In-plane Temperature Gradient Research Articles

Independent enhancement of the in-plane Seebeck effect in 2D PtSe2/PtSe2 homostructures via a facile interface tuning method

Atomically thin two-dimensional (2D) transition-metal dichalcogenide (TMDC) films have emerged as promising semiconducting materials for use in thermoelectric (TE) applications. However, the utilization of such materials remains challenging owing to the relatively high intrinsic resistance as the size of the TMDC thin films increases to the centimeter scale. These 2D TMDC films can also form vertically stacked homo- or heterostructures at large interfaces with other 2D TMDC films, resulting in unique TE properties at room temperature. This article reports on the in-plane TE properties when the interfaces formed within a PtSe2/PtSe2 (3 nm/3 nm) homostructure are modulated as a function of O2 plasma treatment time. The results show enhanced Seebeck coefficients compared with that of the single-layer PtSe2 with the same thickness. The independent enhancement in the Seebeck coefficient while keeping the electrical conductivity leads to a substantial increase in the power factor. Such extra Seebeck voltage in 2D PtSe2/PtSe2 homostructures is mainly as a result of momentum exchange by charge carriers caused by the temperature gradient in the vertical direction, which occurs in-plane Seebeck coefficient measurements, at the interface between the PtSe2 layers in the in-plane temperature gradient along the samples. These results resemble the characteristics of the phonon drag effect at low temperatures, which can independently increase the Seebeck coefficient at room temperature.

High-efficiency solar-driven water purification enhanced by the in-plane temperature gradient and hydrated ions

Solar-driven water purification has become a promising way to overcome the freshwater crisis because of its environmentally-friendly features. Improving the evaporation rate and evaporation efficiency are eternal topics. In this work, we redesign the solar-driven vapor generation (SVG) device and a unique in-plane temperature gradient is established due to the oriented water transportation. The input energy is maximized and the superb evaporation rate of 6.40 kg m−2 h−1 with an efficiency of 243.8 % is achieved. By investigating the hydration state in NaCl solution and aqueous acid, the interaction mechanism between hydrated ions and non-woven fabrics is developed. Owing to the increased intermediate water proportion, the evaporation rate of the SVG device in 5 wt% NaCl solution can reach 6.38 kg m−2 h−1, which is almost the same as that in DI water. Moreover, the unique reversible doping properties make the non-woven fabrics a reusable and stable volatile acid purifier. The evaporation rate in pH = 4.0 aqueous acid can be enhanced to 6.75 kg m−2 h−1, while the generated water maintains a pH higher than 6.5. Our work provides a new perspective for designing high-efficiency and multifunctional SVG devices.

High-performance flexible thermoelectric generators with tunable in-plane and out-of-plane architectures

Although thermoelectric generators (TEGs) based on organic/inorganic composite films have made great achievements in recent years, rational design of flexible TEGs with tunable in-plane or out-of-plane architecture still remains a great challenge. Herein, flexible films of poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate)/single-walled carbon nanotube (PEDOT:PSS/SWCNT) composite with an optimized power factor of 97 ± 2.4 μW m−1 K−2 are prepared by a facile solution mixing, followed by vacuum filtration and sequential solvents post-treatment. The effects of geometric parameters of thermoelectric (TE) legs on the generator output performance were investigated. Subsequently, the designed TEG prototypes, assembled in a "back-to-back" pattern with 5 or 10 p-n couples (TEG-5pn or TEG-10pn), can effectively utilize both in-plane and cross-plane temperature gradients. The out-of-plane TEG-10pn exhibits a higher output power density (337.4 μW cm−2 or 0.069 μW cm−2 K−2 at temperature difference of 70 K). Furthermore, the designed TEGs displayed versatile applications, efficiently achieving heat-to-electricity conversion by harvesting both in-plane and cross-plane temperature gradients induced by hot water in a cylindrical beaker, human body, or a hot plate. This work provides a convenient and practical strategy for the development of film-based TEGs, considering device architecture design, packing density and the geometric parameters of the TE legs.

