Dipartimento di Fisica - Tesi di Dottorato

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Questa collezione raccoglie le Tesi di Dottorato afferenti al Dipartimento di Fisica dell'Università della Calabria.

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Methane Physisorption processes on porous nanostructured materials
(2001-11-03) Myrsini Kyriaki, Antoniou; Agostino, Raffaele Giuseppe; Carbone, Vincenzo; Bartolino, Roberto
Rappresentazioni proiettive: applicazioni nella teoria quantistica
(2005) Filippelli, Gianluigi; Nisticò, Giuseppe; Giuliano, Domenico; Chiarello, Gennaro
Study of SU(N) gauge theories on the lattice
(2006) Falcone, Rossella; Papa, Alessandro; Falcone, Giovanni
Polarization holographic recording in polymeric and liquid crystalline materials
(2006) Provenzano, Clementina; Cipparrone, Gabriella; Longeri, Marcello
Optical studies related to polarization holographic recording in photosensitive materials, as azo compounds, liquid crystals and polymeric mixtures, and dye doped polymers, were carried out. The interest in this type of holographic recording is due to the improved signal to noise ratio and the possibilities for image and signal processing, optical switch, beam steering, optical polarizers and selective erasure. We focused our investigation on the mechanisms that can possibly induce diffraction gratings in these different types of photosensitive materials, on the peculiarities of the achieved diffractive devices and on their possible applications. In particular we investigated the effects of polarization holography on azo-dye Langmuir-Blodgett films, on polymer dispersed liquid crystal (PDLC), and on liquid crystal films confined by dye-doped polymers aligning layers. In the first system, conventionally used for polarization holographic recording, we investigated the influence of the particular Langmuir-Blodgett deposition technique on the features of the recorded structures in order to obtain pure polarization gratings. The absence of surface reliefs gratings (SRG), the stability of the recorded devices and the high induced birefringence of the selected material, open up the possibility of interesting applications. In particular, we report the design and the implementation of a photopolarimeter for simultaneous measurements of Stokes parameters of light, in which the basic element is the actual polarization grating. PDLC is a non conventional system for polarization holographic recording, because no azocompounds are present in the polymeric and liquid crystalline mixtures. Polarization holographic storage produces diffraction gratings that originate mainly from the liquid crystal alignment inside the droplets of the solid polymeric matrix, created during the polymerization and phase separation processes. Polarization properties and electro-optical switching behaviour of the gratings are studied. We also report the unexpected observation of SRG in a system without azo compound, where photoisomerization and chromophore reorientation processes do not occur. In the last systems, we exploit a new method for spatially varying liquid-crystal alignment using patterned surfaces obtained by means of a polarization holographic exposure on a dye-doped polyimide. This idea is based on the fact that holographic gratings on some photosensitive material provide a periodic alignment of the nematic liquid crystals. In fact, putting in contact a Polarization holographic recording in polymeric and liquid crystalline materials ii thin film of liquid crystal with the aligning layers, we obtain a replica-grating in the bulk with the same properties of the gratings recorded on photosensitive layers. We describe the high flexibility of these replica-gratings, related to the control of the diffraction efficiency by means of an external electric field, and the very singular properties of the polarization states of the beams diffracted from this device. We also obtain two dimensional (2D) gratings consisting of a 2D array of differently twisted structures of nematic liquid crystal, achieved by a crossed assembling of polarization holograms recorded at the surfaces of the aligning substrates. These devices diffract the incident beam in several diffracted beams with various polarization states at the same time. The energy distribution can be controlled by means of the polarization state of the incident beam. Additionally, the distribution of the intensity on the diffracted beams can be completely controlled by means of a low external applied voltage. These features make the optical devices very interesting for beam steering, beam shaping and other modifications of light intensity or phase.
Order reconstruction in nematics
(2006-11-30) Ayeb, Habib; Barbieri, Riccardo; Gharbi, Abdelhafidh; Longeri, Marcello
Study of transparent thin film oxide and they interaction with nematic liquid crystals
(2006-11-30) Marino, Salvatore; Scaramuzza, Nicola; Longeri, M.
Innovative Electro-Optic and Photonic Effects in Liquid Crystals
(2006-11-30) Barna, Valentin; Scaramuzza, N.; Strangi, G.; Longeri, M.
Laser action in liquid crystals: from random to periodic syatems
(2007) Ferjani, Sameh; Strangi, Giuseppe; Versace, Carlo
Modellization of optical radiation - Liquid crystal interaction in complex geometries
(2007-11-30) Pezzi, Luigia; Blinov, Lev; Versace, Carlo
Nanostructured Soft Matter: Mirror-less Lase
(2008) Matranga, Mario Ariosto; Versace, Carlo; Barberi, Riccardo
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.
