This thesis presents experimental work developing silicon nanocrystal based light emitting devices for silicon photonics. The chapters are organized as follows: In chapter 2, fabrication and characterization of silicon nanocrystal based devices are presented. In collaboration with Intel Corporation and Bruno Kessler Foundation and thanks to the support of European Commission through the project No. ICT-FP7-224312 HELIOS and through the project No. ICT-FP7-248909 LIMA, it is shown that layers and devices containing silicon nanocrystals can be formed in a production silicon-fab on 4 and 8 inch silicon substrates via PECVD and subsequent thermal annealing. Devices produced by single layer and multilayer deposition are studied and compared in terms of structural properties, conduction mechanisms and electroluminescence properties. Power efficiency is evaluated and studied in order to understand the relation between exciton recombination and electrical conduction. A band gap engineering method is proposed in order to better control carrier injection and light emission in order to enhance the electroluminescence power efficiency. In chapter 3, the power efficiency of silicon nanocrystal light-emitting devices is studied in alternating current regime. An experimental method based on impedance spectroscopy is proposed and an electrical model based on the constant phase element (CPE) is derived. It is, then, given a physical interpretation of the electrical model proposed by considering the disordered composition of the active material. The electrical model is further generalized for many kinds of waveforms applied and it is generalized for the direct current regime. At the end, time-resolved electroluminescence and carrier injection in alternate current regime are presented. In chapter 4, erbium implanted silicon rich oxide based devices are presented. The investigation of opto-electrical properties of LED in direct current and alternate current regime are studied in order to understand the injection mechanism and estimate the energy transfer between silicon nanocrystals and erbium. At the end a device layout and process flow for an erbium doped silicon nanocrystal based laser structure are shown. In chapter 5, some other applications of silicon nanocrystal are presented. An example of all-silicon solar cell is shown. The photovoltaic properties and carrier transport of silicon nanocrystal based solar are studied. At the end, the combination of emitting and absorbing properties of silicon nanocrystal based LED are used to develop an all-silicon based optical transceiver.

Porous silicon (Psi) and nanocellulose (NC) hydrogels are nanostructured materials with several properties that make them promising for drug delivery applications. In this work, Î2-carotene (BC) and clofazimine (CFZ) are used as model molecules to investigate the physical and chemical processes governing the interactions of hydrophobic molecules with both inorganic (Psi) and organic (NC) nanostructured carriers. Despite the large number of advantages, Psi does not perform well as carrier for BC, since it stimulates the molecule degradation even if its surface is carefully passivated. Furthermore, during the release experiments, BC tends to nucleate on Psi surface forming aggregates whose dissolution is much slower than the BC molecules release, thus they negatively impact on the control over the drug release. On the other hand NC hydrogels do not pose heavy issues to the release of lipophilic drugs, provided that a suitable surfactant (either Tween-20 or Tween-80) mediates the molecule solvation and its subsequent release into aqueous media. Moreover, NC gels protect BC from degradation much better than its storage in freezer or in organic solvent, making these carriers interesting for DD.

This thesis work presents the results of experimental studies on the gas transport properties of three polymer-based membrane systems: (i) amine-modified epoxy resins, (ii) epoxy resin nanocomposites containing Few Layer Graphene (FLG) nanoplatelets as dispersed fillers and (iii) nanocellulose-based membranes. The gas transport properties of the present membrane systems were studied by gas phase permeation techniques changing sample temperature and penetrant molecules; results were discussed in the framework of the free volume theory of diffusion, using information on the samples’ free volume structure as experimentally obtained by Positron Annihilation Lifetime Spectroscopy (PALS). Results evidenced that the transport properties of small penetrant molecules are controlled by the membranes’ free volume structure, which determines, in fact, the penetrant diffusion kinetics. The free volume of epoxy resins was changed by changing their crosslink density but maintaining same chemical environment for penetrant molecules: it was observed that, reducing the free volume structure, the gas diffusivity decreases but no relevant changes in the gas solubility occurred. The experimentally obtained fractional free volume values permitted to reproduce the measured diffusivity values and their variation with temperature, using equations provided by the free volume theory of diffusion. Increasing the amount of FLG fillers in epoxy-based nanocomposites, we observed a progressive gas permeability decrease, which was accompanied by a progressive reduction of their free volume. This correlation was attributed to the formation of constrained, gas-impermeable polymer regions at the filler-matrix interfaces. The thickness of these regions was evaluated by the reduction of the nanocomposites’ fractional free volume with respect to the free volume of the pure polymer matrix; its value permits to reproduce quantitatively the experimental permeation data of the nanocomposites at all examined temperatures, filler concentrations and test gases. Few micrometers thick nanocellulose films deposited on polylactic acid substrates act as impermeable barriers for CO2, O2, and N2 and reduce the D2 (deuterium) and He permeation flux by a factor of approx. 10^3. Penetrant transport through this biopolymer is controlled by the solution-diffusion mechanism and barrier properties are due to the extremely low penetrant diffusivity. The free volume in the nanocellulose coatings consists of interconnected elongated cavities with sub-nanometer cross-sectional size where the selective transport of the small size penetrants is due to sieving effects. D2 and He diffusion has thermally activated character and occurs in configurational regime.

