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Microstructure and thermoelectric properties of In2O3/ITO thin film thermocouples with Al2O3 protecting layer
摘要： In2O3/ITO thin film thermocouples (TFTCs) with alumina protecting layer were fabricated on alumina substrates. The effects of protecting layer on their performance at higher temperature and long term service were investigated accordingly. In2O3 and ITO thin films were prepared by radio frequency magnetron sputtering methods, while the alumina protecting layer was prepared by traditional spin-coating methods. Microstructural and thermoelectric properties of the In2O3/ITO TFTCs with and without alumina (Al2O3) protecting layer were investigated as a function of sintering time from 2 to 10 h at 1250 °C. The results show that, the existence of alumina protecting layer can effectively increase the performance capabilities of thermocouples at high temperatures by inhibiting the volatilization of the thin film. In2O3/ITO TFTCs with protecting layer can work normally over 10 h at 1250 °C while Seebeck coefficient is 131.7 μV/°C. The drift rate can reach 3.05 °C/h, which is much better than those without protecting layer.
关键词： high temperature,thermoelectric properties,Al2O3 protecting layer,long term service,In2O3/ITO thin film thermocouples
更新于2025-09-10 09:29:36
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Thermoelectric performance of monolayer InSe improved by convergence of multivalley bands
摘要： We theoretically investigate a possibility of improving the thermoelectric performance of monolayer InSe through convergence of multivalley energy bands, in which some distinct valleys become almost degenerate. The convergence of energy bands is achieved by applying mechanical strain. We find that the thermoelectric power factor of monolayer InSe can be significantly enhanced by nearly a factor of 3 through the band convergence in both valence (p-type) and conduction (n-type) bands under a biaxial compressive stress of about 1.16 GPa. However, the maximum enhancement of the figure of merit ZT in the p-type and n-type InSe differs each other depending on how the valleys converge in each case. The optimal scenario is that the heavy valleys approach the light valleys in the band convergence, which leads to an increase in the power factor and, at the same time, a decrease in the thermal conductivity of an electron. This optimal condition can be obtained in the strained n-type InSe that gives the largest enhancement of ZT as high as 230% ZT of unstrained InSe. In contrast, the enhancement of ZT in the strained p-type InSe, which exhibits opposite valley convergence (light valleys joining heavy ones), gives only 26% ZT of unstrained InSe.
关键词： mechanical strain,thermoelectric performance,power factor,figure of merit,multivalley bands,monolayer InSe
更新于2025-09-10 09:29:36
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Coherent Acoustic Phonon and Its Chirping in Dirac Semimetal Cd <sub/>3</sub> As <sub/>2</sub>
摘要： Ultrafast optical spectroscopy of a single crystal of a Dirac semimetal Cd3As2 is carried out. An acoustic phonon (AP) mode with central frequency ?? = 0.037 THz (i.e., 1.23 cm?1 or 0.153 meV) is unambiguously generated and detected, which we attribute to laser-induced thermal strain. An AP chirping (i.e., variation of the phonon frequency) is clearly detected, which is ascribed to heat capacity variation with time. By comparing our experimental results and the theoretical model, we obtain a chirping time constant, which is 31.2 ps at 6 K and 19.8 ps at 300 K, respectively. Significantly, we identify an asymmetry in the AP frequency domain peak and find that it is caused by the chirping, instead of a Fano resonance. Moreover, we experimentally demonstrate that the central frequency of AP is extremely stable with varying laser fluence, as well as temperature, which endows Cd3As2 application potentials in thermoelectric devices.
关键词： Cd3As2,chirping,acoustic phonon,Dirac semimetal,thermoelectric devices,thermal strain
更新于2025-09-09 09:28:46
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Temperature and pressure induced Raman studies of C 60 oxide
摘要： We present temperature, laser power, and pressure dependent Raman spectral analysis of C60 oxide (C60O) thin films prepared by the photolysis method. The first order temperature, laser power, and pressure coefficients of the Raman frequencies are evaluated and are utilized for evaluating the thermal conductivity of C60O. Its thermal conductivity is found to be 0.7 W m-1 K-1 which is marginally higher than that of bulk C60. Raman frequencies corresponding to C–O and C–C bonds blue-shift with a decrease in temperature which is attributed to the thermal contraction of C60O molecules. The density functional measurements have been performed to optimize C60O structure. The contraction in the C–O bond length has been corroborated with the experimental Raman shifts at different temperatures and is used to evaluate the linear expansion coefficient of C60O. Pressure induced compression and polymerization of C60O clusters are also illustrated. This study highlights the interplay between thermal and mechanical transformations in the C60O cluster which may regulate its thermoelectric properties by tuning the intermolecular interactions.
