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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Item Laser action in liquid crystals: from random to periodic syatems(2007) Ferjani, Sameh; Strangi, Giuseppe; Versace, CarloItem TiO2 nanotubes in nanotechnologies(2010-12-14) Jimenez, Leticia; Versace, CarloItem TiO2 nanotubes in nanotechnologies(2010-12-14) Jimenez, Leticia; Versace, CarloItem Advanced Materials (Ceramics in particular) for Structural Applications(2015-12-15) Koduru, Hari Krishna; Bartolino, Roberto; Versace, Carlo; Scaramuzza, NicolaThe study of ‘Intrinsic and Metal nano particles doped polymer thin films for soft matter applications and nanostructured Hyperbolic metamaterials’ is an challenging and dynamic field of research with significant implications in the development of novel technologies, like gas sensors, bio-medical application and engineering of spontaneous emission of florescent molecules. In the present investigation, we presented research work in two directions. We prepared Polymer thin films by homemade Cold Plasma Polymerization technique and studied their Microstructural, Optical and dielectric responses as a function of thin film growth parameters, in view of gas sensor applications. In other direction, we fabricated lamellar structured Hyperbolic Metamaterials by employing physical and chemical vapour thin film deposition techniques and employed them as effective substrates to engineer the life time of florescent dye molecules. The first part of this thesis is devoted to preparing Polypyrrole (PPy) thin films of nano sized thickness, by Cold plasma polymerization technique and analyzing the influence of Plasma power on Microstructural, Optical, wetting and dielectric properties of grown PPy films. Fabricating layered structures of “PVA/AgNPs/PVA” thin films to investigate the influence of rate of distribution of AgNPs on dielectric responses of PVA matrix to employ them as a gas sensor applications, whose study is still open and is getting substantial interest in industrial and academic environments. Enhancement of spontaneous emission is a dynamic and challenging fundamental quantum phenomenon in optics and in nutshell it opens new avenues for spectrum of futuristic applications. Metamaterials are artificially designed nanocomposite materials, in which bulk electromagnetic properties arise due to underlying structural resonances and near field coupling between the designed sub-wavelength building blocks. Metamaterials promise to alleviate the classical limitations of optics and led to exotic applications such as negative refraction, sub-wavelength resolution imaging, invisibility devices and perfect absorbers. In the second part of this thesis, we fabricated Hyperbolic metamaterials and proposed new grating coupled hyperbolic metamaterial (GCHMM) configuration for the enhancement of spontaneous emission rate of dye molecules by exploiting the unique property of a hypergrating to outcouple and extract the non-radiative plasmonic modes.Item Across Scales Approach Based on Exciton-Plasmon Coupling for Low Loss Optical Metamaterials(2015-12-15) Dhama, Rakesh; Bartolino, Roberto; Versace, Carlo; De Luca, AntonioItem Atomic forcemicroscopy of corneal biomechanics(2014-11-28) Labate, Cristina; Bartolino, Roberto; Versace, Carlo; Barberi, Riccardo; De Santo, Maria P.Item New methods for characterization and dating in material of cultural heritage(2014-11-03) Bosco, Stefania; Versace, Carlo; Chidichimo, GiuseppeItem Optical systems for diagnostics: Near-Infrared Imaging technique for detection of dental demineralisation(2012-11-30) Salsone, Silvia; Versace, Carlo; Lombardo, Giuseppe; Zakian, Christian; Bartolino, RobertoIn dentistry, a correct detection of caries severity is still a challenging descision-making task that crucially a ects the choice for the best treatment plan. The challenge is to nd both the most objective parameters to detect caries at di erent stages (from an early reversibile stage to a severe one) and the most reliable method(s) that should be used to distinguish these stages. Currently, methods used in clinics are visual inspection, aided with light probe and pick inspection tools, and radiography. The main issue rising by the use of these methods is that both of them are subjective, with possibility for intra- and inter-examiner variability. For this reason, radiography needs an extreme care of interpretation especially when assessing occlusal caries. Visual methods, instead, are a ected by confounding factors, such as stain or uorosis, a ecting the accurate assessment of early caries lesions. Radiography, moreover, should be performed with care considering that the emission of ionising radiation may cause malignant change in tissues, especially for young age patients and are counter-indicated during pregnancy. They are also inadequate for the detection of initial caries and to locate the lesions looking at the superimposition of the tooth along its buccal-lingual axis. The aim of this study was to overcome the limits of the current detection techniques, o ering a non-invasive, objective method for the detection of caries at any stage of the demineralisation process. The proposed method measures the near-infrared (NIR) re ectance response of the tooth at three speci c wavelengths. It is then possible to investigate properties of the sample at the surface and in depth and get an image that maps the lesions on the occlusal view of the sample when combining these wavelengths. Due to the properties of the NIR light, this method is non-invasive, non-contact and allows for detection both at the enamel and at the dentine level. The NIR method o ers objective supporting information to quantify and detect dental caries and is especially suitable for areas a ected by confounding factors, such as stain. The objective of the study was to design and implement a NIR multispetral imaging system, developing e cient image analysis algorithms. In order to prove this objective, an in vitro validation of the technique against gold standard histology was performed together with a comparison to other detection methods - International Caries Detection and Assessment System (ICDAS - clinical visual inspection), bre optic transillumination method (FOTI - visual inspection with light probe), radiography and Quantitative Light-induced Fluorescence method (QLF), used in clinics or in research. A