Impurity Concentration Research Articles

Enhancing up-conversion luminescence in Yb/Er co-doped CsPbCl3 single crystals

The search for and fabrication of materials for the near-infrared range of the spectrum, including telecommunication windows, is an extremely important task in modern technology. This work presents the results of studies on the photoluminescence of CsPbCl3 single crystals with varying contents of ytterbium and erbium impurities, grown using the Bridgman method. The existence of electrically neutral Yb3+–VPb–Er3+ complexes within the crystal structure was confirmed. Resonant absorption of excitation radiation λ = 980 nm by Yb3+ ions reveals a three-step energy transfer channel from Yb3+ to Er3+ ions within a single complex. The estimated quantum yield of up-conversion luminescence at λ = 524 nm (0.02%) associated with erbium ions indicates the presence of electronic transitions to higher energy levels, with the possibility of subsequent emission within the third telecommunication window.

The Influence of Iron Particle Contamination on the Breakdown Characteristics of Circulating Mineral Oil under DC Voltage

The presence of metallic particles can lead to the degradation of transformer oil due to the intensification of the electric fields near the conductive components. The primary objective of this research was to investigate the impact of iron impurities on the electrical properties of Mineral Oil (MO), particularly under conditions of continuous flow. Five distinct samples with varying levels of contaminants were carefully prepared for analysis. A specialized chamber was designed to replicate the circulation conditions of oil within an operating transformer. The focus of the investigation was on the breakdown characteristics under DC voltages. The results indicated that higher concentrations of iron impurities were associated with a reduction in breakdown voltage although the circulation of oil exhibited a beneficial effect. To validate these findings, Finite Element Method (FEM)-based simulations were conducted. The analysis of the electric field distribution revealed that iron impurities amplified the electric field intensity, while circulation served to mitigate this effect. Furthermore, the simulations tracking the trajectory of iron particles demonstrated that circulation hindered the particles from reaching the electrodes, thereby diminishing discharge events and lowering the risk of dielectric failure. In conclusion, the circulation of MO enhanced its breakdown voltage, although the presence of iron contamination could still pose a risk under DC voltage conditions.

Experimental study on metallic impurity behavior with boronization wall conditioning in EAST tokamak

Operation of EAST tokamak with full metal wall without any wall conditioning are attempted in 2023 and 2024 experimental campaign to address the issues related to ITER tungsten wall operation. It is found that H-mode plasma could be sustained even with a substantial increase in metallic impurity content caused by strong plasma-wall interaction under uncoated metal wall. Boronization wall conditioning is therefore performed to improve the plasma performance with higher injected power. This study aims to quantitatively assess the impact of boronization wall conditioning on metallic impurity concentration and behavior in the EAST tokamak. It is then proved to be an effective wall conditioning approach for significantly controlling high-Z impurity content. In this work, the impurity spectra at extreme ultraviolet (EUV) wavelength range measured by sets of fast-time-response and space-resolved EUV spectrometers are widely used in the data analysis. The variation in the boron content in plasma after boronization are investigated by monitoring the 2nd order of B V line at 48.59 Å. It is found that the persistence time of boron in EAST device after a boronization with 10 g of carborane (C2B10H12) is about 2000 s (∼150 shots) of discharge duration. The impact of different wall conditions (uncoated metal wall and boron coated wall) on metallic impurity content are then quantitatively studied. After boronization, the concentration of tungsten (CW) and molybdenum (CMo) dropped by 85 %, e. g., from 2.0 × 10-4 to 4.1 × 10-5 and from 4.6 × 10-5 to 6.3 × 10-6, respectively. While the concentration of copper (CCu) and iron (CFe) decreased by approximately 50 % and 65 %, respectively, e. g., from 4.3 × 10-5 to 2.1 × 10-5 and from 2.0 × 10-4 to 6.9 × 10-5. A comparison of the line emission profiles from tungsten ions of W26+ − W32+ and W43+ before and after boronization reveals an overall reduction in the intensity while without obvious change in the profile shape, which suggests a reduction in metallic impurities source after boronization instead of altering impurity transport in core plasma significantly.

