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1.
V. Kumar 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2003,24(1-3):227-232
We report the recent findings of metal (M) encapsulated
clusters of silicon from computer experiments based on
ab initio total energy
calculations and a cage shrinkage and atom removal approach. Our
results show that using a guest atom, it is possible to wrap
silicon in fullerenelike (f)
structures, as sp2 bonding is not
favorable to produce empty cages unlike for carbon. Transition M
atoms have a strong bonding with the silicon cage that are
responsible for the compact structures. The size and structure
of the cage change from 14 to 20 Si atoms depending upon the
size and valence of the M atom. Fewer Si atoms lead to
relatively open structures. We find cubic,
f, Frank-Kasper (FK)
polyheral type, decahedral, icosahedral and hexagonal structures
for M@Sin with n = 12-16 and several different M
atoms. The magic behavior of 15 and 16 atom Si cages is in
agreement with experiments. The FK polyhedral cluster,
M@Si16 has an exceptionally large density
functional gap of about 2.35 eV calculated within the
generalized gradient approximation. It is likely to give rise to
visible luminescence in these clusters. The cluster-cluster
interaction is weak that makes such clusters attractive for
cluster assembled materials. Further studies to stabilize
Si20 cage with M = Zr, Ba, Sr, and Pb
show that in all cases there is a distortion of the
f cage. Similar studies on M
encapsulated germanium clusters show FK polyhedral and
decahedral isomers to be more favorable. Also perfect
icosahedral M@Ge12 and
M@Sn12 clusters have been obtained with
large gaps by doping with divalent M atoms. Recent results of
the H interaction with these clusters, hydrogenated silicon
fullerenes as well as assemblies of clusters such as nanowires
and nanotubes are briefly presented. 相似文献
2.
M.P. Machado P. Piquini R. Mota 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2003,23(1):91-93
The geometric structures, energetics and electronic properties of the recently discovered BN nanocones are investigated using
first-principles calculations based on the density-functional theory. We have proposed one particular structure for BN nanocones
associated with the 240° disclination, derived by the extraction of four 60° segments, presenting as characteristic four pentagons at the apex and termination in two atoms. The cones are simulated by
three clusters containing 58 B plus N atoms and additional 12 H atoms to saturate the dangling bonds at the edge. The most
stable configuration is obtained when the two terminating atoms are one B and one N. For the cases where the two terminating
atoms are of the same kind, the tip with B atoms is determined to have lower binding energy than with N atoms. The local densities
of states of these BN nanocones are investigated and sharp states are found in the regions close (below and above) to the
Fermi energy.
Received 14 October 2002 / Received in final form 6 December 2002 Published online 11 February 2003
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ID="a"e-mail: ppiquini@smail.ufsm.br 相似文献
3.
Q. Sun Q. Wang X.G. Gong V. Kumar Y. Kawazoe 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2002,18(1):77-81
We report results of the atomic and electronic structures of Al7C cluster using ab initio molecular dynamics with ultrasoft pseudopotentials and generalized gradient approximation. The lowest energy structure is
found to be the one in which carbon atom occupies an interstitial position in Al7 cluster. The electronic structure shows that the recent observation [Chem. Phys. Lett. 316, 31 (2000)] of magic behavior of Al7C- cluster is due to a large highest occupied and lowest unoccupied molecular orbital (HOMO-LUMO) gap which makes Al7C- chemically inert. These results have further led us to the finding of a new neutral magic cluster Al7N which has the same number of valence electrons as in Al7C- and a large HOMO-LUMO gap of 1.99 eV. Further, calculations have been carried out on (Al7N)2 to study interaction between magic clusters.
Received 28 July 2001 相似文献
4.
A. Srinivasan M. N. Huda A. K. Ray 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2006,39(2):227-236
Fullerene-like silicon nanostructures with twenty and twenty-four carbon
atoms on the surface of the Si60 cage by substitution, as well as
inside the cage at various orientations have been studied within the
generalized gradient approximation to density functional theory. Full
geometry optimizations have been performed without any symmetry constraints
using the Gaussian 03 suite of programs and the LANL2DZ basis set. Thus, for the
silicon atom, the Hay-Wadt pseudopotential with the associated basis set is
used for the core electrons and the valence electrons, respectively. For the
carbon atom, the Dunning/Huzinaga double zeta basis set is employed.
