NanoPlasMeta 2021 Abstracts


Area 1 - Nanophotonics, Plasmonics and Metamaterials

Nr: 2
Title:

An Overview of New Effects in Molecular Optomechanics

Authors:

Ruben Esteban

Abstract: The interaction between molecular vibrations at infrared frequencies and optical nanocavities that support plasmonic resonances at significantly larger energies can be understood in terms of quantum optomechanics [1-2]. This molecular optomechanical framework offers a very complete description of the Raman scattering that occurs in the system, whereby a plasmon excited by a laser of frequency ωl interchanges energy with the molecular vibrations that oscillate with frequency ωv, resulting in an increase of the vibrational population and the emission of Stokes and anti-Stokes photons at a shifted energy ħ(ωl - ωv) or ħ(ωl + ωv), respectively . For simple conditions, this description fully recovers the well-known scaling of the Raman signal with the fourth power of the classical enhancement of the local electric fields near the plasmonic particle, which is at the origin of the huge increase of the emitted signal in Surface Enhanced Raman Spectroscopy. It also correctly predicts the quadratic increase of the anti-Stokes signal with laser intensity that is found when the vibrational population is induced by the Stokes scattering instead of by a thermal process, in the vibrational pumping regime [3-5]. This contribution presents the molecular optomechanics framework and describes how it can be used to explore a variety of novel or less well understood effects in Surface Enhanced Raman spectroscopy, which include a signal divergence called parametric instability [1,3], collective effects in the presence of many molecules [6], a rich scenery of correlations of the emitted photons[7] and coupling between vibrational and electronic degrees of freedom of the molecule at large intensities [8,9]. We also describe how, although a single-mode description of the plasmonic response is advantageous to understand the main optomechanical effects, it is essential in many situations to consider the full plasmonic behaviour [10,11]. This work can thus serve as a guide of experiments investigating new effects in Surface Enhanced Raman Spectroscopy [12,13]. REFERENCES [1] P. Roelli, C. Galland, et al., Nat. Nanotech. 11, 164 (2016). [3] M. K. Schmidt, R. Esteban, et al., ACS Nano 10, 6291 (2016). [3] M. K. Schmidt, R. Esteban et al., Faraday Discuss. 205, 31 (2017). [4] E. C. Le Ru and P. G. Etchegoin. Faraday Discuss. 132, 63 (2006). [5] K. Kneipp, Y. Wang,et al., Phys. Rev. Lett. 76, 2444 (1996). [6] Y. Zhang, J. Aizpurua, and R. Esteban, ACS Photonics 7, 1676 (2020). [7] M. K. Schmidt, R. Esteban et al., arXiv:2009.06216. [8] T. Neuman, R. Esteban et al. , Phys. Rev A 100, 043422 (2019). [9] T. Neuman, J. Aizpurua and R. Esteban Nanophotonics 9, 295 (2020). [10] M. K. Dezfouli and S. ACS Photonics, 4, 1245 (2017). [11] Y Zhang, R. Esteban et al., Accepted in Nanoscale [12] A. Lombardi, M. K. Schmidt et al. Phys. Rev. X, 8, 011016 (2018). [13] F. Benz, M. K. Schmidt et al., Science 354, 726 (2016).

Nr: 3
Title:

Controlling Light Emission and Light Wavefronts with Dielectric Nanoantennas

Authors:

Ramon Paniagua-Dominguez, Parikshit Moitra, Xu Xuewu, Rasna M. Veetil, Liang Xinan, Mengfei Wu, Son Tung Ha, Zhenying Pan, Vytautas Valuckas and Arseniy Kuznetsov

Abstract: Recent years have witnessed a tremendous development in the field of optical nanoantennas and metasurfaces, artificially structured surfaces whose electromagnetic response to an external stimulus can be engineered almost at will [1]. Using subwavelength inclusions to locally modify the fundamental properties of light (phase, amplitude and/or polarization), metasurfaces allow manipulation of light waves with unprecedented resolution, opening venues to substitute traditional bulk optics by miniaturized and planar components with enhanced functionalities, so called flat optics components. Starting from the initial demonstrations based on plasmonic structures, the field has steadily moved towards using dielectric materials, offering lower dissipative losses, richer phenomenology of optical modes [2] and, ultimately, higher efficiencies, which may reach values competing with those of traditional refractive optics [3]. Beyond the static manipulation of wavefronts provided by flat optical components, recent research efforts have shifted focus towards active or tunable metasurfaces, aiming to obtain control over light emission processes and dynamic manipulation of light wavefronts [4]. In this talk, we will present our recent advances in these two directions. Regarding light emission, we will show how the rich phenomenology of optical modes available in resonant dielectric nanoantennas allow enhancing and tailoring light emission processes. In particular, we will show how the eigenmodes of these systems can be engineered to suppress radiation loses, enabling high quality factors with very small form factors and, ultimately, nano- and micro-scale laser with intriguing emission properties [5-8]. Regarding dynamic manipulation of light, we will show hoe interfacing dielectric nanoantennas and liquid crystals (LC), it is possible to dynamically modulate the phase of light at the single or few particle level by applying external biases. We employ this concept to obtain a proof-of-principle spatial light modulator (SLM) consisting of individually addressable linear pixels containing few nanoantennas that is in turn used to realize tunable beam steering [9]. We will discuss future prospect in this two research lines and how this findings may find relevant applications in areas spanning from LIDAR and 3D mapping to near-eye and holographic displays. References [1] N. Yu and F. Capasso, “Flat optics with designer metasurfaces”, Nature Mater. 13, 139-150 (2014). [2] A. I. Kuznetsov et al., “Optically resonant dielectric nanostructures”, Science 354, aag2472 (2016). [3] S. Kruk and Y. Kivshar, “Functional meta-optics and nanophotonics governed by Mie resonances”, ACS Phot. 4, 2638-2649 (2017). [4] R. Paniagua-Dominguez et al., “Active and tunable nanophotonics with dielectric nanoantennas”, Proceedings of the IEEE 108, 749-771 (2019). [5] S. T. Ha et al. “Directional lasing in resonant semiconductor nanoantenna arrays”, Nature Nano. 13, 1042-1047 (2018). [6] V. Mylnikov et al. “Lasing action in single subwavelength particles supporting supercavity modes”, ACS Nano 14, 7338–7346 (2020). [7] T. X. Hoang et al. “Collective Mie Resonances for Directional On-chip Nanolasers”, Nano Lett. 20, 5655-5661 (2020). [8] M. Wu et al. “Room-Temperature Lasing in Colloidal Nanoplatelets via Mie-Resonant Bound States in the Continuum”, Nano Lett. 20, 6005-6011 (2020). [9] S.Q. Li et al., “Phase-only transmissive spatial light modulator based on tunable dielectric metasurface,” Science 364, 1087-1090 (2019).

