Laser parameters requirement for third-generation ground-based gravitational wave detection
Li Qing-Hui, Li Wei, Sun Yu, Wang Ya-Jun, Tian Long, Chen Li-Rong, Zhang Peng-Fei, Zheng Yao-Hui, et al.
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Gravitational waves (GWs), predicted by the general relativity of Albert Einstein, are ripples in space-time caused by massive accelerating objects. Since the first direct observation of GWs in 2015, more and more binary black hole mergers and neutron star merger were detected by the laser interferometer gravitational-wave observatory (LIGO) and the Virgo interferometric detector. The construction of the third-generation (3G) gravitational wave detector(GWD), whose sensitivity is ten times that of the second-generation (2G) GWD (Advanced LIGO and Virgo), can not only push the gravitational wave astronomy towards the edge of the observable universe, but also test the fundamental laws of physics and study the nature of matter. By utilizing the abandoned underground mines, Shanxi university proposes to construct a 3G ground-based gravitational wave detector with an arm length of 10 km and a strain sensitivity of 10–24 Hz–1/2, improving the location accuracy of wave source by participating in the global GWD network. The construction of 3G GWD has many technical challenges, including ultrahigh large-scale vacuum system, ultrastable seismic isolation system, high-precision control system, high-quality laser and quantum source. Theoretically, the sensitivity of GWD with equal arm length is not limited by the laser source noise. However, in the actual scenario, the sensitivity is limited by the differences in arm length, arm cavity linewidth, arm reflectivity, arm mass, arm power, and the laser parameters. In this work, based on the design sensitivity (10–24 Hz–1/2) of dual-recycled Fabry-Perot Michelson interferometer, we propose the requirements for an ultra low-noise laser, including wavelength, amplitude noise, frequency noise, beam pointing noise and fundamental mode purity. The results show that in order to achieve the design sensitivity at the Fourier frequency of 100 Hz, the wavelength of the laser source should be 1.5 μm, the output power should be higher than 200 W, the amplitude noise should be better than 10–8 Hz–1/2, and the frequency noise should be better than 10–6 Hz/Hz1/2. To achieve the sensitivity of 10–24 Hz–1/2 at 10 Hz analysis frequency, the requirements for the amplitude and frequency noise of the laser source are much more stringent. This study lays a solid foundation for the analysis of laser source noise and the decomposition of interferometer indexes .
Phase regulation of lightwave transmission in inhomogeneous atmospheric medium using plane acoustic field*
Wang Ming-Jun, Wang Wan-Rou, Li Yong-Jun, et al.
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Based on the acousto-optic effect and the Gladstone–Dale relationship, the relationship about variations of the refractive index of the isotropic homogeneous atmospheric medium and the inhomogeneous atmospheric medium with the sound pressure under the disturbance of the plane sound field is derived. Models for the transmission of plane light waves and Laguerre-Gaussian beams through homogeneous atmospheric medium and inhomogeneous atmospheric medium disturbed by plane acoustic waves are established. The results show that the refractive index distribution of the homogeneous atmospheric medium exhibits a homogeneous periodic distribution after being disturbed by the plane sound field. For large-scale angles of longitudinal variation of atmospheric pressure, the plane sound field has little effect on the distribution of the refractive index of the inhomogeneous atmosphere. For small-scale angles, the inhomogeneous atmospheric refractive index gradually decreases with height and fluctuates with the influence of sound pressure. When the plane acoustic wave disturbs the homogeneous atmospheric medium, the isophase plane of the plane light wave will fluctuate significantly due to the influence of the acoustic wave. The phase of the LG beam rotates and always returns to the original phase. When the plane acoustic wave disturbs the inhomogeneous atmospheric medium, the phase change of the plane light wave will change periodically with the change law of the sound wave. The overall optical path is an inclined plane, but due to the disturbance of the sound wave, the optical path will fluctuate. The phase of the LG beam still rotates, but unlike the homogeneous medium, its phase does not return to its original phase due to the change of its refractive index with height.
