Nano-optical and photocurrent characterization of WSe2/MoSe2
heterostructures
Thomas Darlington1, Emanuil Yanev1, Kevin W.C. Kwok2, Xuehao Wu3, Natalie Fardian-Melamed1, Abhay N.
Pasupahy3, James C. Hone1, P. James Schuck1
1. Department of Mechanical Engineering, Columbia University, New York, USA
2. Department of Electrical Engineering, Columbia University, New York, USA
3. Department of Physics, Columbia University, New York, USA
Email: td2583@columbia.edu, pjs2191@columbia.edu

The stacking of two-dimensional (2D) crystals represent a new frontier in materials engineering, offering a
degree of control that is not possible with bulk materials. Through choice of 2D material and their twist orientation,
fundamental materials parameters can be tuned, such as the bandgap and nonlinear susceptibility. Among the most
exciting phenomena currently being studied are effects that arise due to the moiré lattice formed between twisted 2D
layers.1,2 For the Mo- and W- transition metal dichalcogenide (TMD) semiconductors, excitons can become trappedin moiré potential wells, resulting in so-called moiré excitons. However, to date, the existence and properties ofmoiré excitons have only been inferred spectroscopically due to the sub-wavelength nanoscale nature of moiré
lattices in these materials. Real-space nano-optical imaging of moiré excitons has proven difficult due to theinherently low oscillator strength of interlayer excitons and poor alignment of exciton transition dipoles with theantenna mode of common nano-optical probes.3
In this presentation, I will show our recent efforts to resolve moiré physics in twisted MoSe2/WSe2 heterobilayers. With combined nano-Raman and nano-photocurrent measurements, we resolve features consistent withdomain wall reconstruction known to occur in low-angle twisted TMD heterostructures. Further, we measure sizable
photocurrents when pumping at zero bias, which correlates with tip enhanced nano-Raman scattering, suggesting astrong interaction of the interlayer exciton and gap-mode plasmonic mode. Our results demonstrate the feasibility of
direct imaging of moiré exciton properties at room temperature at their native length scales and show the potential
for new optoelectronic phenomena in TMDs.

References:[1] Tran, K. et al. 2019, Nature 567, 71.
[2] Rosenberger, M. R. et al. 2020. ACS Nano 14, 4550-4558.
[3] Sigl, L. et al. 2022, Phys. Rev. B 105, 035417.

Ultrabroadband nanocavity of hyperbolic phonon polaritons in 1D-like
α-MoO3Ingrid D. Barcelos1, Thalita A. Canassa2, Rafael A. Mayer1,3, Flavio H. Feres1,3, Eynara G. de Oliveira4, AlemMar B. Goncalves2, 4, Hans A. Bechtel5, Raul O. Freitas1, Francisco C. B. Maia1, Diego C. B. Alves2,41

Brazilian Synchrotron Light Laboratory (LNLS), Brazilian Center for Research in Energy and Materials (CNPEM), Zip Code 13083-970,
Campinas, Sao Paulo, Brazil.
2
Instituto de Química, Universidade Federal de Mato Grosso do Sul (UFMS), Zip Code 79070-900, Campo Grande, Mato Grosso do Sul, Brazil.
3
Physics Department, Gleb Wataghin Physics Institute, University of Campinas (Unicamp), 13083-859 Campinas, Sao Paulo, Brazil
4
Instituto de Física, Universidade Federal de Mato Grosso do Sul (UFMS), Zip Code 79070-900, Campo Grande, Mato Grosso do Sul, Brazil.
5
Advanced Light Source, Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA.
E-mail: Ingrid.barcelos@lnls.br

Polaritons, which are quasiparticles composed of a photon coupled to an electric or
magnetic dipole, are a major focus in nanophotonic research of low-dimensional materials.
Polaritons can be active in a broad range of the electromagnetic spectrum (meVs to eVs) and exhibit
momenta much higher than the corresponding free-space radiation. Hence, the use of highmomentum broadband sources or probes is imperative to excite those quasiparticles and measure
the frequency-momentum dispersion relations, which provide insights into polariton dynamics.
Synchrotron infrared nanospectroscopy[1] (SINS) is a technique that combines the nanoscale spatial
resolution of scattering-type scanning near-field optical microscopy with synchrotron infrared
radiation, making it highly suitable to probe and characterize a variety of polaritons. Here, theadvances enabled by SINS on the study of key different types of polaritons from the THZ to midinfrared will be described[2,3]. In this work, I will exploit the polaritonic response of α-MoO3
nanobelts, with reduced dimensionality approaching “1D-like”. The polaritons in α-MoO3
nanobelts feature Fabry-Perot (FP) resonances, primarily from type I HP2s in the 970-1100 cm-1
range. The modes show dependence on the geometric form factor (thickness and width) of the
nanobelt and propagate along the [100] crystal direction. In the same crystalline axis, we also show
the first infrared nanoimages of type I polaritonic modes in the far-IR band extending from 440 to
490 cm-1. Those analyses are confirmed by a robust convergence among experiment and numericalsimulations[3]. Hence, α-MoO3 nanobelts are presented as an HP2 nanocavity directly synthesized
without the need of lithography or other post-synthetic sculpting processes. This low-dimensionalpolaritonic material opens new avenues for integrated planar IR photonics, dictating polaritonscontrol and nanoresonators for phonon-enhanced molecular vibrational spectroscopy.
References:[1]
I. D. Barcelos, et al; Adv. Opt. Mater. 2020, 8, 1.
[2]
I. D. Barcelos, et al; ACS Photonics 2018, acsphotonics.7b01017.
[3]
F. H. Feres, et al; Nat. Commun. 2021, 12, 1.

Active Tuning of Highly Anisotropic Phonon Polaritons in Van der Waals
Crystal Slabs by Gated Graphene
Gonzalo Álvarez-Pérez1,2,3, Arturo González-Morán4, Nathaniel Capote-Robayna4, Kirill V. Voronin5, Jiahua
Duan1,2, Valentyn S. Volkov5, Pablo Alonso-González1,2, and Alexey Y. Nikitin4,6
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. Donostia International Physics Center (DIPC), Donostia-San Sebastián 20018, Spain
5. Center for Photonics and 2D Materials, Moscow Institute of Physics and Technology, Dolgoprudny 141700, Russia
6. IKERBASQUE, Basque Foundation for Science, Bilbao 48013, Spain.
E-mail: gonzaloalvarez@uniovi.es

Phonon polaritons (PhPs)─lattice vibrations coupled to electromagnetic fields─in highly anisotropic media [1-4]display a plethora of intriguing optical phenomena, including ray-like propagation, anomalous refraction [5], andoptical topological transitions [6], among others, which have potential for unprecedented manipulation of the flow oflight at the nanoscale. However, the properties of these PhPs are intrinsically dictated by the anisotropic crystal
structure of the host material [6-8]. Although in-plane anisotropic PhPs can be steered, and even canalized, by twisting
individual crystal slabs in a van der Waals (vdW) stack [9-12], active control of their propagation via external stimuli,
key for their implementation in nano-optical technologies, presents a significant challenge.
Here [13], we report a technology in which anisotropic PhPs supported by biaxial vdW slabs can be tuned actively
and in-situ by integrating a gated graphene layer. Excitingly, we predict active tuning of optical topological transitionsof the polaritonic IFCs (the optical version of Lifshitz transitions in electronic systems), which enable controlling lowloss canalization of PhPs along different in-plane directions in both single slabs and twisted heterostructures (Fig. 1).
Our theoretical and numerical results demonstrate that such tunable topological transitions, leading to canalization ofpolaritons, are highly dependent on the Fermi level of charge carriers in graphene. Therefore, by simply applying a
voltage, the in-plane canalization direction can be controlled in a wide range of angles, opening the door to steer
infrared light along specific directions on demand. Excitingly, the propagating properties of the resulting hybrid
polaritons, such as propagation length or lifetime, key for applications requiring long-lived light-matter interactions
such as strong coupling or mid-infrared (bio)sensing, are not undermined by the ohmic losses in graphene. Apart fromtheir fundamental relevance, our findings pave the way to obtaining optical topological transitions not only actively
tunable but also electrically, enabling the integration of anisotropic PhPs with dynamically controllable properties in
nano-optoelectronic studies and devices, such as sensors and photodetectors.

Fig. 1. Phonon polaritons supported by biaxial van der Waals slabs can be tuned actively and in-situ by integrating a gated graphene
layer. This enables to guide nanolight along very specific directions by simply applying an external voltage.

References[1] Dai, S.; et al. 2014. Science 343,1125.
[2] Caldwell J. D.; et al. 2014. Nat. Commun., 5, 5221.
[3] Ma, W.; Alonso-González, P.; Li, S.; et al. 2018. Nature, 562, 557−562.
[4] Ma, W.; Hu, G.; Hu, D.; Chen, R.; et al. 2021, Nature 596, 362–366.
[5] Duan, J.; Álvarez-Pérez, G.; et al. 2021. Nat. Commun., 12, 4325.
[6] Duan, J.; Álvarez-Pérez, G.; et al. 2021. Sci. Adv., 7, eabf2690.
[7] Álvarez-Pérez, G.; Voronin, K. V.; et al. 2019. Phys. Rev. B, 100, 235408.
[8] Álvarez-Pérez, G.; et al. 2020. Adv. Mater., 32, 1908176.
[9] Duan, J.; et al. 2020. Nano Lett., 20, 5323–5329.
[10] Hu, G.; et al. 2020, Nature, 582, 209−213.
[11] Zheng, Z.; et al. 2020, Nano Lett. 20, 5301−5308.
[12] Chen, M.; et al. 2020, Nat. Mater. 19, 1307−1311.
[13] Álvarez-Pérez, G.; González-Morán, A.; et al. 2022. ACS Photonics. DOI: 10.1021/acsphotonics.1c01549.

Twist-tunable polaritonic nanoresonators
O. G. Matveeva1†, A. I. F. Tresguerres-Mata2†, R. V. Kirtaev1, K. V. Voronin1,
J. Taboada-Gutiérrez2,3, C. Lanza-García2, J. Duan2,3, J. Martín-Sánchez2,3, V. S. Volkov1,4, P. AlonsoGonzález2,3*, A. Y. Nikitin5,6*
1. Center for Photonics and 2D Materials, Moscow Institute of Physics and Technology, Dolgoprudny 141700, Russia
2. Department of Physics, University of Oviedo, Oviedo 33006, Spain
3. Center of Research on Nanomaterials and Nanotechnology, CINN (CSIC-Universidad de Oviedo), El Entrego 33940, Spain
4. GrapheneTek, Skolkovo Innovation Center, Moscow 143026, Russia
5. Donostia International Physics Center (DIPC), Donostia/San Sebastián 20018, Spain
6. IKERBASQUE, Basque Foundation for Science, Bilbao 48013, Spain
E-mail: pabloalonso@uniovi.es† These authors contributed equally to this work

Optical nanoresonators are fundamental building blocks in a number of nanotechnology applications (e.g. inspectroscopy) due to their ability to efficiently confine light at the nanoscale. Recently, nanoresonators based on the
excitation of phonon polaritons (PhPs) – light coupled to lattice vibrations – in polar crystals (e.g. SiC, or h-BN) haveattracted much attention due to their strong field confinement, high quality factors, and potential to enhance thephotonic density of states at mid-infrared (IR) frequencies [1]. Here, we go one step further by introducing PhPs
nanoresonators that not only exhibit these extraordinary properties but also incorporate a new degree of freedom: twist
tuning, i.e. the possibility to be spectrally controlled by a simple rotation (Fig. 1a). To that end, we both take advantageof the low-loss in-plane hyperbolic propagation of PhPs in the van der Waals crystal -MoO3 [2], and realize adielectric engineering of a pristine -MoO3 slab placed on top of a metal ribbon grating, which preserves the highquality of the polaritonic resonances. By simply rotating the -MoO3 slab in the plane (from 0 to 45º), we demonstrateby far- and near-field measurements that the narrow polaritonic resonances (with quality factors Q up to 200) can betuned in a broad range (up to 32 cm-1, i.e. up to ̴ 6 times its full width at half maximum, FWHM ̴ 5 cm-1) (Fig. 1b).
Our results open the door to the development of tunable low-loss nanotechnologies at IR frequencies with applicationin sensing, emission, or photodetection.

abFig. 1 PhPs nanoresonators in -MoO3 defined by placing a pristine -MoO3 slab on top of metal ribbons. a. Schematics of thestudied structure that allows defining the nanoresonators by “dielectric engineering” and controlling them by a twist angle, . b.
Measured relative reflection spectra, R for twist angles  =0,15,30 and 45º.

References[1] Li, Peining. et al., 23 Feb 2018, Science, Volume 359, 892-896.
[2] Ma, W. et al., 25 Oct 2018, Nature, Volume 562, 557-562.

Super-resolved identification of nanoscale defects in low-dimensional
materials by near-field photoluminescence mapping
Jiatai Huang, Benfeng Bai, Pengyi Feng, Tong Cui, and Hong-Bo Sun

State Key Laboratory of Precision Measurement Technology and Instruments, Department of Precision Instrument, Tsinghua University,
Beijing 100084, China
E-mail: hjt20@mails.tsinghua.edu.cn

Low-dimensional materials, especially Monolayer transition-metal dichalcogenides, have emerged as potential
candidate materials for next-generation ultra-thin optoelectronics devices. The quality inspection and control in the
production of such materials are crucial for their applications, including the detection and identification of the spatial
heterogeneity caused by various nanoscale defects.
Here we provide a super-resolved defects identification method based on scanning near-field optical microscopy(SNOM) to explore the photoluminescence (PL) distribution of transferred monolayer WS2 with sub-diffraction
spatial resolution (140 nm) in a large range (10×10 um2) in ambient environment. By performing topography
mapping and photoluminescence nanospectroscopy, the nature of different nanoscale defects in monolayer WS2,
such as the stack, bubble, and wrinkle, can be identified through their light emission properties, which strongly
correlate with exciton emission modulation and tensile strain arose from local structural deformations.
According to our study, the PL intensity drops down sharply at the stack region because of the direct-to-indirect
bandgap transition when 1L-WS2 increases to multi-layer[1]. In the bubble region, the peeling off of WS2 from thesubstrate and the water molecules trapped inside the bubble induce a relative p-doping effect[2], leading toaccumulation of holes in the transferred monolayer WS2 with electrical neutrality and resulting in the enhancementof the AT emission and weakening of the A0 emission. The resonance peak showed relative enhancement and redshift of about 60% and 5 nm (~15 meV) in the peak of the wrinkle. With the help of high-resolution PL mapping
passed above the wrinkle, the red-shift of the PL peak can ascribe to the modified band structure due to the tensile
strain induced by the structural deformation[3], and the enhancement of PL intensity at wrinkle peak can be
explained by exciton funneling effect[4] since the photo-generated excitons tend to drift to the lower bandgap region.
(a)

(b)

(c)

Fig. 1 (a) Schematic of the near-field PL measurement system with a pyramid SNOM probe. A WS2 sample is excited by a focused 532 nm laser
beam through the probe, and the PL signal is collected by a high numerical aperture (NA) objective. The inset shows the optical image of theworking probe acquired by a charge-coupled device (CCD), where a focused beam spot is seen. (b) Near-field PL mapping of the sample withintegral from 614 nm to 634 nm. (c) near field spectra of various defects in monolayer WS2.

The presented approach and results deepen the understanding of the spatial emission behaviors in monolayer
TMDs and provided a powerful tool for the identification of different local nanoscale defects in low-dimensional
materials, which could be necessary for next-generation ultra-thin optoelectronics devices.
References[1] K. F. Mak, C. Lee, J. Hone, J. Shan, 202 and T. F. Heinz, “Atomically thin mos(2): a new direct-gap semiconductor,” Phys Rev Lett 105,
136805 (2010).
[2] Y. Lee, S. J. Yun, Y. Kim, M. S. Kim, G. H. Han, A. K. Sood, and J. Kim, “Near-field spectral mapping of individual exciton complexes ofmonolayer ws2 correlated with local defects and charge population,” Nanoscale 9, 2272–2278 (2017).
[3] D. J. Trainer, Y. Zhang, F. Bobba, X. Xi, S. W. Hla, and M. Iavarone, “The effects of atomic-scale strain relaxation on the electronic
properties of monolayer mos2,” ACS Nano 13, 8284–8291 (2019).
[4] A. Castellanos-Gomez, R. Roldan, E. Cappelluti, M. Buscema, F. Guinea, H. S. van der Zant, and G. A. Steele, “Local strain engineering inatomically thin mos2,” Nano Lett 13, 5361–6 (2013).

Nano-PL mapping of room-temperature strain-localized excitons in arrayguided nanowrinkles
Emanuil S. Yanev1, Thomas P. Darlington1, Matthew Strasbourg2, Nicholas J. Borys2, James C. Hone1, P.
James Schuck1
1. Columbia University, 550 W 120th St, New York, NY 10027
2. Montana State University, 1325 S 6th Ave, Bozeman, MT 59715
emanuil.yanev@columbia.edu

Since their discovery, two-dimensional (2D) materials have garnered much interest in the condensed matter
community, both as platforms to investigate new physics, and as promising candidates for a variety of technologicaladvances. Notably, their reduced dimensionality and tunable properties offer intriguing potential for applications inquantum systems and quantum information science. The strain-controlled single-photon emitters (SPEs) observed in
2D semiconductors provide several advantages over SPEs in other materials, which tend to be limited in wavelength
tunability, deterministic spatial control, and integrability with other device components.
Motivated by our previous nano-optical studies of strain-localized quantum-dot-like states in tungsten diselenide(WSe2) [1], this work explores strain-directed and controlled localized emission with the potential of realizing
tunable SPEs at room temperature. Here, monolayer sheets of WSe2 are transferred onto lithographically patterned
arrays of sharp conical structures. Owing to the low defect density and single crystal nature of this material, it is able
to strongly conform to the substrate features without breaking. In doing so, nanoscale wrinkles are formed aroundand in-between the cones, with directionality clearly influenced by the array lattice. These highly strained regions
can effectively localize excitons, as evidenced by near-field mapping (Figure 1b), and produce similar low-energy
emission to that seen in our previous work on nanobubbles [1]. A host of sharp spectral features emerge from theseareas at low temperatures, which suggests that the emission is quantum in nature and tunable with strain.

ab

250 nm

250 nmcFig. 1. (a) AFM topography of wrinkles in monolayer WSe2 on a patterned substrate. (b) Hyperspectral map of the same region
showing integrated emission intensity between 780-900 nm. Colored crosses and arrows indicate the locations of the selected
spectra shown in (c).

References[1] Darlington, T.P., Carmesin, C., Florian, M., Yanev, E.S. et al. 2020. Nat. Nanotechnol, 15, 854-860.

