Li Wan-jiao, Guan Yun-Xia, Bao Xi, Wang Cheng, Song Jia-Yi, Xu Shuang, Peng ke-Ao, Chen Li-jia, Niu Lian-Bin
Tandem organic electroluminescent devices (OLEDs) have attracted widespread attention due to their long lifetime and high current efficiency. In this study, a double-emitting unit tandem OLED was fabricated using Alq3/HAT-CN as an interconnect layer. Its photovoltaic properties and exciton regulation mechanism were investigated. The results show that the luminance (11189.86 cd/m2) and efficiency (13.85 cd/A) of the tandem OLED reached 2.7 times that of the single EL unit OLED (luminance and efficiency of 4007.14 cd/m2 and 5.00 cd/A, respectively) at a current density of 80 mA/cm2. This proves that Alq3/HAT-CN is an efficient interconnect layer. At room temperature, the polaron pair undergoes intersystem crossing (ISC) due to hyperfine interaction (HFI) when a magnetic field is applied to the device. This increases the concentration of the triplet exciton (T1), which favours charg the scattering. The result is a rapid increase in the low magnetic field and a slow increase in the high magnetic field of the MEL. When the injection current strength is constant, there is less uncompounded charge in the Alq3/HAT-CN device than in other connected layer devices. Triplet-charge annihilation (TQA) is weak, resulting in a relative increase in the concentration of T1, which is not involved in TQA. This suppresses the ISC and leads to a minimal increase in the MEL. As the current strength increases, the T1 concentration increases, causing TQA toincrease and ISC to decrease. Since TQA is related to charge and T1 concentration, lowering the temperature decreases the carrier mobility in the device, resulting in a relative decrease in charge concentration and a weakening of TQA. Lowering the temperature decreases the quenching of thermal phonons and increases the concentration of T1 while extending its lifetime, resulting in enhanced triplet-triplet annihilation (TTA). At low temperatures, the high magnetic field shape of the MEL changes from slowly increasing to rapidly decrease. Therefore, the concentration of T1 can be regulated by varying the current strength and temperature, which further affects the strength of ISC, TQA and TTA, and the luminescence and efficiency of the device can be effectively improved by reducing TQA and ISC. This work is important for the understanding of the luminescence mechanism of small molecule tandem devices and investigating the investigation of the mechanism for improving their photovoltaic performance.
{"title":"Investigation of the exciton regulation mechanism of Alq3/HAT-CN tandem electroluminescent devices","authors":"Li Wan-jiao, Guan Yun-Xia, Bao Xi, Wang Cheng, Song Jia-Yi, Xu Shuang, Peng ke-Ao, Chen Li-jia, Niu Lian-Bin","doi":"10.7498/aps.72.20230973","DOIUrl":"https://doi.org/10.7498/aps.72.20230973","url":null,"abstract":"Tandem organic electroluminescent devices (OLEDs) have attracted widespread attention due to their long lifetime and high current efficiency. In this study, a double-emitting unit tandem OLED was fabricated using Alq3/HAT-CN as an interconnect layer. Its photovoltaic properties and exciton regulation mechanism were investigated. The results show that the luminance (11189.86 cd/m2) and efficiency (13.85 cd/A) of the tandem OLED reached 2.7 times that of the single EL unit OLED (luminance and efficiency of 4007.14 cd/m2 and 5.00 cd/A, respectively) at a current density of 80 mA/cm2. This proves that Alq3/HAT-CN is an efficient interconnect layer. At room temperature, the polaron pair undergoes intersystem crossing (ISC) due to hyperfine interaction (HFI) when a magnetic field is applied to the device. This increases the concentration of the triplet exciton (T1), which favours charg the scattering. The result is a rapid increase in the low magnetic field and a slow increase in the high magnetic field of the MEL. When the injection current strength is constant, there is less uncompounded charge in the Alq3/HAT-CN device than in other connected layer devices. Triplet-charge annihilation (TQA) is weak, resulting in a relative increase in the concentration of T1, which is not involved in TQA. This suppresses the ISC and leads to a minimal increase in the MEL. As the current strength increases, the T1 concentration increases, causing TQA toincrease and ISC to decrease. Since TQA is related to charge and T1 concentration, lowering the temperature decreases the carrier mobility in the device, resulting in a relative decrease in charge concentration and a weakening of TQA. Lowering the temperature decreases the quenching of thermal phonons and increases the concentration of T1 while extending its lifetime, resulting in enhanced triplet-triplet annihilation (TTA). At low temperatures, the high magnetic field shape of the MEL changes from slowly increasing to rapidly decrease. Therefore, the concentration of T1 can be regulated by varying the current strength and temperature, which further affects the strength of ISC, TQA and TTA, and the luminescence and efficiency of the device can be effectively improved by reducing TQA and ISC. This work is important for the understanding of the luminescence mechanism of small molecule tandem devices and investigating the investigation of the mechanism for improving their photovoltaic performance.","PeriodicalId":6995,"journal":{"name":"物理学报","volume":"31 1","pages":""},"PeriodicalIF":1.0,"publicationDate":"2023-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"76449979","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
We used admittance spectroscopy to characterize the energy distribution of defects in CIGSe solar cells before and after annealing to investigate the mechanism of the annealing process improving battery performance. In this article, we annealed the prepared CIGSe solar cells in compressed air at 150℃ for 10 minutes. We conducted dark I-V, C-V, admittance spectroscopy, and illumination I-V tests on CIGSe solar cells before and after annealing to characterize the changes in battery performance before and after annealing. The test results of dark I-V characteristics showed that the reverse dark current of CIGSe solar cells decreased by about an order of magnitude after annealing, and the ideal factor of the cells also decreased from 2.16 before annealing to 1.85 after annealing. This means that the annealing process reduces the recombination of carriers in CIGSe solar cells. Under reverse bias, the capacitance of CIGSe solar cells is higher than that after annealing, and their C-V characteristics are linearly fitted with 1/C2 vs. V. The fitting results show that the slope of the curve increases after annealing, which means that the annealing process leads to a decrease in the free carrier concentration in the absorption layer of CIGSe solar cells, that is, a decrease in the carrier concentration contributed by defects after annealing. In addition, the built-in potentials before and after annealing of CIGSe solar cells were also obtained through fitting, which are 0.52V and 0.64V, respectively. The admittance spectrum test results of CIGSe solar cells before and after annealing showed that the defect activation energy in the absorption layer significantly decreased after annealing, but the defect concentration remained almost unchanged. The decrease in defect activation energy means that the Shockley Read Hall (SRH) recombination probability of defects in copper indium gallium selenium solar cells is reduced. In addition, the test results of the optical I-V characteristics of the battery indicate that the open circuit voltage and parallel resistance of the battery significantly increase after annealing, which is consistent with the test results of the dark I-V characteristics, C-V characteristics, and admittance spectroscopy of the solar cell. Therefore, the annealing process of CIGSe solar cells leads to a weakening of the SRH recombination of carriers in the absorption layer of the battery, thereby improving the performance of the solar cell's performances.
