Directive giant upconversion by supercritical bound states in the continuum.

Photonic bound states in the continuum (BICs), embedded in the spectrum of free-space waves with diverging radiative quality factor, are topologically non-trivial dark modes in open-cavity resonators that have enabled important advances in photonics. However, it is particularly challenging to achieve maximum near-field enhancement, as this requires matching radiative and non-radiative losses. Here we propose the concept of supercritical coupling, drawing inspiration from electromagnetically induced transparency in near-field coupled resonances close to the Friedrich-Wintgen condition.

Integrating collapsible plasmonic gaps on near-field probes for polarization-resolved mapping of plasmon-enhanced emission in 2D material.

Scanning near-field optical microscopy (SNOM) is an important technique used to study the optical properties of material systems at the nanoscale. In previous work, we reported on the use of nanoimprinting to improve the reproducibility and throughput of near-field probes including complicated optical antenna structures such as the 'campanile' probe. However, precise control over the plasmonic gap size, which determines the near-field enhancement and spatial resolution, remains a challenge.

Near-Field Coupling with a Nanoimprinted Probe for Dark Exciton Nanoimaging in Monolayer WSe.

Tip-enhanced photoluminescence (TRPL) is a powerful technique for spatially and spectrally probing local optical properties of 2-dimensional (2D) materials that are modulated by the local heterogeneities, revealing inaccessible dark states due to bright state overlap in conventional far-field microscopy at room temperature. While scattering-type near-field probes have shown the potential to selectively enhance and reveal dark exciton emission, their technical complexity and sensitivity can pose challenges under certain experimental conditions. Here, we present a highly reproducible and easy-to-fabricate near-field probe based on nanoimprint lithography and fiber-optic excitation and collection.

Transferable nano-patterned ALD membrane.

We demonstrate fabrication of nano-patterned thin ALD (Atomic layer deposition) membrane (suspended/transferable) by using a bi-layer resist process where the bottom layer resist acts as a sacrificial layer. This method enables an all dry deterministic transfer of nano-patterned ALD membrane on desired substrate, allowing assembly of multitude of hetero-structures and functionalities that are not yet accessible. Unlike conventional ways of achieving patterned alumina membrane reported in literature our technique requires significantly less fabrication steps and paves the way for novel ALD membrane-based technology.

Sharp, high numerical aperture (NA), nanoimprinted bare pyramid probe for optical mapping.

The ability to correlate optical hyperspectral mapping and high resolution topographic imaging is critically important to gain deep insight into the structure-function relationship of nanomaterial systems. Scanning near-field optical microscopy can achieve this goal, but at the cost of significant effort in probe fabrication and experimental expertise. To overcome these two limitations, we have developed a low-cost and high-throughput nanoimprinting technique to integrate a sharp pyramid structure on the end facet of a single-mode fiber that can be scanned with a simple tuning-fork technique.

Small footprint optoelectrodes using ring resonators for passive light localization.

The combination of electrophysiology and optogenetics enables the exploration of how the brain operates down to a single neuron and its network activity. Neural probes are in vivo invasive devices that integrate sensors and stimulation sites to record and manipulate neuronal activity with high spatiotemporal resolution. State-of-the-art probes are limited by tradeoffs involving their lateral dimension, number of sensors, and ability to access independent stimulation sites.

Visualizing delocalized correlated electronic states in twisted double bilayer graphene.

The discovery of interaction-driven insulating and superconducting phases in moiré van der Waals heterostructures has sparked considerable interest in understanding the novel correlated physics of these systems. While a significant number of studies have focused on twisted bilayer graphene, correlated insulating states and a superconductivity-like transition up to 12 K have been reported in recent transport measurements of twisted double bilayer graphene. Here we present a scanning tunneling microscopy and spectroscopy study of gate-tunable twisted double bilayer graphene devices.

Scalable nanophotonic neural probes for multicolor and on-demand light delivery in brain tissue.

