Impurity Concentration Research Articles

Oxygen Incorporation as a Route to Nondegenerate Zinc Nitride Semiconductor Thin Films.

Zinc nitride (Zn3N2) comprises earth-abundant elements, possesses a small direct bandgap, and is characterized by high electron mobility. While these characteristics make the material a promising compound semiconductor for various optoelectronic applications, including photovoltaics and thin-film transistors, it commonly exhibits unintentional degenerate n-type conductivity. This degenerate character has significantly impeded the development of Zn3N2 for technological applications and is commonly assumed to arise from incorporation of oxygen impurities. However, consistent understanding and control of the role of native and impurity defects on the optoelectronic properties of this otherwise promising semiconductor have not yet emerged. Here, we systematically synthesize epitaxial Zn3N2 thin films with controlled oxygen impurity concentrations of up to 20 at % by plasma-assisted molecular beam epitaxy (PA-MBE). Contrary to expectations, we find that oxygen does not lead to degenerate conductivity but instead serves as a compensating defect, the control of which can be used to achieve nondegenerate semiconducting thin films with free electron concentrations in the range of 1017 cm-3, while retaining high mobilities in excess of 200 cm2 V-1 s-1. This understanding of the beneficial role of oxygen thus provides a route to controllably synthesize nondegenerate O-doped Zn3N2 for optoelectronic applications.

Determination of O-isobutylmethylphosphonate in industrial emissions by gas chromatography using pulsating flame photometric detector

A procedure for gas chromatographic determination of O-isobutylmethylphosphonate micro-quantities in industrial emissions with a concentration range from 0.5 to 50 mg/m3 has been developed. The target analyte was collected and concentrated using an aspirator of the required volume of the test medium taken from sources of industrial emissions through sampling tubes equipped with ready-made filter materials, two layers of filters of the PFC (Petryanova filter cloth) type, 12 mm in diameter, two layers of filters of the appropriate size, washed in ethyl alcohol and dried in air, made of dense cotton material «moleskin». Recovery of concentrated substances from the sample tubes was performed by extraction with isopropanol. Methylation with diazomethane was carried out to convert the desired substance to a volatile product for subsequent chromatography, by a method improved to obtain micro-quantities of dialkyl esters of MPA and its monoesters. The high efficiency of the proposed methylation method as a factor for obtaining solutions with a low content of impurities of both starting reagents and non-target reaction products has been experimentally proven, which leads to higher accuracy of microconcentration measurements. Trace impurities, including diazomethane residues, were removed by vacuuming the methylated solution for 2 – 5 min. The use of other methods to remove excess diazomethane does not give positive results: blowing diazomethane from the solution with an inert gas does not lead to noticeable changes even for 15 – 20 min, during which time part of the solvent is removed and, therefore, the concentration of the target product changes; the addition of additional chemicals, for example acetic acid, leads to contamination with two products at once-excess acetic acid and methyl acetate, in addition, the addition of excess competing reagent can lead to transalkylation with the participation of the target product and, as a result, to incomplete progress of the target reaction. Quantitative data were obtained by gas chromatography using a Varian CP-3800 gas chromatograph equipped with a pulsed flame photometric detector, the mixture was separated on a CP WAX CB capillary column. The methodology was tested at real control facilities, appropriately certified and implemented in environmental control and monitoring programs.

Temperature Dependence of Electrical Properties of Ammonothermal GaN

The electrical properties at different temperatures of GaN grown by the basic ammonothermal method are studied. In the temperature range of 95–500 K, the scattering mechanism of GaN changes from ionized impurity scattering at low temperature to polar optical phonon scattering at high temperatures. It is found that the experimental measurement value at room temperature is lower than the calculated value, due to the multi‐ion scattering effect caused by high impurity concentrations, which are believed to result from the compensation of Mg, Mn, and VGa‐Hx.