Vector spin Seebeck effect and spin swapping effect in antiferromagnetic insulators with non-collinear spin structure

Antiferromagnets (AFs) are prospective for next-generation high-density and high-speed spintronic applications due to their negligible stray field and ultrafast spin dynamics, notwithstanding the challenges in detecting and manipulating AF order with no magnetization (M = 0). Among the AFs, non-collinear AFs are of particular interest because of their unique properties arising from the non-collinear spin structure and the small magnetization M. In this work, we describe the recently observed vector spin Seebeck effect in non-collinear LuFeO3, where the magneto-thermovoltage under an in-plane temperature gradient, not previously observed, is consistent with the predicted spin swapping effect. Our results shed light on the importance of the non-collinear spin structure in the emerging spin phenomena in non-collinear AFs and offer a new class of materials for AF spintronics and spin caloritronics.

Asymmetric thermal rectifier with designed in-plane temperature gradient zones for thermoelectric generator

Temperature difference and its duration are two main factors that affect thermoelectric performance. One can obtain the desired temperature distributions by manipulating heat flow directions; however, it is generally neglected when designing thermoelectric generators (TEGs). In this study, thermal rectifiers work in forward directions to produce in-plane temperature differences (ΔTh), where hot and cold zones are, respectively, provided by the small terminals of rectifiers and gaps between these areas. Thermoelectric legs placed above are arranged in an “X”-shape, keep TEGs' internal resistances, and have a stable range from 0.7 to 2 Ω; even heating temperatures Th have a significant range from 30 to 80 °C. When the rectification coefficient of thermal rectifiers was 1.63 and the thickness of thermoelectric legs decreased from 1 mm to 10 μm, simulated-ΔTh in the steady state rises from 2.62 to 27.10 °C rather than falling. An experimental thermal rectifier with a PI film thickness of 25 μm demonstrates that ΔTh can reach up to 14.7 °C, and the time duration is more than 60 s, where Th and ambient are 50 and 20 °C, respectively. The maximum output power can reach up to 92.48 μW when the temperature bias between Th and ambient increases to 65.33 °C. These novel thin-TEGs with designed in-plane temperature gradient zones by asymmetric thermal rectifiers are expected to be applied in distributed sensors, wearable devices, etc.

Zebra-inspired stretchable, biodegradable radiation modulator for all-day sustainable energy harvesters.

Recent advances in passive radiative cooling systems describe a variety of strategies to enhance cooling efficiency, while the integration of such technology with a bioinspired design using biodegradable materials can offer a research opportunity to generate energy in a sustainable manner, favorable for the temperature/climate system of the planet. Here, we introduce stretchable and ecoresorbable radiative cooling/heating systems engineered with zebra stripe-like patterns that enable the generation of a large in-plane temperature gradient for thermoelectric generation. A comprehensive study of materials with theoretical evaluations validates the ability to accomplish the target performances even under external mechanical strains, while all systems eventually disappear under physiological conditions. Use of the zebra print for selective radiative heating demonstrates an unexpected level of temperature difference compared to use of radiative cooling emitters alone, which enables producing energy through resorbable silicon-based thermoelectric devices. The overall result suggests the potential of scalable, ecofriendly renewable energy systems.

Compensation of Thermal Gradients Effects on a Quartz Crystal Microbalance

Quartz Crystal Microbalances (QCM) are widely used instruments thanks to their stability, low mass, and low cost. Nevertheless, the sensitivity to temperature is their main drawback and is often a driver for their design. Though the crystal average temperature is mostly considered as the only disturbance, temperature affects the QCM measurements also through the in-plane temperature gradients, an effect identified in the past but mostly neglected. Recently, it has been shown that this effect can prevail over that of the average temperature in implementations where the heat for thermal control is released directly on the crystal through deposited film heaters. In this study, the effect of temperature gradients for this kind of crystal is analyzed, the sensitivity of frequency to the average temperature gradient on the electrode border is determined, and a correction is proposed and verified. A numerical thermal model of the QCM has been created to determine the temperature gradients on the electrode borders. The frequency versus temperature-gradient function has been experimentally determined in different thermal conditions. The correction function has been eventually applied to a QCM implementing a crystal of the same manufacturing lot as the one used for the characterization. The residual errors after the implementation of the correction of both average temperature and temperature gradients were always lower than 5% of the initial temperature disturbance. Moreover, using the correlation between the heater power dissipation and the generated temperature gradients, it has been shown that an effective correction strategy can be based on the measurement of the power delivered to the crystal without the determination of the temperature gradient.

