Flexible and wearable technologies in environmental monitoring, healthcare, and industrial safety have been made possible by the advancement of chemiresistive sensors. Ammonia is an important sign of food going bad and kidney problems, so we need detection systems that are sensitive, stable, and can work at room temperature, which many traditional metal oxide sensors can't provide. In this study, we present a flexible ammonia sensor based on a Ti-doped ZnO/polymer composite, fabricated via a cost-effective electrospinning method. This approach enabled uniform integration of Ti-doped ZnO nanoparticles into polymeric fibers, improving electron transport and enhancing sensing performance under mechanical deformation. Obtained material also showed good flexible properties. The sensor exhibited strong mechanical stability and maintained high sensitivity across various bending conditions, showing the same response at both 0° and 90° angles. The synergistic effects between the doped metal oxide and the flexible substrate offer a reliable, non-invasive platform for real-time ammonia monitoring in wearable applications. 

Acknowledgments. This research has been funded by the Science Committee of the Ministry of Science and Higher Education of the Republic of Kazakhstan (Grant No. AP23489498, Development of advanced polymer-based sensor containing biowaste-derived carbon for detection of NH3).

Carbon nanotubes (CNTs) exhibit exceptional electrical, optical, thermal, magnetic, and mechanical properties, making them promising materials for a wide range of applications. Among various configurations, the synthesis of vertically aligned CNTs is particularly valuable, however, their synthesis relies heavily on catalyst nanoparticles with well-defined size, composition and catalyst support films. Controlling these parameters remains a significant challenge, since the physical properties of CNTs such as specific chirality and diameter are typically determined by the catalyst. This talk will be about demonstrating a true bottom-up approach synthesis of vertically aligned CNTs using bimetallic oxide nanoparticles (biMO-NPs) where catalyst nanoparticles were synthesized in liquid phase without the need of expensive thin films deposition equipment.^[1] Iron based (FeAlOx) and cobalt based (CoAlOx) discrete nanoparticles with tunable geometries were synthesized in the liquid phase from aluminum, iron and cobalt oleate precursors respectively.^[2] These nanoparticles were assembled into monolayer films on silicon oxide (SiO₂) substrates using bifunctional organic linker molecules. The linker molecules, with terminal functional groups, enable controlled anchoring of the nanoparticle substrates, forming a uniform catalyst monolayer of particles with nanoscale thickness. This monolayer assembly approach ensures consistent particle distribution and avoids aggregation of nanoparticles, critical for the uniform growth of CNTs. biMO-NPs composed of FeAlOx and CoAlOx, assembled as monolayer films enabled the successful growth of long VA-CNTs, even on unmodified SiO₂ surfaces. Structural and chemical characterization confirmed the uniformity and composition of the bimetallic nanoparticles as well as the CNT characteristics. 

This study demonstrates that a bottom-up, fully wet-chemistry approach can achieve a high degree of control over the catalyst nanoparticles composition and spatial arrangement. The ability to synthesize and organize bimetallic nanoparticles into functional monolayers offers a simple, scalable, and cost-effective alternative to traditional physical vapor deposition methods for catalyst preparation. Moreover, this work highlights the potential for tuning CNT growth and moving closer to the rational synthesis of CNTs with specific physical properties, including chirality. 

The third-generation semiconductors, gallium nitride (GaN) and silicon carbide (SiC), have attracted extensive attention due to their exceptional material properties and potential in high-performance electronic and optoelectronic devices. Among them, GaN is especially fascinating for high-frequency applications. This advantage arises from the formation of a two-dimensional electron gas (2DEG) at the AlGaN/GaN heterojunction interface, which enables high electron mobility and supports device architectures such as high electron mobility transistors (HEMTs). By contrast, SiC is renowned for its superior thermal conductivity, wide bandgap, and high critical electric field, which together inspire its capability for handling high power density and ensuring robust thermal management. When these two materials are combined—namely, GaN epitaxially grown on SiC substrates—the resulting heterostructure becomes a highly attractive platform for realizing high-power and high-frequency HEMTs. Such devices are promised to play a critical role in next-generation wireless communication systems, power electronics, and radar applications.

