Variation of Surface Nanostructures on (100) PbS Single Crystals during Argon Plasma Treatment

The nanostructuring of the (100) PbS single crystal surface was studied under varying argon plasma treatment conditions. The initial PbS single crystals were grown by high-pressure vertical zone melting, cut into wafer samples, and polished. Subsequently, the PbS single crystals were treated with inductively coupled argon plasma under varying treatment parameters such as ion energy and sputtering time. Plasma treatment with ions at a minimum energy of 25 eV resulted in the formation of nanotips with heights of 30–50 nm. When the ion energy was increased to 75–200 eV, two types of structures formed on the surface: high submicron cones and arrays of nanostructures with various shapes. In particular, the 120 s plasma treatment formed specific cruciform nanostructures with lateral orthogonal elements oriented in four <100> directions. In contrast, plasma treatment with an ion energy of 75 eV for 180 s led to the formation of submicron quasi-spherical lead structures with diameters of 250–600 nm. The nanostructuring mechanisms included a surface micromasking mechanism with lead formation and the vapor–liquid–solid mechanism, with liquid lead droplets acting as self-forming micromasks and growth catalysts depending on the plasma treatment conditions (sputtering time and rate).

Study on Black Phosphorus Characteristics Using a Two-Step Thinning Method

A mild two-step method of black phosphorus (BP) flake thinning was demonstrated in this article. Slight ultraviolet–ozone (UVO) radiation followed by an argon plasma treatment was employed to oxidize mechanically exfoliated BP flakes and remove the surface remains of previous ozone treatment. The annealing process introduced aims to reduce impurities and defects. Low damage and efficient electronic devices were fabricated in terms of controlling the thickness of BP flakes through this method. These results lead to an important step toward the fabrication of high-performance devices based on two-dimensioned materials.

Исследование влияния обработки поверхности Si-подложек на морфологию слоев GaP, полученных методом плазмохимического атомно-слоевого осаждения

Investigations of atomic-layer deposition of GaP layers on Si substrates with different orientations and with different preliminary surface treatment have been carried out. The deposition of GaP was carried out by the method of plasma enhanced atomic-layer deposition using in situ treatment in argon plasma. It was shown that at the initial stage of the growth of GaP layers on precisely oriented (100) Si substrates and with misorientation, two-dimensional growth occurs both after chemical and plasma surface treatment. Upon growth on (111) substrates, after plasma treatment of the surface, a transition to three-dimensional growth is observed, at which the size of islands reaches 30–40 nm. The smallest root-mean-square roughness of the surface of the growing GaP layers (<0.1 nm) was achieved for (100) substrates with a misorientation of 4 °. The GaP layers grown on (100) substrates had a roughness of ~ 0.1 nm, and on substrates with the (111) orientation - 0.12 nm. It was found that the surface treatment of Si substrates with the (100) orientation in hydrogen plasma leads to a slight increase in the surface roughness of growing GaP layers (0.12–0.14 nm), which is associated with the effect of inhomogeneous etching of silicon in hydrogen plasma. When treating the (100) silicon surface in argon plasma, the surface roughness does not change significantly in comparison with the chemical surface treatment. On the surface of substrates with preliminary deposition of an epitaxial Si layer with a thickness of 4 nm, the morphology of GaP layers is the same as in the case of using hydrogen plasma.

Numerical study of atmospheric-pressure argon plasma jet propagating into ambient nitrogen

In this paper, a two-dimensional fluid model is used to study the properties of atmospheric-pressure argon plasma jet propagating into ambient nitrogen driven by a pulsed voltage, emphasizing the influence of gas velocity on the dynamic characteristics of the jet. The simulation results show that the argon jet exhibits a cylindrical shape channel and with the increase of propagation length, the jet channel gradually shrinks. The jet propagation velocity varies with time. Inside the dielectric tube, the plasma jet accelerates propagation and reaches its maximum value near the nozzle. Exiting from the tube, the propagation velocity of the plasma jet quickly decreases and when approaching the metal plane, the decrease of jet velocity slows down. The increase of gas speed leads to the variation of the jet spatial distribution. The electron density presents a solid structure at lower gas flow speeds, whereas an annular structure can be observed under the higher gas flow velocity in the ionization head. The jet length increases with the gas flow velocity. However, when the flow velocity exceeds a critical value, the increased rate of the plasma jet length becomes slow. Additionally, the influence of the gas flow speed on the production and transport of the reactive species is also studied and discussed.

