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Lectures

Alexander O. Govorov

Department of Physics and Astronomy, Ohio University, Athens, USA; govorov@ohio.edu

Lecture : Short Stories from the World of Optical Metamaterials: DNA-Origami, The Origin of Chirality, Chiral Plasmonic Photochemistry, and More

Seminar: "Hot Electrons and Electromagnetic Effects in Achiral and Chiral plasmonic nanostructures"

Chirality refers to objects whose geometry is such that the mirror image cannot coincide with the object [1]. Numerous molecular and biomolecular systems of prime importance are chiral (e.g., DNA, sugar, lactic acid, proteins). Recently, the fields of plasmonics and bio-photonics have begun to actively involve the concept of chirality. Why plasmonics? This talk will address this point.

Plasmonic nanostructures and metamaterials are very efficient at the absorption and scattering of light. The studies presented in this talk concern unique designs of hybrid nanostructures with electromagnetic hot spots, where the electromagnetic field becomes strongly enhanced and spatially concentrated [2-12]. In particular, nanocrystal assemblies and metastructures with plasmon resonances can be designed to be strongly chiral, demonstrating unprecedented numbers of Circular Dichroism (CD) for a nanoscale system [9]. Simultaneously, when conjugated with biomolecules, plasmonic hot spots allow us to enhance chiral optical responses (CD) of biomolecular species, whereas, in an inorganic environment, plasmonic nanocrystals are efficient at inducing chiral photochemical effects [8-12].

^{[1] W. T. B. Kelvin. The molecular tactics of a crystal, Clarendon Press Oxford (1894).}

^{[2] E.-M. Roller et al., Nature Physics, 13, 761 (2017).}

^{[3] A. O. Govorov, H. Zhang, H.V. Demir and Y. K. Gun’ko, Nano Today 9, 85 (2014).}

^{[4] H. Harutyunyan et al., Nature Nanotech. 10, 770 (2015).}

^{[5] A. O. Govorov and H. Richardson, Nano Today 2, 20 (2007).}

^{[6] C. Jack et al., Nat. Commun. 7, 10946 (2016).}

^{[7] X.-T. Kong et al., Nano Letters, 18, 2001 (2018).}

^{[8] A. O. Govorov et al., Nano Letters 10, 1374–1382 (2010).}

^{[9] A. Kuzyk et al., Nature 483, 311 (2012).}

^{[10] T. Liu et al., Nano Letters, 19, 1395–1407 (2019).}

^{[11] K. Martens, et al., Nat. Commun., 12, 2025 (2021).}

^{[12] S. Rej, A. Naldoni, et al., Nano Energy,}^{104(B), 107989 (2022)}.

Giulia Tagliabue

EPFL, Laboratory of Nanoscience for Energy Technologies, Lausanne, Switzerland

Lecture: Nanophotonics for Energy: an Opportunity for Photochemical Devices

Seminar: Nanophotonic Engineering for Light-Energy Storage Devices

In the last decade, optical nanoantennas have revolutionized light manipulation and control at the nanoscale. Interestingly, generation of hot carriers in metals upon light absorption have opened new pathways for controlling activity and selectivity of photo(electro)chemical processes. Concurrently, semiconductor nanostructures enable optimization of charge transport and light absorption. Yet, fundamental questions remain about the microscopic details of these complex light-matter interactions. I will first present our recent results on quantifying the energy-resolved injection probability of hot electrons and hot holes across the metal/semiconductor interface. We demonstrate the importance of small scale nanoantennas to maximize the chance of ballistic collection and we unravel microscopic details of charge transfer via inner or outer sphere pathways [1,2]. Furthermore, I will show how morphology of semiconducting nanostructures dramatically impacts the performance of solar redox flow batteries [3]. In particular, we demonstrate that high photovoltages are attainable in single-material photoanode, enabling unassisted recharging up to high state of charge. Overall, using an internal quantum efficiency perspective, our work unravel the interplay of light absorption, charge generation and in plasmonic and semiconducting photocatalysts.

Javier Aizpurua

Donostia International Physics Center (DIPC), and University of the Basque Country (UPV/EHU), Theory of Nanophotonics Group, San Sebastian, Spain

Lecture: Picocavities and Strong Coupling

Seminar: Exploiting picocavities in field-enhanced fluorescence and in surface-enhanced Raman scattering

Plasmonic nanocavities provide a remarkable effective mode volume reduction, with the corresponding localization and enhancement of local electromagentic fields. A particularly useful extra-localization of light due to the presence of atomic protrusions in surfaces and metallic tips, so-called picocavities, provides the ultimate paradigm of light localization, boosting light-matter interaction at the atomic scale. The extreme fields produced in picocavities can be exploited in field-enhanced spectroscopy and microscopy for instance to reach strong coupling regimes of light-matter interaction as well as to achieve extreme resolution in spatially-resolved molcecular excitations mapping, as in flurescence or in Raman scattering. A description of picocavity-assisted molecular fluorescence of organic chromophores, as well as molecular optomechanical effects driven by a picocavity on a metallic tip will be provided with a strong connection to state-of-the-art experiments in nanophotonics.

Ludovic Douillard

CEA, IRAMIS SPEC, Gif sur Yvette, France

Lecture: Probing the near-field with electrons

Seminar: Plasmonic nanoparticles for the exploration of strong field physics

At small scale, the interaction of light with a metallic object leads to the occurrence of remarkable resonances in the absorption spectrum, known as plasmon resonances. These modes correspond to coherent collective oscillations of charge carriers and generate localised electric fields of high amplitudes. Plasmonics thus offers the possibility of exploring new physical properties in extreme regimes, in particular the physics of strong fields.

This work reports the use of plasmonic nanoparticles and surfaces to study different electronic emission regimes. The emission mechanism can be continuously adjusted from a non-linear photoelectric emission characteristic of a low-field regime to a cold tunnel emission in a high-field regime. The study is carried out at the scale of the individual object by monitoring the kinetic energy distribution of the electrons emitted at resonance [Dombi 2013]. In the strong-field regime, the electrons see their energy distributions widen as a result of a ponderomotive effect up to a large cut-off energy. A cut-off energy of 10 eV is easily obtained for a modest irradiance of the order of 1 - 10 GW/cm² in the infrared wavelength range. The importance of plasmonic particles for strong field physics will be discussed.

^{[Dombi 2013] P. Dombi, et al. Nano Lett. 13 (2013) 674−678}

Romain Quidant

Dept. of Mechanical and Process Engineering, Nanophotonic Systems Laboratory, ETH Zürich, Switzerland

Lecture: Current trends in nanophotonic sensing

Seminar: Revisiting biosensing with digital holography

Digital holography, initially utilized for imaging, has recently experienced a resurgence due to its promising applications in molecular sensing. A prime example is the recent breakthrough in single-protein detection using the iScat technique. Beyond single-molecule detection, access to both the amplitude and phase of optical fields unlocks a plethora of opportunities in diverse sensing applications. This presentation delves into our recent advancements in merging digital holography with cutting-edge microfluidics and nanophotonics to push the boundaries of bioassays and extract deeper insights into bioanalytes.

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