Neural probes arebrain-invasive devices that record and manipulate neural circuits using electricity, light, or drugs. The capability to shine distinct wavelengths and control their respective output locations for activation or deactivation of specific groups of neurons is desirable but remains unachieved. Here, we discuss our probe's capability to deliver two independently controllable wavelengths (450 and 655 nm) in the location(s) of interest using nanophotonic directional couplers and ring resonators.

Antiferromagnetic switching driven by the collective dynamics of a coexisting spin glass.

The theory behind the electrical switching of antiferromagnets is premised on the existence of a well-defined broken symmetry state that can be rotated to encode information. A spin glass is, in many ways, the antithesis of this state, characterized by an ergodic landscape of nearly degenerate magnetic configurations, choosing to freeze into a distribution of these in a manner that is seemingly bereft of information. Here, we show that the coexistence of spin glass and antiferromagnetic order allows a novel mechanism to facilitate the switching of the antiferromagnet FeNbS, rooted in the electrically stimulated collective winding of the spin glass.

Being a Gambler during the COVID-19 Pandemic: A Study with Italian Patients and the Effects of Reduced Exposition.

The COVID-19 pandemic, with the consequent lockdown of about 3 months, can be viewed as an experimental model to observe the impact of the depletion of environmental factors that stimulate gambling, particularly electronic gambling machines (EGMs) that were set to zero. The effects of some structural characteristics of gambling activities that increase gambling behavior were studied among disordered gamblers in treatment in this unique scenario. In fact, studies investigating the effects of the lockdown on problem gamblers (PGs) under treatment are missing.

Tunable rainbow light trapping in ultrathin resonator arrays.

Rainbow light trapping in plasmonic devices allows for field enhancement of multiple wavelengths within a single device. However, many of these devices lack precise control over spatial and spectral enhancement profiles and cannot provide extremely high localised field strengths. Here we present a versatile, analytical design paradigm for rainbow trapping in nanogroove arrays by utilising both the groove-width and groove-length as tuning parameters.

Gallium phosphide optical metasurfaces for visible light applications.

There are few materials that are broadly used for fabricating optical metasurfaces for visible light applications. Gallium phosphide (GaP) is a material that, due to its optical properties, has the potential to become a primary choice but due to the difficulties in fabrication, GaP thin films deposited on transparent substrates have never been exploited. In this article we report the design, fabrication, and characterization of three different amorphous GaP metasurfaces obtained through sputtering.

Probing the Mechanisms of Strong Fluorescence Enhancement in Plasmonic Nanogaps with Sub-nanometer Precision.

Plasmon-enhanced fluorescence is demonstrated in the vicinity of metal surfaces due to strong local field enhancement. Meanwhile, fluorescence quenching is observed as the spacing between fluorophore molecules and the adjacent metal is reduced below a threshold of a few nanometers. Here, we introduce a technology, placing the fluorophore molecules in plasmonic hotspots between pairs of collapsible nanofingers with tunable gap sizes at sub-nanometer precision.

Near-field enhancement in oxidized close gap aluminum dimers.

Aluminum bowtie nanoantennas represent a possibility to confine and enhance electromagnetic (EM) field at optical frequencies in subwavelength regions by using an abundant and inexpensive metal. The native oxidation process of this metal is often viewed as a limitation for its application in plasmonics. Here, we show that in close gap configurations, the high refractive index of the native aluminum oxide helps in squeezing the plasmonic mode in extremely reduced size volumes, providing a higher EM near-field confinement and enhancement in the bowtie antenna gaps than achieved in the pure aluminum counterpart.

Selectively accessing the hotspots of optical nanoantennas by self-aligned dry laser ablation.

Plasmonic nanostructures serve as optical antennas for concentrating the energy of incoming light in localized hotspots close to their surface. By positioning nanoemitters in the antenna hotspots, energy transfer is enabled, leading to novel hybrid antenna-emitter-systems, where the antenna can be used to manipulate the optical properties of the nano-objects. The challenge remains how to precisely position emitters within the hotspots.

