Publications
795 results found
Dagdeviren OE, Glass D, Sapienza R, et al., 2021, The effect of photoinduced surface oxygen vacancies on the charge carrier dynamics in TiO2 films, Nano Letters: a journal dedicated to nanoscience and nanotechnology, Vol: 21, Pages: 8348-8354, ISSN: 1530-6984
Metal-oxide semiconductors (MOS) are widely utilized for catalytic and photocatalytic applications in which the dynamics of charged carriers (e.g., electrons, holes) play important roles. Under operation conditions, photoinduced surface oxygen vacancies (PI-SOV) can greatly impact the dynamics of charge carriers. However, current knowledge regarding the effect of PI-SOV on the dynamics of hole migration in MOS films, such as titanium dioxide, is solely based upon volume-averaged measurements and/or vacuum conditions. This limits the basic understanding of hole-vacancy interactions, as they are not capable of revealing time-resolved variations during operation. Here, we measured the effect of PI-SOV on the dynamics of hole migration using time-resolved atomic force microscopy. Our findings demonstrate that the time constant associated with hole migration is strongly affected by PI-SOV, in a reversible manner. These results will nucleate an insightful understanding of the physics of hole dynamics and thus enable emerging technologies, facilitated by engineering hole-vacancy interactions.
Mao P, Liu C, Li X, et al., 2021, Single-step-fabricated disordered metasurfaces for enhanced light extraction from LEDs., Light: Science and Applications, Vol: 10, ISSN: 2047-7538
While total internal reflection (TIR) lays the foundation for many important applications, foremost fibre optics that revolutionised information technologies, it is undesirable in some other applications such as light-emitting diodes (LEDs), which are a backbone for energy-efficient light sources. In the case of LEDs, TIR prevents photons from escaping the constituent high-index materials. Advances in material science have led to good efficiencies in generating photons from electron-hole pairs, making light extraction the bottleneck of the overall efficiency of LEDs. In recent years, the extraction efficiency has been improved, using nanostructures at the semiconductor/air interface that outcouple trapped photons to the outside continuum. However, the design of geometrical features for light extraction with sizes comparable to or smaller than the optical wavelength always requires sophisticated and time-consuming fabrication, which causes a gap between lab demonstration and industrial-level applications. Inspired by lightning bugs, we propose and realise a disordered metasurface for light extraction throughout the visible spectrum, achieved with single-step fabrication. By applying such a cost-effective light extraction layer, we improve the external quantum efficiency by a factor of 1.65 for commercialised GaN LEDs, demonstrating a substantial potential for global energy-saving and sustainability.
Wang J, Kuehne J, Karamanos T, et al., 2021, All-dielectric crescent metasurface sensor driven by bound states in the continuum, Advanced Functional Materials, Vol: 31, ISSN: 1616-301X
Metasurfaces based on quasi-bound states in the continuum (quasi-BICs) constitute an emerging toolkit in nanophotonic sensing as they sustain high quality factor resonances and substantial near-field enhancements. It is demonstrated that silicon metasurfaces composed of crescent shaped meta-atoms provide tailored light-matter interaction controlled by the crescent geometry. Significantly, this metasurface not only exhibits a fundamental quasi-BIC resonance, but also supports a higher-order resonance with tunable electromagnetic field enhancement and advantageous properties for sensing. The higher-order resonance shows twice the sensitivity of the fundamental one for bulk refractive index sensing. It is further demonstrated that both the fundamental and higher-order resonances can be exploited for sensing ultrathin layers of biomolecules in air and buffer solutions. Specifically, when measuring in buffer solution, the figure of merit of the sensor, defined as the change in the spectral position of the resonance normalized to its full width at half maximum, is a factor of 2.5 larger for the higher-order resonance when compared to the fundamental one. Due to its high sensitivity and potential for straightforward microfluidic integration, the silicon crescent metasurface is ideally suited for real-time and in situ biosensing, enabling compact sensing devices for a wide range of diagnostic applications.
Ren H, Wang X, Li C, et al., 2021, Orbital-angular-momentum-controlled hybrid nanowire circuit, Nano Letters: a journal dedicated to nanoscience and nanotechnology, Vol: 21, Pages: 6220-6227, ISSN: 1530-6984
Plasmonic nanostructures can enable compact multiplexing of the orbital angular momentum (OAM) of light; however, strong dissipation of the highly localized OAM-distinct plasmonic fields in the near-field region hinders on-chip OAM transmission and processing. Superior transmission efficiency is offered by semiconductor nanowires sustaining highly confined optical modes, but only the polarization degree of freedom has been utilized for their selective excitation. Here we demonstrate that incident OAM beams can selectively excite single-crystalline cadmium sulfide (CdS) nanowires through coupling OAM-distinct plasmonic fields into nanowire waveguides for long-distance transportation. This allows us to build an OAM-controlled hybrid nanowire circuit for optical logic operations including AND and OR gates. In addition, this circuit enables the on-chip photoluminescence readout of OAM-encrypted information. Our results open exciting new avenues not only for nanowire photonics to develop OAM-controlled optical switches, logic gates, and modulators but also for OAM photonics to build ultracompact photonic circuits for information processing.
