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1.
The structures and properties of Wn (n=2-14) clusters were studied by using the density functional theory (DFT) at LSDA level. The most stable structures of Wn (n=2-14) clusters with global minimum were determined. The average binding energy (Eb), the first and second difference of total energy (△E,△2E), the vertical detachment energy (VDE), and the HOMO-LUMO gap versus the size were also discussed. The abrupt decrease of VDE and HOMO-LUMO gap at size n=8 and 10 implied that tungsten clusters of W8 and W10 appeared to have metallic features. These changes were also accompanied by the delocalization of electron charge density and the strong hybridization between 5d and 6s orbits in W8 and W10 clusters. Our results are in good agreement with the available experimental data.  相似文献   

2.
Quantum Theory of Electronic Double-Slit Diffraction   总被引:1,自引:0,他引:1       下载免费PDF全文
Phenomena of electron, neutron, atomic and molecular diffraction have been studied in many experiments, and these experiments have been explained by some theoretical works. We study electronic double-slit diffraction with a quantum mechanical approach and obtain the following results: (1) When the ratio of d + a /a=n (n = 1,2, 3,...), orders n, 2n, 3n,... are missing in diffraction pattern. (2) When the ratio of d+a/a≠ n (n =1,2, 3,...), there is a not missing order in diffraction pattern. (3) The slit thickness c has a large affect on the electronic diffraction pattern, which is a new quantum effect. We believe that all the predictions in our work can be tested by the electronic double slit diffraction experiment.  相似文献   

3.
Cross sections for electron impact excitation of lithium from the ground state 1s^22s to the excited states 1s2s^2, 1s2p^2, 1s2snp (n = 2-5), 1s2sns (n = 3 5), 1s2pns (n = 3-5), and 1s2pnp (n = 3-5) are calculated by using a full relativistic distorted wave method. The latest experimental electron energy loss spectra for inner-shell electron excitations of lithium at a given incident electron energy of 2500 eV [Chin. Phys. Lett. 25 (2008)3649] have been reproduced by the present theoretical investigation excellently. At the same time, the structures of electron energy loss spectra of lithium at low incident electron energy are also predicted theoretically, it is found that the electron energy loss spectra in the energy region of 55-57eV show two-peak structures.  相似文献   

4.
张贺  骆军  朱航天  刘泉林  梁敬魁  李静波  刘广耀 《中国物理 B》2012,21(10):106101-106101
Polycrystalline p-type Ag 0.9 Sb 1.1 x Mn x Te 2.05(x = 0.05,0.10,and 0.20) compounds have been prepared by a combined process of melt-quenching and spark plasma sintering.The sample composition of Ag 0.9 Sb 1.1 x Mn x Te 2.05 has been specially designed in order to achieve the doping effect by replacing part of Sb with Mn and to present the uniformly dispersed Ag 2 Te phase in the matrix by adding insufficient Te,which is beneficial for optimizing the electrical transport properties and enhancing the phonon scattering effect.All the samples have the NaCl-type structure according to our X-ray powder diffraction analysis.After the treatment of spark plasma sintering,only the sample with x = 0.20 has a small amount of MnTe 2 impurities.The thermal analysis indicates that a tiny amount of Ag 2 Te phase exists in all these samples.The presence of the MnTe 2 impurity with high resistance and high thermal conductivity leads to the deteriorative thermoelectric performance of the sample with x = 0.20 due to the decreased electrical transport properties and the increased thermal conductivity.In contrast,the sample with x = 0.10 exhibits enhanced thermoeletric properties due to the Mn-doping effect.A dimensionless thermoelectric figure of merit of 1.2 is attained for the sample with x = 0.10 at 573 K,showing promising thermoelectric properties in the medium temperature range.  相似文献   

