共查询到20条相似文献,搜索用时 31 毫秒
1.
H. Ohtsuka K. Hojou H. Maeta H. Otsu H. Sugai H. Yamamoto 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,16(1):309-311
We investigated defect formation within nanostructured materials using a transmission electron microscope (TEM) and ion accelerators.
Controlling diffusion coefficient of the defects we have first observed changes in pattern of defect clusters, namely, the
diffusion-limited reaction of defects in nanocrystals.
Received 30 November 2000 相似文献
2.
M.N. Huda A.K. Ray 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2003,22(2):217-227
The formalisms of many body perturbation theory and coupled cluster theory have been used to study the electronic and geometric
structures of neutral, cationic, and anionic small silver clusters. Hay-Wadt relativistic effective core potentials replacing
the twenty-eight core electrons and a Gaussian basis set have been used. Topologically different clusters and clusters belonging
to different symmetry groups have been identified and studied in detail. Full geometry optimizations have been carried out
at four different correlated levels of theories. Ionization potentials, electron affinities, and fragmentation energies of
the optimized clusters have been compared with other experimental and theoretical results available in the literature. No
convergence problems are encountered at the various levels of correlated theories. This is noteworthy since it has been claimed
in the literature that for d elements the MP series does not converge very well.
Received 16 April 2002 / Received in final form 12 September 2002 Published online 21 January 2003
RID="a"
ID="a"e-mail: akr@uta.edu 相似文献
3.
I. Vodenska-Chitkushev F. Z. Wang P. Weber K. Yamasaki S. Havlin H. E. Stanley 《The European Physical Journal B - Condensed Matter and Complex Systems》2008,61(2):217-223
We analyze the S&P 500 index data for the 13-year period, from
January 1, 1984 to December 31, 1996, with one data point every 10
min. For this database, we study the distribution and clustering
of volatility return intervals, which are defined as the time
intervals between successive volatilities above a certain threshold
q. We find that the long memory in the volatility leads to a
clustering of above-median as well as below-median return intervals.
In addition, it turns out that the short return intervals form
larger clusters compared to the long return intervals. When
comparing the empirical results to the ARMA-FIGARCH and fBm models
for volatility, we find that the fBm model predicts scaling better
than the ARMA-FIGARCH model, which is consistent with the argument
that both ARMA-FIGARCH and fBm capture the long-term dependence in
return intervals to a certain extent, but only fBm accounts for the
scaling. We perform the Student's t-test to compare the empirical
data with the shuffled records, ARMA-FIGARCH and fBm. We analyze
separately the clusters of above-median return intervals and the
clusters of below-median return intervals for different thresholds
q. We find that the empirical data are statistically different
from the shuffled data for all thresholds q. Our results also
suggest that the ARMA-FIGARCH model is statistically different from
the S&P 500 for intermediate q for both above-median and
below-median clusters, while fBm is statistically different from
S&P 500 for small and large q for above-median clusters and for
small q for below-median clusters. Neither model can fully explain
the entire regime of q studied. 相似文献
4.
P. Specht J.C. Ho X. Xu R. Armitage E.R. Weber R. Erni C. Kisielowski 《Solid State Communications》2005,135(5):340-344
Valence electron energy loss spectroscopy (VEELS) was applied to determine band transitions in wurtzite InN, deposited by molecular beam epitaxy on (0001) sapphire substrates or GaN buffer layers. The GaN buffer layer was used as VEELS reference. At room temperature a band transition for wurtzite InN was found at (1.7±0.2 eV) and for wurtzite GaN at (3.3±0.2 eV) that are ascribed to the fundamental bandgap. Additional band transitions could be identified at higher and lower energy losses. The latter may be related to transitions involving defect bands. In InN, neither oxygen related crystal phases nor indium metal clusters were observed in the areas of the epilayers investigated by VEELS. Consequently, the obtained results mainly describe the properties of the InN host crystal. 相似文献
5.
Spatial sensitometry variations in a liquid crystal light valve are studied as well as signal induced noise and differences
in global and local contrast ratio. The device's off state is investigated and spatial variations in the thickness of the
LC layer are used to quantify the results obtained. Operation with low frequency applied ac voltages appears preferable from
noise considerations, whereas operation at high frequency appears preferable for improved uniformity. 相似文献
6.
