Search

Grup de Treball. Perspectiva de Gènere en la Docència, la Recerca i la Transferència, Les rúbriques transversals despleguen les recomanacions recollides en el III Pla d’Igualtat de la Universitat de Barcelona. S’han proposat seguint el model de la Guia per a la incorporació de la perspectiva de gènere en els plans docents i les assignatures de la Universitat de Barcelona (2021) elaborada per la Comissió d’Igualtat que, al seu torn, s’ajusta al que disposa l’AQU en el seu Marc general per a la incorporació de la perspectiva de gènere en docència (2018). Les rúbriques poden ser d’aplicació a tots els graus i màsters de la Universitat de Barcelona. Som conscients que no tots els ensenyaments poden aplicar la perspectiva de gènere a la docència de la mateixa manera, per això cada centre i cada ensenyament haurà de prendre la decisió estratègica que més afavoreixi l’ensenyament dels continguts de l’àrea. Es pot fer incorporant-hi una assignatura sencera sobre perspectiva de gènere (com s’ha distingit incloent la casella “temàtica” en les rúbriques transversals). També es pot decidir, segons convingui, adaptar metodologies, fer canvis en els entorns d’aprenentatge o en les referències bibliogràfiques, o idear una combinació de diferents pràctiques transversals o específiques.

La Universitat de Barcelona, en el seu III Pla d’igualtat, s’ha compromès a incloure i desplegar la perspectiva de gènere en tots els seus àmbits d’actuació. Un dels eixos que estructuren aquest pla (concretament, l’eix 4) està dedicat a la perspectiva de gènere en la docència. La Comissió d’Igualtat, el Vicerectorat de Política Docent, el Vicerectorat de Política Acadèmica i Qualitat, el Vicerectorat d’Igualtat i Gènere i la Unitat d’Igualtat volem facilitar-vos la tasca d’incorporar la perspectiva de gènere a totes les assignatures. Us proposem d’avançar cap a una UB més inclusiva començant pels plans docents, tal com preveu la legislació vigent. Aquesta proposta s’anirà acompanyant, al llarg del curs, d’accions de formació i d’altres materials que esperem que us siguin útils.

Traducció a cura de Sònia Estradé de l'article d'Evelyn Fox Keller de 1977

Una educación en Ciencias Físicas abre un notable abanico de posibilidades de carrera profesional; sin embargo, estas oportunidades no están igualmente disponibles para todos a causa de que los grupos subrepresentados entre el estudiantado y el corpus de profesionales de la Física y los campos relacionados, especialmente las mujeres, acaban teniendo un acceso limitado a los recursos que deberían permitirles desarrollar plenamente su potencial. Con ligeras variaciones, este es el caso en toda el área de investigación europea. En el presente trabajo presentaremos un análisis del proyecto Erasmus+ “Diversity in the Cultures of Physics”, centrado en acompañar y apoyar a las mujeres que están al final de sus estudios de Física (o al inicio de sus doctorados) para que accedan en el futuro a la investigación y a la enseñanza, a la innovación, a la industria, conscientes de los sesgos de género que deben afrontar e, idealmente, con las herramientas que les permitan sortearlos An education in physics offers a remarkable diversity of career options; however, these opportunities are not equally open to all because underrepresented groups within the students and scientists in physics and related fields, most notably women, are granted only limited access to fully realize their individual potentials. With only slight variations, this is the case across the European research area. In the present work we will undertake an analysis of the Erasmus+ project "Diversity in the Cultures of Physics", focused on coaching and supporting women who are at the end of their physics degrees (or at the beginning of their PhDs) so that they can, in the future, get an access to research and teaching, to innovation, to industry, well aware of the gender biases they are to face and, ideally, having the tools to overcome them.

Here it is demonstrated that multiple-energy, anomalous small-angle X-ray scattering (ASAXS) provides significant enhancement in sensitivity to internal material boundaries of layered nanoparticles compared with the traditional modeling of a single scattering energy, even for cases in which high scattering contrast naturally exists. Specifically, the material-specific structure of monodispersed Fe₃O₄|γ-Mn₂O₃ core|shell nanoparticles is determined, and the contribution of each component to the total scattering profile is identified with unprecedented clarity. We show that Fe₃O₄|γ-Mn₂O₃ core|shell nanoparticles with a diameter of 8.2 ± 0.2 nm consist of a core with a composition near Fe₃O₄ surrounded by a (Mn(x)Fe(1-x))₃O₄ shell with a graded composition, ranging from x ≈ 0.40 at the inner shell toward x ≈ 0.46 at the surface. Evaluation of the scattering contribution arising from the interference between material-specific layers additionally reveals the presence of Fe₃O₄ cores without a coating shell. Finally, it is found that the material-specific scattering profile shapes and chemical compositions extracted by this method are independent of the original input chemical compositions used in the analysis, revealing multiple-energy ASAXS as a powerful tool for determining internal nanostructured morphology even if the exact composition of the individual layers is not known a priori.

High resolution monochromated Electron Energy Loss Spectroscopy (EELS) at subnanometric spatial resolution and

Podeu consultar el llibre complet a: http://hdl.handle.net/2445/32166, In the present work we review the way in which the electron-matter interaction allows us to perform electron energy loss spectroscopy (EELS), as well as the latest developments in the technique and some of the most relevant results of EELS as a characterization tool in nanoscience and nanotechnology.

Spinel ferrites are being considered for advanced spintronic applications. Here, we report on the magnetic properties of ultrathin (3-37 nm) epitaxial films of NiFe2O4 (NFO) on MgAl2O4 (MAO) and SrTiO3 (STO) single crystalline substrates. It is found that NFO films on STO display superparamagnetic response down to 50 K, whereas films grown on MAO display ferrimagnetic response up to room temperature. Microstructural information indicates that this distinct response can be attributed to the different growth mechanisms of the spinel ferrite on the isostructural MAO substrate (two-dimensional growth) and the perovskite STO (Volmer-Weber three-dimensional growth). We discuss the reasons for this distinct behavior and its relevance for the integration of ferrites in epitaxial heterostructures for tunnel devices.

Epitaxial thin films of biferroic Bi1−xLax 2NiMnO6 have been grown on SrTiO3 001 substrates. High resolution electron microscopy, energy-loss spectroscopy and synchrotron radiation have been used to demonstrate that, under appropriate growth conditions, stoichiometric, and fully oxidized thin films with long-range order of Ni2+ and Mn4+ ions can be obtained, despite the presence of randomly distributed dissimilar cations Bi, La at the A-site. This ordering leads to Ni2+OMn4+ ferromagnetic interactions and its preservation in thin films is key for implementation of these biferroic materials in practical devices.

