共查询到20条相似文献,搜索用时 15 毫秒
1.
S. Duffe T. Irawan M. Bieletzki T. Richter B. Sieben C. Yin B. von Issendorff M. Moseler H. Hövel 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2007,45(3):401-408
The low energy deposition of silver cluster cations with
561 (±5) atoms on a cold fullerene covered gold surface has
been studied both by scanning tunneling microscopy and molecular
dynamics simulation. The special properties of the
C60/Au(111) surface result in a noticeable fixation of the
clusters without a significant change of the cluster shape. Upon
heating to room temperature we observe a flattening or shrinking
of the cluster samples due to thermal activation. Similar changes were observed also for mass selected Ag clusters with other
sizes. For comparison
we also studied Ag islands of similar size, grown by low
temperature deposition of Ag atoms and subsequent annealing. A
completely different behavior is observed with much broader size
distributions and a qualitatively different response to
annealing. 相似文献
2.
D. Cheng S. Huang W. Wang 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2006,39(1):41-48
We have investigated segregation phenomena in Cu–Au
bimetallic clusters with decahedral structures at 100 K and 300 K, based on
the second-moment approximation of the tight-binding (TB-SMA) potentials by
using Monte Carlo method. The simulation results indicate that there are
three regions (split, three-shell onion-like and core-shell region) at 100 K
and two regions (split and core-shell) at 300 K with the structure of
decahedral clusters, as the chemical potential difference Δμ
changes. It is found that the structure of decahedral clusters undergoes a
division into smaller clusters in the split region. In the core-shell
structure, Au atoms are enriched in surface and Cu atoms occupy the core of
the clusters because of the different surface energy of Cu and Au. The Au
atoms are enriched in the surface shell, and the Cu atoms are in the middle
shell, while a single Au atom is located in the center to form the
three-shell onion-like structure. The structure and binding energy of
smaller clusters after splitting are also discussed. The Au atoms generally
lie on the surface of the smaller clusters after splitting. 相似文献
3.
P. Moskovkin S. Pisov M. Hou C. Raufast F. Tournus L. Favre V. Dupuis 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2007,43(1-3):27-32
Model and real cobalt-platinum alloy clusters are compared in terms of structure, composition and segregation. Canonical and
semi grand canonical Metropolis Monte Carlo simulations are performed to model these clusters,
using embedded atom (EAM) and modified embedded atom (MEAM) potentials. All
of them correctly predict the bulk L12 Co3Pt and CoPt3
structures as well as the L10 CoPt phase. However, the lattice
parameters, phase stability and the L10-fcc order-disorder transition
temperature are at variance. Segregation predictions with EAM and MEAM
potentials are contradictory. Experimentally, mixed clusters with various
compositions were deposited by Low Energy Cluster Beam on amorphous carbon
at room temperature. Their size distribution, crystalline structure and
composition were examined by Transmission Electron Microscopy (TEM).
Clusters with the same size distributions were modelled. Both experiment and
modelling show their crystallographic parameters to continuously correspond
to the fcc CoPt chemically disordered phase. Diffraction measurements
indicate surface segregation of the specie in excess, in agreement with EAM
predictions for the Co-rich phase. The consequences on magnetic properties
are discussed. 相似文献
4.
C. Bréchignac Ph. Cahuzac F. Carlier C. Colliex M. de Frutos N. Kébaïli J. Le Roux A. Masson B. Yoon 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2003,24(1-3):265-268
We studied shape relaxation of nano-fractal islands,
during annealing, after their growth from antimony cluster
deposition on graphite surface. Annealing at
180°C shows evidence of an increase
of the fractal branch width with time followed by branch
fragmentation, without changing the fractal dimension. The time
evolution of the width of the arm suggests the surface
self-diffusion mechanism as the main relaxation process. With
Monte Carlo simulations, we confirmed the observed behavior.
Comparison is done with our previous results on fragmentation of
nano-fractal silver islands when impurity added to the incident
cluster promotes rapid fragmentation by surface self-diffusion
enhancement [1]. 相似文献
5.
