Broadband absorbers capable of attenuating electromagnetic radiation from terahertz (THz) to deep-ultraviolet (DUV) frequencies are critical components in spectroscopy, imaging, sensor technology, and energy harvesting systems. However, most conventional absorbers are limited by their narrow operational bandwidth and often require complex or costly nanostructuring. In this study, we present a black nickel (b-Ni) coating fabricated via scalable electrodeposition onto copper substrates, followed by controlled acid etching, as a cost-effective and robust broadband absorber. The resulting b-Ni films, characterized by scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS), demonstrate ultrabroadband absorption spanning from 30 to 1500 THz, with absorptivity exceeding 95% throughout this range. Compared to nanostructured metamaterials and moth-eye analogs, the b-Ni coating offers significant advantages in fabrication simplicity and scalability. This work positions chemically etched b-Ni coatings as a highly promising material for large-area applications in spectral and imaging instrumentation, including emerging systems operating within the THz frequency range.

Coherent anti-Stokes Raman scattering (CARS) enables chemically specific vibrational imaging of a wide range of samples. Because CARS is a third-order nonlinear optical process, it requires high-intensity laser pulses to generate measurable signals, which can, however, risk damaging the sample. Metal nanostructures can enhance the local electromagnetic field via plasmonic effects, leading to a stronger CARS signal without further increasing laser intensity. In this work, we investigated polycrystalline diamond films decorated with various metal nanostructures to identify which types of metals can enhance the CARS signal. We demonstrate that gold and titanium nanostructures effectively boost the resonant CARS response, while for nickel, copper, and silver, high laser intensities lead to thermal modification of the nanostructures, limiting their practical use for signal enhancement.

Single‐crystal diamond needles (SCDNs) have emerged as promising candidates for optical and quantum sensing applications due to their unique shape, high‐quality crystalline structure, and availability for relatively simple mass production. In this study, morphology modification and luminescence features of SCDNs subjected to high‐temperature oxidation in air at 650 °C and 700 °C are investigated. Significant morphological changes, including sharpening, length reduction, and surface feature formation, are revealed as a result of oxidation with scanning electron microscopy observations. The morphology modifications are dependent on oxidation temperature. Gradual sharpening and formation of surface protrusions with (100) and (111) surfaces during oxidation at 650 °C significantly accelerate at oxidation temperature increase to 700 °C. Observed formation of the surface protrusions is explained by local variation in resistance to oxidation at diamond needle surface. Furthermore, photon correlation measurements reveal that oxidation duration may be optimized allowing obtaining of SCDNs with single nitrogen‐vacancy centers situated in their tips, and confirming the viability of these diamonds for quantum sensing. This findings highlight the superior optical properties and structural integrity of SCDNs, making them highly suitable for single‐photon emission and other quantum technological applications.

Efficient catalysts for both photo- and electrocatalytic applications are essential for sustainable technologies. The combination of In2O3 and TiO2 offers tunable structural and electronic properties, supporting multifunctional catalytic applications. We prepare nanostructured In2O3/TiO2 composites with varying oxide ratios and at different temperatures. The resulting powders and thin films are thoroughly characterized to assess their structure, crystallinity, and surface area. Photocatalytic activity depends strongly on composition, with 70-90 wt% TiO2 samples showing the highest enhancement in hydroxyl radical generation and rhodamine B degradation, attributed to increased specific surface area and improved charge separation. In oxygen electroreduction, catalytic activity increases for TiO2 and In2O3 as the annealing temperature rises from 200 to 450 degrees C. Formation of composites between the two oxides does not result in a significant inprovement in electrocatalytic activity. These findings highlight the potential of In2O3/TiO2 systems as tailored and multifunctional catalysts for environmental remediation and energy conversion.

Carbon nitride quantum dots (CNQDs) are emerging as versatile photocatalytic materials with promising applications in biomedicine and environmental remediation. In this study, we synthesized pristine and sulfur-doped CNQDs via a hydrothermal method, and characterized them using transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and UV-vis absorption spectroscopy. For the first time, the quantum yields of superoxide and singlet oxygen generation were measured for CNQDs. Sulfur doping was found to significantly enhance superoxide generation while concurrently suppressing singlet oxygen production, offering a powerful mechanism for tailoring reactive oxygen species (ROS) output. In addition, all CNQD samples produced hydrogen peroxide and hydroxyl radicals. The ability of these nanomaterials to produce multiple ROS types underscores their potential as hypoxia-resistant photosensitizers (PSs) for photodynamic therapy (PDT) and as efficient photocatalysts for pollutant degradation.