5.
Polycrystalline p-type Ag 0.9 Sb 1.1 x Mn x Te 2.05(x = 0.05,0.10,and 0.20) compounds have been prepared by a combined process of melt-quenching and spark plasma sintering.The sample composition of Ag 0.9 Sb 1.1 x Mn x Te 2.05 has been specially designed in order to achieve the doping effect by replacing part of Sb with Mn and to present the uniformly dispersed Ag 2 Te phase in the matrix by adding insufficient Te,which is beneficial for optimizing the electrical transport properties and enhancing the phonon scattering effect.All the samples have the NaCl-type structure according to our X-ray powder diffraction analysis.After the treatment of spark plasma sintering,only the sample with x = 0.20 has a small amount of MnTe 2 impurities.The thermal analysis indicates that a tiny amount of Ag 2 Te phase exists in all these samples.The presence of the MnTe 2 impurity with high resistance and high thermal conductivity leads to the deteriorative thermoelectric performance of the sample with x = 0.20 due to the decreased electrical transport properties and the increased thermal conductivity.In contrast,the sample with x = 0.10 exhibits enhanced thermoeletric properties due to the Mn-doping effect.A dimensionless thermoelectric figure of merit of 1.2 is attained for the sample with x = 0.10 at 573 K,showing promising thermoelectric properties in the medium temperature range.  相似文献   

6.
The lowest-energy structures and the electronic properties of CdnSn (n = 1 - 8) clusters have been studied by using denslty-functional theory simulating package DMol^3 in the generalized gradient approximation (GGA). The ring-like structures are the lowest-energy configurations for n = 2, 3 and the three-dimensional spheroid configurations for n = 4 - 8. The three-dimensional structures may be considered as being built from the Cd2S2 and Cd3S3 rings. Compared to the previous reports, we have found the more stable structures for CdnSn(n = 7, 8). Calculations show that the magic numbers of CdnSn (n = 1-8) clusters are n = 3 and 6. As cluster size increases, the properties of CdnSn clusters tend to bulk-like ones in binding energy per CdS unit and Mulliken atomic charge, obtained by comparing with the calculated results of the wurtzite and zinc blende CdS for the same simulating parameters.  相似文献   

7.
The electric field in a surface discharge type ac-PDP cell with He or He/Xe(0.1%) mixture has been measured over a wide range of pressure (5-50 kPa) using laser induced fluorescence detection. The wall voltage was estimated from the measured electric field. The Stark manifolds of triplet atomic helium Rydberg state (2s^3S) with principal quantum numbers (n=8 and 9) have been used to measure the electric field, as the lifetime of 2s^3S is longer than the single atomic helium Rydberg state (2s^1S) in high pressure discharge. Comparison of the Stark manifolds between the n=9 and n=8 shows that the measurement accuracy of electric field can be increased by 10%. The maximum electric field strength during discharge and the wall voltage at the end of pulse decreases with the increase of pressure. The comparison of He and He/Xe(0.1%) discharge at 13 kPa showed that He/Xe gas mixture discharge can accumulate more wall charge on MgO surface and the electric field was somewhat higher than those of pure helium discharge during pulse off period under the same discharge conditions.  相似文献   

8.
High-spin states in ~(126)Te have been investigated by using in-beam γ ray spectroscopy with the ~(124)Sn(~7Li,1p4n)~(126)Te reaction at a beam energy of 48 MeV.The previously known level scheme has been enriched,and a new negative-parity sequence has been established.The yrast positive-parity band shows a shape change between triaxial shape and collective oblate shape as a function of spin.In particular,three competitive minima appear in the potential energy surface for the I~π=8~+ states,with one aligned state at γ =-120° and two triaxial states atγ ~30° and-45°,respectively.The signature splitting behavior of the negative-parity band is discussed.The shape change with increasing angular momentum and the signature splitting can be interpreted well in terms of the Cranked Nilsson-Strutinsky-Bogoliubov and Cranked Nilsson-Strutinsky model calculations.  相似文献   

9.
《中国物理快报》2004,21(1):187-190
Structural measurements have revealed nonlinear changes of lattice parameters in the layered-perovskite manganires La2-xSrxMnO4 with increasing Sr content; these changes can be well understood by means of interactions among the charge, crystal lattice and the orbital degree of freedom in this strongly correlated system. A probably spin-glass transition was detected for the first time in the x=1.75 sample at the temperature of around 44K. Fundamental properties of charge ordering appearing in the range of 1.5 ≤x≤1.75 have been observed at low-temperatures and are interpreted in terms of the Mn^3 -dz^2 orbital ordering.  相似文献   