Optical biosensors, and in particular label-free optical biosensors have become one of the most active and attractive fields within the biosensing devices. The portability and the possibility to set free from the laboratory settings gave a new hint for integrated photonic biosensors development and use in numerous applications. Integrated photonic sensors have shown very promising results, and in particular, devices like WGM resonators and interferometers are showing high sensitivities and miniaturization abilities, which allow the realization of an integrated complete lab-on-chip device. The main goal of this thesis is the development of an optical biosensor for the fast and comprehensive detection of carcinogenic Aflatoxin M1 (AFM1) mycotoxin. The acceptable maximum level of AFM1 in milk according to European Union regulations is 50 ng/L equivalent to 152 pM for the adults and 25 ng/L equivalent to 76 pM for the infants, respectively. Within a European Project named SYMPHONY, we develop an integrated silicon-photonic biosensor based on the optical microring resonators (MRR) and the asymmetric Mach-Zehnder Interferometers (aMZI). The sensing is performed by measuring the resonance wavelength shift in the MRR transmission or the phase shift of aMZI caused by the binding of the analyte to the ligand immobilized on the sensor surface. The experimental characterization of the bulk refractometric sensing of the devices is performed in a continuous flow. This characterization assesses the high resolution of both device types, which are able to resolve variations in the refractive index of the liquids with a limit of detection down to 10E-6 refractive index units (RIU). Furthermore, the SYMPHONY sensor optimization based on the Fab' and DNA-aptamer functionalization strategies is realized. It is therefore demonstrated, that the Fab' functionalization strategy provides more reproducible results with respect to the DNA-aptamer one. However, for both strategies, the specificity of the sensor functionalization to detect AFM1 molecules is achieved with respect to non-specific Ochratoxin molecules at high concentrations. In the final stage of the SYMPHONY project, the Fab'-based functionalized aMZI sensor is tested with real milk samples (eluates) prepared in the SYMPHONY system that consists of the three main modules: the defatting module, the concentrator module and the sensor module. The system calibration yields the minimum concentration of AFM1 at 40 pM to be detectable. The detection of the ligand-analyte binding in real-time enabled the study of the kinetics of the binding reaction, and we measured for the first time the kinetic rate constants of the Fab'-AFM1 interaction with our sensors. Finally, a MRR based affinity biosensor is developed dedicated to the biotinylated BSA - anti-biotin binding study. An affinity constant of 10E6 1/M is measured. The sensor is successfully regenerated up to eight times by applying a longer incubation period.

X-ray photon correlation is used to probe the dynamics of the strong glass former boron trioxide and of a series of alkali borate glasses, (M2O)x(B2O3)1-x where M is the alkali modifier (M=Li, Na and K). The decay times τ of the obtained correlation functions in B2O3 are consistent with visible light scattering results and independent of the incoming beam intensity in the undercooled liquid phase; are instead temperature independent and show a definite dependence on the X-ray beam intensity in the glass. We are therefore witnessing an atomic dynamics induced by the X-ray beam. Furthermore, we clearly demonstrate that the value of τ is related to absorption by investigating a series of alkali borate glass with the same molar ratio and as a function of the alkali modifier. Finally, we highlight the role played by the structure in the X-ray induced dynamics by studying a series of lithium borate glasses with different molar ratios, and by investigating the wave vector dependence. Despite the observed dynamics is clearly intensity dependent, we obtain very interesting information on glasses not available with other experimental techniques.

In this thesis, second order optical nonlinearities in silicon waveguides are studied. At the beginning, the strained silicon platform is investigated in detail. In recent years, second order nonlinearities have been demonstrated on this platform. However, the origin of these nonlinearities was not clear. This thesis offers a clear answer to this question, demonstrating that this nonlinearity does not originate on the applied strain, but on the presence of trapped charges that induce a static electric field inside the waveguide. Based on this outcome, a way to induce larger electric fields in silicon waveguide is studied. Using lateral p-n junctions, strong electric fields are introduced in the waveguides, demonstrating both electro-optic effects and second-harmonic generation. These results, together with a detailed modeling of the system, pave the way through the demonstration of spontaneous parametric down-conversion in silicon.

