The comparative analysis of modem mathematical models for 3D problems in electron optics is presented. The new approach to solve the electron optics problems in three dimensions is presented. It is based on the princi...The comparative analysis of modem mathematical models for 3D problems in electron optics is presented. The new approach to solve the electron optics problems in three dimensions is presented. It is based on the principal ray method suggested by G. Grinberg in 1948. That perspective approach was not realized before for full three-dimensional electron optic systems, probably because of the complexity of its mathematical apparatus. We describe the analytical technique of the BEM （boundary element method） for the field evaluation, and 3rd order aberration expansion for the trajectory analysis. The first version of such computer code ＂OPTICS-3＂ and some results of numerical simulations with this code were presented.展开更多
The decomposition method was successfully used in solving of 3D problems with complex geometry shape in electron optics for the FDM （Finite Difference Method） and FEM （Finite Element Method） mostly to implement fa...The decomposition method was successfully used in solving of 3D problems with complex geometry shape in electron optics for the FDM （Finite Difference Method） and FEM （Finite Element Method） mostly to implement fast and robust parallel algorithms and computer codes. We suggest a new version of similar approach for the BEM （Boundary Element Method） based on the alternating method by Schwartz. This approach substantially reduce the dimension of dense global matrix of algebraic system produced by BEM algorithm to solve a complex problem on as single CPU （Central Processor Unit） desktop computer. New algorithm is iterative one, but exponential convergence for the Schwatlz＇s algorithm creates the fast numerical procedures. We describe the results of numerical simulation for a multi electrode ion transport system. The algorithms were implemented in the computer code ＂POISSON-3＂.展开更多
Compound eyes(CEs)that feature ultra-compact structures and extraordinary versatility have revealed great potential for cutting-edge applications.However,the optoelectronic integration of CEs with available photodetec...Compound eyes(CEs)that feature ultra-compact structures and extraordinary versatility have revealed great potential for cutting-edge applications.However,the optoelectronic integration of CEs with available photodetectors is still challenging because the planar charge-coupled device(CCD)/complementary metal oxide semiconductor(CMOS)detector cannot match the spatially distributed images formed by CE ommatidia.To reach this end,we report here the optoelectronic integration of CEs by manufacturing 3D nonuniform ommatidia for developing an ultra-compact on-chip camera.As a proof-of-concept,we fabricated microscale CEs with uniform and nonuniform ommatidia through femtosecond laser two-photon photopolymerization,and compared their focusing/imaging performance both theoretically and experimentally.By engineering the surface profiles of the ommatidia at different positions of the CE,the images formed by all the ommatidia can be tuned on a plane.In this way,the nonuniform CE can be directly integrated with a commercial CMOS photodetector,forming an ultra-compact CE camera.Additionally,we further combine the CE camera with a microfluidic chip,which can further serve as an on-chip microscopic monitoring system.We anticipate that such an ultra-compact CE camera may find broad applications in microfluidics,robotics,and micro-optics.展开更多
Directly resolving structural changes in material on the atomic scales of time and space is desired in studies of many disciplines.Ultrafast electron diffraction(UED),which combines the temporal resolution of femtosec...Directly resolving structural changes in material on the atomic scales of time and space is desired in studies of many disciplines.Ultrafast electron diffraction(UED),which combines the temporal resolution of femtosecond-pulse laser and the spatial sensitivity of electron diffraction,is an advancing methodology serving such a goal.Here we present the design of a UED apparatus with multiple operation modes for observation of collective atomic motions in solid material of various morphologies.This multi-mode UED employs a pulsed electron beam with propagation trajectory of parallel and convergent incidences,and diffraction configurations of transmission and reflection,as well utilities of preparation and characterization of cleaned surface and adsorbates.We recorded the process of electron-phonon coupling in single crystal molybdenum ditelluride following excitation of femtosecond laser pulses,and diffraction patterns of polycrystalline graphite thin film under different settings of electron optics,to demonstrate the temporal characteristics and tunable probe spot of the built UED apparatus,respectively.展开更多
The inverse design of electron lens is realized by two different methods in this paper. One is damped least square method and the other is the artificial neural network method. Their merits and defects are discussed a...The inverse design of electron lens is realized by two different methods in this paper. One is damped least square method and the other is the artificial neural network method. Their merits and defects are discussed according to our calculation results in the paper. In the condition of selecting the learning samples properly, the artificial neural network has obvious advantages in the inverse design of electron lens. It is an effective method to solve the inverse design problem in the electron optic system.展开更多
