Search

Bi2Te3 is a thermoelectric material with high thermoelectric conversion efficiency near room temperature. The control of its components is an effective method to improve the thermoelectric properties of Bi–Te based materials. In this paper, seven-layer Bi–Te thin films with Te content ranging from 36.29% to 77.29% were deposited on non-rotating glass substrates by co-sputtering and the samples were rapidly thermally annealed in a nitrogen atmosphere. The films were characterized by x-ray diffraction, scanning electron microscopy, and Hall effect measurement methods, and the effects of the components on the film morphology and thermoelectric properties were investigated. The results showed that the films were composed of mainly Bi2Te3 after annealing. As the Te element content increased, the grain size in the film surface first increased and then decreased, the layers between the interfaces became less obvious, and the number of voids decreased. Subsequently, thin films with Te content between 60% and 75% were deposited on a rotating substrate; the thermoelectric properties were relatively high and stable after annealing. A film with Te content of 69.29% had a good crystallization quality and large grain size with a maximum power factor of 8.17 µW/(K2 cm) after annealing at 350 °C for 17 min. [ABSTRACT FROM AUTHOR]

Although electrospinning is considered a powerful and generic tool for the preparation of nanofiber webs, several issues still need to be overcome for real-world applications. Most of these problems are caused by needle-based systems, where the key factor influencing successful electrospinning is limited by the low yield of nanofibers prepared by needle-type electrospinning and the balance between the electric field force and the surface tension of the droplets. In order to solve these two issues, we use the roller type electrospinning system to prepare nanofibers. The characteristic of the system is that the roller is made of glass, and the voltage is connected to the liquid bath and the auxiliary electrode is added. We demonstrate that needle-disk electrospinning produces nanofiber with super-high throughput of 15.9 g/h, which is 177 times higher than traditional electrospinning under similar spinning conditions. Not only does it increase productivity, but also it facilitates handling and cleaning work. In addition, the auxiliary electrode can optimize the electric field and reduce the edge effect of the collecting plate. This method should help expand the range of applications for electrospun nanofiber webs in the near future. [ABSTRACT FROM AUTHOR]

The lattice vibrations and optical properties of α-Ga2O3 are investigated by polarized Raman scattering and spectroscopic ellipsometry measurements at room temperature. Three types of epitaxial α-Ga2O3 film samples were grown on c-plane sapphire substrates by halide vapor phase epitaxy (HVPE) in three different growth modes, namely by O2-control, Ga-control, and reference mode. Seven Raman active phonons and three infrared active phonons are determined experimentally for all samples. The relative intensities of Eg(2), Eg(4), and Eg(5) modes in Raman spectra varies as a function of growth mode. The growth mode has no obvious effect on the infrared active Eu(2) and Eu(4) modes, while phonon lifetime of the Eu(3) mode drastically changes. For the Eu(3) mode, the O2-control sample exhibits a significantly reduced broadening factor of 7.6 cm−1 compared with that of the reference (10 cm−1), and the Ga-control (16.6 cm−1) samples. All the three types of samples show similar complex ordinary dielectric functions in the spectral range between 0.5 and 6.5 eV indicating no obvious changes within the band structure by changing the growth mode. [ABSTRACT FROM AUTHOR]

The electrical transport properties of gallium phosphide (GaP) under high pressure (up to 50 GPa) are investigated using in situ impedance‐spectrum and Hall‐effect measurements. A discontinuous resistance is observed at 9.9 GPa because of the pressure‐induced grain boundary effect, whereas the pressure‐induced metallization of GaP occurred at ≈24.6 GPa. The metallization transition is determined by measuring the temperature‐dependent resistance and resistivity, and the transition is observed to be reversible. The main cause of the sharp decrease in the resistance and resistivity is a pressure‐induced structural phase transition at 39.3 GPa, as reflected by the measured Hall parameters. [ABSTRACT FROM AUTHOR]

The thermoelectric cooler (TEC) is a kind of cooling equipment which used to dissipate heat from the devices by Peltier effect. The cooling capacity (Qc) and coefficient of performance (COP) are both significant performance parameters of a thermoelectric cooler. In this article, three-dimensional numerical simulations are carried out by finite element analysis based on the temperature-dependent materials properties. The experimental and geometrical parameters have important effects on the TEC performance which have been analysed, such as electrical current, geometric configuration of thermoelectric leg, Thomson effect, thermal contact resistances and electrical contact resistances. The results show when the Thomson effect is ignored, the maximum difference in the cooling capacity is 7.638 W while the maximum difference in the COP is 0.09. When contact effect is not considered, the maximum difference in the cooling capacity is 22.06 W while the maximum difference in the COP is 0.75. Furthermore, the cooling capacity and COP have also been simultaneously optimized according to the multi-objective genetic algorithm. The best optimal value is obtained making use of TOPSIS (technique for order preference by similarity to an ideal solution) method from Pareto frontier. Investigated on these optimal design parameters which were anticipated to provide real guidance in industry. [ABSTRACT FROM AUTHOR]

The electric forces are the main factor responsible for the characteristic jet path and stretching in electrospinning. The distribution of the electric field determines the quality of the electrospinning. In this paper, a glass flywheel nozzle is designed, and a ring electrode and a capacitor are added between the nozzle and the receiving plate. Theoretical calculations prove the feasibility of the design. The finite element analysis software COMSOL Multiphysics5.0 is used for electric field simulation. The effect of the voltage across the ring electrode and capacitor on the electric field was studied. It is found that when the ring electrode is connected to 10 kV voltage and the voltage across the capacitor is 5 kV, the uniformity of the electric field is significantly improved, which provides a reference for the future optimization of the electrostatic spinning electric field. [ABSTRACT FROM AUTHOR]

