Nanophotonics and Optoelectronics with surface phonon polaritons
Christopher R. Gubbin, Simone De Liberato
School of Physics and Astronomy, University of Southampton, Southampton, SO17 1BJ, United Kingdom
E-mail: s.de-liberato@soton.ac.uk

Surface phonon polaritons, electromagnetic modes supported at the interface of polar materials have opened new
avenues for mid-infrared nanophotonics and optoelectronics, thanks to their extremely sub-wavelength confinement
and long lifetimes1. Given the lack of adequate materials with bandgap in the mid-infrared region, electrical excitationof phonon polaritons has until now been performed either thermally, leading to narrowband directional thermal
emitters2, or using quantum cascade structures 3. Notwithstanding their merits, the former approach has intrinsicallylimited efficiency and cannot lead to lasing, while the latter presents the usual complexity and cost constraints ofstandard quantum cascade lasers. An important dissipation channel in polar materials is the emission of longitudinal
optical phonons via the Fröhlich interaction, which accounts for a large part of Ohmic losses. Due to their longitudinal
nature these phonons do not couple with light. Transverse optical phonons couple with light instead, and they canhybridize with photons to create phonon polaritons.

Fig. 1 In panel (a) we show the reflectance of a nanometric dielectric multilayer. The experimental data shows resonances which
are not correctly described by a local response theory (LRA) ignoring the phonon dispersion. Our nonlocal theory from Ref. 4
correctly reproduces the resonances and identifies them as LTPP modes. In panel (b) we sketch the concept of LTPP emission, in
which the Fröhlich interaction in polar semiconductors is dressed by the photonic field, leading to the resonant electrical emissionof LTPPs.

We discovered that longitudinal and transverse optical phonons, which are perfectly decoupled at small wavevectors,
can become coupled when the large-wavevector dispersion of the phonons is taken into account. Our nonlocal theory
predicted the existence of novel quasiparticles with a hybrid longitudinal and transverse nature, which we named
longitudinal-transverse phonon polaritons (LTPP). We initially experimentally observed them in polytypes of siliconcarbide (SiC) characterized by elongated unit cells which fold longitudinal phonons back into the light-line5. We thendemonstrated that LTPP are a ubiquitous feature of polar nanostructures when the crystal features are small enough tocouple photons to large wavevector phonon modes4 (see Fig. 1(a)). The LTPPs can thus be electrically excited thanks
to their longitudinal component, while emitting mid-infrared light in the far-field thanks to their transverse one, as
schematized in Fig. 1(b).
I will conclude this talk showing some recent theoretical results describing the LTPP-mediated electrical emission of
mid-infrared radiation from polar dielectrics. Our results demonstrate that this emission channel has the features toempower a novel generation of efficient and ubiquitous mid-infrared optoelectronic devices.
References
(1)
(2)
(3)
(4)
(5)

Gubbin, C. R.; De Liberato, S.; Folland, T. G. 2022. J. Appl. Phys., 131, 030901.
Lu, G.; Gubbin, C. R.; Nolen, J. R.; Folland, T.; Tadjer, M. J.; De Liberato, S.; Caldwell, J. D. 2021. Nano Lett., 21, 1831.
Ohtani, K.; Meng, B.; Franckié, M.; Bosco, L.; Ndebeka-Bandou, C.; Beck, M.; Faist, J. 2019. Sci. Adv., 5, eaau1632.
Gubbin, C. R.; De Liberato, S. 2020. Phys. Rev. X, 10, 021027.
Gubbin, C. R.; Berte, R.; Meeker, M. A.; Giles, A. J.; Ellis, C. T.; Tischler, J. G.; Wheeler, V. D.; Maier, S. A.; Caldwell, J. D.; De Liberato,
S. 2019. Nat Commun, 10, 1682.

Anisotropic Polaritons in Heterostructures made of Rotated Thin
Layers and Dielectric Spacers
Christian Lanza1,2, Aitana Tarazaga Martín-Luengo1,2 , Gonzalo Álvarez-Pérez1,2,3 , Kirill V.
Voronin4, Nathaniel Capote-Robayna5, Javier Martín-Sánchez1,2, Alexey Y. Nikitin5,6 and Pablo
Alonso-González1,2
1. Department of Physics, University of Oviedo, Oviedo 33006, Spain.
2. Center of Research on Nanomaterials and Nanotechnology, CINN (CSIC-Universidad de Oviedo), El Entrego 33940, Spain.
3. Department of Physics, Columbia University, New York, NY, 10027, USA
4. Center for Photonics and 2D Materials, Moscow Institute of Physics and Technology, Dolgoprudny 141700, Russia.
5. Donostia International Physics Center (DIPC), Donostia-San Sebastián 20018, Spain.
6. IKERBASQUE, Basque Foundation for Science, Bilbao 48013, Spain.
E-mail: lanzachristian@uniovi.es

Polaritons in strongly anisotropic media have recently emerged as a promising tool for controlling lightat the nanoscale. Among them, understanding phonon polaritons (PhPs) in biaxial van der Waals crystals[1] arise as one of the cornerstones for future communication and sensing devices at the mesoscopic regime.
In this sense, twisted heterostructures made of biaxial slabs offer singular properties, such as confinement[2], canalization, ultralow losses and topological transitions [3], among others. However, a general
theoretical model that describes the light propagation in these systems is still needed. Moreover, lightpropagation in systems made of the stacking of biaxial slabs and dielectric media [4] remain exempt of ageneral theoretical model. Here [5], a complete general derivation of a model for such a system isperformed, considering three rotated biaxial slabs separated by dielectric media, as well as a quantitative
characterization of the coupling of the electromagnetic modes of the anisotropic materials. An extension tosimpler systems made of anisotropic materials and a comparison with their analytical models is also detailed
in this paper, showing a perfect agreement with previous models [4,6]. All calculations are compared withfull-wave electromagnetic simulations. This work lays the foundations for future experiments in the fieldof twistoptics, allowing for a theoretical prediction and justification of the behavior of electromagnetic
modes in heterostructures made of twisted biaxial slabs measured by near-field techniques.

References[1] Ma, W. et al. 2018. Nature, 562, 557−562..
[2] Álvarez-Pérez, G. et al. 2020. Adv. Mater., 32, 1908176.
[3] Duan, J. et al. 2021. Sci. Adv., 7, eabf2690.
[4] Duan, J. et al. 2020. Nano Lett., 20, 5323–5329.
[5] Lanza .C et al. 2022. To be published.
[6] Álvarez-Pérez, G. et al. 2019. Phys. Rev. B, 100, 235408.

Quasinormal mode theory of Purcell factors and chiral radiation from
nanophotonic resonators near an exceptional point
Juanjuan Ren1, Sebastian Franke2,1, Stephen Hughes1
1. Queen’s University, 99 University Avenue, Kingston, ON, K7L 3N6, Canada
2. Technische Universität Berlin, Institut für Theoretische Physik, Nichtlineare Optik und Quantenelektronik, Hardenbergstraße 36, 10623
Berlin, Germany
E-mail: jr180@queensu.ca

Non-Hermitian optical physics has been intensively investigated recently, exploring aspects of parity-timesymmetry and exceptional points (EPs). One general design consists of two resonators or coupled modes, e.g.,
one with material loss and the other with gain. Coupled normal mode (NM) theory predicts that a perfect EP
can occur when the loss and gain is balanced. However, describing open cavities with NM theory is
ambiguous, where the loss is usually added phenomenologically, which motivates one to develop a morequantitative non-Hermitian theory for the cavity modes. Here we use quasinormal modes (QNMs) to study
coupled cavity resonators, and describe the new physics that emerges in these systems. We show how one canuse just the bare QNMs of the individual resonators to have a quantitatively accurate theory of the emerging
hybrid modes, using coupled QNM theory. We also show how the criteria for finding EPs is generalized.
Furthermore, we show a drastic breakdown of the widely used classical Purcell formula for coupled gain-loss
media [1] and show how this is fixed [2]. A second way to achieve EP-like phenomena is through amodulated refractive index in a single whispering gallery mode resonator, as demonstrated experimentally in[3], where they also reported chiral emission for linear dipole emitters and explained this in terms of adecoupling of the eigenmodes to a “missing dimension”. We show how our QNM theory can successfully
explain the chiral radiation close to an EP in terms of only the underlying two QNMs [4], and we show how
the chirality can be controlled in terms of dipole position and frequency.

Fig. 1 (a) Schematic of a coupled loss-gain resonator and computed classical Purcell factors for a dipole placed in the gap.
‘QNM +/-’ are the two hybrid modes obtained from coupled QNM theory. Their separate contribution (green/blue curves) andtotal contribution (black curve) are shown, which agree very well with the full numerical dipole results (red circles). For
comparison, ‘QNM L’ shows the case with the bare lossy cavity only, which is multiplied by 12 for clarity (orange curve). (b)Schematic of a refractive index modulated ring and the chiral radiation of a linear (polarized) dipole from QNM/NM solutions
and full numerical dipole calculations. The QNM solutions recover the full dipole results, while the NM solutions fail.

References[1] Ren, J., Franke, S., and Hughes, S. 2021, “Quasinormal Modes, Local Density of States, and Classical Purcell Factors for Coupled Loss-Gain
Resonators”, Phys. Rev. X, 11, 041020.
[2] Franke, S., Ren, J., Richter, M., Knorr A., and Hughes, S., 2021, “Fermi’s Golden Rule for Spontaneous Emission in Absorptive andAmplifying Media”, Phys. Rev. Lett., 127, 013602.
[3] Chen, H.-Z., Liu, T., Luan, H.-Y., Liu, R.-J., Wang, X.-Y., Zhu, X.-F., Li, Y.-B., Gu, Z.-M., Liang, S.-J., Gao, H., Lu, L., Ge, L., Zhang, S.,
Zhu, J., and Ma, R.-M., 2020, “Revealing the missing dimension at an exceptional point”, Nat. Phys., 16, 571–578.
[4] Ren, J., Franke, S., and Hughes, S. 2021, “Quasinormal mode analysis of chiral power flow from linearly polarized dipole emitters coupled toindex-modulated microring resonators close to an exceptional point”, arXiv: 2112.02010 (ACS photonics, in press).

Topological transitions and surface umklapp scattering in periodicallymodulated metasurfaces beyond the effective medium
Guy Bartal
Technion – Israel institute of technology, E-mail: Guy@ee.technion.ac.il

Metamaterials and metasurfaces are at the pinnacle of wave propagation engineering, with their design been
mainly focused on deep-subwavelength periodicities, practically forming an effective medium. Such an approachoverlooks important structural degrees-of-freedom, e.g. the interplay between modulation amplitude and periodicity,which determine the properties of waves, guided in the meta-structure. Metasurfaces (MSs) – the interfaces between
two materials structured in the subwavelength scale[1] – have been widely investigated in recent years for theirability to manipulate light for various applications. Additionally, they play an important role in surface wave
engineering, attaining unidirectional and spin-selective coupling, as well as surface wave-guidance at low
frequencies. Interestingly, the surface wave properties can be strongly influenced even by simple periodic
structuring of the interface, exhibiting tunable propagation characteristics. In this respect, one-dimensional depth
modulation was shown to produce hyperbolic metasurfaces (HMSs), wherein the modulation amplitude tuned thespatial dispersion anisotropy from elliptic to hyperbolic [2-4), giving rise to a topological transition predicted byeffective medium theory. Here, we show control and manipulation of surface waves achived by periodicallymodulated interface that go beyond the effective medium. We reveal dispersion regimes and topological transitions
unattainable in effective media and utilize phase-resolved near-field microscopy to observe geometry-dependenttransitions in the surface-wave transport as well as unique phenomenon of backward focusing – mediated byumklapp scattering. Our findings offer a comprehensive approach for engineering surface and guided waves in
artificial periodic systems and can be implemented to produce novel kinds of photonic circuity and electromagnetic
modes with intricate and unique dispersion features.

Fig. 1 control over surface wave diffraction. (a) a “phase diagram” comprising different surface-propagation regimes depending on the
periodicity and depth of the structuring. (b-c)Fourier plane extraction from phase-resolved near-field measurements of the E-field under different
structuring. (b) varying depth (c) varying peridocity. (d) near-field measurement of anomalous focusing based on the band marked by the redboxes. (1) Umklapp-mediated and (2) hyperbolic focusing.

References[1] Bomzon, Z., Biener, G., Kleiner, V. & Hasman, E. Radially and azimuthally polarized beams generated by space-variant dielectricsubwavelength gratings. Opt. Lett. 27, 285–287 (2002).
[2] Liu, Y. & Zhang, X. Metasurfaces for manipulating surface plasmons. Applied Physics Letters 103, 141101 (2013).
[3] High, A. A. et al. Visible-frequency hyperbolic metasurface. Nature 522, 192–196 (2015).
[4] Li, P. et al. Infrared hyperbolic metasurface based on nanostructured van der Waals materials. Science 359, 892–896 (2018).

Quantitative modelling and engineering of photoluminescence from lightemitting metasurfaces via absorption calculations
Elise Bailly1, Camilo R. Pérez de la Vega2, Kevin Chevrier2, Jean-Paul Hugonin1,
Yannick de Wilde2, Valentina Krachmalnicoff2, Benjamin Vest1, Jean-Jacques Greffet1
1. Université Paris-Saclay, Institut d'Optique Graduate School, CNRS, Laboratoire Charles Fabry, 91127 Palaiseau, FRANCE
2. Institut Langevin, ESPCI Paris, Université PSL, CNRS, 75005 Paris FRANCE
E-mail: benjamin.vest@institutoptique.fr

Light-emitting metasurfaces are ultrathin devices consisting of a nanostructured surface covered with dense
ensemble of emitters. The interaction between emitters and the metasurface allows for a precise control of the emission
properties. In the standard model, the emitters are considered as a collection of electric dipoles randomly oriented
inside the structure, whose contribution can be added incoherently. Their emission spectrum is a Stokes-shifted
counterpart of their absorption spectrum. The emission spectrum of the whole structure is then described as resulting
from the modification of the fluorophore photoluminescence via radiative decay rate enhancement and extraction
efficiency of the device [1]. However, this approach does not account for modifications of the spectrum influenced bytemperature and pumping conditions and cannot predict the intensity of the emitted signal.
In this presentation, we first present a procedure to model emission by light-emitting metasurfaces using a(𝑙𝑙)generalized Kirchhoff’s law formalism. We show that the power 𝑑𝑑𝑃𝑃𝑒𝑒 (𝒖𝒖, 𝜔𝜔) emitted by a metasurface in a direction
𝒖𝒖 at a frequency 𝜔𝜔 can be expressed as [2]:𝑑𝑑𝑃𝑃𝑒𝑒 (𝒖𝒖, 𝜔𝜔) = 𝑑𝑑Ω ∭ 𝛼𝛼𝑎𝑎𝑎𝑎𝑎𝑎 (−𝒖𝒖, 𝒓𝒓′ , 𝜔𝜔)

𝜔𝜔2

ℏ𝜔𝜔

8𝜋𝜋3 𝑐𝑐 2 exp�ℏ𝜔𝜔−𝜇𝜇(𝒓𝒓′)�−1
𝑘𝑘𝐵𝐵 𝑇𝑇(𝒓𝒓′ )𝑑𝑑 3 𝒓𝒓′ ;This expression shows a product of the local absorptivity rate 𝛼𝛼𝑎𝑎𝑎𝑎𝑎𝑎 by a Planckian exponential contribution
depending on the temperature 𝑇𝑇 and the photon chemical potential 𝜇𝜇. 𝛼𝛼𝑎𝑎𝑎𝑎𝑎𝑎 encompasses the angular and polarization
dependance of the structure. Therefore, the directivity of the system as well as its polarization features can be designed
by engineering its local absorptivity, whereas the Planckian exponential explains spectral modifications between
absorption and emission.
In the second part of the presentation, we apply our procedure to model the photoluminescence features of complex
systems consisting of ensembles J-aggregated dyes (TDBC) deposited on metallic substrates [3]. We will highlight an
important aspect of light-emitting metasurfaces engineering: far from material resonances, the absorptivity is extremely
low - however, light emission can still occur provided that the Planckian factor takes significant values. Therefore, aquantitative and reliable modelling of emission also require accurate permittivity models in the low energy tail of theabsorption spectrum. In an example involving various types of emitters (quantum dots and dye molecules, see Fig. 1),
we will show that Brendel-Bormann models of permittivity overcome limitations faced when using Lorentzian models.
Our work paves the way towards a reliable engineering procedure to design ultrathin light sources with on-demand
properties, such as controlled directivity, polarization state and emission spectrum.

