Search Results (260)

Ternary and quaternary compounds offer vast potential for tailoring material properties through compositional adjustments and complex interactions among their constituent elements. However, many of their compositional possibilities still need to be investigated. Energy-dispersive X-ray spectroscopy (EDX) is crucial for determining elemental composition but is inadequate for identifying chemical bonds and physical properties. This work introduces a novel methodology using a stoichiometric deviation vector (SDV) to estimate the physical and compositional feature characteristics of Si, N, and O compounds by comparing actual molar ratios with ideal stoichiometric references. We validated this method by estimating Si-O bonds in silicon oxynitride samples, demonstrating strong agreement with FTIR and refractive index results. We also extended our proof of principle for SiAlON compounds and established an adaptable procedure to analyze compounds with more than three elements. This flexible methodology will significantly value the materials research community, providing valuable compositional features and physical insights by performing elemental EDX characterizations. Full article

A large number of the thin-film organic structures (polyimides, 2-cyclooctylarnino-5-nitropyridine, N-(4-nitrophenyl)-(L)-prolinol, 2-(n-Prolinol)-5-nitropyridine) sensitized with the different types of the nano-objects (fullerenes, carbon nanotubes, quantum dots, shungites, reduced graphene oxides) are presented, which are studied using the holographic technique under the Raman–Nath diffraction conditions. Pulsed laser irradiation testing of these materials predicts a dramatic increase of the laser-induced refractive index, which is in several orders of the magnitude greater compared to pure materials. The estimated nonlinear refraction coefficients and the cubic nonlinearities for the materials studied are close to or larger than those known for volumetric inorganic crystals. The role of the intermolecular charge transfer complex formation is considered as the essential in the refractivity increase in nano-objects-doped organics. As a new idea, the shift of charge from the intramolecular donor fragment to the intermolecular acceptors can be proposed as the development of Janus particles. The energy losses via diffraction are considered as an additional mechanism to explain the nonlinear attenuation of the laser beam. Full article

Colloidal Cu₂O nanoparticles can exhibit both photocatalytic activity under visible light illumination and resonant Mie scattering, but, for their practical application, they have to be immobilized on a substrate. Butterfly wings, with complex hierarchical photonic nanoarchitectures, constitute a promising substrate for the immobilization of nanoparticles and for the tuning of their optical properties. The native wax layer covering the wing scales of Polyommatus icarus butterflies was removed by simple ethanol pretreatment prior to the deposition of Cu₂O nanoparticles, which allowed reproducible deposition on the dorsal blue wing scale nanoarchitectures via drop casting. The samples were investigated by optical and electron microscopy, attenuated total reflectance infrared spectroscopy, UV–visible spectrophotometry, microspectrophotometry, and hyperspectral spectrophotometry. It was found that the Cu₂O nanoparticles integrated well into the photonic nanoarchitecture of the P. icarus wing scales, they exhibited Mie resonance on the glass slides, and the spectral signature of this resonance was absent on Si(100). A novel bio-nanohybrid photonic nanoarchitecture was produced in which the spectral properties of the butterfly wings were tuned by the Cu₂O nanoparticles and their backscattering due to the Mie resonance was suppressed despite the low refractive index of the chitinous substrate. Full article

With advances in terahertz technology, achieving high and nearly constant birefringence over a wide frequency range plays an extreme role in many advanced applications. In the past decade, significant research efforts have been devoted to creating new systems or elements with high birefringence. To our knowledge, the maximum birefringence attainable using artificial crystals, intrinsic liquid crystals or fiber-based systems has been less than unity. More importantly, the birefringence created in previous studies has exhibited a strong frequency dependence, limiting their practical applications. In this work, we propose a novel approach to achieve extraordinarily high birefringence over a broad terahertz frequency band (>100 GHz). To address the limitation of frequency dependence, we combined the principle of metamaterials with the form birefringence concept. First, we designed a metamaterial with an exceptionally high refractive index, thoroughly characterizing it using simulations and analytical analysis. Next, we systematically investigated the form birefringence concept, exploring its frequency response, geometric limitations, and complex refractive index differences between constituent elements. Finally, we designed a hybrid material system, combining the strengths of both metamaterials and form birefringence. Our results demonstrate the feasibility of achieving a birefringent medium exceeding three orders of magnitude higher than previous reports while maintaining a time-invariant frequency response in the sub-terahertz regime. Full article