We investigate theoretically the electron-reflection phenomenon in a graphene n＋n junction based on electron optics, where the local potential in the left n ＋ region is higher than that in the right n region. It is ...We investigate theoretically the electron-reflection phenomenon in a graphene n＋n junction based on electron optics, where the local potential in the left n ＋ region is higher than that in the right n region. It is demonstrated numerically that electrons emitting from a point source in the n ＋ region will experience total internal reflection through the interface of the junction. The reflection becomes stronger and the transmission becomes weaker with decrease of the local potential in the right graphene ribbon. It is also found that when a nonideal interface is considered in the junction, the electron-reflection effect is enhanced due to interracial backseattering.展开更多
Atomized, pre-alloyed Ti-24Nb-4Zr-7.9Sn （wt%） powder was used to fabricate solid, prototype components by electron beam melting （EBM）. Vickers microindentation hardness values were observed to average 2 GPa for th...Atomized, pre-alloyed Ti-24Nb-4Zr-7.9Sn （wt%） powder was used to fabricate solid, prototype components by electron beam melting （EBM）. Vickers microindentation hardness values were observed to average 2 GPa for the precursor powder and 2.5 GPa for the solid, EBM-fabricated products. The powder and solid product microstructures were examined by optical and electron microscopy. X-ray diffraction analyses showed that they had bcc β-phase microstructure. However, it was found by transmission electron microscopy that the EBM-fabricated product had plate morphology with space -100-200 nm. Although the corresponding selected area diffraction patterns can be indexed by β-phase plus α＂-martensite with orthorhombic crystal structure, the dark-field analyses failed to observe the α＂-martensite. Such phenomenon was also found in deformed gum metals and explained by stress-induced diffusion scattering due to phonon softening.展开更多
We investigated the properties of polarons in a wurtzite ZnO/MgxZn1-xO quantum well by adopting a modified Lee–Low–Pines variational method, giving the ground state energy, transition energy, and phonon contribution...We investigated the properties of polarons in a wurtzite ZnO/MgxZn1-xO quantum well by adopting a modified Lee–Low–Pines variational method, giving the ground state energy, transition energy, and phonon contributions from various optical-phonon modes to the ground state energy as functions of the well width and Mg composition. In our calculations, we considered the effects of confined optical phonon modes, interface-optical phonon modes, and half-space phonon modes, as well as the anisotropy of the electron effective band mass, phonon frequency, and dielectric constant. Our numerical results indicate that the electron–optical phonon interactions importantly affect the polaronic energies in the ZnO/MgxZn1-xO quantum well. The electron–optical phonon interactions decrease the polaron energies. For quantum wells with narrower wells, the interface optical phonon and half-space phonon modes contribute more to the polaronic energies than the confined phonon modes. However, for wider quantum wells, the total contribution to the polaronic energy mainly comes from the confined modes. The contributions of the various phonon modes to the transition energy change differently with increasing well width. The contribution of the half-space phonons decreases slowly as the QW width increases, whereas the contributions of the confined and interface phonons reach a maximum at d ≈ 5.0 nm and then decrease slowly. However,the total contribution of phonon modes to the transition energy is negative and increases gradually with the QW width of d.As the composition x increases, the total contribution of phonons to the ground state energies increases slowly, but the total contributions of phonons to the transition energies decrease gradually. We analyze the physical reasons for these behaviors in detail.展开更多
The electronic structures and optical properties of the [llO]-oriented Sil-xGex nanowires （NWs） passivated with different functional groups （-H, -F and-OH） are investigated by using first-principles calculations. ...The electronic structures and optical properties of the [llO]-oriented Sil-xGex nanowires （NWs） passivated with different functional groups （-H, -F and-OH） are investigated by using first-principles calculations. The results show that surface passivation influences the characteristics of electronic band structures significantly： the band gap widths and types （direct or indirect） of the Si1-xGe, NWs with different terminators show complex and robust variations, and the effective masses of the electrons in the NWs can be modulated dramatically by the terminators. The study of optical absorption shows that the main peaks of the parallel polarization component of Si1-x Gex NWs passivated with the functional groups exhibit prominent changes both in height and position, and are red-shifted with respect to those of corresponding pure Si NWs, indicating the importance of both the terminators and Ge concentrations. Our results demonstrate that the electronic and optical properties of Si1-xGex NWs can be tuned by utilizing selected functional groups as well as particular Ge concentrations for customizing purposes.展开更多
The outstanding properties of CVD diamond film such as electronic, optical, thermal and mechanical and the high radiation hardness have made it an ideal candidate material for radiation detectors in severe environment...The outstanding properties of CVD diamond film such as electronic, optical, thermal and mechanical and the high radiation hardness have made it an ideal candidate material for radiation detectors in severe environments. Fabrication of ＇detector grade＇ CVD diamond films and development of CVD diamond detectors have been leading edge subjects. Micro-strip gas chamber （MSGC） fabricated on CVD diamond substrate would overcome the charge-up effect and the substrate instability, which has been a hotspot in the research of gas detectors.展开更多