Nr: 10
Title:

Numerical Analysis of Metallic and High Refractive Index Nanoparticles for Enhancing the Emission of Single Quantum Dots

Authors:

Angela I. Barreda, Sebastian Hell, Alexander Minovich, Thomas Pertsch and Isabelle Staude

Abstract: The confinement of electromagnetic energy to subwavelength volumes through nanometer sized particles can be used to enhance the spontaneous emission of quantum emitters. With this aim, different configurations of metallic and high refractive index dielectric nanoparticles have been explored. Here, we carry out a comparison analysis of metallic, high refractive index dielectric and hybrid nanostructures attending to the Purcell enhancement, quantum yield and directionality properties. We focus our study on different geometries and material combinations of a dimer of cylinders. A dimer system made of two gold nanocylinders is the most promising candidate for improving the spontaneous emission. While two small gold cylinders (r < λ/10, being λ the emission wavelength of the quantum dot, λ = 800 nm) exhibit the largest electric field enhancement and Purcell factor of our study, larger gold cylinder dimers (r = λ/4) show a directional far-field radiation pattern which allows for a more efficient collection of single photons. With the aim to improve the directionality properties, silicon nanocylinders are used as directors of the scattered radiation. This work has applications in the development of single quantum sources.

Nr: 12
Title:

Design and Comparative Analysis of Aluminum-MoS2 based Plasmonic Devices with Enhanced Sensitivity and Figure of Merit for Biosensing Applications in the Near-infrared Region

Authors:

Sambhavi Shukla and Pankaj Arora

Abstract: To study the minuscule interactions at the biomolecular level, the Surface Plasmon Resonance (SPR) phenomenon has emerged as a major player in the field of label-free detection techniques. In SPR based sensors, of late, Aluminum (Al) has gained leverage over conventionally used gold or silver plasmonic metals, because of its economic value. Also, the ability of Al to cover a wider spectrum range and its increased biocompatibility with the optoelectronic devices makes it a suitable choice for initiating the plasmonic activity at the surface media. To further enhance the biomolecular interactions, Graphene (Gr) has emerged as one of the attractive alternatives. But with Gr layers, the sensitivity is found to be increasing at the cost of deteriorated Full Width at Half Maximum (FWHM). To overcome such ambiguity with Gr layers, recently, Transition Metal Dichalcogenides (TMDCs) have become exceedingly popular for better plasmonic activity. Molybdenum Disulfide (MoS2), often referred to as the “Beyond Graphene” material, is one of the most exclusively researched nanomaterial, among the other TMDCs. Gr-MoS2 when stacked together are among the effective biocompatible composites as has been reported previously. Nevertheless, all the research is entirely focused on the visible region. Hence investigation of MoS2 based plasmonic devices in the Near-Infrared (NIR) region becomes imperative. Moreover, browsing through the previous reports, MoS2 based plasmonic sensors were proposed either for higher Figure of Merit (FOM) but with a lower sensitivity or for an enhanced sensitivity but with a lower FOM. Hence, there is a need to focus our research on plasmonic devices which can provide cumulative results with perfect trade-offs amongst all the geometrical parameters, to achieve maximum sensitivity along with FOM. The present study takes into account multiple Aluminum-MoS2 based Kretschmann configurations, in the NIR region. Important performance parameters (Sensitivity and FOM) are studied for the following four engineered structures: Al-Si-MoS2-Gr, Al-MoS2-Gr, Al-Si-MoS2, and Al-MoS2. Such a comparative analysis yields a platform that can provide an exhaustive approach towards the behavior of 2D materials in the NIR region (1550nm). After studying the effect of Al thickness on the conventional configuration, the intermediate layers between the metal layer and the analyte are optimized. The effect of including silicon is also studied for sensitivity enhancement. Besides, a comparative analysis of sensor performances of the proposed devices is presented taking into account both the sensitivity and FOM. Among the optimized multi-layered MoS2 based configurations, a maximum sensitivity of about 141°/RIU is obtained along with FOM of about 335.13 RIU-1. Finally, the single-stranded DNA sensing on the engineered devices shows that the proposed nanomaterial-based devices prove to be much more promising configurations in the NIR regime as both the important parameters i.e. sensitivity as well FOM is sufficiently high as compared to the works in the existing literature.

Nr: 13
Title:

Stacked Photonic Systems Consisting of All-dielectric Metasurfaces and Other Functional Layers

Authors:

Isabelle Staude

Abstract: Metasurfaces composed of designed dielectric nanoresonators arranged in a plane offer unique opportunities for controlling the properties of light fields. Such metasurfaces can e.g. impose a spatially variant phase shift onto an incident light field, thereby providing control over its wave front with high transmittance efficiency [1]. While most research on dielectric metasurfaces realized so far focussed on the isolated scattering properties of single layer metasurfaces on a bulk substrate, the opportunities offered by stacking of several dielectric metasurface and other functional layers are often neglected, likely because of the difficulty of fabricating such stacked dielectric systems. A notable exceptions includes reflective metasurfaces for wavefront shaping [2] based on a three-layer geometry, where a resonant dielectric metasurface is separated from a metallic mirror by a dielectric spacer layer. This talk will provide an overview of our recent and ongoing research activities in stacking dielectric metasurface and other functional layers in order to obtain new optical response features and functionalities. In particular, we consider two different stacked metasurface systems. The first system are chiral bilayer dielectric metasurfaces [3]. More specifically, we experimentally and numerically demonstrate three-dimensional chiral dielectric metasurfaces exhibiting multipolar resonances and examine their chiro-optical properties. In particular, we demonstrate that record high circular dichroism of 0.7 and optical activity of 2.67 × 105 degree/mm can be achieved based on the excitation of electric and magnetic dipolar resonances inside the chiral structures. These large values are facilitated by a small amount of dissipative loss present in the dielectric nanoresonator material and the formation of a chiral supermode in the 4-fold symmetric metasurface unit cell. Our results highlight the mechanisms for maximizing the chiral response of photonic nanostructures and offer important opportunities for high-efficiency, ultrathin polarizing elements, which can be used in miniaturized devices. The second system is a resonant dielectric metasurface, which is separated from a metallic mirror by a dielectric spacer layer. We analytically, numerically and experimentally investigate how systematic changes in the spacer layer thickness of such structures influence the optical reflection spectra of the metasurfaces. We consider a silicon nanocylinder metasurface exhibiting electric and magnetic dipolar Mie-type resonances at near-infrared frequencies, which is situated on a gold mirror. The metasurface and the mirror are separated by a dielectric spacer layer with a gradually varying thickness. A transition from near perfect reflection to near perfect absorption occurs for a very small spacer layer thickness change of about 10 nm as a consequence of an interference effect of different types of modes supported by the structure, which may be useful for applications in actively tunable photonic devices. Altogether, our results show that stacked photonic systems consisting of all-dielectric metasurfaces and other functional layers offer interesting additional degrees of freedom to tailor the response of dielectric metasurface systems. REFERENCES [1] I. Staude und J. Schilling, “Metamaterial-inspired silicon nanophotonics”, Nature Photon. 11, 274 (2017). [2] Y. Yang, W. Wang, P. Moitra, I. I. Kravchenko, D. P. Briggs, and J. Valentine, “Dielectric Meta-Reflectarray for Broadband Linear Polarization Conversion and Optical Vortex Generation”, Nano Lett. 14, 3, 1394 (2014). [3] K. Tanaka, D. Arslan, S. Fasold, M. Steinert, J. Sautter, M. Falkner, T. Pertsch, M. Decker, and I. Staude, “Chiral Bilayer All-Dielectric Metasurfaces“, ACS Nano, https://doi.org/10.1021/acsnano.0c07295 (2020).

