Publications
795 results found
Ren H, Maier SA, 2023, Nanophotonic Materials for Twisted-Light Manipulation, ADVANCED MATERIALS, Vol: 35, ISSN: 0935-9648
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- Citations: 12
Zhang C, Huang B, Li H, et al., 2023, Plasmonic Nanoneedle Arrays with Enhanced Hot Electron Photodetection for Near-IR Imaging, ADVANCED FUNCTIONAL MATERIALS, ISSN: 1616-301X
Lv J, Wu Y, Liu J, et al., 2023, Hyperbolic polaritonic crystals with configurable low-symmetry Bloch modes, NATURE COMMUNICATIONS, Vol: 14
Tirole R, Vezzoli S, Galiffi E, et al., 2023, Double-slit time diffraction at optical frequencies, Nature Physics, Vol: 19, Pages: 999-1002, ISSN: 1745-2473
Double-slit experiments—where a wave is transmitted through a thin double aperture in space—have confirmed the wave–particle duality of quantum objects, such as single photons, electrons, neutrons, atoms and large molecules. Yet, the temporal counterpart of Young’s double-slit experiment—a wave interacting with a double temporal modulation of an interface—remains elusive. Here we report such a time-domain version of the classic Young’s double-slit experiment: a beam of light twice gated in time produces an interference in the frequency spectrum. The ‘time slits’, narrow enough to produce diffraction at optical frequencies, are generated from the optical excitation of a thin film of indium tin oxide near its epsilon-near-zero point. The separation between time slits determines the period of oscillations in the frequency spectrum, whereas the decay of fringe visibility in frequency reveals the shape of the time slits. Surprisingly, many more oscillations are visible than expected from existing theory, implying a rise time that approaches an optical cycle. This result enables the further exploration of time-varying physics, towards the spectral synthesis of waves and applications such as signal processing and neuromorphic computation.
Gargiulo J, Herran M, Violi IL, et al., 2023, Impact of bimetallic interface design on heat generation in plasmonic Au/Pd nanostructures studied by single-particle thermometry, NATURE COMMUNICATIONS, Vol: 14
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- Citations: 3
Weber T, Kühner L, Sortino L, et al., 2023, Intrinsic strong light-matter coupling with self-hybridized bound states in the continuum in van der Waals metasurfaces., Nature Materials, Vol: 22, Pages: 970-976, ISSN: 1476-1122
Photonic bound states in the continuum (BICs) provide a standout platform for strong light-matter coupling with transition metal dichalcogenides (TMDCs) but have so far mostly been implemented as traditional all-dielectric metasurfaces with adjacent TMDC layers, incurring limitations related to strain, mode overlap and material integration. Here, we demonstrate intrinsic strong coupling in BIC-driven metasurfaces composed of nanostructured bulk tungsten disulfide (WS2) and exhibiting resonances with sharp, tailored linewidths and selective enhancement of light-matter interactions. Tuning of the BIC resonances across the exciton resonance in bulk WS2 is achieved by varying the metasurface unit cells, enabling strong coupling with an anticrossing pattern and a Rabi splitting of 116 meV. Crucially, the coupling strength itself can be controlled and is shown to be independent of material-intrinsic losses. Our self-hybridized metasurface platform can readily incorporate other TMDCs or excitonic materials to deliver fundamental insights and practical device concepts for polaritonic applications.
Lin T, Yang T, Cai Y, et al., 2023, Transformation-optics-designed plasmonic singularities for efficient photocatalytic hydrogen evolution at metal/semiconductor interfaces, Nano Letters: a journal dedicated to nanoscience and nanotechnology, Vol: 23, Pages: 5288-5296, ISSN: 1530-6984
Inspired by transformation optics, we propose a new concept for plasmonic photocatalysis by creating a novel hybrid nanostructure with a plasmonic singularity. Our geometry enables broad and strong spectral light harvesting at the active site of a nearby semiconductor where the chemical reaction occurs. A proof-of-concept nanostructure comprising Cu2ZnSnS4 (CZTS) and Au-Au dimer (t-CZTS@Au-Au) is fabricated via a colloidal strategy combining templating and seeded growth. On the basis of numerical and experimental results of different related hybrid nanostructures, we show that both the sharpness of the singular feature and the relative position to the reactive site play a pivotal role in optimizing photocatalytic activity. Compared with bare CZTS, the hybrid nanostructure (t-CZTS@Au-Au) exhibits an enhancement of the photocatalytic hydrogen evolution rate by up to ∼9 times. The insights gained from this work might be beneficial for designing efficient composite plasmonic photocatalysts for diverse photocatalytic reactions.
