In this work an improved methodology for the study of hydrogen storage material (HSM) is presented, for the characterization of smaller samples of HSM at increased accuracy. It includes: the realization of innovative differential instrument; a novel approach to the detailed micro kinetic modelling; increase the comprehension of absorption and desorption mechanisms; support research efforts in this topic. As side results, a macro and lumped model for the design of generic hydrogen storage tank are developed and validated. The study of a novel IDA (Isochoric Differential apparatus) is presented, describing all the steps from the initial theoretical approach, to the detailed design and the definition of an experimental proceeding. It includes the necessary technical improvements to increase the measure uncertainty compared to the classical SIevert. Novel microkinetic modelling for HSM is explained as variation of classic nucleation and growth model (JMAK model). The nuclei’s growth is assumed to be limited by surface or even by radius of powder’s particles. Micro modelling is applied on Mg-based material, introducing high accurate kinetic measures obtained by IDA. This leads to extrapolate information about kinetic parameters and kinetic mechanisms of hydrogen sorption. The obtained micro modelling is used as core for the development of a model at a higher scale (macro) which keeps in consideration also heat and hydrogen diffusion in porous materials typical in hydrogen storage tank. Experimental data collected by a prototipal realization of hydrogen storage tank are used to validate macro modelling. Moreover, a lumped model is developed with the scope to built a numerical tool able to give preliminary indications on proper design/layout of hydrogen storage tank, based on hydrogen flow, temperature or pressure requirements. Lumped modelling is finally compared with results by the numerical simulation of validated macro model. Finally, micro kinetic model is applied on high accuracy sorption data (by IDA) on innovative catalysed Mg-material. Material is produced by a novel approach, where catalyst, Nb2O5, is deposited by PVD techniques at extremely low concentration on the surface of powder to exploit its higher catalyst proprieties.

This thesis work is focused on the investigation of a peculiar phenomenon observed in germanium: the formation of a regular network of columnar nanovoids induced by heavy ion and high fluence irradiation at room temperature. This phenomenon can represent a possible way to produce wide nanostructured areas on semiconductor surfaces by a well-established semiconductor technology process such as ion implantation. However, the formation mechanism of this regular network of Ge columnar nanovoids is still under debate. Therefore, the work has been focused on the investigation of the formation mechanisms and on the possible strategies to control the geometry and the composition of these structures, in order to exploit the results for possible technological applications. In particular, ion implantation was carried out using Sn+ ions with the double aim of creating Ge1-xSnx nanostructures and following the depth distribution of the impinging ions. Furthermore, ion implantation through ultra-thin (10-20 nm) films of silicon nitride (SiNx) was investigated as a possible way to impact on nanovoid formation kinetics, prevent ambient contaminations and prevent Sn out-diffusion upon thermal treatments. Firstly, low temperature Sn+ implants were carried out in order to define a recipe to prepare Ge1-xSnx alloy: Ge1-xSnx alloy films with thickness of 15-30 nm were obtained by implanting Sn+ in Ge at liquid nitrogen temperature and subsequent thermal annealing (600 °C for 10 s). High Sn substitutionality, no relevant diffusion, limited surface segregation and excellent crystallinity were achieved, a tin concentration of x=6-7 at.% was reached. Secondly, Ge nanostructures were prepared by high fluence ion implantation at room temperature and then morphologically and chemically characterized, determining that the obtained nanostructures are constituted by Sn-rich Ge. Nanovoids developed under the SiNx film, with reduced oxygen contamination. The first stages of nanovoid formation were observed for samples with and without the SiNx layer. The SiNx layer seems to induce a retarded nanovoid nucleation in terms of threshold fluence, without hindering nanovoid growth. The experimental data were interpreted on the basis of the vacancy clustering theory. SRIM simulations were performed to compare the distributions of point defects and implanted ions at different conditions in the SiNx/Ge stack. These helped to show that the depth distribution of energy deposition is the relevant parameter. Moreover, it was highlighted that both the redistribution in depth of the SiNx atoms and the implanted Sn+ contribute to a lowering of the Ge concentration causing the formation of a layer where nanovoid nucleation does not occur. Taking into account the ion mixing effect including the introduction of Sn, threshold value of the deposited energy was found. The thermal treatments investigated for the Ge1-xSnx alloy thin films were applied on nanostructured samples, causing a dramatic deformation of the nanovoids probably due to a melting temperature decreased by the presence of tin. The investigation of possible technological applications of Ge nanostructures was carried out, in particular in thermoelectric applications, in lithium ion batteries and gas sensors. Several samples were designed and ad-hoc substrates were produced.