Electronic and geometric properties of these nanostructures are presented
and discussed in detail. Optimized silicon-carbon fullerene like
nanostructures are found to have increased stability compared to the bare
Si60 cage and the stability depends on the number and the orientation
of carbon atoms, as well as on the nature of silicon-carbon and
carbon-carbon bonding. 相似文献
5.
F. Hagelberg C. Xiao B. Marsen M. Lonfat P. Scheier K. Sattler 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,17(1):37-41
In a series of recent experiments, the HOMO-LUMO energy gaps of small Si clusters deposited on a graphite substrate have been
determined by Scanning Tunneling Microscopy (STM). The values obtained were found to be substantially smaller than the energy
gaps of corresponding passivated clusters. This work considers dimensional reduction as a possible mechanism for a sizeable
energy gap narrowing by the example of the system Si5. The impact of the graphite substrate on the deposited species is investigated in the framework of a pseudocluster model.
Received 30 November 2000 相似文献
6.
D. V. Kolesnikov V. A. Osipov 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,49(4):465-470
The low-energy electronic structure of icosahedral
fullerenes is studied within the field-theory model. In the field
model, the pentagonal rings in the fullerene are simulated by two
kinds of gauge fields. The first one, non-abelian field, follows
from so-called K spin rotation invariance for the spinor field
while the second one describes the elastic flow due to pentagonal
apical disclinations. For fullerene molecule, these fluxes are
taken into account by introducing an effective field due to
magnetic monopole placed at the center of a sphere.
Additionally, the spherical geometry of the
fullerene is incorporated via the spin connection term. The exact
analytical solution of the problem (both for the eigenfunctions
and the energy spectrum) is found. 相似文献
7.
L. Kronik R. Fromherz E. Ko G. Ganteför J. R. Chelikowsky 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2003,24(1-3):33-36
We compare experimentally measured and
ab initio computed
photoelectron spectra of negatively charged deuterated silicon
clusters (
, 4m10, 0n2) produced in a plasma environment.
Based on this comparison, we discuss the kinetics and
thermodynamics of the cluster formation and the effect of
deuterium on the geometrical and electronic structure of the
clusters. 相似文献
8.
E. S. Dy H. Kasai 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2007,41(2):241-245
We study the interaction between tin(II) porphyrin (SnPor) with platinum and
non-precious Group 8B metals (iron, cobalt and nickel) by density functional
theory and discuss the electronic properties of the resulting products. We
also model the interaction of the resulting compounds with water where
applicable. Our studies indicate that, SnPor-Ni possesses electronic
properties similar to SnPor-Pt, suggesting that it may possess similar
photocatalytic properties for reduction reactions, such as converting water
to hydrogen gas. 相似文献
9.
M. Yamada H. Nishihara 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2003,24(1-3):257-260
Biferrocene-modified gold nanoparticles
(Aun-BFc) comprising 1.7, 2.2 and 2.9 nm
in average core diameter, d,
were synthesized by a substitution reaction of octyl
thiolate-covered nanoparticles with biferrocene-terminated
alkanethiol, 1-(9-thiononyl-1-one)-1, 1-biferrocene (BFcS).
All sizes of Aun-BFc undergo two-step
oxidation reactions in 0.1 mol dm-3
Bu4NClO4-CH2Cl2
and consecutive potential scans including the second oxidation
process lead to the formation of an adhesive redox-active gold
nanoparticle film on an electrode. The thickness of the
Aun-BFc film is controllable by the
number of potential scans. The scanning tunneling microscope
images reveal that the Aun-BFc (d = 2.9 nm) film forms many domains of
the assembled Aun-BFcs, especially the
particles are isotropically assembled in line. 相似文献
10.
