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The growing demand for flexible and low-cost electronics has driven research towards the study of novel semiconducting materials to replace traditional semiconductors like silicon and germanium, which are limited by mechanical rigidity and high production cost. Some of the most promising semiconductors in this sense are metal halide perovskites (MHPs), which combine low-cost fabrication and solution processability with exceptional optoelectronic properties like high absorption coefficient, long charge carrier lifetime, and high mobility. These properties, combined with an impressive effort by many research groups around the world, have enabled the fabrication of solar cells with record-breaking efficiencies, and photodetectors with better performance than commercial ones. However, MHP devices are still affected by issues that are hindering their commercialization, such as degradation under humidity and illumination, ion migration, electronic defects, and limited resistance to mechanical stress. The aim of this thesis work is the experimental characterization of these phenomena. We investigated the effects of several factors, such as X-ray irradiation, exposure to environmental gases, and atmosphere during synthesis, on the optoelectronic properties of MHP single crystals. We achieved this by means of optical spectroscopy, electrical measurements, and chemical analyses. We identified the cause of mechanical delamination in MHP/silicon tandem solar cells by atomic force microscopy measurements. We characterized electronic defects and ion migration in MHP single crystals by applying for the first time the photo-induced current transient spectroscopy technique to this class of materials. This research allowed to gain insight into both intrinsic defects, like ion migration and electron trapping, and extrinsic defects, induced by X-ray irradiation, mechanical stress, and exposure to humidity. This research paves the way to the development of methods that heal and passivate these defects, enabling improved performance and stability of MHP optoelectronic devices.

Ionizing radiations are important tools employed every day in the modern society. For example, in medicine they are routinely used for diagnostic and therapy. The large variety of applications leads to the need of novel, more efficient, low-cost ionizing radiation detectors with new functionalities. Personal dosimetry would benefit from wearable detectors able to conform to the body surfaces. Traditional semiconductors used for ionizing radiation direct detectors offer high performance but they are intrinsically stiff, brittle and require high voltages to operate. Hybrid lead-halide perovskites emerged recently as a novel class of materials for ionizing radiation detection. They combine high absorption coefficient, solution processability and high charge transport capability, enabling efficient and low-cost detection. The deposition from solution allows the fabrication of thin-film flexible devices. In this thesis, I studied the detection properties of different types of hybrid perovskites, deposited from solution in thin-film form, and tested under X-rays, gamma-rays and protons beams. I developed the first ultraflexible X-ray detector with exceptional conformability. The effect of coupling organic layers with perovskites was studied at the nanoscale giving a direct demonstration of trap passivation effect at the grain boundaries. Different perovskite formulations were deposited and tested to improve the film stability. I report about the longest aging studies on perovskite X-ray detectors showing that the addition of starch in the precursors’ solution can improve the stability in time with only a 7% decrease in sensitivity after 630 days of storage in ambient conditions. 2D perovskites were also explored as direct detector for X-rays and gamma-rays. Detection of 511 keV photons by a thin-film device is here demonstrated and was validated for monitoring a radiotracer injection. At last, a new approach has been used: a 2D/3Dmixed perovskite thin-film demonstrated to reliably detect 5 MeV protons, envisioning wearable dose monitoring during proton/hadron therapy treatments.

This book contain the abstracts presented the XXII ICMMB, held in Bologna in September 2022. The abstracts are divided following the sessions scheduled during the conference.

Recent research in the field of organic spintronics highlighted the peculiar spin-dependent properties of the interface formed by an organic semiconductor (OSC) chemisorbed over a 3d ferromagnetic metal, also known as spinterface. The hybridization between the molecular and metallic orbitals, typically π orbitals of the molecule and the d orbitals of the ferromagnet, give rise to spin dependent properties that were not expected by considering the single components of interfaces, as for example the appearance of a magnetic moment on non-magnetic molecules or changes in the magnetic behavior of the ferromagnet. From a technological viewpoint these aspects provide novel engineering schemes for spin memory and for spintronics devices, featuring unexpected interfacial magnetoresistance, spin-filtering effects and even modulated magnetic anisotropy. Applications of these concepts to devices require nevertheless to transfer the spinterface effects from an ideal interface to room temperature operating thin films. In this view, my work presents for the first time how spinterface effects can be obtained even at room temperature on polycrystalline ferromagnetic Co thin films interfaced with organic molecules. The considered molecules were commercial and widely used in the field of organic electronics: Fullerene (C60), Gallium Quinoline (Gaq3) and Sexithiophene (T6). An increase of coercivity, up to 100% at room temperature, has been obtained on the Co ultra-thin films by the deposition of an organic molecule. This effect is accompanied by a change of in-plane anisotropy that is molecule-dependent. Moreover the Spinterface effect is not limited to the interfacial layer, but it extends throughout the whole thickness of the ferromagnetic layer, posing new questions on the nature of the 3d metal-molecule interaction.

