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@article{nokey,

title = {A Comparative Analysis of Plasmonic and Dielectric Metasurface Sensing Platforms Powered by Bound States in the Continuum},

author = {T Jiang and A Bhattacharya and M Barkey and A Aigner and L Rohrer and T Weber and J Wang and S A Maier and A Tittl},

url = {\<Go to ISI\>://WOS:001558957300001},

doi = {10.1002/adfm.202516021},

issn = {1616-301X},

year  = {2025},

date = {2025-08-28},

journal = {Advanced Functional Materials},

abstract = {Nanophotonic platforms based on surface-enhanced infrared absorbance spectroscopy (SEIRAS) have emerged as an effective tool for molecular detection. Sensitive nanophotonic sensors with robust resonant modes and amplified electromagnetic near fields are essential for spectroscopy, especially in lossy environments. Metasurfaces driven by bound state in the continuum (BICs) have unlocked a powerful platform for molecular detection due to their exceptional spectral selectivity. While plasmonic BIC metasurfaces are preferred for molecular spectroscopy due to their high surface fields, enhancing the interaction with analytes, dielectric BICs have become popular due to their high-quality factors and, thus, high sensitivity. However, their sensing performance has largely been demonstrated in air, neglecting the intrinsic infrared (IR) losses found in common solvents. This study evaluates the suitability of plasmonic versus dielectric platforms for in situ molecular spectroscopy. Here, the sensing performance of plasmonic (gold) and dielectric (silicon) metasurfaces is assessed across liquid environments with varying losses resembling typical solvents. The results show that dielectric metasurfaces excel in dry conditions, while plasmonic BIC metasurfaces outperform them in lossy solvents, with a distinct crossover point where both show similar performance. The results provide a framework for selecting the optimal metasurface material platform for SEIRAS studies based on environmental conditions.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{nokey,

title = {Optical control of resonances in temporally symmetry-broken metasurfaces},

author = {A Aigner and T Possmayer and T Weber and A A Antonov and L D Menezes and S A Maier and A Tittl},

url = {\<Go to ISI\>://WOS:001545391600001},

doi = {10.1038/s41586-025-09363-7},

issn = {0028-0836},

year  = {2025},

date = {2025-08-06},

journal = {Nature},

abstract = {Tunability in active metasurfaces has mainly relied on shifting the resonance wavelength1,2 or increasing material losses3,4 to spectrally detune or quench resonant modes, respectively. However, both methods face fundamental limitations, such as a limited Q factor and near-field enhancement control and the inability to achieve resonance on-off switching by completely coupling and decoupling the mode from the far field. Here we demonstrate temporal symmetry breaking in metasurfaces through ultrafast optical pumping, providing an experimental realization of radiative-loss-driven resonance tuning, allowing resonance creation, annihilation, broadening and sharpening. To enable this temporal control, we introduce restored symmetry-protected bound states in the continuum. Even though their unit cells are geometrically asymmetric, coupling to the radiation continuum remains fully suppressed, which, in this work, is achieved by two equally strong antisymmetric dipoles. By using selective Mie-resonant pumping in parts of these unit cells, we can modify their dipole balance to create or annihilate resonances as well as tune the linewidth, amplitude and near-field enhancement, leading to potential applications in optical and quantum communications, time crystals and photonic circuits.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{nokey,

title = {Reflection-Enhanced Raman Identification of Single Bacterial Cells Patterned Using Capillary Assembly},

author = {J Lee and E Rho and M Kim and S Huh and S Kim and S A Maier and E Cort\'{e}s and S Jo and Y S Jung and Y Nam},

url = {\<Go to ISI\>://WOS:001543629000001},

doi = {10.1021/acssensors.5c01225},

issn = {2379-3694},

year  = {2025},

date = {2025-08-03},

journal = {Acs Sensors},

abstract = {Raman spectroscopy is an enticing tool for the rapid identification of pathogenic bacteria and has the potential to meet the demand for early diagnosis and timely treatment of patients. However, it remains a challenge to devise a reliable Raman detection platform to obtain reproducible signals from single bacterial cells. Herein, we utilize a reflective Ag/SiO2 film that enhances the intrinsically weak Raman signals by re-excitation of the bacteria and reflection of downward-scattered photons, with maximum Raman intensities recorded by exciting the central edge of each single cell. The reflection-based configuration is simple, and its reliability as a sensing platform is validated by deep learning analysis. Importantly, given the positional dependence of the laser light on the Raman intensity, we employ capillarity-assisted particle assembly (CAPA) to selectively position single bacterial cells into a reflective topographical template to align the most Raman active region of the cell per the trap site geometry. Moreover, CAPA is utilized to directly isolate single cells from a suspension of artificial urine, eradicating any additional steps previously required to separate bacteria from biological samples. The proposed system has positive implications for future clinical settings that require simple, accurate, and reproducible detection of bacteria at the single-cell level.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{nokey,

title = {Fabrication Optimization of van der Waals Metasurfaces: Inverse Patterning Boosts Resonance Quality Factor},

author = {J Biechteler and C Heimig and T Weber and D Gryb and L Sortino and S A Maier and L S De Menezes and A Tittl},

url = {\<Go to ISI\>://WOS:001508031900001},

doi = {10.1002/adom.202500920},

issn = {2195-1071},

year  = {2025},

date = {2025-06-09},

journal = {Advanced Optical Materials},

abstract = {Van der Waals (vdW) materials have garnered growing interest for use as nanophotonic building blocks that offer precise control over light-matter interaction at the nanoscale, such as optical metasurfaces hosting sharp quasi-bound states in the continuum resonances. However, traditional fabrication strategies often rely on lift-off processes, which inherently introduce imperfections in resonator shape and size distribution, ultimately limiting the resonance performance. Here, an optimized fabrication approach for vdW-metasurfaces is presented that implements inverse patterning of the etching mask, resulting in increased resonator quality solely limited by the resolution of the electron beam lithography resist and etching. Applying this inverse fabrication technique on hexagonal boron nitride (hBN), quality (Q) factors exceeding 103 in the visible spectral range are demonstrated, significantly surpassing previous results shown by lift-off fabricated structures. Additionally, the platform's potential as a biosensor is displayed, achieving remarkable sensitivity and figure of merit of 220 in a refractive index sensing experiment. The inverse technique is applied to create chiral metasurfaces from hBN, using a two-height resonator geometry to achieve up to 50% transmittance selectivity. This inverse lithography technique paves the way toward high-performances vdW-devices with high-Q resonances, establishing hBN as a cornerstone for next-generation nanophotonic and optoelectronic devices.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{nokey,

title = {Atomic-layer assembly of ultrathin optical cavities in van der Waals heterostructure metasurfaces},

author = {L Sortino and J Biechteler and L Lafeta and L K\"{u}hner and A Hartschuh and L D Menezes and S A Maier and A Tittl},

url = {\<Go to ISI\>://WOS:001495232400001},

doi = {10.1038/s41566-025-01675-4},

issn = {1749-4885},

year  = {2025},

date = {2025-05-26},

journal = {Nature Photonics},

abstract = {Photonics has been revolutionized by advances in optical metasurfaces, unlocking design and engineering opportunities for flat optical components. Similarly, layered two-dimensional materials have enabled breakthroughs in physics via the deterministic assembly of vertical heterostructures, allowing precise control over the atomic composition of each layer. However, integrating these fields into a single system has remained challenging, limiting progress in atomic-scale optical cavities and metamaterials. Here we demonstrate the concept of van der Waals heterostructure metasurfaces, where ultrathin multilayer van der Waals material stacks are shaped into precisely engineered resonant nanostructures for enhancing light-matter interactions. By leveraging quasi-bound states in the continuum physics, we create intrinsic high-quality-factor resonances originating from WS2 monolayers encapsulated in hexagonal boron nitride at thicknesses below 130 nm, achieving room-temperature strong coupling and polaritonic photoluminescence emission. Furthermore, the metasurface-coupled exciton-polaritons exhibit strong nonlinearities, leading to a saturation of the strong-coupling regime at ultralow fluences of \<1 nJ cm(-2), three orders of magnitude lower than in previous two-dimensional-material-based cavity systems. Our approach monolithically integrates metasurfaces and van der Waals materials and can be extended to the vast library of existing two-dimensional materials, unlocking new avenues for ambient operation of ultrathin polaritonic devices with atomic-scale precision and control.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{nokey,

title = {Angular dispersion suppression in deeply subwavelength phonon polariton bound states in the continuum metasurfaces},

author = {L Nan and A Mancini and T Weber and G L Seah and E Cort\'{e}s and A Tittl and S A Maier},

doi = {10.1038/s41566-025-01670-9},

issn = {1749-4885 

1749-4893},

year  = {2025},

date = {2025-05-16},

journal = {NATURE PHOTONICS},

abstract = {Quasi-bound states in the continuum (qBICs) achieved through symmetry breaking in photonic metasurfaces are a powerful approach for engineering resonances with high quality factors and tunability. However, miniaturization of these devices is limited as the in-plane unit-cell size typically scales linearly with the resonant wavelength. By contrast, polariton resonators can be deeply subwavelength, offering a promising solution for achieving compact devices. Here we demonstrate that low-loss mid-infrared surface phonon polaritons enable metasurfaces supporting qBICs with unit-cell volumes up to 105 times smaller than the free-space volume lambda 03documentclass[12pt]minimal usepackageamsmath usepackagewasysym usepackageamsfonts usepackageamssymb usepackageamsbsy usepackagemathrsfs usepackageupgreek setlength\oddsidemargin-69pt begindocument$$\lambda_0\<^\>3$$enddocument. Using 100-nm-thick free-standing silicon carbide membranes, we achieve highly confined qBIC states with exceptional robustness against incident-angle variations, a feature unique among qBIC systems. This absence of angular dispersion enables mid-infrared vibrational sensing of thin, weakly absorbing molecular layers using a reflective objective, a method that typically degrades resonance quality in standard qBIC metasurfaces. We introduce surface-phonon-polariton-based qBICs as a platform for ultraconfined nanophotonic systems, advancing the miniaturization of mid-infrared sensors and devices for thermal radiation engineering.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{nokey,

title = {Control and enhancement of optical nonlinearities in plasmonic semiconductor nanostructures},

author = {A Rossetti and H T Hu and T Venanzi and A Bousseksou and F De Luca and T Deckert and V Giliberti and M Pea and I Sagnes and G Beaudoin and P Biagioni and E Ba\`{u} and S A Maier and A Tittl and D Brida and R Colombelli and M Ortolani and C Cirac\`{i}},

url = {\<Go to ISI\>://WOS:001495020200001},

doi = {10.1038/s41377-025-01783-4},

issn = {2095-5545},

year  = {2025},

date = {2025-05-13},

journal = {Light-Science \& Applications},

volume = {14},

number = {1},

abstract = {The efficiency of nanoscale nonlinear elements in photonic integrated circuits is hindered by the physical limits to the nonlinear optical response of dielectrics, which cannot be engineered as it is a fundamental material property. Here, we experimentally demonstrate that ultrafast optical nonlinearities in doped semiconductors can be engineered and can easily exceed those of conventional undoped dielectrics. The electron response of heavily doped semiconductors acquires in fact a hydrodynamic character that introduces nonlocal effects as well as additional nonlinear sources. Our experimental findings are supported by a comprehensive computational analysis based on the hydrodynamic model. In particular, by studying third-harmonic generation from plasmonic nanoantenna arrays made out of heavily n-doped InGaAs with increasing levels of free-carrier density, we discriminate between hydrodynamic and dielectric nonlinearities. Most importantly, we demonstrate that the maximum nonlinear efficiency as well as its spectral location can be engineered by tuning the doping level. Crucially, the maximum efficiency can be increased by almost two orders of magnitude with respect to the classical dielectric nonlinearity. Having employed the common material platform InGaAs/InP that supports integrated waveguides, our findings pave the way for future exploitation of plasmonic nonlinearities in all-semiconductor photonic integrated circuits.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{nokey,

title = {All-optical permittivity-asymmetric quasi-bound states in the continuum},

author = {R Bert\'{e} and T Possmayer and A Tittl and L D S Menezes and S A Maier},

url = {https://doi.org/10.1038/s41377-025-01843-9},

doi = {10.1038/s41377-025-01843-9},

issn = {2047-7538},

year  = {2025},

date = {2025-05-07},

journal = {Light: Science \& Applications},

volume = {14},

number = {1},

pages = {185},

abstract = {Resonances are usually associated with finite systems\textemdashthe vibrations of clamped strings in a guitar or the optical modes in a cavity defined by mirrors. In optics, resonances may be induced in infinite continuous media via periodic modulations of their optical properties. Here we demonstrate that periodic modulations of the permittivity of a featureless thin film can also act as a symmetry-breaking mechanism, allowing the excitation of photonic quasi-bound states in the continuum (qBICs). By interfering two ultrashort laser pulses in the unbounded film, transient resonances can be tailored through different parameters of the pump beams. We show that the system offers resonances tunable in wavelength and quality-factor, and spectrally selective enhancement of third-harmonic generation. Due to a fast decay of the permittivity asymmetry, we observe ultrafast dynamics, enabling time-selective near-field enhancement with picosecond precision. Optically induced permittivity asymmetries may be exploited in on-demand weak to ultrastrong light-matter interaction regimes and light manipulation at dynamically chosen wavelengths in lithography-free metasurfaces.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{nokey,

title = {Coherent Acoustic Phonons in Plasmonic Nanoparticles: Elastic Properties and Dissipation at Low Temperatures},

author = {H D Boggiano and T Possmayer and L Morguet and L Nan and L Sortino and S A Maier and E Cort\'{e}s and G Grinblat and A V Bragas and L De S. Menezes},

url = {https://doi.org/10.1021/acsnano.4c09193},

doi = {10.1021/acsnano.4c09193},

issn = {1936-0851},

year  = {2024},

date = {2024-11-19},

journal = {ACS Nano},

volume = {18},

number = {46},

pages = {31903-31911},

abstract = {We studied the frequency and quality factor of mechanical plasmonic nanoresonators as a function of temperature, ranging from ambient to 4 K. Our investigation focused on individual gold nanorods and nanodisks of various sizes. We observed that oscillation frequencies increase linearly as temperature decreases until saturation is reached at cryogenic temperatures. This behavior is explained by the temperature dependence of the elastic modulus, with a Debye temperature compatible with reported bulk values for gold. To describe the behavior of the quality factor, we developed a model considering the nanostructures as anelastic solids, identifying a dissipation peak around 150 K due to a thermally activated process, likely of the Niblett-Wilks mechanism type. Importantly, our findings suggest that external dissipation factors are more critical to improving quality factors than internal friction, which can be increased by modifying the nanoresonator’s environment. Our results enable the future design of structures with high vibration frequencies and quality factors by effectively controlling external losses.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{nokey,

title = {Chiral nonlinear polaritonics with van der Waals metasurfaces},

author = {C Heimig and A A Antonov and D Gryb and T Possmayer and T Weber and M Hirler and J Biechteler and L Sortino and L D S Menezes and S A Maier},

year  = {2024},

date = {2024-11-14},

journal = {arXiv preprint arXiv:2410.18760},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{nokey,

title = {All-Optical Generation and Detection of Coherent Acoustic Vibrations in Single Gallium Phosphide Nanoantennas Probed Near the Anapole Excitation},

author = {H D Boggiano and N A Roqueiro and H Zhang and L Krivitsky and E Cortes and S A Maier and A V Bragas and A Kuznetsov and G Grinblat},

year  = {2024},

date = {2024-10-03},

journal = {arXiv preprint arXiv:2410.02431},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{nokey,

title = {Photoluminescence modal splitting via strong coupling in hybrid Au/WS2/GaP nanoparticle-on-mirror cavities},

author = {M G\"{u}lm\"{u}s and T Possmayer and B Tilmann and P Butler and I D Sharp and L D S Menezes and S A Maier and L Sortino},

url = {http://dx.doi.org/10.1039/D4NR03166K},

doi = {10.1039/D4NR03166K},

issn = {2040-3364},

year  = {2024},

date = {2024-09-18},

journal = {Nanoscale},

volume = {16},

number = {40},

pages = {18843-18851},

abstract = {By integrating dielectric and metallic components, hybrid nanophotonic devices present promising opportunities for manipulating nanoscale light\textendashmatter interactions. Here, we investigate hybrid nanoparticle-on-mirror optical cavities, where semiconductor WS2 monolayers are positioned between gallium phosphide (GaP) nanoantennas and a gold mirror, thereby establishing extreme confinement of optical fields. Prior to integration of the mirror, we observe an intermediate coupling regime from GaP nanoantennas covered with WS2 monolayers. Upon introduction of the mirror, enhanced interactions lead to modal splitting in the exciton photoluminescence spectra, spatially localized within the dielectric-metallic gap. Using a coupled harmonic oscillator model, we extract an average Rabi splitting energy of 22.6 meV at room temperature, at the onset of the strong coupling regime. Moreover, the characteristics of polaritonic emission are revealed by the increasing Lorentzian linewidth and energy blueshift with increasing excitation power. Our findings highlight hybrid nanophotonic structures as novel platforms for controlling light\textendashmatter coupling with atomically thin materials.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{nokey,

title = {Engineering of Active and Passive Loss in High-Quality-Factor Vanadium Dioxide-Based BIC Metasurfaces},

author = {A Aigner and F Ligmajer and K Rovensk\'{a} and J Holobr\'{a}dek and B Idesov\'{a} and S A Maier and A Tittl and L De S. Menezes},

url = {https://doi.org/10.1021/acs.nanolett.4c01703},

doi = {10.1021/acs.nanolett.4c01703},

issn = {1530-6984},

year  = {2024},

date = {2024-09-04},

journal = {Nano Letters},

volume = {24},

number = {35},

pages = {10742-10749},

abstract = {Active functionalities of metasurfaces are of growing interest in nanophotonics. The main strategy employed to date is spectral resonance tuning affecting predominantly the far-field response. However, this barely influences other essential resonance properties like near-field enhancement, signal modulation, quality factor, and absorbance, which are all vital for numerous applications. Here we introduce an active metasurface approach that combines temperature-tunable losses in vanadium dioxide with far-field coupling tunable symmetry-protected bound states in the continuum. This method enables exceptional precision in independently controlling both radiative and nonradiative losses. Consequently, it allows for the adjustment of both the far-field response and, notably, the near-field characteristics like local field enhancement and absorbance. We experimentally demonstrate continuous tuning from under- through critical- to overcoupling, achieving quality factors of 200 and a relative switching contrast of 78%. Our research marks a significant step toward highly tunable metasurfaces, controlling both near- and far-field properties.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{nokey,

title = {Environmental permittivity-asymmetric BIC metasurfaces with electrical reconfigurability},

author = {H Hu and W Lu and A Antonov and R Bert\'{e} and S A Maier and A Tittl},

url = {https://doi.org/10.1038/s41467-024-51340-7},

doi = {10.1038/s41467-024-51340-7},

issn = {2041-1723},

year  = {2024},

date = {2024-08-15},

journal = {Nature Communications},

volume = {15},

number = {1},

pages = {7050},

abstract = {Achieving precise spectral and temporal light manipulation at the nanoscale remains a critical challenge in nanophotonics. While photonic bound states in the continuum (BICs) have emerged as a powerful means of controlling light, their reliance on geometrical symmetry breaking for obtaining tailored resonances makes them highly susceptible to fabrication imperfections, and their generally fixed asymmetry factor fundamentally limits applications in reconfigurable metasurfaces. Here, we introduce the concept of environmental symmetry breaking by embedding identical resonators into a surrounding medium with carefully placed regions of contrasting refractive indexes, activating permittivity-driven quasi-BIC resonances (ε-qBICs) without altering the underlying resonator geometry and unlocking an additional degree of freedom for light manipulation through active tuning of the surrounding dielectric environment. We demonstrate this concept by integrating polyaniline (PANI), an electro-optically active polymer, to achieve electrically reconfigurable ε-qBICs. This integration not only demonstrates rapid switching speeds and exceptional durability but also boosts the system’s optical response to environmental perturbations. Our strategy significantly expands the capabilities of resonant light manipulation through permittivity modulation, opening avenues for on-chip optical devices, advanced sensing, and beyond.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{nokey,

