Strong coupling typically occurs between two separate objects or between an object and its environment (such as an atom and a cavity). However, it can also occur between two different excitations within the same object, a situation that has been much less studied. In this study, we observe strong coupling between localized surface plasmon resonances and the interband transition in aluminum nanorods, as evidenced by optical spectroscopy and electron energy loss spectroscopy, and corroborated with numerical simulations. Strong coupling is observed between the interband transition and multiple orders of the surface plasmon mode, including dark ones. We also obtain experimental maps of the hybrid modes at the nanoscale. In each case, the associated Rabi energy, which corresponds to the energy splitting between the two polaritonic branches, is obtained. Moreover, a dedicated numerical model was employed to calculate the hot electron generation rate in the nanorods. The calculations demonstrate that efficient generation of hot electrons can be achieved in the near-infrared region when the interband transition is strongly coupled with a plasmon resonance. This high generation rate stems from the hybrid nature of the mode, as its plasmonic component provides a high absorption cross-section, while the interband transition part ensures efficient conversion to hot electrons. Consequently, aluminum nanorods represent an efficient source of hot electrons in the visible and near-infrared regions, with potential applications in local photochemistry, photodetection, and solar energy harvesting.

Thermal transport in nanostructures plays a critical role in modern technologies. As devices shrink, techniques that can measure thermal properties at nanometer and nanosecond scales are increasingly needed to capture transient, out-of-equilibrium phenomena. We present a novel pump-probe photon-electron method within a scanning transmission electron microscope (STEM) to map temperature dynamics with unprecedented spatial and temporal resolutions. By combining focused laser-induced heating and synchronized time-resolved monochromated electron energy loss spectroscopy (EELS), we track phonon, exciton and plasmon signals in various materials, including silicon nitride, aluminum thin film, and transition metal dichalcogenides. Our results demonstrate the technique's ability to follow temperature changes at the nanometer and nanosecond scales. The experimental data closely matched theoretical heat diffusion models, confirming the method's validity. This approach opens new opportunities to investigate transient thermal phenomena in nanoscale materials, offering valuable insights for applications in thermoelectric devices and nanoelectronics.

The work of Luis M. Liz-Marzán, his colleagues, and other nanochemists has been essential in the emergence of electron spectroscopies for nano-optics applications. After a brief presentation of these techniques and their applications to individual plasmonic nanoparticles, this paper focuses on a short review of the study of the coupling between optical excitations at the nanometer scale, made possible by recent advances in electron spectroscopies. In particular, plasmon–plasmon, plasmon–exciton, and plasmon–phonon couplings are reviewed.

Scanning transmission electron microscopy coupled with electron energy loss spectroscopy (STEM-EELS) provides spatially resolved chemical information down to the atomic scale. However, studying radiation-sensitive specimens such as organic-inorganic composites remains extremely challenging. Here, we analyzed metal-organic framework nanoparticles (nanoMOFs) at low-dose (10 e-/Å2) and liquid nitrogen temperatures, similar to cryo-TEM conditions usually employed for high-resolution imaging of biological specimens. Our results demonstrate that monochromated STEM-EELS enables damage-free analysis of nanoMOFs, providing in a single experiment, signatures of intact functional groups comparable with infrared, ultraviolet, and X-ray data, with an energy resolution down to 7 meV. The signals have been mapped at the nanoscale (<10 nm) for each of these energy spectral ranges, including the chemical features observed for high energy losses (X-ray range). By controlling beam irradiation and monitoring spectral changes, our work provides insights into the possible pathways of chemical reactions occurring under electron exposure. These results demonstrate the possibilities for characterizing at the nanoscale the chemistry of sensitive systems such as organic and biological materials.

The acquisition of a hyperspectral image is nowadays a standard technique used in the scanning transmission electron microscope. It relates the spatial position of the electron probe to the spectral data associated with it. In the case of electron energy loss spectroscopy (EELS), frame-based hyperspectral acquisition is much slower than the achievable rastering time of the scan unit (SU), which sometimes leads to undesirable effects in the sample, such as electron irradiation damage, that goes unperceived during frame acquisition. In this work, we have developed an event-based hyperspectral EELS by using a Timepix3 application-specific integrated circuit detector with two supplementary time-to-digital (TDC) lines embedded. In such a system, electron events are characterized by their positional and temporal coordinates, but TDC events only by temporal ones. By sending reference signals from the SU to the TDC line, it is possible to reconstruct the entire spectral image with SU-limited scanning pixel dwell time and thus acquire, with no additional cost, a hyperspectral image at the same rate as that of a single channel detector, such as annular dark-field. To exemplify the possibilities behind event-based hyperspectral EELS, we have studied the decomposition of calcite (CaCO$_3$) into calcium oxide (CaO) and carbon dioxide (CO$_2$) under the electron beam irradiation.