Davidson-Marquis F, Gargiulo J, Gomez-Lopez E, et al., 2021, Coherent interaction of atoms with a beam of light confined in a light cage, Light: Science and Applications, Vol: 10, ISSN: 2047-7538
Li C-H, Maier SA, Ren H-R, 2021, Optical vortices in nanophotonics, CHINESE OPTICS, Vol: 14, Pages: 792-811, ISSN: 2095-1531
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- Citations: 9
Wang X, Liu C, Gao C, et al., 2021, Self-constructed multiple plasmonic hotspots on an individual fractal to amplify broadband hot electron generation., ACS Nano, Vol: 15, Pages: 10553-10564, ISSN: 1936-0851
Plasmonic nanoparticles are ideal candidates for hot-electron-assisted applications, but their narrow resonance region and limited hotspot number hindered the energy utilization of broadband solar energy. Inspired by tree branches, we designed and chemically synthesized silver fractals, which enable self-constructed hotspots and multiple plasmonic resonances, extending the broadband generation of hot electrons for better matching with the solar radiation spectrum. We directly revealed the plasmonic origin, the spatial distribution, and the decay dynamics of hot electrons on the single-particle level by using ab initio simulation, dark-field spectroscopy, pump-probe measurements, and electron energy loss spectroscopy. Our results show that fractals with acute tips and narrow gaps can support broadband resonances (400-1100 nm) and a large number of randomly distributed hotspots, which can provide unpolarized enhanced near field and promote hot electron generation. As a proof-of-concept, hot-electron-triggered dimerization of p-nitropthiophenol and hydrogen production are investigated under various irradiations, and the promoted hot electron generation on fractals was confirmed with significantly improved efficiency.
Jang B, Gargiulo J, Kim J, et al., 2021, Fiber-integrated hollow-core light cage for gas spectroscopy, APL PHOTONICS, Vol: 6, ISSN: 2378-0967
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- Citations: 7
Mao P, Liu C, Niu Y, et al., 2021, Disorder-Induced Material-Insensitive Optical Response in Plasmonic Nanostructures: Vibrant Structural Colors from Noble Metals, ADVANCED MATERIALS, Vol: 33, ISSN: 0935-9648
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- Citations: 19
Davidson-Marquis F, Gargiulo J, Gomez-Lopez E, et al., 2021, Coherent interaction of atoms with a beam of light confined in a light cage, Light: Science and Applications, Vol: 10, ISSN: 2047-7538
Controlling coherent interaction between optical fields and quantum systems in scalable, integrated platforms is essential for quantum technologies. Miniaturised, warm alkali-vapour cells integrated with on-chip photonic devices represent an attractive system, in particular for delay or storage of a single-photon quantum state. Hollow-core fibres or planar waveguides are widely used to confine light over long distances enhancing light-matter interaction in atomic-vapour cells. However, they suffer from inefficient filling times, enhanced dephasing for atoms near the surfaces, and limited light-matter overlap. We report here on the observation of modified electromagnetically induced transparency for a non-diffractive beam of light in an on-chip, laterally-accessible hollow-core light cage. Atomic layer deposition of an alumina nanofilm onto the light-cage structure was utilised to precisely tune the high-transmission spectral region of the light-cage mode to the operation wavelength of the atomic transition, while additionally protecting the polymer against the corrosive alkali vapour. The experiments show strong, coherent light-matter coupling over lengths substantially exceeding the Rayleigh range. Additionally, the stable non-degrading performance and extreme versatility of the light cage provide an excellent basis for a manifold of quantum-storage and quantum-nonlinear applications, highlighting it as a compelling candidate for all-on-chip, integrable, low-cost, vapour-based photon delay.