Vortex reconnections and interactions play a fundamental role in the dynamics of fluids and turbulent flows, both in the classical and quantum regime. Studying vortices in a clean system like ultracold gases can therefore help, as a bottom-up approach, to understand the physics in a wider context, including superfluid helium, polariton condensates, fluid dynamics and turbulence, neutron stars and cosmological models. So far vortex-vortex interaction was studied in Bose-Einstein condensates either in rotating systems with the observation of regular Abrikosov lattices or in flat condensates across the Berezinskii-Kosterlitz-Thouless transition. In both cases the geometrical constraints allowed to study just a planar interaction among aligned or anti-aligned vortices. The present study instead is carried out in an axisymmetric cigar-shaped Bose-Einstein condensate. Vortices in prolate structures are also known as solitonic vortices. This geometry is especially suitable for investigating vortex interactions. Indeed vortices are oriented perpendicularly to the condensate axis to minimize their length, hence energy, and, because of the cylindrical symmetry, the orientation of a vortex in the radial plane has no constraints. These facts permit interactions to occur with different incoming relative angles between the vortex lines and with different relative velocities. The strong confinement, acting along the radial axis, enhances also interesting effects due to the boundaries.

This work shows that it is possible to fabricate phosphate-based planar wave-guides activated by rare earth ions both by sol-gel and RF-sputtering techniques. The objective of this thesis has been to evaluate various methodologies for fab-rication Phosphorous-based planar waveguides. In this context sol-gel and RF-sputtering techniques for planar waveguides fabrication has been investigated. RF-process has been optimized. In case of sol-gel technique a further thermo-dynamical study is required. Each of technique has drawbacks, in sol-gel method the principal question is related to the kinetics of the reaction, since it is too fast, to better control of the reaction rates, and better adjustment of the technological films fabrication, which effects on spectroscopic properties of the waveguiding systems: losses, refractive index. In case of RF-sputtering is no-ticeable that the refractive index is low, and the losses are less than 0.2 dB/cm, however the multicomponent target material increase the complexity of the structure.

The study presented in this thesis is focused on the investigation of Arsenic ultra-shallow distributions in Si for applications as source-drain extension dopant in CMOS technology. Using the Ultra-low energy SIMS measurements the evolution of arsenic shallow distribution was investigated with reference to the metastable electrical activation and the successive deactivation under moderate thermal treatment (550-700°C). Three different approaches to form As USJ were investigated to understand their physical mechanisms to verify their possible application in next generation microelectronics devices. First two activation approaches were based on low energy beamline ion implanted material. The first one is the low temperature (550°C) solid-phase epitaxial re-growth and the second activation approach is a sub-melt laser annealing at different temperatures. A range of deactivation studies was performed using these two classes of material with more attention given to the laser annealed ones. Plasma ion immersion implantation together with the LA was considered as the third approach of arsenic ultra-shallow junction formation. Samples created by AsH3+ plasma were investigated with respect to arsenic distribution, silicon oxide thickness and arsenic local order using SIMS, INAA, and EXAFS analysis.

