Thermal Robustness Research Articles

Suppressing the Shuttle Effect in Lithium-Sulfur Batteries by a UiO-66-Modified Polypropylene Separator.

The lithium–sulfur battery is one of the most promising battery technologies with high energy density that exceeds the presently commercialized ones. The shuttle effect caused by the migration of soluble polysulfides to the lithium anode is known as one of the crucial issues that prevent the Li–S batteries from practical application. Modification of the separator is regarded as a convenient yet efficient strategy to alleviate the shuttle effect. In this report, we use a thermally stable and chemically robust metal–organic framework (MOF), UiO-66, as a physical and chemical barrier for soluble polysulfides to functionalize the commercial polypropylene separator. The Li–S cell assembled with such a separator shows a significantly improved cycling stability with an average specific capacity of ca. 720 mA h g–1 at a current rate of 0.5 C for 500 cycles. Experimental and theoretical investigations indicate that the cell performance enhancement results from the physical restriction of the MOF barrier layer and strong chemical interaction between UiO-66 and polysulfides. The excellent thermal stability and chemical robustness (in acid/alkali solutions, conventional organic solvents, and polysulfide electrolytes) of UiO-66 make it highly competitive among various materials developed for separator modification in Li–S batteries.

Comparative study on thermal robustness of GaN and AlGaN/GaN MOS devices with thin oxide interlayers

Similarities and differences in the design of the interfaces between gate dielectrics and GaN-based semiconductors were systematically investigated with a focus on the thermal stability of the interlayers. Although the excellent electrical properties of a SiO2/GaN interface with a thin Ga-oxide interlayer (SiO2/GaOx/GaN) were deteriorated by high-temperature treatment at around 1000 °C, the thin oxide on the AlGaN surface (SiO2/GaOx/AlGaN) exhibited superior thermal stability and interface quality even after treatment at 1000 °C. Physical characterizations showed that thermal decomposition of the thin GaOx layer on the GaN surface is promoted by oxygen transfer, which produces volatile products, leading to remarkable roughening of the GaN surface. In contrast, decomposition of the thin GaOx layer was suppressed on the AlGaN surface under the high temperatures, preserving a smooth oxide surface. The mechanisms behind both the improved and degraded electrical properties in these GaN-based MOS structures are discussed on the basis of these findings.

Recent Studies on Fluorinated Silica Nanometer-Sized Particles.

Since initially being reported, fluorinated silica nanometer-sized particles (F-SiNPs) have gained much interest in the scientific community, due to their unique properties. These properties, include, low surface energies, increased mechanical strength, thermal robustness, and chemical resistance, and are a direct result of the incorporation of fluorine with a nanometer-sized silica network. This review aims to summarize the synthetic methods that have, and are still, being utilized to prepare these specialized materials. Following this, applications for F-SiNPs, with an emphasis on recent examples, will be presented in further detail.

Improving the phase stability of inorganic lead halide perovskites through K/Rb doping

All-inorganic perovskites have gained considerable significance. Despite their superior thermal robustness, poor phase stability has rendered inorganic perovskites adverse. Herein, on the basis of first-principles calculations, we find that the incorporation of rubidium (Rb) and potassium (K) in an appropriate ratio will stabilize CsPbI2Br perovskites considerably, in which the cooperative interactions between Rb/K, I and Br play an important role. Besides, it is verified that 2D orthorhombic CsPbI3 with a thickness of ∼1 nm exhibits outstanding stability, even exceeding the non-perovskite, yellow structure and has a suitable band gap for solar cell applications.

Thermal Analysis of the Solar Orbiter PHI Electronics Unit

This paper presents the thermal design of the electronics unit of the instrument Polarimetric Helioseismic Imager, onboard the European Space Agency mission Solar Orbiter. The thermal design procedure, along with the problems encountered during this design phase, and the solutions found to fix them are described, proving in this way the thermal feasibility and robustness of the unit. Its final thermal behaviour, obtained from thermal analyses correlated with data from thermal tests performed in a vacuum environment, is presented.

Global Quantum Discord in Transverse‐Field Ising Models on N × N Square Lattices

Global quantum discord (GQD) in two‐dimensional (2D) transverse‐field Ising models on N × N square lattices at zero temperature and finite temperatures are studied. First, the GQD defined on the reduced density matrix of a 2 × 2 sub‐square in the center of the N × N lattices, with is studied. It is found that shows little size dependence in the strong‐field and weak‐field limit, and presents dramatic size dependence in the middle‐field region. The results are explained by short‐range correlations in non‐critical regions and long‐range correlations in critical regions of the models, respectively. Then the scaling behavior of the GQD of the ground states for the entire N × N squares is studied. It is found that contains a 1D contribution (corresponding to the side length of the squares) and a 2D contribution (corresponding to the area of the squares). Furthermore, the effect of thermodynamic fluctuations on GQD by investigating the thermal‐state GQD is considered. In high‐temperature regions, GQD is always destroyed by thermodynamic fluctuations for any strength of the magnetic field. However, in low‐temperature regions, some thermal enhancement of GQD under weak fields and some thermal robustness of GQD under strong fields is observed. The results are explained by the low‐lying energy states and the energy gap of the models.