Tip-enhanced nano-imaging and control of dark excitons in WSe2
Kathryn Hasz1, Zucheng Hu1, Kyoung-Duck Park2, and Markus B. Raschke1
1. Department of Physics, and JILA, University of Colorado, Boulder, CO 80303, USA.
2. Department of Physics, Ulsan National Institute of Science and Technology (UNIST)Ulsan 44919, Republic of Korea
E-mail: kathryn.hasz@colorado.edu

Formatted: Space After: 8 pt
Formatted: Bottom: 2.03 cm
Formatted: Line spacing: single
Formatted: Space After: 6 pt, Line spacing: single

Dark excitons in transition metal dichalcogenides provide new opportunities for optoelectronic devices due to theirlong lifetimes. SThe strong spin-orbit coupling causes the conduction band to split (Fig. 1a), with the dark state notoptically active due to a forbidden spin transition, making it difficult to access spectroscopically. It To date, it has
primarily been detected using strong magnetic fields at low temperatures to tip the spin to allow for a some degree of
optical emission.
Using tip- enhanced photoluminescence (TEPL), we are able to optically detect and control the dark exciton XD
emission as demonstrated in WSe2. A Here, a gold tip acts as a nanoantenna with polarization parallel to the tip tocouple with the out-of-plane moment of the dark exciton (Fig. 1b) [1]. In contrast, pPerpendicular polarization issenses only preferentially sensitive to the in-plane moment and thus does not show darkbright moment of the bright
excitons X0. The A tip-sample pico-cavity coupling with the out-of-plane moment allows for Purcell enhancement of≥2x103 ahow much?d Allows for efficient XD emission of the dark exciton even at room temperature (Fig. 1c);, andby dynamically controlling the tip-sample distance and associated pico-cavity mode volume we modulate the relative
strengths of dark and brightX0 and XD emission [2].
RecentPrevious work has demonstrated the ability to detect a dark exciton signal through a pico-cavity with local
probe spectroscopy [1]. fFar- field studies have detected evidence of dark excitons, they yet intrinsically provide only
a spatial average that would obscures any surface heterogeneities. In order to study and control spatial heterogeneity
in dark exciton behavior as also desirable for exciton condensation [3], and associated with nano-bubbles [4] andedges, here we extend this workwe perform correlated to TEPL dark exciton nano-imaging with AFM force
spectroscopy with few nanometer spatial resolution.

Formatted: Space After: 0 pt

FIGURE 1: (a) Split-band configurations of bright and dark exciton states. (b) Schematic of TEPL setup. (c) Bright Tip-sample
distance dependence of bright excitonexciton intensity (red dash) increases as tip-sample distance decreases andwith emergenceof pico-cavity enhanced emission of dark exciton satellite peak of the dark exciton (blue dash) in Wse2 appears. (d) Bright exciton
intensity increases before contact, with dark exciton intensity increasing after contactDistinct distance dependence reflecting
enhancement and quenching reflecting different X0 and XD lifetimes. (e)(e) Pico-cavity Intensity shows spatial variation.XD TEPL
nano-imaging of nano-bubbles of WSe2 showing spatial heterogeneity of XD emission with <10 nm spatial resolution.

Formatted: Space Before: 0 pt

As seen in Fig. 1c, we see an enhancement of the main Bbright exciton peak (1.65 eV) and a satellite peakcorresponding to the dark excitons (1.61 eV) exhibit characteristic tip-sample distance dependent behavior (Fig. 1c)with long range field enhancement for X0, followed by short range pico-cavity induced emission of XD, transitioning
into non-radiative quenching, with relative intensities and characteristic length scales controlled by the competition
between Purcell-enhancement, relative lifetimes, temperature activated conversion of XD to X0 population, and nonradiative quenchingas the tip approaches the sample surface. The bright exciton peak intensity increases dramaticallystarting 5-10 nm before the sample surface then begins to quench upon contact, The data are modelled using coupled
rate equations [2], and correlated with where contact is defined as the point at which the force on the cantilevertransitions from the attractive to repulsive regime (Fig. 1d). In contrast, the dark exciton signal emerges right at the
sample surface and increases in intensity for the next 5-10 nm in which force is being applied. It then also begins toquench. We also see aspectral redshifts of both the bright and dark exciton under an applied force, which further allows
to relate tip-induced to sample built in local strain suggesting strain as a mechanism to perturbing the excitonic
emission in TMD monolayers.
We then image the spatial heterogeneity of the dark exciton intensity revealing . There is a clear variation in strength
X0 and XD emission of the detected dark exciton intensity (Fig. 1e), on few-nanometer length scales, with the strongest
XD intensity occurring around the peakcorrelating in intensity with topographic of nano- of nanoscale bubbles in WSe2
on Au. Au? What substrate?. The highly strained and non-equilibrium stress state a of WSe2 nano-bubbles have

Formatted: Font: Bold

Formatted: Indent: First line: 0 cm, Space After: 0 pt
Formatted: Font: Bold
Formatted: Highlight
Formatted: Font: Bold
Formatted: Indent: First line: 0 cm

Formatted: Indent: First line: 0 cm, Space After: 0 pt
Formatted: Font: Bold

Formatted: Space After: 0 pt
Formatted: Font: Bold
Formatted: Highlightpreviously shown a strain-localized exciton developing at nano-bubble edges [5], but the detected intensity of the dark
exciton is not confined to the nano-bubble edges.t the nano-bubbles along with potential polymeric residue could
increase light scattering, strengthening the detected intensity of the dark exciton signal. … what do you intend to say?
I believe there was a paper by Jim Schuck maybe 2-3 years ago who imaged the bright exciton in TEPL and sees
emission correlated with the periphery of the bubbles where they strain is largest. I would check into that, in factinclude this references, and maybe say that dark exciton emission of bubbles is different from bright excition emission.
In summary, in full spatio-spectral nano-imaging of we image and detect dark excitons in WSe2 w. We resolve spatial
heterogeneities in both intensity and energy associated with bubbles, and edges, and correlated with local internal andapplied strain . By applying strain, we actively change the intensity and energy of the brightswitching and controllingand dark exciton emission. With better understanding of the sample, structural, and tip-plasmonic coupling conditions
for dark excitons , they become more accessible candidates for new optoelectronic applications.
References[1] K. D. Park, et al. “Radiative control of dark excitons at room temperature by nano-optical antenna-tip Purcell effect,” Nat. Nanotechnol, 13,
59-64 (2018).
[2] M. A. May, et al. “Nanocavity Clock Spectroscopy: Resolving Competing Exciton Dynamics in WSe2/MoSe2 Heterobilayers,” Nano Lett. 21,
522-528 (2020).
[3] M. Combescot, et al. “Bose-Einstein Condensation in Semiconductors: The Key Role of Dark Excitons,” Phys. Rev. Let, 99, 176403 (2007).
[4] M. Rahaman, et al. “Observation of Room-Temperature Dark Exciton Emission in Nanopatch-Decorated Monolayer WSe2 on Metal
Substrate,” Adv. Opt. Mat. 9, 2101801 (2021).
[5] T. P. Darlinton, et al. “Imaging strain-localized excitons in nanoscale bubbles of monolayer WSe2
at room temperature,” Nat. Nanotechnol. 15, 854 (2020).

Formatted: Highlight
Formatted: Highlight
Formatted: Indent: First line: 0 cm, Space After: 0 pt

Formatted: Font: Not Bold
Formatted: Space Before: 0 pt

[1] Park, K. D.; Jiang, T.; Clark, G.; Xu, X.; and Raschke, M. B. 2018. Nat. Nanotechnol, 13, 59.
[2] May, M. A.; Jiang, T.; Du, C.; Park, K. D.; Xu, X.; Belyanin, A.; and Raschke, M. B. 2020. Nano Lett. 21, 522.
[3] Combescot, M.; Betberder-Matibet,O.; and Combescot, R. 2007. Phys. Rev. Lett, 99, 176403.
[4] Rahaman, M.; Selyshchev, O.; Pan, Y.; Schwartz, R.; Milekhin, I.; Sharma, A.; Salvan, G.; Gemming, S.; Korn, T.; and Zahn, D.R.T. 2021.
Adv. Opt. Mat. 9, 2101801.

Formatted: Normal

References: add titles, and if not enough space, abbreviate authors as First author, et al.

Formatted: Font: Not Bold, Highlight

Formatted: Font: 11 pt

Formatted: Font: Not Bold

Effects of the Dielectric Environment on the Propagation of Phonon Polaritonsin Twisted Polaritonic Slabs
Aitana Tarazaga Martín-Luengo1, Jiahua Duan1, Christian Lanza1, Javier Taboada-Gutiérrez1, GonzaloÁlvarez-González1, Ana Isabel F Tresguerres‐Mata1, Javier Martín-Sánchez1, Alexey Y. Nikitin2, Pablo
Alonso-González1
1. University of Oviedo, Department of Physics c/ García Lorca, Oviedo, Spain
2. Donostia International Physics Center (DIPC), Donostia-San Sebastián, Spain.
E-mail: aitana555@gmail.com

Phonon polaritons (PhPs) -hybrid light-matter excitations- in van der Waals (vdW) materials present very
interesting properties for applications in nanooptics such as high field confinement, low losses and in-plane highly
anisotropic propagation [1-3]. Recently, it was shown that by stacking two slabs of α-phase molybdenum trioxide (αMoO3) van der Waals material, the propagation of the polaritons along the surface of the top slab can be controlled.
Specifically, guiding of PhPs along predetermined directions can be obtained for certain critical twisting angles
between the relative crystal directions of the two slabs [4,5]. On the other hand, the propagation of PhPs in a α-MoO3
slab is strongly affected by the surrounding dielectric environment, as the propagation direction can be switched alongpreviously forbidden directions by inducing a topological transition when the slab is placed on a substrate with a given
negative permittivity (the case of silicon carbide) [6].
In this work, we realize combined optical near-field and numerical simulation studies on twisted slabs of α-MoO3
on a silicon carbide substrate. Particularly, we study the dependence of the relative crystal axes orientation between
the two slabs on the propagation of the PhPs, and as a function of the illumination frequency. We find a topologicallyinduced transition in the propagation of PhPs along the surface of the bilayer from a nearly isotropic regime to a highly
anisotropic ray-like propagation. Our results provide in-depth fundamental knowledge about the propagation of PhPs
in twisted slabs placed on different dielectric environments.
References[1] Dai,S., Fei, Z., Ma, Q., Rodin, A.S., Wagner, M., McLeod, A.S., Liu, M.K., Gannett, W., Regan, W., Watanabe, K, Taniguchi, T., Thiemens,M., Dominguez, G., Castro Neto, A.H., Zettl, A., Keilmann, F., Jarillo-Herrero, P., Fogler, M.M., Basov, D.N. 2014. Science, 343, 1125.
[2] Ma, W., Alonso-González, P., Li, S., Nikitin, A.Y., Yuan, J., Martín-Sánchez, J., Taboada-Gutiérrez, J., Amenabar, I., Li, P., Vélez, S., Tollan,C., Dai, Z., Zhang, Y., Sriram, S., Kalantar-Zadeh, K., Lee, S.T., Hillenbrand, R., Bao, Q. 2018. Nature, 562, 557.
[3] Zheng, Z., Xu, N., Oscurato, S.L., Tamagnone, M., Sun, F., Jiang, Y., Ke, Y., Chen, J., Huang, W., Wilson, W.L., Ambrosio, A., Deng1, S.,
Che, H. 2019. Sci. Adv., 5, eaav8690.
[4] Duan, J., Capote-Robayna, N., Taboada-Gutiérrez, J., Álvarez-Pérez, G., Prieto, I., Martín-Sánchez, J., Nikitin, A.Y., Alonso-González, P.
2020. Nano Lett., 20, 5323.
[5] Hu, G., Ou, Q., Si, G., Wu, Y., Wu, J., Dai, Z., Krasnok, A., Mazor, Y., Zhang, Q., Bao, Q., Qiu, C.W., Alù, A. 2020. Nature, 582, 209.
[6] Duan, J., Álvarez-Pérez, G., Voronin, K.V., Prieto, I., Taboada-Gutiérrez, J., Volkov, V.S., Martín-Sánchez, J., Nikitin, A.Y., AlonsoGonzález, P. 2021. Sci. Adv., 7, eabf2690.

Brobdingnagian photon bunching in cathodoluminescence of excitonsin WS2 monolayer
Saskia Fiedler1, Sergii Morozov1,2, Leonid Iliushyn2,3, Sergejs Boroviks1,
Martin Thomaschewski1, Jianfang Wang4, Timothy J. Booth2,3, Nicolas Stenger2,5,
Christian Wolff1, and N. Asger Mortensen1,2,6

1. Center for Nano Optics, University of Southern Denmark, Campusvej 55, Odense 5230, Denmark
2. Center for Nanostructured Graphene, Technical University of Denmark, DK-2800 Kongens Lyngby, Denmark
3. Department of Physics, Technical University of Denmark, DK-2800 Kongens Lyngby, Denmark
4. Department of Physics, The Chinese University of Hong Kong, Shatin, Hong Kong SAR, China
5. Department of Photonics Engineering, Technical University of Denmark, DK-2800 Kongens Lyngby, Denmark
6. Danish Institute for Advanced Study, University of Southern Denmark, Campusvej 55, DK-5230 Odense M, DenmarkE-mail: semo@mci.sdu.dk

Cathodoluminescence spectroscopy in conjunction with second-order auto-correlation measurements of 𝑔𝑔2 (𝜏𝜏)allows to extensively study the synchronization of quantum light sources in low-dimensional structures [1]. Co-existing
excitons in two-dimensional transition metal dichalcogenide monolayers provide a great source of identical quantum
emitters which can be simultaneously excited by an electron. In this article, we demonstrate large photon bunchingwith 𝑔𝑔2 (𝜏𝜏) up to 156±16 of a tungsten disulfide monolayer, exhibiting a strong dependence on the electron-beamcurrent density. To further improve the excitation synchronization and the electron-emitter interaction, we show
exemplary that the careful selection of a simple and compact geometry - a thin, monocrystalline gold nanodisk - canbe used to realize a record-high bunching 𝑔𝑔2 (0) of up to 2152±236 [2]. This approach to control the electron excitationof excitons in a WS2 monolayer allows for the synchronization of quantum emitters in an ensemble, which is importantto further advance quantum information processing and computing technologies.

.

Fig. 1 a Artistic view for generation of highly bunched light. A high-energy electron generates multiple electron-hole pairs in hBN
sandwich, which experience synchronized radiative recombination in the WS2 monolayer. b Strong photon bunching in hBNencapsulated WS2 monolayer and the same structure with a gold nanodisk measured at the same electron beam current (8 pA) andacceleration voltage (30 kV). c The photon bunching amplitude 𝑔𝑔2 (0) is limited by the lowest electron beam current attainable by
the instrument, while the addition of a gold nanodisk can further boost 𝑔𝑔2 (0) through the local manipulation of electron beam
current.

References[1] Meuret S., Adv. Imaging Electron Phys. 215, 47 (2020).
[2] Saskia Fiedler, Sergii Morozov. Leonid Iliushyn. Sergejs Boroviks, Martin Thomaschewski, Jianfang Wang, Timothy J. Booth, Nicolas
Stenger, Christian Wolff, and N. Asger Mortensen, arXiv:2111.07596, (2021).

In-situ optical tracking of memristive switching in 2D materials
Joanna Symonowicz1,2, Giuliana Di Martino1
1. Department of Materials Science and Metallurgy, University of Cambridge, Cambridge, UK
2. Cavendish Laboratory, University of Cambridge, Cambridge, UK
E-mail: jks68@cam.ac.uk

Up to 80% of the computing energy is consumed in the data-transfer between logic and memory units [1]. Resistive
switching memories enable modern in-memory computing architectures, where memory and logic are no longer
separated, avoiding inefficient shuttling of information. Materials suitable for memristive switches are thus in highdemand and among the contenders are MoS2 and h-BN nanosheets. However, their switching mechanisms are still
debated [2,3].
In our work, we tightly confine light, i.e. plasmonic hotspots, within the electrically switched nanosheets [4]. This
allows to optically track in-situ and in real-time morphological changes happening in nanoscale Au/MoS2/Au andAu/h-BN/Au memristive cells. This novel non-destructive and fully optical technique enables Raman, darkfield
scattering, and photoluminescence analysis from single-digit nanometer areas, hence providing unprecedented insights
into the underlaying mechanism of the MoS2 and h-BN memristive switching.

Fig. 1 A schematics of our technique used to optically track morphological changes occurring in nanosheets upon voltage changes.

References[1] Miller, D. A. B. (2009) IEEE Proceedings 97, 7, 1166.
[2] Hus, S. et al., (2021) Nature Nanotechnology 16, 58–62.
[3] Ge, R. et al., (2020) Advanced Materials 33, 7, 2007792.
[4] Di Martino, G. et al., (2020) Nature Electronics 3, 687.

Orientation-Dependent Interaction between the Magnetic Plasmons in Gold
Nanocups and the Excitons in WS2 Monolayer and Multilayer
Ruoqi Ai, Xinyue Xia, Jianfang Wang*
Department of Physics, The Chinese University of Hong Kong, Shatin, Hong Kong SAR, China
E-mail: jfwang@phy.cuhk.edu.hk

Typically, a quantum emitter in free space cannot interact strongly with photons due to the large mismatch between
the emitter size and the light wavelength. Metallic nanostructures, which can support localized surface plasmon
resonances and concentrate light into the sub-wavelength scale, are highly potential candidates for enhancing thelight–matter interactions [1]. The interaction between plasmons in metal nanostructures and excitons in twodimensional transition-metal dichalcogenides has attracted tremendous attention due to its fundamental importance incavity quantum-electrodynamics research and great potential in quantum information applications [2]. In this work,
we investigate the interaction between the magnetic plasmons in differently orientated Au nanocups and excitons in
WS2 monolayer and multilayer (Fig. 1a). By varying the orientation and size of the Au nanocups, spectral overlap
between the magnetic plasmon mode of the Au nanocups and the excitons of WS2 monolayer is achieved (Fig. 1b and1c, upper and middle panel). Different resonance coupling regimes have been reached with the individual nanocups
by adjusting the nanocup orientation on WS2 monolayer, resulting in weak to strong coupling (Fig. 1c, lower panel).
The finite-difference time-domain (FDTD) shows that the strong coupling for the downward configuration has
benefited from the magnetic mode, which can induce the strong near-field electric enhancement in the WS2 layer andintensely interact with the in-plane excitons. By varying the diameter and opening size of the downward Au nanocup,
the magnetic plasmon resonance can be successfully adjusted to accurately match the excitons of WS2 monolayer,
giving rise to a splitting energy up to 106 meV for the magnetic plasmon–exciton system. Both the simulated scatteringand absorption spectra indicate that the system is in the strongly coupled regime. The coupling strength also increases
as the number of layers increases due to more excitons participating in the coupling. The magnitude of the couplingstrength increases with the number of layers and then saturates at ~4 layers. Our study provides a feasible approach
toward the realization of different coupling regimes in such an individual particle/exciton transition system.

