The local density of optical states(LDOS)is an important physical concept,which can characterize the spontaneous emission of microcavities.In order to calculate the LDOS,the relationship between the mode spectrum and ...The local density of optical states(LDOS)is an important physical concept,which can characterize the spontaneous emission of microcavities.In order to calculate the LDOS,the relationship between the mode spectrum and the LDOS is established.Then,based on the transfer matrix method and the effective resonator model,the leaky loss of the leaky mode and the mode spectrum in the one-dimensional photonic bandgap crystal waveguide are calculated,results of which indicate that the mode spectrum can characterize the leaky loss of the leaky mode.At last,the density of optical states(DOS),and the LDOS in each layer are calculated.The partial DOS and the partial LDOS in the quantum well,related to the fundamental leaky mode,can be used to find out the optimal location of the quantum well in the defect layer to couple more useful photons into the lasing mode for lasers.展开更多
The recently reported quasi-nonvolatile memory based on semi-floating gate architecture has attracted extensive attention thanks to its potential to bridge the large gap between volatile and nonvolatile memory.However...The recently reported quasi-nonvolatile memory based on semi-floating gate architecture has attracted extensive attention thanks to its potential to bridge the large gap between volatile and nonvolatile memory.However,the further extension of the refresh time in quasi-nonvolatile memory is limited by the charge leakage through the p-n junction.Here,based on the density of states engineered van der Waals heterostructures,the leakage of electrons from the floating gate to the channel is greatly suppressed.As a result,the refresh time is effectively extended to more than 100 s,which is the longest among all previously reported quasi-nonvolatile memories.This work provides a new idea to enhance the refresh time of quasi-nonvolatile memory by the density of states engineering and demonstrates great application potential for high-speed and low-power memory technology.展开更多
The spatial distribution of vortex bound states is often anisotropic,which is correlated with the underlying property of materials.In this work,we examine the effects of Fermi surface anisotropy on vortex bound states...The spatial distribution of vortex bound states is often anisotropic,which is correlated with the underlying property of materials.In this work,we examine the effects of Fermi surface anisotropy on vortex bound states.The large-scale calculation of vortex bound states is introduced in the presence of fourfold or twofold Fermi surface by solving the Bogoliubov–de Gennes(BdG)equations.Two kinds of quasiparticles’behaviors can be extracted from the local density of states(LDOS)around a vortex.The angle-dependent quasiparticles will move from high energy to low energy when the angle varies from curvature maxima to minima of the Fermi surface,while the angle-independent quasiparticles tend to stay at a relatively higher energy.In addition,the weight of angle-dependent quasiparticles can be enhanced by the increasing anisotropy degree of Fermi surface.展开更多
A theoretical study on discrete vortex bound states is carried out near a vortex core in the presence of a van Hove singularity(VHS) near the Fermi level by solving Bogoliubov–de Gennes(Bd G) equations. When the VHS ...A theoretical study on discrete vortex bound states is carried out near a vortex core in the presence of a van Hove singularity(VHS) near the Fermi level by solving Bogoliubov–de Gennes(Bd G) equations. When the VHS lies exactly at the Fermi level and also at the middle of the band, a zero-energy state and other higher-energy states whose energy ratios follow integer numbers emerge. These discrete vortex bound state peaks undergo a splitting behavior when the VHS or Fermi level moves away from the middle of the band. Such splitting behavior will eventually lead to a new arrangement of quantized vortex core states whose energy ratios follow half-odd-integer numbers.展开更多
We investigate the topological phase transition driven by non-local electronic correlations in a realistic quantum anomalous Hall model consisting of d_(xy)–d_(x^(2)-y^(2)) orbitals. Three topologically distinct phas...We investigate the topological phase transition driven by non-local electronic correlations in a realistic quantum anomalous Hall model consisting of d_(xy)–d_(x^(2)-y^(2)) orbitals. Three topologically distinct phases defined in the noninteracting limit evolve to different charge density wave phases under correlations. Two conspicuous conclusions were obtained: The topological phase transition does not involve gap-closing and the dynamical fluctuations significantly suppress the charge order favored by the next nearest neighbor interaction. Our study sheds light on the stability of topological phase under electronic correlations, and we demonstrate a positive role played by dynamical fluctuations that is distinct to all previous studies on correlated topological states.展开更多
The analysis of the density of states for electrons in single quantum well, the conduction band nonparabolicity take is account. It is shown that the degree of conduction band nonparabolicity pronounces depending on t...The analysis of the density of states for electrons in single quantum well, the conduction band nonparabolicity take is account. It is shown that the degree of conduction band nonparabolicity pronounces depending on the energy density of states. With increasing temperature, a step change in the density of states smoothes and at high temperatures is completely blurred. Nonparabolicity dispersion law manifests itself in a wide range of temperatures. Calculations are carried out for the example of the quantum wells in InAs and InSb.展开更多
For nonparabolic dispersion law is determined by the density of the energy states (Ns) in a quantizing magnetic field. The effect of temperature on the expansion of the Lan-dau levels of electrons semiconductors with ...For nonparabolic dispersion law is determined by the density of the energy states (Ns) in a quantizing magnetic field. The effect of temperature on the expansion of the Lan-dau levels of electrons semiconductors with the nonquadratic dispersion is studied. The density of states at low temperatures is calculated from data on high-tem- perature Ns.展开更多
