Bulletin of the Russian Academy of Sciences: Physics最新文献

The different cases of degenerate defect modes in one-dimensional photonic crystals with two defect layers are studied. Degenerate defect modes occur when two or more defect modes merge at a given wavelength in the photonic crystal reflection spectrum. Such defect modes have a variety of potential practical applications, including the increase of sensitivity in optical sensors. The appearance of each type of degenerate defect modes is determined by the structural features and parameters of the photonic crystal. For this reason, we have derived analytical equations containing the photonic crystal parameters describing each type of defect modes merging. Analytical expressions for the zero imaginary phase for any type of defect mode merging have been also obtained. These general relationships can be used to simplify the modeling of one-dimensional photonic crystals with two defect layers and for further analysis of degenerate defect modes.

Ultrathin metal films are an important element for transparent optoelectronics including displays, photovoltaics and sensors, where the use of flexible and durable electrodes is needed. Nevertheless, fabrication of ultrathin, continuous and smooth metal films is quite challenging and restricted by a variety of factors, including deposition techniques and substrate. Much effort has been expended in creating ultrathin gold and silver films as transparent conductor, but the methods developed have often been limited to the choice of substrate and its surface modification, thus transferring the already resulted ultrathin film to the target surface looks promising. Here, we introduce a facile technique for fabrication and transfer of ultrathin (<10 nm) gold films onto target substrate presenting their structural morphology and electrical properties analysis, which showed high quality and low sheet resistance of the obtained gold films.

The research is devoted to the development of a method for identifying skin tumors based on multimodal joint analysis of Raman scattering data and dermatoscopic images. Experimental skin Raman spectra were recorded using a portable setup that includes a laser source with a central wavelength of 785 nm. The spectra were recorded in the range from 792 to 1874 cm^–1. Dermatoscopic images of skin neoplasms were obtained using a digital dermatoscope. Machine learning methods, in particular, convolutional neural networks, were used to analyze the registered data. The classification model for malignant melanoma and benign pigmented neoplasms has shown an increase in classification accuracy compared to the analysis of Raman spectra or dermatoscopic images alone. As a result, combined multimodal method for diagnosing skin cancer, which simultaneously takes into account both specific spectral features of neoplasms and spatial inhomogeneities in the distribution of absorbance, has been proposed. The studied approaches to the analysis of optical biopsy data can be further used as part of the software for automated screening diagnostics of skin pathologies in order to detect neoplasms at an early stage of development.

Microbubbles have numerous applications in fields such as drug delivery, diagnostic imaging, and localized therapies. In this study, we propose a method for generating microbubbles with controlled size, confined by the dimensions of a hollow shell. The hollow capsules were fabricated from trithiocyanuric acid and further modified with gold nanoparticles to enhance their photothermal properties. We demonstrate that irradiation with a near-infrared laser can induce the formation of microbubbles within these capsules. The bubbles remain spatially confined by the shell and stable for the duration of the laser operation. This approach offers a versatile platform for applications requiring targeted control of microbubble formation and heat generation in biomedical and microfluidic systems.

We studied the properties of a plasmonic nanoantenna in the form of a subwavelength metal sphere partly buried in a metal substrate with a hollow gap between the sphere and the substrate. Using a nickel sphere in a nickel substrate as an example, it is shown that imbedding a metal sphere deep into the substrate leads to the broadening and a strong red shift of its dipole resonance. Significant enhancement of the near electromagnetic field of the sphere in the gap region is demonstrated. The effect of all geometric parameters of the nanoantenna under study on its optical performance is studied. Enhanced transmission of a metal film with defects in the form of spherical particles embedded in it is demonstrated, which results from the leaking of the near electromagnetic field from the gaps to the opposite side of the film. The obtained results can find application in nanooptics for designing plasmonic nanoantennas for concentration, enhancement and redistribution of the electromagnetic field.

We presented results of applying an adaptive interferometry technique, based on dynamic holograms recorded in photorefractive crystal, to accurately determine the mass of biofilm bacteria colonies by the measuring of microcantilever frequency shift. During the experimental testing, biofilms of Escherichia coli were grown on the surface of a cantilever previously coated with a BaF₂ film. The proposed experimental setup is completely non-contact due to using an optical method of excitation and detection of cantilever oscillations. Based on the measured shift in the resonant frequency, the mass of the biofilm grown on the cantilever was calculated to be (2.072 ± 0.003) × 10^–9 gram.

We report highly transparent in the wide band optical range of (0.4–7) µm mesh electrodes fabricated on thin semimetal films of semimetal calcium disilicide (CaSi₂) by utilizing femtosecond laser ablation technique with flat top beam shaped geometry. Compared with continuous films, mesh electrodes demonstrate an increase in the figure of merit as transparent conducting materials from 0.3 up to 0.9 Ω^–1. Of importance, CaSi₂ retains low sheet resistance not exceeding 20 Ω/sq after laser processing. Obtained material parameters allowed testing CaSi₂ mesh electrodes under actual conditions as transparent heater. The surface temperature as high as 150°C under low applied DC voltage of 8 V has been approved by infrared camera. CaSi₂ heater possess hysteresis free behavior with response as fast as 40 s and excellent stability under the cyclic operation. Thus, laser perforated CaSi₂ thin films could be considered as a material of choice for the infrared optoelectronic applications, smart windows and miniature heaters for microscopic observations of biological samples.

This study was focused on development of a rapid and sensitive method for detection of food spoilage marker histamine based on surface-enhanced raman spectroscopy (SERS) using quickly produced laser-textured Ag film as a SERS substrate. Optimization of fs-laser fabrication parameters has reduced the substrate fabrication time to less than a minute. Label-free SERS-detection of histamine adsorbed onto a spallated Ag surface over the concentration range of 10^–6 to 10^–10 M was demonstrated. The method addresses the need for large number of disposable SERS-substrates required in various biosensing applications.

Nowadays various perovskite devices are aimed to generate a new revolution in thin-film electronics. Besides perovskite solar cells and LED, many types of photodiodes are perspective for personal medicine, light control technologies and Internet of Things. This research is dedicated to find new ways of light absorption improvement of perovskite photodiodes in visible and near infrared range where classic narrow band gap-based perovskite devices have poor light sensitivity. There are few new models with improved thickness of perovskite devices improved by Mie-resonant 160 nm Si nanoparticles possess both electric and magnetic multipoles in visible and near IR range which can improve light absorption of thick perovskite photodiodes by 10%.

This study investigates the use of deep eutectic solvents (DES) in direct laser metallization (DLM) for the deposition of cobalt patterns on glass substrates. In order to extend the DLM technique to cobalt, a systematic study was conducted to synthesize a DES containing cobalt salts, specifically cobalt acetate and cobalt chloride, in different molar ratios. By optimizing the scanning speed and laser power, metallic structures with electrical conductivity were fabricated. Characterization techniques, including X-ray diffraction (XRD) and energy dispersive X-ray spectroscopy (EDX), confirmed the successful formation of cobalt patterns, while morphological studies revealed a well-developed structure without cracks or discontinuities. The results underscore the potential of DES in laser fabrication and demonstrate its versatility in facilitating the deposition of metal patterns.