Doiron B, Li Y, Bower R, et al., 2023, Optimizing hot electron harvesting at planar metal–semiconductor interfaces with titanium oxynitride thin films, ACS Applied Materials and Interfaces, Vol: 25, Pages: 30417-30426, ISSN: 1944-8244
Understanding metal-semiconductor interfaces is critical to the advancement of photocatalysis and sub-bandgap solar energy harvesting where electrons in the metal can be excited by sub-bandgap photons and extracted into the semiconductor. In this work, we compare the electron extraction efficiency across Au/TiO2 and titanium oxynitride (TiON)/TiO2-x interfaces, where in the latter case the spontaneously forming oxide layer (TiO2-x) creates a metal-semiconductor contact. Time-resolved pump-probe spectroscopy is used to study the electron recombination rates in both cases. Unlike the nanosecond recombination lifetimes in Au/TiO2, we find a bottleneck in the electron relaxation in the TiON system, which we explain using a trap-mediated recombination model. Using this model, we investigate the tunability of the relaxation dynamics with oxygen content in the parent film. The optimized film (TiO0.5N0.5) exhibits the highest carrier extraction efficiency (NFC ≈ 2.8 × 1019 m-3), slowest trapping, and an appreciable hot electron population reaching the surface oxide (NHE ≈ 1.6 × 1018 m-3). Our results demonstrate the productive role oxygen can play in enhancing electron harvesting and prolonging electron lifetimes, providing an optimized metal-semiconductor interface using only the native oxide of titanium oxynitride.
Berger LM, Duportal M, Menezes LDS, et al., 2023, Improved In Situ Characterization of Electrochemical Interfaces Using Metasurface-Driven Surface-Enhanced IR Absorption Spectroscopy, ADVANCED FUNCTIONAL MATERIALS, Vol: 33, ISSN: 1616-301X
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- Citations: 1
Pessoa AR, Galindo JAO, dos Santos LF, et al., 2023, Correction Due to Nonthermally Coupled Emission Bands and Its Implications on the Performance of Y<sub>2</sub>O<sub>3</sub>:Yb<SUP>3+</SUP> /Er<SUP>3+</SUP> Single-Particle Thermometers, JOURNAL OF PHYSICAL CHEMISTRY C, Vol: 127, Pages: 9673-9680, ISSN: 1932-7447
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- Citations: 1
Oulton R, 2023, Emission enhancement of erbium in a reverse nanofocusing waveguide, Nature Communications, Vol: 14, Pages: 1-10, ISSN: 2041-1723
Since Purcell’s seminal report 75 years ago, electromagnetic resonators have been used to control light-matter interactions to make brighter radiation sources and unleash unprecedented control over quantum states of light and matter. Indeed, optical resonators such as microcavities and plasmonic antennas offer excellent control but only over a limited spectral range. Strategies to mutually tune and match emission and resonator frequency are often required, which is intricate and precludes the possibility of enhancing multiple transitions simultaneously. In this letter, we report a strong radiative emission rate enhancement of Er3+-ions across the telecommunications C-band in a single plasmonic waveguide based on the Purcell effect. Our gap waveguide uses a reverse nanofocusing approach to efficiently enhance, extract and guide emission from the nanoscale to a photonic waveguide while keeping plasmonic losses at a minimum. Remarkably, the large and broadband Purcell enhancement allows us to resolve Stark-split electric dipole transitions, which are typically only observed under cryogenic conditions. Simultaneous radiative emission enhancement of multiple quantum states is of great interest for photonic quantum networks and on-chip data communications.