The Influence of a Second Ground Electrode on Hydrogen Peroxide Production from an Argon Plasma Jet and Correlation to Antibacterial Efficacy and Mammalian Cell Cytotoxicity

This study investigates how addition of a second ground electrode in an argon plasma jet influences the production of hydrogen peroxide (H2O2) in deionised water (DIW). Briefly, plasma is ignited by purging argon gas through a quartz tube at 1 litre per minute and applying a sinusoidal voltage of 7 kV (peak-peak) at 23.5 kHz to a high voltage stainless steel needle electrode sealed inside the quartz tube surrounded by single or double copper ring(s) situated downstream of the high voltage electrode that served as the ground electrode(s). The mechanisms of H2O2 production are investigated through the electrical and optical plasma properties and chemical analysis of the treated DIW. We discover that the addition of a second ground electrode results in higher accumulation of charges on the wall of quartz tube of the plasma jet assembly resulting in an increase in the discharge current and dissipated power. This further leads to an increase in the electron temperature that more than doubles the H2O2 production through dissociative recombination of water vapour molecules, whilst still maintaining a biological tissue tolerable gas temperature. The double ground electrode plasma jet is shown to be highly effective at reducing the growth of common wound pathogens (Pseudomonas aeruginosa and Staphylococcus aureus) in both planktonic and biofilm states whilst inducing a low level of cytotoxicity in HaCaT keratinocyte skin-like cells under certain conditions. The information provided in this study is useful in understanding the complex physicochemical processes that influence H2O2 production in plasma jets, which is needed to optimise the development of plasma sources for clinical applications.

Morphofunctional characterization of rat thymus mast cells after administration of magnesium orotate mechanically activated forms

Relevance. The topicality of the work is determined by the wide spread of hypomagnesemia among the people, which makes it necessary to correct it. The aim of the work is to elucidate the cell-mediated response of the thymus mastocytic link to magnesium deficiency and its correction by the mechanoactivated form of magnesium orotate. Materials and Methods . Animals with drug-induced magnesium deficiency (administration of furosemide 30 mg/kg for 14 days) were administered either the initial preparation Magnerot (Magnerot, Vervag Pharma, Germany), or its mechanoactivated form. The level of magnesium in the blood was determined by test systems ARKREY (Japan). The concentration of magnesium in the thymus tissue was determined by the method of emission spectroscopy with inductively coupled (argon) plasma on an atomic emission spectrometer. Density of mastocytes and the indices of degranulation and granulolosis were calculated on paraffin sections of the thymus after coloration with toluidine blue. Results and Discussion . It was shown that furosemide administration the amount of magnesium decreased in the blood (from 1,750,08 to 0,9020,18 mmol/l, p0,05), but increased in the thymus (from 1,60,6 in the control to 3,71,2 mg/l); in the gland tissue, the number of mastocytes of morphotype A decreased and the number of mastocytes of morphotype D, after active degranulation, increased (by 7,1 times, p0,05). The type of mastocyte secretion in hypomagnesemia is represented by the merocrine variant. The administration of the initial magnesium orotate led to an increase in the concentration of magnesium in the blood to 1,150,25 mmol/l, which is 65,7% of the initial level, the amount of magnesium in the thymus remained elevated (3,41,1 mg/l), the number of actively degranulating cells (morphotype D) was increased. Mechanoactivated magnesium orotate restored the concentration of Mg2+ in the blood to 89,1% (1,560,18 mmol/l, p0,05) and decreased in the thymus (to 2,30,7 mg/l), restored the subpopulation of mastocytes saturated with heparin (type A), reduced the number of mastocytes of morphotype D. Conclusion . The mechanoactivated form of magnesium orotate has a normalizing effect on the population of thymic mastocytes, shows pronounced immunomodulatory activity, which allows us to consider it as a potential therapeutic agent for clinical testing in the complex therapy of hypomagnesemia and associated immunodeficiency.