title = {Tracking surface charge dynamics on single nanoparticles},

author = {R Dagar and W Zhang and P Rosenberger and T M Linker and A Sousa-Castillo and M Neuhaus and S Mitra and S Biswas and A Feinberg and A M Summers and A Nakano and P Vashishta and F Shimojo and J Wu and C C Vera and S A Maier and E Cort\'{e}s and B Bergues and M F Kling},

url = {https://doi.org/10.1126/sciadv.adp1890},

doi = {10.1126/sciadv.adp1890},

year  = {2024},

date = {2024-08-07},

journal = {Science Advances},

volume = {10},

number = {32},

pages = {eadp1890},

abstract = {Surface charges play a fundamental role in physics and chemistry, in particular in shaping the catalytic properties of nanomaterials. However, tracking nanoscale surface charge dynamics remains challenging due to the involved length and time scales. Here, we demonstrate time-resolved access to the nanoscale charge dynamics on dielectric nanoparticles using reaction nanoscopy. We present a four-dimensional visualization of the spatiotemporal evolution of the charge density on individual SiO2 nanoparticles under strong-field irradiation with femtosecond-nanometer resolution. The initially localized surface charges exhibit a biexponential redistribution over time. Our findings reveal the influence of surface charges on surface molecular bonding through quantum dynamical simulations. We performed semi-classical simulations to uncover the roles of diffusion and charge loss in the surface charge redistribution process. Understanding nanoscale surface charge dynamics and its influence on chemical bonding on a single-nanoparticle level unlocks an increased ability to address global needs in renewable energy and advanced health care. Time-resolved visualization of surface charge dynamics on single nanoparticles shows bond-weakening effects for surface molecules.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{nokey,

title = {Van der Waals heterostructure metasurfaces: atomic-layer assembly of ultrathin optical cavities},

author = {L Sortino and J Biechteler and L Lafeta and L K\"{u}hner and A Hartschuh and L D S Menezes and S A Maier and A Tittl},

year  = {2024},

date = {2024-07-23},

journal = {arXiv preprint arXiv:2407.16480},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{nokey,

title = {Multiplication of the orbital angular momentum of phonon polaritons via sublinear dispersion},

author = {A Mancini and L Nan and R Bert\'{e} and E Cort\'{e}s and H Ren and S A Maier},

url = {https://doi.org/10.1038/s41566-024-01410-5},

doi = {10.1038/s41566-024-01410-5},

issn = {1749-4893},

year  = {2024},

date = {2024-07-01},

journal = {Nature Photonics},

volume = {18},

number = {7},

pages = {677-684},

abstract = {Optical vortices (OVs) promise to greatly enhance optical information capacity via orbital angular momentum multiplexing. The need for the on-chip integration of orbital angular momentum technologies has prompted research into subwavelength-confined polaritonic OVs. However, the topological order imprinted by the structure used for transduction from free-space beams to surface polaritons is inherently fixed after fabrication. Here we overcome this limitation via dispersion-driven topological charge multiplication. We switch the OV topological charge within a small frequency range (~3%) by leveraging the strong sublinear dispersion of low-loss surface phonon polaritons on silicon carbide membranes. Applying the Huygens principle, we quantitatively evaluate the topological order of experimental OVs detected by near-field imaging. We further explore the deuterogenic effect, which predicts the coexistence of multiple topological charges in higher-order polaritonic OVs. Our work demonstrates a viable method to manipulate the topological charge of polaritonic OVs, paving the way for the exploration of novel orbital-angular-momentum-enabled light\textendashmatter interactions at mid-infrared frequencies.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{nokey,

title = {Si metasurface supporting multiple quasi-BICs for degenerate four-wave mixing},

author = {G Q Moretti and T Weber and T Possmayer and E Cort\'{e}s and L D S Menezes and A V Bragas and S A Maier and A Tittl and G Grinblat},

url = {https://doi.org/10.1515/nanoph-2024-0128},

doi = {doi:10.1515/nanoph-2024-0128},

year  = {2024},

date = {2024-06-05},

journal = {Nanophotonics},

volume = {13},

number = {18},

pages = {3421-3428},

abstract = {Dielectric metasurfaces supporting quasi-bound states in the continuum (qBICs) enable high field enhancement with narrow-linewidth resonances in the visible and near-infrared ranges. The resonance emerges when distorting the meta-atom’s geometry away from a symmetry-protected BIC condition and, usually, a given design can sustain one or two of these states. In this work, we introduce a silicon-on-silica metasurface that simultaneously supports up to four qBIC resonances in the near-infrared region. This is achieved by combining multiple symmetry-breaking distortions on an elliptical cylinder array. By pumping two of these resonances, the nonlinear process of degenerate four-wave mixing is experimentally realized. By comparing the nonlinear response with that of an unpatterned silicon film, the near-field enhancement inside the nanostructured dielectric is revealed. The presented results demonstrate independent geometric control of multiple qBICs and their interaction through wave mixing processes, opening new research pathways in nanophotonics, with potential applications in information multiplexing, multi-wavelength sensing and nonlinear imaging.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{nokey,

title = {Focusing Surface Acoustic Waves with a Plasmonic Hypersonic Lens},

author = {H D Boggiano and L Nan and G Grinblat and S A Maier and E Cort\'{e}s and A V Bragas},

url = {https://doi.org/10.1021/acs.nanolett.4c01251},

doi = {10.1021/acs.nanolett.4c01251},

issn = {1530-6984},

year  = {2024},

date = {2024-05-29},

journal = {Nano Letters},

volume = {24},

number = {21},

pages = {6362-6368},

abstract = {Plasmonic nanoantennas have proven to be efficient transducers of electromagnetic to mechanical energy and vice versa. The sudden thermal expansion of these structures after an ultrafast optical pulsed excitation leads to the emission of hypersonic acoustic waves to the supporting substrate, which can be detected by another antenna that acts as a high-sensitivity mechanical probe due to the strong modulation of its optical response. Here, we propose and experimentally demonstrate a nanoscale acoustic lens comprised of 11 gold nanodisks whose collective oscillation at gigahertz frequencies gives rise to an interference pattern that results in a diffraction-limited surface acoustic beam of about 340 nm width, with an amplitude contrast of 60%. Via spatially decoupled pump\textendashprobe experiments, we were able to map the radiated acoustic energy in the proximity of the focal area, obtaining a very good agreement with the continuum elastic theory.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{nokey,

title = {Pixelated High-Q Metasurfaces for in Situ Biospectroscopy and Artificial Intelligence-Enabled Classification of Lipid Membrane Photoswitching Dynamics},

author = {M Barkey and R B\"{u}chner and A Wester and S D Pritzl and M Makarenko and Q Wang and T Weber and D Trauner and S A Maier and A Fratalocchi and T Lohm\"{u}ller and A Tittl},

url = {https://doi.org/10.1021/acsnano.3c09798},

doi = {10.1021/acsnano.3c09798},

issn = {1936-0851},

year  = {2024},

date = {2024-04-23},

urldate = {2024-04-23},

journal = {ACS Nano},

volume = {18},

number = {18},

pages = {11644-11654},

abstract = {Nanophotonic devices excel at confining light into intense hot spots of electromagnetic near fields, creating exceptional opportunities for light\textendashmatter coupling and surface-enhanced sensing. Recently, all-dielectric metasurfaces with ultrasharp resonances enabled by photonic bound states in the continuum (BICs) have unlocked additional functionalities for surface-enhanced biospectroscopy by precisely targeting and reading out the molecular absorption signatures of diverse molecular systems. However, BIC-driven molecular spectroscopy has so far focused on end point measurements in dry conditions, neglecting the crucial interaction dynamics of biological systems. Here, we combine the advantages of pixelated all-dielectric metasurfaces with deep learning-enabled feature extraction and prediction to realize an integrated optofluidic platform for time-resolved in situ biospectroscopy. Our approach harnesses high-Q metasurfaces specifically designed for operation in a lossy aqueous environment together with advanced spectral sampling techniques to temporally resolve the dynamic behavior of photoswitchable lipid membranes. Enabled by a software convolutional neural network, we further demonstrate the real-time classification of the characteristic cis and trans membrane conformations with 98% accuracy. Our synergistic sensing platform incorporating metasurfaces, optofluidics, and deep learning reveals exciting possibilities for studying multimolecular biological systems, ranging from the behavior of transmembrane proteins to the dynamic processes associated with cellular communication.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{nokey,

title = {Highly confined incident-angle-robust surface phonon polariton bound states in the continuum metasurfaces},

author = {L Nan and A Mancini and T Weber and G L Seah and E Cort\'{e}s and A Tittl and S A Maier},

year  = {2024},

date = {2024-03-27},

journal = {arXiv preprint arXiv:2403.18743},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{nokey,

title = {Emergent resonances in a thin film tailored by optically-induced small permittivity asymmetries},

author = {R Bert\'{e} and T Possmayer and A Tittl and L D S Menezes and S A Maier},

year  = {2024},

date = {2024-03-08},

journal = {arXiv preprint arXiv:2403.05730},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{nokey,

title = {Nonlinear Dielectric Epsilon Near-Zero Hybrid Nanogap Antennas},

author = {R Tirole and B Tilmann and L D S Menezes and S Vezzoli and R Sapienza and S A Maier},

url = {https://doi.org/10.1002/adom.202302069},

doi = {https://doi.org/10.1002/adom.202302069},

issn = {2195-1071},

year  = {2024},

date = {2024-03-01},

journal = {Advanced Optical Materials},

volume = {12},

number = {9},

pages = {2302069},

abstract = {Abstract High-index Mie-resonant dielectric nanostructures provide a new framework to manipulate light at the nanoscale. In particular their local field confinement together with their inherently low losses at frequencies below their bandgap energy allows to efficiently boost and control linear and nonlinear optical processes. Here, nanoantennas composed of a thin indium-tin oxide (ITO) layer in the center of a dielectric gallium phosphide (GaP) nanodisc are investigated. While the linear response is similar to that of a pure GaP nanodisc, it is shown that second harmonic generation is enhanced across a broadband wavelength range. On the other hand, third harmonic generation is only marginally enhanced around the epsilon-near-zero wavelength of ITO. Linear and nonlinear finite-difference time-domain simulations show that despite the high refractive index contrast leading to strong field confinement inside the antenna's ITO layer, the nanogap enhancement effect is mitigated by the low nonlinear volume of the nanogap layer and the antenna's behavior at the harmonic wavelength. Measurement of ITO and GaP nonlinear susceptibilities additionally show a comparative advantage for harmonic generation in GaP. These investigations deliver insights on the mechanisms at play in nonlinear nanogap antennas and their potential applications as nanoscale devices.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{nokey,

title = {Surface-Enhanced Raman Scattering in BIC-Driven Semiconductor Metasurfaces},

author = {H Hu and A K Pal and A Berestennikov and T Weber and A Stefancu and E Cort\'{e}s and S A Maier and A Tittl},

url = {https://onlinelibrary.wiley.com/doi/abs/10.1002/adom.202302812},

doi = {https://doi.org/10.1002/adom.202302812},

issn = {2195-1071},

year  = {2024},

date = {2024-02-05},

journal = {Advanced Optical Materials},

volume = {12},

number = {14},

pages = {2302812},

abstract = {Abstract Semiconductor-based surface-enhanced Raman spectroscopy (SERS) substrates, as a new frontier in the field of SERS, are hindered by their poor electromagnetic field confinement and weak light-matter interaction. Metasurfaces, a class of 2D artificial materials based on the electromagnetic design of nanophotonic resonators, enable strong electromagnetic field enhancement and optical absorption engineering for a wide range of semiconductors. However, the engineering of semiconductor substrates into metasurfaces for improving SERS activity remains underexplored. Here, an improved SERS metasurface platform is developed that leverages the combination of titanium oxide (TiO2) and the emerging physical concept of optical bound states in the continuum (BICs) to boost the Raman emission. Moreover, fine-tuning of BIC-assisted resonant absorption offers a pathway for maximizing the photoinduced charge transfer effect (PICT) in SERS. High values of BIC-assisted electric field enhancement (|E/E0|2 ≈103) are achieved, challenging the preconception of weak electromagnetic (EM) field enhancement on semiconductor SERS substrates. The BIC-assisted TiO2 metasurface platform offers a new dimension in spectrally-tunable SERS with earth-abundant and bio-compatible semiconductor materials, beyond the traditional plasmonic ones.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{nokey,

title = {Unraveling the Chirality Transfer from Circularly Polarized Light to Single Plasmonic Nanoparticles},

author = {S Lee and C Fan and A Movsesyan and J B\"{u}rger and F J Wendisch and L De S. Menezes and S A Maier and H Ren and T Liedl and L V Besteiro and A O Govorov and E Cort\'{e}s},

url = {https://onlinelibrary.wiley.com/doi/abs/10.1002/anie.202319920},

doi = {https://doi.org/10.1002/anie.202319920},

issn = {1433-7851},

year  = {2024},

date = {2024-01-18},

journal = {Angewandte Chemie International Edition},

volume = {63},

number = {11},

pages = {e202319920},

abstract = {Abstract Due to their broken symmetry, chiral plasmonic nanostructures have unique optical properties and numerous applications. However, there is still a lack of comprehension regarding how chirality transfer occurs between circularly polarized light (CPL) and these structures. Here, we thoroughly investigate the plasmon-assisted growth of chiral nanoparticles from achiral Au nanocubes (AuNCs) via CPL without the involvement of any chiral molecule stimulators. We identify the structural chirality of our synthesized chiral plasmonic nanostructures using circular differential scattering (CDS) spectroscopy, which is correlated with scanning electron microscopy imaging at both the single-particle and ensemble levels. Theoretical simulations, including hot-electron surface maps, reveal that the plasmon-induced chirality transfer is mediated by the asymmetric distribution of hot electrons on achiral AuNCs under CPL excitation. Furthermore, we shed light on how this plasmon-induced chirality transfer can also be utilized for chiral growth in bimetallic systems, such as Ag or Pd on AuNCs. The results presented here uncover fundamental aspects of chiral light-matter interaction and have implications for the future design and optimization of chiral sensors and chiral catalysis, among others.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{nokey,

title = {Unraveling the Chirality Transfer from Circularly Polarized Light to Single Plasmonic Nanoparticles},

author = {S Lee and C Fan and A Movsesyan and J B\"{u}rger and F J Wendisch and L De S. Menezes and S A Maier and H Ren and T Liedl and L V Besteiro and A O Govorov and E Cort\'{e}s},

url = {https://onlinelibrary.wiley.com/doi/abs/10.1002/anie.202319920},

doi = {https://doi.org/10.1002/anie.202319920},

issn = {1433-7851},

year  = {2024},

date = {2024-01-18},

journal = {Angewandte Chemie International Edition},

volume = {63},

number = {11},

pages = {e202319920},

abstract = {Abstract Due to their broken symmetry, chiral plasmonic nanostructures have unique optical properties and numerous applications. However, there is still a lack of comprehension regarding how chirality transfer occurs between circularly polarized light (CPL) and these structures. Here, we thoroughly investigate the plasmon-assisted growth of chiral nanoparticles from achiral Au nanocubes (AuNCs) via CPL without the involvement of any chiral molecule stimulators. We identify the structural chirality of our synthesized chiral plasmonic nanostructures using circular differential scattering (CDS) spectroscopy, which is correlated with scanning electron microscopy imaging at both the single-particle and ensemble levels. Theoretical simulations, including hot-electron surface maps, reveal that the plasmon-induced chirality transfer is mediated by the asymmetric distribution of hot electrons on achiral AuNCs under CPL excitation. Furthermore, we shed light on how this plasmon-induced chirality transfer can also be utilized for chiral growth in bimetallic systems, such as Ag or Pd on AuNCs. The results presented here uncover fundamental aspects of chiral light-matter interaction and have implications for the future design and optimization of chiral sensors and chiral catalysis, among others.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{nokey,

title = {Continuous spectral and coupling-strength encoding with dual-gradient metasurfaces},

author = {A Aigner and T Weber and A Wester and S A Maier and A Tittl},

url = {https://arxiv.org/abs/2312.05600},

doi = {https://doi.org/10.48550/arXiv.2312.05600},

year  = {2023},

date = {2023-12-09},

journal = {arXiv preprint arXiv:2312.05600},

abstract = {Optical metasurfaces excel at enhancing and controlling light-matter interactions, which are primarily dictated by two factors: the spectral overlap of the resonances with target excitations in the material and the coupling-strength between them, where resonance linewidth and localized field enhancement are the governing influences. Current metasurface designs are limited to sampling a few discrete points within this vast 2D interaction parameter space or have varied only a single parameter. Symmetry-protected bound states in the continuum (BICs) allow precise control over the wavelength and linewidth of individual resonances, but rely on large arrangements of identical unit cells, limiting the continuous mapping of the parameter space. Therefore, optical platforms that concurrently probe the spectral and coupling parameters, so far, remained elusive. Here, we introduce the concept of dual-gradient metasurfaces for the continuous and simultaneous encoding of the spectral and coupling-strength of light-matter interactions, enabled by smooth local variations of the unit cell parameters. Contrary to conventional understanding, we demonstrate that BICs can be excited in such non-periodic systems provided the parameter variations are sufficiently small. Our dual-gradient metasurface exhibits an extraordinary resonance density, with each unit cell supporting a unique mode. This results in up to 27,500 distinct modes, all contained within a compact footprint. We apply this technology to surface-enhanced molecular sensing, capturing not only the spectral fingerprint of molecules but also unveiling an additional coupling-based dimension of spectroscopic data. This advancement in metasurface design paves the way for generalized light-matter coupling with metasurfaces, with applications ranging from on-chip spectrometer, to chirality encoding and AI-driven biochemical spectroscopy.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{nokey,

title = {Active Loss Engineering in Vanadium Dioxide Based BIC Metasurfaces},

author = {A Aigner and F Ligmajer and K Rovensk\'{a} and J Holobr\'{a}dek and B Idesov\'{a} and S A Maier and A Tittl and L D S Menezes},

url = {https://arxiv.org/abs/2312.00547},

doi = {https://doi.org/10.48550/arXiv.2312.00547},

year  = {2023},

date = {2023-12-01},

journal = {arXiv preprint arXiv:2312.00547},

abstract = {Metasurfaces have unlocked significant advancements across photonics, yet their efficient active control remains challenging. The active materials required often lack continuous tunability, exhibit inadequate refractive index (RI) changes, or suffer from high losses. These aspects pose an inherent limitation for resonance-shifting based switching: when RI changes are small, the resulting shift is also minor. Conversely, high RI changes typically come with high intrinsic losses necessitating broad modes because narrow ones cannot tolerate such losses. Therefore, larger spectral shifts are required to effectively detune the modes. This paper introduces a novel active metasurface approach that converts the constraint of high intrinsic losses into a beneficial feature. This is achieved by controlling the losses in a hybrid vanadium dioxide (VO2) - silicon metasurface, supporting symmetry-protected bound states in the continuum (BICs) within the infrared spectrum. By leveraging the temperature-controlled losses in VO2 and combining them with the inherent far-field-coupling tunability of BICs, we gain unprecedented precision in independently controlling both the radiative and nonradiative losses of the resonant system. Our dual-control mechanism allows us to optimize our metasurfaces and we experimentally demonstrate quality factors above 200, a maximum reflectance amplitude of 90%, a relative switching contrast of 78%, and continuous tuning from under- to over-coupling within the infrared spectral range. This study provides a foundation for experimentally and technologically simple, fine-tunable, active metasurfaces for applications ranging from molecular sensors to filters and optical modulators.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{nokey,