The effect of In composition on two-dimensional electron gas in wurtzite AlGaN/InGaN heterostructures is theoretically investigated. The sheet carrier density is shown to increase nearly linearly with In mole fraction...The effect of In composition on two-dimensional electron gas in wurtzite AlGaN/InGaN heterostructures is theoretically investigated. The sheet carrier density is shown to increase nearly linearly with In mole fraction x, due to the increase in the polarization charge at the AlGaN/InGaN interface. The electron sheet density is enhanced with the doping in the AlGaN layer. The sheet carrier density is as high as 3.7×1013 cm^-2 at the donor density of 10×1018 cm^-3 for the HEMT structure with x=0.3. The contribution of additional donor density on the electron sheet density is nearly independent of the In mole fraction.展开更多
Theoretical investigations have been performed to explore the variation in electronic,optical,and charge transport properties upon the change of the chemical composition along the backbone in 2,1,3-benzothiadiazole（...Theoretical investigations have been performed to explore the variation in electronic,optical,and charge transport properties upon the change of the chemical composition along the backbone in 2,1,3-benzothiadiazole（BTD）-based derivative.Narrow difference between hole and electron transportations with the charge hopping model indicates studied BTD-based derivative can be used as good ambipolar transport material in organic light-emitting diodes.展开更多
By using first-principles calculation,we study the properties of h-BN/BC_(3)heterostructure and the effects of external electric fields and strains on its electronic and optical properties.It is found that the semicon...By using first-principles calculation,we study the properties of h-BN/BC_(3)heterostructure and the effects of external electric fields and strains on its electronic and optical properties.It is found that the semiconducting h-BN/BC_(3)has good dynamical stability and ultrahigh stiffness,enhanced electron mobility,and well-preserved electronic band structure as the BC_(3)monolayer.Meanwhile,its electronic band structure is slightly modified by an external electric field.In contrast,applying an external strain can mildly modulate the electronic band structure of h-BN/BC_(3)and the optical property exhibits an apparent redshift under a compressive strain relative to the pristine one.These findings show that the h-BN/BC_(3)hybrid can be designed as optoelectronic device with moderately strain-tunable electronic and optical properties.展开更多
The searches for large-gap quantum spin Hall insulators are important for both practical and fundamental inter- ests. In this work, we present a theoretical observation of the two-dimensional fully fluorinated stanene...The searches for large-gap quantum spin Hall insulators are important for both practical and fundamental inter- ests. In this work, we present a theoretical observation of the two-dimensional fully fluorinated stanene （SnF） by means of density functional theory. Remarkably, a significant spin-orbit coupling is observed for the SnF monolayer in the valence band at the F point, with a considerable indirect band gap of 278 meV. The direct gap of the SnF monolayer is at the F point, which is slightly larger by as much as 381 meV. In addition, the elastic modulus of the SnF monolayer is about 20J/m^2, which is comparable with the in-plane stiffness of black phos- phorus monolayer along the x-direction （~28.94 J/m^2）. Finally, the optical properties of stanene, SnF monolayer and stanene/SnF bilayer are calculated, in which the stanene/SnF bilayer is supposed to be an attractive sunlight absorber.展开更多
A new GaAs（100） spin polarized electron source with an optical polarimeter, which is employed in the field of polarized electron and gas atom collision, is presented in detail. The apparatus is passive-magnetic-shie...A new GaAs（100） spin polarized electron source with an optical polarimeter, which is employed in the field of polarized electron and gas atom collision, is presented in detail. The apparatus is passive-magnetic-shielded by a box and a cylinder made of nickel-iron-molybdenum soft magnetic alloy without Helmholtz coil arrangement. And a uniformly distributed residual magnetic field of less than 5 × 10^-7T is obtained near the collision area. The spin polarized electron beam is transmitted and focused onto collision point from photocathode by a set of electron optics with more than 25% transmission 95 cm distance through an 1 mm diameter aperture. Construction and operation of the apparatus, such as vacuum and magnetic shielding system, photocathode, laser optics, electron optics and polarimeter are discussed. The polarization of the spin polarized electron beam is determined to be 30.8 ±3.5% measured with a He optical polarimeter.展开更多
High signal-to-noise ratio can be achieved with the electron multiplying charge-coupled-device（EMCCD） applied in the Shack–Hartmann wavefront sensor（S–H WFS） in adaptive optics（AO）.However,when the brightness ...High signal-to-noise ratio can be achieved with the electron multiplying charge-coupled-device（EMCCD） applied in the Shack–Hartmann wavefront sensor（S–H WFS） in adaptive optics（AO）.However,when the brightness of the target changes in a large scale,the fixed electron multiplying（EM） gain will not be suited to the sensing limitation.Therefore an auto-gain-control method based on the brightness of light-spots array in S–H WFS is proposed in this paper.The control value is the average of the maximum signals of every light spot in an array,which has been demonstrated to be kept stable even under the influence of some noise and turbulence,and sensitive enough to the change of target brightness.A goal value is needed in the control process and it is predetermined based on the characters of EMCCD.Simulations and experiments have demonstrated that this auto-gain-control method is valid and robust,the sensing SNR reaches the maximum for the corresponding signal level,and especially is greatly improved for those dim targets from 6 to 4 magnitude in the visual band.展开更多
