Search

To increase the sensitivity and efficiency of a gas sensor, nanostructured ZnO and Co3O4 layers were obtained by hydrothermal synthesis directly on the electrode surface, eliminating the use of binders. Scanning electron microscope images showed that the resulting nanostructured coatings were characterised by good adhesion to the surface and high porosity, which opened up the possibility of their further use in the process of developing a gas sensor. The efficiency of the obtained nanostructured coatings and their sensitivity at room temperature to various concentrations of CO2 were determined. The resistance curves of the samples were obtained as a function of gas concentration in the chamber, for Co3O4 and ZnO nanostructures.

Amongst the most popular methods for the production of metal oxide nanostructures is hydrothermal synthesis. For producing ZnO nanostructures, a nitrate-based precursor reaction with equimolar amounts of hexamethylenetetramine (HMTA) is commonly used. In these reactions, zinc nitrate provides the source of Zn2+ ions, and HMTA produces the desired amount of OH− ions. The growth process occurs due to a dissolution-secondary precipitation mechanism. ZnO nanostructures are characterized by anisotropic growth with different growth rates of the individual faces, where (v(0001) > v(100) > v(10) > v(101) > v(000)). Therefore, considering the principle of energy minimization, the most favorable is vertical growth perpendicular to the (0001) plane, which ensures the formation of characteristic rod-like nanostruchtures of ZnO. The mentioned process takes place when chemical reactions are in equilibrium. Shifting from the equilibrium conditions by varying the parameters of reaction, or using capping agents, makes it possible to change the growth rate of individual crystallographic planes and, as result, affect the morphology of the obtained nanostructure. In this paper the influence of concentration and composition of the reagents, growth time and temperature, pH of the solution, and the presence of different capping agents on the growth process of nanostructured ZnO were investigated. Optimal synthesis parameters for obtaining nine independent ZnO morphologies have been determined. The distinctive feature of these experiments is the fact that the samples were obtained as durable, homogeneous, epitaxial coatings on hard surfaces. This can be especially interesting for the development of sensors and other fields where surface area is crucial, and it opens up more possibilities than use of the nanostructured ZnO powders.

This research presents a comparative analysis of water-gated thin film transistors based on a copper oxide (CuO) semiconductor in the form of a smooth film and a nanostructured surface. A smooth CuO film was deposited through reactive magnetron sputtering followed by annealing in atmosphere at a temperature of 280 (Formula presented.) C. Copper oxide nanostructures were obtained by hydrothermal synthesis on a preliminary magnetron sputtered 2 nm thick CuO precursor followed by annealing at 280 (Formula presented.) C. An X-ray diffraction (XRD) analysis of the samples revealed the presence of a tenorite (CuO) phase with a predominant orientation of (002). Scanning electron microscopy (SEM) and atomic force microscopy (AFM) studies of the samples revealed a highly developed surface with crystallites having a monoclinic syngony and dimensions of 15–20 nm in thickness, 150 nm in length, and 100 nm in height relative to a 2.5 nm height for the CuO crystallites of the smooth film. Electric measurements of the studied devices revealed typical current–voltage characteristics of semiconductors with predominant hole conductivity. The maximum ON/OFF ratio at a rain-source voltage of 0.4 volts and −1.2 volts on the gate for a smooth film was (Formula presented.), and for a nanostructured transistor, it was (Formula presented.). However, a much stronger saturation of the channel was observed for the nanostructured channel than for the smooth film. A test solution containing glyphosate dissolved in deionized water in three different concentrations of 5, 10, and 15 (Formula presented.) mol/L was used during the experiments. The principle of operation was based on the preliminary saturation of the solution with Cu ions, followed by the formation of a metal–organic complex alongside glyphate. The glyphosate contents in the analyte led to a decrease in the conductivity of the transistor on the axis of the smooth film. In turn, the opposite effect was observed on the nanostructured surface, i.e., an increase in conductivity was noted upon the introduction of an analyte. Despite this, the overall sensitivity of the nanostructured device was twice as high as that of the device with a thin film channel. The relative changes in the field-effect transistor (FET) conductivity at maximum glyphosate concentrations of 15 (Formula presented.) mol/L reached 19.42% for the nanostructured CuO film and 3.3% for the smooth film. © 2022 by the authors. --//-- This is an open access article Ogurcovs A, Kadiwala K, Sledevskis E, Krasovska M, Mizers V., "Glyphosate Sensor Based on Nanostructured Water-Gated CuO Field-Effect Transistor", Sensors (2022) 22(22):8744, doi: 10.3390/s22228744 published under the CC BY 4.0 licence., This research was supported by State Education Development Agency, Project No. 1.1.1.2/16/I/001, Research Proposal No. 1.1.1.2/VIAA/4/20/590 “Portable diagnostic device based on a biosensor array of 2D material sensing elements”. Institute of Solid-State Physics, University of Latvia has received funding from the European Union's Horizon 2020 Framework Programme H2020-WIDESPREAD-01-2016-2017-Teaming Phase 2 under grant agreement No. 739508, project CAMART2.

