Barrier Thickness Research Articles

Systematical Theoretical Study of the Nonpoint Source Effects in Nuclear Medicine Shielding Calculation

Abstract The objective of this note was to systematically study the effects from nonpoint radiation sources on the nuclear medicine imaging room or uptake room shielding design. The dose from a nonpoint source to a location at a certain distance to the center of the source was calculated. A correction factor could be applied to the dose calculated using a point source model with the same distance to compensate the nonpoint source effects. The correction factor was a function only depending on the source relative dimension, the ratio of the source’s geometric dimension to the distance. Theoretical and numerical calculation were performed to calculate the correction factor on a one-dimensional line source, two-dimensional circular disc source, three-dimensional sphere, and cylinder sources. Our study indicated that for large nuclear medicine imaging rooms, the point source model was a good approximation for shielding design. For a small uptake room, a nonpoint source correction may be considered to calculate the barrier thickness.

Estimation of barrier layer thickness from satellite-derived sea surface parameters in the north Indian Ocean using machine learning

ABSTRACT Oceanic barrier layer thickness (BLT) has been estimated from sea surface parameters through four machine learning (ML) models. The BLT used for training and testing of ML models has been computed from 19 years (2005–2023) of Argo data of vertical temperature and salinity profile in the north Indian ocean. It is observed that thick barrier layer (BL) exists in three regions within the north Indian ocean: the Bay of Bengal (BoB), Eastern Arabian Sea (EAS) and the East Equatorial Indian Ocean (EEIO) off the Sumatra. The observed BLT ranges from 0 to 80 m in the north Indian ocean with a seasonal cycle. Four ML models, i.e. multiple linear regression, artificial neural network (ANN), Random Forest and XGBoost have been trained for 2010–2018 to learn the relationship between sea surface parameters (input features) and BLT (target/output variable) in three thick BL regions within the north Indian Ocean. Thereafter, the trained models have been tested for the estimation of BLT in the same regions for the time period of 2019–2023. The ML models are well able to estimate the BLT from sea surface parameters (SST, SSS) with RMSE less than 5 m in the BoB and EAS, which is less than 8 percentile of the model testing datasets. The ‘Random Forest Regressor’ turns out to perform better than the other three ML models for estimation of BLT. Further, the Random Forest estimated BLT has been compared with the BLT computed using ORAS5 reanalysis data of vertical temperature and salinity profile. This study explores the capability of the ML models for capturing the signature of a subsurface variable on the surface owing to the limitation of costly subsurface measurement.

Enhanced tunnel magnetoresistance of Fe/MgGa2O4/Fe(001) magnetic tunnel junctions by interface-tuning with atomic-scale MgO insertion layers

We demonstrate a significant effect of atomic-scale MgO insertion layers on the tunnel magnetoresistance (TMR) in epitaxial magnetic tunnel junctions (MTJs) using a small bandgap oxide MgGa2O4. An enhanced TMR ratio of 151% at room temperature (resistance area product, RA: 23 kΩ ⋅ μm2) and 291% at 5 K (RA: 26 kΩ ⋅ μm2) were observed using 0.3 nm MgO insertion layers at the bottom and top barrier interfaces in Fe/MgGa2O4/Fe(001) MTJs with a total barrier thickness of 2.3 nm. The TMR showed a strong MgO thickness dependence. Microstructure analyses revealed that after MgO insertion, a homogeneous rock-salt structured Mg0.55Ga0.45O(001) barrier is formed, which differs from the nominal spinel crystal MgGa2O4. Elemental mapping of the MTJ showed that Ga diffusion into the adjacent Fe can be effectively suppressed while maintaining perfect lattice-matching at the Fe/barrier interfaces, thereby improving effective tunneling spin polarization through the barrier. The RA of the Mg0.55Ga0.45O (2.3 nm) MTJ is smaller than that of a comparable MgAl2O4 barrier (2.3 nm), thanks to the lower barrier height of the Mg0.55Ga0.45O as confirmed by the current–voltage characteristics.

