Plasmonic nanocrystals with complex shapes for photocatalysis and growth: Contrasting anisotropic hot-electron generation with the photothermal effect

In plasmonics, and particularly in plasmonic photochemistry, the effect of hot-electron generation is an exciting phenomenon driving new fundamental and applied research. However, obtaining a microscopic description of the hot-electron states represents a challenging problem, limiting our capability to design efficient nanoantennas exploiting these excited carriers. This paper addresses this limitation and studies the spatial distributions of the photophysical dynamic parameters controlling the local surface photochemistry on a plasmonic nanocrystal. We found that the generation of energetic electrons and holes in small plasmonic nanocrystals with complex shapes is strongly position-dependent and anisotropic, whereas the phototemperature across the nanocrystal surface is nearly uniform. Our formalism includes three mechanisms for the generation of excited carriers: the Drude process, the surface-assisted generation of hot-electrons in the sp-band, and the excitation of interband d-holes. Our computations show that the hot-carrier generation originating from these mechanisms reflects the internal structure of hot spots in nanocrystals with complex shapes. The injection of energetic carriers and increased surface phototemperature are driving forces for photocatalytic and photo-growth processes on the surface of plasmonic nanostructures. Therefore, developing a consistent microscopic theory of such processes is necessary for designing efficient nanoantennas for photocatalytic applications

Universal imprinting of chirality with chiral light by employing plasmonic metastructures

Chirality, either of light or matter, has proved to be very practical in biosensing and nanophotonics. However, the fundamental understanding of its temporal dynamics still needs to be discovered. A realistic setup for this are the so-called metastructures, since they are optically active and are built massively, hence rendering an immediate potential candidate. Here we propose and study the electromagnetic-optical mechanism leading to chiral optical imprinting on metastructures. Induced photothermal responses create anisotropic permittivity modulations, different for left or right circularly polarized light, leading to temporal-dependent chiral imprinting of hot-spots, namely imprinting of chirality. The above effect has not been observed yet, but it is within reach of modern experimental approaches. The proposed nonlinear chiroptical effect is general and should appear in any anisotropic material; however, we need to design a particular geometry for this effect to be strong. These new chiral time-dependent metastructures may lead to a plethora of applications.Comment: Main (29 pages, 6 figures) and supplemental (46 pages, 35 figures

Hot electrons and electromagnetic effects in the broadband Au, Ag, and Ag-Au nanocrystals: The UV, visible, and NIR plasmons

Energetic and optical properties of plasmonic nanocrystals strongly depend on their sizes, shapes, and composition. Whereas using plasmonic nanoparticles in biotesting has become routine, applications of plasmonics in energy are still early in development. Here, we investigate hot electron (HE) generation and related electromagnetic effects in both mono- and bi-metallic nanorods (NRs) and focus on one promising type of bi-metallic nanocrystals - core-shell Au-Ag nanorods. The spectra of the NRs are broadband, highly tunable with their geometry, and have few plasmon resonances. In this work, we provide a new quantum formalism describing the HE generation in bi-metallic nanostructures. Interestingly, we observe that the HE generation rate at the UV plasmon resonance of Au-Ag NRs appears to be very high. These HEs are highly energetic and suitable for carbon-fuel reactions. Simultaneously, the HE generation at the longitudinal plasmon (L-plasmon) peaks, which can be tuned from the yellow to near-IR, depends on the near-field and electromagnetic Mie effects, limiting the HE efficiencies for the long and large NRs. These properties of the L-plasmon relate to all kinds of NRs (Au, Ag, and Au-Ag). We also consider the generation of the interband d-holes in Au and Ag, since the involvement of the d-band is crucial for the energetic properties of UV plasmons. The proposed formalism is an important development for the description of bi-metallic (or tri-metallic, or more complex) nanostructures, and it paves the way to the efficient application of the plasmonic HEs and hot holes in sensing, nanotechnology, photocatalysis, and electrophotochemistry

Worldwide trends in underweight and obesity from 1990 to 2022: a pooled analysis of 3663 population-representative studies with 222 million children, adolescents, and adults

