In view of the important application of GaAs and GaN photocathodes in electron sources, differences in photoe- mission behaviour, namely the activation process and quantum yield decay, between the two typical types of...In view of the important application of GaAs and GaN photocathodes in electron sources, differences in photoe- mission behaviour, namely the activation process and quantum yield decay, between the two typical types of III-V compound photocathodes have been investigated using a multi-information measurement system. The activation exper- iment shows that a surface negative electron affinity state for the GaAs photocathode can be achieved by the necessary Cs-O two-step activation and by Cs activation alone for the GaN photocathode. In addition, a quantum yield decay experiment shows that the GaN photocathode exhibits better stability and a longer lifetime in a demountable vacuum system than the GaAs photocathode. The results mean that GaN photocathodes are more promising candidates for electron source emitter use in comparison with GaAs photocathodes.展开更多
If an electron emits all of its rest mass energy mec2, the relativistic energy of the electron will become zero. According to the special theory of relativity, an electron whose relativistic energy is zero does not ha...If an electron emits all of its rest mass energy mec2, the relativistic energy of the electron will become zero. According to the special theory of relativity, an electron whose relativistic energy is zero does not have photon energy. In this paper, however, an electron is regarded as having photon energy mec2 and negative energy −mec2, even when its relativistic energy is zero. The state where relativistic energy is zero is achieved due to the positive energy and negative energy canceling each other out. Relativistic energy becomes zero for an electron in a hydrogen atom when the principle quantum number n is zero. The author has already pointed out the existence of an energy level with n=0. If this model is used, it is possible for an electron in the state with n=0 to emit additional photons, and transition to negative energy levels. The existence of negative energy specific to the electron has previously been nothing more than a conjecture. However, this paper aims to theoretically show the existence of negative energy based on a discussion using an ellipse. The results show that the electron has latent negative energy.展开更多
The formulae for parameters of a negative electron affinity semiconductor(NEAS)with large mean escape depth of secondary electrons A(NEASLD)are deduced.The methods for obtaining parameters such asλ,B,E_(pom)and the m...The formulae for parameters of a negative electron affinity semiconductor(NEAS)with large mean escape depth of secondary electrons A(NEASLD)are deduced.The methods for obtaining parameters such asλ,B,E_(pom)and the maximumδandδat 100.0 keV≥E_(po)≥1.0 keV of a NEASLD with the deduced formulae are presented(B is the probability that an internal secondary electron escapes into the vacuum upon reaching the emission surface of the emitter,δis the secondary electron yield,E_(po)is the incident energy of primary electrons and E_(pom)is the E_(po)corresponding to the maximumδ).The parameters obtained here are analyzed,and it can be concluded that several parameters of NEASLDs obtained by the methods presented here agree with those obtained by other authors.The relation between the secondary electron emission and photoemission from a NEAS with large mean escape depth of excited electrons is investigated,and it is concluded that the presented method of obtaining A is more accurate than that of obtaining the corresponding parameter for a NEAS with largeλ_(ph)(λ_(ph)being the mean escape depth of photoelectrons),and that the presented method of calculating B at E_(po)>10.0 keV is more widely applicable for obtaining the corresponding parameters for a NEAS with largeλ_(ph).展开更多
In this paper a negative electron affinity （NEA） multialkali photocathode of （Na<sub>2</sub>KSb-Cs）-O-Cs structure is fabricated by new technology. It is found that its emission stability is much bette...In this paper a negative electron affinity （NEA） multialkali photocathode of （Na<sub>2</sub>KSb-Cs）-O-Cs structure is fabricated by new technology. It is found that its emission stability is much better than that of the NEA GaAs photocathode, but is inferior to that of the conventional Na<sub>2</sub>KSb（Cs）. After 70 hour performance in a pumping vacuum system, the emission sensitivity of the NEA （Na<sub>2</sub>KSb-Cs）-O-Cs photocathode drops only by 2.5%. The emission stability is closely related to the states of the activation cesium and oxygen during activation, best results being obtained with cesium ions and excited oxygen. Furthermore, better photoemission sensitivity and emission stability may be obtained if the cathode is illuminated by intense white light during the activation process. The performance of the NEA （Na<sub>2</sub>KSb-Cs）-O-Cs cathode which has not been illuminated by intense white light during activation may be improved by the illumination even during operation intermission.展开更多
In a previous publication, the author discussed the electron mass and charge inconsistencies resulting from classical models. A model was proposed using classical equations and two opposite charges to resolve the char...In a previous publication, the author discussed the electron mass and charge inconsistencies resulting from classical models. A model was proposed using classical equations and two opposite charges to resolve the charge inconsistency. The model proposed in that article is modified herein using classical equations to define a model that also resolves the mass inconsistency. The positive mass of the outer shell of the electron core is replaced with a negative mass. The small negatively-charged core at the center still has positive mass.展开更多