We have investigated the energy states of a one-dimensional electron gas and analyzed the temperature dependence of the density of states. It is shown that with increasing temperature due to thermal broadening of quan...We have investigated the energy states of a one-dimensional electron gas and analyzed the temperature dependence of the density of states. It is shown that with increasing temperature due to thermal broadening of quantum, levels are blurred.展开更多
We discussed the oxidation differential and mechanisms on different planes of pyrite. The experimental results show that the oxidation priority is:(222) plane>(200) plane>(200) plane, and there is no direct corr...We discussed the oxidation differential and mechanisms on different planes of pyrite. The experimental results show that the oxidation priority is:(222) plane>(200) plane>(200) plane, and there is no direct correlation between the crystal plane index, the atom numbers, and the oxidation priority. However, with more exchanged charge among atoms, the oxidation could be conducted more easily, and the distribution rule of the electric charge conforms with the variation trend of adsorption energy, which will provide more overall cognition on the oxidation mechanism of pyrite from the atomic scale.展开更多
Some important insights into the electron-states-architecture (ESA) and its dimensionality (from 3 to 0) in a semiconductor (or generally crystalline) material are obtained. The self-consistency of the set of density ...Some important insights into the electron-states-architecture (ESA) and its dimensionality (from 3 to 0) in a semiconductor (or generally crystalline) material are obtained. The self-consistency of the set of density of states (DOS) expressions with different dimensionalities is remediated through the clarification and rearrangement of the wave-function boundary conditions for working out the eigenvalues in the wave vector space. The actually too roughly observed and theoretically unpredicted critical points for the dimensionality transitions referring to the integer ones are revealed upon an unusual assumption of the intrinsic energy-level dispersion (ELD). The ELD based quantitative physical model had been established on an immediate instinct at the very beginning and has been properly modified afterwards. The uncertainty regarding the relationship between the de Broglie wavelength of electrons and the dimensionality transitions, seeming somewhat mysterious before, is consequentially eliminated. The effect of the material dimensions on the ELD width is also predicted and has been included in the model. The continuous evolution of the ESA dimensionality is convincingly and comprehensively interpreted and thus the area of the fractional ESA dimensionalities is opened. Another new assumption of the spatial extension shrinkage (SES) closely related to the ELD has also been made and thus the understanding of the behavior of an electron or, in a general sense, a particle has become more comprehensive. This work would manifest itself a new basis for further development of nanoheterostructures (or low dimensional heterostructures including the quantum wells, quantum wires, quantum dots and especially the hetero-dimensional structures). Expected should also be the possible inventions of some novel electronic and optoelectronic devices. More basically, it leads to a new quantum mechanical picture, the essential modifications of Schrödinger equation and Newtonian equation that give rise to a full cosmic-scope picture, and a super-low-speed relativity assumption.展开更多
This research paper is on Density Functional Theory (DFT) within Local Density Approximation. The calculation was performed using Fritz Haber Institute Ab-initio Molecular Simulations (FHIAIMS) code based on numerical...This research paper is on Density Functional Theory (DFT) within Local Density Approximation. The calculation was performed using Fritz Haber Institute Ab-initio Molecular Simulations (FHIAIMS) code based on numerical atomic-centered orbital basis sets. The electronic band structure, total density of state (DOS) and band gap energy were calculated for Gallium-Arsenide and Aluminium-Arsenide in diamond structures. The result of minimum total energy and computational time obtained from the experimental lattice constant 5.63 A for both Gallium Arsenide and Aluminium Arsenide is -114,915.7903 eV and 64.989 s, respectively. The electronic band structure analysis shows that Aluminium-Arsenide is an indirect band gap semiconductor while Gallium-Arsenide is a direct band gap semiconductor. The energy gap results obtained for GaAs is 0.37 eV and AlAs is 1.42 eV. The band gap in GaAs observed is very small when compared to AlAs. This indicates that GaAs can exhibit high transport property of the electron in the semiconductor which makes it suitable for optoelectronics devices while the wider band gap of AlAs indicates their potentials can be used in high temperature and strong electric fields device applications. The results reveal a good agreement within reasonable acceptable errors when compared with the theoretical and experimental values obtained in the work of Federico and Yin wang [1] [2].展开更多
The dc conductivity in vacuum evaporated amorphous thin films of the glassy alloys Se100–xZnx(2 ≤ x ≤ 20) are meas-ured in the temperature range (308 - 388 K). The dc conductivity (σdc) is increases with increased...The dc conductivity in vacuum evaporated amorphous thin films of the glassy alloys Se100–xZnx(2 ≤ x ≤ 20) are meas-ured in the temperature range (308 - 388 K). The dc conductivity (σdc) is increases with increased of Zn concentration in the glassy alloys. The activation energy (ΔE) decreases with increase of Zn content. The conduction is explained on the basis of localized state in the mobility gap. To study the effect of electric field, a Current-Voltage characteristic has been measured at various fixed temperatures. The Current-Voltage data are fitted into the theory of space charge limited conduction in case of uniform distribution of traps in mobility gap at high electric fields (E ~104 V/cm) of these materials. The density of localized state (g0) are estimated by fitting in theory of space charge limited conduction (SCLC) at the temperature range of (352 - 372 K) in the glassy Se100–xZnx. The density of localized state (0) near the Fermi level are increases with increase of Zn concentration in the (Se100–xZnx) thin films and explain on the basis of increase of the Zn-Se bond.展开更多