title = {All-Dielectric Structural Coloration Empowered by Bound States in the Continuum},

author = {H Zheng and H Hu and T Weber and J Wang and L Nan and B Zou and S A Maier and A Tittl},

url = {https://arxiv.org/abs/2311.13315},

doi = {https://doi.org/10.48550/arXiv.2311.13315},

year  = {2023},

date = {2023-11-28},

journal = {arXiv preprint arXiv:2311.13315},

abstract = {The technological requirements of low-power and high-fidelity color displays have been instrumental in driving research into advanced coloration technologies. At the forefront of these developments is the implementation of dye-free coloration techniques, which overcome previous constraints related to insufficient resolution and color fading. In this context, resonant dielectric nanostructures have emerged as a promising paradigm, showing great potential for high efficiency, remarkably high color saturation, wide gamut palette, and realistic image reproduction. However, they still face limitations related to color accuracy, purity, and simultaneous brightness tunability. Here, we demonstrate an all-dielectric metasurface empowered by photonic bound states in the continuum (BICs), which supports sharp resonances throughout the visible spectral range, ideally suited for producing a wide range of structural colors. The metasurface design consists of titanium dioxide (TiO2) ellipses with carefully controlled sizes and geometrical asymmetry, allowing versatile and on-demand variation of the brightness and hue of the output colors, respectively.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{nokey,

title = {Spatial Distributions of Single-Molecule Reactivity in Plasmonic Catalysis},

author = {S Ezendam and J Gargiulo and A Sousa-Castillo and J B Lee and Y S Nam and S A Maier and E Cort\'{e}s},

url = {https://doi.org/10.1021/acsnano.3c07833},

doi = {10.1021/acsnano.3c07833},

issn = {1936-0851},

year  = {2023},

date = {2023-11-16},

journal = {ACS Nano},

abstract = {Plasmonic catalysts have the potential to accelerate and control chemical reactions with light by exploiting localized surface plasmon resonances. However, the mechanisms governing plasmonic catalysis are not simple to decouple. Several plasmon-derived phenomena, such as electromagnetic field enhancements, temperature, or the generation of charge carriers, can affect the reactivity of the system. These effects are convoluted with the inherent (nonplasmonic) catalytic properties of the metal surface. Disentangling these coexisting effects is challenging but is the key to rationally controlling reaction pathways and enhancing reaction rates. This study utilizes super-resolution fluorescence microscopy to examine the mechanisms of plasmonic catalysis at the single-particle level. The reduction reaction of resazurin to resorufin in the presence of Au nanorods coated with a porous silica shell is investigated in situ. This allows the determination of reaction rates with a single-molecule sensitivity and subparticle resolution. By variation of the irradiation wavelength, it is possible to examine two different regimes: photoexcitation of the reactant molecules and photoexcitation of the nanoparticle’s plasmon resonance. In addition, the measured spatial distribution of reactivity allows differentiation between superficial and far-field effects. Our results indicate that the reduction of resazurin can occur through more than one reaction pathway, being most efficient when the reactant is photoexcited and is in contact with the Au surface. In addition, it was found that the spatial distribution of enhancements varies, depending on the underlying mechanism. These findings contribute to the fundamental understanding of plasmonic catalysis and the rational design of future plasmonic nanocatalysts.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{nokey,

title = {Optical Readout of the Mechanical Properties of Silica Mesoporous Thin Films Using Plasmonic Nanoantennas},

author = {H D Boggiano and J I Ramallo and L Nan and A Litwiller and E Cort\'{e}s and S A Maier and G Grinblat and M C Fuertes and P C Angelom\'{e} and A V Bragas},

url = {https://doi.org/10.1021/acsphotonics.3c00874},

doi = {10.1021/acsphotonics.3c00874},

year  = {2023},

date = {2023-11-15},

journal = {ACS Photonics},

volume = {10},

number = {11},

pages = {3998-4005},

abstract = {In this work, we apply the recently developed frequency shift of nanoantennas (FRESA) technique to measure the Young’s modulus of thin mesoporous films at GHz frequencies as a function of porosity with local precision. The method measures changes in the mechanical oscillation frequency of optically excited plasmonic nanoantennas with modification of their surrounding medium. The values obtained range from 4 to 10 GPa for porosities extending from 35 to 4%, compatible with reports on films grown under similar conditions. We further find comparable results when using the well-established nanoindentation (NI) technique, validating the new method. By analysis of the nanoresonator’s quality factor, the measurement reveals an excellent interfacial adhesion of the films to the nanoantennas. Different from most other characterization techniques, FRESA provides elastic modulus determination at GHz frequencies, relevant for the operation of current devices. Furthermore, FRESA exhibits, in principle, no limitations in terms of film thickness, in contrast to the NI, which is strongly affected by the stiffness of the substrate for ultrathin films.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{nokey,

title = {Fluorescence enhancement in topologically optimized gallium phosphide all-dielectric nanoantennas},

author = {C Vidal and B Tilmann and S Tiwari and T Raziman and S A Maier and J Wenger and R Sapienza},

url = {https://arxiv.org/abs/2310.07309},

doi = {https://doi.org/10.48550/arXiv.2310.07309},

year  = {2023},

date = {2023-10-11},

journal = {arXiv preprint arXiv:2310.07309},

abstract = {Nanoantennas capable of large fluorescence enhancement with minimal absorption are crucial for future optical technologies from single-photon sources to biosensing. Efficient dielectric nanoantennas have been designed, however, evaluating their performance at the individual emitter level is challenging due to the complexity of combining high-resolution nanofabrication, spectroscopy and nanoscale positioning of the emitter. Here, we study the fluorescence enhancement in infinity-shaped gallium phosphide (GaP) nanoantennas based on a topologically optimized design. Using fluorescence correlation spectroscopy (FCS), we probe the nanoantennas enhancement factor and observed an average of 63-fold fluorescence brightness enhancement with a maximum of 93-fold for dye molecules in nanogaps between 20 nm and 50 nm. The experimentally determined fluorescence enhancement of the nanoantennas was confirmed by numerical simulations of the local density of optical states (LDOS). Furthermore, we show that beyond design optimisation of dielectric nanoantennas, increased performances can be achieved via tailoring of nanoantenna fabrication.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{nokey,

title = {Semiconductor Metasurfaces for Surface-enhanced Raman Scattering},

author = {H Hu and A K Pal and A Berestennikov and T Weber and A Stefancu and E Cortes and S A Maier and A Tittl},

url = {https://arxiv.org/abs/2309.10732},

doi = {https://doi.org/10.48550/arXiv.2309.10732},

year  = {2023},

date = {2023-09-19},

journal = {arXiv preprint arXiv:2309.10732},

abstract = {Semiconductor-based surface-enhanced Raman spectroscopy (SERS) substrates, as a new frontier in the field of SERS, are hindered by their poor electromagnetic field confinement, and weak light-matter interaction. Metasurfaces, a class of 2D artificial materials based on the electromagnetic design of nanophotonic resonators, enable strong electromagnetic field enhancement and optical absorption engineering for a wide range of semiconductor materials. However, the engineering of semiconductor substrates into metasurfaces for improving SERS activity remains underexplored. Here, we develop an improved SERS metasurface platform that leverages the combination of titanium oxide (TiO2) and the emerging physical concept of optical bound states in the continuum (BICs) to boost the Raman emission. Moreover, fine-tuning of BIC-assisted resonant absorption offers a pathway for maximizing the photoinduced charge transfer effect (PICT) in SERS. We achieve ultrahigh values of BIC-assisted electric field enhancement (|E/E0|^2 ~ 10^3), challenging the preconception of weak electromagnetic (EM) field enhancement on semiconductor SERS substrates. Our BIC-assisted TiO2 metasurface platform offers a new dimension in spectrally-tunable SERS with earth-abundant and bio-compatible semiconductor materials, beyond the traditional plasmonic ones.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{nokey,

title = {Anti Stokes Thermometry of Plasmonic Nanoparticle Arrays},

author = {S Ezendam and L Nan and I L Violi and S A Maier and E Cort\'{e}s and G Baffou and J Gargiulo},

url = {https://onlinelibrary.wiley.com/doi/abs/10.1002/adom.202301496},

doi = {https://doi.org/10.1002/adom.202301496},

issn = {2195-1071},

year  = {2023},

date = {2023-09-14},

journal = {Advanced Optical Materials},

volume = {n/a},

number = {n/a},

pages = {2301496},

abstract = {Abstract Metallic nanoparticles possess strong photothermal responses, especially when illuminated as ensembles due to collective effects. However, accurately quantifying the temperature increase remains a significant challenge, impeding progress in several applications. Anti Stokes thermometry offers a promising solution by enabling direct and non-invasive temperature measurements of the metal without the need for labeling or prior calibration. While Anti Stokes thermometry is successfully applied to individual nanoparticles, its potential to study light-to-heat conversion with plasmonic ensembles remains unexplored. In this study, the theoretical framework and the conditions that must be fulfilled for applying Anti Stokes thermometry to ensembles of nanoparticles are discussed. Then, this technique is implemented to measure the light-induced heating of square arrays of Au nanodisks. The obtained temperature measurements are validated using wavefront microscopy, demonstrating excellent agreement between the two thermometry methods. These results showcase the extension of Anti Stokes thermometry to plasmonic ensembles, highlighting its potential for implementation in the diverse photothermal applications involving these systems.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{nokey,

title = {Photo-induced enhanced Raman spectroscopy as a probe for photocatalytic surfaces},

author = {S Ben-Jaber and D Glass and T Brick and S A Maier and I P Parkin and E Cort\'{e}s and W J Peveler and R Quesada-Cabrera},

url = {https://royalsocietypublishing.org/doi/abs/10.1098/rsta.2022.0343},

doi = {doi:10.1098/rsta.2022.0343},

year  = {2023},

date = {2023-09-11},

journal = {Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences},

volume = {381},

number = {2259},

pages = {20220343},

abstract = {Photo-induced enhanced Raman spectroscopy (PIERS) has emerged as a highly sensitive surface-enhanced Raman spectroscopy (SERS) technique for the detection of ultra-low concentrations of organic molecules. The PIERS mechanism has been largely attributed to UV-induced formation of surface oxygen vacancies (Vo) in semiconductor materials, although alternative interpretations have been suggested. Very recently, PIERS has been proposed as a surface probe for photocatalytic materials, following Vo formation and healing kinetics. This work establishes comparison between PIERS and Vo-induced SERS approaches in defected noble-metal-free titanium dioxide (TiO2-x) films to further confirm the role of Vo in PIERS. Upon application of three post-treatment methods (namely UV-induction, vacuum annealing and argon etching), correlation of Vo kinetics and distribution could be established. A proposed mechanism and further discussion on PIERS as a probe to explore photocatalytic materials are also presented. This article is part of the theme issue ‘Exploring the length scales, timescales and chemistry of challenging materials (Part 2)’.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{nokey,

title = {Pixelated high-Q metasurfaces for in-situ biospectroscopy and AI-enabled classification of lipid membrane photoswitching dynamics},

author = {M Barkey and R B\"{u}chner and A Wester and S D Pritzl and M Makarenko and Q Wang and T Weber and D Trauner and S A Maier and A Fratalocchi},

url = {https://arxiv.org/abs/2308.15644},

doi = {https://doi.org/10.48550/arXiv.2308.15644},

year  = {2023},

date = {2023-08-29},

journal = {arXiv preprint arXiv:2308.15644},

abstract = {Nanophotonic devices excel at confining light into intense hot spots of the electromagnetic near fields, creating unprecedented opportunities for light-matter coupling and surface-enhanced sensing. Recently, all-dielectric metasurfaces with ultrasharp resonances enabled by photonic bound states in the continuum have unlocked new functionalities for surface-enhanced biospectroscopy by precisely targeting and reading out molecular absorption signatures of diverse molecular systems. However, BIC-driven molecular spectroscopy has so far focused on endpoint measurements in dry conditions, neglecting the crucial interaction dynamics of biological systems. Here, we combine the advantages of pixelated all-dielectric metasurfaces with deep learning-enabled feature extraction and prediction to realize an integrated optofluidic platform for time-resolved in-situ biospectroscopy. Our approach harnesses high-Q metasurfaces specifically designed for operation in a lossy aqueous environment together with advanced spectral sampling techniques to temporally resolve the dynamic behavior of photoswitchable lipid membranes. Enabled by a software convolutional neural network, we further demonstrate the real-time classification of the characteristic cis and trans membrane conformations with 98% accuracy. Our synergistic sensing platform incorporating metasurfaces, optofluidics, and deep learning opens exciting possibilities for studying multi-molecular biological systems, ranging from the behavior of transmembrane proteins to the dynamic processes associated with cellular communication.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{nokey,

title = {Optimization of p-Type Cu2O Nanocube Photocatalysts Based on Electronic Effects},

author = {R Lin and H Chen and T Cui and Z Zhang and Q Zhou and L Nan and W-C Cheong and L Schr\"{o}ck and V Ramm and Q Ding and X Liang and S Saris and F J Wendisch and S A Maier and R A Fischer and Y Zhu and D Wang and E Cortes},

url = {https://doi.org/10.1021/acscatal.3c02710},

doi = {10.1021/acscatal.3c02710},

year  = {2023},

date = {2023-08-14},

journal = {ACS Catalysis},

pages = {11352-11361},

abstract = {The size effect in semiconductor photocatalysis has been widely investigated but still remains elusive. Herein, employing p-type Cu2O nanocubes as the heterogeneous photocatalysts, we propose a feasible size optimization strategy to enhance the photocatalytic performance of semiconductors. With the size of Cu2O increasing from 2.5 nm (exciton Bohr radius) to 5 nm (twice the exciton Bohr radius), the corresponding calculated band gap of Cu2O decreases from 3.39 to 2.41 eV, indicating that controlling the size to above twice the exciton Bohr radius is vital for retaining the visible-light response of Cu2O. Based on the theoretical calculations and experimental measurements of the charge carrier dynamics, we found that the synthesized 30 nm Cu2O nanocubes have an electron diffusion length of 191 nm, while 229 nm Cu2O nanocubes show an electron diffusion length of 45 nm. An electron diffusion length larger than the semiconductor particle size lowers the electron\textendashhole recombination, resulting in a visible-light CO generation rate 23.4 times higher for the smaller Cu2O nanocubes than that for the larger ones. These results verify that confining Cu2O size to within the minority carrier diffusion length and above twice the exciton Bohr radius is a promising way to enhance Cu2O photocatalytic activity.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{nokey,

title = {Multi-band metasurface-driven surface-enhanced infrared absorption spectroscopy for improved characterization of in-situ electrochemical reactions},

author = {M Duportal and L M Berger and S A Maier and A Tittl and K Krischer},

url = {https://arxiv.org/abs/2307.10951},

doi = {https://doi.org/10.48550/arXiv.2307.10951},

year  = {2023},

date = {2023-07-20},

journal = {arXiv preprint arXiv:2307.10951},

abstract = {Surface-enhanced spectroscopy techniques are the method-of-choice to characterize adsorbed intermediates occurring during electrochemical reactions, which are crucial in realizing a green sustainable future. Characterizing species with low coverages or short lifetimes have so far been limited by low signal enhancement. Recently, metasurface-driven surface-enhanced infrared absorption spectroscopy (SEIRAS) has been pioneered as a promising narrowband technology to study single vibrational modes of electrochemical interfaces during CO oxidation. However, many reactions involve several species or configurations of adsorption that need to be monitored simultaneously requiring reproducible and broadband sensing platforms to provide a clear understanding of the underlying electrochemical processes. Here, we experimentally realize multi-band metasurface-driven SEIRAS for the in-situ study of electrochemical CO2 reduction on a Pt surface. We develop an easily reproducible and spectrally-tunable platinum nano-slot metasurface. Two CO adsorption configurations at 2030 cm-1 and 1840 cm-1 are locally enhanced as a proof of concept that can be extended to more vibrational bands. Our platform provides a 41-fold enhancement in the detection of characteristic absorption signals compared to conventional broadband electrochemically roughened platinum films. A straightforward methodology is outlined starting by baselining our system in CO saturated environment and clearly detecting both configurations of adsorption, in particular the hitherto hardly detectable CO bridge configuration. Then, thanks to the signal enhancement provided by our platform, we find that the CO bridge configuration on platinum does not play a significant role during CO2 reduction in an alkaline environment. We anticipate that our technology will guide researchers in developing similar sensing platforms.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{nokey,

title = {Probing the micro- and nanoscopic properties of dental materials using infrared spectroscopy: A proof-of-principle study},

author = {M Beddoe and T G\"{o}lz and M Barkey and E Bau and M Godejohann and S A Maier and F Keilmann and M Moldovan and D Prodan and N Ilie and A Tittl},

url = {https://www.sciencedirect.com/science/article/pii/S1742706123004026},

doi = {https://doi.org/10.1016/j.actbio.2023.07.017},

issn = {1742-7061},

year  = {2023},

date = {2023-07-19},

journal = {Acta Biomaterialia},

volume = {168},

pages = {309-322},

abstract = {The preservation of oral health over a person's lifespan is a key factor for a high quality of life. Sustaining oral health requires high-end dental materials with a plethora of attributes such as durability, non-toxicity and ease of application. The combination of different requirements leads to increasing miniaturization and complexity of the material components such as the composite and adhesives, which makes the precise characterization of the material blend challenging. Here, we demonstrate how modern IR spectroscopy and imaging from the micro- to the nanoscale can provide insights on the chemical composition of the different material sections of a dental filling. We show how the recorded IR-images can be used for a fast and non-destructive porosity determination of the studied adhesive. Furthermore, the nanoscale study allows precise assessment of glass cluster structures and distribution within their characteristic organically modified ceramic (ORMOCER) matrix and an assessment of the interface between the composite and adhesive material. For the study we used a Fourier-Transform-IR (FTIR) microscope and a quantum cascade laser-based IR-microscope (QCL-IR) for the microscale analysis and a scattering-type scanning near-field optical microscopy (s-SNOM) for the nanoscale analysis. The paper ends with an in-depth discussion of the strengths and weaknesses of the different imaging methods to give the reader a clear picture for which scientific question the microscopes are best suited for. Statement of significance Modern resin-based composites for dental restoration are complex multi-compound materials. In order to improve these high-end materials, it is important to investigate the molecular composition and morphology of the different parts. An emergent method to characterize these materials is infrared spectroscopic imaging, which combines the strength of infrared spectroscopy and an imaging approach known from optical microscopy. In this work, three state of the art methods are compared for investigating a dental filling including FTIR- and quantum cascade laser IR-imaging microscopy for the microscale and scattering-type scanning near-field optical microscopy for the nanoscale.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{nokey,

title = {Optimizing Hot Electron Harvesting at Planar Metal\textendashSemiconductor Interfaces with Titanium Oxynitride Thin Films},

author = {B Doiron and Y Li and R Bower and A Mihai and S Dal Forno and S Fearn and L H\"{u}ttenhofer and E Cort\'{e}s and L F Cohen and N M Alford and J Lischner and P Petrov and S A Maier and R F Oulton},

url = {https://doi.org/10.1021/acsami.3c02812},

doi = {10.1021/acsami.3c02812},

issn = {1944-8244},

year  = {2023},

date = {2023-06-28},

journal = {ACS Applied Materials \& Interfaces},

volume = {15},

number = {25},

pages = {30417-30426},

abstract = {Understanding metal\textendashsemiconductor 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\textendashx interfaces, where in the latter case the spontaneously forming oxide layer (TiO2\textendashx) creates a metal\textendashsemiconductor contact. Time-resolved pump\textendashprobe 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\textendash3), slowest trapping, and an appreciable hot electron population reaching the surface oxide (NHE ≈ 1.6 × 1018 m\textendash3). Our results demonstrate the productive role oxygen can play in enhancing electron harvesting and prolonging electron lifetimes, providing an optimized metal\textendashsemiconductor interface using only the native oxide of titanium oxynitride.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{nokey,