利用导纳光谱对CIGSe太阳能电池退火前后缺陷的能量分布进行了表征，探讨了退火工艺改善电池性能的机理。在本文中，我们将制备好的CIGSe太阳能电池在压缩空气中150℃退火10分钟。我们对退火前后的CIGSe太阳能电池进行了暗I-V、C-V、导纳光谱和照明I-V测试，表征了退火前后电池性能的变化。暗I-V特性测试结果表明，CIGSe太阳能电池的反向暗电流在退火后下降了约一个数量级，电池的理想因子也从退火前的2.16下降到退火后的1.85。这意味着退火过程减少了载流子在CIGSe太阳能电池中的复合。在反向偏压下，CIGSe太阳电池的电容高于退火后的电容，其C-V特性与1/C2 vs. v呈线性拟合。拟合结果表明，退火后曲线斜率增大，说明退火过程导致CIGSe太阳电池吸收层中自由载流子浓度降低，即退火后缺陷贡献的载流子浓度降低。此外，通过拟合得到了CIGSe太阳能电池退火前后的内嵌电势，分别为0.52V和0.64V。退火前后CIGSe太阳电池的导纳谱测试结果表明，退火后吸收层缺陷活化能明显降低，但缺陷浓度基本保持不变。缺陷激活能的降低意味着铜铟镓硒太阳电池中缺陷的Shockley Read Hall (SRH)重组概率降低。此外，该电池的光学I-V特性测试结果表明，退火后电池的开路电压和并联电阻显著增加，这与该太阳能电池的暗I-V特性、C-V特性和导纳光谱测试结果一致。因此，CIGSe太阳能电池的退火工艺导致电池吸收层载流子的SRH复合减弱，从而提高了太阳能电池的性能。
{"title":"Characterization of the Defect in CIGS Solar Cell by Admittance Spectroscopy","authors":"Rui Jia, Xiaorang Tian","doi":"10.7498/aps.72.20230292","DOIUrl":"https://doi.org/10.7498/aps.72.20230292","url":null,"abstract":"We used admittance spectroscopy to characterize the energy distribution of defects in CIGSe solar cells before and after annealing to investigate the mechanism of the annealing process improving battery performance. In this article, we annealed the prepared CIGSe solar cells in compressed air at 150℃ for 10 minutes. We conducted dark I-V, C-V, admittance spectroscopy, and illumination I-V tests on CIGSe solar cells before and after annealing to characterize the changes in battery performance before and after annealing. The test results of dark I-V characteristics showed that the reverse dark current of CIGSe solar cells decreased by about an order of magnitude after annealing, and the ideal factor of the cells also decreased from 2.16 before annealing to 1.85 after annealing. This means that the annealing process reduces the recombination of carriers in CIGSe solar cells. Under reverse bias, the capacitance of CIGSe solar cells is higher than that after annealing, and their C-V characteristics are linearly fitted with 1/C2 vs. V. The fitting results show that the slope of the curve increases after annealing, which means that the annealing process leads to a decrease in the free carrier concentration in the absorption layer of CIGSe solar cells, that is, a decrease in the carrier concentration contributed by defects after annealing. In addition, the built-in potentials before and after annealing of CIGSe solar cells were also obtained through fitting, which are 0.52V and 0.64V, respectively. The admittance spectrum test results of CIGSe solar cells before and after annealing showed that the defect activation energy in the absorption layer significantly decreased after annealing, but the defect concentration remained almost unchanged. The decrease in defect activation energy means that the Shockley Read Hall (SRH) recombination probability of defects in copper indium gallium selenium solar cells is reduced. In addition, the test results of the optical I-V characteristics of the battery indicate that the open circuit voltage and parallel resistance of the battery significantly increase after annealing, which is consistent with the test results of the dark I-V characteristics, C-V characteristics, and admittance spectroscopy of the solar cell. Therefore, the annealing process of CIGSe solar cells leads to a weakening of the SRH recombination of carriers in the absorption layer of the battery, thereby improving the performance of the solar cell's performances.","PeriodicalId":6995,"journal":{"name":"物理学报","volume":"332 1","pages":""},"PeriodicalIF":1.0,"publicationDate":"2023-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"76588495","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Convergence-zone (CZ) sound propagation is one of the most important hydro-acoustic phenomenons in the deep ocean, that allows long-range transmission of acoustic signals with high intensity and low distortion. Accurate prediction and identification of CZ is of great significance for remote detection or communication, but there is still no standard definition in sense of mathematical physics for convergence zone. Especially on the issue of systematic error of computation introduced by the earth curvature, with no exact propagation model, curvature-correction methods always lead to imprecision of the ray phase. In previous research work, we realize that the Riemannian geometric meaning of the caustics phenomena caused by ray convergence is that the caustic points are equivalent to the conjugate points, which form on geodesics with positive section curvature. In this paper, we presents a spherical layered acoustic ray propagation model for CZ based on the Riemannian geometric theory. With direct computation in the curved manifolds of the earth instead of in the European space, a Riemannian geometric description of CZ is provided for the first time, on the basis of comprehensive analysis about it’s characteristics. And it shows that the mathematical expression of section curvature adds an additional item $frac{{hat c(l)hat c'(l)}}{l}$ after considering the earth curvature, which reflects the influence of the earth curvature on the ray topology and CZ. By means of Jacobi field theory of Riemannian geometry, computational rule and methods of the location and distance of CZ in deep water are proposed. Taking the Munk sound speed profile as an typical example, the new Riemannian geometric model of CZ is compared with the normal mode and curvature-correction method. Simulation and analysis shows that the Riemannian geometric model of CZ given in this paper is a mathematical form naturally considering the earth curvature with theoretical accuracy, which lays more solid scientific foundations for research of convergence zone. Moreover, we find that the location of CZ moves towards sound source when considering the earth curvature, and the width of CZ near the sea surface increases first and then decreases with sound propagation. The maximum width is about 20 km and the minimum is about 4 km.