Physicochemical origin of improvement of magnetic and transport properties of STT-MRAM cells using tungsten on FeCoB storage layer

We investigated and compared the structural and magnetic properties of MgO/FeCoB based out-of-plane magnetized tunnel junctions at the thin film level and the magneto-transport properties of the corresponding patterned spin transfer torque magnetic random access memory(STT-MRAM) cells comprising either Ta1 nm or W2/Ta1 nm cap layers for different annealing temperatures up to 455 °C. The W material in the cap was found to improve the structural stiffness of the perpendicular magnetic tunnel junctions (pMTJs) and most importantly prohibits Fe diffusion from the FeCoB storage layer to the cap layer, remarkably improving the thermal robustness and magneto-transport properties of the stacks and of the corresponding patterned memory cells. As a result, the interfacial anisotropy constant of the MgO/FeCoB interfaces is improved by 17%–29% compared to the Ta cap. The STT-MRAM cells fabricated from the pMTJ stacks with the W/Ta cap reveal a significant improvement of the tunneling magnetoresistance and thermal stability factor, which are 120% and 52 as compared to 70% and 35 for the stack with the Ta cap, respectively. This improvement is ascribed to the enhancement of MgO crystallinity upon higher temperature annealing (425 °C) and prohibition of Fe out-diffusion.

Determination of Polariton Condensates’ Critical Temperature

The thermal robustness of traveling polariton condensates is investigated. We create remote condensates that have never been in contact, and study their interference in momentum space, when they travel with the same velocity, by means of time‐resolved photoluminescence. We determine the condensed to thermal, uncondensed polariton fraction, which shows a gradual decay with increasing temperature, and obtain the critical temperature for the Bose‐Einstein‐like condensate (BEC) phase transition. We tentatively compare our experimental findings with theoretical models, developed for atomic condensates, to describe the condensates’ coherence fading with temperature.

Effects of Ti transition layers and thermal annealing on the adhesive property of Ag nanorods-based SERS sensors

Adhesion strength of surface-enhanced Raman scattering (SERS) substrates is an important factor for practical applications. Ag nanorods (AgNRs) based SERS sensors possess many outstanding merits, while the film adhesion is very weak. To strengthen the bonding of AgNRs on supporting bases, two effective approaches of adding transition layers and subsequent thermal annealing were utilized. Before AgNRs deposition, a Ti intermediate layer was deposited onto silicon wafers to relieve the large internal stress caused by the physical property differences between Ag and Si films. An ultrathin Al2O3 layer was then coated onto AgNRs surfaces, which enhanced both the thermal stability and mechanical robustness of the Ti-AgNRs substrate. Thereafter, Ti-AgNRs@Al2O3 was annealed to further facilitate the atomic diffusion and interaction between Ag, Ti and Si films. The optimized substrate exhibited a much improved scratch resistance property, and could sustain long-term ultrasonic vibration measurement. The excellent adhesive property ensures the stability of SERS substrates during transportation, storage and employment. Such a structure design leads to robust and reliable SERS sensors for real-life applications, and provides a valuable guidance for the adhesion enhancement of thin films.

Unique supramolecular complex of diclofenac: structural robustness, crystal-to-crystal solvent exchange, and mechanochemical synthesis.

We describe an unexpected, cyclic supramolecular complex that results from self-assembly of the nonsteroidal anti-inflammatory drug, diclofenac and 4,4'-azopyridine. The cycles self-assemble into 1D columns occupied by solvent, which can be removed at elevated temperatures (>100 °C) while retaining crystallinity. The complex exhibits solvent exchange ability that occurs through crystal-to-crystal transformations. Finally, the complex can be synthesized using mechanochemistry. Materials exhibiting the structural framework and robustness described here could be applied to removal of hazardous materials or undesirable solvents.

Preliminary Thermal Evaluation of Actuator for Steer-by-Wire Vehicle

Automotive industry is moving toward the electrification of the steering system due to efficiency and active safety integration concerns. Studies on actuators for steer-by-wire (SBW) application is very limited, and no thermal effects on the actuator related to utilization in the SBW have yet been looked into. Using a valid thermal model, and steer torque data collected from a journey mapping, a temperature profile of a prototype synchronous reluctance machine (Syncrel) has been established as if it was utilized as SBW actuator to verify the thermal robustness of the machine in that particular application. The maximum temperature in the winding is shown to not exceed the limit temperature for the winding insulation if the winding resistance can be divided by half of the current resistance in the prototype machine, thus, allowing us to consider Syncrel as another actuator solution for the SBW.

