Fabricación, caracterización estructural y óptica de capas plasmónicas y puntos cuánticos: aplicaciones

This Thesis introduces a new chemistry methodology to synthesize in situ metallic nanocomposites thin films, made of Au and Ag nanoparticles embedded in solid dielectric matrices of TiO2 and SiO2. By this methodology, it is possible to control the size, shape and filling factor of the nanoparticles, being corroborated by different electronic microscopy techniques (SEM, TEM, HAADF-STEM) and surface characterization (AFM). Moreover, the optical properties of these layers were measured using different techniques, like extinction, transmittance and reflectance, as well as the indices of refraction were determined by means of ellipsometry, confirming the typical localized surface plasmon resonance of these metallic nanoparticles. These properties were explained using the Maxwell-Garnett effective medium approximation within the picture of Fresnel equations in order to explain the origin of reflectance and extinction spectra. Using these layers in combination with a controlled wet chemical etching, we obtain antireflectance layers by means of the formation of a porous inside the layer that allows the formation of a gradient-index multilayer, which traduces in a dramatic diminution of the reflectance in samples deposited over Si, showing a minimum in the spectral region dominated by the plasmon resonance. This gradual diminution of the reflectance with the etching time is explained with calculations in a multilayer structure. When the layers are doped with Ag nanoparticles, we observe the interaction with the organic molecule 2-mercaptoethanol in aqueous medium. This interaction provokes the diminution in the intensity of the optical extinction, as well as a shift in the wavelength of the plasmon resonance to larger energies. This opens the path to the development of potential applications in the field of chemical sensors. Colloidal quantum dots with diameters between 3-8 nm were synthesized and their optical properties were characterized by means of absorption and photoluminescence in the regimes of low temperature and high hydrostatic pressures. Taking into account the linear dependence of the effective masses with the temperature and the successfully applied finite potential wall model to explain the confinement energy alongside the non-parabolicity of the bands, a similar model has been employed in order to explain the ecotonic dynamics at high pressure regime and compared with the measurements in the spectral region of the infrared for the bulk material. We have obtained a good agreement with the experimental data, comparing with the differences obtained using a simplified model with the mechanical diminution of quantum dot’s size. Three different kind of bilayer nanocomposites have been fabricated containing metallic nanoparticles and quantum dots based on CdSe, observing in all these samples an photon-plasmon coupling, resulting in a enhancement or quenching in the emission of the quantum dots, that could be controlled by adding a dielectric spacer layer.En esta tesis se ha desarrollado una nueva metodología de síntesis química (sol-gel) para la fabricación in situ de nanocomposites metálicos en forma de capa delgada, compuestos por nanopartículas de Au y Ag embebidas en matrices dieléctricas sólidas de TiO2 y SiO2. Con dicha metodología se puede controlar el tamaño y el factor de llenado de las nanopartículas, que se han caracterizado mediante el uso de técnicas de microscopía electrónica (SEM, TEM, HAADF-STEM) y de caracterización de superficie (AFM). Además, se han empleado diversas técnicas para medir las propiedades ópticas de estas capas, como son la extinción, transmitancia y reflectancia, así como el índice de refracción por medio de elipsometría, verificando la existencia de la resonancia plasmónica superficial localizada típica de las nanopartículas hechas de estos metales. Estas propiedades se han modelizado haciendo uso de la aproximación de medio efectivo de Maxwell-Garnett y dentro del marco de las ecuaciones de Fresnel para explicar el origen de la reflectancia y la extinción. Utilizando estas capas, y mediante un ataque químico controlado, se han obtenido capas antireflejantes al conseguir una estructura porosa que permite la formación de un gradiente de índice de refracción, provocando un mínimo de reflectancia en la región espectral dominada por la resonancia plasmónica con muestras en substrato de Si. El gradual descenso de la reflectancia con el incremento del tiempo de ataque ha sido explicado satisfactoriamente mediante cálculos con estructuras multicapa. Con esta misma estructura porosa generada en las capas de TiO2 dopadas con nanopartículas de Ag, además del mismo comportamiento antireflejante, se ha observado la interacción con la molécula orgánica 2-mercaptoetanol en medio acuoso, registrándose un descenso en la intensidad de la extinción óptica en muestras depositadas sobre vidrio, así como un corrimiento hacia energías mayores de la longitud de onda de la resonancia plasmónica, lo que plantea la potencial aplicación de estas capas como sensores químicos. Se han sintetizado puntos cuánticos de PbSe, con diámetros entre 3-8 nm, y caracterizado sus propiedades ópticas mediante medidas de absorción y fotoluminiscencia en los regímenes de baja temperatura y altas presiones. Basándonos en la dependencia lineal de la masa efectiva con la temperatura y el buen acuerdo que presenta la energía de confinamiento experimental con un modelo de paredes de potencial finitas teniendo en cuenta la no parabolicidad de las bandas, se ha planteado un modelo similar para explicar la dinámica excitónica en el regímen de altas presiones, comparándose con las medidas en el infrarojo del material masivo. Se ha obtenido un buen acuerdo con los experimentos, haciendo hincapié en las diferencias obtenidas usando un modelo que solo tiene en cuenta la disminución mecánica del tamaño del punto cuántico con la presión. Se han fabricado tres tipos distintos de nanocomposites en forma de bicapa conteniendo nanopartículas metálicas y puntos cuanticos basados en CdSe, observándose en todos los casos una interacción foton-plasmón, que se traduce en un incremento o un descenso en la emisión de los puntos cuánticos, que se intenta controlar mediante la adición de una capa separadora

