Efficient conversion of mid-infrared (MIR) radiation into electricity remains a challenge for thermoelectric devices. We present multiresonant Ag–Si:B–Ni bowtie cross nanoantenna (BCN) arrays that exploit plasmon-enhanced photothermal effects to achieve broadband MIR absorption and voltage generation via the Seebeck effect. The 9×9 BCN arrays, fabricated by electron beam lithography, exhibit multiple plasmonic resonances from 18 to 48 THz with a ∼30 THz bandwidth. COMSOL simulations reveal strong field confinement and open-circuit voltages up to 11.19 μV under 1000 W·m2 illumination, which are experimentally validated by Fourier Transform Infrared measurements. The broadband response, geometry-dependent tunability, and efficient heat-to-electric conversion establish BCNs as promising candidates for waste-heat harvesting, MIR sensing, and plasmonic metasurface thermoelectrics.

Deep learning has emerged as a transformative approach for on-demand inverse design of chiral metamaterials and nanophotonic devices. However, the inherent black-box nature of neural networks (NNs) poses significant challenges in interpreting the multimodal optical responses predicted by data-driven models. We develop a hybrid architecture that integrates an expanding-width NN with a Gaussian parsing NN to achieve spectral decoding and inverse design of chiral plasmonic nanoantennas. The expanding-width NN adopts a neuron-doubling architecture across successive layers, effectively broadening gradient propagation pathways to mitigate vanishing gradients, thereby enabling accurate predictions of nanoantenna scattering, absorption, and near-field spectra (mean squared error <0.0077). Importantly, the Gaussian parsing NN decomposes complex plasmonic spectral responses into fundamental eigenmodes, quantitatively resolving critical parameters such as the dominant mode count, linewidth, and resonance wavelengths. Furthermore, we utilize this framework to establish an end-to-end mapping from geometric parameters to tailored plasmonic modes that govern circular dichroism and Fano resonance. Our methodology not only bridges data-driven design with physical interpretability but also paves the way for new applications in topological photonic circuits, single-molecule biosensors, and hyperspectral computational imaging.

Within an optical nanocavity, the temperature dependence of the emission wavelength defines its emission energy stability. Thermal management, therefore, is crucial in controlling wavelength drift, and/or radiative recombination rates, especially in electrically-driven light sources. Our results show that heat accumulation in a nanocavity directly depends on its geometry, orientation and interface area with the underlying substrate. We use the temperature-dependence of the bandgap to compare the heat retention in nanocavities with lateral and standing orientations. For this purpose, we compare lateral nanofins (fins), and free-standing nanopillars, a.k.a., nanowires (NWs). Hyperspectral cathodoluminescence (CL) microscopy is used to monitor the temperature dependence of the bandgap. Results show that the emission energy of a lateral nanocavity is less dependent on temperature variation compared to that of a standing one. This variation in temperature dependence is attributed to the extent of heat accumulation in the lattice. It is shown that the retained heat in a nanocavity depends on its interface area with the underlying substrate and its surface-to-volume ratio, where the former is the predominant factor. Theoretical modeling shows that introducing a short heat pulse to a standing-nanostructure results in a rapid temperature increase. The initial heating is due to the ultrafast phonon-phonon couplings and build-up of lattice heat. By increasing the interface area between the nanostructure and the substrate the temperature spike disappeared. Results show the interface area has a far more important contribution than a larger surface-to-volume ratio in heat dissipation. These findings are particularly significant in thermal management of electrically-driven optical nanocavities, where operating temperatures could exceed 350 K. As such, while the design and fabrication of efficient nanocavities are essential, controlling their thermal interactions with the surrounding are equally important. Interfacial engineering thus plays a vital role in developing built-in mechanisms for realization of efficient and stable nanoscale light sources.

The large-area epitaxial growth of wafer-scale hexagonal boron nitride (h-BN) with a uniform surface and high crystalline quality is crucial for the fabrication and application of h-BN-based two-dimensional (2D) material devices. We investigate the influence of the V/III ratio on the crystal quality of h-BN by varying the triethylboron flow rate in metal-organic chemical vapor deposition. The results indicate that a lower V/III ratio enhances boron atom mobility, facilitating the lateral growth of h-BN, but too low V/III ratio will lead to a high concentration of carbon impurity doping. By optimizing the V/III ratio, we successfully achieve the growth of h-BN films on 2-in. sapphire substrate, with a particle-free surface, low impurity concentrations, and high crystalline quality. Based on high-quality h-BN, a deep ultraviolet photodetector is fabricated, demonstrating excellent response under 193 nm illumination. At 50 V and a light power density of 15.95 μW/mm2, the detector achieves a responsivity of 0.72 mA/W, a specific detectivity of 9.53×1011 Jones, and an on-off ratio of 103, with a response time in the millisecond range. We optimize the growth conditions for high-quality h-BN and realize the fabrication of optoelectronic devices, thereby paving the way for future wafer-scale 2D semiconductor electronic devices.