T. Döppner S. Teuber Th. Diederich Th. Fennel P. Radcliffe J. Tiggesbäumker K. H. Meiwes-Broer 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2003,24(1-3):157-160
Lead clusters are exposed to strong femtosecond light
pulses. The dependence of the recoil energy on the charge state
of the atomic ion is now investigated using a new detection
setup, i.e., a Thomson
analyser. First results show that in contrast to laser-induced
overdense plasmas at surfaces the recoil energy distribution
appears much narrower. Comparing free lead clusters with lead
clusters embedded in large helium droplets, the charging
dynamics show distinct differences on the femtosecond time
scale. In the embedded case the maximum ionization enhancement
is reached earlier. 相似文献
7.
Y. Chushak L.S. Bartell 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,16(1):43-46
A set of molten gold clusters, each with 1157 gold atoms, was studied by molecular dynamics simulations as the clusters underwent
freezing at three different temperatures. Most of the clusters attained an icosahedral structure upon freezing, a structure
found to be stable to mild annealing. Other structures observed were imperfect truncated decahedral, truncated octahedral
and hexagonal close packed structures. The role of kinetics in the process of cluster solidification is discussed.
Received 6 November 2000 相似文献
8.
M.E. Garcia 《Applied Physics A: Materials Science & Processing》2001,72(3):261-271
A theoretical study of different ultrafast nonequilibrium processes taking place during and after ultrashort excitation of
clusters is presented. We discuss similarities and differences for several processes involving nonequilibrium ultrafast motion
of atoms and electrons. We study ultrashort relaxation of clusters in response to excitations produced by femtosecond laser
pulses of different intensities. We show how different relaxation processes, such as bond breaking, melting, fragmentation,
emission of atoms, or Coulomb explosion, can be induced, depending on the laser intensity and laser pulse duration. We also
discuss processes involving nonequilibrium electron dynamics, such as intraband Auger decay in clusters and ultrafast electronic
motion during collisions between clusters and surfaces. We show that this electron dynamics leads to Stückelberg-like oscillations
of measurable quantities, such as the electron emission yield.
Received: 4 April 2000 / Accepted: 6 November 2000 / Published online: 9 February 2001 相似文献
9.
N. S. Maslova S. I. Oreshkin V. I. Panov S. V. Savinov A. Depuydt C. Van Haesendonck 《JETP Letters》1998,67(2):146-152
We have used scanning tunneling microscopy and scanning tunneling spectroscopy at liquid helium temperature to study the electronic
structure of in situ cleaved, (110) oriented surfaces of InAs single crystals. Both unperturbed, atomically flat areas and areas with an atomic-size
defect cluster have been investigated. We show that the anomalous behavior of the local tunneling conductivity, which indicates
a pronounced enhancement of the semiconductor band gap for the flat areas, is consistent with band bending induced by charges
localized at the apex of the tip. Atomic-size defect clusters contain additional charges which modify the band bending; this
explains the different behavior of the tunneling conductivity near the defect cluster. The experimentally observed oscillations
of the tunneling conductivity near the band gap edges can be directly related to resonant tunneling through quantized surface
states which appear because of the band bending.
Pis’ma Zh. éksp. Teor. Fiz. 67, No. 2, 130–135 (25 January 1998)
Published in English in the original Russian journal. Edited by Steve Torstveit. 相似文献
10.
E. Kasabova D. Alamanova M. Springborg V. G. Grigoryan 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2007,45(3):425-431
The soft deposition of Ni13 and Cu13 clusters on Ni(111) and Cu(111) surfaces is studied by
means of constant-energy molecular-dynamics simulations.
The atomic interactions are described by the Embedded Atom Method.
