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Metal nanocrystals (NCs) display unique physicochemical features that are highly dependent on the nanoparticle dimensions, anisotropy, structure, and composition. The development of synthesis methodologies that allow us to tune such parameters finely emerges crucial for the application of metal NCs in catalysis, optical materials, or biomedicine. Here, we describe a synthetic methodology to fabricate hollow multimetallic heterostructures using a combination of seed-mediated growth routes and femtosecond pulsed laser irradiation. The envisaged methodology relies on the co-reduction of Ag and Pd ions on gold nanorods (Au NRs) to form Au@PdAg core–shell nanostructures containing small cavities at the Au-PdAg interface. The excitation of Au@PdAg NRs with low fluence femtosecond pulses was employed to induce the coalescence and growth of large cavities, forming multihollow anisotropic Au@PdAg nanostructures. Moreover, single-hollow alloy AuPdAg could be achieved in high yield by increasing the irradiation energy. Advanced electron microscopy techniques, energy-dispersive X-ray spectroscopy (EDX) tomography, X-ray absorption near edge structure (XANES) and FDTD (finite differences in the time domain) simulationsallowed us to characterize the morphology, structure, and elemental distribution of the irradiated NCs in detail. The ability of the reported synthesis route to fabricate multimetallic NCs with unprecedented hollow nanostructures brings attractive prospects for the fabrication of tailored high-entropy alloy nanoparticles., Ministerio de Ciencia e Innovación (España), Comunidad de Madrid, European Commission, Depto. de Química Física, Fac. de Ciencias Químicas, TRUE, inpress

We studied by means of an atomistic model based on molecular dynamics the thermal evolution of surface atoms in amorphous silica under high electronic excitation produced by irradiation with swift heavy ions. The model was validated with the total and differential yields measured in sputtering experiments with different ions and ion energies showing a very good quantitative prediction capability. Three mechanisms are behind the evolution of the surface region: (1) an ejection mechanism of atoms and clusters with kinetic energy exceeding their binding energy to the sample surface, which explains the experimentally observed angular distributions of emitted atoms, and the correlation of the total sputtering yield with the electronic stopping power and the incidence angle. (2) A collective mechanism of the atoms in the ion track originated by the initial atom motion outwards the track region subsequently followed by the return to the resulting low-density region in the track center. The collective mechanism describes the energy dissipation of bulk atoms and the changes in density, residual stress, defect formation and optical properties. (3) A flow mechanism resulting from the accumulation and subsequent evolution of surface atoms unable to escape. This mechanism is responsible for the crater rim formation.

We studied by means of an atomistic model based on molecular dynamics the thermal evolution of surface atoms in amorphous silica under high electronic excitation produced by irradiation with swift heavy ions. The model was validated with the total and differential yields measured in sputtering experiments with different ions and ion energies showing a very good quantitative prediction capability. Three mechanisms are behind the evolution of the surface region: (1) an ejection mechanism of atoms and clusters with kinetic energy exceeding their binding energy to the sample surface, which explains the experimentally observed angular distributions of emitted atoms, and the correlation of the total sputtering yield with the electronic stopping power and the incidence angle. (2) A collective mechanism of the atoms in the ion track originated by the initial atom motion outwards the track region subsequently followed by the return to the resulting low-density region in the track center. The collective mechanism describes the energy dissipation of bulk atoms and the changes in density, residual stress, defect formation and optical properties. (3) A flow mechanism resulting from the accumulation and subsequent evolution of surface atoms unable to escape. This mechanism is responsible for the crater rim formation. Graphic Abstract: [Figure not available: see fulltext.].