{"title":"Riemannian Geometric Modeling of Underwater Acoustic Ray Propagation · Application——Riemannian Geometric Model of Convergence Zone in the Deep Ocean","authors":"Ma S Q, Guo X J, Zhang L L, Lan Q, Huang C X","doi":"10.7498/aps.72.20221495","DOIUrl":"https://doi.org/10.7498/aps.72.20221495","url":null,"abstract":"Convergence-zone (CZ) sound propagation is one of the most important hydro-acoustic phenomenons in the deep ocean, that allows long-range transmission of acoustic signals with high intensity and low distortion. Accurate prediction and identification of CZ is of great significance for remote detection or communication, but there is still no standard definition in sense of mathematical physics for convergence zone. Especially on the issue of systematic error of computation introduced by the earth curvature, with no exact propagation model, curvature-correction methods always lead to imprecision of the ray phase. In previous research work, we realize that the Riemannian geometric meaning of the caustics phenomena caused by ray convergence is that the caustic points are equivalent to the conjugate points, which form on geodesics with positive section curvature. In this paper, we presents a spherical layered acoustic ray propagation model for CZ based on the Riemannian geometric theory. With direct computation in the curved manifolds of the earth instead of in the European space, a Riemannian geometric description of CZ is provided for the first time, on the basis of comprehensive analysis about it’s characteristics. And it shows that the mathematical expression of section curvature adds an additional item $frac{{hat c(l)hat c'(l)}}{l}$ after considering the earth curvature, which reflects the influence of the earth curvature on the ray topology and CZ. By means of Jacobi field theory of Riemannian geometry, computational rule and methods of the location and distance of CZ in deep water are proposed. Taking the Munk sound speed profile as an typical example, the new Riemannian geometric model of CZ is compared with the normal mode and curvature-correction method. Simulation and analysis shows that the Riemannian geometric model of CZ given in this paper is a mathematical form naturally considering the earth curvature with theoretical accuracy, which lays more solid scientific foundations for research of convergence zone. Moreover, we find that the location of CZ moves towards sound source when considering the earth curvature, and the width of CZ near the sea surface increases first and then decreases with sound propagation. The maximum width is about 20 km and the minimum is about 4 km.","PeriodicalId":6995,"journal":{"name":"物理学报","volume":"462 1","pages":""},"PeriodicalIF":1.0,"publicationDate":"2023-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"76691060","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Underwater sound propagation models are generally established from the extrinsic perspective, that is, embedding acoustic channels in Euclidean space with fixed coordinate system. Riemannian geometry is intrinsic for curved space, that can describe the essential properties of background manifolds. The underwater acoustic Gaussian beam was originally adopted from seismology. Till now it is the most important method used in acoustic ray based modeling and applications. Due to the advantages of Gaussian beam method over the traditional ray counterpart, it is the mainstream technology of ray propagation computational software such as the famous Bellhop. With the assumption of Euclidean space, it is hard to grasp the naturally curved characteristics of the Gaussian beam. In this paper, we propose the Riemannian geometry theory of underwater acoustic ray propagation, and obtain the following results : (1) The Riemannian geometric intrinsic forms of the eikonal equation, paraxial ray equation and the Gaussian beam under radially symmetric acoustic propagation environments are established, that provide a Riemannian geometric interpretation of the Gaussian beam. In fact, the underwater acoustic eikonal equation is equivalent to the geodesic equation in Riemannian manifolds, and the intrinsic geometric spreading of the Gaussian beam corresponds to the lateral deviation of geodesic curve along the Jacobian field. (2) Some geometric and topological properties of acoustic ray about conjugate points and section curvature are acquired by the Jacobi field theory, indicating that the convergence of ray beam corresponds to the intersection of geodesics at the conjugate point with positive section curvature. (3)The specific modeling method under horizontal stratified and distance-related environment is presented using the above theory. And we point out that the method proposed here is also applicable to other radially symmetric acoustic propagation environments. (4) Simulation and comparative analysis of three typical underwater acoustic propagation examples, confirms the feasibility of the Riemannian geometric model for underwater acoustic propagation. And shows that the Riemannian geometric model has exact mathematical physics meaning over the Euclidean space method adopted by the Bellhop model. The basic theory given in this paper can be extended to curved surface, three-dimensional and other complex propagation environments. And especially it lays a theoretical foundation for the further research of long-range acoustic propagation considering curvature of the earth.
