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排序方式: 共有142条查询结果,搜索用时 31 毫秒
61.
Albert Prodan Herman J.P. van Midden Sao turm Rok
itko Erik Zupani
J. Craig Bennett Robert MacDougall Pawel Starowicz 《Solid State Sciences》2009,11(9):1556-1561
High-resolution transmission electron microscopy (HRTEM), resistivity measurements and electronic band structure calculations performed by means of the extended Hückel tight-binding method are presented for the quasi one-dimensional compounds AxNb3Te4 (A = In, Tl, Zn, Ag, Hg). HRTEM and electron diffraction performed on pure Nb3Te4 at room- and liquid nitrogen temperatures, reveal both the basic structure and the low-temperature charge-density waves (CDWs) modulation. Resistivity vs. temperature plots show characteristic CDW anomalies, dependent on the type and concentration of the atoms, intercalated into the large hexagonal tunnels of the host structure. It is shown that intercalation of Tl and In results in a flattening of the corresponding Fermi surfaces and that CDW formation is largely dependent on the coincidence between the Fermi level EF and a small peak in the density of states spectrum, mainly developed from the Nb dz2 orbitals. This peak is positioned in a minimum between the filled and empty states of the spectrum and tends to split into a doublet as a consequence of intercalation. 相似文献
62.
A.N. Pisarchik R. Meucci F.T. Arecchi 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,13(3):385-391
The discrete distribution of homoclinic orbits has been investigated numerically and experimentally in a CO2 laser with feedback. The narrow chaotic ranges appear consequently when a laser parameter (bias voltage or feedback gain)
changes exponentially. Up to six consecutive chaotic windows have been observed in the numerical simulation as well as in
the experiments. Every subsequent increase in the number of loops in the upward spiral around the saddle focus is accompanied
by the appearance of the corresponding chaotic window. The discrete character of homoclinic chaos is also demonstrated through
bifurcation diagrams, eigenvalues of the fixed point, return maps, and return times of the return maps.
Received 28 September 2000 and 27 October 2000 相似文献
63.
We consider quantum heat flow in two-terminal junctions and inquire on the connection between the transport mechanism and the junction functionality. Using simple models, we demonstrate that the violation of the Landauer behavior in asymmetric junctions does not necessarily imply the onset of thermal rectification. We also demonstrate through a simple example that a spatial inhomogeneity of the energy spectra is not a necessary condition for thermal rectification. 相似文献
64.
P. Galatola G. Coupier M. Saint Jean J.-B. Fournier C. Guthmann 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,50(4):549-557
Macroscopic Wigner islands present an interesting
complementary approach to explore the properties of two-dimensional
confined particles systems. In this work, we characterize theoretically
and experimentally the interaction between their basic components, viz.,
conducting spheres lying on the bottom electrode of a plane condenser.
We show that the interaction energy can be approximately described by a
decaying exponential as well as by a modified Bessel function of the
second kind. In particular, this implies that the interactions in this
system, whose characteristics are easily controllable, are the same as
those between vortices in type-II superconductors. 相似文献
65.
Single-crystal nanowires of hexagonal tungsten trioxide in a large scale have been successfully prepared by a simple hydrothermal method without any templates and catalysts. Uniform h-WO3 nanowires with diameter of 25-50 nm and length of up to several micrometers are obtained. It is found that the morphology and crystal form of the final products are strongly dependent on the amount of the sulfate and pH value of the reaction system. The electrochemical performances of the as-prepared h-WO3 nanowires as anodic materials of Li-ion batteries have also been investigated. It deliveres a discharge capacity of 218 mAh g−1 for the first cycle. In addition, the cycle ability of the nanocrystals is superior to that of bulk materials, which implies the morphology and particle size have the influence on the electrochemical performances. 相似文献
66.
Photoinduced optiсal second harmonic generation was studied in nanocrystalline SiC films prepared by the method of direct ion deposition. For the studies were chosen three types of polytypes (with different degree of hexagonality) – 24R with degree hexagonality G=25, 27R-G=44, 33R with – G=36. The bicolor photoinduced treatment was performed by the wavelengths 1064nm/532 nm by 15 ns YAG:Nd laser. The efficiency of the output SHG was evaluated by ratio of the corresponding signal intensities with respect to the references and by the time delay between the SHG and the fundamental maxima. Explanation of the observed effect is given within a framework of the occurrence of the nano-trapping levels in the film crystalline interfaces. 相似文献
67.