Observation of the giant magneto-Seebeck effect in a metastable Co50Fe50/Cu multilayer

We report the observation of the giant magneto-Seebeck (GMS) effect in an epitaxially grown Co50Fe50/Cu multilayer film with metastable bcc Cu spacers under an in-plane temperature gradient. The magnetization-dependent switching ratio of the Seebeck coefficient, GMS ratio, and switching ratio of the thermoelectric power factor reach approximately −50% and 280% at room temperature, respectively, which are higher than those previously reported in magnetic multilayers with the current-in-plane geometry. By measuring the temperature dependence of both GMS and giant magnetoresistance (GMR) effects, we found that the GMS ratio remains high at high temperatures, while the GMR ratio quickly decreases with increasing temperature, where the spin-dependent electron scattering dominantly affects the large GMS effect in the Co50Fe50/Cu multilayer.

Characterization of Thermal Gradient Effects on a Quartz Crystal Microbalance.

Quartz crystal microbalances are widely used sensors with applications for the detection of very-low-mass deposition in many different fields, from contamination monitoring in the high vacuum of deep space missions to the monitoring of biological activity or pollution using specifically designed active substrates. These sensors are very stable over time; nevertheless, their sensitivity to the temperature is well known, and different implementations have been devised to correct it, e.g., through compensation with a dual crystal. This paper deals with the effects of temperature on QCM but separates the case of uniform crystal temperature from the case of in-plane temperature gradients considering a QCM based on quartz crystals with deposited film resistors used as both RTDs and heaters. This configuration allows both an accurate temperature measurement and efficient thermal control, allowing the achievement of crystals temperatures in the order of 400 °C higher than the environment with a low power dissipation of the order of 1 W. The film resistors deposited around the electrodes allow directly measuring the average crystal temperature and directly delivering power to the crystal for thermal control. The localized delivery of the heat nevertheless also determines uncommon temperature fields on the crystal, and thus, an analysis of both the effects of temperature on the new microbalance was performed. The temperature gradient has strong effects on the frequency; therefore, along with the temperature, the thermal gradients have tobe compensated. The calibration of the QCM thermometers and the assessment of the achievable measurement accuracy were performed, as well as the determination of the frequency–temperature relationship. The comparison between frequency changes in the case of uniform temperature and those observed while using crystal heaters proved that temperature gradients have a strong effect on the crystal frequency. To identify the temperature field on the crystal surface of a QCM crystal, the gold coating of the deposited films was removed to achieve an emissivity acceptable for thermal imaging with an IR camera. Moreover, image processing for emissivity correction was developed. In order to correlate the temperature gradient with the frequency variation, a test campaign was performed to measure the frequency changes derived from different power levels delivered to the crystal heaters. From this test campaign and thermal analysis, the effect of the thermal gradient was assessed.

Modeling the inhomogeneous lithium plating in lithium-ion batteries induced by non-uniform temperature distribution

Under fast-charging or low-temperature charging conditions, large-format lithium-ion batteries are prone to inhomogeneous lithium plating, resulting in localized degradation and even internal short circuit, thus requiring a thorough investigation. This study establishes a three-dimensional electrochemical model to analyze the inhomogeneous lithium plating behavior in lithium-ion batteries. The model is validated with the voltage profiles and temperature distributions of a 24Ah pouch lithium-ion battery during low-temperature charging. The inhomogeneous lithium plating induced by non-uniform temperature distribution and the underlying mechanism are investigated using the model. The local current density and overpotential turn out to be the key factors affecting the spatial distribution of plated lithium. Moreover, the effects of temperature gradients on the lithium plating and stripping behaviors are explored. In-plane temperature gradient shows little effect on the total amount of plated lithium, but leads to apparent inhomogeneity in the distribution of plated lithium, with the differences between the concentrations of plated lithium in the upper and lower half of battery reach 57.61%, 103.06% and 159.68% of the average concentration in the whole battery during 1C charging at -5, 5 and 10°C, respectively. The temperature gradient also significantly influences the battery voltage relaxation profile related to the lithium stripping process. The characteristic plateau in the battery voltage relaxation profile disappears when the temperature gradient increases to larger than 6°C, leading to difficulty in detecting inhomogeneous lithium plating in large-format lithium batteries. The results presented in this study can provide helpful guidance for the design and management of large-format lithium-ion batteries.