Scanning probe spectroscopy of sulfur vacancies and MoS2 monolayers in side-contacted van der Waals heterostructures

Abstract We investigate the interplay between vertical tunneling and lateral transport phenomena in electrically contacted van der Waals heterostructures made from monolayer MoS2, hBN, and graphene. We compare data taken by low-temperature scanning tunneling spectroscopy to results from room-temperature conductive atomic force spectroscopy on monolayer MoS2 with sulfur vacancies and with varying hBN layers. We show that for thick hBN barrier layers, where tunneling currents into the conductive substrate are suppressed, a side-contact still enables addressing the defect states in the STM via the lateral current flow. Few-layer hBN realizes an intermediate regime in which the competition between vertical tunneling and lateral transport needs to be considered. The latter is relevant for device structures with both a thin tunneling barrier and a side contact to the semiconducting layers.

Optimizing breakdown voltage in rod-plane gaps with barrier design for positive DC voltage: an experimental study

Traditional air insulation in high-voltage equipment becomes bulky for high voltage withstand. The research so far conducted is related to electrode shape optimization, without fully exploiting the potential of strategically placed dielectric barriers. This paper introduces a new concept toward miniaturized high-voltage equipment by proposing glass barriers within rod-gap electrodes insulated with air and subjected to positive DC voltage. Barrier thickness and its positioning with regard to withstand characteristics are studied in order to optimize the design of such equipment. Three regimes of barrier thickness have been studied, and how that influences breakdown voltage and path type is presented. It was seen that with increasing barrier thickness, breakdown voltage improves more considerably. Interestingly, while the vertical position influences the breakdown path type, breakdown voltages remain similar for different paths at the same location. This paper, therefore, reveals that strategically placed glass barriers can enhance the dielectric strength of air-insulated systems. The present study leads to the optimization of the thickness and placement of barriers in future work by understanding the interplay with breakdown path to maximize the dielectric strength in miniaturized high-voltage equipment.

Polarization-induced two-dimensional hole gases in N-polar AlGaN/GaN heterostructures

We report the observation of two-dimensional hole gases (2DHGs) in N-polar AlGaN/GaN heterostructures grown on single-crystal GaN substrates by plasma-assisted molecular beam epitaxy. A systematic study varying AlGaN barrier thickness is performed. The presence of 2DHGs is confirmed by persistent p-type conductivity and high hole mobility observed in temperature-dependent Hall-effect measurements down to 10 K, and the dependence of 2DHG density on the AlGaN barrier thickness indicates its polarization induced origin. 2DHG with a sheet density of 7.5×1012 cm−2 shows a relatively high hole mobility of 273 cm2 V−1 s−1 at 10 K. Mobility model fit suggests that acoustic phonon scattering is the dominant scattering mechanism in the sub-room temperature region. This work indicates that the quality of N-polar 2DHGs is comparable to that of state-of-the-art metal-polar 2DHGs, contributing to a building block for potential high-quality N-polar p-channel devices.

Simulation of Quantum Tunnelling in Semiconductors: Analysis of Barrier Thickness Variation through the High Order FDTD Method

The time-dependent Schrödinger equation is fundamental to quantum mechanics, describing the temporal evolution of quantum systems. This research presents a High-Order Finite-Difference Time-Domain (HO-FDTD) method, employing Taylor series expansion to solve the equation with enhanced efficiency and accuracy. By advancing beyond traditional methods like first-order Taylor series (Crank-Nicolson, forward or backward Euler) or computationally intensive Runge-Kutta schemes, the HO-FDTD method leverages higher-order Taylor expansion for the time evolution operator while simultaneously refining the Laplacian operator. This dual improvement enhances precision, allowing for accurate modeling of complex quantum phenomena. Focusing on quantum tunneling, a critical process where electrons traverse potential barriers despite insufficient classical energy, the study examines tunneling probabilities and electron behavior across barriers of varying thickness in semiconductors. The simulations reveal that thicker barriers reduce tunneling probabilities, amplify deviations in electron positions, and indicate energy transfer during interactions, with increased resistance lowering kinetic energy and raising potential energy. These findings emphasize the significant influence of barrier thickness on quantum tunneling and highlight the HO-FDTD method’s capability to capture intricate quantum dynamics, establishing it as a robust tool for advancing research and applications in quantum mechanics.

BKa, BH*(10) and BH* for 70, 90 and 120 kV X-rays in clay based bricks

Clay-based bricks are used worldwide in the construction industry due to their mechanical properties and durability. To design or evaluate the shielding of a room having a X-ray radiation source, is necessary to determine the walls thickness (barriers) necessary to reduce the dose due to primary, scattered and leakage radiation. For these calculations is required to know the dose transmission of room walls materials. In this work, Monte Carlo methods were used to estimate the Ka, H*(10) and H* transmission values of the red brick for X-rays produced when 70, 90 and 120 keV electrons collide with a tungsten target and pass through a 0.28 cm-thick aluminum filter. Dose transmission values in function of shielding thickness were fitted to a semiempirical function. Curves of dose transmission, and the parameters obtained by the fitting process, can be used to evaluate or to design a shielding based on clay bricks.