Wearable electronic textiles are an emerging research field playing a pivotal role among several different technological areas such as sensing, communication, clothing, health monitoring, information technology, and microsystems. The possibility to realise a fully-textile platform, endowed with various sensors directly realised with textile fibres and fabric, represents a new challenge for the entire research community. Among several high-performing materials, the intrinsically conductive poly(3,4-ethylenedioxythiophene) (PEDOT), doped with poly(styrenesulfonic acid) (PSS), or PEDOT:PSS, is one of the most representative and utilised, having an excellent chemical and thermal stability, as well as reversible doping state and high conductivity. This work relies on PEDOT:PSS combined with sensible materials to design, realise, and develop textile chemical and physical sensors. In particular, chloride concentration and pH level sensors in human sweat for continuous monitoring of the wearer's hydration status and stress level are reported. Additionally, a prototype smart bandage detecting the moisture level and pH value of a bed wound to allow the remote monitoring of the healing process of severe and chronic wounds is described. Physical sensors used to monitor the pressure distribution for rehabilitation, workplace safety, or sport tracking are also presented together with a novel fully-textile device able to measure the incident X-ray dose for medical or security applications where thin, comfortable, and flexible features are essential. Finally, a proof-of-concept for an organic-inorganic textile thermoelectric generator that harvests energy directly from body heat has been proposed. Though further efforts must be dedicated to overcome issues such as durability, washability, power consumption, and large-scale production, the novel, versatile, and widely encompassing area of electronic textiles is a promising protagonist in the upcoming technological revolution.

This thesis aims to study the modifications induced by vanadium in titanium dioxide, an oxide semiconductor used for photoelectrocatalytic applications, such as water-splitting for hydrogen production and air and water remediation. The modification of this material is necessary to improve its conversion efficiency of light into chemical energy. In fact, its main limitation is the poor visible light absorption due to its wide energy gap (3.2 eV). In this work, V was introduced during the preparation of the sample, either in form of thin films or nanoparticles, using radio-frequency magnetron sputtering and inert gas phase condensation technique, respectively. A structural characterization by X-ray diffraction, Raman spectroscopy, and X-ray photoelectron spectroscopy showed that V does not induce critical changes in TiO2 matrix; X-ray near edge absorption spectroscopy was used to determine the local environment of V and Ti, revealing that V is substitutional. Femtosecond transient absorbance spectroscopy was adopted to provide the basis for the interpretation of the photoelctrocatalytic behavior of V-modified and unmodified TiO2, used as photoanodes in a photoelectrochemical cell. FTAS revealed that vanadium accelerates electron-hole recombination upon UV irradiation, explaining the lower conversion efficiency in the UV spectral range with respect to unmodified TiO2. In the visible range, for modified samples, FTAS revealed the presence of a transient signal due to free electrons and trapped holes after pumping at 530 nm. These results were supported by the new photoelectrocatalytic activity in the visible range, attributed to a V-induced introduction of intragap levels at ≈ 2.2 eV below the conduction band. Similar results were obtained for thin films and nanoparticle based samples. IPCE spectra showed that incorporation of vanadium in TiO2 extends water splitting in the visible range up to ≈ 530 nm, a significant improvement compared to unmodified TiO2 that is active only in the UV range.

Brillouin optical time domain analysis (BOTDA) is one of the most important distributed optical fiber sensor technologies thanks to its capability of monitoring both temperature and strain distribution over tens of kilometers of sensing fibers with a single interrogator. BOTDA sensors have found important applications in structural health monitoring, safety and environmental engineering. Their employment is still limited by two factors: on one hand, the high complexity (and cost) for a single interrogator unit reduces the applications where BOTDA can compete with classical point-like sensors. On the other, the time required to obtain a single temperature/strain distribution is in the order of several minutes, limiting BOTDA to static or quasi-static measurements. In this thesis solutions are proposed for these limitations. In the first part, two different pump-probe laser sources based on Brillouin ring lasers (BRL) are shown and evaluated as low-cost alternatives to traditional sources employed in BOTDA. The first source, which is based on a long cavity BRL, is shown to be successfully employable in BOTDA measurements up to at least 10 km of range. The second source, which is based on a doubly resonant short cavity BRL, shows further improvements in intensity noise, output light spectral linewidth and tunability of the pump-probe frequency shift, at the cost of a slightly more complex hardware requirement, which still remains less severe than traditional sources. In the second part, a fast BOTDA design based on a closed-loop control was explored and improved, with a particular focus in its signal processing methods. Finally, a new adaptive signal filtering technique to improve noise suppression is proposed and demonstrated.

Microbial communities are ubiquitous and play crucial roles in many natural processes (e.g., biogeochemical cycles and industrial processes). Despite their importance, however, there are still many aspects of microbial community dynamics that we do not fully understand. In this Thesis we provide two improvements to the approach used to study competition in microbial communities that can help us in this direction. The theoretical framework on which we build is MacArthur’s consumer-resource model, commonly used to describe mathematically competition between microbes. The first improvement consists in introducing an optimization principle in the dynamics of such systems, so that we can include in mathematical models the well known fact that microbes can switch between different energy sources depending on environmental conditions. We require that each species does so in order to maximize its own relative fitness, and we explore the consequences of this choice on the biodiversity of competitive communities, comparing also the model with experimental data. Then, we reconsider the consumer-resource framework in light of experimental evidence showing that the allocation of cellular internal resources affects microbial growth. This new framework describes community dynamics at an intermediate level of complexity, allowing us to explore the relationship between population dynamics and microbial metabolism, which has attracted the attention of the scientific community in recent years. We compare the predictions of our new model with experimental data in a simple case, and then we study its predictions analytically and numerically to understand how biodiversity in competitive communities can be maintained.