Tungsten trioxide (WO3) is a well-known electrochromic material with a wide band gap, while rhenium trioxide (ReO3) is a “covalent metal” with an electrical conductivity comparable to that of pure metals. Since both WO3 and ReO3 oxides have perovskite-type structures, the formation of their solid solutions (ReO3–WO3 or RexW1–xO3) can be expected, which may be of significant academic and industrial interest. In this study, layered WO3/ReO3, ReO3/WO3, and mixed ReO3–WO3 thin films were produced by reactive DC magnetron sputtering and subsequent annealing in air at 450 °C. The structure and properties of the films were characterized by X-ray diffraction, optical spectroscopy, Hall conductivity measurements, conductive atomic force microscopy, scanning and transmission electron microscopy, energy-dispersive X-ray spectroscopy, and X-ray photoemission spectroscopy. First-principles density functional theory calculations were performed for selected compositions of RexW1–xO3 solid solutions to model their crystallographic structure and electronic properties. The calculations predict metallic conductivity and tetragonal distortion of solid solutions in agreement with the experimental results. In contrast to previously reported methods, our approach allows us to produce the WO3–ReO3 alloy with a high Re content (>50%) at moderate temperatures and without the use of high pressures.

Direct experimental proof of the existence of several mechanisms of strengthening of polymer composites modified with single-walled carbon nanotubes was obtained by the method of high-resolution scanning electron microscopy.

Crystal growth & design 20(9), 6147 - 6156 (2020). doi:10.1021/acs.cgd.0c00848, Thin films of rhenium trioxide (ReO$_3$) were produced by reactive DC magnetron sputtering from a metallic rhenium target, followed by annealing in the air in a range of temperatures from 200 to 350 °C. Nanocrystalline single-phase ReO$_3$ films were obtained after being annealed at about 250 °C. The thin films appeared bright red in reflected light and blue-green in transmitted light, thus showing an optical transparency window in the spectral range of 475–525 nm. The film exhibited a high conductivity as evidenced by macro- and nanoscale conductivity measurements. The long-range and local atomic structures of the films were studied in detail by structural methods, such as X-ray diffraction and X-ray absorption spectroscopy. The oxidation state (6+) of rhenium was confirmed by X-ray photoemission and X-ray absorption spectroscopy. The nanocrystalline morphology of the annealed films was evidenced by scanning electron microscopy (SEM), transmission electron microscopy (TEM), and atomic force microscopy (AFM). The obtained results allowed us to propose a mechanism of rhenium oxide conversion from the initially amorphous ReO$_x$ phase to cubic ReO$_3$., Published by ACS Publ., Washington, DC