10.
于荣梅  程勇军  王旸  周雅君 《中国物理 B》2012,21(5):53402-053402
Investigations of resonances and threshold behaviors in positron-helium scattering have been made using the momentum-space coupled-channels optical method.The positronium formation channels are considered via an equivalent-local complex potential.The s-wave resonances and the Wigner cusp feature at the positronium(n = 1) formation threshold are compared with the previous reports.The p-and the d-wave resonances and a Wigner cusp feature at the positronium(n = 2) formation threshold are reported for the first time.  相似文献   

11.
In the two-dimensional electron systems with strong coupling in MgZnO/ZnO heterostructures, the thermal behavior of Ising quantum Hall ferromagnets at the filling factor ν = 2 has been studied. The spin polarization of Hall ferromagnets has been detected by measuring the signal related to the inelastic light scattering by intrasubband spin excitons. A stepwise change in the spin polarization at the phase transition at the filling factors ν = 2,3, and 4 in the heterostructures with different electron densities has been observed. The thermal stability of the Hall ferromagnetic phases at ν = 2 has been studied and the Curie temperature has been estimated. It has been shown that the Curie temperature is determined by the formation energy for domain walls in the Ising quantum Hall ferromagnets.  相似文献   

12.
New experiments are reported which improve our estimates of the bandwidth and energy flux of the observed radiation. These include search for coincident, sudden increases in power of newly instrumented detectors at 1661 Hertz and 1581 Hertz, at opposite ends of a 1000 kilometer baseline, and search for coincidences between outputs of detectors at 1661 Hertz and 5000 Hertz. Coincidences are observed for the detectors separated by 80 Hertz, implying a radiation bandwidth exceeding 80 Hertz.The new instrumentation is a modification of the earlier technique for bonding ferroelectric crystals to aluminium cylinders. Three detectors are fully operational with sensitivity one order better than earlier ones.Progress has been made in data retrieval employing a computer and magnetic tape. Earlier results on the coincidence rates and time delay experiments have been confirmed.A 1661 Hertz detector has been developed for operation at liquid helium temperatures. It is now undergoing tests at the Argonne National Laboratory.An experiment has been approved by NASA to employ the moon as a gravitational radiation detector. Equipment has been designed by Bendix and the University of Maryland for emplacement by the Apollo 17 astronauts.Supported in part by the U.S. National Science Foundation.Presented at the International Conference on Gravitation and Relativity, Copenhagen, 5–10 July, 1971.  相似文献   

13.
Cluster-based nanostructured films of Si clusters embedded in SiO nanoparticles have been prepared by low energy deposition of SiO cluster beam formed by inert gas aggregating method. The microstructures of the nanofilms have been characterized by TEM and the chemical components of the nanofilms have been analyzed by XPS spectra. It is shown that the film is assembled by the ultrafine spherical nanoparticles, which are distributed randomly and uniformly in the film, while the Si clusters produced by SiO disproportionation reaction are embedded dispersedly in the nanoparticles. Furthermore, the photoluminescence properties of the films have been measured and a blue PL band at wavelength of 400 nm with a shoulder peak at 393 nm has been observed. The PL band at 400 nm may be attributed to quantum confinement effect of the Si cores confined in SiO nanoparticles and energy potential barrier effect of outer SiO layer, while the 393 nm PL shoulder peak may be caused by the oxygen-deficient-associated defect centers.  相似文献   

14.
15.
The temperature dependence of the frequency spectrum of tantalum in the temperature range from room temperature to 2300 K has been studied for the first time using inelastic slow-neutron scattering. The inelastic slow-neutron scattering spectra have been measured at different temperatures on a DIN-2PI time-of-flight spectrometer installed at the IBR-2 nuclear reactor (Joint Institute for Nuclear Research, Dubna, Russia) with the use of a TS3000K high-temperature thermostat. From the measured spectra, the frequency spectra of the tantalum crystal lattice have been determined at temperatures of 293, 1584, and 2300 K by the iteration method. As the temperature increases, the frequency spectrum, on the whole, is softened and the specific features manifested themselves at room temperature are smoothed. The variations observed have been explained by the increase in the role of the effects of vibration anharmonism at high temperatures.  相似文献   