Nowadays the development of real-time ionizing radiation detection system operating over large areas is crucial. Increasing quest for flexible, portable, low cost and low power consumption sensors pushed the scientific community to look for alternative materials and technologies able to fulfill these new requirements. In this thesis the potentiality of organic semiconductors and metal oxides as material platforms for novel ionizing radiation sensors is demonstrated. In particular, organic semiconductors are human tissue-equivalent and this represents a unique and desirable property for the development of dosimeters to be employed in the medical field. The ionizing radiation sensors described in this thesis have been designed, fabricated and characterized during my PhD research and are realized onto polymeric foils leading to flexible devices operating at low voltages, in ambient condition and able to directly detect X-rays, gamma-rays and protons. Following the study of the properties and of the mechanisms of interaction between the radiation and the active layers of the sensors, several strategies have been adopted to enhance the efficiency of these detectors. X-rays dosimeters based on organic semiconductors have been realized presenting record sensitivity values compared with the state of the art for large area radiation detection. The unprecedentedly reported performance led to the possibility to testing these devices in actual medical environments. Moreover, the proof-of-principle demonstration of a dosimetric detection of proton beams by organic-based sensors is reported. Finally, a new sensing platform based on metal oxides is introduced. Combining the advantages of amorphous high mobility oxide semiconductors with a multilayer dielectric, novel devices have been designed, capable of providing a sensitivity one order of magnitude higher than the one shown by the standard RADFETs. Thanks to their unique properties, these sensors have been integrated with a wireless readout system based on a commercial RFID tag and its assessment is presented.

Nanomaterials are not simply miniaturized materials. In this world halfway between the atomic and the bulk scale, high density of interfaces and surfaces, elemental composition, unique geometries and interactions constitute a virtually infinite set of parameters that allows to tailor material properties at the nanoscale. The aim of this Thesis is to contribute to the development of strategies for the growth of nanomaterials featuring complex morphologies and tailorable structures by careful design of Gas Phases Condensation (GPC) experiment. The proposed strategies are demonstrated for the growth of nanomaterials with applications in the energy storage field. The co-evaporation of Mg and Ti in a H enriched atmosphere is the key to grow small Mg-Ti-H nanoparticles (NPs), in which TiH2 and Mg/MgH2 coexist at the single NP level, despite the bulk immiscibility of Mg and Ti. The high density of MgH2/TiH2 interfaces gives rise to outstanding H-absorption and desorption kinetics in the 373-423 K temperature range. Moreover, a theoretical model is proposed to explain the altered thermodynamics induced by interface energetics. Thermal GPC and Pulsed Laser GPC were employed to grow Fe-Co alloy nanoparticles. The influence of the two techniques over the morphology of the nanoparticles is discussed and an application in the catalysis of CO2 reduction is presented. Finally, a novel strategy for the one-step synthesis of Fe-Co alloy nanoparticles supported on Ti oxide nanoparticles via Thermal GPC is presented. This new approach relies on the independent evaporation of two metallic precursors with strongly different oxidation enthalpies in an O2 enriched atmosphere. TEM and XRD morphological and structural characterizations clearly show that less negative enthalpy gives birth to metallic NPs, while the other to oxide NPs.

Bioeletronics aims at the direct coupling of biomolecular function units with standard electronic devices. The main limitations of this field are the material needed to interface soft living entities with hard inorganic devices. Conducting polymers enabled the bridging between these two separate worlds, owing to their biocompatibility, soft nature and the ability to be tailored according to the required application. In particular, the intrinsically conductive poly(3,4-ethylenedioxythiophene):poly(styrenesulfonic acid) (PEDOT:PSS) is one of the most promising polymers, having an excellent chemical and thermal stability, reversible doping state and high conductivity. This thesis relies on the use of PEDOT:PSS as semiconducting material for biological interfaces and biosensors. In detail, OECTs were demonstrated to be able to real-time monitor growth and detachment of both strong-barrier and no-barrier cells, according to the patterning of the device active area and the selected geometry. Thus, these devices were employed to assess silver nanoparticles (AgNPs) toxicity effects on cell lines, allowing further insights on citrate-coated AgNPs uptake by the cells and their toxic action, while demonstrating no cytotoxic activity of EG6OH-coated AgNPs. Moreover, PEDOT:PSS OECTs were proved to be capable of detecting oxygen dissolved in KCl or even cell culture medium, in the oxygen partial pressure range of 0-5%. Furthermore, PEDOT:PSS OECTs were biofunctionalized to impart specificity on the device sensing capabilities, through a biochemical functionalization strategy, electrically characterized. The resulting devices showed a proof of concept detection of a fundamental cytokine for cells undergoing osteogenic differentiation. Finally, PEDOT:PSS thickness-controlled films were employed as biocompatible, low-impedance and soft interfaces between the animal nerve and a gold electrode. The introduction of the plasticizer polyethylene glycol (PEG) enhanced the elasticity of the polymer, while keeping good conductivity and low-impedance properties. An in-vivo, chronic recording of the renal sympathetic nerve activity in rats demonstrated the efficiency of the device.

