Física (Dr.)

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Propagating reaction fronts in moving fluids
(Pontificia Universidad Católica del Perú, 2015-10-20) Vilela Proaño, Pablo Martin; Vásquez Rodríguez, Desiderio Augusto
La presente tesis tuvo como objetivo estudiar frentes de reacción modelados mediante la ecuación de Kuramoto-Sivashinsky sujetos a diferentes tipos de movimiento de fluido: flujo externo de Poiseuille, el cual es contrastado con el flujo de Couette, y flujo convectivo debido a la inestabilidad de Rayleigh-Taylor. En el primer caso, los frentes se propagan a favor o en contra de un flujo estacionario bidimensional entre dos placas paralelas que se conoce como flujo de Poiseuille. Para pequeñas distancias entre las placas, encontramos frentes estacionarios que pueden ser planos, simétricos o asimétricos, dependiendo de la separación de las placas y de la velocidad promedio del fluido externo. Adicionalmente, descubrimos que los frentes simétricos estables que se propagan en sentido opuesto al flujo simétrico externo se vuelven asimétricos al incrementar la rapidez del flujo externo. En el caso del flujo externo de Couette, el flujo es producido por el movimiento de dos placas paralelas en sentidos opuestos. Hallamos que la estabilidad y la forma de los frentes estacionarios dependen de la velocidad relativa entre las placas y de su separación. Estos parámetros desempeñan un papel importante, puesto que pueden convertir frentes inestables en estables. En el último caso, las inestabilidades en el frente producidas cuando un fluido más denso se encuentra encima de un fluido menos denso se conocen como inestabilidades de Rayleigh-Taylor y son causadas por la diferencia de densidades a través del frente bajo la acción de la gravedad. El frente describe la interfaz delgada que separa los fluidos de diferente densidad dentro de dos placas paralelas verticales; mientras que la convección causada por las fuerzas de flotación a través de la interfaz delgada determina el flujo debido a la inestabilidad de Rayleigh-Taylor. Para el estudio de los efectos del flujo externo sobre los frentes de reacción, primero obtuvimos los frentes y luego realizaremos un análisis de estabilidad lineal para determinar la estabilidad de los frentes bajo los tres tipos de movimiento del fluido. La forma de los frentes y sus respectivas regiones de estabilidad fueron contrastadas con los frentes en ausencia de flujo externo. Los resultados de la investigación fueron publicados en tres revistas internacionales arbitradas e indexadas: Physical Review E (2012), Chaos (2014), y European Physics Journal (2014). Adicionalmente, la tesis presenta resultados para frentes oscilantes y sus transiciones al caos debido a la interacción del frente de reacción con los flujos externos antes mencionados.
Optical characterization and thermal activation of Tb doped amorphous SiC, AlN and SiN thin films
(Pontificia Universidad Católica del Perú, 2017-08-10) Guerra Torres, Jorge Andrés; Weingärtner, Roland; Winnacker, Albrecht
En la presente tesis se evalúan las propiedades ópticas y las características de emisión de luz de películas delgadas amorfas de AlN, SiN y SiC:H dopadas con Tb. La caracterización óptica se centra en la determinación del ancho de banda, la energía de Urbach y el foco de Urbach a partir de mediciones ópticas. Se desarrolla un modelo, basado en fluctuaciones térmicas de la banda, para describir la absorción fundamental sobrepuesta con las colas de Urbach. Luego, se realiza un análisis de la existencia y significado del foco de Urbach y se contrasta con modelo anterior. Uno de los principales resultados en esta parte es la capacidad del modelo antes mencionado para distinguir las regiones de Urbach y Tauc del coeficiente de absorción. En este caso, películas delgadas de a-SiC:H depositadas en distintas condiciones de dilución de hidrógeno exhibieron un ancho de banda no correlacionado con la energía de Urbach al usar este modelo, en contraste a lo que se observa típicamente después de utilizar el modelo de Tauc. El análisis de características de emisión de luz se centra al proceso de activación térmica que sufren los iones de tierras raras cuando se calientan las muestras. El efecto de la temperatura de recocido, temperatura de la muestra y concentración de tierras raras en la intensidad de la emisión de luz se evalúa bajo fuentes de excitación de fotones y electrones. Se utiliza un modelo de tasa de transiciones para ajustar la intensidad de luz global asociada al Tb en películas delgadas de a-SiC:H:Tb3+ frente a la concentración de Tb después de diferentes temperaturas de recocido. Se recupera una energía de activación asociada a la activación térmica. Finalmente, en el caso de a-SiC: H: Tb3+, se observa una disminución del efecto de enfriamiento de la concentración, lo que sugiere un mecanismo adicional para aumentar la intensidad de emisión de luz relacionada con Tb.
An analysis of the roles played by Born’s rule, Bell’s theorem and Bohr’s complementarity in the establishment of the quantum-classical boundary
(Pontificia Universidad Católica del Perú, 2018-08-28) De Zela Martínez, Francisco; Massoni Kamimoto, Eduardo Rubén
This work contains a series of contributions that are related, in one form or another, with the placement of the quantum-classical boundary. Three results that have been widely taken as characteristic traits of quantum phenomena are here shown to appear in purely classical contexts as well. These are: Born’s rule, Bell violations and Bohr’s complementarity. This work discusses how Born’s rule may be derived from some basic assumptions that relate to measurements in general, thereby showing that said rule applies when dealing with both classical and quantum cases. Bell violations are ultimately based upon Born’s rule. Therefore, the applicability of the latter in a classical context leads to Bell violations in this very same context. We can therefore predict non-quantum Bell violations. Moreover, we report experimental results confirming these violations. Finally, we address Bohr’s complementarity in a quantitative way and derive an equation that links visibility and distinguishability – two complementary features of an interferometric array – with polarization, which can be seen as an “internal” degree of freedom.