High order waveguide modes are nowadays of great interest for the development of new functionalities in photonics. Because of this, efficient mode couplers are required. In this thesis a new strategy for mode coupling is investigated, based on the interference arising from two coherent tilted beams superimposed in a star-coupler. Handling the high order modes allows to explore new processes within the photonics platform, as the intermodal four wave mixing. Intermodal four wave mixing is a new nonlinear optical process in waveguide, and it is here demonstrated on a silicon chip. Via intermodal four wave mixing it is possible to achieve a large and tunable frequency conversion, with the generation of photons spanning from the near to the mid infrared. The broadband operation of this process is of interest for the field of quantum photonics. Single photon sources are the main building block of quantum applications, and they need to be pure and efficient. Via intermodal four wave mixing, it is here demonstrated the generation of single photons above 2000 nm heralded by the idler at 1260 nm. Thanks to the discrete band phase matching of this nonlinear process, high purity single photons without narrow band spectral filters are demonstrated. Intermodal four wave mixing enables a new class of classical and quantum sources, with unprecedent flexibility and spectral tunability. This process is particularly useful for the developing field of mid infrared photonics, where a viable integrated source of light is still missing.

The NEXT experiment is one of the most innovative ones looking for the neutrinoless double beta decay, which finding will answer one of the most important questions in the last years physics: is the neutrino its own antiparticle? Or in other words, is it a Majorana particle? With that purpose NEXT uses a TPC (Time Projection Chamber) filled with enriched xenon gas at high pressure, and two photosensors planes, one on each end. The first plane contains PMTs (PhotoMultiplier Tube), that collect the light emitted by the xenon when an event happens and precisely measures its energy. The second plane is a SiPM (Silicon PhotoMultiplier) matrix that allows to 3D-reconstruct the event track. Both planes together allows NEXT to have a great background rejection, which makes a difference with the other experiments aiming for the neutrinoless double beta decay. In addition, SiPMs are a new technology which nowadays is evolving to, in the future, displace the classical PMTs. For that reason the study of these sensors starts from zero, as there were not previous uses as pixel-tracking, and lead a new path in the physics detectors, for both high and low energy. This thesis is focused on the study and design of the electronics involving the tracking plane, which includes some technical solutions related also with mechanical issues. From the sensors placed inside the detector, the SiPMs, to the front-end electronic boards, there are few elements on the chain; as the support boards for the SiPMs which must satisfy severe outgassing and radiopurity levels. Also the inner and outer cabling has been designed, focusing on obtaining the best signal-noise ratio; and also the feedthrough for the tracking plane, which solved at low cost the huge problem of taking out about 4000 lines from the pressurized xenon to the outside. Finally, one of the most important elements on this chain and the one that this thesis is focused on, is the front-end board. Starting with the experience acquired with the first prototype, NEXT-DEMO, the electronics have been improved, able to condition, integrate and digitize the signals from all the tracking plane SiPMs; allowing the further acquisition and processing through an ATCA-based system (Advanced Telecommunications Computing Architecture). All the elements designed have been produced and assembled on the NEW detector, a large-scale prototype of the final detector, placed at the Laboratorio Subterra'neo de Canfranc, an underground laboratory at the aragonese Pyrenee. / El experimento NEXT es uno de los más innovadores en la búsqueda de la desintegración doble beta sin neutrinos, cuyo hallazgo daría con la respuesta a una de las cuestiones más importantes de la física en los últimos años: ¿es el neutrino su propia antipartícula? O dicho de otro modo, ¿es una partícula de Majorana? Para ello NEXT hace uso de una TPC (Time Projection Chamber) llena de gas xenón enriquecido a alta presión, y con dos planos de fotosensores, uno en cada extremo. El primero de ellos está formado por PMTs (Photo Multiplier Tube), que recogen la luz generada por el xenón cuando ocurre un evento, y miden la energía de éste. El segundo consiste en una matriz de SiPMs (Silicon PhotoMultipliers) que permiten reconstruir tridimensionalmente la traza de dicho evento. El conjunto de ambos planos de fotosensores otorga al experimento NEXT un gran rechazo a eventos de fondo, lo que marca la diferencia con otros experimentos en busca de la desintegración doble beta sin neutrinos. Además, los SiPMs son una tecnoloía de reciente aparición que en la