Background/Objective: Atherosclerosis is becoming increasingly common in modern society. Owing to the increasing number of complex angioplasty procedures, there is an increasing need for training in cases where the risk of periprocedural complications is high. Methods: A procedure was developed to obtain three-dimensional (3D) models and printing of blood vessels. The mechanical and optical properties of the printed materials were also examined. Angioplasty and stent implantation were tested, and the phantom was compared with the clinical data of patients who underwent interventional treatment. Both laser techniques and cone-beam computed tomography of the phantoms were used for comparison. Results: The printed material exhibited mechanical parameters similar to those of blood vessel walls. The refractive index of 1.473 ± 0.002 and high transparency allowed for non-invasive laser examination of the interior of the print. The printed models behaved similarly to human arteries in vivo, allowing training in treatment procedures and considering vessel deformation during the procedure. Models with stents can be analyzed using laser and cone-beam computed tomography to compare stents from different manufacturers. Conclusions: The developed methodology allows for simple and time-efficient production of personalized vessel phantoms. Full article

Fluorescence flow cytometry is a powerful instrument to distinguish cells or particles labelled with high-specificity fluorophores. However, traditional flow cytometry is complex, bulky, and inconvenient for users to adjust fluorescence channels. In this paper, we present a modular fluorescence flow cytometry (M-FCM) system in which fluorescence channels can be flexibly arranged. Modules for particle focusing and fluorescence detection were developed. After hydrodynamical focusing, the cells were measured in the detection modules, which were integrated with in situ illumination and fluorescence detection. The signal-to-noise ratio of the detection reached to 33.2 dB. The crosstalk among the fluorescence channels was eliminated. The M-FCM system was applied to evaluate cell viability in drug screening, agreeing well with the commercial cytometry. The modular cytometry presents several outstanding features: flexibility in setting fluorescence channels, cost efficiency, compact construction, ease of operation, and the potential to upgrade for multifunctional measurements. The modular cytometry provides a multifunctional platform for various biophysical measurements, e.g., electrical impedance and refractive-index detection. The proposed work paves an innovative avenue for the multivariate analysis of cellular characteristics. Full article

The research referred to in this study examines the morphological, structural, and optical characteristics of kesterite (Cu_1−xAg_x)₂ZnSnS₄ (CAZTS) thin films, which are produced using a process known as thermal evaporation (TE). The study’s main goal was to determine how different Ag contents affect the characteristics of CAZTS systems. X-ray diffraction (XRD) and Raman spectroscopy were used to confirm the crystal structure of the CAZTS thin films. Using a mathematical model of spectroscopic ellipsometry, the refractive index (n) represented the real part of the complex thin films, the extinction coefficient (k) portrayed the imaginary part, and the energy bandgap of the fabricated thin films was calculated. The energy bandgap is a crucial parameter for solar cell applications, as it determines the wavelength of light that the material can absorb. The energy bandgap was found to decrease from 1.74 eV to 1.55 eV with the increasing Ag content. The ITO/n-CdS/p-CAZTS/Mo heterojunction was well constructed, and the primary photovoltaic characteristics of the n-CdS/p-CAZTS junctions were examined for use in solar cells. Different Ag contents of the CAZTS layers were used to determine the dark and illumination (current–voltage) characteristics of the heterojunctions. The study’s findings collectively point to CAZTS thin layers as potential absorber materials for solar cell applications. Full article

