In this Thesis we will theoretically address some issues concerning the Physics of ultracold Fermi gases, all of them with experimental relevance. The field of ultracold gases, and more recently of ultracold Fermi gases, is gathering a lot of experimental and theoretical interest for two main reasons: the great control on the relevant parameters of the problem and the relative simplicity of the minimal theory which is able to correctly describe the system. Building upon this solid background, ultracold gases provided an ideal laboratory for testing more refined theories and also for addressing fundamental issues of quantum mechanics as well as for simulating more complex physical systems such as those encountered in condensed matter. Even if the effective hamiltonian of ultracold gases can be simple, due to the diluteness of the system and the low temperature, which imply low energy physics, the solution of the quantum mechanic equations governing the state of these systems is not always simple. For the static properties usually mean-field solutions exist or perturbative expansions can be produced in some regimes. However Quantum Monte Carlo (QMC) techniques provide more accurate results especially in the strongly interacting regimes. For confined systems it is possible to use QMC only for a few particles, so that, for large number of particles, a fruitful combined use of Density Functional Theory (DFT) and QMC is necessary. The study of the dynamics of ultracold gases has received little attention with QMC techniques, due to the intrinsic computational difficulty of the many-body problem, so that general hydrodynamic equations are often used for studying the propagation of smoothly varying perturbations. In this Thesis we use QMC techniques for studying the problem of ferromagnetism in repulsive or effectively repulsive ultracold gases without a lattice and the problem of the Bardeen-Cooper-Schrieffer to Bose-Einstein-Condensation (BCS-BEC) crossover in two dimensions. We use DFT in the Local Density Approximation (LDA) for calculating the density profiles of ultracold Fermi gases in harmonic magneto-optical traps, starting from QMC equations of state. We study the propagation of first and second sound in ultracold Fermi gases in cylindrical geometry, using the hydrodynamic equations of superfluids.

GIXRF (Grazing incidence X-Ray Fluorescence) is an analytical technique with high potential in the study of depth profiles and in the characterization of thin layered structures. To extract information from a GIXRF measurement and determine the layer composition it is necessary to compare the experimental data with simulation. However at the moment this thesis has been written, there is no software widely recognized from the scientific community as the reference software for the analysis. For this reason this work of thesis deals with the development of an analytical software and its application to several case studies. A program called GIMPy is presented. The program is capable to perform simulations of the expected GIXRF signal from a given model, but also of the expected fluorescence signal at high angle of incidence and the reflectivity (XRR). The use of a programming language like Python makes the library extremely portable, easily extendible and flexible thanks to its object oriented syntax and scripting capabilities. GIMPy bases the modelling of the electric field propagation inside the sample and the expected fluorescence from the theoretical description found in literature. Moreover a series of methods were developed to account for the effect of the instrumental set-up geometry, the detector response, indirect excitation and primary beam shape and energy composition. A round-robin related to GIXRF comparison with several institutes developing an analytical software has been organised. The comparison showed a good agreement between the results obtained with GIMPy and the other programs. GIXRF has then been applied to the characterisation of several systems. A combined XRR and GIXRF analysis of multi-layered transparent and conductive oxide films (TCO) of technological interest resulted in a nondestructive and precise characterization of their structures. Measurements were performed at the ESRF synchrotron facility and in the laboratory using a Cu tube as source. Combining the measurements performed with dif- ferent instrumental set-ups the effectiveness of the combined XRR-GIXRFapproach, that has proved already effective in the past, has been further shown. It has been possible to evidence the existence of a thin inter dif- fusion profile induced by annealing the samples, showing a sensitivity to structural changes in the depth of 0.5-1 nm. GIXRF measurements performed on Sn implants in Ge provided information about the total dose retained by the sample after an implantation process. Synchrotron tunable excitation energy was extremely valuable for the fluorescence analysis.The two different modelling strategies used for data fitting, one using a SIMS profile as an input the other an analytical description of the depth profile, and returned values close to the one obtained with other techniques. A new technology based on the deposition of ALD coatings for the preservation of cultural heritage object has been characterised with XRR and GIXRF. The XRR measurements were effective in revealing the deterioration of the coatings after the effect of an accelerated ageing process. Moreover the analysis of GIXRF also revealed the formation of nano-particles at the top of the surface, and allowed the characterisation of their size and composition. The last chapter shows some theoretical calculations investigating GIXRF potential in the size and chemical characterisation of nano-particles. It is shown how the experimental setup and the sample preparation can influ- ence the outcome of the measurement. The theoretical calculations are also reinforced by the result obtained on some preliminary experiments on Gold nano-particles.