Non‐Perovskite Hybrid Material, Imidazolium Lead Iodide, with Enhanced Stability

AbstractA systematic study of a new hybrid organic‐inorganic material where the cation has been replaced with imidazolium is presented. Imidazolium lead iodide (ImPI) shares the same stoichiometry of ABX3 as a perovskite, however, it has a hexagonal structure. This material shows a vastly improved thermal stability as compared to the more popular hybrid perovskite, methyl ammonium lead iodide (MAPI). ImPI also exhibits a dramatic phase stability as compared to MAPI as demonstrated by the variable temperature XRD data (both low temperature and high temperature). In addition to the enhanced thermal robustness, ImPI shows three times better stability than MAPI under ambient conditions. The stability can be attributed to better packing efficiency of the ImPI lattice which in turn depends on the symmetrical and bulkier organic cation, imidazolium. Optoelectronic measurements were also performed and specifically, unlike for MAPI, photoluminescence measurements of ImPI showcased a broad emission over a range of 500 nm to 900 nm which could be attributed to the presence of self‐trapped excitons and as such this broad emission holds promise for light emitting device applications.

Multipartite Entanglement at Finite Temperature

The interplay of quantum and thermal fluctuations in the vicinity of a quantum critical point characterizes the physics of strongly correlated systems. Here we investigate this interplay from a quantum information perspective presenting the universal phase diagram of the quantum Fisher information at a quantum phase transition. Different regions in the diagram are identified by characteristic scaling laws of the quantum Fisher information with respect to temperature. This feature has immediate consequences on the thermal robustness of quantum coherence and multipartite entanglement. We support the theoretical predictions with the analysis of paradigmatic spin systems showing symmetry-breaking quantum phase transitions and free-fermion models characterized by topological phases. In particular we show that topological systems are characterized by the survival of large multipartite entanglement, reaching the Heisenberg limit at finite temperature.

Linear Hybrid Reluctance Motor with High Density Force

Linear switched reluctance motors are a focus of study for many applications because of their simple and sturdy electromagnetic structure, despite their lower thrust force density when compared with linear permanent magnet synchronous motors. This study presents a novel linear switched reluctance structure enhanced by the use of permanent magnets. The proposed structure preserves the main advantages of the reluctance machines, that is, mechanical and thermal robustness, fault tolerant, and easy assembly in spite of the permanent magnets. The linear hybrid reluctance motor is analyzed by finite element analysis and the results are validated by experimental results. The main findings show a significant increase in the thrust force when compared with the former reluctance structure, with a low detent force.

Upgrading of Biomass Monosaccharides by Immobilized Glucose Dehydrogenase and Xylose Dehydrogenase

AbstractDirect upgrading and separation of the monosaccharides from biomass liquors is an overlooked area. In this work we demonstrate enzymatic production of gluconic acid and xylonic acid from glucose and xylose present in pretreated birchwood liquor by glucose dehydrogenase (GDH, EC 1.1.1.47) and xylose dehydrogenase (XDH, EC 1.1.1.175), respectively. The biocatalytic conversions were compared using two different kinds of silica support materials (silica nanoparticles (nanoSiO2) and porous silica particles with hexagonal pores (SBA 15 silica) for enzyme immobilization. Upon immobilization, both enzymes showed significant improvement in their thermal stability and robustness at alkaline pH and exhibited over 50 % activity even at pH 10 and 60 °C on both immobilization matrices. When compared to free enzymes at 45 °C, GDH immobilized on nanoSiO2 and SBA silica displayed a 4.5 and 7.25 fold increase in half‐life, respectively, whilst XDH immobilized on nanoSiO2 and SBA showed a 4.7 and 9.5 fold improvement in half‐life, respectively. Additionally, after five reaction cycles both nanoSiO2GDH and nanoSiO2XDH retained more than 40 % activity and GDH and XDH immobilized on SBA silica maintained around 50 % of their initial activity resulting in about 1.5–1.6 fold increase in biocatalytic productivity compared to the free enzymes.

A MEMS Resonant Accelerometer With High Performance of Temperature Based on Electrostatic Spring Softening and Continuous Ring-Down Technique

Temperature fluctuations seriously damage the performance of resonant accelerometers. Two approaches have been proposed in this paper to address this problem. In structural design, an electrostatic softening spring is utilized to modulate the external acceleration on the frequency of resonator’s anti-phase modal without any stress transmission and thus improve the thermal robustness of the accelerometer. In control circuit, a continuous ring-down technique is employed for real-time quality factor (utilized as a virtual thermometer) monitoring, which attenuates measuring hysteresis and improves the precision of temperature compensation. A prototype is implemented to verify the proposed approaches. Experiments show that this accelerometer is insensitive to stress and has better performance of temperature compared with the vibration beam resonant accelerometer. The bias stability of acceleration output was improved from 35.2 to 0.08 mg with real-time quality factor compensation ranging from −40 °C to +40 °C.