Effect of transverse magnetic field on magnetogasdynamic flow and heat transfer characteristics in insulated / conductive circular tubes
Zhao Qi-Jin, Mao Bao-Quan, Bai Xiang-Hua, Yang Yu-Ying, Chen Chun-Lin, et al.
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The regulating effect of magnetic field on magnetogasdynamic flow and heat transfer characteristics in circular tubes has important applications in many fields, but there is still a lack of relevant basic research. Considering the conductivity of the tube wall and the insufficient development of turbulence, the physical model and mathematical model of magnetogasdynamic flow in a circular tube under a given transverse magnetic field are constructed, and the numerical algorithm is designed within a theoretical framework of the finite volume method. The effect of factors including Hartman number (Ha) and wall conductivity ratio (C) on the flow and heat transfer characteristics are obtained through analyzing the distributions of velocity, turbulent kinetic energy, and temperature. Furthermore, the regulation mechanism of the transverse magnetic field is discussed by analyzing the spatial distribution of induced current, electromagnetic force and Joule heat. The results show that the distribution of velocity and the distribution of turbulent kinetic energy in the circular tube under a given transverse magnetic field are both anisotropic. The turbulent kinetic energy near the Hartmann boundary layer is much lower than that near the Roberts boundary layer, and the anisotropic distribution of velocity and turbulent kinetic energy become more and more evident with the increase of Ha and the extension of the flow. The transverse magnetic field has a suppression effect on the heat transfer in the tube. For different values of C, the average Nusselt number ($ \overline {Nu} $) shows a first-decreasing-and-then-increasing trend with Ha increasing, that is, there is a “saturation effect” in heat transfer suppression. When the wall conductivity is small (C $\leqslant $ 0.67), the change of $ \overline {Nu} $ under the condition of conductive wall is basically consistent with that of an insulating wall. However, when C exceeds a certain value (C $\geqslant $ 66.67), the $ \overline {Nu} $ under the condition of small Ha increases in comparison with that of the insulating wall, while the $ \overline {Nu} $ decreases under the condition of large Ha . The change of flow characteristics in the circular tube results from the variation of electromagnetic force under the coupling of magnetic field and fluid, while the change of heat transfer characteristics originates from the coupling effect of the suppression of turbulence and the Joule heating. When Ha is small, the suppression effect of the magnetic field on turbulence is dominant, and the $ \overline {Nu} $ decreases with the increase of Ha. When Ha exceeds a certain value (Ha $\geqslant $ 222), the large accumulation of Joule heat in the circular tube enhances the heat transfer, resulting in the increase of the $ \overline {Nu} $ with the continuous increase of Ha.
Research on terahertz real-time near-field spectral imaging
Feng Long-Cheng, Du Chen, Yang Sheng-Xin, Zhang Cai-Hong, Wu Jing-Bo, Fan Ke-Bin, Jin Biao-Bing, Chen Jian, Wu Pei-Heng, et al.
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In this paper, a real-time near-field high-resolution THz (terahertz, THz) spectral imaging system is designed and built by using optical rectification and wave-front tilting to generate strong-field terahertz signals and based on electro-optical detection. The system can switch between large beam THz imaging and tight-focusing THz imaging, which provides a method for implementing the integrated application of the system. Since the imaging is based on the traditional THz time-domain spectroscopy method, the spectral amplitude and phase information of the sample can be obtained simultaneously. The spectral resolution is about 15 GHz. A series of micromachining samples is measured and studied by using the system, and the performance of the imaging system is analyzed by using the micron structure. The results show the superiority of the real-time high-resolution terahertz spectral imaging system in terms of spatial resolution and imaging speed. The real-time imaging frame rate is up to 20 f/s (1200 frames/min) at 1024 pixel × 512 pixel. In the large-field THz imaging, the optimal spatial resolution reaches λ/4 at 1.5 THz. In the tightly focused THz imaging, the optimal spatial resolution reaches λ/12 at 0.82 THz. These properties make the system suitable for the applications in biomedical imaging, bbological effects and other areas .
Cryogenic blackbody calibration source for superconducting terahertz detectors
Wu Man-Jin, Yao Bo-Zhi, Shi Li-Li, Chen Ben-Wen, Wu Jing-Bo, Zhang Cai-Hong, Jin Biao-Bing, Chen Jian, Wu Pei-Heng, et al.