It is shown that the shape of the nickel clusters deposited on Cu(111) surfaces remains rather intact,
while the copper clusters impacting on Ni(111) surfaces collapse forming double and triple layered
products. Furthermore, it is found that for an impact energy of 0.5 eV/atom the structures of all
investigated clusters show the lowest similarity to the original structures, except for the case of
nickel clusters deposited on a Cu(111) surface. Finally, it is demonstrated that when cluster and
substrate are of different materials, it is possible to control whether the deposition results in
largely intact clusters on the substrate or in a spreading of the clusters. This separation into
hard and soft clusters can be related to the relative cohesive energy of the crystalline materials. 相似文献
11.
G. Grégoire M. Mons C. Dedonder-Lardeux C. Jouvet 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》1998,1(1):5-7
clusters (solvents being , or ) have been studied by resonance enhanced two photons ionization, leading to the detection of clusters. When water is the solvent, large clusters up to n>50 can be observed, whereas for and no clusters larger than 10 could be evidenced. Because the first step in the ionization process is the excitation from the
ground solvated () ion pair state to a covalent excited state, the differences in the cluster size distribution for different solvent may be
interpreted as a difference in cluster structures leading to a difference in the charge separation in the ground state.
Received: 30 September 1997 / Revised in final form: 30 October 1997 / Accepted: 30 October 1997 相似文献
12.
Arkhipkin VG Gunyakov VA Myslivets SA Zyryanov VY Shabanov VF 《The European physical journal. E, Soft matter》2007,24(3):297-302
A one-dimensional ZrO2/SiO2 photonic crystal with a 4-n -pentyl-4' -cyanobiphenyl (5CB) nematic defect layer was used to investigate the transmission spectra of light polarized
parallel and perpendicular to the liquid-crystal director at different angles of incidence. The spectra of the photonic crystal
were shown to split into four polarized components Tij at oblique incidence. When the incident angle increased, the bandgap edges and the defect modes shifted towards short wavelengths,
while the amplitudes of the defect modes increased for the transverse magnetic polarization and decreased for the transverse
electric polarization. The observed discrepancy between the defect mode amplitudes in the center and near the edges of the
photonic bandgap was found to be related to the radiation losses inside the defect layer of a non-ideal photonic crystal.
The simulated transmission spectra obtained using recurrence relations and taking into account the decay of defect modes are
in good agreement with the experimental data. 相似文献
13.
Abstract The kinetics of radiation defect accumulation and subsequent recovery during/after electron irradiation below 273 K, at 323 K and 373 K were investigated for the Fe-15.7 at.% Cr using positron annihilation measurements at room temperature. Formation of vacancy clusters was observed at all of the irradiation temperatures. The formation of clusters and kinetics of their accumulation point to mobility of vacancies at least at room temperature. The cluster rearrangement and variations in the cluster configuration take place during annealing. 相似文献
14.
J.C. Pivin M.A. García H. Hofmeister A. Martucci M. Sendova Vassileva M. Nikolaeva O. Kaitasov J. Llopis 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2002,20(2):251-260
Precipitation of silver clusters in silica is achieved by different methods: ion implantation, ion beam mixing of superimposed
layers and ion irradiation of films deposited by means of co-sputtering or sol-gel technique. Main features of the nanoparticles
depending on the preparation method are investigated by TEM. The optical extinction resonance of these clusters is analysed
in terms of sizes and interaction between the clusters on the basis of calculations. We found that resonances in sputtered
and gel films with low metal concentrations are well described by plasmon polaritons in isolated clusters and calculations
based on Mie theory allow the study of their growth under irradiation. This theory is not appropriate to describe the optical
response of silver clusters in silica implanted with Ag concentrations higher than 5 at.% or in ion beam mixed films, because
of the interaction between clusters. Using an effective medium model, it is demonstrated that the random dispersion of clusters
in implantation films causes fluctuations and, on average, an increase of the clusters polarization. On the contrary, the
particular arrangement of the clusters with a bimodal size distribution in ion beam mixed films induces a screening effect
between the clusters of largest size.
Received 10 January 2002 / Received in final form 26 April 2002 Published online 19 July 2002 相似文献
15.
G. Cattapan P. Lotti A. Pascolini 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,53(3):387-394
We consider a T-shaped, one-dimensional quantum waveguide containing
an attractive or repulsive impurity in the lateral stub, and study how
the resonance poles move in the complex k-plane when the strength or
the position of the defect changes. Similarities and differences with
respect to standard potential scattering problems are highlighted. 相似文献
16.