title = {Impact of bimetallic interface design on heat generation in plasmonic Au/Pd nanostructures studied by single-particle thermometry},

author = {J Gargiulo and M Herran and I L Violi and A Sousa-Castillo and L P Martinez and S Ezendam and M Barella and H Giesler and R Grzeschik and S Schl\"{u}cker and S A Maier and F D Stefani and E Cort\'{e}s},

url = {https://doi.org/10.1038/s41467-023-38982-9},

doi = {10.1038/s41467-023-38982-9},

issn = {2041-1723},

year  = {2023},

date = {2023-06-27},

journal = {Nature Communications},

volume = {14},

number = {1},

pages = {3813},

abstract = {Localized surface plasmons are lossy and generate heat. However, accurate measurement of the temperature of metallic nanoparticles under illumination remains an open challenge, creating difficulties in the interpretation of results across plasmonic applications. Particularly, there is a quest for understanding the role of temperature in plasmon-assisted catalysis. Bimetallic nanoparticles combining plasmonic with catalytic metals are raising increasing interest in artificial photosynthesis and the production of solar fuels. Here, we perform single-particle thermometry measurements to investigate the link between morphology and light-to-heat conversion of colloidal Au/Pd nanoparticles with two different configurations: core\textendashshell and core-satellite. It is observed that the inclusion of Pd as a shell strongly reduces the photothermal response in comparison to the bare cores, while the inclusion of Pd as satellites keeps photothermal properties almost unaffected. These results contribute to a better understanding of energy conversion processes in plasmon-assisted catalysis.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{nokey,

title = {Intrinsic strong light-matter coupling with self-hybridized bound states in the continuum in van der Waals metasurfaces},

author = {T Weber and L K\"{u}hner and L Sortino and A Ben Mhenni and N P Wilson and J K\"{u}hne and J J Finley and S A Maier and A Tittl},

url = {https://doi.org/10.1038/s41563-023-01580-7},

doi = {10.1038/s41563-023-01580-7},

issn = {1476-4660},

year  = {2023},

date = {2023-06-22},

journal = {Nature Materials},

volume = {22},

number = {8},

pages = {970-976},

abstract = {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.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{nokey,

title = {Intrinsic strong light-matter coupling with self-hybridized bound states in the continuum in van der Waals metasurfaces},

author = {T Weber and L K\"{u}hner and L Sortino and A Ben Mhenni and N P Wilson and J K\"{u}hne and J J Finley and S A Maier and A Tittl},

url = {https://doi.org/10.1038/s41563-023-01580-7},

doi = {10.1038/s41563-023-01580-7},

issn = {1476-4660},

year  = {2023},

date = {2023-06-22},

journal = {Nature Materials},

volume = {22},

number = {8},

pages = {970-976},

abstract = {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.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{nokey,

title = {Optically addressable spin defects coupled to bound states in the continuum metasurfaces},

author = {L Sortino and A Gale and L K\"{u}hner and C Li and J Biechteler and F J Wendisch and M Kianinia and H Ren and M Toth and S A Maier},

url = {https://arxiv.org/abs/2306.05735},

doi = {https://doi.org/10.48550/arXiv.2306.05735},

year  = {2023},

date = {2023-06-09},

journal = {arXiv preprint arXiv:2306.05735},

abstract = {Van der Waals (vdW) materials, including hexagonal boron nitride (hBN), are layered crystalline solids with appealing properties for investigating light-matter interactions at the nanoscale. hBN has emerged as a versatile building block for nanophotonic structures, and the recent identification of native optically addressable spin defects has opened up exciting possibilities in quantum technologies. However, these defects exhibit relatively low quantum efficiencies and a broad emission spectrum, limiting potential applications. Optical metasurfaces present a novel approach to boost light emission efficiency, offering remarkable control over light-matter coupling at the sub-wavelength regime. Here, we propose and realise a monolithic scalable integration between intrinsic spin defects in hBN metasurfaces and high quality (Q) factor resonances leveraging quasi-bound states in the continuum (qBICs). Coupling between spin defect ensembles and qBIC resonances delivers a 25-fold increase in photoluminescence intensity, accompanied by spectral narrowing to below 4 nm linewidth facilitated by Q factors exceeding 10 ^2. Our findings demonstrate a new class of spin based metasurfaces and pave the way towards vdW-based nanophotonic devices with enhanced efficiency and sensitivity for quantum applications in imaging, sensing, and light emission.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{nokey,

title = {Comparison of Harmonic Generation from Crystalline and Amorphous Gallium Phosphide Nanofilms},

author = {B Tilmann and T Huq and T Possmayer and J Dranczewski and B Nickel and H Zhang and L Krivitsky and A I Kuznetsov and L De S. Menezes and S Vezzoli and R Sapienza and S A Maier},

url = {https://onlinelibrary.wiley.com/doi/abs/10.1002/adom.202300269},

doi = {https://doi.org/10.1002/adom.202300269},

issn = {2195-1071},

year  = {2023},

date = {2023-06-02},

journal = {Advanced Optical Materials},

volume = {11},

number = {16},

pages = {2300269},

abstract = {Abstract Gallium phosphide (GaP) is a promising material for nanophotonics, given its large refractive index and a transparency over most of the visible spectrum. However, since easy phase-matching is not possible with bulk GaP, a comprehensive study of its nonlinear optical properties for harmonic generation, especially when grown as thin films, is still missing. Here, second harmonic generation is studied from epitaxially grown GaP thin films, demonstrating that the absolute conversion efficiencies are comparable to a bulk wafer over the pump wavelength range from 1060 to 1370 nm. Furthermore, the results are compared to nonlinear simulations, and the second order nonlinear susceptibility is extracted, showing a similar dispersion and magnitude to that of the bulk material. Furthermore, the third order nonlinear susceptibility of amorphous GaP thin films is extracted from third harmonic generation to be more than one order of magnitude larger than that of the crystalline material, and generation of up to the fifth harmonic is reported. The results show the potential of crystalline and amorphous thin films for nonlinear optics with nanoantennas and metasurfaces, particularly in the visible to near infrared part of the spectrum.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{nokey,

title = {Metallic and All-Dielectric Metasurfaces Sustaining Displacement-Mediated Bound States in the Continuum},

author = {L M Berger and M Barkey and S A Maier and A Tittl},

url = {https://arxiv.org/abs/2306.00591},

doi = {https://doi.org/10.48550/arXiv.2306.00591},

year  = {2023},

date = {2023-06-01},

journal = {arXiv preprint arXiv:2306.00591},

abstract = {Bound states in the continuum (BICs) are localized electromagnetic modes within the continuous spectrum of radiating waves. Due to their infinite lifetimes without radiation losses, BICs are driving research directions in lasing, non-linear optical processes, and sensing. However, conventional methods for converting BICs into leaky resonances, or quasi-BICs, with high-quality factors typically rely on breaking the in-plane inversion symmetry of the metasurface and often result in resonances that are strongly dependent on the angle of the incident light, making them unsuitable for many practical applications. Here, we numerically analyze and experimentally demonstrate an emerging class of BIC-driven metasurfaces, where the coupling to the far field is controlled by the displacement of individual resonators. In particular, we investigate both all-dielectric and metallic as well as positive and inverse displacement-mediated metasurfaces sustaining angular-robust quasi-BICs in the mid-infrared spectral region. We explore their behavior with changes in the incidence angle of illumination and experimentally show their superior performance compared to two conventional alternatives: silicon-based tilted ellipses and cylindrical nanoholes in gold. We anticipate our findings to open exciting perspectives for bio-sensing, conformal optical devices, and photonic devices using focused light.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{nokey,

title = {Transformation-Optics-Designed Plasmonic Singularities for Efficient Photocatalytic Hydrogen Evolution at Metal/Semiconductor Interfaces},

author = {T Lin and T Yang and Y Cai and J Li and G Lu and S Chen and Y Li and L Guo and S A Maier and C Liu and J Huang},

url = {https://doi.org/10.1021/acs.nanolett.3c01287},

doi = {10.1021/acs.nanolett.3c01287},

issn = {1530-6984},

year  = {2023},

date = {2023-05-26},

journal = {Nano Letters},

volume = {23},

number = {11},

pages = {5288-5296},

abstract = {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\textendashAu dimer (t-CZTS@Au\textendashAu) 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\textendashAu) 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.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{nokey,

title = {Active Huygens' metasurface based on in-situ grown conductive polymer},

author = {W Lu and L D S Menezes and A Tittl and H Ren and S A Maier},

url = {https://arxiv.org/abs/2305.07356},

doi = {https://doi.org/10.48550/arXiv.2305.07356},

year  = {2023},

date = {2023-05-12},

journal = {arXiv preprint arXiv:2305.07356},

abstract = {Active metasurfaces provide unique advantages for on-demand light manipulation at a subwavelength scale for emerging applications of 3D displays, augmented/virtual reality (AR/VR) glasses, holographic projectors and light detection and ranging (LiDAR). These applications put stringent requirements on switching speed, cycling duration, controllability over intermediate states, modulation contrast, optical efficiency and operation voltages. However, previous demonstrations focus only on particular subsets of these key performance requirements for device implementation, while the other performance metrics have remained too low for any practical use. Here, we demonstrate an active Huygens' metasurface based on in-situ grown conductive polymer with holistic switching performance, including switching speed of 60 frames per second (fps), switching duration of more than 2000 switching cycles without noticeable degradation, hysteresis-free controllability over intermediate states, modulation contrast of over 1400%, optical efficiency of 28% and operation voltage range within 1 V. Our active metasurface design meets all foundational requirements for display applications and can be readily incorporated into other metasurface concepts to deliver high-reliability electrical control over its optical response, paving the way for compact and robust electro-optic metadevices.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{nokey,

title = {Improved In Situ Characterization of Electrochemical Interfaces Using Metasurface-Driven Surface-Enhanced IR Absorption Spectroscopy},

author = {L M Berger and M Duportal and L D S Menezes and E Cort\'{e}s and S A Maier and A Tittl and K Krischer},

url = {https://onlinelibrary.wiley.com/doi/abs/10.1002/adfm.202300411},

doi = {https://doi.org/10.1002/adfm.202300411},

issn = {1616-301X},

year  = {2023},

date = {2023-03-20},

urldate = {2023-03-20},

journal = {Advanced Functional Materials},

volume = {33},

issue = {25},

pages = {2300411},

abstract = {Abstract Electrocatalysis plays a crucial role in realizing the transition toward a zero-carbon future, driving research directions from green hydrogen generation to carbon dioxide reduction. Surface-enhanced infrared absorption spectroscopy (SEIRAS) is a suitable method for investigating electrocatalytic processes because it can monitor with chemical specificity the mechanisms of the reactions. However, it remains difficult to detect many relevant aspects of electrochemical reactions such as short-lived intermediates. Herein, an integrated nanophotonic-electrochemical SEIRAS platform is developed and experimentally realized for the in situ investigation of molecular signal traces emerging during electrochemical experiments. A platinum nano-slot metasurface featuring strongly enhanced electromagnetic near fields is implemented and spectrally targets the weak vibrational mode of the adsorbed carbon monoxide at ≈2033 cm−1. The metasurface-driven resonances can be tuned over a broad range in the mid-infrared spectrum and provide high molecular sensitivity. Compared to conventional unstructured platinum films, this nanophotonic-electrochemical platform delivers a 27-fold improvement of the experimentally detected characteristic absorption signals, enabling the detection of new species with weak signals, fast conversions, or low surface concentrations. By providing a deeper understanding of catalytic reactions, the nanophotonic-electrochemical platform is anticipated to open exciting perspectives for electrochemical SEIRAS, surface-enhanced Raman spectroscopy, and other fields of chemistry such as photoelectrocatalysis.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{nokey,

title = {Nanomechanics with plasmonic nanoantennas: ultrafast and local exchange between electromagnetic and mechanical energy},

author = {A V Bragas and S A Maier and H D Boggiano and G Grinblat and R Bert\'{e} and L D S Menezes and E Cort\'{e}s},

url = {https://opg.optica.org/josab/abstract.cfm?doi=10.1364/JOSAB.482384},

doi = {https://doi.org/10.1364/JOSAB.482384},

year  = {2023},

date = {2023-03-10},

journal = {J. Opt. Soc. Am. B},

abstract = {Converted into mechanical nanoresonators after optical pulsed excitation and electron decay into coherent acoustic phonons, plasmonic nanoantennas produce a periodic modulation of their optical properties, allowing, in turn, an optical reading of these extremely small movements. In this work we review the physics of these nanoresonators and their acoustic vibrations, whose frequencies are in the range of a few to tens of GHz. The accurate determination of their oscillation frequencies allows them to act as mechanical nanoprobes, measure local mechanical moduli of the environment, and perform high-resolution imaging using phononic reconstruction. Furthermore, the internal and external damping mechanisms which affect the quality factor of the nanoresonator and, in particular, the role of the substrate when the nanoantennas are integrated into platforms and probed individually are also reviewed. Finally, we discuss the all-optical generation of hypersonic surface acoustic waves with nanoantennas and the importance of their manipulation for potential acousto-plasmonic devices operating in the GHz range and the nanoscale.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{nokey,

title = {Highly Efficient Sum-Frequency Generation in Niobium Oxydichloride NbOCl2 Nanosheets},

author = {I Abdelwahab and B Tilmann and X Zhao and I Verzhbitskiy and R Bert\'{e} and G Eda and W L Wilson and G Grinblat and L De S. Menezes and K P Loh and S A Maier},

url = {https://onlinelibrary.wiley.com/doi/abs/10.1002/adom.202202833},

doi = {https://doi.org/10.1002/adom.202202833},

issn = {2195-1071},

year  = {2023},

date = {2023-02-05},

journal = {Advanced Optical Materials},

volume = {11},

number = {7},

pages = {2202833},

abstract = {Abstract Parametric infrared (IR) upconversion is a process in which low-frequency IR photons are upconverted into high-frequency ultraviolet/visible photons through a nonlinear optical process. It is of paramount importance for a wide range of security, material science, and healthcare applications. However, in general, the efficiencies of upconversion processes are typically extremely low for nanometer-scale materials due to the short penetration depth of the excitation fields. Here, parametric IR upconversion processes, including frequency doubling and sum-frequency generation, are studied in layered van der Waals NbOCl2. An upconversion efficiency of up to 0.004% is attained for the NbOCl2 nanosheets, orders of magnitude higher than previously reported values for nonlinear layered materials. The upconverted signal is sensitive to layer numbers, crystal orientation, excitation wavelength, and temperature, and it can be utilized as an optical cross-correlator for ultrashort pulse characterization.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{nokey,

title = {Disorder-Induced Topological State Transition in the Optical Skyrmion Family},

author = {C Liu and S Zhang and S A Maier and H Ren},

url = {https://link.aps.org/doi/10.1103/PhysRevLett.129.267401},

doi = {10.1103/PhysRevLett.129.267401},

year  = {2022},

date = {2022-12-23},

journal = {Physical Review Letters},

volume = {129},

number = {26},

pages = {267401},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{nokey,

title = {Plasmonic bound states in the continuum to tailor light-matter coupling},

author = {A Aigner and A Tittl and J Wang and T Weber and Y Kivshar and S A Maier and H Ren},

url = {https://doi.org/10.1126/sciadv.add4816},

doi = {10.1126/sciadv.add4816},

year  = {2022},

date = {2022-12-09},

journal = {Science Advances},

volume = {8},

number = {49},

pages = {eadd4816},

abstract = {Plasmon resonances play a pivotal role in enhancing light-matter interactions in nanophotonics, but their low-quality factors have hindered applications demanding high spectral selectivity. Here, we demonstrate the design and 3D laser nanoprinting of plasmonic nanofin metasurfaces, which support symmetry-protected bound states in the continuum up to the fourth order. By breaking the nanofins? out-of-plane symmetry in parameter space, we achieve high-quality factor (up to 180) modes under normal incidence. The out-of-plane symmetry breaking can be fine-tuned by the nanofins? triangle angle, opening a pathway to precisely control the ratio of radiative to intrinsic losses. This enables access to the under-, critical, and over-coupled regimes, which we exploit for pixelated molecular sensing. We observe a strong dependence of the sensing performance on the coupling regime, demonstrating the importance of judicious tailoring of light-matter interactions. Our demonstration provides a metasurface platform for enhanced light-matter interaction with a wide range of applications. 3D-nanoprinted plasmonic nanofin metasurfaces with high-quality factor resonances can achieve enhanced light-matter interaction.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{nokey,

title = {Mirror-coupled plasmonic bound states in the continuum for tunable perfect absorption},

author = {J Wang and T Weber and A Aigner and S A Maier and A Tittl},

url = {https://arxiv.org/abs/2211.03673},

doi = {https://doi.org/10.48550/arXiv.2211.03673},

year  = {2022},

date = {2022-11-07},

journal = {arXiv preprint arXiv:2211.03673},

abstract = {Tailoring critical light-matter coupling is a fundamental challenge of nanophotonics, impacting diverse fields from higher harmonic generation and energy conversion to surface-enhanced spectroscopy. Plasmonic perfect absorbers (PAs), where resonant antennas couple to their mirror images in adjacent metal films, have been instrumental for obtaining different coupling regimes by tuning the antenna-film distance. However, for on-chip uses, the ideal PA gap size can only match one wavelength, and wide range multispectral approaches remain challenging. Here, we introduce a new paradigm for plasmonic PAs by combining mirror-coupled resonances with the unique loss engineering capabilities of plasmonic bound states in the continuum (BICs). Our BIC-driven PA platform leverages the asymmetry of the constituent meta-atoms as an additional degree of freedom for reaching the critical coupling (CC) condition, delivering resonances with unity absorbance and high quality factors approaching 100 in the mid-infrared. Such a platform holds flexible tuning knobs including asymmetry parameter, dielectric gap, and geometrical scaling factor to precisely control the coupling condition, resonance frequency, and selective enhancement of magnetic and electric fields while maintaining CC. We demonstrate a pixelated PA metasurface with optimal absorption over a broad range of mid-infrared frequencies (950 ~ 2000 1/cm) using only a single spacer layer thickness and apply it for multispectral surface-enhanced molecular spectroscopy in tailored coupling regimes. Our concept greatly expands the capabilities and flexibility of traditional gap-tuned PAs, opening new perspectives for miniaturized sensing platforms towards on-chip and in-situ detection.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{nokey,

title = {Permittivity-asymmetric quasi-bound states in the continuum},

author = {R Bert\'{e} and T Weber and L D S Menezes and L K\"{u}hner and A Aigner and M Barkey and F J Wendisch and Y S Kivshar and A Tittl and S A Maier},

url = {https://arxiv.org/abs/2211.01176},

doi = {https://doi.org/10.48550/arXiv.2211.01176},

year  = {2022},

date = {2022-11-02},

journal = {arXiv preprint arXiv:2211.01176},

abstract = {Broken symmetries lie at the heart of nontrivial physical phenomena. Breaking the in-plane geometrical symmetry of optical systems allows to access a set of electromagnetic states termed symmetry-protected quasi-bound states in the continuum (qBICs). Here we demonstrate, theoretically, numerically and experimentally, that such optical states can also be accessed in metasurfaces by breaking the in-plane symmetry in the permittivity of the comprising materials, showing a remarkable equivalence to their geometrically-asymmetric counterparts. However, 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 up the possibility of infinitesimal permittivity asymmetries for on-demand, and dynamically tuneable optical resonances of extremely high quality factors. 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 refractive index contrast of the dissimilar materials, surpassing any unwanted asymmetries from nanofabrication defects or angular deviations of light from normal incidence. ε-qBICs can also be excited in 1D gratings, where quality-factor enhancement and tailored interference phenomena via the interplay of geometrical and permittivity asymmetries are numerically demonstrated. The emergence of ε-qBICs in systems with broken symmetries in their permittivity may enable to test time-energy uncertainties in quantum mechanics, and lead to a whole new class of low-footprint optical and optoelectronic devices, from arbitrarily narrow filters and topological sources, biosensing and ultrastrong light-matter interaction platforms, to tuneable optical switches.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{nokey,

