The surprising discovery of the X(3872) resonance by the Belle experiment in 2003, and subsequent confirmation by BaBar, CDF and D0, opened up a new chapter of QCD studies and puzzles. Since then, detailed experimental and theoretical studies have been performed in attempt to determine and explain the proprieties of this state. Since the end of 2009 the world’s largest and highest-energy particle accelerator, the Large Hadron Collider (LHC), started its operations at the CERN laboratories in Geneva. One of the main experiments at LHC is CMS (Compact Muon Solenoid), a general purpose detector projected to address a wide range of physical phenomena, in particular the search of the Higgs boson, the only still unconfirmed element of the Standard Model (SM) of particle interactions and, new physics beyond the SM itself. Even if CMS has been designed to study high energy events, it’s high resolution central tracker and superior muon spectrometer made it an optimal tool to study the X(3872) state. In this thesis are presented the results of a series of study on the X(3872) state performed with the CMS experiment. Already with the first year worth of data, a clear peak for the X(3872) has been identified, and the measurement of the cross section ratio with respect to the Psi(2S) has been performed. With the increased statistic collected during 2011 it has been possible to study, in bins of transverse momentum, the cross section ratio between X(3872) and Psi(2S) and separate their prompt and non-prompt component.

Ultra-relativistic heavy ions generate strong electromagnetic fields which offer the possibility to study γ-γ and γ-nucleus processes at the LHC in the so called ultra-peripheral collisions (UPC). The photoproduction of J/ψ vector mesons in UPC is sensitive to the gluon distribution of the interacting nuclei. In this thesis the study of coherent and incoherent J/ψ production in Pb-Pb collisions at √sNN = 2.76 TeV is described. The J/ψ has been measured via its leptonic decay in the rapidity range -0.9 < y < 0.9. The cross section for coherent and incoherent J/ψ are given. The results are compared to theoretical models for J/ψ production and the coherent cross section is found to be in good agreement with those models which include nuclear gluon shadowing consistent with EPS09 parametrization. In addition the cross section for the process γ γ→ e+e− has been measured and found to be in agreement with the STARLIGHT Monte Carlo predictions. The analysis has been published by the ALICE Collaboration in the European Physical Journal C, with one of its main plot depicted on the cover-front of the November 2013 issue.

Semiconductor nanowires (NWs) are one- or quasi one-dimensional systems whose physical properties are unique as compared to bulk materials because of their nanoscaled sizes. They bring together quantum world and semiconductor devices. NWs-based technologies may achieve an impact comparable to that of current microelectronic devices if new challenges will be faced. This thesis primarily focuses on two different, cutting-edge aspects of research over semiconductor NW arrays as pivotal components of NW-based devices. The first part deals with the characterization of electrically active defects in NWs. It has been elaborated the set-up of a general procedure which enables to employ Deep Level Transient Spectroscopy (DLTS) to probe NW arrays’ defects. This procedure has been applied to perform the characterization of a specific system, i.e. Reactive Ion Etched (RIE) silicon NW arrays-based Schottky barrier diodes. This study has allowed to shed light over how and if growth conditions introduce defects in RIE processed silicon NWs. The second part of this thesis concerns the bowing induced by electron beam and the subsequent clustering of gallium arsenide NWs. After a justified rejection of the mechanisms previously reported in literature, an original interpretation of the electron beam induced bending has been illustrated. Moreover, this thesis has successfully interpreted the formation of NW clusters in the framework of the lateral collapse of fibrillar structures. These latter are both idealized models and actual artificial structures used to study and to mimic the adhesion properties of natural surfaces in lizards and insects (Gecko effect). Our conclusion are that mechanical and surface properties of the NWs, together with the geometry of the NW arrays, play a key role in their post-growth alignment. The same parameters open, then, to the benign possibility of locally engineering NW arrays in micro- and macro-templates.

This PhD thesis presents two measurements of differential production cross section of top and anti-top pairs tt ̅ decaying in a lepton+jets final state. The normalize cross section is measured as a function of the top transverse momentum and the tt ̅ mass, transverse momentum and rapidity using the full 2011 proton-proton (pp) ATLAS data taking at a center of mass energy of √s=7 TeV and corresponding to an integrated luminosity of L=4.6 〖fb〗^(-1). The cross section is also measured at the particle level as a function of the hadronic top transverse momentum for highly energetic events using the full 2012 data taking at √s=8 TeV and with L=20 〖fb〗^(-1). The measured spectra are fully corrected for detector efficiency and resolution effects and are compared to several theoretical predictions showing a quite good agreement, depending on different spectra.