Simulations of nanocrystalline iron formation under high shear strain

High-shear methods have long been used in experiments to refine grain structures in metals, yet the underlying mechanisms remain elusive. We demonstrate a refinement process using molecular dynamic simulations of iron wherein nanocrystalline structures are generated from initially perfect lattices under high-shear strain. The simulation cells undergo a highly disordered state, followed by an atomic reordering and grain coarsening, resulting in nanograins. We explore the dependence on parameters such as temperature, heat dissipation rate, shear strain rate, and carbon impurity concentration. Higher temperatures lead to the formation of larger and longer grains. The faster heat dissipation sample initially yields more small grains, but their number subsequently reduces and is lower than the slower heat dissipation sample at approximately γ=1.5. Slower strain rates do not promote nanograin formation. The presence of carbon impurities appears to have little effect on grain formation. This detailed analysis affords insight into the mechanisms that control the formation of nanograins under high-shear conditions. Published by the American Physical Society 2025

First‐Principles Study on the Influence of Cu/Ag/Au Doping with Different Valence States and Point Defects on the p‐Type Conductivity of ZnO

Herein, the impact of Cu/Ag/Au doping with different valence states on the p‐type conductivity of ZnO‐doped materials, as well as the coexistence of Zn vacancy (VZn) and H interstitial (Hi), is investigated using first‐principles calculations within the context of density functional theory. Under rich O conditions, dopant systems are more accessible to create and steady. The Fermi level of the dopant enters the valence band, resulting in an ionization impurity concentration that exceeds the critical threshold for ionization impurities, thereby exhibiting the characteristics of p‐type degeneracy. Hi can promote conductivity in the a‐axis while reducing conductivity in the c‐axis direction. The Zn34Ag2+HiO36(VZn0) system has the highest p‐type conductivity along the a‐axis direction, whereas the Zn34Ag2+HiO36(VZn0) system has the highest p‐type conductivity along the c‐axis direction.

Low-Temperature, Highly Sensitive Ammonia Sensors Based on Nanostructured Copper Iodide Layers

Chemiresistive ammonia gas sensors with a low limit of detection of 0.15 ppm and moisture-independent characteristics based on p-type copper iodide (CuI) semiconductor films have been developed. CuI films were deposited on glass and polyethylene terephthalate (PET) substrates using a Successive Ionic Layer Adsorption and Reaction method to fabricate CuI/glass and CuI/PET gas sensors, respectively. They have a nanoscale morphology, an excess iodine and sulfur impurity content, a zinc blende γ-CuI crystal structure with a grain size of ~34 nm and an optical band gap of about 2.95 eV. The high selective sensitivity of both sensors to NH3 is explained by the formation of the [Cu(NH3)2]+ complex. At 5 °C, the responses to 3 ppm ammonia in air in terms of the relative resistance change were 24.5 for the CuI/glass gas sensor and 28 for the CuI/PET gas sensor, with short response times of 50 s to 210 s and recovery times of 10–70 s. The sensors have a fast response–recovery and their performance was well maintained after long-term stability testing for 45 days. After 1000 repeated bends of the flexible CuI/PET gas sensor in different directions, with bending angles up to 180° and curvature radii up to 0.25 cm, the response changes were only 3%.

Development of a General Pharmacopoeial Monograph for Determining the Content of N-Nitrosoamine Impurities in Pharmaceutical Substances of the Sartan Group and Metformin Substances for Inclusion in the State Pharmacopoeia

Development of a General Pharmacopoeial Monograph for Determining the Content of N-Nitrosoamine Impurities in Pharmaceutical Substances of the Sartan Group and Metformin Substances for Inclusion in the State Pharmacopoeia

Effect of Major Impurity in the Vanadium‐Rich Solution on the Growth of NaV2O5 Crystals under Hydrothermal Conditions