Evidence for spin swapping in an antiferromagnet

Antiferromagnetic insulators offer strategic advantages in spintronic applications because of their negligible stray fields and ultrafast magnetic dynamics. Control of their magnetization and readout of their magnetic state are essential for these applications but remain challenging. Here we report the electrical detection of room-temperature magnetization switching in the canted antiferromagnetic insulator LaFeO3, capped with a Pt or W overlayer. The observation of a large magneto-thermovoltage with an in-plane temperature gradient suggests that the mechanism is the swapping of spin currents in the antiferromagnet. This effect provides a sensitive electrical probe of the tiny net magnetization in the insulator, which can be manipulated by a magnetic field on the order of 10 mT. Our results highlight a new material class of insulating canted antiferromagnets for spintronics and spin caloritronics and suggests a method for the electrical readout of magnetic signals in an antiferromagnetic insulator.

Thermal Concentration on Thermoelectric Thin Film for Efficient Solar Energy Harvesting

Thermoelectric generators can directly harvest and convert ambient thermal energy into electricity, which makes it ideal for thermal energy conversion. However, the limited working temperature gradient developed by direct solar radiation severely restricts the performance and the application of solar thermoelectric generators. Here, we report a multilayer thin film integrating a solar selective absorbing coating and a thermoelectric layer, where an in-plane temperature gradient was established. The temperature gradient was relatively large since the absorbed solar energy could only flow through the restricted cross-section of the thin film, representing a high thermal concentration. The fabricated thin-film solar thermoelectric generators (100 mm × 15 mm) achieve an open-circuit voltage of about 300 mV, and an output power of 0.83 μW under AM 1.5G conditions. Our work opens up a promising new strategy to achieve the simple and cost-effective conversion of solar energy into electricity by thermal concentration.

Influence of kerosene flame on fire-behaviour and mechanical properties of hybrid Carbon Glass fibers reinforced PEEK composite laminates

This work examines the influence of kerosene flame exposure on the residual mechanical behavior (tension and compression) of hybrid quasi-isotropic composite laminates consisting of carbon/glass fibers and a PEEK thermoplastic matrix. The influence of a kerosene flame exposure (116 kW/m2 and 1100 °C), on the composites structural integrity was examined as a function of exposure time (5–10-15 min). The changes in the tensile and compressive properties (axial stiffness and strength) were compared with respect to the virgin materials (experiencing no prior flame exposure). The discussions on fire- and mechanically-induced damage mechanisms are supported by fractographic analysis of specimens. It is therefore possible to better understand how the fire-induced damages within the laminates micro- and meso-structures modify the mechanical behavior of flame-exposed laminates.Regardless the exposure time, the kerosene flame exposure involves in-plane and through-thickness temperature gradients, which ultimately create two well defined areas within the laminates: an extensively delaminated one (the one close to the exposed surface) and a relatively well preserved one (close to the back surface). From the present work, it is possible to conclude that the mechanical properties in tension are severely affected (-50% in stiffness and −70% in strength) by prolonged exposures to kerosene flame (15 min) with respect to as-received specimens. When compared to the 5 min case, flame exposure time (ranging from 5 to 15 min) seems to have little very influence on tensile properties and the effect is moderate on compressive properties. The barrier formed by an extensive thermally-induced delamination contributes to relatively preserve the structural integrity of the plies close to the back surface. The mechanical loading is taken up by the 0° fibers in non-delaminated areas of the specimens, resulting in preserving the residual mechanical in tension and in compression.