The electron transport of linear atomic chain trodes was investigated by using the density Green＇s function method. We have calculated of MgB2 sandwiched between Au（100） elecfunctional theory with the non-equilibri...The electron transport of linear atomic chain trodes was investigated by using the density Green＇s function method. We have calculated of MgB2 sandwiched between Au（100） elecfunctional theory with the non-equilibrium the corresponding cohesion energy and conductance of junctions in different distance. It is found that, at the equilibrium position, the Au-B bond-length is 1.90 A, the B-Mg bond-length is 2.22 A, and the equilibrium conductance is 0.51G0 （Go=2e^2/h）. The transport channel is almost formed by the π antibonding orbitals, which was made up of the Px and Py orbital electrons of B and Mg atoms. In the voltage range of -1.5 to 1.5 V, the junctions show the metallic behaviors. When the voltage is larger than 1.5 V, the current decreases gradually and then negative differential resistance appears almost symmetrically on both positive and negative bias.展开更多
We explore the electronic and transport properties of zigzag graphene nanoribbons （GNRs） with nitrogen-vacancy defects by performing fully self-consistent spin-polarized density functional theory calculations combin...We explore the electronic and transport properties of zigzag graphene nanoribbons （GNRs） with nitrogen-vacancy defects by performing fully self-consistent spin-polarized density functional theory calculations combined with non-equilibrium Green＇s function technique. We observe robust negative di erential resistance （NDR） effect in all examined molecular junctions. Through analyzing the calculated electronic structures and the bias-dependent transmission coefficients, we find that the narrow density of states of electrodes and the bias-dependent effective coupling between the central molecular orbitals and the electrode subbands are responsible for the observed NDR phenomenon. In addition, the obvious di erence of the transmission spectra of two spin channels is observed in some bias ranges, which leads to the near perfect spin-filtering effect. These theoretical findings imply that GNRs with nitrogenvacancy defects hold great potential for building molecular devices.展开更多
Based on non-equilibrium Green’s function method combined with the density functional theory, we have studied the electronic properties of a graphene nanoribbon (GNR) which is composed of two GNRs with different widt...Based on non-equilibrium Green’s function method combined with the density functional theory, we have studied the electronic properties of a graphene nanoribbon (GNR) which is composed of two GNRs with different widths. The results show that the electron transmission is greatly modulated by the applied bias. The current of the system displays negative differential resistance effect, which is attributed to the broadening of the transmission gap with the increase of the bias around the Fermi level.展开更多
The photodetachment of a hetero-nuclear diatomic molecular negative ion is studied by using a two-centre model. An analytic formula is presented for the electron flux distribution of a heteronuclear diatomic molecular...The photodetachment of a hetero-nuclear diatomic molecular negative ion is studied by using a two-centre model. An analytic formula is presented for the electron flux distribution of a heteronuclear diatomic molecular negative ion. Taking HF- as an example, we calculated the electron flux distributions of this ion for various detached electron energies. The results show that the electron flux distributions exhibit oscillatory structures, which are caused by the interference effect between the two nuclei. Besides, the laser light polarization also has a great influence on the electron flux distribution. The oscillation amplitude is the largest when the laser polarization is parallel to the z-axis; when the laser polarization is perpendicular to the z-axis, the oscillation almost vanishes. This study provides a new understanding of the photodetachment of a heteronuclear diatomic molecular negative ion.展开更多
By using the first-principle calculations and nonequilibrium Green functions method, the electronic transport properties of molecular devices constructed by C82, C80BN and C80N2 were studied. The results show that the...By using the first-principle calculations and nonequilibrium Green functions method, the electronic transport properties of molecular devices constructed by C82, C80BN and C80N2 were studied. The results show that the electronic transport properties of molecular devices are affected by doped atoms. Negative differential resistance (NDR) behavior can be observed in certain bias regions for C82 and C80BN molecular devices but cannot be observed for C80N2 molecular device. A mechanism for the negative differential resistance behavior was suggested.展开更多
Using a full configuration-interaction method with Hylleraas-Gaussian basis function, this paper investigates the 1^10^＋, 1^1（-1）^＋ and 1^1（-2）6＋ states of the hydrogen negative ion in strong magnetic fields. T...Using a full configuration-interaction method with Hylleraas-Gaussian basis function, this paper investigates the 1^10^＋, 1^1（-1）^＋ and 1^1（-2）6＋ states of the hydrogen negative ion in strong magnetic fields. The total energies, electron detachment energies and derivatives of the total energy with respect to the magnetic field are presented as functions of magnetic field over a wide range of field strengths. Compared with the available theoretical data, the accuracy for the energies is enhanced significantly. The field regimes 3 〈 γ 〈 4 and 0.02 〈 γ 〈 0.05, in which the 1^1（-1）6＋ and 1^1（-2）^＋ states start to become bound, respectively, are also determined based on the calculated electron detachment energies.展开更多
