Plasmonic Silver Nanoparticles by Dewetting process: Applications in SERS and Thin Film Solar Cells

The exploration of materials at the nanoscale, and their integration into optoelectronic devices, can be developed via new nanophotonic strategies based on plasmonic effects, which are nowadays regarded as the preferential solutions to overcome performance limitations in different types of applications. Those explored here concern the increase of efficiency of physically thin film silicon (Si) solar cells and of weak Raman signals for molecular detection (one scattered photon per million incident), employing metal nanoparticle (MNP) structures made of silver (Ag) which is the most effective material for plasmon-enhancement in solar cells and Raman Spectroscopy. The present thesis explored these effects employing thermal evaporation assisted by electron beam (e-beam) to deposit uniform thin layers of Ag, which then underwent a thermally-induced morphology transformation from a thin film (TF) to an array of NPs by a solid-state dewetting (SSD) mechanism. A novel procedure, involving a one-step methodology, without any post-deposition thermal procedures, is presented. This resulted in the direct arrangement of individual nanoparticles suitable for Raman amplification, with good control of their size and shape. The nanostructures that require a post-annealing process were essentially used for light trapping in solar cells. In this case a rapid thermal annealing (RTA) method was developed that yields highly reproducible and uniform plasmonic surfaces within a very fast (<10 min) annealing time when compared to other commonly employed annealing processes (>1 hour). The final results showed that microcrystalline silicon (μc-Si:H) solar cells deposited on improved ultra-fast plasmonics back reflectors (PBR), with Ag NPs with sizes of about 200 nm, exhibit an overall 11% improvement on device efficiency, corresponding to a photocurrent of 24.4 mA/cm2 and an efficiency of 6.78 %; against 21.79 mA/cm2 and 6.12 %, respectively, obtained on flat structures without NPs. For surface enhanced Raman spectroscopy (SERS) application, a remarkable 109 signal enhancement was obtained using rhodamine 6G (10-8 M) as the test analyte, and a new kind of costefficient SERS substrate (cardboard plates) was investigated for low-cost, flexible and disposable bio-detection devices. Besides such advantages, cardboard substrate proved to be a high-efficient, uniform and stable SERS substrate

Control óptico de la expresión génica en sistemas biológicos mediante nanopartículas de oro: Expresión génica fototérmica en Escherichia coli y silenciamiento génico en Chlamydomonas reinhardtii