Fig. 1 a) Schematic of the system under study: a layer of quantum dots (QDs) embedded in PMMA are deposited on a layer of Jaggregate dye (TDBC molecules) and on silver. The system is excited at 445 nm and the emitted light is collected in a spectrometer.
b) Photoluminescence map obtained experimentally. c) Photoluminescence map obtained by numerical simulations based on our
local Kirchhoff’s approach used with Brendel-Bormann’s models of permittivities.

References[1] Vaskin, A., Kolkowski, R., Koenderink, A. F., & Staude, I. (2019). Light-emitting metasurfaces. Nanophotonics, 8(7), 1151–1198.
https://doi.org/10.1515/nanoph-2019-0110[2] Wojszvzyk, L., Monin, H., & Greffet, J. J. (2019). Light Emission by a Thermalized Ensemble of Emitters Coupled to a Resonant Structure.
Adv. Opt. Mater.. https://doi.org/10.1002/adom.201801697[3] Bailly, E., Hugonin, J.-P., Vest, B., & Greffet, J.-J. (2021). Spatial coherence of light emitted by thermalized ensembles of emitters coupled tosurface waves. Phys. Rev. Research, 3(3), L032040. https://doi.org/10.1103/PhysRevResearch.3.L032040

Nanophotonics controlling free-electron-light-matter interactions
Matthias Liebtrau1, Aviv Karnieli2, Dolev Roitman2, Shai Tsesses4, Nika van Nielen1,
Hannah Niese1, Ady Arie3, Ido Kaminer4, and Albert Polman1
1. Center for Nanophotonics, NWO-Institute AMOLF, 1098 XG Amsterdam, The Netherlands
2. Raymond and Beverly Sackler School of Physics and Astronomy, Tel Aviv University, 69978 Tel Aviv, Israel
3. School of Electrical Engineering, Fleischman Faculty of Engineering, Tel Aviv University, 69978 Tel Aviv, Israel
4. Andrew and Erna Viterbi Department of Electrical Engineering, Technion – Israel Institute of Technology, 32000 Haifa, Israel
E-mail: m.liebtrau@amolf.nl

The time-varying evanescent electric field of a free electron can couple to a broad spectral range of electromagnetic
modes in a material, rendering a unique interplay between free electrons and light at the nanoscale [1]. In this work,
we apply nanophotonics to manipulate free electron radiation mechanisms, and – vice versa – design optical near fields
that permit a quantum-coherent modulation of the electron wave function.
Smith Purcell (SP) radiation is a broadband phenomenon occurring upon coherent excitation of periodicallyarranged emitters by a grazing free electron, with the excitation phase-lag giving rise to discrete diffraction orders in
the far field [2]. By designing nano-gratings with a non-linear chirp [3], we show – for the first time in experiment –that the wavefront of SP radiation can be shaped to induce lensing effects of focusing and defocusing near the grating
surface (Fig. 1a, b). The corresponding cylindrical emission wavefronts are observed in the far field using in-situ
hyperspectral angle-resolved light detection in a scanning electron microscope (SEM) at 30 keV incident electronenergy. Our data (Fig. 1c) are found in good agreement with the results of analytical theory as well as a hybridsimulation approach (Fig. 1c), combining full-wave numerical near-field calculations with a ray-tracing model of ourlight collection setup. To further exemplify the wide-ranging functionalities that can be embedded with electron-driven
light sources, we design a metasurface composed of split-ring-resonantor (SRR) meta-atoms, permitting simultaneous
SP focusing and tunable polarization control via spatially-selective SRR mode excitation.

Fig. 1 a) Metagratings of 20 µm length with opposing chirp along the electron beam axis were patterned into a 40 nm thin gold
film on a silicon substrate. b) Full-wave numerical simulations of the near field induced upon 30 keV free-electron excitation,
revealing focusing (top) or defocusing (bottom) near the grating surface at a design operational wavelength of 580 nm. c) Simulated
and d) measured hyperspectral angle-resolved far field emission patterns, featuring multiple characteristic curved emission bands.

Free electrons not only provide a unique source of electromagnetic excitation. Under external stimulation, theirinteraction with optical fields also permits a quantum-coherent manipulation of the electron wave function itself [4].
To this end, phase-matching is required between the optical field and the incident electron wave packet – a condition
that can be only fulfilled in the presence of matter [5]. In particular, sub-relativistic electrons, as routinely provided by
SEM, can undergo strong interactions with tightly-confined near fields at the nanoscale [6]. Here, we tailor the mode
profile of a layered metasurface to enhance electron-light-matter coupling over short interaction ranges, permitting us
to observe the quantum-coherent energy modulation of 6 keV-electrons in our new quantum scanning electron
microscope (QSEM). Our work merges the worlds of nanophotonics and free-electron-light-matter interactions,rendering a prosperous platform for both fundamental research and advanced technological applications.
References[1] Polman, A, Kociak, M, and García de Abajo, F J. 2019. Nature Mater., 18, 1558-1171.
[2] Smith, S J, and Purcell, E M. 1953. Phys. Rev., 92, 1069.
[3] Remez, R, Shapira , N, Roques-Carmes, C, Tirole, R, Yang, Y, Lereah, Y, Soljačić, M, Kaminer, I, Arie, A, 2017. Phys. Rev. A, 96, 061801[4] Feist, A, Echternkamp, K E, Schauss, J, Yalunin, S V, Schäfer, S, and Ropers, C. 2015. Nature, 521, 200-203.
[5] García de Abajo, F J, Asenjo-Garcia, A, Kociak, M., 2010. Nano Lett., 10, 1859-1863[6] Talebi, N. 2020. Phys. Rev. Lett., 125, 080401

2D chemical mapping of light driven reactions by plasmonic nanostructures
Olivier Henrotte1, Luca Mascaretti1, Štěpán Kment1, Alberto Naldoni1
1. Regional Centre of Advanced Technologies and Materials, Czech Advanced Technology and Research Institute, Palacký University Olomouc,
Slechtitelů 27, 78371 Olomouc, Czech Republic
e-mail: olivier.henrotte@upol.cz

Upon light illumination, surface plasmons (SPs) produce very intense electric fields localized in nanoscale
volumes. SPs decay by generating non-thermal (hot) electron-hole pairs having enough energy to drive chemical
reactions. Plasmonic photocatalysis received soaring interest due to the possibility of using plasmonic effects toenhance reactions rates or activate non-trivial reaction pathways [1].
Herein, we present an original methodology to investigate locally the photoactivity of plasmon nanostructures byscanning probe microscopy (SPM) techniques. As presented in Fig.1, we investigate the material morphology (a,d),
optical properties (b,e) and photochemical activity (c) thanks to SEM, scanning spectrophotometer microscopy (SSM)
and scanning photoelectrochemical microscopy (SPECM), respectively. The collected data unravel structure-activity
relationships at the origin of the plasmonic activity. For instance, the localized surface plasmon resonance (LSPR)
peak shift observed in Fig.1.b is directly related to the morphology disparity (Fig.1.d). Moreover, the optical properties
corresponded well with the observed photoactivity (Fig.1.f).

Fig. 1. Investigation of the Au NPs on TiO2/ITO substrate morphology, optically and photochemically wise. (a) SEM image of the Au NPs on
TiO2/ITO substrate. (b) SSM map presenting the LSPR peak position at the different positions. (c) Photoactivity map of the Au NPs, with the probe
depicted to scale on (c), at 530 nm at 4.7 µW. (d) Mean diameter (left axis, filled squares) and population density (right axis, empty squares) of
the different positions from (a). (e) Absorbance from the line across the center of the square at 455 (blue), 530 (green), 580 (orange) and 660(red) nm. (f) Photoactivity (left axis, solid lines) and absorbance (right axis, dashed lines with filled circles) at the same line position for 530(green) and 660 (red) nm. SPECM measurement conditions: rT = 5 µm, RG = 5, Z = 20 µm, vscan = 20 µm/s in 1 mM Fc(MeOH)2 and 0.1 M KCl.

The presented results are set up on a reference model including Au nanoparticles deposited on asemiconductor/charge collector substrate formed by a TiO2/ITO substrate, which is already well-referenced in theliterature [3]. Ultimately, we aim to shed light on plasmonic material properties and their impact on thephotochemichestry thanks to correlation between the plasmonic system (e.g. size, shape, composition, interface andembedding media) and its activity at the nanoscale.
References[1] Zhang, Y.; He, S.; Guo, W.; Hu, Y.; Huang, J.; Mulcahy, J. R.; Wei, W. D., 2018, Chem. Rev., 118, 2927−2954[2] Casillas, N.: James, P.; Smyrl, W.H., J., 1995, Electrochem. Soc., 142, L16[3] Yu, Y.; Wijesekara, K. D.; Xi, X.; Willets, K. A., 2019, ACS Nano, 13, 3629–3637

Hot Electron Extraction Enabled by Single-Crystal
Metal Films and Nanostructures
Finlay C. MacNab, Sasan V. Grayli, Gary W. Leach1

1. Simon Fraser University, 8888 University Dr. Burnaby, BC Canada V5A 1S6
E-mail: gleach@sfu.ca

Surface plasmons concentrate the extended three-dimensional fields of propagating electromagnetic waves tonanometer-scale structures, where their enhanced and confined local fields can drive new physical and chemical
phenomena. Plasmon-mediated hot carrier generation is particularly interesting and can provide a means for directenergy harvesting, photocatalytic chemistry, and the development of new optical sensor technologies. However,identifying and optimizing the factors that lead to efficient hot electron extraction have remained a challenge and have
limited the utility of surface plasmon-based devices for these applications. Here, we describe the requirements for
efficient hot electron extraction in smooth and nanostructured Ag/ZnO plasmonic photovoltaic devices. Device
efficiency is found to be highly correlated with material quality and the electronic character of the interfaces.
Our findings have driven the development of a new scalable and environmentally friendly electroless deposition
method for single-crystal epitaxial noble metals films and nanostructures [1]. The method produces smooth, low-loss,
single-crystal noble metal films ideal for subtractive patterning of nanostructures through ion beam milling, and highdefinition, sub-wavelength single-crystal nanostructured arrays through lithographic patterning. We describe thenucleation and growth of these metal films and nanostructures in the absence and presence of anionic shape-control
agents and examine the role of specific anions in determining the resulting film and nanostructure morphologies via
scanning electron microscopy (SEM) and high-resolution transmission electron microscopy (HRTEM) [2]. These
effects have been exploited to yield large area patterned, and shape-controlled nanoarrays of single-crystal metalnanostructures, yielding plasmonic metasurfaces with tailored local fields that can be tuned to exploit local fieldenhancements. These approaches offer new and cost-effective routes to achieve crystalline, shape-controlled surface
nanostructure for nanophotonic and nanodevice applications.

Fig. 1. ZnO deposited on single-crystal a) planar and b) nanostructured silver to form plasmonic photovoltaic structures. c) device
structure for free space-coupled hot electron extraction measurements.

References[1] V. Grayli, S.; Zhang, X.; MacNab, F.C.; Kamal, S.; Star, D.; Leach, G. W., Scalable, Green Fabrication of Single-Crystal
Noble Metal Films and Nanostructures for Low-Loss Nanotechnology Applications., ACS Nano, (2020) 14, 7581−7592.
[2] V. Grayli, S.; Zhang, X.; Star, D.; Leach, G. W., “Shape-Controlled, Single-Crystal Gold Surface Nanostructures”, (2019)
ChemRxiv.9956450.v1, published online Oct. 11, 2019.

NFO16 Template
TERS study of phonon localization in low-angle twisted bilayer graphene andother two-dimensional Systes
Ado Jorio1,2, A. C. Gadelha1, R. Nadas1, C. Rabelo2, T. L. Vasconcelos3, L. G. Cançado1
1. Physics Department, Universidade Federal de Minas Gerais, Belo Horizonte, MG 31270-901, Brazil.
2. Electrical Engineering Graduate Program, Universidade Federal de Minas Gerais, Belo Horizonte, MG 31270-901, Brazil.
3. Divisão de Metrologia de Materiais, Inmetro, Duque de Caxias, RJ 25250-020 Brazil.
E-mail: adojorio@fisica.ufmg.br

This talk reports hyperspectral tip-enhanced Raman spectral (TERS [1]) imaging of the crystal superlattice inreconstructed (low-angle) twisted bilayer graphene and other local effects in two-dimensional systems [2]. Gateinduced homojunctions are formed and imaged in graphene and MoS2 [3]. For small twist angles, twisted bilayer
graphene undergoes a self-organized lattice reconstruction, leading to the formation of a periodically repeated domain,which can be observed in TERS experiments (see Fig.1) [4,5]. The resulting superlattice modulates the vibrational andelectronic structures within the material, leading to changes in the behaviour of electron–phonon coupling [6]. The
results are rationalized by an atomistic model that enables evaluation of the local density of the electronic andvibrational states of the superlattice. Our observations highlight the relevance of solitons and topological points for thevibrational and electronic properties of the structures, particularly for small twist angles, and they represent a step
towards understanding the relevance of electron-phonon interaction in these systems, relevant in context of twistronics.
Technical details about samples preparation and characterization are also discussed [7,8].