The possible defect models of Y^3+:PbWO4 crystals are discussed by defect chemistry and the most possible substituting positions of the impurity Y^3+ ions are studied by using the general utility lattice program (GULP). The calculated results indicate that in the lightly doped Y^3+ :PWO crystal, the main compensating mechanism is [2Ypb^+ + VPb^2-], and in the heavily doped Y^3+ :PWO crystal, it will bring interstitial oxygen ions to compensate the positive electricity caused by YPb^+, forming defect clusters of [2Ypb^+ +Oi^2-] in the crystal. The electronic structures of Y3+ :PWO with different defect models are calculated using the DV-Xα method. It can be concluded from the electronic structures that, for lightly doped cases, the energy gap of the crystal would be broadened and the 420nm absorption band will be restricted; for heavily doped cases, because of the existence of interstitial oxygen ions, it can bring a new absorption band and reduce the radiation hardness of the crystal. 相似文献
17.
Effect of vacancy defect clusters on the optical property of the aluminium filter used for the space solar telescope 下载免费PDF全文
We investigate the microstructures of the pure aluminium foil
and filter used on the space solar telescope, irradiated by photons
with different doses. The vacancy defect clusters induced by proton
irradiation in both samples are characterized by transmission
electron microscopy, and the density and the size distribution of
vacancy defect clusters are determined. Their transmittances are
measured before and after irradiating the samples by protons
with energy E=100~keV and dose φ =6× 1011/mm2.
Our experimental results show that the density and the size of
vacancy defect clusters increase with the increase of irradiation
doses in the irradiated pure aluminium foils. As irradiation dose
increases, vacancies incline to form larger defect clusters. In the
irradiated filter, a large number of banded void defects are
observed at the agglomerate boundary, which results in the
degradation of the optical and mechanical performances of the
filter after proton irradiation. 相似文献
18.
采用分子动力学模拟研究了具有面心立方(fcc)晶格结构的截断八面体Ag309团簇升温过程中结构演变。对团簇的能量曲线变化、快照图演变和键对分析表明:无缺陷截断八面体Ag309团簇在410 K时转变为二十面体,在840 K时熔化;不同缺陷诱导二十面体结构转变温度异常变化,沿晶面滑移缺陷使二十面体转变温度升高,沿晶面旋转缺陷使二十面体结构转变温度降低;不同缺陷对团簇键型和势能产生的影响是使二十面体结构转变温度异常变化的主要诱导因素。这种通过缺陷控制团簇结构转变的研究为新型纳米结构的可控制备提供理论基础。 相似文献
19.
Plasma Bragg grating (PBG) is composed of periodic variations of plasma and dielectric or vacuum. The defect mode characteristic of the PBG with a cavity-defect is studied by one-dimensional particle-in-cell (1D PIC) simulation. It is shown that the laser pulse with the defect frequency can be localized around the defect partly and at the same time leak out of both sides of the grating slowly because of the few number of the grating period. This results in local high laser field intensity and high plasma density produced at the defect area, from which the third harmonic is enhanced by one order of magnitude. With the enhancement of the light coupled to the defect and the decrease of the light leaking out of the defect, the conversion efficiency of the third harmonic from the incident laser can be increased. 相似文献
20.
Clusters as new materials 总被引:1,自引:0,他引:1
Over the past two decades methods have been developed to produce clusters with an exactly determined number of atoms. Due to their finite size these small particles have totally different structures and `materials properties' than their bulk crystalline counterparts. Even more, these properties sometimes change drastically whenever a single atom is added to or removed from the cluster. This opens the pathway for a whole new world of tailor made materials in the future. In this article we describe the present state of the knowledge of the properties of clusters of atoms which in their bulk form conventional metals or semiconductors. The questions addressed include the development of the electronic structure as a function of cluster size and for example what remains of the `metallic' properties of the bulk solid in these very small clusters. Technological advances are expected using clusters on a specific support material in the areas of catalysis, magnetic storage media or electronic materials, and even solids assembled totally from clusters. Examples from each of these fields will be discussed in the context of this article. 相似文献