[ES] La irradiación de nanopartículas de oro (AuNPs) esféricas en una suspensión coloidal con pulsos láser de nanosegundos puede inducir su metamorfosis, dando lugar a la aparición de esferas con cavidades internas. La concentración del surfactante estabilizador de las partículas, el uso de fluencias de láser moderadas y el tamaño de las partículas, determinan la eficiencia y características del proceso. Las partículas huecas resultantes se obtienen cuando las moléculas del medio circundante (ej., agua, materia orgánica del surfactante) quedan atrapadas durante la irradiación láser. Estas observaciones experimentales sugieren la existencia de un balance sutil entre los procesos de calentamiento y enfriamiento. El primero induce la expansión y paso a un estado amorfo y, el segundo, la subsecuente recristalización manteniendo en su interior el material atrapado. Estas observaciones experimentales han sido explicadas satisfactoriamente con las simulaciones de dinámica molecular clásica desarrolladas en el marco de esta tesis. Específicamente, la dinámica molecular confirma que es necesaria la existencia de moléculas en el interior de las cavidades que se forman dentro de las AuNPs para que se produzca su estabilización. En la segunda parte de esta tesis, se detallan las simulaciones de dinámica molecular clásica y los cálculos de propiedades ópticas de la irradiación de nanopartículas esféricas de oro con pulsos láser de femtosegundos, para predecir los cambios de forma que se producen en las mismas, bajo una exploración de los diferentes parámetros involucrados, es decir, la fluencia y duración del láser, el tamaño de las nanopartículas cristalinas esféricas y la capacidad de enfriamiento del medio circundante. El objetivo fundamental de las simulaciones es brindar una guía para la síntesis de nanopartículas con morfologías determinadas. Los resultados de las simulaciones indican que, para la formación de nanopartículas huecas, las mismas deben ser calentadas hasta un, [CA] La irradiació de nanopartícules d'or (AuNPs) esfèriques en una suspensiócolloidal amb polsos làser de nanosegons pot induir la seua metamorfosi, donant lloc a l'aparició d'esferes amb cavitats internes. La concentració del surfactante estabilitzador de les partícules, l'ús de fluencias de làser moderades i la grandària de les partícules, determinen l'eficiència i característiques del procés. Les partícules buides resultants s'obtenen quan les molècules del mitjà circumdant (ex., aigua, matèria orgànica del surfactante) queden atrapades durant la irradiació làser. Aquestes observacions experimentals suggereixen l'existència d'un balanç subtil entre els processos de calfament i refredament. El primer indueix l'expansió i passe a un estat amorf i, el segon, la subseqüent recristalización mantenint en el seu interior el material atrapat. Aquestes observacions experimentals han sigut explicades satisfactòriament amb les simulacions de dinàmica molecular clàssica desenvolupades en el marc d'aquesta tesi. Específicament, la dinàmica molecular confirma que és necessària l'existència de molècules a l'interior de les cavitats que es formen dins de les AuNPs perquè es produïsca la seua estabilització. En la segona part d'aquesta tesi, es detallen les simulacions de dinàmica molecular clàssica i els càlculs de propietats òptiques de la irradiació de nanopartícules esfèriques d'or amb polsos làser de femtosegundos, per a predir els canvis de manera que es produeixen en aquestes, sota una exploració dels diferents paràmetres involucrats, és a dir, la fluencia i duració del làser, la grandària de les nanopartícules cristal·lines esfèriques i la capacitat de refredament del mitjà circumdant. L'objectiu fonamental de les simulacions és brindar una guia per a la síntesi de nanopartícules amb morfologies determinades. Els resultats de les simulacions indiquen que, per a la formació de nanopartícules buides, les mateixes han de ser calfades fins a una temperatura entre 2500 i 3500, [EN] The irradiation of gold nanoparticles (AuNPs) in a colloid with nanosecond laser pulses can give rise to the formation of cavities. The concentration of the surfactant used to stabilize the particles, the laser fluency, and the size of the nanoparticles, determine the efficiency and features of the process. The resulting hollow particles are obtained when the right balance between the heating and cooling processes is given. The first process induces an expansion and the melting of the particle, while the second, leads to the recrystallization, keeping the extraneous matter trapped in the inside. These experimental observations have been satisfactorily explained by the molecular dynamics simulations carried out in this thesis. Specifically, the simulations have confirmed that it is necessary the existence of trapped molecules in the inside of the cavities to stabilize the cavities. In the second part of this thesis, the molecular dynamics simulations and calculation of optical properties when gold nanoparticles (in a colloid) are irradiated with femtosecond laser pulses. The simulations allowed to predict the the shape changes under different conditions for the laser fluency and duration, the size of the nanoparticles and the cooling rate, which is driven by the properties of the solvent and the surfactant. These simulations provide a guidance for the synthesis of nanoparticles with specific morphological features. The results show that the nanospheres should be heated up to 2500 y 3500 K, followed by a fast cooling (time constant of 120 ps). Therefore, the experimental conditions for the efficient production of hollow nanoparticles are described what opens a broad range of possibilities for applications in areas such as energy storage and catalysis. MD simulations are carried out in the last part of this thesis to gain insights into the pump-probe experiments using AuNPs in reference [R. Fuentes-Domínguez et al. Appl. Sci. 2017, 7(8), 819.]. Upon femtosecond la