actualidad está evolucionando a grandes pasos para, en un futuro, desplazar a los fotomultiplicadores clásicos. Por ello el estudio de estos fotosensores parte prácticamente desde cero, ya que no existen aplicaciones previas de su uso como pixel-tracking, y ha permitido abrir un nuevo camino en los detectores de física, tanto de alta como baja energía. Esta tesis doctoral tiene como objetivo el estudio y diseño de la electrónica involucrada en el plano de reconstrucción de trazas, y que involucran en menor medida dar solución a problemas técnicos de aspecto mecánico. Partiendo de los sensores ubicados dentro del detector, los SiPMs, hasta las tarjetas de front-end, se incluyen varios elementos de la cadena; como son las tarjetas empleadas como soporte para los SiPM en el interior de la cámara, las cuáles deben cumplir rigurosas medidas de radiopureza y degasificación. También se ha diseñado el cableado tanto interno como externo, haciendo énfasis en conseguir la mayor relación posible señal-ruido; y el pasamuros específico para el plano de reconstrucción de trazas, el cual ha resuelto a bajo coste el problema de extraer casi 4000 líneas desde la zona de xenón a alta presión hasta el exterior. Por último, uno de los elementos más importantes de esta cadena y en el cuál se centra principalmente esta tesis, es la tarjeta de front-end. Partiendo de la experiencia adquirida del primer prototipo del experimento, NEXT-DEMO, se ha perfeccionado una electrónica capaz de tratar, integrar y adquirir las señales de todos los SiPM del plano de reconstrucción de trazas, permitiendo su posterior adquisición y procesado mediante un sistema basado en la estructura ATCA (Advanced Telecommunications Computing Architecture). Todos los elementos diseñados han sido ensamblados y puestos en marcha en el detector NEW, un prototipo a gran escala del detector final, que está ubicado en el Laboratorio Subterráneo de Canfranc, en el Pirineo Aragonés. / L'experiment NEXT és un dels més innovadors en la recerca de la desintegració doble beta sense neutrins, i aquesta troballa donaria amb la resposta a una de les quèstions més importants de la física en els últims anys: és el neutrí la seua pròpia antipartícula? O dit d'una altra manera, és una partícula de Majorana? Per açò NEXT fa ús d'una TPC (Time Projection Chamber) plena de gas xenó enriquit a alta presió, i amb dos plànols de fotosensors, un a cada extrem. El primer d'ells està format per PMTs (Photo Multiplier Tube), que arrepleguen la llum generada pel xenó quan ocorre un esdeveniment, i mesuren l'energía d'aquest. El segon consisteix en una matriu de SiPMs (Silicon PhotoMultipliers) que permeten reconstruir tridimensionalment la traça d'aquest esdeveniment. El conjunt de tots dos plànols de fotosensors atorga a l'experiment NEXT un gran rebuig a esdeveniments de fons, la qual cosa marca la diferència amb altres experiments a la recerca de la desintegració doble beta sense neutrins. A més, els SiPMs so'n una tecnología de recent aparició que en l'actualitat està evolucionant a grans passos per a, en un futur, desplaçar als fotomultiplicadors clàssics. Per això l'estudi d'aquests fotosensors part pràcticament des de zero, ja que no hi ha aplicacions prèvies del seu ús com a pixel-tracking, i ha permés obrir un nou camí en els detectors de física, tant d'alta com de baixa energia. Aquesta tesi doctoral té com a objectiu l'estudi i diseny de l'electrònica involucrada en el plànol de reconstrucció de traces, i que involucra en menor mesura donar solució a problemes tècnics d'aspecte mecànic. Partint dels sensors situats dins del detector, els SiPMs, fins a les targetes de front-end, s'inclouen diversos elements de la cadena; com són les targetes emprades com a suport per als SiPMs a l'interior de la càmera, les quals han de complir rigoroses mesures de radioactivitat i degasificació. També s'ha disenyat el cablejat tant intern com extern, fent èmfasi en aconseguir la major relació possible senyal-soroll; i el passamurs específic per al plànol de reconstrucció de traces, el qual ha resolt a baix cost el problema d'extraure quasi 4000 línies des de la zona de xenó a alta presió fins a l'exterior. Finalment, un dels elements més importants d'aquesta cadena i en el qual es centra principalment aquesta tesi, és la targeta de front-end. Partint de l'experiència adquirida del primer prototip de l'experiment, NEXT-DEMO, s'ha perfeccionat una electrònica capaç de tractar, integrar i adquirir les senyals de tots els SiPM del plànol de reconstrucció de traces, permetent la seua posterior adquisició i processament mitjançant un sistema basat en l'estructura ATCA (Advanced Telecommunications Computing Architecture). Tots els elements disenyats han sigut muntats i engegats en el detector NEW, un prototip a gran escala del detector final, que està situat en el Laboratorio Subterráneo de Canfranc, al Pirineu Aragonés. / Rodríguez Samaniego, J. (2017). Study and design of the front-end and readout electronics for the tracking plane in the NEXT experiment [Tesis doctoral]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/86285