Within the framework of the density functional theory and the pseudopotential method,the electronic structure calculations of the“metal-Si(100)”systems with Li,Be and Al as metal coverings of one to four monolayers(...Within the framework of the density functional theory and the pseudopotential method,the electronic structure calculations of the“metal-Si(100)”systems with Li,Be and Al as metal coverings of one to four monolayers(ML)thickness,were carried out.Calculations showed that band gaps of 1.02 eV,0.98 eV and 0.5 eV,respectively,appear in the densities of electronic states when the thickness of Li,Be and Al coverings is one ML.These gaps disappear with increasing thickness of the metal layers:first in the Li-Si system(for two ML),then in the Al-Si system(for three ML)and then in the Be-Si system(for four ML).This behavior of the band gap can be explained by the passivation of the substrate surface states and the peculiarities of the electronic structure of the adsorbed metals.In common the results can be interpreted as describing the possibility of the formation of a two-dimensional silicide with semiconducting properties in Li-Si(100),Be-Si(100)and Al-Si(100)systems.展开更多
The structural, electronic, optical and thermodynamic properties of Mo_2Ga_2C are investigated using density functional theory(DFT) within the generalized gradient approximation(GGA). The optimized crystal structure i...The structural, electronic, optical and thermodynamic properties of Mo_2Ga_2C are investigated using density functional theory(DFT) within the generalized gradient approximation(GGA). The optimized crystal structure is obtained and the lattice parameters are compared with available experimental data. The electronic density of states(DOS) is calculated and analyzed. The metallic behavior for the compound is confirmed and the value of DOS at Fermi level is 4.2 states per unit cell per e V. Technologically important optical parameters(e.g., dielectric function, refractive index, absorption coefficient, photo conductivity, reflectivity, and loss function) are calculated for the first time. The study of dielectric constant(ε1) indicates the Drude-like behavior. The absorption and conductivity spectra suggest that the compound is metallic.The reflectance spectrum shows that this compound has the potential to be used as a solar reflector. The thermodynamic properties such as the temperature and pressure dependent bulk modulus, Debye temperature, specific heats, and thermal expansion coefficient of Mo_2Ga_2C MAX phase are derived from the quasi-harmonic Debye model with phononic effect also for the first time. Analysis of T c expression using available parameter values(DOS, Debye temperature, atomic mass,etc.) suggests that the compound is less likely to be superconductor.展开更多
To clarify the effect of pressure on a(TaNb)0.67(HfZrTi)0.33 alloy composed of a solid solution with a single body-centered-cubic crystal structure,we used first-principles calculations to theoretically investigate th...To clarify the effect of pressure on a(TaNb)0.67(HfZrTi)0.33 alloy composed of a solid solution with a single body-centered-cubic crystal structure,we used first-principles calculations to theoretically investigate the structural,elastic,and electronic properties of this alloy at different pressures.The results show that the calculated equilibrium lattice parameters are consistent with the experimental results,and that the normalized structural parameters of lattice constants and volume decrease whereas the total enthalpy differenceΔE and elastic constants increase with increasing pressure.The(TaNb)0.67(HfZrTi)0.33 alloy exhibits mechanical stability at high pressures lower than 400 GPa.At high pressure,the bulk modulus B shows larger values than the shear modulus G,and the alloy exhibits an obvious anisotropic feature at pressures ranging from 30 to 70 GPa.Our analysis of the electronic structures reveals that the atomic orbitals are occupied by the electrons change due to the compression of the crystal lattices under the effect of high pressure,which results in a decrease in the total density of states and a wider electron energy level.This factor is favorable for zero resistance.展开更多
The performance of lithium-sulfur batteries is deteriorated by the inferior conductivity of sulfur,the shuttle effect of lithium polysulfides(LiPSs),sluggish redox kinetics of polysulfide intermediates and serious vol...The performance of lithium-sulfur batteries is deteriorated by the inferior conductivity of sulfur,the shuttle effect of lithium polysulfides(LiPSs),sluggish redox kinetics of polysulfide intermediates and serious volumetric expansion of sulfur.To overcome these challenges,we report a versatile route to prepare multi-functional nanocomposites with tuable hierarchical structure via ammonium hydroxide(NH_(3)·H_(2) O)induced self-assembly.The versatility of the system has been demonstrated that the organization of the hierarchical structure can be regulated by adding different amounts of NH_(3)·H_(2) O,and WS_(2) and Co_(9)S_(8) with nitrogen-doped carbon coating(denoted as WS_(2)@NC and Co_(9)S_(8)@NC)can be prepared by adding different precursor salts.When the as-prepared materials are applied for Li-S batteries,the WS_(2)@NC composite exhibits a reversible capacity of 1107.4 mAh g^(-1) at 0.1 C after 500 cycles and even 728.9 mAh g^(-1) at2 C for 1000 cycles,which is significantly better than the Co_(9)S_(8) counterpart and other reported WS_(2) sulfur hosts.Experimentally,the advantageous performance of WS_(2) could be attributed to its higher surface area and total pore volume,giving rise to the easier access to electrolyte and better ability to buffer the volume change during the charge/discharge process.Theoretically,the density function theory(DFT)calculation reveals that the as-prepared WS_(2) has a higher binding energy towards LiPSs as well as a lower energy barrier for Li^(+)diffusion on the surface than Co_(9)S_(8).More significantly,the density of states(DOS)analysis further confirms that the superior performance is mainly ascribed to the more prominent shifting and the more charge compensation from d band of W than Co,which increase electronic concentration and give more hybridization of d-p orbitals in the Fermi level of the adsorbed Li2 S4 to accelerate the lithium polysulfide interfacial redox and conversion dynamics in WS_(2).By proposing this mechanism,this work sheds new light on the understanding of catalytic conversion of lithium polysulfides at the atomic level and the strategy to develop advanced cathode materials for high-performance lithium-sulfur batteries.展开更多