As its title announces, the general aim of this doctoral thesis is to investigate the growth and use of nanostructured materials in order to make them suitable for sensoristics. Sensors applications have become very important in the last years because of a new sensibility towards pollution of the urban world and its effects on human health. Only very recently people and countries discovered the importance of environment preservation and monitoring. After a period of fast and uncontrolled industrial progress, we are now aware of this danger. Thus we need to monitor the environment and the changes which are happening directly or indirectly because of human presence. During the last decades, solid-state gas sensors have played an important role in environmental monitoring and chemical process control. The strong investigation which followed, made clear that the field of science and sensor technology cannot search for new sensor materials which are ideal, because different applications (e.g. different transformations of energy and different goals for sensors) require different materials. However materials are important drivers in sensor technology. The combination of the right materials (new or existing) to the right application can result in smarter, cheaper, or more reliable sensors. In order to give a contribution to this important evolving situation, during these three years the PhD candidate investigated two of the most important areas related to nanostructured materials used in sensing applications. On one side, the recent interesting field of metal oxide nanowires has been studied, both in terms of fundamentals (growth mechanism and structural properties) and sensor properties towards different gases. On the other side, the less exploited (in terms of sensor devices) field of organic thin films has been investigated, in terms of growth and fundamental properties (charge carriers mobility) which are required to use them as sensors. While nanostructured metal oxides are already in use in commercial sensors (usually in the form of porous thick or thin films), organic materials are still in a prototypal phase, and need further investigation in order to be effectively used. This different evolution step is reflected also in the present thesis: in which zinc and tin oxide nanowires are characterized as gas sensing devices, while molecular materials are only optimized towards a better order and a higher carrier mobility, which is one of the bottlenecks towards a higher response. For this reason, the chapters concerning metal oxide nanowires will give a wide picture, from their growth mechanism to their structure until their use (in different architectures) in sensing applications. Oxide nanowires have been used as passive (resistive) sensors (they have been used also as active sensors, but such data are still under analysis) both in order to develop new real sensors, and to better understand the sensing mechanism behind the high response of such nanostructured materials. Their nanoscale dimensions, comparable to the depletion layer, makes them almost ideal intrinsic on-off devices, and this can be exploited to fabricate a new generation of sensors characterized by a huge response. The problems of metal oxide sensors are however their poor selectivity and high working temperature. In this direction goes the investigation of the molecular materials. Concerning the organic complement in this thesis, the aim of the experimental work was the optimization of the overall field effect mobility of carriers (holes) along the whole device, which means several microns (tens of microns, due to the impossibility to use standard lithography techniques on organic delicate materials). This meant the minimization of grain boundaries, that are one of the steps hindering the charge carrier mobility, and even the recently found domain boundaries. Exploiting the high kinetic energy achievable by SuMBD, we found that it is partially transformed in surface mobility, increasing the order of the fundamental building blocks inside each monolayer, and decreasing the grain and domain boundary density (because of wider and less fractal grains). At the end of the thesis we will show a first combination of the two families of materials, just as a sample of what the exploitation of the best features of each family (high response for metal oxides and good selectivity for organic materials) can provide.

In this thesis we investigate the properties of impurities immersed in a dilute Bose gas at zero temperature using quantum Monte-Carlo methods. The interactions between bosons are modeled by a hard sphere potential with scattering length a, whereas the interactions between the impurity and the bosons are modeled by a short-range, square-well potential where both the sign and the strength of the scattering length b can be varied by adjusting the well depth. We calculate the binding energy, the effective mass and the pair correlation functions of a impurity along the attractive and the repulsive polaron branch. In particular, at the unitary limit of the impurity-bosons interaction, we find that the binding energy is much larger than the chemical potential of the bath signaling that many bosons dress the impurity thereby lowering its energy and increasing its effective mass. We characterize this state by calculating the bosons-boson pair correlation function and by investigating the dependence of the binding energy on the gas parameter of the bosonic bath. We also investigate the ground-state properties of M impurities in a Bose gas at T=0. In particular, the energy and the phase diagram by using both quantum Monte-Carlo and mean field methods.