Abstract There is a growing concern related to increasing energy requirement and greenhouse gas emissions. Hydrogen gas is recognised as a desirable clean fuel and may be a sustainable solution. Hydrogen gas can be directly used as an anodic fuel for Proton Exchange Membrane Fuel Cell that converts chemical energy of hydrogen into electrical energy with no environmentally harmful by-products. Chemical hydrides with high hydrogen storage capacity in terms of gravimetric and volumetric efficiencies are the most promising candidates to supply pure hydrogen at room temperature. Among them, Sodium borohydride (SBH) and Ammonia borane (AB) have drawn a lot of interest as they are stable, non-flammable, nontoxic, and have a high hydrogen storage capability. Large amount of pure hydrogen gas is released during the hydrolysis of these chemical hydrides in presence of certain catalysts. The by-products are non-toxic, environmentally safe and can be recycled. Noble catalysts like Pt and Pd, used in the past to enhance the hydrogen production rate, do not seem to be viable for industrial application considering their cost and availability. Co and Ni borides are considered as good candidates for catalyzed hydrolysis owing to their good catalytic activity, low cost and effortlessly synthesis. Transition metals with varying (metal)/(Co + metal) molar ratio were doped in Co-B catalyst and the effect of metal doping on surface morphology, electronic interaction, and catalytic efficiency of the alloy catalyst powder on hydrogen production by hydrolysis of SBH and AB were studied. On the basis of characterization results, the role of each metal species, involved in hydrolysis and enhanced catalytic performance is discussed. The stability, reusability, and durability of these catalysts have also been investigated. Nanoparticle-assembled Co-B-P thin films on Ni foam (by electroless deposition), along with supported and unsupported Co-B nanoparticles over carbon films were synthesized by Pulsed Laser Deposition and studied for catalytic hydrolysis.

Oxide-based transparent conductors constitute a novel class of materials, which finds applications in many technological fields such as photovoltaics and organic light emitting devices. They can be employed in the new generation solar cells as transparent charge collectors. The transparent and conductive oxide mostly used nowadays is indium tin oxide (ITO), however due to the high cost and scarcity of indium, other materials are under research and development as potential substitutes. Many candidates are currently under study, mainly doped-ZnO, doped-CdO, doped-SnO2, doped-TiO2. The work undertaken in this thesis is a study of the doping processes of thin films of TiO2 and ZnO, two cheap, chemically stable and non-toxic materials. Two main objectives were pursued in this work: (i) the optimization of the film deposition and doping conditions for a potential replacement of ITO and (ii) the understanding of the factors dominating the doping process as well as its limitations. The approach was to explore three doping methods of the films: intrinsic doping, extrinsic doping and, with the aim to combine the benefits of both, intrinsic-extrinsic co-doping. Since the structural defects (such as oxygen vacancies) are at the basis of the intrinsic doping, a control of their formation was searched through the variation of the growth process conditions of the ZnO and TiO2 films. Niobium was selected for the extrinsic doping of the TiO2 films. The films were grown by RF plasma sputtering in different atmospheres (Argon, Ar-O2 and Ar-H2 gas mixtures) and under different plasma power conditions and substrate temperature, onto silicon and quartz substrate. The Nb-containing films were obtained by co-sputtering of either a single composite TiO2 -Nb target or two distinct niobium and TiO2 targets. Many characterization techniques were applied to define the film structural, electronic, electrical and optical properties obtained upon doping. For chemical analysis, X-ray Photoelectron Spectroscopy (XPS) was used. The structure and morphology of the films were analyzed by X-ray Diffraction (XRD) and Scanning Electron Microscopy (SEM). The chemical species present in various plasmas used in deposition process were investigated by Optical Emission Spectroscopy (OES). Further, the defect structure and properties of the obtained films were studied by Positron Annihilation Spectroscopy. Analysis by this technique shed more light on the nature of the vacancies/open volume and on the effect of the latter on the electrical and structural properties of the films. A study based on a joint use of XPS and optical measurements allowed to define the electronic properties of the films (valence band edge, Fermi level position, work function, ionization potential and electron affinity). Structural analysis results revealed the formation of both anatase and rutile nanocrystalline phases for intrinsic and extrinsic doping of