Characterization of thin transparent polymeric films obtained by plasma polymerization technique and their application to liquid crystal cells
(2008-10-17) Nicastro, Gaetano; Scaramuzza, Nicola; Versace, Carlo
The aim of this work Although liquid crystal displays (LCD) are quite ubiquitous in the modern world, there is still a great run for better and cheaper LCD. The main physical phenomenon that makes LCD as valuable consists in the particular way polarized light propagates through anisotropic media in general and liquid crystals in particular. Different from solid anisotropic media, the actual anisotropy of liquid crystals is imposed by surface interactions. The concepts of aligning layer and anchoring have been coined. Normally, a thin lightly dielectric polyimide film separates the liquid crystal from conducting transparent electrodes. An applied electric field between these electrodes can reorient the liquid crystal inside (the bulk) and change the transmittance of the cell. An electric field can rather easily do so such that the response time to the applied film, τon, is normally less than 1 ms. Switching off the field, liquid crystal relaxes to the initial state, the only “driving force” now, in the absence of the electric field, remains the anchoring of the liquid crystal to the surface. If this anchoring is not very strong the relaxation time, τoff, can be as large as seconds, a unsuitable value for practical purposes. Much stronger anchoring overwhelms this shortcut by the expense of using thin film transistors, difficult to insert and quite costly. Not long ago, a “fast switching response” has been observed using conducting polymers. [1] as aligning films. Conducting electro active polymers such as polypyrrole (PPyr), Polyaniline (PAn), polythiophene (PTh), or poly-o-anisidine (PoA) are complex dynamic structures that captivate the imagination of those involved in intelligent materials research [2]. Although promising response times, τoff 1. The chemical nature of the substance used, for instance polyaniline, or polypyrrole; , of 1-2 ms, even 0.5 ms, have been observed, the rate of defected samples is unacceptable high. Therefore, there is a strong incentive to carry on investigation in the field. There are many parameters that should be considered; among them we quote: 2. The way of inducing the polymerization process, either chemically, electrelectro-chemically, by DC or Rf plasma reactor; 3. the nature and number of doping or included ions; 4. Their mobility 5. Possible red-ox reactions at ITO/polymer and/or polymer/liquid crystal interfaces; 6. Thickness of the aligning films 7. Roughness or porosity of the film In this thesis we will present all the results obtained with these films about “the fast switching response”, a characterization study made with various instruments like SEM, AFM ecc. on these films and other measurements like current curves on the LC cells made with these films, all realized for better understand the properties of these films deposited via DC plasma polymerization
Critical aspects of quantum field theories on the lattice
(2008-12-31) Gravina, Mario; Alessandro Papa; Giovanni Falcone
Remediaciòn de unsitio contaminado (Pertusola):modelaciòn del transporte subterraneo Y anàlisis de riesgo sanitario
(2009) Rivera Velasquez, Maria Fernanda; Troisi, Salvatore; Guerra, Ignazio
This work applies deterministic and probabilistic methodology to the analysis of health risk of a contaminated site. The risks we have calculated are both cancerogenous and no-cancerogenous. The area we studied was formerly used for chemical industry, and is called “Pertusola South Crotone”. Due to its high concentrations of heavy metals it has been declared “area of national interest”. The receptors we have considered are adults, children and workers. As point where the target is exposed to the contamination we have taken the coast line. The contaminants that were considered are As, Cd y Zn. A mathematical model is utilized for the simulation of destination and transportation of contaminants from the point of origin of the contamination to that of exposition. The methodology of risk analysis is applied in direct and inverse way. The direct calculation allows the estimate of health risk to which the target is exposed in presence of a strong contamination. The inverse calculation makes possible to determine the maximum acceptable contamination of the target, compatible with an acceptable level of risk. The deterministic methodology has been used to calculate the RME and MLE values. The probabilistic one (based on Monte Carlo method) has been used to calculate the estimated average value, UCL 95%, UCL 99%. If the exposition rate RME is considered and deterministic and probabilistic results are compared, one obtains an overestimate of the risk in the case of the deterministic values. The probabilistic calculation allows to fulfil less conservative remediation objectives. This leads to a lower cost of the remediation work. From the uncertainty and sensitivity analysis one finds that toxicological factors contribute to the risk equation more than hydrogeological factors.
Atomic force microscopy study of physico-chemical and nanotribological properties of hydrophobin protein
(2009-11-09) Houmadi, M. Said; Giocondo, Michele; Lacaze, Emmanuelle
Scanning probe microscopy studies and dynamic behaviour of ferroelectric domains in PbZr0.53Ti0.47O3 thin films
(2009-11-09) Bruno, Emanuela; Scaramuzza, Nicola; Versace, Carlo
Ferroelectric domains play an essential role in all ferroelectric materials applications, for example, microelectromechanical sensors systems (MEMS) and integrated optical systems. The prime interest in recent years is, however, in non-volatile random accesses memories (FRAM) based on ferroelectric thin film. This requires substantial improvement in the understanding of the basic proprieties at the nanometer length scale. Especially the domain nucleation and growth processes in ferroelectric is of key importance. As the optical methods are limited by diffraction, novel high resolution techniques are required. The scanning force methods introduced during this thesis offer the required high resolution together with high sensitivity. In this thesis experimental and theoretical evidence for the origin of the force acting on the tip, the cantilever deflection and the image contrast mechanisms is given for various SFM (Scanning Force Microscopy) operation modes. For imaging ferroelectric domains the best suited SPM technique is the piezoresponse SFM that is performed with the tip in contact with the sample. The spontaneous growth of the domains 1 nucleating in lead zirconate titanate sample is investigated in detail using the EFM (Electrostatic Force Microscopy) technique. Even more interesting is the case where the domains are intentionally created switching the spontaneous polarization by means of an electric field between the EFM tip and an electrode below the sample. This allows to create any desired pattern of domains. The ability to use the same tip for domain switching and imaging is another advantage of the EFM. The domain formed in this way varies in size from few nanometers to few micrometers. Using EFM technique we demonstrate ferroelectrostatic switching in Lead Zircanate Titanate (PZT) thin film. This has important technological implication because the ferroelectric switching must be used in ferroelectric devices.