Optical and luminiscent properties of terbium / ytterbium doped aluminum oxynitride and terbium doped aluminum nitride thin films
(Pontificia Universidad Católica del Perú, 2020-08-06) Tucto Salinas, Karem Yoli; Guerra Torres, Jorge Andrés; Grieseler, Rolf
In the present thesis the optical and light emission properties of two systems consisting of Tb3+ and Yb3+ doped amorphous AlOxNy thin ﬁlms and Tb3+ doped polycrystalline AlN thin ﬁlms were analyzed. In the two ions system, to obtain an adequate luminescent emission, commonly a signiﬁcant eﬀort must be made to ﬁnd a suitable concentration of dopants and elemental composition of the host material. An interesting and highly eﬃcient method is a combinatorial approach, allowing a high velocity screening of a wider range of properties. In the present work a combinatorial gradient based thin ﬁlm libraries of amorphous AlOxNy:Yb3+, AlOxNy:Tb3+ and AlOxNy:Tb3+:Yb3+ have been prepared by radio frequency co-sputtering from more than one target. In the prepared libraries, the Tb and Yb concentration range spreads along with the oxygen to nitrogen ratio of the host matrix all over the substrate area. Concentrations ranges for each ion were established for producing high emission intensity samples, along with an analysis of the light emission features of Yb3+ ions with Tb3+ ions as sensitizers for cooperative down conversion process. Using diﬀerent annealing temperatures the activation energy of the rare earth ions and thermal-induced activation mechanisms are evaluated. Here we show that the diﬀerent oxygen to nitrogen ratios in the host composition aﬀect the light emission intensity. According to experimental results, there is a strong enhancement of the Yb3+ related emission intensity over the Tb3+ emission in codoped ﬁlms with Tb:Yb concentration ratios near to 1:2, at 850°C. Thus, suggesting the sensitization of Tb3+ ions through an AlOxNy matrix and the cooperative energy transfer between Tb3+ and Yb3+ ions as the driven mechanism for down conversion process with promising applications in silicon solar cells. At the end of this ﬁrst part, the optimal elemental composition and optimal annealing temperature in the investigated ranges to achieve the highest Yb3+ emission intensity upon sensitization of Tb3+ ions is reported. The second system studied consists of Tb3+ doped AlN layers prepared by reactive magnetron sputtering and analyzed using the conventional one at a time approach. In this work, two types of thermal treatments have been applied: substrate heating during deposition of the ﬁlms and post deposition rapid thermal annealing, with varying temperature from non intentional heating up to 600°C. The composition, morphology and crystalline structure of the ﬁlms under diﬀerent thermal processes and temperatures were investigated along with their optical and light emission properties, with the aim of maximizing the Tb3+ emission intensity. The polycrystalline nature of the ﬁlms was conﬁrmed by X-ray diﬀraction under grazing incidence, and the inﬂuence of substrate temperature on the crystalline structure was reported. Atomic force microscopy and scanning electron microscopy has revealed the smooth grainy surface quality of the AlN:Tb3+ ﬁlms. The highest Tb3+ photoluminescence emission intensity was achieved in the ﬁlm treated with rapid thermal annealing process. For a more detailed study of the post deposition annealing treatments, temperature was further increased up to 900°C, and the inﬂuence of annealing temperature on the emission properties was investigated by photoluminescence and photoluminescence decay measurements. An increase in the photoluminescence intensity and photoluminescence decay time was observed upon annealing for the main transition of Tb3+ ions at 545 nm, which was attributed to a decrease of non radiative recombination and increase of the population of excited Tb3+ ions upon annealing. Additionally, using the characterized ﬁlms as active layer, direct current and alternate current thin ﬁlm electroluminescence devices were designed and investigated.
Characterization of maintenance industrial alkyd resins prepared with Plukenetia volubilis L. oil.
(Pontificia Universidad Católica del Perú, 2021-08-11) Hadzich Girola, Antonella; Flores Merino, Santiago Eleodoro
In this doctoral thesis, alkyd resins synthesized with high unsaturation renewable plant sources and polyols with different functionalities were characterized. Alkyds are synthetic resins modified with vegetable oils, whose level of unsaturation provides the resin the ability to cure in air without using a catalyst. Oil sources with high content of fatty acids and elevated concentration of double bonds are preferred in the surface coating field as they increase the crosslinking density of alkyd resins, forming a continuous film that acts as a barrier against corrosive species. In the present work, Sacha inchi oil, a Peruvian low cost agricultural feedstock, was used due to its high content of unsaturated fatty acids and its similarity to linseed oil’s composition, a drying oil widely used in the coating industry. This commercial oil was used also for comparative purposes. Glycerol and pentaerythritol, polyols with dissimilar levels of crosslinking, were used for resin manufacturing. The use of a multifunctional polyol such as pentaerythritol sought to increase branching and promote the obtainment of high solid alkyds with better film properties and weathering resistance. This study focuses on comparing the effect of the polyol and oil/fatty acid type on alkyd’s physical properties such as colour, density, viscosity, and thermal stability, and film coating’s performance (drying, hardness, chemical resistance). FT-IR, One- (1D) and two-dimensional (2D) 1H- and 13C-NMR spectroscopy were performed for alkyd structural verification. Curing process was also evaluated by a standard proceeding and Raman spectroscopy. The oxidative crosslinking time tendency was corroborated by the quartz crystal microbalance (QCM) technique. This technique has been recently applied for resin characterization and proves to be a useful tool for monitoring more precisely curing stages. Gel permeation chromatography was also carried out to characterize the molecular weight distribution and dispersity of alkyds. The protective capacity of oil-based resin films on aluminium substrates was studied by Electrochemical Impedance Spectroscopy. Moreover, the anticorrosive behaviour of primers prepared with the most representative synthesized oil-based resins was verified by accelerated corrosion tests. In general, the performance of the Sacha inchi-based alkyd resins was found to be comparable to an alkyd resin prepared with linseed oil. Accelerated weathering tests showed that the mixture of pentaerythritol and Sacha inchi oil improves properties of alkyd resins and enhances the anticorrosive performance of alkyd primers. From this study, it can be concluded that Sacha inchi oil and fatty acids extracted from it have the necessary characteristics to be used as raw materials for the production of alkyd resins. The exploitation of a Peruvian non-traditional vegetable oil as a raw material in a new sector of the economy could generate direct or indirect income in the production chain collaborating with the development of the Amazon region and improving the competitiveness of the Peruvian market worldwide.
A study on the response of the LR-115 detector exposed inside a diffusion chamber and in unconventional bare mode
(Pontificia Universidad Católica del Perú, 2021-12-17) Bertin Andrés, Pérez Ancaya; López Herrera, María Elena
Several methodologies for radon concentration measurements have been used for monitoring radon in homes and workplaces to minimize health hazards due to indoor radon exposure. One of them is the Nuclear Track Methodology (NTM), commonly used for passive long-term measurements. The LR-115 type II (cellulose nitrate), as an NTM’s detector, is often located inside a diffusion chamber. The set formed by the detector and the chamber hereinafter will be called a monitor. Commercial monitors, e.g., RadOUT , Radosys, NRPB, are routinely used for radon measurements; they are calibrated in Certified and/or Accredited Laboratories. However, many laboratories have developed their own monitors, varying some characteristics as geometric shapes, dimensions, and material properties. They also do not have access to calibrate them in Certified and/or Accredited Laboratories. In the present thesis, we studied the detector response given the characteristics of the diffusion chamber that we use, and to know how these characteristics influence radon measurements. The results of this study can provide a fast-calibration of the detector that can be compared to calibrations in Certified and/or Accredited Laboratories. This study is based on Monte Carlo methods that imitate the experimental procedure commonly-used in estimating the calibration factor. This calibration method is more accesible than calibrations performed in Certified and/or Accredited Laboratories due to its low cost, feasibility and applicability. For these purposes, a monitor (LR-115 + a non-commercial diffusion chamber made of polypropylene -usually used as cosmetic pot-) was used in this research. LR-115 detector response in this set-up is reported by taking into account the geometric shape, dimensions and material (conductive or non-conductive) of the chamber, the transmission factor (the ratio of final steady state concentration of radon or thoron at the entrance of the chamber to the concentration of radon or thoron just inside this entrance), radon exposure level, and etching and reading process. Regarding the level of radon exposure, it was possible to correct the track overlap effect for high exposure levels, as can occur in radon measurements in soil pores, by applying a mathematical model. Mainly, these researches show that a non-commercial monitor can work as well as commercial ones. Besides, using an LR-115 in bare mode exposed by unconventional exposition results in concentric ring-shaped tracks, caused by UV natural radiation. The repeatability and reproducibility of the observed phenomenon were experimentally demonstrated. We also studied the ability of the LR-115 detector to register alpha particles from nuclear (n,α) reactions, or radon/thoron progeny. This study is also based on Monte Carlo methods and can provide an estimation of the efficiency of the detector to neutron or radon/thoron progeny.