Negative staining is an effective method that can be used for electron microscopic study to observe fine structural morphology without destruction of bacterial structure. Although uranium acetate is used worldwide as ...Negative staining is an effective method that can be used for electron microscopic study to observe fine structural morphology without destruction of bacterial structure. Although uranium acetate is used worldwide as a general dyeing solution, it is extremely difficult to use it by a new purchase at a research institution because it falls under the nuclear regulation substance in Japan. Therefore, we examined alternative reagents for negative staining that could replace uranium acetate through bacterial observation with an electron microscope. Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus, and Streptococcus pyogenes were examined by four stain reagents (phosphotungstic acid (PTA), EMstainer, TI blue, and uranium acetate). Pre cultured bacteria were stained with each stain reagents on a copper grid, washed with PBS, and observed with a transmission electron microscope. In the comparison between bacterial structures, the cell wall structure and bacterial flagella could be observed well in the order of PTA, EMstainer, and uranium acetate. With TI blue staining, flagella could be observed very poorly. In comparison between bacteria, gram negative bacteria such as Escherichia coli and Pseudomonas aeruginosa, could be observed well as compared with gram positive cocci such as Staphylococcus aureus and Streptococcus pyogenes. The uranium acetate looked very coarse in background particles. Since crystals tend to precipitate, TI blue also required filtering, and electron beams were absorbed by the agglomerated crystals, and the frequency of electronic burning occurred high frequency. In this study, there was clear difference in the observation conditions depending on the type of bacteria and the kind of the staining reagents. Especially, it was confirmed that good negative staining features of Pseudomonas aeruginosa by electron microscope were obtained by PTA and EMstainer staining. These alternative reagents are considered to be a candidate for a negative staining.展开更多
We theoretically study current dynamics of graphene nanoribbons subject to DC-AC driven fields. We show that graphene exhibits negative differential conductivity (NDC) at high-harmonics. NDC occurs in the neighborhood...We theoretically study current dynamics of graphene nanoribbons subject to DC-AC driven fields. We show that graphene exhibits negative differential conductivity (NDC) at high-harmonics. NDC occurs in the neighborhood where a constant electric field is equal to amplitude of ac field. We also observe NDC at both even and odd harmonics and at wave mixing of two commensurate frequencies. The even harmonics are more pronounced than the odd harmonics. A possible use of the present method for generating terahertz frequencies at even harmonics in graphene is suggested.展开更多
Diamond has an ultrawide bandgap with excellent physical properties,such as high critical electric field,excellent thermal conductivity,high carrier mobility,etc.Diamond with a hydrogen-terminated(H-terminated)surface...Diamond has an ultrawide bandgap with excellent physical properties,such as high critical electric field,excellent thermal conductivity,high carrier mobility,etc.Diamond with a hydrogen-terminated(H-terminated)surface has a negative electron affinity(NEA)and can easily produce surface electrons from valence or trapped electrons via optical absorption,thermal heating energy or carrier transport in a PN junction.The NEA of the H-terminated surface enables surface electrons to emit with high efficiency into the vacuum without encountering additional barriers and promotes further development and application of diamond-based emitting devices.This article reviews the electron emission properties of H-terminated diamond surfaces exhibiting NEA characteristics.The electron emission is induced by different physical mechanisms.Recent advancements in electron-emitting devices based on diamond are also summarized.Finally,the current challenges and future development opportunities are discussed to further develop the relevant applications of diamond-based electronemitting devices.展开更多
In quantum mechanics, the energy of a hydrogen atom is minimized when the principal quantum number n is 1. However, the author has previously pointed out that the hydrogen atom has a state where n=0. An electron in th...In quantum mechanics, the energy of a hydrogen atom is minimized when the principal quantum number n is 1. However, the author has previously pointed out that the hydrogen atom has a state where n=0. An electron in the state where n=0has zero rest mass energy. However, a hydrogen atom has an energy level even lower than the n=0state. This is hard to accept from the standpoint of common sense. Thus, the author has previously pointed out that an electron at the energy level where n=0has zero energy because the positive energy mec2and negative energy −mec2cancel each other out. This paper elucidates the strange relationship between the momentum of a photon emitted when a hydrogen atom is formed by an electron with such characteristics, and the momentum acquired by the electron.展开更多
The electron flux distributions in the photodetachment of HF- near an interface are studied using a two-center model and the theoretical imaging method. An analytical expression for electron flux distributions is deri...The electron flux distributions in the photodetachment of HF- near an interface are studied using a two-center model and the theoretical imaging method. An analytical expression for electron flux distributions is derived, which displays oscillations on an observation plane similar to the recent results published by Wang but in the presence of a static electric field. We also discuss the expressions for soft and hard wall cases in detail. A comparison is made with the previous work. The expression is a more general result, and we can deduce from it the electron flux distributions for the photodetachment of H2 near an interface. Finally, we show that the expression reveals similar results as those in [Chin. Phys. B 19 020306 （2010）] when the wall effect is neglected.展开更多