An optical antenna can convert a propagative optical radiation into a localized excitation and the reciprocal. Although optical antennas can be readily created using resonant nanoparticles (metallic or dielectric) as elementary building blocks, the realization of antennas sustaining multiple resonances over a broad range of frequencies remains a challenging task. Here, we use aluminum self-similar, fractal-like structures as broadband optical antennas. Using electron energy loss spectroscopy, we experimentally evidence that a single aluminum Cayley tree, a simple self-similar structure, sustains multiple plasmonic resonances. The spectral position of these resonances is scalable over a broad spectral range spanning two decades, from ultraviolet to midinfrared. Such multiresonant structures are highly desirable for applications ranging from nonlinear optics to light harvesting and photodetection, as well as surface-enhanced infrared absorption spectroscopy.

Aerosol-assisted catalytic chemical vapor deposition (AACCVD) is a powerful one-step process to produce vertically aligned carbon nanotubes (VACNTs), characterized by the continuous supply of the catalyst precursor (metallocene). The behavior of catalyst species all along the synthesis is essential for the continuous growth of VACNTs. It is there investigated through detailed observations and elemental analyses at scales of VACNT carpets and of individual CNTs. Our approach is based on two complementary experiments: quenching of the sample cooling, and sequential injection of two distinct metallocenes. Metal-based nanoparticles nucleated in the gas-phase during the whole synthesis duration are shown to diffuse in between the growing VACNTs from the top of the CNT carpet towards the substrate. They are much smaller than the catalyst particles formed on the substrate in the initial steps of the process and evidences are given that they continuously feed these catalyst particles at the VACNT roots. Particularly, the electron energy-loss spectroscopy (EELS) analyses of metal-based segments found into a single CNT show that the second injected metal is very gradually incorporated in the particle initially formed from the metal firstly injected. The feeding of the catalyst particles by the nanoparticles continuously nucleated in the gas-phase is therefore an essential feature of the base-growth of CNTs by AACCVD.

Journal Article Unveiling Single Particle Coupling of Metallic Nanoparticles and Whispering Gallery Mode Resonators Get access Yves Auad, Yves Auad Laboratoire de Physique des Solides, Orsay, 91405, France Search for other works by this author on: Oxford Academic Google Scholar Cyrille Hamon, Cyrille Hamon Laboratoire de Physique des Solides, Orsay, 91405, France Search for other works by this author on: Oxford Academic Google Scholar Marcel Tencé, Marcel Tencé Laboratoire de Physique des Solides, Orsay, 91405, France Search for other works by this author on: Oxford Academic Google Scholar H Lourenço-Matins, H Lourenço-Matins Max Planck Institute for Biophysical Chemistry, G̈ottingen, 37077, GermanyIV. Physical Institute, University of G̈ottingen, G̈ottingen 37077, Germany Search for other works by this author on: Oxford Academic Google Scholar Vahagn Mkhitaryan, Vahagn Mkhitaryan ICFO-Institut de Ciencies Fotoniques, The Barcelona Institute of Science and Technology, 08860 Castelldefels (Barcelona), Spain Search for other works by this author on: Oxford Academic Google Scholar Odile Stéphan, Odile Stéphan Laboratoire de Physique des Solides, Orsay, 91405, France Search for other works by this author on: Oxford Academic Google Scholar F Javier García de Abajo, F Javier García de Abajo ICFO-Institut de Ciencies Fotoniques, The Barcelona Institute of Science and Technology, 08860 Castelldefels (Barcelona), SpainICREA-Institució Catalana de Recerca i Estudis Avançats, Passeig Lluís Companys 23, 08010 Barcelona, Spain Search for other works by this author on: Oxford Academic Google Scholar Luiz H G Tizei, Luiz H G Tizei Laboratoire de Physique des Solides, Orsay, 91405, France Search for other works by this author on: Oxford Academic Google Scholar Mathieu Kociak Mathieu Kociak Laboratoire de Physique des Solides, Orsay, 91405, France Search for other works by this author on: Oxford Academic Google Scholar Microscopy and Microanalysis, Volume 28, Issue S1, 1 August 2022, Pages 1962–1964, https://doi.org/10.1017/S1431927622007656 Published: 01 August 2022