Preparación y optimización de películas delgadas de sistemas de carbono-sílice dopados con tierras raras para aplicaciones luminiscentes
(Pontificia Universidad Católica del Perú, 2022-02-01) Flores Escalante, Loreleyn Flor; Grieseler, Rolf
El uso de elementos de tierras raras (RE) en materiales de luminiscencia ha permitido introducir mejoras en diversas aplicaciones. En iluminación, por ejemplo, los fósforos amarillos YAG (Y3Al5O12:Ce3+) son ampliamente utilizado en LED blancos. En los sistemas de telecomunicaciones e Internet, se utilizan amplificadores de fibra dopada con erbio (Er3+) para aplicaciones en la región de longitud de onda de las telecomunicaciones (1530- 1550 nm). En láseres, YAG:Nd3+ encuentran su aplicación en láseres de estado sólido con una línea de emisión de 1,06 μm. Los YAG también pueden estar dopados con Tm3+ (1,93- 2,04 μm) o Er3+ (2,94 μm) y se utilizan principalmente en aplicaciones médicas. En las células solares, las capas de convertidor espectral están diseñadas para aumentar la eficiencia de las células solares. El espectro solar AM1.5G se puede modificar mediante procesos llamados Up-conversion, quantum cutting, and down-shifting. Por tanto, se mejoraría el EQE de las células solares. El estudio central de este trabajo fue la preparación y optimización de la luminiscencia de los iones Tb3+ e Yb3+ en la relativamente nueva matriz de a-SiOC: H para aplicaciones luminiscentes como convertidores espectrales descendentes. El método utilizado para la optimización de la luminiscencia se basa en tratamientos de recocido, composición de la matriz y co-dopaje con elementos Tb e Yb. Los detalles experimentales se presentan en el Capítulo 3. El primer objetivo de este trabajo se centró en la preparación de capas de a-SiOC: H que pueden cultivarse en la superficie de una célula solar de prueba (célula de Si + capa antirreflejante). La literatura reporta trabajos previos sobre SiOC. Sin embargo, la mayoría de ellos se basan principalmente en la preparación a temperaturas cercanas a los 1000 °C, lo que provocaría daños en la celda solar debido a la alta temperatura. Por esta razón, se utilizó un sistema de pulverización catódica de RF con enfriamiento del sustrato. Las propiedades ópticas de la matriz dependen de la composición de Si, C y O. por lo que, el Capítulo 4 se enfoca en el estudio de (1) el análisis de composición y la estructura, (2) el cálculo de la banda prohibida y la energía de Urbach, (3) el efecto del tratamiento de recocido en la estructura de la red atómica y (4) los procesos que impulsan la luminiscencia de matriz. El segundo objetivo de este trabajo fue la optimización de la fotoluminiscencia de los iones Tb3+ e Yb3+ en muestras de a-SiOC:H dopadas con uno de los dos iones. Una luminiscencia creciente de los iones de RE3+ requiere (1) aumentar el número de iones RE3+ activos, (2) reducir las fuentes de pérdida de energía y (3) aumentar el número de sensibilizadores. El Capítulo 5 examina estos procesos en detalle. En la literatura, la emisión de iones RE3+ está bien reportada. Sin embargo, los mecanismos de transferencia no radiativa de energía de los estados de defecto (en materiales amorfos basados en silicio) a los dopantes de RE son poco discutidos. Además, el ion RE3+ en tales materiales no reemplazará a ninguno de los iones en la matriz como si lo hace en el caso de los materiales cristalinos dopados con elementos de RE. En materiales amorfos (que contienen oxígeno), el ion RE3+ se ubicará en un sitio rodeado localmente por átomos de oxígeno. Por lo tanto, este trabajo estudia y propone mecanismos de excitación para los iones Tb3+ e Yb3+. Estos mecanismos pueden aplicarse en la matriz a-SiOC: H y extenderse a materiales basados en Si y SiOx. Finalmente, estudios previos del efecto del carbono mostraron una mejora de la luminiscencia de los iones RE3+. Por tanto, se llevó a cabo un estudio sistemático de luminiscencia basado en el cambio de composición del carbono. Este trabajo estudia las ventajas y desventajas del dopaje con carbono en la activación de la luminiscencia de los iones RE3+. Los resultados también se presentan en el Capítulo 5. El tercer objetivo de este trabajo fue la optimización de la luminiscencia del Yb en muestras de a-SiOC:H co-dopadas. Entre los diferentes sistemas de iones RE3+ para aplicaciones de corte cuántico (QC) en el infrarrojo cercano, los que incluyen iones Yb3+ parecen ser los más apropiados porque el ión Yb3+ tiene una transición a aproximadamente 980 nm (~ 1,22 eV) justo por encima de la banda prohibida del silicio cristalino de 1,1 eV. Los iones Tb3+ se utilizaron para mejorar la emisión de los iones Yb3+. Por lo tanto, los convertidores descendentes de infrarrojo cercano encuentran una posible aplicación en las células solares de silicio. La capa de convertidor espectral se colocará en la parte superior de la superficie de la célula solar, por lo que la capa de QC tiene la ventaja de que se puede optimizar independientemente de la celda. En este trabajo se identifican y estudian los mecanismos asociados a la transferencia de energía del huésped a los iones RE3+. Se estimó el rendimiento cuántico de fotoluminiscencia de la capa convertidora espectral. Además, se prepararon las capas en la superficie frontal de las células de mc-silicio, y se estudió su efecto en la eficiencia cuántica externa. Por último, se estudió el mecanismo de transferencia cooperativa entre los iones Tb3+ e Yb3+; los cuales son utilizados para explicar el proceso de QC. Este mecanismo cooperativo se ha atribuido a los procesos de QC en muchas matrices cristalinas y amorfas. Sin embargo, a pesar de numerosos documentos que adscriben sus resultados al mecanismo de transferencia cooperativa, pocos realmente lo prueban. Por lo tanto, también se analiza el papel de los iones Tb3+ en la luminiscencia del Yb. Los resultados se presentan en el Capítulo 6.