Understanding the negative thermal expansion(NTE)mechanism remains an important and challenging thing.In this work,we selected the case of YFe(CN)_(6)to investigate the structure-mechanism relation on the base of crys...Understanding the negative thermal expansion(NTE)mechanism remains an important and challenging thing.In this work,we selected the case of YFe(CN)_(6)to investigate the structure-mechanism relation on the base of crystal structure,electro nic structure and lattice dynamics.We expanded the NTE of YFe(CN)_(6)to 150 K,and the temperature dependence of volume and lattice constants was determined by temperature-variable synchrotro n X-ray diffraction measure ments.A large NTE was found in the system.Our theoretical calculations indicate that the Y-N bond exhibits a strong ionic feature through the calculated electron localization function(ELF),which has a strong influence on the anisotropic vibration of the N atom.The detailed lattice dynamics simulations suggest that the NTE of YFe(CN)_(6)may be related to the presence of the unusual low-frequency modes of the YN_(6)triangular prism(tri-prism)units.The optical branches with low frequencies are mainly related to the distortion and twisting modes of the YN_(6)tri-prism units,which contribute most to the NTE effect in the crystal.展开更多
The addition of electrons to form gas-phase multiply charged anions(MCAs)normally requires sophisticated experiments or calculations.In this work,the factors stabilizing the MCAs,the maximum electron uptake of gas-pha...The addition of electrons to form gas-phase multiply charged anions(MCAs)normally requires sophisticated experiments or calculations.In this work,the factors stabilizing the MCAs,the maximum electron uptake of gas-phase molecules,X,and the electronic stability of MCAs X^(Q-),are discussed.The drawbacks encountered when applying computational and/or conceptual density functional theory(DFT)to MCAs are highlighted.We develop and test a different model based on the valence-state concept.As in DFT,the electronic energy,E(N,v_(ex)),is a continuous function of the average electron number,N,and the external potential,v_(ex),of the nuclei.The valence-state-parabola is a second-order polynomial that allows extending E(N,v_(ex))to dianions and higher MCAs.The model expresses the maximum electron acceptance,Q_(max),and the higher electron affinities,A_Q,as simple functions of the firstelectron affinity,A_1,and the ionization energy,I,of the"ancestor"system.Thus,the maximum electron acceptance is Q_(max,calc)=1+12A_1/7(I-A_1).The ground-state parabola model of the conceptual DFT yields approximately half of this value,and it is termed Q_(max,GS)=?+A_1/(I-A_1).A large variety of molecules are evaluated including fullerenes,metal clusters,super-pnictogens,super-halogens(OF_3),super-alkali species(OLi_3),and neutral or charged transition-metal complexes,AB_(m )L_n^(0/+/-).The calculated second electron affinity A_(2,calc)=A_1-(7/12)(I-A_1)is linearly correlated to the literature references A_(2,lit) with a correlation coefficient R=0.998.A_2 or A_3 values are predicted for further 24 species.The appearance sizes,n_(ap)^(3-),of triply charged anionic clusters and fullerenes are calculated in agreement with the literature.展开更多
In previous publications, the author has proposed a model of the electron’s internal structure, wherein a positively-charged negative mass outer shell and a negatively-charged positive mass central core are proposed ...In previous publications, the author has proposed a model of the electron’s internal structure, wherein a positively-charged negative mass outer shell and a negatively-charged positive mass central core are proposed to resolve the electron’s charge and mass inconsistencies. That model is modified in this document by assuming the electron’s radius is exactly equal to the classical electron radius. The attributes of the internal components of the electron’s structure have been recalculated accordingly. The shape of the electron is also predicted, and found to be slightly aspherical on the order of an oblate ellipsoid. This shape is attributed to centrifugal force and compliant outer shell material. It is interesting to note that all of the electron’s attributes, both external and internal, with the exception of mass and angular moment, are functions of the fine structure constant a, and can be calculated from just three additional constants: electron mass, Planck’s constant, and speed of light. In particular, the ratios of the outer shell charge and mass to the electron charge and mass, respectively, are 3/2a. The ratios of the central core charge and mass to the electron charge and mass, respectively, are 1-(3/2a). Attributes of the electron are compared with those of the muon. Charge and spin angular momentum are the same, while mass, magnetic moment, and radius appear to be related by the fine structure constant. The mass of the electron outer shell is nearly equal to the mass of the muon. The muon internal structure can be modeled exactly the same as for the electron, with exactly the same attribute relationships.展开更多