El presente proyecto consiste en un estudio de la energía que depositan los distintos tipos de iones a lo largo de su trayectoria, durante su uso en la terapia hadrónica. Para obtener los resultados, se utiliza un software de simulación basado en el método de Monte Carlo, e implementado a partir de la herramienta GEANT4. Se estudian dos tipos de cáncer. El cáncer de pulmón y el cáncer de ojo. Para el cáncer de pulmón, se han obtenido resultados similares con todos los iones considerados. Para el de ojo, se obtiene que es favorable el uso de He-4. Abstract This project consists in a study of the deposited energy of different types of ions through their trajectory, during their use in hadron therapy. In order to obtain the results, it is used a simulation software based on the Monte Carlo technique and developed with the GEANT4 toolkit. Two types of cancer are studied. Lung cancer and eye cancer. Regarding the lung cancer, results are similar for all the ions studied. Regarding eye cancer, results are favourable for He-4.

A lo largo de los últimos años, con los diferentes avances tecnológicos y una mayor accesibilidad a todo tipo de estudios, la ciencia de materiales, sobre todo el área orientada a materiales avanzados y nanomateriales, ha tenido un gran auge de la investigación y la experimentación. Estas líneas de desarrollo tienen como uno de sus objetivos la creación de materiales con propiedades específicas, lo que se consigue mediante técnicas y procesos de combinación de materiales. Es aquí donde entra la implantación iónica. La implantación iónica es una técnica que consiste en la aceleración de iones de un elemento elegido, hasta una cierta energía, con la que penetrarán en un blanco, quedando así implantados en su interior, modificando el material y dotándolo de propiedades nuevas. Este proyecto se realiza dentro del área de la simulación de esta técnica y en él se llevará a cabo el análisis de cuatro casos diferentes de implantación:  Oro de 1,5 MeV implantado en un sustrato de silicio.  Oro de 4 MeV implantado en un sustrato de dióxido de silicio (SiO2).  Iodo de 1 MeV implantado en un sustrato de zafiro (Al2O3).  Níquel de 600 keV implantado en un sustrato de silicio. Las condiciones de estas implantaciones serán simuladas mediante dos programas diferentes, SRIM y Strata, que darán la información necesaria para posteriormente hacer una comparación con los datos experimentales obtenidos del Centro de Micro-Análisis de Materiales (CMAM) de la Universidad Autónoma de Madrid. Para el completo entendimiento de estos casos

One of the most important and distinctive features of plasmonic nanostructures is their ability to confine large electromagnetic fields on nanometric volumes; i.e., the so-called hot spots. The generation, control and characterization of the hot spots are fundamental for several applications, like surface-enhanced spectroscopies. In this work, we characterize the near-field distribution and enhancement of nanostructured gold thin films fabricated by glancing angle deposition magnetron sputtering. These films are composed of columnar nanostructures with high roughness and high density of inter-columnar gaps, where the electromagnetic radiation can be confined, generating hot spots. As expected, the hot spots are localized in the gaps between adjacent nanocolumns and we use scattering-type scanning near-field optical microscopy to image their distribution over the surface of the samples. The experimental results are compared with finite-difference time-domain simulations, finding an excellent agreement between them. The spectral dependence of the field-enhancement is also studied with the simulations, together with surface-enhanced Raman spectroscopy at different excitation wavelengths in the visible-NIR range, proving a broad-band response of the substrates. These findings may result in interesting applications in the field of surface-enhanced optical spectroscopies or sensing.

