Using an excitonic basis, we investigate the intraband polarization, optical absorption spectra, and terahertzemission of semiconductor superlattice with the density matrix theory. The excitonic Bloch oscillation is d...Using an excitonic basis, we investigate the intraband polarization, optical absorption spectra, and terahertzemission of semiconductor superlattice with the density matrix theory. The excitonic Bloch oscillation is driven by thedc and ac electric fields. The slow variation in the intraband polarization depends on the ac electric field frequency. Theintraband polarization increases when the ac electric field frequency is below the Bloch frequency. When the ac electricfield frequency is above the Bloch frequency, the intraband polarization downwards and its intensity decreases. Thesatellite structures in the optical absorption spectra are presented. Due to excitonic dynamic localization, the emissionlines of terahertz shift in different ac electric field and dc electric field.展开更多
The structural and thermodynamic properties of TiAI intermetallics under high pressure have been investigated by ab initio plane-wave pseudopotential density functional theory method. It is found that the ratio of lat...The structural and thermodynamic properties of TiAI intermetallics under high pressure have been investigated by ab initio plane-wave pseudopotential density functional theory method. It is found that the ratio of lattice parameter c to a keeps almost constant with a value of 1.02 under the pressure from 0 to 20 GPa, which agrees well with the experimental results. With the pressure increasing from 20 to 45 GPa the values of c/a decrease almost linearly from 1.02 to 0.99. These calculated results indicate under low pressure the variation rate for a-axis is almost the same to that for c-axis, but under higher pressure the variation for a-axis is smaller than along e-axis. Through the quasi-harmonic Debye model, the equation of state （EOS） of TiAI intermetallies, as well as the thermal expansion and heat capacity at various pressures and temperatures are also studied.展开更多
The structural and thermodynamic properties of Zr2A1C at high pressure and high temper- ature are investigated by first principles density functional theory method. The calculated lattice parameters of Zr2A1C are in g...The structural and thermodynamic properties of Zr2A1C at high pressure and high temper- ature are investigated by first principles density functional theory method. The calculated lattice parameters of Zr2A1C are in good agreement with the available theoretical data. The pressure dependences of the elastic constants, bulk modulus, shear modulus, Young＇s mod- ulus, and Vickers hardness of Zr2A1C are successfully obtained. The elastic anisotropy is examined through the computation of the direction dependence of Young＇s modulus. By using the quasiharmonic Debye model, the thermodynamic properties including the Debye temperature, heat capacity, volume thermal expansion coefficient, and Griineisen parameter at high pressure and temperature are predicted for the first time.展开更多
Layered double hydroxides(LDHs)with decent oxygen evolution reaction(OER)activity have been extensively studied in the fields of energy storage and conversion.However,their poor conductivity,ease of agglomeration,and ...Layered double hydroxides(LDHs)with decent oxygen evolution reaction(OER)activity have been extensively studied in the fields of energy storage and conversion.However,their poor conductivity,ease of agglomeration,and low intrinsic activity limit their practical application.To date,improvement of the intrinsic activity and stability of NiFe-LDHs through the introduction of heteroatoms or its combination with other conductive substrates to enhance their water-splitting performance has drawn increasing attention.In this study,vertically interlaced ternary phosphatised nickel/iron hybrids grown on the surface of titanium carbide flakes(NiFe P/MXene)were successfully synthesised through a hydrothermal reaction and phosphating calcination process.The optimised NiFe P/MXene exhibited a low overpotential of 286 m V at 10 m A cm^(-2) and a Tafel slope of 35 m V dec^(-1) for the OER,which exceeded the performance of several existing NiFe-based catalysts.NiFe P/MXene was further used as a water-splitting anode in an alkaline electrolyte,exhibiting a cell voltage of only 1.61 V to achieve a current density of 10 m A cm^(-2).Density functional theory(DFT)calculations revealed that the combination of MXene acting as a conductive substrate and the phosphating process can effectively tune the electronic structure and density of the electrocatalyst surface to promote the energy level of the d-band centre,resulting in an enhanced OER performance.This study provides a valuable guideline for designing high-performance MXenesupported NiFe-based OER catalysts.展开更多
This study used density functional theory and the quantum transport method to investigate the interfacial coupling and spin transport of transition metals(TMs)with a Fe,Co,and Ni/2H-VSe_(2)hybrid nanostructure.Because...This study used density functional theory and the quantum transport method to investigate the interfacial coupling and spin transport of transition metals(TMs)with a Fe,Co,and Ni/2H-VSe_(2)hybrid nanostructure.Because the indirect coupling of TM-Se-V led to an obvious reduction of the magnetic moment and the disappearance of the half-metal characteristics of 2H-VSe_(2),the expected spin-filtering effect of individual TMs and 2H-VSe_(2)deteriorated at the contact region.Nevertheless,all the TM/2H-VSe_(2)-based dual-probe devices exhibited an interesting bias-dependent spin-injection efficiency with a maximum output spin-polarized current of 666 mA mm-1 in Co/2H-VSe_(2).The proposed TM/2H-VSe_(2)-based spin-field-effect transistor demonstrated outstanding performance.The Ni/2H-VSe_(2)-based transistor achieved a maximum output spin-polarized current of 3117 m A mm-1 and demonstrated a good switching characteristic of 106 mV dec-1.Importantly,all transistors achieved a widely tunable scale of spin-extraction efficiency ranging consistently between 96%and-92%with gate bias.These results indicate a promising candidate for use in high-performance spintronic devices.展开更多
基金Supported by National Science Foundation of China under Grant No.10647132the Scientific Research Fund of Hunan Provincial Education Department under Grant No.05B014
文摘Using an excitonic basis, we investigate the intraband polarization, optical absorption spectra, and terahertzemission of semiconductor superlattice with the density matrix theory. The excitonic Bloch oscillation is driven by thedc and ac electric fields. The slow variation in the intraband polarization depends on the ac electric field frequency. Theintraband polarization increases when the ac electric field frequency is below the Bloch frequency. When the ac electricfield frequency is above the Bloch frequency, the intraband polarization downwards and its intensity decreases. Thesatellite structures in the optical absorption spectra are presented. Due to excitonic dynamic localization, the emissionlines of terahertz shift in different ac electric field and dc electric field.