We report a new method to deeply analyze the scrambling characteristic of polarization scramblers based on density of polarization states(DPS)statistics that makes it possible to describe the DPS distribution in detai...We report a new method to deeply analyze the scrambling characteristic of polarization scramblers based on density of polarization states(DPS)statistics that makes it possible to describe the DPS distribution in detail on the whole Poincarésphere,thus easy to locate accurately the nonuniform areas of defective polarization scramblers,which cannot be realized by existing methods.We have built a polarization scrambling system to demonstrate the advantages of our method compared with others by experiments and suggested effective evaluation indexes whose validity is well confirmed by applying to a commercial scrambler.Our conclusions are valuable for accurately analyzing and diagnosing the performance of any polarization scrambler,and quality evaluation of polarization controllers or other polarization devices.展开更多
Chemical reactivity towards electron transfer is captured by the Fukui function.However,this is not well defined when the system or its ions have degenerate or pseudo-degenerate ground states.In such a case,the first-...Chemical reactivity towards electron transfer is captured by the Fukui function.However,this is not well defined when the system or its ions have degenerate or pseudo-degenerate ground states.In such a case,the first-order chemical response is not independent of the perturbation and the correct response has to be computed using the mathematical formalism of perturbation theory for degenerate states.Spatialpseudo-degeneracy is ubiquitous in nanostructures with high symmetry and totally extended systems.Given the size of these systems,using degenerate-state perturbation theory is impractical because it requires the calculation of many excited states.Here we present an alternative to compute the chemical response of extended systems using models of local softness in terms of the local density of states.The local softness is approximately equal to the density of states at the Fermi level.However,such approximation leaves out the contribution of inner states.In order to include and weight the contribution of the states around the Fermi level,a model inspired by the long-range behavior of the local softness is presented.Single wall capped carbon nanotubes(SWCCNT) illustrate the limitation of the frontier orbital theory in extended systems.Thus,we have used a C360 SWCCNT to test the proposed model and how it compares with available models based on the local density of states.Interestingly,a simple Hü ckel approximation captures the main features of chemical response of these systems.Our results suggest that density-of-states models of the softness along simple tight binding Hamiltonians could be used to explore the chemical reactivity of more complex system,such a surfaces and nanoparticles.展开更多
The recently reported quasi-nonvolatile memory based on semi-floating gate architecture has attracted extensive attention thanks to its potential to bridge the large gap between volatile and nonvolatile memory.However...The recently reported quasi-nonvolatile memory based on semi-floating gate architecture has attracted extensive attention thanks to its potential to bridge the large gap between volatile and nonvolatile memory.However,the further extension of the refresh time in quasi-nonvolatile memory is limited by the charge leakage through the p-n junction.Here,based on the density of states engineered van der Waals heterostructures,the leakage of electrons from the floating gate to the channel is greatly suppressed.As a result,the refresh time is effectively extended to more than 100 s,which is the longest among all previously reported quasi-nonvolatile memories.This work provides a new idea to enhance the refresh time of quasi-nonvolatile memory by the density of states engineering and demonstrates great application potential for high-speed and low-power memory technology.展开更多
Electrides are unique materials with the anionic electrons confined to the interstitial sites,expecting important applications in various areas.In this work,the electronic structure and detailed physical properties of...Electrides are unique materials with the anionic electrons confined to the interstitial sites,expecting important applications in various areas.In this work,the electronic structure and detailed physical properties of topological electride Ca_(3)Pb are studied theoretically.By comparing the crystal structures and band structures of Ca_(3)Pb and Ca_(3)PbO,we find that after removing O^(2-)ions from Ca_(3)PbO,the remaining electrons are confined in the vacancies of the Ca6 octahedra centers,playing the role as anions and forming an additional energy band compared with that of Ca_(3)Pb.These interstitial electrons partially result in the low work function of Ca_(3)Pb.Moreover,the calculated mechanic properties imply that Ca_(3)Pb has a strong brittleness.In addition,the dielectric functions and optical properties of Ca_(3)Pb are also analyzed.展开更多
基金Project supported by the National Key Research and Development Program of China(Grant Nos.2021YFA1400604 and 2021YFB2801400)the National Natural Science Foundation of China(Grant Nos.91850206,62075213,62135001,and 62205328)。
文摘The local density of optical states(LDOS)is an important physical concept,which can characterize the spontaneous emission of microcavities.In order to calculate the LDOS,the relationship between the mode spectrum and the LDOS is established.Then,based on the transfer matrix method and the effective resonator model,the leaky loss of the leaky mode and the mode spectrum in the one-dimensional photonic bandgap crystal waveguide are calculated,results of which indicate that the mode spectrum can characterize the leaky loss of the leaky mode.At last,the density of optical states(DOS),and the LDOS in each layer are calculated.The partial DOS and the partial LDOS in the quantum well,related to the fundamental leaky mode,can be used to find out the optimal location of the quantum well in the defect layer to couple more useful photons into the lasing mode for lasers.