ZnO nanostructures are promising candidates for use in sensors, especially in electrochemical sensors and biosensors, due to their unique physical and chemical properties, as well as sensitivity and selectivity to several types of contamination, including heavy metal ions. In this work, using the hydrothermal method, nanostructures of ZnO were synthesized in four different morphologies: nanorods, nanoneedles, nanotubes and nanoplates. To determine the peculiarities of adsorption for each morphology, a series of electrochemical measurements were carried out using these nanostructured ZnO coatings on the working electrodes, using aqueous solutions of Pb(NO3)2 and Cd(NO3)2 as analytes with different concentrations. It was found that the sensitivity of the resulting electrochemical sensors depends on the morphology of the ZnO nanostructures: the best results were achieved in the case of porous nanostructures (nanotubes and nanoplates), whereas the lowest sensitivity corresponded to ZnO nanorods with a large diameter (i.e., low surface-to-volume ratio). The efficiency of sedimentation is also related to the electronegativity of adsorbate: it has been shown that all observed ZnO morphologies exhibited significantly higher sensitivity in detecting lead ions compared to cadmium ions.

The present study highlights the beneficial effects of premixing of highly loaded poly (butylene succinate) (PBS) / nanofibrillated cellulose (NFC) nanocomposites under solution conditions and its use as a masterbatch for melt blending. The proposed masterbatch process strategy is a very promising manufacturing technique for nanocomposites. Herein, we show the preparation of masterbatch with NFC with a very high loading of 50 wt.%. Research is aimed towards understanding the solution and melt processing effects on the structure and exploitation properties. The composites with NFC loadings from 5 up to 15 wt.% have been prepared by diluting the masterbatch and compared to conventional solvent casting. The masterbatch process significantly reduced overall solvent usage and improved the NFC dispersion within the polymer matrix. The samples prepared by solution casting showed excellent mechanical performance with an increase in elastic modulus up to 1.6-fold and storage modulus up to 2-fold at room temperature (20 °C) compared to the neat PBS, while masterbatch processed samples showed even higher overall mechanical properties – 1.8-fold and 2.5-fold increase in elastic modulus and storage modulus, correspondingly. Scanning electron microscopy (SEM) imaging indicated a homogeneous NFC dispersion for masterbatch samples and revealed agglomeration of NFC for the solvent cast ones. Biodegradation studies in the composting conditions were performed to underpin the weight, visual changes, calorimetric properties, while chemical changes were studied using spectroscopy. The NFC significantly accelerated the nanocomposites' biodegradation process from 80 days for the neat PBS to 60 days for the nanocomposites. The calorimetric studies indicate that NFC promoted crystalline phase formation and reduced crystallinity, but thermal stability was not significantly affected. In addition, the reinforcement factor analysis shows that the suitable masterbatch NFC nanocomposite preparation method's choice has a high potential to obtain high-performance materials for PBS films and packaging applications.

Glyphosate, commonly known by its original trade name Roundup™, is the world's most widely used herbicide. Glyphosate and its metabolites have a profound negative environmental impact and long-term toxicity risk, including carcinogenicity, genotoxicity, and endocrine disruption, even at concentration levels too low to have a herbicidal effect. Therefore, the detection of these pollutants at low concentrations is an important task. To increase the sensitivity of the sensor, nanostructures were used. To analyze the presence of glyphosate and its metabolites in rye juice, two groups of samples were selected. In the first case, glyphosate at different concentrations was added to the water for irrigation on the first day, and then the rye samples were watered with pure water for 7 days. In the second case, the samples were watered with pure water for all 8 days, and glyphosate was artificially added just before the measurement. The obtained samples were studied by the Different Pulse Voltammetry (DPV) employing nanostructured working electrodes. To analyze changes in the DNA sequence, a Polymerase chain reaction (PCR) product obtained from samples of the first group was electrochemically studied. To confirm the results obtained, an electrophoresis method was also applied. The results indicate that the DPV signal obtained from samples with artificially added glyphosate has significant differences compared to the signal obtained from the juice of plants absorbing glyphosate in a natural way during growth. However, in both cases, the CuO nanostructure based sensor detects the presence of glyphosate or its metabolites compared to the control sample. The experiment also found significant changes in the DNA caused by exposure with glyphosate during the growth process of rye sprouts. A nanostructured electrochemical sensor was used for the detection of glyphosate residuals and genetic changes caused by glyphosate in untreated rye juice.