We show both theoretical and experimental evidences of the appearance of ferromagnetism in MgO thin films. First-principles calculations allow predicting the possibility of the formation of a local moment in MgO, provided the existence of Mg vacancies which create holes on acceptor levels near the O 2p-dominated valence band. Magnetic measurements evidence of the existence of room-temperature ferromagnetism in MgO thin films. High-resolution transmission electron microscopy demonstrates the existence of cation vacancies in our samples. Finally, by applying the element specificity of the x-ray magnetic circular dichroism technique, we also demonstrate that the magnetic moments of the system arise from the spin polarization of the 2p electrons of oxygen atoms surrounding Mg vacancies.

Màster en Nanociència i Nanotecnologia curs 2006-2007. Directors: Francesca Peiró i Martínez and Jordi Arbiol i Cobos, In the present work Transmission Electron Microscopy (TEM) and Electron Energy Loss Spectroscopy (EELS) are applied for the evaluation of trivalent cationic migration in epitaxial thin films of La2/3Ca1/3MnO3 (LCMO). The first part of the work shows the comparative results of the growth by RF-sputtering of both annealed and as grown La2/3Ca1/3MnO3 (LCMO) layers of various thicknesses on (001) LaAlO3 (LAO) substrates. Lanthanum diffusion is detected for LCMO films grown on LAO as a function of annealing and layer thickness and is determined to play a major role in the degradation of the magnetic properties found in this system. In the second part, thin LCMO layers simultaneously grown, also by RF-sputtering, on (001) and (110) SrTiO3 (STO) are evaluated. La diffusion is also found in thin LCMO films grown on STO and the correlation with magnetic properties depending on the film thickness is discussed.

We report on a growth study of MgO films deposited on Al2O3(0001) substrates by magnetron sputtering. The films exhibited a preferred rocksalt MgO(111) orientation. Surprisingly, depending on the O2 gas flow ratio, a structure of graphiticlike wurtzite MgO(0001) has been revealed. The observed Mg-O perpendicular bond length reduction is accompanied by an atomically flat surface morphology for the development of MgO(111) films; the transition to the bulk rocksalt structure occurs in the 3-6 nm coverage range. Previously, relaxation of the electrostatic instability of MgO(111) films accompanied by an in-plane lattice increase has been suggested theoretically [Phys. Rev. Lett. 98, 205701 (2007)]. Here, relying on ab initio calculations, we infer that Mg vacancies facilitate the lattice match with the substrate. This mechanism suggests methods to engineer oxide heterostructures.

The structural and optical properties of three different kinds of GaAs nanowires with 100% zinc-blende structure and with an average of 30% and 70% wurtzite are presented. A variety of shorter and longer segments of zinc-blende or wurtzite crystal phases are observed by transmission electron microscopy in the nanowires. Sharp photoluminescence lines are observed with emission energies tuned from 1.515 eV down to 1.43 eV when the percentage of wurtzite is increased. The downward shift of the emission peaks can be understood by carrier confinement at the interfaces, in quantum wells and in random short period superlattices existent in these nanowires, assuming a staggered band offset between wurtzite and zinc-blende GaAs. The latter is confirmed also by time-resolved measurements. The extremely local nature of these optical transitions is evidenced also by cathodoluminescence measurements. Raman spectroscopy on single wires shows different strain conditions, depending on the wurtzite content which affects also the band alignments. Finally, the occurrence of the two crystallographic phases is discussed in thermodynamic terms.

[eng] Transmission Electron Microscopy (TEM), since its first implementation by Ernst August Friedrich Ruska and Max Knoll in 1931, has been an essential technique in the nanoscience and nanotechnology field. In the beginning, the real resolution was just a small fraction of the potential resolution expected by the fact of using electrons as a “light” source. The wavelength of the electrons accelerated at hundreds of electronvolts would involve a subatomic resolution; however, all the aberrations related to electromagnetic lenses caused a dramatic decrease. In addition, the energy resolution was highly affected by the chromatic aberration of the electron beam. Nowadays, all these initial problems have been solved by the development of the image aberration correctors and the monochromators. Since atomic resolution together with 10 meV energy resolution are a reality for researchers, new and higher horizons have been set for the transmission electron microscopy, such as orbital imaging, phonon imaging, or real time atom monitoring amongst others. TEM could be described at its most fundamental as the analysis of the result of impacting electrons with a specific compound or structure. From, this impact different data can be obtained which can be rapidly classified between imaging and spectroscopy. With the recent increases in energy and spatial resolution, a huge amount of information can be directly extracted from very large experimental datasets; however, for a deeper understanding, most of the times the support from theoretical calculations is also needed. Solid state physics with quantum considerations can contribute to an accurate description of the studied systems. Whereas in the past, materials science, solid state physics, quantum mechanics and chemistry were disciplines with a huge separation between them, nowadays they merge in the field of nanoscience and nanotechnology. When the object size is reduced to the nanoscale the quantum effects cannot be neglected anymore, any change on the synthesis can in turn change the structure which plays an essential role on the compound properties. Thus, modelling has become an essential step in the materials synthesis and characterization. The knowledge of the structure allows to compute the interaction of the electrons with any well described crystalline structure and generate images and spectra comparable with experimental data, but not just as a check, but to gain deeper insight. The interaction of the electrons with matter must be computed by solving the Schrödinger equation of the electrons interacting with the sample. The sample, the system, can be considered as a periodic potential. Imaging, measuring, modelling and manipulating matter are the basis of the promising field of nanoscience, and they can be carried out using a TEM, with the continuous support of theoretical calculations to obtain the most. The present thesis uses three main types of calculations to interpret TEM data: atomic simulations applied to imaging, Boundary Element Method (BEM) based calculations for surface plasmon distributions and Density Functional Theory (DFT) for EELS analysis. Even if they will be presented separately, they are not independent; the essence is always the same but depending on the desired results different considerations are needed. The materials science problems solved through these kinds of simulations presented in the thesis are the analysis of CuPtB ordering effects in GaInP, the influence of oxygen vacancies in the EELS of Bi2O3, the consequences of the Fe3O4 Verwey transition in its electronic structure and how it is observed in EELS and, finally, the surface plasmon distribution in gold-nanodomes as a function of the dome shape. To conclude, the simulations have been presented as an essential tool to complement TEM studies to link the experimental results with the most fundamental aspects which are determined by the structure of the studied materials., [cat] Aquesta tesi doctoral s'ha centrat en la realització de càlculs teòrics que permetin comprendre i extreure la major quantitat d'informació possible de les dades experimentals de microscòpia de transmissió d’electrons (TEM), i de les tècniques espectroscòpiques relacionades, concretament, l'espectroscòpia de pèrdua d’energia dels electrons (EELS). S’hi utilitzen tres tipus principals de càlculs per interpretar les dades del TEM: simulacions atòmiques aplicades a l'obtenció d'imatges, càlculs basats en el mètode d'elements de contorn (BEM) per a les distribucions de plasmons superficials i la teoria del funcional de la densitat (DFT) per a l'anàlisi d’EELS. Tot i que es presentin per separat, no són independents; l'essència sempre és la mateixa, però depenent dels resultats desitjats es necessiten diferents consideracions. En aquest sentit, primerament s'han presentat les bases físiques de diferents mètodes de simulació: simulació multislice per calcular imatges de contrast de número atòmic i de contrast de fase, càlculs (DFT) per calcular dades EELS de baixa pèrdua i de pèrdues profundes i, simulacions basades en BEM per a plasmons de superfície. Un cop presentades les bases, s’han resolt problemes de la ciència dels materials mitjançant aquest tipus de simulacions: l'anàlisi dels efectes d'ordenació del CuPtB al GaInP, la influència de les vacants d'oxigen a l'EELS del Bi2O3, les conseqüències de la transició Fe3O4 Verwey en la seva estructura electrònica i com s'observa a l'EELS i, finalment, la distribució de plasmons superficials als nanodoms d'or en funció de la forma de la cúpula. En resum, al llarg la tesi doctoral les simulacions han demostrat ser una eina essencial per complementar els estudis de TEM, per vincular els resultats experimentals amb els aspectes més fonamentals determinats per l'estructura dels materials estudiats.