A model for the internal structure of the electron using classical physics equations has been previously published by the author. The model employs both positive and negative charges and positive and negative masses. ...A model for the internal structure of the electron using classical physics equations has been previously published by the author. The model employs both positive and negative charges and positive and negative masses. The internal attributes of the electron structure were calculated for both ring and spherical shapes. Further examination of the model reveals an instability for the ring shape. The spherical shape appears to be stable, but relies on tensile or compressive forces of the electron material for stability. The model is modified in this document to eliminate the dependency on material forces. Uniform stability is provided solely by balancing electrical and centrifugal forces. This stability is achieved by slightly elongating the sphere along the spin axis to create a prolate ellipsoid. The semi-major axis of the ellipsoid is the spin axis of the electron, and is calculated to be 1.20% longer than the semi-minor axis, which is the radius of the equator. Although the shape deviates slightly from a perfect sphere, the electric dipole moment is zero. In the author’s previously published document, the attributes of the internal components of the electron, such as charge and mass, were calculated and expressed as ratios to the classically measured values for the composite electron. It is interesting to note that all of these ratios are nearly the same as the inverse of the Fine Structure Constant, with differences of less than 15%. The electron model assumed that the outer surface charge was fixed and uniform. By allowing the charge to be mobile and the shape to have a particular ellipticity, it is shown that the calculated charge and mass ratios for the model can be exactly equal to the Fine Structure Constant and the Constant plus one. The electron radius predicted by the model is 15% greater than the Classical Electron Radius.展开更多
基金supported by the National Natural Science Foundation of China (Grant Nos. 60801036 and 61067001)the Research and Innovation Plan for Graduate Students of Jiangsu Higher Education Institutions (Grant No. CX09B 096Z)the Research Foundation of Nanjing University of Science and Technology (Grant No. 2010ZYTS032)
文摘In view of the important application of GaAs and GaN photocathodes in electron sources, differences in photoe- mission behaviour, namely the activation process and quantum yield decay, between the two typical types of III-V compound photocathodes have been investigated using a multi-information measurement system. The activation exper- iment shows that a surface negative electron affinity state for the GaAs photocathode can be achieved by the necessary Cs-O two-step activation and by Cs activation alone for the GaN photocathode. In addition, a quantum yield decay experiment shows that the GaN photocathode exhibits better stability and a longer lifetime in a demountable vacuum system than the GaAs photocathode. The results mean that GaN photocathodes are more promising candidates for electron source emitter use in comparison with GaAs photocathodes.
文摘If an electron emits all of its rest mass energy mec2, the relativistic energy of the electron will become zero. According to the special theory of relativity, an electron whose relativistic energy is zero does not have photon energy. In this paper, however, an electron is regarded as having photon energy mec2 and negative energy −mec2, even when its relativistic energy is zero. The state where relativistic energy is zero is achieved due to the positive energy and negative energy canceling each other out. Relativistic energy becomes zero for an electron in a hydrogen atom when the principle quantum number n is zero. The author has already pointed out the existence of an energy level with n=0. If this model is used, it is possible for an electron in the state with n=0 to emit additional photons, and transition to negative energy levels. The existence of negative energy specific to the electron has previously been nothing more than a conjecture. However, this paper aims to theoretically show the existence of negative energy based on a discussion using an ellipse. The results show that the electron has latent negative energy.
基金Project supported by the National Natural Science Foundation of China(Grant No.11873013)。
文摘The formulae for parameters of a negative electron affinity semiconductor(NEAS)with large mean escape depth of secondary electrons A(NEASLD)are deduced.The methods for obtaining parameters such asλ,B,E_(pom)and the maximumδandδat 100.0 keV≥E_(po)≥1.0 keV of a NEASLD with the deduced formulae are presented(B is the probability that an internal secondary electron escapes into the vacuum upon reaching the emission surface of the emitter,δis the secondary electron yield,E_(po)is the incident energy of primary electrons and E_(pom)is the E_(po)corresponding to the maximumδ).The parameters obtained here are analyzed,and it can be concluded that several parameters of NEASLDs obtained by the methods presented here agree with those obtained by other authors.The relation between the secondary electron emission and photoemission from a NEAS with large mean escape depth of excited electrons is investigated,and it is concluded that the presented method of obtaining A is more accurate than that of obtaining the corresponding parameter for a NEAS with largeλ_(ph)(λ_(ph)being the mean escape depth of photoelectrons),and that the presented method of calculating B at E_(po)>10.0 keV is more widely applicable for obtaining the corresponding parameters for a NEAS with largeλ_(ph).
基金This work is supported by the Natural Science Foundation of Fujian Province, China.
文摘In this paper a negative electron affinity （NEA） multialkali photocathode of （Na<sub>2</sub>KSb-Cs）-O-Cs structure is fabricated by new technology. It is found that its emission stability is much better than that of the NEA GaAs photocathode, but is inferior to that of the conventional Na<sub>2</sub>KSb（Cs）. After 70 hour performance in a pumping vacuum system, the emission sensitivity of the NEA （Na<sub>2</sub>KSb-Cs）-O-Cs photocathode drops only by 2.5%. The emission stability is closely related to the states of the activation cesium and oxygen during activation, best results being obtained with cesium ions and excited oxygen. Furthermore, better photoemission sensitivity and emission stability may be obtained if the cathode is illuminated by intense white light during the activation process. The performance of the NEA （Na<sub>2</sub>KSb-Cs）-O-Cs cathode which has not been illuminated by intense white light during activation may be improved by the illumination even during operation intermission.
