Imperial College London

ProfessorStefanMaier

Faculty of Natural SciencesDepartment of Physics

Lee-Lucas Chair in Experimental Physics
 
 
 
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Contact

 

+44 (0)20 7594 6063s.maier Website CV

 
 
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Location

 

Huxley 903Huxley BuildingSouth Kensington Campus

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Summary

 

Publications

Publication Type
Year
to

799 results found

Cortes E, Grzeschik R, Maier SA, Schluecker Set al., 2022, Experimental characterization techniques for plasmon-assisted chemistry, NATURE REVIEWS CHEMISTRY, Vol: 6, Pages: 259-274

Journal article

Wang J, Maier SA, Tittl A, 2022, Trends in Nanophotonics-Enabled Optofluidic Biosensors, ADVANCED OPTICAL MATERIALS, Vol: 10, ISSN: 2195-1071

Journal article

Yang B, Liu K, Li H, Liu C, Fu J, Li H, Huang JE, Ou P, Alkayyali T, Cai C, Duan Y, Liu H, An P, Zhang N, Li W, Qiu X, Jia C, Hu J, Chai L, Lin Z, Gao Y, Miyauchi M, Cortés E, Maier SA, Liu Met al., 2022, Accelerating CO2 electroreduction to multicarbon products via synergistic electric-thermal field on copper nanoneedles., Journal of the American Chemical Society, Vol: 144, Pages: 3039-3049, ISSN: 0002-7863

Electrochemical CO2 reduction is a promising way to mitigate CO2 emissions and close the anthropogenic carbon cycle. Among products from CO2RR, multicarbon chemicals, such as ethylene and ethanol with high energy density, are more valuable. However, the selectivity and reaction rate of C2 production are unsatisfactory due to the sluggish thermodynamics and kinetics of C-C coupling. The electric field and thermal field have been studied and utilized to promote catalytic reactions, as they can regulate the thermodynamic and kinetic barriers of reactions. Either raising the potential or heating the electrolyte can enhance C-C coupling, but these come at the cost of increasing side reactions, such as the hydrogen evolution reaction. Here, we present a generic strategy to enhance the local electric field and temperature simultaneously and dramatically improve the electric-thermal synergy desired in electrocatalysis. A conformal coating of ∼5 nm of polytetrafluoroethylene significantly improves the catalytic ability of copper nanoneedles (∼7-fold electric field and ∼40 K temperature enhancement at the tips compared with bare copper nanoneedles experimentally), resulting in an improved C2 Faradaic efficiency of over 86% at a partial current density of more than 250 mA cm-2 and a record-high C2 turnover frequency of 11.5 ± 0.3 s-1 Cu site-1. Combined with its low cost and scalability, the electric-thermal strategy for a state-of-the-art catalyst not only offers new insight into improving activity and selectivity of value-added C2 products as we demonstrated but also inspires advances in efficiency and/or selectivity of other valuable electro-/photocatalysis such as hydrogen evolution, nitrogen reduction, and hydrogen peroxide electrosynthesis.

Journal article

Aigner A, Dawes JM, Maier SA, Ren Het al., 2022, Nanophotonics shines light on hyperbolic metamaterials (vol 11, 9, 2022), LIGHT-SCIENCE & APPLICATIONS, Vol: 11, ISSN: 2047-7538

Journal article

Liu C, Maier SA, 2022, High-Quality Optical Hotspots with Topology-Protected Robustness, ACS PHOTONICS, Vol: 9, Pages: 241-248, ISSN: 2330-4022

Journal article

Aigner A, Dawes JM, Maier SA, Ren Het al., 2022, Nanophotonics shines light on hyperbolic metamaterials, LIGHT-SCIENCE & APPLICATIONS, Vol: 11, ISSN: 2047-7538

Journal article

Güsken NA, Fu M, Zapf M, Nielsen MP, Dichtl P, Roder R, Maier SA, Ronning C, Brongersma ML, Oulton RFet al., 2022, Fluorescence enhancement of Er<sup>3+</sup>-ions using reverse hybrid plasmonic nano-focusing

We report the broadband fluorescence enhancement of erbium ions embedded in a single non-resonant reverse nano-focusing waveguide. We measure a large radiative Purcell enhancement of a total emission rate enhancement of > 250 across the entire measured spectrum including the prominent telecoms C-band. Further, we observe the enhancement of single electric dipole transitions from Stark-split levels at room temperature.