Treballs Finals de Grau de Física, Facultat de Física, Universitat de Barcelona, Curs: 2022, Tutores: Sònia Estradé, Gemma Viscasillas, The objective of this work is to use python-based big data tools to perform a gender study of doctoral theses carried out at the Faculty of Physics of the University of Barcelona. The data used for the study is a total of 561 theses that have been obtained from the Dipòsit Digital of the University of Barcelona through Web Scraping and have been analyzed using Python

Treballs Finals de Grau de Física, Facultat de Física, Universitat de Barcelona, Curs: 2021, Tutors: Sònia Estradé, Daniel Del Pozo Bueno, In this work we test machine learning tools such as the Support Vector Machine algorithm and neural network models on the task of Electron Energy-Loss Spectroscopy (EELS) spectra classification. Given many sample spectra of EELS applied on wüstite and magnetite nanocubes, we train both models to determine the oxidation state of iron. We show that SMV exhibits a good performance on classifying clean data, and we demonstrate the capability of neural networks of producing robust results given shifted data

[eng] This thesis has been primarily dedicated to the exploration and implementation of new computational analysis tools and techniques for the characterisation of nanomaterials and devices via transmission electron microscopy (TEM). In particular, the focus is set on the fields of electron energy loss spectroscopy (EELS) and electron tomography (ET). In the context of this PhD, EELS is used for the quantitative and qualitative analysis of elemental distributions at the nanoscale for several different materials, mainly transition metal and rare earth oxides. It is also used for the investigation of the distribution of elemental oxidation states at the nanoscale through the analysis of the so-called energy-loss near-edge structures (ELNES) of core-loss edges. The ever-growing size and complexity of the acquired spectral datasets, as well as a paradigmatic change towards the acquisition of larger but noisier spectral datasets, is the driving force behind the continuous push by the TEM community towards the implementation of new analysis techniques from the field of machine learning into the standard EELS characterization pipelines. The linear matrix factorization algorithms of principal component analysis (PCA) and non-negative matrix factorization (NMF) are among the first algorithms implemented for EELS analysis. Recently, several clustering analysis algorithms, such as K-means and hierarchical agglomerative clustering, have been used for the spectral segmentation of EELS spectrum images (SI) as well. In this thesis the combined use of a non-linear dimensionality reduction algorithm called uniform manifold approximation and projection (UMAP) for dimension reduction, and a clustering algorithm called hierarchical density-based spatial clustering of applications with noise (HDBSCAN), was explored as a viable solution towards a fully-data driven methodology for the spectral segmentation of EELS SI. Furthermore, a systematic revision of these new DRM and clustering methods (UMAP and HDBSCAN), the already stablished ones (PCA, NMF, K-means, etc.), and some of the possible combinations between them, was conducted. This revision includes several qualitative and quantitative performance analysis experiments, which are carried out for a series of specially designed synthetic datasets. The acquired experience with these techniques is later applied to characterize a wide variety of materials. Also, the combination of clustering and non-linear least-squares (NLLS) fitting has also been proven as a promising solution to improve the stability of the latter. This methodology was addressed as part of work done during this PhD to provide a ready-to-go software solution for all these machine learning methodologies applied to EELS and ELNES analysis, leading to the development of a complete and independent software solution called WhatEELS. This modular tool provides the resources required to quantitatively resolve complex problems involving ELNES analysis. A clear example of its powerful capabilities is showcased through the characterization of a set of Pr-Gd doped CeO2 mesoporous materials. In this series of experiments, the local changes in the Ce oxidation state and the localized dopant segregation were successfully resolved. The field of ET provides the materials scientist with one of the most versatile toolsets for the characterization of materials at the nanoscale, as it allows the reconstruction of 3D volumes from a limited set of 2D projections acquired. In this PhD thesis, the work is mainly focused on the implementation of advanced algorithms for the ET reconstruction of nanomaterials in Python programming language. The attention is centred on the TVAL3 algorithm, a solver for the total variation minimization (TVM) problem with its theoretical foundations in the mathematical field of compressed sensing. This methodology based on the TVAL3 algorithm is used for the experimental characterisation of the 3D morphology and chemical composition of a wide variety of different nanomaterials, such as the 3D resolution of the dopant segregation in the CeO2 mesoporous material., [spa] Esta tesis se centra, principalmente, en la exploración e implementación de nuevas herramientas y técnicas de análisis computacional para la caracterización de nanomateriales mediante espectroscopía de pérdida de energía de los electrones (EELS) y tomografía electrónica (TE). En el contexto de este doctorado, el EELS se utiliza para el análisis cuantitativo y cualitativo de distribuciones elementales a la nanoescala, principalmente para óxidos de metales de transición y de tierras raras. También se utiliza para la investigación de la distribución de estados de oxidación mediante el análisis de la estructura fina (ELNES). Para hacer dichos análisis, en esta tesis se demuestra que el uso combinado de un algoritmo de reducción de dimensionalidad (DRM) no lineal, UMAP, y un algoritmo jerárquico de agrupamiento (‘clustering’), HDBSCAN, es una solución viable hacia una metodología totalmente basada en los datos para la segmentación de imágenes de espectros de EELS. Además, se realizó una revisión sistemática de estos nuevos métodos de DRM y ‘clustering’ (UMAP y HDBSCAN), de los ya establecidos (PCA, NMF, K-means, etc.), y de algunas de sus posibles combinaciones. El uso combinado de ‘clustering’ y del ajuste de mínimos cuadrados no lineales (NLLS) se muestra también como una solución prometedora para el análisis de ELNES. Dicha metodología fue implementada como parte de una nueva herramienta de software llamada WhatEELS. Esta herramienta modular y de acceso gratuito proporciona los recursos necesarios para resolver cuantitativamente problemas complejos que involucran el análisis ELNES. Su potencial fue demostrado mediante el análisis de la segregación de dopantes y del cambio localizado del estado de oxidación catiónico para una serie de muestras de Ceria mesoporosa. Finalmente, parte de esta tesis también está dedicada a la implementación de algoritmos para el muestreo disperso en TE. En concreto, el algoritmo TVAL3 fue traducido al lenguaje de programación Python y utilizado para varios experimentos, incluida la resolución de la segregación de dopantes en 3D para los materiales mesoporosos de ceria ya mencionados.