基金This work was supported by the National Natural Science Foundation of China(61925402,61851402 and 61734003)Science and Technology Commission of Shanghai Municipality(19JC1416600)+2 种基金National Key Research and Development Program(2017YFB0405600)Shanghai Education Development Foundation and Shanghai Municipal Education Commission Shuguang Program(18SG01)China Postdoctoral Science Foundation(2019M661358,2019TQ0065).
文摘The recently reported quasi-nonvolatile memory based on semi-floating gate architecture has attracted extensive attention thanks to its potential to bridge the large gap between volatile and nonvolatile memory.However,the further extension of the refresh time in quasi-nonvolatile memory is limited by the charge leakage through the p-n junction.Here,based on the density of states engineered van der Waals heterostructures,the leakage of electrons from the floating gate to the channel is greatly suppressed.As a result,the refresh time is effectively extended to more than 100 s,which is the longest among all previously reported quasi-nonvolatile memories.This work provides a new idea to enhance the refresh time of quasi-nonvolatile memory by the density of states engineering and demonstrates great application potential for high-speed and low-power memory technology.
基金the National Natural Science Foundation of China(Grant No.11804154)Scientific Research Foundation of NJIT(Grant No.YKJ201853).
文摘The spatial distribution of vortex bound states is often anisotropic,which is correlated with the underlying property of materials.In this work,we examine the effects of Fermi surface anisotropy on vortex bound states.The large-scale calculation of vortex bound states is introduced in the presence of fourfold or twofold Fermi surface by solving the Bogoliubov–de Gennes(BdG)equations.Two kinds of quasiparticles’behaviors can be extracted from the local density of states(LDOS)around a vortex.The angle-dependent quasiparticles will move from high energy to low energy when the angle varies from curvature maxima to minima of the Fermi surface,while the angle-independent quasiparticles tend to stay at a relatively higher energy.In addition,the weight of angle-dependent quasiparticles can be enhanced by the increasing anisotropy degree of Fermi surface.
基金the National Natural Science Foundation of China (Grant No. 11804154)the Scientific Research Foundation of NJIT (Grant Nos. YKJ201853 and CKJA201807)。
文摘A theoretical study on discrete vortex bound states is carried out near a vortex core in the presence of a van Hove singularity(VHS) near the Fermi level by solving Bogoliubov–de Gennes(Bd G) equations. When the VHS lies exactly at the Fermi level and also at the middle of the band, a zero-energy state and other higher-energy states whose energy ratios follow integer numbers emerge. These discrete vortex bound state peaks undergo a splitting behavior when the VHS or Fermi level moves away from the middle of the band. Such splitting behavior will eventually lead to a new arrangement of quantized vortex core states whose energy ratios follow half-odd-integer numbers.
基金supported by the National Natural Science Foundation of China (Grant No. 11874263)the National Key R&D Program of China (Grant No. 2017YFE0131300)Shanghai Technology Innovation Action Plan (2020-Integrated Circuit Technology Support Program 20DZ1100605,2021-Fundamental Research Area 21JC1404700)。
文摘We investigate the topological phase transition driven by non-local electronic correlations in a realistic quantum anomalous Hall model consisting of d_(xy)–d_(x^(2)-y^(2)) orbitals. Three topologically distinct phases defined in the noninteracting limit evolve to different charge density wave phases under correlations. Two conspicuous conclusions were obtained: The topological phase transition does not involve gap-closing and the dynamical fluctuations significantly suppress the charge order favored by the next nearest neighbor interaction. Our study sheds light on the stability of topological phase under electronic correlations, and we demonstrate a positive role played by dynamical fluctuations that is distinct to all previous studies on correlated topological states.