T. Van Hoof A. Dzhurakhalov M. Hou 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2007,43(1-3):159-163
Molecular Dynamics is used to study the formation of an interface between a
single crystalline Ag matrix and core-shell AgCo nanoclusters deposited with
energies ranging from 0.25 eV to 1.5 eV per atom. As a consequence of the
slowing down, clusters deform, may become epitaxial with the substrate and
keep their core-shell structure. The consequences of the cluster-surface
interaction are studied in detail for a realistic size and energy range and
the accumulation of clusters is modelled. It is found that the interface
formed is no more than a few atomic layers thick and that both the cobalt
cluster cores and the silver shells display limited epitaxy with the
substrate. The effect is not much energy dependent and is larger for the Ag
shells that for the Co cores. 相似文献
6.
Structural and electronic properties of Bin (n = 2-14) clusters from density-functional calculations
J. M. Jia G. B. Chen D. N. Shi B. L. Wang 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2008,47(3):359-365
The structural and electronic properties of Bin
(n = 2-14) clusters have been systematically studied using gradient-corrected
density-functional theory. For each cluster size, a number of structural
isomers were constructed and optimized to search for the lowest-energy
structure. The competition of several structural patterns such as cages,
superclusters, and layered structures leads to the alternating appearance of
these configurations as global minima. Although the tendency of Bi to form
puckered-layer structures is already well-known, the electronic states of
Bin clusters are still far from that of the bulk. As well, a remarkable
even-odd atom number oscillation is observed in the structural and
electronic properties of the clusters, implying that the stability of
Bin clusters is mainly dominated by the electron shell effect rather
than by geometrical packing. The theoretically calculated values for
electron affinities agree well with available experimental data. 相似文献
7.
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
8.
O. Diéguez R.C. Longo C. Rey L.J. Gallego 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》1999,7(4):573-576
Using the noncentral embedded atom model potential recently proposed by Besson and Morillo for bulk alloys (), we performed computer simulations to predict the ground-state configurations of and clusters (). The computed structures of clusters are in general agreement with such theoretical results as have been obtained by density functional calculations
(i.e. for ). The results for Fe-rich clusters show surface segregation of Al, which is in keeping with the findings of a previous study of clusters.
Received 29 April 1999 相似文献
9.
J. F. Zhou Z. Chen L. B. He C. H. Xu L. Yang M. Han G. H. Wang 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2007,43(1-3):283-286
InSb nanostructures have been synthesized by the use of
gas aggregation process. Nanoparticles with different shapes are obtained by
controlling the growth and deposition temperature of the InSb nanoclusters.
Triangular nanocrystals are commonly observed when the clusters are
extracted from the condensation chamber of the source and deposited on the
room temperature substrate at high vacuum. When the deposition is performed
inside the condensation chamber at high temperature near the melting point
of bulk InSb, nanoparticles formed on the substrate surface show several
kinds of 3-dimensional morphologies, such as triangular or rectangular
prisms, as well as hexagonal tablets. Keeping the same conditions for the
cluster source operation and deposition, after long time growth, nanorods
with hexagonal and quadrangular cross sections are formed through
vapor-liquid-solid (VLS) process. The origin of the difference on the
morphologies and shapes of the nanostructures is attributed to the
anisotropic growth of InSb, which is temperature dependent. 相似文献
10.
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
11.
K.-L. Jonas V. von Oeynhausen J. Bansmann K.-H. Meiwes-Broer 《Applied Physics A: Materials Science & Processing》2006,82(1):131-137
Morphology and electronic properties of silver islands and deposited silver clusters on Ge(001) have been studied using scanning tunnelling microscopy (STM) and spectroscopy (STS) at low temperatures. Already the clean surface bears an interesting electronic structure, which is obvious from the STS. The tunnelling spectra exhibit strong peaks associated with dangling bond-derived surface states and an antibonding σ-state of the surface dimer. For silver islands of only few monolayers in height, complex spectra are interpreted to be dominated by metal–semiconductor interface states. These islands show energy gaps which are not observed for larger ones beyond 1 nm in height. Spectra of the larger islands contain a series of distinct peaks originating from lateral and three-dimensional electron confinement, respectively. Silver clusters – preformed in the gas phase using a cluster source – have been fabricated, size selected and deposited onto germanium(001). In tunnelling spectra dips at the Fermi level are accompanied by two maxima. These characteristics seem to be almost independent from the cluster size. Additional weak structures are found at higher bias voltages, which are understood in terms of quantized states. PACS 36.40.Cg; 61.46.+w; 73.20.At 相似文献
12.
