Electrochemical interfaces are ubiquitous in sensing, catalysis, and energy storage, yet understanding molecular interactions with the electrochemical double layer (EDL) remains limited. Here, we use electrochemical surface-enhanced Raman spectroscopy (EC-SERS) to probe analyte-EDL interactions in real time. Precision SERS electrodes with robust electrochemically recleanable gold nanogaps allow us to detect subtle molecular spectral changes during cyclic voltammetry, revealing distinct intensity and frequency oscillations. Quantum mechanics/molecular mechanics simulations show that these effects arise from electrochemical potential-induced molecular reorientation and surface restructuring driven by dynamic interactions with the EDL. For sensing, this mechanism reduces detection limits for DNA nucleobases by more than 25-fold and enables label-free multiplexed sensing. Beyond improved sensor performance, this work provides a framework for understanding EC-SERS and gives insight into neutral molecule behavior within the EDL.

Stable radicals are spin-active species with a plethora of proposed applications in fields from energy storage and molecular electronics to quantum communications. However, their optical properties and vibrational modes are so far not well understood. Furthermore, it is not yet clear how these are affected by the radical oxidation state, which is key to understanding their electronic transport. Here, we identify the properties of 1,2,4-benzotriazin-4-yl, a stable doubly thiolated variant of the Blatter radical, using surface-enhanced Raman scattering (SERS). Embedding molecular monolayers in plasmonic nanocavities gives access to their vibrational modes, photoluminescence, and optical response during redox processes. We reveal the influence of the adjacent metallic surfaces and identify fluctuating SERS signals that suggest a coupling between the unpaired radical electron and a spatially overlapping vibrational mode. This can potentially be exploited for information-storage devices and chemically designed molecular qubits.

Extreme plasmonic confinement to the nanoscale can be used to probe the configuration of molecules at metallic surfaces. Exploring low-frequency (hν < kBT) inelastic light scattering from molecular-monolayer-filled plasmonic nanocavities reveals additional low-frequency excitations not previously observed. We identify these as terahertz Lamb shear modes in the nanogap, exhibiting cross sections even larger than the surface-enhanced Raman scattering (SERS) of the vibrating molecules. Comparing different molecules and metals shows the influence on these Lamb modes of surface binding of the molecular monolayer as well as the strong impact of damping. The large occupation of such modes at room temperature implies their role across many fields, from electrochemistry, molecular electronics, and thermoelectrics to photocatalysis and sensing.

Nitrogen-vacancy (N-V) centers are diamond lattice defects that may be manipulated and controlled by visible light and microwave irradiation. They are considered a promising solid-state platform for a broad range of quantum technologies, such as magnetic field sensing. A major limitation in realizing such applications is the weak optical signal attained from the NVs, making the readout inefficient and prone to noise. Here, we report the increased brightness and shortened lifetime of N-V centers coupled to hyperbolic metamaterial photonic cavities with optimized dispersion characteristics. As a result, we demonstrate the enhancement of magnetic field sensitivity and measurement SNR. These results introduce a broadly applicable, robust, and technically accessible platform, promising improved performance relevant for a multitude of solid-state defects and their applications.

Anti-Stokes photoluminescence (PL) is light emission at a higher photon energy than the excitation, with applications in optical cooling, bioimaging, lasing, and quantum optics. Here, we show how plasmonic nano-cavities activate anti-Stokes PL in WSe2 monolayers through resonant excitation of a dark exciton at room temperature. The optical near-fields of the plasmonic cavities excite the out-of-plane transition dipole of the dark exciton, leading to light emission from the bright exciton at higher energy. Through statistical measurements on hundreds of plasmonic cavities, we show that coupling to the dark exciton leads to a near hundred-fold enhancement of the upconverted PL intensity. This is further corroborated by experiments in which the laser excitation wavelength is tuned across the dark exciton. We show that a precise nanoparticle geometry is key for a consistent enhancement, with decahedral nanoparticle shapes providing an efficient PL upconversion. Finally, we demonstrate a selective and reversible switching of the upconverted PL via electrochemical gating. Our work introduces the dark exciton as an excitation channel for anti-Stokes PL in WSe2 and paves the way for large-area substrates providing nanoscale optical cooling, anti-Stokes lasing, and radiative engineering of excitons.