关键词： pressure dependence,thermoelectric properties,Raman spectroscopy,thermal conductivity,C60 oxide,laser power dependence,temperature dependence
更新于2025-09-09 09:28:46
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Handbook of Smart Cities (Software Services and Cyber Infrastructure) || Energy Harvesting in Smart Building Sensing: Overview and a Proof-of-Concept Study
摘要： Modern “smart” buildings require a plethora of sensors to be installed at various locations during the construction phase. Wiring costs and limited ?exibility of installation make wired installations less attractive. An alternative, ?exible, approach is to introduce wireless sensors and endow them with ways to harvest energy from the environment such that they attain the same “zero cost” of maintenance as their wired counterparts. The chapter reviews the sensing needs of smart buildings, and the related merits of energy harvesting to power embedded wireless sensor nodes. A proof-of-concept device exploiting thermoelectric harvesting is designed, built and tested to demonstrate how todays wireless sensing devices enable sustained continuous operation with minor energy harvesting requirements. In multi-hop environments, the underlying optimization problems are described and simple strategies that forego the solution of the hard computation problems but appear effective are outlined.
关键词： thermoelectric harvesting,smart buildings,energy harvesting,wireless sensor networks,multi-hop environments
更新于2025-09-09 09:28:46
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Characteristics of electrodeposited bismuth telluride thin films with different crystal growth by adjusting electrolyte temperature and concentration
摘要： Bismuth telluride (Bi2Te3) thin films were prepared with various electrolyte temperatures (10°C–70 °C) and concentrations [Bi(NO3)3 and TeO2: 1.25–5.0 mM] in this study. The surface morphologies differed significantly between the experiments in which these two electrodeposition conditions were separately adjusted even though the applied current density was in the same range in both cases. At higher electrolyte temperatures, a dendrite crystal structure appeared on the film surface. However, the surface morphology did not change significantly as the electrolyte concentration increased. The dendrite crystal structure formation in the former case may have been caused by the diffusion lengths of the ions increasing with increasing electrolyte temperature. In such a state, the reactive points primarily occur at the tops of spiked areas, leading to dendrite crystal structure formation. In addition, the in-plane thermoelectric properties of Bi2Te3 thin films were measured at approximately 300 K. The power factor decreased drastically as the electrolyte temperature increased because of the decrease in electrical conductivity due to the dendrite crystal structure. However, the power factor did not strongly depend on the electrolyte concentration. The highest power factor [1.08 μW/(cm·K2)] was obtained at 3.75 mM. Therefore, to produce electrodeposited Bi2Te3 films with improved thermoelectric performances and relatively high deposition rates, the electrolyte temperature should be relatively low (30 °C) and the electrolyte concentration should be set at 3.75 mM.
关键词： Electrolyte temperature,Bismuth telluride,Electrolyte concentration,Thermoelectric,Electrodeposition
更新于2025-09-09 09:28:46
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Attaining reduced lattice thermal conductivity and enhanced electrical conductivity in as-sintered pure n-type Bi2Te3 alloy
摘要： Undoped n-type Bi2Te3 bulks were prepared via the liquid state manipulation (LSM) with subsequent ball milling and spark plasma sintering processes. The sample with LSM obtains higher carrier concentration and larger effective mass compared with that without LSM, exhibiting favourable electrical transport properties. More importantly, a much reduced lattice thermal conductivity * 0.47 W m-1 K-1 (decreased by 43%) is obtained, due to the enhanced multiscale phonon scattering from hierarchical microstructures, including boundaries, nanograins and lattice dislocations. Additionally, due to the increased carrier concentration and enlarged band gap, the bipolar effect is effectively suppressed in sample BT-LSM. Consequently, zTmax * 0.66 is achieved in the sample with LSM at higher temperature of 475 K, almost 22% improvement compared with that of the contrast.