Las nanopartículas de oro pueden ser encontrados de diferentes formas, tamaños y que determinan sus características químicas y físicas. Las propiedades físicas y químicas de las nanopartículas metálicas pueden ser moduladas al cambiar su forma, tamaño y la química de su superficie. Por lo tanto, esto ha permitido su uso en una gran variedad de aplicaciones en los sectores industriales y académicos. Una de las características de las nanopartículas metálicas es su habilidad para actuar como convertidos de energía optotérmicos. Esta característica ha sido utilizada en muchas aplicaciones donde las nanopartículas son acopladas con sistemas de respuesta térmica para generar una respuesta óptica. En este estudio, nosotros sintetizamos nanopartículas metálicas que son mayormente esféricas en su forma con un promedio de diámetro de 20.07 nm. En este estudio, nosotrosutilizamos dos fuentes de luz: LED y láser. Diferentes enfoques estadísticos fueron utilizados para medir la potencia y capacidad funcional de la luz láser y LED así como identificar a la variable más necesaria para incrementar la temperatura en una solución de nanopartículas de oro. En este trabajo se realizaron simultáneamente técnicas teóricas y experimentales para evaluar los diferentes factores que afectan la generación de calor en la superficie de nanopartículas cuando son expuestas a una longitud de onda específica por la luz láser y LED. Respecto al láser, los resultados mostraron que los factores que más contribuyeron al cambio de temperatura exhibido en la solución de nanopartículas resultaron ser el poder del láser, la concentración de las nanopartículas de oro, la interacción tiempo × láser y el tiempo de iluminación. Nosotros reportamos un modelo de regresión que permite predecir la generación de calor y cambios de temperatura con errores estándares residuales en menos de 4%. Los resultados son altamente relevantes para diseños futuros y en el desarrollo de aplicaciones donde las aplicaciones de nanopartículas sean incorporadas en los sistemas para inducir un cambio en la temperatura a partir de la exposición de con luz. Respecto al LED, nosotros analizamos estadísticamente la temperatura producida en la superficie de las nanopartículas de oro cuando utilizando LED como fuente de luz. Los resultados mostrados que los efectores principales y las interacciones de todos los factores fueron significativos. Finalmente, basados en el modelo de regresión presentado, los coeficientes de regresión y los resultados de ANOVA nos permiten presentan un poderoso modelo de regresión que muestra las relaciones entre la temperatura de cambio y sus variables. Nosotros simulamos el cambio de generación de nuestras nanopartículas de oro cuando la solución con nanopartículas de oro era iluminada con una fuente de luz LED. Nosotros demostramos que el máximo incremento de temperatura en la solución de nanopartículas (resultados de simulación) cotejaron excelentemente con nuestras observaciones (resultados prácticos). Para evaluar nuestra aplicación fototérmica obtenida a partir de nanopartículas de oro en un sistema biológico en células, evaluamos su factibilidad en la producción de proteína con enfoque fototérmico por primera vez. Para lograr este objetivo, utilizamos luz LED en vez de un dispositivo láser al considerarse como un método nuevo, barato, inofensivo y conmutable para sistemas biológicos vivos. Después de sintetizar las nanopartículas de oro y obtener su perfil de temperatura, nosotros diseñamos un gen sintético, donde el sitio de unión a ribosoma pudiera ser activo y trabajar eficientemente a 37°C. Basado en el modelo de regresión lineal y en análisis de respuesta de superficie de curva, nosotros encontramos el cómo proveer la temperatura necesaria. De esta manera, nosotros mostramos el uso de nanopartículas metálicas y LED como fuente de luz pueden trabajar eficientemente en una estructura tipo stem – loop que contiene un sitio a unión a ribosoma y consecuentemente una alta producción de mCherry es logrado. Además, para mostrar su factibilidad en la desbridamiento de dsDNA unido a nanopartículas metálicas a partir de LED como fuente de luz, nosotros elaboramos conmutadores (nanopartículas de oro acoplados con dsDNA) y finalmente fueron caracterizados. Entonces, nosotros mostramos la factibilidad del desbridamiento del dsDNA unido a nanopartículas de oro (prueba in vitro) utilizando LED como fuente de luz bajo diferentes longitudes de onda. La prueba demostró ser exitosa y se mostró la probabilidad de que el calor generado fototérmica pueda ser utilizado para el silenciamiento de genes por antisentido en células de microalgas vivas

Polymer-Nanoparticle Hybrid Materials for Plasmonic Hydrogen Detection

Plasmonic metal nanoparticles and polymer materials have independently undergone rapid development during the last two decades. More recently, it has been realized that combining these two systems in a hybrid or nanocomposite material comprised of plasmonically active metal nanoparticles dispersed in a polymer matrix leads to systems that exhibit fascinating properties, and some first attempts had been made to exploit them for optical spectroscopy, solar cells or even pure art. In my thesis, I have applied this concept to tackle the urgent problem of hydrogen safety by developing Pd nanoparticle-based “plasmonic plastic” hybrid materials, and by using them as the active element in optical hydrogen sensors. This is motivated by the fact that hydrogen gas, which constitutes a clean and sustainable energy vector, poses a risk for severe accidents due to its high flammability when mixed with air. Therefore, hydrogen leak detection systems are compulsory in the imminent large-scale dissemination of hydrogen energy technologies. To date, however, there a several unresolved challenges in terms of hydrogen sensor performance, whereof too slow sensor response/recovery times and insufficient resistance towards deactivation by poisoning species are two of the most severe ones. In this thesis, I have therefore applied the plasmonic plastic hybrid material concept to tackle these challenges. In summary, I have (i) developed hysteresis-free plasmonic hydrogen sensors based on PdAu, PdCu and PdAuCu alloy nanoparticles; (ii) demonstrated ultrafast sensor response and stable sensor operation in chemically challenging environments using polymer coatings; (iii) introduced bulk-processed and 3D printed plasmonic plastic hydrogen sensors with fast response and high resistance against poisoning and deactivation

