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Esponges, Esponjas, Sponges, Ecologia marina, Ecología marina, Marine ecology, Silici, Silicio, Silicon, and Ciències Experimentals i Matemàtiques

Silicon (Si), in its dissolved form of silicic acid (DSi), is a key nutrient in the ocean. The availability of such nutrient in marine ecosystems is regulated through its use by silica-secreting organisms, a variety of groups including protists, algae, and animals that consume DSi to build their silica (BSi) skeletons. The interest in determining how Si cycles in the ocean is high, since it interacts with the cycling of other major nutrients and ocean primary productivity. Because diatoms are the most abundant Si users, the scientific attempts to quantify the Si utilization in the ocean have been only focused on these organisms, considering negligible the role of other Si users. Over the last decades, some studies have suggested that at least another group, the siliceous sponges, are also playing a non-negligible role in the consumption of Si in marine ecosystems. Marine sponges are conspicuous animals in benthic ecosystems. They are common across the world ocean, irrespective of the latitude and depth, being able to form enormous aggregations that may extend over large areas. Both their ubiquity and their abundance make sponges good candidates to develop relevant functional roles in marine ecosystems. Regarding the use of Si, it is surprising that, despite about 80% of the sponge species require from DSi to elaborate their skeleton, almost no information is available about how sponges consume such nutrient. In fact, before the beginning of this PhD, only few studies had investigated DSi consumption in marine sponges, with kinetic models available for only four species in two genera of demosponges. This lack of knowledge sparked this PhD, which has been developed in the frame of three research grants: 1) “A research action to quantify fluxes and sinks of silicon through sponges: a neglected circuit within the marine cycle” (MEC–CTM2012-37787); 2) “Exploring the biological production of silica and its applications in science and technology” (MINECO-CTM2015-67221- R); and 3) WP4 —Ecosystem functions, services, and goods— in the EU’s project SponGES (H2020-No. 679849). The main objective of the work was to improve the general understanding on how sponges utilize DSi, to facilitate further assessment of the quantitative role of the sponges as Si users. Here we investigated the kinetics of DSi consumption in five sponge species: four temperate, shallow-water demosponges and, for the first time, a cold, deep-water hexactinellid sponge. We also examined the sources of between-species and between-individual variability in DSi consumption responses. Interestingly, we detected that DSi consumption kinetics can change seasonally in some species, what may have important implications when quantifying the role of sponges as Si users. Additionally, we determined for the first time the rate of DSi utilization by a sponge species in situ. The results significantly matched those estimated from the kinetic models obtained in the laboratory, supporting the use of long (>24h) incubations in laboratory to investigate DSi consumption kinetics in sponges, in contrast to the very short periods traditionally recommended for diatoms (< 3h). Finally, we used the empirically information gained on DSi consumption over the development of this PhD to estimate the utilization of DSi by a sponge assemblage at the ecosystem level, using as case study the bay of Brest (France). In summary, this research showed that sponges have a noticeable role as Si users, even in a shallow-water ecosystem (the bay of Brest) where diatoms largely contribute to the phytoplankton biomass. Our results also indicated that sponges increase their role in marine ecosystems with increasing availability of DSi in seawater. Thus, sponges are predicted to play a relevant role as Si users in high-latitude and deep-water habitats, characterized by high DSi availability. All together, the siliceous sponges should be considered as Si users if we aim to accurately quantify the cycling of Si in marine ecosystems.

Silici, Silicio, Silicon, Detectors de física d'altres energies, Detectores de física de altas energias, High energy particle detectors, and Ciències Experimentals

Aquesta tesi tracta el desenvolupament de detectors de silici de tecnologia avançada per experiments de Física d'Altes Energies (HEP en anglès). La mida dels detectors de silici per determinar traces en experiments de HEP ha de disminuïr per millorar la resolució espacial en les mesures i millorar l'ocupancia en l'electrònica. Els experiments al CERN hauran de funcionar amb fluencies de fins a 2·10 16 n eq 1cm2 , i els detectors de silici més petits tindran menys atrapament de les parelles electró-forat generats al volum, que porta a un millor comportament sota un medi amb alts nivells de radiació. Aquesta tesi estudia detectors de silici fabricats al CNM-Barcelona per aplicacions de HEP amb dos tipus d'arquitectura nou: 3D i detectors d'allau amb guany moderat (LGAD en anglès). Els detectors 3D afavoreixen la reducció de la mida de la regió buidada dins del detector i permet treballar a voltatges més baixos, mentres que els detectors LGAD tenen guany intern que incrementa la senyal col·leccionada amb un mecanisme de multiplicació. El capítol 1 introdueix els detectors de silici aplicats a HEP. Els capítols 2 i 3 exploren els dissenys de detectors 3D de silici fabricats al CNM-Barcelona. Els detectors 3D de silici van ser introduïts per primera vegada a un experiment de HEP durant el 2013 per una nova capa del experiment ATLAS, la Insertable B-Layer (IBL), i alguns d'aquests detectors han sigut caracteritzats durant aquest treball. Actualment, detectors 3D de silici amb dimensions de píxel més petites seran operatius per noves posades a punt de l'ATLAS, i aquests detectors s'han simulat en aquest treball. El capítol 4 està dedicat a detectors LGAD segmentats i fabricats en oblies epitaxials amb la intenció de disminuïr el gruix dels detectors i augmentar la càrrega col·leccionada amb el mecanisme de multiplicació. Aquesta tesi mostra simulacions tecnològiques, el procés de fabricació, simulació elèctrica i caracterització elèctrica i de càrrega d'aquests detectors.