基金Support from Ph. D. Program Foundation (B2009-59)the National Science Foundations of China under Grant No. 50802024+1 种基金Henan Educational Committee under Grant No. 2011A140007Young Key Teacher by Henan Polytechnic University
文摘The structural and thermodynamic properties of TiAI intermetallics under high pressure have been investigated by ab initio plane-wave pseudopotential density functional theory method. It is found that the ratio of lattice parameter c to a keeps almost constant with a value of 1.02 under the pressure from 0 to 20 GPa, which agrees well with the experimental results. With the pressure increasing from 20 to 45 GPa the values of c/a decrease almost linearly from 1.02 to 0.99. These calculated results indicate under low pressure the variation rate for a-axis is almost the same to that for c-axis, but under higher pressure the variation for a-axis is smaller than along e-axis. Through the quasi-harmonic Debye model, the equation of state （EOS） of TiAI intermetallies, as well as the thermal expansion and heat capacity at various pressures and temperatures are also studied.
基金This work was supportted by the National Natural Science Foundation of China （No.11447176 and No.11447152）, the National Natural Science Foundation of China and the China Academy of Engineering Physics （No.U1230201）, and the Doctor Foundation of Southwest University of Science and Technology （No.13zx7137 and No.14zx7167）.
文摘The structural and thermodynamic properties of Zr2A1C at high pressure and high temper- ature are investigated by first principles density functional theory method. The calculated lattice parameters of Zr2A1C are in good agreement with the available theoretical data. The pressure dependences of the elastic constants, bulk modulus, shear modulus, Young＇s mod- ulus, and Vickers hardness of Zr2A1C are successfully obtained. The elastic anisotropy is examined through the computation of the direction dependence of Young＇s modulus. By using the quasiharmonic Debye model, the thermodynamic properties including the Debye temperature, heat capacity, volume thermal expansion coefficient, and Griineisen parameter at high pressure and temperature are predicted for the first time.
基金supported by the National Natural Science Foundation of China(21875048)the Outstanding Youth Project of Guangdong Natural Science Foundation(2020B1515020028)+1 种基金the Yangcheng Scholars Research Project of Guangzhou(201831820)the Science and Technology Research Project of Guangzhou(202002010007)。
文摘Layered double hydroxides(LDHs)with decent oxygen evolution reaction(OER)activity have been extensively studied in the fields of energy storage and conversion.However,their poor conductivity,ease of agglomeration,and low intrinsic activity limit their practical application.To date,improvement of the intrinsic activity and stability of NiFe-LDHs through the introduction of heteroatoms or its combination with other conductive substrates to enhance their water-splitting performance has drawn increasing attention.In this study,vertically interlaced ternary phosphatised nickel/iron hybrids grown on the surface of titanium carbide flakes(NiFe P/MXene)were successfully synthesised through a hydrothermal reaction and phosphating calcination process.The optimised NiFe P/MXene exhibited a low overpotential of 286 m V at 10 m A cm^(-2) and a Tafel slope of 35 m V dec^(-1) for the OER,which exceeded the performance of several existing NiFe-based catalysts.NiFe P/MXene was further used as a water-splitting anode in an alkaline electrolyte,exhibiting a cell voltage of only 1.61 V to achieve a current density of 10 m A cm^(-2).Density functional theory(DFT)calculations revealed that the combination of MXene acting as a conductive substrate and the phosphating process can effectively tune the electronic structure and density of the electrocatalyst surface to promote the energy level of the d-band centre,resulting in an enhanced OER performance.This study provides a valuable guideline for designing high-performance MXenesupported NiFe-based OER catalysts.
基金the 111 project(B12026)the National Natural Science Foundation of China(61904142)the Natural Science Basic Research Plan in Shaanxi Province of China(2019ZDLGY16-03)。
文摘This study used density functional theory and the quantum transport method to investigate the interfacial coupling and spin transport of transition metals(TMs)with a Fe,Co,and Ni/2H-VSe_(2)hybrid nanostructure.Because the indirect coupling of TM-Se-V led to an obvious reduction of the magnetic moment and the disappearance of the half-metal characteristics of 2H-VSe_(2),the expected spin-filtering effect of individual TMs and 2H-VSe_(2)deteriorated at the contact region.Nevertheless,all the TM/2H-VSe_(2)-based dual-probe devices exhibited an interesting bias-dependent spin-injection efficiency with a maximum output spin-polarized current of 666 mA mm-1 in Co/2H-VSe_(2).The proposed TM/2H-VSe_(2)-based spin-field-effect transistor demonstrated outstanding performance.The Ni/2H-VSe_(2)-based transistor achieved a maximum output spin-polarized current of 3117 m A mm-1 and demonstrated a good switching characteristic of 106 mV dec-1.Importantly,all transistors achieved a widely tunable scale of spin-extraction efficiency ranging consistently between 96%and-92%with gate bias.These results indicate a promising candidate for use in high-performance spintronic devices.