Il presente lavoro di tesi ha come obiettivo principale lo studio di materiali innovativi per lo sviluppo di componenti ottici nella regione spettrale dell’estremo ultravioletto (EUV) e dell’ultravioletto da vuoto (VUV). I campi di applicazione sono molteplici e spaziano dalla litografia EUV all’esplorazione spaziale. Questo tipo di ricerca richiede contemporaneamente l’utilizzo e la messa a punto di adeguati metodi di caratterizzazione, che permettano una completa analisi delle proprietà nella regione spettrale di interesse. Il risultato più interessante presentato è sicuramente l’analisi ottica e strutturale di strati di grafene (singolo e triplo) depositati su silicon oxide, nella regione spettrale dell’ultravioletto da vuoto. Lo studio è stato affrontato combinando diverse tecniche sperimentali e partendo dalle proprietà ottiche dell’ossido di silicio depositato su silicio (SiO2/Si), che costituisce il substrato. Il SiO2/Si è stato caratterizzato alla hydrogen Lyman-alpha (121.6 nm) utilizzando un riflettometro dedicato alla riflettometria nell’ultravioletto e recentemente implementato per misure polarimetriche (CNR-IFN Padova). Sono stati determinati i parametri ellissometrici, ratio (ρ) and phase shift (), le costanti ottiche e le proprietà polarimetriche del silicon oxide. Il SiO2 si comporta effettivamente come una lamina di ritardo introducendo una differenza di fase tra le componenti s- e p- della radiazione incidente. La differenza di fase introdotta varia dai 18° ai 160° e dipende dall’angolo di incidenza. Successivamente, lo stesso tipo di analisi sperimentale è stata completata per i campioni con uno strato di grafene depositato sull’ossido di silicio (1LG/SiO2/Si). E’ stato osservato che, nonostante il sottile spessore, il singolo strato di grafene migliora la riflettività del substrato. Dall’analisi polarimetrica, non si può invece affermare che il grafene introduca un ritardo di fase osservabile. Le costanti ottiche del singolo e triplo strato di graphene cresciuto su SiO2/Si sono state studiate alla hydrogen Lyman-alpha utilizzando misure in riflettometria in polarizzazione s- e p- acquisite utilizzando luce di sincrotrone (ELETTRA Trieste, BEAR beamline). Si notano differenze misurabile nella riflettività dei campioni. Le differenze dipendono dal numero di strati di graphene. Queste misure sono state utilizzate per ricavare le costanti ottiche. E’ stata inoltre sperimentalmente osservato una anisotropia ottica con asse di simmetria quasi perpendicolare alla superficie e coerentemente correlata all’orientamento degli orbitali π. Le costanti ottiche efficaci sono state ricavate simulando l’interazione della radiazione elettromagnetica con la struttura del campione. Inoltre, l’attendibilità delle costanti ottiche trovate è stata qualitativamente testata ricavando la “surface differential reflectance (SDR)” dalle misure di riflettività. Un altro effetto molto interessante indotto dal grafene è lo spostamento dell’angolo di pseudo-Brewster rispetto a quanto osservato per il substrato. Lo spostamento, che cresce in valore assoluto con il numero di strati, induce un downshift contrariamente a quanto osservato in altre regioni spettrali. La qualità della superficie, la morfologia e il numero di layer sono stati caratterizzati con misure di microscopia a forza atomica e spettroscopia Raman. Per quanto ne sappiamo, questi risultati relativi allo studio delle proprietà ottiche del grafene nel VUV sono assolutamente nuovi. L’ultima parte della tesi riguarda lo studio dello strato di stagnazione che si forma sul fronte di collisione di due plasmi collidenti. La tecnica utilizzata è una spettroscopia risolta in tempo. Il tempo di evoluzione e le dinamiche dei plasmi collidenti di Al-Al e Al-Si sono stati studiati con tecniche spettroscopiche risolte in tempo. È stato osservato che nel caso di un "wedge target" lo strato di ristagno produce uno spettro più luminoso e in precedenza sono comparsi stati di ionizzazione più elevati con un'intensità relativamente più elevata di un "flat target". Il tempo di evoluzione della densità elettronica è stato studiato e confrontato nel caso delle due configurazioni con i target diversi e una densità elettronica relativamente più alta è stata osservata nel caso di “wedge target”.