[eng] The application of electron diffraction to crystallographically characterize all kinds of materials has experienced new developments that have attracted some attention in recent years. A large number of structural analyses from different compounds have been already carried out with the help of 3D electron diffraction data that were not possible with the available X-ray methods. The use of a transmission electron microscope as an electron nano-diffractometer has proved to be advantageous when diffraction data from single nanocrystals are required, for instance in phase mixtures. In this way, the individual phases do not have to be purely synthesized, which always involves the risk of structural changes. The work presented here includes the development and implementation of a novel and universal routine for the accurate and reliable acquisition of electron diffraction data. It contains the alignment of the transmission electron microscope in order to set a quasi-parallel and precessed beam suitable for the acquisition of this kind of data, and the description and comparison of the developed technique to the other methods already available. This novel acquisition method has been called fast and automated diffraction tomography (Fast-ADT) and it is based on two consecutive tilt scans of the goniometric stage of the microscope; one to image the crystal and generate a crystal tracking file, and a second one to acquire the diffraction patterns while the beam is automatically shifted to follow the crystal at the different tilt angles. Such technique has been implemented in different experimental setups to test different detectors as well as different samplings of the diffraction space to point out their advantages and hindrances. The potential of this new data collection strategy to solve various crystallographic problems is illustrated using three known materials: barite, an inorganic salt stable under the electron beam used to check the level of accuracy that can be obtained from electron diffraction, RUB-5, a layered silicate with disordered features to show the advantage of high frame-rate cameras, and the pi-ferrosilicide, a crystalline phase from a commercial alloy measured to demonstrate how electron diffraction can reliably determine absolute structures. In addition, two unknown crystal structures from commercial products are fully determined and refined. The first one is the dehydrated DRED1 molecular crystal, an inorganic dye used in textile applications, which has been solved ab initio revealing the 46 non-hydrogen atoms of the two independent molecules in P-1. Furthermore, the structure refinement based on intensities calculated according to the dynamical diffraction theory has proved the position of some of the hydrogens, confirming the square-like H-bond network initially found from a Rietveld refinement based on a X-ray powder diffractogram. Finally, the incommensurate modulated structure of one of the polymorphs of dicalcium silicate (belite), a major constituent of cement, has been comprehensively characterized only by means of electron diffraction. Such crystal structure has been known since 1971 but the observed modulation has never been fully studied. Here, the Fast-ADT technique is presented as a robust acquisition method to systematically identify and properly characterize different crystallographic phases and features of powder mixtures. In this particular case, the precise knowledge of the different crystal structures in cement clinkers, such as the alpha’H-C2S, enables the exact phase analysis of these industrial phase mixtures directly from the manufacturing process, and paves the way for its CO2 emissions reduction that, at the moment, adds up to 5% of the global anthropogenic emission. In this context, a novel technique for the collection of 3D electron diffraction datasets has been successfully developed and implemented to increase the range of reliable available tools for the characterization of atomic structures from different materials., [cat] L’aplicació de la difracció d’electrons per caracteritzar cristal·logràficament tot tipus de materials ha experimentat nous desenvolupaments que han cridat certa atenció durant aquests últims anys. Un gran nombre d’anàlisis estructurals en diferents compostos ja s’han dut a terme amb l’ajut de dades tridimensionals de difracció d’electrons que no eren possibles amb els habituals mètodes de raigs X. L’ús d'un microscopi electrònic de transmissió com a nano-difractòmetre d’electrons ha demostrat ser molt més beneficiós quan es requereixen dades de difracció de nanocristalls individuals, per exemple en mescles de fases cristal·logràfiques. D’aquesta manera, les fases individuals no s’han de sintetitzar en estat pur, fet que sempre comporta el risc de canvis estructurals. El treball presentat aquí inclou el desenvolupament i implementació d’una nova rutina universal per l’adquisició precisa i fiable de dades de difracció d’electrons. El potencial d’aquesta nova estratègia de recopilació de dades per resoldre diversos problemes cristal·logràfics s’il·lustra mitjançant tres materials coneguts. A més a més, dues estructures cristal·lines desconegudes de productes comercials han estat determinades i refinades completament; un colorant orgànic de baixa simetria i una estructura modulada incommensurada d’un component principal del ciment. En particular, el coneixement precís de les diferents estructures cristal·lines dels clinkers de ciment, com ara la alpha’H-C2S, permet l’anàlisi exacta de les fases d'aquestes mescles industrials extretes directament del procés de fabricació, i facilita el seu estudi per reduir les emissions de CO2.