Nr: 14
Title:

Raman Tweezers for Small Microplastics and Nanoplastics Identification in Seawater

Authors:

Raymond Gillibert, Alessandro Magazzù, David Bronte-Ciriza, Maria Grazia Donato, Antonino Foti, Morgan Tardivel, Quentin Deshoules, Florent Colas, Gireeshkumar Balakrishnan, Marc Lamy de La Chapelle, Fabienne Lagarde, Onofrio M. Maragò and Pietro G. Gucciardi

Abstract: Our understanding of the fate and distribution of micro- and nano- plastics in the marine environment is limited by the intrinsic difficulties of the techniques currently used for the detection, quantification, and chemical identification of small particles in liquid (light scattering, vibrational spectroscopies, and optical and electron microscopies). Here we introduce Raman Tweezers (RTs), namely optical tweezers combined with Raman spectroscopy, as an analytical tool for the study of micro- and nanoplastics in seawater. We show optical trapping and chemical identification of sub-20 μm plastics, down to the 50 nm range. Analysis at the single particle level allows us to unambiguously discriminate plastics from organic matter and mineral sediments, overcoming the capacities of standard Raman spectroscopy in liquid, intrinsically limited to ensemble measurements. Being a microscopy technique, RTs also permits one to assess the size and shapes of particles (beads, fragments, and fibers), with spatial resolution only limited by diffraction. Applications are shown on both model particles and naturally aged environmental samples, made of common plastic pollutants, including polyethylene, polypropylene, nylon, and polystyrene, also in the presence of a thin eco-corona. The analysis is then extended to samples of Tire and Road Wear Particles (TRWP) collected from a brake test platform, where we highlight the presence of sub-micrometric agglomerates of rubber and brake debris. Our results show the potential of Raman Tweezers in environmental pollution analysis. We acknowledge financial contribution from the agreement ASI-INAF n. 2018-16-HH.0, project “SPACE Tweezers” and the MSCA ITN (ETN) project “Active Matter”.

Nr: 15
Title:

Optical Tweezers: From Nano to Space Applications

Authors:

Onofrio M. Maragò, Alessandro Magazzù, David Bronte-Ciriza, Paolo Polimeno, Anna Musolino, Antonino Foti, Maria Grazia Donato, Pietro G. Gucciardi, Maria Antonia Iati, Rosalba Saija, Luigi Folco and Alessandra Rotundi

Abstract: Optical tweezers are powerful tools based on focused laser beams. They are able to trap, manipulate and investigate a wide range of nanoscopic particles in different media, such as liquids, air, and vacuum. After an introduction to optical forces, we will give an overview of results on optical trapping, optical binding, and characterization of particles at the nanoscale. Furthermore, we will describe how optical tweezers can be used to trap and characterize extraterrestrial particulate matter. On one side, we exploit light scattering theory in the T-matrix formalism to calculate radiation pressure and optical trapping properties of a variety of complex particles of astrophysical interest. On the other side, we show results on micro and nanoscopic particles in controlled laboratory experiments. Our results open perspectives non-destructive, non-contact and non-contaminating investigation of extraterrestrial particles, aiming for space tweezers applications. We acknowledge financial contribution from the agreement ASI-INAF n. 2018-16-HH.0, project “SPACE Tweezers” and the MSCA ITN (ETN) project “Active Matter”.

Nr: 16
Title:

Plasmonic Nanomotors using Optical Forces Induced by Directional Control of Scattered Light

Authors:

Yoshito Y. Tanaka

Abstract: Plasmonic nanoantennas provide means to control light on subwavelength scale. The direction of the light they scatter can be modified by engineering the phase distribution of the plasmon modes excited. The unidirectional side scattering of light by a pair of two nanorods with different lengths has been demonstrated. In this study, we focus on the transfer of momentum from photons to the nanoantennas in such side scattering process. We have demonstrated a linear nanomotor employing lateral optical forces acting on a plasmonic nanoparticle, in which the force direction is determined by the orientation of the nanoparticle rather than a field gradient or propagation direction of the illumination light beam. The arrangements of the nanoparticles provide the lateral force distributions with nanoscale spatial precision and resolution, resulting in not only linear but also rotational movement of a micrometer-sized object. Our nanomotors would provide a paradigm shift in optical manipulation as it removes the need for oblique incidence, focusing and steering of the light beam.

Nr: 17
Title:

Multifunctional Devices based on Metasurfaces, 2D Crystals and Molecular Compounds

Authors:

Josep Canet-Ferrer

Abstract: During the last decades, Nanotechnology developments have been encouraged by the needs of Emerging Technologies, continuously demanding to scale down the size of optoelectronical devices. However, the demands of Optoelectronics have been changed as limit of the miniaturization of silicon devices has been achieved. One of the most successful alternatives consists of the integration of components of different nature into a single platform for the development of multifunctional devices. Able to perform different tasks in parallel multifunctional devices can improve the performance of silicon based devices while reducing the size and energy consumption. With the aim to contribute in this field, we have recently launched a new research line for the design of a new class of hybrid devices based on the combination of metasurfaces with 2D crystals and molecular compounds. In this talk, I will describe the mechanisms involved in the interaction among those materials at the nanoscale. This way, we can identify the main features that allow the synergic cooperation among such different building blocks looking for insights for the design of more efficient realization of thermoelectric, thermoplasmonic and magnetoplasmonic applications.

