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180 p., Esta tesis recoge los resultados obtenidos durante los primeros pasos en el desarrollo de un quemo-sensor de bario dicatión para el experimento NEXT. Su funcionamiento se basa en convertir propiedades químicas del analito en una señal detectable, como una señal eléctrica u óptica. Recientemente se ha explorado el uso de quemo-sensores fluorescentes como herramienta potencialmente única en el campo de la física de neutrinos. El experimento NEXT busca detectar la desintegración doble beta sin neutrinos del isótopo 136Xe. En esta desintegración se producen dos electrones y un dicatión 136Ba2+. Si el ión Ba2+se detectase en coincidencia con los electrones, el experimento NEXT funcionaría sin background. Para identificar el ión Ba2+ se ha propuesto utilizar quemo-sensores fluorescentes. El uso de esta técnica en el campo de física de partículas es completamente novedoso y requiere adaptar estos sensores al entorno extremadamente seco de una cámara de xenon gaseoso a alta presión. La fabricación del sensor requiere inmobilizar las moléculas en una superficie que preserve la sensibilidad de la señal fluorescente. Este enfoque requiere el uso de técnicas de deposición molecular y caracterización en superficies con precisión atómica y el desarrollo de un microscopio de fluorescencia adaptado a estas condiciones.

127 p., En esta Tesis, estudiamos a escala nanométrica materiales con aplicabilidad en tecnologías cuánticas, centrándonos, principalmente, en sensores de radiación electromagnética basados en el efecto termoeléctrico gigante. Este efecto tiene lugar en heteroestructuras basadas en superconductores que se encuentran en contacto con un aislante ferromagnético, el cual crea un desequilibrio de espín en su densidad de estados, conocido como spin-splitting. Este efecto depende de muchos factores, entre los que se encuentran la calidad de la interfaz superconductor/aislante ferromagnético y las propiedades de todos los materiales que conforman la heteroestructura.Mediante una combinación de técnicas de caracterización en ultra alto vacío y ex-situ, hemos demostrado cómo las condiciones de preparación afectan a las propiedades estructurales, químicas y magnéticas de los materiales, pudiendo controlar y modificar esas propiedades de acuerdo a las necesidades del dispositivo en que se quieran incorporar. Además, hemos fabricado uniones de tipo túnel, estudiando también las condiciones de fabricación que tienen impacto en el transporte a través de dichas uniones.

Earth-abundant electrocatalysts for the oxygen evolution reaction (OER) able to work in acidic working conditions are elusive. While many first-row transition metal oxides are competitive in alkaline media, most of them just dissolve or become inactive at high proton concentrations where hydrogen evolution is preferred. Only noble-metal catalysts, such as IrO2, are fast and stable enough in acidic media. Herein, we report the excellent activity and long-term stability of Co3O4-based anodes in 1 M H2SO4 (pH 0.1) when processed in a partially hydrophobic carbon-based protecting matrix. These Co3O4@C composites reliably drive O-2 evolution a 10 mA cm(-2) current density for >40 h without appearance of performance fatigue, successfully passing benchmarking protocols without incorporating noble metals. Our strategy opens an alternative venue towards fast, energy efficient acid-media water oxidation electrodes. While water electrolysis offers a renewable way to produce hydrogen, there are few Earth-abundant, acid-stable water oxidation catalysts. Here, authors show Co3O4, when protected by a partially hydrophobic environment, to sustain 40 h activity without structural or chemical transformations.

