共查询到20条相似文献,搜索用时 329 毫秒
1.
2.
A new pseudo-three-dimensional electron hole in a magnetized plasma is possible when the low-frequency ion dynamics is taken into account. The newly found nonlinear Bernstein-Greene-Kruskal stationary solution, whose parallel phase velocity ranges between almost zero and the electron thermal speed, has the form of a cylinder that is tilted relative to the magnetic field. These structures are interpreted as three-dimensional electron holes coupled with hydrodynamic vortices, and provide a possible theoretical explanation for the POLAR and FAST satellite observations of coherent structures characterized by bipolar spikes of the parallel electric field and large perpendicular ion kinetic energies. 相似文献
3.
D. H. Fan 《Applied Physics A: Materials Science & Processing》2009,96(3):655-660
ZnO hollow spherical structures with different surface-to-volume ratios were prepared using solid Zn microspheres as template
via a simple oxygen-controlled thermal evaporation approach. The results of scanning electron microscopy testify that ZnO
hollow spherical structures with different morphologies can be realized by changing oxygen supply. The corresponding transmission
electron microscopy images further reveal that the prepared spherical structures are hollow, and nanorods epitaxially grow
from the surface of the sphere shell along the [0001] direction. A series of experiments indicates that the formation of hollow
spherical structures involves the oxidization on the surface of Zn microspheres, sublimation of Zn, and growth of ZnO nanorods. 相似文献
4.
We have measured the coherent optical transition radiation emitted by an electron beam from laser-plasma interaction. The measurement of the spectrum of the radiation reveals fine structures of the electron beam in the range 400-1000 nm. These structures are reproduced using an electron distribution from a 3D particle-in-cell simulation and are attributed to microbunching of the electron bunch due to its interaction with the laser field. When the radiator is placed closer to the interaction point, spectral oscillations have also been recorded, signature of the interference of the radiation produced by two electron bunches delayed by 74 fs. The second electron bunch duration is shown to be ultrashort to match the intensity level of the radiation. Whereas transition radiation was used at longer wavelengths in order to estimate the electron bunch length, this study focuses on the ultrashort structures of the electron beam. 相似文献
5.
Helical carbon nanofibers are synthesized by thermal chemical vapor deposition using copper nanocrystals as a catalyst and acetylene as a source gas at the low temperature of 195 °C. These nanocoils are symmetrically grown on copper nanocrystals in the form of twin helices. They contain high content of hydrogen. Their molecular structures are different from polyacetylene. They can be classified as a new type of amorphous carbon nanofibers. They present novel elasticity and interesting processability. The twin helices exhibit not only the reversible extension of the nanocoil itself but also the reversible angle change between the two nanocoils. They can be easily separated into two by electron beam heating. However, if a certain section of the nanocoil is heated by electron beam in a scanning mode, it will adjust its structures along the scanning line of the electron beam. 相似文献
6.
Electron localization is studied in formamide cluster anions. The isolated
formamide molecule has a large dipole moment and its clusters can give birth
to multipole-bound anions as well as valence anions. The vertical valence
electron affinity of the isolated molecule is determined by electron
transmission spectroscopy. The anion formation process is studied as a
function of cluster size with Rydberg electron transfer spectroscopy. DFT
calculations of the neutral and negatively-charged cluster structures show
that the anion excess electron localizes on a single molecule. The adiabatic
valence electron affinity of isolated formamide is deduced from the
observation of the cluster size threshold for valence attachment. 相似文献
7.
We numerically investigate the injection process of electrons from metal electrodes to one-dimensional organic molecules by combining the extended Su-Schrieffer-Heeger (SSH) model with a nonadiabatic dynamics method. It is found that a match between the Fermi level of electrodes and the highest occupied molecular orbital (HOMO) or the lowest unoccupied molecular orbital (LUMO) of organic molecules can be greatly affected by the length of the organic chains, which has a great impact on electron injection. The correlation between oligomers and electrodes is found to open more efficient channels for electron injection as compared with that in polymer/electrode structures. For oligomer/electrode structures, we show that the Schottky barrier essentially does not affect the electron injection as the electrode work function is smaller than a critical value. This means that the Schottky barrier is pinned for a small work-function electrode. For polymer/electrode structures, we find that it is possible for the Fermi level of electrodes to be pinned to the polaronic level. The condition under which the Fermi level of electrodes exceeds the polaronic level of polymers is shown to not always lead to spontaneous electron transfer from electrodes to polymers. 相似文献
8.