NaV2O5 is a promising cathode material for ion batteries with high capacity and good cycle performance. The high concentration of vanadium and low impurity in vanadium‐rich solution makes it possible to be used as raw material for vanadium product preparation. Vanadium solution containing impurity was prepared to investigate its influence mechanism on NaV2O5 crystal precipitation. The influence of four major impurity elements on the precipitation of NaV2O5 following the order of P > Al > Si > Fe. With the increase of impurity concentrations, vanadium conversion rate and V content of the precipitates decreased to varying degrees, while impurity content increased. When concentrations of Fe, Al and Si were high, the resulting precipitate was still NaV2O5, but the crystal structure changed. The AlOH and SiOH hider the condensation between VOH and broke the rod into irregular flakes and blocks. As P concentration gradually increased, the precipitates changed from NaV2O5 to VO2(H2O) 0.5 and then to Na3.053((V5O9)(PO4)2(OH)0.1(H2O)8, meanwhile, the morphologies changed from rod to plate, then to cross‐like, and finally to cube. Revealing the influence of impurity in vanadium‐rich solution on the growth of NaV2O5 crystal is conducive to the popularization of the process.

Correlation of srf performance to oxygen diffusion length of medium temperature heat treated cavities*

Abstract This comprehensive study, being part of the European XFEL R\&D effort, elucidates the influence of medium temperature (mid-T) heat treatments between 250°C and 350°C on the performance of 1.3~GHz superconducting radiofrequency (SRF) niobium cavities. 
Utilizing a refurbished niobium retort furnace equipped with an inter-vacuum chamber and cryopumps at DESY, we have embarked on an investigation to enhance the state-of-the-art SRF cavity technology. Our research reveals that mid-T heat treatments significantly boost the quality factor ($Q_0$) of the cavities, achieving values between $2\cdot10^{10}$ to $5\cdot10^{10}$ at field strengths around 16~MV/m, while the maximum field strengths are limited to 25-35~MV/m and enhanced sensitivity to trapped magnetic flux is observed. Moreover, we delve into the effects of surface impurity concentration changes, particularly the diffusion of oxygen content, and its impact on performance enhancements. By categorizing treatments based on calculated diffusion lengths using the whole temperature profile, we recognize patterns that suggest an optimal diffusion length conducive to optimizing cavity performance. SIMS results from samples confirm the calculated oxygen diffusion lengths in most instances. Deviations are primarily attributed to grain boundaries in fine-grain materials, necessitating repeated measurements on single-crystal materials to further investigate this phenomenon. Investigations into cooling rates and the resulting spatial temperature gradients across the cavities ranging from 0.04 to 0.2~K/mm reveal no significant correlation with performance following a mid-T heat treatment. However, the increased sensitivity to trapped magnetic flux leads to new challenges in the quest for next-generation accelerator technologies since the requirement for magnetic hygiene gets stricter.

Optimization of microstructure to improve Si3N4 ceramics with thermal conductivity and mechanical properties: effect of Si and α-Si3N4 powder composition

The heat dissipation capacity and mechanical reliability of silicon nitride (Si3N4) ceramic substrates determine the service life of power devices. In this work, a two-step sintering method was designed to produce Si3N4 ceramics with excellent performance using Si and α-Si3N4 powders with different ratios as raw materials. The nitridation mechanism and the microstructural evolution mechanism were clarified. The in-situ-generated β-Si3N4 seeds regulated the microstructure of the post-sintered Si3N4 ceramics. The introduction of Si powder reduced the content of oxygen impurities and regulated the microstructure of Si3N4 ceramics, thereby improving thermal conductivity while maintaining excellent mechanical properties. When the mass ratio of Si powder nitridation to α-Si3N4 was 0.75, its thermal conductivity was 120W·m-1·K-1, fracture toughness was 11.92±0.36MPa·m1/2, and bending strength was 712±20.6MPa. This study provides a strategy to reduce the introduction of oxygen impurities while optimizing the microstructure to prepare Si3N4 ceramics with excellent performance.