Since the growing interest in Lab-On-a-Chip (LOC) applications, the demand for a high multifunctional and portable devices in order to increase the achievement of complex laboratories analysis on a small size chips. This need pushed the research to integrate in the substrates several tools with different tasks, and consequently, the requirements of the material exploited become rapidly more restricted. In particular, the performances of multiple toolkit device are related to its capabilities of combining and matching stages, thus avoiding any detrimental interferences between the material properties needed for their realization. During the last 20 years, several materials have been proposed for the combination of different tools on the same device. Only recently our group proposed Lithium Niobate (LiNbO3) as a valid alternative for a monolithic substrate in LOC application. This material is well-known in the field of integrated optics, due to its interesting optical properties, that brought it to be the main component in optical modulators in the telecom devices. The excellent performances in this field can be combined to the microfluidic for the realization of reliable optofluidic stages for LOC application. Moreover, LiNbO3 was demonstrated as a substrate for several micro-manipulation tools, exploiting its further properties, such as photovoltaic tweezers of micro-sized objects, nano-droplets pipetting with pyroelectric induced field, acoustic driven particle transports via piezoelectric generated surface acoustic wave respectively. For these reasons, the merge of all these tools on the same monolithic substrate could represent the optimal improvement to push even further the LOC technology. This thesis aimed to demonstrate that a multifunctional opto-microfluidic platform can be realized in one monolithic substrate of lithium niobate, achieving properties that can be properly exploited for LOC application. In particular, the attention was focused on combining integrated optics and microfluidics in a unique platform, where light is confined in an optical waveguide and crossed a microfluidic channel allowing for a transmission detection. The realization of microchannel for the coupling with microphotonic structures is presented: so in particular channel configurations, such as droplet generator, are characterized and compared to those achieved with other standard material, in order to show the better performances provided by LiNbO3. In this platform the crucial aspect was played by the optical quality of the lateral walls of the microfluidic channel in order to guarantee an optimized optical coupling of the integrated optical waveguide and the microchannel. Such an optical grade quality allows for the integration of microchannels with Ti-indiffused waveguide, in an unexplored way alternative to the standards in optofluidics. This optofluidic coupling is performed by crossing the waveguide with an engraved microfluidic channel. This configuration enables the analysis of the transmitted light guided by the first half of the waveguide to the second half of it. The self-aligned geometry allows for the traveling of the light beam from one waveguide (input waveguide) across the channel until it recouples in the other part of the waveguide (output waveguide). This optical transmission signal of the medium inside the channel is exploited for LOC applications, such as optical measurements of the droplet geometrical properties (such as frequency, length, volume), and controlled microfluidic pH titration, which allows for the pH determination and the neutralization of strong acidic or basic solution, and finally as an optical multiplexer actuated microfluidically. In all these applications, the devices showed not only high level of integration and accurate response, but also superior performances than the standard procedures and materials. Moreover, a further tool was integrated to this optofluidic platform: a photovoltaic tweezers, exploiting the lithium niobate capability of photoinducing electric field on its surfaces. These multifunctional stages are proposed for the effectively manipulation of the orientation liquid crystal inside a microchannel, and the consequent polarization control waveguide transmission beam.

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.

The R&D program reported in this thesis (develop of cryogenic setups, analysis software and characterizations) has delivered the NUV HD Cryo technology of Silicon Photomultipliers (SiPM) developed in FBK to the DS-20k experiment for the research of Dark Matter. NUV HD Cryo technology currently represents the best cryogenic SiPM performance and fully satisfies the experiment requirements. These developments are relevant also to nEXO experiment and have attracted the attention of other large experiments, such as DUNE, which require large active areas of SiPMs operated in cryogenic noble liquids

The atomic mean square displacement (MSD, ¯(σ_i^2 ) ) is often used in computational materials science studies to calculate measurable properties from the atomic trajectories of simulations; for example, the diffusion coefficient, which according to Einstein relations (Einstein 1905) on the random walk is 1/6 of the slope of the trend of ¯(σ_i^2 ) vs. time (Chandler 1987). Equally relevant is the mean square relative displacement (MSRD, ¯(σ_ij^2 )), used in X-ray Spectroscopies, mainly EXAFS, to describe the atomic disorder in solids (Calvin 2013) (Fornasini 2014). Less known is the relevance of the MSRD in X-ray scattering from nanoparticles. In particular, in Total Scattering methods (Pair Distribution Function and Debye Scattering Equation), which rely on an atomistic description of the nanoparticles, the MSRD is the key to distinguish dynamic (thermal) and static disorder (Krivoglaz 1969) (Kuhs 2006). Interestingly, the trend of the MRSD with the distance is characteristic of the nanoparticle shape, an aspect investigated in some detail in this Thesis work. More generally it can be shown that beyond the expected effect of nanocrystal size, the shape alters the contribution of the surface, which is quite relevant for the MSRD. The importance of the shape and of the surface region holds also in case of clusters of nanoparticles, not only in isolated particles. Besides the MSRD, the atomic configurations simulated by molecular dynamics (MD) can also be used to calculate the so-called Warren plot (or diagram), originally introduced in the seminal work of Warren & Averbach of the ‘50s to describe the effects of plastic deformation in metals (Warren B.E. 1950). Recent work has shown how to obtain Warren plots from the analysis of the diffraction line profiles according to the Whole Powder Pattern Modelling (WPPM) (L. M. Scardi P. 2002) (Scardi P 2017) (P. E.-W. Scardi 2018), in particular from the analysis of the strain component of the diffraction peak profile broadening. As proposed in this work, If the Warren plot can be calculated directly from MD simulations, then it is possible to proceed backwards, and construct more reliable strain functions from an atomistic knowledge of the local atomic displacement caused by static and dynamic disorder components. This thesis is divided in two main parts, discussing two different but complementary topics: atomistic modelling and calculations of displacement quantities, application of the above results to experimental case studies, based on the modelling of diffraction data from nanocrystalline systems. We start by describing the atomistic simulations and vibrational properties calculated for several atomic configurations. The main case study concerns Palladium nanoparticles of different sizes and shapes, for which we show that vibrational properties and correlation properties between atoms pairs are greatly influenced by the geometric shape of the nanoparticle and to a lesser extent by their size. The interest is on truncated cubes, i.e. cubes whose edges and corners are progressively removed, as in the series of so-called Wulff solids, ranging from the cubic to the octahedral shape (Wulff G. 1901). As shown in (ii), these are the object of several experimental studies. The developed methodologies are nevertheless applicable to other cases, like the clusters of nanocrystals observed in powders produced by high-energy ball milling, which is also a topic discussed in (ii). The work aims to show a general approach to atomistic modelling, both for isolated nanoparticles with definite shapes, and grains of unspecified shape in plastically deformed polycrystalline materials. We then use the values for displacement quantities (e.g., MSD, MSRD) calculated for the simulated systems to compare them to the experimental results. An underlying fact that seems to hold in all the different cases is that the surface behaviour of nanomaterials has the largest influence on the displacement quantities. For isolated particles we observe strong correlation between displacement quantities and the shape; whereas in the case of a nanocrystalline grain clusters (Figure 1 1) we see that no matter the defects inside the grain, the main contribution to MSRD is given by the grain boundary.