A wider bio-optical waveguide is always desirable for large-field illumination of an optical waveguide microscopy. However, a wider waveguide leads to non-uniform illumination due to non-uniform evanescent field excited by multi-mode interference (MMI) patterns of waveguides. We introduce a seven-layer model of bio-waveguide for optical waveguide microscopy to analyze the waveguide-cell system. We also develop an averaging strategy of MMI pattern images by moving the coupling position to generate uniform illumination inside a wide bio-optical waveguide. Then, we systematically investigate the averaging strategy of MMI pattern images due to wide waveguide, at the wavelengths of 488, 532, and 646 nm. Finally, we demonstrate a 25% uniform improvement by the averaging strategy inside a wide bio-optical waveguide, compared with the conventional strategy.

Motivated by the demand for achieving high modulation depth of optical signal in three-dimensional (3D) imaging light detection and ranging (LIDAR), the electro-optic (EO) modulation depth of KTa1−x NbxO3 (KTN) crystal and its stability under the electric field have been investigated. The strong field-enhanced effect of dielectric permittivity occurs owing to the dielectric resonance, the modulation depth is enhanced, and half-wave voltage is further reduced. Only when the alternating current (AC) electric field is applied, the modulation depth increases with the increment of the electric field and trends to remain unchanged under the high owing to the saturation of polar nanoregions (PNRs) in KTN crystal. The modulation depth fluctuates with time, which can reduce the ranging accuracy of 3D imaging LIDAR. We found it can be attributed to the instability of PNRs. After applying the direct current (DC) electric field, the modulation depth was increased and its stability was enhanced owing to the improved polarization and enhanced stability of PNRs. The result reveals that the DC + AC electric field can increase the ranging accuracy of LIDAR compared to the AC electric field. We will provide guidance for designing the EO modulator in high-accuracy 3D imaging LIDAR from the perspective of nanodomain engineering and electric field-driven systems.

Plasmonic supercrystals (PSCs) made by colloidal self-assembly metallic nanoparticles can be regarded as a special kind of optical metamaterials with intriguing properties, such as engineered refractive indices and densely distributed near field “hot spots.” Analysis of the Purcell effect of PSCs is crucial for many applications related to light-emission processes, such as surface-enhanced Raman scattering and spontaneous emission enhancement. We present a detailed theoretical and numerical study on the Purcell effect of films and nanocavities made of PSCs. We first demonstrate that the spectral response of the Purcell effect of a monolayer PSC can be basically divided into the surface plasmon polariton regime, the collective plasmon (CP) regime, and the dielectric regime. In particular, we reveal that the resonances in the CP regime have rich fine structures of near fields, resulting in a strong dependence of the Purcell effect on the position and polarization of emitters. We further show that nanocavities consist of PSCs that sustain Mie-like electric and magnetic multipolar resonances that can be utilized to enhance the Purcell effect in the near-infrared band. Our results are helpful for understanding the light–matter interactions at nanoscale and may promote applications of PSCs in light-emission engineering.

Nitrogen and sulfur co-doped green fluorescent carbon dots (G-CDs) with quantum yield (QY) of 28.26% were synthesized by hydrothermal method with p-phenylenediamine and thiosemicarbazone as precursors. The synthesized G-CDs exhibit good sensitivity and anti-interference ability for detecting copper ion (Cu2+) by fluorescence quenching (λex=390 nm, λem=535 nm) with a linear range of 20 to 200 μM and the limit of detection of 4.8 μM. This analytical method has been applied to detect Cu2+ of the local lake with good accuracy and recovery.

Temporally periodic physical vapor deposition (TP-PVD) is commonly used to fabricate Bragg mirrors on planar surfaces. These devices are notionally of infinite transverse extent and homogeneity, but they have periodically nonhomogeneous electromagnetic constitutions in the thickness direction. Undertaking TP-PVD in two different formats, we found that the Bragg phenomenon can be avoided in certain thin-film applications by undertaking TP-PVD on surfaces roughened randomly on the scale of the wavelength.

Hybrid plasmonic waveguides (HPWs) are capable of supporting subwavelength optical modes. In a composite HPW (CHPW), the propagation loss can be minimized by adjusting the geometrical parameters of its component layers to reduce field flux inside its lossy metal layer. A ring resonator-based plasmonic sensor based on a waveguide structure of suspended CHPW (SCHPW) is designed for gas sensing applications. SCHPWs are applied for the introduced sensor's 200-nm-wide bus waveguide and 1-μm-radius ring resonator. The operational parameters of the sensor, such as sensitivity and figure of merit (FOM), are investigated in the near-infrared region using a three-dimensional finite-difference time-domain method. For two considered resonances of the proposed sensor, sensitivities of 236.2 and 270 nm / RIU with FOMs of 67.4 and 37.5 RIU − 1 are achieved, respectively. Additionally, for the proposed sensor, a straightforward mechanism for sensing the mass density of the polarizable hydrogen gas is introduced using the theoretical index–density relation of Lorentz–Lorenz. The mass density sensitivities of 358.2 and 409.3 nm / ( g / cm3 ) are achieved for the two considered resonances for the hydrogen gas at the range of 0 to 0.05 g / cm3.