High-index dielectric metasurfaces have gradually become one of the most promising platforms in the field of nanophotonics due to the ease in engineering their optical behavior and their small size. Several numerical and experimental studies have been conducted in the fields of plasmonic metasurfaces and dielectric metasurfaces on in-plane symmetry-breaking nanodisk metasurfaces supporting high -Q states called "quasi-BICs", where these devices are useful for applications such as imaging and biodetection. This article studies numerically and experimentally symmetry-breaking metasurfaces made of amorphous silicon (alpha-Si) nanodisks in the visible-to-near-infrared range. It is reported that the angular response of the quasi-BICs for type I symmetry breaking metasurfaces can be blue-shifted with respect to incident light tilted parallel to the axis of mirror symmetry and red-shifted when tilted perpendicular to it due to changes in the in-plane momentum. Comparatively, the angular response of the quasi-BICs of type II symmetry-breaking metasurfaces can only be red shifted due to mirror symmetries in both axis directions.

We demonstrate a tunable metasurface made of aluminum nanodisk array coated with ITO on a thin film of lithium niobate. A spectral resonant shift of few nanometers and modulation contrast of ~40% are observed.

We study numerically and experimentally symmetry-breaking dielectric metasurfaces and found that the angular response of the localized magnetic dipole resonance for a 1-fold symmetry is blue-shifted, while for a 2-fold symmetry it is red-shifted.

Many consumer technologies and scientific methods rely on photodetection of infrared light. We report a Schottky photodetector operating below silicon's band gap energy, through hot carrier injection from a nanoscale metallic absorber. Our design relies on simple CMOS-compatible 'bottom up' fabrication of fractally nanostructured aluminium films. Due to the fractal nature of the nanostructuring, the aluminium films support plasmonically enhanced absorption over a wide wavelength range. We demonstrate two orders of magnitude improvements of responsivity, noise-equivalent-power, and detectivity as compared to bulk metal, over a broad spectral and angular range. We attribute this to momentum relaxation processes from the nanoscale fractal geometry. Specifically, we demonstrate a direct link between quantum efficiency enhancement and structural parameters such as perimeter to surface ratio. Finally, our devices also function as bulk refractive index sensors. Our approach is a promising candidate for future cost effective and robust short wave infrared photodetection and sensing applications.

Due to their atomic layer thickness, direct bandgap, mechanical robustness and other superior properties, transition metal dichalcogenides (TMDCs) monolayers are considered as an attractive alternative to graphene for diverse optoelectronic applications. Yet, due to the very nature of atomic layer thickness, the interaction of light with TMDCs is limited, hindering overall efficiency for optical applications. Therefore, in order for TMDCs to become a true candidate as the material of choice for optoelectronics, there is a need for a mechanism which significantly enhances the interaction of light with TMDCs. In this paper, we demonstrate about 30-fold enhancement of the overall photoluminescence emission intensity from a WS2 monolayer, by its coupling to a hyperbolic metamaterial nanoantenna array. This enhancement corresponds to nearly 300-fold enhancement per individual nanoantenna. This overall enhancement is achieved by the combination of enhancing the excitation (absorption) efficiency, alongside with enhancing the radiative decay rate. Our result paves the way for the use of TMDCs in diverse optoelectronic applications, ranging from light sources and photodetectors to saturated absorbers and nonlinear media.

A metric for evaluation of overall metalens performance is presented. It is applied to determination of optimal operating spectral range of a metalens, both theoretically and experimentally. This metric is quite general and can be applied to the design and evaluation of future metalenses, particularly achromatic metalenses.