Nr: 18
Title:

Improving the Optical Response of Solar Cell using Dielectric Metastructures

Authors:

Braulio Garcia-Camara, Eduardo Lopez-Fraguas, Ricardo Vergaz, Mahmoud Elshorbagy and José M. Sánchez-Pena

Abstract: In this contribution, we will explain our latest proposals to include dielectric metasurfaces in the structure of either conventional or tandem solar cells, with the aim of improving both the light absorption in the active layers and decreasing the global reflection (Figure 1). This is obtained by a convenient design of the geometrical and optical properties in order to excite Mie resonances and/or produce diffraction effects. From our point of view, this can be a promising solution that completes the improvements produced by materials engineering and the optimization of current structures and produces a new generation of solar cells.

Nr: 19
Title:

Strain-tunable Optical Emission from Site-controlled Quantum Emitters

Authors:

Javier Martín-Sánchez

Abstract: The physical properties of crystalline materials ultimately depend on the inter-distance between their constitutive atoms. Hence, the deliberate introduction of elastic deformation fields (strain) in materials with a full control of the strain tensor would allow a complete control of their properties. In this regard, the future development of ultra-compact two-dimensional (2D) photonic technologies for quantum information processing relies on our ability to tailor the optical properties of single photon sources in 2D nanomaterials [1]. A promising strategy is based on the use of a novel class of customized micro-machined piezoelectric actuators allowing for the introduction of controlled deformation fields in nanomaterials, which can be operated under extreme working conditions [2–5]. In this talk, I will present the capabilities of this kind of devices with a reduced fingerprint to introduce fully controlled in-plane strain fields in semiconductor nanomaterials in a reversible manner operated at cryogenic temperatures. The successful fabrication and applicability of hybrid 2D-piezoelectric devices will be demonstrated for the manipulation and understanding of the optical emission properties of site-controlled single photon sources in WSe2 semiconductor monolayers. [1] O. Iff et al. Nano Lett. 19 6931 (2019) [2] J. Martín-Sánchez et al. Adv. Opt. Mater. 4 682 (2016) [3] J. Martín-Sánchez et al. Semicond. Sci. Technol. 33 013001 (2017) [4] R. Trotta et al. Nature Commun. 7 10375 (2016) [5] X. Yuan et al. Nature Commun. 9 3058 (2018)

Nr: 23
Title:

Optically Induced Aggregation by Radiation Pressure of Gold Nanorods on Graphene for SERS Detection of Biomolecules

Authors:

Antonino Foti, Maria Grazia Donato, Onofrio M. Maragò and Pietro G. Gucciardi

Abstract: Radiation pressure is used to push gold nanorods on multilayered graphene and create hybrid active surfaces for Surface-Enhanced Raman Spectroscopy (SERS) in liquid. As a proof of concept, ultrasensitive detection of bovine serum albumin (BSA) is shown, and the aggregation kinetics is studied as a function of the irradiation time. We observe that optical aggregation on graphene is 3.5 times slower compared to glass. We attribute the difference to the peculiar surface properties of graphene and, in particular, to its efficient thermal conductivity. Despite the slowdown of the aggregation kinetics, the usage of graphene as substrate in this process offers manifold benefits: an almost negligible fluorescence background when using near-infrared light (785 nm), the absence of thermal absorption as well as the possibility to easily functionalize the surface to enhance the affinity with the analytes. Our results highlight the importance of the physical properties of the surfaces on which optical aggregation is carried out for SERS biomolecular detection.

Nr: 24
Title:

Plasmon-molecule Coupling: Electromagnetic Field Quantization and Effect of Vibrational Modes

Authors:

Antonio I. Fernandez Dominguez

Abstract: Nanocativies enable a wide range of weak and strong light-matter coupling phenomena at the single molecule level. In this talk, I will explore classical and quantum optical effects behind strong plasmon-molecule interactions, with particular focus on two different topics. First, I will treat the quantization of the electromagnetic fields in both purely metallic [1] and hybrid metallo-dielectric [2] nanostructures. Secondly, I will explore the impact of molecular vibrations in the so-called plasmonic Purcell effect [3]. [1] R.-Q. Li et al., Phys. Rev. Lett. 117, 107401 (2016), ACS Photonics 5, 3082 (2018). [2] I. Medina et al., arXiv:2008.00349 (2020). [3] D. Zhao et al., ACS Photonics (ASAP, 2020).

Nr: 25
Title:

Photonic Fractal Metamaterials for Enhanced Volatile Compound Sensing

Authors:

Mohsen Rahmani, Zelio Fusco, Thanh Tran-Phu, Chiara Ricci, Alexander Kiy, Patrick Kluth, Enrico Dellagaspera, Nunzio Motta, Dragomir Neshev and Antonio Tricoli

Abstract: The advance of photonics media is restrained by the lack of structuring techniques for the 3D fabrication of active materials with long-range periodicity. Recently, aggregates of metallic nanoparticles exhibiting fractal properties has been introduced as efficient scattering enhancers [1] and have shown promising results in several research areas including giant local optical field [2] multifunctionality [3], and stabilized broadband optical chirality [4]. Here, a methodology is reported for the engineering of tunable resonant photonic media with thickness exceeding the plasmonic near-field enhancement region by more than two orders of magnitude. The media architecture consists of a stochastically ordered distribution of plasmonic nanocrystals in a fractal scaffold of high-index semiconductors. This plasmonic-semiconductor fractal media supports the propagation of surface plasmons with drastically enhanced intensity over multiple length scales, overcoming 2D limitations of established metasurface technologies. The fractal media are used for the fabrication of plasmonic optical gas sensors, achieving a limit of detection of 0.01 vol% at room temperature and sensitivity up to 1.9 nm/vol%, demonstrating almost a five fold increase with respect to an optimised planar geometry [5]. Beneficially to their implementation, the self-assembly mechanism of this fractal architecture allows fabrication of micrometer-thick media over surfaces of several square centimeters in a few seconds. The designable optical features and intrinsic scalability of these photonic fractal metamaterials provide ample opportunities for applications, bridging across transformation optics, non-invasive biomedical sensing and light harvesting. References: [1] M. Stockman, Physics 2010, 3. [2] K. Li, M. I. Stockman, D. J. Bergman, Phys. Rev. Lett. 2003, 91, 227402. [3] T. Tran-Phu, R. Daiyan, Z. Fusco, Z. Ma, L. R. A. Rahim, A. Kiy, P. Kluth, X. Guo, Y. Zhu, H. Chen, R. Amal, A. Tricoli, J. Mater. Chem. A 2020. [4] M. L. Tseng, Z.-H. Lin, H. Y. Kuo, T.-T. Huang, Y.-T. Huang, T. L. Chung, C. H. Chu, J.-S. Huang, D. P. Tsai, Adv. Opt. Mater. 2019, 7, 1900617. [5] Z. Fusco, M. Rahmani, T.P. Thanh, R. Chiara, K. Alexander, P. Kluth, E. Della Gaspera, N. Motta, D. Neshev, and A.Tricoli" Adv. Mater. 2020, 2002471.