Coherencia como recurso en los sistemas cuánticos abiertos
(Pontificia Universidad Católica del Perú, 2022-07-26) Yugra Carcasi, Yonny Daniel; De Zela Martinez, Francisco Antonio
In this thesis, we address open quantum systems subjected to Markovian and non- Markovian evolutions. We diagnose these two regimes using the relative entropy of coherence. We specially address the case of two qubits encoded in the polarization degree of freedom of photon beams. The two qubits play the roles of system and ancilla. In our experimental setup, we need only two parameters to control Markovian and non-Markovian regimes. We also propose and provide a proof-of-concept for the implementation of a quantum gate that drives an open system so that it can reach maximal coherence. Our ndings also illustrate possibilities for generating non-Markovian processes, which are important to recover information that has gone from the system to its environment. We thereby show how non-Markovianity can be considered as a resource in open quantum systems.
From light neutrino decay phenomenology to muon neutrino cross-section measurement at MINERvA experiment
(Pontificia Universidad Católica del Perú, 2022-08-15) Ascencio Sosa, Marvin Vladimir; Gago Medina, Alberto Martín
This thesis tackles two essential topics of neutrino physics: neutrino decay and neutrino cross-section measurement. First, the invisible and visible neutrino decay is analyzed through a phenomenological approach, considering future long-baseline neutrino experiments such as DUNE and a hypothetical neutrino beam toward the ANDES laboratory. The study takes into account the νμ and νe disappearance and appearance, respectively, for both FHC and RHC flux modes. The results showed a negligible matter effect for DUNE but significantly more notable at ANDES. At 90% C.L., the sensitivity to the decay parameter α3 can be as small as 2 × 10−6 eV2 for a chosen coupling. The impact of neutrino decay in the determination of θ23 and δCP were also shown. Second, the double-differential cross-section measurement for νμ-carbon interactions with three-momentum transfer |q| < 1.2 GeV obtained with medium energy exposures in the NuMI beam at MINERvA experiment are reported. The measurement is presented as a function of |q| and Eavail and reviews different interaction models and nuclear effects along quasi-elastic to resonance processes to define a new model for a better agreement. The double differential cross sections are compared to the MnvTunes, GENIE, and NuWro predictions.
Contribution to the characterization and modeling of photovoltaic generators
(Pontificia Universidad Católica del Perú, 2023-01-10) Angulo Abanto, Jose Ruben; Palomino Töfflinger, Jan Amaru
A crucial aspect of evaluating and maintaining a photovoltaic (PV) installation connected to the grid is the availability of models that describe its operation reliably in real operating conditions. The nominal power of the PV generator (P*M) is considered an essential input parameter, and several models have been proposed to estimate P*M for characterizing the PV system. In the case of PV generators in outdoor conditions, the American Society for Testing and Materials, the International Electrotechnical Commission, and others have proposed procedures to determine the P*M of the generator. As part of these procedures, monitoring days with ideal conditions is mandatory, notably days with a clear sky, high irradiance values, and low wind speeds. Such restrictions can limit the number of suitable monitoring days, especially in places where clouds frequently form. This thesis proposes a new approach that allows estimating the P*M with data even from non-ideal, partially cloudy days. Based on non-parametric statistics, this procedure identifies and filters out noise as well as deviations from ideal conditions of irradiance, allowing for an estimation of P*M with similar accuracy as for a clear-sky day. This new procedure enables the characterization of a PV generator on a daily basis without the requirement to meet ideal conditions, thus, considerably enhancing the number of suitable monitoring days. To overcome the limitation in the P*M estimation and considerably extend the number of monitoring days, the new procedure can be applied to ideal and non-ideal conditions, such as partially cloudy days. This procedure determines the most probable nominal power value within one monitoring day using non-parametric statistics. In order to test the new procedure, a 109.44 kW photovoltaic plant in Granada, Spain, was monitored for six months. A referential procedure reported in the literature for large PV plants under ideal climatic conditions is first applied to estimate its nominal power. The results indicate that the nominal power can be estimated reliably in non-ideal conditions, maintaining the same precision as in ideal conditions. Then validating the procedure for a smaller PV generator and under different conditions, two small grid-connected 1.5 kW PV arrays were used. The PV systems in question are located in two different cities in Peru: Chachapoyas (tropical highland) and Lima (coastal desert). The objective of this study in Chachapoyas was to validate the methodology in a tropical climate with a high presence of clouds but at the same time with high irradiance values above 800 W/m2. According to the results obtained, under these conditions, the nominal power of the system can be calculated with reasonable certainty. As a precaution, monitoring for more than one day is recommended to obtain more data (at least 3 hours with high irradiance) to reduce uncertainties. Lima, Peru's second location under study, has a particular climate. Since the capital is located in a desert with high relative humidity values, dust deposition increases and power output decreases due to these conditions. For this purpose, the nominal power was used as a parameter to determine the maintenance schedule. Since keeping the system in optimal performance, considering this in future installations for operation and maintenance costs, is essential. The new procedure developed in this work can be applied to facilitate technical due diligence and quality control processes for PV generators of different sizes and under different operating conditions that are being re-purchased or have been recently installed. The possibility of daily monitoring of the P*M also enables long-term monitoring of a PV generator to ensure the correct operation or identify possible degradation effects
Testing new physics in long baseline neutrino oscillation experiments
(Pontificia Universidad Católica del Perú, 2023-01-10) Díaz Desposorio, Félix Napoleón; Gago Medina, Alberto Martín
In this thesis, we focus on analyzing the different ways in which new physics scenarios, such as Violation of the Equivalence Principle (VEP) and Quantum Decoherence, can manifest themselves in the context of the neutrino oscillation phenomenon. Within the framework of the DUNE experiment, we examine several effects of the VEP, such as the possibility of getting a misconstructed neutrino oscillation parameter region provoked by our ignorance of VEP in nature, as well as the impact on the DUNE sensitivity for CPV and mass hierarchy. Additionally, we set limits for the different textures of the gravitational matrix and the diverse scenarios of energy dependencies associated with the Lorentz Violation. On the other hand, we demonstrate that the quantum decoherence phenomenon applied to the neutrino system leads us to fascinating phenomenological scenarios. One of the scenarios analyzed, within the context of quantum decoherence, is the one that breaks the fundamental CPT symmetry. For the latter, we identify what textures that include certain nondiagonal elements of the decoherence matrix are necessary. In this line, we propose a way to measure the CPT violation in the DUNE experiment using the muon neutrino and antineutrino channels for different energy dependencies. Another intriguing effect of considering the neutrino as an open quantum system is the possibility of discovering the neutrino nature by measuring the Majorana phase at the DUNE experiment achieving a competitive precision. As a consequence of the latter, we find that the crucial measurement of the CP violation phase (δCP), planned to be performed at the DUNE experiment, can be spoiled by the introduction of the decoherence and the Majorana phases in nature. Thus, a signature of a non-null Majorana phase is a sizable distortion in the measurement of the Dirac CP violation phase δCP at DUNE when compared with T2HK measurement. Subsequently, via simulation, we measured the Majorana phase for values of ϕ1/π = ±0.5 and decoherence parameter Γ = 4.5(5.5) × 10−24GeV, reaching a precision of 23 (21) %. This precision is consistent with the corresponding to the Dirac CP phase at T2K experiment.