The aim of this thesis is the study of electronic transport and mechanical properties of materials using computer simulations. In particular, we dealt with the charge transport in semiconduc- tor and metallic samples and with the peeling of a graphene layer from bulk graphite. The computational methods used to investigate the samples are (i) the Monte Carlo (MC) statis- tical method to simulate the transport of electrons in solids and (ii) the molecular dynamic (MD) approach to study the mechanical characteristics. A relevant part of this thesis is focused on carbon-based material, such as diamond and graphite, and the stable two-dimensional al- lotrope, graphene. The response of diamond and graphite to external electromagnetic pertur- bations, due to e.g. an impinging electron beam, was investigated by calculating reflection electron energy loss (REEL) spectra with MC simulations. By comparing the calculated spec- tra, obtained using different dielectric models, and in-house recorded experimental results, the most effective dielectric model better describing the plasma losses was identified. Moreover, an extension to these models to describe the anisotropic response of graphite to an external electromagnetic perturbation was developed and included in the MC approach. Owing to the central role of carbon for future electronic and technological applications, also its mechanical properties were investigated by means of MD simulations. In particular, the peeling process of a layer of graphene from a bulk of graphite was investigated. This process is exploitable for graphene production and for adhesive applications of this material. Moreover, the MC approach, employed for calculating REEL spectra, was tested and compared to other com- putational techniques based on the solution of the Ambartsumian-Chandrasekhar equations. This consistency test was realized by considering three metals (copper, silver and gold) as tar- get materials. Further studies were carried out on these materials by calculating secondary electron emission yields as a function of the electron beam energy. A remarkable good agreement with experimental data was obtained. The MC approach was also used to investigate the growth of particles in a W(CO)6 layer deposited on a SiO2 substrate upon irradiations by an electron beam in the context of the focused electron beam induced deposition technique. In particular, by applying the MC method, the radial distribution of emitted secondary electrons was calculated and then utilized as input data for further MD simulations. Moreover, the study of electron transport in an organic polymer (P3HT) was performed in order to understand how the molecular ordering affects the secondary electron emission. This aspect is of paramount importance to construct efficient organic electronic devices.

This thesis deals with the theoretical and computational modelling of materials by using a variety of ab-initio approaches to accurately predict the properties of realistic structures. A number of known and novel carbon-based materials are studied, exploiting the unique versatility of carbon to bind into several bonding configurations, with the aim of tailoring their electronic and mechanical characteristics. In this regard, the methods used to carry out electronic structure simulations depend on the system size: from the Dirac-Hartree-Fock approach to model molecular properties, to Density Functional Theory used for periodic solids, such as diamond and graphene-related materials composed by a few to some hundred of atoms, to Density Functional Tight Binding or plane Tight Binding to study nanowires or Beltrami pseudospheres, which are composed by some hundreds to a few millions atoms. The details of these methods are introduced in the chapters where they are used. The criterion used to present these concepts is to organize the chapters, with the exception of the last one, according to the increasing dimension of the systems. More in details, the first chapter uses the Dirac-Hartree-Fock approach to simulate atoms and molecules, such bromotrifluoromethane; the second chapter deals with periodic systems characterized by unit cells with a relatively small number of atoms, such as diamond and graphite; the third one discusses graphene and graphene-related materials with lower density; the fourth one present a new computational and experimental model of silicon carbide nanowires coated with silicon dioxide shell; the fifth chapter is focused on the study of sp2-hybridized carbon atoms, arranged on a Beltrami surface. The latter topic spans different research fields such as geometrical topology, physics and mechanical engineering. Finally, the last chapter is dedicated to an on going work which deals with the Non-Adiabatic Molecular Dynamics simulation of amorphous silica samples where we couple the nuclear dynamic of the system to the electronic structure.