Although the lattice constant mismatch between GaN and SiC is relatively small, the dislocation density in conventional GaN-on-SiC epitaxial structures remains on the order of 10^9 cm^−2. This high density of threading dislocations and related crystalline defects significantly degrades device performance, limiting the reliability, efficiency, and lifetime of HEMTs. Traditional approaches to mitigate defect density mainly rely on optimizing epitaxial growth parameters through methods such as buffer layer engineering, substrate miscut angle control, and multi-step growth processes. However, these approaches are both time-consuming and highly costly, demanding extensive iterative experimentation that is impractical for large-scale production. Consequently, innovative substrate engineering concepts have been explored as an alternative pathway to address these challenges.

One promising strategy is the use of patterned SiC substrates to improve GaN epitaxial quality. By introducing micro-/nano-sized structures onto the SiC surface, epitaxial strain can be more effectively distributed, and dislocation propagation can be hindered, leading to a significant reduction in defect density within the active GaN layer. Building upon this concept, our team has recently developed a new class of engineered substrates, referred to as meta-substrates. These are fabricated by creating periodic meta-structures directly on 4H-SiC substrates, designed to enhance defect annihilation, suppress dislocation propagation, and tailor strain relaxation during GaN epitaxy. Unlike conventional patterned substrates, the meta-substrate approach offers new degrees of freedom for crystal quality optimization.

In this presentation, we report on the complete HEMT device fabrication processes carried out on these SiC meta-substrates, including ohmic and Schottky contact formation, passivation strategies, and gate metallization. Also, we evaluate the radio-frequency (RF) performance of the fabricated devices, highlighting their advantages in terms of cut-off frequency and device performance when compared with conventional GaN-on-SiC HEMTs.

The results confirm that meta-substrates provide a viable pathway for advancing GaN-on-SiC technologies, enabling scalable and cost-effective solutions for high-power and high-frequency electronics. This work demonstrates how advanced substrate design can unlock new performance benchmarks in GaN-based HEMTs. We believe that the meta-substrate concept represents not only a significant advancement in semiconductor device fabrication but also a strategic opportunity to accelerate the deployment of GaN/SiC HEMTs in emerging applications such as 5G/6G communications, electric vehicles, and next-generation radar systems.

Perfect vortex beams (PVBs) represent a compelling advancement in the field of structured light due to their unique property of maintaining a constant annular intensity ring diameter across different topological charges (TCs). This distinct feature contrasts with conventional optical vortex beams, whose ring diameters vary with TC, making PVBs particularly advantageous for multiplexed beam applications. The uniform ring size facilitates efficient spatial coupling of multiple vortex beams with different TCs simultaneously, which is crucial for high-dimensional optical communication systems, parallel optical trapping, and quantum photonic networks. Despite these advantages, practical deployment of PVBs remains constrained by the bulky and often complex optical setups required to generate them. Conventional PVB generation relies on interferometric arrangements or combinations of axicons and spiral phase plates, which are not compatible with compact or integrated platforms. These limitations hinder their integration into on-chip photonic devices or CMOS-compatible systems, particularly when high-order TCs are required. To overcome these challenges, this work presents a novel approach to realizing perfect vortex beams using flat, subwavelength-structured optical components—specifically, metasurfaces [1]. We experimentally demonstrate metasurface-generated perfect vortex beams (MPVBs) with TCs as high as +16 and −32 in the visible spectrum [2]. These MPVBs exhibit annular intensity distributions that remain largely invariant with respect to their TC, confirming the generation of perfect vortex beam profiles. In addition to their compactness and integrability, these metasurfaces show broadband functionality, enabling consistent performance across a range of visible wavelengths. The metasurfaces are carefully engineered to encode both the radial and azimuthal phase profiles necessary to form the PVBs. By manipulating the local phase delay through nano-resonators with spatially varying orientations and geometries, we achieve the desired field distribution without the need for bulk optics. The result is a highly efficient and compact optical device capable of generating complex vortex beam states with topological diversity and spatial uniformity. A particularly innovative aspect of this study is the integration of the optical eraser concept with the MPVBs. The optical eraser technique involves the interference of two vortex beams with opposite or different TCs, producing flower-like interference patterns that can be used to selectively suppress or modulate specific spatial modes. In our experiments, the interference of MPVBs with carefully chosen TCs results in helicity switching, a phenomenon in which the angular momentum characteristics of the beam are inverted or neutralized. This effect leads to the uniformization of the ring-shaped intensity distributions, helping to stabilize and homogenize the output for a range of topological charges. This ability to erase or modify the intensity profiles of high-order vortex beams has far-reaching implications. It provides a powerful method for dynamically controlling structured light fields, which is of particular interest in areas such as quantum optics, where phase coherence and modal purity are essential. The helicity switching observed in the flower-like interference patterns could also offer a new pathway to study spin–orbit interactions and quantum entanglement phenomena in optical fields. Moreover, the compact, CMOS-compatible nature of these metasurface-based devices makes them highly suitable for integration into lab-on-chip systems, high-density optical interconnects, and adaptive optics platforms. Their robustness, tunability, and high-resolution phase control position MPVBs as a scalable and versatile solution for future optical technologies. In conclusion, this work not only demonstrates the generation of high-order, broadband, and spatially uniform perfect vortex beams using metasurfaces but also introduces a novel method for their dynamic modulation through interference-based helicity control. These findings pave the way for miniaturized, multifunctional vortex beam generators with applications ranging from quantum information processing to next-generation optical sensing and beam shaping.