Fig. 1 Fig. (a) Schematic illustrating the heterostructures composed of Au nanocups in different orientations on the WS2
monolayer. (b) SEM images of the three representative Au nanocups in the three typical orientations on WS2 monolayer. (c)Measured scattering spectra of the three differently orientated Au nanocups on the SiO2 substrate (upper), PL spectrum of WS2
monolayer (middle), and scattering spectra of the three differently orientated Au nanocups coupled to WS2 monolayer (lower),whose SEM images are shown in (b).

References[1] Hugall, J. T.; Singh, A.; Hulst, N. F. 2018. ACS Photonics. 5, 43.
[2] Torma, P.; Barnes, W. L. 2015. Rep. Prog. Phys. 78, 013901.

Manipulating the fluorescence contrast in liquid-gel phases
Jia-Ru Yu1, 2, He-Chun Chou1, Wei-Ssu Liao2, and Chi Chen12
1. Research Center for Applied Sciences, Academia Sinica, Taipei, 115, Taiwan
2. Department of Chemistry, National Taiwan University, Taipei, 106, Taiwan*e-mail: chenchi@gate.sinica.edu.tw

Fluorescence tagging of the supported lipid bilayers (SLBs) is an essential technique for imaging the particularcomponents in the biological membrane. It is generally believed that the tagged lipids would participate in the liquiddisordered (fluid) phase rather than the liquid-ordered (gel) phase. Such partition behavior of tagged lipids usually
guides the interpretation of the fluorescence-bright or dark domain on the membrane. Here, we employ our homebuilt
liquid-phase scanning near field microscopy (SNOM) to study lipid bilayers [1] (Fig. 1 (a) and (b)). A heating circuitand temperature feedback is equipped in the liquid cell for observing the movement and phase segregation of lipids
under temperature control. We can manipulate local lipid molecules from gel phase to fluid phase by the a-SNOM tip,which caused the reverse of fluorescence contrast (Fig. 1 (c)). It demonstrates that there is no preferable partition for
the fluorescence tag in the fluid or gel phases. The packing and relative motion among neighbor lipids determine thedipole orientation and lead to distinct EET efficiency between the gel and fluid phase. Our results not only reveal thefundamental issue of fluorescence tag partition but also offer a practical guide in interpreting the fluorescence contrast.

Fig. 1 (a) Schematic illustration of the homebuilt liquid-phase SNOM system. (b) Schematic illustration of a a-SNOM tip to scan
lipid bilayers. (c) The sequential a-SNOM images of the DPPC:DOPC = 1:1 SLB with 3% Texas red-DHPE fluorescence probe.
Top row is the a-SNOM topography and the bottom row is the simultaneous recorded a-SNOM fluorescence intensity map.

References[1] Yu, J.R.; Chou, H.C.; Yang, C. W.; Liao, W. S.; Hwang, I. S.; Chen, C 2020, Rev. Sci. Instrum. 910, 73703.

Imparting spectrally selective optical properties to metallic substrates throughsurface engineering
Sraboni Dey and J. Mitra
School of Physics, Indian Institute of Science Education and Research, Thiruvananthapuram-695551, India
E-mail: srabonidey20@iisertvm.ac.in

Recent advancements in nanoscience and nanotechnology have revolutionized applications of plasmonics andphotonics. Direct optical excitation of surface plasmons on nanostructures and thin films with free carriers brings
about unique ways to influence light matter interactions. Novel optical materials, innovative new devices have beendeveloped with significant potential to contribute to the growing technology [1] where degenerately doped, wide band
gap metal oxides such as Al doped ZnO, ITO, doped CdO etc can replace metals as plasmonic materials. This isenabled by their controllable carrier density that allows tuning of their dielectric to metallic transition wavelength
known as epsilon near zero (ENZ) wavelength (𝜆𝜆ENZ) [2]. A niche application of ENZ materials and their plasmonic
properties is evidenced in the development of spectrally selective coatings, where the optical property of a reflecting
metallic surface is XXX with the ability to selectively absorb light below a tailored wavelength and reflect at higher
wavelengths. Such coatings have potential applications in areas such as solar energy conversion, thermal management,
radiative cooling, smart windows etc [3]. The challenges being the overall complexity and thickness of the coatings
along with their angular dependence of their spectral selectivity.
Here we demonstrate using how surface engineering can impart spectrally selective optical properties to a ubiquitous
substrate like stainless steel (SS) from visible to near IR. The surface engineering has been executed by coating a trilayer thin film (ITO/Cr/Cr2O3) each of optimal thicknesses on SS with an elementary periodic grating of ITO
nanostructures of optimized dimensions over the substrate. Investigated from 400 – 4000 nm the coated substrateshows high average absorption (~90%) over the entire visible up to a particular wavelength λ0 beyond which thereflectivity becomes ~ 80%. In other words, the reflection coefficient is like a “step function” at that particular
wavelength λ0 (here around ~1670 nm), which is an omnidirectional feature realized between 0֩ to 60֩, as shown in Fig
1b. Importantly, λ0 can be tuned using proper selection of materials which has been showcased here through theutilization of an ENZ material i.e. ITO both in thin film and nanostructured form supported by the absorbing coating
underneath.
The focus is not only on the optical response which has been achieved but also on the roles played by the individual
building blocks of this system which has been depicted in Fig 1c. The power dissipation calculation performed forvarious wavelengths from visible to IR exhibits the contribution of the underlying Cr/Cr2O3 coatings on stainless steel
and proves its significance in bringing down the reflectivity to nearly 10% in the visible regime and also for ITO in
playing the major role as the reflector in the near IR. Overall, the opportunistic employment of these materials in theright forms and dimensions has proven to develop this unique response. Therefore, the system that has been developed
not only demands direct applications in optical devices but also exploring it from the fundamental material research
point of view.

Fig. 1a. Magnitude of electric field variation across the system, b. Simulated reflectance spectra, c. Power dissipation across different layers

References[1] Halas, Naomi J., 2010, Nano Letters, 10, 3816-3822.
[2] Johns, Ben Puthoor, Navas Meleth Gopalakrishnan, Harikrishnan Mishra, Akhileshwar Pant, Ravi Mitra, J., Journal of Applied Physics,2020,
127,043102.
[3] Li, Yang Lin, Chongjia Huang, Jingyuan Chi, Cheng Huang, Baoling,, Global Challenges, 2021,5,2000058.

Light-controlled microdroplet robot on nanophotonic substrate
Masayuki Naya1,2, Nanami Ohhara1, Akinobu Yamaguchi2 and Toshiharu Saiki1
1. Graduate school of Science and Technology, Keio University, 3-14-1, Hiyoshi, Kohoku-ku,Yokohama, Kanagawa 223-8533, Japan
2. Laboratory of Advanced Science and Technology for Industry, University of Hyogo, 3-1-2 Kouto, kamigori, Ako-gun, Hyogo 678-1205, Japan
E-mail: masa@naya-lab.com

The formation of microdroplets and their behavior are important subjects for the investigation of the origin of life
[1] and applications such as precise material transport. Recently, the artificial formation of a micro-droplet driven by
Marangoni convection, which is generated by irradiating a laser beam onto a thin film of light-absorbing liquid, hasbeen reported [2,3]. We have found that artificial droplet generation is possible even with non-light-absorbing liquid
by using light-absorbing substrates such as a GeSbTe film, a gold film, and plasmonic-films. Furthermore, we foundthat the generated droplet performs self-excited motion such as vibration and rotation.
Figure1 shows the experimental setup. By sandwiching a volatile liquid (ethanol) mixed with a small amount of
non-volatile polymer liquid (PEG) between a gold substrate and a glass substrate, a reservoir of liquid and an air gap
with wetting film are created between the substrates. A sessile droplet can be formed on a gold film surface in the air
gap area by irradiating a 532 nm CW laser spot (Fig. 2 and Fig. 3). We found that the droplet moves spontaneously
even when the laser spot is fixed. The mechanism of this phenomenon is thermal Marangoni convection due to the
local heating by the optical absorption of the gold film and the soluto Marangoni convection due to the local increaseof PEG concentration caused by evaporation of ethanol in the light-irradiated area.
Since the concentration of PEG in the droplet generated by the soluto Marangoni convection should be higher thanthat in the wetting film surrounding the droplet, the droplet formation involves liquid-liquid phase separation. The
liquid-liquid phase separation is a phenomenon, in which a polymer in a liquid moves such as due to thermalinteractions, causing the separation into a polymer-rich phase and a dilute phase [4]. It has attracted strong attention
due to its relevance to the origin and activities of life and its potential applications including drug delivery in cells.
Although inducing phase separation by chemical reaction is common, it is not applicable to generating and controlling
single droplets, making it difficult to precisely analyze the phenomenon. In contrast to this, our method enables
creation, annihilation, and transportation of single droplets at a desired position. More interestingly, we found that the
droplets exhibit spontaneous motion such as vibration and rotation. These phenomena suggest the possibility ofrealizing a droplet robot controlled by light. A possible application includes collection and transport of targeted
nanoparticles. We will also demonstrate that microdroplets can be generated by irradiating white light over a wide
area on a patterned nanophotonic substrate.

Fig.1 Experimental setup for droplet formation

References

Fig.2 Droplet formation process

Fig.3 Optical Microscope image of droplet[1] D. Twicker, R. Seyboldt, C.A. Weber, A.A. Hyman and F. Julicher, 2017, Nature Physics, 13, 408–413.
[2] N.A. Ivanova and B.A. Bezuglyi, 2007, Colloid J., 69, 735–740 .
[3] K.A. Tatosova, A.Y. Mallyuk and B.A. Bezugly, 2017, Colloid and Surface A., 521, 22–29.
[4] C.D. Keating, 2012, ACC Chem. Res. 45, 2114–2124.

“Photonics in Canada”
By: Nikki Bulgarea and Robert Corriveau, Photons Canada.

As the main organization representing the Canadian photonics industry andresearchers, Photons Canada is organizing Events like, workshops, webinars,
and networking events with the objective of increasing, fostering and accelerating
the collaboration between industry, R&D centres and university researchers
ensuring Canada growth through innovation in photonics.
In 2021, Photons Canada has initiated and developed a report looking atstrength, weakness, opportunity, and threat (SWOT) analysis for the following six
technologies in Canada:-biophotonics,-

Imaging, sensors and fusion,-Laser processing for advanced manufacturing,-

Photonics integrated circuits,-

photovoltaics and-quantum technologies.

It was concluded that these photonics technologies are present and covered in
Canada.
In 2022, we will proceed with a more detailed SWOT analysis by region:
Western Provinces, Ontario, Quebec and the Maritimes.
After an overview of the global photonics in Canada, the different aspects for theWestern Provinces SWOT analysis will be presented for an open discussion withthe participants.

Ultrasensitive analysis of nano-matter via scattering:from single proteins and viruses to sub-cellular features
Vahid Sandoghdar
Max Planck Institute for the Science of Light,
Max-Planck-Zentrum für Physik und Medizin,
91058 Erlangen, Germany
Email: vahid.sandoghdar@mpl.mpg.de
The last two decades have witnessed the insatiable potential of optical techniques for sensitive studies.
Optical detection of small nanoparticles and single molecules have often relied on fluorescence, but
limited photophysics and the need for labeling pose severe restrictions for the broad application ofthis approach. The ubiquitous process of Rayleigh scattering offers a powerful alternative. Although
the common intuition might be that detection of individual nanoparticles and single molecules is notwithin reach via the measurement of their Rayleigh scattering, interferometric scattering (iSCAT)
microscopy introduced in 2004 has demonstrated the contrary [1]. Indeed, it is now possible to reacha remarkable real-time detection sensitivity down to single unlabeled proteins [2]. In this presentation,
I will present the most recent advances in iSCAT analysis, reaching an exquisite sensitivity for detecting
single unlabeled bio-particles as light as 10 kDa [3,4]. I also discuss new results in three-dimensional
imaging and tracking of sub-cellular structures in live cells [5].
References:
1- R. W. Taylor and V. Sandoghdar,
Interferometric Scattering Microscopy: Seeing Single Nanoparticles and Molecules via Rayleigh
Scattering,
Nano Letters 19, 4827-4835 (2019).
2- M. Piliarik and V. Sandoghdar, Direct optical sensing of single unlabelled proteins and superresolution imaging of their binding sites, Nature Communications 5 4495 (2014).
3- A. D. Kashkanova, M. Blessing, A. Gemeinhardt, D. Soulat, V. Sandoghdar,
Precision size and refractive index analysis of weakly scattering nanoparticles in polydispersions,
Nature Methods 19, 586-593 (2022)
4- M. Dahmardeh, H. Mirzaalian Dastjerdi, H. Mazal, H. Köstler, V. Sandoghdar,
Self-supervised machine learning pushes the sensitivity limit in label-free detection of single proteins
below 10 kDa,
https://doi.org/10.21203/rs.3.rs-1635524/v1 (2022).
5- M. Küppers, D. Albrecht, A. D. Kashkanova, J. Lühr, V. Sandoghdar,
Confocal Interferometric Scattering Microscopy Reveals 3D Nanoscopic Structure and Dynamics inLive Cells,
https://doi.org/10.21203/rs.3.rs-1690188/v1 (2022).

High throughput imaging of thermal conductivity and interfacial thermal
conductance with nanoscale resolution
Andrea Centrone1, Mingkang Wang,1,2 Georg Ramer,1,2 Vladimir Aksyuk2
1. National Institute of Standards and Technology, Gaithersburg, MD 20899 USA
2. University of Maryland, College Park, MD 20742, USA
E-mail: andrea.centrone@nist.gov

Accurate knowledge of thermal conductivity (η) and interfacial thermal conductance (G) at the nanoscale is criticalfor engineering thermoelectrics, memristors and other advanced electronic devices and for studying thermal transport
in nanostructured or quantum materials. State of the art, time-domain thermoreflectance (TDTR) is a high signal-tonoise, pump-probe, technique that measures η and G by reconstructing the sample time-domain photothermal
expansion as a function of the probe delay time. However, TDTR spatial resolution is limited to the micrometer scaleand requires long measurement times (≈ 120 s per point), even when coating the sample with a metallic (reflective)
transducer layer to increase its sensitivity. Photothermal induces resonance (PTIR) [1,2] is a scanning probe techniquethat uses the tip on an AFM to transduce the sample photothermal expansion and to enable IR spectroscopy at thenanoscale. However, conventional AFM probes do not have sufficient sensitivity or bandwidth to capture the fastsample thermalization that could be used to extract the sample thermal properties at the nanoscale.
Here, we develop an optomechanical cantilever probe and customize PTIR setup to directly capture at once theentire time-domain sample thermal expansion dynamic due to the absorption of IR laser pulses with nanoscale
resolution. This novel setup can measure thermal dynamic events with ≈ 10 ns temporal resolution, ≈ 35 nm spatial
resolution, and high sensitivity concurrently, thanks to a very low detection noise (≈ 1 fm/Hz1/2) over a wide (> 100
MHz) bandwidth. Such high sensitivity, wide bandwidth measurement enables fast data acquisition (≈ 20 ms) andnanoimaging of η and G with a throughput ≈ 6000 × faster than macroscale-resolution TDTR and ≈ 500000 × fasterthan for measurements with conventional AFM cantilevers. This feat is achieved by improving the nanophotonic AFM
transducers design (≈ 5 × higher lateral stiffness, ≈ 3 × lower measurement noise, and ≈ 4 × larger bandwidths thanprevious attempts [3]), by integrating a novel wavelength-tunable IR excitation laser with a 200 × faster repetition rate
(200 kHz) and by developing a custom FPGA data acquisition system that digitizes and process the data at the highrates (0.8 GHz) required by fast scanning.
As a proof-of-principle demonstration, we obtain 100 × 100 pixel maps of η and G in 200 s with a small relative
uncertainty (∆η ≈ 10 % and ∆G ≈ 5 %) on a ≈ 3 µm wide polymer particle. Importantly, such measurements do not
require extensive probe calibration (as for other AFM-based measurements) or a metallic transducer layer on thesample (as for TDTR).
This work paves the way to study fast thermal dynamics in materials and devices with nanoscale resolution, whichis critical, for example, to study the thermal properties of grain boundaries and of filaments in memristive devices.
References[1] Centrone, A., Annu. Rev. Anal. Chem. 2015, 8 (1), 101-126.
[2] Kurouski, D. ; Dazzi, A.; Zenobi, R. ; Centrone, A, Chem. Soc. Rev., 2020, 49, 3315-3347[3] Cahe, J.; et al, Nano Lett. 2017, 17, 5587–5594

Bloch Surface Waves for surface enhanced Mid-Infrared spectroscopy
Raffaella Polito1, Agostino Occhicone1, Marialilia Pea2, Alberto Sinibaldi1, Francesco Mattioli2, Sara
Cibella2, Andrea Notargiacomo2, Alessandro Nucara1, Paolo Biagioni3, Francesco Michelotti1,
Michele Ortolani1, and Leonetta Baldassarre1
1
Sapienza University of Rome, Rome, 00185 Italy
CNR – Institute for Photonics and Nanotechnologies, Rome, 00154 Italy
3
Politecnico di Milano, Milano, 20133 Italy
E-mail: raffaella.polito@uniroma1.it

2

Mid-Infrared (mid-IR) spectroscopy in the 2-20 µm spectral region could play a relevant role in the field of labelfree biosensors, being a valuable tool for the chemical identification of molecular species and even for probing themolecule conformations in some cases, due to the specificity of mid-IR vibrational fingerprints. Nevertheless, the longwavelengths of IR radiation and the small dipole moment of most molecules prevent the routine application of mid-IR
spectroscopy to study nanometer-thick layers. In the mid-IR, a promising alternative to Surface Plasmon Polariton(SPP)-assisted biosensors, widely exploited in the visible range, could be represented by Bloch Surface Wave (BSW)based biosensors. BSWs are electromagnetic states sustained at the interface between a continuous dielectric medium(in biosensors, this is usually the liquid solution containing the molecules of interest) and a periodic stack of dielectricmaterials with alternating high/low refractive indices, i.e., a one-dimensional photonic crystal (1DPC) [1]. BSWs areusually excited in a total reflection configuration, hence depositing the 1DPC on the surface of a prism.
The proposed 1DPC consists of a periodic structure of alternating ZnS/CaF2 layers, both transparent up to 10 µm
wavelength (Fig. 1a,b). The 1DPC structure was designed and optimized by means of numerical simulations carriedout by the transfer matrix method (TMM) and the multilayers were directly deposited onto CaF2 prisms by thermal
evaporation under high vacuum. The evaporated stack was characterized by slice-and-view with focused ion
beam/scanning electron microscopy. Atomic force microscopy and normal-incidence mid-IR reflectancemeasurements were employed to verify the optical quality of the stack. BSWs spectra were collected in the
Kretschmann-Raether configuration by means of a Fourier Transform spectrometer modified so as to produce a quasicollimated input beam for several different excitation angles θ inside the prism, in order to measure the BSW dispersion(Fig 1c).
We have observed clear spectroscopic evidence of BSWs excitation for both transverse electric (σ) and transverse
magnetic (π) polarization in the wavelength range between 3 and 8 μm [2]. At λ=5.6 µm we calculated an evanescentfield decay length as short as lσd ~810 nm (Fig. 1d), instead of several wavelengths such as in mid-IR SPPs supported
by noble metal [2]. More importantly, the nonzero horizontal propagation length of BSWs compared to the simple
attenuated total internal reflection (ATR) may increase the interaction length with thin layers. Also, BSW sensors canprobe both polarizations, while SPPs can probe only the π polarization. All these features could make BSW biosensors
promising candidates for label-free molecule-specific detection of nanometer-thick layers such as antigen-antibody
pairs.
(a)
(c)
(d)

R

(b)
(b)

Fig. 1 (a) Pictorial sketch of the 1DPC deposited on the CaF2 prism. The IR beam impinges on the 1DPC with an incidence angle
θ (Kretschmann-Raether configuration). (b) Cross-sectional scanning electron microscopy picture of the 1DPC. (c) BSW spectralfeatures obtained by mid-IR spectroscopy at variable internal reflection angle θ with σ polarized light. (d) Square modulus of theelectric field along the direction x perpendicular to the surface. When the incident angle is θσ BSW= 55.13°, the σ-BSW is excitedat 5.6 µm showing a penetration distance lσd ~810 𝑛𝑛𝑛𝑛 and a field enhancement, evaluated as the ratio between the electromagnetic
field intensity in the external medium with (|Esurf σ |2) and without (|E0|2) the 1DPC, of about two orders of magnitude. The dashed
red lines indicate the refractive index profile of the 1DPC.