Long-Range Exciton Diffusion in Two-Dimensional Assemblies of Cesium Lead Bromide Perovskite Nanocrystals.

Förster resonant energy transfer (FRET)-mediated exciton diffusion through artificial nanoscale building block assemblies could be used as an optoelectronic design element to transport energy. However, so far, nanocrystal (NC) systems supported only diffusion lengths of 30 nm, which are too small to be useful in devices. Here, we demonstrate a FRET-mediated exciton diffusion length of 200 nm with 0.

Tuning the exponential sensitivity of a bound-state-in-continuum optical sensor.

In this work, we investigate the evanescent field sensing mechanism provided by an all-dielectric metasurface supporting bound states in the continuum (BICs). The metasurface is based on a transparent photonic crystal with subwavelength thickness. The BIC electromagnetic field is localized along the direction normal to the photonic crystal nanoscale-thin slab (PhCS) because of a topology-induced confinement, exponentially decaying in the material to detect.

A nanochannel through a plasmonic antenna gap: an integrated device for single particle counting.

Plasmonic nanoantennas are ideal for single molecule detection since they nano-focus the light beyond diffraction and enhance the optical fields by several orders of magnitude. But delivering the molecules into these nanometric hot-spots is a real challenge. Here, we present a dynamic sensor, with label-free real-time detection capabilities, which can detect and count molecules and particles one by one in their native environment independently of their concentration.

Strongly coupled magnon-phonon dynamics in a single nanomagnet.

Polaritons are widely investigated quasiparticles with fundamental and technological significance due to their unique properties. They have been studied most extensively in semiconductors when photons interact with various elementary excitations. However, other strongly coupled excitations demonstrate similar dynamics.

Very High Refractive Index Transition Metal Dichalcogenide Photonic Conformal Coatings by Conversion of ALD Metal Oxides.

Materials for nanophotonic devices ideally combine ease of deposition, very high refractive index, and facile pattern formation through lithographic templating and/or etching. In this work, we present a scalable method for producing high refractive index WS layers by chemical conversion of WO synthesized via atomic layer deposition (ALD). These conformal nanocrystalline thin films demonstrate a surprisingly high index of refraction (n > 3.

Atomic layer deposition for spacer defined double patterning of sub-10 nm titanium dioxide features.

The next generation of hard disk drive technology for data storage densities beyond 5 Tb/in will require single-bit patterning of features with sub-10 nm dimensions by nanoimprint lithography. To address this challenge master templates are fabricated using pattern multiplication with atomic layer deposition (ALD). Sub-10 nm lithography requires a solid understanding of materials and their interactions.

Optical Biosensors Based on Photonic Crystals Supporting Bound States in the Continuum.

A novel optical label-free bio-sensing platform based on a new class of resonances supported in a photonic crystal metasurface is reported herein. Molecular binding is detected as a shift in the resonant wavelength of the bound states in the continuum of radiation modes. The new configuration is applied to the recognition of the interaction between protein p53 and its protein regulatory partner murine double minute 2 (MDM2).

Nanoimprinted High-Refractive Index Active Photonic Nanostructures Based on Quantum Dots for Visible Light.

A novel method to realizing printed active photonic devices was developed using nanoimprint lithography (NIL), combining a printable high-refractive index material and colloidal CdSe/CdS quantum dots (QDs) for applications in the visible region. Active media QDs were applied in two different ways: embedded inside a printable high-refractive index matrix to form an active printable hybrid nanocomposite, and used as a uniform coating on top of printed photonic devices. As a proof-of-demonstration for printed active photonic devices, two-dimensional (2-D) photonic crystals as well as 1D and 2D photonic nanocavities were successfully fabricated following a simple reverse-nanoimprint process.

Hybrid photonic-plasmonic near-field probe for efficient light conversion into the nanoscale hot spot.

In this Letter, we present a design and simulations of the novel hybrid photonic-plasmonic near-field probe. Near-field optics is a unique imaging tool that provides optical images with resolution down to tens of nanometers. One of the main limitations of this technology is its low light sensitivity.