Electrònica, Electrónica, Electronics, Semiconductors, Semiconductores, Silici, Silicio, Silicon, Nitrurs, Nitruros, Nitrides, Espectroscòpia de pèrdua d'energia d'electrons, Espectroscopía por pérdidas de energía de electrones, Electron energy loss spectroscopy, and Ciències Experimentals i Matemàtiques

This thesis explores the analytical capabilities of low-loss electron energy loss spectroscopy (EELS), applied to disentangle the intimate configuration of advanced semiconductor heterostructures. Modern aberration corrected scanning transmission electron microscopy (STEM) allows extracting spectroscopic information from extremely constrained areas, down to atomic resolution. Because of this, EELS is becoming increasingly popular for the examination of novel semiconductor devices, as the characteristic size of their constituent structures shrinks. Energy-loss spectra contain a high amount of information, and since the electron beam undergoes well-known inelastic scattering processes, we can trace the features in these spectra down to elementary excitations in the atomic electronic configuration. In Chapter 1, the general theoretical framework for low-loss EELS is described. This formulation, the dielectric model of inelastic scattering, takes into account the electrodynamic properties of the fast electron beam and the quantum mechanical description of the materials. Low-loss EELS features are originated both from collective mode (plasmons) and single electron excitations (e.g. band gap), that contain relevant chemical and structural information. The nature of these excitations and the inelastic processes involved has to be taken into account in order to analyze experimental data or to perform simulations. The computational tools required to perform these tasks are presented in Chapter 2. Among them, calibration, deconvolution and Kramers-Kronig analysis (KKA) of the spectrum constitute the most relevant procedures, that ultimately help obtain the dielectric information in the form of a complex dielectric function (CDF). This information may be then compared to the one obtained by optical techniques or with the results from simulations. Additional techniques are explained, focusing first on multivariate analysis (MVA) algorithms that exploit the hyperspectral acquisition of EELS, i.e. spectrum imaging (SI) modes. Finally, an introduction to the density functional theory (DFT) simulations of the energy-loss spectrum is given. In Chapter 3, DFT simulations concerning (Al, Ga, In)N binary and ternary compounds are introduced. The prediction of properties observed in low-loss EELS of these semiconductor materials, such as the band gap energy, is improved in these calculations. Moreover, a super-cell approach allows to obtain the composition dependence of both band gap and plasmon energies from the theoretical dielectric response coefficients of ternary alloys. These results are exploited in the two following chapters, in which we experimentally probe structures based on group-III nitride binary and ternary compounds. In Chapter 4, two distributed Bragg reflector structures are examined (based upon AlN/GaN and InAlN/GaN multilayers, respectively) through different strategies for the characterization of composition from plasmon energy shift. Moreover; HAADF image simulation is used to corroborate he obtained results; plasmon width, band gap energy and other features are measured; and, KKA is performed to obtain the CDF of GaN. In Chapter 5, a multiple InGaN quantum well (QW) structure is examined. In these QWs (indium rich layers of a few nanometers in width), we carry out an analysis of the energy-loss spectrum taking into account delocalization and quantum confinement effects. We propose useful alternatives complementary to the study of plasmon energy, using KKA of the spectrum. Chapters 6 and 7 deal with the analysis of structures that present pure silicon-nanocrystals (Si-NCs) embedded in silicon-based dielectric matrices. Our aim is to study the properties of these nanoparticles individually, but the measured low-loss spectrum always contains mixed signatures from the embedding matrix as well. In this scenario, Chapter 6 proposes the most straightforward solution; using a model-based fit that contains two peaks. Using this strategy, the Si-NCs embedded in an Er-doped SiO2 layer are characterized. Another strategy, presented in Chapter 7, uses computer-vision tools and MVA algorithms in low-loss EELS-SIs to separate the signature spectra of the Si-NCs. The advantages and drawbacks of this technique are revealed through its application to three different matrices (SiO2, Si3N4 and SiC). Moreover, the application of KKA to the MVA results is demonstrated, which allows to extract CDFs for the Si-NCs and surrounding matrices.

Cèl·lules solars, Células solares, Solar cells, Silici, Silicio, Silicon, Pel·lícules fines, Películas delgadas, Thin films, and Ciències Experimentals i Matemàtiques