Metasurfaces can be used to enhance the absorption in metallic and dielectric thin films. Taking advantage of this property, we experimentally demonstrate the use of a commercially available thermoelectric device as a thermoelectric photodetector by integrating it with a metallic metasurface array operating as an absorption enhancer for both the visible and the short-wave infrared. Electrical measurement shows that the responsivity of the nanostructured region is an order of magnitude higher than the flat film region. The absorption spectrum and correspondingly the spectral response of the device can be tailored by optimizing the metasurface dimensions. As such, the device can be used as a multiband photodetector for diverse applications.

We design and experimentally demonstrate ultra-small mode volume hyperbolic metamaterial nano cavities in the visible frequency band. These HMM cavities show enhancement of light-matter interaction with 2D TMDC materials in the deep sub-wavelength limit.

We experimentally demonstrate a thermoelectric photodetector combined with nanostructured thin-film broadband super-absorber in the visible to short wave infrared with an order of magnitude enhanced sensitivity as compared to a flat metal film device.

We present a method of optimizing the operating spectral range of a metalens. This is of importance for practical applications, and as a metric for comparing the performance of different metalens designs.

Many consumer technologies rely on photodetection of infrared light, such as lidar, low visibility imaging, proximity sensors/range finders, etc. However, silicon, the standard material of the semiconductor industry, becomes transparent for wavelengths above 1.1 µm, as the photons no longer have sufficient energy to stimulate direct band-to-band absorption. We report here a Schottky photodetector design that extends silicon’s optical detection range beyond this 1.1 µm limit, by utilizing internal photoemission of hot carriers. Our design relies on an ultra-thin fractally nanostructured aluminum optical absorber and yet remarkably achieves over 50% absorption of incident light. We demonstrate 2 orders of magnitude improvements of responsivity, noise-equivalent power, and specific detectivity as compared to a reference Schottky photodetector made of bulk metal films. We attribute this to the combination of superior transport and momentum relaxation processes from the nanoscale fractal geometries. Specifically, we show a direct link between internal quantum efficiency enhancement and structural parameters such as perimeter-to-surface ratio. Finally, our devices also function as bulk refractive index sensors. Our approach uses an exceedingly simple complementary metal-oxide-semiconductor (CMOS)-compatible “bottom up” fabrication that is cheap and scalable and is a promising candidate for future cost-effective and robust shortwave infrared photodetection and sensing applications.

The field of metasurfaces is rapidly growing. Nowadays, metasurfaces are considered at the front of artificial optical materials. With metasurfaces, it is possible to control the properties of light for variety of applications, from beam shaping, structural colors, and polarization control to tight focusing, scanning, spatial and spectral filtering, etc. One of the major challenges in the construction of metasurfaces is the need for precise control over their dimensions and consequently their spectral response. In this paper, we demonstrate an approach for postfabrication trimming of dielectric metasurfaces consisting of amorphous silicon layer on top of a quartz substrate, by using local oxidation of silicon technique. The oxidation effectively reduces the radius of the silicon disk, resulting in a blue shift in the observed spectral response. Blue shift of up to 100 nm is demonstrated. Relaxing fabrication tolerances and enabling post-processing techniques is expected to play an important role in promoting the scientific advances of metasurfaces into viable and useful technology. We thus believe that the demonstrated approach will provide an additional important tool to the rapidly developed toolkit of metasurface science and technology.

The absorption in amorphous silicon nano antennas is engineered for the purpose of post process structural change via resonant laser printing by illumination, thus shifting transmission and reflection spectrum in a controlled manner.

The ongoing effort to implement compact and cheap optical systems is the main driving force for the recent flourishing research in the field of optical metalenses. Metalenses are a type of metasurface, used for focusing and imaging applications, and are implemented based on the nanopatterning of an optical surface. The challenge faced by metalens research is to reach high levels of performance, using simple fabrication methods suitable for mass-production. In this paper we present a Huygens nanoantenna based metalens, designed for outdoor photographic/surveillance applications in the near-infra-red. We show that good imaging quality can be obtained over a field-of-view (FOV) as large as +/-15 degrees. This first successful implementation of metalenses for outdoor imaging applications is expected to provide insight and inspiration for future metalens imaging applications.