Several studies have demonstrated the antioxidant and anti-inflammatory effects of plant polyphenols (PP) [1, 2]. However, despite their biological potential, the clinical application of PP is limited primarily by their poor water solubility, which results in low bioavailability when administered orally. Micro- and nanoparticles loaded with plant polyphenols have shown high pharmacological activity, making the development of such delivery systems and the investigation of their biological effects highly relevant [3]. The objective of this study was to compare the protective effects of native and nanostructured quercetin on the initiation of oxidative stress in human keratinocytes exposed to tert-butyl hydroperoxide (tBHP). Quercetin was encapsulated within gelatin-based microcontainers, forming nanoparticles with diameters ranging from 160 to 190 nm. Two formulations were used: uncoated gelatin nanoparticles (nano 1) and  gelatin nanoparticles coated with a  shell composed of dextran sulfate and a chitosan-dextran copolymer (nano 2). Cell viability was assessed using PrestoBlue™ reagent. Keratinocyte damage was evaluated via lactate dehydrogenase (LDH) release. Apoptotic and necrotic cells were identified through flow cytometry using an Annexin V-FITC/PI staining kit. DNA damage was analyzed using the comet assay. The results demonstrate that gelatin nanoparticles effectively encapsulate quercetin, and the nanostructured form enables its application in aqueous suspensions without compromising its antioxidant, gene-protective, and cytoprotective effects under conditions of cellular oxidative stress. Both free and nanoparticle-loaded quercetin significantly protected keratinocytes from oxidative DNA damage and apoptosis induced by tBHP. These findings suggest that gelatin nanoparticles are effective carriers for quercetin, exhibiting high efficiency in its release.

Conclusion: The use of gelatin nanoparticles represents a promising strategy for enhancing the bioavailability and therapeutic efficacy of phytochemicals.

Surfactant-gas flooding is one of the new methods for enhanced oil recovery. In this method, the simultaneous injection of gas and surfactant solution leads to the formation of foam. Foam reduces the mobility of injected fluids and improves the displacement efficiency of enhanced oil recovery process. Currently, surfactant is used to produce and stabilize foam. Surfactants generally lose their desirable physical properties at high temperature and salinity and are wasted due to adsorption on the rock surface in the porous medium. The most important weakness of foam formed with surfactant is its short-term stability; Nevertheless, if nanoparticles are used instead of surfactant or together with it to produce and stabilize foam, it can eliminate the limitations of using surfactant. By using nanoparticles, a stable foam which have long-term stability in reservoir conditions can be designed to use it as a control agent for the mobility of injected fluids in enhanced oil recovery.