Spin Nernst and anomalous Nernst effects and their signature outputs in ferromagnet/nonmagnet heterostructures

The spin Nernst effect (SNE) and anomalous Nernst effect (ANE) convert a heat current generated by a temperature gradient to a spin current in nonmagnetic metals and ferromagnets, respectively. We present a diffusive spin transport theory of the combination of these thermoelectric effects in ferromagnet (F)/nonmagnet (N) heterostructures and their respective output signals. In a F/N bilayer, in the presence of an in-plane temperature gradient, electrical voltages are induced by the SNE in N and the ANE in the F layers, via the inverse spin Hall effect in the N. The analytical expression of the thermally driven spin Hall magnetoresistance (TSMR) output is derived, which captures both the local SNE contribution in the N and the nonlocal mixing contribution due to the ANE in the adjacent F. Interestingly, the SNE and ANE give additive contributions to the transverse TSMR voltages but subtract from each other for the longitudinal component. This anisotropic response suggests a possible means to extract the individual SNE and ANE contributions, as well as spin-dependent polarization parameters. In a F1/N/F2 trilayer, both SNE and ANE contribute to spin torques on the free F2 layer. We analyze the ferromagnetic resonance (FMR) of the free layer and show that both thermoelectric effects contribute additively to the FMR magnitude and linewidth for the considered magnetization configuration. Finally, we show that TSMR can provide a more sensitive experimental detection of SNE and ANE down to a threshold thermal gradient of the order of ${10}^{\ensuremath{-}6}$ K/nm.

Magnon thermal Edelstein effect detected by inverse spin Hall effect

In an easy-plane antiferromagnet with the Dzyaloshinskii–Moriya interaction (DMI), magnons are subject to an effective spin-momentum locking. An in-plane temperature gradient can generate interfacial accumulation of magnons with a specified polarization, realizing the magnon thermal Edelstein effect. We theoretically investigate the injection and detection of this thermally driven spin polarization in an adjacent heavy metal with a strong spin Hall effect. We find that the inverse spin Hall voltage depends monotonically on both temperature and the DMI but non-monotonically on the hard-axis anisotropy. Counterintuitively, the magnon thermal Edelstein effect is an even function of a magnetic field applied along the Néel vector.

Double Point Temperature Measurements Under Rib and Channel in an Operating PEFC Using MEMS Sensors

Introduction For more spread of polymer electrolyte fuel cells (PEFCs), investigating the temperature distribution inside an operating PEFC is important. Last year, correlation between local through-thickness temperature gradient and the PEFC performance was investigated [1]. In this case, temperature gradient was critical to the PEFC performance under certain operating conditions. Moreover, local in-plane temperature gradient should be suggested as an important factor to the PEFC performance. Therefore, in this study, two local temperature measurement on the interface of the cathode catalyst layer (CL) and the microporous layer (MPL) in a PEFC was performed while it was operated. Experimental method Thin-Film Thermocouple (TFTC) For the local temperature measurement inside a PEFC, in-house thin-film thermocouple (TFTC) was fabricated using micro electromechanical system (MEMS). The thermocouple was made from Au and Ni. Its measurement point was about 30 µm width and about 6 µm thick, which was so fine and thin that it wouldn’t disturb a reaction inside a PEFC.Cell Configuration An active area of 1 cm2 PEFC cell was used, and is has five 1mm width gas channels and five 1mm width ribs with parallel flow configuration. 15 µm thick reinforces type PEM was used. TGP-H-060 (with MPL 2.0 mg/cm2) was used and in both anode and cathode side. TFTCs were inserted between interface of cathode CL/MPL, and two TFTCs were set on rib and channel, respectively.Operation Conditions Power generation was performed by sweeping the cell voltage from OCV to 0 V at a rate of 1 mV/s. K-type thermocouples were used to measure the bi-polar plates with gas channels and sensor terminal temperatures. An impedance analyzer was used to measure the cell resistance. O2 and air were used as a cathode supply gas, respectively. Pure H2 was used as an anode supply gas. The flow rates of anode gas / cathode gas were set in two conditions, 500/500 mL/min, and 30/75 mL/min. Results and Discussion Here, results in one operating condition is being shown, when the high flow rate has been chosen, and O2 has been chosen as a cathode supply gas. Fig.1 (a) shows the cell voltage and cell resistance transition with current density. In this case, the cell voltage decrease due to diffusion overvoltage didn’t occur. And Fig.1 (b) shows the temperature increase from the beginning operating the PEFC on the CL/MPL interface under rib and channel. The temperature on the channel was higher than that on the rib. Due to the condensed water which was generated with the PEFC operation, the effective thermal conductivity got decreased. The amount of the condensed water on the rib was larger than that on the channel. Therefore, total amount of the condensed water might affect on the effective thermal conductivity and caused the temperature difference on the rib and channel. Reference [1] K. Shigemasa, et al., ECS Trans., 92(8),161-4 (2019) Figure 1

Observation of Thermal Spin-Orbit Torque in W/CoFeB/MgO Structures.