Optimization of liquefaction cycles applied to CO2 coming from onshore pipeline to offshore ship transportation

In the field of the CO2 transportation for the Carbon Capture, Utilization and Storage (CCUS) process chain, several analyses show that, for a large-scale CO2 transportation, pipeline transportation is the preferred method on land due to its lower cost. Barges also present a feasible alternative if the capture site is near a waterway. Maritime transport becomes more advantageous than pipelines, particularly over long distances and across ocean. Despite the need to liquefy CO2 and to add temporary storage facilities for loading and unloading onto ships, beyond a certain distance at fixed CO2 transported and plant life, ship transport optimal at pressures of 7 or 15 bar depending on the type of vessel. Impurities in CO2, arising from various industrial processes and variable performances of capture technologies, increase energy consumption during compression and could cause corrosion risks. Specifications for CO2 ship transport limit the concentration of certain impurities with strict thresholds. Methods for purifying CO2, such as the two-flash system and stripping column, have been proposed to meet these specifications. The studied CO2 liquefaction methods show that hybrid cycles, combining open cycle with Joule-Thompson expansion and closed cycle with cooling machine offer reduced energy consumption and improved CO2 recovery compared to open or closed cycles. In the presence of the maximum threshold of impurities in the pipeline, energy consumption can nearly double from 21.8 kWh/tCO2 to 40.9 kWh/tCO2, with the highest recovery rising 98.1 %. This research underscores the importance of optimizing CO2 transport strategies to facilitate the deployment of CCUS technologies.

Density compensation with pellet fueling during ELM suppression with n = 4 RMP on metal-wall EAST tokamak

Pellet injection is the most promising fueling method to achieve a deep particle deposition for future fusion reactors. On metal-wall EAST tokamak, a full density compensation has been achieved by the pellet fueling during ELM suppression with n = 4 RMP which will be used in ITER’s operation. During the pellet injection, ELM suppression is terminated and small ELMs reappear. The plasma stored energy does not have a reduction with the pellet injection. Meanwhile, large sawtooth accompanied with RMP application is modified by the pellet injection. The amplitude of sawtooth crash decreases and high frequency small sawtooth crashes appear during the pellet fueling. The concentration of heavy impurities in the plasma core, such as tungsten and molybdenum, has an obvious reduction with the ELM reappearance and sawtooth modification. Although the same ELM behaviors also appears after divertor gas fueling, pellet fueling can modify the core plasma more significantly. All these experimental results will provide a good support to the ITER operation in the future.

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.

Initial design concepts for solid boron injection in ITER

As part of ITER’s consideration to change its first wall material from beryllium to tungsten, the ITER Organization has proposed studying the feasibility of real-time solid boron injection (SBI) into the plasma to coat the walls and divertor to supplement glow discharge boronization (GDB) [1]. Boron deposits getter oxygen and reduce sputtering of tungsten from plasma facing components (PFCs). Particularly in areas with significant plasma wall interactions, boron coatings are expected to be short-lived under high performance plasma conditions. The proposed SBI system aims to maintain boron layers in these areas to avoid excessive radiation from tungsten in the plasma as a risk mitigation to ensure ITER will be able to reach and sustain Q = 10 conditions. The system will be used sparingly, as redeposition of boron can lead to significant tritium retention, which must be minimized in ITER to comply with nuclear safety concerns. SBI is proposed to limit and precisely control the amount of boron injected in real-time during plasma operation. Here, some of the design requirements and initial concepts for an SBI system in ITER are presented based on previous results carried out with SBI systems on a number of tokamaks and stellarators around the world [2–18].Previous results using SBI systems installed by PPPL have injected boron particles from 5 µm–2 mm diameter at calibrated rates of 2–200 mg/s in real-time during plasma operation on AUG [4], DIII-D [5], EAST [6], KSTAR [7], LHD [8], TFTR [9], WEST [10], and W7-X [11,12], leading to improved wall conditions with reduced plasma impurity concentrations and radiated power and improved plasma performance. The boron is ionized in the plasma edge and then deposited on plasma-wetted surfaces. On AUG [4], EAST [6] and WEST [10] reduced tungsten sputtering sources were observed following several discharges with SBI. Extrapolation of these SBI results are presented to estimate the amount of boron needed for wall conditioning in ITER. Real-time SBI control requirements and plasma operation scenarios for ITER are also described.