In this study, glass microspheres (GMs) of varying sizes, both pure and decorated with nano-sized bimetallic Ni (80)Fe(20) particles, were incorporated into epoxy-based composites filled with 3 wt% graphite nanoparticles (GNPs) to create 2D and 3D structures. The electromagnetic interference (EMI) shielding properties were analyzed in the Ka-band (25-36 GHz). The addition of GMs altered the frequency dependence of shielding efficiency (SET) and shifted the balance between shielding by reflection (SER) and absorption (SEA). In GNPs-only composites, SEA was much smaller than SER, whereas in all GMs-containing materials, SEA significantly exceeded SER. At higher frequencies, the absorption-to-reflection loss ratio increased, reaching 4 at 36 GHz. For 2D GM structures with a thickness of 0.6-0.8 mm, absorption exhibited a sharp frequency dependence at lower frequencies. In contrast, 3D GM structures with a thickness greater than 2.5 mm maintained a frequency-independent absorption with a value of 0.95. These results highlight that incorporating GMs into epoxy/3% GNP composites enhances absorption mechanisms in their interaction with electromagnetic waves.

This work presents the design, the development and the experimental validation of a portable, low-cost sensing system for the detection of waterborne pollutants. The proposed system is based on Electrochemical Impedance Spectroscopy and PPF+Ni nanomembrane sensors. Designed in response to the increasing demand for in situ water quality monitoring, the system integrates a simplified, scalable EIS acquisition architecture compatible with microcontroller-based platforms. The sensing configuration utilises the voltage divider principle, ensuring simplicity in signal conditioning by allowing compatibility with different electrode types through passive impedance matching. In addition, new merit figures have been proposed and implemented to analyse the measures. The proposed platform was experimentally characterised for its measurement stability, accuracy and environmental robustness. Sensitivity tests using benzoquinone as a target analyte demonstrated the capability of detecting concentrations as low as 0.1 mM with a monotonic response over increasing concentrations. A comparative study with a commercial electrochemical system (PalmSens4) under identical conditions highlighted the higher resolution and practical advantages of the proposed method despite operating with a lower impedance range. Additionally, the system exhibited reliable discrimination across tested concentrations and greater adaptability for integration into field-deployable environmental monitoring platforms. Future developments will focus on optimising selectivity through new sensor materials and analytical modelling of uncertainty propagation in the analysis based on defined figures of merit.

This study presents a comprehensive analysis aimed at validating the use of an innovative nanosensor based on graphitic nanomembranes for the smart monitoring of industrial wastewater. The validation of the potential of the nanosensor was carried out through the development of advanced analytical methodologies, a direct experimental comparison with commercially available electrode sensors commonly used for the detection of chemical species, and the evaluation of performance under conditions very similar to real-world field applications. The investigation involved a series of controlled experiments using an organic pollutant—benzoquinone—at varying concentrations. Initially, data analysis was performed using classical linear regression models, representing a conventional approach in chemical analysis. Subsequently, a more advanced methodology was implemented, incorporating machine-learning techniques to train a classifier capable of detecting the presence of pollutants in water samples. The study builds upon an experimental protocol previously developed by the authors for the nanomembranes, based on electrochemical impedance spectroscopy. The results clearly demonstrate that integrating the nanosensor with machine-learning algorithms yields significant performance. The intrinsic properties of the nanosensor make it well-suited for potential integration into field-deployable platforms, offering a real-time, cost-effective, and high-performance solution for the detection and quantification of contaminants in wastewater. These features position the nanomembrane-based sensor as a promising alternative to overcome current technological limitations in this domain.

This study presents a detailed investigation into the fluorescence properties of color centers in single-crystal diamond needles (SCDNs) synthesized via chemical vapor deposition. Using steady-state and time-resolved photoluminescence (PL) techniques, we identified color centers with zero-phonon lines at 389 nm, 468 nm, 575 nm (NV0), 637 nm (NV-), and 738 nm (SiV-). PL excitation spectroscopy conducted at room temperature revealed the complex electronic structure of some of these centers, paving the way for further investigation into their fluorescence properties. Lifetime measurements were performed for each center, with the 389 nm one exhibiting the longest decay time (∼30 ns), which is advantageous for enhancing quantum coherence, improving photon emission efficiency, and reducing power consumption. Altogether, these findings highlight the potential of SCDNs for quantum applications and confirm their promise as a platform for next-generation photonic and quantum devices.