The objective of this work was to study two different light management approaches to enhance the efficiency of thin film Si solar cells and these were the manipulation of the light path (light trapping) and changing the incoming photon energy (upconversion). In the first approach the light path was manipulated by creating either periodic or random textured interfaces. Periodic patterns were created at the front AZO by means of direct laser ablation. Amongst all the patterns assessed, the best result was achieved with a linear pattern of 10 lam of pitch and 360 nm of groove depth, that yielded to an Rs of 11 SI/sq and a haze of 12.7% at 600 nm. However structures in the sub-micrometer range cannot be created because the minimum period is limited by the laser spot. By means of the Aluminum Induced Texturing method (AIT) random textures were performed on glass substrates. In this method, a thin Al film is deposited onto a glass substrate and a redox reaction between the Al and the SiO2 of the glass is induced by high temperature annealing. The reaction products are wet-etched and the result is a uniform and rough glass surface. The process parameters were varied in order to control the resultant glass roughness and it was found that the most critical was the Al deposition method. By using evaporation smooth U-shaped craters morphology and roughness up to 90 nm were created, whereas the sputtered films resulted in rough and porous textures with roughness until 145 nm. AZO grown over the U-shape crater morphology led to a double texture with haze values above 10% at 600 nm, transparency above 84%, and Rs-7 SI/sq whereas AZO over very rough glass resulted in a cauliflower-like surface with haze values >32% at 600 nm, Rs around 9.5 SI/sq and transmittance of 74%. A-Si:H solar cells were deposited on different AIT textures and an improvement of the short circuit current, as well as a reduction of the device reflectivity was achieved in all cases in comparison to the cells deposited on smooth glass textures. The second approach was to create a transparent and conducting upconverter to be used on top of the rear reflector of a thin film Si solar cell. For that purpose, ZnO was doped with Er and Yb ions and was post-annealed under different treatments. The unique spectral properties of rare earth (RE) elements due to their electronic configuration occur as a result of their intra 4f-4f shell transitions. In the case of Er, its excitation takes places at 1500 nm and 980 nm and the upconverted photons are emitted within the Si absorption range. Moreover, codoping with Yb can enhance the Er visible emission because they cooperate together due to the matching of their energy levels for k=980 nm. As deposited ZnO doped with rare earths (RE) was found to be transparent and conducting but not luminescent. RE ions need to be surrounded by 6 oxygen in a distorted octahedron to be optically active and REs replacing zinc in the ZnO lattice do not present this symmetry; hence, a post deposition treatment is needed. When the films were post-annealed in air, visible upconversion (UC) was seen at 660 nm under 980 nm laser excitation, however, the films become almost insulating. When the films were annealed in vacuum, lower UC luminescence was achieved, and the resistivity increased 1 order of magnitude. By using CW laser radiation, the electrical properties were maintained and high UC was observed. UC came from clusters of RE06 as well as from RE203 inside or outside the matrix. When annealing in air, in vacuum or by laser radiation, oxygen from the atmosphere bound to the RE to form RE oxides and/or RE06 complexes but just laser annealing was able to preserve the conductivity while producing optically active centers.

Electrònica, Electrónica, Electronics, Transport d'electrons, Transporte de electrones, Electron transport, Luminescència, Luminiscencia, Luminescence, Fotònica, Fotónica, Photonics, Silici, Silicio, Silicon, Terres rares, Tierras raras, Rare earths, and Ciències Experimentals i Matemàtiques

This thesis presents the work carried out towards the implementation of RE-doped Si-based light emitting devices as integrated optoelectronic building blocks for Silicon Photonics. This work spans from the fundamentals such as the structure, the morphology of active layers containing Si-ncs and/or RE ions or the origin of the EL emission under different voltage excitations, to the development of advanced Si-based light emitting devices, providing insights on the device design, mask layout, device fabrication and the optoelectronic characterization. Also, novel layer architectures are proposed to overcome some of the inherent limitations of studied devices, paving the way towards efficient and reliable Si-based light emitting devices. This thesis is divided in two main blocks: one dedicated to the study of Er-doped Si-based light emitting devices emitting at 1.54 µm for on-chip optical data routing, and another one focussed on the structural and luminescence properties of Tb3+ and Ce3+ doped silicon oxide and oxynitride thin films with different layer compositions as enabling materials for sensing and RGB micro display applications. Also, different multilayer architectures containing alternated RE-doped single layers are explored.

Nanoelectrònica, Nanoelectrónica, Nanoelectronics, Nanoestructures, Nanoestructuras, Nanostructures, Fotònica, Fotónica, Photonics, Silici, Silicio, Silicon, Metall-òxid-semiconductors complementaris, Semiconductores de metal-óxido complementarios, Complementary metal oxide semiconductors, and Ciències Experimentals i Matemàtiques

This project presents the study of luminescent devices and materials based on silicon for its use in the fabrication of an optical system that integrates light emitter, waveguide, and light sensor in a single chip obtained by the use of standard CMOS techniques and materials. The atomic and structural characteristics of the materials are analysed and related to its luminescent response. Taking into account the results from the active material characterization, the design, fabrication, and characterization of electroluminescent devices based on such materials is presented. Finally, the design, fabrication and characterization of a complete CMOS compatible Integrated Optical System consisting of a transceiver, is discussed and analysed. The active materials used for light emission were different Silicon Rich Silicon Dioxide(SRO) and SRO-Si3 N4 bi-layers, obtained by a variety of CMOS compatible techniques and fabrication parameters. Two contributing mechanisms to photoluminescence in SRO were identified in all cases, respectively linked to the presence of radiative defects, and to Quantum Confinement phenomena. It is proposed and tested a model to describe the latter, based on the effective mass approximation, and the relation between the amount of Si-Si links and the volume of nano-agglomerates present in the material. In bi-layer samples, an additional luminescence band was observed, found to be generated in the transition material between silicon nitride and dioxide, and related to energy states introduced by defects. Samples with SRO thickness ten times higher than that of nitride, presented a clear dominance of the photoluminescence related to the dioxide. The centres responsible for electroluminescence in the electronicd evices were found to be fundamentally the same as those for photoluminescence despite the differences in measured spectra, and it was concluded that the influence of the architecture on the light output is of significant importance. It was shown that bi-layered devices delivered better results in terms of efficiency, light emission control, distribution and stability. The carrier transport mechanisms observed in the devices were dominated by material breakdown in single-layered devices, and Trap-assisted Tunnelling in the bi-layers. The Optical System integrating the light emitter, a waveguide, and a light detector, was designed and fabricated based on the results from the fabrication and analysis of the stand alone light emitting devices. During the design stage, it was corroborated by computer simulations that the characteristics of thelight emittedby thedevices thatpresented thehighest e.ciency and reliability, were suitable for its transmission trough the pro­posed waveguide architecture. The detection capabilities of the designed light sensors were also theoretically corroborated to be appropriated for the detection of the emitted light type. The proper functioning of the elements conforming the finally fabricated system was probed. Differences were found in the operation of the stand alone light emitting devices and those integrated, but the resulting luminescence was within the boundaries of the transmittable spectrum. The operation of the Integrated Optical System was tested and preliminarily studied, obtaining positive results in its stimulus-detection response, fulfilling the main objective of the work, and opening the door for further studies which can lead to the optimization of the design for particular applications.