Diodes are characterized by mono-directional flow of current, yet this simplicity belies their critical importance in electronics and optics. Here, Strambini et al demonstrate a superconducting quasi-particle equivalent, achieved by the use of a thin ferromagnetic insulator. Diodes are key elements for electronics, optics, and detection. Their evolution towards low dissipation electronics has seen the hybridization with superconductors and the realization of supercurrent diodes with zero resistance in only one direction. Here, we present the quasi-particle counterpart, a superconducting tunnel diode with zero conductance in only one direction. The direction-selective propagation of the charge has been obtained through the broken electron-hole symmetry induced by the spin selection of the ferromagnetic tunnel barrier: a EuS thin film separating a superconducting Al and a normal metal Cu layer. The Cu/EuS/Al tunnel junction achieves a large rectification (up to similar to 40%) already for a small voltage bias (similar to 200 mu V) thanks to the small energy scale of the system: the Al superconducting gap. With the help of an analytical theoretical model we can link the maximum rectification to the spin polarization (P) of the barrier and describe the quasi-ideal Shockley-diode behavior of the junction. This cryogenic spintronic rectifier is promising for the application in highly-sensitive radiation detection for which two different configurations are evaluated. In addition, the superconducting diode may pave the way for future low-dissipation and fast superconducting electronics.

Diodes are characterized by mono-directional flow of current, yet this simplicity belies their critical importance in electronics and optics. Here, Strambini et al demonstrate a superconducting quasi-particle equivalent, achieved by the use of a thin ferromagnetic insulator. Diodes are key elements for electronics, optics, and detection. Their evolution towards low dissipation electronics has seen the hybridization with superconductors and the realization of supercurrent diodes with zero resistance in only one direction. Here, we present the quasi-particle counterpart, a superconducting tunnel diode with zero conductance in only one direction. The direction-selective propagation of the charge has been obtained through the broken electron-hole symmetry induced by the spin selection of the ferromagnetic tunnel barrier: a EuS thin film separating a superconducting Al and a normal metal Cu layer. The Cu/EuS/Al tunnel junction achieves a large rectification (up to similar to 40%) already for a small voltage bias (similar to 200 mu V) thanks to the small energy scale of the system: the Al superconducting gap. With the help of an analytical theoretical model we can link the maximum rectification to the spin polarization (P) of the barrier and describe the quasi-ideal Shockley-diode behavior of the junction. This cryogenic spintronic rectifier is promising for the application in highly-sensitive radiation detection for which two different configurations are evaluated. In addition, the superconducting diode may pave the way for future low-dissipation and fast superconducting electronics.

Diodes are characterized by mono-directional flow of current, yet this simplicity belies their critical importance in electronics and optics. Here, Strambini et al demonstrate a superconducting quasi-particle equivalent, achieved by the use of a thin ferromagnetic insulator. Diodes are key elements for electronics, optics, and detection. Their evolution towards low dissipation electronics has seen the hybridization with superconductors and the realization of supercurrent diodes with zero resistance in only one direction. Here, we present the quasi-particle counterpart, a superconducting tunnel diode with zero conductance in only one direction. The direction-selective propagation of the charge has been obtained through the broken electron-hole symmetry induced by the spin selection of the ferromagnetic tunnel barrier: a EuS thin film separating a superconducting Al and a normal metal Cu layer. The Cu/EuS/Al tunnel junction achieves a large rectification (up to similar to 40%) already for a small voltage bias (similar to 200 mu V) thanks to the small energy scale of the system: the Al superconducting gap. With the help of an analytical theoretical model we can link the maximum rectification to the spin polarization (P) of the barrier and describe the quasi-ideal Shockley-diode behavior of the junction. This cryogenic spintronic rectifier is promising for the application in highly-sensitive radiation detection for which two different configurations are evaluated. In addition, the superconducting diode may pave the way for future low-dissipation and fast superconducting electronics.

Earth-abundant electrocatalysts for the oxygen evolution reaction (OER) able to work in acidic working conditions are elusive. While many first-row transition metal oxides are competitive in alkaline media, most of them just dissolve or become inactive at high proton concentrations where hydrogen evolution is preferred. Only noble-metal catalysts, such as IrO2, are fast and stable enough in acidic media. Herein, we report the excellent activity and long-term stability of Co3O4-based anodes in 1 M H2SO4 (pH 0.1) when processed in a partially hydrophobic carbon-based protecting matrix. These Co3O4@C composites reliably drive O-2 evolution a 10 mA cm(-2) current density for >40 h without appearance of performance fatigue, successfully passing benchmarking protocols without incorporating noble metals. Our strategy opens an alternative venue towards fast, energy efficient acid-media water oxidation electrodes. While water electrolysis offers a renewable way to produce hydrogen, there are few Earth-abundant, acid-stable water oxidation catalysts. Here, authors show Co3O4, when protected by a partially hydrophobic environment, to sustain 40 h activity without structural or chemical transformations.

