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Avalanche ruggedness is one of the key factors for safe and reliable power converters deployed in various automotive subsystems. In this article, the avalanche capability of power MOSFETs is tested under different repetitive avalanche conditions to differentiate the die degradation and package degradation. While examining the degradation mechanisms, the corresponding electrical parameter shifts are analyzed to better understand the structural changes and root causes and identify potential precursors for condition monitoring. For this purpose, a high-resolution and cost-effective nanosecond current pulse generator (CPG) is designed. Due to the high-resolution pulsewidth modulation function of a digital signal processor (DSP), short current pulses can be generated in the order of 100 ps where the magnitude and duration of the current pulsewidth can be adjusted precisely. During the experiments, power MOSFETs are stressed under two different pulsewidths. It is observed that the ON-state resistance gradually increases in both cases, yet the roots of the degradations are different. The die degradation and package degradation are responsible for the changes in short pulse and long pulse, respectively. In the short pulse case, some devices show saturation in drain leakage current and ON-state resistance, while some others show a significant threshold voltage drop, which leads to a noticeable shift of transfer and output characteristics. The electrical parameter shifts indicate a possible gate degradation after the device aging. At the end of the tests, failure analyses are conducted on both devices under test (DUTs) under different stress conditions, revealing different failure mechanisms.

Herein, the influence of platinum (Pt) catalyst on the interface between SiO 2 nanofiller and addition cure silicone rubber (ALSR) matrix is investigated with different concentrations of Pt catalyst. It is found through various tests that Si–O–Si covalent bonds and hydrogen bonds form at the interface with a moderate amount of Pt catalyst. Based on these observations, a model for the interfacial structure of ALSR/SiO 2 nanocomposites is proposed. In particular, it is demonstrated, without changing the mass fraction and surface modifier of the filler, a more compact interface is obtained by increasing the amount of added Pt catalyst by a few ppm, resulting in a 25% increase of breakdown strength, 10% increase in thermal conductivity, 50% increase in tensile strength, and a 31% increase in the elongation at break.

This article proposes a new complete condition monitoring method which can independently monitor both the threshold voltage drift and the packaging degradation accurately by monitoring only the reverse body diode voltage drop at different gate bias levels. The SiC MOSFETs are aged through an accelerated aging method and the corresponding changes in electrical parameters are periodically measured to assess their correlation with the state of the device's health. It has been revealed that the on -state resistance reveals the combination of gate oxide and package-related degradation while the threshold voltage mainly depicts gate oxide-related issues. Unlike these two parameters, the body diode voltage drop is found to independently indicate the state of device health both for package and gate oxide. This is caused by a unique secondary conduction mode of SiC MOSFETs in third-quadrant operation which is clearly disclosed with transition boundaries by a proposed body diode transfer characterization curve. In order to have a detailed condition information of the device with a simple circuit, monitoring the reverse body diode voltage drop at 0 and $-$ 5 V gate bias is proposed. The proposed condition monitoring method is implemented on a gate drive circuit and experimental results are given for two artificially degraded devices. The experimental results confirm that the proposed method can independently monitor both the gate oxide and packaging degradations accurately by monitoring a single precursor parameter. The proposed method can be integrated into the gate driver or converter itself to monitor SiC devices.

An unusual tensile deformation behaviour in the form of a propagating band along the sample gauge was observed in two neutron-irradiated 316 stainless steel samples during room-temperature tests, leading to a combination of high strength and high ductility. These bands were not observed in an unirradiated counterpart. With the help of in situ high-energy synchrotron x-ray diffraction, the phase-specific crystal information was tracked at different deformation levels in each sample. Post-irradiation and post-deformation samples were examined using electron microscopy to characterize various microstructural features. All samples displayed a deformation-induced martensitic phase transformation, which was identified as a second strain-hardening mechanism accompanying the dislocation hardening. The deformation-induced martensitic transformation was rationalized by the effect of applied stress on the effective martensite start temperature. The results showed that the irradiation did not alter the dislocation hardening and the martensitic transformation mechanisms, but the increased yield strength in irradiated materials facilitated the localized phase transformation at the onset of plastic deformation, in contrast to the unirradiated material which required pre-straining. The hardening effect of the martensitic transformation reduced the tendency towards necking and mitigated the loss of ductility in the irradiated material by carrying the deformation in the form of a propagating band. Despite the beneficial effect from the martensitic transformation, this study indicates that this mechanism cannot not be activated at typical operating temperatures of nuclear reactors.

Orientation-controlled growth of two-dimensional (2D) transition metal dichalcogenides (TMDCs) may enable many new electronic and optical applications. However, previous studies reporting aligned growth of WSe2 usually yielded very small domain sizes. Herein, we introduced gold vapor into the chemical vapor deposition (CVD) process as a catalyst to assist the growth of WSe2 and successfully achieved highly aligned monolayer WSe2 triangular flakes grown on c-plane sapphire with large domain sizes (130 µm) and fast growth rate (4.3 µm·s−1). When the aligned WSe2 domains merged together, a continuous monolayer WSe2 was formed with good uniformity. After transferring to Si/SiO2 substrates, field effect transistors were fabricated on the continuous monolayer WSe2, and an average mobility of 12 cm2·V−1·s−1 was achieved, demonstrating the good quality of the material. This report paves the way to study the effect of catalytic metal vapor in the CVD process of TMDCs and contributes a novel approach to realize the growth of aligned TMDC flakes.