Nr: 26
Title:

Theory of ``hot'' Photo-luminescence from Drude Metals

Authors:

Yonatan Sivan and Yonatan Dubi

Abstract: Using our previously developed comprehensive theory for the non-thermal electron distribution in metals, we provide a complete quantitative theory for light emission from Drude metals under continuous wave illumination. We show that the electronic contribution to the emission exhibits a dependence on the emission frequency which is essentially identical to the energy dependence of the non-equilibrium distribution. We also provide what is to our knowledge, the first ever analytic description of the (polynomial) dependence of the metal emission on the electric field, its dependence on the pump laser frequency, and its non-trivial exponential dependence on the electron (and lattice) temperature, both for the Stokes and anti-Stokes regimes. We also provide first predictions for the quantum yield and explain the spectral shape of the emission in great detail using our recently developed modal method. Our results imply that, the emission does not originate from either fermion statistics (due to e-e interactions), and even though one could have expected the emission to follow boson statistics due to involvement of photons (like for (Planck's) Black Body emission), it turns out to deviate from that form as well. These results resolve many of the arguments on the origin of the light emission from metals.

Nr: 27
Title:

Surface-enhanced Infrared Spectroscopy for In-vitro Detection of Conformational Changes

Authors:

Frank Neubrech, Rostyslav Semenyshyn, Mario Hentschel, Florian Mörz and Harald Giessen

Abstract: Plasmonic nanoantennas confine electromagnetic fields at infrared wavelengths to volumes of only a few cubic nanometers, resulting in huge local fields in the vicinity of the resonantly excited metal particles. These near fields can be used to enhance the infrared vibrational bands of molecular monolayers and thus enable a spectroscopic detection with ultra-high sensitivity. In our experiments, we applied this approach of resonant surface-enhanced infrared spectroscopy to detect secondary structural changes of biomolecular monolayers composed of minicollagens or polypeptides. Plasmonic nanostructures (either slits or linear antennas) have been resonantly matched to the amide vibrational bands of the minicollagens and polypeptides, respectively. To ensure a good spatial overlap between the enhanced electromagnetic fields and the molecules, the minicollagens and the polypeptides have been functionalized on top of the gold nanostructures’ surfaces. By applying different external stimuli, such as temperature or different pH values, we induced structural changes of the secondary structure of the respective biomolecule. Depending on the molecular species, the structural change resulted in an intensity change and/or shift of the vibrational frequency of the amid vibration. Utilizing principle component data analysis, even reversible conformational transitions of the monolayers could be monitored in-vitro. The detection limit of resonant surface enhanced infrared spectroscopy was further reduced to only a few thousands of polypeptides attached to a single nanostructure by the implementation of a high power and broadband mid infrared laser source. The demonstrated concept could lead to integrated chip-level technology for biological and medical applications, where the detection of minute concentrations of biological entities is essential, e.g. for early disease diagnostics. With further advances in nanostructure design or laser development, it could be possible to push the detection limit to a few or even single proteins and observe structural changes of individual entities.

Nr: 33
Title:

Unveiling Directional Polaritons along Previously Forbidden Directions via a Topological Transition

Authors:

Pablo Alonso-González

Abstract: Polaritons in single and twisted slabs of biaxial van der Waals (vdW) crystals, have recently opened the door for unprecedented manipulation of the flow of light at the nanoscale due to a strongly directional propagation with low losses. However, despite this potential, these polaritons present a fundamental limitation: their propagation is restricted to specific directions dictated by the crystal structure. Here, we theoretically predict and experimentally demonstrate that biaxial crystals can host a unique optical topological transition that triggers the existence of directional polaritons propagating along previously forbidden directions in such media. Importantly, this transition emerges naturally by simply placing the biaxial crystal on a substrate with a given negative permittivity. As a proof of principle, we show real-space visualizations of phonon polaritons in α-MoO3 featuring hyperbolic propagation centered along the previously non-polaritonic (in the studied spectral range) [100] direction by placing the crystal on 4H-SiC. Moreover, due to the low-loss nature of this topological transition, we are able to visualize in real space exotic intermediate polaritonic states between mutually orthogonal hyperbolic regimes, which permit to unveil the origin of the transition, characterized by a gap opening in the polaritonic dispersion. This work provides new insights into the emergence of low-loss optical topological transitions in vdW crystals, offering a general and simple route to steer the flow of energy at the nanoscale along previously forbidden directions.

Nr: 34
Title:

New Insight on the Aptamer Conformation and Aptamer/Protein Interaction by SERS and Multivariate Statistical Analysis

Authors:

Marc Lamy de La Chapelle, Wafa Safar, Andra-Sorina Tatar, Aymeric Leray, Monica Potara, Qiqian Liu, Mathieu Edely, Nadia Djaker, Jolanda Spadavecchia, Weiling Fu, Sarra Derouich, Nordin Felidj, Simion Astilean and Eric Finot

Abstract: We study the interaction between one aptamer with its analyte (the MnSOD protein) by the combination of Surface Enhanced Raman Scattering and multivariate statistical analysis and observe the aptamer structure and its evolution during the interaction in different experimental conditions (in air or in buffer). Through the spectral treatment by principal component analysis of a large set of SERS data, we were able to probe the aptamer conformations and orientations relatively to the surface assuming that the in plane nucleoside modes are selectively enhanced. We demonstrate that the aptamer orientation and thus its flexibility relies strongly on the presence of a spacer of 15 thymines and on the experimental conditions with aptamers laying on surface in air and standing in buffer. We reveal for the first time that the interaction with the MnSOD induces a large loss of flexibility and freezes the aptamer structure in a single conformation.