This thesis deals with the study of the yarn interlacing. The interlacing process is commonly employed by textile industries to impart cohesion points to a multi-filament yarn. Indeed, this work has been realized in the framework of a collaboration between the Department of Physics of the University of Trento (Italy) and Aquafil S.p.A., a company producing Nylon 6 yarn. The interlacing of the filaments into periodic knots is caused by their interaction with a turbolent flow, but the full dynamics is not well characterized. Additionally, one problem that textile industries need to face is the irregularity of the process, still difficult to improve. A regular knots distance is required to ensure the homogeneous appearance of the final fabric. Hence, it is interesting to understand which are the key parameters affecting and influencing interlacing, to improve its regularity. For this reason, the present work focuses on a deeper understanding of the process dynamics. Then, different on-line sensing techniques that measure the knots distance are investigated and compared. The evaluation of the process regularity during yarn production allows, as a further step, to change the machine parameters on-line, avoiding waste of time and material. In Chapter 1 is given the background knowledge about the yarn production process, starting from the raw material. The attention will be focused on interlacing, with an overview of the state of the art literature on that topic. In Chapter 2 the yarn-air interaction is investigated, with a high speed analysis of the yarn motion in an interlacer. A dynamics of interlacing is proposed, indicating the key role played by the turbolent pattern, observed by means of a tracer. Chapter 3 studies the vibrations close to the interlacer, to monitor a possible flow modulation caused by the yarn-air interaction. In Chapter 4 and Chapter 5 two sensing techniques have been approached, based on the use of a microphone and a photodiode. The issues related to those measurements have been investigated, for a final comparison of their performance in terms of capability of detecting the cohesion points distance on-line, on a running yarn.

Microresonators are fundamental building blocks in the growing field of integrated photonics and several resonator-based devices such as filters, switches and routers are currently used in common optical telecommunication networks. In order to exploit the peculiar features offered by integrated resonators, a complete and consistent comprehension of their physics and of the processes they can accommodate is needed. More specifically, coupling of light to and from a resonator represents a crucial point: a correct comprehension of the coupling dynamics, a proper model for the system and its validation through experimental procedure are all essential elements for a fruitful exploitation of the device. Among the different resonator-waveguide coupling schemes, the most widely used is the in-plane coupling and it consists of a waveguide placed near to a microresonator and laying on the same plane. However, an alternative approach is represented by the vertical coupling scheme, where the waveguide lays under the resonator edge. The peculiar position of the waveguide in this last configuration causes the device to show specific properties not present in other common coupling schemes: namely, a working range spanning from almost visible wavelengths (780nm) to the near IR domain (1600nm), the selective excitation of high order resonator radial modes and the possibility to fabricate wedge and free-standing resonators without any detrimental effect on the bus waveguide. In order to fully exploit these and other features of the vertical coupling scheme, a detailed investigation has been carried out throughout this thesis. The waveguide-microresonator system has been studied at different levels, from the general coupling dynamics to more specific and peculiar phenomena. In particular, the basic model proposed for the vertical coupling has been extended to consider wavelength dependences and an experimental validation has been carried out consequently. The reactive coupling model, which describes the internal dynamics of a vertically coupled resonator in the case of multimodal operation, has been experimentally proven. A general model considering the presence counterpropagating modes has been theoretically proposed and experimentally investigated. Finally, the bistable behaviour generated by thermo-optic effect when a large amount of power circulates in the microresonator has been experimentally studied. In order to better characterize the system response, a specific interferometric setup has been implemented. It consists in a Mach-Zehnder computer driven interferometer, whose peculiar characteristic is the ability to perform simultaneous pump and probe transmittance and phase measurements of any integrated photonic device provided with input and output ports. In this way, the information carried by the phase of the propagating optical signal is added to the one provided by its intensity and contributes to produce a more complete picture of the investigated system. In the case of microresonators this phase information becomes even more fundamental. Indeed, the phase response of a resonating structure is highly influenced by variations in the coupling strength, and the phase spectrum of a single resonance allows to clearly identify the resonator coupling regime for that specific resonance. This fact does not hold in the case of transmittance measurements, where single resonance spectrum carries information only on the total losses of the system. Finally, in order to exploit the combined information provided by this measurement procedure, a phasor plot representation is extensively used throughout the thesis work.