Contribution to the characterization of emerging photovoltaics technologies in Lima-Peru
(Pontificia Universidad Católica del Perú, 2023-01-13) Conde Mendoza, Luis Angel; Palomino Töfflinger, Jan Amaru
This Doctoral Thesis contributed to forming a new photovoltaic (PV) laboratory in Lima-Peru, by developing an outdoor characterization system for PV modules. This system enables performance studies of different PV technologies under outdoor conditions. The new laboratory is the first of its kind in Peru due to its appropriate instrumentation for various PV performance research. This system was installed in the outdoor-PV laboratory of the Physics section (12◦2′S, 77◦1′W) at the Pontifical Catholic University of Peru (PUCP) in collaboration with the IDEA research group of the University of Jaén (UJA) in Spain. Seven PV modules of different technologies, and instruments are currently installed to measure environmental conditions. This system measures the current-voltage (I-V) curve of each PV module at five-minute intervals and simultaneously measures module temperature and irradiance. Additionally, the solar spectrum and environmental conditions are measured. With these experimental data, it is possible to carry out characterization and performance studies of PV modules or systems. The system started working in March 2019 and continues to work automatically to date. Three types of PV technologies began to be characterized: Aluminum Back Surface Field (Al- BSF), Hetero-junction with Intrinsic Thin-Layer (HIT), and Amorphous/micro-crystalline silicon tandem (a-Si/μc-Si). Four additional technologies were installed in 2020: Interdigitated Back Contact (IBC), Passivated Emitter Rear Totally Diffused (PERT), Amorphous Silicon (a- Si), and Copper Indium Gallium Selenide (CIGS). The first part describes the characterization system composed of an I-V curve tracer, a multiplexing system, and environmental sensors. PV modules, measuring instruments, sensors, components for circuit boards, and connection diagrams are listed. The automated control section describes the architecture of the software developed in LabVIEW for measurement, visualization, and data storage. In the second part, an analysis of the data extracted from the I-V curves is made, mainly in the maximum power point. For this, a methodology was developed to calibrate the PV modules outdoors. Simple methods such as Osterwald and Constant Fill Factor (FFk) were used to model the maximum power of HIT, Al-BSF, and tandem a-Si/μc-Si, for a year (May 2019 – April 2020). Next, the energy conversion efficiency is analyzed using the Performance Ratio (PR) in the following PV technologies: HIT, Al-BSF, tandem a-Si/μc-Si, IBC, PERT, a-Si, and CIGS for another year (March 2020 – February 2022). In the third part, an experimental study of the solar spectrum was carried out during one year (March 2019 – February 2020). The spectrum was characterized by the Average Photon Energy (APE). It was found that the yearly APE for the study period was 1.923 eV, indicating that the spectrum in Lima has a blue shift with respect to the AM1.5G standard spectrum. Additionally, the variation of the monthly APE during the year is negligible. Then, a theoretical evaluation of the Mismatch Factor (MM) and spectral gain was made for the spectral response (SR) of seven PV technologies: a-Si, Perovskite, CdTe, two CIGS with different SRs, multi-Si, and mono-Si. In the part of conclusions and future works, the objectives achieved and the current state of the research laboratory with the new systems and instruments installed are summarized. Finally, in the appendixes there is more detailed additional information on the circuits, algorithms, and mathematical arrangements that were necessary for the development of the thesis.
Testing pALPIDE sensors for particle detection and Characterization of a Laser beam using a webcam CMOS sensor
(Pontificia Universidad Católica del Perú, 2023-01-16) Soncco Meza, Carlos; Gago Medina, Alberto Martín
The upgrade program of the Large Hadron Collider (LHC) was implemented during the second Long Shutdown program (2019/2020). For this program, the ALICE Collaboration (A Large Ion Collider Experiment) proposed, among others, a new detector called Muon Forward Tracker (MFT). The primary goal of the MFT detector, installed on December 2021 and located between the Inner Tracker System (ITS) and the Muon Spectrometer, is to improve the capability of vertex reconstruction. The MFT is equipped with the same pixel sensors used for the ITS upgrade. These sensors are the ALICE Pixel Detectors (ALPIDE), a kind of monolithic active pixel sensor. The MFT is composed of five arrays of pixel sensors which are configured as parallel discs covering −3.6 < η < −2.45. Some prototypes were designed in order to achieve the final version of the ALPIDE, such as the pALPIDE family, which was divided into three versions (i.e., pALPIDE-1,2,3). The ALICE upgrade also included a new system for the data taking and simulation called Online-offline (O2) to replace AliRoot. We designed the geometry of two non-active parts of the MFT and included them in the O2 system. The first goal of this thesis is focused on the characterization of the pALPIDE-2. This sensor is segmented into four groups corresponding to four types of pixels. This characterization includes the test of analogue and digital. According to these tests, we identified a group of pixels that do not work correctly. The threshold scan tests showed the threshold level in each pixel is influenced by the input capacitance according to its n-well size and the surrounding area. Also, we studied the response of the pALPIDE-2 when it was exposed to a soft x-ray source, varying the distance between them. This test showed that the hit count changed according to the inverse square of the distance. iv The second goal of this thesis was to implement a low-cost tool based on a CMOS sensor to characterize laser beams. This tool comprises a Raspberry, a Pi Camera with a pitch size of 1.4 µm, and an optical system. To test the accuracy of the results of this tool, we made similar measurements with other sensors. A photodiode and a light-dependent resistor performed these measurements, which showed the spot radius size compatibility. However, the CMOS sensor expressed the highest precision and is a more affordable tool than commercial devices.