Nr: 35
Title:

Self-assembled DNA-mediated Optical Antennas for Single Molecule Nanophotonics

Authors:

Guillermo P. Acuna

Abstract: Over the last decade, the DNA origami1 technique has consolidated into the state-of-the-art approach for the self-assembly of nanophotonic structures2 since it provides unique control and versatility to organize different molecules and nanoparticles in well-defined geometric arrangements. In particular, this technique has proven extremely useful to fabricate nanophotonic devices with specific functions by setting single-photon emitters, such as fluorescent molecules or quantum dots, and metallic nanoparticles in precise geometries with high positional and stoichiometric control. In this contribution, we will first introduce this technique and discuss its strengths and limitations together with a comparison with state-of-the-art top down approaches. Then we will show how this technique can be applied to study light-matter interaction at the single molecule level in order to enhance fluorescence3, direct single molecule fluorescence emission4, affect and shift the apparent fluorescence emission center5, combined with graphene6, natural light harvesting complexes7 and lithographic structures8. 1. Rothemund, P. W. K. Folding DNA to create nanoscale shapes and patterns. Nature 440, 297–302 (2006). 2. Kuzyk, A., Jungmann, R., Acuna, G. P. & Liu, N. DNA Origami Route for Nanophotonics. ACS Photonics 5, 1151–1163 (2018). 3. Puchkova, A. et al. DNA Origami Nanoantennas with over 5000-fold Fluorescence Enhancement and Single-Molecule Detection at 25 μm. Nano Lett. 15, 8354–8359 (2015). 4. Hübner, K. et al. Directing Single-Molecule Emission with DNA Origami-Assembled Optical Antennas. Nano Lett. (2019). doi:10.1021/acs.nanolett.9b02886 5. Raab, M., Vietz, C., Stefani, F. D., Acuna, G. P. & Tinnefeld, P. Shifting molecular localization by plasmonic coupling in a single-molecule mirage. Nat. Commun. 8, 13966 (2017). 6. Kaminska, I. et al. Distance Dependence of Single-Molecule Energy Transfer to Graphene Measured with DNA Origami Nanopositioners. Nano Lett. Just accep, acs.nanolett.9b00172 (2019). 7. Kaminska, I., Bohlen, J., Mackowski, S., Tinnefeld, P. & Acuna, G. P. Strong Plasmonic Enhancement of a Single Peridinin–Chlorophyll a –Protein Complex on DNA Origami-Based Optical Antennas. ACS Nano 12, 1650–1655 (2018). 8. Pibiri, E., Holzmeister, P., Lalkens, B., Acuna, G. P. & Tinnefeld, P. Single-molecule positioning in zeromode waveguides by DNA origami nanoadapters. Nano Lett. 14, 3499–3503 (2014).

Nr: 36
Title:

Transparent Metals

Authors:

Vincenzo Giannini

Abstract: Metals are highly opaque, yet we show numerically and experimentally that densely packed arrays of metallic nanoparticles can be more transparent to infrared radiation than dielectrics such as germanium, even for arrays that are over 75% metal by volume. Despite strong interactions between the metallic particles, these arrays form effective dielectrics that are virtually dispersion-free, making possible the design of optical components that are achromatic over ultra-broadband ranges of wavelengths from a few microns up to millimetres or more. Furthermore, the local refractive indices may be tuned by altering the size, shape, and spacing of the nanoparticles, allowing the design of gradient-index lenses that guide and focus light on the microscale. The electric field is also strongly concentrated in the gaps between the metallic nanoparticles, and the simultaneous focusing and squeezing of the electric field produces strong ‘doubly-enhanced’ hotspots which could boost measurements made using infrared spectroscopy and other non-linear processes over a broad range of frequencies, with minimal heat production.

Nr: 37
Title:

Metallic and Dielectric Nanostructures for the UV Range

Authors:

Fernando Moreno, Yael Gutiérrez, Francisco González, José M. Saiz, Dolores Ortiz, Javier González, Andrea Fernández, Gonzalo Santos, Saúl A. Rosales and Pablo Albella

Abstract: Extending the analysis of radiation-nanomatter interaction into the UV has triggered a lot of interest due to the new challenges in areas like biomedicine, photocatalysis, imaging or surface-enhanced spectroscopy techniques. Coinage nanostructured metals, such as Ag or Au, are not effective in the UV because both present interband transitions in this spectral range. Recent studies have presented Al, Mg, Ga and Rh as very promising candidates for this purpose [1]. However, Mg, Al and Ga nanoparticles (NPs) made of tend to oxidize with a native oxide layer whose thickness strongly depends on the ambient conditions and that affects its plasmonic behavior. A more recent numerical study has presented Rh as a promising metal for plasmonics in the UV not only for its good plasmonic performance but also for its low tendency to oxidation and chemical stability [2]. Moreover, Rh NPs can be easily fabricated through chemical means with a wide variety of shapes (cubes [3], tetrahedrons [4], tripod stars [2],…) and sizes smaller down to 10 nm. Their potential for photocatalysis applications, makes this material very attractive for building plasmonic tools in the UV. At the nanoscale, dielectric NPs, and in particular those made with materials of high refractive index (HRI), have not been exploited in this spectral range yet [5]. This type of materials presents several advantages as compared to metals: they do not oxidize, and resistive losses are absent. In addition, HRI dielectric NPs can support both magnetic and electric resonances whose scattered fields and their coherent interference leads to interesting scattering directionality properties. In this contribution we will make an overview on our latest research on metallic and HRI dielectric nanostructures for photon energies above 3 eV. This will mainly focus on near-field enhancement, directionality and chiral features [6] in the UV for applications in matter analysis and light guiding. References: 1. Y. Gutiérrez et al., Plasmonics in the Ultraviolet with Aluminum, Gallium, Magnesium and Rhodium. Appl. Sci. 2018, 8, 64. 2. A. M. Watson et al., Rhodium nanoparticles for ultraviolet plasmonics. Nano Lett. 2015, 15, 1095–100. 3. X. Zhang et al., Size-tunable rhodium nanostructures for wavelength-tunable ultraviolet plasmonics. Nanoscale Horizons 2016, 1, 75–80. 4. C.S. Kuo et al., Aqueous Synthesis of Concave Rh Nanotetrahedra with Defect-Rich Surfaces: Insights into Growth-, Defect-, and Plasmon-Enhanced Catalytic Energy Conversion. Chem. Mater. 2018, 30, 4448–4458. 5. Y. Gutiérrez et al., Ortiz, D.; Saiz, J.; González, F.; Albella, P.; Moreno, F. The Quest for Low Loss High Refractive Index Dielectric Materials for UV Photonic Applications. Appl. Sci. 2018, 8, 2065. 6. S. A. Rosales, F. González, F. Moreno, Y. Gutiérrez. Non-Absorbing Dielectric Materials for Surface-Enhanced Spectroscopies and Chiral Sensing in the UV. Nanomaterials 2020, 10, 1–22.