Coupling of spin and heat currents enables the spin Nernst effect, the thermal generation of spin currents in nonmagnets that have strong spin-orbit interaction. Analogous to the spin Hall effect that electrically generates spin currents and associated electrical spin-orbit torques (SOTs), the spin Nernst effect can exert thermal SOTs on an adjacent magnetic layer and control the magnetization direction. Here, the thermal SOT caused by the spin Nernst effect is experimentally demonstrated in W/CoFeB/MgO structures. It is found that an in-plane temperature gradient across the sample generates a magnetic torque and modulates the switching field of the perpendicularly magnetized CoFeB. The W thickness dependence suggests that the torque originates mainly from thermal spin currents induced in W. Moreover, the thermal SOT reduces the critical current for SOT-induced magnetization switching, demonstrating that it can be utilized to control the magnetization in spintronic devices.

Nonlocal Detection of Out-of-Plane Magnetization in a Magnetic Insulator by Thermal Spin Drag.

We demonstrate a conceptually new mechanism to generate an in-plane spin current with out-of-plane polarization in a nonmagnetic metal, detected by nonlocal thermoelectric voltage measurement. We generate out-of-plane (∇T_{OP}) and in-plane (∇T_{IP}) temperature gradients, simultaneously, acting on a magnetic insulator-Pt bilayer. When the magnetization has a component oriented perpendicular to the plane, ∇T_{OP} drives a spin current into Pt with out-of-plane polarization due to the spin Seebeck effect. ∇T_{IP} then drags the resulting spin-polarized electrons in Pt parallel to the plane against the gradient direction. This finally produces an inverse spin Hall effect voltage in Pt, transverse to ∇T_{IP} and proportional to the out-of-plane component of the magnetization. This simple method enables the detection of the perpendicular magnetization component in a magnetic insulator in a nonlocal geometry.

Planar thermal Hall effect in Weyl semimetals

Weyl semimetals are intriguing topological states of matter that support various anomalous magneto-transport phenomena. One such phenomenon is a negative longitudinal ($\mathbf{\nabla} T \parallel \mathbf{B}$) magneto-thermal resistivity, which arises due to chiral magnetic effect (CME). In this paper we show that another fascinating effect induced by CME is the planar thermal Hall effect (PTHE), i.e., appearance of an in-plane transverse temperature gradient when the current due to $\mathbf{\nabla} T$ and the magnetic field $\mathbf{B}$ are not aligned with each other. Using semiclassical Boltzmann transport formalism in the relaxation time approximation we compute both longitudinal magneto-thermal conductivity (LMTC) and planar thermal Hall conductivity (PTHC) for a time reversal symmetry breaking WSM. We find that both LMTC and PTHC are quadratic in B in type-I WSM whereas each follows a linear-B dependence in type-II WSM in a configuration where $\mathbf{\nabla} T$ and B are applied along the tilt direction. In addition, we investigate the Wiedemann-Franz law for an inversion symmetry broken WSM (e.g., WTe$_{2}$) and find that this law is violated in these systems due to both chiral anomaly and CME.

Dynamic Response of a Thermally Stressed Plate with Reinforced Edges

Conditions in hypersonic flight generate non-uniform temperature distributions that affect the performance and longevity of aircraft components. Historically, a limited amount of experimental work has been performed on the mechanical behaviour of reinforced aircraft structures subjected to very high temperatures. In this work on Hastelloy-X plates, non-contact techniques were used to measure the full-field temperature and deflection of a 1 mm thick plate with reinforced edges. The geometry was designed to emulate an aircraft’s skin with the reinforced edges performing the function of stringers and ribs. High temperatures were achieved using quartz lamps arranged in various configurations with controllable power output. Digital image correlation (DIC) was used to measure surface displacements and a micro-bolometer mapped the temperature distribution across the plate. Deflection results for the reinforced plate showed it to behave as a dynamic system that buckles out-of-plane when heated before relaxing to a steady state. It is demonstrated that the out-of-plane displacement field experienced by the plate is influenced both by the in-plane temperature gradient and the energy supplied.