Reducing disorder in Ge quantum wells by using thick SiGe barriers

We investigate the disorder properties of two-dimensional hole gases in Ge/SiGe heterostructures grown on Ge wafers, using thick SiGe barriers to mitigate the influence of the semiconductor–dielectric interface. Across several heterostructure field effect transistors, we measure an average maximum mobility of (4.4±0.2)×106 cm2/Vs at a saturation density of (1.72±0.03)×1011 cm−2, corresponding to a long mean free path of (30±1)μm. The highest measured mobility is 4.68×106 cm2/Vs. We identify uniform background impurities and interface roughness as the dominant scattering mechanisms limiting mobility in a representative device, and we evaluate a percolation-induced critical density of (4.5±0.1)×109 cm−2. This low-disorder heterostructure, according to simulations, may support the electrostatic confinement of holes in gate-defined quantum dots.

Sr Migration and Gd-Ce-Zr Interdiffusion in Solid Oxide Cells Under Different Fabrication and Testing Conditions

This work aims to understand how solid oxide cell (SOC) fabrication methods and SOC operating conditions affect Sr migration into the yttria stabilized zirconia (YSZ) electrolyte through the rare-earth doped ceria barrier layer. Ni-YSZ electrode-supported SOCs and coupons were fabricated using (La0.6Sr0.4)0.95Co0.2Fe0.8O3-δ-Gd0.1Ce0.9O2-δ (LSCF-GDC) oxygen electrode and GDC or samaria-doped ceria (SDC) barrier layer. Barrier layers were either screen printed and sintered to YSZ electrolyte layer at 1260 °C for 2h, or deposited using thin film deposition techniques such as PLD, electron beam and sputtering. LSCF-GDC electrode layer was sintered onto the GDC barrier at different temperatures from 950 to 1100°C for 2h to determine the effect of firing temperature and barrier layer thickness on Sr migration. Several SOCs were tested at 750°C in a wide range of operating conditions, both in SOFC and SOEC mode, for up to 12,000 hours. The GDC/YSZ interfaces in coupons and SOCs were examined using scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDS). Sr-Zr rich phase formation at GDC/YSZ interface was observed in coupons with LSCF-GDC sintered at 1100°C, but not in the other coupons sintered below 1100°C, unless the barrier layer was too thin and porous. Furthermore, no Sr migration into YSZ was observed in SOECs with varying testing time from 0 h to12,000 h. In addition, Gd and Ce diffusion into YSZ occurred when GDC was fired at 1260°C, but not in cells with GDC deposited using thin film techniques without additional high temperature firing. No significant difference was noted in the GDC-YSZ interdiffusion layer growth after SOC testing for 1,000-12,000 h. Aberration-corrected scanning transmission electron microscopy (STEM) was involved to identify the composition and crystal structure of the Sr-Zr rich phase, which was demonstrated to be SrZrO3 phase. After the long-term SOC tests, no SrZrO3 phase or Sr migration through GDC grain boundaries was observed in cells with 5-7 microns thick porous GDC barrier. This presentation will demonstrate how optimization of fabrication conditions, thermal treatment and fabrication techniques, could mitigate the formation of the insulating SrZrO3 phase.

Formation of Porous Anodic Aluminum Oxide with a Thick Barrier Layer and High Porosity By Anodizing Aluminum in Sodium Metaborate Solutions

