共查询到20条相似文献,搜索用时 62 毫秒
1.
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
2.
Q. L. Lu Q. Q. Luo A. F. Jalbout J. G. Wan G. H. Wang 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2009,51(2):219-223
Density functional theory has been employed in order to investigate the structure and stability of Si@Al12Hn () clusters. Hydrogenated Si@Al12 clusters exhibit pronounced stability for even numbers of H atoms. Large binding energy, HOMO-LUMO gaps and increased ionization
potentials imply that these clusters should be physically and chemically stable. The analysis of the charge density of the
HOMO plot illustrates that a pair of hydrogen atoms prefer to occupy opposing on-top sites for clusters with an even n number.
Studies of deformation charge density plots demonstrate that significant charge transfer occurs from the Si@Al12 to the H atoms. 相似文献
3.
M. Han J.F. Zhou F. Q. Song C. R. Yin M. D. Liu J. G. Wan G. H. Wang 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2003,24(1-3):269-272
Free beam of silicon oxide nanoclusters is produced by a
gas aggregation source from SiO precursor. Due to the
disproportionation reaction during the condensation of SiO vapor
the generated clusters are Si-riched. The clusters are
collimated to be a fine beam and deposited on the substrate at
room temperature. The microstructures of the cluster-based
nanofilm are characterized by TEM. It is shown that with
appropriate impacting parameters, Si-riched oxide nanofilms
assembled from uniformly distributed isolated clusters can be
obtained. And the clusters can self-organize into partially
densely ordered packing within local domains. XPS spectra are
taken to analyze the chemical components of the nanofilms.
Photoluminescence from the Si-riched oxide nanofilms has also
been observed. 相似文献
4.
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
5.
D.L. Peng T.J. Konno K. Wakoh T. Hihara K. Sumiyama 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,16(1):329-332
Cluster-cluster coalescence process of monodispersed Co clusters with mean diameter d = 8.5 and 13 nm deposited a plasma-gas-condensation-type cluster beam deposition system was investigated by in situ electrical conductivity measurements and ex situ scanning electron microscopy (SEM) and transmission electron microscopy (TEM), and analyzed by percolation concept. The electrical
conductivity measurement and TEM observation indicated that, below temperature T≈ 100°C, the Co clusters in the assemblies maintain their original structure as deposited at room temperature, while that the inter-cluster
coalescence takes place at T > 100°C, although the size distribution and the interface morphology of the clusters showed no marked change at substrate temperatures
T
s≤200°C.
Received 29 November 2000 相似文献
6.
D.J. Kenny S.C. Weller M. Couillard R.E. Palmer C.F. Sanz-Navarro R. Smith 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,16(1):115-118
Scanning tunnelling microscopy (STM) and molecular dynamics (MD) simulations have been used to investigate the implantation
of Ag7
- clusters into the graphite surface. An experimental measure of the implantation depth of individual clusters is gained via thermal oxidation of the bombarded graphite surfaces. This process results in etching of the cluster-induced defects to form
etch pits which grow laterally whilst retaining the depth of the implanted cluster. STM imaging of the etch pits reveals the
distribution of implantation depths for deposition energies of 2 keV and 5 keV. Molecular dynamics simulations for clusters
of 5 keV energy show that the implantation depth for Ag7
- is largely independent of the impact site on the graphite surface and the cluster orientation. The implantation depth found
by MD lies at the upper edge of the experimental depth distribution.
Received 30 November 2000 相似文献
7.
T. Rander M. Lundwall A. Lindblad G. Öhrwall M. Tchaplyguine S. Svensson O. Björneholm 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2007,42(2):253-257
Resonant Auger spectra of O2 clusters excited at the O1s edge are reported. After excitation to the repulsive 1s-13σ* state, the resulting resonant Auger spectrum displays features that remain constant in kinetic energy as the photon energy
is detuned. The shift between known atomic fragment features and these features is consistent with that observed for atoms
and clusters in singly charged states in direct photoemission. These findings are strong evidence for the existence of molecular
ultrafast dissociation processes within the clusters or on their surface. 相似文献
8.
An experimental photoelectron spectroscopy study is presented highlighting several aspects of importance for the study of deposited metal clusters and particles with photoemission. It is shown that the Fermi level is the correct energy reference for the core level binding energies. The choice of different deposition conditions, well within the range of soft landing, has a strong impact on the outcome of the spectroscopic experiments. Single adatoms as well as clusters deposited with some excess energy display relatively narrow core level spectra at much lower binding energies than previously reported, even when atomic mass selection is not performed. In contrast, single sized Pt19 clusters, deposited onto a thin Ar film before being exposed to the graphite surface show spectral broadening and shifts to higher binding energies. We discuss our results in terms of the cluster substrate interaction and the influence of deposition conditions on the metal adsorbate structure. 相似文献
9.