References[1] Descrovi, E., Sfez, T., Quaglio, M., Brunazzo, D., Dominici, L., Michelotti, F., Herzig, H.P., Martin, O. and Giorgis F. 2010. Nano Lett. 10,
2087–2091.
[2] Occhicone, A., Pea, M., Polito, R.., Giliberti, V., Sinibaldi, A., Mattioli, F., Cibella, S., Notargiacomo, A., Nucara, A., Biagioni, P., Michelotti,F., Ortolani, M. and Baldassarre, L. 2021. ACS Photonics 8 (1), 350-359.

Monitoring Tautomerization of Single Hypericin Molecules in a Tunable
Optical 𝜆𝜆/2 Microcavity

Quan Liu1,2, Liangxuan Wang1,4, Frank Wackenhut1,3, Marc Brecht1,3, Pierre-Michel Adam2, Johannes
Gierschner4, and Alfred J. Meixner1

1 Institute of Physical and Theoretical Chemistry, Eberhard Karls University Tübingen, 72076 Tübingen, Germany.
2 Laboratoire Lumière, Nanomatériaux & Nanotechnologies (L2N), CNRS ERL 7004, Universitéde Technologie de Troyes, 10000 Troyes,
France3 Reutlingen Research Institute, Process Analysis and Technology (PA&T), Reutlingen University, 72762 Reutlingen, Germany
4 Madrid Institute for Advanced Studies, IMDEA in Nanoscience, C/ Faraday 9, Ciudad Universitaria Cantoblanco, 28049 Madrid, Spain.
E-mail: quan.liu@uni-tuebingen.de

Many molecules, such as porphines, porphycenes, or phenanthroperylene quinones, exhibit a reorientation of thetransition dipole moment (TDM) during tautomerization. [1] Here, we study single hypericin molecules, which is aprominent phenanthroperylene quinone showing antiviral, antidepressive, and photodynamical properties. [2]Hypericin tautomerization that involves the migration of the labile protons is believed to be the primary photophysicalprocess relevant to its light-activated antiviral activity. Despite the difficulty to isolate individual tautomers, it can bedirectly observed in single-molecule experiments.
Confocal fluorescence microscopy combined with radially polarized excitation scanning was used to monitor the
spatial orientation of TDM of single hypericin molecules in a Poly (vinyl alcohol) matrix. Observing abrupt ﬂippingof the image pattern (as illustrated in Fig. 1) combined with time-dependent density functional theory calculations
allows drawing conclusions about the coexistence of four tautomers and their conversion path which are difficult todistinguish in ensemble spectroscopy due to the overlap of the spectra. [3,4] This approach allows the unambiguous
assignment of a TDM orientation to a speciﬁc tautomer and enables the determination of the chemical structure in situ.

Fig. 1 Illustration of reorientation of the TDM during tautomerization

Moreover, the study can be extended to a λ/2 Fabry–Pérot microcavity. [5] The modification of the local photonic
environment by a microcavity is well simulated with a theoretical model that shows good agreement with theexperimental data. The excited state lifetime and fluorescence intensity of single hypericin inside a microcavity arecorrelated, and a distinct jump of the lifetime and fluorescence intensity reveal the temporal behavior of thetautomerization with high sensitivity and high temporal resolution. The observed changes are also consistent with TDDFT calculations. Our approach paves the way to monitor and even control reactions for a wider range of molecules
at the single molecule level.
References[1] Piatkowski L, Schanbacher C, Wackenhut F, Jamrozik A, Meixner AJ, Waluk J. 2018. J Phys Chem Lett. 9(6):1211-1215.
[2] Liu Q, Wackenhut F, Hauler O, et al. 2020. J Phys Chem A. 124(12):2497-2504.
[3] Liu Q, Wackenhut F, Wang L, et al. 2021. J Phys Chem Lett. 12(3):1025-1031.
[4] Liu Q, Wang L, Roldao JC, et al. 2021. Advanced Photonics Research. 2(6):2000170.
[5] Wang L, Liu Q, Wackenhut F, et al. 2022. J Chem Phys. 156(1):014203.

Plasmon Enhanced High-Frequency Electron Paramagnetic Resonance utilization of plasmonic metasurface resonators for magnetic fieldenhancement at THz frequencies
Martin Hrtoň1,2, Lorenzo Tesi3, Peter Kepič1,2, Katarína Rovenská1,2, Dominik Bloos3, Martin Konečný1,2,
Zdeněk Nováček1,2, Vlastimil Křápek1,2, Reiner Hillenbrandt4, A. Leavesly5, Joris van Slageren3, and Tomáš.
Šikola1,2
1. CEITEC BUT, Brno University of Technology, Purkyňova 123, 612 00 Brno, Czech Republic
2. Institute of Physical Engineering, Brno University of Technology, Technická 2, 616 69 Brno, Czech Republic
3 Institute of Physical Chemistry and Center for Integrated Quantum Science and Technology, University of Stuttgart, Pfaffenwaldring 55,
70569 Stuttgart, Germany
4 CICnanoGUNE BRTA and Department of Electricity and Electronics, UPV/EHU, Tolosa Hiribidea 76, 20018 Donostia-San Sebastián, Spain
5 Thomas Keating Ltd., Station Mills, RH14 9SH Billinsgshurst, UK
E-mail: sikola@fme.vutbr.cz

Plasmonic effects, based on localized surface plasmons (LSP) have been used in spectroscopic methods for increasing
sensitivity and spatial resolution beyond diffraction limit – one can name Surface-enhanced Raman Spectroscopy(SERS), Tip-enhanced Raman spectroscopies (TERS), Surface-enhanced Infrared Absorption (SEIRA), Plasmonenhanced fluorescence, etc. In these methods, the electric component of electromagnetic field generated by plasmonicresonant structures (antennas or tips) and its local enhancement are utilized in spectroscopic probes, which corresponds
to the fact that this component is in most cases responsible for the interaction with a matter [1]. However, contrary tothat, in some methods, for instance in electron paramagnetic resonance (EPR), the magnetic component ofelectromagnetic radiation is essential [2].
Although, in principle, THz EPR provides high-resolution access to their properties, lack of sensitivity has precluded
realizing this potential. To resolve this issue, the plasmonic enhancement of the magnetic component of THz
electromagnet near fields by a new type of resonators has been proposed. A resonator composed of an array of diaboloantennas with a back-reflecting mirror was designed and fabricated. Simulations and THz EPR measurements
demonstrate a 30-fold signal increase for thin film samples [3]. This enhancement factor increases to a theoreticalvalue of 7500 for samples confined to the active region of the antennas. These findings open the door to the elucidationof fundamental processes in nanoscale samples, including junctions in spintronic devices or biological membranes.

Fig. 1 a) FFMR map measured in HFEPR for 1PMR in the active orientation at 10 K; the PMR resonance area is highlighted in the inset. The colour
scale is linear and normalized to unity. b) Comparison of the frequency profiles extracted by the experimental FFMR maps for the PMR in the active(1PMR-ACT), nonactive (1PMR-NA) orientations and for the reference sample constituted by bare quartz (1REF). The simulation of the PMR
nearfield intensity is scaled for comparison [3].

References[1] Mivelle, M; Grosjean, T.; Burr, G.W.; Fischer, U.C.; et al., 2015, ACS Photonics 2, 1071.
[2] Pake, G.E.; Estle, T.L.: The Physical Principles of EPR, W. A. Benjamin, Addison Wesley, Reading, Mass. 1974.
[3] Tesi, L.; Bloos, D.; Hrtoň, M.; Beneš, A.; Hentschel, M.; Kern, M.; Leavesley, A.; Hillenbrand, R.; Křápek, V.; Šikola, T.; and van Slageren,J., Small Methods 2021, 5, 210037.

AFM-TERS measurements in liquid environment with sideillumination/collection
Patrick Hsia1, Pierre Burgos2, Marc Chaigneau1

1. HORIBA France SAS, 14, Bd. Thomas Gobert - Passage Jobin Yvon CS 45002 - 91120 Palaiseau - France
2. HORIBA UK Ltd., Kyoto Cl, Moulton Park Industrial Estate, Northampton NN3 6FL - UK
E-mail: patrick.hsia@horiba.com

The new breakthrough in Raman nanoscale chemical imaging is the measurement in liquid environment. TERS
measurements in liquid will significantly broaden the potential application of TERS across scientific disciplines suchas heterogeneous catalysis[1,2], electrochemistry[3,4], cellular biology [5], and biomaterials [6]. Implementation of
TERS in liquid brings out some instrumental difficulties. AFM-TERS in liquid have been published quite recently but
mainly in bottom [7], and top [6], optical accesses.
In this talk, specifics of the TERS setup that enables measurements in liquid with side illumination/collectionin order to keep optimal polarization conditions will be discussed: the design of a side access liquid cell that allows
high-throughput optics, the possibility to perform AFM imaging in true non-contact mode in liquid, the alignment
procedure of the Raman laser to the AFM-TERS tip in liquid using objective scanner (Fig. 1).

Fig. 1 Laser pre-aligned on the tip in liquid environment. The tip and its reflection on the substrate can both be seen on thispictureThanks to those latest instrumental developments, we will present the nanoscale imaging in liquid of graphene
oxide and carbon nanotubes immersed in water. TERS resolution in liquid down to 20 nm is demonstrated along withtrue non-contact AFM images (Fig. 2).

Fig. 2 (a) AFM imaging (true non-contact mode) of graphene oxide flake in liquid, (b) TERS map of the 2D band and (c) TERS
map of the D band.

References[1] Li, Z. et al., 2021, Chem. Commun., 57, 891-894[2] Cai, Z.-F. et al., 2021, J. Am. Chem. Soc., 144, 538-546[3] Touzalin, T. et al., 2019, Electrochem. Commun., 108, 106557[4] Huang, S.-C. et al., 2019, Anal. Chem., 91, 11092‑11097[5] Lipiec, E. et al., 2014, Angew. Chem. Int. Ed., 53, 169‑172[6] Lipiec, E. et al., 2021, Angew. Chem. Int. Ed., 60, 4545‑4550[7] Bhattarai, A. et al., 2019, J. Phys. Chem. C, 123, 7376‑7380

Molecular Stark Effect at the Nanoscale
Demelza Wright1†, Sara Sangtarash2, Niclas S. Mueller1, Qianqi Lin1, Hatef Sadeghi2, Jeremy J. Baumberg1
1. NanoPhotonics Centre, Department of Physics, Cavendish Laboratory, University of Cambridge, Cambridge, UK.
2. Device Modelling Group, School of Engineering, University of Warwick, Coventry, UK
E-mail: daw85@cam.ac.uk

Sensing local electric field is important to gain insights into catalysis, biomolecular binding (e.g., in medical
devices), or in molecular electronics. The smallest field sensor is a single polar chemical bond, whose vibrational
resonance shifts in electric fields and is known as a Stark probe. Here, we show for the first time how ionic double
layers can sometimes penetrate molecular layers, and how this can be measured and controlled.
Molecular self-assembled monolayers (SAMs) support polar bonds for sensing. However, little is understood aboutcharge transport or ionic movement within SAMs because direct measurements are extremely challenging. We findhere that ions are excluded from SAMs by surrounding phenyl groups, preventing the formation of a penetrating
electrical double layer and thus directly modifying the local field on the nanoscale. This has important consequences
for driving-force sensitive surface reactions taking place in mixed, multi-molecular, or ‘dirty’ environments.[1]Plasmonic nanogaps using the NanoParticle-on-Mirror (NPoM) geometry enhance Raman intensities by 108,
facilitating high signal-to-noise spectroscopy of only a few hundred molecules and significantly increasing spectral
quality by minimizing averaging effects.[2] Our previous work utilized this to perform a mechanistic analysis ofmolecular catalysts: revealing the first direct evidence of an intermediate state involving a thiol linker.[3] Co-opting
this approach, we now address a topic with little agreement in literature: the interaction of the electrical double layer
and SAMs. We combine theoretical and experimental approaches in tracking multiple vibrational modes of a SAM
with a C≡N Stark reporter group moiety in response to electrochemical fields (Fig.1a).[4]We observe Stark shifts in multiple vibrational modes that cannot be described by the commonly used linear-fielddensity functional theory model. Instead, we show that modelling the movement of a single local ion close to the C≡N
group describes the results well, with ion movement of only 2 Å accounting for most vibrational changes. By stericallyhindering ions from accessing the C≡N group using a mixed SAM system with a larger biphenyl molecule (Fig.1b)
we observe strong impacts on the Stark shifts. We fully suppress Stark shifting in heavily diluted mixtures and decrease
the Stark effect for intermediate mixtures (Fig.1c), supporting our conclusion that stacking of phenyl groups prevents
electrical double layer formation within SAM layers. We thus identify and control the position of the electrical double
layer at a SAM interface.

Fig. 1 a. Electrochemical nanogap spectroscopy from single plasmonic junctions. b. Schematic of ion movement near pure andmixed self-assembled monolayers. c. Molecular Stark shifting in pure and mixed self-assembled monolayers.
†

Present address: Department of Electrical and Computer Engineering, University of Victoria, Victoria, British Columbia, Canada

References[1] Moore, E.E.; Cobb, S.J.; Coito, A.M.; Oliveira, A.R.; Pereira, I.A.C.; Reisner, E. 2022, PNAS 119, e2114097119.
[2] Kamp, M.; de Nijs, B.; Kongsuwan, N.; Saba, M.; Chikkaraddy, R.; Readman, C.A.; Deacon, W.M.; Griffiths, J.; Barrow, S.J.; Ojambati,
O.S.; Wright, D.; Huang,J.; Hess, O.; Scherman, O.A.; Baumberg, J.J. 2020, PNAS 117, 14819[3] Wright, D.; Lin, Q.; Berta, D.; Földes, T.; Wagner, A.; Griffiths, J.; Readman, C., Rosta, E.; Reisner, E.; Baumberg, J.J. 2021, Nat Catal, 4,
157.
[4] Wright, D.; Sangtarash, S.; Mueller, N.S.; Lin, Q.; Sadeghi, H.; Baumberg, J.J.; submitted (2022)

Terahertz Spoof Surface Plasmon Polariton sensor on thin Silicon-Nitride
membrane
Mohsen Haghighat1, Levi Smith1, Thomas Darcie1
1. Department of Electrical and Computer Engineering, University of Victoria,
Victoria, BC V8P 5C2, Canada
E-mail: mohsenh@uvic.ca

Our Terahertz System-On-Chip (TSoC) enables high-speed baseband pulse transmission along with low-loss andlow-dispersion by creating circuits on a thin (1 μm) Silicon Nitride membrane [1]. Spoof surface plasmon polariton(SSPP) waveguides are candidates to enable miniaturized terahertz integrated circuits and systems [2]. Tapered SSPP
structures have been used for focusing or channeling terahertz radiation to micron-scale volumes for near-fieldimaging, spectroscopy, and sensing applications [3]. Previous work related to this application has used a conicalstructure [3]. Here we focus on a planar on-chip integration using a Goubau line [4]. We use an open-circuited line tocreate a high-intensity field at the tip of a tapered Goubau line.
In this work, we simulate a tapered and corrugated SSPP device integrated onto our experimentally compatible
TSoC platform for THz focusing. Fig. 1 shows the electric field magnitude of simulated Tapered SSPP at threedifferent frequencies (e.g., 0.25, 0.50, and 0.75 THz). The simulation is used by the commercial finite element method(FEM) solver ANSYS HFSS, and a terminal solution with a single wave port is used to simulate the structure. The
conductor is Gold (Au) with 200nm thickness on a 1 μm Silicon-Nitride substrate with a length and width of 2mm.
The length waveguide is 0.5mm shorter (e.g., 1.5mm) to observe the focusing on the surface of metal and dielectric.
By integrating a tapered SSPP Goubau transmission line we can increase the local field intensity
at the tip by more than 15dB from 0.1 to 1 THz. The reflection magnitude intensity changes in the presenceof different chemicals, and it can be optimized based on a particular analyte.
Frequency / Mag.
E field Ratio

Electrical field intensity on the surface:

The magnitude of E field along the waveguide:

250GHz /24.2dB45dB(Mag. E[V/m])

40

500GHz /23.3dB

35

FocusingdB(Mag. E[V/m]) at 250GHz
dB(Mag. E[V/m]) at 500GHz
dB(Mag. E[V/m]) at 750GHz

30
25
20
15
10
5
0.00

750GHz /18.6dB

0.50

1.00

Distance from port (mm)Fig. 1. The simulation of the planar tapered SSPP Goubau line on Si3N4 membrane for THz focusing and Magnitude of Electricfield (in dB Scale) along the waveguide

References[1] L. Smith, V. Shiran, W. Gomaa, and T. Darcie, 2021, "Characterization of a split-ring-resonator-loaded transmission line at terahertz
frequencies," Opt. Express 29, 23282-23289.
[2] M. A. Unutmaz and M. Unlu, 2019 “Terahertz Spoof Surface Plasmon Polariton Waveguides: A Comprehensive Model with Experimental
Verification,” Scientific Reports, vol. 9, no. 1, p. 7616
[3] S. A. Maier, S. R. Andrews, L. Martín-Moreno, and F. J. García-Vidal, 2006, “Terahertz Surface Plasmon-Polariton Propagation and Focusing
on Periodically Corrugated Metal Wires,”, 2006, Phys. Rev. Lett., vol. 97, no. 17, p. 176805.
[4] T. Akalin, A. Treizebre and B. Bocquet, "Single-wire transmission lines at terahertz frequencies,", 2006, IEEE TMTT, vol. 54, no. 6, pp. 27622767.