Nr: 38
Title:

Deep Learning Enabled Design of Free-space and Integrated Nanophotonic Devices

Authors:

Otto Muskens, Nicholas Dinsdale, Matthew Delaney and Peter Wiecha

Abstract: Data-driven approaches are being considered as alternatives to conventional numerical simulations for a range of applications in evaluating the optical response of nanostructures. In recent years, artificial neural networks (ANNs) have been designed to faithfully reproduce optical response of a wide range of systems, however in many cases these are highly specific to a given parametrization and a more generalized approach is desirable [1]. In the first part of my presentation I will present our efforts in developing a generalized ANN approach for evaluating the internal field of nanostructures defined in free space [2]. By training the network using a pre-defined set of very general examples, we find that it is able to correctly extract general behaviours related to the near-field coupling, internal resonances, and polarization effects in complex assemblies of nanostructures. We have successfully applied this approach to both plasmonic (gold) and dielectric (silicon) nanostructures. The inferral of internal field distributions offers a powerful starting point for deriving secondary properties, such as external near-field distributions, far-field radiation patterns, and optical cross sections, which indeed can be obtained with high accuracy for the majority of cases. Current work is aimed at extension to arbitrary angles of incidence, wavelengths, and material permittivity values. In the second part of this presentation, I will discuss new approaches for controlling light on a chip by producing nanophotonic scattering patterns using a neural network approach [3]. Here, we not only address the forward problem of predicting response for a given geometry, but also the inverse challenge of designing a geometry to achieve a desired optical response. For this to work, we use a tandem neural network consisting of a pre-trained forward ANN and a generator inverse network. This approach has been shown very successful recently in inverse design of nanostructures. We have obtained the first promising results where we are able to design multi-port routers by perturbing a multi-mode waveguide with a pixelated pattern of nanophotonic scattering elements. Crucial here is to find the solutions with a high throughput, which are sparse in the design space. By combining a conventional single-objective forward optimization scheme as a seed for the training dataset, with an iterative training loop where new training solutions are generated by the ANN itself, we find that the network is able to converge to finding appropriate sets of solutions for multi-objective problems. This has allowed us to define 3x3 multi-port transmission matrices with both amplitude and phase design. The method opens up new routes for universal optical elements in photonic integrated circuits. [1] P. R. Wiecha, A. Arbouet, C. Girard, O. L. Muskens, Deep learning in nano-photonics: inverse design and beyond, arXiv:2011.12603 (2020) [2] P. R. Wiecha, O. L. Muskens, Deep learning meets nanophotonics: A generalized accurate predictor for near fields and far fields of arbitrary 3D nanostructures, Nano Letters 20 (1), 329-338 (2020) [3] N. J. Dinsdale, P. R. Wiecha, M. Delaney, J. Reynolds, M. Ebert, I. Zeimpekis, D. J. Thomson, G. T. Reed, P. Lalanne, K. Vynck, O. L. Muskens, Deep learning enabled design of complex transmission matrices for universal optical components, arXiv:2009.11810 (2020)

Nr: 39
Title:

Atomically Thin Optical Modulators

Authors:

Giancarlo Soavi

Abstract: Optical modulators are fundamental building blocks in a large variety of modern technological applications: phase, frequency, amplitude and polarization modulators such as electro-optic (EOM) and acousto-optic modulators (AOM) are widely used in fibre optic communication systems, ultrafast spectroscopy, metrology, active Q switching/mode locking of lasers and quantum information. The research and technological interest in optical modulators further increased with the advent of integrated photonics, which refers to a class of compact microchip devices (µm size) that associatively incorporate optical and optoelectronic functionalities, with the ultimate goal to replace electrical interconnects with optical interconnects to provide faster response time, wider transmission bandwidth, and lower power consumption. The first great challenge towards the realization of photonic circuits is to find materials which are easy to integrate on-chip and fibres and display suitable optical properties for realizing active and passive photonic functionalities. In addition, novel functionalities for photonic circuits could be enabled by active modulation of nonlinear optical effects. Finally, to achieve even higher speed interconnects and quantum computing, electro-optic modulators could be replaced by all-optical modulators. Atomically thin two-dimensional (2D) materials could be ideal for such applications. Thanks to their high mechanical flexibility, ease of fabrication and robustness, 2D materials have already been successfully integrated on waveguides, microdisks, microrings and fibres and different kinds of electro-optic, thermo-optic and magneto-optic modulators have been realized. Moreover, 2D materials display strong nonlinear optical response and are thus ideal to enhance the performances and functionalities of standard photonic devices and to allow all-optical modulation of light. In this talk I will discuss our current efforts towards the realization of electro-optical and all-optical nonlinear modulators based on graphene and related atomically thin materials.

Nr: 41
Title:

Directional Surface Plasmon Polaritons using Gold Grating-based Platforms: Direct Application in Sensing

Authors:

Pablo Albella, Javier González-Colsa, Guillermo Serrera, Alfredo Franco, Dolores Ortiz, José M Saiz, Fernando Moreno and Francisco González

Abstract: Optical biosensing is currently a highly active research area, with an increasing demand of high sensitivity-enhanced, strong selective and low-cost devices. Different approaches to this problem have been suggested from the field of plasmonics, such as ATR structures [1], directional emission polarization-controlled gratings [2] and simple grating structures [3]. The main sensing mechanism is based on Surface Plasmon Polariton (SPP) excitation via a diffraction grating. This is due to its dependance on the optical properties of both, the metal grating and the surrounding dielectric medium. Thus, the reflectivity spectrum of such a system will detect changes in the refractive index of the surrounding medium, showing displacements of the SPP absorption wavelength. These displacements can be exploited to build optical biosensors that can identify and quantify very small refractive index changes. In this talk, we will present our current research in plasmonic grating-based sensors. First, we will describe the sensing platform able to detect small changes in the refractive index of a target sample upon wavelength interrogation. Later, a careful optimization of the structural parameters of this platform will lead to a 1500 nm / RIU sensitivity in an aqueous environment under normal incidence illumination. To conclude, we will show how this structure can act as a selective plasmon coupler offering the possibility to control the propagation direction of surface plasmons. REFERENCES [1] C. Striebel, A. Brecht, and G. Gauglitz, “Characterization of biomembranes by spectral ellipsometry, surface plasmon resonance and interferometry with regard to biosensor application,” Biosens. Bioelectron., vol. 9, no. 2, pp. 139–146, 1994. [2] J. Lin et al., “Polarization-controlled tunable directional coupling of surface plasmon polaritons,” Science (80-. )., vol. 340, no. 6130, pp. 331–334, 2013. [3] J. Cao, Y. Sun, Y. Kong, and W. Qian, “The sensitivity of grating-based SPR sensors with wavelength interrogation,” Sensors (Switzerland), vol. 19, no. 2, 2019.