Thermal robustness evaluation of nonvolatile memory using Pt nanogaps

We investigated the thermal robustness of a nonvolatile memory using polycrystalline platinum (Pt) nanogap electrodes. The temperature dependences of resistance states were evaluated from room temperature to 773 K. At high temperatures, the resistance of the high-resistance state (HRS) was slightly altered as the temperature changed. This slight alteration could be neglected, and the thermal robustness was improved by etching a SiO2 layer just under the nanogap. This indicated that the thermal alteration was caused by current leakage through the SiO2 layer. The nonvolatile memory employing Pt nanogaps is expected to be potentially useful as a thermally robust memory up to 773 K.

(High Temperature Materials Division Outstanding Achievement Award) Recent Advances in Intermediate-Temperature Fuel Cells: Surface Modification and In Situ/Operando Characterization

The performances of electrochemical systems are often limited by the charge and mass transfer along surfaces and across interfaces. Fundamental understanding of these electrochemical processes, especially the rate-limiting steps, is vital to achieving rational design of a new generation of intermediate-temperature fuel cells powered by a wide variety of readily available fuels. Also, surface modification has been successfully used to dramatically enhance electro-catalytic activity and durability of electrode materials. This presentation will highlight some recent advances in surface modifications and characterization of electrodes in energy storage and conversion systems. Surface enhanced Raman spectroscopy (SERS) has been used for probing and mapping new phases and reaction intermediates on electrode surfaces under or near operating conditions. It has also been demonstrated that SiO2 shell isolated Ag nanoparticles have excellent chemical and thermal robustness and stability for in situ SERS study of electrode materials under in situ or operando conditions, providing valuable information on reaction intermediates or structural changes that critically influence the performance and stability of the electrodes. Further, synchrotron-based X-ray absorption spectroscopy (XAS) and XPS have been used to characterize the local atomistic structure and oxidation state of electrode surfaces and interfaces, which may critically affect the activation or degradation processes of electrodes. These experimental studies, together with modeling and simulation, have helped us to gain important insights into the mechanisms of chemical and energy transformation, electro-catalytic reactions, and degradation processes, providing valuable guidelines for rational design of new electrode materials, surfaces, and interfaces with desired functionalities.

Large exchange coupling field in perpendicular synthetic antiferromagnetic structures with CoPt alloy

We have investigated the magnetic properties and thermal stability of perpendicular synthetic antiferromagnetic (p-SAF) layers with a [Co/Pt]x/Ru/[Co/Pt]x structure. A very large exchange coupling field (Hex) of 7.0 kOe was obtained in as-deposited p-SAF structures owing to the large perpendicular magnetic anisotropy of [Co/Pt] and exchange coupling with Ru. We found that a smooth surface of the Ru buffer layer is effective for improving the thermal robustness of [Co/Pt] and demonstrating a large Hex of 2.6 kOe even after annealing at 400 °C, which is as high as the integration temperature for Si-based circuits. Such a thermally robust p-SAF layer is promising for developing magnetic sensor devices.

A Programmable Cryogenic Waveguide Calibration Load With Exceptional Temporal Response and Linearity

We have developed a programmable, fast switching, accurate, and miniaturized calibration load for use in millimeter and submillimeter low-noise amplifier characterization, and Earth/planetary science radiometers. The proposed solution uses a thermally conductive waveguide vane attenuator with low thermal mass, integrated heater, and silicon thermometer. In the present design, we utilize a 125- $\mu$ m-thick z-cut crystal quartz vane due to its low dielectric constant (relative to silicon), high cryogenic thermal conductivity, chemical robustness, and small thermal contraction. To provide adequate attenuation, the bottom side of the quartz fabrication wafer has an nm thick resistive Ti metal layer deposited. On the top of the quartz wafer, a pattern of Au is deposited to allow adhesion of the heater resistor, thermometer, and internal heat strap. The z-cut quartz vane is mounted on three low thermally conductive Torlon posts, centered on the maximum E-field, and positioned across the waveguide. With this approach the quartz vane, protruding all the way into the waveguide, approximates a blackbody with a physical temperature T . The design uniqueness lies in the choice of cryogenically suitable materials coupled with detailed thermal analyses and proper miniaturization. When operated in a proportional $-$ integral $-$ derivative loop, these properties combine to facilitate a programmable calibration load with a switching speed of $\lesssim$ 10 s. It will be shown that the W-band design operates overmoded to $\sim$ 230 GHz and that the concept is in principle scalable to terahertz frequencies.