Fig. 1 (left) optical image of a twiste bilayer graphene sample, with the green pointed showing the location where AFM and TERS
were acquired; (meddle) AFM-based topography of the sample at the location shown in the left panel; (right) TERS based imageof the 2D band intensity, at the location shown in the left panel [4].

References[1] Costa, M. D. D., Cançado, L. G., Jorio, A. (2021) Journal of Raman Spectroscopy 52 (3), 587-599[2] Malard, L. M., et al. (2021) Physical Chemistry Chemical Physics 23 (41), 23428-23444[3] Gadelha, A. C., et al. (2021) The Journal of Physical Chemistry Letters 12 (31), 7625-7631[4] AC Gadelha, A. C., et al. (2021) Nature 590 (7846), 405-409[5] TC Barbosa, T. C., et al. (2022) arXiv preprint arXiv:2201.01762[6] Gadelha A. C., et al. (2022) arXiv:2110.14916[7] Gadelha, A. C., et al. (2021) ACS Applied Nano Materials 4 (2), 1858-1866[8] Ohlberg, D. A A., et al. (2021) Nature Communications 12 (1), 1-6

THz-Light Canalization by Phonon Polaritons in 2D van der Waals Materials
Maximilian Obst1,2, Tobias Nörenberg1,2, Gonzalo Álvarez-Pèrez3, Pablo Alonso-González3, Alexey Nikitin4,
Thales V.A.G. de Oliveira5, J. Michael Klopf5, Susanne C. Kehr1, Lukas M. Eng1,2
1. Technische Universität Dresden, Nöthnitzer Straße 61, 01187 Dresden, Germany
2. Würzburg-Dresden Cluster of Excellence - EXC 2147 (ct.qmat), 01062 Dresden, Germany
3. University of Oviedo, Edif. Severo Ochoa, C/Fernando Bonguera s/n, Oviedo, 33006 Asturias, Spain
4. Donostia International Physics Center, Paseo Manuel de Lardizabal 4, 20018 Donostia-San Sebastián (Gipuzkoa), Spain
5. Helmholtz-Zentrum Dresden-Rossendorf, Bautzner Landstraße 400, 01328 Dresden, Germany
E-mail: maximilian.obst@tu-dresden.de

Terahertz (THz) electromagnetic radiation is key to optically accessing collective excitations such as magnons(spins), plasmons (electrons), and phonons (atomic vibrations) bridging between optical and solid-state physics. In
particular, confining THz light at nanometer length scales is desirable for the local probing of such excitations in low
dimensional systems, thus inherently circumventing the large spatial distribution and low spectral power density of
far-field THz optics. For that purpose, hyperbolic phonon polaritons (PhP) in anisotropic, 2D van der Waals (vdW)
materials present a promising platform for THz nanooptics [1], as they not only allow strong confinement of THz
radiation but, furthermore, also for energy transport directed along specific crystallographic axes without the need of
topographical structuring. However, the lateral spread due to the hyperbolic shape of these polaritons entails
undesirable losses. To that end, the demonstration of diffraction-less propagating “canalized” PhPs in vertically stacked
and twisted α-MoO3-flakes (so called “twisted bilayer (TBL) MoO3”) in early 2020 introduced a major breakthroughin polariton physics [2-5]. Spectrally, the canalization regime of TBL-MoO3-polaritons is determined by the hyperbolic
optical material response 𝜀𝜀̅(𝜐𝜐) as well as by the specific twist angle θ, and so far has been studied exclusively at MIR
wavelengths. In this talk we explore canalized polaritons in TBL-MoO3 at THz wavelengths, where recently hyperbolic
PhP have been demonstrated [6] and where long wavelengths make strong confinement even more desirable.
Subsequently, we contrast the intriguing THz PhP channeling properties predicted in the 2D vdW material GeS basedon the flattening of the elliptical iso-frequency-curve.
In particular, we experimentally study the spectral response of PhPs in TBL α-MoO3 between 𝜈𝜈 = 8.28 and 9.38
THz. For this purpose, the free-electron laser FELBE (HZDR, Germany) is combined as the tunable narrow-band lightsource with scattering scanning near-field optical microscopy (s-SNOM) (Fig. 1a). For a twist angle of θ = 50°, wefind canalized PhPs at 𝜈𝜈 = 8.67 THz (Fig. 1b,c) with a 6.8 µm wavelength, a propagation length of 7 µm, a quality
factor of 6.5, and a confinement perpendicular to the propagation direction of 1 µm. These results are directly comparedwith single flake PhP and the elliptical response of orthogonally θ = 90° twisted TBLs. Moreover, as an alternative
material for THz light canalization, we introduce α-germanium(II) sulfide (α-GeS) in this talk, a novel highly anisotropic 2D vdW semiconductor that suggests natural PhP canalization even within a single slab (Fig. 1d) [7,8] due tothe unique interaction of a phonon in out-of-plane direction with the PhP and the substrate. The resulting shape of the
PhPs in k-space around 8.57 THz (Fig. 1e) resembles the one found for canalization in TBL α-MoO3.

Fig. 1 a) Schematic of the experimental setup using the free electron laser for THz near-field excitation in s-SNOM on the TBL
α-MoO3 (twist angle θ = 50°); b) canalized polariton propagation observed at 𝜈𝜈 = 8.67 THz; c) Fast-Fourier-transform (FFT) of
the near-field image in (b) featuring two parallel lines corresponding to the PhP’s directive propagation; d) outline formeasurements on a single GeS-flake mounted on a silicon substrate, showing the full-wave simulated real-space field distributionof the single- 𝛼𝛼-GeS-flake polaritons at 𝜈𝜈 = 8.57 THz [8]; e) FFT of the field distribution in (d) featuring two strong straight lines
closely resembling the canalized response in (c).

References:[1] Basov, D.N. et al. 2016. Science 354, 6309; https://doi.org/10.1126/science.aag1992[2] Hu, G. et al. 2020. Nature 582, 209; https://doi.org/10.1038/s41586-020-2359-9.
[3] Duan, J. et al. 2020. Nano Lett. 20, 5323; https://dx.doi.org/10.1021/acs.nanolett.0c01673.
[4] Zheng, Z. et al. 2020. Nano Lett. 20, 5301 https://dx.doi.org/10.1021/acs.nanolett.0c01627.
[5] Chen, M. et al. 2020. Nat. Mater. 19, 1307; https://doi.org/10.1038/s41563-020-0732-6.
[6] de Oliveira, T.V.A.G. et al. 2021. Adv. Mater. 33, 2005777; https://doi.org/10.1002/adma.202005777[7] Liu, Y. 2019. PhD Thesis, UC Berkeley; https://escholarship.org/uc/item/7r2524dv.
[8] Nörenberg, T. et al. 2021. https://arxiv.org/abs/2110.13295v2.

Imaging the Bandgap Shifting in WxMo1-xS2 by Near-Field Broadband
Transmittance Microscopy
Po-Wen Tang1, Shiue-Yuan Shiau2, He-Chun Chou1, Xin-Quan Zhang3, Jia-Ru Yu1, Chun-Te Sung1,3,
Yi-Hsien Lee3, and Chi Chen1*
1. Research Center for Applied Sciences, Academia Sinica, Taipei,115, Taiwan
2. Physics Division, National Center for Theoretical Sciences, Taipei, 106, Taiwan
3. Department of Materials Science and Engineering, National Tsing-Hua University, Hsinchu, 300, Taiwan
E-mail: chenchi@gate.sinica.edu.tw

Two-dimensional (2D) transition metal dichalcogenide (TMD) alloys allow tunable bandgap, which enable a broad
range in optoelectronics applications. The WxMo1-xS2 alloy was synthesized by gradually changing temperate in onepot CVD growth, [1] which exhibits spatially-varied bandgaps shift as a function of constitutional atoms (x/1-x) fromthe pure MoS2 at the center to the WS2 at the edge. Typically, Photoluminescence (PL) spectroscopy is utilized tocharacterize the A exciton of single-layer TMDs since they exhibit direct bandgap. However, in the cases of multilayers
or highly-defective TMDs, the PL emission are quenched due to the non-radiative exciton recombination. Here, we
introduce home-built broadband near-field transmittance (NF-tr) microscopy to overcome the problems of PL detection.
[2] Collimated white light was focused into the apertured tip by a 50× objective lens (N.A. 0.5). The transmittancelight was collected by a 100× objective lens (N.A. 0.9) and then coupled into a spectrometer. Absorption spectrum
mapping of alloy TMD flake can be recorded in the energy range from 1.8 to 2.7 eV, which contains all A, B, and C
exciton bands and has never been realized for TMDs up to now.

Figure (a) The schematic of the WxMo1-xS2 sample. (b) The optical setup for NF-tr measurement. (c) The far-field transmittanceimage of WxMo1-xS2 and (d) the NF-tr image of WxMo1-xS2 at 520 nm (2.38 eV). (e) Energy-location diagram along the yellow
line in (d).

The far-field (FF) and the near-field (NF) transmittance images at 520 nm are shown in fig. c and d. The far-field
image is blurred due to the chromatic aberration of the optical system. Oppositely, the NF image shows sub-diffractionlimited and aberration-free contrast in transmittance. The energy-location diagram (fig. e) presents the locationdependent band shift of the A and B excitons. However, both the shift of the A and B excitons are not a linear functionof x, so the bowing factor is introduced as a prominent indication of the bending curvature relative to x. In summary,our NF- transmittance technique provides an aberration-free and sub-diffraction-limited imaging and spectroscopy tool
to reveal the spatial variance of alloy TMDs. This technology can make a very useful tool for investigating the various
layered structures in the era of “stacking materials” in quest of novel quantum devices.

References(1)

Zhang, X.-Q.; Lin, C.-H.; Tseng, Y.-W.; Huang, K.-H.; Lee, Y.-H. Synthesis of Lateral Heterostructures of Semiconducting Atomic Layers.
Nano Lett. 2015, 15 (1), 410–415.

(2)Yu, J.-R.; Chou, H.-C.; Yang, C.-W.; Liao, W.-S.; Hwang, I.-S.; Chen, C. A Horizontal-Type Scanning Near-Field Optical Microscope with
Torsional Mode Operation toward High-Resolution and Non-Destructive Imaging of Soft Materials. Rev. Sci. Instrum. 2020, 91 (7), 073703.

Probing vibrational strong coupling with tip-enhanced near-field spectroscopy
Carlos Maciel Escudero1,2, Irene Dolado1, Elizaveta Nikulina1, Evgenii Modin1, Francesco Calavalle1, Shu
Chen1, Andrei Bylinkin1, Francisco Javier Alfaro-Mozaz3, Felix Casanova1,4, Luis E. Hueso1,4, Ruben
Esteban2,3, Javier Aizpurua2,3, and Rainer Hillenbrand4,5
1. CIC nanoGUNE BRTA, 20018 Donostia-San Sebastián, Spain
2. Materials Physcis Center, CSIC-UPV/EHU, 20018 Donostia-San Sebastián, Spain
3. Donostia International Physics Center (DIPC), Donostia-San Sebastián, Spain
4. IKERBASQUE, Basque Foundation for Science, 48009 Bilbao, Spain
5. CIC nanoGUNE BRTA and Department of Electricity and Electronics, UPV/EHU, 20018 Donostia-San Sebastián, Spainc.maciel@nanogune.eu

Vibrational strong coupling (VSC) occurs when the coherent energy exchange between infrared cavity photons andmolecular vibrations exceeds the decay rates of both, the cavity mode and the molecular vibration [1]. In this strong
light–matter interaction regime, new hybrid states – polaritons – are formed exhibiting interesting possibilities forultra-sensitive vibrational spectroscopy and for modifying chemical reactions [2,3]. Typically, VSC is achieved byfilling microcavities with a high concentration of organic molecules limiting access to quantum phenomena that canoccur for a single or a few number of molecules. Phonon–polariton (PhP) nanoresonators could be ideal candidates toachieve VSC at the nanoscale, due to their small mode volumes and large quality factors [4]. Although VSC employing
arrays of PhP resonators has been reported before [5], the study of VSC with individual PhP resonators is challenged
by their extremely small extinction cross sections, which makes difficult to use conventional far-field opticaltechniques to probe VSC on single resonators.

Fig. 1 (a) Sketch of the system. The blue rod represents the h-BN nanoresonator of length L. The green rectangular structure
represents the CBP layer covering half of the h-BN nanoresonator. The elongated conical structure at the top-left part of the blue
rod represents the non-resonant tip being illuminated with a broadband infrared laser. The height of the tip oscillates with frequency
Ω. (c) Experimental nano-FTIR amplitude spectra, obtained for different nanoresonator lengths L. (b) Theoretical calculation of
the near-field amplitude below the tip for different L. Red lines are guide to the eye and mark peak positions. The dashed verticalline marks the CBP molecular vibration frequency at 1450 cm-1. In the theoretical calculations the tip is simulated as a pointdipole. (c) Numerical simulation of ǀEzǀ around an h-BN nanorod, whose right half is covered by a CBP layer. 1 nm above the left
nanorod extremity a tip of 25 nm apex radius is placed. Tip and nanorod are illuminated with a plane wave of ν = 1442 cm-1 at anangle of 60° relative to the tip axis.

In this work, we experimentally and theoretically address the use of tip-enhanced near-field spectroscopy to probe
and map the hybrid polaritonic modes of single hexagonal boron nitride (h-BN) nanoresonators coupled to molecularvibrations. We achieve this by covering half of the h-BN nanoresonator with CBP (4,4′-bis(N-carbazolyl)-1,1′biphenyl; organic semiconductor) molecules having a well-defined molecular vibration at νCBP = 1450 cm-1 [see Fig.
1(a)]. In addition, at the region between ν =1400-1500 cm-1, the h-BN nanoresonator supports phonon polaritons
exhibiting Fabry–Perot (FP) resonances [see Figs. 1(b)-1(c)] and thus, by varying the nanoresonators length, we cantune the 2nd-order FP resonance [see Fig. 1(d)] with respect to νCBP. We probe the nanoresonator–molecule coupledsystem with a non-resonant tip and minimize the potential influence of the tip by probing only the part of thenanoresonator not covered with CBP molecules. Our results can constitute an avenue for near-field imaging of strongly
coupled systems that are not accessible by far-field spectroscopy.
References[1] Dovzhenko, D. D., Ryabchuk, S. V., Rakovich, Y. P. and Nabiev, I. R. 2018. Nanoscale, 10, 3589-3605.
[2] Hutchison, J. A., Schwartz, T., Genet, C., Devaux, E. and Ebbesen, T. W. 2012. Angewandte Chemie – International Edition, 51, 1592-1596.
[3] Galego, J., Garcia-Vidal, F. J. and Feist, J. 2016. Nat. Commun., 7, 13841.
[4] Alfaro-Mozaz F. J., Alonso-González P., Vélez S., Dolado I., Autore M., Mastel S, Casanova F., Hueso L. E., Li. P., Nikitin A. Y. andHillenbrand R. 2017. Nat. Commun., 8, 15624.
[5] Autore, M., Li, P., Dolado, I., Alfaro-Mozaz, F. J., Esteban, R., Atxabal, A., Casanova, F., Hueso, L. E., Alonso-González, P., Aizpurua, J.,
Nikitin, A. Y., Vélez, S. and Hillenbrand, R. 2018. Light Sci. Appl., 7, 17172.