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Blackbody radiation source has been widely used as a calibration source for terahertz (THz) radiometers in recent decades with the applications of THz detection technology in the fields of aerospace, astronomy and remote sensing. We develop a THz blackbody calibration source capable of working in the cryogenic environment and having adjustable radiation power for the calibration of THz superconducting detectors. The ideal blackbody source has an emissivity and absorptivity of 1 and the reflectance coefficient is used to indirectly characterise the performance of the developed blackbody source. In this work, we use a mixture of epoxy, catalyst, carbon black and glass beads as blackbody absorbing material. The real part and imaginary part of the complex dielectric constant of Berkeley blackbody material are extracted from the THz time-domain spectra, and its reflection coefficient is measured. We use this material to design a conical blackbody radiation source , and simulate it as well. The simulation result show that it has low reflectivity below –35 dB in a frequency range of 0.2–0.5 THz. We fabricate a conical blackbody radiation source that is mounted in a dilution refrigerator, and use filters and light-guiding systems to make the detector for measuring the radiation by the THz light of a specific wavelength. The radiation power can be tuned by changing its temperature. The relationship between radiation power and temperature shows a power tuning range of 10–12–10–9 W in the frequency range of 0.2–0.5 THz with a minimum power value of 2.13 × 10–12 W. The designed blackbody radiation source can meet the calibration requirements of THz superconducting detectors, and will contribute to the development and application of highly sensitive THz radiometers.
Research on Error Compensation Method of Photomultiplier Tube Time Measurement
Wang Chong, Dang Wen-Bin, Zhu Bing-Li, Yang Kai, Yang Jia-Hao, Han Jiang-Hao, et al.
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In order to improve the temporal resolution of photomultiplier tubes, our research group has conducted in-depth research on photomultiplier tubes based on microchannel plates that are widely used at present. The time resolution of photomultiplier tube based on microchannel plate is limited by the transit time of photoelectric signal in each part, including the transit time of photoelectric signal in the transmission process of photocathode to microchannel plate, the transit time of photoelectric signal in microchannel plate time, the transit time of the photoelectric signal from the microchannel plate to the detector anode, and the transit time of the photoelectric signal on the anode to the electrode port. The transit time of the whole process has a certain degree of influence on the time information measurement of the optoelectronic signal. In this study, various parameters affecting the time resolution of the photomultiplier tube were analyzed, and it was found that the different positions of the photoelectron signal on the anode would bring errors to the measurement of the arrival time of the signal at the anode, and the photoelectric signal was transmitted to the electrode port at the impact point of the anode The time spent will cause the signal measurement time to lag behind the real time, which indirectly affects the time resolution of the system. Therefore, a specific study was carried out on the time measurement error of the signal on the anode, and it was determined that the difference of the photoelectron signal on the anode position was an important factor causing the signal time measurement error, and a simple and effective error compensation method was proposed. In the research process, the delay line anode is used, and the positional resolution principle of the photoelectric signal is used to obtain the position information of the photoelectron signal on the anode, and the position information is converted into the time information transmitted from the position to the electrode port. The theoretical value of the transit time on the anode is offset, eliminating unnecessary time in the time-of-arrival measurement of the photoelectron signal. The time measurement error of the optoelectronic signal is compensated by this time information. The experimental results show that the error compensation method can effectively improve the time measurement accuracy of optoelectronic signals, and provide solutions and theoretical basis for improving the time resolution of photomultiplier tubes based on microchannel plates.
Influence of sand and dust turbulent atmosphere on the performance of free space quantum communication
Yang Rui-Ke, Li Fu-Jun, Wu Fu-Ping, Lu Fang, Wei Bing, Zhou Ye, et al.