The electronic and optical properties of TiS2 are studied of density functional theory. A linearized and augmented by using an ab-initio calculation within the frame plane wave basis set with the generalized gradient ...The electronic and optical properties of TiS2 are studied of density functional theory. A linearized and augmented by using an ab-initio calculation within the frame plane wave basis set with the generalized gradient approximation as proposed by Perdew et al. is used for the energy exchange-correlation determination. The results show a metallic character of TiS2, and the plots of total and partial densities of states of TiS2 show the metallic character of the bonds and a strong hybridization between the states d of Ti and p of S below the Fermi energy. The optical properties of the material such as real and imaginary parts of dielectric constant （ε（w） = ε1（w） ＋ iε2（w））, refractive index n（w）, optical reflectivity R（w）, for E / /x and E / /z are performed for the energy range of 0-.14 eV.展开更多
Optical electron polarimetry is suitable for calibration of a spin-polarized electron source, especially for measurement of polarization of spin-polarized electron beam. In this paper, a new optical electron polarimet...Optical electron polarimetry is suitable for calibration of a spin-polarized electron source, especially for measurement of polarization of spin-polarized electron beam. In this paper, a new optical electron polarimeter is described, which is based on the circularly polarized He radiation induced by the bombarding of He atoms with spin-polarized electrons. The theoretical basis of the optical electron polarimetry and the structure of the optical electron polarimeter are discussed. The measurement of polarization of spin-polarized electrons produced from a new GaAs （100） spin-polarized electron source is carried out. The result of polarization of 30.8% for our spin-polarized electron source is obtained using the He optical electron polarimeter.展开更多
Photoelectrochemical water splitting using solar energy,generating oxygen and hydrogen is one of the clean fuel production processes.Inspired by surface-dependent characteristics of Janus structures,a newly designed J...Photoelectrochemical water splitting using solar energy,generating oxygen and hydrogen is one of the clean fuel production processes.Inspired by surface-dependent characteristics of Janus structures,a newly designed Janus monolayer Silicon Phosphorous Arsenide(SiPAs)was analyzed with Density Functional Theory(DFT)methods.Hybrid exchange-correlation functional(HSE06)combined with Wannier90-based analysis for electronic and optical properties of SiPAs reveals that it can act as a photocatalyst.SiPAs show an indirect bandgap of 1.88 eV,absorbing visible light range is 350 to 500 nm.The phonon spectrum confirms dynamic stability.The exciton binding energy is computed with GW/BSE methods.The electronic band edge positions are at-5.75 and-4.43 eV,perfectly straddling the water redox potentials.Interestingly the strain application modifies the bandgap and also non-homogenously widens the absorption band.A novel range of photocatalyst designs with Group IV-V elements with great promise for water-splitting,photovoltaic,and narrow bandgap semiconductor(optoelectronics)applications may be feasible.展开更多
With the help of the first-prlnciples full potential linearized augmented plane wave method, absorption coefficients, reflect/vity, dielectric behavior and electronic properties, including electronic energy bands, den...With the help of the first-prlnciples full potential linearized augmented plane wave method, absorption coefficients, reflect/vity, dielectric behavior and electronic properties, including electronic energy bands, density of states and charge density distributions, are studied for the tetragonal and cubic CaTiO3. By considering the thermal expansion effects, an approximate method is proposed for the study of the stability of ground state and a tendency of phase transition, based on the minimum free energy principle. Subsequently, numerical calculations are carried out by using the first-principles perturbation method. We demonstrate that the high-temperature phase is cubic. It is shown that optical spectra in tetragonal phase exhibit single-peak feature and differ from multi-peak character in cubic. We find that strong orbital hybridization results in the co-valent bonds between Ti 3d and O 2p electrons and forms two-type dipoles （Ti-Ol and Ti-02） in tetragonal, while the Ti-O dipoles are identical in cubic. It is argued that crystal structure determines the dipole distributions and leads to some electron states among which the dipole-dipole transit/on forbidden is a key, causing such anomalous optical phenomena with the insulator characteristics. The predicted charge density distribution and the tendency of phase transition from tetragonal to cubic are in good agreement with experimental observations.展开更多
文摘The comparative analysis of modem mathematical models for 3D problems in electron optics is presented. The new approach to solve the electron optics problems in three dimensions is presented. It is based on the principal ray method suggested by G. Grinberg in 1948. That perspective approach was not realized before for full three-dimensional electron optic systems, probably because of the complexity of its mathematical apparatus. We describe the analytical technique of the BEM （boundary element method） for the field evaluation, and 3rd order aberration expansion for the trajectory analysis. The first version of such computer code ＂OPTICS-3＂ and some results of numerical simulations with this code were presented.