title = {Near-Field Retrieval of the Surface Phonon Polariton Dispersion in Free-Standing Silicon Carbide Thin Films},

author = {A Mancini and L Nan and F J Wendisch and R Bert\'{e} and H Ren and E Cort\'{e}s and S A Maier},

url = {https://doi.org/10.1021/acsphotonics.2c01270},

doi = {10.1021/acsphotonics.2c01270},

year  = {2022},

date = {2022-10-20},

journal = {ACS Photonics},

abstract = {Surface phonon polaritons (SPhPs) are mixed light-matter states originating from strong coupling of photons with lattice vibrations. Thin films of polar dielectrics feature a splitting of the SPhP branch due to the hybridization of the top and bottom interface modes. Recently, enhanced in-plane thermal conductivity and near-field energy transfer have been experimentally demonstrated in free-standing polar films. These effects are determined by the SPhP dispersion in these systems, which, however, is yet to be reported experimentally. In this work, we retrieve the SPhP dispersion in silicon carbide free-standing membranes few hundreds of nanometers thick through near-field spectroscopy. We find several branches in the experimental dispersion, which we rationalize as multiple reflections of tip and edge launched SPhPs, in good agreement with theoretical predictions. Our work paves the way to employ large-area free-standing membranes as a platform for phonon polaritonics, with foreseeable applications in the field of thermal management at the nanoscale.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{nokey,

title = {High-Q nanophotonics over the full visible spectrum enabled by hexagonal boron nitride metasurfaces},

author = {L K\"{u}hner and L Sortino and B Tilmann and T Weber and K Watanabe and T Taniguchi and S A Maier and A Tittl},

url = {https://arxiv.org/abs/2210.11314},

doi = {https://doi.org/10.48550/arXiv.2210.11314},

year  = {2022},

date = {2022-10-20},

journal = {arXiv preprint arXiv:2210.11314},

abstract = {All-dielectric optical metasurfaces with high quality (Q) factors have so far been hampered by the lack of simultaneously lossless and high refractive index (RI) materials over the full visible spectrum. To achieve broad spectral coverage, the use of low-index materials is, in fact, unavoidable due to the inverse correlation between the band-gap energy (and therefore the optical losses) and the RI. However, for Mie resonant photonics, smaller RIs are associated with reduced Q factors and mode volume confinement. In this work, we leverage symmetry-broken bound states in the continuum (BICs) to efficiently suppress radiation losses from the low-index (n~2) van der Waals material hexagonal boron nitride (hBN), realizing metasurfaces with high-Q resonances over the complete visible spectrum. In particular, we analyze the rational use of low and high RI materials as resonator components and harness our insights to experimentally demonstrate sharp BIC resonances with Q factors above 300, spanning wavelengths between 400 nm and 1000 nm from a single hBN flake. Moreover, we utilize the enhanced electric near-fields to demonstrate second harmonic generation (SHG) with enhancement factors above 102. Our results provide a theoretical and experimental framework for the implementation of low RI materials as photonic media for metaoptics.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{nokey,

title = {Unlocking the out-of-plane dimension for photonic bound states in the continuum to achieve maximum optical chirality},

author = {L K\"{u}hner and F J Wendisch and A A Antonov and J B\"{u}rger and L H\"{u}ttenhofer and L D S Menezes and S A Maier and M V Gorkunov and Y Kivshar and A Tittl},

url = {https://arxiv.org/abs/2210.05339},

doi = {https://doi.org/10.48550/arXiv.2210.05339},

year  = {2022},

date = {2022-10-11},

journal = {arXiv preprint arXiv:2210.05339},

abstract = {The realization of lossless metasurfaces with true chirality crucially requires the fabrication of three-dimensional structures, constraining their feasibility for experiments and hampering practical implementations. Even though the three-dimensional assembly of metallic nanostructures has been demonstrated previously, the resulting plasmonic resonances suffer from high intrinsic and radiative losses. The concept of photonic bound states in the continuum (BICs) is instrumental for tailoring radiative losses in diverse geometries, especially when implemented using lossless dielectrics, but applications have so far been limited to planar and intrinsically achiral structures. Here, we introduce a novel nanofabrication approach to unlock the height of generally flat all-dielectric metasurfaces as an accessible parameter for efficient resonance and functionality control. In particular, we realize out-of-plane symmetry breaking in quasi-BIC metasurfaces and leverage this design degree of freedom to demonstrate, for the first time, an optical all-dielectric quasi-BIC metasurface with maximum intrinsic chirality that responds selectively to light of a particular circular polarization depending on the structural handedness. Our experimental results not only open a new paradigm for all-dielectric BICs and chiral nanophotonics but also promise advances in the realization of efficient generation of optical angular momentum, holographic metasurfaces, and parity-time symmetry-broken optical systems.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{nokey,

title = {Metasurface Measuring Twisted Light in Turbulence},

author = {T Dinter and C Li and L K\"{u}hner and T Weber and A Tittl and S A Maier and J M Dawes and H Ren},

url = {https://doi.org/10.1021/acsphotonics.2c00800},

doi = {10.1021/acsphotonics.2c00800},

year  = {2022},

date = {2022-09-09},

journal = {ACS Photonics},

volume = {9},

number = {9},

pages = {3043-3051},

abstract = {Orbital angular momentum (OAM) of light represents an independent degree of freedom using orthogonal helical modes for optical and quantum multiplexing, offering great potential to transform future ultrahigh-bandwidth information systems. Practical OAM communication systems suffer from turbulence-induced phase distortions to the propagating beams, decreasing the orthogonality of OAM modes through introduced modal crosstalk. To date, optical systems used for measuring OAM orthogonality breakdown in different turbulence conditions are too bulky and slow (e.g., one OAM mode at a time) for any practical use. Here, we demonstrate the use of an ultrathin OAM mode-sorting metasurface for characterizing the OAM orthogonality breakdown under different turbulence conditions. Our approach allows the measurement of the whole OAM spectrum at the same time. This metasurface exhibits strong OAM selectivity with an average modal crosstalk below −42.4 dB for OAM modes with topological charges ranging from −15 to +15. Our results suggest that higher-order OAM modes are as robust as lower-order modes in particular turbulence environments, paving the way for future practical free-space OAM communications harnessing high-dimensional OAM multiplexing. We demonstrated that a flat optical device with a small form factor can be integrated with practical communication systems for compact, fast, and efficient generation and detection of twisted light.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{nokey,

title = {Strong light-matter interaction with self-hybridized bound states in the continuum in monolithic van der Waals metasurfaces},

author = {T Weber and L K\"{u}hner and L Sortino and A B Mhenni and N P Wilson and J K\"{u}hne and J J Finley and S A Maier and A Tittl},

url = {https://arxiv.org/abs/2209.01944},

doi = {https://doi.org/10.48550/arXiv.2209.01944},

year  = {2022},

date = {2022-09-05},

journal = {arXiv preprint arXiv:2209.01944},

abstract = {Photonic bound states in the continuum (BICs) are a standout nanophotonic platform for strong light-matter coupling with transition metal dichalcogenides (TMDCs), but have so far mostly been employed as all-dielectric metasurfaces with adjacent TMDC layers, incurring limitations related to strain, mode overlap, and material integration. In this work, we experimentally demonstrate for the first time asymmetry-dependent BIC resonances in 2D arrays of monolithic metasurfaces composed solely of the nanostructured bulk TMDC WS2 with BIC modes exhibiting sharp and tailored linewidths, ideal for selectively enhancing light-matter interactions. Geometrical variation enables the tuning of the BIC resonances across the exciton resonance in bulk WS2, revealing the strong-coupling regime with an anti-crossing pattern and a Rabi splitting of 116 meV. The precise control over the radiative loss channel provided by the BIC concept is harnessed to tailor the Rabi splitting via a geometrical asymmetry parameter of the metasurface. Crucially, the coupling strength itself can be controlled and is shown to be independent of material-intrinsic losses. Our BIC-driven monolithic metasurface platform can readily incorporate other TMDCs or excitonic materials to deliver previously unavailable fundamental insights and practical device concepts for polaritonic applications.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{nokey,

title = {3D-Nanoprinted Antiresonant Hollow-Core Microgap Waveguide: An on-Chip Platform for Integrated Photonic Devices and Sensors},

author = {J B\"{u}rger and V Schalles and J Kim and B Jang and M Zeisberger and J Gargiulo and L De S. Menezes and M A Schmidt and S A Maier},

url = {https://doi.org/10.1021/acsphotonics.2c00725},

doi = {10.1021/acsphotonics.2c00725},

year  = {2022},

date = {2022-09-02},

journal = {ACS Photonics},

volume = {9},

number = {9},

pages = {3012-3024},

abstract = {Due to their unique capabilities, hollow-core waveguides are playing an increasingly important role, especially in meeting the growing demand for integrated and low-cost photonic devices and sensors. Here, we present the antiresonant hollow-core microgap waveguide as a platform for the on-chip investigation of light-gas interaction over centimeter-long distances. The design consists of hollow-core segments separated by gaps that allow external access to the core region, while samples with lengths up to 5 cm were realized on silicon chips through 3D-nanoprinting using two-photon absorption based direct laser writing. The agreement of mathematical models, numerical simulations and experiments illustrates the importance of the antiresonance effect in that context. Our study shows the modal loss, the effect of gap size and the spectral tuning potential, with highlights including extremely broadband transmission windows (\>200 nm), very high contrast resonance (\>60 dB), exceptionally high structural openness factor (18%) and spectral control by nanoprinting (control over dimensions with step sizes (i.e., increments) of 60 nm). The application potential was demonstrated in the context of laser scanning absorption spectroscopy of ammonia, showing diffusion speeds comparable to bulk diffusion and a low detection limit. Due to these unique properties, application of this platform can be anticipated in a variety of spectroscopy-related fields, including bioanalytics, environmental sciences, and life sciences.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{nokey,

title = {Introducing a Symmetry-Breaking Coupler into a Dielectric Metasurface Enables Robust High-Q Quasi-BICs},

author = {G Q Moretti and A Tittl and E Cort\'{e}s and S A Maier and A V Bragas and G Grinblat},

url = {https://onlinelibrary.wiley.com/doi/abs/10.1002/adpr.202200111},

doi = {https://doi.org/10.1002/adpr.202200111},

issn = {2699-9293},

year  = {2022},

date = {2022-08-21},

journal = {Advanced Photonics Research},

volume = {n/a},

number = {n/a},

pages = {2200111},

abstract = {Dielectric metasurfaces supporting quasibound states in the continuum (quasi-BICs) exhibit very high-quality factor resonances and electric field confinement. However, accessing the high-Q end of the quasi-BIC regime usually requires marginally distorting the metasurface design from a BIC condition, pushing the needed nanoscale fabrication precision to the limit. This work introduces a novel concept for generating high-Q quasi-BICs, which strongly relaxes this requirement by incorporating a relatively large perturbative element close to high-symmetry points of an undistorted BIC metasurface, acting as a coupler to the radiation continuum. This approach is validated by adding a ≈100 nm diameter cylinder between two reflection-symmetry points separated by a 300 nm gap in an elliptical disk metasurface unit cell, using gallium phosphide as the dielectric. It is found that high-Q resonances emerge when the cylindrical coupler is placed at any position between such symmetry points. This metasurface's second harmonic generation capability in the optical range is further explored. Displacing the coupler as much as a full diameter from a BIC condition produces record-breaking normalized conversion efficiencies \>102 W−1. The strategy of enclosing a disruptive element between multiple high-symmetry points in a BIC metasurface can be applied to construct robust high-Q quasi-BICs in many geometrical designs.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{nokey,

title = {Strong Polarization Dependent Nonlinear Excitation of a Perovskite Nanocrystal Monolayer on a Chiral Dielectric Nanoantenna Array},

author = {I Vin\c{c}on and F J Wendisch and D De Gregorio and S D Pritzl and Q A Akkerman and H Ren and L De S. Menezes and S A Maier and J Feldmann},

url = {https://doi.org/10.1021/acsphotonics.2c00159},

doi = {10.1021/acsphotonics.2c00159},

year  = {2022},

date = {2022-08-17},

urldate = {2022-08-17},

journal = {ACS Photonics},

volume = {9},

issue = {11},

pages = {3506-3514},

abstract = {With their unique optoelectronic properties, perovskite nanocrystals are highly advantageous semiconductor materials for tailored light applications including an interaction with circularly polarized light. Although chiral perovskite nanocrystals have been obtained by the adsorption of chiral molecules, their chiroptical response is still intrinsically weak. Alternatively, perovskites have been combined with artificial chiral surfaces demonstrating enhanced chiroptical responses. However, bulk perovskite films of considerable thickness were required, mitigating the perovskite’s photoluminescence efficiency and processability. Here we developed a hybrid system of a dielectric chiral nanoantenna array that was coated with a monolayer of cubic all-inorganic lead halide perovskite nanocrystals. By tuning the thickness of the perovskite film down to one monolayer of nanocrystals, we restricted the interactions exclusively to the near-field regime. The chiral surface built of z-shaped Si nanoantennas features pronounced chiral resonances in the visible to IR region. We demonstrate that the two-photon excited photoluminescence emission of the nanocrystals can be enhanced by up to one order of magnitude in this configuration. This emission increase is controllable by the choice of the excitation wavelength and polarization with an asymmetry in emission of up to 25% upon left and right circularly polarized illumination. Altogether, our findings demonstrate a pathway to an all-optical control and modulation of perovskite light emission via strong polarization sensitive light\textendashmatter interactions in the near-field, rendering this hybrid system interesting for sensing and display technologies.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{nokey,

title = {Catalytic Metasurfaces Empowered by Bound States in the Continuum},

author = {H Hu and T Weber and O Bienek and A Wester and L H\"{u}ttenhofer and I D Sharp and S A Maier and A Tittl and E Cort\'{e}s},

url = {https://doi.org/10.1021/acsnano.2c05680},

doi = {10.1021/acsnano.2c05680},

issn = {1936-0851},

year  = {2022},

date = {2022-08-11},

journal = {ACS Nano},

volume = {16},

number = {8},

pages = {13057-13068},

abstract = {Photocatalytic platforms based on ultrathin reactive materials facilitate carrier transport and extraction but are typically restricted to a narrow set of materials and spectral operating ranges due to limited absorption and poor energy-tuning possibilities. Metasurfaces, a class of 2D artificial materials based on the electromagnetic design of nanophotonic resonators, allow optical absorption engineering for a wide range of materials. Moreover, tailored resonances in nanostructured materials enable strong absorption enhancement and thus carrier multiplication. Here, we develop an ultrathin catalytic metasurface platform that leverages the combination of loss-engineered substoichiometric titanium oxide (TiO2\textendashx) and the emerging physical concept of optical bound states in the continuum (BICs) to boost photocatalytic activity and provide broad spectral tunability. We demonstrate that our platform reaches the condition of critical light coupling in a TiO2\textendashx BIC metasurface, thus providing a general framework for maximizing light\textendashmatter interactions in diverse photocatalytic materials. This approach can avoid the long-standing drawbacks of many naturally occurring semiconductor-based ultrathin films applied in photocatalysis, such as poor spectral tunability and limited absorption manipulation. Our results are broadly applicable to fields beyond photocatalysis, including photovoltaics and photodetectors.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{nokey,

title = {Mechanistic Insights into OC\textendashCOH Coupling in CO2 Electroreduction on Fragmented Copper},

author = {K Yao and J Li and H Wang and R Lu and X Yang and M Luo and N Wang and Z Wang and C Liu and T Jing and S Chen and E Cort\'{e}s and S A Maier and S Zhang and T Li and Y Yu and Y Liu and X Kang and H Liang},

url = {https://doi.org/10.1021/jacs.2c01044},

doi = {10.1021/jacs.2c01044},

issn = {0002-7863},

year  = {2022},

date = {2022-07-29},

journal = {Journal of the American Chemical Society},

volume = {144},

number = {31},

pages = {14005-14011},

abstract = {The carbon\textendashcarbon (C\textendashC) bond formation is essential for the electroconversion of CO2 into high-energy-density C2+ products, and the precise coupling pathways remain controversial. Although recent computational investigations have proposed that the OC\textendashCOH coupling pathway is more favorable in specific reaction conditions than the well-known CO dimerization pathway, the experimental evidence is still lacking, partly due to the separated catalyst design and mechanistic/spectroscopic exploration. Here, we employ density functional theory calculations to show that on low-coordinated copper sites, the *CO bindings are strengthened, and the adsorbed *CO coupling with their hydrogenation species, *COH, receives precedence over CO dimerization. Experimentally, we construct a fragmented Cu catalyst with abundant low-coordinated sites, exhibiting a 77.8% Faradaic efficiency for C2+ products at 300 mA cm\textendash2. With a suite of in situ spectroscopic studies, we capture an *OCCOH intermediate on the fragmented Cu surfaces, providing direct evidence to support the OC\textendashCOH coupling pathway. The mechanistic insights of this research elucidate how to design materials in favor of OC\textendashCOH coupling toward efficient C2+ production from CO2 reduction.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{nokey,

title = {Giant second-harmonic generation in ferroelectric NbOI2},

author = {I Abdelwahab and B Tilmann and Y Wu and D Giovanni and I Verzhbitskiy and M Zhu and R Bert\'{e} and F Xuan and L D S Menezes and G Eda and T C Sum and S Y Quek and S A Maier and K P Loh},

url = {https://doi.org/10.1038/s41566-022-01021-y},

doi = {10.1038/s41566-022-01021-y},

issn = {1749-4893},

year  = {2022},

date = {2022-06-30},

journal = {Nature Photonics},

abstract = {Implementing nonlinear optical components in nanoscale photonic devices is challenged by phase-matching conditions requiring thicknesses in the order of hundreds of wavelengths, and is disadvantaged by the short optical interaction depth of nanometre-scale materials and weak photon\textendashphoton interactions. Here we report that ferroelectric NbOI2 nanosheets exhibit giant second-harmonic generation with conversion efficiencies that are orders of magnitude higher than commonly reported nonlinear crystals. The nonlinear response scales with layer thickness and is strain- and electrical-tunable; a record \>0.2% absolute SHG conversion efficiency and an effective nonlinear susceptibility $$chi _mathrmeff^(2)$$in the order of 10−9 m V−1 are demonstrated at an average pump intensity of 8 kW cm\textendash2. Due to the interplay between anisotropic polarization and excitonic resonance in NbOI2, the spatial profile of the polarized SHG response can be tuned by the excitation wavelength. Our results represent a new paradigm for ultrathin, efficient nonlinear optical components.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{nokey,

title = {Imaging elliptically polarized infrared near-fields on nanoparticles by strong-field dissociation of functional surface groups},

author = {P Rosenberger and R Dagar and W Zhang and A Sousa-Castillo and M Neuhaus and E Cortes and S A Maier and C Costa-Vera and M F Kling and B Bergues},

url = {https://doi.org/10.1140/epjd/s10053-022-00430-6},

doi = {10.1140/epjd/s10053-022-00430-6},

issn = {1434-6079},

year  = {2022},

date = {2022-06-27},

journal = {The European Physical Journal D},

volume = {76},

number = {6},

pages = {109},

abstract = {We investigate the strong-field ion emission from the surface of isolated silica nanoparticles aerosolized from an alcoholic solution, and demonstrate the applicability of the recently reported near-field imaging at 720 nm [Rupp et al., Nat. Comm., 10(1):4655, 2019] to longer wavelength (2 $$mu $$m) and polarizations with arbitrary ellipticity. Based on the experimental observations, we discuss the validity of a previously introduced semi-classical model, which is based on near-field driven charge generation by a Monte-Carlo approach and classical propagation. We furthermore clarify the role of the solvent in the surface composition of the nanoparticles in the interaction region. We find that upon injection of the nanoparticles into the vacuum, the alcoholic solvent evaporates on millisecond time scales, and that the generated ions originate predominantly from covalent bonds with the silica surface rather than from physisorbed solvent molecules. These findings have important implications for the development of future theoretical models of the strong-field ion emission from silica nanoparticles, and the application of near-field imaging and reaction dynamics of functional groups on isolated nanoparticles.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{nokey,