文摘The analysis of the density of states for electrons in single quantum well, the conduction band nonparabolicity take is account. It is shown that the degree of conduction band nonparabolicity pronounces depending on the energy density of states. With increasing temperature, a step change in the density of states smoothes and at high temperatures is completely blurred. Nonparabolicity dispersion law manifests itself in a wide range of temperatures. Calculations are carried out for the example of the quantum wells in InAs and InSb.
文摘For nonparabolic dispersion law is determined by the density of the energy states (Ns) in a quantizing magnetic field. The effect of temperature on the expansion of the Lan-dau levels of electrons semiconductors with the nonquadratic dispersion is studied. The density of states at low temperatures is calculated from data on high-tem- perature Ns.
文摘We have investigated the energy states of a one-dimensional electron gas and analyzed the temperature dependence of the density of states. It is shown that with increasing temperature due to thermal broadening of quantum, levels are blurred.
基金Funded by the Academician Workstation of Yi Chang Hui Long Science and Technology Co.Ltd. Association of Science and Technology of Hubei Province[2013]104-22
文摘We discussed the oxidation differential and mechanisms on different planes of pyrite. The experimental results show that the oxidation priority is:(222) plane>(200) plane>(200) plane, and there is no direct correlation between the crystal plane index, the atom numbers, and the oxidation priority. However, with more exchanged charge among atoms, the oxidation could be conducted more easily, and the distribution rule of the electric charge conforms with the variation trend of adsorption energy, which will provide more overall cognition on the oxidation mechanism of pyrite from the atomic scale.
基金supported by the National Basic Re-search Program of China(No.2010CB327601)the Na-tional Natural Science Foundation of China(No.61020106007,61108048)+1 种基金International Science&Technology Cooperation Program of China(No.2011DFR11010)the 111 Project(No.B07005).
文摘Some important insights into the electron-states-architecture (ESA) and its dimensionality (from 3 to 0) in a semiconductor (or generally crystalline) material are obtained. The self-consistency of the set of density of states (DOS) expressions with different dimensionalities is remediated through the clarification and rearrangement of the wave-function boundary conditions for working out the eigenvalues in the wave vector space. The actually too roughly observed and theoretically unpredicted critical points for the dimensionality transitions referring to the integer ones are revealed upon an unusual assumption of the intrinsic energy-level dispersion (ELD). The ELD based quantitative physical model had been established on an immediate instinct at the very beginning and has been properly modified afterwards. The uncertainty regarding the relationship between the de Broglie wavelength of electrons and the dimensionality transitions, seeming somewhat mysterious before, is consequentially eliminated. The effect of the material dimensions on the ELD width is also predicted and has been included in the model. The continuous evolution of the ESA dimensionality is convincingly and comprehensively interpreted and thus the area of the fractional ESA dimensionalities is opened. Another new assumption of the spatial extension shrinkage (SES) closely related to the ELD has also been made and thus the understanding of the behavior of an electron or, in a general sense, a particle has become more comprehensive. This work would manifest itself a new basis for further development of nanoheterostructures (or low dimensional heterostructures including the quantum wells, quantum wires, quantum dots and especially the hetero-dimensional structures). Expected should also be the possible inventions of some novel electronic and optoelectronic devices. More basically, it leads to a new quantum mechanical picture, the essential modifications of Schrödinger equation and Newtonian equation that give rise to a full cosmic-scope picture, and a super-low-speed relativity assumption.
文摘This research paper is on Density Functional Theory (DFT) within Local Density Approximation. The calculation was performed using Fritz Haber Institute Ab-initio Molecular Simulations (FHIAIMS) code based on numerical atomic-centered orbital basis sets. The electronic band structure, total density of state (DOS) and band gap energy were calculated for Gallium-Arsenide and Aluminium-Arsenide in diamond structures. The result of minimum total energy and computational time obtained from the experimental lattice constant 5.63 A for both Gallium Arsenide and Aluminium Arsenide is -114,915.7903 eV and 64.989 s, respectively. The electronic band structure analysis shows that Aluminium-Arsenide is an indirect band gap semiconductor while Gallium-Arsenide is a direct band gap semiconductor. The energy gap results obtained for GaAs is 0.37 eV and AlAs is 1.42 eV. The band gap in GaAs observed is very small when compared to AlAs. This indicates that GaAs can exhibit high transport property of the electron in the semiconductor which makes it suitable for optoelectronics devices while the wider band gap of AlAs indicates their potentials can be used in high temperature and strong electric fields device applications. The results reveal a good agreement within reasonable acceptable errors when compared with the theoretical and experimental values obtained in the work of Federico and Yin wang [1] [2].