Màster en Nanociència i Nanotecnologia, Facultat de Física, Universitat de Barcelona, Curs: 2018-2019. Tutors: Sònia Estradé Albiol, Javier Blanco Portals, In this work a sample of iron oxide nanoparticles is studied with a variety of techniques. In order to map its oxidation states, a characterization through indexing its crystallographic structure is attempted, but it is an EELS big data treatment through model creation of individual components in conjunction with clustering what will ultimately reveal a distribution map of different oxidation states across the sample

Treballs Finals de Grau de Física, Facultat de Física, Universitat de Barcelona, Curs: 2019, Tutors: Sònia Estradé Albiol, Enric Pérez Canals., I Premi al millor Treball Final de Grau amb perspectiva de gènere de la Universitat de Barcelona - Clara Campoamor - Curs: 2018-2019. Accèssit a la branca de Ciències experimentals i Enginyeria., The aim of the project is to find an objective tool to analyze relevant data on gender studies. Over the total proven methods, K-modes has been chosen as the most suitable tool for the analysis due to the categorical nature of the variables in the data-set. The algorithm implementation produces sub-groupings of the samples depending on the dis/similarities between them. The input data were obtained from a survey answered by Spanish physics professors

[eng] The aim of this thesis has been two-fold. First, to develop new processing and analysis tools and strategies for extracting information from EELS data, and second, to apply the methods to different nanoparticle systems to shed light to relevant phenomena related to their synthesis and properties. In this regard, chapter 1 presented and overview of the EELS fundamentals and of the state of the art of the technique. Chapter 2 was focused on the advanced computational methods related to EELS data analysis. Moreover, the application of cluster analysis to EELS was introduced, showing its possibilities as an image segmenting and phase identification tool. The following chapters were devoted to the investigation of different material science problems related to NPs that take advantage of the capabilities of quantitative EELS. The results were grouped by increasing complexity of the performed analysis, with chapter 3 devoted to characterizations that were mainly carried out using EELS elemental mapping, chapter 4 being related to ELNES analysis and chapter 5 to EELS tomography. In chapter 2, the adaptation of data clustering algorithms to the analysis of EELS data, developed within the scope of the present thesis, has been undertaken. In chapter 3.1 the organic synthesis of FeOx@SiO2 NPs was assessed. Several findings were obtained through the HRTEM, STEM-HAADF and EELS characterization of the FeOx@SiO2 NPs at different stages of its synthesis. In chapter 3.2, concerning Au-Ag-Se and the Au-Ag-S system cation exchange reactions several findings were made. Chapter 4 was devoted to the characterization of different NPs with an emphasis on the direct observation the oxidation state of its constituents through EELS. In chapter 4.1, the synthesis of MnOx/Fe3O4 core/shell NPs was assessed. In chapter 4.2, the measurement of oxidation state at atomic resolution in spinel crystals was proposed as a method to assess cation inversion in the crystal. The necessary methods were developed and applied to iron oxide/manganese oxide core/shell NPs. Chapter 5 was devoted to the combination of EELS and tomography. In chapter 5.1 the synthesis of cobalt oxide/cobalt ferrite (CoO@CFO) core/shell NPs and cobalt oxide/manganese ferrite (CoO@MFO) NPs was investigated. Chapter 5.2 was focused on the achievement of an oxidation state-sensitive tomographic reconstruction., [cat] L’adveniment de la nanotecnologia està portant amb ell l’aparició d’una gran quantitat de nous materials, compostos i aplicacions. En el seu desenvolupament, sovint té lloc fenomenologia sorprenent, o encara no ben entesa. Per omplir aquest forats en el nostre coneixement i poder desenvolupar noves aplicacions és de vital importància esbrinar la configuració estructural i química a nivell subnanomètric d’aquests components. Per la seva gran resolució espacial, la microscòpia electrònica de transmissió ha esdevingut una eina indispensable en aquest context. A més, en un microscopi electrònic es poden combinar una gran varietat de tècniques que poden donar una quantitat d’informació enorme. Una d’aquestes tècniques és l’espectroscòpia de pèrdua d’energia dels electrons (EELS). Aquesta tècnica ha permès en els últims anys el mapejat d’elements químics i ions columna atòmica per columna atòmica, arribant a uns dels nivells més íntims als que es pot conèixer la matèria en estat sòlid. L’objectiu d’aquesta tesi ha estat fer ús de l’EELS i d’altres tècniques emprades en microscòpia electrònica per entendre els processos químics que tenen lloc en diferents síntesis de nanopartícules. En aquest procés s’han desenvolupat també una sèrie d’eines enfocades al processat de les dades d’EELS ja sigui per a facilitar la seva interpretació, limitar problemes derivats de la seva adquisició (i. e. soroll) o calcular propietats concretes del material estudiat. A més aquesta tècnica s’ha combinat amb mètodes de reconstrucció 3D per obtenir una informació completa dels sistemes estudiats.

Màster en Nanociència i Nanotecnologia, Facultat de Física, Universitat de Barcelona, Curs: 2018-2019. Tutores: Sònia Estradé, Francesca Peiró, Electron magnetic circular dichroism (EMCD) is a novel technique used for the magnetic characterization at the nanoscale using the electron energy loss spectroscopy (EELS) in a transmission electron microscope (TEM). The EMCD is analogous to the X-ray magnetic circular dichroism technique (XMCD). However, this technique offers some bene ts in comparison with XMCD, such as the high spatial resolution at which the magnetic information of the sample is obtained, and magnetic depth sensitivity of the whole sample. In this master thesis, the EMCD technique was used to study magnetic nanocubes with a core/shell structure, formed by an iron II oxide core (FeO) covered by a magnetite shell (Fe3O4). The EMCD experiments were carried out using an intrinsic two-beam conditions as a scattering configuration to perform the experiment. In these Fe3O4/FeO nanocubes, it is imperative to probe the dichroic signal from the core and shell regions separately, in order to characterize the magnetic properties of the magnetite shell. For this purpose, EEL spectra were classified using data mining algorithms. Once both contributions were separated, the dichroic signal from both core and shell were obtained. Also, the spin magnetic moment ratio mL/mS is calculated for the magnetic shell. The difference in the dichroic signal between EMCD experiments carried out at room and low temperature are discussed