title = {Low Band Gap Perovskite Concentrator Solar Cells: Physics, Device Simulation, and Experiment},

author = {T Ma and Y An and S Li and Y Zhao and H Wang and C Wang and S A Maier and X Li},

url = {https://doi.org/10.1021/acsami.2c06393},

doi = {10.1021/acsami.2c06393},

issn = {1944-8244},

year  = {2022},

date = {2022-06-22},

journal = {ACS Applied Materials \& Interfaces},

volume = {14},

number = {26},

pages = {29856-29866},

abstract = {Perovskite solar cells (PSCs) own rapidly increasing power conversion efficiencies (PCEs), but their concentrated counterparts (i.e., PCSCs) show a much lower performance. A deeper understanding of PCSCs relies on a thorough study of the intensive energy losses of the device along with increasing the illumination intensity. Taking the low band gap Sn\textendashPb PCSC as an example, we realize a device-level optoelectronic simulation to thoroughly disclose the internal photovoltaic physics and mechanisms by addressing the fundamental electromagnetic and carrier-transport processes within PCSCs under various concentration conditions. We find that the primary factor limiting the performance improvement of PCSCs is the significantly increased bulk recombination under the increased light concentration, which is attributed mostly to the inferior transport/collection ability of holes determined by the hole transport layer (HTL). We perform further electrical manipulation on the perovskite layer and the HTL so that the carrier-transport capability is significantly improved. Under the optoelectronic design, we fabricate low band gap PCSCs, which exhibit particularly high PCEs of up to 22.36% at 4.17 sun.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{nokey,

title = {Optical Metasurfaces for Energy Conversion},

author = {E Cort\'{e}s and F J Wendisch and L Sortino and A Mancini and S Ezendam and S Saris and L De S. Menezes and A Tittl and H Ren and S A Maier},

url = {https://doi.org/10.1021/acs.chemrev.2c00078},

doi = {10.1021/acs.chemrev.2c00078},

issn = {0009-2665},

year  = {2022},

date = {2022-06-21},

journal = {Chemical Reviews},

volume = {122},

number = {19},

pages = {15082-15176},

abstract = {Nanostructured surfaces with designed optical functionalities, such as metasurfaces, allow efficient harvesting of light at the nanoscale, enhancing light\textendashmatter interactions for a wide variety of material combinations. Exploiting light-driven matter excitations in these artificial materials opens up a new dimension in the conversion and management of energy at the nanoscale. In this review, we outline the impact, opportunities, applications, and challenges of optical metasurfaces in converting the energy of incoming photons into frequency-shifted photons, phonons, and energetic charge carriers. A myriad of opportunities await for the utilization of the converted energy. Here we cover the most pertinent aspects from a fundamental nanoscopic viewpoint all the way to applications.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{nokey,

title = {Radial bound states in the continuum for polarization-invariant nanophotonics},

author = {L K\"{u}hner and L Sortino and R Bert\'{e} and J Wang and H Ren and S A Maier and Y S Kivshar and A Tittl},

url = {https://arxiv.org/abs/2206.05206},

doi = {https://doi.org/10.48550/arXiv.2206.05206},

year  = {2022},

date = {2022-06-10},

journal = {arXiv preprint arXiv:2206.05206},

abstract = {All-dielectric nanophotonics underpinned by bound states in the continuum (BICs) have demonstrated breakthrough applications in nanoscale light manipulation, frequency conversion and optical sensing. Leading BIC implementations range from isolated nanoantennas with localized electromagnetic fields to symmetry-protected metasurfaces with controllable resonance quality (Q) factors. However, they either require structured light illumination with complex beamshaping optics or large, fabrication-intense arrays of polarization-sensitive unit cells, hindering tailored nanophotonic applications and on-chip integration. Here, we introduce radial quasi bound states in the continuum (rBICs) as a new class of radially distributed electromagnetic modes controlled by structural asymmetry in a ring of dielectric rod pair resonators. The rBIC platform provides polarization-invariant and tunable high-Q resonances with strongly enhanced near-fields in an ultracompact footprint as low as 2 μm2. We demonstrate rBIC realizations in the visible for sensitive biomolecular detection and enhanced second-harmonic generation from monolayers of transition metal dichalcogenides, opening new perspectives for compact, spectrally selective, and polarization-invariant metadevices for multi-functional light-matter coupling, multiplexed sensing, and high-density on-chip photonics.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{nokey,

title = {All-optical nanoscopic spatial control of molecular reaction yields on nanoparticles},

author = {W Zhang and R Dagar and P Rosenberger and A Sousa-Castillo and M Neuhaus and W Li and S A Khan and A S Alnaser and E Cortes and S A Maier and C Costa-Vera and M F Kling and B Bergues},

url = {http://opg.optica.org/optica/abstract.cfm?URI=optica-9-5-551},

doi = {10.1364/OPTICA.453915},

year  = {2022},

date = {2022-05-20},

journal = {Optica},

volume = {9},

number = {5},

pages = {551-560},

abstract = {Molecular adsorbate reactions on nanoparticles play a fundamental role in areas such as nano-photocatalysis, atmospheric, and astrochemistry. They can be induced, enhanced, and controlled by field localization and enhancement on the nanoparticle surface. In particular, the ability to perform highly controlled near-field-mediated reactions is key to deepening our understanding of surface photoactivity on nanosystems. Here, using reaction nanoscopy, we experimentally demonstrate all-optical nanoscopic control of surface reaction yields by tailoring the near fields on nanoparticles with waveform-controlled linear and bicircular two-color laser pulses, respectively. We observe site-selective proton emission from the dissociative ionization of adsorbate molecules on SiO2 nanoparticles as a function of the polarization and relative phase of the two-color pulses. The angularly resolved close-to-uniform mapping between the surface reaction yields and the measured ion momentum enables the observation and spatial control of molecular reactions on the nanoparticle surface with nanoscopic resolution. The experimental results are modeled and reproduced qualitatively by classical trajectory Monte Carlo simulations. Our work paves the way toward reliable all-optical control of photocatalytic chemical reactions on nanoscale surfaces.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{nokey,

title = {Controlling Plasmonic Chemistry Pathways through Specific Ion Effects},

author = {A Stefancu and L Nan and L Zhu and V Chiș and I Bald and M Liu and N Leopold and S A Maier and E Cortes},

url = {https://onlinelibrary.wiley.com/doi/abs/10.1002/adom.202200397},

doi = {https://doi.org/10.1002/adom.202200397},

issn = {2195-1071},

year  = {2022},

date = {2022-05-11},

journal = {Advanced Optical Materials},

volume = {n/a},

number = {n/a},

pages = {2200397},

abstract = {Abstract Plasmon-driven dehalogenation of brominated purines has been recently explored as a model system to understand fundamental aspects of plasmon-assisted chemical reactions. Here, it is shown that divalent Ca2+ ions strongly bridge the adsorption of bromoadenine (Br-Ade) to Ag surfaces. Such ion-mediated binding increases the molecule's adsorption energy leading to an overlap of the metal energy states and the molecular states, enabling the chemical interface damping (CID) of the plasmon modes of the Ag nanostructures (i.e., direct electron transfer from the metal to Br-Ade). Consequently, the conversion of Br-Ade to adenine almost doubles following the addition of Ca2+. These experimental results, supported by theoretical calculations of the local density of states of the Ag/Br-Ade complex, indicate a change of the charge transfer pathway driving the dehalogenation reaction, from Landau damping (in the lack of Ca2+ ions) to CID (after the addition of Ca2+). The results show that the surface dynamics of chemical species (including water molecules) play an essential role in charge transfer at plasmonic interfaces and cannot be ignored. It is envisioned that these results will help in designing more efficient nanoreactors, harnessing the full potential of plasmon-assisted chemistry.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{nokey,

title = {Introducing a Symmetry-Breaking Coupler into a Dielectric Metasurface Enables Robust High-Q Quasibound States in the Continuum and Efficient Nonlinear Frequency Conversion},

author = {G Q Moretti and A Tittl and E Cort\'{e}s and S A Maier and A V Bragas and G Grinblat},

url = {https://doi.org/10.48550/arXiv.2204.07097},

doi = {https://doi.org/10.48550/arXiv.2204.07097},

year  = {2022},

date = {2022-04-14},

journal = {arXiv preprint arXiv:2204.07097},

abstract = {Dielectric metasurfaces supporting quasi-bound states in the continuum (quasi-BICs) exhibit very high quality factor resonances and electric field confinement. However, accessing the high-Q end of the quasi-BIC regime usually requires marginally distorting the metasurface design from a BIC condition, pushing the needed nanoscale fabrication precision to the limit. This work introduces a novel concept for generating high-Q quasi-BICs, which strongly relaxes this requirement by incorporating a relatively large perturbative element close to high-symmetry points of an undistorted BIC metasurface, acting as a coupler to the radiation continuum. We validate this approach by adding a ∼100 nm diameter cylinder between two reflection-symmetry points separated by a 300 nm gap in an elliptical disk metasurface unit cell, using gallium phosphide as the dielectric. We find that high-Q resonances emerge when the cylindrical coupler is placed at any position between such symmetry points. We further explore this metasurface's second harmonic generation capability in the optical range. Displacing the coupler as much as a full diameter from a BIC condition produces record-breaking normalized conversion efficiencies \>102 W−1. The strategy of enclosing a disruptive element between multiple high-symmetry points in a BIC metasurface could be applied to construct robust high-Q quasi-BICs in many geometrical designs.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{nokey,

title = {High-Throughput Fabrication of Triangular Nanogap Arrays for Surface-Enhanced Raman Spectroscopy},

author = {S Luo and A Mancini and F Wang and J Liu and S A Maier and J C De Mello},

url = {https://doi.org/10.1021/acsnano.1c09930},

doi = {10.1021/acsnano.1c09930},

issn = {1936-0851},

year  = {2022},

date = {2022-04-05},

journal = {ACS Nano},

abstract = {Squeezing light into nanometer-sized metallic nanogaps can generate extremely high near-field intensities, resulting in dramatically enhanced absorption, emission, and Raman scattering of target molecules embedded within the gaps. However, the scarcity of low-cost, high-throughput, and reproducible nanogap fabrication methods offering precise control over the gap size is a continuing obstacle to practical applications. Using a combination of molecular self-assembly, colloidal nanosphere lithography, and physical peeling, we report here a high-throughput method for fabricating large-area arrays of triangular nanogaps that allow the gap width to be tuned from ∼10 to ∼3 nm. The nanogap arrays function as high-performance substrates for surface-enhanced Raman spectroscopy (SERS), with measured enhancement factors as high as 108 relative to a thin gold film. Using the nanogap arrays, methylene blue dye molecules can be detected at concentrations as low as 1 pM, while adenine biomolecules can be detected down to 100 pM. We further show that it is possible to achieve sensitive SERS detection on binary-metal nanogap arrays containing gold and platinum, potentially extending SERS detection to the investigation of reactive species at platinum-based catalytic and electrochemical surfaces.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{nokey,

title = {Experimental characterization techniques for plasmon-assisted chemistry},

author = {E Cort\'{e}s and R Grzeschik and S A Maier and S Schl\"{u}cker},

doi = {10.1038/s41570-022-00368-8},

issn = {2397-3358},

year  = {2022},

date = {2022-03-28},

journal = {Nat Rev Chem},

volume = {6},

number = {4},

pages = {259-274},

abstract = {Plasmon-assisted chemistry is the result of a complex interplay between electromagnetic near fields, heat and charge transfer on the nanoscale. The disentanglement of their roles is non-trivial. Therefore, a thorough knowledge of the chemical, structural and spectral properties of the plasmonic/molecular system being used is required. Specific techniques are needed to fully characterize optical near fields, temperature and hot carriers with spatial, energetic and/or temporal resolution. The timescales for all relevant physical and chemical processes can range from a few femtoseconds to milliseconds, which necessitates the use of time-resolved techniques for monitoring the underlying dynamics. In this Review, we focus on experimental techniques to tackle these challenges. We further outline the difficulties when going from the ensemble level to single-particle measurements. Finally, a thorough understanding of plasmon-assisted chemistry also requires a substantial joint experimental and theoretical effort.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{nokey,

title = {Trends in Nanophotonics-Enabled Optofluidic Biosensors},

author = {J Wang and S A Maier and A Tittl},

url = {https://onlinelibrary.wiley.com/doi/abs/10.1002/adom.202102366},

doi = {https://doi.org/10.1002/adom.202102366},

issn = {2195-1071},

year  = {2022},

date = {2022-02-22},

journal = {Advanced Optical Materials},

volume = {n/a},

number = {n/a},

pages = {2102366},

abstract = {Abstract Optofluidic sensors integrate photonics with micro/nanofluidics to realize compact devices for the label-free detection of molecules and the real-time monitoring of dynamic surface binding events with high specificity, ultrahigh sensitivity, low detection limit, and multiplexing capability. Nanophotonic structures composed of metallic and/or dielectric building blocks excel at focusing light into ultrasmall volumes, creating enhanced electromagnetic near-fields ideal for amplifying the molecular signal readout. Furthermore, fluidic control on small length scales enables precise tailoring of the spatial overlap between the electromagnetic hotspots and the analytes, boosting light-matter interaction, and can be utilized to integrate advanced functionalities for the pre-treatment of samples in real-world-use cases, such as purification, separation, or dilution. In this review, the authors highlight current trends in nanophotonics-enabled optofluidic biosensors for applications in the life sciences while providing a detailed perspective on how these approaches can synergistically amplify the optical signal readout and achieve real-time dynamic monitoring, which is crucial in biomedical assays and clinical diagnostics.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{nokey,

title = {Ultrafast sub-100 fs all-optical modulation and efficient third-harmonic generation in Weyl semimetal niobium phosphide thin films},

author = {B Tilmann and A K Pandeya and G Grinblat and L D S Menezes and Y Li and C Shekhar and C Felser and S S P Parkin and A Bedoya-Pinto and S A Maier},

url = {https://onlinelibrary.wiley.com/doi/abs/10.1002/adma.202106733},

doi = {https://doi.org/10.1002/adma.202106733},

issn = {0935-9648},

year  = {2022},

date = {2022-02-16},

journal = {Advanced Materials},

volume = {n/a},

number = {n/a},

pages = {2106733},

abstract = {Abstract Since their experimental discovery in 2015, Weyl semimetals generated a large amount of attention due their intriguing physical properties that arise from their linear electron dispersion relation and topological surface states. In particular in the field of nonlinear (NL) optics and light harvesting, Weyl semimetals have shown outstanding performances and achieved record NL conversion coefficients. In this context, we perform first steps towards Weyl semimetal nanophotonics by thoroughly characterizing the linear and NL optical behavior of epitaxially grown niobium phosphide (NbP) thin films, covering the visible to near-infrared regime of the electromagnetic spectrum. Despite the measured high linear absorption, third-harmonic generation studies demonstrate high conversion efficiencies up to 10-4%, that can be attributed to the topological electron states at the surface of the material. Furthermore, nondegenerate pump-probe measurements with sub-10 fs pulses reveal a maximum modulation depth of about 1%, completely decaying within 100 fs and therefore suggesting the possibility of developing devices based on NbP with all-optical switching bandwidths of up to 10 THz. Altogether, our work reveals promising NL optical properties of Weyl semimetal thin films that are outperforming bulk crystals of the same material, laying the grounds for nanoscale applications, enabled by top-down nanostructuring, such as light-harvesting, on-chip frequency conversion and all-optical processing. This article is protected by copyright. All rights reserved},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{nokey,

title = {Accelerating CO2 Electroreduction to Multicarbon Products via Synergistic Electric\textendashThermal Field on Copper Nanoneedles},

author = {B Yang and K Liu and H Li and C Liu and J Fu and H Li and J E Huang and P Ou and T Alkayyali and C Cai and Y Duan and H Liu and P An and N Zhang and W Li and X Qiu and C Jia and J Hu and L Chai and Z Lin and Y Gao and M Miyauchi and E Cort\'{e}s and S A Maier and M Liu},

url = {https://doi.org/10.1021/jacs.1c11253},

doi = {10.1021/jacs.1c11253},

issn = {0002-7863},

year  = {2022},

date = {2022-02-03},

urldate = {2022-02-03},

journal = {Journal of the American Chemical Society},

abstract = {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\textendashC 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\textendashC 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\textendashthermal 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\textendash2 and a record-high C2 turnover frequency of 11.5 ± 0.3 s\textendash1 Cu site\textendash1. Combined with its low cost and scalability, the electric\textendashthermal 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.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{nokey,

title = {High-Quality Optical Hotspots with Topology-Protected Robustness},

author = {C Liu and S A Maier},

url = {https://doi.org/10.1021/acsphotonics.1c01445},

doi = {10.1021/acsphotonics.1c01445},

year  = {2021},

date = {2021-12-23},

journal = {ACS Photonics},

abstract = {Optical hotspots underpin a wide variety of photonic devices ranging from sensing, nonlinear generation to photocatalysis, taking advantage of the strong light\textendashmatter interaction at the vicinity of photonic nanostructures. While plasmonic nanostructures have been widely used for strongly localized electromagnetic energy on surfaces, they suffer from high loss and consequently a low quality factor. Resonance-based dielectric structures provide an alternative solution with a larger quality factor, but there is a mismatch between the maximum values of the light confinement (quality factor) and the leakage (intensity in the near-field). Here, we propose to apply the concept of topological photonics to the formation of hotspots, producing them in both topological edge states and topological corner states. The topology secures strong light localization at the surface of the nanostructures where the underlying topological invariant shows a jump, generating a field hotspot with simultaneous increment of quality factor and light intensity. Meanwhile, it leverages a good robustness to fabrication imperfection including fluctuation in shape and misalignment. After a systematic investigation and comparison of the robustness between 1D and 2D topological structures, we conclude that the hotspots from 1D topological edge states promise a fertile playground for emerging applications that require both enhanced light intensity and high spectral resolution.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{nokey,

title = {Probing the Role of Atomic Defects in Photocatalytic Systems through Photoinduced Enhanced Raman Scattering},

author = {D Glass and R Quesada-Cabrera and S Bardey and P Promdet and R Sapienza and V Keller and S A Maier and V Caps and I P Parkin and E Cort\'{e}s},

url = {https://doi.org/10.1021/acsenergylett.1c01772},

doi = {10.1021/acsenergylett.1c01772},

year  = {2021},

date = {2021-11-10},

journal = {ACS Energy Letters},

pages = {4273-4281},

abstract = {Even in ultralow quantities, oxygen vacancies (VO) drastically impact key properties of metal oxide semiconductors, such as charge transport, surface adsorption, and reactivity, playing central roles in functional materials performance. Current methods used to investigate VO often rely on specialized instrumentation under far from ideal reaction conditions. Hence, the influence of VO generated in situ during catalytic processes has yet to be probed. In this work, we assess in situ extrinsic surface VO formation and lifetime under photocatalytic conditions which we compare to photocatalytic performance. We show for the first time that lifetimes of in situ generated atomic VO play more significant roles in catalysis than their concentration, with strong correlations between longer-lived VO and higher photocatalytic activity. Our results indicate that enhanced photocatalytic efficiency correlates with goldilocks VO concentrations, where VO densities must be just right to encourage carrier transport while avoiding charge carrier trapping.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{nokey,

