preparata e caratterizzata una nuova serie di “soft salt” di Ir(III) contenenti i nuovi complessi anionici ottenuti accoppiati ad opportuni complessi cationici di Ir(III) già noti in letteratura. Sono stati infine preparati e caratterizzati nuovi complessi luminescenti neutri di Ir(III) elettropolimerizzabili. Utilizzando tali complessi sono stati anche ottenuti film sottili elettrogenerati di alta qualità.
Strategies to control linear anisotropy and chirality in polymeric materials:from the basic issues to the micro-devices developments
(2016-10-05) Lepera, Eugenia; Bartolino, Roberto; Versace, Carlo C.; Cipparrone, Gabriele
The development of devices with increasing levels of functionality represents an important technological issue. To this aim, innovative materials with tunable functionalities play a crucial role. The challenge is to obtain multifunctional materials through simple procedures with high performance and low cost, and eventually external control parameters. Moreover the understanding of multifunctionality of materials is hence an exciting scientific opportunity. For these purpose, the main objectives of the present work have been to explore two main strategies. In the first one, azobenzene based materials and their light induced functionalities has been exploited to develop microdevices for polarimetric applications. Already know effects of linear and circular photoinduced optical anisotropies in azobenzene based polymers was investigated coupling the materials properties with holographic techniques, both to characterize the photoinduced properties of the materials and to develop diffractive devices useful for the above cited applications. The second topic is addressed towards the development of a materials science approach to build up polymeric matrices with controllable supramolecular chiral structures and subnanometric cavities. Both explored features are connected to intriguing topics as chirality and small size cavities. Their chirooptical properties and supramolecular structures suggest high potentiality for development of chiral sensors or filtration devices. Key words: micro-devices, azo-polymers, polarization holography, syndiotactic polystyrene, supramolecular chirality.
Synthesis and characterization of enstatite and talc doped with zinc and manganese
(2013-11-11) Catalano, Manuela; Bartolino, Roberto; Cazzanelli, Enzo; Versace, Carlo C.; Bloise, Andrea
In recent years, particular interest has been addressed by researchers in the synthesis and study of silicates such as enstatite MgSiO3 and talc Mg3Si4O10(OH)2. The first one is useful for several technological applications such as substrates in electronics, high frequency insulators, thermal insulators in high temperatures applications, and as luminescent materials in laser technology. The latter, because of the low cost and good properties (i.e. resistant to heat and acids, hydrophobic, electrical insulating) is widely used in many different products such as ceramics, papers, cosmetics, foods, polymers and filler in composites. The usual presence of foreign ions (e.g., Mn, Ti, Ni, etc.) and their inconstant amounts in natural enstatite and talc hinder the use of these minerals as high-performance materials. For these reasons, in recent years pure and doped enstatite and talc have been grown and characterized in several different ways. Nevertheless, there are still various problems to be solved in order to obtain very high quality crystals and the desired changes in the physical and chemical properties of them when they are doped with metal elements. In this work, Zn-doped enstatite, Mn-doped enstatite, Zn-doped talc and Mn-doped talc have been grown and characterized with different techniques. The starting materials and the final products were characterized and studied by binocular microscope, powder crystal X-ray diffraction (XRPD), scanning electron microscopy with energy-dispersive spectrometry (SEM/EDS), single-crystal X-ray diffraction (XRD), micro-Raman (μ-R), cathodoluminescence (CL), differential scanning calorimetry, thermogravimetric analysis (DSC-TG) and Fourier transform infrared spectroscopy (FT-IR). Zn- and Mn-doped enstatite was successfully produced by slow-cooling flux growth method, using MoO3, V2O5, Li2CO3 as melting agent. Several starting mixtures, with different MnO or ZnO concentrations, were first held at 1350 °C, 1250 °C 1050 °C and 950 °C and then slowly cooled down to 700 °C or 600 °C with different cooling rate (3.75 °C/h, 2.1 °C/h, 1.8 °C/h 1.7 °C/h). Enstatite crystallizes in the orthorhombic and monoclinic systems as revealed by XRD and Raman spectra. Transparent Zn-doped enstatite ( max length of 3.5 mm) and reddish Mn-doped enstatite (max length of 8 mm) single crystals are euhedral in form, not homogeneous in width and inclusion free. Maximum content of Mn-dopant is 14.52 wt %, while the maximum amount of Zn-dopant is 10.49 wt%. Crystals grow under equilibrium conditions only when the dopant content is maintained at low value. When either Zn or Mn is totally substituted for Mg in the starting material, no enstatite is produced. The presence of the dopant in the enstatite structure causes a decrease in unit cell volume respect to the pure one and strongly affects the CL-signal and micro-Raman spectra. CL spectrum of Mn-doped enstatite contains a broad emission located at 677 nm and attributed to the 4T1g(G)→6A1g(S) transition of octahedral Mn2+ centres. The presence of Zn in enstatite induces very remarkable peak broadening by the mode at 133 cm-1 and 343 cm-1 in the Raman spectra; for these modes a strong component of metal ion displacement must be postulated. Raman spectra of Mn-enstatite show: i) a general decrease of Raman intensity due to the increase in surface reflection when the MnO dopant concentration increases; ii) a widening and a down shifting of the peak positions indicating changes in vibrational modes because of the increasing presence of MnO. Zn- and Mn-doped talc was successfully synthesized in hydrothermal conditions at temperatures of 300, 500 and 650 °C, under constant pressure of 2 kbar and reaction time of 160 hours. Talc morphology and content of dopant within the crystals show strong dependence on crystallization temperature. Talc exhibits a cabbage-like morphology, its classical hexagonal tabular morphology and fibrous morphology. The best temperature to obtain the highest abundance of Zn- and Mn-doped talc is 650 °C. A decrease in temperature from 650 to 300 °C: i) worsens the reactions and poorly crystallized Zn- and Mn-doped talc is obtained; ii) increases the content of zinc or manganese dopant. Talc only grows when Mg is not totally substituted by either zinc or manganese in the starting mixture. Zn-doped talc formation is increased by treating the starting mixture with H2O + HCl; conversely, the reactant H2O + CaCl2 inhibits the growth of talc. In order to increase doped talc yield, large amounts of aqueous solution is as crucial as high temperatures. The presence of varying amounts of metal elements replacing Mg in talc influences its temperature decomposition. Indeed, the thermal stability of Zn- and Mn-doped talc decreases with respect to pure one. Zn-dopant in talc mainly affected the hydroxyl stretching fundamental peak (3674 cm-1), splitting itself into as many as four peaks with respect to non-doped talc, which displayed only a sharp band. The splitting appears to be dependent on the degree of substitution of the magnesium in the octahedral layer and related to the electronegativity difference between Zn and Mg. Future studies will be carried out on these materials to have a better knowledge of other physical properties, useful in novel applications.