Porous-type anodic aluminum oxide (AAO) can be fabricated by anodizing an aluminum substrate in suitable aqueous electrolyte solutions. The morphological properties of the AAO, including the interpore distance, pore size, and thickness, are controlled by various operating parameters, such as the applied voltage, temperature, and anodizing time. However, their structural controllability is limited because the fabrication process is based on the typical anodizing method in acidic solutions. The authors previously found that AAO with a novel nanostructure can be fabricated by anodizing using alkaline ammonium carbonate and sodium tetraborate. Therefore, further research on aluminum anodizing using various alkaline solutions opens the possibility of novel AAO fabrication. Herein, we report the fabrication of a new AAO film, which is different from the typical nanostructure formed in acidic solutions, by anodizing in alkaline sodium metaborate (NaBO2).Electropolished aluminum specimens were anodized at a constant voltage of 0.1-200 V in a 0.3 M sodium metaborate electrolyte solution (pH = 11.9) at 278 K. The surface and cross-section of the anodized specimens were examined by field-emission scanning electron microscopy (FE-SEM), atomic force microscopy (AFM), and Cs-corrected scanning transmission electron microscopy (STEM). The elemental depth profile of the specimens was analyzed by radiofrequency glow discharge optical emission spectroscopy (rf-GDOES).An AAO film consisting of an outer porous layer and an inner hemispherical cap barrier layer, similar to typical AAO films formed in acidic solutions, was formed at lower voltages below 50 V. In contrast, an AAO film with a flat barrier layer, deviating from the typical Keller-Hunter-Robinson model, was obtained at voltages above 100 V. The porosities of the porous layer obtained above 20 V were almost constant (0.16-0.19). However, there was a significant increase in the porosity at lower voltages (0.93 at 0.1 V). The AAO formed in sodium metaborate was composed of amorphous, anion-free aluminum oxide. Figure 1

Solid State YSZ Electrolyte Oxygen Partial Pressure Under Dynamic Operation

Idaho National Lab has developed a time dependent model of oxygen partial pressure in the electrolyte of a solid oxide cell. This model is of a standard cell used commonly throughout literature and is the reference cell of the H2New consortium. The cell is composed of a generic material set for solid oxide electrolysis. The electrolyte is a 7 micron thick layer of YSZ, 5 micron thick barrier layer of GDC, and an electrode layer of LSCF. During cell operation, there is a slow increase of oxygen partial pressure in the electrolyte. This can be observed to reach a critical threshold which induces micro-cracking. This is one of the underlying degradation mechanisms of solid oxide cells. At high current, the time to reach the threshold changes. By switching between a safe threshold and an unsafe threshold, a meta-stable relaxation and redistribution of oxygen partial pressure avoids reaching the critical threshold. The time scale of the threshold can be between seconds and hours depending on the current and voltage applied. Models have been developed to reduce the impact of oxygen partial pressure using different cycling timescales, as well as identifying safe short-term overproduction rates.

(Invited) A New Perspective on Pore Growth in Anodic Alumina Films

Pores in the porous-type anodic oxide film of aluminum have conventionally been thought to grow vertically in a straight tube-like manner. However, branching and nano-branching pores (referred to as feather-like) typically observed in films generated in chromic acid solutions are considered non-steady-state morphologies. However, are these formed only under specific conditions? These have also been observed in neutral borate electrolytes, highlighting the need to clarify the dominant factors governing pore morphology. In this study, we report the results of observations and discussions on the fine structure of pore morphology, including typical films grown in oxalic acid or sulfuric acid, using state-of-the-art analytical techniques to elucidate the dominant factors influencing pore formation [1].Observation of the initial pore formation in the three types of electrolytes, sulfuric acid, oxalic acid, and phosphoric acid, reveals that the initial pores are considerably smaller in diameter and more numerous than the main pores. This is presumed to be due to pore formation through dissolution under low electric field strength caused by the presence of a thick barrier layer. Observation of the growth process of pores generated in sulfuric acid and oxalic acid electrolytes using high-resolution TEM revealed that neither film grows in a tubular manner but rather undergoes repeated branching at a fine scale. The cause of nano-branching in the main pores is similarly attributed to thickening of the barrier layer for some reason in the electrolyte, resulting in a decrease in the electric field. Thus, it is considered that pores do not grow in a straight tube-like manner but rather universally involve branching, and the grown pores are subsequently smoothed out by chemical dissolution.These results thus indicate that the formation of radial nano-branched pores is not unique to chromic acid films. Instead, this is a universal phenomenon of anodic films that frequently occurs when the electric field strength decreases during anodizing for the same reason. When Thompson et al. first reported horizontal cross-section observations of various porous anodic films in 1978, they stated that “steady-state anodizing is not as regular as previously assumed”. This remains true, and elucidation of the actual structure of the porous film is important for more effective application of the film.[1] S. Ono, H. Asoh, Electrochem. Comm. (2021). Figure 1

Investigation of inter-dot tunnelling effect in hybrid coupled QDs heterostructures for short-wave infrared detection (SWIR) application

