Enhancing Magnetic Light Emission with All-Dielectric Optical Nanoantennas

Electric and magnetic optical fields carry the same amount of energy. Nevertheless, the efficiency with which matter interacts with electric optical fields is commonly accepted to be at least 4 orders of magnitude higher than with magnetic optical fields. Here, we experimentally demonstrate that properly designed photonic nanoantennas can selectively manipulate the magnetic versus electric emission of luminescent nanocrystals. In particular, we show selective enhancement of magnetic emission from trivalent europium-doped nanoparticles in the vicinity of a nanoantenna tailored to exhibit a magnetic resonance. Specifically, by controlling the spatial coupling between emitters and an individual nanoresonator located at the edge of a near field optical scanning tip, we record with nanoscale precision local distributions of both magnetic and electric radiative local densities of states (LDOS). The map of the radiative LDOS reveals the modification of both the magnetic and electric quantum environments induced by the presence of the nanoantenna. This manipulation and enhancement of magnetic light-matter interaction by means of nanoantennas opens up new possibilities for the research fields of opto-electronics, chiral optics, nonlinear&nano-optics, spintronics and metamaterials, amongst others.Peer ReviewedPostprint (author's final draft

Direct imaging of fluorescence enhancement in the gap between two gold nanodisks

We present an analysis of the optical coupling between two gold nanodisks by near-field fluorescence microscopy. This is achieved by simultaneously scanning and measuring the light emitted by a single Er3þ/Yb3þ doped nanocrystal glued at the end of an atomic force microscope tip. The excitation of the nanocrystal was performed at k ¼ 975 nm via upconversion, and fluorescence was detected in the visible part of the spectrum at k ¼ 550 nm. For an isolated nanodisk, the near-field presents a two-lobe pattern oriented along the direction of the incident polarization. For two nanodisks with a sizable separation distance (385 nm) illuminated with the polarization along the interparticle axis, we observe a negative effect of the coupling with a slight decrease in fluorescence in the gap. For smaller gap values (195, 95, and 55 nm), a strong increase in fluorescence is observed as well as a reduced spatial localization of the field as the distance decreases. Finally, when the disks touch each other (0 nm), the dipolar–dipolar interaction between them disappears and no fluorescence enhancement occurs. A new plasmon mode is created at another wavelength. Our experimental results are in good agreement with numerical simulations of the nearfield intensity distribution at the excitation wavelength on the surface of the structures. Combining fluorescence mapping and far-field scattering spectroscopy should be of strong interest to develop bio-chemical sensors based on field enhancement effects.The authors thank the support from the DIM Nano-K program from “Region Ile de France,” from the Idex Paris Sciences & Lettres through Grant No. ANR-10-IDEX-0001-02 PSL from the CNRS and the CSIC through the Spanish-French program PICS (Grant Nos. SolarNano PICS07687 and PIC2016FR2), and from the Spanish Ministerio de Ciencia e Innovacion through Grant No. PID2019-109905GA-C22.Peer reviewe

Nanostructure strategies for improved perovskite solar cells

Resumen del trabajo presentado en la Conferencia Española de Nanofotónica (CEN2021), celebrada de forma virtual del 20 al 22 de septiembre de 2021Organic-inorganic hybrid perovskite solar cells have attracted much attention due to their high power conversion efficiency (¿23%) and low-cost fabrication. Directions to further improve these solar cells include strategies to enhance their stability and their efficiency by modifying either the perovskite absorber layer or the electron/hole transport layer. For example, the transparent electron transport layer (ETL) can be an important tuning knob influencing the charge extraction, [1] light harvesting, [2] and stability [3] in these solar cells, or the use of up-conversion nanoparticles to get better performance in the near IR part of the visible spectrum. [4] Here we present two strategies based on nanostructuration, first a fundamental study of upconversion fluorescence enhancement effects near Au nanodisks by scanning near-field optical microscopy and second the effects of a nanocolumnar TiO2 layer on the performance and the stability of Cs0.05(FA0.83MA0.17)0.95Pb(I0.83Br0.17)3 perovskite solar cells. For the first case, the enhancement and localization of light near the metallic structures are directly visualized by using a single Er/Yb-codoped fluorescent nanocrystal glued at the end of a sharp scanning tip. [5] For the second we find that, compared to devices with planar TiO2 ETLs, the TiO2 nanocolumns can significantly enhance the power conversion efficiency of the perovskite solar cells by 17 % and prolong their shelf life. By analyzing the optical properties, solar cells characteristics, as well as transport/recombination properties by impedance spectroscopy, we observed light-trapping and reduced carrier recombination in solar cells associated with the use of TiO2 nanocolumn arrays. [6] References: [1] S.S. Mali, et al., Chemistry of Materials 27, 1541 (2015). [2] C. Liu, et al., Journal of Materials Chemistry A 5, 15970 (2017). [3] M. Salado, et al., Nano Energy 35, 215 (2017) [4] M. Bauch et al., Plasmonics 9, 781 (2014) [5] L. Aigouy, et al., Nanoscale 11, 10365 (2019) [6] Z. Hu, et al., ACS Appl. Mater. Interfaces 12, 5979 (2020