The influence of external action on the dynamics of elastic, thermal and concentration waves propagation

This paper presents the nonlinear coupled mathematical model allowing investigating the interrelation between the mechanical, thermal and diffusion processes in solid body. The model takes into account the finiteness of relaxation times of mass and heat fluxes. This is of interest for dynamical processes with characteristic times comparable to relaxation times, when the changes in the temperature and impurity concentration are described by hyperbolic thermal conductivity and diffusion equations. Additionally, the model takes into account the temperature and concentration dependencies of the diffusion coefficients; it gives rise to additional nonlinearity. The model is thermodynamically consistent and follows from the nonlinear equations of the thermoelastic diffusion theory. The implicit difference scheme of second approximation order in time and spatial steps, linearization relatively to known time moment and double-sweep method are used for the numerical implementation of the equation system. Examples of interrelating wave propagating under external actions are considered. The results show that distortions in the strain/stress and temperature distributions appear due to the interaction between the phenomena of different physical nature. The specific rates of different physical processes are different. Although diffusion is the slowest of them all, the influence of the diffusion wave is reflected in stress and strain waves far beyond the diffusion wave front. It is shown that regardless of the external action character and impulse form, the influence of the considered processes on each other does not change, but the wave picture becomes much more complicated with increasing number of actions.

Improvement of End-of-Synthesis Radiochemical Purity of 177Lu-DOTA-PSMA-Ligands with Alternative Synthesis Approaches: Conversion Upswing and Side-Products Minimization

Background: Radiochemical purity is a key criterion for the quality of radiopharmaceuticals used in clinical practice. The joint improvement of analytical methods capable of identifying related radiochemical impurities and determining the actual radiochemical purity, as well as the improvement of synthesis methods to minimize the formation of possible radiochemical impurities, is integral to the implementation of high-tech nuclear medicine procedures. PSMA-targeted radionuclide therapy with lutetium-177 has emerged as an effective treatment option for prostate cancer, and [177Lu]Lu-PSMA-617 and [177Lu]Lu-PSMAI&T have achieved global recognition as viable radiopharmaceuticals. Recently, it was shown that specific radiochemical impurities can form during the synthesis of [177Lu]Lu-PSMA-617 because of a spontaneous, thermally mediated condensation of the Glu-C(O)-Lys fragment, resulting in the formation of three different cyclic forms (with no affinity for PSMA). During this study, we identified another impurity, a product of detachment of the Glu-CO fragment from PSMA-617, caused by heating. The total content of all four thermally mediated degradation products may reach 9–11% during classical incubation for 30 min at 95 °C, reducing the radiochemical purity to an unacceptable level (albeit with high levels of radiochemical conversion). It is reasonable to assume that the formation of similar impurities is characteristic of all PSMA-specific vectors that contain Glu-C(O)-Lys pharmacophores. Because the formation of these impurities directly depends on the temperature and incubation time, to reduce their content in the reaction mixture at the end of the synthesis, it is necessary to select conditions to achieve a high level of radiochemical conversion for the minimum possible time and/or at the minimum sufficient temperature. Methods: In this study, using [177Lu]Lu-PSMA-617 as an example, we evaluated the efficiency of alternative methods of synthesis with microwave heating and co-solvent (ethanol) addition to ensure radiochemical yield and radiochemical purity in the shortest possible time and at the minimum necessary and sufficient synthesis temperature. Results: Both approaches achieved a significant reduction in the impurities content, while achieving satisfactory synthesis yields in a short time. In addition to improving the synthesis parameters and radiochemical purity, the use of microwave heating and the addition of ethanol reduces the negative influence of other auxiliaries on labeling kinetics. Notably, the addition of ethanol under certain conditions allowed [177Lu]Lu-PSMA-617 to be synthesized at room temperature for only 10 min. This makes it possible to achieve exceptionally high real radiochemical purity of the preparations, determined only by the quality of the original precursor. The approaches considered in this study can be successfully applied to improve the synthesis process and quality parameters of the finished product, both for known radiopharmaceuticals and for those under development.