文摘In a previous publication, the author discussed the electron mass and charge inconsistencies resulting from classical models. A model was proposed using classical equations and two opposite charges to resolve the charge inconsistency. The model proposed in that article is modified herein using classical equations to define a model that also resolves the mass inconsistency. The positive mass of the outer shell of the electron core is replaced with a negative mass. The small negatively-charged core at the center still has positive mass.
基金V. ACKNOWLEDGMENTS This work was supported by the National Natural Science Foundation of China （No.11174214 and No.11204192）, the Research Project of Education Department in Sichuan Province （No.13ZB0207）, and Scientific Research Project of Yibin University （No.2013YY05）.
文摘The electron transport of linear atomic chain trodes was investigated by using the density Green＇s function method. We have calculated of MgB2 sandwiched between Au（100） elecfunctional theory with the non-equilibrium the corresponding cohesion energy and conductance of junctions in different distance. It is found that, at the equilibrium position, the Au-B bond-length is 1.90 A, the B-Mg bond-length is 2.22 A, and the equilibrium conductance is 0.51G0 （Go=2e^2/h）. The transport channel is almost formed by the π antibonding orbitals, which was made up of the Px and Py orbital electrons of B and Mg atoms. In the voltage range of -1.5 to 1.5 V, the junctions show the metallic behaviors. When the voltage is larger than 1.5 V, the current decreases gradually and then negative differential resistance appears almost symmetrically on both positive and negative bias.
基金This work was partially supported by the National Natural Science Foundation of China （No.20903003 and No.21273208）, the Anhui Provincial Natural Science Foundation （No.1408085QB26）, the China Postdoctoral Science Foundation （No.2012M511409）, the Supercomputer Center of Chinese Academy of Sciences, and University of Science and Technology of China and Shanghai Supercomputer Centers.
文摘We explore the electronic and transport properties of zigzag graphene nanoribbons （GNRs） with nitrogen-vacancy defects by performing fully self-consistent spin-polarized density functional theory calculations combined with non-equilibrium Green＇s function technique. We observe robust negative di erential resistance （NDR） effect in all examined molecular junctions. Through analyzing the calculated electronic structures and the bias-dependent transmission coefficients, we find that the narrow density of states of electrodes and the bias-dependent effective coupling between the central molecular orbitals and the electrode subbands are responsible for the observed NDR phenomenon. In addition, the obvious di erence of the transmission spectra of two spin channels is observed in some bias ranges, which leads to the near perfect spin-filtering effect. These theoretical findings imply that GNRs with nitrogenvacancy defects hold great potential for building molecular devices.
文摘Based on non-equilibrium Green’s function method combined with the density functional theory, we have studied the electronic properties of a graphene nanoribbon (GNR) which is composed of two GNRs with different widths. The results show that the electron transmission is greatly modulated by the applied bias. The current of the system displays negative differential resistance effect, which is attributed to the broadening of the transmission gap with the increase of the bias around the Fermi level.
基金supported by the National Natural Science Foundation of China (Grant No. 10604045)the University Science and Technology Planning Program of Shandong Province of China (Grant No. J09LA02)
文摘The photodetachment of a hetero-nuclear diatomic molecular negative ion is studied by using a two-centre model. An analytic formula is presented for the electron flux distribution of a heteronuclear diatomic molecular negative ion. Taking HF- as an example, we calculated the electron flux distributions of this ion for various detached electron energies. The results show that the electron flux distributions exhibit oscillatory structures, which are caused by the interference effect between the two nuclei. Besides, the laser light polarization also has a great influence on the electron flux distribution. The oscillation amplitude is the largest when the laser polarization is parallel to the z-axis; when the laser polarization is perpendicular to the z-axis, the oscillation almost vanishes. This study provides a new understanding of the photodetachment of a heteronuclear diatomic molecular negative ion.
基金Project(50721003)supported by the National Natural Science Foundation of ChinaProject(10C1171)supported by the Scientific Research Fund of Hunan Provincial Education Department,ChinaProject(11JJ3073)supported by the Natural Science Foundation of Hunan Province,China
文摘By using the first-principle calculations and nonequilibrium Green functions method, the electronic transport properties of molecular devices constructed by C82, C80BN and C80N2 were studied. The results show that the electronic transport properties of molecular devices are affected by doped atoms. Negative differential resistance (NDR) behavior can be observed in certain bias regions for C82 and C80BN molecular devices but cannot be observed for C80N2 molecular device. A mechanism for the negative differential resistance behavior was suggested.
基金Project supported by the National Natural Science Foundation of China (Grant No. 10874133)
文摘Using a full configuration-interaction method with Hylleraas-Gaussian basis function, this paper investigates the 1^10^＋, 1^1（-1）^＋ and 1^1（-2）6＋ states of the hydrogen negative ion in strong magnetic fields. The total energies, electron detachment energies and derivatives of the total energy with respect to the magnetic field are presented as functions of magnetic field over a wide range of field strengths. Compared with the available theoretical data, the accuracy for the energies is enhanced significantly. The field regimes 3 〈 γ 〈 4 and 0.02 〈 γ 〈 0.05, in which the 1^1（-1）6＋ and 1^1（-2）^＋ states start to become bound, respectively, are also determined based on the calculated electron detachment energies.