Imagerie thermique par microscopie en champ proche à sonde fluorescente

Ce travail présente le développement d'une nouvelle technique d'imagerie thermique utilisant une nanoparticule fluorescente comme capteur de température. La particule est fixée à l'extrémité d'une pointe de microscope à force atomique. En contact avec une surface ou un dispositif plus ou moins chaud, la fluorescence de la particule varie et permet de déterminer la température. La particule utilisée contient des ions de terres rares (erbium et ytterbium) dont certaines raies d'émission sont en équilibre thermique. La mesure de l'intensité relative de ces raies permet de déterminer la température absolue du matériau, et donc de la surface avec lequel il est en contact. Nous avons tout d'abord utilisé cette technique pour étudier l'échauffement de pistes résistives (aluminium et nickel) parcourues par un courant continu. Dans le cas de pistes d'aluminium, la résolution latérale thermique que nous avons obtenue est d'environ 250 nm, de l'ordre de la taille de la particule fluorescente. Nous avons ensuite utilisé cet instrument pour observer l'échauffement de pistes parcourues par un courant alternatif. Ce mode permet d'observer où sont localisées les variations de température, mais ne permet pas pour l'instant de déterminer la température absolue du dispositif. A l'aide de ce mode de fonctionnement, nous avons observé l'échauffement dans des pistes de nickel dont la largeur est de l'ordre de 200 nm. Enfin, en effectuant des courbes d'approche/retrait, nous avons aussi pu mesurer l'importance relative des différents mécanismes de transfert de chaleur entre la pointe et la surface. Dans le cas de pistes de taille submicronique, le transfert de chaleur par contact direct est de loin le plus efficace.PARIS-BIUSJ-Physique recherche (751052113) / SudocSudocFranceF

Heating effects in micro and nanowires probed by flourescence scanning thermal microscopy

Dans ce manuscrit, nous avons étudié le comportement thermique de micro et nano-dispositifs métalliques, grâce à une nouvelle technique utilisant une nanoparticule fluorescente comme capteur de température. Cette technique a été développée au laboratoire LPEM de l'ESPCI. Ce travail est motivé par la demande croissante de caractérisations thermiques à des échelles micro et nanométriques. Nous avons montré que, en fixant une nanoparticule fluorescente à l'extrémité d'une pointe d'AFM, nous pouvons reconstruire une cartographie thermique de dispositifs nanostructurés, excités par effet Joule. En recueillant les variations d'intensité de fluorescence de la nanoparticule, nous pouvons mesurer la température de nanostructures avec une résolution latérale inférieure à 200nm. La technique fonctionne en mode alternatif et continu, pour mesurer des variations de température. Dans ce cas, nous avons décrit un processus de normalisation, avec l'aide duquel nous pouvons nous affranchir d'effets indésirables liés au champ proche optique, et qui nous permet d'extraire la température locale des dispositifs. En effectuant des balayages, nous avons observé différents mécanismes de transferts de chaleur pointe/surface. Nous avons montré que, bien que le transfert de chaleur par contact direct soit très efficace, un transfert existe aussi par conduction dans l'air au voisinage de la pointe. Nous avons ensuite étudié le rôle d'une couche interfaciale sur la propagation de la chaleur. Nous avons observé que la température d'un nano fil fabriqué sur un substrat de silicium oxydé augmente si l'épaisseur d'oxyde augmente. Nos résultats sont en bon accord avec des simulationsIn this manuscript, we have studied the thermal behavior of metallic micro and nanodevices, obtained by a specific Scanning Thermal Microscope, which uses a fluorescent nanoparticle as a very sensitive sensor of temperature. This home-made technique has been developed at ESPCI-LPEM. This work is motivated by the increasing demand of understanding the heat propagation at micro& nanoscale. We have shown that, by gluing a fluorescent nanoparticle at the extremity of an AFM tip, and by scanning the surface of the sample, we can reconstruct the thermal cartography of metallic nanostructured devices heated by Joule effect. By collecting the variations of the fluorescence intensity of the nanoparticle, we can measure the temperature of the nanostructures, with a lateral resolution better that 200nm.The technique can operate for measuring steady state temperatures and also the alternating mode, and measure temperature variations. We have described a normalization process, by the help of which, one can get rid of the unwanted nearfield optical effects, to extract the temperature of the devices very locally. By performing scans, we have observed how heat is transferred between the surface and the tip. We have shown that, although the most efficient transfer occurs when the tip is in direct contact with the surface, some transfer also occurs through the air. We have then investigated the role of the interfacial layer on the heat propagation. We have observed that the temperature of a Joule-heated nanowire fabricated on an oxidized silicon substrate strongly increases when the thickness of the oxide increases. Our experimental results are in good agreement with numerical simulationsPARIS-BIUSJ-Biologie recherche (751052107) / SudocSudocFranceF