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Quantum communication is a frontier hot field of research at home and abroad, with ideal information security. In order to enable quantum systems in arid and desertified areas to work almost all-weather, it is necessary to carry out research on the attenuation of free-space quantum signal transmission and the impact on communication performance caused by the turbulence atmosphere with carrying sand and dust. Using Mie scattering theory, multiple scattering simulation method and atmospheric turbulence theory, the attenuation of optical wave transmission in sand and dust turbulent atmospheric channels with different visibility, and the influence of multiple scattering and turbulence on attenuation are studied. It shows that the effect of multiple scattering increases with the decrease of visibility, the turbulence effect gradually strengthens with the increase of distance. Based on the quantum amplitude damped channel model, the effects of multiple scattering and turbulence in the sand and dust turbulent atmosphere with different visibility on the quantum channel capacity, fidelity and bit error rate are analyzed. The results show that as the visibility decreases, the multiple scattering effect increases, resulting in a decrease in attenuation and bit error rate, while an increase in channel capacity, fidelity and the boundaries of security key rate. The existence of turbulence in the dust atmosphere will increase the attenuation and bit error rate, but the channel capacity, fidelity and security key rate will decrease. It can be seen that the influence of multiple scattering and turbulence on the communication performance when the visibility of the sand and dust atmosphere is low cannot be ignored. In practical applications, the relevant parameters of quantum communication should be adaptively adjusted according to the visibility and turbulence intensity to improve the probability, efficiency and reliability of quantum communication.
Λ-type electromagnetically induced transparency and absorption by controlling atomic coherence
Pei Li-Ya, Zheng Shi-Yang, Niu Jin-Yan, et al.
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In a Λ-type electromagnetically induced transparency system, it shows that on the Doppler-broadened linear absorption background, as the probe intensity increases, the single narrow line-width window gradually evolves into 3 windows and 2 absorption peaks alternately. In this paper, the mechanism of probe intensity is studied in detail by using the dressed-state model. We propose that when the probe field is not so weak, the atomic Raman coherence can be manipulated by its intensity. For a Doppler-broadened system, there will appear the discontinuous energy variation of the dressed-states, and the large Raman loss due to the double resonance for dressed-states, which are the key factors for the evolution of the transparency window.
Two-dimensional radiation hydrodynamic simulations on the high-speed collisions of high-density plasma jets
Yang Mengqi, Wu Fuyuan, Chen Zhibo, Zhang Yixiang, Chen Yi, Zhang Jinchuan, Chen Zhizhen, Fang Zhifan, Rafael Ramis, Zhang Jie, et al.
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Collisions of plasma jets are common hydrodynamic phenomena in astrophysical and laser-plasma interaction processes. Deriving scaling relationships between colliding plasmas and initial conditions of plasma jets is of great significance for the optimization design and data analysis of the relevant experiments. Double-Cone Ignition (DCI) scheme is an excellent platform for the study of plasma jets collision, since the collision of high-speed, high-density plasma jets can be easily generated and characterized in both simulations and experiments.
In this paper, we employ the upgraded two-dimensional arbitrary Eulerian-Lagrange (ALE) program MULTI-2D to simulate collision process of plasma jets with high speed (≥ 100 km/s) and high density (≥ 10 g/cc). Using the database obtained from the simulations, hydrodynamic scaling laws that describing the collision process of plasma jets are derived with the Bayesian inference method in machine learning. The Bayesian inference method not only has the parameter estimation function of traditional least square method, but also has other potential advantages such as giving the probability distribution of estimated parameters. Numerical results show that the collision of plasma jets with open boundaries is easy to form an isochoric plasma distribution with high-density. Increasing the initial density and velocity of the plasma jets is helpful to enhance the density and temperature of the colliding plasmas. Increasing the initial temperature of plasma jets is beneficial to achieve colliding plasmas with a higher temperature, while leading to a decreased plasma density and pressure after collision. When the initial density, temperature and velocity of the plasma jets are set to be 15 g/cc, 30 eV and 300 km/s, respectively, the colliding plasma density can reach more than 300 g/cc. This is very favorable for the following fast electron heating process in the double-cone ignition (DCI) scheme.