total of 112 teeh, molars and premolars, with di erent lesion severities were used for this study. Histologcal sections were obtained to con rm the lesion severities and used as a gold standard to compare the sensitivity and speci cty among techniques. Visual inspection methods recorded the highest values of sensitivity (ICDAS: >99%, FOTI: 93%) and speci city to dental caries (FOTI: >99%, ICDAS: 90%). However, these methods could have been highly facilitated by the in-vitro viewing of the samples. Sensitivity to dental caries was higher for NIR (91%) than for QLF (88%) and radiography (63%) while speci city was higher for radiography (81%) than for NIR (73%) and QLF (63%). The results from this study suggest that the NIR method has the ability to detect dental caries when other methods fail, providing an alternative to assist in the decision-making process with the further advantage of removing the confounding e ect of stain. This method can enhance patient communication and o ers an objective and safe alternative to ionising radiation methods.Item Dielectric characterization of different mesogenic substances and a mixture with non-conventional gold nanoparticles(2012-11-28) Marino, Lucia; Versace, Carlo; Bertolini, Roberto; Scaramuzza, NicolaThe study of liquid-crystalline matter and nano-structured materials is an important and vast field of research with potential implications in the development of new technologies, like sensors and displays. In this work we have analyzed and characterized different systems by dielectric spectroscopy. The first part of this thesis is devoted to the characterization of an orthoconic liquid-crystalline mixture, W-129, with ferroelectric properties. The analysis of the dielectric response of this material has revealed a plurality of ferroelectric smectic C* subphases; they represent smectic intermediate variants situated between the ferroelectric phase and the antiferroelettric one, known like antiferrielectric phases (SmCFI*, SmCFII*, ... ), whose study is still open and is collecting a lot of interest in academic environments. The same liquid crystalline mixture was then doped with unconventional gold nanoparticles. These nanoparticles are functionalized with a hydrophilic polymer which becomes hydrophobic exceeded 40°C. The nano-composite material obtained by the dispersion of the gold nanoparticles presents interesting characteristics, such as an enhancement of dielectric increments (or strengths) probably due to the molecular interactions between the ferroelectric liquid crystal and the gold nanoparticles, which translates into an increase of the order of the liquid crystal host, in a stabilization of the smectic subphases and in an enhanced memory effect already seen in the pure liquid-crystalline mixture. The third and last part is devoted to the characterization of a new "banana-shaped" liquid crystal, which exhibits some unusual physical properties during the nematic phase, in particular, the presence of regions of more ordered molecules, organized in a smectic C phase inside a nematic one. The dielectric spectra acquired during the nematic phase show the presence of a relaxation response between 10 and 20 Hz which, with the addition of relatively large values of permittivity, may suggest the presence of a ferroelectric response due to the existence of cybotactic clusters.Item Optical trapping and manipulation exploiting liquid crystalline systems(2012-11-30) Hernandez, Raul Josue; Versace, Carlo; Cipparrone, GabriellaThis thesis and all the research contained within, pretends to develop new ideas and concepts on liquid crystals (LC) and optical trapping and manipulation. The combination between optical tweezers and LC systems promises unique and exciting results. The content on the thesis is presented for those with some experience in the elds of liquid crystal and optical manipulation, and for those who are interested in begin to learn about these matters, proposing an overview of much existing work and a correlation between di erent science branches like soft matter, photonics and optical control. Two main research lines has been developed involving liquid crystalline systems and polarized optical tweezers. In the rst part, nematic LC droplets in water have been adopted to study the mechanical properties of light elds with a polarization gradient, i.e. optical tweez- ers based on polarization holographic techniques with non conventional trapping in an extended interferometric optical trap. For this purpose, LC emulsions in wa- ter were prepared, obtaining droplets with radial or bipolar director con guration, which result in optically isotropic or anisotropic particles. Exploiting the vecto- rial nature of the light and its interaction with LC droplets, an unconventional opto-hydrodynamical control and trapping has been demonstrated. The planned experiments shown that a hydrodynamic force, known as Magnus force, never con- sidered in optical micromanipulation experiments, can play an important role in the optical micromanipulation and should be considered whenever particles are forced to spin and dragged in a uid. In the second part, the study was mainly focused into developing an innovative and versatile soft matter object, namely chiral-solid microspheres. They were created by combining very simple self-assembling and photoinduced processes of the soft mat- ter, i.e. photopolymerizing cholesteric LC droplets in water emulsion. The ability to control the internal helical geometry using chemical agents in the precursor LC emulsion enables to obtain solid microspheres with radial, conical, or cylindrical con gurations of the helical structures that exhibit unique optical properties. Their exclusive capabilities were demonstrated by optical manipulation experiments in- volving optical tweezers. A unique and dichotomous behavior has been revealed by polarized circularly polarized tweezers: an attractive or repulsive optical force is ex- erted by varying the light polarization. Moreover, the application of the chiral-solid microspheres as optical microresonators for creating microlasers was also demon- strated. The high performance as well as the novel and exclusive properties make these chiral microparticles good candidates for developing new concepts in colloidal materials science, microphotonics, microlasers, optical trapping and manipulation, micro- and opto uidics and microsensors.