title = {Scalable Fabrication of Metallic Nanogaps at the Sub-10 nm Level},

author = {S Luo and B H Hoff and S A Maier and J C De Mello},

doi = {10.1002/advs.202102756},

issn = {2198-3844},

year  = {2021},

date = {2021-10-31},

journal = {Adv Sci (Weinh)},

pages = {e2102756},

abstract = {Metallic nanogaps with metal-metal separations of less than 10 nm have many applications in nanoscale photonics and electronics. However, their fabrication remains a considerable challenge, especially for applications that require patterning of nanoscale features over macroscopic length-scales. Here, some of the most promising techniques for nanogap fabrication are evaluated, covering established technologies such as photolithography, electron-beam lithography (EBL), and focused ion beam (FIB) milling, plus a number of newer methods that use novel electrochemical and mechanical means to effect the patterning. The physical principles behind each method are reviewed and their strengths and limitations for nanogap patterning in terms of resolution, fidelity, speed, ease of implementation, versatility, and scalability to large substrate sizes are discussed.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{nokey,

title = {Metasurface Photoelectrodes for Enhanced Solar Fuel Generation},

author = {L H\"{u}ttenhofer and M Golibrzuch and O Bienek and F J Wendisch and R Lin and M Becherer and I D Sharp and S A Maier and E Cort\'{e}s},

url = {https://onlinelibrary.wiley.com/doi/abs/10.1002/aenm.202102877},

doi = {https://doi.org/10.1002/aenm.202102877},

issn = {1614-6832},

year  = {2021},

date = {2021-10-27},

journal = {Advanced Energy Materials},

volume = {11},

number = {46},

pages = {2102877},

abstract = {Abstract Tailoring optical properties in photocatalysts by nanostructuring them can help increase solar light harvesting efficiencies in a wide range of materials. Whereas plasmon resonances are widely employed in metallic catalysts for this purpose, latest advances of nonradiative, dielectric nanophotonics also enable light confinement and enhanced visible light absorption in semiconductors. Here, a design procedure for large-scale nanofabrication of semiconductor photoelectrodes using imprint lithography is developed. Anapole excitations and metasurface lattice resonances are combined to enhance the absorption of the model material, amorphous gallium phosphide (a-GaP), over the visible spectrum. It is shown that cost-effective, high sample throughput is achieved while retaining the precise signature of the engineered photonic states. Photoelectrochemical measurements under hydrogen evolution reaction conditions and sunlight illumination reveal the contributions of the respective resonances and demonstrate an overall photocurrent enhancement of 5.7, compared to a planar film. These results are supported by optical and numerical analysis of single nanodisks and of the upscaled metasurface.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{nokey,

title = {Tip Coupling and Array Effects of Gold Nanoantennas in Near-Field Microscopy},

author = {R B\"{u}chner and T Weber and L K\"{u}hner and S A Maier and A Tittl},

url = {https://doi.org/10.1021/acsphotonics.1c00744},

doi = {10.1021/acsphotonics.1c00744},

year  = {2021},

date = {2021-10-14},

journal = {ACS Photonics},

abstract = {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\textendashantenna 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.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{nokey,

title = {The Effect of Photoinduced Surface Oxygen Vacancies on the Charge Carrier Dynamics in TiO2 Films},

author = {O E Dagdeviren and D Glass and R Sapienza and E Cort\'{e}s and S A Maier and I P Parkin and P Gr\"{u}tter and R Quesada-Cabrera},

url = {https://doi.org/10.1021/acs.nanolett.1c02853},

doi = {10.1021/acs.nanolett.1c02853},

issn = {1530-6984},

year  = {2021},

date = {2021-09-28},

journal = {Nano Letters},

volume = {21},

number = {19},

pages = {8348-8354},

abstract = {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.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{nokey,

title = {Acoustic Coupling between Plasmonic Nanoantennas: Detection and Directionality of Surface Acoustic Waves},

author = {M Poblet and R Bert\'{e} and H D Boggiano and Y Li and E Cort\'{e}s and G Grinblat and S A Maier and A V Bragas},

url = {https://doi.org/10.1021/acsphotonics.1c00741},

doi = {10.1021/acsphotonics.1c00741},

year  = {2021},

date = {2021-09-17},

urldate = {2021-09-17},

journal = {ACS Photonics},

abstract = {Hypersound waves can be efficient mediators between optical signals at the nanoscale. Having phase velocities several orders of magnitude lower than the speed of light, they propagate with much shorter wavelengths and can be controlled, directed, and even focused in a very small region of space. This work shows how two optical nanoantennas can be coupled through an acoustic wave that propagates with a certain directionality. An “emitter” antenna is first optically excited to generate acoustic coherent phonons that launch surface acoustic waves through the underlying substrate. These waves travel until they are mechanically detected by a “receiver” nanoantenna whose oscillation produces a detectable optical signal. Generation and detection are studied in detail, and new designs are proposed to improve the directionality of the hypersonic surface acoustic wave.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{nokey,

title = {Engineering gallium phosphide nanostructures for efficient nonlinear photonics and enhanced spectroscopies},

author = {G Q Moretti and E Cort\'{e}s and S A Maier and A V Bragas and G Grinblat},

url = {https://doi.org/10.1515/nanoph-2021-0388},

doi = {doi:10.1515/nanoph-2021-0388},

year  = {2021},

date = {2021-09-16},

journal = {Nanophotonics},

number = {000010151520210388},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{nokey,

title = {Single-step-fabricated disordered metasurfaces for enhanced light extraction from LEDs},

author = {P Mao and C Liu and X Li and M Liu and Q Chen and M Han and S A Maier and E H Sargent and S Zhang},

url = {https://doi.org/10.1038/s41377-021-00621-7},

doi = {10.1038/s41377-021-00621-7},

issn = {2047-7538},

year  = {2021},

date = {2021-09-06},

journal = {Light: Science \& Applications},

volume = {10},

number = {1},

pages = {180},

abstract = {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\textendashhole 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.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{nokey,

title = {Fabrication robustness in BIC metasurfaces},

author = {J K\"{u}hne and J Wang and T Weber and L K\"{u}hner and S A Maier and A Tittl},

url = {https://doi.org/10.1515/nanoph-2021-0391},

doi = {doi:10.1515/nanoph-2021-0391},

year  = {2021},

date = {2021-09-06},

journal = {Nanophotonics},

volume = {10},

number = {17},

pages = {4305-4312},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{nokey,

title = {All‐Dielectric Crescent Metasurface Sensor Driven by Bound States in the Continuum},

author = {J Wang and J K\"{u}hne and T Karamanos and C Rockstuhl and S A Maier and A Tittl},

issn = {1616-301X},

year  = {2021},

date = {2021-08-13},

journal = {Advanced Functional Materials},

pages = {2104652},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{,

title = {Self-Constructed Multiple Plasmonic Hotspots on an Individual Fractal to Amplify Broadband Hot Electron Generation},

author = {X Wang and C Liu and C Gao and K Yao and S S M Masouleh and R Bert\'{e} and H Ren and L D S Menezes and E Cort\'{e}s and I C Bicket and H Wang and N Li and Z Zhang and M Li and W Xie and Y Yu and Y Fang and S Zhang and H Xu and A Vomiero and Y Liu and G A Botton and S A Maier and H Liang},

url = {https://doi.org/10.1021/acsnano.1c03218},

doi = {10.1021/acsnano.1c03218},

issn = {1936-0851},

year  = {2021},

date = {2021-06-11},

journal = {ACS Nano},

abstract = {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\textendashprobe measurements, and electron energy loss spectroscopy. Our results show that fractals with acute tips and narrow gaps can support broadband resonances (400\textendash1100 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.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{nokey,

title = {Disorder-Induced Material-Insensitive Optical Response in Plasmonic Nanostructures: Vibrant Structural Colors from Noble Metals},

author = {P Mao and C Liu and Y Niu and Y Qin and F Song and M Han and R E Palmer and S A Maier and S Zhang},

url = {https://doi.org/10.1002/adma.202007623},

doi = {https://doi.org/10.1002/adma.202007623},

issn = {0935-9648},

year  = {2021},

date = {2021-06-01},

journal = {Advanced Materials},

volume = {33},

number = {23},

pages = {2007623},

abstract = {Abstract Materials show various responses to incident light, owing to their unique dielectric functions. A well-known example is the distinct colors displayed by metals, providing probably the simplest method to identify gold, silver, and bronze since ancient times. With the advancement of nanotechnology, optical structures with feature sizes smaller than the optical wavelength have been routinely achieved. In this regime, the optical response is also determined by the geometry of the nanostructures, inspiring flourishing progress in plasmonics, photonic crystals, and metamaterials. Nevertheless, the nature of the materials still plays a decisive role in light?matter interactions, and this material-dependent optical response is widely accepted as a norm in nanophotonics. Here, a counterintuitive system?plasmonic nanostructures composed of different materials but exhibiting almost identical reflection?is proposed and realized. The geometric disorder embedded in the system overwhelms the contribution of the material properties to the electrodynamics. Both numerical simulations and experimental results provide concrete evidence of the insensitivity of the optical response to different plasmonic materials. The same optical response is preserved with various materials, providing great flexibility of freedom in material selection. As a result, the proposed configuration may shed light on novel applications ranging from Raman spectroscopy, photocatalysis, to nonlinear optics.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{nokey,

title = {Massively Parallel Arrays of Size-Controlled Metallic Nanogaps with Gap-Widths Down to the Sub-3-nm Level},

author = {S Luo and A Mancini and R Bert\'{e} and B H Hoff and S A Maier and J C De Mello},

url = {https://onlinelibrary.wiley.com/doi/abs/10.1002/adma.202100491},

doi = {https://doi.org/10.1002/adma.202100491},

issn = {0935-9648},

year  = {2021},

date = {2021-05-03},

journal = {Advanced Materials},

volume = {33},

number = {20},

pages = {2100491},

abstract = {Abstract Metallic nanogaps (MNGs) are fundamental components of nanoscale photonic and electronic devices. However, the lack of reproducible, high-yield fabrication methods with nanometric control over the gap-size has hindered practical applications. A patterning technique based on molecular self-assembly and physical peeling is reported here that allows the gap-width to be tuned from more than 30 nm to less than 3 nm. The ability of the technique to define sub-3-nm gaps between dissimilar metals permits the easy fabrication of molecular rectifiers, in which conductive molecules bridge metals with differing work functions. A method is further described for fabricating massively parallel nanogap arrays containing hundreds of millions of ring-shaped nanogaps, in which nanometric size control is maintained over large patterning areas of up to a square centimeter. The arrays exhibit strong plasmonic resonances under visible light illumination and act as high-performance substrates for surface-enhanced Raman spectroscopy, with high enhancement factors of up to 3 × 108 relative to thin gold films. The methods described here extend the range of metallic nanostructures that can be fabricated over large areas, and are likely to find many applications in molecular electronics, plasmonics, and biosensing.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{,

title = {Anapole-Assisted Absorption Engineering in Arrays of Coupled Amorphous Gallium Phosphide Nanodisks},

author = {L H\"{u}ttenhofer and A Tittl and L K\"{u}hner and E Cort\'{e}s and S A Maier},

url = {https://doi.org/10.1021/acsphotonics.1c00238},

doi = {10.1021/acsphotonics.1c00238},

year  = {2021},

date = {2021-04-26},

journal = {ACS Photonics},

abstract = {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\textendashanapole 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 conversion applications.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{,

title = {Bright single photon emitters with enhanced quantum efficiency in a two-dimensional semiconductor coupled with dielectric nano-antennas},

author = {L Sortino and P G Zotev and C L Phillips and A J Brash and J Cambiasso and E Marensi and A M Fox and S A Maier and R Sapienza and A I Tartakovskii},

year  = {2021},

date = {2021-04-05},

journal = {arXiv preprint arXiv:2103.16986},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{,

title = {Template Dissolution Interfacial Patterning of Single Colloids for Nanoelectrochemistry and Nanosensing},

author = {J B Lee and H Walker and Y Li and T W Nam and A Rakovich and R Sapienza and Y S Jung and Y S Nam and S A Maier and E Cort\'{e}s},

url = {https://doi.org/10.1021/acsnano.0c09319},

doi = {10.1021/acsnano.0c09319},

issn = {1936-0851},

year  = {2020},

date = {2020-12-03},

urldate = {2020-12-03},

journal = {ACS Nano},

abstract = {Deterministic positioning and assembly of colloidal nanoparticles (NPs) onto substrates is a core requirement and a promising alternative to top-down lithography to create functional nanostructures and nanodevices with intriguing optical, electrical, and catalytic features. Capillary-assisted particle assembly (CAPA) has emerged as an attractive technique to this end, as it allows controlled and selective assembly of a wide variety of NPs onto predefined topographical templates using capillary forces. One critical issue with CAPA, however, lies in its final printing step, where high printing yields are possible only with the use of an adhesive polymer film. To address this problem, we have developed a template dissolution interfacial patterning (TDIP) technique to assemble and print single colloidal AuNP arrays onto various dielectric and conductive substrates in the absence of any adhesion layer, with printing yields higher than 98%. The TDIP approach grants direct access to the interface between the AuNP and the target surface, enabling the use of colloidal AuNPs as building blocks for practical applications. The versatile applicability of TDIP is demonstrated by the creation of direct electrical junctions for electro- and photoelectrochemistry and nanoparticle-on-mirror geometries for single-particle molecular sensing.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{nokey,

title = {Mode-Matching Enhancement of Second-Harmonic Generation with Plasmonic Nanopatch Antennas},

author = {A Noor and A R Damodaran and I-H Lee and S A Maier and S-H Oh and C Cirac\`{i}},

url = {https://doi.org/10.1021/acsphotonics.0c01545},

doi = {10.1021/acsphotonics.0c01545},

year  = {2020},

date = {2020-11-25},

journal = {ACS Photonics},

volume = {7},

number = {12},

pages = {3333-3340},

abstract = {Plasmonic enhancement of nonlinear optical processes confront severe limitations arising from the strong dispersion of metal susceptibilities and small interaction volumes that hamper the realization of desirable phase-matching-like conditions. Maximizing nonlinear interactions in nanoscale systems require simultaneous excitation of resonant modes that spatially and constructively overlap at all wavelengths involved in the process. Here, we present a hybrid rectangular patch antenna design for optimal second-harmonic generation (SHG) that is characterized by a non-centrosymmetric dielectric/ferroelectric material at the plasmonic hot spot. The optimization of the rectangular patch allows for the independent tuning of various modes of resonances that can be used to enhance the SHG process. We explore the angular dependence of SHG in these hybrid structures and highlight conditions necessary for the maximal SHG efficiency. Furthermore, we propose a novel configuration with a periodically poled ferroelectric layer for an orders-of-magnitude enhanced SHG at normal incidence. Such a platform may enable the development of integrated nanoscale light sources and on-chip frequency converters.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{,

title = {Electron tunneling at the molecularly thin 2D perovskite and graphene van der Waals interface},

author = {K Leng and L Wang and Y Shao and I Abdelwahab and G Grinblat and I Verzhbitskiy and R Li and Y Cai and X Chi and W Fu and P Song and A Rusydi and G Eda and S A Maier and K P Loh},

url = {https://doi.org/10.1038/s41467-020-19331-6},

doi = {10.1038/s41467-020-19331-6},

issn = {2041-1723},

year  = {2020},

date = {2020-10-30},

journal = {Nature Communications},

volume = {11},

number = {1},

pages = {5483},

abstract = {Quasi-two-dimensional perovskites have emerged as a new material platform for optoelectronics on account of its intrinsic stability. A major bottleneck to device performance is the high charge injection barrier caused by organic molecular layers on its basal plane, thus the best performing device currently relies on edge contact. Herein, by leveraging on van der Waals coupling and energy level matching between two-dimensional Ruddlesden-Popper perovskite and graphene, we show that the plane-contacted perovskite and graphene interface presents a lower barrier than gold for charge injection. Electron tunneling across the interface occurs via a gate-tunable, direct tunneling-to-field emission mechanism with increasing bias, and photoinduced charge transfer occurs at femtosecond timescale (~50 fs). Field effect transistors fabricated on molecularly thin Ruddlesden-Popper perovskite using graphene contact exhibit electron mobilities ranging from 0.1 to 0.018 cm2V−1s−1 between 1.7 to 200 K. Scanning tunneling spectroscopy studies reveal layer-dependent tunneling barrier and domain size on few-layered Ruddlesden-Popper perovskite.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{,

title = {Electron tunneling at the molecularly thin 2D perovskite and graphene van der Waals interface},

author = {K Leng and L Wang and Y Shao and I Abdelwahab and G Grinblat and I Verzhbitskiy and R Li and Y Cai and X Chi and W Fu and P Song and A Rusydi and G Eda and S A Maier and K P Loh},

url = {https://doi.org/10.1038/s41467-020-19331-6},

doi = {10.1038/s41467-020-19331-6},

issn = {2041-1723},

year  = {2020},

date = {2020-10-30},

journal = {Nature Communications},

volume = {11},

number = {1},

pages = {5483},

abstract = {Quasi-two-dimensional perovskites have emerged as a new material platform for optoelectronics on account of its intrinsic stability. A major bottleneck to device performance is the high charge injection barrier caused by organic molecular layers on its basal plane, thus the best performing device currently relies on edge contact. Herein, by leveraging on van der Waals coupling and energy level matching between two-dimensional Ruddlesden-Popper perovskite and graphene, we show that the plane-contacted perovskite and graphene interface presents a lower barrier than gold for charge injection. Electron tunneling across the interface occurs via a gate-tunable, direct tunneling-to-field emission mechanism with increasing bias, and photoinduced charge transfer occurs at femtosecond timescale (~50 fs). Field effect transistors fabricated on molecularly thin Ruddlesden-Popper perovskite using graphene contact exhibit electron mobilities ranging from 0.1 to 0.018 cm2V−1s−1 between 1.7 to 200 K. Scanning tunneling spectroscopy studies reveal layer-dependent tunneling barrier and domain size on few-layered Ruddlesden-Popper perovskite.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{,

title = {Nanostructured amorphous gallium phosphide on silica for nonlinear and ultrafast nanophotonics},

author = {B Tilmann and G Grinblat and R Bert\'{e} and M \"{O}zcan and V F Kunzelmann and B Nickel and I D Sharp and E Cort\'{e}s and S A Maier and Y Li},

url = {http://dx.doi.org/10.1039/D0NH00461H},

doi = {10.1039/D0NH00461H},

issn = {2055-6756},

year  = {2020},

date = {2020-09-30},

journal = {Nanoscale Horizons},

volume = {5},

number = {11},

pages = {1500-1508},

abstract = {Nanophotonics based on high refractive index dielectrics relies on appreciable contrast between the indices of designed nanostructures and their immediate surrounding, which can be achieved by the growth of thin films on low-index substrates. Here we propose the use of high index amorphous gallium phosphide (a-GaP), fabricated by radio-frequency sputter deposition, on top of a low refractive index glass substrate and thoroughly examine its nanophotonic properties. Spectral ellipsometry of the amorphous material demonstrates the optical properties to be considerably close to crystalline gallium phosphide (c-GaP), with low-loss transparency for wavelengths longer than 650 nm. When nanostructured into nanopatches, the second harmonic (SH) response of an individual a-GaP patch is characterized to be more than two orders of magnitude larger than the as-deposited unstructured film, with an anapole-like resonant behavior. Numerical simulations are in good agreement with the experimental results over a large spectral and geometrical range. Furthermore, by studying individual a-GaP nanopatches through non-degenerate pump\textendashprobe spectroscopy with sub-10 fs pulses, we find a more than 5% ultrafast modulation of the reflectivity that is accompanied by a slower decaying free carrier contribution, caused by absorption. Our investigations reveal a potential for a-GaP as an adequate inexpensive and CMOS-compatible material for nonlinear nanophotonic applications as well as for photocatalysis.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{nokey,

title = {Electrical control of single-photon emission in highly charged individual colloidal quantum dots},