The issue about quantum degeneracy after collision is discussed in this work. Under the typical initial conditions of plasma jets in DCI scheme (100km/s ≤V0≤500km/s, 10eV ≤T0≤ 100eV, 10g/cc ≤ρ0≤ 50g/cc, both quantum degenerate plasma and classical non-degenerate plasma can be obtained with the temperature between 0.3TF (Fermi temperature) and 3TF. By comparing the plasma temperature and Fermi temperature of the collision, the criterion for achieving quantum degenerate plasma or non-degenerate plasma under given initial conditions is obtained with the help of the derived hydrodynamic scaling laws. The criterion shows that higher initial velocity, higher temperature and lower density of plasma jets are required if we want to obtain non-degenerate plasma after collision.
The Crystal Growth and Electronic Transport Property of Ternary Pd-based Tellurides
Qiu Hang-Qiang, Xie Xiao-Meng, Liu Yi, Li Yu-Ke, Xu Xiao-Feng, Jiao Wen-He, et al.
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Ternary transition-metal chalcogenides are a series of compounds that possess both low-dimensional structures and correlated electrons, and display rich electronic ground states according to its different compositions. Among the chalcogen (S, Se, Te), Te has lower electronegativity and heavier atomic mass than S and Se. Thus, transition-metal tellurides take on distinct crystal structures, electronic structures and physical properties. In recent years, we successively discovered novel superconductors Ta4Pd3Te16and Ta3Pd3Te14, topological Dirac semimetals TaTMTe5(TM=Pd, Pt, Ni) and so on, further expanding the investigations of physical properties on the family of tellurides and laying a foundation for exploring the potential applications of them. The basis of further investigations and exploring the potential applications is that obtaining the high-quality crystals with large dimensions. In this work, we first introduce the whole procedures of the single-crystal growth in growing the four ternary Pd-based tellurides (Ta4Pd3Te16, Ta3Pd3Te14, TaPdTe5, and Ta2Pd3Te5) by employing the self-flux method and chemical vapor transport method, and then gives the chemical reaction equations in chemical vapor transport. The superconducting transition widths of the Ta4Pd3Te16 and Ta3Pd3Te14crystals are as small as 0.61K and 0.13K, and by fitting the temperature-dependent resistivity of the topological insulator Ta2Pd3Te5, the band gap is derived to be 23.37 meV. Finally, we comparatively analyse the crystal-growth processes of the four ternary Pd-based tellurides by employing the flux method, which can provide inspiration and reference for growing the crystals of other transition-metal tellurides by employing the similar methods.
Synthesis of h-BN/diamond heterojunctions and its electrical characteristics
Yanwei Jia, Jian He, Meng He, Xiaohua Zhu, Shangman Zhao, Jinlong Liu, Liangxian Chen, Junjun Wei, Chengming Li, et al.
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Conductive channels on the surface of hydrogen terminated diamonds with two-dimensional h-BN passivation exhibit high hole mobility. However, the current h-BN passivated diamond mainly uses the method of mechanical peeling, which cannot achieve a large-size conductive channel and is difficult to meet the actual application requirements. In this study, the effect of classical transfer h-BN on the conductive channel on the surface of hydrogen terminated diamond was studied. High-quality single crystal diamonds are epitaxially grown by microwave chemical vapor deposition (MPCVD) and hydrogen terminated diamonds were obtained by surface hydrogenation treatment. H-BN/H-diamond heterojunctions with different layers of h-BN were prepared by wetting transfer, and the characteristics of channel carrier transport were systematically studied. The results show that the channel conductivity is significantly enhanced after h-BN transfer, and with the increase of h-BN thickness, the enhancement effect of channel conductivity tends to be stable. The transfer of multilayer h-BN can increase the carrier density on the surface of hydrogen terminated diamond by nearly 2 times, and the square resistance is reduced to 50%. The current results show that the h-BN/H-diamond heterojunction may have a transfer doping effect, resulting in a significant increase in carrier density. With the increase of the channel carrier density, the channel mobility on the surface of the h-BN passivated diamond remains stable. H-BN absorbs on the surface of the diamond, so that the negative charge originally on the surface of the hydrogen termination moves to the surface of h-BN, and the distance of action increases, weakening the coupling of the negative charge of the hole and the negative charge of the dielectric layer in the conductive channel of the hydrogen terminated diamond, which makes the mobility stable.