K. Nagaya H. Murakami H. Iwayama Y. Ohmasa M. Yao 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2007,43(1-3):69-72
The spectra of deep inner-core excited mixed rare-gas clusters were recorded by using electron ion coincidence (EICO) and
multi-hit momentum imaging (MHMI) techniques.
The EICO spectra for Ar99Kr1 clusters reveal that singly charged ions are emitted from the inner-core excited clusters in addition to the multiple charged
ions.
The dependence of the EICO spectra on photon energy and cluster size suggests that the holes created through vacancy cascade
on the krypton atoms are transferred to the surrounding atoms, and that the singly charged ions are the primary product of
the krypton photoabsorption.
Charge localization is suggested for the inner-core excited mixed rare-gas clusters from the analysis of the EICO peak width.
The MHMI measurements give us direct evidence for the strong charge migration from X-ray absorbing atoms to surrounding atoms.
The photon energy dependence of the PSD image for fragment ions suggests that the momentum of the fragment ions depends on
the number of charges generated by the vacancy cascade. 相似文献
10.
11.
F.v. Gynz-Rekowski W. Quester R. Dietsche D. C. Lim N. Bertram T. Fischer G. Ganteför M. Schach P. Nielaba Y. D. Kim 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2007,45(3):409-413
The possibility of using magic Si7 clusters to form a cluster material was studied experimentally and theoretically. In experiments Si7 clusters were deposited on carbon surfaces, and the electronic structure and chemical properties of the deposited clusters
were measured using X-ray photoelectron spectroscopy (XPS). A non bulk-like electronic structure of Si7 was found in the Si 2p core level spectra. Si7 is suggested to form a more stable structure than the non-magic Si8 cluster and Si atoms upon deposition on carbon surfaces. Theoretically it was possible to study the interaction between the
clusters without the effect of a surface. Density functional theory (DFT) calculations of potential curves of two free Si7 clusters approaching each other in various orientations hint at the formation of cluster materials rather than the fusion
of clusters forming bulk-like structures. 相似文献
12.
P. Mélinon F. Tournus B. Masenelli A. Perez M. Pellarin J. Lermé M. Broyer B. Champagnon 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,16(1):337-340
This paper deals with a new type of SiC bonding where silicon atom seems to bridge C60 molecules. We have studied films obtained by deposition of (C60)nSim clusters prepared in a laser vaporization source. Prior deposition, free ionized clusters were studied in a time-of-flight
mass spectrometer. Mixed clusters (C60)nSim were clearly observed. Abundance and photofragmentation mass spectroscopies revealed the relatively high stability of the
(C60)nSi
n
+
, (C60)nSi
n - 1
+
and (C60)nSi
n - 2
+
species. This observation is in favor of the arrangement of these complexes as polymers where the C60 cages may be bridged by a silicon atom. Free neutral clusters are then deposited onto substrate making up a nanogranular
thin film (≃ 100 nm). The film is probed by Auger and X-ray photoemission spectroscopies, but above all by surface enhanced Raman scattering.
The results suggest an unusual chemical bonding between silicon and carbon and the environment of the silicon atom is expected
to be totally different from the sp3 lattice: ten or twelve carbon neighbors might surround silicon atom. The bonding is discussed to the light of the so-called
fullerene polymerization as observed for pure fullerite upon laser irradiation. This opens a new route for bridging C60 molecules together with an appreciable energy bonding, since the usual van der Waals bonding in fullerite could be replaced
by an ionocovalent bond. Such an assumption must be checked in the future by XAS and EXAFS experiments.
Received 15 November 2000 相似文献
13.
M. Hedén M. Kjellberg A. V. Bulgakov K. Hansen E. E.B. Campbell 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2007,43(1-3):255-259
Molecular fusion is induced in clusters of fullerene molecules on excitation with fs laser pulses. The dependence of the mass
distributions of the fused products on the initial cluster distribution are studied and results for (C60)N and (C70)N clusters are compared. The fused products decay by emitting C2 molecules and the fragmentation spectrum is used to determine the initial excitation energy of the fused species. The threshold
excitation energy needed to induce fusion is consistent with the energetic thresholds for molecular fusion of fullerenes determined
previously in single collision experiments. 相似文献
14.