Nanoparticles influence on genome is investigated worldwide. The appearance of somaclonal variation is a cause of great concern for any micropropagation system. Somaclonal variation describes the tissue-culture-induced phenotypic and genotypic variations. This paper shows the results of somaclonal variation in two resistance genes pectin methylesterase and Mlo-like protein in all tissue culture development stages, as donor plant, calluses, and regenerants ofLinum usitatissimuminduced by gold and silver nanoparticles. In this paper, it was essential to obtain DNA material from all tissue culture development stages from one donor plant to record changes in each nucleotide sequence. Gene region specific primers were developed for resistance genes such asMloandPme3to define the genetic variability in tissue culture ofL. usitatissimum. In recent years, utilization of gold and silver nanoparticles in tissue culture is increased and the mechanisms of changes in genome induced by nanoparticles still remain unclear. Obtained data show the somaclonal variation increase in calluses obtained from one donor plant and grown on medium supplemented by gold nanoparticles (Mlo14.68±0.98;Pme32.07±0.87) or silver nanoparticles (Mlo12.01±0.43;Pme310.04±0.46) and decrease in regenerants. Morphological parameters of calluses showed a number of differences between each investigated culture group.

Experimental investigations of single-wall carbon nanotubes (CNT) effect on the mechanical properties of polymeric composite materials based on epoxy matrix have been carried out. It has been found that addition of CNT at low concentration dramatically increases tensile strength (20 – 30 per cent growth) and Young’s modulus of the samples under study. Structure of polymeric composites with CNT was characterized by atomic force microscopy (AFM) and scanning electron microscopy (SEM). AFM images of the samples under study confirm strong interaction between polymeric matrix and nano-additives, demonstrating intimate contact between CNT and epoxy surroundings which is of great importance for composite material reinforcement. Dependences of tensile strength and those of Young’s modulus on CNT concentration are discussed using micromechanics models for nanocomposites.

Optimal growing parameters have been found using the hydrothermal method to obtain well-aligned vertical ZnO nanorod and nanotube arrays. The influence of different growing factors (such as temperature, growing solution concentration, method of obtaining seed layer and condition) on nanotube morphology and size is described in the paper. Well-structured ZnO nanotubes have been obtained by using a selfselective etching method with lowering temperatures of growth during the hydrothermal process. It is shown that the optical properties of the nanostructure arrays obtained are sensitive to the medium in which they are placed, which is why they can be used as sensors for pure substance detection and in different solutions for impurity determination.

The present paper presents the method for obtaining core/shell CuO-ZnO nanoparticles and nanocoatings by using a commercially available vacuum coating system. Initially generated Cu-Zn core/shell nanoparticles have been oxidised with a highly reactive atomic oxygen beam. Second-harmonic generation has been observed in the obtained samples. The dependence of second- harmonic intensity on the wavelength of the exciting radiation is shown in the paper.

Metal-dielectric nanocomposite optical materials based on colloidal crystals have been prepared by electro-thermo-diffusion or magnetron sputtering of silver. Optical properties of these photonic crystals have been studied by angle-resolved reflectance and transmission spectroscopy. The interpretation of observed spectra has been made taking into account the Bragg diffraction, Fano resonance, Fabry-Perot resonance and surface plasmon-polaritons, which excitations contribute to the optical properties of plasmonic-photonic crystals.