Ferromagnetic insulators (FI) can induce a strong exchange field in an adjacent superconductor (S) via the magnetic proximity effect. This manifests as spin splitting of the BCS density of states of the superconductor, an important ingredient for numerous superconducting spintronics applications and the realization of Majorana fermions. A crucial parameter that determines the magnitude of the induced spin splitting in FI/S bilayers is the thickness of the S layer d: In very thin samples, the superconductivity is suppressed by the strong magnetism. By contrast, in very thick samples, the spin splitting is absent at distances away from the interface. In this work, we calculate the density of states and critical exchange field of FI/S bilayers of arbitrary thickness. From here, we determine the range of parameters of interest for applications, where the exchange field and superconductivity coexist. We show that for d > 3.0 xi(s), the paramagnetic phase transition is always of the second order, in contrast to the first-order transition in thinner samples at low temperatures. Here xi(s), is the superconducting coherence length. Finally, we compare our theory with the tunneling spectroscopy measurements in several EuS/Al/AlOx/Al samples. If the Al film in contact with the EuS is thinner than a certain critical value, we do not observe superconductivity, whereas, in thicker samples, we find evidence of a first-order phase transition induced by an external field. The complete transition is preceded by a regime in which normal and superconducting regions coexist. We attribute this mixed phase to inhomogeneities of the Al film thickness and the presence of superparamagnetic grains at the EuS /Al interface with different switching fields. The steplike evolution of the tunnel-barrier magnetoresistance supports this assumption. Our results demonstrate on the one hand, the important role of the S layer thickness, which is particularly relevant for the fabrication of high-quality

Next-generation neutrinoless double beta decay experiments aim for half-life sensitivities of similar to 10(27) yr, requiring suppressing backgrounds to < 1 count/tonne/yr. For this, any extra background rejection handle, beyond excellent energy resolution and the use of extremely radiopure materials, is of utmost importance. The NEXT experiment exploits differences in the spatial ionization patterns of double beta decay and single-electron events to discriminate signal from background. While the former display two Bragg peak dense ionization regions at the opposite ends of the track, the latter typically have only one such feature. Thus, comparing the energies at the track extremes provides an additional rejection tool. The unique combination of the topology-based background discrimination and excellent energy resolution (1% FWHM at the Q-value of the decay) is the distinguishing feature of NEXT. Previous studies demonstrated a topological background rejection factor of 5 when reconstructing electron-positron pairs in the Tl-208 1.6 MeV double escape peak (with Compton events as background), recorded in the NEXT-White demonstrator at the Laboratorio Subterraneo de Canfranc, with 72% signal efficiency. This was recently improved through the use of a deep convolutional neural network to yield a background rejection factor of similar to 10 with 65% signal efficiency. Here, we present a new reconstruction method, based on the Richardson-Lucy deconvolution algorithm, which allows reversing the blurring induced by electron diffusion and electroluminescence light production in the NEXT TPC. The new method yields highly refined 3D images of reconstructed events, and, as a result, significantly improves the topological background discrimination. When applied to real-data 1.6 MeV e(-)e(+) pairs, it leads to a background rejection factor of 27 at 57% signal efficiency.