Conference paper

Kühner L, Wendisch F, Maier SA, Kivshar YS, Tittl Aet al., 2022, Height-Driven Symmetry Breaking for High-Q Resonances in All-Dielectric Metasurfaces

We demonstrate a novel approach to control photonic bound states in the continuum induced by a symmetry-breaking with tailored resonator heights leading to more precisely engineered system asymmetries and new metasurface functionalities.

Conference paper

Kühner L, Wendisch F, Maier SA, Kivshar YS, Tittl Aet al., 2022, Height-Driven Symmetry Breaking for High-Q Resonances in All-Dielectric Metasurfaces

We demonstrate a novel approach to control photonic bound states in the continuum induced by a symmetry-breaking with tailored resonator heights leading to more precisely engineered system asymmetries and new metasurface functionalities.

Conference paper

Güsken NA, Fu M, Zapf M, Nielsen MP, Dichtl P, Röder R, Maier SA, Ronning C, Brongersma ML, Oulton RFet al., 2022, Fluorescence enhancement of Er<sup>3+</sup>-ions using reverse hybrid plasmonic nano-focusing

We report the broadband fluorescence enhancement of erbium ions embedded in a single non-resonant reverse nano-focusing waveguide. We measure a large radiative Purcell enhancement of a total emission rate enhancement of > 250 across the entire measured spectrum including the prominent telecoms C-band. Further, we observe the enhancement of single electric dipole transitions from Stark-split levels at room temperature.

Conference paper

Dinter T, Kühner L, Li C, Weber T, Tittl A, Maier SA, Dawes JM, Ren Het al., 2022, Metasurface measuring twisted light in turbulence

Practical free-space communication systems suffer from turbulence-induced phase distortions to propagating beams, destroying the orthogonality of orbital angular momentum (OAM) modes used for space-division multiplexing and introducing modal crosstalk. Here we present the design and use of an ultrathin OAM mode-sorting metasurface for investigating the deterioration of OAM orthogonality under different turbulence conditions, offering a compact, fast and efficient way to measure the OAM spectrum.

Conference paper

Tirole R, Vezzoli S, Galiffi E, Tilmann B, Huidobro PA, Alù A, Maier SA, Pendry JB, Sapienza Ret al., 2022, Single and double slit time diffraction at optical frequencies

In a temporal version of a single slit and Young's double slit experiments, newly generated optical frequencies form a diffraction pattern. The spectral extent of these frequencies is beyond the expected bandwidth of the modulation.

Conference paper

Boggiano HD, Nam L, Tilmann B, Maier SA, Grinblat G, Cortés E, Bragas AVet al., 2022, Focusing a nano-earthquake

Plasmonic nanoantennas are optomechanical transducers for converting laser pulses into surface hypersound waves traveling through the underlying substrate, similar to the seismic waves after an earthquake. Here we introduce a novel design consisting of an array of plasmonic nanodisks allowing the focusing of the generated waves in the nanoscale.

Conference paper

Kim J, Bürger J, Schalles V, Jang B, Zeisberger M, Gargiulo J, Menezes LDS, Maier SA, Schmidt MAet al., 2022, The optofluidic 3D-nanoprinted hollow core micro-gap waveguide spectroscopy

We present a novel on-chip optofluidic hollow core micro-gap waveguide based on a strong light guidance through anti-resonant effect. We show gas and liquid-based spectroscopic experiments with simulations.

Conference paper

Aigner A, Wang J, Tittl A, Maier SA, Ren Het al., 2022, Out-of-plane symmetry-protected bound states in the continuum in a plasmonic nanofin metasurface

We present a plasmonic nanofin metasurface harnessing the out-of-plane symmetry breaking in parameter space by tuning the triangle angle of 3D laser nanoprinted polymer triangles (named as nanofins) coated with gold. The plasmonic nature of the out-of-plane symmetry-protected BICs enables high field enhancement together with high q-factors from the near- to mid-infrared regions, which were utilised for refractive index and pixelated molecular sensing.