Development of nanotechnology leads to the increasing release of nanoparticles in the environment that results in accumulation of different NPs in living organisms including plants. This can lead to serious changes in plant cultures which leads to genotoxicity. The aims of the present study were to detect if iron oxide NPs pass through the flax cell wall, to compare callus morphology, and to estimate the genotoxicity in Linum usitatissimum L. callus cultures induced by different concentrations of Fe3O4 nanoparticles. Two parallel experiments were performed: experiment A, where flax explants were grown on medium supplemented with 0.5 mg/l, 1 mg/l, and 1.5 mg/l Fe3O4 NPs for callus culture obtaining, and experiment B, where calluses obtained from basal MS medium were transported into medium supplemented with concentrations of NPs identical to experiment A. Obtained results demonstrate similarly in both experiments that 25 nm Fe3O4 NPs pass into callus cells and induce low toxicity level in the callus cultures. Nevertheless, calluses from experiment A showed 100% embryogenesis in comparison with experiment B where 100% rhizogenesis was noticed. It could be associated with different stress levels and adaptation time for explants and calluses that were transported into medium with Fe3O4 NPs supplementation.

Development of methods for direct delivery of different bioactive substances into the cell is a promising and intensively approached area of research. It has become a subject of serious research for multidisciplinary team of scientists working in such areas as physics, biology, and biotechnology. Plant calluses were grown on medium supplemented with different nanoparticles to be used as a model for biotechnological research. Gold nanoparticles with mesoporous silica coating were used as hormone carriers, since they possess many of critical properties required for cellular transportation instrument. Some of those properties are great biocompatibility and controlled release of carried molecules. Significant changes in hormones common impact were detected. The great increase in ploidy numbers, embryogenesis, induction, and methylation level was observed when compared to the "conventional" methods of targeted hormones delivery that embrace usage of Au nanoparticles as a main hormone carrier. The authors suppose the research under consideration can provide a new pathway to the design of a novel targeted plant hormone and bioactive substances carrier., Institute of Solid State Physics, University of Latvia as the Center of Excellence has received funding from the European Union’s Horizon 2020 Framework Programme H2020-WIDESPREAD-01-2016-2017-TeamingPhase2 under grant agreement No. 739508, project CAMART²

A DNA electrochemical sensor's construction based on ZnO nanostructured electrodes is described in the article. As object of the study, DNA primers and PCR products of Trichinella britovi and Trichinella spiralis were chosen. The sensors were prepared with different morphologies of ZnO structures on the surfaces of the working electrodes: thin film of zinc oxide, nanorods and nanotubes. Immobilization processes of DNA primers were studied. Differential Pulse Voltammetry was used as a method of measurements of electrochemical characteristics. The measurements have shown an eligible difference of signals for confident distinction of Trichinella britovi and Trichinella spiralis PCR products. Keywords: DNA electrochemical sensor, ZnO nanostructures, Trichinella, DNA hybridization, DPV

CuInSe2 (CISe) compound was produced by high-temperature synthesis. After mechanical milling, the average CISe particle size decreased to 10μm. The authors study structural changes of the compound after ablation in liquid by a 1064 nm pulsed laser. The SEM examination indicated the presence of spherical particles with the average size of ~ 450 nm. A nonlinear relationship was established between the laser radiation dose and the quantity of spherical particles. The XRD analysis has shown an improvement in the CISe crystalline structure and the absence of significant changes in its stoichiometry. The 3 μm thick experimental CISe samples were screen-printed on planar Ni electrodes, and improvement also was revealed in their photosensitivity. The conclusion is that the pulsed-laser ablation can be applied to chalcopyrite structures like CISe without destruction of their initial properties.