Scaling laws in solar wind turbulence
(2009-11-27) Marino,Raffaele; Falcone, Giovanni; Carbone, Vincenzo; Noullez, Alain; Sorriso Salvo, Luca
Search for a light U boson in e+e− → μ+μ−γ channel with the KLOE experiment at DAΦNE collider at LNF and application of the GEM technology for the KLOE-2 Inner Tracker
(2010) Morello, Gianfranco; Schioppa, Marco; Falcone, Giovanni; Bencivenni, Giovanni; Venanzoni, Graziano
L’esperimento KLOE ai Laboratori Nazionali di Frascati ha accumulato una luminosit`a integrata di R L dt 2.5 fb−1 (nel periodo 2002-2005) alla - factory DA NE, un acceleratore e+e− con energia nel centro di massa di 1020 MeV corrispondente alla massa del mesone . L’esperimento ha for- nito molteplici misure di precisione nella fisica dei kaoni e degli adroni. Un upgrade del rivelatore KLOE con nuovi rivelatori `e stato approvato e KLOE- 2 inizier`a la presa dati in pochi mesi (inizio del 2011). Il programma di fisica di KLOE-2 si focalizzer`a sull’interferometria dei kaoni neutri, sugli studi dei decadimenti del KS, e ′ e su un nuovo bosone di gauge previsto in alcune estensioni del Modello Standard. Nel primo capitolo troviamo una sintesi della fisica dell’interferometria dei kaoni neutri e sono introdotte le ragioni per ricerche di Dark Matter a KLOE e KLOE-2. Questa ricerca ha una semplice segnatura (una coppia di muoni con fotone associato) che sar`a descritta in dettaglio nell’ultima parte del capi- tolo. La descrizione dell’apparato sperimentale KLOE sar`a data nel secondo capi- tolo: le caratteristiche della Camera a Deriva, del Calorimetro e del sistema di Trigger saranno riportate. Il programma KLOE-2 sar`a introdotto nel terzo capitolo, con una descrizione dei nuovi rivelatori previsti nell’apparato. In particolare, l’inserimento di un Tracciatore Interno sar`a presentato, oltre all’impatto sulle misure di fisica. Nel quarto capitolo si discuter`a della tecnologia (GEM) che `e stata usata per realizzare il Tracciatore Interno. I principali vantaggi di questa tecnologia saranno spiegati, per finire con un breve sguardo sulle nuove tecniche in fase di sviluppo. Il quinto capitolo si occuper`a della contruzione del prototipo del Tracciatore Interno con la tecnologia GEM e delle misure fatte su di esso. La parte finale del capitolo sar`a centrata sulla caratterizzazione del comportamento di una GEM planare in campo magnetico con il readout finale progettato per il TI. Nell’ultimo capitolo si discuter`a in dettaglio l’analisi per la ricerca di un bosone leggero (U) negli eventi μμ a sar`a presentato un nuovo taglio che `e 1 stato sviluppato per migliorare la reiezione del fondo (principalmente eventi
Study of Z0 and Higgs production at ATLAS & Dream calorimetry
(2010-10-21) Venturelli, Tommaso; La Rotonda, Laura; Falcone, Giovanni
Turbulence and Stochastic Processes in Nematic Liquid Crystals
(2010-10-22) Carbone, Francesco; Strangi, Giuseppe; Versace, Carlo
In this work we studied the electrohydrodynamics instabilities (EHD) from a different point of view. We used the traditional tools, belonging to the traditional fluid turbulence framework, to the world of liquid crystals. This tools in addition, for the first time, a 3D scanning of the NLC sample driven in these turbulent regimes, give us some interesting results. As an example a fragmentation of the large scale structures (Williams Domains) whit characteristics similar to the Richardson cascade. We also studied, for the first time, the intensity fluctuation at different depth z inside the sample, and we found a strong non gaussianity in the probability density function of this fluctuation. Further information has been obtained by by studying the decorrelation processes in EHD. We found a local transition between two different regimes: the classical Kolomokorov K41 law in the y direction, and a random sweeping decorrelation in the opposite x direction. Finally we study the weak localization of light obtained during the EHD. We found a drastic reduction in the scattering mean free path `? and a strong enhancement of the backscattering cone.