This paper explores the coupling between two different types of dots for enhancing the performance of p type/hole based (p-i-p) quantum dot infrared photodetectors (QDIPs). There are two possible con: Stranski-Krastanov (SK) QDs can be deposited on submonolayer (SML) QDs, or the SML QDs can be deposited first, followed by SK QDs. Here, both configurations are tried, and the fact that the tunnelling improves with a decrease in the barrier is exploited. The tunnelling of carriers from one QD to another QD is facilitated by the overlap of their wavefunctions, which depends on their spatial separations between the dots. A smaller barrier will lead to enhanced tunnelling probability. Utilising this idea, samples with 20 nm and 7.5 nm barriers between the QDs are grown with both types of configurations. An enhancement is anticipated in the absorption and carrier lifetime of the p-i-p QDIP structures, making them well-suited for detection in short-wavelength infra-red regions. The p-i-p configuration with the active layers of coupled QDs sandwiched between p-type dopped layers, can effectively absorb SWIR photons and generate long-lived carriers for improved photodetection performance. With the help of Photoluminescence (PL), Photoluminescence Excitation (PLE), and X-ray Diffraction (XRD) experiments, we expect large dispersion in SK on SML configuration, significantly improved carrier transfer via tunnelling and thermalisation and, changes in dot density for both of the configurations. Development of a more efficient SWIR device is expected by the insightful understanding of carrier transfer by tunnelling and thermalization with respect to the barrier thickness in the coupled QD based heterostructures.

20(R)-ginsenoside Rg3 alleviates diabetic retinal injury in T2DM mice by attenuating ROS-mediated ER stress through the activation of the Nrf2/HO-1 axis

BackgroundAlthough our previous work confirmed 20(R)-ginsenoside Rg3 (R-Rg3), which is an active ingredient in the Panax Ginseng C.A. Meyer, to have good anti-diabetic activity, its beneficial effect on diabetic retinal injury was found to be limited. PurposeThis study aims to investigate the protective effects of R-Rg3 on diabetes-induced retinal injury and the associated molecular mechanisms of action. MethodsDiabetic retinal injury was induced in mice using a combination of a high-fat diet (HFD) and intraperitoneal injection of streptozotocin (STZ). R-Rg3 (10 and 20 mg/kg) was subsequently administered for 6 weeks. The human retinal endothelial cells (HRECs) were subjected to high glucose (HG)-induced injury for the in vitro analysis and treated with R-Rg3 (4, 8, 16 μM), antioxidant N-Acetylcysteine (NAC, 1 mM) and Nrf2 inhibitor ML385 (5 μM). The mice retinas then underwent functional and histopathological analysis. Expression levels of proteins related to the Nrf2/HO-1 axis, tight junction proteins, endoplasmic reticulum (ER) stress and the apoptosis in retinal tissue and HRECs were determined by western blot. Expressions of ZO-1 and Nrf2 in the retina and HRECs were assessed by immunofluorescence. Additional evaluations included measuring body weights, fasting blood glucose (FBG), lipid levels and oxidative markers. ResultsThe results showed 6 weeks of R-Rg3 treatment significantly restored the functional changes and redox system imbalance that was induced by HFD/STZ in mice. R-Rg3 was also found to significantly reduce retinal barrier damage and thickness changes resulting from hyperglycaemia exposure. At the same time, R-Rg3 also protected HRECs from HG-induced damage. R-Rg3 could also activate Nrf2/HO-1 axis and inhibit endoplasmic reticulum stress as a means of alleviating retinal endothelial cells apoptosis. The molecular docking results also demonstrated that R-Rg3 had a good binding ability with Nrf2. ConclusionOur study suggested Nrf2/HO-1 axis might be crucial for the ability of R-Rg3 to prevent diabetic retinal injury.

Hypertension is associated with the reduction in epidermal small fibres independently of sural nerve inflammation in type 2 diabetic subjects.