The present thesis is focused on the study of innovative Si-based materials for third generation photovoltaics. In particular, silicon oxi-nitride (SiOxNy) thin films and multilayer of Silicon Rich Carbide (SRC)/Si have been characterized in view of their application in photovoltaics. SiOxNy is a promising material for applications in thin-film solar cells as well as for wafer based silicon solar cells, like silicon heterojunction solar cells. However, many issues relevant to the material properties have not been studied yet, such as the role of the deposition condition and precursor gas concentrations on the optical and electronic properties of the films, the composition and structure of the nanocrystals. The results presented in the thesis aim to clarify the effects of annealing and oxygen incorporation within nc-SiOxNy films on its properties in view of the photovoltaic applications. Silicon nano-crystals (Si NCs) embedded in a dielectric matrix were proposed as absorbers in all-Si multi-junction solar cells due to the quantum confinement capability of Si NCs, that allows a better match to the solar spectrum thanks to the size induced tunability of the band gap. Despite the efficient solar radiation absorption capability of this structure, its charge collection and transport properties has still to be fully demonstrated. The results presented in the thesis aim to the understanding of the transport mechanisms at macroscopic and microscopic scale. Experimental results on SiOxNy thin films and SRC/Si multilayers have been obtained at macroscopical and microscopical level using different characterizations techniques, such as Atomic Force Microscopy, Reflection and Transmission measurements, High Resolution Transmission Electron Microscopy, Energy-Dispersive X-ray spectroscopy and Fourier Transform Infrared Spectroscopy. The deep knowledge and improved understanding of the basic physical properties of these quite complex, multi-phase and multi-component systems, made by nanocrystals and amorphous phases, will contribute to improve the efficiency of Si based solar cells.

This thesis reports on the results of the so-called free-fall experiment performed on LISA Pathfinder (LPF). After an introduction to the measurement of space-time curvature from space and its application to gravitational wave observation, overviews of LISA and the precursor mission, LISA Pathfinder, are described. Then a specific source of noise arising on LPF, the actuation noise, is investigated, also with reference to the free-fall experiment. Then, the physics and the design of the experiment are described as well as the analysis technique adopted to analyze the free-fall data. Finally, the results of the free-fall data campaign are shown, with a discussion regarding the possible implications for LISA and space-based gravity gradiometers.

My work was carried out with the aim of devising and characterize novel integrated devices for signal routing in optical networks on chip. Several type of optical microresonators, both in a single and coupled configuration (CROW, SCISSOR), are discussed starting from the fundamental theory till dealing with novel configurations. The coupling between a Mach-Zehnder interferometer and such configuration of microresonators is also investigated. Since the used material platform is the silicon on insulator (SOI), an in depth study of the microresonators behaviour has demanded an investigation in both in the linear and non-linear regime. All devices were fabricated through a standard CMOS facility by using deep UV lithography in order to verify the reliability of resolution and throughput similar to those required for commercial applications. Particular attention has been paid in the study of structures robust with respect to manufacturing defects. All the steps necessary to develop a device for integrated optics are studied in deep: device conception, device simulations through analytic and FEM simulations, GDS mask design, experimental characterizations. All the devices parameters are carefully reported to allow the reproduction of the experimental results. Where it was possible, suggestions on how to improve the fabricated devices performance were given.

In the present thesis work, we have developed two different experimental setups for the optical detection of the OH radical in discharges at atmospheric pressure. The first one allows us to improve the time-resolved broad-band absorption spectroscopy. The main advances of the new set up are a better collimation of the UV light and a novel gating scheme. They both significantly reduce the interference of the plasma-induced emission on the absorption measurement. The second setup is dedicated to an improved laser induced fluorescence experiment, which takes advantage of a novel multi-transition excitation scheme. This permits the simultaneous measurements of both the OH density and its ground state rotational temperature. In addition, we have developed a new rate-equation model to rationalize LIF spectra, by taking into account the electronic quenching, the vibrational and rotational energy transfers, and the spatial profile of the laser beam. Finally, the electrical power dissipated in the discharge was accurately measured.

