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

609 results found

Dagdeviren OE, Glass D, Sapienza R, Cortés E, Maier SA, Parkin IP, Grütter P, Quesada-Cabrera Ret al., 2021, The Effect of Photoinduced Surface Oxygen Vacancies on the Charge Carrier Dynamics in TiO2 Films., Nano Lett

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.

Journal article

Poblet M, Berté R, Boggiano HD, Li Y, Cortés E, Grinblat G, Maier SA, Bragas AVet al., 2021, Acoustic Coupling between Plasmonic Nanoantennas: Detection and Directionality of Surface Acoustic Waves, ACS Photonics, ISSN: 2330-4022

Journal article

Mao P, Liu C, Li X, Liu M, Chen Q, Han M, Maier SA, Sargent EH, Zhang Set 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.

Journal article

Wang J, Kuehne J, Karamanos T, Rockstuhl C, Maier SA, Tittl Aet al., 2021, All-dielectric crescent metasurface sensor driven by bound states in the continuum, Advanced Functional Materials, 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.

Journal article

Ren H, Wang X, Li C, He C, Wang Y, Pan A, Maier SAet al., 2021, Orbital-Angular-Momentum-Controlled Hybrid Nanowire Circuit, NANO LETTERS, Vol: 21, Pages: 6220-6227, ISSN: 1530-6984

Journal article

Li C-H, Maier SA, Ren H-R, 2021, Optical vortices in nanophotonics, CHINESE OPTICS, Vol: 14, Pages: 792-811, ISSN: 2095-1531

Journal article

Davidson-Marquis F, Gargiulo J, Gomez-Lopez E, Jang B, Kroh T, Muller C, Ziegler M, Maier SA, Kubler H, Schmidt MA, Benson Oet al., 2021, Coherent interaction of atoms with a beam of light confined in a light cage (vol 10, 114, 2021), LIGHT-SCIENCE & APPLICATIONS, Vol: 10, ISSN: 2047-7538

Journal article

Wang X, Liu C, Gao C, Yao K, Masouleh SSM, Berté R, Ren H, Menezes LDS, Cortés E, Bicket IC, Wang H, Li N, Zhang Z, Li M, Xie W, Yu Y, Fang Y, Zhang S, Xu H, Vomiero A, Liu Y, Botton GA, Maier SA, Liang Het 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.

Journal article

Jang B, Gargiulo J, Kim J, Buerger J, Both S, Lehmann H, Wieduwilt T, Weiss T, Maier SA, Schmidt MAet al., 2021, Fiber-integrated hollow-core light cage for gas spectroscopy, APL PHOTONICS, Vol: 6, ISSN: 2378-0967

Journal article

Davidson-Marquis F, Gargiulo J, Gomez-Lopez E, Jang B, Kroh T, Mueller C, Ziegler M, Maier SA, Kuebler H, Schmidt MA, Benson Oet 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.

Journal article

Hüttenhofer L, Tittl A, Kühner L, Cortés E, Maier SAet 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

Journal article

Luo S, Mancini A, Berte R, Hoff BH, Maier SA, de Mello JCet 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

Journal article

Mao P, Liu C, Niu Y, Qin Y, Song F, Han M, Palmer RE, Maier SA, Zhang Set al., 2021, Disorder-Induced Material-Insensitive Optical Response in Plasmonic Nanostructures: Vibrant Structural Colors from Noble Metals, ADVANCED MATERIALS, Vol: 33, ISSN: 0935-9648

Journal article

Kepic P, Ligmajer F, Hrton M, Ren H, Menezes LDS, Maier SA, Sikola Tet 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.

Journal article

BURGER JOHANNES, KIM JISOO, JANG BUMJOON, GARGIULO JULIAN, SCHMIDT MARKUSA, MAIER STEFANAet 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

Journal article

Aizpurua J, Atwater HA, Baumberg JJ, Bozhevolnyi SI, Brongersma ML, Dionne JA, Giessen H, Halas N, Kivshar Y, Kling MF, Krausz F, Maier S, Makarov SV, Mikkelsen M, Moskovits M, Norlander P, Odom T, Polman A, Qiu CW, Segev M, Shalaev VM, Torma P, Tsai DP, Verhagen E, Zayats A, Zhang X, Zheludev NIet al., 2021, Mark Stockman: Evangelist for Plasmonics, ACS PHOTONICS, Vol: 8, Pages: 683-698, ISSN: 2330-4022

Journal article

Plidschun M, Ren H, Kim J, Foerster R, Maier SA, Schmidt MAet al., 2021, Ultrahigh numerical aperture meta-fibre for flexible optical trapping, LIGHT-SCIENCE & APPLICATIONS, Vol: 10, ISSN: 2047-7538