16.
徐庆宇  温峥  高锦龙  吴迪  邱腾  唐少龙  徐明祥 《中国物理 B》2011,20(8):87505-087505
N-doped ZnO films were prepared in nitrogen plasma by pulsed laser deposition.Clear room temperature ferro-magnetism has been observed in the film prepared at a substrate temperature of 500 C.The structural characterizations of X-ray diffraction,Raman,and X-ray photoelectron spectroscopy confirm the substitution of O by N in ZnO,which has been considered to be the origin of the observed ferromagnetism.Furthermore,ferroelectricity has been observed at room temperature by piezoelectric force microscopy,indicating the potential multiferroic applications.  相似文献   

17.
The features of the kinetics of the initiation of detonation condensation waves in carbon suboxide and acetylene have been experimentally studied at high pressures near the low-temperature limits. The role of quantum effects in the expansion of detonation limits has been analyzed. Quantum corrections to the endothermic reaction rates, which are caused by an increase in the high-energy tails of the momentum distribution functions at high pressures due to the manifestation of the uncertainty principle for the energy of colliding particles at a high collision frequency, have been quantitatively estimated. It has been shown that experimentally observed deviations in Arrhenius dependences of the induction periods of the initiation of detonation condensation waves are well described by the proposed quantum corrections.  相似文献   

18.
Optical Tamm states localized at the edges of a photonic crystal bounded from one or both sides by a nanocomposite have been studied. The nanocomposite consists of metallic nanoinclusions, which have a spherical or orientationally ordered spheroidal shape and are dispersed in a transparent matrix, and is characterized by the resonant effective permittivity. The transmission, reflection, and absorption spectra have been calculated for waves with longitudinal and transverse polarizations in such structures at the normal incidence of light. The spectral manifestation of Tamm states that is due to the existence of negative values of the real part of the effective permittivity has been analyzed for the visible spectral range. It has been established that the characteristics of Tamm states localized at the edge of the photonic crystal depend strongly both on the concentration of nanoballs in the nanocomposite film and on its thickness. Modes formed by two coupled Tamm plasmon polaritons localized at the edges of the photonic crystal adjacent to two nanocomposite layers have been examined. It has been shown that, in the case of the anisotropic nanocomposite layer adjacent to the photonic crystal, each of two orthogonal polarizations of the incident wave corresponds to a specific frequency of the Tamm state localized at the edge; owing to this property, the transmission spectra of such a structure are polarization sensitive.  相似文献   

19.
Microwave cyclotron resonance of electrons and holes at the metal-to-semimetal transition in HgTe quantum wells with an inversed band structure has been investigated. The resonance has been studied by measuring microwave photoresistance in the frequency range of 35–170 GHz. The effective cyclotron masses of electrons and holes have been determined. A shift of the cyclotron resonance of the two-dimensional electrons at the metal-to-semimetal transition possibly caused by plasma effects in the two-dimensional semimetal has been discovered.  相似文献   

20.
The structure, Young’s modulus defect, and internal friction in aluminum-germanium alloys have been studied under conditions of longitudinal elastic vibrations with a strain amplitude in the range of 10?6?3 × 10?4 at frequencies about 100 kHz. The ribbon-shaped samples of the alloys with the germanium content from 35 to 64 wt % have been produced by drawing from the melt by the Stepanov method at a rate of 0.1 mm/s. It has been shown that the dependences of the Young’s modulus defect, logarithmic decrement, and vibration stress amplitude on the germanium content in the alloy at a constant strain amplitude have an extremum at 53 wt % Ge. This composition corresponds to the eutectic composition. The dependences of the Young’s modulus defect, the decrement, and vibration stress amplitude at a constant microstrain amplitude have been explained by the vibrational displacements of dislocations, which depend on the alloy structure.  相似文献   

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