Herranz J Pastor I Castejon F de La Luna E Garcia-Cortes I Barth CJ Ascasibar E Sanchez J Tribaldos V 《Physical review letters》2000,85(22):4715-4718
Fine structures are found in the TJ-II stellarator electron temperature and density profiles, when they are measured using a high spatial resolution Thomson scattering system. These structures consist of peaks and valleys superimposed to a smooth average. Some irregularities remain in an ensemble average of discharges with similar macroscopic parameters such as line density, central temperature, and plasma current. They are found in all the magnetic configurations explored in plasmas heated by electron cyclotron waves. Their characteristics are shown and their possible origin is discussed. 相似文献
9.
Technical Physics - Dielectric waveguides are being intensively studied as accelerating structures excited by an electron bunch. Rectangular dielectric structures are used both to test the... 相似文献
10.
Correlative light and electron microscopy (CLEM) is a method of imaging in which the same specimen is observed by both light microscopy and electron microscopy. Specifically, CLEM compares images obtained by light and electron microscopy and makes a correlation between them. After the advent of fluorescent proteins, CLEM was extended by combining electron microscopy with fluorescence microscopy to enable molecular-specific imaging of subcellular structures with a resolution at the nanometer level. This method is a powerful tool that is used to determine the localization of specific molecules of interest in the context of subcellular structures. Knowledge of the localization of target proteins coupled with the functions of the structures to which they are localized yields valuable information about the molecular functions of these proteins. However, this method has been mostly applied to adherent cells due to technical difficulties in immobilizing non-adherent target cells, such as yeasts, during sample preparation. We have developed a method of CLEM applicable to yeast cells. In this report, we detail this method and present its extension to Live CLEM. The Live CLEM method enabled us to link the dynamic properties of molecules of interest to cellular ultrastructures in the yeast cell. Since yeasts are premier organisms in molecular genetics, combining CLEM with yeast genetics promises to provide important new findings for understanding the molecular basis of the function of cellular structures. 相似文献
11.
J. M. Kikkawa I. P. Smorchkova N. Samarth D. D. Awschalom 《Physica E: Low-dimensional Systems and Nanostructures》1998,2(1-4)
Magnetic two-dimensional electron gases are studied using time-resolved Kerr and Faraday rotation spectroscopy in the Voigt geometry. The data directly reveal both electron and Mn spin precession in modest transverse fields. Scattering by Mn ions dominates the electron spin relaxation processes in these materials, and prevents the electron gas from acquiring a long-lived spin polarization as observed in non-magnetic structures. Nonetheless, a persistent Mn spin polarization occurs which creates a oscillating magnetic field within the electron gas for hundreds of picoseconds. 相似文献
12.
P. Bushev D. Bothner J. Nagel M. Kemmler K. B. Konovalenko A. Lörincz K. Ilin M. Siegel D. Koelle R. Kleiner F. Schmidt-Kaler 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2011,63(1):9-16
We propose to couple a trapped single electron to superconducting structures located at a variable distance from the electron. The electron is captured in a cryogenic Penning trap using electric fields and a static magnetic field in the tesla range. Measurements on the electron will allow investigating the properties of the superconductor such as vortex structure, damping and decoherence. We propose to couple a superconducting microwave resonator to the electron in order to realize a circuit QED-like experiment, as well as to couple superconducting Josephson junctions or superconducting quantum interferometers (SQUIDs) to the electron. The electron may also be coupled to a vortex which is situated in a double well potential, realized by nearby pinning centers in the superconductor, acting as a quantum mechanical two level system that can be controlled by a transport current tilting the double well potential. The electron may also be coupled to a single vortex, thus hybridizing an elementary excitation of a superconductor and an elementary particle. 相似文献
13.
The study of misfit structures by means of transmission electron microscopy and associated techniques is reviewed. It is complementary to X-ray crystallography and provides a local and direct view of the beautiful complexity of these systems. Three different types are presented in this work. Misfit columnar structures can be contemplated as a case of one-dimensional misfit structures while misfit layer structures are considered as two-dimensional misfit structures. Some extra dimensionality is added when these misfit layer structures wrap to give rise to tubular crystals. Electron microscopy/diffraction shows clearly in many examples the presence of structural modulations as weak satellite reflections that are very difficult to detect by X-ray diffraction methods. Besides, high-resolution images show the presence of stacking defects in some of these misfit layer structures. 相似文献
14.