Electrònica, Electrónica, Electronics, Fotònica, Fotónica, Photonics, Luminescència, Luminiscencia, Luminescence, Nanoestructures, Nanoestructuras, Nanostructures, Silici, Silicio, Silicon, Light-emitting diode (LED), Díode emissor de llum (LED), Led, and Ciències Experimentals i Matemàtiques

This thesis presents experimental work on developing rare-earth ions and Si nanostructures as a material platform for light emitting devices (LEDs) in the visible and near-infrared range. The realization of the different electroluminescent devices, based on a single, bi- or tri-layer approach of silicon oxide and/or silicon nitride co-doped or not with rare earth ions, is successfully performed. Several complementary metal-oxide-semiconductor (CMOS) compatible fabrication techniques such as co-magnetron sputtering, plasma-enhanced chemical vapor deposition (PECVD), low-pressure chemical vapor deposition (LPCVD) and ion implantation are used. By using characterization techniques such as time of flight secondary ion mass spectrometry (TOF-SIMS), secondary ion mass spectrometry (SIMS), X-ray photoelectron spectroscopy (XPS), energy-filtered transmission electron microscopy (EFTEM), focused ion beam (FIB) and ellipsometry, the structural and compositional properties of the studied active layers are determined. In addition, electro-optical properties at room and at high temperatures (25 0C – 300 0C) under quasi-static and dynamic regimes are studied in both visible and near-infrared spectral region. Typically, the used electro-optical techniques have been current-voltage, capacitance-voltage, charge to breakdown, electroluminescence (EL)-current, EL-voltage and time-resolved EL.

Electrònica, Electrónica, Electronics, Nanopartícules, Nanopartículas, Nanoparticles, Silici, Silicio, Silicon, and Ciències Experimentals i Matemàtiques

Introduction It is undisputed that the silicon became the material most widely used in electronics in recent decades[1,2]. The qualities of silicon are well known, from its abundance and low cost to its ability to easily combine with oxides, so that the material has become essential in integrated electronic circuits and CMOS technology. A step further, though, is the idea of integrating electronics and photonics on the same silicon-based technology[3]. However, new strategies are needed to overcome the two principal obstacles of a possible bulk Si photonics: the indirect band gap and the band gap amplitude, suitable for operation only in the infrared range. Due to the quantum confinement of electric charges in silicon quantum dots (Si QDs)[4], the value of the energy gap of the material increases as the size of QD decreases, giving values greater than bulk Si and making Si QDs good candidates for tunable-band gap devices. Several applications have been developed in recent years using these new properties, from light-emitting devices [5] to solar cell tandem type [6] or other opto-electronic devices [7]. Objectives of this Thesis This Thesis initiated a collaboration between our group and the group of Prof. Ossicini of the University of Modena and Reggio Emilia, who has been modeling Si QDs for the last five years[8-14]. In this context, we contributed with the capacity to study the transport properties of these models by taking advantage of mixing two different techniques, Transfer Hamiltonian (TH) and Density Functional Theory (DFT). Thus, the aim of this work was to develop an approach to study transport in nanostructures by taking advantage of the atomistic information that ab initio methods can provide. In particular, the transport through a single Si QD embedded in a SiO2 dielectric matrix and the influence of the Si QD size, the amorphization level, and the doping were studied. Results and conclusions About the size of QDs In the case of embedded QDs of few nanometers, the strong non-planar interface between Si and SiO2 require a different treatment with respect to common planar Si/SiO2 devices. In this PhD Thesis, we have shown that, for small QD sizes, the particle-in-a-box model cannot describe accurately DOS and band offset, because of the large contribution of interface states. In this regime an ab initio approach is necessary to take into account the atomistic detail of the interface between the Si QD and the first shell of O atoms surrounding it. Regarding the electronic transport in Si QDs, a correlation between electron (hole) barrier value and electron (hole) current was found, obtaining larger current values for smaller energy barriers. Specifically, a contrary dependence on Si QD size and amorphization level is found for electron and hole current. On one hand, electron (hole) current is higher for large (small) Si QDs, and, on the other hand, it is enhanced for amorphous (crystalline) systems. On the effects of doping Finally, the DFT-TH technique was used to study the influence of impurity atoms, B for p-doping and P for n-doping, in embedded Si QDs. It is remarkable that this study is one of the first attempts to model with DFT the inclusion of impurity atoms in embedded Si QDs, after the wide knowledge of ab initio works on free-standing Si QDs of the last years. The principal features that we found were: • The impurity positions with lower formation energy are inside the dot for P-doping (P-dot) and at the interface for B-doping (B-int). • Relation between shift of the Fermi energy and improvement of conductivity in doped systems (due to the change in energy barriers). • Improvement of the conductivity for the most energetically favorable position of P-doping (P-dot) but not for the position of B-doping (B-int). • Change in the conductivity between doped and undoped is higher for P-doping than B-doping for a given Si QD size and impurity position, and decreases with QD size for a given specie and impurity position. Bibliography [1] M. Segal. Material history: Learning from silicon. Nature, 483, S43 (2012). [2] H. J. Leamy and J. H.Wernick. Semiconductor silicon: the extraordinary made ordinary. MRS Bulletin, 22, 47 (1997). [3] X. Hao, E.-C. Cho, G. Scardera, Y. Shen, E. Bellet-Amalric, D. Bellet, G. Conibeer and M. Green. Phosphorus-doped silicon quantum dots for all-silicon quantum dot tandem solar cells. Sol. Energ. Mat. Sol. C, 93, 1524 (2009). [4] J. P. Proot, C. Delerue and G. Allan. Electronic structure and optical properties of silicon crystallites: Application to porous silicon. Appl. Phys. Lett., 61, 1948 (1992). [5] Y. Berencen, J. M. Ramirez, O. Jambois, C. Dominguez, J. A. Rodriguez and B. Garrido. Correlation between charge transport and electrolumi-nescence properties of Si-rich oxide/nitride/oxide-based light emitting capacitors. J. Appl. Phys., 112, 033114 (2012). [6] G. Conibeer, I. Perez-Wur, X. Hao, D. Di and D. Lin. Si solid-state quantum dot-based materials for tandem solar cells. Nanoscale Res. Lett., 7, 193 (2012). [7] L. Pavesi, L. D. Negro, C. Mazzoleni, G. Franzo and F. Priolo. Optical gain in silicon nanocrystals. Nature, 408, 440 (2000). [8] M. Luppi and S. Ossicini. Ab initio study on oxidized silicon clusters and silicon nanocrystals embedded in SiO2: Beyond the quantum confinement effect. Phys. Rev. B, 71, 035340 (2005). [9] R. Guerra, I. Marri, R. Magri, L. Martin-Samos, O. Pulci, E. Degoli and S. Ossicini. Silicon nanocrystallites in a SiO2 matrix: Role of disorder and size. Phys. Rev. B, 79, 155320 (2009). [10] R. Guerra, E. Degoli and S. Ossicini. Size, oxidation, and strain in small Si/SiO2 nanocrystals. Phys. Rev. B, 80, 155332 (2009). [11] R. Guerra and S. Ossicini. High luminescence in small Si/SiO2 nanocrystals: A theoretical study. Phys. Rev. B, 81, 245307 (2010). [12] R. Guerra, E. Degoli, M. Marsili, O. Pulci and S. Ossicini. Local-fields and disorder effects in free-standing and embedded Si nanocrystallites. Phys. Status Solidi B, 247, 2113 (2010). [13] R. Guerra, M. Marsili, O. Pulci and S. Ossicini. Local-field effects in silicon nanoclusters. Phys. Rev. B, 84, 075342 (2011). [14] M. Govoni, I. Marri and S. Ossicini. Auger recombination in Si and GaAs semiconductors: Ab initio results. Phys. Rev. B, 84, 075215 (2011).