{"title":"Riemannian Geometric Modeling of Underwater Acoustic Ray Propagation · Basic Theory","authors":"Guo X J, Ma S Q, Zhang L L, Lan Q, Huang C X","doi":"10.7498/aps.72.20221451","DOIUrl":"https://doi.org/10.7498/aps.72.20221451","url":null,"abstract":"Underwater sound propagation models are generally established from the extrinsic perspective, that is, embedding acoustic channels in Euclidean space with fixed coordinate system. Riemannian geometry is intrinsic for curved space, that can describe the essential properties of background manifolds. The underwater acoustic Gaussian beam was originally adopted from seismology. Till now it is the most important method used in acoustic ray based modeling and applications. Due to the advantages of Gaussian beam method over the traditional ray counterpart, it is the mainstream technology of ray propagation computational software such as the famous Bellhop. With the assumption of Euclidean space, it is hard to grasp the naturally curved characteristics of the Gaussian beam. In this paper, we propose the Riemannian geometry theory of underwater acoustic ray propagation, and obtain the following results : (1) The Riemannian geometric intrinsic forms of the eikonal equation, paraxial ray equation and the Gaussian beam under radially symmetric acoustic propagation environments are established, that provide a Riemannian geometric interpretation of the Gaussian beam. In fact, the underwater acoustic eikonal equation is equivalent to the geodesic equation in Riemannian manifolds, and the intrinsic geometric spreading of the Gaussian beam corresponds to the lateral deviation of geodesic curve along the Jacobian field. (2) Some geometric and topological properties of acoustic ray about conjugate points and section curvature are acquired by the Jacobi field theory, indicating that the convergence of ray beam corresponds to the intersection of geodesics at the conjugate point with positive section curvature. (3)The specific modeling method under horizontal stratified and distance-related environment is presented using the above theory. And we point out that the method proposed here is also applicable to other radially symmetric acoustic propagation environments. (4) Simulation and comparative analysis of three typical underwater acoustic propagation examples, confirms the feasibility of the Riemannian geometric model for underwater acoustic propagation. And shows that the Riemannian geometric model has exact mathematical physics meaning over the Euclidean space method adopted by the Bellhop model. The basic theory given in this paper can be extended to curved surface, three-dimensional and other complex propagation environments. And especially it lays a theoretical foundation for the further research of long-range acoustic propagation considering curvature of the earth.","PeriodicalId":6995,"journal":{"name":"物理学报","volume":"2 1","pages":""},"PeriodicalIF":1.0,"publicationDate":"2023-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"76898557","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
High-energy nuclear physics aims at exploring and understanding the physics of matter constituted by quark and gluon. However, it is intrinsically diffculty to simulate high-energy nuclear physics from the first principle based on quantum chromodynamics with classical computers. In recent years, quantum computing has received intensive attention because it is expected to provide an ultimate solution for simulating high-energy nuclear physics. In this paper, we firstly review recent advances in quantum simulation of high-energy nuclear physics. Then some standard quantum algorithms will be introduced, such as state preparation and measurements of light-cone correlation function. Lastly, we demonstrate the advantage of quantum computing for solving the real-time evolution and the sign problems by studying hadronic scattering amplitude and phase structure of finitetemperature and finite-density matter, respectively.
{"title":"High-energy nuclear physics by quantum computing","authors":"Li Tian-Yin, Xing Hong-Xi, Zhang Dan-Bo","doi":"10.7498/aps.72.20230907","DOIUrl":"https://doi.org/10.7498/aps.72.20230907","url":null,"abstract":"High-energy nuclear physics aims at exploring and understanding the physics of matter constituted by quark and gluon. However, it is intrinsically diffculty to simulate high-energy nuclear physics from the first principle based on quantum chromodynamics with classical computers. In recent years, quantum computing has received intensive attention because it is expected to provide an ultimate solution for simulating high-energy nuclear physics. In this paper, we firstly review recent advances in quantum simulation of high-energy nuclear physics. Then some standard quantum algorithms will be introduced, such as state preparation and measurements of light-cone correlation function. Lastly, we demonstrate the advantage of quantum computing for solving the real-time evolution and the sign problems by studying hadronic scattering amplitude and phase structure of finitetemperature and finite-density matter, respectively.","PeriodicalId":6995,"journal":{"name":"物理学报","volume":"2 1","pages":""},"PeriodicalIF":1.0,"publicationDate":"2023-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"72706742","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Wave-wave resonance mechanism plays a fundamental and prominent role in the process of energy transmission and distribution in whether microscopic or macroscopic materials. For the most extensive and intuitive ocean surface wave motion on earth, it is bound to be even more so. Can we extract the general wave-wave resonance law from it? Especially the most special and brief resonance one for single wave train. To this end, according to a set of classical methods proposed by Phillips for initiating modern water wave dynamics with the specific 4-wave resonance conditions, and starting from the basic governing equations of ocean deep-water surface capillary-gravity waves, the first-order differential equation of the Fourier component of free surface displacement and the second-, third- and fourth-order integral differential ones which are becoming more and more complex but tend to be complete are given in turn by the Fourier-Stieltjes transformation and perturbation method. Under a set of symbol system which are self-created, self-evident and concise, these equations are solved in turn to obtain the first-order free surface displacement of single wave train, the Fourier coefficients of the second-, third- and fourth-order non-resonant and resonant free surface ones and the second-, third- and fourth-order resonant conditions, thus leading to the general nth-order self-resonance law of single wave train. This completely reveals the rich connotation of single wave resonance dynamics of ocean surface capillary-gravity waves, effectively expands the application range of the classical single wave resonance solutions given by Phillips for ocean surface gravity waves, lays the foundation for depicting single and multiple resonance interaction mechanisms of double and multi-wave trains of ocean surface waves, and so provides a typical example for the exploration of single-wave resonance law in all wave fields.