Conference paper

Dinter T, Kühner L, Li C, Weber T, Tittl A, Maier SA, Dawes JM, Ren Het al., 2022, Metasurface measuring twisted light in turbulence

Practical free-space communication systems suffer from turbulence-induced phase distortions to propagating beams, destroying the orthogonality of orbital angular momentum (OAM) modes used for space-division multiplexing and introducing modal crosstalk. Here we present the design and use of an ultrathin OAM mode-sorting metasurface for investigating the deterioration of OAM orthogonality under different turbulence conditions, offering a compact, fast and efficient way to measure the OAM spectrum.

Conference paper

Aigner A, Wang J, Tittl A, Maier SA, Ren Het al., 2022, Out-of-plane symmetry-protected bound states in the continuum, Pages: 509-510

Symmetry-protected bound states in the continuum (BICs) combines high-quality factors (q-factors) with a large spectral tunability, offering an ideal platform for optical sensing. We present a plasmonic nanofin metasurface harnessing the out-of-plane symmetry breaking in parameter space by tuning the opening angle of 3D laser nanoprinted polymer triangles coated with gold. The plasmonic nature of the out-of-plane symmetry-protected BICs enables high surface field enhancement together with high q-factors, which have been utilised for refractive index and pixelated molecular sensing.

Conference paper

Li C, Schdmit MA, Maier SA, Ren Het al., 2022, All-on-fiber generation of higher-order Poincaré sphere beams via 3D lasernanoprinted metasurfaces, Pages: 1218-1219

We present a new metafiber platform for all-on-fiber polarization manipulation through implementing 3D laser-nanoprinted metasurfaces on the end face of polarizationmaintaining fibers. The unlocked height degree of freedom in 3D polymer meta-atoms eases the simultaneous polarization and phase control, leading to the generation of arbitrary higherorder Poincare sphere beams carrying different orbital angular momentum modes.

Conference paper

Kepič P, Ligmajer F, Hrtoň M, Ren H, de Menezes LS, Maier SA, Šikola Tet al., 2022, Exploiting Mie resonances in VO2 nanoantennas for achieving optically tunable metasurfaces in the visible range, Pages: 680-681

We study the optical properties of VO2 nanodiscs in the visible range. These nanostructures present strong Mie resonances not only in the known high-temperature, plasmonic phase, but also in the low-temperature phase, in which the material’s behavior is predominantly dielectric. A large extinction modulation is observed when the nanodiscs go upon phase transition. The nanodiscs present large potential for being used as building blocks of a metasurface which can be tuned by shining a CW laser on it.

Conference paper

Schmidt MA, Schneidewind H, Hübner U, Zeisberger M, Plidschun M, Kim J, Yermakov O, Kivshar Y, Bogdanov A, Ren H, Maier SAet al., 2022, Metasurfaces meet optical fibers: a novel platform for flexible optical trapping and boosting in-coupling efficiencies, Pages: 344-345

In this talk, we show that the combination of optical fibers with nanostructures defines a new class of fiber integrated devices — nanostructured fibers — which opensup new application areas for optical fiber research. Using 3D nanoprinting and modified electron beam lithography, we integrate high-NA meta-lenses and dielectric ring gratings onto the end faces of single-mode fibers. These devices enable efficient light coupling at angles up to 80° and trapping of Escherichia coli bacteria with an individual single-mode fiber device.

Conference paper

Sortino L, Maier SA, 2022, All-dielectric nanophotonics with quantum emitters in Transition Metal Dichalcogenides semiconductors

Transition metal dichalcogenides (TMDs) semiconductors offer a platform for merging nanophotonics and two-dimensional (2D) materials. They are exceptional quantum materials in the monolayer form and possess appealing optical properties as bulk materials, such as a high index of refraction and giant anisotropy. Here we show that the combination of monolayer TMDs and all-dielectric nanostructures, also made from bulk TMDs, provides new approaches for enhanced light-matter interaction of 2D excitons and quantum emitters with Mie-resonant nanophotonic devices.