Thermodynamic modeling of the processes of purification of primary aluminum from vanadium impurities

This article discusses the interaction of chemical elements in the three-component Al-V-B system. Vanadium reduces electrical conductivity in primary aluminum, which requires its reduction during aluminum electrolysis to values less than 0.02%. In order to reduce the concentration of vanadium impurities, thermodynamic calculations were carried out for the reactions of separation of the metallic phase of aluminum and impurities of vanadium intermetallic compounds through the use of a boron-containing flux. The calculation of thermodynamic parameters was carried out in HSC Chemistry 9.0. for AlB2 and VB2 compounds, the chemical reaction AlB2 + V = VB2 + Al within the operating temperatures of electrolysis and casting of primary aluminum of 650–950°С and the conditions of immersion of boron-containing flux into the melt to a ladle depth of 0.5, 1.0, 1.5 and 2 m, i.e. within the pressure range of 102.39–148.99 kPa. Thermodynamic analysis showed that the Gibbs energy (ΔGT) values in the entire range of operating temperatures of the electrolysis and casting of primary aluminum for VB2 are significantly lower than AlB2, therefore, they will be formed predominantly in this temperature range. The order of stability also suggests that vanadium can be easily removed from aluminum melts by adding boron. The results obtained allow us to conclude that chemical reactions of primary aluminum purification from vanadium impurities can occur due to boron additives.

Impurity study in the dimensionless and dimensional isotope identity experiment between JET Deuterium and Tritium L-mode plasmas

Abstract The behaviour of impurities in fusion plasmas is of crucial importance for achieving sustained fusion reactions, and understanding similarities and differences between Deuterium (D) and Tritium (T) plasmas is needed to assess potential changes from DD to DT in ITER and future reactors. The first dimensionless and dimensional isotope identity experiments between Deuterium (D) and Tritium (T) L-mode plasmas were conducted at the JET W/Be wall. In the first approach, the discharges with matched ρ∗, ν∗, βn, q, and Te/Ti were compared to emphasize direct isotope effects, while in the dimensional approach engineering parameters such as toroidal magnetic field BT, plasma current Ip, plasma electron density and NBI power PNBI were matched. The dimensionless isotope scaling showed an improvement in global confinement and local transport in T plasmas in comparison to the matched D one [1]. Detailed impurity analyses using VUV, visible spectroscopy, SXR cameras, and bolometry revealed that T plasmas exhibited higher radiation and impurity content, particularly Ni and W, compared to D plasmas. Understanding the origin of the increased impurity content is addressed in this paper. The dimensionless experiments showed differences in impurity transport. The Be source behaviour varied: D plasmas had higher Be influx in the dimensionless approach due to lower electron density and enhanced sputtering [2], while T plasmas showed a higher Be source in the dimensional experiments, highlighting isotope mass effects. W in the divertor region was not sputtered by hydrogen isotopes. W in the divertor region was not sputtered by hydrogen isotopes. In the dimensionless experiments, W sputtering was primarily influenced by Ni in T plasmas and by Be in D plasmas. However, in the dimensional approach, Be played a more significant role in W sputtering within T plasmas. MHD instabilities, including sawtooth oscillations, were present in all cases other ones were correlated with NBI power levels; higher NBI power led to elevated levels of Be, Ni, and W impurities. The comprehensive comparison underscores the necessity of accounting for isotope mass effects in predictive modelling and optimization of plasma performance in fusion reactors.