Study on spectral characteristics of low excited state of strontium monobromide molecule
WU Donglan, GUO Ziyi, ZHOU Junjie, RUAN Wen, ZENG Xuefeng, XIE Andong, et al.
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The electronic structure and single point energy of 14 lowest electronic states of 88Sr79Br molecule are optimized by using internal contraction multi-reference configuration interaction method and relativistic effective core pseudo-potential basis. Because 88Sr79Br molecule belongs to heavy element system, the single point energy must be corrected to obtain more accurate spectral parameters. Therefore, Davidson is introduced to correct the energy inconsistency, nuclear valence correlation is used to correct the electron correlation effect of inner shell and valence shell, and the relativistic scalar effect is corrected by calculating the third-order Douglas-Kroll-Hess Hamilton single electron integral. According to the single point energy calculated by the modified optimization, the potential energy curves, electric dipole moments and transition dipole moments of 14 lowest electronic states are obtained. Using the latest LEVEL8.0 program to fit the modified potential energy curve, the spectral constants, molecular constants and vibration energy levels of 5 lowest bound states of 88Sr79Br molecule are given. In order to explain the changing trend of spectral constants of homologous compounds, the spectral parameters of each compound are compared and analyzed in this paper. At the same time, the vibration energy levels and molecular constants of 88Sr81Br molecule are also fitted and calculated for analysis the influence of isotopes. Comparative analysis shows that the results of 88Sr79Br molecule are in better agreement with the experimental values. Finally, the Franck-Condon factors are gained by fitting the optimized single point energy and transition dipole moment of 88Sr79Br molecule. The transition band with the largest factor and obvious diagonalization is selected by analyzing the Franck-Condon factor of each transition band, and whether it meets the conditions for selecting laser cooling molecular system is judged. The radiation lifetimes of the lowest two excited states to the ground state transitions are calculated by combining the transition dipole moment, Franck-Condon factor, single point energy and vibration energy level of each electronic state. The results of this paper are in good agreement with the experimental values, which shows that the method in this paper is reliable. These spectral characteristic parameters provide theoretical support for further experimental measurement and construction of molecular laser cooling scheme of 88Sr79Br molecule.
Mechanisms and effects of metalloid elements addition on glass-forming ability and magnetic properties of Co-Y-B metallic glasses
Ma Shuang, Hao Wei-ye, Wang Xu-dong, Zhang Wei, Yao Man, et al.
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Co-based metallic glasses (MGs) are a new class of soft magnetic materials, which have promising application value in high-frequency fields due to their high magnetic permeability and low coercivity. However, these kinds of MGs have poor glass-formation ability (GFA) and relatively low saturated magnetic flux density, so their application scope is limited. The atomic size of metalloid elements M (B, C, Si, and P) is small, which can easily enter the gap between atoms, and there is a relatively large negative enthalpy of mixing between metalloid elements and metal elements. Therefore, alloying with metalloid elements M is an effective method to improve the GFA while maintaining superior soft magnetic properties for Co-based MGs. In this paper, the formation process of Co72Y3B15M10 (M=B, C, Si, P) MGs was simulated by ab initio molecular dynamics (AIMD) methods, and the effects of the addition of metalloid elements M (C, Si, P) on the GFA and magnetic properties of Co-Y-B MGs have been investigated. It is devoted to analyzing the relationship between local atomic structures and properties from different perspectives at the atomic level.
According to the results of the characterization parameters of local atomic structures (pair distribution function, coordination numbers, chemical short-range order, Voronoi polyhedron index, local five-fold symmetry, and mean square displacement), it is found that the GFA of the four alloys is different due to their different local atomic structures. Co72Y3B15C10 and Co72Y3B15P10 alloys possess a higher fraction of prism structures, and the solute segregation between B/C-C and B/P-P atoms is weak, resulting in the higher atomic diffusivity in the supercooled state (1100 K), and hence weaken the GFA of the alloys. The Co72Y3B15Si10 alloy has a higher fraction of icosahedral-like structures, the stronger attraction between Co-Si atoms and solute segregation between B/Si-Si atoms reduce the atomic diffusivity in the supercooled state, whilst improving the thermal stability of alloy melts, stability of the local atomic structures, and the degree of five-fold symmetry, thereby increasing the GFA. Based on the analysis of the local atomic structures, it is speculated that the addition of Si is beneficial for enhancing the GFA, while the addition of C or P will reduce the GFA, that is, the GFA of the four alloys decreases in the order of Co72Y3B15Si10 > Co72Y3B25 > Co72Y3B15P10 > Co72Y3B15C10. In terms of magnetic properties, with metalloid elements M addition, the total magnetic moment of Co72Y3B15M10 (M=B, C, Si, P) alloys decreases as follows Co72Y3B25 > Co72Y3B15Si10 > Co72Y3B15C10 > Co72Y3B15P10. The stronger p-d orbital hybridization between Co-Si atoms enhances the ferromagnetic exchange interaction, leading to the total magnetic moment less affected by Si addition.