1.50

Evaluation of SERS substrates through average and high fluctuation regimes
Arash Azarakhshi1, Alexandre G. Brolo2
1. Department of Physics and astronomy, University of Victoria, Victoria BC Canada
2. Department of Chemistry, University of Victoria, Victoria BC Canada
E-mail: agbrolo@uvic.ca

Surface-Enhanced Raman scattering (SERS) is a well-known phenomenon that provides an increment of up to 10 in
the number of Raman scattered photons.1 SERS is achieved through the excitation of surface plasmon polaritons(SPP’s) at the surface of metal nanoparticles/nanostructures leading to highly concentrated local electrical fieldhotspots (HS) beyond the diffraction limit.2 Presence of a probe molecule inside of a strong HS results in a SERS signal
which could pass the instrumental detection threshold. While the enhancement factor (EF) is the most common
parameter to report the quality of the SERS substrates,3 but the broad ranges of definitions, experimental and theoreticalprocedures and the lack of a temporal and spatial resolution make this parameter an unreliable factor. Providing theuniversal standards to evaluate and compare different SERS substrates based on the temporal and spatial variations of
the SERS signals is the central pursuit of our work. Though evaluation of the signal in the average SERS regime would
provide useful insight toward the quality of the substrate, we also implement the high fluctuation regime to relate thesignal characteristics to physical features of the HSs either density or strength. As shown in Fig.1, for the average
SERS regime the signal fluctuates symmetrically around the mean value with the small Mean Absolute Deviation(MAD) while in the high fluctuation regime SERS signal could fluctuate further from the mean value which would
lead to higher MAD.
(a)(b)

Fig1. Temporal fluctuation of the SERS signal obtained from the same substrate for two different regimes. a. 1mMPyridine, b. 50 nM Nile Blue

Fig.2 implies the evaluation parameters and results for two commercial gold substrates in both average and highfluctuation SERS regimes. Additionally, we collect data in the solution phase to benefit from the dynamic variation of
the signal.
(a)(b)

Fig2. Evaluation Parameters of the SERS substrate. a. Average SERS regime, b. High fluctuation regime

According to Fig.2, substrate A demonstrates higher temporal fluctuations but its stronger signal leads to a smaller
RMAD. The higher mean and maximum intensity from Substrate A could root from different possible scenarios: higher
density of HSs, possession of stronger HSs, or both. To link the behavior of substrates to their physical properties wemove to the high fluctuation regime which reveals that the Density of Active Area (DAA)-the fraction of nonzero
events- for both substrates are similar, however, substrate B still produces higher counts. Thus the better performanceof Substrate A arises from the stronger HSs rather than a higher density of HSs. Consequently, our analysis directs
how to employ the various evaluation parameters in different regimes to evaluate and compare the SERS substrates.
References[1] Ru, E. C. L.; Blackie, E.; Meyer, M.; Etchegoin, P. G. 61. SERS A Comprehensive Study. 2007, 13794 13803.
[2] Willets, K. A. Super-resolution imaging of SERS hot spots. Chemical Society Reviews 2014, 43, 3854 3864.
[3] Rodrigues, D. C.; De Souza, M. L.; Souza, K. S.; Dos Santos, D. P.; Andrade, G. F.; Temperini, M. L. Critical assessment of enhancement factor
measurements in surface enhanced Raman scattering on different substrates. Physical Chemistry Chemical Physics 2015, 17, 21294 21301.

Monitoring metabolic alterations in cancer cells upon radiotherapy by SERS
Xiangyu Chen1, Javier Plou2
1. University of Victoria, 3800 Finnerty Road, Victoria, BC, Canada
2. CIC biomaGUNE, Basque Research and Technology Alliance (BRTA), 20014 Donostia-San Sebastián, Spain.
E-mail: xiangyuchen@uvic.ca

Abstract: Surface-enhanced Raman scattering (SERS) spectroscopy has been recognized as apromising technology for biomedical analysis and clinical diagnosis thanks to its high sensitivity
and label-free operation. As a real-time probe of the exogenous metabolites of cells, SERS exhibits
simpler, faster, and less expensive advantages. The tumor microenvironment (TME) is a very
complex cellular ecosystem characterized by an altered metabolism. Analysis of the SERS spectraof the metabolisms from breast cancer cells allows the identification of characteristic patterns in
the extracellular environment of breast cancer cells before and after radiotherapy treatment. The
release of specific metabolites from cells that have resisted radiotherapy treatment may havesignificant implications in tumor recurrence after therapy. Here, we fabricated the plasmonic
substrates based on silver nanoparticles enhancing the Raman signal of metabolites from the cellsupernatant and performing irradiation of cells with different irradiation doses (Gy5 and Gy20).
The recorded SERS spectra from the extracellular environment after 2-week of radiotherapy
exhibit meaningful differences between control and irradiated cells (see Fig.1).

Fig. 1 SERS spectra (left) and Two-Dimensional Principal Component Analysis (right) of extracellular environment of breast
cancer before treatment and after 2 weeks of treatment

Unveiling the role of chemical and electronic structure in plasmon catalysis
using alkoxyamines as a chemical probe
Darya Votkina,1 Pavel Petunin, 1 Andrii Trelin, 2 Oleksiy Lyutakov,2 Gérard Audran,3 Rashid Valiev,4,5
Sylvain R. A. Marque,3 and Pavel Postnikov,1,2 Yusuke Yamauchi6, Olga Guselnikova1
1

Research School of Chemistry and Applied Biomedical Sciences, Tomsk Polytechnic University, Russian Federation.
Department of Solid-State Engineering, University of Chemistry and Technology, Prague, Czech Republic.
Aix-Marseille Univ, CNRS, ICR case 551, Avenue Escadrille Normandie-Niemen, 13397 Marseille Cedex 20, France
4.
Tomsk State University, 36, Lenin Avenue, 634050 Tomsk, Russia.
University of Helsinki, Department of Chemistry, P.O. Box 55, (A.I. Virtanens plats 1), FIN-00014 University of Helsinki, Finland
JST-ERATO Yamauchi Materials Space-Tectonics Project, International Center for Materials Nanoarchitectonics (WPI-MANA),
National Institute for Materials Science, 1-1 Namiki, Tsukuba, Ibaraki, Japan
2

3
5.
6.

.

guselnikova.olga@nims.go.jp

The excitation of localized plasmon resonance on nanoparticles followed by the interaction with organic molecules
leads to new pathways of chemical reactions [1]. Although a number of physical factors (temperature, illumination
regime, type of nanoparticles, etc.) are affecting this process, the role of the chemical factors is underestimated [2, 3,
4, 5]. Challenging this assumption, here we studied the kinetic of plasmon-induced homolysis of five alkoxyamines(AAs) with different chemical and electronic structures using electron paramagnetic resonance (EPR) (Fig. 1).

Fig. 1. Overview of the experimental strategy. A - Scheme for the direct intramolecular excitation mechanism via localized surface plasmon (LSP)
resonance and location of HOMO, LUMO levels, B - Scheme of plasmon-induced homolysis of alkoxyamines using AuNPs-C4H9, C - the structureof organic layer, D -TEM image, and UV-Vis spectra of AuNPs-C4H9, E- structures of alkoxyamines investigated.

The kinetic data revealed the dependence of plasmonic homolysis rate constant (kd) with the HOMO energy of AAs,
which cannot be described by the kinetic parameters derived from thermal homolysis experiments. The observed trend
in kd allowed to suggest the key role of intramolecular excitation mechanism supported by the DFT calculations,additional spectroscopic characterization, and control experiments. This observation suggests that the electronic
structure of organic molecules may play a key role in other related reactions in plasmon catalysis
References[1]
Zhang Z., Zhang C., Zheng H. and Xu, H. 2019, Acc. Ahem. Res., 52, 2506–2515.
[2]
Guselnikova O., Váňa, J., Phuong, P., Panov, I., Rulíšek, L., Trelin, A., Postnikov, P.,Švorčík, V., Andris, E. Lyutakov, O. 2021, Chem. Sci., 12, 5591–5598.
[3]
Olshtrem, A., Guselnikova, O., Postnikov, P., Trelin, A., Yusubov, M., Kalachyova, Y.,
Lapcak, L., Cieslar, M., Ulbrich, P., Svorcik, V., Lyutakov, O., 2020, Nanoscale, 12, 14581–
14588.
[4]
Ezina, M., Guselnikova, O., Miliutina, E., Trelin, A., Postnikov, P., Svorcik, V.,
Lyutakov, O., 2021, J. Phys. Chem. C, 125, 10318–10325.
[5]
Guselnikova, O., Audran, G., Joly, J.-P., Trelin, A., Tretyakov, E., Svorcik, V.,
Lyutakov, O., Marque, S. R. S., Postnikov, P., 2021, Chem. Sci., 12, 4154–4161.

Near Infrared Waveguide using multilayer ITO metamaterial
Shashwata Chattopadhyay and J Mitra
School of Physics, Indian Institute of Science Education and Research Thiruvananthapuram, kerala (695551), INDIA.
E-mail: shash00817@iisertvm.ac.in

Optical waveguides of subwavelength dimensions, for enabling on-chip all optical or electro-optic modulation has
remained a challenge in terms of efficient light coupling with low propagation losses. Epsilon near zero (ENZ)
materials like indium tin oxide (ITO) offer multiple advantages for realizing such a on-chip device. Transparent in thevisible ITO undergoes a dielectric to metal transition at the ENZ wavelength, at which the real part of its dielectric
constant (Re(𝜖𝜖)) becomes zero[1]. The near zero relative permittivity and refractive index below 1 nucleates interesting
optical properties therein like perfect absorption (PA)[2], local electric field enhancement and high nonlinearities[3].
In parallel the conducting nature of the oxide allows for electro-optic modulation where the refractive index of thematerial may be modulated by an applied voltage. Here we propose a sandwich waveguide structure of stacked ITO
multilayers on glass substrate, with a low electron density ITO (n= 1e27 m ) having ENZ wavelength 2.22 µm ofthickness 10 nm in between two higher electron density ITO (n= 2e27 m ) having ENZ wavelength 1.52 µm ofthickness 50 nm and 90 nm respectively. In the attenuated total internal reflection (ATR) configuration this stackallows for exciting modes in the middle ITO waveguide in wavelength regimes where the stack behaves as a metallicdielectric-metallic metamaterial.
-3-3

Finite element modelling simulations performed on the above structure shows feasibility of efficient light coupling
into the waveguide in the spectral range 1.7 - 2.1 µm. Figure 1a shows the effective dielectric constant of the sandwich
waveguide showing a protracted spectral region with Re(𝜖𝜖) close to zero. Figure 1b plots the y-component of the
Poynting vector quantifying the energy transport along the dielectric ITO channel in an analogous ITO waveguidewhere the third ITO layer is replaced by 40 nm of Au, for incident excitation of 1.88 µm. Figure 1c then shows thevariation of the Poynting vector along the dashed line in figure 1b showing the energy localization within the 10 nm
waveguide. Across the applicable spectral window our results show that approximately 1/3rd of the incident power issuccessfully coupled into the proposed waveguide using a simple stacked multilayer of ITO. We further discuss
experimental realisation of the waveguide and electro-optic modulation of the same by application of bias across the
ITO channel.

Relative Permittivity

W/m2
(b)

(a)

glass

Wavelength (nm)ITO1 Au

Simulation Domain (µm)

W/m2
(c)

Air

Simulation Domain (µm)

Fig. 1 (a) Effective relative permittivity vs wavelength of the stacked multilayer ITO. (b) Y-Component of Poynting's vector mapped acrossthe simulation model domain with ITO1 (n=1e27 m-3)-ITO2 (n=2e27 m-3)-Au (c) Y-Component of Poynting's vector along the dashed line
in figure 1(b).

References[1] Johns, B., Puthoor, N. M., Gopalakrishnan, H., Mishra, A., Pant, R., & Mitra, J. 2020. Epsilon-near-zero response in indium tin oxide thinfilms: Octave span tuning and IR plasmonics. Journal of Applied Physics, 127(4).
[2] Johns,Ben Chattopadhyay,Shashwata Mitra,Joy ,2022, Advanced Photonics Research, Volume 3, Issue 1, 2100153.
[3] Suresh, S., Reshef, O., Alam, M. Z., Upham, J., Karimi, M., & Boyd, R. W. 2021. Enhanced Nonlinear Optical Responses of Layered Epsilonnear-Zero Metamaterials at Visible Frequencies. ACS Photonics, 8(1), 125–129.

Creation of wide stopbands by loading split-ring-resonators to a terahertz
guided-wave coplanar strip transmission line
Saeid Asadi1, Levi Smith,1 Thomas Darcie1
1. Department of Electrical and Computer Engineering, University of Victoria, BC, V8W, Canada
saeid.asadi86@gmail.com, levismith@uvic.ca, tdarcie@ece.uvic.ca

In this paper, split-ring-resonator (SRR) meta-atoms (metamaterials) are placed between the two conductors of a
coplanar strip (CPS) THz transmission line (TL). This CPS TL is designed on a thin (1μm) Silicon Nitride membrane
which enables operation up-to 3 THz. Adding a SRR in a TL introduces a resonance corresponding to a negative
permeability (𝜇𝜇 < 0) [1] which appears as a stopband [2]. In the previous work [3], equal sized meta-atoms are placednear a guided-wave CPS TL which led to a single resonance and narrow stopband. In this work, we widen the stopband
by varying the radius of each meta-atom. This study has been performed by the ABCD matrix approach [4].
Fig. 1(a) illustrates a CPS TL loaded with a single SRR. In Figs. 1(b, c), obtained by simulation (HFSS), the electricfield intensity is observed off and on resonance, respectively. Modifying the radius of a SRR changes its resonant
frequencies. In Fig. 2, the TL containing one SRR is compared with TL containing three and four SRRs in terms of
the 𝑆𝑆21 parameter. In Fig. 2(a), all the SRRs have the same radius in both configurations; however, the TL with three
SRRs has a wider stopband. In Fig. 2 (b), the radii of SRRs, of the TL with three SRRs, are changed which corresponds
to a variation in the equivalent inductance and capacitance and a wide stopband (about 0.1 THz). Therefore, by adding
more SRRs, not only is it possible to further widen the stopband and thus the region where 𝜇𝜇 < 0, also we can further
weaken components in the stopband as depicted in Fig. 2 (c) which the TL contains four different radii SRRs.
(a)

(b)

(c)

Fig. 1. (a) CPS TL containing a single SRR. (b) and (c) Electric field pattern in off and on
resonance, respectively.

(a)

(b)

(c)

Fig. 2. 𝑆𝑆21 parameter of CPS TL containing SRRs. The dashed line characterizes a TL containing one SRR. The solid line
characterizes a TL including three and four SRRs. (a) All the SRRs have equal radii. (b) The three SRRs have different
radii. (c) Four SRRs with different radii.

References[1] Pendry, J, B. Holden, A, J. Robbins, D, J. Stewart, W, J. 1999. IEEE Transactions on Microwave Theory and Techniques, 47, 2075-2084.
[2] Syms, R, R, A. Shamonina, E. Kalinin, V. Solymar, L. 2005. J. Appl. Phys, 97, 064909.
[3] Smith, L. Shiran, V. Gomaa, W. Darcie, T. 2021. Optics Express, 29, 15-19.
[4] Pozar, D, M. Microwave Network Analysis, Microwave Engineering. 2012, John Wiley & Sons, Inc, United States, 188-194.

Broadband absorber utilizing nonlocal metamaterials
Won-Heum Han1, Q-Han Park2
1,2 Korea University/Nanooptics lab, 145 Anam-ro, Seongbuk-gu, Seoul, 02841, Rep. of Korea.
E-mail: hanwh.mail@gmail.com1, qpark@korea.ac.kr2

Electromagnetic wave absorbers are widely used for various applications including stealth technology andminimizing EM wave interference between automobile electronic components. There are many previous studies
especially in the X-band(8-12GHz) region to design an absorber attached to PEC with design methods such as thefrequency selective surface(FSS) [2], metamaterial and multilayer methods[3]. In the case of the FSS study, theabsorption performance reaches about -15dB reflectance (lower reflectance refers to better absorption performance).
Reflectance below -20dB has been reported when either TE or TM polarization has been specifically selected. In themulti-layer case aimed for a broadband operation, the thickness of an absorber has to increase significantly to assure
the absorption performance. Earlier studies have shown a -10dB reflectance with thickness 3.04mm and -20dB withthickness 10mm. For practical applications, it is highly desirable to design a thin X-band absorber with reflectance lessthan -20dB covering all polarizations and broadband.
To achieve the high absorption performance with ultrabroadband operation, nonlocal absorbers enabling theuniversal impedance matching(UIM) have been suggested[1]. In this study, we present a nonlocal metamaterial
absorber which was designed to meet the UIM condition approximately. A broadband absorber is made of silicone
rubber with an embedded double layered conductive wire. Wires of each layer contains a resistor, marked in cyan color
in Fig. 1(a). The overall thickness of an absorber is about a quaterwavelength while the size of an unit is also of
subwavelenth scale. Full wave numerical calculations shows a good performance with results on the reflectance in the
X-band of the proposed structure illustrated in Fig.1 (b). We achieve a reflectance less than -20dB which is smallerwhen compared to other studies of similar thickness. Other additional strengths of our work are summarized in the
Table 1 with comparisons to previous studies.
Reflectance

TE, TM coverThickness

Number of materials

Flexibility

FSS method[2]-15dB

some possible

3~7mm

2~3

X

Multilayer[3]-10dB

possible

3mm~

3~5

X

This study-20dB

possible

4mm

3

O

Table. 1 Comparison Analysis of X-band Absorbers.