LiAl-layered double hydroxide (LiAl-LDH) has been reported as a potential hardening accelerator of calcium sulfoaluminate (CSA) cement. Until now, little has been known about the effect of synthesis conditions and post-synthetic treatments of LiAl-LDH on the performance of CSA cement. The present work shows two methods for the synthesis of LiAl-LDH – a solvothermal method and a separate nucleation and aging steps method (SNAS) – and two methods for the post-synthetic treatments of LiAl-LDH, with and without drying process. The effect of the resultant LiAl-LDH on the performance of CSA cement was studied in relation to the strength, hydration process and products. Results indicate that specimens containing LiAl-LDH showed a greatly enhanced performance with regard to setting time and compressive strength at early and later ages. Compared to LiAl-LDH prepared with the solvothermal method, LiAl-LDH from SNAS synthesis is more effective to increase the compressive strength and shorten setting time. Moreover, the post-synthetic treatments affect the performance of LiAl-LDH. LiAl-LDH without a drying process has better dispersion stability, higher compressive strength and a shorter setting time. Owing to the crystal seed effect, LiAl-LDH enhanced the hydration rate and improved the amount of hydration products, resulting in a higher compressive strength.

Due to a lack of facile methods for evaluating the reheat cracking susceptibility of the coarse grain heat-affected zone (CGHAZ), a simple notched C-ring reheat cracking test method and evaluation criteria were proposed. Accordingly, a suitable C-ring sampling method and heat treatment procedure were established. The C-ring specimens were taken from thick plate joints welded under five different heat inputs and testing was carried out. Reheat cracks were observed and identified under different stress loadings. Subsequently, related with the evaluation criteria of the Gleeble® test, the evaluation criteria based on notched C-ring tests were developed. This method can reflect both the microstructure and restraint stress of actual welded joints, and the stress relaxation during heat treatment. Moreover, the experimental operation is simple and repeat-able. It is expected that an evaluation standard for reheat cracking sensitivity in CGHAZ will be established.

Nonwoven-based microfluidics is an emerging field in low-cost microfluidics as another alternative to paper-based microfluidics. Comparing with the conventional paper material that has been widely used in low-cost microfluidics, the cost of nonwoven fabric material is the same range, but with the advantages of higher mechanical strength and a wider choice of chemical/physical properties. In this study, we proposed a novel method for defining a programmable and single-use wax valve on nonwoven-based microfluidic devices. The nonwoven-based microfluidic devices were fabricated using wax-printing and thermal reflow approach to define the basic microchannels for fluid penetration. Then, another layer of wax material contain valve structures were deposited on the surface of the microchannels, each wax valve structure has a corresponding heater resistor that can trigger the wax penetration to block (close) the microchannel. With the controlled thermal actuator operation, the fluid penetration inside the porous media of nonwoven fabric microchannel can be programmed with the control of wax valves. A chemical method for reopening the microchannels was also introduced in this study. The proposed programmable wax valve on nonwoven-based microfluidics is easily accessible with low-cost for point-of-care applications in biological and medical fields.

In this article, an in situ SiC mosfet degradation monitoring method using readily available converter sensors is presented. Device's drain-source resistance in saturation and ohmic regions are employed as aging precursors to, respectively, indicate die and package-related degradations. The presented findings in this article are essential for low-cost and practical early warning systems in power electronics applications. To verify the effectiveness of the proposed method, a number of power-cycling tests are conducted to analyze aging process and fatigue mechanism. Device static parameters are measured throughout accelerated aging tests and the physical causes behind them are discussed in detail. It is shown that the drain-source resistance within saturation region at low gate bias can be used to indicate die-related degradation. Similarly, at full positive gate bias, device on -state drain-source resistance can be used to detect package-related degradation. In order to find out optimal variables such as applied gate bias, pulse duration, etc., a comprehensive single pulse test is conducted and the results are reported. Finally, the proposed degradation monitoring method is experimentally validated in the context of a three-phase inverter considering different sensor configurations and load types.

This study proposed a novel method for the fabrication of non-woven based microfluidic devices with a wax hydrophobic barrier. Current microfluidic devices were fabricated with glass or polymer material, and paper is also widely used for the fabrication of low-cost microfluidic devices. The application of non-woven fabric based microfluidic devices provides a new option of bulk materials for microfluidics. Compared with the glass or polymer material used in microfluidics, non-woven fabric is low-cost, easy to process and disposable. Fluid can penetrate through the non-woven fabric material with capillary force without the requirement of external pumps. As fiber-based material, comparing with paper, non-woven fabric material is more durable with higher mechanical strength, and various types of non-woven fabric material also provide a board choice of surface chemical/physical properties for microfluidic applications. In this study, the hydrophilic non-woven fabric is chosen as the bulk material for microfluidic devices, a wax pattern transfer protocol is also proposed in this study for the deposition of hydrophobic barriers. For a demonstration of the proposed fabrication technique, a microfluidic mixer was also fabricated in this study.