[eng] The main goal of this thesis has been to apply in-situ Transmission Electron Microscopy (TEM) electrical measurements using a Scanning Tunneling Microscopy (STM) tip, combined with TEM imaging and spectroscopic techniques, in order to address the characterization of relevant nanomaterials. This system has not only been used to measure electrical properties, but also to carry out in-situ experiments with Joule heating and to apply mechanical stresses. A review of the different in-situ TEM techniques, their development over the years and their impact in the scientific community has been presented. Moreover, the instrumental used in this thesis, in particular, the TEM-STM system, has been described. In addition, two techniques for the preparation of specific samples for in-situ TEM-STM experiments have been presented: for nanostructured samples (2D materials, nanowires, etc), and for localized samples (devices, thin layers, bulk samples, etc). A gridcase that allows the use of conventional TEM grids in the TEM-STM system has been designed and fabricated in the context of this thesis. The use of this homemade gridase has allowed us to improve the experiments, offering more reproducibility and versatility. Finally, the calibration of the electrical measurements of the system has been carried out. Using the TEM-STM system, different type of nanostructures have been characterized during the present thesis, from 2D nanostructures, as the elucidation of the effects of electrical current through a single graphene oxide sheet, to functional devices, as the study of the ferroelectric and piezoelectric behavior of structures based on La2WO6, the study of the anisotropic electrical conductivity of GaInP CuPtB type ordering layers used for multijunction solar cells or the study of the conductive filament (CF) formation mechanism in three different Resistive random-access memory (ReRAM) devices. In summary, in-situ microscopy expands the horizons of the characterization and study of materials and, in particular, in the context of this thesis, an in-situ TEM-STM system has been used to electrically characterize samples from nanomaterials to functional devices., [cat] En aquesta Tesi, s'ha emprat una tècnica de Microscopia Electrònica de Transmissió (TEM, Transmission Electron Microscopy en anglès) in-situ que permet realitzar mesures elèctriques utilitzant una sonda de microscòpia d'efecte túnel (STM, Scanning Tunneling Microscopy en anglès), tot combinant-la amb imatge TEM i tècniques d'espectroscòpia. A més, aquest sistema no només s'ha utilitzat per a mesurar les propietats elèctriques, sinó també per a dur a terme experiments in-situ amb escalfament per efecte Joule o aplicant una tensió mecànica a la superfície de la mostra. D'aquesta manera s'han pogut caracteritzar nanomaterials, des de nanoestructures 2D, estudiant l’efecte del pas de corrent a través d'un sol full d'òxid de grafè, fins a dispositius completament funcionals, com la caracterització piezoelèctrica i ferroelèctrica de capes primes d'òxids funcionals lliures de plom, l'estudi de l’anisotropia en la conductivitat d’estructures ternàries III-V ordenades utilitzades en cèl·lules solars tàndem multicapa i l'estudi amb TEM de la formació de filaments conductors (CF) i del mecanisme de commutació resistiva en tres dispositius ReRAM diferents. En els diferents capítols d'aquesta tesi s'ha donat resposta a problemes de ciència de materials amb l'ajut d'una tècnica de TEM in-situ tot combinant-la amb altres tècniques d'espectroscòpia i difracció. El desenvolupament d'aquesta tècnica ha permès caracteritzar les propietats del materials a nivell nano.

Màster en Nanociència i Nanotecnologia, Facultat de Física, Universitat de Barcelona, Curs: 2017-2018. Tutors: Sònia Estradé Albiol, Víctor Izquierdo Roca and Javier Blanco Portals, In the present work, we study a kesterite Cu2ZnSnSe4 solar cell at the nanoscale level in order to analyze the defects that lower its energy conversion efficiency. First of all, current density{voltage characteristics, quan- tum effciency, photoluminiscence, and Raman spectroscopy are studied to obtain macroscopic and microscopic information about the device. Then, High Resolution Transmission Electron Microscopy (HRTEM) is performed to observe the cross-section and, for the first time, the front interface of the absorber with nanoscopic detail

Treballs Finals de Grau de Física, Facultat de Física, Universitat de Barcelona, Curs: 2018, Tutors: Sonia Estradé Albiol, Javier Blanco Portals, In order to characterize an unknown sample, big data and machine learning methods are proposed. An electron energy loss (EEL) spectrum image obtained in the transmission electron microscope is analyzed. Applying principal component analysis (PCA) to image EEL spectra, the noise present in the raw data can be discarded, and comparing with existing datasets and alternatively through clustering analysis, the presence of vanadium and oxygen in the sample over a substrate with lanthanum and oxygen can be recognized

Treballs Finals de Grau de Física, Facultat de Física, Universitat de Barcelona, Curs: 2017, Tutors: Sònia Estradé Albiol i Pau Torruella Besa, In the present work, we focus on the study of nanoparticles of the Ag-Au-S ternary system. The nanoscopic dimensions recquire the use of powerful instruments and effcient techniques, so High Resolution Transmission Electron Microscopy (HRTEM) is performed. Using the Gatan DigitalMicrograph and the CaRIne Crystallography softwares, the nanostructures are identified and characterized.

Treballs Finals de Grau de Física, Facultat de Física, Universitat de Barcelona, Curs: 2016, Tutores: Sònia Estradé Albiol and Catalina Coll Benejam, Lanthanum nickel oxide, LaNiO3, is often used as an electrode in many electronic devices due to its low resistivity. The study of its properties requires understanding them in the nanoscale and, for this purpose, the electron transmission microscope is an indispensable tool. In the present work, we aim to examine the defects observed in High Angular Annular Dark Field (HAADF) images of a lanthanum nickel oxide thin film grown epitaxially on a lanthanum aluminate substrate. For this end, High Resolution Transmission Electron Microscopy (HRTEM) and HAADF images are simulated following the multislice method, implemented by Temsim, a software provided freely by E.J. Kirkland. Results show that the multislice method is a powerful tool so as to interpret the defects in the structure

Treballs Finals de Grau de Física, Facultat de Física, Universitat de Barcelona, Any: 2015, Tutors: Sònia Estradé Albiol i Lluís López Conesa, The use of High Resolution Tranmission Electron Microscopy (HRTEM) image simulation to interpret images of complex materials has gained popularity because of the progress in the field of simulation that has taken place in the last decades. In this work, we will explain one of the methods to simulate images, the multislice approach, and we will apply it to a tetragonal tungsten bronze (TTB) material, Sr0,67Ba0.33O2 (SBN-67), which is an interesting material for the technology of sensors because of its electrooptical, pyroelectrical and piezoelectrical properties. Then, these simulated images will be compared to the experimental ones, acquired with a JEOL 2010F TEM, to obtain the simulated image that best fits the experimental one, as to identify which atoms are present in this structure. To simulate the images we use a C++ code provided by Earl J. Kirkland, TEMsim, which is free for download. The results of these simulations demonstrate that the multislice approach is a powerful tool to interpret TEM images in spite of the huge amount of approximations that need to be introduced.