RECYCLING OF DOMESTIC AND INDUSTRIAL WASTEWATER USING VERMIFILTRATION TECHNOLOGY

One of the biggest problems of our time is the growing shortage of fresh water. According to the World Health Organization, by the middle of the 21st century, half of the planet's inhabitants will experience an acute shortage of fresh water. Simultaneously with the growing consumption of clean water, the annual volume of wastewater from municipal, agricultural and industrial enterprises also increases. At the same time, the volume of water used annually is more than an order of magnitude higher than the volume of treated wastewater. Untreated wastewater is characterized by a high content of organic impurities and pathogenic microorganisms capable of causing diseases that are dangerous for human life. In connection with the outlined extremely urgent task is to ensure effective purification of wastewater from pollution with subsequent recycling of purified effluents - their reuse for other purposes: in the circulating system of industrial enterprises, agricultural and landscape irrigation systems. From this point of view, the process of vermifiltration - wastewater treatment using earthworms - is of great interest. The technology is based on the ability of worms to work as "biofilters". Worms absorb organic and inorganic pollutants from wastewater, digest them and release them in the form of their excrement (coprolites) into the environment. With such processing, wastewater is cleaned, disinfected, and detoxified; treated effluents are suitable for reuse. There is also a transformation of organic and inorganic components into organo-mineral fertilizer - vermicompost and biomass of earthworms, which can serve as raw materials for the fodder and pharmaceutical industry.

Detachment scalings derived from 1D scrape-off-layer simulations

Fusion power plants will require detachment to mitigate sputtering and keep divertor heat fluxes at tolerable levels. Controlling detachment on these devices may require the use of real-time scrape-off-layer modeling to complement the limited set of available diagnostics. In this work, we use the configurable Hermes-3 edge modeling framework to perform time-dependent, fixed-fraction-impurity 1D detachment simulations. Although currently far from real-time, these simulations are used to investigate time-dependent effects and the minimum physics set required for control-relevant modeling. We show that these simulations reproduce the expected rollover of the target ion flux — a typical characteristic of detachment onset. We also perform scans of the input heat flux and impurity concentration and show that the steady-state results closely match the scalings predicted by the 0D time-independent Lengyel–Goedheer model. This allows us to indirectly compare to SOLPS simulations, which find a similar scaling but a lower value for the impurity concentration required for detachment for given upstream conditions. We use this result to suggest a series of improvements for the Hermes simulations, and finally show simulations demonstrating the impact of time-dependence.

Preliminary Beneficiation Studies of Quartz Samples from the Northwest Territories, Canada

Three quartz-rich geologic materials—vein quartz from the Great Bear Magmatic Zone, massive quartz from the Nechalacho rare earth deposit, and quartz sands from the Chedabucto silica sand deposit along the shores of the Northern Arm of the Great Slave Lake, Northwest Territories of Canada—were evaluated for their amenability to physical beneficiation into high-purity quartz (HPQ). The samples were subjected to various treatment processes, including crushing, grinding, calcining and quenching, acid leaching, wet high-intensity magnetic separation (WHIMS), and reverse flotation. After treatment, both the core and sand quartz samples met the requirements for HPQ, making them suitable for use in the production of semiconductor filters, liquid crystal displays (LCDs), and optical glass. However, the Al-bearing impurity content in the vein quartz products remained relatively high, and most of these impurities were dispersed in the quartz lattice, requiring further processing to meet the purity standards for HPQ required by these industries.

