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21.
T. Bergmann T. Gasenzer O. Nachtmann 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2007,45(2):197-210
A system of metastable plus unstable states is discussed. The mass matrix governing the time development
of the system is supposed to vary slowly with time. The adiabatic limit for this case is studied and it is shown that only
the metastable states obtain the analogs of the dynamical and geometrical phase factors familiar from stable states. Abelian
and non-Abelian geometric phase factors for metastable states are defined. 相似文献
22.
In the present investigations, we have grown the nano-crystallites of Si by metal induced crystallization process. Layers of two different metals (Al and Au) were deposited on either side of Si using thermal evaporation technique to study metal induced crystallization. Annealing of such samples was carried out in the hot stage of TEM. We have found that the crystallization of amorphous silicon starts at 150 °C through the formation of metal silicides. Formation of metal silicides was observed through selected area diffraction. Nearly complete formation of nano crystallites of Si throughout the sample was observed at 200 °C. High-resolution TEM studies confirm the formation of nano-crystallites of Si all along the film. 相似文献
23.
N. Maruyama 《Journal of solid state chemistry》2009,182(2):246-25798
Transparent crystallized glasses consisting of nonlinear optical Ba2TiSi2O8 nanocrystals (diameter: ∼100 nm) are prepared through the crystallization of 40BaO-20TiO2-40SiO2-0.5Dy2O3 glass (in the molar ratio), and photoluminescence quantum yields of Dy3+ ions in the visible region are evaluated directly by using a photoluminescence spectrometer with an integrating sphere. The incorporation of Dy3+ ions into Ba2TiSi2O8 nanocrystals is confirmed from the X-ray diffraction analyses. The total quantum yields of the emissions at the bands of 4F9/2→6H15/2 (blue: 484 nm), 4F9/2→6H13/2 (yellow: 575 nm), and 4F9/2→6H11/2 (red: 669 nm) in the crystallized glasses are ∼15%, being about four times larger compared with the precursor glass. It is found that the intensity of yellow (575 nm) emissions and the branching ratio of the yellow (575 nm)/blue (484 nm) intensity ratio increase largely due to the crystallization. It is suggested from Judd-Ofelt analyses that the site symmetry of Dy3+ ions in the crystallized glasses is largely distorted, giving a large increase in the yellow emissions. It is proposed that Dy3+ ions substitute Ba2+ sites in Ba2TiSi2O8 nanocrystals. 相似文献
24.
T. Bergmann T. Gasenzer O. Nachtmann 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2007,45(2):211-227
We discuss and calculate parity conserving (PC) and parity violating (PV) geometric phases for the metastable 2S states of
hydrogen and deuterium. The atoms are supposed to be subjected to slowly varying electric and magnetic fields which act as
external parameters for the atoms. Geometric flux density fields are introduced which allow for an easy overview how to choose
the paths in parameter space in order to obtain only PC or only PV geometric phases. The PV phases are calculated in the Standard
Model of particle physics. Even if numerically they come out small they have interest of principle as a new manifestation
of parity violation in atomic physics.
Electronic supplementary material Supplementary Online Material 相似文献
25.
E. Jahier J. Guéna Ph. Jacquier M. Lintz M.A. Bouchiat 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,17(2):221-229
We demonstrate the production of an electric field inside a high temperature cesium vapor cell with external electrodes. This external control of the electric field, which is not possible with a glass cell in presence of a cesium
vapor, is achieved using a cell made of sapphire, and is of particular interest for our ongoing Parity Violation experiment.
We describe the main components and the implementation on the set-up, including the pulsed high voltage generator. With pulse
duration not exceeding 200 ns the system provides a reversible longitudinal E-field of up to 2 kV/cm in the vapor at a density of ∼ 2×1014 at/cm3 without discharge. Atomic signals attest the application of the electric field in the cell, with the predicted value. Further
improvements obtained with sapphire cells are also presented.
Received 15 September 2000 相似文献
26.
The spinel NiCo2O4 nanofibers with diameters of 50-100 nm were prepared by high temperature calcinations of a simple inorganic-polymer composite fibers, which were obtained by electrospinning of the PVA/cobalt acetate/nickel acetate composite precursor. The crystallinity, purity, and surface morphology of the as-prepared NiCo2O4 nanofibers were investigated by XRD, FT-IR, SEM, respectively. 相似文献
27.
2 + Na2S → CdS + 2NaCl induced by mechanical milling resulted in the formation of CdS particles with an average diameter of < 8 nm.
The average particle size was controlled within the range of 4 to 8 nm by varying the size of the grinding media. The onset
energy of optical absorption showed a blue shift with decreasing particle size.
Received: 29 August 1997/Accepted: 25 September 1997 相似文献
28.
G. Palasantzas 《Solid State Communications》2003,127(3):219-222
We have fabricated cobalt-silicide nanowires on silicon by removing hydrogen from a passivated Si(001)2×1 surface with a scanning tunnelling microscope, followed by evaporation of cobalt. The apparent shape of the wires depends on the bias applied to the tip. This is due to the Fermi level pinning close to the valence edge by the high work function Pt-Ir tips, and the Co acceptor levels 0.35 eV above the valence band. Moreover, the decrement in the image contrast with increasing bias voltage is related to decrement in the local density of states, which is in qualitative agreement with former studies of nanosized cobalt disilicide islands. 相似文献
29.
Aluminum nitride nanorods were grown during rapid thermal annealing of multi-layered Al2S3 /BaS thin films. Depending on the thickness ratio between the BaS and Al2S3 layers, nanowires or straight nanorods were obtained. Typical dimensions for the nanorods were a diameter in the range of 50-100 nm and a length of 2-5 μm. The nanostructures are formed upon annealing at a relatively low temperature of 900 °C when aluminum evaporates from the thin film, but remains trapped between the thin film surface and the Si wafer, which is used as a support during the annealing. The nitrogen is provided by N2 gas flushed through the annealing chamber. High-resolution transmission electron microscopy showed crystalline, wurtzite-structured AlN nanorods. The growth mechanism in terms of thin film composition, annealing parameters and the role of catalysts is discussed. 相似文献
30.
Inorganic-organic intercalation compounds comprised of montmorillonite (MMT) and aniline salts with different counter anions were prepared by a mechanochemical processing. The intercalation process and the formed structure of intercalation compounds were investigated via X-ray diffraction analysis. The amounts of intercalated species were very likely dependent on the types of counter anions and increased with decreasing the size of counter anions during the mechanochemical processing. Very interestingly, much larger interlayer expansions of 1.51 nm was observed for aniline hydrofluoride AnF- and aniline hydrochloride AnCl-MMT systems in higher intercalates loading levels, suggesting that neutral guest molecules also introduce within the interlayer regions together with anilinium cations by van der Waals interactions. Judging from the larger interlayer expansions and the size of guest molecules, intercalated species are expected to prefer a tri-molecular layer arrangement with their aromatic rings perpendicular to the silicate sheets. In contrast, for aniline hydrobromide AnBr-MMT, the interlayer expansion was ca. 0.52 nm, which reveals that only anilinium cations are introduced by ion exchange and they probably adopt a vertical orientation in the interlayers. It is inferred that aniline hydroiodide AnI-MMT compounds have a heterogeneous structure containing both anilinium and sodium cations in the interlayers. Different intercalation behaviors during the mechanochemical processing strongly suggest the smaller the size of counter anions, the more guest molecules can be intercalated into the confined clay interlayers in highly ordered arrangements. 相似文献