Bragas AV, Maier SA, Boggiano HD, et al., 2023, Nanomechanics with plasmonic nanoantennas : ultrafast and local exchange between electromagnetic and mechanical energy, JOURNAL OF THE OPTICAL SOCIETY OF AMERICA B-OPTICAL PHYSICS, Vol: 40, Pages: 1196-1211, ISSN: 0740-3224
Xiao X, Gillibert R, Foti A, et al., 2023, Plasmonic Polarization Rotation in SERS Spectroscopy, NANO LETTERS, Vol: 23, Pages: 2530-2535, ISSN: 1530-6984
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- Citations: 1
Berté R, Weber T, de Souza Menezes L, et al., 2023, Permittivity-asymmetric quasi-bound states in the continuum., Nano Letters: a journal dedicated to nanoscience and nanotechnology, Vol: 23, Pages: 2651-2658, ISSN: 1530-6984
Breaking the in-plane geometric symmetry of dielectric metasurfaces allows us to access a set of electromagnetic states termed symmetry-protected quasi-bound states in the continuum (qBICs). Here we demonstrate that qBICs can also be accessed by a symmetry breaking in the permittivity of the comprising materials. While the physical size of atoms imposes a limit on the lowest achievable geometrical asymmetry, weak permittivity modulations due to carrier doping, and electro-optical Pockels and Kerr effects, usually considered insignificant, open the possibility of infinitesimal permittivity asymmetries for on-demand, dynamically tunable resonances of extremely high quality factors. As a proof-of-principle, we probe the excitation of permittivity-asymmetric qBICs (ε-qBICs) using a prototype Si/TiO2 metasurface, in which the asymmetry in the unit cell is provided by the permittivity contrast of the materials. ε-qBICs are also numerically demonstrated in 1D gratings, where quality-factor enhancement and tailored interference phenomena of qBICs are shown via the interplay of geometrical and permittivity asymmetries.
Abdelwahab I, Tilmann B, Zhao X, et al., 2023, Highly Efficient Sum-Frequency Generation in Niobium Oxydichloride NbOCl<sub>2</sub> Nanosheets, ADVANCED OPTICAL MATERIALS, Vol: 11, ISSN: 2195-1071
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- Citations: 1
Kuehner L, Sortino L, Tilmann B, et al., 2023, High-<i>Q</i> Nanophotonics over the Full Visible Spectrum Enabled by Hexagonal Boron Nitride Metasurfaces, ADVANCED MATERIALS, ISSN: 0935-9648
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- Citations: 2
Kalinic B, Cesca T, Balasa IG, et al., 2023, Quasi-BIC modes in all-dielectric slotted nanoantennas for enhanced Er3+ emission, ACS Photonics, Vol: 10, Pages: 534-543, ISSN: 2330-4022
In the quest for new and increasingly efficient photon sources, the engineering of the photonic environment at the subwavelength scale is fundamental for controlling the properties of quantum emitters. A high refractive index particle can be exploited to enhance the optical properties of nearby emitters without decreasing their quantum efficiency, but the relatively modest Q-factors (Q ∼ 5–10) limit the local density of optical states (LDOS) amplification achievable. On the other hand, ultrahigh Q-factors (up to Q ∼ 109) have been reported for quasi-BIC modes in all-dielectric nanostructures. In the present work, we demonstrate that the combination of quasi-BIC modes with high spectral confinement and nanogaps with spacial confinement in silicon slotted nanoantennas lead to a significant boosting of the electromagnetic LDOS in the optically active region of the nanoantenna array. We observe an enhancement of up to 3 orders of magnitude in the photoluminescence intensity and 2 orders of magnitude in the decay rate of the Er3+ emission at room temperature and telecom wavelengths. Moreover, the nanoantenna directivity is increased, proving that strong beaming effects can be obtained when the emitted radiation couples to the high Q-factor modes. Finally, via tuning the nanoanntenna aspect ratio, a selective control of the Er3+ electric and magnetic radiative transitions can be obtained, keeping the quantum efficiency almost unitary.
Kim J, Buerger J, Jang B, et al., 2023, 3D-nanoprinted on-chip antiresonant waveguide with hollow core and microgaps for integrated optofluidic spectroscopy, OPTICS EXPRESS, Vol: 31, Pages: 2833-2845, ISSN: 1094-4087
Güsken NA, Fu M, Zapf M, et al., 2023, Emission enhancement of erbium in a reverse nanofocusing waveguide, Pages: 584-585
We report emission enhancement of Er3+-ions across the telecommunications C-band in a single plasmonic waveguide based on the Purcell effect. Our gap waveguide uses a reverse nanofocusing approach to efficiently enhance, extract and guide emission from the nanoscale to a photonic waveguide while keeping plasmonic losses at a minimum. A large and broadband Purcell enhancement allows us to resolve Stark-split electric dipole transitions. Simultaneous enhancement of multiple quantum states is of great interest for photonic and quantum networks.