Hierarchical macro/mesoporous γ-Al2O3 as column matrix for development of low specific activity 99Mo/99mTc generator via 100Mo (γ, n)99Mo reaction

Abstract 99mTc, the daughter product of 99Mo, is a γ-emitting radionuclide with essential diagnostic applications in nuclear medicine. In this paper, an accelerator-based method (100Mo (γ, n)99Mo) for production of 99Mo and 99mTc has been explored. Approximately 68.3 MBq of 99Mo was successfully produced by the irradiation of 100Mo metallic target for 40 h using electron beam with energy of 50 MeV and current of 0.2 μA at electron linear accelerator (Institute of Modern Physics, Chinese Academy of Sciences, IMPCAS). Different types of 99Mo/99mTc generators were prepared using hierarchical macro/mesoporous γ-Al2O3 (HMMA) as column adsorbent, and their performances were evaluated for over one week. 99Mo/99mTc generator with a column (3 mL, 4.2 × 0.95 cm) packed with 0.6 g HMMA exhibited excellent eluting performance. 99mTc could be collected within 4.0 mL of saline solution with high purity, and the elution efficiency could reach >85 %. Furthermore, 99Mo breakthrough in the eluates was negligible (<2 × 10−3 %) and concentration of impurity (<10 ppm) was acceptable. Finally, the enriched 100Mo was eluted from the spent 99Mo/99mTc generator using 1.0 mol/L ammonium hydroxide, and then reduced by high-temperature hydrogen reduction process with a total recovery of 95.3 %. This work demonstrated that the preparation of 99Mo via 100Mo (γ, n)99Mo reaction and isolating 99mTc using HMMA column chromatography have a potential in application.

Effect of H3PO4 coordination on vanadium extraction and iron separation in a H2SO4 leaching system.

The selectivity of the full wet leaching process for vanadium extraction using H2SO4 is low, resulting in a high impurity content in vanadium extracted from vanadium-bearing shale. This study focused on vanadium extraction and iron separation from vanadium-bearing shale, involving the coordination of H3PO4 in an H2SO4 leaching system. The effects of the ratio and quantity of H2SO4-H3PO4, leaching time, leaching temperature, and liquid-to-solid ratio on vanadium-bearing shale leaching were investigated. The dissolution processes of various minerals and the mechanism of iron coordination precipitation were analyzed. Results showed that vanadium leaching efficiency was 91.07% and iron leaching efficiency decreased from 84% to 23.86% under optimal leaching conditions-H2SO4-to-H3PO4 ratio of 2 : 1, H+ content of 8 mol kg-1, liquid-to-solid ratio of 0.8 L kg-1, and leaching time of 12 h at 95 °C. Leaching kinetics showed that the leaching process of vanadium shale was a mixed-control process in the H3PO4-H2SO4 leaching system; additionally, the leaching process was mainly controlled by a chemical reaction with an activation energy of 67 kJ mol-1. The preferential dissolution order of minerals in the vanadium-bearing shale was calcite, apatite, magnetite, muscovite, and pyrite. Under the H2SO4-H3PO4 leaching system, the iron content was reduced by inhibiting the dissolution of pyrite and coordination precipitation of Fe3+ with PO4 3-, thus separating iron and vanadium from the source. This provides guidance for vanadium extraction and impurity separation from vanadium-bearing shale using an all-wet method.

Low-Acid Leaching for Preferential Lithium Extraction and Preparation of Lithium Carbonate from Rare Earth Molten Salt Electrolytic Slag

In this work, lithium was preferentially recovered through the low-acid leaching from rare earth molten salt electrolytic slag (REMSES) with a leaching temperature of 60 °C. The influence on lithium extraction was investigated in detail in different leaching conditions. The optimal conditions were as follows: liquid-to-solid ratio (10 mL/g), sulfuric acid concentration (0.8 mol/L), leaching time (60 min) and leaching temperature (60 °C). This yielded a lithium extraction rate of 98.52% and a lithium carbonate purity of 99.5%. It was fitted using an empirical model; the kinetics showed that internal diffusion control conformed to the low-acid leaching reaction, which had an apparent activation energy of 10.81 kJ/mol for lithium. The total profit from the whole process was USD 0.2576 when dealing with 1.0 kg of REMSES. Moreover, in the sulfuric acid system, the leaching reaction mechanism was carefully investigated between 30 and 90 °C. An innovative process of recovering lithium from REMSES was achieved with environmental friendliness and good economic returns. Compared to traditional leaching using concentrated sulfuric acid, this cleaner recycling method conforms to the concept of green, low-carbon sustainable development, with high lithium selectivity, low impurity content in the filtrate and low acid consumption.