The design and optimization of plasmonic nanohole arrays (NHAs) as transducers for efficient bioanalytical sensing is a rapidly growing field of research. In this work, we present a rational method for tailoring the optical and functional properties of Au NHAs realized on planar transparent substrates. Experimental and numerical results demonstrate how the far- and near-field properties of the NHAs can be controlled and optimized for specific sensing applications, proving a valuable insight into the distribution of electric fields generated on the nanostructured metal surface and the depth of penetration into the surrounding media. Metal thickness is found to play a crucial role in determining the sensing volume, while the diameter of the nanoholes affects the localization of the electromagnetic field and the extent of the decay field. The remarkable surface and bulk refractive index sensitivities observed a rival performance of more complex geometric designs reported in the recent literature, showcasing their outstanding potential for chemo-biosensing applications. Full article

A preliminary investigation of the optical properties of complex Cr-based hard coatings and their connection with the compound structure of the coatings is presented. Cr/CrN, Cr/CrN/CrAlN, Cr/CrN/CrTiAlN, and Cr/CrN/CrAlTiN coating structures were deposited through unbalanced magnetron sputtering. Their mechanical properties, especially nanohardness, coefficient of friction, and adhesion, were measured. The structure and composition of the coatings were characterised through SEM, FIB, XPS, and TEM. Their optical properties were investigated by UV-VIS ellipsometry. The optical parameters’ phase difference Δ, the amplitude ratio Ψ, the frequency-dependent real (ε₁(ω)) and imaginary (ε₂(ω)) part of the dielectric function, and the corresponding refractive and extinction indexes n(ω) and k(ω) were measured and modelled via regression analysis implemented using the WVASE© software version 3.686. Satisfactory coincidence was achieved between the measured optical data and the corresponding fitting models. The physical polycrystalline optical constants of the industrial samples were extracted from modelling data with roughness. The analysis of the data showed that ellipsometric characterisation can be used in order to determine the physical properties of Cr-based hard coatings with complex structure and composition, as well as for repeatability control of the deposition process. However, more detailed research is needed to predict the composition based on measured optical properties. Full article

Optical fibre sensors have the potential to be overly sensitive and responsive, making them useful in various applications to detect the presence of pollutants in the environment, toxic gasses, or pesticides in soil. Deoxyribonucleic acid (DNA) as biopolymer active surfaces for fibre sensors can be designed to detect specific molecules or compounds accurately. In the article, we propose to use an optical fibre taper and DNA complex with surfactant-based sensors to offer a promising approach for gas detection, including ammonia solution, 1,4 thioxane, and trimethyl phosphate imitating hazardous agents. The presented results describe the influence of the adsorption of evaporation of measured agents to the DNA complex layer on a light leakage outside the structure of an optical fibre taper. The DNA layer with additional gas molecules becomes a new cladding of the taper structure, with the possibility to change its properties. The process of adsorption causes a change in the layer’s optical properties surrounding a taper-like refractive index and increasing layer diameter, which changes the boundary condition of the structure and interacts with light in a wide spectral range of 600–1200 nm. The research’s novelty is implementing a DNA complex active surface as the biodegradable biopolymer alignment for optical devices like in-line fibre sensors and those enabled for hazardous agent detection for substances appearing in the environment as industrial or even warfare toxic agents. Full article

Tilted fibre Bragg gratings are optical fibre structures used as sensors of various physical quantities. Their unique measurement capabilities result from the high complexity of the optical spectrum consisting of several dozen cladding mode resonances. TFBG spectra demodulation methods generate signal features that highlight changes in the spectrum due to changes in the interacting quantities. Such methods should enable the distinction between two slightly different values of the measured quantity. The paper presents an effective method of processing the TFBG spectrum for use in measuring the refractive index of liquids. The use of Gabor and log-Gabor filters and their adaptive version eliminates the problem of discontinuity in determining the SRI value related to the existence of the cladding mode comb. The Gabor filters used make visible the shifting and fading of spectral features related to the decrease in the intensity of leaking modes. Subsequent modifications of the proposed algorithm led to an increase in the quality factor of the processed spectrum. Full article