Hong-Kang Zhao 《The European Physical Journal B - Condensed Matter and Complex Systems》2003,33(3):365-372
The ac Stark effect is investigated in the toroidal carbon nanotube system threaded with an ac magnetic flux. The Floquet
theory is employed to deal with the time-dependent quantum problems. The time-averaged energy of the system is derived and
is found to exhibit a strong relationship with an external field, and the modified energy gap has been presented. The ac flux
enhances energy gaps to cause metal-semiconductor transition. The steady current has been obtained by employing the free energy
approach, and the persistent current is a special case as the magnitude of the ac flux approaches zero. The photon-assisted
current is quite different from the persistent current due to the absorption and emission of photons. The local density of
states is obtained by calculating the Green's function in the Floquet state, and photon-resonant structures are observed.
All of the novel features are associated with the ac Stark effect, which is caused by the modification of energy levels.
Received 20 November 2002 / Received in final form 7 February 2003 Published online 20 June 2003
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ID="a"e-mail: zhaohonk@yahoo.com 相似文献
11.
M.-H. Du L.-L. Wang A. Kolchin H.-P. Cheng 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2003,24(1-3):323-326
The interaction of water with SiO
2 is an important problem in geophysics,
materials physics, and environmental science. In this paper, we
present recent results on studies of H
2
O-silica clusters from first-principles
Born-Oppenheimer molecular dynamics calculations. Bond strength
and chemical stability are investigated as a function of cluster
size and chemical composition. Both physisorption and
chemisorption of water molecules on the clusters are discussed
via analysis of energetics.
Calculations of clusters are compared with the results from
extended surfaces. The validity of clusters as models of
surfaces is discussed. 相似文献
12.
X.P. Yang H.M. Weng J. Dong 《The European Physical Journal B - Condensed Matter and Complex Systems》2003,32(3):345-350
The structural, electronic, and optical properties of 4 ? single-walled carbon nanotubes (SWNTs) contained inside the zeolite
channels have been studied based upon the density-functional theory in the local-density approximation (LDA). Our calculated
results indicate that the relaxed geometrical structures for the smallest SWNTs in the zeolite channels are much different
from those of the ideal isolated SWNTs, producing a great effect on their physical properties. It is found that all three
kinds of 4 ? SWNTs can possibly exist inside the Zeolite channels. Especially, as an example, we have also studied the coupling
effect between the ALPO4-5 zeolite and the tube (5,0) inside it, and found that the zeolite has real effects on the electronic structure and optical
properties of the inside (5,0) tube.
Received 26 January 2003 Published online 11 April 2003
RID="a"
ID="a"e-mail: yxptl@hotmail.com 相似文献
13.
A. Md. Asaduzzaman M. Springborg 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2007,43(1-3):213-216
Using a parameterized density-functional tight-binding method we have calculated the electronic and structural properties
of Ge–Si nanoparticles. Starting with a spherical part of a zinc-blende/diamond crystal (with the center of the sphere at
the mid-point of a nearest-neighbour bond) we have constructed initial structures that subsequently were allowed to relax.
Structures consisting solely of Ge atoms or solely of Si atoms were studied, together with core-shell structures for which
one semiconductor forms a shell on the core of the other semiconductor. Moreover, homogeneous, ordered SiGe structures as
well as structures with a semisphere of one semiconductor and a semisphere of the other were also considered.
In analysing the results special emphasis is put on identifying particularly stable structures, on explaining the occurrence
of those, on the spatial distribution of the frontier orbitals, and on the variation of the total energy with structure and
composition. 相似文献
14.
G. Ballentine M. Heßler M. Kinza K. Fauth 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2007,45(3):535-537
Fe clusters of 105±2 atoms/cluster were mass selectively deposited onto Cu(111) at cryogenic temperatures.
XMCD was used to measure temperature and direction dependent magnetization curves.
The clusters are superparamagnetic at the lowest temperature measured (10 K). Their magnetization curves are consistent with
magnetic moments of ≈2.5μB per atom which are thus enhanced over the bulk values.