Being able to directly relate the final properties with the intimate structure provides a unique insight into the functionality of materials and devices, especially when compared to the necessarily statistical nature of the information that can be retrieved by macroscopic measurements. In particular, the scale reduction associated with the Nanoscience and Nanotechnology revolution demands characterization tools capable of reaching an unprecedented resolution, in a wide range of fields, not only for standard quality control, but in order to understand the properties of matter at the nanoscale. Going from bigger to smaller devices, but also from elemental building blocks (even atoms) to bigger assemblies, basic properties and device functionalities meet. With its ability to provide different kinds of information at a very high spatial resolution, state-of-the-art TEM and related techniques are in the core of this multidisciplinary and rapidly growing field. The first major topic is related to the assessment of local atomic ordering/disordering phenomena in functional materials. A series of rare earth niobates (RE3NbO7) will be studied in order to understand the microstructural origin of their proton conduction properties, that make them excellent candidates to be used as electrode materials in solid oxide fuel cells. Also, single crystals of the tetragonal tungsten bronze (TTB) Sr0.33Ba0.66Nb2O6 (SBN-67) will be studied by different TEM techniques in order to assess the possible short range structural and/or chemical disorder. These features are thought to be responsible for the observed macroscopic uniaxial polarization vector of the material as well as its relaxor properties. A second major topic of interest will be the phenomena taking place at interfaces. This includes the characterization of a set of LaNiO3 perovskite thin films grown on different substrates (LAO, LSAT, STO, YAO). The effect of the substrate-induced compressive/tensile strain, given by lattice mismatch, on the structure of the films will be assessed and related to the observed electric transport properties. The interfaces in a GaN/InAlN multilayered system designed as a Bragg reflector for laser cavities applications will be investigated in order to account for a lower than expected reflectivity of the devices. The presence of structural defects and the detection of intergrowth of wurtzite and zinc blende phases of GaN in thin films will be addressed. Also regarding interfaces and strain conditions, the characterization of the free surface of Nb2O5 nanorods, as a key point for their humidity sensing properties. Expanding on this, the strain state of Nb2O5 when grown on SnO2 nanowires will also be studied. The coupling of the sensing capabilities of Nb2O5 with the electrical transport properties of SnO2 is of particular interest for functional sensing devices. Therefore, defects at the interface and strain state are of capital interest in order to understand the band structure alignment of the system. Interfaces in lower dimensionality systems will also be studied, as in the case of Ag@Fe3O4 dimers for applications in magnetoplasmonics. The epitaxial quality, strain, and the possible chemical diffusion through the contact surface of the two phases of the dimer are key aspects in order to properly tailor their optical properties. The last major topic is the mapping of magnetic fields at the nanoscale. The magnetic configurations of different geometric arrangements of magnetite Fe3O4 nanocubes will be studied. This characterization is aimed at obtaining enhanced responses in magnetic hyperthermia treatments for cancer. Given the strong interrelationship between the problems under study, the chapter structure follows the dimensionality of the systems under study (3D, 2D, 1D and 0D systems)., La reducció en l'escala espacial associada a la revolució de la Nanociència i la Nanotecnologia fa necessari comptar amb una sèrie d'eines capaces d'assolir una resolució sense precedents en una gran varietat d'àress, ja no tan sols com a control de qualitat, sinó per tal d'entendre les propietats de la matèria a la nanoescala. La correlació de la configuració estructural, la composició química i les distribucions de càrrega amb les propietats funcionals és imprescindible pel disseny de nous dispositius, tant des de la perspectiva 'top down' (reducció de les dimensions dels dispositius) com de la perspectiva 'bottom up' (fabricació d'estructures complexes a partir de blocs més petits, fins i tot àtoms). La capacitat de la Microscòpia Electrònica de Transmissió (TEM) de proporcionar diferents tipus d'informació amb una alta resolució espacial, situa les tècniques avançades de TEM com a peça clau en el desenvolupament d'aquest camp multidisciplinari i creixent. L'objectiu principal d'aquesta tesi ha estat l'aplicació de tècniques quantitatives d'imatge TEM per la resolució de problemes en ciència dels materials. La tesi cobreix un espectre ampli pel que fa al tipus de materials estudiats i els seus camps d'aplicació. El Capítol 1 presenta una introducció general a la teoria de formació d'imatge aplicada a la microscopia TEM. S'hi exposen els diferents fenòmens d'interacció electró-matèria que són responsables dels diferents tipus de contrast que es poden trobar a les imatges TEM. El Capítol 2 presenta les tècniques experimentals que es faran servir en la caracterització dels materials, en concret la simulació d'imatges d'alta resolució (HRTEM), l'holografia electrònica i l'anàlisi de la fase geomètrica (GPA). S'hi pot trobar una descripció del marc teòric i dels fonaments experimentals, juntament amb un resum dels resultats més recents en aquests camps. Els resultats experimentals s'agrupen en els capítols posteriors segons la dimensionalitat dels sistemes estudiats. En ordre decreixent de dimensionalitat s'hi inclouen: materials massius (3D), capes primes (2D), nanofils (1D) i nanopartícules (1D).

[spa] Este trabajo explora las posibilidades analíticas que ofrece la técnica de espectroscopia electrónica de bajas pérdidas (low-loss EELS), capaces de revelar la configuración estructural de los más avanzados dispositivos semiconductores. El uso de modernos microscopios electrónicos de transmisión-barrido (STEM) nos permite obtener información espectroscópica a partir de volúmenes reducidos, hasta llegar a resolución atómica. Por ello, EELS es cada vez mas popular para la observación de los dispositivos semiconductores, a medida que los tamaños característicos de sus estructuras constituyentes se miniaturiza. Los espectros de pérdida de energía contienen mucha información: dado que el haz de electrones sufre unos bien conocidos procesos de dispersión inelástica, podemos trazar relaciones entre estos espectros y excitaciones elementales en la configuración atómica de los elementos y compuestos constituyentes de cada material. Se describe un marco teórico para el estudio del low-loss EELS: el modelo dieléctrico de dispersión inelástica, que toma en consideración las propiedades electrodinámicas del haz de electrones y la descripción mecano-cuántica de los materiales. Adicionalmente, se describen en detalle las herramientas utilizadas en el análisis de datos experimentales o la simulación teórica de espectros. Monitorizando las energías de band gap y plasmon en los datos experimentales de low-loss EELS se obtiene información directa sobre propiedades electrónicas de los materiales. Además, usando análisis Kramers-Kronig en los espectros se obtiene información dieléctrica que puede ser comparada con las simulaciones o con otras técnicas (ópticas). Se demuestra el uso de estas herramientas con una serie de estudios sobre estructuras basadas en nitruros del grupo-III. Por otro lado, el uso de algoritmos para el análisis multivariante permite separar las contribuciones individuales que se miden mezcladas en espectros de estructuras complicadas. Hemos utilizado estas avanzadas herramientas para el análisis de estructuras basadas en silicio que contienen nano-cristales embebidos en matrices dieléctricas., [eng] 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.

Treballs Finals de Grau de Física, Facultat de Física, Universitat de Barcelona, Any: 2014, Tutores: Francesca Peiró Martínez i Sonia Estradé Albiol, Er-doped silicon nanocrystal-based oxides/nitrides have been investigated. These layers are grown between a polycrystalline silicon electrode and a monocrystalline silicon substrate to allow electrical injection. Energy Filtered (EF-) and High Resolution (HR-) TEM characterization has been performed to provide microscopic insight onto the macroscopic optoelectronic properties of the samples. Evident Er-clustering has been observed in silicon dioxides but not in silicon nitrides, suggesting a better Er solubility and local environment when nitrogen is incorporated. Silicon nanocrystals have been observed in silicon-rich nitride layers, as expected, but also in a region close to the silicon dioxide-polysilicon interface in a layer with no nitrogen or Si excesses. This unexpected Si clusterization has been attributed to Si diffusion from the polycrystalline silicon electrode into the silicon dioxide as a consequence of the annealing treatment. The structural characterization carried out by HRTEM and EFTEM has been correlated with the optoelectronic properties of the devices.