Graphene's exceptional nonlinear optical properties combined with resonant photonic structures offer a promising pathway for efficient nonlinear applications at terahertz (THz) frequencies. In this work, we propose and demonstrate a fabrication-friendly hybrid nonlinear metasurface composed of gold patches integrated with uniform graphene, circumventing the need for complex graphene patterning. The structure supports strong localized resonances that enhance nonlinear interactions. By exploiting resonant enhancement at both the fundamental and third harmonic frequencies, we predict via simulations third-harmonic generation efficiencies as high as -15 dB (3.2%) under continuous-wave excitation at modest intensities (0.1 MW/cm2). The metasurface is fabricated via electron-beam lithography and experimentally characterized under pulsed excitation using THz time-domain spectroscopy. The broadband excitation spectrum prevents unambiguous isolation of a third-harmonic signal; however, we experimentally observe pronounced nonlinear frequency shifts up to 0.5 THz (12.5% fractional change), driven by self-phase modulation, consistent with simulation results. Our findings highlight the potential of tailored graphene-based metasurfaces for efficient nonlinear THz photonic devices.

Pyrolyzed photoresist films (PPFs), of 150 nm thickness were developed via vacuum annealing of a photoresist. The high frequency conductivity of PPF was investigated via contactless THz time-domain spectroscopy (TDS). The PPF sheet resistance was found to be comparable to that of CVD graphene. Our findings open a path for simple and scalable fabrication of graphitic-film-based high frequency nanocircuits.

We analyzed theoretically and experimentally the inter-element coupling behavior between the periodic structure's so-called "meta-atoms" by varying the number of meta-atoms arranged periodically in the array. For this reason a planar metamaterial consisting of ring-shaped subwavelength periodic structures on a thin metal film was developed to exhibits a resonant transparency at the frequency of about 0.35 THz. The cross-talk between the meta-atoms due to electromagnetic multipole interferences lead to a significant change in resonance bandwidth and the quality (Q) factor. We anticipate that found coupling behavior between inter-element with subwavelength dimensions can potentially be used for a variety of applications such as filters, multi-pixel emitter and detector arrays, etc. for broad THz frequencies.

Monitoring of tiny intracell temperature variations is of high importance to understand the mechanisms of exothermic/endothermic processes inside the living cells. Small shifts in thermal balance may drastically influence cell functioning and induce pathological conditions. By using biocompatible diamond single‐crystal microneedles enriched with nitrogen‐vacancy (NV)/silicon‐vacancy (SiV) color centers, this study demonstrates all‐optical in vitro temperature monitoring in the physiologically significant range (25–55 °C). Zero‐phonon line (ZPL) of SiV centers belonging to the “therapeutic window” is used to improve measurement precision via suppression of the tissue autofluorescence. The simultaneous detection of the NV and SiV fluorescence enables two‐band visualization of the living cells combined with the temperature sensing. This study demonstrates experimentally that temperature can be measured by lifetime, full‐width at half maximum, and peak position of SiV ZPL, while accuracy can be further improved by normalizing the photoluminescence (PL) ZPL peak intensity on the PL signal measured at the wavelength where it is temperature independent. According to performed numerical simulations diamond microneedles enable real‐time temperature measurements because their characteristic heating time is less than 10 ns. The results open a way toward accurate, noninvasive, precise, and real‐time monitoring of temperature variations accompanying intracellular biochemical reactions and processes on the single‐cell level.

We demonstrated that wide-field second harmonic generation (SHG) microscopy of lung tissue in combination with quantitative analysis of SHG images is a powerful tool for fast and label-free visualization of the fibrosis pathogenesis in pulmonary arterial hypertension (PAH). Statistical analysis of the SHG images revealed changes of the collagen content and morphology in the lung tissue during the monocrotaline-induced PAH progression in rats. First order statistics disclosed the dependence of the collagen overproduction on time, the second order statistics indicated tightening of collagen fiber network around blood vessels and their spreading into the alveolar region. Fourier analysis revealed that enhancement of the fiber orientation in the collagen network with PAH progression was followed with its subsequent reduction at the terminating phase of the disease. Proposed approach has potential for assessing pulmonary fibrosis in interstitial lung disease, after lung(s) transplantation, cancer, etc.