Within experimental accuracy, the clusters do not present magnetocrystalline anisotropy in the temperature range
of 10 K to 60 K. 相似文献
15.
M. Imamura T. Miyashita A. Tanaka H. Yasuda Y. Negishi T. Tsukuda 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2007,43(1-3):233-236
We have carried out optical and X-ray photoemission
studies of the dendrimer-encapsulated Au nanoclusters. The
dendrimer-encapsulated Au nanoclusters are prepared by the chemical
reduction of Au ions loaded within the dendrimer templates.
Photoluminescence spectrum of the dendrimer-encapsulated Au nanoclusters with
diameter of about 1.0 nm shows the visible luminescence centered at about
2.8 eV. In addition, we have measured the nanocluster-size dependent
photoemission spectra in the valence-band region. From line shape analysis
of Au 4f X-ray photoemission spectra, Au 4f core-level spectra of
the dendrimer-encapsulated Au nanoclusters reflect the size dependent
chemical-states. From these results, we discuss electronic structures and
chemical states of the dendrimer-encapsulated Au nanoclusters. 相似文献
16.
M. Tchaplyguine S. Peredkov A. Rosso J. Schulz G. Öhrwall M. Lundwall T. Rander A. Lindblad H. Bergersen W. Pokapanich S. Svensson S. L. Sorensen N. Mårtensson O. Björneholm 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2007,45(2):295-299
Synchrotron-based X-ray photoelectron spectroscopy on copper and silver
cluster beams created by a magnetron-based gas-aggregation source has
allowed mapping the electron density of states (DOS) of free metallic
nanoparticles. The cluster DOS profiles obtained in the experiments strongly
resemble the infinite solid DOS shapes, but the extracted cluster
work-functions are lower than those for the bulk metal. The latter
observation is explained by the initial negative charge on most of the
clusters, created by the source. 相似文献
17.
T. Kodaira S. Inoue Y. Murakami 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2007,43(1-3):267-270
Arrayed cationic K clusters including one 4s-electron in each cluster, i.e., Km+1
m+, were incorporated into α-cages of zeolite LTA with Si/Al=1.5. Although no magnetic phase transition was observed regarding
the temperature (T) dependence of magnetic susceptibilities originating from the 4s-electron spins (χspin) between 2 and 300 K, the χspin-T curve could be fitted by the sum of magnetic susceptibilities based on the Curie-Weiss law and Pauli paramagnetism. A possible
explanation of this behavior is the existence of a narrow energy band formed out of 1s-cluster orbitals of arrayed K clusters,
and the existence of a finite density of state at the Fermi energy. 相似文献
18.
Y. P. Chen Y. E. Xie X. H. Yan 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,49(3):333-338
We have studied the transmission resonances for a confined array of
antidots, using the lattice Green's function method. Two kinds of resonant
peaks via quasibound states are found. One kind of resonant peak corresponds
to the split quasibound states. The split states originate from the
superposition of quasibound states respectively localized in different (T or
crossed) junctions, while the number of quasibound states in each junction
is associated with the arm-width of the junction. Electrons in these split
states are mainly localized in the junctions. The other kind of resonant
peaks correspond to the high quasibound states which exist in (transverse
and longitude) multi-period confined arrays of antidots. It is interesting
to note that electrons in some of the high quasibound states are mainly
localized in the intersection of the junctions rather than in the junctions
themselves. 相似文献
19.
S. Bornemann J. Minár J. B. Staunton J. Honolka A. Enders K. Kern H. Ebert 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2007,45(3):529-534
We present results of magnetic torque calculations using the fully relativistic
spin-polarized Korringa-Kohn-Rostoker approach applied to small Co and Fe
clusters deposited on the Pt(111) surface. From the magnetic torque one can
derive amongst others the magnetic anisotropy energy (MAE). It was found that
this approach is numerically much more stable and also computationally less
demanding than using the magnetic force theorem that allows to calculate the
MAE directly. Although structural relaxation effects were not included our
results correspond reasonably well to recent experimental data. 相似文献
20.
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