{"title":"The nth-order self-resonance law of single wave train for surface capillary-gravity waves in deep water","authors":"Huang Hu, Tian Ze-Bing","doi":"10.7498/aps.72.20221281","DOIUrl":"https://doi.org/10.7498/aps.72.20221281","url":null,"abstract":"Wave-wave resonance mechanism plays a fundamental and prominent role in the process of energy transmission and distribution in whether microscopic or macroscopic materials. For the most extensive and intuitive ocean surface wave motion on earth, it is bound to be even more so. Can we extract the general wave-wave resonance law from it? Especially the most special and brief resonance one for single wave train. To this end, according to a set of classical methods proposed by Phillips for initiating modern water wave dynamics with the specific 4-wave resonance conditions, and starting from the basic governing equations of ocean deep-water surface capillary-gravity waves, the first-order differential equation of the Fourier component of free surface displacement and the second-, third- and fourth-order integral differential ones which are becoming more and more complex but tend to be complete are given in turn by the Fourier-Stieltjes transformation and perturbation method. Under a set of symbol system which are self-created, self-evident and concise, these equations are solved in turn to obtain the first-order free surface displacement of single wave train, the Fourier coefficients of the second-, third- and fourth-order non-resonant and resonant free surface ones and the second-, third- and fourth-order resonant conditions, thus leading to the general nth-order self-resonance law of single wave train. This completely reveals the rich connotation of single wave resonance dynamics of ocean surface capillary-gravity waves, effectively expands the application range of the classical single wave resonance solutions given by Phillips for ocean surface gravity waves, lays the foundation for depicting single and multiple resonance interaction mechanisms of double and multi-wave trains of ocean surface waves, and so provides a typical example for the exploration of single-wave resonance law in all wave fields.","PeriodicalId":6995,"journal":{"name":"物理学报","volume":"34 1","pages":""},"PeriodicalIF":1.0,"publicationDate":"2023-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"72975561","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Compositing the solid-liquid phase change material with the metal foam is an effective way to improve the heat transfer performance of the latent heat thermal energy storage system. In this paper, the three-dimensional numerical structure of the copper foam is reconstructed by using the micro CT, and then the pore-scale numerical simulation of the melting process in a cubic cavity filled with the phase change material composited with the copper foam is performed via the lattice Boltzmann method. The effects of the hollow skeleton on the melting process are discussed in detail under different Rayleigh numbers and ratios of thermal conductivity between the copper foam and the phase change material. The results show that, compared with the solid skeleton copper foam, the hollow skeleton copper foam leads to a lower average Nusselt number along the left wall at the early stage of the melting process, together with a slower melting rate and a higher energy storage efficiency η. Compared with the skeleton region of the copper foam, the heat transfer rate entering the cubic cavity through the hollow region of the skeleton is almost negligible. Because of the competition between heat conduction and natural convection, the heat transfer enhancement efficiency of copper foam ζ first increases, then decreases, and then increases again with the increase of the Fourier number. When the Rayleigh number decreases, the energy storage efficiency η increases, and the natural convection also weakens. Meanwhile, the fluctuation of the heat transfer enhancement efficiency ζ decreases as the Fourier number increases, and the gap of the heat transfer enhancement efficiency ζ between the hollow and solid skeleton copper foams tends to be smaller. When the ratio of the thermal conductivity between the copper foam skeleton and the phase change material kλ increases, the energy storage efficiency η is relatively high at the early stage of the melting process but becomes relatively low when the melting process is completed. With a larger thermal conductivity ratio kλ , the heat transfer rate entering the cubic cavity through the skeleton region of the copper foam becomes dominant, which reduces the effect of the hollow skeleton on the heat transfer, and thus the gap of the heat transfer enhancement efficiency ζ between the hollow and solid skeleton copper foams becomes relatively small.