Background Underweight and obesity are associated with adverse health outcomes throughout the life course. We estimated the individual and combined prevalence of underweight or thinness and obesity, and their changes, from 1990 to 2022 for adults and school-aged children and adolescents in 200 countries and territories. Methods We used data from 3663 population-based studies with 222 million participants that measured height and weight in representative samples of the general population. We used a Bayesian hierarchical model to estimate trends in the prevalence of different BMI categories, separately for adults (age ≥20 years) and school-aged children and adolescents (age 5–19 years), from 1990 to 2022 for 200 countries and territories. For adults, we report the individual and combined prevalence of underweight (BMI <18·5 kg/m2) and obesity (BMI ≥30 kg/m2). For schoolaged children and adolescents, we report thinness (BMI <2 SD below the median of the WHO growth reference) and obesity (BMI >2 SD above the median). Findings From 1990 to 2022, the combined prevalence of underweight and obesity in adults decreased in 11 countries (6%) for women and 17 (9%) for men with a posterior probability of at least 0·80 that the observed changes were true decreases. The combined prevalence increased in 162 countries (81%) for women and 140 countries (70%) for men with a posterior probability of at least 0·80. In 2022, the combined prevalence of underweight and obesity was highest in island nations in the Caribbean and Polynesia and Micronesia, and countries in the Middle East and north Africa. Obesity prevalence was higher than underweight with posterior probability of at least 0·80 in 177 countries (89%) for women and 145 (73%) for men in 2022, whereas the converse was true in 16 countries (8%) for women, and 39 (20%) for men. From 1990 to 2022, the combined prevalence of thinness and obesity decreased among girls in five countries (3%) and among boys in 15 countries (8%) with a posterior probability of at least 0·80, and increased among girls in 140 countries (70%) and boys in 137 countries (69%) with a posterior probability of at least 0·80. The countries with highest combined prevalence of thinness and obesity in school-aged children and adolescents in 2022 were in Polynesia and Micronesia and the Caribbean for both sexes, and Chile and Qatar for boys. Combined prevalence was also high in some countries in south Asia, such as India and Pakistan, where thinness remained prevalent despite having declined. In 2022, obesity in school-aged children and adolescents was more prevalent than thinness with a posterior probability of at least 0·80 among girls in 133 countries (67%) and boys in 125 countries (63%), whereas the converse was true in 35 countries (18%) and 42 countries (21%), respectively. In almost all countries for both adults and school-aged children and adolescents, the increases in double burden were driven by increases in obesity, and decreases in double burden by declining underweight or thinness. Interpretation The combined burden of underweight and obesity has increased in most countries, driven by an increase in obesity, while underweight and thinness remain prevalent in south Asia and parts of Africa. A healthy nutrition transition that enhances access to nutritious foods is needed to address the remaining burden of underweight while curbing and reversing the increase in obesit

Propriétés plasmoniques des nanoparticules métalliques : au-delà de la résonance dipolaire

Ces dernières années, l’intérêt pour les nanoparticules métalliques a grandement augmenté du fait de la spécificité de leurs propriétés optiques. Ces propriétés se réfèrent aux résonances de plasmon de surface localisées pour les nanoparticules métalliques dont la taille est plus petite que la longueur d’onde d’illumination. Ces résonances sont directement liées à l’oscillation des électrons de conduction du métal et mènent à un champ proche électromagnétique fort localisé à la surface de la nanoparticule. Les nanoparticules métalliques sont utilisées dans des applications variées, telles que la détection biochimique, les lasers, la génération de couleurs, la spectroscopie exaltée de surface, la thérapie photo thermique du cancer, etc. Le plus souvent, les applications sont basées sur des facteurs externes. Dans cette thèse, nous étudions en profondeur les facteurs qui peuvent affecter la position spectrale de ces modes. De plus, nous parlerons de l’influence du montage expérimental sur les spectres optiques enregistrés. Outre le mode dipolaire, une nanostructure plasmonique peut montrer plusieurs autres modes qui peuvent être potentiellement utilisés pour des applications. Nous étudierons l’excitation et les mécanismes révélant les modes plasmoniques « cachés ». Dans la dernière étape de cette étude, nous utiliserons les propriétés multi-résonantes d’un nanocylindre d’or pour démontrer l’exaltation de fluorescence de boîtes quantiques par un effet plasmonique résonant double. Cette approche possède un grand potentiel pour être utilisée dans des applications d’énergie solaire.Last decades the interest in metallic nanoparticles increased enormously due to their optical tremendous properties. These properties refer to the localized surface plasmon resonances, which are characteristic for metallic nanoparticles of smaller sizes than the illumination wavelength. These resonances are directly linked to the oscillation of the conduction electrons of the metal and lead to a strong electromagnetic near-field localized at the nanoparticle surface. The plasmonic nanoparticles are successfully used in various application such as bio-chemical sensing, lasing, color generation, surface enhanced spectroscopies, photo-thermal therapy of cancer and etc.. Mostly, the applications are based on a single plasmonic resonance (mode) called dipolar. These modes are sensitive to many internal and external factors. In this thesis, we deeply study the factors, which may act on the spectral position of these modes. Moreover, we introduce the experimental set-ups influence on the recorded optical spectra. Besides the dipolar mode, a plasmonic nanostructure may exhibit many other modes which can be potentially used in applications. We investigate the excitation and the revealing mechanisms of so-called “hidden” plasmonic modes. In the final stage of the study we used the multi-resonant properties of a gold nanocylinder to demonstrate the enhancement of the quantum dots fluorescence by a doubly resonant plasmonic effect. This approach has a strong potential to be used in the solar energy applications