文摘Negative staining is an effective method that can be used for electron microscopic study to observe fine structural morphology without destruction of bacterial structure. Although uranium acetate is used worldwide as a general dyeing solution, it is extremely difficult to use it by a new purchase at a research institution because it falls under the nuclear regulation substance in Japan. Therefore, we examined alternative reagents for negative staining that could replace uranium acetate through bacterial observation with an electron microscope. Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus, and Streptococcus pyogenes were examined by four stain reagents (phosphotungstic acid (PTA), EMstainer, TI blue, and uranium acetate). Pre cultured bacteria were stained with each stain reagents on a copper grid, washed with PBS, and observed with a transmission electron microscope. In the comparison between bacterial structures, the cell wall structure and bacterial flagella could be observed well in the order of PTA, EMstainer, and uranium acetate. With TI blue staining, flagella could be observed very poorly. In comparison between bacteria, gram negative bacteria such as Escherichia coli and Pseudomonas aeruginosa, could be observed well as compared with gram positive cocci such as Staphylococcus aureus and Streptococcus pyogenes. The uranium acetate looked very coarse in background particles. Since crystals tend to precipitate, TI blue also required filtering, and electron beams were absorbed by the agglomerated crystals, and the frequency of electronic burning occurred high frequency. In this study, there was clear difference in the observation conditions depending on the type of bacteria and the kind of the staining reagents. Especially, it was confirmed that good negative staining features of Pseudomonas aeruginosa by electron microscope were obtained by PTA and EMstainer staining. These alternative reagents are considered to be a candidate for a negative staining.
文摘We theoretically study current dynamics of graphene nanoribbons subject to DC-AC driven fields. We show that graphene exhibits negative differential conductivity (NDC) at high-harmonics. NDC occurs in the neighborhood where a constant electric field is equal to amplitude of ac field. We also observe NDC at both even and odd harmonics and at wave mixing of two commensurate frequencies. The even harmonics are more pronounced than the odd harmonics. A possible use of the present method for generating terahertz frequencies at even harmonics in graphene is suggested.
基金the National Natural Sci-ence Foundation of China(Grant No.62274084)the Fun-damental Research Funds for the Central Universities(Grant No.0210-14380193).
文摘Diamond has an ultrawide bandgap with excellent physical properties,such as high critical electric field,excellent thermal conductivity,high carrier mobility,etc.Diamond with a hydrogen-terminated(H-terminated)surface has a negative electron affinity(NEA)and can easily produce surface electrons from valence or trapped electrons via optical absorption,thermal heating energy or carrier transport in a PN junction.The NEA of the H-terminated surface enables surface electrons to emit with high efficiency into the vacuum without encountering additional barriers and promotes further development and application of diamond-based emitting devices.This article reviews the electron emission properties of H-terminated diamond surfaces exhibiting NEA characteristics.The electron emission is induced by different physical mechanisms.Recent advancements in electron-emitting devices based on diamond are also summarized.Finally,the current challenges and future development opportunities are discussed to further develop the relevant applications of diamond-based electronemitting devices.
文摘In quantum mechanics, the energy of a hydrogen atom is minimized when the principal quantum number n is 1. However, the author has previously pointed out that the hydrogen atom has a state where n=0. An electron in the state where n=0has zero rest mass energy. However, a hydrogen atom has an energy level even lower than the n=0state. This is hard to accept from the standpoint of common sense. Thus, the author has previously pointed out that an electron at the energy level where n=0has zero energy because the positive energy mec2and negative energy −mec2cancel each other out. This paper elucidates the strange relationship between the momentum of a photon emitted when a hydrogen atom is formed by an electron with such characteristics, and the momentum acquired by the electron.
文摘The electron flux distributions in the photodetachment of HF- near an interface are studied using a two-center model and the theoretical imaging method. An analytical expression for electron flux distributions is derived, which displays oscillations on an observation plane similar to the recent results published by Wang but in the presence of a static electric field. We also discuss the expressions for soft and hard wall cases in detail. A comparison is made with the previous work. The expression is a more general result, and we can deduce from it the electron flux distributions for the photodetachment of H2 near an interface. Finally, we show that the expression reveals similar results as those in [Chin. Phys. B 19 020306 （2010）] when the wall effect is neglected.