TiO2, while with the co-doping method only anatase phase was obtained, a phase known to be favorable for Nb incorporation in TiO2 lattice. The intrinsic doping of TiO2 films showed high transparency in the visible range, but resulted in still high resistivity values (101-103 ï —xcm). The latter could be lowered by using Ar-H2 gas mixtures during film deposition. The same trend was observed in the case of intrinsically-doped ZnO films, an increase in the electrical conductivity was observed when the concentration of defects was increased. The lowest resistivity was achieved with niobium doping of TiO2, 5x10-3 ï —xcm, with an optical absorption coefficient in the visible range of ~1x104 cm-1, however the combination of the internal defects and Nb, in co-doping, did not improve the conductivity. Nonetheless, it was found that co-doping method strongly modified the electronic properties of the TiO2 films, allowing a control of the work function, an important parameter for transparent electrodes. Low cost transparent conductive oxides were obtained when niobium was successfully incorporated in TiO2 lattice. By optimization of the deposition process of the films (dopant concentration, RF power, atmosphere, and annealing temperature) the electronic, electrical and optical properties of doped- TiO2 films can be improved. The obtained results can contribute to the development of transparent electrodes and charge collectors by RF sputtering, a suitable technique for coating on large area substrates.

The development of new materials represents the recent frontier in hydrogen storage technologies. In the last few decades the preparation of nanostructured materials has had an increasing interest, because the hydrogen storage capacity is closely linked to the material dimensions, and increases considerably with the reduction of the particles sizes. The chemical synthesis plays an important role in the development of new materials for hydrogen absorption because it allows a good control of the hydride phase sizing, and thus of the kinetics/ thermodynamics of such materials. The aim of the work concerns the synthesis by chemical techniques of metals nanoparticles. Nanostractured metals embedded into a polymeric matrix are prepared. The polymer was used for achieving nanoparticles with tailored properties.

Cu2ZnSnS4 (CZTS) quaternary compound has attracted much attention in the last years as new abundant, low cost and non-toxic material, with desirable properties for thin film photovoltaic (PV) applications. In this work, CZTS thin films were grown using two different processes, based on vacuum deposition of precursors, followed by a heat treatment in sulphur atmosphere. The precursors were deposited using two different approaches: (i) electron-beam evaporation of multiple stacks made of ZnS, Sn and Cu and (ii) co-sputtering deposition of the three binary sulphides CuS, SnS and ZnS. All the materials were characterized both as isolated films and as absorber layer in solar cells, produced using the typical structure Mo/CZTS/CdS/i:Zno/AZO. Both growth processes were found to give good quality kesterite films, showing CZTS as the main phase, large grains and suitable properties for PV application, but higher homogeneity and stoichiometry control were achieved using the co-sputtering route. A detailed investigation on CZTS optical properties, microstructure, intrinsic defect density and their correlation with the material composition is presented. A strong effect of the tin content on the bandgap energy, sub-gap absorption coefficient, crystalline domain and grain size is shown and a model based on the increase of the intrinsic defect density induced by a reduced tin content is proposed. These studies suggested a correlation between the increase of the bandgap energy and the improvement of the material quality, which was also confirmed by the performances of the final devices. CZTS thin films were then assembled into the solar cells and their properties as absorber layer were optimized by varying both composition and thickness. CZTS samples produced from stacked evaporated precursors allowed achieving a maximum efficiency of 3.2%, but reproducibility limits of the evaporation process made difficult to obtain further and rapid efficiency improvements. The co-sputtering route was demonstrated to be a more successful strategy, assuring a fine-control of the film composition with good process reproducibility. A fast improvement of solar cell efficiency was obtained using this approach and a maximum efficiency of 5.7% was achieved. The relationship between the absorber layer stoichiometry and the device performances was investigated: the effect of the Zn enrichment and a possible influence of the Cu/Sn ratio on the device performances are discussed. Investigation on CZTS/CdS and CZTS/MoS2 interfaces revealed that the optimization of both buffer-layer and back-contact technology is a primary need for further improvement of CZTS solar cells.