Measured conductivity of Pyrolytic carbon. Ac conductivity measured in THz frequency range by time domain THz spectrometer, reconstructed from transmittance and reflectance measurements for different types of synthesised directly on dielectric SiO2 substrates at 1000C by annealing at 900 C using different carbon precursors (photoresists, mentioned in data sheets). Last column corresponds to conductivity of those samples calculated in effective medium theory, see details for measurements and theory in: P. Kuzhir, A. Celzard, and X. Chen, “Microwave absorption by carbon-based materials and structures (Editorial),” Journal of Applied Physics, 131, 200401 (2022)

We experimentally and theoretically investigated the effects of ionizing radiation on a stack of graphene sheets separated by polymethyl methacrylate (PMMA) slabs. The exceptional absorption ability of such a heterostructure in the THz range makes it promising for use in a graphene-based THz bolometer to be deployed in space. A hydrogen/carbon ion beam was used to simulate the action of protons and secondary ions on the device. We showed that the graphene sheets remain intact after irradiation with an intense 290 keV ion beam at the density of 1.5×1012 cm−2. However, the THz absorption ability of the graphene/PMMA multilayer can be substantially suppressed due to heating damage of the topmost PMMA slabs produced by carbon ions. By contrast, protons do not have this negative effect due to their much longer mean free pass in PMMA. Since the particles’ flux at the geostationary orbit is significantly lower than that used in our experiments, we conclude that it cannot cause tangible damage of the graphene/PMMA based THz absorber. Our numerical simulations reveal that, at the geostationary orbit, the damaging of the graphene/PMMA multilayer due to the ions bombardment is sufficiently lower to affect the performance of the graphene/PMMA multilayer, the main working element of the THz bolometer, which remains unchanged for more than ten years.

The dielectric/electric properties of the Ni@C (carbon-coated Ni)/epoxy composites and Ni@C/MWCNTs (multi-walled carbon nanotubes)/epoxy composites loaded with fixed MWCNTs amount just below the percolation threshold (0.09 vol.%) and Ni@C at different concentrations up to 1 vol.% were investigated in broad frequency (20 Hz–40 GHz) and temperature (30 K–500 K) regions. In composites with the only Ni@C nanoparticles, the electrical percolation threshold was determined between 10 and 15 vol.%. Above the percolation threshold the dielectric permittivity (ε’) and the electrical conductivity (σ) of the composites loaded with Ni@C only are high enough, i.e., ε’ = 105 and σ = 0.6 S/m at 100 Hz for composites with 30 vol.% Ni@C, to be used for electromagnetic shielding applications. The annealing to 500 K was proved to be an effective and simple tool to decrease the percolation threshold in epoxy/Ni@C composites. For hybrid composites series an optimal concentration of Ni@C (0.2 vol.%) was determined, leading to the conductivity absolute values several orders of magnitude higher than that of a composite filled with MWCNTs only. The synergy effects of using both fillers have been discussed. Below room temperature the electrical transport is mainly governed by epoxy resin compression in all composites, while the electron tunnelling was observed only in hybrid composites below 200 K. At higher temperatures (above 400 K), in addition to the nanoparticles redistribution effects, the electrical conductivity of epoxy resin makes a significant contribution to the total composite conductivity. The dielectric relaxation spectroscopy allows estimating the nanoparticles distributions in polymer matrix and could be used as the non-destructive and fast alternate to microscopy techniques for general polymer composite fabrication control.

The scattering theory for two crossing metallic single-walled carbon nanotubes of finite length exposed to an electromagnetic field has been developed based on a synthesis of the quantum transport formalism and classical electrodynamics. The model of the point contact has been developed to be incorporated into the Hall\'en and Pocklington equations for crossing carbon nanotubes. The influence of the contact conductance and position as well as the angle between the tube axes on the tube polarizability has been analyzed in the range of 1 GHz to 10 THz. The physical mechanisms responsible for the electromagnetic interaction between crossing tubes with zero and nonzero intertube contact conductance are shown and discussed. The influence of the coupling between the tubes on the localized plasmon resonance in them has been demonstrated.

Composite materials with 83 wt.% of the 0.7Pb(Mg1/3Nb2/3)O3-0.3PbTiO3 distributed in phosphate-bonded ceramics were prepared at three different pressures. A phosphate matrix comprises a mixture of an aluminum phosphate binder and melted periclase, MgO. All samples demonstrate a homogeneous distribution of the ferroelectric perovskite phase and are thermally stable up to 900 K. At higher temperatures, the pyrochlore cubic phase forms. It has been found that the density of the composites non-monotonously depends on the pressure. The dielectric permittivity and losses substantially increase with the density of the samples. The fabricated composites demonstrate diffused ferroelectric–paraelectric transition and prominent piezoelectric properties.