Fig. 1 (a) CST modeling. (b) Simulation result

References[1] Im K, Kang JH and Park QH. 2018. Nature Photon 12, 143-149.
[2] Sohrab A P, Atlasbaf Z. 2013. IEEE Antennas and Wireless Propagation Letters, vol. 12, 276-279[3] Choi WH, Shin JH, Song TH, Kim JB, Lee WY, Kim CG. 2015 Composite Structures Volume 124, 310-316

NFO16
FIB defined curved architectures toward asymmetric chiral metasurfaces
Ruhao Pan1, Changzhi Gu1*, Junjie Li1*
Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190, China
E-mail: panruhao@iphy.ac.cn

3D chiral metasurfaces show great advantages in modulating the spin-states of the electromagnetic waves, and thus
give crucial opportunities to next-generation bio-sensors and optical communication devices[1,2]. However, the lack ofarbitrary structure controls and giant CDs hinders the application of 3D metasurface.
Here, we have developed a focused ion beam (FIB) defined origami method, which can generate 3D curved
configurations in micro/nano-scale by FIB global irradiation of the planar cantilevers, showing great potential in therealization of multifunctional metasurface that can hardly be achieved by 2D patterns. The curved deformation during
the FIB irradiation comes from the tensile stress that induced by the ion-matter interaction. As shown in Fig.1, by
simultaneously modulating the cantilevers’ patterns and FIB irradiation parameters, the curved 3D architectures with
controllable shapes and curvature down to 175 nm are taken shaped over a large scale.
A chiral metasurface consisting of curved asymmetric split ring resonators (SRR) with intrinsic chirality is designed
and shown in Fig.2. Because the curved arm of the SRR breaks the symmetry in z-space, the chiral metasurface shows
asymmetric chirality for the light illuminate from different directions. Greater CDs at 5.2 μm can be observed for the
backward incident compared to the forward incident. The CDs change with the curved angle of the metasurface, andmetasurface with 60° curved angle show highest CD of 0.85/0.71 by simulation/experiment for backward beamincidence, while the CD is shrunk to -0.29/-0.29 for forward incidence. The near-filed distribution shows theasymmetric chirality comes from the electronic and magnetic dipoles are neither parallel nor vertical, which results in��⃗ ≠ 0 and |p�⃗ × �m��⃗| ≠ 0.
that 𝑝𝑝⃗ ∙ 𝑚𝑚
FIB defined origami not only shows a new method to build up 3D metasurfaces with asymmetric chirality, butalso inspiring a new approach to designing multifunctional and high efficiency photonic devices.
Fig. 1 Diverse curved structures fabricated by FIB defined origami method

Fig.2 The SEM image and the optical properties of the asymmetric chiral metasurface

References[1] Liang, Y; Lin, H; Koshelev, K,; et al. 2021. Nano Lett., 21, 1090-1095.
[2]Wang C; Li, Z; Pan, R; et al. 2020. ACS Photonics, 7, 3415-3422.

Infrared Near-Field Spectroscopy at the
National Synchrotron Light Source II
Lukas Wehmeier1, Ziheng Yao2, Mengkun Liu1,2, and G. Lawrence Carr1
1. National Synchrotron Light Source II, Brookhaven National Laboratory, Upton, New York 11973, USA
2. Department of Physics and Astronomy, Stony Brook University, Stony Brook, New York 11794, USA
E-mail: lwehmeier@bnl.gov

Infrared near-field spectroscopy provides unique capabilities for exploration of the nanoworld as it combines theinformation density of optical techniques with the spatial resolution of atomic force microscopy of ~10 nm. Despite
rapid technological development in the past decades, the availability of suitable table-top laser sources still severely
limits the accessible infrared spectral range [1].

Fig. 1 Synchrotron light sources allow for infrared near-field spectroscopy in an ultrabroadband spectral range. (a) Infrared spectral
radiance of different synchrotron light sources in comparison to blackbody (BB) radiation at 2000 K. The large gap (LG) bending
magnet at the National Synchrotron Light Source II (NSLS-II) in Upton, USA provides one of the highest infrared spectral
radiances of existing synchrotron light sources. Figure adapted from reference [2]. (b) Sketch of a synchrotron infrared near-field
spectroscopy (SINS) setup. Figure adapted from reference [3].

In the large part of the infrared spectral region where no suitable table-top laser sources are available, acceleratorbased near-field techniques provide an alternative approach [3–6]. As shown in Fig. 1a, synchrotron light sourcesdeliver infrared radiation with several orders of magnitude higher spectral radiance than thermal blackbody
radiation [2]. Thus, synchrotron infrared near-field spectroscopy (SINS) enables nanoscale material studies in an
ultrabroadband spectral range down to 320 cm-1 (9.7 THz) (sketch of a SINS setup shown in Fig. 1b) [3–5].
Referring to Fig. 1a, the National Synchrotron Light Source II (NSLS-II) at Brookhaven National Lab, Upton,
USA has a mid- to far-infrared spectral radiance that is among the highest of existing synchrotron light sources [2].
Exploiting this high spectral density, we are currently commissioning a new SINS setup at NSLS-II. At its final
stage, we expect our setup to push the spectral limit of SINS to wavenumbers in the range of 100 cm-1 [2]. We will
illustrate our current SINS capabilities via near-field spectroscopy data of isotropic and anisotropic bulk materials,
thin films, and polariton interferometry of 2D and van der Waals materials.
References[1] Chen, X. et al. 2019. Adv. Mater. 31, 1804774.
[2] Dumas, P. & Carr, G.L. Infrared Spectroscopy and spectro-microscopy with synchrotron radiation. 2020. Brookhaven National Lab. (BNL),
Upton, NY (United States).
[3] Khatib, O. et al. 2018. ACS Photonics 5, 2773.
[4] Barcelos, I.D. et al. 2020. Adv. Opt. Mater. 8, 1901091.
[5] Yao, Z. et al. 2021. Nat. Commun. 12, 2649.
[6] Oliveira, T.V.A.G. et al. 2021. Adv. Mater. 33, 2005777.

Near-field hyper-spectral imaging of resonant Mie modes in a dielectric island
Francesca Intonti1, Nicoletta Granchi1, Michele Montanari1, Andrea Ristori1 Mario Khoury2, Mohammed
Bouabdellaoui2, Chiara Barri3, Luca Fagiani3, Massimo Gurioli1, Monica Bollani3, Marco Abbarchi2
1.

3.

Department of Physics and Astronomy and LENS, University of Florence, Sesto Fiorentino (FI), Italy
2. Aix Marseille Univ, Université de Toulon, CNRS, IM2NP, Marseille, France
Istituto di Fotonica e Nanotecnologie (IFN-CNR) and Department of Physics, Politecnico di Milano, 22100 Como, Italy
E-mail: intonti@lens.unifi.it

All-dielectric sub-wavelength sized Mie resonators have emerged in the last decade as promising building blocks for
optoelectronic devices, since they provide the possibility to efficiently redirect and concentrate light with low
absorption losses [1]. The optical modes in high-index dielectric nanoparticles originate from the excitation of opticallyinduced displacement currents and can be both magnetic and electric in nature. The combination of these two kinds ofresonant modes and the exploitation of higher order multipolar modes offers opportunities for directional andpolarization controlled emission from nanoemitters [2]. However, the investigation of the intricacies of the Mieresonances at the sub-wavelength scale has been hampered by the limitations of conventional near-field methods. In
this work, we address the spatial and spectral mapping of multipolar modes of a Si island by near-field hyper-spectral
imaging. A Si resonator, realized by solid state dewetting [3], with diameter of 320 nm and sitting atop a 2 µm SiO2
substrate, Fig. 1a), is investigated by scanning near-field optical microscopy (SNOM) in scattering configuration, Fig.
1b). The normalized near-field spectrum collected at the apex of the island, illuminated by a tilted supercontinuum
laser source, is reported in Fig. 1c), together with the finite difference time domain (FDTD) near-field spectrum.
Simulated and experimental spectra are in good agreement, allowing to identify the main higher order multipolar
resonances that result from the resonant modes of the antenna. Fig. 1d) shows the near-field map of the resonance at
730 nm, and exploiting the morphology of the sample simultaneously acquired [the island position is highlighted bywhite circles in Fig. 1d) and e)] allows a direct comparison with the FDTD map of the same resonance, Fig. 1e).
Experimental and simulated maps show striking similarities in the spatial distribution of the hot spots that are typicalof the mode.

Fig. 1 a) SEM image of a single Si resonator. b) Sketch of the experimental setup: the tilted illumination from the supercontinuum
laser is scattered by the island and the scattered light (yellow cone) is collected by an aperture near-field probe. c) Normalized
SNOM scattering spectrum collected on top of the dewetted island (purple) and corresponding FDTD spectrum (dark green), thespectral positions of different high order resonances (magnetic and electric quadrupole and hexapoles) are indicated. d) and e)
Experimental SNOM and simulated maps relative to the magnetic quadrupole MQ’.

The combination of numerical and experimental results allows a full comprehension of the sensitivity of magnetic lightwith respect to the thickness of the substrate and the angle of illumination [4]. Moreover, this detailed analysis indicates
how such sensitivity affects the near-field scattering pattern of the antenna, suggesting a novel approach to control the
position of the localized electric field maxima to engineer an important aspect of the coupling between emitters andantenna: instead of placing the emitter on the hotspot, the hotspot can be moved on the emitter position, offering a
versatile tuning tool to control the absorption of the emitter itself.
References[1] Kuznetsov, A. I. et al., 2016, Science 354, 2472.
[2] Van de Groep , J. et al., 2013, Opt. Express 21, 26285.
[3] Abbarchi, M. et al., 2014, ACS Nano 8, 11181.
[4] Granchi, N. et al., 2021, APL Photonics, 2, 126102.

Observation of the History Dependence of Two Nano-Photoisomerization
Pathways in Photochromic Single Crystals
Yuji Arakawa1, Kazuharu Uchiyama¹, Yuki Hashimoto², Kingo Uchida²,
Hirotsugu Suzui3, Makoto Naruse³, and Hirokazu Hori¹

1. University of Yamanashi, 4-3-11 Takeda, Kofu, Yamanashi 400-8511, Japan
2. Ryukoku University, 1-5 Yokotani, Oe-cho, Seta, Otsu, Shiga 520-2194, Japan
3. 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
E-mail: g21tz002@yamanashi.ac.jp

Toward realizing intelligent devices based on the interactions of light and matter, we utilize a photochromic
diarylethene single crystal, which is reversibly isomerized into colored and colorless states while maintaining theircrystalline state by light irradiation (Fig. 1(a)) [1,2]. Previously, we reported local excitation by local electric fieldenhancement with an Au-coated metal probe to the surface of a colored photochromic crystal. We found that a chainof photoisomerization was spontaneously formed where nanometer-scale transparent pathways were generated [1]. In
other words, a complex pattern was memorized as a result of near-field light excitation. In this study, we examined the
addition of another memory to existing photon pathways in the photochromic material. We characterized the effectsof such additive memory on the original memory or originally formed pathways.
The measurements were performed using a double-probe scanning near-field optical microscope with two probes;
one probe was on the upper and the other on the lower side of the crystal sample. After forming a memory path withthe upper metal probe, the optical near-field on the rear side was measured within a 2-μm square area by scanning theoptical fiber probe (Fig. 1(b)). After forming and observing such a path, which is referred to as “P1” hereafter, we
horizontally displaced the local excitation point by an amount of 1 μm and formed another path, of which observation
was called “P2”. We then returned the local excitation point to the original position and observed the path again (called“P1’”) (Fig. 1(c)). Nanoscale near-field optical structures were observed, indicating the formation of two memories.
The cross-correlation between P1 and P2 and that between P1’ and P2 are demonstrated in Figs. 1(c,i) and 1(c,ii),
respectively, for the size of the extracted structure. A negative correlation was observed in the optical near-field scale(~100 nm), indicating that the nanometer-scale memory paths were different from each other regarding different local
optical excitation points. The mechanical distortion caused by the first path generation (P1) exclusively constrained
the formation of the second path (P2), leading to the formation of different pathways. In other words, a historydependent effect was observed due to optical near-field excitations added via different positions. Finally, we comparedP1 and P1’, where local optical excitations were generated at the same point before and after the addition of anothermemory P2 (Fig. 1(c,iii)). These structures are positively correlated; that is, the structures are consistent for the same
local optical excitation even after the addition of path P2. This indicates the conservation of the memory pathways.
These results suggest that the nano-photoisomerization in the photochromic diarylethene single-crystal implements
sequential multiple memory structures, where the original memory provides constraints for the subsequent memory
formations and is preserved even after the additional path formations. This paves the way for novel functionalities bynear-field optics combined with photoisomerization in photochromic materials on the nanometer scale.

Fig. 1 (a) Photochromic diarylethene molecules and the photoisomerizations. (b) Schematics of the experiments.(c) (i) Cross-correlation of P1 andP2. (ii) Cross-correlation of P1’ and P2.(iii) Cross-correlation of P1 and P1’ for the size of the extracted structure.

References[1] Nakagomi, R., Uchiyama, K., Kubota, S., Hatano, E., Uchida, K., Naruse, M., Hori, H., 2018. App. Phys. A 124, 10.
[2] Uchiyama, K., Suzui, H., Nakagomi, R., Saigo, H., Uchida, K., Naruse, M., Hori, H., 2020. Sci. Rep. 10, 2710.

A Review of Nanoscale Chemical Imaging Applications Using Photo Induced
Force Microscopy
Derek B. Nowak1, Padraic O’Reilly1 Sung I. Park1
1. Molecular Vista Inc, 6840 Via Del Oro Suite 110, San Jose CA
E-mail: derek@molecularvista.com

Since the original concept of image force microscopy was demonstrated by Kumar Wickramasinghe’s group at
the University of California, Irvine in 2010 [1], Photo-induced force microscopy (PiFM) as it is now commonly called
has seen an incredible expansion into many different scientific disciplines. Applications ranging from biophysics [2],polymer studies [3] and nanoplastics [4], nanocomposites [5], semiconductors [6], geosciences [7], nanoplasmonics[8], and renewables [9]. The ability for PiFM to be sensitive to both organic and inorganic material, operate in a noncontact mode of atomic force microscopy, operate on rough to smooth samples and to be sensitive to monolayers, allwhile demonstrating the highest spatial resolution nano-IR modality, have all contributed to this success.
The mechanism of PiFM uses mechanical force instead of optical detection to measure the near-field opticalinteraction between the tip and sample. PiFM leverages local polarization of the sample by tip-enhanced optical
illumination, resulting in highly localized forces acting between the tip and sample which are easily detected by AFM.
Mechanical detection eliminates the problem of background scattering seen in s‑SNOM, giving PiFM a superior SNR
and greatly enhancing ease-of-use and quality of data on most samples. The basic tip-sample optical interaction in sSNOM and PiFM is quite similar – the same near field illumination and local polarization of the sample that emits
scattered photons in s-SNOM also generates the mechanical forces detected in PiFM [1]. Thus, one might expect sSNOM and PiFM to have similar spatial resolution; however, PiFM generally shows superior resolution by virtue of
its increased SNR for a given tip radius. In PiFM, the tip-sample interface generates two types of short-range forces:(1) the usual van der Waals (vdW) force that NC-AFM relies on for mapping the topography of the sample surface,and (2) the photo-induced force (PiF) generated by near field illumination. Both forces act over a very short range,
coming into play only when the tip is atomically close to the sample surface (~10 nm or less). PiFM utilizes two
vibrational modes of the rectangular AFM cantilever to measure the two forces independently – the interatomic vdW
force with one mode, and the photo-induced force (PiF) with another. Since the vibration of the two modes iscompletely independent, motion in one mode generally does not influence the other. Assigning each of these forces to
its own vibrational mode of the cantilever is accomplished by modulating the vdW force at or near the resonant
frequency of one mode (as is normally done in NC-AFM by mechanically driving the cantilever vibration andmonitoring its response) and modulating or pulsing the excitation light so that it generates the PiF at the resonant
frequency of another cantilever mode. Due to the high quality-factor Q of the cantilever resonance, even tiny forces in
the range of pN can excite measurable oscillations, making this approach ideal for measuring small photo-induced
forces.
A review of published PiFM work on nanoscale applications will be presented, showcasing this new-frontier
technique and it’s potential. Many recent developments in real world applications, in process monitoring and defectreview on unpublished applications and use cases will be presented.
References[1] Rajapaksa, I.; Uenal K.; Wickramasinghe H. K., Appl. Phys. Lett. 2010, 97, 073121.
[2] Eesaee, M.; et.al. ACS Appl, Polym. Mater. 2022, 4, 4, 301-312.
[3] Sunday, D. F.; et. al. Chem. Mater. 2020, 32, 6.
[4] I. C. ten Have; et. al. Chemistry – Methods 2021, 1(5), 205–209.
[5] Eichmann, S.; Nowak, D.; Jacobi, D., Burnham, N. Microsc Microanal, 2018, 24, S1, 1040-1041.
[6] Huang, Y.; et. al. ACS Photonics 2018, 5, 11, 4352-4359.
[7] Otter, L.M.; Förster, M.W.; et.al. GGR Cutting-Edge Review: Geostand Geoanal Res. 2021, 45, 5–27.
[8] Tumkur, T. U.; Yang, X.; Cerjan, B.; Halas, N. J.; Nordlander, P.; Thomann, I. Nano Lett. 2016, 16 (12), 7942-7949.
[9] Song, J.; et. al. Adv Sci Comm 2020, 7, 2001986

Structural and Optical Identification of
Planar Side-Chain Stacking P3HT Nanowires
He-Chun Chou1, Chung-Kai Fang2, Pei-Yun Chung3, Jia-Ru Yu1, Ing-Shouh Hwang2, Jiun-Tai Chen3, andChi Chen1,*
1. Research Center for Applied Sciences, Academia Sinica, Taipei, Taiwan
2. Institute of Physics, Academia Sinica, Taipei, Taiwan
3. Department of Applied Chemistry, National Yang Ming Chiao Tung University, Hsinchu, Taiwan
E-mail: chenchi@gate.sinica.edu.tw

Poly(3-hexylthiophene) (P3HT) is well-recognized for forming π−π stacked crystalline films and nanowires. In thisstudy, we identified a new planar crystalline P3HT architecture assembled by hexyl side chains by building a homemade scanning near-field optical microscopy and confocal microscopy in glove box.[1] The atomic force microscopy
results indicated that both the π−π stacking and side-chain stacking nanowires were crystalline ribbons decorated withamorphous fringes. The different stacking structures of the nanowires led to different interchain coupling strengths andhence spectroscopic properties. Both types of nanowires were characterized using confocal microscopy and homemade scanning near-field optical microscopy. The coexistence of the planar side-chain stacking structure in P3HT
films and nanowires along with the π−π stacking architecture leads to multiplicity in their optical properties.[2]Fig. 1 SNOM-fluorescence imaging of the P3HT NWs. (a and b) Simultaneously recorded AFM topography (a) and SNOMfluorescence intensity map (b) of the P3HT NWs. Cross-sectional profiles of the linecuts in (a) and (b), respectively. (e) Structuralmodel of the transition from the π−π stacking to the side-chain stacking in the NWs. The directions of interchain and intrachain
coupling were also indicated.