A.S. Eggeman A.K. Petford-Long P.J. Dobson J. Wiggins T. Bromwich R. Dunin-Borkowski T. Kasama 《Journal of magnetism and magnetic materials》2006
Nanoparticles of cobalt were produced by direct reduction in aqueous solution. These were subsequently coated in silica by a very slow hydrolysis reaction. Electrostatic and magnetic forces between the nanoparticles led to ordered structures forming, which were analysed by high resolution transmission electron microscopy. SQUID magnetometry showed that the nanoparticles were ferromagnetic with an additional magnetic signal from highly disordered surface states. Off-axis electron holography of the structures was undertaken and gives evidence for the mechanism by which the structures form. 相似文献
15.
The general theory of parametric coupling between space-charge waves and drifting charge carriers in thin-film semiconductor structures has been worked out. This theory is applicable, in particular, to n-GaAs and n-InP semiconductors with negative differential conductance due to intervalley electron transitions under high electric fields. We started from the electrodynamic theory of waveguide excitation by extraneous currents, which was extended for arbitrary waveguide structures with composite active media. Our theory makes it possible to study parametric interaction between space-charge waves in semiconductor films with regard for boundary conditions, diffusion, the anisotropy and the frequency dispersion of the differential electron mobility, as well as the multifrequency and multimode nature of a wave process in thin-film structures. 相似文献
16.
17.
AlSb/InAs quantum well (QW) structures and InAs films on GaAs (001) substrates were grown by molecular beam epitaxy (MBE). We investigated the dependence of electron mobility and two-dimensional electron gas (2DEG) concentration on the thickness of an InAs channel. It is found that electron mobility as high as 19050 cm2·V-1·s-1 has been achieved for an InAs channel of 22.5 nm. The Hall devices with high sensitivity and good temperature stability were fabricated based on the AlSb/InAs QW structures. Their sensitivity is markedly superior to Hall devices of InAs films. 相似文献
18.
N. A. Golodze G. A. Kartsivadze N. I. Kurdiani É. R. Kuteliya 《Russian Physics Journal》1984,27(7):627-630
The effect of irradiation with 3.5-MeV electrons on the properties of GaAlAs-based light-emitting structures is investigated. It is shown that the considerable reduction in the intensity of light emitted as a result of electron irradiation is not accompanied by changes in the recombination and electrical properties of the structures mentioned. Electron microscope and Auger spectral measurements have established that electron irradiation leads to the appearance on the external surface of the n layer of the structure regions of free aluminum accumulation, the number and size of which depend on the electron dose. The assumption is advanced that the regions mentioned may play the role of a gray filter for the light emitted by the structure.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 7, pp. 97–100, July, 1984. 相似文献
19.
Caldes MT Deniard P Zou XD Marchand R Diot N Brec R 《Micron (Oxford, England : 1993)》2001,32(5):497-507
X-ray diffraction can be used for accurately determining not only classical, ordinary structures, but also modulated ones. For structures with weak modulations, the modulation induced satellite reflections are often hard to be observed by X-ray diffraction, but they appear clearly in electron diffraction. In these cases, X-ray diffraction will give only average structures whereas electron diffraction will yield information about the modulations. Sr(1.4)Ta(0.6)O(2.9) is a complex modulated compound with weak modulation and small modulated domains. Here we demonstrate the power of combining X-ray and electron crystallography for studying modulated structures on powders. The modulations of Sr(1.4)Ta(0.6)O(2.9) were determined from electron diffraction (SAED) and high resolution electron microscopy (HREM) images. With specially developed image processing techniques, the weak modulations were enhanced, facilitating the interpretation of HREM images in terms of atomic structure. 相似文献
20.
A variational approach is used to study the surface states of an electron in a semi-infinite wurtzite nitride semiconductor. The surface-state energy of the electron is calculated, by taking the effects of the electron-surface optical phonon interaction and structure anisotropy into account. The numerical computation has been performed for the energies of the electronic surface states as a function of the surface potential V0 for wurtzite GaN, AlN, and InN, respectively. The results show that the electron-phonon interaction lowers the surface state energy. It is also found that the energies of the electronic surface-state in wurtzite structures are lower than that in the zinc-blende structures by hundreds of meV for the materials calculated. The influence of e-p-interactions on the surface state of electron cannot be neglected. 相似文献