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- ItemStudy on the properties of CO2 adsorption and CO detection by materials based on modified graphene oxide and copper oxide composites(2025) Roble Albeal, Martín Cristián; Díaz, Donovan; Pontificia Universidad Católica de Chile. Instituto de FísicaThis doctoral thesis focused in two related topics, carbon dioxide (CO2) adsorption and carbon monoxide (CO) detection. Both research areas shared a common material, graphene oxide (GO). For CO2 adsorption, chemical modification of GO, which produced modified GO (mGO), was done using a variety of chemical compounds. For CO detection, composite materials based on hydrothermally-produced copper oxide (CuO) and GO were studied. GO was synthesized via Tour’s method and modified using ammonia (mGO-N1), hydrazine (mGO-N2), sodium sulfide (mGO-S1), sodium sulfate (mGO-S2), and pure water (mGO-H), using a condensation reflux system and under the same reaction temperature and time. Modifications aimed to introduce heteroatoms (N, S) and alter the oxygen functional groups inGO. The obtained materials were characterized by a variety of techniques, and their CO2 adsorption capacity measured using a quartz crystal microbalance (QCMB) setup. As determined from UV-Visible absorption and X-ray Photoelectron spectroscopies, the modified GO presented shifts in their UV-Vis absorption peak (π→π* transition going from 228 nm in GO to 277 nm in mGO-N2), and nitrogen doping (4.5 at% for mGO-N1), while S-doping was ineffective (only 0.4% for mGO-S2). Raman analysis suggested that vacancy-type defects could dominate over other vacancy types, but the significance of this result was limited by the low crystallinity of the materials. Scanning electron Microscopy (SEM) revealed significant differences in the conformation of the mGO films. From QCMB measurements, it was found that mGO-N1 achieved the highest CO₂ adsorption capacity (~1.2 wt% at 45 torr), attributed mostly to N-dopants acting as Lewis base sites. On the contrary, mGO-H exhibited the lowest capacity due to its lack of adsorption sites (N-doping, oxygen functional groups) and visible diffusion channels. Furthermore, it was observed that film thickness in GO influenced kinetics, with medium thicknessoptimizing CO2 adsorption capacity in the adsorption timeframes studied. Selectivity tests confirmed mGO-N1’s superior CO₂/CO discrimination, over GO and mGO-H. For CO detection, CuO microplates with estimated lengths and thicknesses of around 2-3mm and 35 nm, respectively, were hydrothermally synthesized with/without addition of GO. Additionally, composites were also prepared by physically mixing CuO with GO, followed by thermal reduction at 150°C and 250°C. The obtained materials were deposited on gold/platinum interdigitated electrodes, and placed inside a testing chamber where their response towards CO was studied under flow-regime.SEM confirmed CuO’s planar morphology, while XRD identified tenorite as the single phase in CuO. For CuO-rGO composites, SEM identified the presence of both phases in composites with high content of GO, but identification of this phase was limited for the composites with low GO content. Similarly, CuO-rGO composite analyzed by XRD lacked a diffraction peak attributable to GO/rGO, due to high dispersion of the GO sheets and low mass content. However, Raman spectroscopy and XPS confirmed the effective formation of a CuO-rGO composite. In particular, XPS analysis revealed a higher reduction at 250°C (90% unoxidized carbon vs. 60% at150°C), as expected. On CO detection, it was found that all the tested materials (CuO, hydrothermal and physically-mixed composites, and rGO) exhibited p-type response towards CO. However, pure CuO sensors outperformed CuO-rGO composites in the studied temperature range, showing a comparable or higher response towards 150 ppm of CO. The optimal response of CuO sensor was found at ~165°C (S = 1.38 for 150 ppm CO, where S = RCO / Rair is the ration between the sensor resistances under CO exposure and pure air, respectively). Physically mixed CuO-GO outperformed thermally reduced CuO-rGO composites, but their unstable response difficult reallife applications. Instability refers to significant dispersion in the response at fixed temperatures of 45 and 55ºC, of 20 and 10%, respectively. Post-thermal reduction (150°C) enhanced stability but reduced sensitivity. It was found that rGO sensor showed negligible recovery at lowtemperatures, requiring thermal "reset" steps. When compared with the literature, the observed superior performance of CuO over CuOrGO composites seems to be against the expected outcomes. It is hypothesized that the planar morphology of the CuO microstructures studied play a role in the response decrease of the composites. Interestingly, the high-yet-unstable responses of unreduced CuO-GO composites suggest that GO/rGO could play a role beyond electrical modulation through heterojunction formation between p-p semiconductors, owing to the insulating nature of GO.