Silici, Silicio, Silicon, Pel·lícules fines, Películas delgadas, Thin films, Energia fotovoltaica, Energía fotovoltaica, Photovoltaic power generation, and Ciències Experimentals i Matemàtiques

El diseño de un sistema de generación eléctrica fotovoltaica requiere la estimación precisa de la producción eléctrica. Las especificaciones técnicas de los módulos proporcionan los parámetros eléctricos relevantes sólo en la condición estándar que la Comisión Electrotécnica Internacional establece en su norma [IEC904-1]: 25 ºC de temperatura de módulo, 1000 Wm(2) de irradiancia, AM1.5 global en la distribución espectral de la radiación e incidencia normal a la superficie del módulo. La potencia eléctrica depende de la temperatura de la célula y la intensidad y el contenido espectral de la radiación incidente, que varía sustancialmente durante la producción. Distintas metodologías de estimación de la producción energética [Raicu 1991, Friesen 2002, Kenny 2002], que previamente han demostrado ser precisas en módulos de silicio cristalino, exhiben considerables desviaciones cuando se aplican a los módulos de silicio amorfo. En particular, la predicción de la eficiencia en los meses cálidos de verano es sistemáticamente inferior al comportamiento real observado. A diferencia de los módulos convencionales, que exhiben pérdidas de eficiencia debido al aumento de temperatura en verano, los módulos de silicio amorfo mejoran su eficiencia. Los modelos convencionales no explican este resultado que, en general, ha sido atribuido a efectos espectrales y de recuperación térmica o “annealing” [Akhmad 1997, delCueto 1997, King 2000, Kleiss 1993, Gottschalg 2003, Gottschalg 2004, Hirata 1995, Hirata 1998, Merten 1998b, Rüther 1994]. La importancia relativa de estos dos fenómenos es controvertida y dificulta el desarrollo de nuevos modelos de predicción. La finalidad de este trabajo de Tesis es obtener un modelo de predicción preciso para la tecnología de silicio amorfo mediante la caracterización y análisis de células solares y módulos fotovoltaicos de esta tecnología. Para ello se trabaja sobre un modelo de circuito eléctrico equivalente que considera las particularidades de las células solares de silicio amorfo. El primer bloque de la Tesis aborda la interpretación de las medidas eléctricas realizadas en el sistema de caracterización del laboratorio. Este sistema se ha adaptado para realizar medidas electro-ópticas automáticas a diferentes temperaturas e iluminación. Se han caracterizado células solares de silicio amorfo de pequeña área suministradas por un fabricante de módulos fotovoltaicos. Las medidas se interpretan mediante un modelo circuital que incluye un modelo analítico para describir el término de fotocorriente. Este modelo analítico es válido para dispositivos cuya fotocolección está asistida por campo eléctrico. La dependencia de la fotocorriente con la tensión aplicada es únicamente descrita mediante dos parámetros: el potencial de difusión V(b) y la tensión de colección V(c) [Merten 1998a, Asensi 1998, Hof 2000]. Del análisis de las medidas se ha determinado las dependencias de V(b) y V(c) con la iluminación y la temperatura. Introduciendo estas dependencias en el modelo circuital se puede reproducir adecuadamente el comportamiento eléctrico de las células solares de silicio amorfo en cualquier nivel de iluminación y temperatura. El segundo bloque de la Tesis está orientado hacia la monitorización en condiciones reales del comportamiento de módulos comerciales de silicio amorfo. Se ha diseñado y montado un sistema de monitorización que registra información detallada de las características eléctricas de los módulos, datos climáticos, temperaturas de módulo e intensidad y contenido espectral de la radiación incidente sobre el plano del módulo. Los datos obtenidos pueden interpretarse utilizando el modelo circuital desarrollado en el bloque anterior. Sin embargo, al no controlar la temperatura e iluminación, la metodología es, necesariamente, distinta. El procedimiento que se presenta permite el cálculo aproximado de los parámetros circuitales del módulo fotovoltaico a partir de los datos habituales de un sistema estándar de monitorización. Los resultados generales han constatado que el rendimiento de los módulos fotovoltaicos de silicio amorfo presenta un comportamiento periódico, cuyo valor máximo tiene lugar en verano. Es decir, cuando aumenta la temperatura y la irradiación. Se ha comprobado que el origen de esta evolución estacional se puede interpretar en términos de los promedios diarios de los principales parámetros característicos normalizados a la condición estándar de irradiancia: la corriente de cortocircuito, < J1000 (sc >d), asociada al efecto espectral, la tensión de circuito abierto, < V 1000 (oc >d), que depende de la temperatura del módulo y el factor de forma, < FF1000 (>d), que representa el comportamiento meta-estable del silicio amorfo. El análisis de estos parámetros concluye que el comportamiento estacional de los módulos monitorizados es principalmente debido al efecto espectral.