文摘The dc conductivity in vacuum evaporated amorphous thin films of the glassy alloys Se100–xZnx(2 ≤ x ≤ 20) are meas-ured in the temperature range (308 - 388 K). The dc conductivity (σdc) is increases with increased of Zn concentration in the glassy alloys. The activation energy (ΔE) decreases with increase of Zn content. The conduction is explained on the basis of localized state in the mobility gap. To study the effect of electric field, a Current-Voltage characteristic has been measured at various fixed temperatures. The Current-Voltage data are fitted into the theory of space charge limited conduction in case of uniform distribution of traps in mobility gap at high electric fields (E ~104 V/cm) of these materials. The density of localized state (g0) are estimated by fitting in theory of space charge limited conduction (SCLC) at the temperature range of (352 - 372 K) in the glassy Se100–xZnx. The density of localized state (0) near the Fermi level are increases with increase of Zn concentration in the (Se100–xZnx) thin films and explain on the basis of increase of the Zn-Se bond.
文摘Within the framework of the density functional theory and the pseudopotential method,the electronic structure calculations of the“metal-Si(100)”systems with Li,Be and Al as metal coverings of one to four monolayers(ML)thickness,were carried out.Calculations showed that band gaps of 1.02 eV,0.98 eV and 0.5 eV,respectively,appear in the densities of electronic states when the thickness of Li,Be and Al coverings is one ML.These gaps disappear with increasing thickness of the metal layers:first in the Li-Si system(for two ML),then in the Al-Si system(for three ML)and then in the Be-Si system(for four ML).This behavior of the band gap can be explained by the passivation of the substrate surface states and the peculiarities of the electronic structure of the adsorbed metals.In common the results can be interpreted as describing the possibility of the formation of a two-dimensional silicide with semiconducting properties in Li-Si(100),Be-Si(100)and Al-Si(100)systems.
文摘The structural, electronic, optical and thermodynamic properties of Mo_2Ga_2C are investigated using density functional theory(DFT) within the generalized gradient approximation(GGA). The optimized crystal structure is obtained and the lattice parameters are compared with available experimental data. The electronic density of states(DOS) is calculated and analyzed. The metallic behavior for the compound is confirmed and the value of DOS at Fermi level is 4.2 states per unit cell per e V. Technologically important optical parameters(e.g., dielectric function, refractive index, absorption coefficient, photo conductivity, reflectivity, and loss function) are calculated for the first time. The study of dielectric constant(ε1) indicates the Drude-like behavior. The absorption and conductivity spectra suggest that the compound is metallic.The reflectance spectrum shows that this compound has the potential to be used as a solar reflector. The thermodynamic properties such as the temperature and pressure dependent bulk modulus, Debye temperature, specific heats, and thermal expansion coefficient of Mo_2Ga_2C MAX phase are derived from the quasi-harmonic Debye model with phononic effect also for the first time. Analysis of T c expression using available parameter values(DOS, Debye temperature, atomic mass,etc.) suggests that the compound is less likely to be superconductor.
基金the National Natural Science Foundation of China(No.51701128)the Scientific Research Project of Education Department of Liaoning Province,China(No.JYT19037).
文摘To clarify the effect of pressure on a(TaNb)0.67(HfZrTi)0.33 alloy composed of a solid solution with a single body-centered-cubic crystal structure,we used first-principles calculations to theoretically investigate the structural,elastic,and electronic properties of this alloy at different pressures.The results show that the calculated equilibrium lattice parameters are consistent with the experimental results,and that the normalized structural parameters of lattice constants and volume decrease whereas the total enthalpy differenceΔE and elastic constants increase with increasing pressure.The(TaNb)0.67(HfZrTi)0.33 alloy exhibits mechanical stability at high pressures lower than 400 GPa.At high pressure,the bulk modulus B shows larger values than the shear modulus G,and the alloy exhibits an obvious anisotropic feature at pressures ranging from 30 to 70 GPa.Our analysis of the electronic structures reveals that the atomic orbitals are occupied by the electrons change due to the compression of the crystal lattices under the effect of high pressure,which results in a decrease in the total density of states and a wider electron energy level.This factor is favorable for zero resistance.
基金financially supported by National Key Research and Development Program(2018YFB1502503)Fundamental Research Funds for the Central Universities(ZYGX2019J030)Sichuan Science and Technology Program(2020YJ0299)。
文摘The performance of lithium-sulfur batteries is deteriorated by the inferior conductivity of sulfur,the shuttle effect of lithium polysulfides(LiPSs),sluggish redox kinetics of polysulfide intermediates and serious volumetric expansion of sulfur.To overcome these challenges,we report a versatile route to prepare multi-functional nanocomposites with tuable hierarchical structure via ammonium hydroxide(NH_(3)·H_(2) O)induced self-assembly.The versatility of the system has been demonstrated that the organization of the hierarchical structure can be regulated by adding different amounts of NH_(3)·H_(2) O,and WS_(2) and Co_(9)S_(8) with nitrogen-doped carbon coating(denoted as WS_(2)@NC and Co_(9)S_(8)@NC)can be prepared by adding different precursor salts.When the as-prepared materials are applied for Li-S batteries,the WS_(2)@NC composite exhibits a reversible capacity of 1107.4 mAh g^(-1) at 0.1 C after 500 cycles and even 728.9 mAh g^(-1) at2 C for 1000 cycles,which is significantly better than the Co_(9)S_(8) counterpart and other reported WS_(2) sulfur hosts.Experimentally,the advantageous performance of WS_(2) could be attributed to its higher surface area and total pore volume,giving rise to the easier access to electrolyte and better ability to buffer the volume change during the charge/discharge process.Theoretically,the density function theory(DFT)calculation reveals that the as-prepared WS_(2) has a higher binding energy towards LiPSs as well as a lower energy barrier for Li^(+)diffusion on the surface than Co_(9)S_(8).More significantly,the density of states(DOS)analysis further confirms that the superior performance is mainly ascribed to the more prominent shifting and the more charge compensation from d band of W than Co,which increase electronic concentration and give more hybridization of d-p orbitals in the Fermi level of the adsorbed Li2 S4 to accelerate the lithium polysulfide interfacial redox and conversion dynamics in WS_(2).By proposing this mechanism,this work sheds new light on the understanding of catalytic conversion of lithium polysulfides at the atomic level and the strategy to develop advanced cathode materials for high-performance lithium-sulfur batteries.