Analysis of the physical properties and photoelectrochemical behavior of c-Si/a-SiC:H(p) photocathodes for solar water splitting
(Pontificia Universidad Católica del Perú, 2023-01-16) Mejia Chueca, María del Carmen; Rumiche Zapata, Francisco Aurelio
Photoelectrochemical (PEC) processes have become an efficient and viable method for solar energy conversion into zero-emission fuels by harnessing and storage the power of the sun, which offers an environment-friendly approach. Hydrogen is considered as a sustainable and suitable energy alternative in comparison to energy systems based on the consumption of conventional hydrocarbon fuels. In particular, hydrogen production by PEC water splitting represents an attractive alternative to enhance the efficiency of water splitting process using sun light. Current research in this field is devoted to the fabrication and evaluation of new photoactive materials that upon sunlight absorption enable water-splitting PEC reactions with high efficiency and durability. Silicon based compounds offer a good opportunity as photoactive material due to its high abundance and current scalable technologies. Silicon is the eighth most abundant element in the universe and constitutes up to 27.2% of the earth’s crust weight [1]. Particularly, hydrogenated amorphous silicon carbide (a-SiC:H) thin films have been tested as photocathode material for photo-assisted electrolysis, exhibiting solar to hydrogen conversion efficiencies up to 7.5 %. Due to the capability to tailor the bandgap (1.8 - 3.3 eV) by the incorporation of carbon in a-Si:H, this material has turned out to be a promising candidate for PEC cells, fulfilling the optical bandgap (Egap) primary requirement, i.e. Egap > 2.2 eV. Additionally, the carbon incorporation leads to an enhancement of the corrosion resistance properties in aqueous media. It has been theoretically estimated that a PEC device with an a-Si0.9C0.1:H absorption layer exhibiting 2.0 eV of energy bandgap, can generate a photocurrent density Jph of 15 mA/cm2 (solar-to-hydrogen conversion efficiency ∼18 %) when submitted to an Air mass (AM) 1.5 solar spectrum [2]. The specific value of 1.5 for the Air mass is selected for standardization purposes, based on the analysis of solar irradiance data in the United States, and corresponds to a power of 1000 W/cm2 [3]. In the present work, a similar material a-Si0.5C0.5:H exhibiting 2.76 eV of energy bandgap generates a Jph of 17 mA/cm2 when submitted to the same light spectrum. This reflects an improvement in the use of a-SiC:H in PEC water splitting. Research on single thin film photoactive materials does not typically consider the role of the silicon substrate in the photoelectrochemical performance. In this sense, the photoelectrode is a system formed by a p-p, n-n or n-p structure, which depending on the depth of the space charge region may have an important impact on the photoelectrode performance. In this work, this substrate effect has been considered and studied. PEC performance of a-SiC:H is often limited by its non-ideal energy band-edge alignment to the H2O/O2 redox potential, thus limiting the oxygen evolution reaction (OER) and the whole water splitting process [4]. To overcome this downside, an external bias needs to be applied, contributing to counteract the overpotential required to trigger the direct water splitting reaction. The external bias also contributes to reduce overpotentials due to the presence of a surface SiO2 barrier layer and compensates interface charge carriers recombination as well. Previous studies have demonstrated that by removing the SiO2 native layer vii from a-SiC:H(i) surface, Jph values over 6 mA/cm2 can be achieved at a potential of -1.4 V vs. Ag/AgCl in contrast to values lower than < 4 mA/cm2 obtained without the oxide removal. In fact, the existence of surface states (SS) originated from the hydroxyl group termination on the oxide surface, form an electronic state that is typically located within the semiconductor bandgap. The theory that such states act as recombination centers for minority photo carriers, fits quite well with the assumption that surface recombination competes with charge transfer from the semiconductor band towards the electrolyte. Additionally, it has been reported that depending on the density and energetic position of SS, these can provide another favorable pathway for indirect charge transfer to the solution, competing with the undesirable recombination mechanism. Knowledge in this field is limitated to full-drift diffusion simulations in steady-state and dynamic regimes for photo-anodic currents in crystalline materials. In the current work, an experimental study has been carried out over an amorphous material (a-SiC:H) acting as photocathode for PEC water splitting. Thus, adding knowledge in this field. Attempts to understand the role of a-SiC defects in PEC water splitting performance have been carried out in 2009 by Simonds et al. [5]. As a result of these, defects density in the bulk of the a-SiC increases with carbon concentration, from ∼9 × 1016 cm−3 (6%C) to ∼8 × 1017 cm−3 (11%C), leading to a reduction of the PEC performance. On the other hand, defect densities in the SiC/SiO2 interface (SS) were approximated by Gaussian distributions with maximums of ∼2 × 1012 cm−2 · eV−1 (Ivanov et al. [6]). The latter finding was retrieved from Capacitance-Voltage (C−V) measurements over metal-oxide-semiconductor (MOS) structures, and fit quite well with the SiC SS density distributions reported in this work. The current work consists in three parts. In the first part, Bandgap engineering of a-SiC:H thin films was carried out to assess the material light absorption without compromising its photoelectrochemical water splitting capabilities. The tailoring was performed by varying the hydrogen concentration in the semiconductor and by post-deposition isochronical annealing treatments from 200 to 700 ◦C. By isochronical annealing, the same sample is submitted to the different temperature steps, from low to high temperature. After this analysis, the most suitable samples for water splitting application were evaluated as photocathodes in 1 M sulfuric acid under chopped light illumination. These a-SiC:H samples were doped with aluminum and deposited on different Silicon substrate conductivity types to assess the substrate influence in the a-SiC:H(Al) photocurrent response. This constitutes the second part or the work. Finally, in the third part, the role of SS in the photocathodic current for a-SiC:H(Al) absorber layers was experimentally analyzed. This analysis was based on steady-state and dynamic electrochemical models. Results concerning a-SiC:H(Al) photocathode stability under darkness and illumination conditions are also shown and discussed in this part. Concerning the findings and the novelty in this work, localized a-SiC:H(Al)/SiO2 SS would take part in a desirable mechanism of indirect electron charge transfer viii to the electrolyte, and thus, conduct hydrogen evolution reaction. Related to the SiO2 native layer, the evidence suggests that the SiO2 layer reduction during PEC tests triggers a favorable semiconductor-electrolyte interface. This interface exhibits less overpotential barriers which promotes photocurrent generation. A correlation exists between the retrieved SS density (NSS) and Urbach energy (EU) values. The EU is associated with disorder-induced electronic tail states or Urbach tails, which are localized states near the semiconductor band-edges. This correlation, as well as other a-SiC:H(Al)/SiO2 interface studies, support the reliability of our NSS calculations for the c-Si(p)/a-SiC:H(Al)/SiO2/electrolyte system. Finally, a charge transfer mechanism assisted by photogenerated minority carriers from the c-Si substrate has been also proposed in this work