Enhancing thermal dissipation ability and electrical performance in GaN-on-GaN HEMTs through stepped-carbon buffer design

This study investigates the thermal dissipation ability and electrical performance of GaN-on-GaN HEMTs through a stepped-C buffer design. We analyzed the relationship between impurity (C and Fe) concentrations and the thermal conductivity of the GaN material by fitting Debye–Callaway model. A stepped-C buffer design is proposed to avoid the Fe impurity and its tailing effect on thermal conduction in GaN epitaxial layers. In addition, the high concentration of C doping is designed to suppress the epitaxial interface leakage in GaN-on-GaN structures. The transducer-less transient thermoreflectance (TL-TTR) technique revealed that the stepped-C structure significantly improves thermal conductivity of epitaxial layers compared with that of Fe/C co-doped structure. Due to the optimization of heat dissipation ability, the peak temperature of the stepped-C sample decreased by ∼30 °C compared to the Fe/C co-doped sample at PDC = 10.4 W/mm. Consequently, the GaN-on-GaN HEMTs with the stepped-C buffer achieved a record output power density (Pout) of 14.8 W/mm and a power-added efficiency (PAE) of 48.2% at 3.6 GHz, underscoring the critical role of thermal management in advancing GaN-on-GaN HEMT RF performance.

Characterization and quantitative understanding of subthreshold swing of Si metal–oxide–semiconductor field effect transistors at cryogenic temperatures

The temperature and drain current (ID) dependencies of sub-threshold swing (SS) values of Si n- and p-channel metal–oxide–semiconductor field effect transistors (MOSFETs) with different substrate impurity concentrations ranging from the 1015 to 1018 cm−3 ranges are systematically and experimentally evaluated at cryogenic temperatures. It is found that SS of p-channel MOSFETs tends to increase with decreasing temperature, which contrasts with saturation of SS of n-MOSFETs at cryogenic temperatures, well reported by many previous works. To explain these SS behaviors quantitatively, we employ a density-of-state (DOS) model with tail states consisting of localized states in a deep energy range and mobile states in a shallow energy range, which are attributable to potential fluctuations caused by substrate impurities. It is shown that this model can quantitatively explain the temperature and ID dependencies of SS of both n-MOSFETs and p-MOSFETs. Then, we are assuming that the Si p-MOSFET has a higher density of localized states than the n-MOSFET. Thus, the increase in SS of the p-MOSFETs with decreasing temperature is explained by an increase in the density of localized states at the Fermi level with decreasing temperature, because the density of localized states increases with elevating the Fermi level position in the employed DOS model.

Thermodynamic Analysis and Synthesis of Metallic Molybdenum Powder via the Solution Combustion Synthesis Process

ABSTRACT This study investigates the production of metallic molybdenum powder through the solution combustion synthesis (SCS) method. Despite thermodynamic challenges posed by potential back-oxidation under equilibrium conditions, the non-equilibrium nature of SCS facilitates the formation of metallic molybdenum. Experimental evidence suggests that Mo6+ actively participates as an oxidizer in the process, leading to the reduction of Mo6+ to Mo4+. Subsequent reduction of MoO2 is primarily driven by reactions with methane, a byproduct of the SCS process. Characterization of the gel precursor reveals the formation of a molybdenum-citric acid dimer. The resulting molybdenum powder exhibits a semi-amorphous structure with a developed specific surface area and low metallic impurity content but contains a significant amount of residual organic compounds. While heat treatment does not effectively remove these impurities, future research efforts should focus on developing purification strategies to minimize organic contamination.