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While phonons and their related properties have been studied comprehensively in bulk materials, a thorough understanding of surface phonons for nanoscale objects remains elusive. Infra-red imaging methods with photons or electrons exist, which can map these vibrational excitations down to the individual atom scale. However, no technique so far was able to directly reveal the complete three-dimensional vectorial picture of the phononic electromagnetic density of states from a nanostructured object. Using a highly monochromated electron beam in a scanning transmission electron microscope, we could visualize varying phonon signatures from nanoscale MgO cubes both as a function of the beam position, energy-loss and tilt angle. The vibrational responses were described in terms of well-defined eigenmodes and were used to tomographically reconstruct the phononic surface fields of the object, disclosing effects invisible by conventional mapping. Surface phonon applications rely critically on the way the electromagnetic field is spatially and vectorially shaped, strongly influencing the optical, thermal and electronic behavior of the materials. Such 3D information therefore promises novel insights in nanoscale physical phenomena and is invaluable to the design and optimization of nanostructures for fascinating new uses.

Hybrid/moiré interlayer and intralayer excitons have been realized in twisted two-dimensional transition metal chalcogenides (2D-TMD) due to variation in local moiré potential within a moiré supercell. Though moiré excitons have been detected in TMD heterostructures by macroscopic spectroscopic techniques, their spatial distribution is experimentally unknown. In the present work, using high-resolution scanning transmission electron microscopy (STEM) and electron energy-loss spectroscopy (EELS), we explore the effect of the twist angle in MoS2/WSe2 heterostructures. We observe weak interaction between the layers at higher twist angles (>5°) and stronger interaction for lower twist angles. The optical response of the heterostructure varies within the moiré supercell, with a lower energy absorption peak appearing in regions with the AA stacking.

Whispering-gallery mode resonators host multiple trapped narrow-band circulating optical resonances that find applications in quantum electrodynamics, optomechanics, and sensing. However, the spherical symmetry and low field leakage of dielectric microspheres make it difficult to probe their high-quality optical modes using far-field radiation. Even so, local field enhancement from metallic nanoparticles (MNPs) coupled to the resonators can interface the optical far field and the bounded cavity modes. In this work, we study the interaction between whispering-gallery modes and MNP surface plasmons with nanometric spatial resolution by using electron-beam spectroscopy with a scanning transmission electron microscope. We show that gallery modes are induced over a selective spectral range of the nanoparticle plasmons, and additionally, their polarization can be controlled by the induced dipole moment of the MNP. Our study demonstrates a viable mechanism to effectively excite high-quality-factor whispering-gallery modes and holds potential for applications in optical sensing and light manipulation.

This file contains the raw dataset used in the manuscript "Tailored Nanoscale Plasmon-Enhanced Vibrational Electron Spectroscopy" published in L. H. G. Tizei et al Nano Letters, 2020 (doi: 10.1021/acs.nanolett.9b04659) Data has been acquired using Nion Swift (https://nionswift.readthedocs.io/en/stable/). Experimental details can be found in L. H. G. Tizei et al Nano Letters, 2020 (doi: 10.1021/acs.nanolett.9b04659). The dataset has been analyzed using the following Python libraries: Numpy, Scipy, Hyperspy, Matplotlib EELS hyperspectral images have been aligned using the Hyperspy "align1D" method. Aligned EELS hyperspectral images are saved in files finished with "_Aligned.hspy": For the strong coupling experiments: Tip 1 is on hBN Tip 2 is on vacuum For each of the nanowires tips, a file with the fitted coefficients are available, as well as a plot of the data and the fitted curve. Datasets have been fitted with gaussian and/or lorentizan functions, as described in the published text. Any question can be forwarded to the corresponding authors of the published text.

The first colour photographs were created by a process introduced by Edmond Becquerel in 1848. The nature of these photochromatic images colours motivated a debate between scientists during the XIXth century, which is still not settled. We present the results of chemical analysis (EDX, HAXPES and EXAFS) and morphology studies (SEM, STEM) aiming at explaining the optical properties of the photochromatic images (UV-visible spectroscopy and low loss EELS). We rule out the two hypotheses (pigment and interferences) that have prevailed since 1848, respectively based on variations in the oxidation degree of the compound forming the sensitized layer and periodically spaced photolytic silver planes. A study of the silver nanoparticles dispersions contained in the coloured layers showed specific localizations and sizes distributions of the nanoparticles for each colour. These results allow us to formulate a plasmonic hypothesis on the origin of the photochromatic images colours.