A unique class of crystalline Ge1–ySny alloys with ultrahigh Sn concentrations reaching 33% as well as Si-doped analogues have been synthesized directly on large-area Si wafers by chemical vapor de...

Metal-free nanocarbons among other unique characteristics, offer the possibility of tuning the local electronic structure of the active sites allowing to identify precisely how to enhance the catalytic activity. Hence N-doped sp3@sp2 hybrid nanocarbons are studied here for the catalytic oxidative synthesis of a broad series of drug-related compounds (23 examples), like 2-substituted benzoxazoles, benzothiazoles and benzimidazoles under mild conditions and they show good catalytic activity and reusability which is comparable to homogeneous /heterogeneous metal-based catalysts. We demonstrate for the first time that the electron-donating capability and intrinsic catalytic activity of pyridinic N and neighboring C atoms can be enhanced by increasing up to c.a. 3 layers of sp2 C over the N-doped sp3@sp2 nanocarbon, which is evidenced by the KPFM measurements and DFT calculations. The mechanistic study suggests that the O2 could be activated to O2•−, which could subsequently react with abstracted H along with the formation of H2O2. This study provides a methodology of applying carbocatalysts for the synthesis of complex drug targets and shed light on the origin of the intrinsic catalytic activity enhancement of the pyridinic N by regulating the sp2 C layers of the catalysts.

In the context of a memory-dependent generalized thermoelasticity, the thermal-induced transient response in an infinite elastic body containing a spherical shell is investigated. A thermal shock i...

The fabrication of a bionic super-hydrophobic metallic surface without any low-surface-energy modification is investigated, in which picosecond laser ablation, electropolishing and electrodeposition are used sequentially. The micro-cone structure is formed via laser ablation, and then the nano-pyramid structure is electrodeposited on the micro-cone structure, resulting in a hierarchical structure that is important for achieving super-hydrophobicity on an intrinsically hydrophilic material surface. In this study, the surface morphology and material removal mechanism are discussed with respect to the laser-ablated surface and the subsequent electropolished/electrodeposited surfaces. The condensation experiments results show that both types of surfaces are associated with relatively high contact angles (CAs) at normal temperatures, and the CAs are 147° and 160°, respectively. However, the CA on the laser-ablated surfaces at low temperatures decreases to as less as 107°, which may be owing to the easy transition from Cassie state to a metastable state or even the Wenzel state, leading to a degraded hydrophobic surface. By contrast, the CA on the sequentially processed surfaces still maintains at 150°, which should be attributed to the densely distributed nano-scale structures. The sequentially processed surfaces also show excellent long-term durability. Furthermore, this technique has been employed for fabricating super-hydrophobic surfaces with CAs > 151° and the sliding angles (SAs)

In the present work, we show the preparation of (In,Ga,Mn)As films with different Ga concentration by Mn ion implantation and pulsed laser melting. All films are confirmed to be well recrystallized by Rutherford backscattering spectrometry/channeling and to be ferromagnetic by magnetometry measurements, respectively. Their Curie temperatures depend on the Ga concentration. Our results show the perspective of ion implantation in the preparation of different III-Mn-V quaternary alloys as new members of diluted ferromagnetic semiconductors.

Severe lithium (Li) dendrite growth during the plating/stripping process, which results in low Coulombic efficiency and safety issues, strongly hinders the practical applications of Li metal anodes. Herein, we propose a novel design of three-dimensional (3D) interconnected graphene (IG) framework synthesized with the help of nickel (Ni) microspheres for stable Li metal anodes. The as-prepared IG framework consists of multiple stacks of two-dimensional (2D) graphene layers and plenty of hollow graphene microspheres in between, and thus provides protective layers on the top to suppress lithium dendrites, sufficient surface area to reduce the effective current density, as well as ion channels for fast Li transport, which is confirmed by post-cycle morphology characterization. When Li foil was used as the counter electrode for Li deposition, the assembled coin cell maintained an average Coulombic efficiency of more than 97.5% for 100 cycles at current density of 1 mA cm−2 with a Li loading of 1 mAh cm−2. Furthermore, we achieved stable cycling for more than 300 h at a current density of 1 mA cm−2 with a Li loading of 2 mAh cm−2 when assembled as symmetric cells. This strategy of vertically stacking 2D materials provides a novel approach towards dendrite-free Li metal anodes for the next-generation energy storage systems.

The temperature of exhaust gas can exceed 800K, which is much higher than surroundings. It’s easy to demonstrate IR and get bombed. Therefore, it’s necessary to lower the temperature of exhaust gas. In this paper, a kind of infrared suppressor which uses engine exhaust to eject cold air and water spray is designed. Water spray is produced by ultrasonic atomization. The mixing process of the ejector is revealed by CFD. CFD results are validated with the experimental values. After validation is satisfied, this paper analyzes the temperature field inside the ejector and compares the performances of ejectors with varying geometries. According to CFD results, a device is made. Test results show that a good performance is achieved: radiation energy is only 36% of the original.