I. L. Garzón M. R. Beltrán G. González I. Guterrez-González K. Michaelian J. A. Reyes-Nava J. I. Rodrguez-Hernández 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2003,24(1-3):105-109
Theoretical and experimental information on the shape and
morphology of bare and passivated gold clusters is fundamental
to predict and understand their electronic, optical, and other
physical and chemical properties. An effective theoretical
approach to determine the lowest-energy configuration (global
minimum) and the structures of low energy isomers (local minima)
of clusters is to combine genetic algorithms and many-body
potentials (to perform global structural optimizations), and
first-principles density functional theory (to confirm the
stability and energy ordering of the local minima). The main
trend emerging from structural optimizations of bare Au clusters
in the size range of 12-212 atoms indicates that many
topologically interesting low-symmetry, disordered structures
exist with energy near or below the lowest-energy ordered
isomer. For example, chiral structures have been obtained as the
lowest-energy isomers of bare Au28 and
Au55 clusters, whereas in the size-range
of 75-212 atoms, defective Marks decahedral structures are
nearly degenerate in energy with the ordered symmetrical
isomers. For methylthiol-passivated gold nanoclusters
[Au28(SCH3)16
and
Au38(SCH3)24],
density functional structural relaxations have shown that the
ligands are not only playing the role of passivating molecules,
but their effect is strong enough to distort the metal cluster
structure. In this work, a theoretical approach to characterize
and quantify chirality in clusters, based on the Hausdorff
chirality measure, is described. After calculating the index of
chirality in bare and passivated gold clusters, it is found that
the thiol monolayer induces or increases the degree of chirality
of the metallic core. We also report simulated high-resolution
transmission electron microscopy (HRTEM) images which show that
defects in decahedral gold nanoclusters, with size between 1-2
nm, can be detected using currently available experimental HRTEM
techniques. 相似文献
15.
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
16.
采用密度泛函(DFT)中的B3LYP方法,选择sto-3g基组,优化并得到了TinMg(n=1—10)小团簇的基态平衡结构,计算出了掺杂团簇的基态结构的平均键长、对称性、原子化能、能级分布、能级间隙、束缚能、总能的二阶差分. 结果表明,随着团簇原子数的增加,镁原子更容易趋于团簇表面位置,镁-钛平均键长大于钛-钛平均键长,以对称性结构为最稳定的基态结构,且呈多个五角双锥结构. 其中Ti5Mg和Ti8Mg的结构更为稳定.
关键词:
密度泛函
钛-镁团簇
基态结构 相似文献
17.
P. M. Dinh F. Fehrer P.-G. Reinhard E. Suraud 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2007,45(3):415-423
Using a combined quantum mechanical/classical method, we study the
dynamics of deposition of small Na clusters on Ar(001) surface. We
work out basic mechanisms by systematic variation of substrate
activity, impact energy, cluster orientations, cluster sizes, and
charges. The soft Ar material is found to serve as an extremely
efficient shock absorber which provides cluster capture in a broad
range of impact energies. Reflection is only observed in combination
with destruction of the substrate. The kinetic energy of the
impinging cluster is rapidly transfered at first impact. The
distribution of the collision energy over the substrate proceeds very
fast with velocity of sound. The full thermalization of ionic and
atomic energies goes at a much slower pace with times of several ps.
Charged clusters are found to have a much stronger interface
interaction and thus get in significantly closer contact with the
surface. 相似文献
18.
S. Tomita J.S. Forster P. Hvelplund A.S. Jensen S.B. Nielsen 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,16(1):119-122
We have measured attenuation cross sections and fragmentation cross sections for protonated water clusters H(H2O)n
+ (n = 1 to 100) colliding with noble gas atoms (He and Xe) at a laboratory energy of 50 keV. In collisions with He, a transparency
effect in the attenuation cross section was observed. For the case of fragmentation in collisions with Xe, a strong enhancement
of small clusters was observed which we attribute to multifragmentation.
Received 30 November 2000 相似文献
19.
Density-functional method PW91 has been selected to investigate the structural, electronic and magnetic properties of Au4M (M =Sc–Zn) clusters. Geometry optimisations show that the M atoms in the ground-state Au4M clusters favour the most highly coordinated position. The ground-state Au4M clusters possess a solid structure for M = Sc and Ti and a planar structure for M = V–Zn. The characteristic frequency of the doped clusters is much greater than that of pure gold cluster. The relative stability and chemical activity are analysed by means of the averaged binding energy and highest occupied molecular orbital and lowest unoccupied molecular orbital energy gap for the lowest energy Au4M clusters. It is found that the dopant atoms can enhance the thermal stability of the host cluster except for Zn atom. The Au4Ti, Au4Mn and Au4Zn clusters have relatively higher chemical stability. The vertical detachment energy, electron affinity and photoelectron spectrum are calculated and simulated theoretically for all the ground-state structures. The magnetism calculations reveal that the total magnetic moment of Au4M cluster is mainly localised on the M atom and vary from 0 to 5 μB by substituting an Au atom in Au5 cluster with different transition-metal atoms. 相似文献
20.
S. A. Nepijko D. N. Ievlev W. Schulze 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2003,24(1-3):115-117
The plasmon energy of Ag clusters produced on an amorphous
carbon substrate by gas-aggregation technique has been measured.
It has been determined from the plasmon peak position in the
light emission spectrum obtained during bombardment of Ag
clusters by low-energy electrons. For Ag cluster films with
maximum of the cluster size distribution at 30, 8 and 2.5 nm,
the plasmon energy comprised 3.76, 4.13 and 4.28 eV (the
wavelength was 330, 300 and 290 nm), respectively. The blue
shift of the plasmon energy is probably related to the effect of
confounding of collective and single-particle excitations. 相似文献