Nr: 42
Title:

Sensing Performance of Hybrid Magnetoplasmonic Systems

Authors:

Antonio Garcia-Martin

Abstract: Plasmonic structures are widely used in low-cost, label-free biosensors, and the investigation of how to improve their sensitivity or to widen their range of applications is a central topic in the field of plasmonics.[1,2] The most commonly used plasmonic sensors are based on the concept of surface plasmon resonance (SPR) and, in particular, on the sensitivity of these resonances to changes in the refractive index of the medium surrounding a metallic structure. In the search for an improved bulk sensitivity of SPR-based sensors, researchers have proposed different strategies. Thus, for instance, it has been shown that the use of the magneto-optical properties of layered systems containing magnetic materials can, in principle, enhance the sensitivity of these sensors.[3,4] Another possibility that is becoming increasingly popular is the use of nanohole arrays or perforated metallic membranes featuring arrays of subwavelength holes. [5,6] These sensors make use of the extraordinary optical transmission phenomenon, which originates from the resonant excitation of surface plasmons in these periodically patterned nanostructures. We present two case studies showing how the use of hybrid magnetoplasmonic systems comprising in one case 2D crystals using ferromagnetic and noble metals and in the other bare noble metal nanoparticles, lead to a notable enhancement of the sensing performance plasmonic sensors. In particular, we present perforated Au−Co−Au films with a periodic array of subwavelength holes as transducers in magneto-optical surface-plasmon-resonance sensors and a random collection of Au nanoparticles supporting localized plasmon resonances deposited over a glass substrate, but using as transducer signal the measurements of the transverse magnetooptical Kerr effect (TMOKE). We demonstrate that this detection scheme results in (i) bulk figures of merit that are two orders of magnitude larger than those of any other type of plasmonic sensor [7], and an increase of ca. 300% in the refractive index sensing lowering at the same time the limit of detection in a ca. 200% [8]. The sensing strategy put forward here can make use of the different advantages of nanohole-based plasmonic sensors such as miniaturization, multiplexing, and its combination with microfluidics. References [1] O. Tokel, F. Inci, U. Demirci, Chem. Rev. 114, (2014) 5728 [2] M.-C. Estevez, M. A. Otte, B. Sepulveda, L. M. Lechuga, Anal. Chim. Acta 806, (2014) 55 [3] B. Sepúlveda, A. Calle, L.M. Lechuga, G. Armelles, Opt. Lett. 31, (2006) 1085 [4] M.G. Manera, et al., Biosens. Bioelectron. 58, (2014) 114 [5] A.A. Yanik, et al., Proc. Natl. Acad. Sci. U. S. A. 108, (2011) 11784 [6] A.E. Cetin, et al., ACS Photonics 2, (2015) 1167 [7] B. Caballero, A. García-Martín, and J. C. Cuevas, ACS Photonics 3, (2016) 203 [8] M.G. Manera, et al., Scientific Reports 8, 12640 (2018)

Nr: 43
Title:

Dielectric Nanostructured Materials for UV Surface Enhanced Spectroscopy Techniques

Authors:

Saúl Antonio R. Mendoza, Fernando Moreno, Francisco González and Yael Gutiérrez

Abstract: Metallic nanomaterials have been extensively studied as novel platforms to harness enhanced lightmatter interactions. Taking advantage of these enhanced interactions, the experimental study of matter properties can become much more efficient. This is the basis of many surface enhanced spectroscopy (SES) techniques, like those based on infrared absorption (SEIRA), Raman scattering (SERS) and fluorescence (SEF) among others. Since these techniques rely on a strong absorption of light, a high value of the near field intensity (NFI) in the surface of the nanostructure is desired. Metals show inherent Joule effect losses when nanostructured that heat their surroundings [1]. In some cases, low heating of the sample is also desired (i.e. for biological samples), making the absorption efficiency of the nanostructure an important parameter to be also considered. Here is where, in general, dielectrics show a good performance due to their low resistive losses. In addition, dielectric nanostructures may generate high optical chiral density (OCD) in their surroundings [2]. The circular dichroism exhibited by a chiral molecule is proportional to the OCD, so dielectric nanostructures that enhance this property may open a new landscape for surface enhanced chiral sensing techniques. In this work, we study a list of 19 dielectric low loss materials for potential SES and chiral sensing applications in the UV [3]. The results of this study become specially interesting for biological material analysis for two reasons: the main absorption bands of the biological material lie in the UV range and when nanostructured, the low losses of some of the selected dielectric materials produce no heating in their surroundings avoiding the possible damage of the analyzed sample. References [1] Sanz, J.M.; Ortiz, D.; de la Osa, R.A.; Saiz, J.M.; González, F.; Brown, A.S.; Losurdo, M.; Everitt, H.O.; Moreno, F. UV Plasmonic Behavior of Various Metal Nanoparticles in the Near- and Far-Field Regimes: Geometry and Substrate Effects. J. Phys. Chem. 2013,117, 19606–19615. doi: 10.1021/jp405773p. [2] Vestler, D.; Ben-moshe, A.; Markovich, G. Enhancement of Circular Dichroism of a Chiral Material by Dielectric Nanospheres Published as part of The Journal of Physical Chemistry virtual special issue “AbrahamNitzan Festschrift”.J. Phys. Chem. 2019,123, 5017–5022. doi: 10.1021/acs.jpcc.8b10975. [3] Rosales S.A.; González F.; Moreno F.; Gutiérrez Y. Non-Absorbing Dielectric Materials for SurfaceEnhanced Spectroscopies and Chiral Sensing in the UV. Nanomaterials, 2020, 10, 2078; doi:10.3390/nano10102078