Modeling of the qualitative state of oilseeds from soybean seeds by multifactorial analysis of factor areas

The production of oil products in Ukraine is a leader not only in the European but also in the world market of food and processing industry products, therefore, the priority areas of scientific research in this field are the effective assessment of the quality of the oil obtained. Existing methods for assessing this product by organoleptic characteristics are subjective and do not allow the use of parameters that require more complex measurement technologies; which in general makes it impossible to conduct a comprehensive analysis of the quality of the studied product. The purpose of this study was to develop and implement a mathematical modeling method for numerical analysis of the quality of soybean oil product varieties. Qualitative assessment of the studied oil varieties was carried out using such indicators as the mass fraction of fat, peroxide, and acid number; content of free fatty acids, phosphatides, moisture, and impurities; it allowed to perform a numerical analysis using dimensionless complexes regarding the condition of the studied oil product varieties and compliance with regulatory indicators. When processing experimental data and calculating the developed quality criteria, programming methods, Excel, and COMPASS mathematical environments were used, which allowed the construction of geometric quality models and the necessary assessment criteria. According to the results of the research, it turned out that the characteristics of the studied varieties "OAS Avatar", "ES Mentor", "Sigalia", "ES Mentor" and "Gallek" do not meet the requirements for compliance with the quality thresholds by 160 - 220%, however, their current characteristics, which were selected for assessment, are within the average normative indicators. The proposed mathematical models can be implemented for practical application in assessing the condition of any complex object of research using an unlimited number of characteristics. At the same time, the main requirements for these parameters are their breadth of coverage of the physical, mechanical, and chemical-biological properties of the product and the ability to provide an objective and thorough assessment of its condition.

Prediction of impurity concentrations in AlN single crystals by absorption at 230 nm using random forest regression

A sample matrix of C, O, and Si doping in PVT-AlN is presented, and links between concentration and absorption coefficient are demonstrated. A trained random forest model offers a promising approach for the prediction of C, O, and Si content.

In Ukrainian

High-quality homogeneous synthetic diamond powders are necessary for the production of modern abrasive tools. The properties of the powder are formed in the process of synthesis, extraction and sorting by various methods. The process of flotation separation of powder is based on differences in the energy state of the surface of the particles. The energy state of the powder surface is influenced by the physico-chemical, physico-mechanical, and morphometric characteristics of the original powder. The purpose of this study is to study at a quantitative level the influence of pretreatment and flotation separation on the physicochemical and morphometric characteristics of synthetic diamond powders. Diamond powders of the AC20 brand with a grain size of 100/80 (Ni-Mn-C system), chemical processing products, separation products (foam and chamber) were studied. The characteristics were determined: strength of the powder under static compression, specific magnetic susceptibility, specific electrical resistance, content of impurities, hydrophilicity of the powder (by the value of the free energy of water saturation). Using the DiaInspect.OSM device, morphometric characteristics were determined, primarily, the indicator of the external specific surface of the powder and the topography of the surface. The obtained results showed that the application of pretreatment of the powder leads to a decrease by an order of magnitude in the specific magnetic susceptibility and specific electrical resistance, a three-fold decrease in the content of impurities, and a 1.4-fold decrease in the hydrophilicity of the original powder. This is reflected in the improvement of the quality of the powders obtained from the foam product. the specific magnetic susceptibility of cis powders is reduced by an order of magnitude; 1.4 times - the content of impurities; 1.25 times - the hydrophilicity of the powder.