Photocatalytic water splitting using solar energy could contribute to the solution of environmental and energy issues related to the hydrogen production. Key research area in this field is the development of photo-catalyst able to provide high energy conversion efficiency. TiO2 has been mostly preferred material as the photo-electrode due to many advantages, mainly related to the cost factor and stability. We have studied on hydrogen production by water splitting in photo-electrochemical cells prepared by using photoanodes made by two different kinds of TiO2: one deposited by RF sputtering and the other one by sol-gel method. Depositions were performed on electrical conducting ITO whose electrical properties plays vital role to reduce the photon energy loss. The photoanodes have been characterised by several techniques to infer on their optical and compositional properties. The observed differences in hydrogen production have been attributed to the peculiarities in absorption properties of the two TiO2 films that in the case of sputter-deposited films are more prone to absorb radiation also because of the produced defects during the deposition process. Metals like Cr and Fe were doped in TiO2 by RF magnetron sputtering and sol-gel methods to increase the efficiency of hydrogen production by water splitting by sensitizing the doped-TiO2 in visible light spectrum. The doping method, dopant concentration, charge transfer from metal dopants to TiO2, and type of dopants used for modification of TiO2 were investigated for their ability to enhance photocatalytic activity. UV-Visible spectra show that the sputter-metaldoped- TiO2 films are much more efficient than the chemically-prepared samples to induce red shift of the absorption edge for absorbing visible light. In addition, we proved that dopant atoms must be located, at low concentration, near the ITO-TiO2 interface to avoid the formation of recombination centers for photo-generated electron-hole pairs. H2 production rate is higher with Fe-doped TiO2 (15.5 μmole/h) than with Cr-doped TiO2 (5.3 μmole/h) because Fe ions trap both electrons and holes thus avoiding recombination. On the other hand, Cr can only trap one type of charge carrier. To increase the light conversion efficiency and reduce the recombination processes of Cr-doped TiO2, a multilayer structure of ITO/Cr-doped-TiO2 (9 at.%) was developed. When the multilayer films were exposed to visible light, we observed that the photocurrent increases as function of the number of bilayers by reaching the maximum with 6-bilayers of ITO/Crdoped-TiO2. The enhanced photocurrent is attributed to: 1) higher absorption of visible light by Cr-doped-TiO2, 2) number of space-charge layers in form of ITO/TiO2 interfaces in multilayer films, and 3) generation of photoelectrons just in/or near to the spacecharge layer by decreasing the Cr-doped-TiO2 layer thickness. The superior photocatalytic efficiency of the 6-bilayers film implies higher hydrogen production rate through water splitting: we obtained indeed 24.4 μmole/h of H2 production rate, a value about two times higher than that of pure TiO2 (12.5 μmole/h). Similar experiment we performed by doing TiO2 with vanadium metal. With 6-ilayers vanadium doped TiO2 film Shows higher hydrogen production rate of about 31.2 μmole/h. This rate is higher than that of CR doped and pure TiO2. A constant H2 generation rate is obtained for long periods of time by all the investigated TiO2 films because of the separate evolution of H2 and O2 gas, thus eliminating the back-reaction effect. Even Ar+ or N+ ion implantation of energy 30 keV was adopted to vary the energy band gap of TiO2 film in order to absorb visible light.The original anatase phase was not changed by implantation. Increase in full visible absorption range was observed for both kinds of ion implanted-TiO2 films which further increases with the ion fluencies, while N+ ion implantation also causes the shift of the absorption edge from UV to visible light range. N+ implanted TiO2 showed narrowing of band gap from 3.2 eV for untreated anatase TiO2 to 2.78 eV for maximum implantation dose. The Ar+ and N+ implantation creates oxygen vacancies related defect energy level in the band gap. In case of N+ implantation, nitrogen also substitutionally replaces the oxygen atoms thus forming an energy level just above the valence band which further interacts with O 2p states resulting in the narrowing of band gap. The black solar absorber material develop over the copper target to absorb concentrated solar radiation and supply heat to the surrounding water. A black copper oxide layer was synthesized over copper substrate by using chemical oxidation treatment. We varied several treatment parameters and optimized the best condition to obtain a black textured layer which has the properties to absorb total solar radiation. The untreated polished copper showed 50 to 60 % reflectance (R) (incidence angle of 15o) and this value decreases to almost zero for whole wavelength range after formation of black copper oxide. The percentage absorption decreases by negligible amount as the angle of incidence increases. The SEM images of the copper oxide layer at high magnification showed a nano-petal like structure which causes the surface texture effect for higher absorption where surface irregularities such as grooves and pores with dimensions similar to the wavelength of the incident radiation simply increase the solar absorptance by multiple reflections. Long time thermal stability and corrosion resistance in hot water was also studied for the copper oxide film. The results revealed that the copper oxide was very stable and showed no changes in optical properties after the test. For the same water heating system a quartz window is used through which the solar radiation is transmitted on the copper target. Thus to acquire high power conversion efficiency it is necessary for quartz window to transmit the entire solar radiation incident on it without much lost due to the reflection on the surface. In general quartz window is able to transmit 90-91 % of the solar radiation while 1-2 % is absorbed and 7-8 % is reflected from the surface. Thus to have nearly complete transmittance it is necessary to cover the surface of quartz window with anti-reflecting (AR) coating: this was the part of my work. We developed single-layer and multi-layer AR coating for single specific wavelength and broad-band wavelength range respectively. Low reflective index material like MgF2 is deposited by e-beam technique to obtain single-layer AR coating. While Al2O3 and ZrO2 layers deposited, by RF-magnetron sputtering, on top of MgF2 forms multi-layer AR coating. The combination of MgF2/ZrO2/Al2O3/MgF2 deposited on both side of quartz showed excellent results with reflectance value of around 0.8% in broad spectral range. The heat exchanger efficiency obtained after using these developed black copper oxide absorber material and AR coating is around 83 % which seems to be significantly higher than the other commercially available water heating system. Concentrating solar power (CSP) systems are utilized to convert sunlight to thermal electric power by using solar absorber. However, the solar absorber are operated at elevated temperature (700-800 oC) and should be spectrally selective to act as perfect absorbers over the solar spectrum (high solar absorptance (α)) and perfect reflectors in the thermal infrared (IR) (low thermal emittance (ε)). Cermet composite solar absorber shows such selective properties at high temperatures. In the present work, we developed Al-AlN based multilayer cermet films by RF magnetron sputtering. We choose combination of Ni/AlxN(1-x)/AlN layers as a solar absorber due to its stability at elevated temperature and high corrosion resistance. In this combination, Ni layer, deposited near to substrate, act as the IR light reflector to provide high thermal emittance. While AlxN(1-x) layer act as an absorber layer for UV-Vis spectrum of solar radiation and transparent AlN layer on top functions as AR coating. To improve absorptance, 3 or 4 layers of AlxN(1-x) film with grading of metal content was synthesized by varying N2 flow during deposition. The optical measurement for these multilayer selective absorber films showed high solar absorptance of 0.92-0.96 and low thermal emittance of around 0.1-0.07. To test the stability of our multilayer coating at high temperature, we annealed these samples at 700 oC with holding time of 2 hrs in air, low vacuum and high vacuum. We observed a slight decrease in solar absorptance value (0.90) for the annealed samples but the results showed that overall performance was not hindered by heat treatment thus proving the thermal stability of our multilayer cermet coating.