关键词： spark plasma sintering,thermoelectric,electrical conductivity,thermal conductivity,liquid state manipulation,ball milling,Bi2Te3
更新于2025-09-09 09:28:46
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Correlation between thermal-vibration-induced large displacement of Cu atoms and phase transition in Cu4SnS4: First-principles investigation
摘要： First-principles (FP) calculations and first-principles molecular dynamics (FPMD) simulations for Cu4SnS4 were performed to clarify the origin of the structural phase transition at 232 K between the high-temperature phase (HP) and low-temperature phase (LP), which leads to an experimentally measured drastic change in the transport properties of Cu4SnS4. The results of the FP and PFMD calculations indicated that, rather than being caused by the so-called freezing of soft modes, the key driving force behind the phase transition in Cu4SnS4 is a large-scale displacement of the Cu atoms located at particular sites due to thermal vibration. In fact, tetrahedrally coordinated CuS4 is stabilized by the effect of the thermal vibration of Cu atoms in the HP whereas CuS3, which is in a trigonal planar environment, is stabilized in the LP.
关键词： first-principles calculation,molecular dynamics simulation,thermoelectric property,electronic structure,phase transition
更新于2025-09-09 09:28:46
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First-principles study of elastic, electronic, optical and thermoelectric properties of newly synthesized K2Cu2GeS4 chalcogenide
摘要： In this article, we report the elastic, electronic, optical and thermoelectric properties of recently synthesized K2Cu2GeS4 chalcogenide. The structural parameters are found to be in good agreement with experimental results. The calculated single crystal elastic constants (Cij) show that K2Cu2GeS4 is mechanically stable. The investigated electronic band structures reveal semiconducting characteristics and are consistent with experiment. Important optical constants such as dielectric constants, refractive index, absorption coefficient, photoconductivity, reflectivity and loss function are calculated and discussed in detail. Optical conductivity is found to be in good qualitative agreement with the results of band structure calculations. The Seebeck coefficients for TB-mBJ potential within the studied temperature range vary from ~450 to ~200 m V/K. The anisotropic electrical conductivity and electronic thermal conductivity are observed in the layered structured K2Cu2GeS4. The power factor and electronic thermal conductivity at 800K along xx-axis using TB-mBJ potential are found to be ~6 m Wcm-1K-2 and 0.578 Wm-1K-1, respectively and the corresponding thermoelectric figure of merit is 0.81. The obtained results predict that K2Cu2GeS4 is a promising material in thermoelectric device applications.
关键词： electronic properties,optical properties,elastic properties,thermoelectric properties,K2Cu2GeS4
更新于2025-09-09 09:28:46
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Direct probing of cross-plane thermal properties of ALD Al <sub/>2</sub> O <sub/>3</sub> /ZnO superlattice films with improved figure of merit and their cross-plane thermoelectric generating performance
摘要： There is a recent interest in semiconducting superlattice films because their low dimensionality can increase the thermal power and phonon scattering at the interface in superlattice films. However, experimental studies in all cross-plane thermoelectric (TE) properties, including thermal conductivity, Seebeck coefficient, and electrical conductivity, has not been performed from these semiconducting superlattice films, because of substantial difficulties in the direct measurement of the Seebeck coefficient and electrical conductivity. Unlike the conventional measurement method, we present technique using a structure of sandwiched superlattice films between two embedded heaters as heating source, and electrodes with two Cu plates, which directly enables the investigation of the Seebeck coefficient and electrical conductivity across the Al2O3/ZnO superlattice films, prepared by atomic layer deposition (ALD) method. Used in combination with the promising cross-plane four-point-probe 3-ω method, our measurements and analysis demonstrate all cross-plane TE properties of Al2O3/ZnO superlattice films in the temperature range from 80 to 500 K. Our experimental methodology and the obtaining results represent a significant advancement in the understating of phonon and electrical transports in nanostructured materials, especially in semiconducting superlattice films in various temperature ranges.
关键词： Thermal conductivity,Cross-plane thermoelectric properties,Seebeck coefficient,Phonon transport,Superlattice films,3-omega measurement,Phonon scattering
更新于2025-09-09 09:28:46