CrSBr is a recently discovered two-dimensional anti-ferromagnet. It has attracted much attention due to its superior properties for potential optoelectronic and spintronic applications. However, its complex refractive index with layer dependence has not been systematically studied yet. In this work, we studied the room-temperature complex refractive indices of thin CrSBr flakes of different thicknesses in the visible light range. Using micro-reflectance spectroscopy, we measured the optical contrast of thin CrSBr flakes with respect to different substrates. The complex refractive index was extracted by modeling the optical contrast with the Fresnel equations. We extracted the band gap values of CrSBr in the few-layer limit. We determined the band gaps for monolayer, bilayer, and trilayer CrSBr to be 1.88 eV, 1.81 eV, and 1.77 eV, respectively. As a comparison, the band gap for multilayer CrSBr is outside our measured range, that is, below 1.55 eV. Our results suggest that the band gap of CrSBr decreases as thickness increases. Full article

Since light propagation in a multimode fiber (MMF) exhibits visually random and complex scattering patterns due to external interference, this study numerically models temperature and curvature through the finite element method in order to understand the complex interactions between the inputs and outputs of an optical fiber under conditions of temperature and curvature interference. The systematic analysis of the fiber’s refractive index and bending loss characteristics determined its critical bending radius to be 15 mm. The temperature speckle atlas is plotted to reflect varying bending radii. An optimal end-to-end residual neural network model capable of automatically extracting highly similar scattering features is proposed and validated for the purpose of identifying temperature and curvature scattering maps of MMFs. The viability of the proposed scheme is tested through numerical simulations and experiments, the results of which demonstrate the effectiveness and robustness of the optimized network model. Full article

Aerosol microphysical properties, including aerosol particle size distribution, complex refractive index and concentration properties, are key parameters evaluating the impact of aerosols on climate, meteorology, and human health. High Spectral Resolution Lidar (HSRL) is an efficient tool for probing the vertical optical properties of aerosol particles, including the aerosol backscatter coefficient (β) and extinction coefficient (α), at multiple wavelengths. To swiftly process vast data volumes, address the ill-posedness of retrieval problems, and suit simpler lidar systems, this study proposes an algorithm (modified algorithm) for retrieving microphysical property profiles from the HSRL optical data targeting fine-mode aerosols, building upon a previous algorithm (basic algorithm). The modified algorithm is based on a look-up table (LUT) approach, combined with the k-nearest neighbor (k-NN) and random forest (RF) algorithms, and it optimizes the decision tree generation strategy, incorporating a self-posed scheme. In numerical simulation tests for different lidar configurations, the modified algorithm reduced retrieval errors by 41%, 30%, and 32% compared to the basic algorithm for 3β + 2α, 3β + 1α, and 2β + 1α, respectively, with a remarkable improvement of stability. In two observation scenes of a field campaign, the median relative errors of the effective radius for 3β + 2α were 6% and −3%, and the median absolute errors of single-scattering albedo were 0.012 and 0.005. This method represents a further step toward the use of the LUT approach, with the potential to provide effective and efficient aerosol microphysical retrieval for simpler lidar systems, which could advance our understanding of aerosols’ climatic, meteorological, and health impacts. Full article

This study presents a novel label-free approach for characterizing cell death states, eliminating the need for complex molecular labeling that may yield artificial or ambiguous results due to technical limitations in microscope resolution. The proposed holographic tomography technique offers a label-free avenue for capturing precise three-dimensional (3D) refractive index morphologies of cells and directly analyzing cellular parameters like area, height, volume, and nucleus/cytoplasm ratio within the 3D cellular model. We showcase holographic tomography results illustrating various cell death types and elucidate distinctive refractive index correlations with specific cell morphologies complemented by biochemical assays to verify cell death states. These findings hold promise for advancing in situ single cell state identification and diagnosis applications. Full article