The effect of thermal stress on the growth of central cracks in inhomogeneous cylindrical superconductors is investigated assuming that the material properties vary linearly with the radial coordinate and temperature differences. General expressions for the temperature distribution and thermal stress in terms of a Bessel equation and the plane strain approach are derived. The results indicate that the distributions and variations in the radial and hoop thermal stresses in an inhomogeneous superconductor differ from those in homogeneous superconductors. However, thermal stress affects the crack growth similarly in both superconductor types. The thermal-stress analysis should be useful for the crack growth prediction regarding inhomogeneous superconductors.

Optically pumped Ge1-ySny lasers operating at low temperature have been recently demonstrated. This article reviews the challenges to efficient lasing that arise from the intrinsic properties of alloys in the Si-Ge-Sn system. The first such challenge is the possibility that even in nominally direct gap Ge1-ySny materials, a significant fraction of pumped carriers reside in the valleys associated with the indirect gap, and therefore are not available for lasing. We find theoretically that this is indeed the case at room temperature, possibly explaining the strong temperature dependence of lasing. A second challenge is finding appropriate barrier materials to reduce the lasing threshold power via spatial confinement. We show that strained layer Ge1-ySny/Ge1-y'Sny' multilayers are unlikely to produce the required direct gap Type-I alignment, and that even the introduction of ternary Ge1-x-ySixSny layers may not lead to suitable lasing structures due to giant bowing parameters in the compositional dependences of their interband transition energies.

The glass forming ability, microstructure, magnetism and magnetocaloric effect (MCE) in two quinary rare-earth rich amorphous ribbons of Tm20Ho20Gd20Co20Ni20 and Tm20Ho20Gd20Co20Cu20 are reported. Both amorphous ribbons exhibit excellent glass forming ability and a table-like MCE. In addition to large magnetic entropy change of ∼14.0 J/kg-K, an extremely high refrigerant capacity of ∼790 J/kg are achieved which can almost cover the temperature range from liquid hydrogen to liquid nitrogen for the magnetic field change of 0–7 T for both ribbons. Therefore, the quinary rare-earth rich amorphous ribbons can be proposed as a new class of promising magnetic refrigeration materials.

We report a versatile chemical vapor deposition (CVD) method to dope Ge films with Ga atoms in situ over a wide concentration range spanning from 3 × 1018 to 2.7 × 1020 cm–3. The method introduces a stable and volatile Ga hydride [D2GaN(CH3)2]2 that reacts readily with Ge4H10 to deliver Ga dopants controllably and systematically at complementary metal-oxide-semiconductor compatible ultralow temperatures of ∼360 °C. Thick and monocrystalline layers (1.3 μm) are produced on Si substrates at growth rates approaching 50 nm/min. The doped crystals are fully epitaxial and devoid of misfit defects and Ga precipitates as evidenced by Rutherford backscattering spectrometry, X-ray diffraction, and cross-sectional transmission electron microscopy. The Ga contents measured by secondary ion mass spectrometry and the active carrier concentrations determined by spectroscopic ellipsometry (as well as Hall effect measurements in several cases) are in close agreement, indicating near full activation. Photoluminescence spec...

Irradiation induced microstructural changes in the NF709 austenitic stainless steel were investigated under 1 MeV Kr ion irradiations to a dose of 3 dpa at room temperature (RT), 300, 400, 500 and 600 °C, and a dose of 20 dpa at RT. The irradiation-induced defects and the stability of precipitates were characterized with transmission electron microscopy (TEM). Frank dislocation loops were observed in all the irradiated samples, and the loop sizes were much larger at 600 °C than those at lower temperatures. “Raft” defect structures, formed through self-alignment of small dislocation loops, were also observed in all irradiated samples. M23C6 precipitates were amorphorized under irradiations at RT and 300 °C, but remained to be crystalline at 400 °C and above. MX precipitates were stable under irradiations at RT up to 20 dpa, and at temperatures below 600 °C to 3 dpa. At 600 °C, some MX precipitates were observed to dissolve during in-situ irradiation, suggesting possible precipitate instability at this irradiation temperature.

Quasi-two-dimensional (2D) β-Ga2O3 is a rediscovered metal-oxide semiconductor with an ultra-wide bandgap of 4.6–4.9 eV. It has been reported to be a promising material for next-generation power and radio frequency electronics. Field effect transistors (FETs) that can switch at high voltage are key components in power and radio frequency devices, and reliable Ohmic contacts are essential for high FET performance. However, obtaining low contact resistance on β-Ga2O3 FETs is difficult since reactions between β-Ga2O3 and metal contacts are not fully understood. Herein, we experimentally demonstrate the importance of reactions at the metal/β-Ga2O3 interface and the corresponding effects of these reactions on FET performance. When Ti is employed as the metal contact, annealing of β-Ga2O3 FETs in argon can effectively transform Schottky contacts into Ohmic contacts and permit a large drain current density of ~ 3.1 mA/μm. The contact resistance (Rcontact) between the Ti electrodes and β-Ga2O3 decreased from ~ 430 to ~ 0.387 Ω·mm after annealing. X-ray photoelectron spectroscopy (XPS) confirmed the formation of oxygen vacancies at the Ti/β-Ga2O3 interface after annealing, which is believed to cause the improved FET performance. The results of this study pave the way for greater application of β-Ga2O3 in electronics.