《Current Applied Physics》2015,15(11):1506-1511
We demonstrate the production of low-dimensional carbon nanomaterials using a solution plasma system and their application to flexible conductive paper. The solution plasma system consists of two graphite electrodes and a beaker filled with ferritin-mixed deionized water. Ferritin molecules are used as the growth catalyst of the carbon nanomaterials. A high voltage of 15 kV at a frequency of 25 kHz is supplied to the electrodes using an alternating-current power source. The effects of the graphite rod diameters and the concentration of ferritin molecules are comparatively investigated. The produced carbon nanomaterials are characterized using Raman spectroscopy, scanning electron microscopy, and transmission electron microscopy. We confirmed the synthesis of graphitic platelets, onion-like structures, and carbon nanotubes. Finally, we fabricated flexible conductive papers using the produced materials with a good electrical conductance. 相似文献
68.
Genuine organic anion-radical salt (N-Me-2,6-di-Me–Py)(TCNQ)2 with pyridine-based cation was synthesized and its crystal structure was resolved. The DC magnetic susceptibility was measured in temperature range from 2 K to 300 K in magnetic fields 10 mT, 100 mT and 1 T. Zero field cooling (ZFC) and field cooling (FC) modes were used. The results were studied in terms of one-dimensional magnetic models and we have found that the most suitable of them is an antiferromagnetic linear Heisenberg S = 1/2 system with small amount of free spins. An additional peak observed at low temperatures can be explained by an interchain coupling between free chain-end spins. 相似文献
69.
《Particuology》2022
Nanomaterials with low-dimensional morphology display unique properties in catalysis and related fields, which are highly dependent on the structure and aspect ratio. Thus, accurate identification of the structure and morphology is the basis to correlate to the performance. However, the widely adopted techniques such as XRD is incapable to precise identify the aspect ratio of low-dimensional nanomaterials, not even to quantify the morphological uniformity with statistical deviation value. Herein, ZnO nanorod and nanosheet featured with one- and two-dimensional morphology were selected as model materials, which were prepared by the hydrothermal method and statistically characterized by transmission electron microscopy (TEM). The results indicate that ZnO nanorods and nanosheets display rod-like and orthohexagnal morphology, which mainly encapsulated with {100} and {001} planes, respectively. The 7.36 ± 0.20 and 0.39 ± 0.02 aspect ratio (c/a) of ZnO nanorods and nanosheets could be obtained through the integration of the (100) and (002) diffraction rings in selected area electron diffraction (SAED). TEM combining with the SAED is favorable compare with XRD, which not only provides more accurate aspect ratio results with standard deviation values but also requires very small amounts of sample. This work is supposed to provide a convenient and accurate method for the characterization of nanomaterials with low-dimensional morphology through TEM. 相似文献
70.
A. M. Panich A. I. Shames H.-M. Vieth E. Ōsawa M. Takahashi A. Ya. Vul' 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,52(3):397-402
We report on a nuclear magnetic resonance (NMR) study of
ultrananocrystalline diamond (UNCD) materials produced by detonation
technique. Analysis of the 13C and 1H NMR spectra, spin-spin and
spin-lattice relaxation times in purified UNCD samples is presented. Our
measurements show that UNCD particles consist of a diamond core that is
partially covered by a sp
2-carbon fullerene-like shell. The uncovered
part of outer diamond surface comprises a number of hydrocarbon groups that
saturate the dangling bonds. Our findings are discussed along with recent
calculations of the UNCD structure. Significant increase in the spin-lattice
relaxation rate (in comparison with that of natural diamond), as well as
stretched exponential character of the magnetization recovery, are
attributed to the interaction of nuclear spins with paramagnetic centers
which are likely fabrication-driven dangling bonds with unpaired electrons.
We show that these centers are located mainly at the interface between the
diamond core and shell. 相似文献