Laser ablation has several advantages over the chemical synthesis of nanoparticles due to its simplicity and because it is a faster and cleaner process. In this paper, we use femtosecond laser ablation to generate highly concentrated silver colloidal nanoparticle solutions. Those high concentrations usually lead to agglomeration of the nanoparticles, rendering the solution nearly useless. We employ two different organic stabilizers (hexadecyltrimethylammonium bromide, CTAB, and polyvinylpyrrolidone, PVP) to avoid this problem and study their effect on the nanoparticle size distribution, structural characteristics, and the solution concentration., Ministerio de Economía y Competitividad (MINECO), Comunidad de Madrid, Depto. de Química Física, Fac. de Ciencias Químicas, TRUE, pub

The irradiation of silica with ions of specific energy larger than ~0.1 MeV/u produces very high electronic excitations that induce permanent changes in the physical, chemical and structural properties and give rise to defects (colour centres), responsible for the loss of sample transparency at specific bands. This type of irradiation leads to the generation of nanometer-sized tracks around the ion trajectory. In situ optical reflection measurements during systematic irradiation of silica samples allowed us to monitor the irradiation-induced compaction, whereas ex situ optical absorption measurements provide information on colour centre generation. In order to analyse the results, we have developed and validated an atomistic model able to quantitatively explain the experimental results. Thus, we are able to provide a consistent explanation for the size of the nanotracks, the velocity and thresholding effects for track formation, as well as, the colour centre yield per ion and the colour centre saturation density. In this work we will discuss the different processes involved in the permanent modification of silica: collective atomic motion, bond breaking, pressure-driven atom rearrangement and ultra-fast cooling. Despite the sudden lattice energy rise is the triggering and dominant step, all these processes are important for the final atomic configuration.

El trabajo de Fin de Grado desarrollado ha consistido en el diseño y fabricación de un microscopio y un espectrómetro para realizar medidas de reflectancia y transmitancia espectroscópicas. También ha sido necesario calibrar este último. Estos equipos han sido financiados por el Instituto de Fusión Nuclear, localizado en la Escuela Técnica Superior de Ingenieros Industriales de la Universidad Politécnica de Madrid, para ser utilizados en docencia y en futuras líneas de investigación de materiales. La caracterización óptica puede clasificarse en dos grandes grupos, atendiendo al momento en que se realizan las mediciones. La caracterización in-situ donde la toma de medidas se realiza durante la fabricación de la muestra. El segundo grupo es la caracterización ex-situ donde el sistema es caracterizado después de su formación, una vez finalizada la deposición del recubrimiento. La caracterización ex-situ será el método empleado en este proyecto por su simplicidad y fiabilidad, aunque el espectrómetro fabricado también podría utilizarse en el otro tipo de caracterización. Se puede afirmar que la caracterización ex-situ es la más sencilla de ejecutar, debido a la menor cantidad de variables a tener en cuenta para obtener una medida fiable y precisa. Se pueden obtener las propiedades del sistema ya crecido, sus propiedades finales, manejando un volumen de datos inferior al de la variante in-situ. Sin embargo, no todo son ventajas ya que presenta serias limitaciones cuando se requiere caracterizar un sistema más allá de sus propiedades finales. Existe una gran variedad de técnicas, de distinta naturaleza, para la caracterización ex-situ e in-situ. En este trabajo se describirán y analizaran algunas de las técnicas de caracterización ópticas más empleadas en la actualidad, centrándose en la reflectancia y transmitancia espectroscópicas de la luz puesto que es la técnica empleada en este trabajo durante la experimentación. El funcionamiento del microscopio diseñado es sencill