In this work we develop Quantum Monte Carlo techniques suitable for exploring both ground state and dynamical properties of interacting many-body systems. We then apply these techniques to the study of excitations in superfluid He4 and to explore the structure of nuclear systems using chiral effective field theory interactions.

Fossil fuels have been critical to the development of modern society, but concerns over pollution, environmental degradation and climate change demand humans transition to renewable sources of energy. Solar energy is, among renewables, by far the largest exploitable resource, providing more energy in 1 hour to the earth than all of the energy consumed by humans in an entire year. The principal problem related to solar energy use is its intermittency. Collecting and storing solar energy in chemical bonds (solar fuel), as nature accomplishes through photosynthesis, is possible through photo-electrochemical water splitting, a clean and sustainable way for hydrogen production. The materials used as photo-electrodes in a photo-electrochemical cell must fulfil a variety of thermodynamic and kinetic requirements to ensure good efficiency and durability. Since there is no material in nature satisfying all these requirements, tailoring the optical, electrical, and morphological properties of the existing materials to construct photo-electrodes with the desired performance is a big task for materials scientists. In this thesis, we study TiO2 based photo-catalysts and Fe2O3 based water oxidation catalysts. TiO2 thin films were deposited by radio frequency magnetron sputtering technique and their optical, electrical and morphological properties were changed to enhance the visible light absorption and/or limit the recombination rate of charge carriers. More specifically, the effect of compensated (V and N) and non compensated (Cu and N) n-p codoping of TiO2 was studied. The role of coupling TiO2 thin films with indium tin oxide films in single and multilayer structures, compact and porous morphologies was underlined. The effect of hydrogen doping in passivating dangling bonds in TiO2 was demonstrated. Fe2O3 nanoparticles assembled coatings were synthesized by pulsed laser deposition and studied for the functionalization of electrodes and absorbers surfaces as water oxidation catalysts. The response of the optical and electrochemical properties of the coating to the tuning of film morphology was studied, ranging from a low-transmittance compact layer to a porous nanoparticle-assembled coating, which resulted to be highly transparent. Materials properties were characterized by various techniques such as Raman spectroscopy, x-ray diffraction, UV-vis spectroscopy, x-ray photoelectron spectroscopy, energy dispersive x-ray spectroscopy, and scanning electron microscopy. Electrochemical and photo-electrochemical properties of the samples were studied by testing them as electrodes in a photoelectrochemical cell. Both materials were chosen because they are widespread, non-hazardous, biocompatible and scalable. This enables the large-scale application of photo-electrochemical water splitting and the full exploitation of the green potential of this technology.