Synthesis, tribology, electro-tribology and mechanical performance of ti2alc and ti3alc2 max phases thin films
(Pontificia Universidad Católica del Perú, 2023-01-26) Quispe Dominguez, Roger; Grieseler, Rolf
This thesis investigates the synthesis, mechanical properties, tribological and electro-tribological behavior of Ti2AlC and Ti3AlC2 MAX phases in the form of thin films. The thin films were obtained by deposition of a multilayer system of Titanium (Ti) - Aluminum (Al) - Carbon (C) and subsequent thermal annealing in a vacuum and controlled atmosphere. The Ti-Al-C multilayer system was deposited by magnetron sputtering on silicon substrates with a SiO2 and SixNy double-layer diffusion barrier. The stoichiometric of the film was controlled through the thickness of the individual monolayers. To obtain a 500 nm thick film, the Ti-Al-C sequence was repeated 22 times with individual thicknesses of 14, 6 and 3.5 nm, respectively. The experimental results show that the Ti2AlC phase is formed at a temperature of 700°C, while the Ti3AlC2 phase is formed at 950°C. The structural properties of the thin films were characterized by X-ray diffraction, Raman microscopy and glow discharge optical emission spectroscopy (GD-OES). The hardness of the thin films was analyzed by nanoindentation tests, obtaining hardness values of 11.6 and 5.3 GPa for Ti2AlC and Ti3AlC2, respectively. The tribological behavior of the thin films was analyzed under dry sliding conditions using a ball-on-flat reciprocating tribometer. The counter body consisted of AISI 52100 steel balls of 3 mm diameter. The friction coefficients obtained were in the range of 0.21 - 0.2 and 0.6 - 0.91 for the Ti2AlC and Ti3AlC2 thin films, respectively. The Ti2AlC phase has a better tribological performance, which can be attributed to its smaller grain size, lower surface roughness and higher hardness compared to the Ti3AlC2 phase. The electrical resistivity of the thin films was 0.73 and 0.45 μΩ·m for Ti2AlC and Ti3AlC2, respectively. The electro-tribological test was carried out using a ball-on-flat reciprocating tribometer under electrical currents of 10, 50 and 100 mA. The coefficient of friction and the electrical contact resistance were measured simultaneously in the same test. The results show that the coefficient of friction and electrical contact resistance could be related to thin-film properties such as hardness, roughness, grain size, and resistivity. These results of the electro-tribological behavior of the films provide valuable information for possible applications such as sliding electrical contacts.
Construction of radon chamber to expose active and passive detectors
(Pontificia Universidad Católica del Perú, 2023-02-14) Rojas Hancco, Jhonny Jonnatan; Lopez Herrera, Maria Elena
In this research and development, we present the design and manufacture of a radon chamber (PUCP radon chamber), a necessary tool for the calibration of passive detectors, verification of the operation of active radon monitors as well as diffusion chamber calibration used in radon measurements in air, and soils. The first chapter is an introduction to describe radon gas and national levels of radon concentration given by many organizations. Parameters that influence the calibration factor of the LR 115 type 2 film detector are studied, such as the energy window, critical angle, and effective volumes. Those are strongly related to the etching processes and counting of tracks all seen from a semi-empirical approach studied in the second chapter. The third chapter presents a review of some radon chambers that have been reported in the literature, based on their size and mode of operation as well as the radon source they use. The design and construction of the radon chamber are presented, use of uranium ore (autunite) as a chamber source is also discussed. In chapter fourth, radon chamber characterization is presented through leakage lambda, homogeneity of radon concentration, regimes-operation modes, and the saturation concentrations that can be reached. Procedures and methodology used in this work are contained in the fifth chapter and also some uses and applications of the PUCP radon chamber are presented; the calibration of cylindrical metallic diffusion chamber based on CR-39 chips detectors taking into account overlapping effect; transmission factors of gaps and pinhole for the same diffusion chambers are determined; permeability of glass fiber filter for 222Rn is obtained after reach equilibrium through Ramachandran model and taking into account a partition function as the rate of track density. The results of this research have been published in indexed journals. Finally, the conclusion and recommendations that reflect the fulfillment aims of this thesis are presented.
Characterization of luminescent ITO:Tb and AZO:Tb thin films prepared by radio frequency magnetron sputtering
(Pontificia Universidad Católica del Perú, 2023-05-09) Llontop López-Dávalos, Paul David; Guerra Torres, Jorge Andres
This thesis investigates the effects of introducing terbium to indium tin oxide (ITO) and aluminum zinc oxide (AZO) thin films on their electrical, optical and light emission properties. The films were prepared by radio frequency magnetron co-sputtering with active cooling during deposition. The samples maintained a high optical transmittance in the ultraviolet and visible spectral regions. ITO:Tb showed a low electrical resistivity ranging from 5×10−3 Ω·cm to 0.3Ω·cm, whilst AZO:Tb resulted with a high resistivity which could not be measured with the available equipment. Tb-related luminescence was obtained in ITO:Tb after annealing at 470 ◦C in air at atmospheric conditions. Contrastingly, AZO:Tb showed characteristic Tb luminescence in the as-grown state and further annealing treatments reduced the Tb-related intensity. For both materials, the optical transmittance was measured at each annealing temperature to track the changes in the optical parameters such as optical band gap and Urbach energy. Additionally, exciton binding energy in the case of AZO:Tb was also registered. Together with cathodoluminescence and photoluminescence (PL) measurements, the compromise between the achieved light emission intensity, optical and electrical properties was assessed for each material. Temperature dependence of the Tb-related luminescence and thermal quenching was assessed by temperature-dependent PL measurements from 83K to 533K under non-resonant indirect excitation. Thermal quenching activation energies suggest an effective energy transfer mechanism from the host to the Tb ions. In the case of ITO:Tb, it is assumed that a short-range charge trapping process and subsquent formation of bound excitons to Tb ion clusters is occuring at low sample temperatures. This indirect excitation mechanism is modeled using a spherical potential-well and a tight-binding one-band approximation models. For AZO:Tb, a similar approach is carried out, although the excitons are assumed to be bound to Tb ion clusters or Tb complexes that arise from the coordination with AZO intrinsic defects.