Molecular optomechanics to address the Raman signal from organic molecules
in complex plasmonic nanocavities
Ruben Esteban1,2, Yuan Zhang3, Tomaš Neuman4, William M. Deacon5, Lukas A. Jakob1, Jeremy J.
Baumberg5 and Javier Aizpurua1,2
1.Center for Material Physics (CSIC – UPV/EHU), San Sebastian,20018. Spain
2 Donostia International Physics Center, San Sebastian,20018. Spain
3. School of Physics and Microelectronics, Zhengzhou University, Zhengzhou 450052, China
4. Institut des Sciences Moléculaires d’Orsay, UMR 8214 CNRS-Université Paris-Sud, 91405 Orsay Cedex
5. Cavendish Laboratory, University of Cambridge, Cambridge CB3 0HE, UK
E-mail: ruben_esteban@ehu.eus

Surface-Enhanced Raman Scattering (SERS) exploits the strong interaction between molecules and plasmonicresonances in metallic nanostructures to enable the characterization of vibrational modes of very small amounts ofmolecules, as desired for sensing applications. An often-used classical description of SERS describes the strong
enhancement of the Raman lines in the emission spectrum, but it assumes that the properties of the molecular vibrations
are fixed. On the other hand, a recent quantum description of SERS based on molecular optomechanics [1,2] showshow, for very intense lasers, the width and the frequency of the Raman lines can change, corresponding to a significant
modification of the effective losses and of the energy of the molecular vibrations, respectively. These changes areaccompanied by a strongly non-linear dependence of the emitted signal on the intensity of the laser illuminating thesystem [3,4].
The molecular optomechanics approach often considers a single plasmonic mode. Here, we use a continuum-fieldmodel [5] to show the importance of including the full plasmonic response in the description of the optomechanicalinteraction under strong laser illumination in configurations where a molecule couples efficiently with higher orderplasmonic modes [6], as in extreme ~1nm-thin plasmonic nanogaps. Higher order plasmonic modes do not only modify
the strength of the Raman signal, but they can also change the general spectral trends, leading, for example, to anincrease instead of a decrease of the Raman spectral width. The effect of the plasmonic modes is particularly evident
in determining the vibrational energy, increasing the vibrational energy shift by up to two orders of magnitude, ascompared with the single-mode results (Fig. 1a)
We further consider the case where multiple molecules are placed in the plasmonic nanocavity. In this case, wefind that in order to capture accurately the optomechanical interaction it is important to consider both the higher-orderplasmonic modes as well as the formation of collective vibrational modes [7]. Different collective modes experience
different vibrational linewidths and frequency shifts, so that, under strong illumination, more peaks can appear in the
spectra: one narrower and less shifted, and another broader and more shifted (Fig 1.b). The results of the calculations
are consistent with experimental results [8] that show a saturation of the intensity of the narrow Raman peak. Thus,
our results show that new intriguing effects can appear in SERS for large laser intensity, as described in the molecular
optomechanics framework.

Fig. 1 a) Change of the vibrational energy of a molecule placed at the gap of a plasmonic nanocavity. The illumination intensity
is 1W µm-2. The results obtained with a single-mode approximation (red line) are much smaller than those obtained when
considering the full plasmonic response (blue line). (b) Raman spectra for 100 molecules placed at the nanocavity gap with weak(brown line) or strong (green line) laser illumination. For strong illumination, a strong change of the vibrational lineshape isobserved due to the emergence of a broad and strongly shifted peak associated with a bright vibrational mode.

References[1] Roelli, P., Galland, C. et al., 2016. Nat. Nanotech. 11, 164.
[2] Schmidt, M. K., Esteban, R. et al., 2016, ACS Nano 10, 6291.
[3] Schmidt, M. K. , Esteban, R. et al., 2017, Faraday Discuss. 205, 31.
[4] Le Ru, E. C. and Etchegoin, P. G. 2006 Faraday Discuss. 132, 63.
[5] Dezfouli M. K. and Hughes, S., 2017, ACS Photonics, 4, 1245.
[6] Zhang, Y., Esteban. R. et al., 2021, Nanoscale 13, 1938
[7] Zhang, Y., Aizpurua. J. and Esteban, R., 2020, ACS Photonics 7, 1676
[8] Deacon, W. M., Zhang, Y. et al., Submitted

Atomically-resolved luminescence mapping of Lamb shift, Stark and Purcell
effects from a single chromophore-picocavity junction
Anna Roslawska1, Tomas Neuman1,2, Benjamin Doppaggne1 Andrei G. Borissov2, Michelangelo Romeo1,
Fabrice Scheurer1, Guillaume Schull1, and Javier Aizpurua32.
3.

1. Universite de Strasbourg, CNRS, IPCMS, UMR 7504, F-67000 Strasbourg, FranceInstitut des Sciences Moleculaires d’Orsay (ISMO), UMR 8214, CNRS, Universite Paris-Saclay, 91405 Orsay Cedex, FranceCenter for Materials Physics (CSIC-UPV/EHU) and DIPC,Paseo Manuel de Lardizabal 5, Donostia-San Sebastian 20018, Spain
4.
E-mail: aizpurua@ehu.eus

Fundamental studies of the optical properties of single molecular emitters have led to the development of superresolution optical microscopy techniques which go beyond the fundamental diffraction limit of optical resolution.
Despite their success, exploited for example in bioimaging, the resolution of these microscopy techniques is still
limited to scales larger than the size of individual organic molecules. This limitation has been lifted using the atomically
sharp tip of a scanning tunnelling microscope (STM) [1] covered by noble metal, which can squeeze opticalelectromagnetic fields into plasmons localized on the atomic scale and conversely collect photons from within
individual molecules with atomic-scale lateral resolution.
Here we present a correlated theoretical and experimental study of the optical properties of an individual free-basephthalocyanine molecule excited electrically by the tip of a STM [2,3]. We theoretically and experimentally show thatthe variation of the spectral position and width of the electroluminescence emission line of the molecular exciton(recorded as a function of the lateral and vertical position of the tip, see Fig.1) can be linked with the tip-positiondependent plasmonic Purcell effect, Lamb shift, and DC Stark effect induced by the static voltage applied across thetip-substrate gap. We demonstrate that the Stark shift is responsible for the observed variations of the luminescence
spectral line energy as a function of the tip position, yielding ~10meV contrast as the tip position is varied. We
computationally show that this Stark shift dominates over the dynamical effect associated to the plasmonic Lamb shift.
This allows us to interpret the tip-position-dependent spectral line shift map as an image of the difference between the
excited- and ground-state electron densities of the molecule (the difference electron density, 𝛥𝛥𝛥𝛥). On the other hand,by analyzing the broadening of the spectra, we are able to map the plasmon-induced lifetime shortening of the exciton(reaching ~ps lifetimes) with atomic-scale resolution, thus revealing a purely optical image of the molecule
unperturbed by the artefacts emerging from the excitation of the molecule by the tunneling current. Our theory thenallows us to interpret the tip-position-dependent map of the excitonic line-width variation as an image of the transition
electron density, 𝜌𝜌𝑒𝑒𝑒𝑒 , representing the oscillating dipole associated with the electronic excitation in the molecule. These
results constitute the foundation for the development of correlated optical and transport atomically resolved
microscopies, but also shed light on the microscopic electrodynamic and electrostatic interactions of molecular
excitons in plasmonic picocavities [4].

Fig. 1 Mapping the excited-state properties of an organic molecule in a STM. (a) The atomically sharp noble-metal STM tip concentrates plasmonic
electric fields to sub-molecular scales in plasmonic gaps. At the same time, DC voltage bias between the tip and the substrate creates a strong
static electric field in the tip-substrate gap. These static and induced dynamical (plasmonic) fields act on the sample molecule and cause shifts andbroadening of photon emission spectra of molecular excitons dependent on the position of the tip, as schematically shown in (b). (c-h) In the far
field, the photon spectra are analysed and used to perform mapping of these line shifts (c,d) and line widths (f,g) that can be interpreted as imagesof the (e) molecular difference electron density 𝛥𝛥𝛥𝛥, and (h) transition electron density 𝜌𝜌𝑒𝑒𝑒𝑒 , respectively.

References[1] Chen, C., et al., 2010. Phys. Rev. Lett., 105(21), 217402.
[2] Doppagne, B., et al., 2020, Nat. Nanotechnol., 15, 207-211.
[3] Roslawska, A., et al., 2022, Phys. Rev. X, 12(1), 011012.
[4] Benz, F., et al., 2016, Science, 354(6313), 726-729.

Single-millisecond SERS measurement of DNA oligonucleotides with singlebase resolution using gold nanoparticle dimers under Brownian motion
Toshiharu Saiki, Ikuya Kataoka, Nozomi Hagiwara, and Keiko Esashika
Department of Electronics and Electrical Engineering, Keio University, 3-14-1 Hiyoshi, Kohoku, Yokohama 223-8522, Japan
E-mail: saiki@elec.keio.ac.jp

Nanopore technologies allow for developing single-molecule DNA sequencing, in which single-stranded DNA
molecules passing through a nanoscale ion channel are observed by detecting current blocking signals. Currently,
nanopore ionic current detection enables discrimination of four nucleotide bases (adenine, thymine, cytosine, andguanine) included in a DNA strand, but it is much more challenging to identify chemically modified bases for
epigenetic sequencing and twenty amino acids for protein sequencing. Optical DNA sequencing based on surfaceenhanced Raman scattering (SERS) is promising as an alternative method for spectroscopic identification of bases.
SERS utilizes extremely high field enhancement in a sub-nanometer volume (hot spot) of metal nanostructures toprovide single-base spatial resolution and sensitivity. In this study, we develop a method to spontaneously form Au
nanoparticle (AuNP) dimers, which sandwiches a single DNA oligonucleotide within a gap of less than 1 nm. SERS
measurement of single AuNP dimers in aqueous suspension demonstrates single-base resolution obtained within a 10ms measurement period.
AuNP dimers sandwiching oligonucleotides are formed in aqueous suspension by using colloidal AuNPs with adiameter of 50 nm and oligonucleotides containing guanine (G) and cytosine (C) bases with a sequence of
CCCCCCCCCCCCGCCCCCCCCCCCC (12C-1G-12C; 25 mers length) as shown in Fig. 1(a). The adsorption ofoligonucleotides on AuNP surface and the formation of AuNP dimer was promoted by protonation of oligonucleotides,
addition of salt, and incubation at elevated temperature. The conditions are carefully examined and optimized forenhancing the dimerization efficiency and for maximizing the probability to find the oligonucleotide in the dimer gap,
which should be minimized to obtain pronounced SERS activity and single-base resolution.
We performed micro-Raman measurements for the AuNP dimers under Brownian motion in aqueous suspension.
The dimer suspension was diluted such that single dimer spectroscopy could be conducted. Although the dwell timeof dimer in the observation volume is approximately 10 ms, the effective measurement time should be less than 10 ms
due to the rotational diffusion of dimers. Figure 1(b) shows Raman spectra obtained from two different single dimers.
The lower spectrum exhibits a characteristic peak only from guanine while the upper one only from cytosine.
According to the principle of bianalyte SERS technique, we demonstrated single-base resolution: Because weobserved nucleotides containing guanine and cytosine, the SERS signal should also include both peaks even in a single
nucleotide observation. The fact that we obtained SERS spectra only from guanine is evidence that the hot spot islocalized in a single-base volume.
(a)

(b)

8
7

Cytosine ring breathing mode

6
5
4
Guanine ring breathing mode

3
2
1
0

600

650

700
750
800
Wavenumber (cm-1)

850

900

Fig. 1 (a) AuNP dimer sandwiching oligonucleotide of 12C-1G-12C. (b) Bianalyte (binucleotide) SERS spectra obtained fromtwo different single AuNP dimers under Brownian motion.

Dynamic Single-Molecule SERS Fluctuations in an Aqueous Environment
Nathan C Lindquist1, Ariadne Tückmantel Bido2, Alexandre G. Brolo2
1. Bethel University, Department of Physics and Engineering, 3900 Bethel Drive, St Paul MN, 55112 USA
2. Department of Chemistry, University of Victoria, 3800 Finnerty Road, Victoria, BC, V8P 5C2, Canada
E-mail: n-lindquist@bethel.edu

Surface enhanced Raman spectroscopy (SERS) is a well-known and highly-studied effect that effectively
represents both the challenges and opportunities inherent to nanophotonics and nanotechnology [1]. This is due to theextremely localized nature of the SERS effect, where intense atomic-scale plasmonic “hotspots” can increase Raman
scattering by orders of magnitude, generating signals from single molecules [2]. These localized SERS signals also
can show significant fluctuations, both in intensity and spectral features. This is considered a hallmark of few tosingle molecule events, and interpreted as being due to the dynamic nature of light-matter interaction at the atomic
scale. Recent experiments have even shown these SERS intensity fluctuations (SIFs) to occur over an extremely
wide range of timescales, from seconds to micro-seconds [3]. While many mechanisms have been proposed for thesefluctuations, such as molecular diffusion or transient plasmonic hotspot generation, the underlying source of thesefluctuations are likely to be a complex interplay of different effects. For example, SERS experiments done with fully
coated, but dry, nanoparticles would have less movement of the probe molecule but may still have transient hotspot
generation due to the mobility of metallic atoms. Alternatively, experiments done with low concentrations of amolecular probe in liquid might tend to see fluctuations caused by freely-diffusing molecules that visit and becometrapped within a static hotspot. In Figure 1 we compare high-speed SIFs in both dry and wet environments.

Fig. 1 Demonstration of SIFs in both a wet and a dry environment with R6G molecules. (a) TEM image of Ag nanoparticle clusters.
(b) After incubating with R6G and dried, the SERS spectrum fluctuated in time. (c) These fluctuations occur on extremely fasttimescales and can be digitized and analyzed. (d) Wet Ag clusters immersed in a 50 nM solution also fluctuated. (e) Analyzingthese fluctuations in time shows distinct regions of delays on the ~Hz timescale and high-speed SIF activity on the >kHz scale. (f)While both wet and dry samples fluctuated on similar timescales, the dry samples tended to have more uniform on-off behavior
whereas (g) the wet samples tended to show noisier SIFs after digitizing. Over dozens of samples and tens of thousands of SIFs,
the coefficient of variation (Standard Deviation / Mean) during a SIF was higher for wet samples (0.82) versus dry (0.65) samples.