The first and foremost goal of the present work was to develop novel theoretical and computational methods and use state-of-the-art techniques in electronic structure theory to interpret a specific set of physical problems mainly related, but not limited to, materials science. Our guiding principle was to relate information obtained from scattering experiments with the numerical solution of the multichannel dynamics of many-body systems, shedding light on the origin of electronic and optical properties of a variety of systems. The general approach adopted in this thesis was not to present separate chapters for theory, rather we introduced methods along with the experiments. In particular, we focused on the modeling of both ground and excited states of materials, on vibrational, core and valence electron spectroscopy of condensed matter systems using computational methods at different level of accuracy and complexity to interpret a number of experimental data. While these methods have been devised for this scope, their applicability, notably the treatment of the continuum states through multichannel scattering formalism, is totally general and can be applied to describe several different experiments, performed with a variety of apparently distant techniques. In particular, the Fano--Fesbach discrete-continuum interaction provides a common framework suitable to this task. Within this scheme, thus, the calculation of the spectral lineshapes measured by XPS, Auger, NEXAFS, and EEL spectroscopy can be reconciled on the same theoretical grounds with the investigation of the properties of ultra-cold Fermi gases at unitarity, or of the electronic capture and decay rate in ultra-hot plasma found in stellar environments or, finally, with the study of the epitaxial growth of nanostructured materials. Crossing the borders between several computational, theoretical and experimental techniques, this thesis should be of interest to a broad community, including those interested in aspects of atomic and molecular physics, electronic structure calculations, experimental and theoretical spectroscopy, astrophysics and scattering theorists in a broad sense.

Photovoltaic technology in the field of renewable energy has reached a high commercial interest over the past decade. The traditional silicon photovoltaic systems that is currently the most widespread, mainly due to government subsidies, have a low energy production. The wide use of material and the low efficiency of the silicon modules required the research and development of photovoltaic systems more efficient. The most promising technology is the photovoltaic concentration that increases the efficiency of the modules by reducing the area of the PV cell. The concentration photovoltaic has had considerable technological progress related to the development of multi-junction PV cells with high efficiency. Another approach is the technology of photovoltaic concentration with the spectral separation, so using the interference filters the solar spectrum is splitted into different optical bands. In this research was designed and built a CPV prototype system with spectral separation. The interference filters such as anti-reflection and dichroic mirror are made up of silicon dioxide and titanium dioxide. These oxides have been realized by means of physical vapor deposition reactive magnetron sputtering technique. The PVD technique allows to deposit thin films with a homogeneous process reproducible and reliable. In the first part of the work, the characterization of individual layers of oxide materials have allowed to extrapolate the optical constants. This is necessary for the design of the optical multilayer. The characterization has nvolved various analyzes such as atomic force microscopy (AFM) to determine the thickness and the roughness, compositional analysis Rutherforf backscattering spectrometry (RBS), and optical analysis UV-Vis-NIR. These analyzes were necesary to calibrate the deposition system in order to subsequently to realize the multilayer optics. The as deposited optical multilayers not confirm the optical design, and it was necessary to carry out an annealing at 350°C. In the second part of the work, there were also micro structural characterizations for evaluating the phase variation of the titanium dioxide with the annealing treatment. The Fourier transform infrared (FT-IR) analysis has checked the absorption peak of the Ti-O-Ti of the crystalline phase. In addition, X-ray diffraction (XRD) analysis verified the phase variation of titanium dioxide from purely amorphous phase with a slight presence of rutile to the anatase phase. Through the optical analysis it was possible to extrapolate the new optical constants corresponding to the phase of anatase. In the third part of the work, the ray tracing design of optical splitting of the CPV prototype was carry out. The CPV system is designed by coupling a concentration