Riesgo radiológico debido a la radiactividad natural y exhalación de radón de suelos y materiales de construcción peruanos
(Pontificia Universidad Católica del Perú, 2023-07-06) Liza Neciosup, Rafael Ángel; Palacios Fernández, Daniel Francisco
La exposición al Radón es una preocupación importante debido a su papel en el aumento del riesgo de cáncer de pulmón. Para evaluar el riesgo de exposición, es necesario realizar mediciones de Radón en el aire interior de los hogares, y tener caracterizado el riesgo radiológico debido a los materiales de construcción y tomar medidas de prevención si es necesario. La exhalación de Radón en materiales de construcción se midió empleando el método de acumulación en una cámara cerrada durante un período de 24 horas para muestra disgregada o pulverizada y de 28 días para material compacto. La concentración de Radón en la cámara se mide regularmente durante este período y se utiliza para calcular la tasa de exhalación en masa y en superficie respectivamente. En el caso de suelos, el riesgo radiológico está asociado con la permeabilidad la concentración de Radón en el suelo. La medición de estos parámetros permitió determinar el potencial geogénico de Radón. Los resultados de este estudio muestran que la exhalación de 222Rn en materiales de construcción y suelos puede variar significativamente. En materiales de construcción, se encontró una tasa de exhalación promedio de 14.01 ± 1.04 mBq kg−1 h −1 , con un rango de [4.50 ± 0.42] a [22.34 ± 1.30] mBq kg−1 h −1 . Además, se encontró una buena correlación entre la concentración total de Radio en los materiales de construcción y la tasa de exhalación de Radón, con un coeficiente de correlación R2 de 0.88. Los dos tipos de ladrillo mostraron las tasas de exhalación más altas, posiblemente debido a la cercanía de la zona de extracción de materia prima para su elaboración con regiones con una alta probabilidad de presentar uranio. Por otro lado, las muestras de yeso no mostraron exhalación significativa de 222Rn, lo que concuerda con la cantidad de Radio en estas muestras. Finalmente, los resultados obtenidos de índices radiológicos de todos los tipos de muestras son importantes ya que demuestran que los materiales de construcción estudiados no representan un riesgo para la salud al usarlos en la construcción de viviendas.
Contribution to the Tb-doped AlNxOy:H/c-Si(p) interface study using Surface Photovoltage (SPV) techniques for potential photovoltaic applications
(Pontificia Universidad Católica del Perú, 2023-07-10) Dulanto Carbajal, Jorge Alejandro; Palomino Töfflinger, Jan Amaru
Hydrogenated Aluminum Oxynitride (AlNxOy:H) is a versatile material for the surface passivation of crystalline silicon (c-Si). The capability of having positive or negative fixed charges makes AlNxOy:H a suitable material for surface passivation of both n-type and p-type c-Si. Terbium (Tb) implemented in thin films is known for its potential for downshifting light. This work studies the electronic properties of the Tb-doped AlNxOy:H/cSi(p) interface. The studied samples’ layers were deposited by reactive direct current (DC) sputtering with different hydrogen flows and then annealed. Due to high leakage currents and high defect densities, the electronic properties of the Tb-doped AlNxOy:H layers could not be analyzed conclusively using standard techniques such as high-frequency capacitance-voltage (HF-CV) or quasi-steady-state photoconductance (QSSPC) measurements, respectively. As an alternative, the non-contact Surface Photovoltage (SPV) characterization technique enabled a profound investigation of the electronic features of the Tb-doped AlNxOy:H/c-Si (p) interface. Both modulated SPV and transient SPV measurements are performed. The capabilities of the SPV measurements make this technique unique and very effective in observing and measuring critical passivation properties of the Tb-doped AlNxOy:H samples. Particularly the transient SPV of the Tb-doped AlNxOy:H samples enabled the observation of different optical transitions (band to band, band to defect, defect to band) and carrier transport mechanisms between the Si surface and the Tb-doped AlNxOy:H. The changes in relaxation times among Tb-doped AlNxOy:H samples are noticeable due to spatial separation among defects (tunneling). This study uses complementary measurements like X-ray reflectometry (XRR), Photoluminescence (PL) and Fourier-transform infrared spectroscopy (FTIR) to obtain valuable information about the AlNxOy:H layer and the AlNxOy:H/c-Si(p) interface that validates the SPV results and observations. In the c-Si, through SPV, we observed strong accumulation with passivation of boron acceptors and the generation of defects near the interface. When the hydrogen flow was increased, the net negative charge in the Tbdoped AlNxOy:H layer decreased, and the surface photovoltage signals associated with defects increased. Transients SPV at higher hydrogen flows decayed faster, and hopping transport via an exponential distribution of trap states in energy replaced trap-limited relaxation of charge carriers separated in space. The particular conditions that these AlNxOy:H samples have, make transient SPV spectroscopy a unique and reliable technique to observe the electronic properties of the AlNxOy:H/c-Si(p) interface.
Nuevo enfoque para estudiar la respuesta del detector LR-115 al 222Rn, 220Rn y progenie. Aplicación en mediciones de radón en interiores de Lima, Perú
(Pontificia Universidad Católica del Perú, 2023-08-23) Pereyra Anaya, Patrizia Edel; Palacios Fernández, Daniel Francisco
Este trabajo se centra en el estudio de la radiactividad y, en particular, en la medición del gas radón en interiores. El objetivo principal es presentar un método alternativo de medición de radón utilizando detectores de huellas nucleares de estado sólido (SSNTDs) que permita realizar un monitoreo a mediana o gran escala y estimar la equivalencia de las mediciones realizadas con detectores desnudos y con una cámara de difusión. La radiactividad es una parte inherente al entorno humano y se ha experimentado exposiciones a dosis superiores a los valores actuales. Los radionucleidos, tanto de origen cósmico como terrestre, están presentes en alimentos, agua, materiales de construcción y seres vivos. Sin embargo, debido a los cambios rápidos y artificiales en el ambiente, la naturaleza no puede mitigarlos con la misma rapidez. Las radiaciones ionizantes pueden tener efectos perjudiciales en los sistemas biológicos y ecológicos, como la degeneración del tejido y el desarrollo de neoplasias. En Perú, los estudios preliminares indican que la población recibe dosis efectiva que de ahora en adelante llamaré dosis, comparables a los valores promedios mundiales, siendo la dosis debido al gas radón significativa en su aporte. Sin embargo, no existen valores propios de intervención establecidos por las organizaciones oficiales encargadas en Perú, lo que se está en la necesidad de realizar un estudio para determinar la concentración del gas radón en el país para determinar valores locales reales. Se conocen ciertas localidades en el mundo con altas concentraciones de radón y se plantea la posibilidad de que podrían existir también zonas anómalas en Perú. En cuanto a la metodología, se utilizarán detectores de huellas nucleares de nitrato de celulosa (LR-115) en modo desnudo y se propone un enfoque novedoso para la calibración de estos detectores. También se describe la estructura del trabajo, con capítulos dedicados a la radiactividad natural, los métodos de medición de radón, el análisis del detector LR-115,la calibración de los detectores y los resultados del monitoreo de radón en la ciudad de Lima. El trabajo concluye destacando la importancia de establecer regulaciones y recomendaciones sobre la protección contra la radiación ionizante del radón en viviendas y lugares de trabajo en Perú. Los resultados obtenidos se utilizarán para establecer valores límites y de intervención de concentración de radón y proporcionarán una base de datos para la creación de un mapa radiológico de Perú.