Ferromagnetic insulators (FI) can induce a strong exchange field in an adjacent superconductor (S) via the magnetic proximity effect. This manifests as spin splitting of the BCS density of states of the superconductor, an important ingredient for numerous superconducting spintronics applications and the realization of Majorana fermions. A crucial parameter that determines the magnitude of the induced spin splitting in FI/S bilayers is the thickness of the S layer d: In very thin samples, the superconductivity is suppressed by the strong magnetism. By contrast, in very thick samples, the spin splitting is absent at distances away from the interface. In this work, we calculate the density of states and critical exchange field of FI/S bilayers of arbitrary thickness. From here, we determine the range of parameters of interest for applications, where the exchange field and superconductivity coexist. We show that for d > 3.0 xi(s), the paramagnetic phase transition is always of the second order, in contrast to the first-order transition in thinner samples at low temperatures. Here xi(s), is the superconducting coherence length. Finally, we compare our theory with the tunneling spectroscopy measurements in several EuS/Al/AlOx/Al samples. If the Al film in contact with the EuS is thinner than a certain critical value, we do not observe superconductivity, whereas, in thicker samples, we find evidence of a first-order phase transition induced by an external field. The complete transition is preceded by a regime in which normal and superconducting regions coexist. We attribute this mixed phase to inhomogeneities of the Al film thickness and the presence of superparamagnetic grains at the EuS /Al interface with different switching fields. The steplike evolution of the tunnel-barrier magnetoresistance supports this assumption. Our results demonstrate on the one hand, the important role of the S layer thickness, which is particularly relevant for the fabrication of high-quality

Next-generation neutrinoless double beta decay experiments aim for half-life sensitivities of similar to 10(27) yr, requiring suppressing backgrounds to < 1 count/tonne/yr. For this, any extra background rejection handle, beyond excellent energy resolution and the use of extremely radiopure materials, is of utmost importance. The NEXT experiment exploits differences in the spatial ionization patterns of double beta decay and single-electron events to discriminate signal from background. While the former display two Bragg peak dense ionization regions at the opposite ends of the track, the latter typically have only one such feature. Thus, comparing the energies at the track extremes provides an additional rejection tool. The unique combination of the topology-based background discrimination and excellent energy resolution (1% FWHM at the Q-value of the decay) is the distinguishing feature of NEXT. Previous studies demonstrated a topological background rejection factor of 5 when reconstructing electron-positron pairs in the Tl-208 1.6 MeV double escape peak (with Compton events as background), recorded in the NEXT-White demonstrator at the Laboratorio Subterraneo de Canfranc, with 72% signal efficiency. This was recently improved through the use of a deep convolutional neural network to yield a background rejection factor of similar to 10 with 65% signal efficiency. Here, we present a new reconstruction method, based on the Richardson-Lucy deconvolution algorithm, which allows reversing the blurring induced by electron diffusion and electroluminescence light production in the NEXT TPC. The new method yields highly refined 3D images of reconstructed events, and, as a result, significantly improves the topological background discrimination. When applied to real-data 1.6 MeV e(-)e(+) pairs, it leads to a background rejection factor of 27 at 57% signal efficiency.

Next-generation neutrinoless double beta decay experiments aim for half-life sensitivities of similar to 10(27) yr, requiring suppressing backgrounds to < 1 count/tonne/yr. For this, any extra background rejection handle, beyond excellent energy resolution and the use of extremely radiopure materials, is of utmost importance. The NEXT experiment exploits differences in the spatial ionization patterns of double beta decay and single-electron events to discriminate signal from background. While the former display two Bragg peak dense ionization regions at the opposite ends of the track, the latter typically have only one such feature. Thus, comparing the energies at the track extremes provides an additional rejection tool. The unique combination of the topology-based background discrimination and excellent energy resolution (1% FWHM at the Q-value of the decay) is the distinguishing feature of NEXT. Previous studies demonstrated a topological background rejection factor of 5 when reconstructing electron-positron pairs in the Tl-208 1.6 MeV double escape peak (with Compton events as background), recorded in the NEXT-White demonstrator at the Laboratorio Subterraneo de Canfranc, with 72% signal efficiency. This was recently improved through the use of a deep convolutional neural network to yield a background rejection factor of similar to 10 with 65% signal efficiency. Here, we present a new reconstruction method, based on the Richardson-Lucy deconvolution algorithm, which allows reversing the blurring induced by electron diffusion and electroluminescence light production in the NEXT TPC. The new method yields highly refined 3D images of reconstructed events, and, as a result, significantly improves the topological background discrimination. When applied to real-data 1.6 MeV e(-)e(+) pairs, it leads to a background rejection factor of 27 at 57% signal efficiency.