- ItemPrimordial Black Holes as Dark Matter Candidate and Possible Feedback Source at Very High Redshift(2025) Casanueva Villarreal, Catalina Isabel; Tissera, Patricia; Padilla, Nelson; Pontificia Universidad Católica de Chile. Instituto de AstrofísicaLos agujeros negros primordiales (Primordial Black Holes, PBHs) son objetos hipotéticos que podrían haberse formado en el Universo temprano, contribuyendo potencialmente a la materia oscura (Dark Matter, DM) y dejando huellas observables en la formación de estructuras cósmicas y en la radiación de fondo. En esta tesis, investigamos su impacto utilizando dos enfoques complementarios: un modelo semianalítico para estudiar el calentamiento inducido por PBHs tanto en los bariones localizados en el medio intergaláctico (Intergalactic Medium, IGM) como en halos de DM a alto corrimiento al rojo (redshift, z), y un marco completamente analítico para calcular sus contribuciones a los fondos de radiación cósmica. Ambos enfoques incorporan un modelo detallado de acreción-emisión, considerando distintos regímenes de acreción, incluidos el flujo de acreción dominado por advección de electrones, el flujo de acreción dominado por advección estándar, el flujo de acreción caliente y luminoso y el régimen de disco delgado. Esto garantiza una caracterización físicamente consistente de la luminosidad de los PBHs en distintos entornos astrofísicos.En el primer enfoque, desarrollamos un modelo semianalítico para cuantificar el calentamiento del gas por PBHs tanto en el IGM como en los halos, incorporando mecanismos de enfriamiento relevantes a alto redshift. Este modelo se aplica sobre una simulación de Cielo a z ~ 23 para evaluar la evolución térmica del gas y analizar el impacto de la acreción de PBHs en la formación temprana de estructuras. Esto nos permite restringir la abundancia de PBHs en función de sus efectos sobre la temperatura y el estado de ionización del medio circundante.En el segundo enfoque, construimos un modelo completamente analítico para evaluar la contribución de los PBHs a los fondos de radiación cósmica, centrándonos en el fondo cósmico de rayos X, el fondo de Lyman-Werner y el fondo cósmico de radio. Comparando la emisión predicha de PBHs con las restricciones observacionales, derivamos límites estrictos sobre su abundancia y evaluamos su posible papel en la configuración de los fondos cósmicos no resueltos.Ambos enfoques producen restricciones consistentes, reforzando la solidez de nuestros resultados. Probando distribuciones de masa monocromática para los PBHs, encontramos que para M_PBH = 1 M_sun, las restricciones combinadas limitan su abundancia a f_PBH ≤ 7 x 10⁻³. Para PBHs en el rango M_PBH = 10 - 100 M_sun, encontramos una restricción más estricta de f_PBH ≤ 6 x 10⁻⁴.Este estudio resalta la complementariedad entre las restricciones derivadas del calentamiento a pequeña escala y las impuestas por los fondos de radiación cósmica a gran escala, proporcionando una perspectiva multiescala sobre la física de los PBHs. Los límites obtenidos se encuentran entre los más estrictos hasta la fecha, lo que refuerza la solidez del análisis. Al integrar simulaciones de alta resolución con técnicas de post-procesamiento y formular un marco analítico exhaustivo, esta tesis ofrece una evaluación rigurosa sobre la viabilidad de los PBHs como candidatos a DM y su influencia en la evolución cósmica temprana.