Deposició en fase de vapor, Deposición en fase de vapor, Vapor-plating, Hot Wire CVD, ECV de alambre caliente, ECV de fil calent, Cat-CVD, Cèl·lules solars, Células solares, Solar cells, Silici, Silicio, Silicon, Pel·lícules fines, Películas delgadas, Thin films, Microcrystalline silicon, Silici microcristal·lí, Silicio microcristalino, and Ciències Experimentals i Matemàtiques

The first block of this thesis deals with the study of the degradation process of tungsten catalytic filaments in the field of silicon deposition with the Hot Wire Chemical Vapour Deposition (HWCVD) technique. The development of technological solutions addressed to the filaments protection will also be dealt as well as the design, fabrication and performance of a novel system for the automatic replacement of used filaments in a HWCVD reactor. The second block deals with the scaling up of HWCVD towards large area deposition and the existence of a scaling law that may allow the deposition of microcrystalline silicon (µc-Si:H) at high rate preserving the material quality.

biosensor, interferometro, silicio, and Ciències Experimentals

Els dispositius òptics biosensors basats en la detecció d’ona evanescent podrien superar les limitacions dels tests de diagnòstic actuals (que són lents i cars) degut a la possibilitat de realitzar les deteccions a temps reals i fent servir un esquema sense la necessitat de marcatges. Entre els diferents transductors òptics, els interferomètrics són els que posseeixen els millors límits de detecció (LOD) deguts a canvis en el índex de refracció de dissolucions (10-7-10-8 Unitats d’Índex de Refracció, RIU) així com per sensibilitat superficial (en el rang dels pg/ml) i un rang lineal més gran. No obstant, les configuracions interferomètriques (l’interferòmetre Mach-Zehnder o el Young) més usuals fan servir un divisor amb forma de Y, que és essencial per dividir o recombinar la llum, lo qual, degut a les toleràncies de les actuals tècniques de fabricació es una gran desavantatge per la reproduibilitat d’aquests dispositius. Per evitar aquests problemes, hem desenvolupat una configuració interferomètrica més simple basada en un guia de ones recte on dos modes de llum de la mateixa polarització interfereixen entre si. Aquesta configuració elimina la complexitat dels interferòmetres més utilitzats i conseqüentment, el biosensors que s’obtenen són més fiables i reproduïbles. Aquesta tesis esta dirigida al desenvolupament i la caracterització d’un nou transductor fotònic per biosensat d’alta sensibilitat i sense marcatges, el dispositiu de guia d’ona bimodal (BiMW). Amb aquest propòsit, els següents punts han estat plantejats: 1. Disseny, fabricació i caracterització òptica del transductor que opera segons el principi de la interferència de dos modes de llum. 2. Desenvolupament i optimització de les estratègies de funcionalització de la superfície transductora fent servir processos de silanització. 3. Estudi de l’aplicabilitat del biosensor amb la demostració del diagnosis analític de problemes clínics rellevants. El transductor es fabrica a nivell d’oblea a la Sala Blanca, lo qual garanteix la producció en massa del dispositiu així com un preu baix del mateix. El dispositiu és molt sensible a variacions en l’índex de refracció de dissolucions, obtenint un límit de detecció de 2×10-7 RIU. La biofuncionalització de l’àrea sensora es un dels aspectes més importants d’aquest treball. Diferents protocols per immobilitzar els diferents bioreceptor en la superfície del dispositiu (cadenes d’ADN, proteïnes i anticossos) han estat desenvolupats. Aquests protocols s’han fet servir per la demostració de diferents bioaplicacions; la detecció d’hormones, bactèries o seqüències d´ADN complementàries. Els resultats presentats en aquesta tesis han destacat pel superior funcionament d’aquest dispositiu en comparació amb els tests de diagnosis convencionals degut a: i) la possibilitat de monitoritzar les interaccions biomoleculars en temps real i fent servir un esquema sense marcadors reduint el temps i el cost de l’assaig, ii) la fabricació del dispositiu fent servir microtecnologia de silici, possibilitant la producció en massa, iii) l’alta sensibilitat (pg/ml, femtomolar) demostrada per les diferents bioaplicacions avaluades i iv) el dispositiu reuneix els requeriments específics per ser miniaturitzat e integrat en una plataforma de sensat multiplexada. Aquest treball obre la porta a la integració d’aquest transductor en un dispositiu lab-on-a -chip, una feina que inclou l’acoblament/detecció de la llum, un sistema capaç de modular la senyal interferomètrica i la incorporació de canals microfluídics per anàlisis multiplexats. Cadascun d’aquests temes afegeix molta complexitat al dispositiu final, han de ser individualment desenvolupades i optimitzades per ser integrades en un biosensor lab-on-a-chip. Finalment, la possibilitat de detectar simultàniament múltiples analits involucra el desenvolupament de noves tècniques per recollir les múltiples senyals així com desenvolupar noves estratègies de biofuncionalització.