Ferromagnetic insulators (FI) can induce a strong exchange field in an adjacent superconductor (S) via the magnetic proximity effect. This manifests as spin splitting of the BCS density of states of the superconductor, an important ingredient for numerous superconducting spintronics applications and the realization of Majorana fermions. A crucial parameter that determines the magnitude of the induced spin splitting in FI/S bilayers is the thickness of the S layer d: In very thin samples, the superconductivity is suppressed by the strong magnetism. By contrast, in very thick samples, the spin splitting is absent at distances away from the interface. In this work, we calculate the density of states and critical exchange field of FI/S bilayers of arbitrary thickness. From here, we determine the range of parameters of interest for applications, where the exchange field and superconductivity coexist. We show that for d > 3.0 xi(s), the paramagnetic phase transition is always of the second order, in contrast to the first-order transition in thinner samples at low temperatures. Here xi(s), is the superconducting coherence length. Finally, we compare our theory with the tunneling spectroscopy measurements in several EuS/Al/AlOx/Al samples. If the Al film in contact with the EuS is thinner than a certain critical value, we do not observe superconductivity, whereas, in thicker samples, we find evidence of a first-order phase transition induced by an external field. The complete transition is preceded by a regime in which normal and superconducting regions coexist. We attribute this mixed phase to inhomogeneities of the Al film thickness and the presence of superparamagnetic grains at the EuS /Al interface with different switching fields. The steplike evolution of the tunnel-barrier magnetoresistance supports this assumption. Our results demonstrate on the one hand, the important role of the S layer thickness, which is particularly relevant for the fabrication of high-quality

131 p., En el presente trabajo estudiamos el crecimiento de nano-estructuras de grafeno (GNR) mediante la reacción de Ullmann en superficies tecnológicamente relevantes.Desde su redescubrimiento allá por el año 2004, el grafeno es conocido como el material del futuro debido, entre otras cosas, a sus excelentes propiedades tanto químicas como electrónicas. Sin embargo, para su implementación en la industria de la nano electrónica y/o nana óptica en forma de dispositivo, necesita poder ser apagado y encendido, es decir, tener un ratio ¿on/off¿. El grafeno es un semimetal por lo que no se puede encender ni apagar intrínsecamente. De las muchas estrategias para conseguir dicho objetivo, uno de los más efectivos se basa en el confinamiento del grafeno, es decir, en disminuir de dos dimensiones a cuasi una dimensión el tamaño del grafeno. En consecuencia, se generan las estructuras llamadas nano grafenos o GNR.Sus excelentes propiedades electrónicas, similares a las del grafeno, así como el gap intrínseco (lo que permite encender o apagarlos) de las estructuras de GNR, hace de ellos componentes idóneos para su implementación en dispositivos electrónicos como por ejemplo los transistores de potencia. Una de las maneras más atractivas de sintetizar estas estructuras de GNR es mediante la reacción de Ullmann, que consiste en ensamblar moléculas previamente prediseñadas en una superficie catalizadora. Sin embargo, por ahora, la reacción de Ullmann solo se ha podido realizar con éxito en superficies metálicas, donde, intrínsecamente, las propiedades del GNR se desvanecen o hibridan. Por ello, una vez sintetizados los GNR, tienen que ser transferidos a superficies modelo, como un semiconductor en el caso del transistor, para poder ser implementados en futuros nano dispositivos, y normalmente la eficacia de dicha transferencia es muy pobre. El siguiente paso en el campo, y el objetivo del presente trabajo, es crecer estructuras de GNR mediante la reacción de Ullmann directamente en supe