Hüttenhofer L, Tittl A, Kühner L, et al., 2021, Anapole-assisted absorption engineering in arrays of coupled amorphous gallium phosphide nanodisks, ACS Photonics, Vol: 8, Pages: 1469-1476, ISSN: 2330-4022
Broadband solar light harvesting plays a crucial role for efficient energy conversion. Anapole excitations and associated absorption engineering in dielectric nanoresonators are a focus of nanophotonic research due to the intricate combination of nonradiating modes and strong electromagnetic field confinement in the underlying material. The arising high field strengths are used for enhanced second-harmonic generation and photocatalysis, where devices require large areas with closely spaced nanoresonators for sizable photonic yields. However, most anapole studies have so far been carried out at the single-particle level, neglecting the influence of anapole–anapole interactions. Here, we present a systematic study of coupling mechanisms in rectangular arrays of amorphous GaP nanodisks that support anapole excitations at 600 nm, which is within the lossy spectral regime of the material. Our experimental findings show that maximum visible light extinction by the array and maximum absorption in the GaP are not achieved by the densest packing of resonators. Counterintuitively, increasing the array periodicities such that collective effects spectrally overlap with the anapole excitation of a single particle leads to an absorption enhancement of up to 300% compared to a single disk. An analysis of coupling in one- and two-dimensional arrays with polarization-dependent measurements and numerical simulations allows us to discriminate between coupling interactions parallel and perpendicular to the polarization axis and evaluate their strengths. Utilizing a multipolar decomposition of excitations in single nanodisks embedded in one-dimensional arrays, we can attribute the coupling to enhanced electric and toroidal dipoles under variation of the interparticle spacing. Our results provide a fundamental understanding of tailored light absorption in coupled anapole resonators and reveal important design guidelines for advanced metasurface approaches in a wide range of energy
Kim J, Jang B, Gargiulo J, et al., 2021, The Light Cage-Integrated on-Chip Spectroscopy Using a Nano-Printed Hollow Core Waveguide
We present a novel platform-the nano-printed optofluidic light cage-that allows for strong light-liquid interactions across centimetre distances via the antiresonant effect. In accordance with simulations we show liquid-based spectroscopic experiments.
Gennaro SD, Roschuk T, Maier SA, et al., 2021, Critical Coupling of a Single Metallic Nanoantenna under Focused Illumination
In this work, we investigate the critical coupling of a single gold disk antenna with a focused beam by evaluating its absorption and scattering using spectral interferometry microcopy.
Jang B, Gargiulo J, Kim J, et al., 2021, Fiber-connected 3D Printed Hollow-core Light Cage for Gas Detection
The light cage is a 3D nanoprinted hollow-core waveguide which can be used as an integrated light-matter interaction platform. Here we present the fiber-connected version of light cage and demonstrate ammonia gas sensing using tunable diode laser absorption spectroscopy.
Kuhner L, Ren H, Berte R, et al., 2021, Radial bound states in the continuum
We experimentally demonstrate a new platform for enhanced light-matter interaction and sensing based on radial bound states in the continuum, which are supported in rings of symmetry-broken dielectric resonators with an ultracompact footprint.
Tirole R, Attavar T, Dranczewski J, et al., 2021, Time Diffraction in an Epsilon-Near-Zero Metasurface
We observe strong, efficient all-optical modulations and frequency-shift due to time diffraction in a thin film of ITO over gold. Excitation of the Berreman mode leads to redshift and spectral broadening from a nonlinear grating.
Luo S, Mancini A, Berte R, et al., 2021, Massively Parallel Arrays of Size-Controlled Metallic Nanogaps with Gap-Widths Down to the Sub-3-nm Level, ADVANCED MATERIALS, Vol: 33, ISSN: 0935-9648
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- Citations: 17
Kepic P, Ligmajer F, Hrton M, et al., 2021, Optically tunable mie resonance VO2 nanoantennas for metasurfaces in the visible, ACS Photonics, Vol: 8, Pages: 1048-1057, ISSN: 2330-4022
Metasurfaces are ultrathin nanostructured surfaces that can allow arbitrary manipulation of light. Implementing dynamic tunability into their design could allow the optical functions of metasurfaces to be rapidly modified at will. The most pronounced and robust tunability of optical properties is provided by phase-change materials such as vanadium dioxide (VO2) and germanium antimony telluride (GST), but their implementations have been limited only to near-infrared wavelengths. Here, we demonstrate that VO2 nanoantennas with widely tunable Mie resonances can be utilized for designing tunable metasurfaces in the visible range. In contrast to the dielectric-metallic VO2 phase transition-induced tunability in previous demonstrations, we show that persisting dielectric Mie resonances in VO2 nanoantennas offer remarkable scattering and extinction modulation depths (5–8 dB and 1–3 dB, respectively) for tunability in the visible. Moreover, these strong resonances are optically switchable using a continuous-wave laser. Our results establish VO2 nanostructures as low-loss building blocks of optically tunable metasurfaces.