Protocells: Milestones and Recent Advances

The origin of life is still one of humankind\u27s great mysteries. At the transition between nonliving and living matter, protocells, initially featureless aggregates of abiotic matter, gain the structure and functions necessary to fulfill the criteria of life. Research addressing protocells as a central element in this transition is diverse and increasingly interdisciplinary. The authors review current protocell concepts and research directions, address milestones, challenges and existing hypotheses in the context of conditions on the early Earth, and provide a concise overview of current protocell research methods

Perspective: Plasmon antennas for nanoscale chiral chemistry

Plasmon nanoantennas are extensively used with molecular systems for the chemical and biological ultra-sensing, for boosting the molecular emissive and energy transfer properties, for the nanoscale catalysis, and for building advanced hybrid nanoarchitectures. In this Perspective we focus on the latest developments of using plasmon nanoantennas for the nanoscale chiral chemistry and for advancing the molecular magnetism. We overview the decisive role nanoplasmonics and nano-optics can play in achieving the chirally-selective molecular synthesis and separation, and in the way such processes might be precisely controlled by potentially merging chirality and magnetism at the molecular level. We give our view on how these insights might lead to the emergence of exciting new fundamental concepts in the nanoscale materials science

Perspective: plasmon antennas for nanoscale chiral chemistry

Plasmon nanoantennas are extensively used with molecular systems for chemical and biological ultra-sensing, for boosting the molecular emissive and energy transfer properties, for nanoscale catalysis, and for building advanced hybrid nanoarchitectures. In this perspective, we focus on the latest developments of using plasmon nanoantennas for nanoscale chiral chemistry and for advancing molecular magnetism. We overview the decisive role nanoplasmonics and nano-optics can play in achieving chirally selective molecular synthesis and separation and the way such processes might be precisely controlled by potentially merging chirality and magnetism at the molecular scale. We give our view on how these insights might lead to the emergence of exciting new fundamental concepts in nanoscale materials science

All-Dielectric and Magnetoplasmonic Nanoantenna Surfaces for the Dynamic Chiroptics

Optical platforms enabling the dynamic real-time control of the fundamental properties of light at visible and near-infrared wavelengths are the essential components for the future optical devices. Combining magnetic materials with the metallic and all-dielectric nano-optics enables a simultaneous enhancement and mutual control of their magneto-optical and chiro-optical properties. Here we examine hybrid nanoantennas made of Si and ferromagnetic metal developing magnetically-controlled chiroptical surfaces

Colony-like protocell superstructures

We report the formation, growth, and dynamics of model protocell superstructures on solid surfaces, resembling single cell colonies. These structures, consisting of several layers of lipidic compartments enveloped in a dome-shaped outer lipid bilayer, emerged as a result of spontaneous shape transformation of lipid agglomerates deposited on thin film aluminum surfaces. Collective protocell structures were observed to be mechanically more stable compared to isolated spherical compartments. We show that the model colonies encapsulate DNA and accommodate nonenzymatic, strand displacement DNA reactions. The membrane envelope is able to disassemble and expose individual daughter protocells, which can migrate and attach via nanotethers to distant surface locations, while maintaining their encapsulated contents. Some colonies feature “exocompartments”, which spontaneously extend out of the enveloping bilayer, internalize DNA, and merge again with the superstructure. A continuum elastohydrodynamic theory that we developed suggests that a plausible driving force behind subcompartment formation is attractive van der Waals (vdW) interactions between the membrane and surface. The balance between membrane bending and vdW interactions yields a critical length scale of 236 nm, above which the membrane invaginations can form subcompartments. The findings support our hypotheses that in extension of the “lipid world hypothesis”, protocells may have existed in the form of colonies, potentially benefiting from the increased mechanical stability provided by a superstructure

Macroscopic magneto-chiroptical metasurfaces

Nanophotonic chiral antennas exhibit orders of magnitude higher circular dichroism (CD) compared to molecular systems. When the structural chirality is merged with magnetism at the nanoscale, efficient magnetic control over the dichroic response is achieved, bringing exciting prospects to active nanophotonic devices. Here, we devise macroscopic enantiomeric magnetophotonic metasurfaces of plasmonic-ferromagnetic spiral antennas assembled on large areas via hole-mask colloidal lithography. The simultaneous presence of 3D- and 2D-features in chiral nanoantennas induces large CD response, where we identify reciprocal and non-reciprocal contributions, respectively. Exploring further this type of magnetophotonic metasurfaces might allow the realization of high-sensitivity chiral sensors and prompts the design of advanced macroscopic optical devices operating with polarized light

Protocells: Milestones and Recent Advances

The origin of life is still one of humankind's great mysteries. At the transition between nonliving and living matter, protocells, initially featureless aggregates of abiotic matter, gain the structure and functions necessary to fulfill the criteria of life. Research addressing protocells as a central element in this transition is diverse and increasingly interdisciplinary. The authors review current protocell concepts and research directions, address milestones, challenges and existing hypotheses in the context of conditions on the early Earth, and provide a concise overview of current protocell research methods