131 p., En el presente trabajo estudiamos el crecimiento de nano-estructuras de grafeno (GNR) mediante la reacción de Ullmann en superficies tecnológicamente relevantes.Desde su redescubrimiento allá por el año 2004, el grafeno es conocido como el material del futuro debido, entre otras cosas, a sus excelentes propiedades tanto químicas como electrónicas. Sin embargo, para su implementación en la industria de la nano electrónica y/o nana óptica en forma de dispositivo, necesita poder ser apagado y encendido, es decir, tener un ratio ¿on/off¿. El grafeno es un semimetal por lo que no se puede encender ni apagar intrínsecamente. De las muchas estrategias para conseguir dicho objetivo, uno de los más efectivos se basa en el confinamiento del grafeno, es decir, en disminuir de dos dimensiones a cuasi una dimensión el tamaño del grafeno. En consecuencia, se generan las estructuras llamadas nano grafenos o GNR.Sus excelentes propiedades electrónicas, similares a las del grafeno, así como el gap intrínseco (lo que permite encender o apagarlos) de las estructuras de GNR, hace de ellos componentes idóneos para su implementación en dispositivos electrónicos como por ejemplo los transistores de potencia. Una de las maneras más atractivas de sintetizar estas estructuras de GNR es mediante la reacción de Ullmann, que consiste en ensamblar moléculas previamente prediseñadas en una superficie catalizadora. Sin embargo, por ahora, la reacción de Ullmann solo se ha podido realizar con éxito en superficies metálicas, donde, intrínsecamente, las propiedades del GNR se desvanecen o hibridan. Por ello, una vez sintetizados los GNR, tienen que ser transferidos a superficies modelo, como un semiconductor en el caso del transistor, para poder ser implementados en futuros nano dispositivos, y normalmente la eficacia de dicha transferencia es muy pobre. El siguiente paso en el campo, y el objetivo del presente trabajo, es crecer estructuras de GNR mediante la reacción de Ullmann directamente en supe

131 p., En el presente trabajo estudiamos el crecimiento de nano-estructuras de grafeno (GNR) mediante la reacción de Ullmann en superficies tecnológicamente relevantes.Desde su redescubrimiento allá por el año 2004, el grafeno es conocido como el material del futuro debido, entre otras cosas, a sus excelentes propiedades tanto químicas como electrónicas. Sin embargo, para su implementación en la industria de la nano electrónica y/o nana óptica en forma de dispositivo, necesita poder ser apagado y encendido, es decir, tener un ratio ¿on/off¿. El grafeno es un semimetal por lo que no se puede encender ni apagar intrínsecamente. De las muchas estrategias para conseguir dicho objetivo, uno de los más efectivos se basa en el confinamiento del grafeno, es decir, en disminuir de dos dimensiones a cuasi una dimensión el tamaño del grafeno. En consecuencia, se generan las estructuras llamadas nano grafenos o GNR.Sus excelentes propiedades electrónicas, similares a las del grafeno, así como el gap intrínseco (lo que permite encender o apagarlos) de las estructuras de GNR, hace de ellos componentes idóneos para su implementación en dispositivos electrónicos como por ejemplo los transistores de potencia. Una de las maneras más atractivas de sintetizar estas estructuras de GNR es mediante la reacción de Ullmann, que consiste en ensamblar moléculas previamente prediseñadas en una superficie catalizadora. Sin embargo, por ahora, la reacción de Ullmann solo se ha podido realizar con éxito en superficies metálicas, donde, intrínsecamente, las propiedades del GNR se desvanecen o hibridan. Por ello, una vez sintetizados los GNR, tienen que ser transferidos a superficies modelo, como un semiconductor en el caso del transistor, para poder ser implementados en futuros nano dispositivos, y normalmente la eficacia de dicha transferencia es muy pobre. El siguiente paso en el campo, y el objetivo del presente trabajo, es crecer estructuras de GNR mediante la reacción de Ullmann directamente en supe