The tensile deformation behavior of a high-temperature, ultrafine-precipitate strengthened (HT-UPS) stainless steel was characterized in-situ with high-energy X-ray diffraction at 20 and 400 °C. The HT-UPS samples were neutron irradiated to 3 dpa at 400 °C. Significant irradiation hardening and ductility loss were observed at both temperatures. Lattice strain evolutions of the irradiated samples showed a strong linear response up to near the onset of the macroscopic yield, in contrast to the unirradiated HT-UPS which showed a pronounced non-linear behavior well below the macroscopic yield. While the room-temperature diffraction elastic moduli in the longitudinal direction increased after irradiation, the 400 °C moduli were similar before and after irradiation. The evolution of the {200} lattice strain parallel to the loading axis ( e { 200 } L ) showed unique characteristics: in the plastic regime, the evolution of e { 200 } L after yield is temperature-dependent in the unirradiated specimens but temperature-independent in the irradiated specimens; and the value of e { 200 } L at the yield is an irradiation-sensitive, temperature-independent parameter. The evolution of e { 200 } L corresponds well with the dislocation density evolution, and is an effective probe of the deformation-induced long-range internal stresses in the HT-UPS steel.

There is a rising prospective in harvesting energy from the environment, as in situ energy is required for the distributed sensors in the interconnected information society, among which the water flow energy is the most potential candidate as a clean and abundant mechanical source. However, for microscale and unordered movement of water, achieving a sustainable direct-current generating device with high output to drive the load element is still challenging, which requires for further exploration. Herein, we propose a dynamic PN water junction generator with moving water sandwiched between two semiconductors, which outputs a sustainable direct-current voltage of 0.3 V and a current of 0.64 μ A. The mechanism can be attributed to the dynamic polarization process of water as moving dielectric medium in the dynamic PN water junction, under the Fermi level difference of two semiconductors. We further demonstrate an encapsulated portable power-generating device with simple structure and continuous direct-current voltage output of 0.11 V, which exhibits its promising potential application in the field of wearable devices and the IoTs.

Lead–sCO2 intermediate heat exchanger (IHX) was designed for lead-cooled fast reactor (LFR). The reactor coolant is lead and flowing through a circular straight channel, meanwhile, sCO2 is heated through 5 channels with different geometries were investigated respectively, including straight channel, zigzag 52° channel, S-shaped fins, offset rectangular fins, and airfoil fins. Considering the thermal-hydraulics characteristics, mechanical structure, corrosion, and flow blockage in the IHX designs, the performance, total cost, and power density of several heat exchanger designs were evaluated and compared. Finally, a printed circuit heat exchanger (PCHE) design using the circular straight (lead) - offset rectangular fins (sCO2) channels was proposed. The straight and S-shaped channels for sCO2 flow were recommended as alternative designs under certain circumstances. However, S-shaped fins and zigzag channels will dramatically increase the cost while straight and airfoil channels will greatly increase the volume.

We demonstrate how the presence of gain-loss contrast between two coupled identical resonators can be used as a new degree of freedom to enhance the modulation frequency response of laser diodes. An electrically pumped microring laser system with a bending radius of 50 μm is fabricated on an InAlGaAs/InP MQW p-i-n structure. The room temperature continuous wave (CW) laser threshold current of the device is 27 mA. By adjusting the ratio between the injection current levels in the two coupled microrings, our experimental results clearly show a bandwidth improvement by up to 1.63 times the fundamental resonant frequency of the individual device. This matches well with our rate equation simulation model.

In our previous study, ultrafine ettringite was prepared in the presence of citric acid by using a nucleation and aging separation method. Due to the seed effect, ultrafine ettringite enhanced the hydration rate and compressive strength of sulfoaluminat cement-based materials at all ages. However, when the particle size of sulfoaluminat cement-based materials became smaller, ultrafine ettringite retarded the hydration rate of ultrafine sulfoaluminat cement-based materials (USCM). In this paper, ettringite was prepared under different citric acid concentrations and characterized by XRD, FT-IR, TG-DSC, PSD and TOC measurements. The effect of ettringite on the properties of USCM was experimentally studied. Results showed that citric acid can absorb on the surface of ettringite. The average particle size of the citric acid-ettringite composites（CECs）were in the range of 100–300 nm, and increasing the concentration of citric acid in composites lead a smaller size of CECs. When present in the alkaline solution of pH 13, the higher citric acid concentration used in the preparation of CECs, the more amount of tartaric acid released from CECs. CECs retarded the cement hydration, modified the pore structure and enhanced the compressive strength of USCM pastes at all ages due to the synergistic effect of nano crystal nucleus and citric acid released from CECs.