The electrical transport properties of indium trisulfide (In2S3) under high pressure were investigated using the in situ Hall-effect and temperature dependent resistivity measurements. Resistivity, Hall coefficient, carrier concentration, and mobility were obtained at pressures up to 41.6 GPa. Pressure induced metallization of In2S3 occurred at approximately 6.8 GPa. This was determined by measuring temperature dependent resistivity. The metallization transition was also determined from compression electrical parameters, and the decompression electrical parameters indicated that the metallization was a reversible transition. The main cause of the sharp decline in resistivity was the increase in carrier concentration at 6.8 GPa. Superconductivity was not observed at the pressures (up to 32.5 GPa) and temperatures (100–300 K) used in the experiment. [ABSTRACT FROM AUTHOR]

As an electroluminescentdevice, the coupling relationship between light-emitting diode (LED) input currents, optical power, and LED junction temperature is a complicated multiphysics process. In this paper, a simplified LED photoelectron-thermal (PET) model by artificial neural network (ANN), which can translatemultiphysics field issue into a singlephysics field problem, ismentioned to study the coupling relationship. In the first, an LED lumens, optical power, and electric power at different temperatures are monitored in a temperature controlling integrating sphere. Then, a backpropagation (BP) ANN is trained by these data to construct an LED Photo-Electron-Thermal (PET) relationship. In addition, LED luminaire thermal analyzing is performed using a finite-element method on the outputs of the BP ANN. Finally, the advantage of this method in terms of saving computing resources and computing time is analyzed by comparing the degrees of freedom in different models. The result shows that at least 6.7 times computing resource are saved by this method, which will reduce the LED thermal management system analyzing time greatly. Finally, the application and extension of this model are discussed. [ABSTRACT FROM PUBLISHER]

A modified model is proposed to describe the dielectric nonlinear behavior in bismuth-based cubic pyrochlores by introducing non-tunable factor into Tagantsev's model. To validate the model, Bi1.5MgNb1.5-x Ti x O7 (BMNT) films were fabricated via chemical solution deposition. Bias field dependence of the permittivity predicted by the modified model agrees well with experimental results. A method for calculating barrier heights for hopping ions is presented based on the modified model. The maximum barrier heights for hopping dipoles in BMNT films derived from the model decrease from 0.206eV to 0.172eV with increasing Ti content from x=0 to x=0.15. [ABSTRACT FROM AUTHOR]

Aiming at the traditional single-needle electrospinning technology, a novel system for the efficient production of multi-production nanofibers through electrospinning is reported. The polymer solution is delivered to the liquid tank, and when the applied voltage exceeds a certain value, a plurality of nozzles is formed. In this paper, the electric field distribution of pinhole cylindrical spinneret structure is studied by simulating the electric field intensity with finite element software. The diameter and yield of the nanofibers were investigated by varying the center electrode voltage and the annular collector radius. The results show that the diameter and productivity of nanofibers are affected by the electric field intensity around the spinneret. Increasing the applied voltage and collecting distance has some significant effect on the diameter of nanofibers. The diameter of nanofibers increases with the concentration of the solution. The maximum yield of nanofibers is 3.1 g/h. It is noteworthy that this method not only greatly improves productivity but also significantly reduces the influence of solvent evaporation during electrospinning. This spinning method provides support for large-scale production of nanofibers in the future. This will be conducive to the further development of electrospinning, increase production, and more accurate control. [ABSTRACT FROM AUTHOR]

In this study, a full-scale three-dimensional trapezoidal thermoelectric cooler model is constructed to study its cooling performance and mechanical reliability using finite element simulation. Temperature dependent material properties are considered in this work. The boundary conditions similar to those in a real experimental environment are applied. The effects of the input electrical current and geometry of the thermoelectric leg on the cooling performance and reliability of a trapezoidal thermoelectric cooler are analyzed, and a comparison is made with a rectangular thermoelectric cooler. The results indicate that increasing the leg height and the variable cross-sectional design of the leg can improve the cooling performance of the trapezoidal thermoelectric cooler. Compared to the original rectangular thermoelectric cooler, the minimum chip temperature was reduced by 0.87% under the trapezoidal thermoelectric cooler with optimized geometry. Furthermore, increasing the leg height enhances the mechanical reliability of the trapezoidal thermoelectric cooler, while the trapezoidal design of the leg reduces its mechanical reliability. The maximum von Mises stress of the leg for the trapezoidal thermoelectric cooler with optimal cooling performance increased by 40.1%. The results of this work provide useful guidance for the structural design of trapezoidal thermoelectric coolers. [ABSTRACT FROM AUTHOR]

The electrical transport properties of SnO 2 (TiO 2 )/MAPbI 3 (MA = CH 3 NH 3 + ) heterojunction interfaces are investigated from ambient pressure to 20 GPa, and the transport properties are calculated by physical parameters such as trap energy density, binding energy, and charge transfer driving force and defect. Based on the partial density of states (PDOS) of the SnO 2 /MAPbI 3 heterojunction interface MAI-termination and PbI 2 -termination, greater charge transfer driving force and higher binding energy are observed, obviously showing the SnO 2 -based heterojunction is more stable. The SnO 2 /MAPbI 3 heterojunction interface possesses stronger electrical transport ability and is less prone to capture electrons compared with the TiO 2 /MAPbI 3 heterojunction interface. The differential charge density spectrum shows that the density is lower in the trap energy level of SnO 2 /MAPbI 3 , whilst the effect of the charge transfer defect is weaker owing to the trap energy level only existing in SnO 2 . The SnO 2 /MAPbI 3 heterostructure interface is less prone to capture electrons. The greater electron concentration difference is attributed to oxygen vacancy (Vo 0 ) in the SnO-like environment, resulting in superior electron transport ability compared with the TiO-like environment., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)