文摘The decomposition method was successfully used in solving of 3D problems with complex geometry shape in electron optics for the FDM （Finite Difference Method） and FEM （Finite Element Method） mostly to implement fast and robust parallel algorithms and computer codes. We suggest a new version of similar approach for the BEM （Boundary Element Method） based on the alternating method by Schwartz. This approach substantially reduce the dimension of dense global matrix of algebraic system produced by BEM algorithm to solve a complex problem on as single CPU （Central Processor Unit） desktop computer. New algorithm is iterative one, but exponential convergence for the Schwatlz＇s algorithm creates the fast numerical procedures. We describe the results of numerical simulation for a multi electrode ion transport system. The algorithms were implemented in the computer code ＂POISSON-3＂.
基金financial supports from Natural Science Foundation of China(Grant No.61935008,T2325014,62205174 and 62275100)。
文摘Compound eyes(CEs)that feature ultra-compact structures and extraordinary versatility have revealed great potential for cutting-edge applications.However,the optoelectronic integration of CEs with available photodetectors is still challenging because the planar charge-coupled device(CCD)/complementary metal oxide semiconductor(CMOS)detector cannot match the spatially distributed images formed by CE ommatidia.To reach this end,we report here the optoelectronic integration of CEs by manufacturing 3D nonuniform ommatidia for developing an ultra-compact on-chip camera.As a proof-of-concept,we fabricated microscale CEs with uniform and nonuniform ommatidia through femtosecond laser two-photon photopolymerization,and compared their focusing/imaging performance both theoretically and experimentally.By engineering the surface profiles of the ommatidia at different positions of the CE,the images formed by all the ommatidia can be tuned on a plane.In this way,the nonuniform CE can be directly integrated with a commercial CMOS photodetector,forming an ultra-compact CE camera.Additionally,we further combine the CE camera with a microfluidic chip,which can further serve as an on-chip microscopic monitoring system.We anticipate that such an ultra-compact CE camera may find broad applications in microfluidics,robotics,and micro-optics.
基金Project supported by the Director Fund of WNLO (Grant No. WNLOZZYJ1501)the Fundamental Research Funds for the Central Universities,HUST (Grant No. 2017KFXKJC001)+1 种基金the Innovation Fund of WNLOthe Fund of State Key Laboratory of Magnetic Resonance and Atomic and Molecular Physics(Grant No. T152012)
文摘Directly resolving structural changes in material on the atomic scales of time and space is desired in studies of many disciplines.Ultrafast electron diffraction(UED),which combines the temporal resolution of femtosecond-pulse laser and the spatial sensitivity of electron diffraction,is an advancing methodology serving such a goal.Here we present the design of a UED apparatus with multiple operation modes for observation of collective atomic motions in solid material of various morphologies.This multi-mode UED employs a pulsed electron beam with propagation trajectory of parallel and convergent incidences,and diffraction configurations of transmission and reflection,as well utilities of preparation and characterization of cleaned surface and adsorbates.We recorded the process of electron-phonon coupling in single crystal molybdenum ditelluride following excitation of femtosecond laser pulses,and diffraction patterns of polycrystalline graphite thin film under different settings of electron optics,to demonstrate the temporal characteristics and tunable probe spot of the built UED apparatus,respectively.
基金the Scientific Research Foundation for Returned Overseas Chinese Scholars, State EducationCommission.
文摘The inverse design of electron lens is realized by two different methods in this paper. One is damped least square method and the other is the artificial neural network method. Their merits and defects are discussed according to our calculation results in the paper. In the condition of selecting the learning samples properly, the artificial neural network has obvious advantages in the inverse design of electron lens. It is an effective method to solve the inverse design problem in the electron optic system.