Generally, the wet environment showed extremely high-speed fluctuations during a single SIF event, whereas adried and more stable molecule-hotspot environment showed SIF events with less overall variation. Both environments
still displayed strong SIF behavior over several orders of magnitude of time-scales, with the dry particles on average
having slightly longer events. These results provide some new insight into the underlying mechanisms of high-speed
SERS fluctuations, and may prompt further studies and applications of SERS in a variety of environments and forvarious metal-molecule systems.
References[1] Langer, J.; Jimenez de Aberasturi, D.; Aizpurua, J.; Alvarez-Puebla, R. A.; Auguié, B.; Baumberg, J. J.; Bazan, G. C.; Bell, S. E.; Boisen, A.;
Brolo, A. G.; Choo, J.; Cialla-May, D.; Deckert, V.; Fabris, L.; Faulds, K.; García de Abajo, F. J.; Goodacre, R.; Graham, D.; Haes, A. J.; Haynes,
C. L.; et al. Present and future of surface-enhanced Raman scattering. ACS Nano 2019, 14, 28-117.
[2] Benz, F.; Schmidt, M. K.; Dreismann, A.; Chikkaraddy, R.; Zhang, Y.; Demetriadou, A.; Carnegie, C.; Ohadi, H.; De Nijs, B.; Esteban, R.;
Aizpurua, J.; Baumberg, J. J. Single-molecule optomechanics in ''picocavities''. Science 2016, 354, 726-729.
[3] Lindquist, N. C.; de Albuquerque, C. D. L.; Sobral-Filho, R. G.; Paci, I.; Brolo, A. G. High-speed imaging of surface-enhanced Raman
scattering fluctuations from individual nanoparticles. Nature Nanotechnology 2019, 14, 981-987.

Exosome detection using a double resonant nanoantenna device in the
mid-infrared range
Maria Eleonora Temperini1,2, Sabrina Romanò3,4, Flavio Di Giacinto3,4, Leonetta Baldassarre1, Valeria
Giliberti2, Marco De Spirito3,4, Gabriele Ciasca3,4, Michele Ortolani1
1. Dipartimento di Fisica, Sapienza Università di Roma, Piazzale Aldo Moro 2, I-00185 Rome, Italy
2. Istituto Italiano di Tecnologia, Center for Life Nano- & Neuro-Science, Viale Regina Elena 291, I-00161 Rome, Italy
3. Fondazione Policlinico Universitario “A. Gemelli”, IRCCS, Largo Agostino Gemelli 8, I-00168 Rome, Italy
4. Dipartimento di Neuroscienze, Sezione di Fisica, Università Cattolica del Sacro Cuore, Largo Francesco Vito 1, I-00168 Rome, Italy
E-mail: mariaeleonora.temperini@uniroma1.it

Infrared (IR) spectroscopy finds application in the field of biomedical sensing as it can provide label-free
information on the molecular composition of a biological sample, targeting even subtle variations or differences. The
limits of IR-based diagnostics are related to the relatively large amount of pure molecule solution required to obtain aspectrum and to the strong IR absorption of the aqueous component required to maintain biomolecules in their
physiological state. The development of plasmonic near-field approaches, such as antenna-enhanced IR spectroscopy,
have allowed to overcome both issues by reducing the required sample volume for sensing, ideally limited to theintense plasmonic hotspots that form on the nanoantenna surface, where target molecules can be attached [1].
In the present work, we realized a microfluidic device based on a gold nanoantenna array with a double resonancein the mid-IR wavelength range, around 4 μm and 6 μm respectively, for the detection of exosomes released by humancell cultures (Fig.1a). These extracellular bodies are lipid bilayer-enclosed structures with nanometer size carrying
biological matter (i.e. proteins, nucleic acids…) (Fig.1b). Since they are involved in the intercellular communication
process, they can be exploited as pathology biomarkers of the parent cells in a so-called “liquid biopsy” [2]. Despite
this potential, the difficulty to gain information on the very small amount of molecules that forms the cargo hampers
their application for clinical diagnostic. The mid-IR device has been designed to detect exosomes through thevibrational absorption of their protein content. Indeed, the nanoantenna array displays a first resonance at 1600 cm-1
that is suitable for surface enhanced IR absorption (SEIRA) spectroscopy of the amide bands of proteins [3]. At thesame time, the sharp reflectivity drop around 1750 cm-1 produced by the interaction of the second resonance with thefirst is strongly sensitive to changes in the refractive index at the interface between the metal antenna and the sample(Fig.1d). The reflectivity drop is thus employed as a surface plasmon resonance (SPR) for mass-sensing [4], allowing
to monitor the presence of non-proteic material on the nanoantenna surface not specifically attached to the antibodyfunctionalization layer. We performed micro-FTIR measurements of 100 µm x 100 µm arrays in reflection mode
during sample solution flow, collecting simultaneously the two sensorgrams (inset of Fig. 1d). First, we demonstrated
the monolayer sensitivity of our device by following the attachment of exosome-specific antibodies on thefunctionalized antenna surface (Fig.1c). We then started to acquire systematic data from exosomes released by humancell cultures.

Fig.1 (a) Schematic view of the plasmonic device. (b) Representative TEM image of exosomes (scale bare: 200 nm). (c) Sketch of thesurface functionalization with antibodies. (d) IR reflectance spectra of the nanoantenna array with incident polarization parallel (greenline) and perpendicular (dashed gray line) to the long axis of the nanoantennas. The inset shows an example of the SEIRA signal
sensorgram in the case of antibody solution.

Acknowledgments This research was funded by Italian Ministry of Health, “Progetto Giovani Ricercatori 2015-2016”,
grant number GR-2016-02363310.
References[1] Neubrech, F., Huck, C., Weber, K., Pucci, A., and Giessen, H. 2017. Chem. Rev.,117 (7), 5110-5145.
[2] Li, S., Yi, M., Dong, B., Tan, X., Luo, S., & Wu, K. 2021. International journal of cancer, 148(11), 2640–2651.
[3] Adato, R., Altug, H. 2013. Nat. Commun., 4, 2154.
[4] Nguyen, H. H., Park, J., Kang, S., & Kim, M. 2015. Sensors, 15(5), 10481–10510.

Mid-IR to Visible Optomechanical Transduction with Molecules in a
Nanocavity
Christophe Galland1, Wen Chen1, Huatian Hu2, Philippe Roelli3
1. Institute of Physics, Ecole Polytechnique Fédérale de Lausanne (EPFL), CH-1015 Lausanne, Switzerland
2. Hubei Key Laboratory of Optical Information and Pattern Recognition, Wuhan Institute of Technology, Wuhan 430205, China
3. Nano-optics Group, CIC nanoGUNE BRTA, E-20018 Donostia, San Sebastián, Spain
E-mail: chris.galland@epfl.ch

The internal vibrational modes of molecules embedded in plasmonic nanogap can be used as ultrahigh frequency(1 – 50 THz) mechanical oscillators and constitute a new form of optomechanical nanocavities [1]. I will first briefly
review recent experiments evidencing quantum correlations that are generated between light and collective molecularvibrations in the process of spontaneous off-resonant Raman scattering [2-5], in the absence of any cavity. Then, I will
introduce our work on plasmonic gap modes [6,7] and show that coupling molecular vibrations to properly designed
dual-resonant plasmonic cavities [8] allows for the observation of coherent optomechanical transduction between midinfrared (~32 THz) and visible (~450 THz) electromagnetic fields [9].

Fig. 1 Coherent frequency conversion with a molecular optomechanical cavity. (a,b) Simulated field enhancement factors for midIR and visible illumination. The lower panel shows an SEM picture of the nanoparticle-in-groove cavity, while the right panel isan artistic rendering of the device. Estimated enhancement factors result in 13 orders of magnitude improvement in per-molecule
upconversion efficiency. (c) Example of high-resolution Raman spectrum (Stokes sideband, laser at 405 THz) with theupconverted signal (colored lines) riding on the spontaneous emission line (grey shade) as the mid-IR laser frequency is tuned
around 32.4 THz (or 1080 cm-1).

References[1] P. Roelli et al., Nature Nano 11, 164-169 (2016)[2] M. Anderson et al., Physical Review Letters 120, 233601 (2018)[3] S. Tarrago Velez et al., https://arxiv.org/abs/2105.00213[4] S. Tarrago Velez et al., Science Adv. eabb0260 (2020)[5] S. Tarrago Velez et al., Physical Review X 9, 041007 (2019)[6] A. Ahmed et al., ACS Photonics 8, 1863–1872 (2021)[7] W. Chen et al., Nature Comm. 12, 2731 (2021)[8] P. Roelli et al., Physical Review X 10, 031057 (2020)[9] W. Chen et al., Science 374 1264-1267 (2021).

Using a novel scanning probe technique to strongly couple a single quantum
dot to a tunable plasmonic nanogap antenna at room-temperature
Michael A. Becker1, Hsuan-Wei Liu1, Korenobu Matsuzaki1, Randhir Kumar1, Stephan Götzinger2,1
and Vahid Sandoghdar1,2
1. Max Planck Institute for the Science of Light, Staudtstr. 2, 91058 Erlangen, Germany
2. Friedrich Alexander University of Erlangen-Nürnberg, Schloßplatz 4, 91054 Erlangen, Germany
E-mail: michael.becker@mpl.mpg.de

Scanning probe techniques are indispensable methods for optical investigations of structures smaller than thediffraction limit. Moreover, techniques like scanning near-field optical microscopy and atomic force microscopy canbe used to probe near-field light–matter interactions and measure electrical and thermal conductance. All these methods
use a sharp tip that is operated in close proximity to the sample surface.
Here, we report on a novel, simple, and versatile tip-less scanning technique (PROscan) capable of performing
high-precision optical near-field measurements [1]. We demonstrate its scanning capabilities and remarkable stability
even in the absence of any feedback stabilization mechanism. Moreover, we utilize the PROscan method to create an
open and tunable nanogap antenna (Fig1.a), where the gap distance can be controlled, allowing one to tune the plasmon
resonance and to modify the fluorescence of single emitters with sub-nanometer resolution (Fig1.b). Locating single
quantum dots at the hotspot of the nanogap antenna and tuning its resonance to the exciton transition, we observe a
clear transition from the weak to the strong light–matter coupling regime, evidenced by a vacuum Rabi splitting in the
fluorescence signal as shown in Fig. 1c [2]. Furthermore, by scanning the plasmon resonance we observe acharacteristic anti-crossing behavior.

Fig. 1, a Schematic of the open and tunable nanogap antenna. b, Left: Measured plasmon resonance for different nanogap sizes.
Right: Simulated scattering cross section of a nanogap antenna for six different gap sizes. c, Photoluminescence spectra ofuncoupled (grey) quantum dot and of the same quantum dot coupled to a nanogap antenna (blue), exhibiting a vacuum Rabi
splitting.

References[1] Liu, H.-W.; Becker, M.A.; Matsuzaki, K.; Kumar, R.; Götzinger, St.; Sandoghdar, V.; „A robust and tip-less positioning device for nanoscopic
investigations”, in submission.
[2] Becker, M.A.; Liu, H.-W.; Matsuzaki, K.; Kumar, R.; Götzinger, St.; Sandoghdar, V.; „Room-temperature strong light–matter coupling
between a quantum dot and a tunable nanogap antenna”, in submission.

Holography, nanothermometry, and quantum correlations in extreme near fields
probed with high-energy electrons
Albert Polman
Center for Nanophotonics, NWO-Institute AMOLF, Amsterdam, The Netherlands
We use time-resolved cathodoluminescence spectroscopy using 30-keV electrons to reveal the emission statistics of
optical emitters, use holography to reveal the phase distribution of plasmonic scattering wavefronts, demonstrate
nanothermometry, and let the electrons climb quantum ladders creating superpositions states in extreme near fields
shaping electron wavepackets in space and time.
[1] Polman, A., Kociak, M. & García de Abajo, F.J. Electron-beam spectroscopy for nanophotonics, Nature Mater. 18, 1158 (2019)[2] K.W. Mauser, M. Solà-Garcia, M. Liebtrau, B. Damilano, P.-M. Coulon, S. Vézian, P. Shields, S. Meuret, and A. Polman,
Employing cathodoluminescence for nanothermometry and thermal transport measurements in semiconductor nanowires,
ACS Nano 15, 11385 (2021)[3] Schilder, N., Agrawal, H., Garnett, E.C. & Polman, A. Phase-resolved surface plasmon scattering probed bycathodoluminescence holography, ACS Photon. 7, 1476 (2020)[4] Feist, A., Echternkamp, K.E., Schauss, J., Yalunin, S.V., Schäfer, S. & Ropers, C. Quantum coherent optical phase modulation in
an ultrafast transmission electron microscope, Nature 521, 200 (2015).
[5] M. Liebtrau, M. Sivis, A. Feist, H. Lourenco-Martins, N. Pazos-Perez, R.A. Alvarez-Puebla, F.J. Garcia de Abajo, A. Polman, and
C. Ropers, Spontaneous and stimulated electron–photon interactions in nanoscale plasmonic near fields, Light Sci. Appl. 10,
82 (2021)[6] Employing cathodoluminescence for nanothermometry and thermal transport measurements in semiconductor nanowires
K.W. Mauser, M. Solà-Garcia, M. Liebtrau, B. Damilano, P.-M. Coulon, S. Vézian, P. Shields, S. Meuret, and A. Polman, ACS
Nano 15, 11385 (2021)[7] Photon statistics of incoherent cathodoluminescence with continuous and pulsed electron beams
M. Solà-Garcia, K.W. Mauser, T. Coenen, M. Lätzel, S. Christiansen, S. Meuret, and A. Polman, ACS Photon. 8, 916 (2021)

Inelastic in-line holography in an ultrafast electron microscope
Sophie Meuret1, Hugo Lourenço-Martins1,2, Sébastien Weber1, Florent Houdellier1 and Arnaud Arbouet1
1. CEMES-CNRS, Université de Toulouse, CNRS, Toulouse, France
2. Max Planck Institute for Multidisciplinary Sciences and 4th Physical Institute, University of Göttingen, 37077 Göttingen, Germany
E-mail: arnaud.arbouet@cemes.fr

Ultrafast Transmission Electron Microscopes (UTEM) combining the femtosecond temporal resolution of ultrafast
optical spectroscopies and the nanometer scale spatial resolution of electron microscopy have opened up many new
possibilities to investigate light-matter at unique spatio-temporal scales [1]. In particular, Photon-Induced Near-field
Electron Microscopy (PINEM) has recently aroused great interest due to its ability to efficiently probe nano-opticalexcitations.
PINEM works on a so-called pump-probe scheme: A first laser pulse (pump) excites the optical nearfieldaround a nanostructure which is then probed by a subsequent electron (probe) pulse (see fig. a and b). During its transit
in the optical near-field, the travelling electron can emit or absorb photons, thus leading to a modification of its energy(see fig. c). This inelastic interaction yields a characteristic electron energy spectrum composed by a series of peaks
reflecting the discrete nature of the photon exchange. The magnitude of these peaks being directly related to thestrength of the optical near-field, the analysis of the electron energy spectrum allows to map the optical near-field at
the nanometer scale. However, conventional PINEM experiments yield an uncomplete picture of the nano-opticalexcitation as the phase of the electromagnetic field is not measured. The situation is different when the investigatedoptical excitation (e.g a plasmon mode) is excited simultaneously with a secondary scattered wave that acts as areference signal. The interference between the two electromagnetic fields then imprints the phase of the plasmon modein the electron/near-field coupling constant extracted from the PINEM signal [2]. These holographic PINEM
experiments are the inelastic analog of the in-line holography technique proposed by D. Gabor in the late 1940s.
We have performed scanning electron energy-loss/gain spectroscopy experiments on our high-brightness UTEM
to investigate the optical near-field excited on gold bowtie antennas. These nanostructures have been fabricated byfocused ion beam milling of a 40 nm thick gold film evaporated on a 50 nm thick Si3N4 membrane. As shown on fig.
f, each nano-antenna is sculpted in a square aperture. At each position of the electron beam, an electron energy spectrum
is acquired. As shown in figure e and g, this 3D dataset yields a complete map of the electron-field coupling constantg. In addition, we observe clear modulations of the PINEM signal around the nano-antenna. The latter are signaturesof the interference between the plasmonic near-field and the wave scattered by the membrane edge and therefore
indicate the realization of the above-mentioned holographic scheme.