Preventive maintenance in urban public transport: the role of engine oil analysis

Engine oil is a valuable source of information on the technical condition of the drive unit. Under the influence of many factors, including operating conditions, time, high temperature, and various types of contamination, the oil gradually degrades, which can result in serious engine damage. The subject of the article focuses on an attempt to answer the questions of how engine failure affects the degradation of engine oil and whether we can use this knowledge to detect potential problems in public transport vehicles at an early stage. The research material consisted of samples of engine oil in the SAE 10 W-40 viscosity class and data on vehicle faults obtained from the service of a public transport company. The oils come from two city buses belonging to the fleet of diesel-powered vehicles, in which critical cooling system failures were diagnosed during engine tests, excluding the vehicle from further use. The conducted studies analyzed the degree of oil degradation, which included determining the changes in kinematic viscosity at 40 °C and 100 °C via a Stabinger SVM 3001 viscometer. The physicochemical parameters of the oil, such as the degree of oxidation, nitration, total acid number (TAN), total base number (TBN), and content of impurities in the form of soot and glycol, were examined via FTIR spectroscopy. The degree of impurities and the general quality of the oil were also determined via a blotter spot test. Additionally, to determine the degree of metal abrasion and changes in the depletion of additives, elemental analysis via the HDXRF method was used. As a result of the tests carried out, potential correlations between the oil condition and the technical condition of the vehicle in real operating conditions were confirmed.

Modified bipolar membrane for electrodialysis processing of highly concentrated sodium nitrate and boric acid solution

We studied the characteristics of two membranes: the industrial bipolar membrane MB-3, consisting of two layers, i.e., an anion exchanger with quaternary ammonium groups and a cation exchanger with phosphonate groups, and the membrane MB-3M, modified on the cation exchange side with a 100 μm thick layer of perfluorosulfonic acid. The analysis of the selectivity of the initial and modified membranes in a wide range of current densities (0.25–4 A/dm2) showed that the application of a perfluorosulfonic acid layer leads to a decrease in the transport of nitrate anions by 18–40 times, depending on the current density, compared to the initial industrial membrane MB-3. Experiments on electrodialysis processing of a mixed 0.5 M NaNO3 and 0.75 M H3BO3 solution showed that the use of a bipolar membrane modified with a perfluorosulfonic acid, at a sodium nitrate processing degree of 75%, allows obtaining a 1.01 M NaOH solution with a low impurity content (0.08 M sodium nitrate and 0.09 M boric acid) and 1.17 M HNO3 (sodium nitrate content 0.09 M, boric acid 0.09 M). When using the initial MB-3 membrane under the same conditions, 0.77 M NaOH with a high content of impurities (0.25 M sodium nitrate and 0.08 M boric acid) and 1.03 M HNO3 (containing 0.09 M sodium nitrate and 0.09 M boric acid) are obtained. The energy consumption for processing is comparable to that for the initial bipolar membrane MB-3 and amounts to 0.15 kW·h/mol.

Snapback in diamond p-i-p structure containing a small amount of n-type impurity in the i-layer

Abstract We studied the snapback phenomenon observed in a diamond p-i-p structure in detail and investigate the effect of n-type impurity concentration in the i-layer. The snapback observed in the p-i-p structure was also observed in the p-i-p structures with a very small amount of n-type impurity and in the p-n-p structure. In addition, since the threshold voltage of snapback changed depending on the n-type impurity concentration, it is considered that n- type impurities are related to the occurrence of snapback. Furthermore, there is a correlation between the voltage and temperature when snapback occurs. These results suggest that the snapback is caused by a small amount of n-type impurity in the i-layer and a parasitic bipolar operation resulting from the applied high voltage and increased leakage current.

Pre-Melting-Assisted Impurity Control of β-Ga2O3 Single Crystals in Edge-Defined Film-Fed Growth.

This study reveals the significant role of the pre-melting process in growing high-quality (100) β-Ga2O3 single crystals from 4N powder (99.995% purity) using the edge-defined film-fed growth (EFG) method. Among various bulk melt growth methods, the EFG method boasts a fast growth rate and the capability of growing multiple crystals simultaneously, thus offering high productivity. The pre-melting process notably enhanced the structural, optical, and electrical properties of the crystals by effectively eliminating impurities such as Si and Fe. Specifically, employing a 100% CO2 atmosphere during pre-melting proved to be highly effective, reducing impurity concentrations and carrier scattering, which resulted in a decreased carrier concentration and an increased electron mobility in the grown Ga2O3 single crystals. These results demonstrate that pre-melting is a crucial technique for substantially improving crystal quality, thereby promising better performance in β-Ga2O3-based device applications.