The electrochemical behavior of plasma electrolytic oxidation (PEO) film on Zirlo alloy in 25–300 °C lithium borate buffer solution was evaluated by in-situ electrochemical impedance spectroscopy (EIS) and potentiodynamic polarization. As the solution temperature rose to a critical value (150 °C), a new relaxation process related to the distinguishable maximum in phase angle vs. frequency curves was observed at medium frequency and became more pronounced with increasing temperature. This relaxation process almost disappeared after a short exposure time under 300 °C. The transition of the relaxation process was closely related to the impedance of PEO film. The new relaxation process was ascribed to the diffusion of corrosion product through the PEO film. In addition, the degradation of the protective properties of PEO film was observed with increasing temperature, which resulted from the enhanced ionic conductivity of doped zirconia under high temperature. Finally, the PEO film hardly changed in morphology and microstructure after in-situ EIS tests at 25–300 °C.

Ge1−xSnx materials with constant and step-graded compositions have been successfully grown on Ge/Si(0 0 1) substrates by using low temperature molecular beam epitaxy (LT-MBE). It has been observed that both completely strained and partially relaxed GeSn materials with the same composition could be formed within the same sample, without adjusting any growth parameters. The residual in-plane strain in GeSn changes in a specific pattern from the GeSn/Ge interface towards the surface. The lower section of the GeSn material remains fully strained and free of dislocations, while most of the threading dislocations are located in the upper section of the layer, causing considerable strain relaxation within this section while maintaining the composition unchanged. This behavior could be explained by kinetic roughening and dislocation generation mechanisms at low temperatures and is remarkably different from GeSn materials grown by chemical vapor deposition (CVD), which exhibit a gradual strain relaxation process as growth continues. This work contributes to the fundamental understanding of the strain relaxation mechanisms of GeSn materials grown by MBE, which is instructive for improving the material quality in the future.

This paper describes the fabrication of Ge1−ySny layers with 2%–13% Sn, utilizing a unique method that combines high-order Ge4H10 and Ge5H12 hydrides and gas source molecular epitaxy techniques. The latter operate at very low working pressures of 10−6–10−7 Torr leading to molecular flow regime conditions, promoting layer-by-layer epitaxy of crystalline materials at ultralow-temperatures (250–160 °C) that cannot be achieved by conventional thermal CVD. In both cases, a “direct injection” approach is employed, using the pure vapor of Ge4H10 and Ge5H12 as the source of the Ge flux, which is then reacted on the substrate surface with SnD4 in the absence of gaseous carriers. Ge4H10 reactions were conducted at 215–190 °C, producing 6%–12% Sn samples. These were grown on both conductive, resistive, single-side, and double-side polished Si(100) with n-type Ge1−xSix buffer layers (x = 2%–3%) to explore conditions and substrate formats that facilitate back-side illumination, enabling transparency and enhanced responsivity at 1550 nm in prototype p-i-n devices. Exploratory reactions of Ge5H12 with SnD4 produced Ge1−ySny with 2%–13% Sn at 250–160 °C for the first time. All samples were characterized by XRD, RBS, IR-ellipsometry, AFM, and TEM to investigate the structure, composition, strain state, and morphology. The samples grow partially relaxed (T > 180 °C) and their compressive strains gradually diminish in situ with increasing film thickness (up to 700 nm) without epitaxial breakdown and Sn segregation. Residual strains are further reduced by RTA processing. The experiments described here demonstrate the practicality of our chemistry-based method as an alternative to thermal CVD for the fabrication of high crystal quality samples on larger area wafers for potential applications in IR devices.

Hyperdoping Si with chalcogens is a topic of great interest due to the strong sub-bandgap absorption exhibited by the resulting material, which can be exploited to develop broadband room-temperature infrared photodetectors using fully Si-compatible technology. Here, we report on the critical behavior of the impurity-driven insulator-to-metal transition in Te-hyperdoped Si layers fabricated via ion implantation followed by nanosecond pulsed-laser melting. Electrical transport measurements reveal an insulator-to-metal transition, which is also confirmed and understood by density functional theory calculations. We demonstrate that the metallic phase is governed by a power law dependence of the conductivity at temperatures below 25 K, whereas the conductivity in the insulating phase is well described by a variable-range hopping mechanism with a Coulomb gap at temperatures in the range of 2-50 K. These results show that the electron wave-function in the vicinity of the transition is strongly affected by the disorder and the electron-electron interaction., Comment: 19 pages, 6 figures

In this work, a systematic investigation on magnetic critical behavior is performed for the first time on an antiperovskite-type Mn3GaN, which is prepared by intentionally modifying stoichiometry. According to the XRD results, the antiperovskite structure is well preserved, even though all lattice parameters shrink upon reducing Ga and N content down to 60%. The sample exhibits a ferromagneticlike feature with a Curie temperature (T-C) of 394K rather than frustrated behavior in stoichiometric Mn3GaN. Most importantly, the modified Arrott plots, Kouvel-Fisher plots, as well as critical isotherm method self-consistently co-confirm the critical exponents of beta=0.33, gamma=1.23, and delta=4.7, unambiguously indicating that the critical behavior follows the 3D-Ising model around T-C. Published under license by AIP Publishing.