Fig. 1 a) ultrafast Transmission Electron Microscope b) close-up of the electron-light interaction on a gold bowtie. c) Electronenergy spectrum showing the sidebands associated with photon absorption/emission by the fast particle. TEM image of a square
aperture (d) and corresponding map of the electron-light coupling constant extracted from the electron spectra. f) and g):corresponding data for a gold bowtie.

Numerical simulations based on the Green Dyadic Method accurately reproduce the experimental results and allow
us to extract the characteristics of the electric field excited around the nano-objects from the holographic data. These
results open promising perspectives for the characterization of optical nano-excitations with unprecedented spatiotemporal resolution.
References[1] Ultrafast Transmission Electron Microscopy: fundamentals, instrumentation and applications. A. Arbouet et al, AIEP, 207, 2018[2] Holographic imaging of electromagnetic fields via electron-light quantum interference. I. Madan et al. Sci. Adv. 2019;5: eaav8358

Near-field optical study of Hyperuniform Disordered photonic structures
Nicoletta Granchi1, Richard Spalding2, Matteo Lodde3, Maurangelo Petruzzella3, Frank W. Otten3, Andrea
Fiore3, Francesca Intonti1, Riccardo Sapienza4, Marian Florescu2 and Massimo Gurioli1
1.

3.

Department of Physics and Astronomy and LENS, University of Florence, Sesto Fiorentino (FI), Italy
2. Advanced Technology Institute and Department of Physics, University of Surrey, Surrey, UK
Department of Applied Physics and Institute for Photonic Integration, Eindhoven University of Technology, Eindhoven, NL
4. The Blackett Laboratory, Department of Physics, Imperial College London, UK
E-mail: granchi@lens.unifi.it

In the last few years, disordered dielectric materials with structural correlations, which fill the gap between random
structures and perfectly ordered photonic crystals, have generated an ever-growing interest. A special class of thesematerials are the Hyperuniform Disordered (HuD) photonic systems [1]. HuD systems have recently been shown todisplay unconventional optical behavior such as transparency in thick optical media and large isotropic photonic bandgaps (PBG) comparable in width to band gaps found in photonic crystals [2], as well as Anderson localization of light.
Within this framework, a complete characterization of luminescent HuD structures in the optical range is still missing.
Here, we tackle this challenge by designing and nanofabricating the first ever optically active hyperuniform structures(SEM image in Fig.1a) with embedded quantum dots emitting at telecom wavelengths (as shown in the inset of Fig.1a)[3]. This breakthrough in the field, which we linked to the very first optical near-field hyper-spectral-imaging of HuD
systems, led to several innovative and unexpected results on the peculiarities of HuD modes. The investigated system
is a HuD dielectric structure on a GaAs slab architecture, with air holes following a specific hyperuniform pattern; we
employ a Near-field Scanning Optical Microscope in illumination-collection configuration (sketch of Fig.1b), whichallows us to have a direct measurement of the local density of states (LDOS) of the system. In Fig.1b are reported three
typical PL enhancement spectra acquired in three different tip positions, obtained by dividing the recorded spectrumby the PL spectrum of the QDs, that are embedded in the middle of the membrane and act as optically active medium.
Many sharp resonances are clearly visible. Doing this procedure for every position of the probe it is possible toreconstruct the near-field spatial distribution of the PL enhancement over a broad range of wavelengths (1165-1265nm), which reflects the distribution of the electric field intensity: this collective map, reported in Fig.1c, shows a highspatial density of modes that exhibit a very high PL enhancement (of the order of 20) and Q factors one order ofmagnitude larger in respect to disordered systems (like it is shown in the upper panel of Fig.1b). The positions (1, 2
and 3) where the spectra of Fig.1b where acquired are indicated also in the map of Fig.1c. The hyper-spectral method
allows also to map the spatial distribution of each mode singularly. This optical characterization allowed to record alarge plethora of interesting properties of the photonic modes in HuD systems, from the Q factor to the localization
length, and to link them to specific light transport regimes. We experimentally demonstrate, after careful support
provided by numerical simulations, that these resonances are intrinsically reproducible and resilient against fabricationinduced disorder and local perturbation. For these reasons, and thanks to special features combining the advantages ofboth ordered and disordered structures, they are eligible as relevant candidates for a large plethora of quantum
electrodynamics applications yet to be explored.

Fig. 1 a) SEM image of the HuD sample; the inset shows the PL emission spectrum of the QDs. (b) Sketch of the near-field
illumination-collection geometry, along with three typical PL enhancement spectra acquired in three tip positions. (c) Near-fieldPL enhancement map filtered around a broad wavelength interval, showing a high density of modes with a maximum PL
enhancement of 20. The white numbers indicate the acquiring positions of the spectra shown in (b).

References[1] Torquato, S. and. Stillinger, F.H, 2003, Physical Review E, 68, 041113.
[2] Florescu, M. et al., 2009, PNAS,106, 20658–20663.
[3] Granchi, N. et al., 2022, Adv. Opt. Mater., accepted.

Invited: Nanophotonics-Enabled Mid-Infrared Microspectrometers
For Chemical Identification and Related Topics
Kenneth B. Crozier1,2,3

1. School of Physics, University of Melbourne, Victoria 3010, Australia
2. Department of Electrical and Electronic Engineering, University of Melbourne, Victoria 3010, Australia
2. ARC Centre of Excellence for Transformative Meta-Optical Systems, University of Melbourne, Victoria 3010, Australia
E-mail: kenneth.crozier@unimelb.edu.au

The identification of chemicals from their mid-infrared spectra has applications that include the industrial
production of chemicals, food production, pharmaceutical manufacturing, and environmental monitoring. This is
generally done using laboratory benchtop tools, such as the Fourier transform infrared spectrometer. Although such
systems offer high performance, alternative platforms offering reduced size, weight, and cost can enable a host of new
applications, e.g. in consumer personal electronics. In this presentation, we will describe our recent work [1] on acompact microspectrometer platform for chemical identification. If time permits, we may describe a selection fromour related work on other topics in nanophotonics from 2021-2022, e.g. microspectrometers [2,3], photodetectors andLEDs based on 2D materials [4], metasurface holograms [5], metasurface lasers [6,7], and optical nanotweezers [8].
Our recent microspectrometer platform [1] comprises a nanophotonic filter chip integrated with a miniaturethermal camera (Fig. 1a). The nanophotonic chip is silicon with a thin gold coating. It contains twenty spectral filters(each 100×100 μm2) that span the wavelength range 6-14 µm. The filters are divided into two categories: bandstop
filters (arrays of gold rings, Fig. 1b-upper) and bandpass filters (arrays of coaxial apertures, Fig. 1b-lower). A
photograph of a prototype IR microspectrometer is provided as Fig. 1c. Experiments are performed by placing thematerial to be studied (“sample”) between the IR blackbody source and the IR microspectrometer (Fig. 1d). A typicalraw (i.e. unprocessed) sensor output is shown as Fig. 1e. The twenty spots of high intensity (Fig. 1e) correspond to
the twenty spectral filters (Fig. 1b). One may regard these as the representation of the IR absorption spectrum of thematerial, divided into twenty spectral channels. Provided that the material has absorption features within the
wavelength range of the filter set (6-14 µm), the resultant sensor output (i.e. Fig. 1e) exhibits a distinctive pattern. We
have demonstrated that this platform can be used with a machine learning (ML) algorithm. After this is trained, it canquickly identify and quantify unknown chemicals with high accuracy from the measured sensor output.

Fig. 1 a). Schematic of integration of nanophotonic filter chip onto thermal camera (FLIR Lepton). b). False-color scanningelectron microscope (SEM) image of nano-optical filter chip. c). Photo of completed microspectrometer. d). Schematic ofexperimental set-up. e). Raw data from microspectrometer..

To evaluate the performance of our IR microspectrometer, we perform experiments in two steps. First, the ML
algorithm is trained on data recorded by the IR microspectrometer while it is subjected to different chemicals at avariety of concentrations. Second, the system is subjected to unknown chemicals. The sensor output (e.g. Fig. 1e) is
provided to the ML algorithm, which then predicts what chemical is present. High accuracy identification of four
liquid chemicals, concentration quantification of ethyl lactate in cyclohexane down to subpercentage levels, and theclassification of food and drug samples is demonstrated.
References[1] Meng, J., Weston, L., Balendhran, S., Wen, D. Cadusch, J.J. Rajasekharan Unnithan, R. and Crozier, K.B. 2022 Laser Photonics Rev.
2100436[2] Cadusch, J.J., Meng, J., Wen, D., Shrestha, V.R., and Crozier, K.B. 2022. ACS Photonics (in press).
[3] Meng, J., Cadusch, J.J. and Crozier, K.B. 2021. ACS Photonics 8, 648-657[4] Kim, H., Uddin, S.Z., Lien, D-H, Yeh, M., Sefidmooye Azar, N., Balendhran, S., Kim, T., Gupta, N., Rho, Y, Grigoropoulos, C.P., Crozier,
K.B. and Javey, A. 2021. Nature, 596, 232-237[5] Wen, D., Cadusch, J.J., Meng, J. and Crozier, K.B. 2021. Nano Letters 21, 1735-1741[6] Wen, D., Meng, J., Cadusch, J.J. and Crozier, K.B. 2021. Advanced Optical Materials 9, 2001780[7] Wen, D. Cadusch, J.J. Fang, Z. and Crozier, K.B. 2021. Nature Photonics 15, 337-338[8] Li, N., Cadusch, J., Liu, A., Barlow, A.J., Roberts, A. and Crozier, K.B. 2021. Advanced Optical Materials 9, 2100758

Order Structure Recognition by Schubert Polynomials Generated by Optical
Near-Field Statistics via Nanometer-Scale Photochromism
Kazuharu Uchiyama1, Ryo Nakagomi1, Hirotsugu Suzui2, Kingo Uchida3, Makoto Naruse2, Hirokazu Hori1

1. University of Yamanashi, 4-3-11 Takeda, Kofu, Yamanashi 400-8511, Japan
2. Department of Information Physics and Computing, Graduate School of Information Science and Technology, The University of Tokyo, 7-3-1
Bunkyo-ku, Tokyo 113-8656, Japan
3. Ryukoku University, 1-5 Yokotani, Oe-cho, Seta, Otsu, Shiga 520-2194, Japan
E-mail: kuchiyama@yamanashi.ac.jp

Light-matter interactions, especially optical near-field interactions, are important in the realization of natural
intelligent devices, which solve problems by mapping them to complex physical processes. The quantum nature of
single photons has been reported to solve decision-making problems [1,2]. We focused on the nanometer-scale photontransfer paths generated by the chain of nano-photochromism due to the near-field photoexcitation on photochromic
crystals [3]. In this study, we demonstrate a strategy to recognize the order structure in the system under study via
utilizing nanometer-scale photon transfer paths generated in photochromic crystals combined with a single photon
detection protocol [4].
The photochromic crystal used in this study consists of diarylethene molecules, which become colored or
decolorized by photoisomerization even in the crystalline state. When near-field photoexcitation is applied to thesurface of the crystal, a nanoscale photoisomerized structure is formed from the surface to inside the crystal due to acomplex local photoisomerization chain formed by the combination of photoisomerization and crystal distortion.
The photoisomerized structures generate the two-dimensional probability map of photons transferring from the exit
positions of the branched photoisomerization pathway to the rear-side sample surface. We extracted the order structurefrom the two-dimensional probability map of the transferring photons via a photon detection protocol [3]. The obtainedorder structures are matrices that show one-to-one correspondence with the Schubert polynomials and are called
Schubert matrices [4]. The series of Schubert matrices has both fluctuation and order, which corresponds topermutations for a statistical system such as a group of slot machines.
We demonstrated recognition of the order structure in a problem without direct probability estimation by a
Schubert-calculus-inspired strategy to map the nano-optical isomerization structure to an ordering problem (such as
solving an order in a set of slot machines). In this strategy, we reorder the rows or columns of the entire matrix series
according to the results of playing the slot machines corresponding to the elements that form the singular structure in
the matrix. The order structure recognition can be used for any ordered structures in optimization and decision-making
problems even when the problem systems include environmental fluctuations based on physical structures. The nanophotochromism encompasses both classical and quantum phenomena, so it can be applied to complex problems suchas social problems where quantum computing is expected to be applied.

Fig. 1 Order structure recognition by Schubert polynomials generated by optical near-field statistics generated by nanometer-scale
photoisomerized structures via a photon detection protocol and a Schubert-calculus-inspired recognition strategy.

