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CHROMATEM

Scientific highlights

Three-dimensional vectorial imaging of surface phonon polaritons

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Surface phonon polaritons (SPhPs) are coupled photon-phonon excitations that emerge at the surfaces of nanostructured materials. Although they strongly influence the optical and thermal behavior of nanomaterials, no technique has been able to reveal the complete three-dimensional (3D) vectorial picture of their electromagnetic density of states. Using our monochromated NION-HERMES CHROMATEM, we could visualize varying SPhP signatures from nanoscale MgO cubes as a function of the beam position, energy loss, and tilt angle. The SPhPs’ response was described in terms of eigenmodes and used to tomographically reconstruct the phononic surface electromagnetic fields of the object. Such 3D information promises insights in nanoscale physical phenomena and might be useful to design and optimize nanostructures. This work was published in Science.

Tailored nanoscale plasmon-enhanced vibrational electron spectroscopy

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Atomic vibrations and phonons are an excellent source of information on nanomaterials that we can access through a variety of methods including Raman Scattering, infrared spectroscopy, and electron energy-loss spectroscopy (EELS). In the presence of a plasmon local field, vibrations are strongly modified, and in particular, their dipolar strengths are highly enhanced, thus rendering Raman scattering and infrared spectroscopy extremely sensitive techniques. Here, we experimentally demonstrate that the interacion between a relativistic electron and vibrational modes in nanostructures is fundamentally modified in the presence of plasmons. We finely tune the energy of surface plasmons in metallic nanowires in the vicinity of hexagonal boron nitride, making it possible to monitor and disentangle both strong phonon-plasmon coupling and plasmon-driven phonon enhancement at the nanometer scale. Due to the near-field character of the electron beam-phonon interaction, optically-inactive phonon modes are also observed. Read more »

Publications

Li, X., et al. Three-dimensional vectorial imaging of surface phonon polaritons. Science 37160, 1364 - 1367 (2021).
Mkhitaryan, V., et al. Can Copper Nanostructures Sustain High-Quality Plasmons?. Nano Letters 21, (2021). Download: acsnanolett0c04667(2).pdf (4.15 MB)
Kociak, M., Galvão Tizei, L.H., Meuret, S., Lourenço-Martins, H. & Stephan, O. Spectromicroscopies électroniques : sonder les propriétés optiques de nanomatériaux avec des électrons rapides. Photoniques 39 - 43 (2020).doi:10.1051/photon/202010239  Download: photon2020102p39.pdf (386.08 KB)
Paulauskas, T., et al. Atomic-Resolution EDX, HAADF, and EELS Study of GaAs1-xBix Alloys. Nanoscale Research Letters 15918, (2020).
Tizei, L.H.G., et al. Tailored nanoscale plasmon-enhanced vibrational electron spectroscopy. Nano Letters (2020).doi:10.1021/acs.nanolett.9b04659
Li, X., et al. Plasmonic Oligomers with Tunable Conductive NanojunctionsPlasmonic Oligomers with Tunable Conductive Nanojunctions. The Journal of Physical Chemistry Letters 10, 7093 - 7099 (2019).
Saito, H., et al. Emergence of point defect states in a plasmonic crystal. Physical Review B 100, (2019).
Tararan, A., et al. Optical gap and optically active intragap defects in cubic BN. Physical Review B 982121, (2018). Download: PhysRevB.98.094106.pdf (2.16 MB)
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