{"title":"Investigation of the effects of the hollow skeleton on the melting peocess in copper foam","authors":"Yang Hao, Zhang Xiao-Jie, Huang Rong-Zong","doi":"10.7498/aps.72.20230151","DOIUrl":"https://doi.org/10.7498/aps.72.20230151","url":null,"abstract":"Compositing the solid-liquid phase change material with the metal foam is an effective way to improve the heat transfer performance of the latent heat thermal energy storage system. In this paper, the three-dimensional numerical structure of the copper foam is reconstructed by using the micro CT, and then the pore-scale numerical simulation of the melting process in a cubic cavity filled with the phase change material composited with the copper foam is performed via the lattice Boltzmann method. The effects of the hollow skeleton on the melting process are discussed in detail under different Rayleigh numbers and ratios of thermal conductivity between the copper foam and the phase change material. The results show that, compared with the solid skeleton copper foam, the hollow skeleton copper foam leads to a lower average Nusselt number along the left wall at the early stage of the melting process, together with a slower melting rate and a higher energy storage efficiency η. Compared with the skeleton region of the copper foam, the heat transfer rate entering the cubic cavity through the hollow region of the skeleton is almost negligible. Because of the competition between heat conduction and natural convection, the heat transfer enhancement efficiency of copper foam ζ first increases, then decreases, and then increases again with the increase of the Fourier number. When the Rayleigh number decreases, the energy storage efficiency η increases, and the natural convection also weakens. Meanwhile, the fluctuation of the heat transfer enhancement efficiency ζ decreases as the Fourier number increases, and the gap of the heat transfer enhancement efficiency ζ between the hollow and solid skeleton copper foams tends to be smaller. When the ratio of the thermal conductivity between the copper foam skeleton and the phase change material kλ increases, the energy storage efficiency η is relatively high at the early stage of the melting process but becomes relatively low when the melting process is completed. With a larger thermal conductivity ratio kλ , the heat transfer rate entering the cubic cavity through the skeleton region of the copper foam becomes dominant, which reduces the effect of the hollow skeleton on the heat transfer, and thus the gap of the heat transfer enhancement efficiency ζ between the hollow and solid skeleton copper foams becomes relatively small.","PeriodicalId":6995,"journal":{"name":"物理学报","volume":"34 1","pages":""},"PeriodicalIF":1.0,"publicationDate":"2023-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"80101308","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Wang Xiao-Fei, Meng Wei-Wei, Zhao Pei-Li, Jia Shuang-Feng, Zheng He, Wang Jian-Bo
Two-dimensional (2D) niobium silicon telluride (Nb2SiTe4) with good stability, a narrow band gap of 0.39 eV, high carrier mobility and superior photoresponsivity, is highly desired for applications as mid-infrared (MIR) detections, ambipolar transistors. Intensive investigations on its ferroelasticity, anisotropic carrier transport, anisotropic thermoelectric property, etc., have also been reported recently. Motivated by the above prominent properties and promising applications, we have systematically studied the electronic properties of single-layer (SL) A2BX4 analogues (A=V, Nb, Ta, B=Si, Ge, Sn, X=S, Se, Te) and found a band-gap anomaly with respect to anions change, which differs from conventional 2D metal chalcogenides. In conventional binary chalcogenides, when cations keep fixed, the bandgap tends to decrease when the atomic numbers of anions in the same group increase. However, in SL A2BX4, when atomic numbers of anions increase, their bandgaps tend to increase with cations kept fixed. In order to find the underlying mechanism of such abnormal bandgap, using first-principles calculations, we have thoroughly investigated the electronic structures of Nb2SiX4 (X=S、Se、Te) as an example. It is found that the valance band maximum (VBM) and conduction band minimum (CBM) are mainly derived from the bonding and antibonding coupling between Nb 4d states. The bandwidth of Nb 4d states determines the relative value of the band gap in Nb2SiX4. We demonstrate that the band gap is largely influenced by the competition effect between Nb-Nb and Nb-X interactions in Nb2SiX4. When the anion atomic number increases, the Nb-Nb bond length also increases, yielding increased bandwidths of Nb 4d states as well as a smaller bandgap of Nb2SiX4. Meanwhile, when Nb-X bond length increases, the bandwidth of Nb 4d however decreases, yielding a larger bandgap. The interaction between Nb and X should be dominant and responsible for the overall bandgap increase of Nb2SiX4 compared with Nb-Nb interaction.