基金supported by the National Natural Science Foundation of China(22071221,21905252)Natural Science Foundation of Henan Province(212300410086)。
文摘Understanding the negative thermal expansion(NTE)mechanism remains an important and challenging thing.In this work,we selected the case of YFe(CN)_(6)to investigate the structure-mechanism relation on the base of crystal structure,electro nic structure and lattice dynamics.We expanded the NTE of YFe(CN)_(6)to 150 K,and the temperature dependence of volume and lattice constants was determined by temperature-variable synchrotro n X-ray diffraction measure ments.A large NTE was found in the system.Our theoretical calculations indicate that the Y-N bond exhibits a strong ionic feature through the calculated electron localization function(ELF),which has a strong influence on the anisotropic vibration of the N atom.The detailed lattice dynamics simulations suggest that the NTE of YFe(CN)_(6)may be related to the presence of the unusual low-frequency modes of the YN_(6)triangular prism(tri-prism)units.The optical branches with low frequencies are mainly related to the distortion and twisting modes of the YN_(6)tri-prism units,which contribute most to the NTE effect in the crystal.
文摘The addition of electrons to form gas-phase multiply charged anions(MCAs)normally requires sophisticated experiments or calculations.In this work,the factors stabilizing the MCAs,the maximum electron uptake of gas-phase molecules,X,and the electronic stability of MCAs X^(Q-),are discussed.The drawbacks encountered when applying computational and/or conceptual density functional theory(DFT)to MCAs are highlighted.We develop and test a different model based on the valence-state concept.As in DFT,the electronic energy,E(N,v_(ex)),is a continuous function of the average electron number,N,and the external potential,v_(ex),of the nuclei.The valence-state-parabola is a second-order polynomial that allows extending E(N,v_(ex))to dianions and higher MCAs.The model expresses the maximum electron acceptance,Q_(max),and the higher electron affinities,A_Q,as simple functions of the firstelectron affinity,A_1,and the ionization energy,I,of the"ancestor"system.Thus,the maximum electron acceptance is Q_(max,calc)=1+12A_1/7(I-A_1).The ground-state parabola model of the conceptual DFT yields approximately half of this value,and it is termed Q_(max,GS)=?+A_1/(I-A_1).A large variety of molecules are evaluated including fullerenes,metal clusters,super-pnictogens,super-halogens(OF_3),super-alkali species(OLi_3),and neutral or charged transition-metal complexes,AB_(m )L_n^(0/+/-).The calculated second electron affinity A_(2,calc)=A_1-(7/12)(I-A_1)is linearly correlated to the literature references A_(2,lit) with a correlation coefficient R=0.998.A_2 or A_3 values are predicted for further 24 species.The appearance sizes,n_(ap)^(3-),of triply charged anionic clusters and fullerenes are calculated in agreement with the literature.
文摘In previous publications, the author has proposed a model of the electron’s internal structure, wherein a positively-charged negative mass outer shell and a negatively-charged positive mass central core are proposed to resolve the electron’s charge and mass inconsistencies. That model is modified in this document by assuming the electron’s radius is exactly equal to the classical electron radius. The attributes of the internal components of the electron’s structure have been recalculated accordingly. The shape of the electron is also predicted, and found to be slightly aspherical on the order of an oblate ellipsoid. This shape is attributed to centrifugal force and compliant outer shell material. It is interesting to note that all of the electron’s attributes, both external and internal, with the exception of mass and angular moment, are functions of the fine structure constant a, and can be calculated from just three additional constants: electron mass, Planck’s constant, and speed of light. In particular, the ratios of the outer shell charge and mass to the electron charge and mass, respectively, are 3/2a. The ratios of the central core charge and mass to the electron charge and mass, respectively, are 1-(3/2a). Attributes of the electron are compared with those of the muon. Charge and spin angular momentum are the same, while mass, magnetic moment, and radius appear to be related by the fine structure constant. The mass of the electron outer shell is nearly equal to the mass of the muon. The muon internal structure can be modeled exactly the same as for the electron, with exactly the same attribute relationships.
文摘A model for the internal structure of the electron using classical physics equations has been previously published by the author. The model employs both positive and negative charges and positive and negative masses. The internal attributes of the electron structure were calculated for both ring and spherical shapes. Further examination of the model reveals an instability for the ring shape. The spherical shape appears to be stable, but relies on tensile or compressive forces of the electron material for stability. The model is modified in this document to eliminate the dependency on material forces. Uniform stability is provided solely by balancing electrical and centrifugal forces. This stability is achieved by slightly elongating the sphere along the spin axis to create a prolate ellipsoid. The semi-major axis of the ellipsoid is the spin axis of the electron, and is calculated to be 1.20% longer than the semi-minor axis, which is the radius of the equator. Although the shape deviates slightly from a perfect sphere, the electric dipole moment is zero. In the author’s previously published document, the attributes of the internal components of the electron, such as charge and mass, were calculated and expressed as ratios to the classically measured values for the composite electron. It is interesting to note that all of these ratios are nearly the same as the inverse of the Fine Structure Constant, with differences of less than 15%. The electron model assumed that the outer surface charge was fixed and uniform. By allowing the charge to be mobile and the shape to have a particular ellipticity, it is shown that the calculated charge and mass ratios for the model can be exactly equal to the Fine Structure Constant and the Constant plus one. The electron radius predicted by the model is 15% greater than the Classical Electron Radius.