The thesis is divided into two topics: silicon nanocrystals based light emitting devices and erbium doped silicon nanocrystals devices. I have studied silicon nanocrystals based devices. Here I have demonstrated the role of the different injection mechanisms in determining the efficiency of the device. I have studied single and multilayer structures, both in diode or transistor configurations. Lastly, the time dependence of the electroluminescence has been studied, clarifying the role of bipolar or unipolar injection in these structures. On the second part of my thesis, I have studied Er and silicon nanocrystals co-doped devices. Firstly, the study was aimed at the understanding of the efficiency of the electrical pumping of Er ions. Then, integrated optical cavities were designed and fabricated and their optoelectronic properties measured. Here I built a specific set-up in order to measure at the same time the optical and electronic properties of active devices on wafer. Unfortunately, the measurements demonstrated that many nonlinear loss mechanisms set in when the devices are heavily injected with current. Therefore, despite the optical cavities are of high qualities, the system did not show any laser emission. On the other hand, I have demonstrated a fully integrated system where the Er doped injection device pumps a waveguide and the emission is then extracted through a grating. Last result was the experimental verification of the existence of intermediate band states through which the silicon nanocrystals to Er energy transfer occurs.

The contents of the present thesis can be divided into three parts. The first three chapters introduce the general context in which this work was developed: the social impact, the motivations and the key concepts of our research field. In particular, in Chapter 1 we discuss about the energy issue, focusing on the problem of sustainability of the energy sources. Through an analysis of updated energy and population statistics, we come to the conclusion that solar energy is the most environmentally, economically and socially sustainable energy source. Then, in Chapter 2 we present the basics of photoelectrochemical water splitting, as a possible strategy of solar hydrogen production. This discussion is inserted in the more general topic of artificial photosynthesis toward solar fuel generation. In view of the experimental work presented in this thesis, we put attention on semiconductor-based photoelectrochemical water splitting and on heterogeneous catalysis with inorganic catalytic materials. More specifically, we propose physical vapor deposition techniques as synthetic methods suitable for the industrial production of thin films for photoelectrochemical applications. In Chapter 3 we introduce the fundamentals of physical vapor deposition techniques (namely, radiofrequency magnetron sputtering, electron-beam deposition and pulsed laser deposition). The second part highlights some fundamental mechanisms that are relevant in the pulsed laser ablation of metals. In particular, we review our recent results on the modeling of liquid nanodroplet formation in the nanosecond laser ablation of pure metals. Chapter 4 develops a simplified model of phase explosion, based on the theory of homogeneous boiling. Through a continuum approach, we describe the liquid nanoparticle formation in a metastable liquid metal, whose temperature is constant over time and space. The results of our computational simulations are presented here for a set of seven metals (Al, Fe, Co, Ni, Cu, Ag and Au), commonly used in pulsed laser deposition. Our modeling was further improved, taking into account a more realistic spatial and temporal dependence of the temperature. In Chapter 5 we design a simulation of the nanosecond laser ablation of aluminum, which considers phase explosion and vaporization mechanisms. A nanosecond Gaussian-shaped laser pulse was assumed and the spatial gradient of the temperature was calculated according to the heat conduction equation. In this way, space–time resolved homogeneous boiling was studied and the size distribution of the produced liquid nanodroplets is presented. After this long digression on the fundamentals of laser ablation mechanisms, we return to focus on the application of physical vapor deposition techniques to the synthesis of solid-state thin layers for photoelectrochemical water splitting. This third part is composed of three chapters, each one dealing with a different physical vapor deposition technique. Chapter 6 presents the synthesis and characterization of tin-doped hematite through radiofrequency magnetron sputtering. That study allowed us to shed some light on the effect of tin doping on the structural, optical and electrochemical properties of hematite. Indeed, tin-doped hematite was studied as a photoanodic material in some considerable experimental works, but the employed techniques made difficult to decouple the effect of the dopant from other structural and morphological features. Chapters 7 and 8 present the results of our work on the pulsed laser deposition and electron-beam deposition of water oxidation catalysts, respectively. In particular, Chapter 7 proposes the synthesis of a porous amorphous iron oxide catalyst employed to functionalize hematite photoanodes. The small-scale nanostructuring obtained through pulsed laser deposition allowed minimizing some issues such as the parasitic light absorption. In Chapter 8 we characterize pure and binary metal oxide thin films based on Fe, Co and Ni, deposited through electron-beam deposition. In our investigation of the electrocatalytic performance of these water oxidation catalysts, NiFe2Ox results as the most active material, in agreement with recent literature.