Diabetic polyneuropathy (DPN) is a multifactorial disease associated not only with hyperglycaemia but also with circulatory disturbances such as hypertension. A close interaction between the immune system and hypertension is known. It remains unclear whether the inflammatory response is associated with hypertension in the pathology of human DPN. Autopsied patients were evaluated: 7 non-diabetic patients (nDM), 11 non-diabetic patients with hypertension (nDMHT), 6 patients with diabetes (DM) and 9 patients with hypertension and diabetes (DMHT). Intraepidermal nerve fibre density (IENFD) was examined by immunofluorescent staining. Dissected sural nerve (SNs) were morphometrically quantified. Dermal and endoneurial macrophage infiltration was evaluated by double immunostaining using anti-CD68 and anti-CD206 antibodies. IENFD was significantly decreased in DM compared to nDM (p < 0.05) and was further decreased in DMHT (p < 0.05). Myelinated nerve fibre density (MNFD) in the SN was significantly decreased in DM compared with nDM (p < 0.05) and further decreased in DMHT (p < 0.01 vs. DM). The infiltration of CD206-/CD68+ proinflammatory macrophages in the SN was significantly increased in DM compared to nDM (p < 0.05), whilst the number of CD206+/CD68+ anti-inflammatory macrophages was decreased in DM (p < 0.05). Hypertension had no impact on macrophage infiltration. The ratio of CD206- and CD206+ macrophage was negatively correlated with MNFD (r = 0.42, p < 0.05) but not IENFD (r = 0.30, p = 0.09). Dermal CD206+ macrophage infiltration was similar amongst all groups. Diabetes complicated by hypertension significantly increased the total diffusion barrier thickness (p < 0.01 vs. DM). Total diffusion barrier thickness was inversely correlated with both IENFD (r = -0.59, p < 0.01) and MNFD (r =-0.62, p < 0.01). Our results suggest that vascular factors and inflammation might be synergistically involved in pathological changes in human diabetic patients through different mechanisms.

Effects of probiotics and fibers on markers of nephropathy, inflammation, intestinal barrier dysfunction and endothelial dysfunction in individuals with type 1 diabetes and albuminuria. The ProFOS Study

AimsTo estimate whether a mix of pre- and probiotics would strengthen the gut barrier and protect the kidneys in individuals with type 1 diabetes and albuminuria. MethodsRandomized, placebo-controlled, crossover study. Forty-one participants received synbiotic (pre- and probiotics) mix or placebo for 12 weeks with 6 weeks washout. Primary endpoint was change from baseline to end-of-period in UACR. Secondary endpoints were changes in endothelial glycocalyx thickness, inflammatory and intestinal barrier dysfunction markers, glomerular filtration rate (GFR) and ambulatory systolic blood pressure. ResultsThirty-five participants completed the study. Mean age was 58 (SD 10) years, 73 % (n = 30) were male, median UACR was 134 (IQR 63–293) mg/g, estimated GFR was 75 (30) ml/min/1.73m2. There was no significant difference in UACR with a mean relative change (CI 95 %) from baseline to end-of-treatment of −3.0 (−18.4; 15.5) % in the synbiotic group and −12.0 (−29.6; 9.6) % in the placebo group with no significant difference between treatment periods (9.37 (−25.2; 44.0) percentage points; p = 0.60). No significant beneficial difference in the secondary end points was demonstrated. ConclusionTwelve weeks treatment with synbiotic mix had no effect on UACR or on any of the secondary endpoints in subjects with type 1 diabetes and albuminuria.

Single-molecule Magnets (SMM) spin channels connecting FeMn antiferromagnet and NiFe ferromagnetic electrodes of a tunnel junction

The integration of single-molecule magnets (SMMs) into magnetic tunnel junctions (MTJs) offers significant potential for advancing molecular spintronics, particularly for next-generation memory devices, quantum computing, and energy storage technologies such as solar cells. In this study, we present the first demonstration of SMM-induced spin-dependent properties in an antiferromagnet-based MTJ molecular spintronic device (MTJMSD). We engineered cross-junction-shaped devices comprising FeMn/AlOx/NiFe MTJs. The AlOx barrier thickness where the exposed junction edges meet was comparable to the SMM length, facilitating the incorporation of SMM molecules as spin channels for spin-dependent transport. The SMM channels enabled long-range magnetic moment ordering around molecular junctions, which were precisely engineered via fabrication processes. The SMM, composed of a [Mn6(μ3-O)2(H2N-sao)6(6-atha)2(EtOH)6] (H2N-saoH = salicylamidoxime, 6-atha = 6-acetylthiohexanoate) complex, featured thioester groups at the ends that upon hydrolysis they form bonds with the magnetic electrodes. SMM-treated junctions demonstrated a significant current enhancement, reaching up to 7 μA at an input voltage of 60 mV. Furthermore, SMM-doped junctions exhibited current stabilization in the μA range at lower temperatures, whereas the bare electrodes showed current suppression to the picoampere range. Magnetization measurements conducted at 55 K and 300 K on pillar-shaped devices revealed a reduction in magnetic moment at low temperatures. Additionally, Kelvin probe atomic force microscopy (KPAFM) measurements confirmed that SMM integration transformed the electronic properties over long ranges.These findings are attributed to the spin channels formed between magnetic metal electrodes, which enhance spin polarization at each magnetic electrode. Our research highlights the potential of using antiferromagnetic materials, characterized by minimal stray fields and zero net magnetization, to transform MTJMSD devices.