.
References[1] Yu, J.-R.; Chou, H.-C.; Yang, C.-W.; Liao, W.-S.; Hwang, I.-S.; Chen, C. 2020, Rev. Sci. Instrum. 91, No. 073703.
[2] Chou, H.-C.; Fang, C.-K.; Chung, P.-Y.; Yu, J.-R.; Liao, W.-S.; Chen, S.-H.; Chen, P.; Hwang, I.-S.; Chen, J.-T. and Chen, C. 2021,
Macromolecules 54, 10750−10757

Using Dispersive Lossy Media to Narrow Plasmon Linewidths
Ryan Peck1, Ali Khademi1, Juanjuan Ren2, Stephen Hughes2, Alex Brolo1, Reuven Gordon1
1. University of Victoria, 3800 Finnerty Rd., Victoria, BC, Canada, V8W 2Y2
2. Queen’s University, 99 University Ave., Kingston, ON, K7L 3N6
E-mail: rpeck34@gmail.com

It is known that the presence of loss in plasmonic systems broadens plasmon linewidths. This relationship isℏexplicitly displayed in the commonly used formula for the linewidth of a plasmon in spectral units: Γ[eV] = , where𝑇𝑇2𝜆𝜆 Γ[eV]𝑇𝑇2 is the total decay time of the plasmon [1]. The linewidth of a plasmon peak in nm is given by Γ[𝑛𝑛𝑛𝑛] = 0

𝐸𝐸0

where 𝜆𝜆0 is the plasmon resonance wavelength and 𝐸𝐸0 is the plasmon resonance energy in eV. Adding loss to thesurrounding medium then allows for plasmons to exchange their energy with the absorbing medium, so that 𝑇𝑇2 isnecessarily decreased which results in an increase in the plasmon linewidth.

Fig. 1 (a) Scattered power for 20 nm gold encased in PMMA and P3HT obtained using a dark field microscope. The linewidths
are the full width at half the maximum (FWHM) of each of the peaks. (b) COMSOL simulations for a 20 nm gold nanoparticle
embedded in 120 nm layers of various surrounding media. The media used in (b) were: 𝜀𝜀1 = 𝜀𝜀P3HT, 𝜀𝜀2 = Re{𝜀𝜀P3HT }, 𝜀𝜀3 =Re{𝜀𝜀P3HT } + 0.3𝑖𝑖, 𝜀𝜀4 = 5 + Im{𝜀𝜀P3HT}𝑖𝑖, 𝜀𝜀5 = 5 + 0.3𝑖𝑖 and , 𝜀𝜀6 = 5.

Dark field microscopy was used to measure the scattering signal from 20 nm gold nanoparticles encased in 120 nm
thin layers of both lossy and non-lossy materials to determine the plasmon linewidths. The organic polymer P3HT,
commonly used in organic photovoltaics, was used as the lossy medium and PMMA was the non-lossy medium. The
results of the dark field measurements are shown in Fig. 1 (a). Intuitively, and as expected from the linewidth formula
shown above, adding loss to the surrounding medium should broaden plasmon linewidths [2], but here we see theopposite; P3HT has a much narrower cross section than PMMA. To verify this odd result, Lumerical FDTD
simulations were performed which showed good agreement with the measured spectra.
Using a Green function scattering theory, it was found that the dispersion in both the real and imaginary parts ofthe permittivity have a significant impact on the plasmon linewidth. Figure 1 (b) shows the results of COMSOL
simulations, which calculated the Green function propagator, S, for a 20 nm gold nanoparticle embedded in a varietyof 120 nm thick surrounding media. PMMA is not dispersive while P3HT has a large dispersion for both the real andimaginary parts of the permittivity near the plasmon peak. In the Rayleigh scattering regime, the plasmon resonancecondition for a small nanoparticle is met when 𝜀𝜀1 = −2𝜀𝜀2 , where 𝜀𝜀1 is the nanoparticle permittivity and 𝜀𝜀2 is thepermittivity of the surrounding medium. The plasmon resonance is swept through much faster for P3HT than for
PMMA due to the high dispersion of P3HT which causes a reduction in the plasmon linewidth. Also, the magnitudeof the permittivity plays an important role in narrowing linewidths. In Fig. 2, the 𝜀𝜀6 = 5 peak has a narrow linewidthof 28 nm, even without dispersion. This is because, although the surrounding medium lacked dispersion, a large real
permittivity red shifts the plasmon peak into a region where gold has a high dispersion, and so this greater dispersion
in the gold nanoparticle narrows the linewidth. Therefore, the commonly used linewidth formula is inaccurate when
considering dispersive and lossy media such as P3HT, and when dispersion is involved, lossy media can even yield
narrower linewidths than non-lossy media.
References[1] Maier, S.A. Localized Surface Plasmons, “Plasmonics: Fundamentals and Applications”. 2007, Springer Science+Business Media LLC, 233
Spring Street, New York, NY, page 75.
[2] Mishchenko, M. I., and Janna M. D. 2019, "Plasmon resonances of metal nanoparticles in an absorbing medium", OSA Continuum 2.12,3415-3421.

Coherent control of plasmon interferences in 2D crystalline cavities for
Boolean calculation
Florian Dell’Ova1, Diana Shakirova1,3, Yoann Brulé1, Laureen Moreaud2, Gérard Colas-Des-Francs1, Erik
Dujardin1,2 and Alexandre Bouhelier1
1. Laboratoire Interdisciplinaire Carnot de Bourgogne, CNRS UMR 6303, Université Bourgogne Franche-Comté, Av. A. Savary, 21000 Dijon,
France2. CEMES, CNRS UPR 8011, 29 rue J. Marvig, 31055 Toulouse, France
3. Faculty of Physics of ITMO University, Ronverksky Pr. 49, bldg. A, St. Petersburg, 197101, Russia.
E-mail: florian.dell-ova@u-bourgogne.fr

We are exploring a strategy for optical information processing by developing an integrated planar plasmonic
calculator [1]. The device we propose is a 2D modal plasmonic cavity made of crystalline gold, as shown in Fig.1A.
The double hexagonal shape of the cavity is engineered by Focus Ion Beam milling. This specific shape offers a richplasmon modal landscape enabling the transport and the treatment of the optical information through the device. The
input and output nodes, defined by the apexes of the double hexagon, are linked via interacting plasmon modes. Surface
plasmons convert the near-infrared incoming laser femtosecond pulses into visible photons in order to build the desired
logical operations in remote region of the device[2,3]. This wavelength up-conversion, called nonlinear
photoluminescence (nPL), is a sensitive nonlinear probe for the plasmon local electric field [4] and characterizes theoutputs of the logic gate (see fig.1 B).
Controlling the interaction between mobilized surface plasmons is a critical point in the operation of thecalculator. This is achieved by adjusting the polarization of the entry nodes and controlling the phase of the plasmon
interference pattern. To do so, we implemented a spatially steerable diffraction-limited temporally-synchronized dual
excitation nodes capable of accommodating any non-trivial device geometry. Our control strategy allows for an agile
reconfiguration of truth table of the logic gate. The Boolean values are encoded on the input nodes into the polarization
states of the two optical stimuli feeding the calculator.
With this specific geometry, we are able to reconstruct the truth table of all basic logic operations [5]. Taking
advantage of the coherent effects when the input nodes are temporally synchronized, we demonstrate an XOR gate anda half-adder based on plasmon interferences.

Fig. 1 A. Colorized scanning electron microscopy image of a double hexagonal shaped Au cavity. The white scale bar
is 500 nm. B. Nonlinear photoluminescence wide field image of the cavity under two beams excitation, positioned in I1
and I2 respectively. Both beams are horizontally polarization (white arrow) and the relative phase between the twopulses is 98 ± 11°.

References[1] Kumar, U. et al. 2018. ACS Photonics, vol. 5, no. 6, pp. 2328–2335.
[2] Viarbitskaya, S., Demichel, O., Cluzel, B., Colas des Francs, G., and Bouhelier, A. 2015. Phys. Rev. Lett., vol. 115, no. 19, p. 197401.
[3] Agreda, A. et al. 2019. ACS Photonics, vol. 6, no. 5, pp. 1240–1247.
[4] Bouhelier, A., Bachelot, R., Lerondel, G., Kostcheev, S., Royer, P. and Wiederrecht, G.P. 2005. Phys. Rev. Lett., vol. 95, no. 26, p. 267405.
[5] Kumar, U. et al. 2021. ACS Nano, vol. 15, no. 8, pp. 13351–13359.

Analytic methods to study the properties of electromagnetic waves inplasmonic slot waveguides
Amrita Pati1& Reuven Gordon1
1. Department of Electrical and Computer Engineering, University of Victoria, 3800 Finnerty Road, Victoria, British Columbia, V8P 5C2, Canada
rgordon@uvic.ca

Plasmonic slot waveguides produce highly localized electromagnetic (EM) fields over a wide range of frequencies
which makes them suitable for applications varying from modulators [1] to optical tweezers [2]. They support modes
with long propagation lengths and high group velocities in the optical communication regime [3], allow sharp bending
angles at lower levels of losses [4], and are easy to fabricate. In addition, the metal layers provide contacts down to thesubwavelength scale and being good thermal conductors, improve heat dissipation in the circuitry [5]. Among several
other applications, these properties of gap plasmon-based waveguides can be used to interface Si photonics andelectronics which can potentially lead to highly miniaturized and faster communication devices.
However, their practical implementation requires reliable computation of several waveguide parameters anddetermination of metal geometry that optimizes the performance of the structure. Several works in the past haveanalyzed the metal-insulator-metal structures but the majority of them use the numerical analysis approach. Numericalsimulations are resource-intensive and do not offer any insights into the actual interactions taking place between the
EM waves and the metal. Our goal here is to build a simple theoretical framework to explain the reflection andpropagation of EM waves in the slot, compute their modal properties, and identify the desired optimal configuration.
In our previous work, we studied the 2-D slit geometry in real metals [6]. We derived an analytic expression forreflection coefficient in the slit using the effective index approximation. Our approach eliminated the need for any
numerical techniques including numerical integration. We compared the values of the reflection phase with a past workand found agreement to within 0.06 rad [7]. The Fabry-Pérot model was used to calculate the optical cross-sections,field intensity, and power inside the slit and this allowed us to establish the condition for maximum power transfer inthe slit as shown in Fig. 1(a). The narrowest slits generated the highest field intensities but in contrast, the power
peaked for slit configurations that produced equal scattering and absorption cross-sections at resonance.

Fig. 1 (a) Variation of power, optical cross-sections with the width of a slit, power in the slit is maximum for equal values of scattering (σs) andabsorption (σa) cross-sections at resonance. (b) Reflection amplitude vs incidence angle in a plasmonic slot waveguide of width 30 nm at different
wavelengths (617 nm, 705 nm, 756 nm). (c) Lumerical FDTD simulations showing the electric field in a 60 nm slot waveguide on a glass substrate

In our current work, we focussed on a 3-D plasmonic slot waveguide. Linearly polarized EM waves were incident
on the slot at an angle θ. First, we derived an analytic equation for the reflection coefficient in the slot by assuming themetal to be a perfect conductor. Next, we invoked the effective index approximation to incorporate the losses of a real
metal into our equation. Fig. 1(b) shows the theoretically calculated values of reflection amplitude in the slot
waveguides for different wavelengths. They were validated against numerical FDTD simulations. The values of thereflection coefficient were used to determine the guiding condition for the waveguide and other modal properties suchas group velocity and propagation length which are key in designing high-performance plasmonic slot waveguides.
References[1] Haffner, C., Heni, W., Fedoryshyn, Y., Niegemann, J., Melikyan, A., Elder, D. L., Salamin, Y., Josten, A., Koch, U., Hoessbacher, C., Ducry,F., Juchli, L., Emboras, A., Hillerkuss, D., Kohl, M., Dalton, L. R., Hafner, C., Leuthold, J., 2015. Nat. Photon., 9, 525-528[2] Pang, Y., Gordon, R., 2012. Nano Lett., 12, 402-406[3] Veronis, G., Fan, S., 2005. Opt. Lett., 30, 3359-3361[4] Liu, L., Han, Z., He, S., 2005. Opt. Express, 13, 6645-6650[5] Gordon, R., Dobinson, M., 2021. Opt. Mater. Express, 11, 2192-2196[6] Pati, A., Gordon, R., 2021. Opt. Express, 29, 38129-38139[7] Sharifi, Z., Gordon, R., 2022. Plasmonics 17, 315–320

Plasmonic nonlinear response from hBN nanoflakes excited with a CW laser
Mirali Seyed Shariatdoust1, Michael Dobinson1, Ghazal hajisalem1, Reuven Gordon1
1. Department of Electrical and Computer Engineering, University of Victoria, Victoria, British Columbia V8P 5C2, Canada
E-mail: mseyedshariatdoust@uvic.ca

Trapping single hexagonal boron nitride (hBN) nanoflakes in a double nanohole using optical tweezers made it
possible to obtain a nonlinear response from sub-diffraction limit area where it was pumped with low power continuous
wave laser (~10 mW). Here, we demonstrate second harmonic generation (SHG) at 486.5 nm from the hBN nanoflakes
mixed with gold nanorods illuminated at 973 nm. It is promising to use the gold nanorods with resonance tuned at 973
nm since they provide around 1000 times more electric field intensity over double nanoholes. The SHG is not resolved
from the nanorods alone, or the nanoflakes in absence of the nanorods. This scheme can be used in telecommunications
band signal detection using silicon-based detectors and ultra-fast imaging [1,2].

Fig. 1 Initial source (973 nm) and second harmonic signal (486.5 nm) spectrum

References[1] Hajisalem, G., Shariatdoust, M. S., Ali, R. F., Gates, B. D., Barclay, P. E., and Gordon, R. 2021. ACS Photonics, Single nanoflake hexagonalboron nitride harmonic generation with ultralow pump power, 8(7), 1922-1926.
[2] Yao, K., Yanev, E., Chuang, H. J., Rosenberger, M. R., Xu, X., Darlington, T., McCreary, K. M., Hanbicki, A.T., Watanbe, K., Taniguchi, T.,
Jonker, B.T., Zhu, X., Basov, D.N., Hone, J.C., and Schuck, P. J. 2019. . ACS Nano, Continuous wave sum frequency generation and imaging ofmonolayer and heterobilayer two-dimensional semiconductors, 14(1), 708-714.

Fundamental limits and complete coupling of light into polaritons
Eduardo J. C. Dias1, F. Javier García de Abajo1,2
1. ICFO - Institut de Ciencies Fotoniques, The Barcelona Institute of Science and Technology, 08860 Castelldefels (Barcelona), Spain
2. ICREA - Institució Catalana de Recerca i Estudis Avançats, Passeig Lluís Companys 23, 08010 Barcelona, Spain
E-mail: eduardo.dias@icfo.eu

Polaritons in metals and 2D materials have been extensively studied over the past decade due to their fundamental
interest and as a platform for applications in telecommunications and sensing. The wavelength of these polaritons isgenerally small compared to that of a photon of the same frequency, making them very attractive to manipulate lightat deep-subwavelength distances. However, it simultaneously introduces a challenge in the coupling between
propagation light and plasmonic modes, since the momentum mismatch between the two makes the in/out-couplingof this process intrinsically weak.
In this work, we address some fundamental limits in the coupling of radiation to surface polaritons [1]. We study
the scattering properties of point-like scatterers over a polariton-supporting surface and quantify the coupling of lightto-polaritons cross-section for this process as a function of the scatterer effective polarizability. We further find ageneralization of the optical theorem to surface polaritons, which remarkably leads to a fundamentally maximum limit
on light-to-polariton coupling cross-section, under plane-wave illumination.
We furthermore show that the fundamental limit described above can be overcome by a small scatterer placed ata suitable distance from a planar surface, under illumination by an adequately focused light beam [2]. We present
rigorous closed-form prescriptions for the modulation of the incident light beam which maximizes this coupling,depending on the characteristics of the scatterer and surface, and show that it can lead to complete coupling to surface
polaritons (Fig. 1a). We corroborate the analytical results by performing rigorous fully-numerical simulations using
realistic setups, which exhibit a very strong enhancement of the absorption into surface plasmons under the prescribed
optimal conditions (Fig. 1b,c).
Our results open a practical route to circumvent the long-standing photon-polariton wavelength mismatch problem
in Nanophotonics.

Fig. 1 (a) Dependence of the maximum coupling fraction 𝐴𝐴max on frequency 𝜔𝜔 and particle-surface separation 𝑎𝑎 for a point

dipole above a semi-infinite Drude metal film with plasma frequency 𝜔𝜔p and damping 𝜔𝜔p /100, approaching 100% for a wide
combination of the two parameters. (b,c) Numerical simulations of the near-field under optimal illumination in the (a) absenceand (b) presence of a Si spherical scatterer with diameter 𝐷𝐷 (represented by open and solid circles, respectively) at a distance 𝑎𝑎
from the surface of a Ag semi-infinite-film. The presence of the Si sphere enhances the absorption into silver plasmons to ~80%.

References[1] E.J.C.Dias and F.J. García de Abajo, "Fundamental Limits to the Coupling between Light and 2D Polaritons by Small Scatterers." ACS Nano
13, 5184 (2019).
[2] E.J.C.Dias and F.J. García de Abajo, "Complete Coupling of Focused Light to Surface Polaritons." Optica 8, 520 (2021).