Berger LM, Duportal M, Menezes LDS, et al., 2023, Metasurface-driven surface-enhanced infrared absorption spectroscopy for superior characterization of electrocatalytic reactions, Pages: 1377-1378
Understanding electrocatalytic processes is crucial to realize the transition toward a sustainable zero-carbon future. Surface-enhanced infrared absorption spectroscopy (SEIRAS) is a suitable method to monitor the mechanisms of these processes with chemical specificity. However, it remains difficult to detect many relevant aspects of electrochemical reactions such as short-lived intermediates. Here, we demonstrate an integrated nanophotonic-electrochemical SEIRAS platform for the in-situ investigation of molecular signal traces emerging during electrochemical experiments.
Moretti GQ, Tilmann B, Tittl A, et al., 2023, Metasurface Design with Robust Resonances for Nonlinear Photonics, Pages: 1015-1016
A metasurface of Gallium Phosphide on glass with a robust design enables high-quality factor (Q) modes, arising from the concept of quasi bound states in the continuum (QBICs). The high enhancement of the incident electric field is used to compute the nonlinear second harmonic (SH) fields in a non-perturbative approach, yielding a theoretical maximum conversion efficiency of 0.5%. Preliminary experimental results will be presented.
Schmidt MA, Schneidewind H, Hübner U, et al., 2023, Merging Nanophotonics with Optical Fibers through 3D Nanoprinting: a novel platform for flexible beam manipulation, Pages: 381-382
Here, we will demonstrate how the fusion of optical fibers with nanostructures creates a new category of fiber-integrated devices 3 hybrid optical fibers - that unlocks novel applications. We achieve this by leveraging 3D nanoprinting, which is highly compatible with the fiber geometry, to integrate high-NA holographic metalenses, achromatic metasurface-based lenses, and dielectric ring-like gratings onto the end faces of single-mode fibers, allowing to trap biological relevant objects, to focus light across the telecommunication range, and to boost incoupling efficiencies.
Vidal C, Tilmann B, Tiwari S, et al., 2023, Performance of gallium phosphide nanoantennas from optimised design
Over the last years, various numerical algorithms have been used to predict the design of a dielectric nanoantenna which maximises the local density of optical states (LDOS) [1-4]. As simulation techniques have evolved and improved in speed and accuracy, the ultimate design for dielectric nanoantennas to enhance a single emitter has to combine resonant modes with nanoscale enhancement. Experiments evaluation of the performance of such antennas is challenging due to the complexity of combining high-resolution nanofabrication and nanoscale positioning of the emitter [5].
Possmayer T, Sortino L, Maier SA, et al., 2023, Microscopic Z-Scan for Measuring Nonlinear Absorption of Mechanically Exfoliated Transition Metal Dichalcogenide Monolayers
The Z-scan technique is commonly used to measure optical nonlinearities of bulk crystals and solutions. By scanning a sample through the focal region of a Gaussian beam and tracking the size and intensity of the transmitted spot, it is possible to retrieve both the Kerr nonlinear refractive index and the nonlinear absorption coefficient of the sample [1]. This enables a higher precision and faster measurement than previously employed methods.