Single-flux-quantum circuits utilizing self-shunted NbN/TaN/NbN Josephson junctions grown on silicon substrates

Abstract We report on the electrical properties of NbN/TaN/NbN Josephson junctions grown on thermally oxidized silicon substrates, along with the design and fabrication of superconducting single-flux-quantum (SFQ) circuits based on these NbN superconductor/normal metal/superconductor (SNS) junctions. The critical current density (J c) of the junctions was found to be relatively sensitive to the barrier thickness, decreasing from 108.0 ± 8.1 kA cm−2 for a 15 nm barrier to 12.8 ± 1.9 kA cm−2 for a 30 nm barrier. For a J c of approximately 24.5 ± 2.1 kA cm−2 and a barrier thickness of 25 nm, the NbN SNS junctions are self-shunted and exhibit nonhysteretic current–voltage (I–V) characteristics. Especially for junctions with diameter (φ) ranging from 0.8 to 1.6 μm, their critical current (I c) falls within the range of 110–450 μA, making them suitable for SFQ circuits. By considering the impact of excess current and incorporating it as an additional term in the conventional resistively and capacitively shunted junction model, the I–V curves of NbN SNS junctions can be precisely described, successfully minimizing the deviation between simulations and test results. The DC-SFQ and SFQ-DC interface circuits can both operate normally, and the bias margins of cell circuits such as Josephson transmission line, confluence buffer, D flip-flop, and splitter are greater than 40%. Compared to Nb superconductor/insulator/superconductor junctions, their self-shunting characteristics and relatively thick 25 nm barriers can also enhance the integration of circuits and increase the yield to complex circuits.

LG = 50 nm T-gated and Fe-doped double quantum well GaN‒HEMT on SiC wafer with graded AlGaN barrier for future power electronics applications

High-performance LG = 50 nm graded double-channel (GDC)-HEMT featuring AlN top barrier, recessed T-gate and graded-AlGaN bottom barrier is designed and investigated. Two quantum wells are formed in the AlN-GaN-graded AlGaN-GaN multilayer structure developed on a SiC substrate and the clear double hump feature of the transconductance (GM), cut-off frequency (fT), and capacitance plots clearly illustrates the double-channel (DC) behavior. The investigations carried out to explore the impact of barrier thickness (both AlN & graded-AlGaN) revealed superior performance with the GM showing two peaks at 181.5 & 488.1 mS/mm, the peak-drive-current (ID_peak) with VGS biased at 3 V is 1.81 A/mm, maximum saturation drain current of 3.08 A/mm (VGS = 3V), and the fT derived from the left- and right-hump are 263.7 GHz & 354.2 GHz, respectively, when both barriers are 6 nm thin, attributable to enhanced 2DEG density due to the coordination of channels because of proximity and lower leakage. It has been noticed that when the bottom barrier is thick, the DC behaviour is less obvious due to insufficient gate access to the lower channel. We investigated the impact of varying the Al % in AlGaN top barrier on the DC/RF performance of GDC-HEMTs, demonstrating enhanced performance with increased Al content, particularly for Al0.35Ga0.65N. By using various metals, this study also investigates how gate engineering affects the electrical characteristics of the GDC-HEMT. The lower ϕm (work function) of the Al-gate led to better DC/RF performance. When the Schottky barrier rises as a result of the conduction band edge being elevated, the performance reduces, and the threshold voltage (Vth) increases. Since it is essential to comprehend the role that source resistance (Rs) & drain resistance (Rd) play in RF design, we have also conducted simulations by varying the source-gate gap (LGS) & drain-gate gap (LGD). Due to low Rs & Rd, it was determined that the GDC-HEMT performed better at the smallest LGS & LGD. The extraordinary performance strongly highlights the immense potential and applicability of the GDC-HEMTs for future broadband power amplifiers.