Microscòpia electrònica, Microscopia electrónica, Electron microscopy, Silici, Silicio, Silicon, and Ciències Experimentals i Matemàtiques

In the last decade transmission electron microscopy (TEM) has become one of the most powerful tools for the structural characterization of crystalline materials. Especially in the field of microelectronics development and production, the information obtained by this analytical tool has been of vital importance for the improvement of the different processing steps. With the reduction of the dimensions of the devices TEM is the only technique that can give information with enough spatial resolution. In this work applications of transmission electron microscopy for the study of processing steps of ULSI technology will be presented. In the first chapter special emphasize is given to the theoretical background of transmission e Some details about Secondary Ion Mass Spectrometry (SIMS) and Spreading Resistance Probe (SRP) are also given, as they will be used for cross-correlation in the following chapters. In semiconducting research and production the processes for the fabrication of devices are restricted to a small volume of the starting material. Only the areas close to the surface, about 5 μm deep, are used for the operation of the devices. Both for plan view and cross-section TEM investigation of integrated circuits special specimen preparation techniques had to be developed. These techniques are described in full detail in chapter two. Chapters 3 and 4 deal with the application of TEM for the characterization of two processing steps that are required for the fabrication of ULSI devices. Chapter 3 presents a structural study of the geometry and the defect generation in the substrate for one of the most important aspects of the process: the device isolation. In it modifications of the LOCOS process will be given, which try to solve the specific problems of LOCOS when applied to submicron devices. In chapter 4 the delineation of shallow junctions is treated. The dopant profiles have to be well characterized and analytical teehniques have to be used which have a high spatial resolution and a high sensitivity for dopant concentration. Especially the determination of two-dimensional dopant profiles poses severe problems. Special TEM techniques will be presented, which allow to determine the lateral dopant spread below implantation masks. Especially promising is the applieation of in-situ electron irradiation in a high voltage transmission electron microscope (HVEM) to this topic. It will be shown that the formation of extended defects in preferential areas of the specimens, induced by the high energy electrons, is dependent on the dopant concentration. Correlation with SIMS or SRP will allow to determine this doping level in a quite accurate way. Finally in chapter 5 the most relevant conclusions of this work will be presented. Further research on the treated topicswill be suggested.