Propriétés plasmoniques des nanoparticules métalliques : au-delà de la résonance dipolaire

Last decades the interest in metallic nanoparticles increased enormously due to their optical tremendous properties. These properties refer to the localized surface plasmon resonances, which are characteristic for metallic nanoparticles of smaller sizes than the illumination wavelength. These resonances are directly linked to the oscillation of the conduction electrons of the metal and lead to a strong electromagnetic near-field localized at the nanoparticle surface. The plasmonic nanoparticles are successfully used in various application such as bio-chemical sensing, lasing, color generation, surface enhanced spectroscopies, photo-thermal therapy of cancer and etc.. Mostly, the applications are based on a single plasmonic resonance (mode) called dipolar. These modes are sensitive to many internal and external factors. In this thesis, we deeply study the factors, which may act on the spectral position of these modes. Moreover, we introduce the experimental set-ups influence on the recorded optical spectra. Besides the dipolar mode, a plasmonic nanostructure may exhibit many other modes which can be potentially used in applications. We investigate the excitation and the revealing mechanisms of so-called “hidden” plasmonic modes. In the final stage of the study we used the multi-resonant properties of a gold nanocylinder to demonstrate the enhancement of the quantum dots fluorescence by a doubly resonant plasmonic effect. This approach has a strong potential to be used in the solar energy applications.Ces dernières années, l’intérêt pour les nanoparticules métalliques a grandement augmenté du fait de la spécificité de leurs propriétés optiques. Ces propriétés se réfèrent aux résonances de plasmon de surface localisées pour les nanoparticules métalliques dont la taille est plus petite que la longueur d’onde d’illumination. Ces résonances sont directement liées à l’oscillation des électrons de conduction du métal et mènent à un champ proche électromagnétique fort localisé à la surface de la nanoparticule. Les nanoparticules métalliques sont utilisées dans des applications variées, telles que la détection biochimique, les lasers, la génération de couleurs, la spectroscopie exaltée de surface, la thérapie photo thermique du cancer, etc. Le plus souvent, les applications sont basées sur des facteurs externes. Dans cette thèse, nous étudions en profondeur les facteurs qui peuvent affecter la position spectrale de ces modes. De plus, nous parlerons de l’influence du montage expérimental sur les spectres optiques enregistrés. Outre le mode dipolaire, une nanostructure plasmonique peut montrer plusieurs autres modes qui peuvent être potentiellement utilisés pour des applications. Nous étudierons l’excitation et les mécanismes révélant les modes plasmoniques « cachés ». Dans la dernière étape de cette étude, nous utiliserons les propriétés multi-résonantes d’un nanocylindre d’or pour démontrer l’exaltation de fluorescence de boîtes quantiques par un effet plasmonique résonant double. Cette approche possède un grand potentiel pour être utilisée dans des applications d’énergie solaire

Polarization switch between parallel and orthogonal collective resonances in aluminum arrays

International audienc

Plasmonic multi-resonances in simple geometric platforms

International audienc

Hidden nanoparticles plasmonic modes revealed via angle resolved optical characterization

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