基金This work was supported by the National Natural Science Foundation of China(Nos.11574026 and 11274037).
文摘We report a new method to deeply analyze the scrambling characteristic of polarization scramblers based on density of polarization states(DPS)statistics that makes it possible to describe the DPS distribution in detail on the whole Poincarésphere,thus easy to locate accurately the nonuniform areas of defective polarization scramblers,which cannot be realized by existing methods.We have built a polarization scrambling system to demonstrate the advantages of our method compared with others by experiments and suggested effective evaluation indexes whose validity is well confirmed by applying to a commercial scrambler.Our conclusions are valuable for accurately analyzing and diagnosing the performance of any polarization scrambler,and quality evaluation of polarization controllers or other polarization devices.
基金This work has been supported by FONDECYT grants 1140313 and 11150164. CC and PF acknowledge support by Financiamiento Basal para Centros Cientificos y Tecnologicos de Excelencia-FB0807, and project RC-130006 CILIS, granted by the Fondo de Innovacion para
文摘Chemical reactivity towards electron transfer is captured by the Fukui function.However,this is not well defined when the system or its ions have degenerate or pseudo-degenerate ground states.In such a case,the first-order chemical response is not independent of the perturbation and the correct response has to be computed using the mathematical formalism of perturbation theory for degenerate states.Spatialpseudo-degeneracy is ubiquitous in nanostructures with high symmetry and totally extended systems.Given the size of these systems,using degenerate-state perturbation theory is impractical because it requires the calculation of many excited states.Here we present an alternative to compute the chemical response of extended systems using models of local softness in terms of the local density of states.The local softness is approximately equal to the density of states at the Fermi level.However,such approximation leaves out the contribution of inner states.In order to include and weight the contribution of the states around the Fermi level,a model inspired by the long-range behavior of the local softness is presented.Single wall capped carbon nanotubes(SWCCNT) illustrate the limitation of the frontier orbital theory in extended systems.Thus,we have used a C360 SWCCNT to test the proposed model and how it compares with available models based on the local density of states.Interestingly,a simple Hü ckel approximation captures the main features of chemical response of these systems.Our results suggest that density-of-states models of the softness along simple tight binding Hamiltonians could be used to explore the chemical reactivity of more complex system,such a surfaces and nanoparticles.
文摘The recently reported quasi-nonvolatile memory based on semi-floating gate architecture has attracted extensive attention thanks to its potential to bridge the large gap between volatile and nonvolatile memory.However,the further extension of the refresh time in quasi-nonvolatile memory is limited by the charge leakage through the p-n junction.Here,based on the density of states engineered van der Waals heterostructures,the leakage of electrons from the floating gate to the channel is greatly suppressed.As a result,the refresh time is effectively extended to more than 100 s,which is the longest among all previously reported quasi-nonvolatile memories.This work provides a new idea to enhance the refresh time of quasi-nonvolatile memory by the density of states engineering and demonstrates great application potential for high-speed and low-power memory technology.
基金the National Natural Science Foundation of China(Grant No.12074013)the Research Innovation Fund for College Students of Beijing University of Posts and Telecommunications,the Fundamental Research Funds for the Central Universities,Chinathe Research Funds of Renmin University of China(Grant No.20XNH064).
文摘Electrides are unique materials with the anionic electrons confined to the interstitial sites,expecting important applications in various areas.In this work,the electronic structure and detailed physical properties of topological electride Ca_(3)Pb are studied theoretically.By comparing the crystal structures and band structures of Ca_(3)Pb and Ca_(3)PbO,we find that after removing O^(2-)ions from Ca_(3)PbO,the remaining electrons are confined in the vacancies of the Ca6 octahedra centers,playing the role as anions and forming an additional energy band compared with that of Ca_(3)Pb.These interstitial electrons partially result in the low work function of Ca_(3)Pb.Moreover,the calculated mechanic properties imply that Ca_(3)Pb has a strong brittleness.In addition,the dielectric functions and optical properties of Ca_(3)Pb are also analyzed.