Pessoa AR, Galindo JAO, dos Santos LF, et al., 2023, Influence of the non-thermally coupled three-photon band on the performance of Y<inf>2</inf>O<inf>3</inf>: Yb<sup>3+</sup>/Er<sup>3+</sup> single-particle nanothermometers
Nanoscale temperature sensing is increasingly being explored to study physical-chemical processes at the nanoscale. Since direct contact thermometers, like thermistors, are usually not suitable for high spatial resolution applications, luminescence thermometry raises as an alternative. In this case, a nanoparticle can be used as a probe and the temperature measurement is done by analyzing the luminescence emission. One of the most exploited candidates as luminescence nanothermometer probes are dielectric nanoparticles doped with lanthanide ions (Ln3+). They offer a high photostability and the possibility of using non-cytotoxic host matrices, targeting biological applications. In a typical approach, one can measure the temperature from Ln3+-based systems by recording their emission luminescence spectrum and computing the Luminescence Intensity Ratio between two so-called thermally coupled levels [1], which should follow the Boltzmann distribution. Another great advantage of using Ln3+-doped systems is to exploit the upconversion (UC) process, being possible to excite the thermally coupled levels with light of lower energy. In this sense, codoped Yb3+/Er3+ systems are among the most efficient ones. In such cases, the electrons in the ground state of the Yb3+ ions can be excited with a laser near 980 nm. Depending on the Yb3+ and Er3+ ions' proximity, the energy can be efficiently transferred from Yb3+ to Er3+ ions. Consecutive energy transfer (ET) steps can thus lead to the UC phenomena, populating higher-lying electronic states. In Er3+ ions, the thermally coupled levels, 2H11/2 and 4S3/2 need a two-step ET of 977 nm excitation. They decay radiatively to the ground state (4I15/2) resulting in luminescent bands in the green spectral region, with central wavelengths of ∼525 nm and ∼550 nm, respectively. Depending on the excitation power density, higher-order multiphoton absorption can also happen, therefore populating states above the thermally coupled ones.
Barkey M, Büchner R, Wester A, et al., 2023, Metasurface-enabled molecular spectroscopy and machine learning resolve lipid membrane photoswitching, Pages: 1621-1623
We present an integrated platform for ultrasensitive in-situ biospectroscopy by combining all-dielectric pixelated metasurfaces and machine learning. Specifically designed metasurfaces with advanced sampling techniques probe the real-time dynamics of lipid membrane photoswitching in an aqueous environment in the mid-infrared, overcoming sensitivity limitations and strong water absorption associated with conventional infrared spectroscopy. Our platform combines metasurfaces, optofluidics, and artificial intelligence (AI) to extend the capabilities of dielectric metasurfaces for analyzing complex biological entities.
Sortino L, Giilmiis M, Tilmann B, et al., 2023, Radiative suppression of exciton-exciton annihilation in a two-dimensional semiconductor
Exciton-exciton annihilation (EEA) processes are a fundamental limit for the efficiency of two-dimensional (2D) semiconductors. Here, we demonstrate suppressed EEA by enhancing light-matter interaction in hybrid 2D-dielectric nanophotonic platforms, by coupling excitons in a transition metal dichalcogenide (TMDC) WS2 monolayer with optical Mie resonances in gallium phosphide (GaP) dielectric nanoantennas. From their ultrafast dynamics, we show reduced EEA processes, even under high exciton density, demonstrating the potential of all-dielectric nanoantennas for low-power integrated nanophotonic devices based on 2D semiconductors.
Hu H, Hüttenhofer L, Bienek O, et al., 2023, Engineering a multifunctional TiO<inf>2</inf> BIC metasurface, Pages: 1542-1541
We develop a multifunctional metasurface platform that leverages the combination of loss-engineered substoichiometric titanium oxide (TiO2-x) and the emerging physical concept of optical bound states in the continuum (BICs) to boost photoinduced charge transfer (PICT) and provide broad spectral tunability, making this semiconductor metasurface not only a competitive platform for surface photocatalytic investigations, but also a promising candidate for boosting sensitivities in in semiconductor-based surface-enhanced Raman scattering (SERS) applications.
Fu M, Mota MPDP, Xiao X, et al., 2023, Near unity Raman β-factor of surface enhanced Raman scattering in a waveguide, Pages: 1327-1328
We show that SERS from monolayer 4-Aminothiophenol (4-ATP) bonded to a plasmonic gap waveguide is directed into a single mode with >99% efficiency. Although sacrificing a confinement dimension, we find a 103 x SERS enhancement across a broad spectral range, enabled by the plasmonic waveguide9s larger sensing volume and non-resonant waveguide mode. Waveguide-SERS (W-SERS) is bright enough to image Raman transport across the waveguides. This exposes the roles of nanofocusing, the Purcell effect and the spontaneous Raman scattering factor, or Raman β-factor.
Liu C, Zhang S, Maier SA, et al., 2022, Disorder-Induced Topological State Transition in the Optical Skyrmion Family, PHYSICAL REVIEW LETTERS, Vol: 129, ISSN: 0031-9007
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- Citations: 3
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