References[1] Aono, M., Naruse, M., Kim, S.-J., Wakabayashi, M., Hori, H., Ohtsu, M., Hara, M., 2013. Langmuir 29, 7557.
[2] Naruse, M., Berthel, M., Drezet, A., Huant, S., Aono, M., Hori, H., Kim, S.-J, 2015. Sci. Rep. 5, 13253.
[3] Uchiyama, K., Suzui, H., Nakagomi, R., Saigo, H., Uchida, K., Naruse, M., Hori, H., 2020. Sci. Rep. 10, 2710.
[4] Uchiyama, K., Nakajima, S., Suzui, H., Chauvet, N., Saigo, H., Horisaki, R., Uchida, K., Naruse, M., Hori, H., 2021. arXiv:2111.09462

Seeing the Forces: Single Avalanching Upconverting Nanoparticles as
Ultrasensitive Local Force Transducers
Natalie Fardian-Melamed1, Artiom Skripka2, Changhwan Lee1, Tom P. Darlington1, Kevin W. C. Kwock1,
Maoji Wang3, Hye Sun Park4, Sang Hwan Nam4, Yung Doug Suh4, Jordan M. Gerton3, Bruce Cohen2, Emory
Chan2, P. James Schuck1
1. Columbia University, New York, NY, USA
2. Lawrence Berkeley National Laboratory, Berkeley, CA, USA
3. University of Utah, Salt Lake City, Utah, USA
4. Korea Research Institute of Chemical Technology (KRICT), DaeJeon, South Korea
E-mail: natalie.melamed@columbia.edu

It has lately been shown that ensembles of lanthanide-doped upconverting nanoparticles (UCNPs) exhibit changes
in their emission spectra due to applied forces in the nano-Newton regime and beyond [1-3]. Avalanching UCNPs(ANPs) [4], possessing steeply nonlinear optical responses, are ideally suited for sensing minute changes in theirenvironments, as small perturbations are expected to usher large changes in signal. Because ANPs absorb and emit
tissue-penetrating near-infrared (NIR) light, they are uniquely positioned for sensing within biological cells and fluids.
In order to characterize and understand the response of these ANPs to local stress and hence determine theirfunctionality as mechano-sensors, it is important to study their mechano-opto-physics on a single particle level.
Utilizing a custom designed combined AFM and inverted optical microscope system (Fig. 1a), we correlate sub-nanoNewton-range applied forces and observable changes in hyperspectral optical signals for isolated single ANPs,
demonstrating their attractiveness as physiologically-relevant local force sensors.
By optimizing ANP lanthanide concentration, core and shell sizes, particle geometry, and host material, we design
ANPs with record-breaking mechano-sensitivity and unprecedented stress-dependent responses. While the decrease
in inter-ionic distance and the change in crystal field with applied pressure usually leads to a decrease in UCNP opticalsignal intensity, newly designed ANPs exhibit optical signal enhancement (Fig. 1b) when subjected to forces as low
as pico-Newtons. The signal enhancement persists for a large range of applied force, from pico-Newtons to microNewtons, in a predictable fashion, over many cycles, for the same particle. Optimally-engineered ANPs - with their
NIR wavelength operating regime, high single particle brightness, substantial mechano-sensitivity, and uniquemechano-response - emerge as highly promising candidates for non-invasive ultra-sensitive force-sensing.

Fig. 1. a) Sub-nano-Newton force is applied to a single ANP with an AFM tip while excited with NIR light from below. b) Forcedependent emission spectra, attained for a single ANP while excited at 1064 nm.

References[1] Lay A, et al. 2017. Nano Lett., 17(7), 4172-4177[2] Lay A, et al. 2019. ACS Cent. Sci., 5(7), 1211-1222[3] McLellan CA, et al. 2022. J. Phys. Chem. Lett., 13, 1547-1553[4] Lee C, et al. 2021. Nature, 589(7841), 230-235

Imaging life at high temperature enabled by plasmonic heatingMaëlle Bénéfice,1 Céline Molinaro,1 Aurore Gorlas,2 Violette Da Cuna,2 Patrick Forterre,2 Guillaume Baffou1*
1
2

Institut Fresnel, CNRS, Aix Marseille University, Centrale Marseille, Marseille, France

Université Paris-Saclay, CEA, CNRS, Institute for Integrative Biology of the Cell (I2BC), Gif-sur-Yvette, France*guillaume.baffou@fresnel.fr

At the bottom of the ocean, close to black smokers, microorganisms can thrive at temperatures higher than 100°C.
Understanding how life can sustain such harsh conditions is of utmost interest for the fundamental understanding of
how Nature copes with high temperatures, and for the development of biological applications at high temperature.
However, it remains very hard to observe thermophilic micro-organisms living in vitro, because it would require
heating a microscope stage at 100°C or more. As a result, most microscopy observations of thermophilic microorganisms today are conducted using electronic microscopy, that is on dead samples, a rather frustrating condition forbiologists.
In this contribution, we show how plasmonic heating can successfully activate thermophilic bacteria using a
conventional microscope, without complex apparatus [1]. Thermophilic bacteria are cultured on a glass coverslip
covered with gold nanoparticles, which are illuminated at their plasmonic resonance wavelength within the field ofview of the microscope at the required temperature (Fig. 1). The temperature distribution is imaged using cross-gratingphase microscopy [2,3]. This work paves the way for the easy study of thermophiles and a better understanding of their
metabolism and interaction.

Fig. 1 Wide field intensity images of the growth of G. stearothermophilus bacteria upon laser heating at different time, (a) t=0
min, (b) 1 h 10 min, (c) 2 h 20 min, (d) 3 h 20 min, extracted from a 200 min long movie, superimposed with the associatedtemperature map. The laser was switched on at time 𝑡𝑡 = 0. Isotherms have been added to the intensity images.

References[1] C. Molinaro, M. Bénéfice, A. Gorlas, V. Da Cunha, H. M. L. Robert, R. Catchpole, L. Gallais, P. Forterre, G. Baffou, under submission (2022)[2] Baffou, G. ; Bon, P. ; Savatier, J. ; Polleux, J. ; Zhu, M. ; Merlin, M. ; Rigneault, H. ; Monneret, S. 2012. ACS Nano 6, 2452-2458[3] Baffou, G. J. Phys. D : Appl. Phys. J. Phys. D: Appl. Phys. 54, 294002 (2021)

Strong coupling of semiconductor nanocrystals withplasmonic resonators at ambient conditions
Daniel Friedrich1, Benedikt Schurr1, Jin Qin1, Heiko Groß1, Philipp Grimm1, Enno Schatz1, Tommaso
Tufarelli2, Joachim M. Hamm3, Ortwin Hess4 and Bert Hecht1

1. Nano-Optics and Biophotonics Group, Department of Experimental Physics 5, Wilhelm-Conrad-Röntgen-Centre for Complex Material
Systems (RCCM), University of Würzburg, 97074 Würzburg, Germany
2. School of Mathematical Sciences and Centre for the Mathematics and Theoretical Physics of Quantum Non-Equilibrium Systems,
University of Nottingham, Nottingham NG7 2RD, United Kingdom
3. The Blackett Laboratory, Department of Physics, Imperial College London, London SW7 2AZ, United Kingdom
4. School of Physics and CRANN Institute, Trinity College Dublin, Dublin 2, IrelandE-mail: daniel.friedrich@physik.uni-wuerzburg.de

Strong coupling and the resultant mixing of light and matter states is an important asset for quantum technologies.
We have successively improved our previously demonstrated deterministic room temperature strong coupling ofa mesoscopic colloidal quantum dot (Fig. 1a) to a plasmonic nanoresonator [1] and substantiated the results ofenormous Rabi splitting up to 110 meV in extensive statistical analysis (Fig. 1c). Furthermore, we developed thescanning experiment into an on-chip platform which provides a stable and continuous strongly coupled system(Fig. 1b). For this purpose, we use ultraprecise He-ion beam milling to fabricate high-quality plasmonic slit
resonators from single-crystalline gold microplatelets in combination with dielectrophoresis to position single
quantum dots close to the slit opening. These novel nanostructures provide additional degrees of freedom as wellas the opportunity to apply electric fields to induce tunability.
We also have recently established a comprehensive theoretical framework for extending the Jaynes-Cummings
model to a multilevel coupling model [2]. Based on the broadband nature of the interaction and the full control of
the coupling, our platform paves the way towards ultrafast coherent manipulation of light-matter interaction in
any 0D, 1D or 2D quantum system at ambient conditions.

Fig. 1 (a) Artistic illustration of a plasmonic nanoresonator (PNR) probe interacting with colloidal semiconductor QDs embedded
in a polymer film. (b) On-chip strong-coupling device. SEM- and AFM images illustrate the geometry as well as a proof of
successful attraction of single QDs to the PNR via dielectrophoresis. In addition, two photoluminescence spectra characterize the
PNR’s plasmonic resonance as well as a clear Rabi-splitting obtained for a coupled system. (c) Compilation of several
measurements and statistical strong coupling mean values. (d) Visual summary of the theoretical light-matter interaction models.

References[1] Groß, H., Hamm, J. M., Tufarelli, T., Hess, O., Hecht, B., Near-field strong coupling of single quantum dots. Sci. Adv. 4, eaar4906(2018).
[2] Tufarelli, T., Friedrich, D., Groß, H., Hamm, J., Hess, O., Hecht, B., Phys. Rev. Research 3, 033103 (2021)

Tunable nano-plasmonic photodetectors
Patrick Pertsch1, René Kullock1, Vinzenz Gabriel1, Luka Zurak1, Monika Emmerling1, and Bert Hecht1
1. NanoOptics & Biophotonics Group, Experimental Physics 5, University of Würzburg, Am Hubland, 97074 Würzburg, Germany
E-mail: patrick.pertsch@physik.uni-wuerzburg.de

The internal photoeffect has been widely used to detect photons with a broadband response in the visible and infrared
regime. By using plasmonic nanostructures, wavelength selectivity can be introduced to these detectors via geometrydependent resonances [1]. Also, additional functionality, like electronic responsivity switching and polarizationsensitive detection have been realized [2,3]. However, previous devices consisted of large arrays of nanostructures toachieve reasonable photocurrents.
Here we show that this concept can be scaled down to a single antenna level, resulting in detector dimensions well
below the resonance wavelength of the device. Our design consists of a single electrically-connected plasmonicnanoantenna covered with a wide-bandgap semiconductor allowing photodetection in the VIS/NIR (Fig. 1). We
demonstrate electrical switching of the resonance wavelength as well as polarization detection. Our results holdpromise for the realization of ultra-small photodetectors with advanced functionality controllable by the antenna
design.

Fig. 1 (a) Schematic drawing of our photodetector consisting of a plasmonic nanoantenna (gold) covered with TiO2
(blue). (b) Geometry dependent scattering and photocurrent of four different nanoantenna-detectors. (c) Cross sectionand (d) energy-diagram of the nanoantenna photodetector.

References[1] Knight, M. W., Sobhani, H., Nordlander, P., Halas, N.. 2011 . Science, Vol 332, Issue 6030, pp. 702-704.
[2] Wang, W., Klots, A., Prasai, D., Yang, Y., Bolotin, K., Valentine, J.. 2015. Nano Lett., 15, 11, 7440-7444.
[3] Hou, Y., Liang, H., Tang, A., Du, X., Mei, Z.. 2021. Appl. Phys. Lett., 118, 063501.

Engineering polariton launchers for nanophotonic chips

Rafael Mayer1,2, Flavio Feres1,2, Francisco Maia2, Ingrid Barcelos2, Alexander Mcleod3, Aleksandr Rodin4,
Raul Freitas2
1. Institute of Physics “Gleb Wataghin”, State University of Campinas (UNICAMP), Campinas, Sao Paulo, Brazil.
2. Brazilian Synchrotron Light Laboratory (LNLS), CNPEM, Campinas, Sao Paulo, Brazil
3. Centre for Advanced 2D Materials, National University of Singapore, Singapore, Singapore
4. School of Physics and Astronomy, University of Minnesota, Minneapolis, Minnesota, USA
E-mail: rafael.mayer@lnls.br

Two-dimensional (2D) crystals have been considered fundamental building blocks for several applications, fromoptical modulators to biosensors. The reason for such success originates in their ability to confine light in the form ofpolaritons, which are quasi-particles that result from the coupling of light and collective excitations in matter. However,coupling polaritons to 2D crystals is challenging, as their momentum may be dozens of times larger than the photon
momentum. On the other hand, studies have shown that metallic antennas can be ideal for the coupling, as they areexcellent light concentrators and can be easily patterned on top of crystals.
Despite the vast literature on plasmonic antennas as polariton launchers [1-3], the basic rules which govern theirlaunching properties are still unspecified. Here, we combine concepts of radiofrequency (RF) antennas and polariton
modeling to deliver insights on the directional launching properties of plasmonic antennas.
Using Finite-Difference Time-Domain calculations, we simulated hyperbolic phonon polaritons (HPhP) in
hexagonal Boron Nitride (hBN) launched by gold antennas (Fig.1a,b,e,f). The waves were modeled as evanescentwaves for a collection of directions outwards the antenna edges. By classifying the region surrounding the antenna into
Fresnel and Fraunhofer zones, we were able to select the directions that optimized the model accuracy. Furthermore,
the classification indicates the type of radiation pattern representation for illustrating the antenna properties(Fig.1c,d,g,h).
Our results show that the antenna geometry, the resonance order, and the illumination setup are crucial for defining
the polariton pattern. For instance, we may design the antenna dimensions to control the local polariton decay. Bychanging the dimensions of the edges, polaritons can propagate as circular or plane-waves. Moreover, asymmetricnear-field distribution on the antennas may lead to highly directive launching (Fig.1d,h). Because the incidence angleof the source and the antenna dimensions strongly influence the antenna polarization, we may tune the directivity bysimply changing these parameters. We envision that our insights will be substantial for planning and designingantennas for near-field experiments on 2D crystals and future photonic chips.

Fig. 1 Simulated near-field patterns on top of disks (a,b) and rod (e,f) antennas for normal (a,e) and oblique incidence (b,f). Polar
representation of the polariton detectable distance, rd (μm), for disks under normal (c) and oblique (d) incidence. Representationof launching properties of a rod for normal (g) and oblique (h) incidence. “Amp.” and “Decay” represent the model-extracted
launching amplitude and geometric spreading decay factor, respectively.

References[1] Dai, Siyuan, et al., 2017, Nano letters, "Efficiency of launching highly confined polaritons by infrared light incident on a hyperbolic material.",17.9: 5285-5290.
[2] Pons-Valencia, Pablo, et al., 2019 Nat. Commun. “Launching of hyperbolic phonon-polaritons in h-BN slabs by resonant metal plasmonic
antennas”, 10.1: 1-8.
[3] Zheng, Zebo, et al., 2021, Adv. Mater "Controlling and Focusing In‐Plane Hyperbolic Phonon Polaritons in α‐MoO3 with a Curved Plasmonic
Antenna.": 2104164.