Fresnel a dichroic mirror. The focus of the radiation on the PV cell, is simulated by two ideal detector. The optical optimization as function of the f-number of the lens has allowed to define the layout for the prototyping phase. A further optimization is to insert a secondary optics element (SOE) of homogenization. The secondary optics will also limits the optical losses due to a misalignment of the CPV prototype. In the last part of this thesis is devoted to the preparation and the characterization of the CPV prototype. Were performed measures of solar radiation, which combined with the characteristic I-V-P curves of the solar cells have enable to evaluate the efficiency of the prototype system. The efficiency of the spectral separation system was compared with concentration multi-junction PV cells. Daily measurement were performed to compare the spectral separation technology than to the multi-junction technology. The results show that the separation system maintains a more constant performance during the day. Finally, thermal measurements were conducted on the component of the CPV prototype separation system. The experimental results allows to guarantee that the spectral separation is also a selective filter of temperature. This allows the solar cells to maximize the photovoltaic conversion and to reduce the overheating.

In this thesis work nanoscrystalline optical properties of diamond and two recent new NCD functionalisation techniques involving UV light (one step method and photochemical oxidation) have been investigated. Firstly the oxidation of diamond surface caused by the irradiation of the surface with UV-light in oxygen atmosphere was considered. Two different experiments in situ were realized in order to understand the physic-chemistry of this method. The chemical bonds between oxygen and surface carbon atoms were investigated by firstly performing an annealing treatment in ultra hight vacuum of a oxidized UV surface and then comparing the obtained result with annealing treatments of two different oxygenated diamond surfaces using other two techniques: plasma oxidation and piranha solution oxidation. An other interesting aspect on which clarity has to be made deal with amination process of diamond surface. As a first fundamental step, the efficiency on hydrogenated diamond surface was investigate. Successively the role of oxygen in the chemistry of amination process was studied performing in situ experiments using different terminated diamond surface (hydrogenated, chemically oxidized, UV oxidized) and different gaese (pure NH3 or NH3 + O2).

In this thesis I present two different research topics investigated during the course of my PhD, regarding the analysis of spatial structures in a Bose Einstein condensate. Ultracold atomic gases offer a privileged platform for such kind of experiments, thanks to the fine control that can be achieved on the system’s parameters and to the availability of advanced imaging schemes allowing for a great measurement accuracy. The first topic is about the shape of quantized vortices in an elongated condensate, with the goal of providing a quantitative analysis of the density structure of a quantized vortex filament hosted in a bulk 3D superfluid. We analyzed the shape of the vortex and studied its dynamics during a free expansion, or time of flight (TOF), of the hosting BEC, with the goal of making a quantitative comparison between theory and experiment for the structure of the core of a quantized vortex in three-dimensional (3D) condensates. Simultaneously imaging the sample along orthogonal directions after a long TOF allowed to map the complete 3D shape of the vortex at the end of the free flight, while the full expansion dynamics has been simulated with numerical solutions of the Gross-Pitaevskii equation. The same data analysis procedure has been applied to both the experimental images and to the density profiles computed with the simulations to ensure a faithful comparison. We were able to detail the evolution of the vortex parameters at all times combining a simple analytic scaling-law model valid at early times, experimental data for the width and the depth of the core at long expansion times, and the numerics that were used to bridge between the two. Additionally, we could check the validity of the predictions on the scaling of vortex parameters with the size of the BEC using the experimental data to interpolate between theoretical limiting models. We concluded that quantized vortex filaments can be optically imaged with standard techniques in 3D atomic BECs, at a level of accuracy which indeed is enough to show good quantitative agreement with the predictions of the GP theory for the width, depth, and overall shape of the vortex core. The second topic is a measurement of the equation of state of a single component BEC. The goal of this project is to verify the non-monotonic behaviour of the chemical