retardante a la llama, silicio, and resina epoxi

Las resinas epoxi son ampliamente utilizadas en soldaduras, recubrimientos, adhesivos y materiales compuestos. En algunas aplicaciones las resinas epoxi requieren de funciones especiales y versátiles, tales como alta adhesión a los sustratos, bajo encogimiento, bajo estrés térmico después del curado, buena dureza, baja inflamabilidad y buena resistencia química. La inflamabilidad de las resinas epoxi es una de las principales desventajas en su aplicación debido a que, como todo polímero orgánico, son inherentemente combustibles y en presencia de una fuente de calor y de oxígeno se queman fácil y rápidamente. Por consiguiente, algunos retardantes al fuego, tales como compuestos bromados, óxidos de antimonio, compuestos fósforo-halogenados, etc. son incorporados en las resinas epoxi para reducir su inflamabilidad. Estos compuestos son excepcionalmente efectivos pero presentan el inconveniente que incrementan las cantidades de humos y productos de descomposición tóxicos y corrosivos que se desprenden durante la combustión del polímero. Por esta serie de inconvenientes en la actualidad se ha incrementado la investigación de otros heteroátomos como retardantes a la llama para reemplazar a los halógenos.En los últimos años se han descrito algunas aproximaciones sobre resinas epoxi con silicio unido covalentemente a la matriz polimérica. Así, han sido descritas modificaciones sobre resinas epoxi comerciales y copolimerizaciones de monómeros glicidílicos que contienen silicio con resinas epoxi comerciales, consiguiéndose una mejora de las propiedades retardantes a la llama sin sacrificar las propiedades mecánicas de la resina curada.En este trabajo se ha planteado como objetivo general el desarrollo de resinas epoxi basadas en silicio con propiedades retardantes a la llama. Así, se ha llevado a cabo la síntesis de monómeros glicidílicos que contienen silicio en su estructura. Para establecer una relación entre la presencia y proporción del silicio y las propiedades físicas de los materiales resultantes, se han preparado polímeros termoestables a partir de mezclas de un glicidilo comercial con los monómeros que contienen silicio así como prepolímeros obtenidos a través de reacciones de crecimiento de cadena entre el DGEBA y un silanodiol. También se han sintetizado monómeros y agentes de curado que contienen fósforo en su estructura y se han preparado polímeros termoestables que contengan ambos heteroátomos. Con objeto de estudiar el mecanismo de reacción de monómeros que contienen silicio con aminas primarias, se ha sintetizado un monómero sililado monofuncional, fenilglicidiloxidimetilsilano (GDMPS), y se ha comparado su reactividad frente a una amina primaria, anilina, con la de un glicidilo comercial, fenilglicidiléter (PGE). El estudio cinético fue llevado a cabo mediante NIR y aplicando a los datos espectrales obtenidos métodos de análisis multivariante de resolución de curvas (MCR-ALS). Se ha llevado a cabo el estudio cinético del curado de un diglicidilo que contiene silicio, fenildiglicidiloximetilsilano (DGPMS), y de las mezclas de éste con DGEBA con una diamina primaria, DDM, mediante DSC isotérmico y dinámico. Además, se han estudiado los fenómenos de gelificacion y vitrificación de estos sistemas mediante DMTA en modo cizalla y TMDSC. Se han preparado polímeros termoestables y se han evaluado sus propiedades termodinamomecánicas, térmicas y de retardancia a la llama. Las propiedades termodinamomecánicas han sido estudiadas mediante DMTA en modo de flexión. La estabilidad térmica de estos compuestos se ha estudiado mediante análisis termogravimétrico en atmósfera de nitrógeno y de aire. Las propiedades de retardancia a la llama fueron evaluadas mediante el test ASTM-D-2683 del índice de oxígeno limitante (LOI). Finalmente, se ha estudiado la degradación térmica de los polímeros obtenidos para establecer el modo de actuación del silicio durante la degradación. Para ello, se ha realizado el estudio cinético de la degradación a partir datos obtenidos por TGA, estudios de las etapas iniciales de la degradación mediante quimioluminiscencia (QL) y la caracterización de los productos formados por TGA-MS, GC-MS, ATR-FTIR y DRX.De los resultados obtenidos se han podido establecer las siguientes conclusiones: (1) Se ha determinado que la presencia del silicio produce un aumento en la reactividad del epóxido probablemente debido a efectos electrónicos. Esta mayor reactividad además reduce la importancia del camino autocatalítico en el curado con aminas primarias. (2) Las resinas epoxi sililadas termoestables muestran una disminución de la Tg y de la densidad de entrecruzamiento con el incremento del porcentaje de silicio.Esta disminución está relacionada con un aumento del volumen libre debido a la mayor longitud de los enlaces Si-O. (3) Los polímeros termoestables que contienen silicio muestran un incremento del LOI a partir de un contenido de silicio del 3%. En los polímeros que contienen silicio y fósforo, se encontraron evidencias de la existencia de sinergia entre los dos heteroátomos. (4) La degradación de los polímeros que contienen silicio, tanto en atmósfera inerte como oxidante, conlleva la formación de oligómeros cíclicos de fenilmetilsiloxano, lo que implica que parte del silicio abandona la fase condensada. El residuo contiene silicio como SiO2, formando probablemente una capa aislante que actúa como barrera térmica y de transferencia de masa disminuyendo de esta manera la producción de volátiles.

Silici, Silicio, Silicon, Semiconductors, Semiconductores, Plasma (Gasos ionitzants), Plasma (Gases ionizados), Plasma (Ionized gases), Descàrregues elèctriques, Descargas eléctricas, Electric discharges, and Ciències Experimentals i Matemàtiques

El silici amorf hidrogenat (a-Si:H) s’ha convertit en el material semiconductor en capa prima més estudiat en els últims anys. Aquest esforç investigador està en gran part motivat pel gran nombre d’aplicacions industrial, com ara les cèl·lules solars en capa prima i baix preu de producció, les matrius de transistors d’efecte de camp per al direccionament de pantalles planes, la nova generació de sensors d’imatge, fotoreceptors per fotocopiadores i impressores làser... El primer silici amorf amb bones propietats semiconductores s’aconseguí el 1969, en desenvolupar-se una nova tècnica per a dipositar silici amorf mitjançant una descàrrega elèctrica en gas silà (SiH(4)) Ja en aquesta fase inicial de la recerca es va intentar utilitzar altres tècniques i s’obtingueren grans diferències segons quina fos la tècnica utilitzada. De totes elles, la descàrrega elèctrica en gas silà és la que permès la producció de a-Si:H en millors propietats. S’ha observat, però, una gran influència de les condicions de descàrrega en les propietats de les capes dipositades. Això fa que sigui molt interessant l’estudi de les característiques del plasma que puguin tenir relació amb les propietats del a-Si:H dipositat, així com la recerca de nous sistemes de dipòsit per tal d’obtenir capes amb bones característiques. L’objectiu del treball és l’estudi dels paràmetres del plasma de silà i la seva correlació amb els paràmetres tecnològics de la descàrrega. S’ha començat estudiant la descàrrega en gas argó, la qual ha facilitat la posta a punt del sistema de mesura. El dispositiu experimental i les tècniques de mesura utilitzades (capítol 1) ens han permès les mesures dels paràmetres corresponents a les poblacions d’electrons en el plasma d’argó (capítol 2) i en el plasma de silà (capítol 3), així com el càlcul de les densitats d’electrons en funció de l’energia per ambdós tipus de plasma i l’ajust d’aquestes mitjançant la suma de distribucions de Maxwell (capítol 4). Finalment, les mesures realitzades amb l’analitzador d’energia iònica ens han permès estudiar el bombardeig dels electrons sobre el substrat (capítol 5).

Semiconductores and Silicio

Microscopía Electrónica de Transmisión, Transistores de Alta Movilidad Electrónica, Nitruros del grupo III, InAlN, InAlGaN, AlGaN, GaN, and Silicio

Semiconductores, Silicio, and Células solares

Raman, Espectroscopia, Semiconductores, Germanio, Silicio, and Física del estado sólido

Semiconductores and Silicio

Semiconductores and Silicio