Parallel collective resonances in arrays of gold nanorods

In this work we discuss the excitation of parallel collective resonances in arrays of gold nanoparticles. Parallel collective resonances result from the coupling of the nanoparticles localized surface plasmons with diffraction orders traveling in the direction parallel to the polarization vector. While they provide field enhancement and delocalization as the standard collective resonances, our results suggest that parallel resonances could exhibit greater tolerance to index asymmetry in the environment surrounding the arrays. The near- and far-field properties of these resonances are analyzed, both experimentally and numerically. © 2014 American Chemical Society.Funding from Spanish MINECO through grants “FUNCOAT” CONSOLIDER CSD2008-00023, “MAPS” MAT2011-29194-C02-01, and from Comunidad de Madrid through grants “NANOBIOMAGNET” S2009/MAT-1726 and “MICROSERES-CM” S2009/TIC-1476. A. V. acknowledges support from Spanish MINECO through FPI grant.Peer Reviewe

Quasi-cylindrical waves at the interface of a semiconductor device

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Strong near-field optical localization on an array of gold nanodisks

5 figuras, 5 páginasBy scanning near-field optical microscopy, we measured the localization of the electromagnetic field on an array of gold nanodisks illuminated in a transmission mode. We experimentally observed that the field is localized between the disks, with a pattern oriented along the incident polarization direction. We also observed that the electromagnetic field rapidly decays above the nanodisks, showing a strong vertical localization. The experimental results are in good agreement with numerical simulations performed by a finite difference time domain method. This study provides quantitative information about the local optical properties of closely-packed nanodisks that can be used for applications in biochemical sensors and nanolithography.This work was supported by the European Union (EU)project Nanomagma under contract NMP3-SL-2008-214107. We also acknowledge the Spanish MICINN for partial funding under “FUNCOAT” CONSOLIDER INGENIO 2010 Grant No. DCS2008-00023 and “MAGPLAS” Grant No.MAT2008-06765-C02-01/NAN.Peer reviewe

Optical quasicylindrical waves at dielectric interfaces

Much effort has been recently devoted to the study of the electromagnetic field launched on a metal-dielectric interface by one-dimensional (1D) subwavelength indentations. In this work, we consider the wave launched on a semiconductor surface that does not support any surface modes, in contrast to the metallic case. Through analytical calculations performed for polarized 2D Dirac line sources, we show that the waves launched by the two orthogonal polarizations (parallel and perpendicular to the surface) have approximately the same form, differing only in phase and magnitude. This finding implies that the wave launched on the surface by an arbitrary subwavelength indentation under an arbitrary illumination, either at grazing, normal, or oblique incidence, is always the same and possesses universal characteristics.We further observe this wave on a silicon substrate with a near-field probe. Through fitting with a simple model, the measured field is found to exhibit characteristics that are reminiscent of quasicylindrical waves on metal surfaces.NANOstructured active MAGneto-plasmonic MAterial

Quasi-cylindrical waves at the interface of a semiconductor device

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