A new targetry system for cyclotron production of pharmaceutical grade indium-111 radioisotope

Abstract The aim of this research is to present a new, fast, simple, low-cost and innovative method for the production and purification of pharmaceutical grade indium-111 chloride for use in nuclear medicine.In the previous methods for cyclotron production of indium-111 radioisotope, besides the need for high amount of enriched cadmium, in electrodeposition of enriched cadmium on copper backings for target preparation and its chemical dissolution step, impurities of isotopes of copper and zinc enter the final product. So, radiolabeling of such products was hard or impossible with some molecules. In this research, due to the proper selection of the target isotope, enriched cadmium-112, and the optimal proton bombardment energy, only very low amount radioisotopic impurities were produced and observed in the sample solution. After the separation process, the amounts of zinc-65 and indium-114 were less than the standard permissible amounts in indium-111 radiopharmaceuticals. The concentration of cadmium impurities in the final product was less than 0.1 ppm. The radionuclidic purity of the sample was confirmed by gamma ray spectroscopy, and it was found to be suitable for use in preclinical studies.

Simulation of snow albedo and solar irradiance profile with the Two-streAm Radiative TransfEr in Snow (TARTES) v2.0 model

Abstract. The Two-streAm Radiative TransfEr in Snow (TARTES) model computes the spectral albedo and the profiles of spectral absorption, irradiance, and actinic fluxes for a multi-layer plane-parallel snowpack. Each snow layer is characterized by its specific surface area, density, and impurity content, in addition to shape parameters. In the landscape of snow optical numerical models, TARTES distinguishes itself by taking into account different shapes of the particles through two shape parameters, namely the absorption enhancement parameter B and the asymmetry factor g. This is of primary importance as recent studies working at the microstructure level have demonstrated that snow does not behave as a collection of equivalent ice spheres, a representation widely used in other models. Instead, B and g take specific values that do not correspond to any simple geometrical shape, which leads to the concept of the “optical shape of snow”. Apart from this specificity, TARTES combines well-established radiative transfer principles to compute the scattering and absorption coefficients of pure or polluted snow, as well as the δ-Eddington two-stream approximation to solve the multi-layer radiative transfer equation. The model is implemented in Python, but conducting TARTES simulations is also possible without any programming through the SnowTARTES web application, making it very accessible to non-experts and for teaching purposes. Here, after describing the theoretical and technical details of the model, we illustrate its main capabilities and present some comparisons with other common snow radiative transfer models (AART, DISORT-Mie, SNICAR-ADv3) as a validation procedure. Overall the agreement on the spectral albedo, when in compatible conditions (i.e., with spheres), is usually within 0.02 and is better in the visible and near-infrared range compared to longer wavelengths.

Trace Metal Impurities Induce Differences in Lithium-Sulfur Batteries.

Carbon nanotubes (CNTs) with exceptional conductivity have been widely adopted in lithium-sulfur (Li-S) batteries. While trace metal impurities in CNTs have demonstrated electrocatalytic activity in various catalytic processes, their influence on sulfur electrocatalysis in Li-S batteries has been largely overlooked. Herein, we reveal that the trace metal impurities content in CNTs significantly improves the specific capacity and cycling performance of Li-S batteries by analyzing both our own results and previous literature with CNTs as the sulfur hosts. Even under lean electrolyte conditions (E/S ratio of 5 μL mgs-1), we demonstrate that a small content of metal impurities in CNTs (∼2 wt %) could account for a 14.3% increase in specific capacity and a 14.1% increase in capacity retention under a high sulfur loading of 3.5 mg cm-2. The electron transfer from confined metal catalysts within CNTs leads to electron accumulation at the carbon interface, facilitating electron donation to adsorbed sulfur species and lowering the energy barrier for Li2S formation.