Undoped ZnO films grown on sapphire by pulsed laser deposition are magnetic at room temperature. A comprehensive study involving x-ray diffraction, positron annihilation spectroscopy, and superconducting quantum Interference device-vibrating sample magnetometer is performed to study the origin of the observed magnetization. Correlations between the saturation magnetization, VZn−2VO concentration and surface to volume ratio of the grain found experimentally show that the magnetization is associated with the vacancy cluster and probably VZn−2VO residing on the grain surface.

Two-dimensional (2D) semiconductors have been extensively explored as a new class of materials with great potential. In particular, black phosphorus (BP) has been considered to be a strong candidate for applications such as high-performance infrared photodetectors. However, the scalability of BP thin film is still a challenge, and its poor stability in the air has hampered the progress of the commercialization of BP devices. Herein, we report the use of hydrothermal-synthesized and air-stable 2D tellurene nanoflakes for broadband and ultrasensitive photodetection. The tellurene nanoflakes show high hole mobilities up to 458 cm2/V·s at ambient conditions, and the tellurene photodetector presents peak extrinsic responsivity of 383 A/W, 19.2 mA/W, and 18.9 mA/W at 520 nm, 1.55 μm, and 3.39 μm light wavelength, respectively. Because of the photogating effect, high gains up to 1.9 × 103 and 3.15 × 104 are obtained at 520 nm and 3.39 μm wavelength, respectively. At the communication wavelength of 1.55 μm, the tellurene photodetector exhibits an exceptionally high anisotropic behavior, and a large bandwidth of 37 MHz is obtained. The photodetection performance at different wavelength is further supported by the corresponding quantum molecular dynamics (QMD) simulations. Our approach has demonstrated the air-stable tellurene photodetectors that fully cover the short-wave infrared band with ultrafast photoresponse.

Thin films of Si1−xMnx were deposited on Al2O3 substrate using pulsed laser deposition(PLD)technique employing time-of-flight separation of the ejected particles with different laser fluence (E = 3.8–7.6 J/cm2). Magnetic properties of these films reveal that the variation in the laser fluence has engineered several magnetic phases in Si1−xMnx films: high temperature (HT) ferromagnetic (FM) phase Si1−xMnx(x = 0.51–0.52) with uniformly distributed Si vacancies, and the low-temperature (LT) FM phases MnSi and Mn4Si7 with Curie temperature ≤40 K. At small fluence, the mesoscopic size MnSi and Mn4Si7 crystallites are formed in the upper layer of Si1−xMnx films with Si excess (x ≈ 0.4–0.5), yielding to inhomogeneous magnetic phase distribution along the film growth direction, while the high and optimal fluence has resulted in uniform distribution of the HT FM phase during the film growth. The XPS, magnetotransport and ferromagnetic resonance (FMR) measurements confirm the presence of several FM phases in the samples and the amplifying role of LT FM for films grown at E ≤ 4.4 J/cm2.

In this paper, we perform a comparison of magnetic and electrical properties between Mn-doped and (Mn, Zn) co-doped GaP dilute ferromagnetic semiconductors. Due to the shallow Zn impurity level (∼20–40 meV above the top of the III-V compounds valence band), the Zn co-doping leads to the increase of conductivity of (Ga,Mn)P, however both the Curie temperature and magnetization reduce, which is probably due to the suppression of active Mn substitution by Zn co-doping.

Microstructural changes resulted from neutron irradiation and post-irradiation annealing in a high-temperature ultra-fine precipitate strengthened (HT-UPS) stainless steel were characterized using transmission electron microscopy (TEM) and atom probe tomography (APT). Three HT-UPS samples were neutron-irradiated to 3 dpa at 500 °C, and after irradiation, two of them were annealed for 1 h at 600 °C and 700 °C, respectively. Frank dislocation loops were the dominant defect structure in both the as-irradiated and 600 °C post-irradiation-annealed (PIAed) samples, and the loop sizes and densities were similar in these two samples. Unfaulted dislocation loops were observed in the 700 °C PIAed sample, and the loop density was greatly reduced in comparison with that in the as-irradiated sample. Nano-sized MX precipitates were observed under TEM in the 700 °C PIAed sample, but not in the 600 °C PIAed or the as-irradiated samples. The titanium-rich clusters were identified in all three samples using APT. The post-irradiation annealing (PIA) caused the growth of the Ti-rich clusters with a stronger effect at 700 °C than at 600 °C. The irradiation caused elemental segregations at the grain boundary and the grain interior, and the grain boundary segregation behavior is consistent with observations in other irradiated austenitic steels. APT results showed that PIA reduced the magnitude of irradiation induced segregations.

High temperature vulcanizing silicone rubber(HTV) and liquid silicone rubber(LSR) are widely used for external insulation of electrical equipments in HVDC converter station. The performance and service life of HTV and LSR materials show some differences, owing to the difference of their components, vulcanization mechanism, molding process, etc. In this paper, one of the key performances of HTV and LSR materials—migration of hydrophobicity was investigated. Besides the comparison of frequently-used HTV and LSR materials, the study found that the best hydrophobicity migration appeared at 60%RH for most samples, which is contradict with the traditional understanding that higher humidity leads to slower migration. In order to analyze the difference of HTV and LSR materials’ hydrophobcity migration in detail, this paper used several microscopic methods, including Fourier transform infrared spectroscopy (FTIR), Gel permeation chromatography (GPC) and liquid chromatography-mass spectrometry (LC-MS). Through these microscopic research, it was found that the distribution of pollution is the decisive factor, but not the amount of LMW siloxanes.