The main goal of this thesis is to combine electron tomography and electron energy loss spectroscopy (EELS) in the TEM, in order to obtain chemical and electronic information in 3D in the nanoscale. Tomography in the TEM has been discussed and the advantages and disadvantages of HAADF STEM tomography have been analyzed. - A Fe3O4 nanocube sample has been considered to illustrate the acquisition, alignment, tilt axis assessment, reconstruction and visualization processes. - HAADF STEM tomography has been used to reconstruct the shape of a series of Cu2O nanoparticles. For one of the samples, the facets of the Cu2O nanoparticles, octahedral in shape, have been found to correspond to {111} planes. The physics and the data analysis methods of core-loss EELS have been briefly summarized. Two relevant contributions have been made: - The effects of beam precession on EELS have been investigated. A signal enhancement due to electron beam precession in the TEM when in zone axis conditions has been discovered for the first time. - A homemade software, Oxide Wizard, for valence state determination of transition metals has been developed and applied to map the Mn oxidation state of a MnOx/FeOy nanoparticle. EELS spectrum imaging and electron tomography have been combined to recover chemical information in 3D for FexCo(3-x)O4@Co3O4 mesoporous nanoparticles. - The samples have been first characterized by HAADF STEM tomography and EELS. - EELS chemical information is, of course, limited to 2D maps, while only structural information is be recovered in 3D form HAADF tomography. . An EELS-SI tilt series has been acquired at 80 kV and low acquisition times, resulting in a very noisy dataset. - Principal component analysis (PCA) has been used to separate the noise from the signal. - Quantifications of the O, Fe and Co signals have been reconstructed, and the shape of the particle recovered. - From the noise clean dataset, components with physical meaning (iron oxide, cobalt oxide and thickness) have been extracted using independent component analysis (ICA), and reconstructed in 3D. - A new kind of signal with chemical and thickness information has been obtained by combining the thickness component with the quantification results. This signal is able to properly reconstruct the chemical structure of the sample in 3D, detecting a higher presence of iron in the surface, and an even distribution of Fe inside of the particle. . Another EELS-SI tilt series has been acquired at 80 kV and low acquisition times with enough spatial resolution to resolve the porous structure. - The noise has been reduced using PCA. - Four signals extracted from the spectrum have been reconstructed: the integrated edge intensities for oxygen, iron and cobalt, and the integrated background prior to the oxygen edge. EELS-SI tomography has been applied to reconstruct CoFe2O4 (CFO) nanocolumns embedded in a BiFeO3 (BFO) matrix grown on LaNiO3 buffered LaAlO3 substrate (BFO-CFO//LNO/LAO). - The nanocomposite sample has been prepared in a nanoneedle shape by means of focused ion beam (FIB). This preparation has the advantage of keeping the thickness of the sample constant throughout the tilting experiment. The nanoneedle contains an island of CFO in a matrix of BFO, as well as the LNO/LAO substrate. - The noise has been discarded using PCA. - The oxygen, iron and lanthanum edges intensities have been extracted and reconstructed. A new kind of data hypercube, the Spectrum Volume, has been proposed. Just as a Spectrum Image contains a spectrum per pixel, a Spectrum Volume is to contain a spectrum per voxel. EELS-SI tomography has been applied to successfully acquire a spectrum volume (SV) of the (BFO-CFO//LNO/LAO) system. - PCA has been used to discard the noise and Bayesian linear unmixing (BLU) has been used to extract independent components (eigenspectra). - Each eigenspectrum has a 2D weighting map for each tilt; weighting maps have been reconstructed into 3D weighting volumes. - Full single spectra for any point in the reconstructed space can now be recovered as a weighed sum of eigenspectra, using the 3D weighting distributions. This approach is used to extract single spectra, spectrum lines and spectrum images from the inside of the sample. In the context of this thesis, tomography and EELS-SI have been combined to successfully recover chemical information in 3D at the nanoscale, and a new kind of data hypercube, the Spectrum Volume, has been proposed and experimentally recovered., En el microscopi electrònic de transmissió (TEM), es poden obtenir imatges d’una mostra des de diferents angles i posteriorment reconstruir aquestes imatges en tres dimensions (3D). Per altra banda, les interaccions dels electrons del feix amb els electrons de la mostra poden ser analitzades mitjançant l’espectroscòpia de pèrdues d’energia dels electrons (EELS), obtenint així informació química de la mostra. L’objectiu d’aquesta tesi és la combinació de l’espectroscòpia EELS amb la tomografia electrònica per obtenir informació química en 3 dimensions a la nanoescala. S’han explicat les bases de la tomografia electrònica i el procediment de la reconstrucció ha estat il•lustrat amb una mostra de nanocubs d’òxid de ferro. Posteriorment, s’ha aplicat a una sèrie de nanopartícules de Cu2O per tal de descriure’n la forma. També s’ha explicat la física en què es basa l’EELS, fent especial atenció als llindars d’altes pèrdues d’energia. A continuació, s’ha mostrat l’augment del senyal obtingut amb precessió electrònica al TEM quan la mostra es troba en condicions d’eix de zona. Seguint amb les aplicacions d’EELS, s’ha explotat la possibilitat de caracteritzar els estats d’oxidació dels metalls de transició mitjançant un programa propi, escrit per a Digital Micrograph i anomenat Oxide Wizard. Una vegada la tomografia electrònica i l’espectroscòpia de pèrdues d’energia dels electrons han estat explicades, s’ha procedit a reconstruir informació extreta d’EELS en 3D. S’han realitzat una sèrie d’experiments amb partícules mesoporoses que han demostrat la utilitat d’aplicar l’anàlisi multivariable per tal de reduir el soroll de les dades i extreure’n els components. Finalment, s’ha dissenyat un experiment en el qual ha estat possible recuperar l’espectre corresponent a cada unitat d’espai com la combinació d’espectres propis en una mostra preparada en forma de nanoagulla. Els espectres recuperats corresponen a la contribució de cada unitat de volum als espectres projectats. Aquest nou tipus de dades permet extreure espectres de l’interior d’una mostra. Finalment, doncs, s’ha pogut combinar amb èxit la tomografia electrònica i EELS per obtenir informació química en tres dimensions a la nanoescala.