Harnessing electron beams to unveil quantum effects in nanoplasmonics
P. André D. Gonçalves1, F. Javier García de Abajo1,2
1. ICFO – The Institute of Photonic Sciences, 08860 Castelldefels (Barcelona), Spain
2. ICREA – Institució Catalana de Recerca i Estudis Avançats, Passeig Lluís Companys 23, 08010 Barcelona, Spain
E-mail: andre.goncalves.icfo.eu

Nonlocal (i.e., q-dependent) response and quantum-mechanical effects are ubiquitous in truly nanometer-scale
plasmonic structures—now well within reach of state-of-the-art nanofabrication techniques—wherein the intrinsicallyquantum-mechanical nature of the plasmon-supporting electron gas manifests itself through nonclassical signatures in
the observed optical response [1–4]. Typically, the impact of quantum nonlocal effects becomes important when thecharacteristic size of the system falls below ~10–20nm or when the optical response is governed by extremely
subwavelength near-fields (i.e., involving field-components with large wavevectors). However, fully quantum
mechanical treatment of the metal’s electrodynamic response [e.g., through time-dependent density-functional theory(TDDFT)] is severely constrained to few-atom clusters or extremely small systems which are, invariably, much smaller
than the typical nanoplasmonic systems of interest in nearly all experiments. As such, common strategies typically relyon simplified quantum-informed models that seek to capture the dominant quantum effects to leading-order [1,2,4].
Among these, the so-called Feibelman d-parameter formalism [2] for nanoscale electrodynamics has been shown toenable the simultaneous incorporation of nonclassical effects including electron spill-out/spill-in, nonlocality, andsurface-assisted Landau damping [2–5]. Crucially, the d-parameter approach has the advantage of being practical to
implement, scalable, and has an amenable computational cost (and even allows analytical treatments in highly
symmetric systems). At its heart, it relies on the introduction of two surface-response functions, 𝑑𝑑⊥ (𝜔𝜔) and 𝑑𝑑∥ (𝜔𝜔),that encode the quantum-mechanical response of the underlying electron gas [2–4]. Naturally, that hinges upon ourability to compute the d-parameters based on a suitable theoretical description, which, in practice, can be challenging(particularly in beyond-jellium TDDFT, as it is required for Au and Ag).
Here, we show that electron-beam spectroscopies can be harnessed to infer such quantum surface-response
functions directly from experimental measurements of electron energy-loss and/or cathodoluminescence spectra,
whereby quantum nonlocal effects imprint nonclassical spectral shifts (~ 𝑅𝑅𝑅𝑅 𝑑𝑑⊥,∥ ) and nonlocal broadening (~ 𝐼𝐼𝐼𝐼 𝑑𝑑⊥,∥ )in the measured spectra [5]. Specifically, we present a quantum-corrected theory of electron energy-loss spectroscopy(EELS) and cathodoluminescence (CL) based on the d-parameter formalism and macroscopic quantum
electrodynamics. Our results establish a brand-new, concrete scheme for interrogating the complex optical response ofplasmonic nanostructures with free-electrons, from which one can retrieve the quantum surface-response [i.e., 𝑑𝑑⊥ and𝑑𝑑∥ ] by capitalizing on the free-electron’s ability to generate near-fields which can be tuned by controlling the electron’s
kinetic energy [5]. Such a quantitative knowledge of the material response is paramount not only from a fundamental
point-of-view but also as a key ingredient for modeling and designing the next-generation of nanophotonic devices
with truly nanometric dimensions.

Fig. 1 (a) Conceptual approach for probing the quantum surface-response of metals using free-electrons. (b)–(c) Classical andquantum (i.e., via the d-parameters) EELS and CL spectra of a metal nanosphere [(b) jellium metal with Wigner–Seitz radius rs=4;(c) silver], showing nonclassical spectral shifting and nonlocal broadening. The nanosphere diameter is 𝐷𝐷 = 10 𝑛𝑛𝑛𝑛, the probing
electron’s kinetic energy is 𝐸𝐸𝑘𝑘 = 20 keV, and the impact parameter is 𝑏𝑏 = 10 𝑛𝑛𝑚𝑚 (measured relative to the nanoparticle’s center).

References[1] Zhu, W., Esteban, R., Borisov, A.G., Baumberg, J.J., Nordlander, P., Lezec, H.J., Aizpurua, J., Crozier, K.B., Nat. Commun. 7, 11495 (2016).
[2] Feibelman, P.J., Prog. Surf. Sci. 12, 287–407 (1982).
[3] Yang, Y., Zhu, D., Yan, W., Agarwal, A., Zheng, M., Joannopoulos, J.D., Lalanne, P., Christensen, T., Berggren, K.K., Soljačić, M., Nature
576, 248 (2019).
[4] Gonçalves, P.A.D., Plasmonics and Light–Matter Interactions in Two-Dimensional Materials and in Metal Nanostructures: Classical andQuantum Considerations (Springer Nature, 2020).
[5] Gonçalves, P.A.D., García de Abajo, F.J., in preparation (2022)

Unidirectional DNA-origami based ultracompact optical antennas for single
molecule emission
Maria Sanz-Paz, Fangjia Zhu, Mauricio Pilo-Pais, Guillermo Acuna
Department of Physics, University of Fribourg, Chemin du Musée 3, Fribourg CH-1700, Switzerland
E-mail: guillermo.acuna@unifr.ch

Optical antennas have been widely used for manipulating light-matter interactions at the nanoscale in order control
the emission intensity, lifetime and directivity of single molecules [1], [2]. In particular, increasing the directionalityof single emitters takes on crucial significance, for example in the context of future integrated optical circuits orquantum communication and computing schemes, which hold potential for lower energy consumption and higher
efficiency using states that can be controlled up to the fundamental quantum limit [3], [4]. To date most efforts werefocused on designs adapted from the Yagi-Uda antenna that can reach high directionality with a significant number of
elements spanned over approximately a wavelength [5]. Despite this tremendous proof of concept, further developmentof these antennas is hindered by the challenges involved in the fabrication and positioning of the single emitters andmetallic elements that limits the coupling control and performance that can be achieved.
In this contribution, we report on the realization of ultra-compact directional antennas for single photon emittersby means of DNA self-assembly. Adapting the design proposed by Pakizeh et al. [6], we used the DNA origami
technique [7] to place two gold nanorods in a side-to-side (or end-fire) arrangement with an overall footprint an orderof magnitude smaller than the optical Yagi-Uda antenna. By coupling a single fluorescent molecule to one of thenanorods, unidirectional emission is registered red-shifted from the bonding mode [8], when the nanorods are driven
close to the antiphase mode.

Fig. 1: Sketch of an ultracompact antenna showing unidirectional emission

References[1] P. Biagioni, J.-S. Huang, and B. Hecht, “Nanoantennas for visible and infrared radiation,” Reports Prog. Phys., vol. 75, no. 2, p. 024402, 2012.
[2] A. F. Koenderink, “Single-Photon Nanoantennas,” ACS Photonics, vol. 4, no. 4. pp. 710–722, 2017.
[3] O. Benson, “Assembly of hybrid photonic architectures from nanophotonic constituents,” Nature, vol. 480, no. 7376. pp. 193–199, 2011.
[4] A. Alù and N. Engheta, “Wireless at the nanoscale: Optical interconnects using matched nanoantennas,” Phys. Rev. Lett., vol. 104, no. 21,
2010.
[5] A. G. Curto, G. Volpe, T. H. Taminiau, M. P. Kreuzer, R. Quidant, and N. F. Van Hulst, “Unidirectional emission of a quantum dot coupled toa nanoantenna,” Science, vol. 329, no. 5994, pp. 930–933, 2010.
[6] T. Pakizeh, M. Käll, M. Ka, and M. Käll, “Unidirectional Ultracompact Optical Nanoantennas,” Nano Lett., vol. 9, pp. 2343–2349, 2009.
[7] P. W. K. Rothemund, “Folding DNA to create nanoscale shapes and patterns,” Nature, vol. 440, no. 7082. pp. 297–302, 2006.
[8] E. Prodan, C. Radloff, N. J. Halas, and P. Nordlander, “A Hybridization Model for the Plasmon Response of Complex Nanostructures,”
Science, vol. 302, no. 5644, pp. 419–422, 2003.

Conformational Dynamics of Single Proteins –Exciting Opportunities with Plasmonic Optical Tweezers
Cuifeng Ying,1,2 Edona Karakaçi,1 Alessandro Ianiro,1 Esteban Bermúdez-Ureña,1,3 Guillermo P. Acuna,4Reuven Gordon,5 Michael Mayer1
1. Adolphe Merkle Institute, University of Fribourg, CH-1700 Fribourg, Switzerland.
2. Advanced Optics and Photonics Lab, Department of Engineering, Nottingham Trent University, United Kingdom.
3.Centro de investigación en Ciencia e Ingeniería de Materiales and Escuela de Física, Universidad de Costa Rica, San José, 11501, Costa Rica
4. Department of Physics, University of Fribourg, CH-1700 Fribourg, Switzerland.
5. Department of Electrical and Computer Engineering, University of Victoria, Victoria, British Columbia V8P 5C2, Canada
Email: michael.mayer@unifr.ch

This talk will present an update of our ongoing efforts to assess the potential of nanoplasmonic optical tweezers
for interrogating the conformational dynamics of single unmodified proteins in aqueous solution. Specifically, we
employ double nanohole (DNH) structures to trap single enzyme proteins [1,2] for minutes to hours. Concurrently,
we monitor changes in transmission through the DNH upon exposure of the trapped protein to substrate, product, or
inhibitor molecules. We show that experiments with trapped enzymes that are known to undergo significant
conformational changes during their catalytic cycle, exhibit multiple, well-defined transmission levels.[3] Increasing
concentration of substrate molecules increases the frequency of transitions between these transmission levels in a dosedependent manner, while the presence of different inhibitors reduces the frequency of transitions by favoring certaintransmission levels (Fig. 1). Step-fitting the transmission recordings makes it possible to follow the rate of transition
between all levels, revealing individual enzymatic cycles, single molecule turnover frequencies, as well as heretofore
unknown enzymatic sub-cycles during catalysis.[3] The talk will conclude with an outlook of applying this approachto additional unmodified enzymes, motor proteins, and transporters as well as a discussion of its current limitations
and possible improvements.

Fig. 1 Monitoring changes in normalized transmission through a double nanohole (DNH) with a single trapped adenylate kinase (AdK) enzyme
in response to increasing concentrations of the enzyme substrate ADP as well as the presence of the inhibitor Ap5A.[3] The magnified area shadedin pink shows a step-fit to three transmission levels and reveals the lifetime of each level as well as the turnover frequency of the enzyme on a single
molecule level. Considering the polarizability [4] of various conformations of AdK, combined with previous observations that AdK populates
predominantly its open conformation in the absence of substrate (0 µM ADP) and that AdK must cycle through the closed conformation duringcatalysis, made it possible to assign the lowest transmission level to AdK’s open (o) conformation, the intermediate transmission level to its partiallyclosed (pc) conformation and the highest transmission level to its fully closed (fc) conformation.

References[1] Juan, M. L.; Gordon, R.; Pang, Y.; Eftekhari, F.; Quidant, R. 2009, Nat. Phys. 5, 915–919[2] Pang, Y.; Gordon, R. 2012, Nano Lett. 12, 402–406.
[3] Ying, C.; Karakaci, E.; Bermudez-Urena, E.; Ianiro, A.; Foster, C.; Awasthi, S.; Guha, A.; Bryan, L.; List, J.; Balog, S. 2021, arXiv Prepr,
arXiv2107.06407.
[4] Booth, L. S.; Browne, E. V.; Mauranyapin, N. P.; Madsen, L. S.; Barfoot, S.; Mark, A.; Bowen, W. P. 2022, Scientific Reports, 12:1995

Near- and far-field properties of few element mid-infrared subwavelength
antennas
Loubnan Abou-Hamdan1,2, Valentina Krachmalnicoff1, Riad Haidar2, Patrick Bouchon2, and Yannick De
Wilde1
1. Institut Langevin, ESPCI Paris, PSL University, CNRS, 1 rue Jussieu, F-75005 Paris, France
2. DOTA, ONERA, Université Paris-Saclay, F-91123 Palaiseau, France
E-mail: Loubnan.abou-hamdan@espci.fr

Tailoring the mid-infrared (mid-IR) optical and thermal radiative properties of individual antennas is of paramountimportance for various pertinent applications, such as, radiative cooling, photo-detection, and solar cell design.
Nevertheless, the electromagnetic radiation emitted by a single mid-IR subwavelength antenna is extremely weak,
and in practice, most studies are limited to periodic arrays, in which the resultant diffraction orders preclude themeasurement of the response of a single antenna. In this study, we push the limits of various highly sensitive IR
microscopy techniques in order to probe the electromagnetic radiation of antennas made of a single or a few
elements, and to understand the fundamental interactions between them.

Fig. 1 (a) Schematic illustration of the MIM pair and the IR-SMS technique. Inset: SEM image of the sample, the scale bar is 1 µm. (b) Measured
thermal emission spectra of the MIM pair for different gaps g. (c) FDTD calculations of emission cross-sections corresponding to themeasurements. The inset shows a sketch of the dimer geometry showing two of the hybrid modes of the MIM pair, for electric field polarizations
parallel and perpendicular to the dimer axis. The positive (+) and negative (-) signs indicate the surface charge distribution [2]. (d) Schematic
illustration of the 3x3 element antenna geometry and the angle-resolved microscope reflectivity setup.

Using infrared spatial modulation spectroscopy (IR-SMS) [1] we have studied the coupling effects between an
asymmetric pair of thermally excited metal-insulator-metal (MIM) antennas [2]. The geometry of the experiment issketched in Fig. 1(a). It is found that for tiny gaps (g ≤ 100 nm) the two gold patches of the MIM antennas form adimer pair and a splitting starts to form in the resonance peak between 7 and 8 µm of the pair’s thermal emission
spectrum (Fig. 1(b), red curve). The obtained splitting is a direct result of the simultaneous excitation of the hybrid
bonding and anti-bonding modes of the dimer [3], shown in the inset of Fig. 1(c). This striking result shows thatvarious coupled modes of a single nano-antenna can be simultaneously excited by thermal fluctuations, anessentially incoherent process arising from fluctuating thermal currents.
Next, we investigate the electromagnetic radiation of a more complex two-dimensional 3x3 element antenna
structure made up of 9 patch MIM antennas in near-field interaction (Fig. 1 (d)). Through angle-resolved
microscope reflectivity measurements, it is found that in contrast to a single patch MIM antenna, the 3x3 element
antenna structure exhibits an angularly dependent optical response. The non-symmetrical optical properties
exhibited by the geometrically symmetric 3x3 antenna structure is a direct consequence of the near-field interaction
among its elements, which we probe via a scattering type scanning near-field optical microscope [4].
References[1] Li, C., et al. , 2018. Phys. Rev. Lett. 121(24), 243901.
[2] Abou-Hamdan, L., et al. 2021. Opt. Lett. 46(5), 981-984.
[3] Nordlander, P., et al., 2004. Nano lett. 4(5), 899-903.
[4] Abou-Hamdan, L., et al. (In preparation)