基金Supported by the Science Research&Train Program of(SRTP)Southeast University for Undergraduates
文摘We investigate theoretically the electron-reflection phenomenon in a graphene n＋n junction based on electron optics, where the local potential in the left n ＋ region is higher than that in the right n region. It is demonstrated numerically that electrons emitting from a point source in the n ＋ region will experience total internal reflection through the interface of the junction. The reflection becomes stronger and the transmission becomes weaker with decrease of the local potential in the right graphene ribbon. It is also found that when a nonideal interface is considered in the junction, the electron-reflection effect is enhanced due to interracial backseattering.
基金supportcd in part by Murchison Endowed Chairs at UTEPan MOST Grant 2012CB933901 at IMR
文摘Atomized, pre-alloyed Ti-24Nb-4Zr-7.9Sn （wt%） powder was used to fabricate solid, prototype components by electron beam melting （EBM）. Vickers microindentation hardness values were observed to average 2 GPa for the precursor powder and 2.5 GPa for the solid, EBM-fabricated products. The powder and solid product microstructures were examined by optical and electron microscopy. X-ray diffraction analyses showed that they had bcc β-phase microstructure. However, it was found by transmission electron microscopy that the EBM-fabricated product had plate morphology with space -100-200 nm. Although the corresponding selected area diffraction patterns can be indexed by β-phase plus α＂-martensite with orthorhombic crystal structure, the dark-field analyses failed to observe the α＂-martensite. Such phenomenon was also found in deformed gum metals and explained by stress-induced diffusion scattering due to phonon softening.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11264027 and 11364030)the Project of Prairie Excellent Specialist of Inner Mongolia,Chinathe "Thousand,Hundred and Ten" Talent Training Project Foundation of Inner Mongolia Normal University,China(Grant No.RCPY-2-2012-K-039)
文摘We investigated the properties of polarons in a wurtzite ZnO/MgxZn1-xO quantum well by adopting a modified Lee–Low–Pines variational method, giving the ground state energy, transition energy, and phonon contributions from various optical-phonon modes to the ground state energy as functions of the well width and Mg composition. In our calculations, we considered the effects of confined optical phonon modes, interface-optical phonon modes, and half-space phonon modes, as well as the anisotropy of the electron effective band mass, phonon frequency, and dielectric constant. Our numerical results indicate that the electron–optical phonon interactions importantly affect the polaronic energies in the ZnO/MgxZn1-xO quantum well. The electron–optical phonon interactions decrease the polaron energies. For quantum wells with narrower wells, the interface optical phonon and half-space phonon modes contribute more to the polaronic energies than the confined phonon modes. However, for wider quantum wells, the total contribution to the polaronic energy mainly comes from the confined modes. The contributions of the various phonon modes to the transition energy change differently with increasing well width. The contribution of the half-space phonons decreases slowly as the QW width increases, whereas the contributions of the confined and interface phonons reach a maximum at d ≈ 5.0 nm and then decrease slowly. However,the total contribution of phonon modes to the transition energy is negative and increases gradually with the QW width of d.As the composition x increases, the total contribution of phonons to the ground state energies increases slowly, but the total contributions of phonons to the transition energies decrease gradually. We analyze the physical reasons for these behaviors in detail.
基金Supported by the National Natural Science Foundation of China under Grant No 11004142the Program for New Century Excellent Talents in University under Grant No 11-035the Project Sponsored by the Scientific Research Foundation for ROCS of the Ministry of Education of China
文摘The electronic structures and optical properties of the [llO]-oriented Sil-xGex nanowires （NWs） passivated with different functional groups （-H, -F and-OH） are investigated by using first-principles calculations. The results show that surface passivation influences the characteristics of electronic band structures significantly： the band gap widths and types （direct or indirect） of the Si1-xGe, NWs with different terminators show complex and robust variations, and the effective masses of the electrons in the NWs can be modulated dramatically by the terminators. The study of optical absorption shows that the main peaks of the parallel polarization component of Si1-x Gex NWs passivated with the functional groups exhibit prominent changes both in height and position, and are red-shifted with respect to those of corresponding pure Si NWs, indicating the importance of both the terminators and Ge concentrations. Our results demonstrate that the electronic and optical properties of Si1-xGex NWs can be tuned by utilizing selected functional groups as well as particular Ge concentrations for customizing purposes.
文摘The outstanding properties of CVD diamond film such as electronic, optical, thermal and mechanical and the high radiation hardness have made it an ideal candidate material for radiation detectors in severe environments. Fabrication of ＇detector grade＇ CVD diamond films and development of CVD diamond detectors have been leading edge subjects. Micro-strip gas chamber （MSGC） fabricated on CVD diamond substrate would overcome the charge-up effect and the substrate instability, which has been a hotspot in the research of gas detectors.