Burger J, Kim J, Jang B, et al., 2021, Ultrahigh-aspect-ratio light cages: fabrication limits and tolerances of free-standing 3D nanoprinted waveguides, OPTICAL MATERIALS EXPRESS, Vol: 11, Pages: 1046-1057, ISSN: 2159-3930
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- Citations: 8
Aizpurua J, Atwater HA, Baumberg JJ, et al., 2021, Mark Stockman: Evangelist for Plasmonics, ACS PHOTONICS, Vol: 8, Pages: 683-698, ISSN: 2330-4022
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- Citations: 2
Plidschun M, Ren H, Kim J, et al., 2021, Ultrahigh numerical aperture meta-fibre for flexible optical trapping, LIGHT-SCIENCE & APPLICATIONS, Vol: 10, ISSN: 2047-7538
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- Citations: 49
Xiao X, Maier SA, Giannini V, 2021, Ultrabroad-Band Direct Digital Refractive Index Imaging Based on Suspended Graphene Plasmon Nanocavities, ACS APPLIED NANO MATERIALS, Vol: 4, Pages: 1635-1642
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- Citations: 1
Barella M, Violi IL, Gargiulo J, et al., 2021, In situ photothermal response of single gold nanoparticles through hyperspectral imaging anti-stokes thermometry, ACS Nano, Vol: 15, Pages: 2458-2467, ISSN: 1936-0851
Several fields of applications require a reliable characterization of the photothermal response and heat dissipation of nanoscopic systems, which remains a challenging task for both modeling and experimental measurements. Here, we present an implementation of anti-Stokes thermometry that enables the in situ photothermal characterization of individual nanoparticles (NPs) from a single hyperspectral photoluminescence confocal image. The method is label-free, potentially applicable to any NP with detectable anti-Stokes emission, and does not require any prior information about the NP itself or the surrounding media. With it, we first studied the photothermal response of spherical gold NPs of different sizes on glass substrates, immersed in water, and found that heat dissipation is mainly dominated by the water for NPs larger than 50 nm. Then, the role of the substrate was studied by comparing the photothermal response of 80 nm gold NPs on glass with sapphire and graphene, two materials with high thermal conductivity. For a given irradiance level, the NPs reach temperatures 18% lower on sapphire and 24% higher on graphene than on bare glass. The fact that the presence of a highly conductive material such as graphene leads to a poorer thermal dissipation demonstrates that interfacial thermal resistances play a very significant role in nanoscopic systems and emphasize the need for in situ experimental thermometry techniques. The developed method will allow addressing several open questions about the role of temperature in plasmon-assisted applications, especially ones where NPs of arbitrary shapes are present in complex matrixes and environments.
Geng D, Abdelwahab I, Xiao X, et al., 2021, One-Pot Confined Epitaxial Growth of 2D Heterostructure Arrays, ACS MATERIALS LETTERS, Vol: 3, Pages: 217-223
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- Citations: 7
Aigner A, Maier SA, Ren H, 2021, Topological-Insulator-Based Gap-Surface Plasmon Metasurfaces, PHOTONICS, Vol: 8
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- Citations: 3
Zhan Y, Zhang L, Rahmani M, et al., 2021, Synthetic Plasmonic Nanocircuits and the Evolution of Their Correlated Spatial Arrangement and Resonance Spectrum, ACS PHOTONICS, Vol: 8, Pages: 166-174, ISSN: 2330-4022
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- Citations: 5
Kim J, Jang B, Gargiulo J, et al., 2021, The Optofluidic Light Cage - On-Chip Integrated Spectroscopy Using an Antiresonance Hollow Core Waveguide, ANALYTICAL CHEMISTRY, Vol: 93, Pages: 752-760, ISSN: 0003-2700
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- Citations: 13
Wang J, Kühne J, Karamanos T, et al., 2021, QUASI-BOUND STATES IN THE CONTINUUM IN ALL-DIELECTRIC METASURFACE TOWARDS BIOSENSING, Pages: 1601-1602
We demonstrate an all-dielectric crescent metasurface made of sub-wavelength silicon meta-atoms, realizing the recently introduced new physics of quasi-bound states in the continuum (quasi-BIC). The crescent metasurface supports a fundamental quasi-BIC together with a higher-order resonance with arbitrarily tunable quality factors and enhanced electromagnetic fields near the resonator surface via finely tailoring the geometry of the crescent shape. Thanks to these unique properties, such a metasurface can serve as an optical label-free sensor for multiplexed bioassays with high sensitivity and low detection limit with the potential for integrating microfluidics for in-situ on chip detection.
Liu C, Mao P, Niu Y, et al., 2021, Material-insensitive optical response from disordered plasmonic nanostructures
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