author = {S Morozov and E L Pensa and A H Khan and A Polovitsyn and E Cort\'{e}s and S A Maier and S Vezzoli and I Moreels and R Sapienza},

url = {https://pubmed.ncbi.nlm.nih.gov/32948584/},

doi = {10.1126/sciadv.abb1821},

issn = {2375-2548},

year  = {2020},

date = {2020-09-18},

urldate = {2020-09-18},

journal = {Sci Adv},

volume = {6},

number = {38},

abstract = {Electron transfer to an individual quantum dot promotes the formation of charged excitons with enhanced recombination pathways and reduced lifetimes. Excitons with only one or two extra charges have been observed and exploited for very efficient lasing or single-quantum dot light-emitting diodes. Here, by room-temperature time-resolved experiments on individual giant-shell CdSe/CdS quantum dots, we show the electrochemical formation of highly charged excitons containing more than 12 electrons and 1 hole. We report the control over intensity blinking, along with a deterministic manipulation of quantum dot photodynamics, with an observed 210-fold increase in the decay rate, accompanied by 12-fold decrease in the emission intensity, while preserving single-photon emission characteristics. These results pave the way for deterministic control over the charge state, and room-temperature decay rate engineering for colloidal quantum dot-based classical and quantum communication technologies.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{nokey,

title = {In Situ Photothermal Response of Single Gold Nanoparticles through Hyperspectral Imaging Anti-Stokes Thermometry},

author = {M Barella and I L Violi and J Gargiulo and L P Martinez and F Goschin and V Guglielmotti and D Pallarola and S Schl\"{u}cker and M Pilo-Pais and G P Acuna and S A Maier and E Cort\'{e}s and F D Stefani},

url = {https://doi.org/10.1021/acsnano.0c06185},

doi = {10.1021/acsnano.0c06185},

issn = {1936-0851},

year  = {2020},

date = {2020-09-17},

journal = {ACS Nano},

volume = {15},

number = {2},

pages = {2458-2467},

abstract = {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.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{nokey,

title = {Direct Detection of Optical Forces of Magnetic Nature in Dielectric Nanoantennas},

author = {M Poblet and Y Li and E Cort\'{e}s and S A Maier and G Grinblat and A V Bragas},

url = {https://doi.org/10.1021/acs.nanolett.0c03157},

doi = {10.1021/acs.nanolett.0c03157},

issn = {1530-6984},

year  = {2020},

date = {2020-09-16},

urldate = {2020-09-16},

journal = {Nano Letters},

volume = {20},

number = {10},

pages = {7627-7634},

abstract = {Optical forces on nanostructures are usually characterized by their interaction with the electric field component of the light wave, given that most materials present negligible magnetic response at optical frequencies. This is not the case however of a high-refractive-index dielectric nanoantenna, which has been recently shown to efficiently support both electric and magnetic optical modes. In this work, we use a photoinduced force microscopy configuration to measure optically induced forces produced by a germanium nanoantenna on a surrounding silicon near-field probe. We reveal the spatial distribution, character, and magnitude of the generated forces when exciting the nanoantenna at its anapole state condition. We retrieve optical force maps showing values of up to 20 pN, which are found to be mainly magnetic in nature, according to our numerical simulations. The results of this investigation open new pathways for the study, detection, and generation of magnetic light forces at the nanometer scale.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{,

title = {Efficient ultrafast all-optical modulation in a nonlinear crystalline gallium phosphide nanodisk at the anapole excitation},

author = {G Grinblat and H Zhang and M P Nielsen and L Krivitsky and R Bert\'{e} and Y Li and B Tilmann and E Cort\'{e}s and R F Oulton and A I Kuznetsov and S A Maier},

url = {https://advances.sciencemag.org/content/advances/6/34/eabb3123.full.pdf},

doi = {10.1126/sciadv.abb3123},

year  = {2020},

date = {2020-08-21},

journal = {Science Advances},

volume = {6},

number = {34},

pages = {eabb3123},

abstract = {High\textendashrefractive index nanostructured dielectrics have the ability to locally enhance electromagnetic fields with low losses while presenting high third-order nonlinearities. In this work, we exploit these characteristics to achieve efficient ultrafast all-optical modulation in a crystalline gallium phosphide (GaP) nanoantenna through the optical Kerr effect (OKE) and two-photon absorption (TPA) in the visible/near-infrared range. We show that an individual GaP nanodisk can yield differential reflectivity modulations of up to ~40%, with characteristic modulation times between 14 and 66 fs, when probed at the anapole excitation (AE). Numerical simulations reveal that the AE represents a unique condition where both the OKE and TPA contribute with the same modulation sign, maximizing the response. These findings highly outperform previous reports on sub\textendash100-fs all-optical switching from resonant nanoscale dielectrics, which have demonstrated modulation depths no larger than 0.5%, placing GaP nanoantennas as a promising choice for ultrafast all-optical modulation at the nanometer scale.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{,

title = {All-Dielectric Silicon Nanoslots for Er3+ Photoluminescence Enhancement},

author = {B Kalinic and T Cesca and S Mignuzzi and A Jacassi and I G Balasa and S A Maier and R Sapienza and G Mattei},

url = {\<Go to ISI\>://WOS:000553352700004},

doi = {10.1103/PhysRevApplied.14.014086},

issn = {2331-7019},

year  = {2020},

date = {2020-07-28},

journal = {Physical Review Applied},

volume = {14},

number = {1},

abstract = {We study, both experimentally and theoretically, the modification of Er3+ photoluminescence properties in Si dielectric nanoslots. The ultrathin nanoslot (down to 5-nm thickness), filled with Er in SiO2, boosts the electric and magnetic local density of states via coherent near-field interaction. We report an experimental 20-fold enhancement of the radiative decay rate with negligible losses. Moreover, via modifying the geometry of the all-dielectric nanoslot, the outcoupling of the emitted radiation to the far field can be strongly improved, without affecting the strong decay-rate enhancement given by the nanoslot structure. Indeed, for a periodic square array of slotted nanopillars an almost one-order-of-magnitude-higher Er3+ PL intensity is measured with respect to the unpatterned structures. This has a direct impact on the design of more efficient CMOS-compatible light sources operating at telecom wavelengths.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{,

title = {Genetic-Algorithm-Aided Meta-Atom Multiplication for Improved Absorption and Coloration in Nanophotonics},

author = {C X Liu and S A Maier and G X Li},

url = {\<Go to ISI\>://WOS:000551497000018},

doi = {10.1021/acsphotonics.0c00266},

issn = {2330-4022},

year  = {2020},

date = {2020-06-15},

journal = {Acs Photonics},

volume = {7},

number = {7},

pages = {1716-1722},

abstract = {For a repertoire of nanophotonic systems, including photonic crystals, metasurfaces, and plasmonic structures, unit cell with a single element is conventionally used for the simplicity of design. The extension of the unit cell with multiple meta-atoms drastically enlarges the parameter space and consequently provides potential configurations with improved device performance. Simultaneously, the multiplication does not induce additional complexity for lithography-based fabrications. However, the substantially increased number of parameters makes the design methodology based on physical intuition and parameter sweep impractical. Here, we show that expanding the number of meta-atoms in the unit cell significantly improves the performance of nanophotonic systems by the virtue of a genetic algorithm-based optimizer. Our approach includes physical intuition endowed in the geometry of meta-atoms, providing additional physical understanding of the optimization process. We demonstrate two photonic applications, including prominent enhancement of a broadband absorption and enlargement of the color coverage of plasmonic nanostructures. Not limited to the two proof-of-concept demonstrations, this methodology can be applied to all meta-atom-based nanophotonic systems, including plasmonic near-field enhancement and nonlinear frequency conversion, as well as a simultaneous control of phase and polarization for metasurfaces.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{nokey,

title = {Near-Field Spectroscopy of Cylindrical Phonon-Polariton Antennas},

author = {A Mancini and C R Gubbin and R Bert\'{e} and F Martini and A Politi and E Cort\'{e}s and Y Li and S De Liberato and S A Maier},

url = {https://doi.org/10.1021/acsnano.0c02784},

doi = {10.1021/acsnano.0c02784},

issn = {1936-0851},

year  = {2020},

date = {2020-06-12},

urldate = {2020-06-12},

journal = {ACS Nano},

volume = {14},

number = {7},

pages = {8508-8517},

abstract = {Surface phonon polaritons (SPhPs) are hybrid light\textendashmatter states in which light strongly couples to lattice vibrations inside the Reststrahlen band of polar dielectrics at mid-infrared frequencies. Antennas supporting localized surface phonon polaritons (LSPhPs) easily outperform their plasmonic counterparts operating in the visible or near-infrared in terms of field enhancement and confinement thanks to the inherently slower phonon\textendashphonon scattering processes governing SPhP decay. In particular, LSPhP antennas have attracted considerable interest for thermal management at the nanoscale, where the emission strongly diverts from the usual far-field blackbody radiation due to the presence of evanescent waves at the surface. However, far-field measurements cannot shed light on the behavior of antennas in the near-field region. To overcome this limitation, we employ scattering-scanning near-field optical microscopy (sSNOM) to unveil the spectral near-field response of 3C-SiC antenna arrays. We present a detailed description of the behavior of the antenna resonances by comparing far-field and near-field spectra and demonstrate the existence of a mode with no net dipole moment, absent in the far-field spectra, but of importance for applications that exploit the heightened electromagnetic near fields. Furthermore, we investigate the perturbation in the antenna response induced by the presence of the AFM tip, which can be further extended toward situations where for example strong IR emitters couple to LSPhP modes.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{,

title = {Determination of Nanoscale Mechanical Properties of Polymers via Plasmonic Nanoantennas},

author = {H D Boggiano and R Berte and A F Scarpettini and E Cortes and S A Maier and A V Bragas},

url = {\<Go to ISI\>://WOS:000542931300008},

doi = {10.1021/acsphotonics.0c00631},

issn = {2330-4022},

year  = {2020},

date = {2020-06-02},

journal = {Acs Photonics},

volume = {7},

number = {6},

pages = {1403-1409},

abstract = {Nanotechnology and the consequent emergence of miniaturized devices are driving the need to improve our understanding of the mechanical properties of a myriad of materials. Here we focus on amorphous polymeric materials and introduce a new way to determine the nanoscale mechanical response of polymeric thin films in the GHz range, using ultrafast optical means. Coupling of the films to plasmonic nanoantennas excited at their vibrational eigenfrequencies allows the extraction of the values of the mechanical moduli as well as the estimation of the glass transition temperature via time-domain measurements, here demonstrated for PMMA films. This nanoscale method can be extended to the determination of mechanical and elastic properties of a wide range of spatially strongly confined materials.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{,

title = {Manipulating disordered plasmonic systems by external cavity with transition from broadband absorption to reconfigurable reflection},

author = {P Mao and C Liu and F Song and M Han and S A Maier and S Zhang},

url = {https://doi.org/10.1038/s41467-020-15349-y},

doi = {10.1038/s41467-020-15349-y},

issn = {2041-1723},

year  = {2020},

date = {2020-03-24},

journal = {Nature Communications},

volume = {11},

number = {1},

pages = {1538},

abstract = {Disordered biostructures are ubiquitous in nature, usually generating white or black colours due to their broadband optical response and robustness to perturbations. Through judicious design, disordered nanostructures have been realised in artificial systems, with unique properties for light localisation, photon transportation and energy harvesting. On the other hand, the tunability of disordered systems with a broadband response has been scarcely explored. Here, we achieve the controlled manipulation of disordered plasmonic systems, realising the transition from broadband absorption to tunable reflection through deterministic control of the coupling to an external cavity. Starting from a generalised model, we realise disordered systems composed of plasmonic nanoclusters that either operate as a broadband absorber or with a reconfigurable reflection band throughout the visible. Not limited to its significance for the further understanding of the physics of disorder, our disordered plasmonic system provides a novel platform for various practical application such as structural colour patterning.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{,

title = {Anapole Excitations in Oxygen-Vacancy-Rich TiO2\textendashx Nanoresonators: Tuning the Absorption for Photocatalysis in the Visible Spectrum},

author = {L H\"{u}ttenhofer and F Eckmann and A Lauri and J Cambiasso and E Pensa and Y Li and E Cort\'{e}s and I D Sharp and S A Maier},

url = {https://doi.org/10.1021/acsnano.9b09987},

doi = {10.1021/acsnano.9b09987},

issn = {1936-0851},

year  = {2020},

date = {2020-02-25},

journal = {ACS Nano},

volume = {14},

number = {2},

pages = {2456-2464},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{,

title = {Broadband SERS detection with disordered plasmonic hybrid aggregates},

author = {P Mao and C X Liu and Q Chen and M Han and S A Maier and S Zhang},

url = {\<Go to ISI\>://WOS:000504106900036},

doi = {10.1039/c9nr08118f},

issn = {2040-3364},

year  = {2019},

date = {2019-10-14},

journal = {Nanoscale},

volume = {12},

number = {1},

pages = {93-102},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{,

title = {Present and Future of Surface-Enhanced Raman Scattering},

author = {J Langer and De D J Aberasturi and J Aizpurua and R A Alvarez-Puebla and B Auguie and J J Baumberg and G C Bazan and S E J Bell and A Boisen and A G Brolo and J Choo and D Cialla-May and V Deckert and L Fabris and K Faulds and De F J G Abajo and R Goodacre and D Graham and A J Haes and C L Haynes and C Huck and T Itoh and M Ka and J Kneipp and N A Kotov and H Kuang and Le E C Ru and H K Lee and J F Li and X Y Ling and S A Maier and T Mayerhofer and M Moskovits and K Murakoshi and J M Nam and S Nie and Y Ozaki and I Pastoriza-Santos and J Perez-Juste and J Popp and A Pucci and S Reich and B Ren and G C Schatz and T Shegai and S Schlucker and L L Tay and K G Thomas and Z Q Tian and Van R P Duyne and T Vo-Dinh and Y Wang and K A Willets and C Xu and H Xu and Y Xu and Y S Yamamoto and B Zhao and L M Liz-Marzan},

url = {\<Go to ISI\>://WOS:000510531500006},

doi = {10.1021/acsnano.9b04224},

issn = {1936-0851},

year  = {2019},

date = {2019-09-03},

journal = {Acs Nano},

volume = {14},

number = {1},

pages = {28-117},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{,

title = {Ultrafast All-Optical Modulation in 2D Hybrid Perovskites},

author = {G Grinblat and I Abdelwahab and M P Nielsen and P Dichtl and K Leng and R F Oulton and K P Loh and S A Maier},

url = {https://doi.org/10.1021/acsnano.9b04483},

doi = {10.1021/acsnano.9b04483},

issn = {1936-0851},

year  = {2019},

date = {2019-08-27},

journal = {ACS Nano},

volume = {13},

number = {8},

pages = {9504-9510},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{,

title = {From Optical to Chemical Hot Spots in Plasmonics},

author = {J Gargiulo and R Bert\'{e} and Y Li and S A Maier and E Cort\'{e}s},

url = {https://doi.org/10.1021/acs.accounts.9b00234},

doi = {10.1021/acs.accounts.9b00234},

issn = {0001-4842},

year  = {2019},

date = {2019-08-20},

journal = {Accounts of Chemical Research},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{,

title = {Nonlinear Pancharatnam−Berry Phase Metasurfaces beyond the Dipole Approximation},

author = {S D Gennaro and Y Li and S A Maier and R F Oulton},

url = {https://doi.org/10.1021/acsphotonics.9b00877},

doi = {10.1021/acsphotonics.9b00877},

year  = {2019},

date = {2019-08-12},

journal = {ACS Photonics},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{,

title = {Ultrawideband Surface Enhanced Raman Scattering in Hybrid Graphene Fragmented-Gold Substrates via Cold-Etching},

author = {T Wu and K Li and N Zhang and J Xia and Q Zeng and X Wen and U S Dinish and M Olivo and Z Shen and Z Liu and Q Xiong and Y Luo and S A Maier and L Wei},

url = {https://doi.org/10.1002/adom.201900905},

doi = {10.1002/adom.201900905},

issn = {2195-1071},

year  = {2019},

date = {2019-08-08},

journal = {Advanced Optical Materials},

volume = {0},

number = {0},

pages = {1900905},

abstract = {Abstract Conventional surface enhanced Raman scattering (SERS) substrates are well known for their supreme electromagnetic enhancements and ultrahigh sensitivity in detecting molecules at low concentrations. However, large-area quasi-uniform SERS substrates are difficult to achieve by standard top-down nanofabrication techniques, resulting in fluctuant SERS responses and unwanted fluorescence interferences, which severely limit their performances in practical applications. To tackle these challenges, a large-scale quasi-uniform hybrid graphene fragmented-gold substrate with stable and reproducible SERS readouts as well as large enhancement factors over an ultrawideband spectrum is developed. The hybrid substrate is fabricated via cold-etching through a controllable break up of a thin gold film followed by a graphene transfer. The stimulated localized surface plasmons interact strongly with the graphene layer, leading to spectrally and spatially modified graphene-mediated surface enhanced Raman scattering (GSERS) responses. The perfect monolayer graphene of the GSERS substrate prevents adsorbates from the atmosphere and direct contact between bonded molecules and gold, thus reducing the catalytic activity of gold and producing clean, stable, and reproducible molecular Raman signals. The easy-fabricated hybrid GSERS substrate not only provides a powerful platform to collect robust molecular Raman spectra but also shows great potentials for future mass production of high-performance nanophotonic devices.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{,

title = {Spectral Screening of the Energy of Hot Holes over a Particle Plasmon Resonance},

author = {E Pensa and J Gargiulo and A Lauri and S Schl\"{u}cker and E Cort\'{e}s and S A Maier},

url = {https://doi.org/10.1021/acs.nanolett.8b04950},

doi = {10.1021/acs.nanolett.8b04950},

issn = {1530-6984},

year  = {2019},

date = {2019-03-13},

journal = {Nano Letters},

volume = {19},

number = {3},

pages = {1867-1874},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{,

title = {Quantifying Figures of Merit for Localized Surface Plasmon Resonance Applications: A Materials Survey},

author = {B Doiron and M Mota and M P Wells and R Bower and A Mihai and Y Li and L F Cohen and N M Alford and P K Petrov and R F Oulton and S A Maier},

url = {https://doi.org/10.1021/acsphotonics.8b01369},

doi = {10.1021/acsphotonics.8b01369},

year  = {2019},

date = {2019-02-20},

journal = {ACS Photonics},

volume = {6},

number = {2},

pages = {240-259},

keywords = {},

pubstate = {published},

tppubtype = {article}

}

@article{,

title = {Phase-matching and Peak Nonlinearity Enhanced Third-Harmonic Generation in Graphene Plasmonic Coupler},

author = {T Wu and Y Luo and S A Maier and L Wei},

url = {https://link.aps.org/doi/10.1103/PhysRevApplied.11.014049},

doi = {10.1103/PhysRevApplied.11.014049},

year  = {2019},

date = {2019-01-24},

journal = {Physical Review Applied},

volume = {11},

number = {1},

pages = {014049},

abstract = {Strong nonlinear optical effects generally require giant optical fields interacting with the nonlinear media. Doped graphene hosts electrically tunable plasmons with long lifetimes that interact strongly with light. We investigate a graphene plasmonic coupler and explore two mechanisms to pursue highly efficient third-harmonic generation (THG): (1) phase matching of graphene plasmons at fundamental- and third-harmonic frequencies and (2) peak third-order nonlinear susceptibility of doped graphene. The third-harmonic wave is mainly converted from the evanescent mode of the incident light and the THG efficiency is found to be enhanced by over 10 orders of magnitude compared with a bare monolayer graphene. The significantly enhanced nonlinear optical responses in the graphene plasmonic coupler make this configuration an ideal platform for the development of alternative frequency generators and for signal processing at midinfrared and terahertz frequencies.},

keywords = {},

pubstate = {published},

tppubtype = {article}

}