Journal article

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, ISSN: 2574-0970

Journal article

Barella M, Violi IL, Gargiulo J, Martinez LP, Goschin F, Guglielmotti V, Pallarola D, Schluecker S, Pilo-Pais M, Acuna GP, Maier SA, Cortes E, Stefani FDet 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

Journal article

Aigner A, Maier SA, Ren H, 2021, Topological-Insulator-Based Gap-Surface Plasmon Metasurfaces, PHOTONICS, Vol: 8

Journal article

Geng D, Abdelwahab I, Xiao X, Cernescu A, Fu W, Giannini V, Maier SA, Li L, Hu W, Loh KP, Yang HYet al., 2021, One-Pot Confined Epitaxial Growth of 2D Heterostructure Arrays, ACS MATERIALS LETTERS, Vol: 3, Pages: 217-223

Journal article

Zhan Y, Zhang L, Rahmani M, Giannini V, Miroshnichenko AE, Hong M, Li X, Maier SA, Lei Det 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

Journal article

Kim J, Jang B, Gargiulo J, Buerger J, Zhao J, Upendar S, Weiss T, Maier SA, Schmidt MAet 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

Journal article

Kühne J, Wang J, Weber T, Kühner L, Maier SA, Tittl Aet al., 2021, Fabrication robustness in BIC metasurfaces, Nanophotonics

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

Busleev N, Kudryashov S, Saraeva I, Danilov P, Rudenko A, Zayarny D, Maier SA, Minh PH, Ionin Aet al., 2021, Few Percent Efficient Polarization-Sensitive Conversion in Nonlinear Plasmonic Interactions Inside Oligomeric Gold Structures, SENSORS, Vol: 21

Journal article

Lee JB, Walker H, Li Y, Nam TW, Rakovich A, Sapienza R, Jung YS, Nam YS, Maier SA, Cortes Eet al., 2020, Template Dissolution Interfacial Patterning of Single Colloids for Nanoelectrochemistry and Nanosensing, ACS NANO, Vol: 14, Pages: 17693-17703, ISSN: 1936-0851

Journal article

Noor A, Damodaran AR, Lee I-H, Maier SA, Oh S-H, Ciraci Cet al., 2020, Mode-Matching Enhancement of Second-Harmonic Generation with Plasmonic Nanopatch Antennas, ACS PHOTONICS, Vol: 7, Pages: 5333-5340, ISSN: 2330-4022

Journal article

Li K, Fitzgerald JM, Xiao X, Caldwell JD, Zhang C, Maier SA, Li X, Giannini Vet al., 2020, Graphene Plasmon Cavities Made with Silicon Carbide (vol 2, pg 3640, 2017), ACS OMEGA, Vol: 5, Pages: 30746-30746, ISSN: 2470-1343

Journal article

Tilmann B, Grinblat G, Berte R, Oezcan M, Kunzelmann VF, Nickel B, Sharp ID, Cortes E, Maier SA, Li Yet al., 2020, Nanostructured amorphous gallium phosphide on silica for nonlinear and ultrafast nanophotonics, NANOSCALE HORIZONS, Vol: 5, Pages: 1500-1508, ISSN: 2055-6756

Journal article

Ren H, Fang X, Jang J, Buerger J, Rho J, Maier Set al., 2020, Complex-amplitude metasurface-based orbital angular momentum holography in momentum space, Nature Nanotechnology, Vol: 15, Pages: 948-955, ISSN: 1748-3387

Digital optical holograms can achieve nanometer-scale resolution thanks to recent advances in metasurface technologies. This has raised hopes for applications in data encryption, data storage, information processing and displays. However, the hologram bandwidth has remained too low for any practical use. To overcome this limitation, information can be stored in the orbital angular momentum (OAM) of light, as this degree of freedom has an unbounded set of orthogonal helical modes that could function as information channels. Thus far, OAM holography has been achieved using phase-only metasurfaces, which however are marred by channels crosstalk. As a result, multiplex information from only 4 channels has been demonstrated. Here we demonstrate an OAM holography technology that is capable of multiplexing up to 200 independent OAM channels. This is achieved by designing a complex-amplitude metasurface in momentum-space capable of complete and independent amplitude and phase manipulation. Information is then extracted by Fourier transform using different OAM modes of light, allowing lensless reconstruction and holographic videos being displayed. Our metasurface can be 3D printed in a polymer matrix on SiO2 for large-area fabrication.

Journal article

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