Avalanche ruggedness is an essential feature to assure robust power converter operations. In this paper, the performance degradation of the power MOSFET under the OFF-state avalanche test is investigated in detail. For this purpose, a high resolution and cost-effective nano-second Current Pulse Generator (CPG) is designed for device avalanche capability test. Using high resolution PWM function of a digital signal processor (DSP), a high resolution current pulse can be generated in the order of 100 picoseconds. Using the same setup, the magnitude and duration of the current pulse width can be adjusted precisely. From the experimental results, a significant drop in the threshold voltage is observed after these tests, which leads to a noticeable shift of transfer and output characteristics. In addition, a large increase in drain leakage current and a gradual increase in on-state resistance were observed over the aging cycles. The electrical parameter shifts indicate a possible gate degradation after the device aging.

In this work, we have fabricated the Al27Cu18Er55 amorphous ribbon with good glassy formation ability by melt-spinning technology. A broad paramagnetic (PM) to ferromagnetic (FM) transition (second ordered) together with a large reversible magnetocaloric effect (MCE) in Al27Cu18Er55 amorphous ribbon was observed around the Curie temperature TC ∼ 11 K. Under the magnetic field change (ΔH of 0–7 T, the values of MCE parameter of the maximum magnetic entropy change (−ΔSMmax) and refrigerant capacity (RC) for Al27Cu18Er55 amorphous ribbon reach 21.4 J/kg K and 599 J/kg, respectively. The outstanding glass forming ability as well as the excellent magneto-caloric properties indicate that Al27Cu18Er55 amorphous could be a good candidate for low temperature magnetic refrigeration.

The tensile stress in a hollow cylindrical superconductor completely restricted by a metal tube in a parallel magnetic field is investigated. Using the plane strain approach, analytical expressions for the stress distribution of the superconductor and the contact stress between the metal tube and the superconductor are obtained and show that both the ratio of Young’s modulus and thickness ratio of the high-temperature superconductors and the metal tube significantly affect the stress distribution in the superconductor explicitly. In addition, the flux pinning-induced stress in the above-mentioned superconductor is systematically studied by the exponential critical state model during the field cooling process. The results indicate that the metal tube can reduce effectively the tensile stress in the hollow cylindrical superconductor during the magnetization process. The findings suggest that the appropriate selection of material parameters and size of the metal tube can improve superconductor performance efficiently.

Manganese (Mn)-based antiperovskite structures (Mn3AX, where A and X represent the 3d transition-metal elements and N or C atoms, respectively) have attracted growing attention because of their novel electronic and magnetic properties. However, the lack of an effective approach to regulate the magnetic coupling in Mn3AX crystal structure, particularly in antiferromagnetic ground states, hinders their further design and applications. Herein, robust high-temperature ferrimagnetic order with a Curie temperature (TC) in the range of ∼390–420 K was successfully achieved in Mn3GaxNx (x = 0.5, 0.6, and 0.7) via composition-deficient engineering. A systematic investigation, including synchrotron X-ray diffraction, neutron powder diffraction, pair distribution function, X-ray absorption near-edge structure, magnetic characterization, and first-principles calculations, convincingly indicated that the redistribution of partial atoms in the antiferromagnetic ground state was responsible for the observed long-range magnetic order. These results not only provide a new perspective into the design and construction of high-temperature ferrimagnets based on the Mn3AX structure, but also open up a promising avenue for the further design of Mn3AX-based spintronic or other multifunctional devices.

Plasma electrolytic oxidation (PEO) and filtered cathodic vacuum arc deposition (FCVAD) techniques were employed to fabricate a ZrO2/Cr composite coating on pure zirconium. The steam oxidation properties of bare and ZrO2/Cr-coated pure Zr were performed in water vapor environment at 900–1100 °C. Their morphologies, microstructures and phase constituents before and after steam oxidation were analyzed. Meanwhile, their composition depth profiles were measured by glow discharge optical emission spectroscopy (GDOES). It was found that the mass gain of ZrO2/Cr-coated Zr was about 22–45% of that of bare Zr after 3600 s steam oxidation at 900–1100 °C, and the PEO and FCVAD composite treatments significantly improved the steam oxidation resistance of Zr. After steam oxidation, the phosphorous element in the outer layer of PEO film from phosphate electrolyte diffused into the residual Cr layer, however, most of the phosphorous in the interior of PEO layer was remained although the phosphorus diffusion in the region was accelerated with the increase of steam temperature. The ZrO2 to Zr3O phase transformation in PEO intermediate layer occurred in high temperature steam. Furthermore, the PEO zirconia interlayer suppressed hydrogen permeation into the Zr substrate during steam oxidation at 900–1100 °C.