In this work we have used in situ reflectance to study structural modifications in silica and quartz irradiated with swift heavy ions. Quantitative analysis of reflectance spectra allowed us to (i) obtain the detailed kinetics of surface modification and (ii) reconstruct the refractive index profiles created in the irradiated materials. We have shown that in situ reflectance yields very accurate results; for instance, track radii and irradiation threshold in silica and quartz obtained from our measurements are similar to those reported in the literature. In particular, reflectance has several advantages over Rutherford Backscattering in the channeling configuration (RBS-C) because it can be measured in situ (allowing recording of detailed kinetics not attainable by RBS-C), requires less sophisticated equipment and, more importantly, can be used with any material whereas RBS-C is restricted to mono-crystalline materials. ©2016 Optical Society of America

Nanoparticles have a fundamental limit as to how much light they can absorb. This limit is based on the finite number of modes excited in the nanoparticle at a given wavelength and maximum absorption capacity per mode. The enhanced absorption can be achieved when each mode supported by the nanoparticle absorbs light up to the maximum capacity. Using a stochastic optimization algorithm, we design multilayer nanoparticles, in which we can make several resonant modes overlap at the same frequency resulting in superabsorption. We further introduce the efficiency of the absorption for a nanoparticle, which is the absorption normalized by the physical size of the particle, and show that efficient absorbers do not always operate in the superabsorption regime.

Ion irradiation on dielectric materials produces several processes, such ionization and defect formation followed by a decay governed by thermal processes such as heat diffusion and atomic rearrangement. Finally in the irradiated region the mechanical properties are altered, strain and stress fields appear, a densification takes places and other properties such as the refractive index are affected. In order to simulate the mechanical response of silica to swift ion irradiation we use a methodology based on molecular dynamics (MD) and finite element methods (FEM). We use information from MD to obtain the local densification generated by an incoming swift ion. Finally we calculate the densification in the ion track using FEM. This method provides information on the strain and stress field along the material as a function of ion irradiation fluence. For this work an experimental campaign using Br ions from 5 to 50 MeV has been done at CMAM accelerator (Madrid). We measured the refractive index and we observe that for high fluences the refractive index decreases. The effect of the strain field on the density could explain the decrease in the refractive index. We check this hypothesis using our methodology coupling MD and FEM.

© 2015 Elsevier B.V. © 2015 Elsevier B.V. All rights reserved. Experimental evidence of synthetic single-crystal diamond amorphization under the effect of irradiation with swift heavy ions is shown. The type of sharp thresholding behavior that characterizes electronic damage is not observed within a range of electronic stopping power covering up to 14 keV/nm. Amorphization is assessed by Rutherford Back Scattering Channeling (RBS-c) measurements done with light ions, after swift heavy ion irradiation. Results are analyzed and discussed in order to confirm the hypothesis of a nuclear damage-induced process, whereby it is concluded that electronic effects are not relevant in the studied range of stopping powers. The evolution of the amorphized fraction as a function of the irradiated fluence and nuclear stopping power is measured and discussed as well.

© 2015 Elsevier B.V. Ion irradiation on dielectric materials produces several processes, such ionization and defect formation followed by a decay governed by thermal processes such as heat diffusion and atomic rearrangement. Finally in the irradiated region the mechanical properties are altered, strain and stress fields appear, a densification takes places and other properties such as the refractive index are affected. In order to simulate the mechanical response of silica to swift ion irradiation we use a methodology based on molecular dynamics (MD) and finite element methods (FEM). We use information from MD to obtain the local densification generated by an incoming swift ion. Finally we calculate the densification in the ion track using FEM. This method provides information on the strain and stress field along the material as a function of ion irradiation fluence. For this work an experimental campaign using Br ions from 5 to 50 MeV has been done at CMAM accelerator (Madrid). We measured the refractive index and we observe that for high fluences the refractive index decreases. The effect of the strain field on the density could explain the decrease in the refractive index. We check this hypothesis using our methodology coupling MD and FEM.