Interface performance of Bi2Te3-based micro thermoelectric devices optimized synergistically by surface modification engineering
Tang Hao, Bai Hui, Lü Jia-Nan, Hua Si-Heng, Yan Yong-Gao, Yang Dong-Wang, Wu Jin-Song, Su Xian-Li, Tang Xin-Feng, et al.
Abstract +
The miniaturization of thermoelectric devices raises a strong requirement for the excellent interfacial properties of thermoelectric elements. Thus, achieving a heterogeneous interface with low interfacial contact resistivity and high interfacial bonding strength is a prerequisite for the successful fabrication of high-performance and high-reliability Bi2Te3-based micro thermoelectric devices. In this work, we adopt the acid pickling method to modify the surface structure of Bi0.4Sb1.6Te3 material to synergistically optimize the interfacial properties of Bi0.4Sb1.6Te3/Ni thermoelectric elements. The acid pickling process effectively modulates the work function of Bi0.4Sb1.6Te3 material, which dramatically reduces the contact barrier height of Ni/Bi0.4Sb1.6Te3 heterojunction from 0.22 to 0.02 eV. As a consequence, the corresponding interfacial contact resistivity of the element is greatly reduced from 14.2 to 0.22 μΩ·cm2. Moreover, the acid pickling process effectively adjusts the surface roughness of the matrix, forming a V-shaped pit of 2–5 μm in depth on the substrate surface and leading to a pinning effect. This significantly enhances the physical bonding between the material surface and the Ni layer, which, together with the metallurgical bond formed by the interfacial diffusion reaction zone of about 50-nm-thick Ni/Bi0.4Sb1.6Te3, greatly enhances the interfacial bond strength from 7.14 to 22.34 MPa. The excellent interfacial properties are further validated by the micro-thermoelectric devices. The maximum cooling temperature difference of 4.7 mm× 4.9 mm micro thermoelectric device fabricated by this process achieves 56.5 K, with hot side temperature setting at 300 K, and the maximum output power reaches 882 μW under the temperature gradient of 10 K. This work provides a new strategy for realizing the synergetic optimization of interfacial properties and opens up a new avenue for improving the performance of micro thermoelectric devices.
OKMC simulation of matrix defect evolution of Fe-C Alloy under irradiation
Shen Zi-Qin, Ai De-Sheng, Lü Sha-Sha, Gao Jie, Lai Wen-Sheng, Li Zheng-Cao, et al.
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The effects of carbon traps in Fe-C alloys on matrix defects and the evolutions of matrix defects in Fe-C alloys under irradiation are investigated in this paper. The object kinetic Monte Carlo (OKMC) modeling is used to establish a bridge between the micro-computational simulation data and the macro-experimental data. The simulation results verify the evolution of the carbon (C)-vacancy (Vac) complex under ideal conditions, and at relatively low temperatures, the complex is mainly C-Vac2. Under the assumption of complex traps, the evolution of matrix defects in Fe-C systems under irradiation is simulated in this work. It is verified that the carbon vacancy complex has an obvious trapping effect on matrix defects, and the simulation results of evolution simulation of matrix defects in the Fe-C system under irradiation are consistent with the experimental results. Furthermore, the effective approximate parameters used in the simulation are compared and discussed. The present research can provide basic support for the research on the evolution of iron-based alloy irradiation defects.
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