Conference paper

Wendisch FJ, Bürger J, Gryb D, Kühner L, Fan C, Lee S, Tittl A, Cortés E, de L, Maier SAet al., 2022, Implementation of an optical setup for investigating chiral nanophotonic structures, Pages: 1110-1111

Chirality is inherent to Nature and happens on all scales from the fundamental biological building blocks up to the structure of galaxies. A pair of mirror-image molecules, called enantiomers, often give rise to tremendous differences in protein function, cell communication and organism health. The chirality of molecules is usually characterized via chiroptical effects using illumination with left and right circularly polarized light beams. However, due to the scale mismatch between the helical pitch of atoms in molecules and the wavelength of light, these chiroptical effects are inherently low and it remains challenging to sense and separate enantiomers. Recent advancements in nanophotonics offer solutions to overcome these limitations by enhancing chiral light-matter interactions by using chiral nanoparticles, metasurfaces or metamaterials. In this work, we report on the development of a setup dedicated to perform linear and nonlinear spectroscopy of chiral photonic nanostructures and on the investigation of the chiral behavior of selected nanophotonic platforms.

Conference paper

Gargiulo J, Barella M, Herran M, Violi IL, Sousa-Castillo A, Ezendam S, Martinez LP, Grzeschik R, Schlücker S, Maier SA, Stefani FD, Cortes Eet al., 2022, In Situ optical thermometry of hybrid plasmonic nanosystems., Pages: 261-262

We present a new implementation of anti-Stokes thermometry that enables the in situ photothermal characterization of individual plasmonic nanoparticles from a single hyperspectral photoluminescence confocal image. We study the photothermal response at the single-particle level of spherical gold NPs with sizes ranging from 50 to 100 nm supported on glass, sapphire and graphene substrates. In addition, we study bimetallic Au@Pd NPs in a core@shell configuration. The developed method allows quantitative assessment of the role of temperature in plasmon-assisted applications.

Conference paper

Kühner L, Sortino L, Berté R, Wang J, Ren H, Maier SA, Kivshar YS, Tittl Aet al., 2022, Radial bound states in the continuum for polarization-invariant nanophotonics, Pages: 336-337

We demonstrate radial bound states in the continuum as a new concept for realizing resonances with high Q factors, strong near-field enhancements, and polarization invariance in a compact footprint, and utilize them for applications in biomolecular sensing and higher harmonic generation from 2D materials.

Conference paper

Aigner A, Wang J, Tittl A, Maier SA, Ren Het al., 2022, Out-of-plane symmetry-protected bound states in the continuum in a plasmonic nanofin metasurface

We present a plasmonic nanofin metasurface harnessing the out-of-plane symmetry breaking in parameter space by tuning the triangle angle of 3D laser nanoprinted polymer triangles (named as nanofins) coated with gold. The plasmonic nature of the out-of-plane symmetry-protected BICs enables high field enhancement together with high q-factors from the near- to mid-infrared regions, which were utilised for refractive index and pixelated molecular sensing.

Conference paper

Altug H, Oh S-H, Maier SA, Homola Jet al., 2022, Advances and applications of nanophotonic biosensors, NATURE NANOTECHNOLOGY, Vol: 17, Pages: 5-16, ISSN: 1748-3387

Journal article

Büchner R, Weber T, Kühner L, Maier SA, Tittl Aet al., 2021, Tip coupling and array effects of gold nanoatennas in near-field microscopy, ACS Photonics, Vol: 8, Pages: 3486-3494, ISSN: 2330-4022

Scattering-type scanning near-field optical microscopy (s-SNOM) is one of the predominant techniques for the nanoscale characterization of optical properties. The optical response of nanoantennas in s-SNOM is highly sensitive to their environment, including influences of the probing tip or neighboring resonators. Dielectric tips are commonly employed to minimize tip-related perturbations, although they provide a comparatively weak scattering signal. Here we show that when using metallic tips, it is possible to select between distinct weak and strong tip–antenna coupling regimes by careful tailoring of the illumination conditions and resonator orientation. This enables the use of highly scattering metallic instead of dielectric tips for mapping plasmonic modes with comparatively higher signal strengths. This is a particular advantage for the retrieval of near-field spectra, which simultaneously require high near-field signals and unperturbed field patterns. We leverage our approach to analyze the collective effects of nanoantenna arrays, phenomena that are well understood in the optical far-field but have not been extensively studied in the near-field. Probing the dependence of the optical response on the array field size, we identify three regimes: the single rod regime, the intermediate regime, and the array-like regime. We show that these array effects give rise to characteristic spectral features originating from a complex interplay of radiative coupling and plasmon hybridization. These results provide evidence that long-range interactions of antennas also influence the local optical response that is probed in s-SNOM and demonstrate how collective resonances emerge from single building blocks, providing guidelines for optimized array designs for near- and far-field applications.