- ItemDesarrollo de un cátodo basado en nanotubos de carbono recubiertos con pentóxido de vanadio para uso en baterías de litio(2025) Picuntureo Jara, Matías; Hevia, Samuel; Cisternas Jiménez, Eduardo Antonio; Pontificia Universidad Católica de Chile. Facultad de FísicaEl desarrollo de cátodos nanoestructurados representa un área de investigación crucial para mejorar el rendimiento de las baterías de ionesde litio. Esta tesis explora el uso de nanotubos de carbono verticalmente alineados (VA-CNT) como plantilla para la fabricación de cátodos basados en pentóxido de vanadio (V₂O₅), un material que destaca por su alta capacidad teórica de intercalación de litio. Se desarrolló un método de síntesis basado en la oxidación controlada de vanadio metálico depositado sobre VA-CNT crecidos directamente sobre electrodos de acero inoxidable. Se encontraron condiciones que permiten simultáneamente la oxidación del vanadio a V₂O₅ y la preservación de la matriz de VA-CNT. El nanomaterial híbrido VA-CNT/V₂O₅ exhibe una morfología tipo nanoesponja sobre la superficie del electrodo y presenta una notable respuesta electroquímica, alcanzando una capacidad específica de descarga reversible de 90 mAh/g a 0.5C, lo que representa un incremento de casi un 300% respecto a los 30 mAh/g desarrollados por el cátodo de V₂O₅ sin VA-CNT, en las mismas condiciones. Esta mejora se atribuye al transporte electrónico facilitado por la red de nanotubos y a las distancias reducidas de difusión iónica en la estructura nanoestructurada. La caracterización exhaustiva del material mediante microscopía electrónica de barrido (SEM), espectroscopía de dispersión de energía (EDX), espectroscopía de fotoelectrones de rayos X (XPS) y espectroscopía Raman permitió comprender en detalle su morfología, composición y estructura. Complementariamente, se realizaron cálculos basados en la teoría del funcional de densidad (DFT) para analizar los Imodos vibracionales del V₂O₅, modelar la interfaz CNT-V₂O₅, estudiar la oxidación de los CNT por V₂O₅ y calcular potenciales de intercalación de litio. Estos últimos resultados teóricos sugieren la formación de sitios favorables para la intercalación de litio en el modelo de la interfaz, lo que podría contribuir a la capacidad de almacenamiento de carga del sistema. La integración de resultados experimentales y teóricos proporciona una comprensión integral del sistema VA-CNT/V₂O₅ como material catódico, validando esta estrategia para la fabricación de cátodos nanoestructurados mediante la oxidación controlada de precursores metálicos.
- ItemBeyond the standard model with scalars: long-lived particles and dimuon Higgs decay(2025) Norero Cárdenas, Sebastián; Díaz, Marco A.; Pontificia Universidad Católica de Chile. Facultad de FísicaThis thesis explores two extensions of the Standard Model. The first modifies the Scotogenic Model to explain deviations in Dimuon Higgs decays, while satisfying LFV constraints. The second extends the Georgi-Machacek model by incorporating a type-II seesaw, leading to a long-lived doubly charged scalar. Both models offer collider signatures, with one probing loop-induced Higgs decays and the other emphasizing LLP searches. Future experiments will be crucial in testing these predictions.
- ItemOutflows from tungsten conical wire arrays. Characterization and applications(2024) Muñoz-Cordovez, Gonzalo; Veloso Espinosa, Felipe Eduardo; Pontificia Universidad Católica de Chile. Facultad de FísicaA tungsten conical wire array is used as load in the Llampudken pulsed power generator(∼400 kA in ∼350 ns) to study the outflows produced by it. At pressures of 10 −4 Torrthe dynamics of the wire array is probe by UV/XUV imaging and laser schlieren andinterferometry. These diagnostics show the expulsion of a dense plasma jet (n e = 3 × 10 24m −3 ) of a couple of centimeters in the axial direction above the anode. This plasma jet havevelocities between 10 4 − 10 5 m/s and its dimensionless parameters are computed in orderto compare the experimentally produced plasma jet with the astronomically producedones. At pressures that varies from 10 −5 Torr to 10 −2 Torr the upwards axial emission ofcharged particles is study using negatively biased Faraday cups. At 10 −5 Torr only ionsare detected by the cups but from 10 −4 Torr to 10 −2 Torr the detection of both electronsand ions moving together in the same direction is observed due to the ionization of thebackground gas. Velocity computed for the electrons and ions is in the order of 10 6 m/simplying MeV ions. Finally, the interaction of these outflows with stationary targets isstudy by placing silicon targets at different heights above the conical wire array. Resultsshow that visible damage over the target was observed from 10 cm to 21 cm above thearray where two main damages are appreciated. For targets located closer to the arraymainly micro-pores are observed but for targets located farther from the array stripes-likeformations are appreciated. These damages indicate that the silicon target boiled and wasfastly heated by the conical wire array outflows. Detail measurements of these outflowsand the damages produced on the silicon targets are shown an discussed in this thesis.