In this thesis we investigate the properties of mixtures of Bose gases in one dimensions at zero temperature using quantum Monte-Carlo methods. First we investigate the limiting case of an impurity interacting with an atomic bath. We characterize the impurity, by calculating its effective mass, binding energy as well as the contact parameter between the impurity and the bath. In particular, we find that the effective mass rapidly increases to very large values when the impurity gets strongly coupled to an otherwise weakly repulsive bath. Then we describe uniform balanced mixtures with repulsive interactions. We investigate the miscibility phase diagram of the two components and find that correlations do not alter the phase diagram predicted by mean-field theories. We investigate the Andreev-Bashkin effect , a non-dissipative drag between the the two components of the gas and find that the drag becomes very large in the strongly interacting regime. In non-homogeneous systems we also investigate the frequency of the spin-dipole mode. Finally we describe mixtures with attractive inter-species interactions, where one can obtain a liquid ground state because of the competition between the inter-species attraction and intra-species repulsion. We characterize the the liquid and we find that the liquid state can be formed if the ratio of coupling strengths between inter-species attractive and intra-species repulsive interactions exceeds a critical value.

Looking at state of the art of optical devices, it is evident that glass-based rare-earth-activated optical structures represent the technological pillar of a huge number of photonic applications covering Health and Biology, Structural Engineering, Environment Monitoring Systems, Lighting, Laser sources and Quantum Technologies. Among different glass-based systems, a strategic place is assigned to transparent glass-ceramics, nanocomposite materials, which offer specific characteristics of capital importance in photonics. Following this strategy, this PhD thesis exploits tin dioxide (SnO2)-based glass-ceramic activated by erbium ions (Er3+) to put the basis for the fabrication of solid state and integrated lasers. The research discussed in my PhD thesis gives a possible solution to two crucial and decisive points in the development of an optically pumped rare-earth-based laser: (i) the low absorption cross section of the rare-earth ions; (ii) the writing of channels and mirrors in the case of waveguide integrated laser, thanks to the demonstration of two innovative and unique characteristics of SnO2-based transparent glass-ceramics, i.e. luminescence sensitizing and photorefractivity. The role of SnO2 nanocrystals as rare-earth ion luminescence sensitizers allows to overcome the low absorption cross section of the Er3+ ion. The photorefractivity in range of 10-3 of SiO2-SnO2:Er3+ glass-ceramics allows applying the robust direct laser photoinscription technique on the systems to fabricate Bragg gratings and channel waveguides for waveguide integrated lasers. Based on an application-oriented approach, a comprehensive study on SiO2-SnO2:Er3+ glass-ceramic planar waveguides and monoliths, has been carried out. The work covers different research stages and aspects from the material preparation to a complete assessment of systems for the applications employing a rich number and variety of experimental techniques. The energy transfer from SnO2 to Er3+ and the efficient pumping scheme exploiting SnO2 as Er3+ luminescence sensitizers were demonstrated. The relaxation dynamic of the electronic states as well as the location of the dopant and density of states are discussed, and a specific modeling has been developed to the proof of concept realization of the considered devices. The obtained photorefractivity in range of 10-3 allowed the inscription of gratings on the fabricated SiO2-SnO2:Er3+ planar waveguides using UV laser direct writing technique. Exploiting the robust femtosecond laser micromachining, the optical waveguides were inscribed in the fabricated SiO2-SnO2:Er3+ monolithic squares. Another important outcome of this research is the design of a solid state laser with lateral pumping scheme and of an integrated waveguide laser in two different distributed feedback structures using all the parameters measured during the experimental activity.

Unlike any other material, graphene is all surface. This means that it is strongly affected by its surroundings, including the substrate it lays upon. In the past few years, it was understood that silicon oxide (SiO2), the most popular substrate material for graphene, limits the performance of graphene devices and obscures interesting physics. Hexagonal boron nitride (hBN) has emerged as “the perfect” substrate that results in graphene devices of astonishing electronic quality. In this Thesis, we explore some peculiar nonlocal effects that are found in such new devices due to quantum transport and electron-electron interactions in the coherent as well as the diffusive regime. Chapters 1-4 are devoted to the introduction of some basic concepts and to the main experimental facts that motivated our work. Since encapsulation in hBN crystals makes graphene practically insusceptible to the environment, electrons can travel micrometer distances without scattering. In Chapter 5, in the framework of the Landauer-Büttiker scattering theory, we have developed a scaling procedure for numerical simulations of tight-binding nonlocal transport in realistic graphene devices. We have tested our method against experimental data on transverse magnetic focusing (TMF). This comparison enables a clear physical interpretation of all the observed features of the TMF signal, including its oscillating sign. Moreover, in graphene/hBN superlattices and in bilayer graphene in a perpendicular electric field, which have broken inversion symmetry, topological currents originating from graphene’s two valleys flow in opposite directions and combine to produce long-range charge neutral flow. This effect translates into a nonlocal voltage at zero magnetic fields in a narrow energy range near Dirac points at distances as large as several micrometers. However, the behavior of the observed long-range nonlocality as a function of temperature, band gap, and carrier concentration remained to be understood. In Chapter 6 and 7, we have showen, using a diffusive theory, that this behavior can be explained with bulk topological transport and Coulomb drag between the electrons belonging to the two different valleys, in good agreement with experimental findings. Finally, in Chapter 8, we have studied the crossed Andreev reflection in a three-terminal hybrid graphene/superconductor system in the quantum Hall regime and its effect on the nonlocal resistances.