Engineering circular dichroism of stretchable chiral metamaterial
Florian Lamaze1, Jérémie Béal1, Julien Proust1, Louis Giraudet2
1 Light, nanomaterials, nanotechnologies EMR 7004, Université de Technologie de Troyes, 10004 Troyes
2. Laboratoire De Recherche en Nanosciences (LRN) - EA 4682, Université de Reims Champagne-Ardenne, 51687 Reims
E-mail: florian.lamaze@utt.fr

Due to their confined and enhanced localized electric field, plasmonic nanostructures are systems providing
extreme sensitivity to their close environment. Consequently, the deformation of a flexible substrate permits themodulation of the Localized Surface Plasmon Resonance (LSPR) of plasmonic gold nanostructures via the inducedchange in the geometry [1]. This should allow the development of high sensitivity deformation sensors.
The 2D chirality of gold nanoparticles on a substrate leads to a large change in the LSPR depending on the directionof rotation of a circularly polarized source. This introduces the notion of circular dichroism (CD) which corresponds
to the difference in response between right and left polarization. Since chirality is strongly dependent on geometry, it
can be expected that a change in the latter via the application of a deformation leads to a significant variation in circulardichroism [2].
The chosen chiral antenna is composed by a central cylinder with six “satellites” ellipsoids, as shown on Fig.1 (a).
We used electron beam lithography to fabricate the structure on solid substrate, as shown on the SEM image on Fig.1(b), and then transferred on a flexible substrate with a homemade process.
Here, we present the results of a combined numerical and experimental study. We used the Finite Difference Time
Domain (FDTD) method to optimize the circular dichroism and its variation, as shown on Fig.1 (c,d), via theimplementation of a homemade deformation model. The circular dichroism variation was experimentally investigatedand compared with numerical simulations thanks to in situ scattering measurement with an integrating sphere.
(a)(d)

Circular Dichroism (%)

(c)

(b)
s

Wavelength (nm)Fig. 1 (a) Schematic of the structure consisting of a central cylinder with six “satellites” ellipsoids and the associated parameters.
(b) SEM image of the structure. (c) FDTD Circular Dichroism spectra of the structure at 0% and 20% of deformation. (d) FDTD
maps of the maximum CD as a function of different parameters.

References[1] Cataldi, U. Caputo, R. Kurylyak, Y. Klein, G. Chekini,C.U. Bürgi, T. 2014. J. Mater. Chem. C, 2(37), 7927-7933[2] Zu, S. Bao, Y. Fang, Z. 2016. Nanoscale, 8(7), 3900-3905

Exciting and mapping directional surface plasmon polaritons using
automated dual-tip scanning near-field optical microscope
Najmeh Abbasirad 1, Angela Barreda2, Michael Steinert1 , Yi-Ju Chen3 , Isabelle Staude 2, Jer-Shing Huang3,
Frank Setzpfandt1, 4 and Thomas Pertsch 1, 4
1. Institute of Applied Physics Abbe Center of Photonics Friedrich-Schiller-Universität Jena, Albert-Einstein-Str. 15, 07745 Jena, Germany
2. Institute for Solid State Physics, Friedrich Schiller University, Helmholtzweg 3, 07743 Jena, Germany
3. Research Department of Nanooptics, Leibniz Institute of Photonic Technology, Albert-Einstein Str. 9, 07745 Jena, Germany
4. Fraunhofer Institute of Applied Optics and Precision Engineering, Albert-Einstein-Str. 7, 07745 Jena, Germany
E-mail: najmeh.abbasirad@uni-jena.de

Using the dual-tip scanning near-field optical microscope (SNOM), we experimentally measured directionalsurface plasmon polaritons (SPPs) at an air-gold interface excited by a dipolar emission from an aperture tip. The
experimental results are supported by numerical simulations based on the Bethe-Bouwkamp model.
Different geometries, including slits and nanoantennas, have been shown to excite SPPs with directional
properties[1-2]. In this work, an automated dual-tip SNOM was used to map directional SPPs in the near-field of an
air-gold interface [3]. Two aperture tips of an automated dual-tip SNOM were exploited to excite and map the SPP
pattern in the near-field. To perform the near-field measurement, the excitation tip was stationary, illuminating a
monocrystalline gold platelet at a wavelength 𝜆0 = 1.55 µ𝑚, and the excitation tip mapped the SPPs near-field
angular pattern around the excitation tip.
Figures 1(a) and (b) show SEM images of the excitation and detection tip apex, respectively. The directional
measured near-field pattern of the SPPs is observed in Fig. 1(c). When the excitation aperture tip is considered as ananoantenna, due to its geometry, the directional pattern results from both in-plane magnetic and out-of-planeelectric dipoles excitation [4-5].

Fig. 1 SEM images of (a) excitation (b) detection tips. (c) Near-field measurements of the SPPs directional propagation due tothe dipolar emission from the excitation aperture tip. (d) Simulated magnetic field intensity. The scale bar denotes 1 µm.

To simulate the SPPs angular distribution pattern, we have used the Bethe-Boukamp model employing an out-of-planeelectric dipole and in-plane magnetic dipole at the center of the aperture. Figure. 1(d) depicts the corresponding
magnetic field intensity calculated in a plane 20 nm above the gold platelet, using the FDTD Solver Lumerical. In
parabolic-like gray regions, no optical data is accessible. The good agreement between the measured near-field andthe simulation verifies that the out-of-plane electric and in-plane magnetic dipoles are excited due to the asymmetryof the aperture tip apex geometry.
References[1] Rodríguez-Fortuño, F. J., Marino, G., Ginzburg, P., O’Connor, D., Martínez, A., Wurtz, G. A., & Zayats, A. V. (2013). Near-field interference
for the unidirectional excitation of electromagnetic guided modes. Science, 340(6130), 328-330.
[2] Xi, Z., Lu, Y., Yu, W., Wang, P., & Ming, H. (2014). Unidirectional surface plasmon launcher: rotating dipole mimicked by opticalantennas. Journal of Optics, 16(10), 105002.
[3] Abbasirad, N., Berzins, J., Kollin, K., Saravi, S., Janunts, N., Setzpfandt, F., & Pertsch, T. (2019). A fully automated dual-tip scanning nearfield optical microscope for localized optical excitation and detection in the visible and near-infrared. Review of Scientific Instruments, 90(5),053705.
[4] Rotenberg, N., Krijger, T. L., Le Feber, B., Spasenović, M., de Abajo, F. J. G., & Kuipers, L. (2013). Magnetic and electric response of single
subwavelength holes. Physical Review B, 88(24), 241408.
[5] Novotny, L., & Hecht, B. (2012). Principles of nano-optics. Cambridge university press.

Towards complete optical coupling to ultraconfined surface polaritons
Saad Abdullah1, Jan Krpensky1, Eduardo J. C. Dias1, Vahagn Mkhitaryan1,2, F. Javier García de Abajo1,3

2

1
ICFO - Institut de Ciencies Fotoniques, The Barcelona Institute of Science and Technology, 08860 Castelldefels (Barcelona), Spain
School of Electrical and Computer Engineering, Birck Nanotechnology Center and Purdue Quantum Science and Engineering Institute, Purdue
University, West Lafayette, IN 47906, USA
3
ICREA-Institució Catalana de Recerca i Estudis Avançats, Passeig Lluís Companys 23, 08010 Barcelona, Spain

Abstract: We experimentally demonstrate high coupling of light to surface polaritons by means ofan optimized scatterer placed at a suitable distance from a polariton-supporting surface.
Specifically, we consider poorly-absorbing gold disks acting as nearly-perfect resonant scatterers,
which we separate from a gold film by means of a dielectric silica spacer. This configuration leads
to resonant coupling between externally incident light and plasmon polaritons in the film withassociated cross sections that approach the fundamental limit ~λ2 imposed by the light wavelength
λ. Our method introduces a disruptive, efficient way to solve the in/out-coupling problem in
nanophotonics.
We experimentally demonstrate a high coupling of light to surface polaritons by means of optimized scatterers
placed at a suitable distance from a polariton-supporting surface. Specifically, we consider poorly-absorbing gold
disks acting as nearly-perfect resonant scatterers, which we separate from a gold film by means of a dielectric silica
spacer. In this configuration, the scatterer develops a strong induced dipole under external illumination tuned to theparticle resonance, which mediates the coupling between light and surface polaritons. However, if the scatterer is too
close to the surface, the resonance is quenched by the very same coupling that we intend to achieve, thus reducing
the overall dipolar strength and, consequently, the efficiency of the coupling scheme. By separating the particle fromthe surface, an optimum distance is found for which a compromise between resonance strength (increasing withseparation) and efficiency of coupling (decreasing with separation) is optimized. Here, we report experimental
results showing nearly complete coupling by means of gold-disk scatterers coupled to plasmon polaritons in a planargold surface. To this end, we measure the infrared reflectance spectra of the scatterer-spacer-surface system, fromwhich we extract the effective polarizability as well as the associated coupling cross sections, which approach thefundamental limit ~λ2 imposed by the light wavelength λ. Our experimental data are in agreement with numericalsimulations, which we complement with analytical theory. These findings provide a disruptive, efficient approach
to solving the long-standing problem of unity-order in/out coupling in nanophotonics.

Fig 1: Scheme of the coupling configuration and working principle. A dipolar scatterer is placed close to apolariton-supporting substrate and illuminated under normal incidence conditions. The scatterer develops an
induced dipole that couples to the surface polaritons. If the scatterer is placed too close to the surface, the lightemission that it produces (i.e., the scattered field) is strongly quenched by the sought-after coupling topolaritons, thus reducing the overall dipolar strength of the combined scattered-substrate system. By separating
the particle from the surface, an optimum distance is found for which the compromise between large strength(increasing with separation) and strong coupling to polaritons (increasing with decreasing distance) is optimized.

References[1] Z. Liang, L. Jiang, X. Chen, ”Plasmonic Enhanced Optoelectronic devices,” Plasmonics 9, 859 (2014).
[2] E. J. C Dias, F. J. García de Abajo, ”Complete coupling of focused light to surface polaritons,” Optica 8, 520 (2021).
[3] P. Grahn, A. Shevchenko, M. Kaivola. ”Electromagnetic multipole theory for optical nanomaterials,” New Journal of Physics, 14 093033(2014).
[4] P. K. Jain, K. S. Lee, I. H. El-Sayed, M. A. El-Sayed. ”Calculated Absorption and Scattering Properties of Gold Nanoparticles of Different
Size, Shape, and Composition: Applications in Biological Imaging and Biomedicine,” The Journal of Physical Chemistry110, 7238-7248(2006).

Aluminum – Zinc Oxide hybrid nanostructures for UV emission
Thomas Simon1, Sergei Kostcheev1, Anna Rumyantseva1, Jérémie Béal1, Davy Gérard1 and Jérôme Martin1
1. Light, nanomaterials and nanotechnologies (L2n), CNRS EMR 7004, Université de Technologie de Troyes,
12 rue Marie Curie, 10004 Troyes cedex, France
E-mail: thomas.simon@utt.fr, jerome.martin@utt.fr

Aluminum nanostructures are now considered as one of the most efficient building blocks for obtaining plasmonicresonances in blue-UV. Moreover, arrays of metallic nanoparticles can sustain hybrid modes between Localized
Surface Plasmon Resonances (LSPR) and grating Rayleigh anomaly, called Surface Lattice Resonances (SLR). These
modes exhibit a Fano-like shape and a lower linewidth compared to the LSP mode of an isolated particle [1].
On the other hand, optical nanoantennas such as plasmonic nanostructures can significantly enhance thephotoluminescence (PL) of nearby emitters. Although enhancement factors of several orders of magnitude have beenreported for quantum dots or molecules, the weak spatial overlap between the emitter and the electromagnetic modesof the nanoantenna lessens the luminescence enhancement magnitude in the case of bulk materials.
Here, we study the coupling between the excitonic emission of a wide-bandgap semiconductor emitter, attachedto the Al metal part, which acts as both an antenna and a light amplifier. The device we propose is composed of a solidstate ultraviolet emitter based on a thin film of zinc oxide coupled with an array of aluminum nanoparticles, as shown
Fig. 1 (a). The Al nanorod array is designed to sustain SLR in the near ultraviolet. We use electron beam lithography
to fabricate the aluminum nanostructures and plasma assisted sputtering to deposit ZnO thin film [2], as shown on the
AFM image on Fig. 1 (b).
We experimentally demonstrate that ZnO’s PL emission can be increased up to a factor of 3 with the addition of
the structures, as shown Fig. 1 (c, d). We also demonstrate that SLRs are more efficient for the ZnO luminescenceenhancement compared to localized surface plasmon resonances and observe the difference in behavior between
possibilities in the tuning wavelength of the structure.

Fig. 1 (a) Schematic of the structures consisting of an array of Aluminum nanoparticles on top of a ZnO thin film. (b) AFM
image of the structure. (c) Photoluminescence spectra of the ZnO film with and without the structures. (d) Corresponding
enhancement spectra.

References[1] Khlopin, D., Laux, F., Wardley, W., Martin, J., Wurtz, G., Plain, J., Bonod, N., Zayats, A., Dickson, W., and Gérard, D. 2017. J. Opt. Soc.
Am. B, 34, 3.
[2] Simon, T., Kostcheev, S., Rumyantseva, A., Béal, J., Gérard, D, and Martin, J. 2021. J. Appl. Phys., 130, 22.

Fast electrical modulation of a single plasmonic nanoresonator
Luka Zurak1, Jessica Meier1, René Kullock1, Bert Hecht1 and Thorsten Feichtner1
1. Nano-Optics and Biophotonics Group, Experimental Physics 5, University of Würzburg, Germany
E-mail: luka.zurak@physik.uni-wuerzburg.de

The resonance of a plasmonic nanoresonator depends on the density of free electrons 𝑛𝑛0 , as the resonant frequencyof the system is proportional to the plasma frequency of the underlying material [1]. A straightforward idea tointroduce a change of 𝑛𝑛0 , and thereby a change in the plasma frequency, is by means of capacitive charging. Since thecapacitance for a typical nanoresonator is on the order of ten attofarads, even for applied voltages in the order of tensof volts only few hundreds of additional electrons can be pushed on the surface of the resonator. Due to the large
intrinsic density of free electrons, the induced relative change in 𝑛𝑛0 is on the order of 10-4. This makes plasmonicresonances pretty robust against charging and corresponding spectral changes difficult to observe.
In order to surpass the limitations of typical capacitive systems, ion gels have been employed in earlier works
leading to an increase in capacitance due to the proximity of additional ions to the metal surface [2,3]. However, oneof the drawbacks of this approach is a very slow switching time as well as occurrence of hysteresis which likely
originate in surface chemistry effects [3].
Here, we demonstrate fast electrical modulation of the plasmonic resonance of a single electrically connected gold
nanorod. We employ lock-in techniques to measure the relative change of the scattering signal 𝛥𝛥 𝑆𝑆 ⁄𝑆𝑆0 in the spectral
range from 500 to 900 nm, while driving our structure with up to 50 kHz in frequency and up to 30 V in voltage
amplitude. The obtained results are of the expected order of magnitude according to existing theories, which we
discuss in detail. Our results form the basis for the thorough understanding of numerous effects in earlier publications
including the so-called plasmoelectric potential [4].

Fig. 1 a) Colored SEM images of the electrically connected gold nanoresonator for capacitive charging. Scale bar is 500 nm, and 100 nm in theinset. b) Unchanged scattering spectra 𝑆𝑆0 (top) and relative change of scattering 𝛥𝛥 𝑆𝑆⁄𝑆𝑆0 under applied potentials (bottom), in experiment (left)
and simulation (right).

References[1] Biagioni, P., Huang, J. S, Hecht, B. 2012 Rep. Prog. Phys., 75, 1-40
[2] Collins, S. S. E., Wei, X., McKenzie, T. G., Funston A. M., Mulvaney, P. 2016 Nano Lett., 16, 6863−6869[3] Maniyara, R. A., Rodrigo, D., Yu, R., Canet-Ferrer, J., Gosh, D. S., Yongsunthon, R., Baker, D. E., Rezikyan, A., Garcia de Abajo, F. J., Pruneri, V.
2019 Nat. Photon., 13, 328-333[4] Sheldon, M. T., Van de Groep, J., Brown, A. M., Polman, A., Atwater, H. A. 2014 Science, 346, 828-831

Fractal-like multiresonant aluminum optical antennas – the Cayley Tree
Thomas Simon1, Xiaoyan Li2, Jérôme Martin1, Dmitry Khlopin1, Odile Stéphan2, Mathieu Kociak2 andDavy Gérard1
1. Light, nanomaterials and nanotechnologies (L2n), CNRS EMR 7004, Université de Technologie de Troyes,
12 rue Marie Curie, 10004 Troyes cedex, France
2. Laboratoire de Physique des Solides, Bâtiment 510, UMR CNRS 8502, Université Paris Saclay, Orsay 91400, France
E-mail: thomas.simon@utt.fr, jerome.martin@utt.fr

An optical antenna is a nanostructure that can convert an incident free radiation into a localized excitation, and thereciprocal. Being able to perform different functions, such as entrance and exit ports, energy harvesting systems,
directional emitters, or substrates for enhanced spectroscopies, they have become vastly used as building blocks fornanophotonic devices [1]. Optical antennas are usually made with resonant nanoparticles, whether metallic or
dielectric, but it is still a challenge to obtain structure exhibiting multiple broadband resonances, over a large span ofwavelengths. This kind of structures could be interesting for fields such as nonlinear optics or multiple harmonics
generation.
Here, we studied a self-similar, fractal-like structures, known as the Cayley Tree, as broadband optical antennas[2]. The aluminum nanoparticles based on this specific shape were fabricated using electron beam lithography on TEM
compatible substrate (15-nm-thick Si3N4 membranes). Using Electron Energy Loss Spectroscopy (EELS), we
experimentally evidenced that a single aluminum Cayley tree, a simple self-similar structure, sustains multiple
plasmonic resonances. The comparison with Finite Difference Time Domain (FDTD) simulations allowed us todistinguish between bright “extremity” modes and dark “core” modes [3].
We experimentally observed that the spectral position of these resonances spans over a wide range of frequencies,
from ultraviolet to thermal infrared, and can be tuned by adapting the length of the different parts of the particle. As
such, Cayley Tree based nanostructures would be of high interest in a variety of applications as photodetection, lightharvesting, surface-enhanced spectroscopy and even nonlinear optics.

Fig. 1 (a) Schematic FDTD-simulated extinction spectra for aluminum Cayley trees with different generations.
(b) Energy-filtered EELS maps at different resonance wavelengths for a Cayley Tree of generation 3, showing the bright“extremity” modes (upper three) and dark “core” modes (lower three).

References[1] Novotny, L., & Van Hulst, N. 2011. Nat. photonics, 5, 2.
[2] S. Gottheim, H. Zhang, A. O. Govorov, N. J. Halas. 2015. ACS Nano, 9, 3.
[3] Simon, T., Li, X., Martin, J., Khlopin, D., Stéphan, O., Kociak, M., Gérard, D. 2022. Proc. Natl. Acad. Sci. U.S.A., 119, 4.