文摘The effect of In composition on two-dimensional electron gas in wurtzite AlGaN/InGaN heterostructures is theoretically investigated. The sheet carrier density is shown to increase nearly linearly with In mole fraction x, due to the increase in the polarization charge at the AlGaN/InGaN interface. The electron sheet density is enhanced with the doping in the AlGaN layer. The sheet carrier density is as high as 3.7×1013 cm^-2 at the donor density of 10×1018 cm^-3 for the HEMT structure with x=0.3. The contribution of additional donor density on the electron sheet density is nearly independent of the In mole fraction.
基金supports from the Education Office of Jilin Province(No2010142)Institute Foundation of Siping City(No2010009) are gratefully acknowledged
文摘Theoretical investigations have been performed to explore the variation in electronic,optical,and charge transport properties upon the change of the chemical composition along the backbone in 2,1,3-benzothiadiazole（BTD）-based derivative.Narrow difference between hole and electron transportations with the charge hopping model indicates studied BTD-based derivative can be used as good ambipolar transport material in organic light-emitting diodes.
基金the National Natural Science Foundation of China(Grant No.11904081)the Natural Science Foundation of Henan Province,China(Grant Nos.202300410247 and 21A140013)。
文摘By using first-principles calculation,we study the properties of h-BN/BC_(3)heterostructure and the effects of external electric fields and strains on its electronic and optical properties.It is found that the semiconducting h-BN/BC_(3)has good dynamical stability and ultrahigh stiffness,enhanced electron mobility,and well-preserved electronic band structure as the BC_(3)monolayer.Meanwhile,its electronic band structure is slightly modified by an external electric field.In contrast,applying an external strain can mildly modulate the electronic band structure of h-BN/BC_(3)and the optical property exhibits an apparent redshift under a compressive strain relative to the pristine one.These findings show that the h-BN/BC_(3)hybrid can be designed as optoelectronic device with moderately strain-tunable electronic and optical properties.
基金Supported by the Science Foundation of Nanjing University of Posts and Telecommunications under Grant No NY215064the China Postdoctoral Science Foundation under Grant No 2015M581824the Jiangsu Post-doctoral Foundation under Grant No1501070B
文摘The searches for large-gap quantum spin Hall insulators are important for both practical and fundamental inter- ests. In this work, we present a theoretical observation of the two-dimensional fully fluorinated stanene （SnF） by means of density functional theory. Remarkably, a significant spin-orbit coupling is observed for the SnF monolayer in the valence band at the F point, with a considerable indirect band gap of 278 meV. The direct gap of the SnF monolayer is at the F point, which is slightly larger by as much as 381 meV. In addition, the elastic modulus of the SnF monolayer is about 20J/m^2, which is comparable with the in-plane stiffness of black phos- phorus monolayer along the x-direction （~28.94 J/m^2）. Finally, the optical properties of stanene, SnF monolayer and stanene/SnF bilayer are calculated, in which the stanene/SnF bilayer is supposed to be an attractive sunlight absorber.
基金Project supported by the National Natural Science Foundation of China （Grant No 10134010）.
文摘A new GaAs（100） spin polarized electron source with an optical polarimeter, which is employed in the field of polarized electron and gas atom collision, is presented in detail. The apparatus is passive-magnetic-shielded by a box and a cylinder made of nickel-iron-molybdenum soft magnetic alloy without Helmholtz coil arrangement. And a uniformly distributed residual magnetic field of less than 5 × 10^-7T is obtained near the collision area. The spin polarized electron beam is transmitted and focused onto collision point from photocathode by a set of electron optics with more than 25% transmission 95 cm distance through an 1 mm diameter aperture. Construction and operation of the apparatus, such as vacuum and magnetic shielding system, photocathode, laser optics, electron optics and polarimeter are discussed. The polarization of the spin polarized electron beam is determined to be 30.8 ±3.5% measured with a He optical polarimeter.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.11174274,61205021,and 61405194)the State Key Laboratory of Applied Optics,Changchun Institute of Optics,Fine Mechanics and Physics,Chinese Academy of Sciences
文摘High signal-to-noise ratio can be achieved with the electron multiplying charge-coupled-device（EMCCD） applied in the Shack–Hartmann wavefront sensor（S–H WFS） in adaptive optics（AO）.However,when the brightness of the target changes in a large scale,the fixed electron multiplying（EM） gain will not be suited to the sensing limitation.Therefore an auto-gain-control method based on the brightness of light-spots array in S–H WFS is proposed in this paper.The control value is the average of the maximum signals of every light spot in an array,which has been demonstrated to be kept stable even under the influence of some noise and turbulence,and sensitive enough to the change of target brightness.A goal value is needed in the control process and it is predetermined based on the characters of EMCCD.Simulations and experiments have demonstrated that this auto-gain-control method is valid and robust,the sensing SNR reaches the maximum for the corresponding signal level,and especially is greatly improved for those dim targets from 6 to 4 magnitude in the visual band.