二维(2D)碲化铌硅(Nb2SiTe4)具有良好的稳定性，0.39 eV的窄带隙，高载流子迁移率和优异的光响应性，是中红外(MIR)探测，双极晶体管等应用的理想材料。近年来，对其铁弹性、各向异性载流子输运、各向异性热电性能等方面也进行了深入的研究。由于上述突出的性质和前景广阔的应用，我们系统地研究了单层(SL) A2BX4类似物(A=V, Nb, Ta, B=Si, Ge, Sn, X=S, Se, Te)的电子性质，并发现了与传统二维金属硫族化合物不同的阴离子变化的带隙异常。在常规的二元硫族化合物中，当阳离子保持固定时，同基团阴离子的原子序数增加，带隙有减小的趋势。而在SL A2BX4中，当阴离子原子序数增加时，其带隙趋于增大，而阳离子保持不变。为了找到这种异常带隙的潜在机制，我们利用第一性原理计算，以Nb2SiX4 (X=S, Se, Te)为例，对其电子结构进行了深入的研究。发现价带最大值(VBM)和导带最小值(CBM)主要来源于Nb - 4d态之间的成键和反键耦合。Nb - 4d态的带宽决定了Nb2SiX4中带隙的相对值。我们证明了带隙在很大程度上受Nb2SiX4中Nb-Nb和Nb-X相互作用之间竞争效应的影响。当阴离子原子序数增加时，Nb-Nb键长也增加，Nb- 4d态的带宽增加，Nb2SiX4的带隙变小。同时，随着Nb- x键长增加，Nb- 4d的带宽减小，产生更大的带隙。与Nb-Nb相互作用相比，Nb和X之间的相互作用应该是Nb2SiX4整体带隙增加的主要原因。
{"title":"Band gap anomaly in single-layer Nb2SiTe4-based compounds","authors":"Wang Xiao-Fei, Meng Wei-Wei, Zhao Pei-Li, Jia Shuang-Feng, Zheng He, Wang Jian-Bo","doi":"10.7498/aps.72.20222058","DOIUrl":"https://doi.org/10.7498/aps.72.20222058","url":null,"abstract":"Two-dimensional (2D) niobium silicon telluride (Nb2SiTe4) with good stability, a narrow band gap of 0.39 eV, high carrier mobility and superior photoresponsivity, is highly desired for applications as mid-infrared (MIR) detections, ambipolar transistors. Intensive investigations on its ferroelasticity, anisotropic carrier transport, anisotropic thermoelectric property, etc., have also been reported recently. Motivated by the above prominent properties and promising applications, we have systematically studied the electronic properties of single-layer (SL) A2BX4 analogues (A=V, Nb, Ta, B=Si, Ge, Sn, X=S, Se, Te) and found a band-gap anomaly with respect to anions change, which differs from conventional 2D metal chalcogenides. In conventional binary chalcogenides, when cations keep fixed, the bandgap tends to decrease when the atomic numbers of anions in the same group increase. However, in SL A2BX4, when atomic numbers of anions increase, their bandgaps tend to increase with cations kept fixed. In order to find the underlying mechanism of such abnormal bandgap, using first-principles calculations, we have thoroughly investigated the electronic structures of Nb2SiX4 (X=S、Se、Te) as an example. It is found that the valance band maximum (VBM) and conduction band minimum (CBM) are mainly derived from the bonding and antibonding coupling between Nb 4d states. The bandwidth of Nb 4d states determines the relative value of the band gap in Nb2SiX4. We demonstrate that the band gap is largely influenced by the competition effect between Nb-Nb and Nb-X interactions in Nb2SiX4. When the anion atomic number increases, the Nb-Nb bond length also increases, yielding increased bandwidths of Nb 4d states as well as a smaller bandgap of Nb2SiX4. Meanwhile, when Nb-X bond length increases, the bandwidth of Nb 4d however decreases, yielding a larger bandgap. The interaction between Nb and X should be dominant and responsible for the overall bandgap increase of Nb2SiX4 compared with Nb-Nb interaction.","PeriodicalId":6995,"journal":{"name":"物理学报","volume":"4 1","pages":""},"PeriodicalIF":1.0,"publicationDate":"2023-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"80267774","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Wang Lu-xuan, Liu Yi-tong, Shi Fang-yuan, Qi Xian-wen, Shen Han, Song Ying-lin, Fang Yu
The ultra-wide bandgap semiconductor gallium oxide β-Ga2O3 with enhanced resistance to the irradiation and temperature is favorable for high-power and high-temperature optoelectronic devices. β-Ga2O3 also exhibits great potential for applications in the field of integrated photonics for its compatibility with the CMOS technique. However, a variety of intrinsic and extrinsic defects and trap states coexist in β-Ga2O3, including vacancies, interstitials, and impurity atoms. The defect-related carrier dynamics in β-Ga2O3 not only adversely affect the optical and electrical properties, but are also directly limit the performance of β-Ga2O3 based devices. Therefore, a comprehensive understanding of the carrier transportation and relaxation dynamics induced by intrinsic defects is crucial. Supercontinuum-probe spectroscopy can provide a fruitful information about the carrier relaxation processes in different recombination mechanisms, and becomes an effective way to study the defect dynamics. In this letter, we report the dynamics of carrier trapping and recombination induced by intrinsic defects in pristine β-Ga2O3 crystal using wavelength-tunable ultrafast transient absorption spectroscopy. The broadband absorption spectra induced by the intrinsic defects are strongly dependent on the polarization of pump and probe pulses. Particularly, two absorption peaks induced by the two defect states can be extracted from the transient absorption spectra by subtracting the absorption transients under two probe polarizations. The observed defect-induced absorption features are attributed to the optical transitions from the valence band to the different charge states of the intrinsic defects (such as gallium vacancy). The data is well interpreted by a proposed carrier capture model based on multi-level. Moreover, the hole capture rate is found to be much greater than that of the electron, and the absorption cross-section of the defect state is at least 10 times larger than that of free carrier. Our findings and results not only clarify the relationship between intrinsic defects and photogenerated carrier dynamics, but also paramount important for the application of β-Ga2O3 crystals in ultrafast and broadband photonics.