Nanoparticles influence on genome is investigated worldwide. The appearance of somaclonal variation is a cause of great concern for any micropropagation system. Somaclonal variation describes the tissue-culture-induced phenotypic and genotypic variations. This paper shows the results of somaclonal variation in two resistance genes pectin methylesterase and Mlo-like protein in all tissue culture development stages, as donor plant, calluses, and regenerants of Linum usitatissimum induced by gold and silver nanoparticles. In this paper, it was essential to obtain DNA material from all tissue culture development stages from one donor plant to record changes in each nucleotide sequence. Gene region specific primers were developed for resistance genes such as Mlo and Pme3 to define the genetic variability in tissue culture of L. usitatissimum. In recent years, utilization of gold and silver nanoparticles in tissue culture is increased and the mechanisms of changes in genome induced by nanoparticles still remain unclear. Obtained data show the somaclonal variation increase in calluses obtained from one donor plant and grown on medium supplemented by gold nanoparticles (Mlo 14.68 ± 0.98; Pme3 2.07 ± 0.87) or silver nanoparticles (Mlo 12.01 ± 0.43; Pme3 10.04 ± 0.46) and decrease in regenerants. Morphological parameters of calluses showed a number of differences between each investigated culture group.

Photoelectric Properties of Screen-Printed Al-Doped ZnO Films The potential of cheap semiconductor materials in the area of solar energy use is illustrated by the example of zinc oxide (pure and Al-doped in various concentrations). Under investigation was the electric conductivity and photoelectric properties of ZnO thin films. The samples were prepared using screen-printing technique. The results of measurements point to non-linear relationships between Al concentration, photosensitivity and electrical conductivity of thin ZnO films. Optimal Al concentration for practical use of ZnO in photovoltaic devices is found to be ~ 1%. The experimental methods, technologies and results described in the paper could be used for further investigations in this area.

The application prospect of zinc oxide (ZnO) nanostructures largely relies on the ability to grow nanoobjects with necessary geometry. In this study well-aligned ZnO nanorod arrays with a high density and uniformity were successfully synthesized on the glass substrates by a hydrothermal method at low-temperature. The aqueous solutions of zinc nitrate hexahydrate and hexamethylenetetramine was used. The effect of seed layer (obtained by electrochemical method and by vacuum deposition method) on the alignment of ZnO nanorods has been investigated. The morphological properties of the ZnO nanorods were also examined in accordance with varying the magnetron sputtering angle for ZnO seeds deposition. It is also shown that the electric field can control the direction of the growth of ZnO nanorods. Morphological, structural and compositional characterizations of obtained films were carried out by scanning electron microscopy, energy-dispersive X-ray spectroscopy and X-ray diffraction analysis methods.

In the experiments, ZnO and CuInSe2 semiconductor powders were used (the latter produced by the high-temperature synthesis method). Microstructural properties of the powders were analyzed using X-Ray diffraction and SEM. The experimental ZnO/CuInSe2 samples were prepared by the screen printing technique. The V–I measurements of the samples indicated the presence of a p-n junction in the ZnO/CuInSe2 contact zone. The samples were exposed to artificial solar radiation, during which an exponential decay of photo-emf was observed. It was shown that the starting conductive properties of the p-n junction restores in ~ 15 min after the exposition. Laser ablation technique was applied to ZnO/CuInSe2 p-n junction with purpose to improve its performance and quality. After several attempts, significant changes in electrical properties of samples was observed. Improvenent of p-n junction can be achieved only at single attempt at certain amount of delivered energy. Futherablation attempt leads to degradation of p-n junction of samples.

The films based on the low-molecular amorphous azochromophore 2-(3-(4-((4- (Ethyl(2-(trityloxy)ethyl)amino)phenyl)diazenyl)styryl)-5,5-dimethylcyclohex-2-enylidene) malononitrile (IWK-2M) were prepared. The optical properties of the material, such as transmittance and reflection spectra of the film, sensitivity to polarization holographic recording by two wavelengths (405 and 532 nm) were studied. The direct relief formation during the polarization holographic recording was explored, relief depth dependence on exposure and record beam intensity was investigated. The holographic matrix on this material base was produced without chemical etching process; the replication of holographic image was performed.