Modeling of plasmonic properties of nanostructures for next generation solar cells and beyond

Plasmonic particles and nanostructures are widely used in photovoltaic and photonics. Surface plasmons were found to enhance different types of solar cells including plasmonic DSSCs, plasmonic solid semiconductor solar cells, plasmonic organic solar cells, and plasmonic perovskite solar cell. Size, composition, and shape of plasmonic nanoparticles as well as nanometer-distance control between particles are key design factors of plasmonic nanostructures. Modeling is rapidly gaining in importance for mechanistic understanding and rational design of plasmonic nanostructures. We review the modeling approaches used to model plasmon resonance features of nanostructures, from classical approaches that can routinely handle most particle sizes used in solar cells to approaches beyond classical electrodynamics such as ab initio approaches based on time-dependent density functional theory (TD-DFT). We highlight recently emerging approaches which have the potential to significantly enhance modeling capabilities in the coming years, in particular, by allowing atomistic (ab initio) modeling at realistic length scales, i.e. of particle sizes beyond 10 nm which are of most interest to plasmonic solar cells but remain problematic with traditional DFT-based techniques, such as density functional tight binding (DFTB) based approaches, time-dependent orbital-free DFT, and machine learning-based approaches, as well as many-body perturbation theory which is expected to gain usage with advances in computing power

Plasmonic Nanoparticles as Light-Harvesting Enhancers in Perovskite Solar Cells: A User’s Guide

In this Perspective we discuss the implications of employing metal particles of different shape, size, and composition as absorption enhancers in methylammonium lead iodide perovskite solar cells, with the aim of establishing some guidelines for the future development of plasmonic resonance-based photovoltaic devices. Hybrid perovskites present an extraordinarily high absorption coefficient which, as we show here, makes it difficult to extrapolate concepts and designs that are applied to other solution-processed photovoltaic materials. In addition, the variability of the optical constants attained from perovskite films of seemingly similar composition further complicates the analysis. We demonstrate that, by means of rigorous design, it is possible to provide a realistic prediction of the magnitude of the absorption enhancement that can be reached for perovskite films embedding metal particles. On the basis of this, we foresee that localized surface plasmon effects will provide a means to attain highly efficient perovskite solar cells using films that are thinner than those usually employed, hence facilitating collection of photocarriers and significantly reducing the amount of potentially toxic lead present in the device.European Union 307081Ministerio de Economía y Competitividad MAT2011-23593, MAT2014-54852-

Dewetting Metal Nanofilms-Effect of Substrate on Refractive Index Sensitivity of Nanoplasmonic Gold

The localized surface plasmon resonance (LSPR) sensitivity of metal nanostructures is strongly dependent on the interaction between the supporting substrate and the metal nanostructure, which may cause a change in the local refractive index of the metal nanostructure. Among various techniques used for the development of LSPR chip preparation, solid-state dewetting of nanofilms offers fast and cost effective methods to fabricate large areas of nanostructures on a given substrate. Most of the previous studies have focused on the effect of the size, shape, and inter-particle distance of the metal nanostructures on the LSPR sensitivity. In this work, we reveal that the silicon-based supporting substrate influences the LSPR associated refractive index sensitivity of gold (Au) nanostructures designed for sensing applications. Specifically, we develop Au nanostructures on four different silicon-based ceramic substrates (Si, SiO2, Si3N4, SiC) by thermal dewetting process and demonstrate that the dielectric properties of these ceramic substrates play a key role in the LSPR-based refractive index (RI) sensitivity of the Au nanostructures. Among these Si-supported Au plasmonic refractive index (RI) sensors, the Au nanostructures on the SiC substrates display the highest average RI sensitivity of 247.80 nm/RIU, for hemispherical Au nanostructures of similar shapes and sizes. Apart from the significance of this work towards RI sensing applications, our results can be advantageous for a wide range of applications where sensitive plasmonic substrates need to be incorporated in silicon based optoelectronic devices