potential of a homogeneous Bose gas of weakly interacting particles as a function of temperature, where one expects to find a maximum across the critical point of transition to the superfluid phase. This effect is believed to be a general feature of the normal-to-superfluid phase transition: it has been already experimentally demonstrated in unitary Fermi gases, and although the same is predicted to happen also in a gas of weakly interacting bosons, no experimental evidence has been reported so far. The measurement relies on the local density approximation, which allows to extract information about the thermodynamics of a homogeneous system from accurate measurements of the local properties of a trapped one. My work has focused on developing a series of imaging and data analysis techniques to measure the 3D density profile of a harmonically trapped gas, even in regimes of extreme density such as inside a Bose condensate. With a new high-dynamic-range method we were able to image the 3D density distribution of a trapped sample, leading to a low-noise measurement of the density distribution. We confirmed the existence of the non-monotonic behaviour of the chemicial potential across, and set the basis for further measurements of the thermodynamics of the system across the transition.In this thesis I present two different research topics investigated during the course of my PhD, regarding the analysis of spatial structures in a Bose Einstein condensate. Ultracold atomic gases offer a privileged platform for such kind of experiments, thanks to the fine control that can be achieved on the system’s parameters and to the availability of advanced imaging schemes allowing for a great measurement accuracy. The first topic is about the shape of quantized vortices in an elongated condensate, with the goal of providing a quantitative analysis of the density structure of a quantized vortex filament hosted in a bulk 3D superfluid. We analyzed the shape of the vortex and studied its dynamics during a free expansion, or time of flight (TOF), of the hosting BEC, with the goal of making a quantitative comparison between theory and experiment for the structure of the core of a quantized vortex in three-dimensional (3D) condensates. Simultaneously imaging the sample along orthogonal directions after a long TOF allowed to map the complete 3D shape of the vortex at the end of the free flight, while the full expansion dynamics has been simulated with numerical solutions of the Gross-Pitaevskii equation. The same data analysis procedure has been applied to both the experimental images and to the density profiles computed with the simulations to ensure a faithful comparison. We were able to detail the evolution of the vortex parameters at all times combining a simple analytic scaling-law model valid at early times, experimental data for the width and the depth of the core at long expansion times, and the numerics that were used to bridge between the two. Additionally, we could check the validity of the predictions on the scaling of vortex parameters with the size of the BEC using the experimental data to interpolate between theoretical limiting models. We concluded that quantized vortex filaments can be optically imaged with standard techniques in 3D atomic BECs, at a level of accuracy which indeed is enough to show good quantitative agreement with the predictions of the GP theory for the width, depth, and overall shape of the vortex core. The second topic is a measurement of the equation of state of a single component BEC. The goal of this project is to verify the non-monotonic behaviour of the chemical potential of a homogeneous Bose gas of weakly interacting particles as a function of temperature, where one expects to find a maximum across the critical point of transition to the superfluid phase. This effect is believed to be a general feature of the normal-to-superfluid phase transition: it has been already experimentally demonstrated in unitary Fermi gases, and although the same is predicted to happen also in a gas of weakly interacting bosons, no experimental evidence has been reported so far. The measurement relies on the local density approximation, which allows to extract information about the thermodynamics of a homogeneous system from accurate measurements of the local properties of a trapped one. My work has focused on developing a series of imaging and data analysis techniques to measure the 3D density profile of a harmonically trapped gas, even in regimes of extreme density such as inside a Bose condensate. With a new high-dynamic-range method we were able to image the 3D density distribution of a trapped sample, leading to a low-noise measurement of the density distribution. We confirmed the existence of the non-monotonic behaviour of the chemicial potential across, and set the basis for further measurements of the thermodynamics of the system across the transition.