Journal article

Moretti GQ, Cortes E, Maier SA, Bragas A, Grinblat Get al., 2021, Engineering gallium phosphide nanostructures for efficient nonlinear photonics and enhanced spectroscopies, Nanophotonics, Vol: 10, Pages: 4261-4271, ISSN: 2192-8606

Optical resonances arising from quasi-bound states in the continuum (QBICs) have been recently identified in nanostructured dielectrics, showing ultrahigh quality factors accompanied by very large electromagnetic field enhancements. In this work, we design a periodic array of gallium phosphide (GaP) elliptical cylinders supporting, concurrently, three spectrally separated QBIC resonances with in-plane magnetic dipole, out-of-plane magnetic dipole, and electric quadrupole characters. We numerically explore this system for second-harmonic generation and degenerate four-wave mixing, demonstrating giant per unit cell conversion efficiencies of up to ∼ 2 W−1 and ∼ 60 W−2, respectively, when considering realistic introduced asymmetries in the metasurface, compatible with current fabrication limitations. We find that this configuration outperforms by up to more than four orders of magnitude the response of low-Q Mie or anapole resonances in individual GaP nanoantennas with engineered nonlinear mode-matching conditions. Benefiting from the straight-oriented electric field of one of the examined high-Q resonances, we further propose a novel nanocavity design for enhanced spectroscopies by slotting the meta-atoms of the periodic array. We discover that the optical cavity sustains high-intensity fields homogeneously distributed inside the slot, delivering its best performance when the elliptical cylinders are cut from end to end forming a gap, which represents a convenient model for experimental investigations. When placing an electric point dipole inside the added aperture, we find that the metasurface offers ultrahigh radiative enhancements, exceeding the previously reported slotted dielectric nanodisk at the anapole excitation by more than two orders of magnitude.

Journal article

Kuehne J, Wang J, Weber T, Kuehner L, Maier SA, Tittl Aet al., 2021, Fabrication robustness in BIC metasurfaces, Nanophotonics, Vol: 10, Pages: 4305-4312, ISSN: 2192-8606

All-dielectric metasurfaces supporting photonic bound states in the continuum (BICs) are an exciting toolkit for achieving resonances with ultranarrow linewidths. However, the transition from theory to experimental realization can significantly reduce the optical performance of BIC-based nanophotonic systems, severely limiting their application potential. Here, we introduce a combined numerical/experimental methodology for predicting how unavoidable tolerances in nanofabrication such as random geometrical variations affect the performance of different BIC metasurface designs. We compare several established all-dielectric BIC unit cell geometries with broken in-plane inversion symmetry including tilted ellipses, asymmetric double rods, and split rings. Significantly, even for low fabrication-induced geometrical changes, both the BIC resonance amplitude and its quality factor (Q-factor) are significantly reduced. We find that the all-dielectric ellipses maintain the highest Q-factors throughout the geometrical variation range, whereas the rod and split ring geometries fall off more quickly. The same behavior is confirmed experimentally, where geometrical variation values are derived from automated processing of sets of scanning electron microscopy (SEM) images. Our methodology provides crucial insights into the performance degradation of BIC metasurfaces when moving from simulations to fabricated samples and will enable the development of robust, high-Q, and easy to manufacture nanophotonic platforms for applications ranging from biomolecular sensing to higher harmonic generation.

Journal article

Luo S, Hoff BH, Maier SA, de Mello JCet al., 2021, Scalable Fabrication of Metallic Nanogaps at the Sub-10 nm Level, ADVANCED SCIENCE, Vol: 8

Journal article

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