文摘The electronic and optical properties of TiS2 are studied of density functional theory. A linearized and augmented by using an ab-initio calculation within the frame plane wave basis set with the generalized gradient approximation as proposed by Perdew et al. is used for the energy exchange-correlation determination. The results show a metallic character of TiS2, and the plots of total and partial densities of states of TiS2 show the metallic character of the bonds and a strong hybridization between the states d of Ti and p of S below the Fermi energy. The optical properties of the material such as real and imaginary parts of dielectric constant （ε（w） = ε1（w） ＋ iε2（w））, refractive index n（w）, optical reflectivity R（w）, for E / /x and E / /z are performed for the energy range of 0-.14 eV.
基金Project supported by the National Natural Science Foundation of China （Grant No 10134010）.
文摘Optical electron polarimetry is suitable for calibration of a spin-polarized electron source, especially for measurement of polarization of spin-polarized electron beam. In this paper, a new optical electron polarimeter is described, which is based on the circularly polarized He radiation induced by the bombarding of He atoms with spin-polarized electrons. The theoretical basis of the optical electron polarimetry and the structure of the optical electron polarimeter are discussed. The measurement of polarization of spin-polarized electrons produced from a new GaAs （100） spin-polarized electron source is carried out. The result of polarization of 30.8% for our spin-polarized electron source is obtained using the He optical electron polarimeter.
基金the financial support for conducting part of the computational work,by the Australian Government through the Australian Research Council(ARC)under the centre of Excellence scheme(Project No.CE170100026)National Computational Infrastructure(NCI),a National Facility for computing resources.S K M also acknowledges the computing system resources’support from the University of Tsukuba,Japan through the International Postdoctoral Fellowship of Japan Society for the Promotion of Science(JSPS)’s KAKENHI(Grant No.JP22F32733)+1 种基金during the computational work and finalization of this studyS K M also acknowledges the support of Mr Matta Sai Aneesh,University of Queensland,Australia while preparing the graphical abstract.
文摘Photoelectrochemical water splitting using solar energy,generating oxygen and hydrogen is one of the clean fuel production processes.Inspired by surface-dependent characteristics of Janus structures,a newly designed Janus monolayer Silicon Phosphorous Arsenide(SiPAs)was analyzed with Density Functional Theory(DFT)methods.Hybrid exchange-correlation functional(HSE06)combined with Wannier90-based analysis for electronic and optical properties of SiPAs reveals that it can act as a photocatalyst.SiPAs show an indirect bandgap of 1.88 eV,absorbing visible light range is 350 to 500 nm.The phonon spectrum confirms dynamic stability.The exciton binding energy is computed with GW/BSE methods.The electronic band edge positions are at-5.75 and-4.43 eV,perfectly straddling the water redox potentials.Interestingly the strain application modifies the bandgap and also non-homogenously widens the absorption band.A novel range of photocatalyst designs with Group IV-V elements with great promise for water-splitting,photovoltaic,and narrow bandgap semiconductor(optoelectronics)applications may be feasible.
基金The project supported by the Natural Science Foundation of Hubei Province under Grant No. 2003ABA004
文摘With the help of the first-prlnciples full potential linearized augmented plane wave method, absorption coefficients, reflect/vity, dielectric behavior and electronic properties, including electronic energy bands, density of states and charge density distributions, are studied for the tetragonal and cubic CaTiO3. By considering the thermal expansion effects, an approximate method is proposed for the study of the stability of ground state and a tendency of phase transition, based on the minimum free energy principle. Subsequently, numerical calculations are carried out by using the first-principles perturbation method. We demonstrate that the high-temperature phase is cubic. It is shown that optical spectra in tetragonal phase exhibit single-peak feature and differ from multi-peak character in cubic. We find that strong orbital hybridization results in the co-valent bonds between Ti 3d and O 2p electrons and forms two-type dipoles （Ti-Ol and Ti-02） in tetragonal, while the Ti-O dipoles are identical in cubic. It is argued that crystal structure determines the dipole distributions and leads to some electron states among which the dipole-dipole transit/on forbidden is a key, causing such anomalous optical phenomena with the insulator characteristics. The predicted charge density distribution and the tendency of phase transition from tetragonal to cubic are in good agreement with experimental observations.