This thesis studies problems concerning the dynamics and thermodynamics of manybody quantum systems. We start by introducing the necessary theoretical concepts and tools forming the basis of this manuscript. The research presented can be split in two parts. The first one deals with the dynamics of many-body quantum systems subject to environmental dissipative effects of various forms, while the second one studies topics of thermodynamics in many-body quantum systems. The first part of the research presented studies the effects of an environment inducing dissipation. We establish and study the adiabatic dynamics of free-fermion models subject to a local Lindblad bath and in the presence of a time-dependent Hamiltonian. The merit of these models is that they can be solved exactly, which thus can help us to study the interplay between non-adiabatic transitions and dissipation in many-body quantum systems. After the adiabatic evolution, we evaluate the excess energy (average value of the Hamiltonian) as a measure of the deviation from reaching the target final ground state. We find a robust evidence of the fact that an optimal working time for the quantum annealing protocol emerges as a result of the competition between the non-adiabatic effects and the dissipative processes. We compare these results with matrix product operator simulations of an Ising system and show that the phenomenology we found applies also for this more realistic case. We then proceed to a scenario in which the environment is not detrimental, but is on the contrary the driving force of the effects studied. We demonstrate that persistent currents can be induced in a quantum system in contact with a structured reservoir, without the need of any applied gauge field. The working principle of the mechanism leading to their presence is based on the extension to the many-body scenario of non-reciprocal Lindblad dynamics. Specifically, we consider an interacting spin/boson model in a ring-shaped one-dimensional lattice coupled to an external bath. By employing a combination of cluster mean-field, exact diagonalization and matrix product operator techniques, we show that solely dissipative effects suffice to engineer steady states with a persistent current that survives in the limit of large systems. We also verify the robustness of such current in the presence of additional dissipative or Hamiltonian perturbation terms. The second part studies many-body quantum systems with a focus on thermodynamics. First, we investigate a quantum battery made of N two-level systems, which is charged by an optical mode via an energy-conserving interaction. We quantify the fraction of energy stored in the battery that can be extracted in order to perform thermodynamic work. We first demonstrate that this fraction is highly reduced by the presence of correlations between the charger and the battery or between the two-level systems composing the battery. We then show that the correlation-induced suppression of extractable energy, however, can be mitigated by preparing the charger in a coherent optical state. We conclude by proving that the charger-battery system is asymptotically free of such locking correlations in the N ! 1 limit. And lastly, we study open questions within the theory of open quantum systems. The Markovian evolution of an open quantum system is characterized by a positive entropy production, while the global entropy gets redistributed between the system and the environmental degrees of freedom. Starting from these premises, we analyse the entropy variation of an open quantum system in terms of two distinct relations: the Clausius inequality, that provides an intrinsic bound for the entropy variation in terms of the heat absorbed by the system, and an extrinsic inequality, which instead relates the former to the corresponding entropy increment of the environment. By modeling the thermalization process with a Markovian collisional model, we compare and discuss the two bounds, showing that the latter is asymptotically saturated in the limit of large interaction time. In this regime not only the reduced density matrix of the system reaches an equilibrium configuration, but it also factorizes from the environmental degrees of freedom.

In solar cell current research, innovative solutions and materials are continuously requested for efficiency improvements. Si-based technology rules over 95% of the market, with silicon heterojunction (SHJ) solar cell reaching 26.7% record efficiency. Nonetheless, hydrogenated amorphous silicon (a-Si:H) layers employed in the structure still have challenges, resolvable with oxygen/nitrogen inclusion. In parallel, new technologies based on different materials still lack in the market due to stability issues or low efficiencies. However, a preliminary study of their properties creates a deeper knowledge exploitable in photovoltaic application. In this perspective, we investigated both innovative Si-based materials (nanocrystalline and amorphous silicon oxy-nitride and oxide thin films, nc-SiOxNy, a-SiOxNy and a-SiOx, respectively) and innovative materials (perovskite lanthanum-vanadium oxide LaVO3 thin films, indium gallium nitride InxGa1-xN and aluminium indium gallium nitride AlxInyGa1-x-yN layers) for solar cell concepts. Different deposition conditions have been employed to extract their influence on compositional, optical, and electrical properties. The study on nc-SiOxNy layers by conductive atomic force microscopy (c-AFM) and surface photovoltage (SPV) has allowed to clarify O, N, and B content, and annealing treatment role on microscopic transport properties. On a-SiOx and a-SiOxNy layers, by spectral ellipsometry, Fourier transform infrared spectroscopy, photoconductance decay and SPV, we can conclude that moderate insertions of O/N in a-Si:H lead to a decrease of optical parasitic absorption, preserving the passivation quality of the layers. The measurements by AFM and Kelvin probe force microscopy on LaVO3 have clearly shown that it is a poor charge-transport medium, thus not suitable for photovoltaic applications. The analysis on InGaN and AlGaInN by SPV measurements has shown how low In content, Si doping and no misfit dislocations in InGaN/GaN structure cause less recombination processes at the interface, whereas, the strain relaxation (tensile and compressive) with the formation of pinholes produces better interfaces in the AlGaInN/GaN samples.