{"title":"Broadband ultrafast photogenerated carrier dynamics induced by intrinsic defects in β-Ga2O3","authors":"Wang Lu-xuan, Liu Yi-tong, Shi Fang-yuan, Qi Xian-wen, Shen Han, Song Ying-lin, Fang Yu","doi":"10.7498/aps.72.20231173","DOIUrl":"https://doi.org/10.7498/aps.72.20231173","url":null,"abstract":"The ultra-wide bandgap semiconductor gallium oxide β-Ga2O3 with enhanced resistance to the irradiation and temperature is favorable for high-power and high-temperature optoelectronic devices. β-Ga2O3 also exhibits great potential for applications in the field of integrated photonics for its compatibility with the CMOS technique. However, a variety of intrinsic and extrinsic defects and trap states coexist in β-Ga2O3, including vacancies, interstitials, and impurity atoms. The defect-related carrier dynamics in β-Ga2O3 not only adversely affect the optical and electrical properties, but are also directly limit the performance of β-Ga2O3 based devices. Therefore, a comprehensive understanding of the carrier transportation and relaxation dynamics induced by intrinsic defects is crucial. Supercontinuum-probe spectroscopy can provide a fruitful information about the carrier relaxation processes in different recombination mechanisms, and becomes an effective way to study the defect dynamics. In this letter, we report the dynamics of carrier trapping and recombination induced by intrinsic defects in pristine β-Ga2O3 crystal using wavelength-tunable ultrafast transient absorption spectroscopy. The broadband absorption spectra induced by the intrinsic defects are strongly dependent on the polarization of pump and probe pulses. Particularly, two absorption peaks induced by the two defect states can be extracted from the transient absorption spectra by subtracting the absorption transients under two probe polarizations. The observed defect-induced absorption features are attributed to the optical transitions from the valence band to the different charge states of the intrinsic defects (such as gallium vacancy). The data is well interpreted by a proposed carrier capture model based on multi-level. Moreover, the hole capture rate is found to be much greater than that of the electron, and the absorption cross-section of the defect state is at least 10 times larger than that of free carrier. Our findings and results not only clarify the relationship between intrinsic defects and photogenerated carrier dynamics, but also paramount important for the application of β-Ga2O3 crystals in ultrafast and broadband photonics.","PeriodicalId":6995,"journal":{"name":"物理学报","volume":"36 1","pages":""},"PeriodicalIF":1.0,"publicationDate":"2023-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"80523795","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Zhang Yi-Fan, Ren Wei, Wang Wei-Li, Ding Shu-Jian, Li Nan, Chang Liang, Zhou Qian
Traditional material calculation methods, such as first principles and thermodynamic simulations, have accelerated the discovery of new materials. However, it is difficult for these methods to construct models flexibly based on various target properties. And they will consume plenty of computational resources while their prediction accuracy is not good. In last decade, data-driven machine learning techniques have gradually been applied in materials science, which has accumulated a large amount of theoretical and experimental data. Machine learning is able to dig out the hidden information in these data and help to predict the properties of materials. In this work, the data source was obtained through the published references. And several performance-oriented algorithms were selected to build a prediction model for the hardness of high entropy alloys. A high entropy alloy hardness dataset containing 19 candidate features was trained, tested, and evaluated using an ensemble learning algorithm: a genetic algorithm was selected to filter the 19 candidate features to obtain an optimized feature set of 8 features; a two-stage feature selection approach was then combined with a traditional solid solution strengthening theory to optimize the features, three most representative feature parameters were chosen and then used to build a Random Forest model for hardness prediction. The prediction accuracy achieved an R2 value of 0.9416 under the ten-fold cross-validation method. To better understand the prediction mechanism, solid solution strengthening theory of the alloy was used to explain the hardness differences. Further, the atomic size, electronegativity and modulus mismatch features were found to have very important effects on the solid solution strengthening of high entropy alloys when using genetic algorithms for feature selection. The machine learning algorithm and features were also further used for prediction of solid solution strengthening properties, resulting in an R2 of 0.8811 using the ten-fold cross-validation method. These screened-out parameters have good transferability for various high entropy alloy system. In view of the poor interpretability of the random forest algorithm, the SHAP interpretable machine learning method was used to dig out the internal reasoning logic of established machine learning model and clarify the mechanism of the influence of each feature on hardness. Especially, the valence electron concentration is found to have the most significant weakening effect on the hardness of high entropy alloys.
{"title":"Machine learning combined with solid solution strengthening model to predict hardness of high entropy alloys","authors":"Zhang Yi-Fan, Ren Wei, Wang Wei-Li, Ding Shu-Jian, Li Nan, Chang Liang, Zhou Qian","doi":"10.7498/aps.72.20230646","DOIUrl":"https://doi.org/10.7498/aps.72.20230646","url":null,"abstract":"Traditional material calculation methods, such as first principles and thermodynamic simulations, have accelerated the discovery of new materials. However, it is difficult for these methods to construct models flexibly based on various target properties. And they will consume plenty of computational resources while their prediction accuracy is not good. In last decade, data-driven machine learning techniques have gradually been applied in materials science, which has accumulated a large amount of theoretical and experimental data. Machine learning is able to dig out the hidden information in these data and help to predict the properties of materials. In this work, the data source was obtained through the published references. And several performance-oriented algorithms were selected to build a prediction model for the hardness of high entropy alloys. A high entropy alloy hardness dataset containing 19 candidate features was trained, tested, and evaluated using an ensemble learning algorithm: a genetic algorithm was selected to filter the 19 candidate features to obtain an optimized feature set of 8 features; a two-stage feature selection approach was then combined with a traditional solid solution strengthening theory to optimize the features, three most representative feature parameters were chosen and then used to build a Random Forest model for hardness prediction. The prediction accuracy achieved an R2 value of 0.9416 under the ten-fold cross-validation method. To better understand the prediction mechanism, solid solution strengthening theory of the alloy was used to explain the hardness differences. Further, the atomic size, electronegativity and modulus mismatch features were found to have very important effects on the solid solution strengthening of high entropy alloys when using genetic algorithms for feature selection. The machine learning algorithm and features were also further used for prediction of solid solution strengthening properties, resulting in an R2 of 0.8811 using the ten-fold cross-validation method. These screened-out parameters have good transferability for various high entropy alloy system. In view of the poor interpretability of the random forest algorithm, the SHAP interpretable machine learning method was used to dig out the internal reasoning logic of established machine learning model and clarify the mechanism of the influence of each feature on hardness. Especially, the valence electron concentration is found to have the most significant weakening effect on the hardness of high entropy alloys.","PeriodicalId":6995,"journal":{"name":"物理学报","volume":"4 1","pages":""},"PeriodicalIF":1.0,"publicationDate":"2023-01-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"80524231","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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