T. Ikeshoji G. Torchet K. Koga 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2003,24(1-3):211-214
Surface tension and pressure (stress) tensors of
Lennard-Jones clusters, in the size range 200 ~ 2700
atoms/cluster, formed from evaporating liquid droplets were
calculated in a Molecular Dynamics simulation. Icosahedral
clusters have a much larger surface tension than decahedral,
fcc, and hcp ones, meanwhile asymmetric icosahedral clusters
have a lower surface tension. Fcc and hcp clusters have a very
small surface tension. Decahedral clusters have a surface
tension closer to that of fcc and hcp ones than to that of
icosahedral ones, though both icosahedral and decahedral
structures have five fold symmetry axis. Binary component
clusters have a higher surface tension than single component
ones. 相似文献
13.
L. Bolotov N. Uchida T. Kanayama 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,16(1):271-274
We present results of scanning tunneling spectroscopy (STS) measurements of hydrogen-saturated silicon clusters islands formed
on Si(111)-( 7×7) surfaces. Nanometer-size islands of Si6H12 with a height of 0.2-4 nm were assembled with a scanning tunneling microscope (STM) using a tip-to-sample voltage larger
than 3 V. STS spectra of Si6H12 cluster islands show characteristic peaks originating in resonance tunneling through discrete states of the clusters. The
peak positions change little with island height, while the peak width shows a tendency of narrowing for the tall islands.
The peak narrowing is interpreted as increase of lifetime of electron trapped at the cluster states. The lifetime was as short
as 10-13 s resulting from interaction with the dangling bonds of surface atoms, which prevents charge accumulation at the cluster
islands.
Received 30 November 2000 相似文献
14.
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
15.
C. Bréchignac Ph. Cahuzac F. Carlier C. Colliex M. de Frutos N. Kébaïli J. Le Roux A. Masson B. Yoon 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,16(1):265-269
The deposition of preformed clusters on surfaces has been established as a new way for growing nano-suctures on surfaces.
It has been shown that supported island morphology relies on the dynamics of clusters, during the growth, giving rise to shapes
from compact to ramified types. This paper identifies and discusses, in the case of antimony cluster deposits, several processes
responsible for the non-equilibrium island shapes: limited kinetic cluster aggregation, size dependent coalescence, “wetting-like
behavior” of antimony clusters on antimony islands. Using successive predetermined cluster sizes during the deposition process
to synthesize polymorphic structure involves the interplay of those mechanisms.
Received 1st December 2000 相似文献
16.
M. Rohmer F. Ghaleh M. Aeschlimann M. Bauer H. Hövel 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2007,45(3):491-499
In this paper we present a combined STM, SEM and
time-resolved PEEM study of silver clusters on a nano-patterned
HOPG-substrate, exhibiting areas of different defect type and defect
densities. The areas show small but distinct differences in the femtosecond
dynamics associated with electronic excitations in the clusters. We assign
these differences to variations in the cluster size distribution and
variations in the cluster-substrate interaction as governed by the bonding
to the different defect types. 相似文献
17.
Pd-induced surface structures on Si(1 1 3) have been studied by scanning tunneling microscopy (STM) and X-ray photoelectron spectroscopy (XPS). In the initial process of the Pd adsorption below 0.10 ML, Pd silicide (Pd2Si) clusters are observed to form randomly on the surface. By increasing the Pd coverage to 0.10 ML, the clusters cover the entire surface, and an amorphous layer is formed. After annealing the Si(1 1 3)-Pd surface at 600 °C, various types of islands and chain protrusions appears. The agglomeration, coalescence and crystallization of these islands are observed by using high temperature (HT-) STM. It is also found by XPS that the islands correspond to Pd2Si structure. On the basis of these results, evolution of Pd-induced structures at high temperatures is in detail discussed. 相似文献
18.
S. R. Bhattacharyya T. K. Chini D. Datta R. Hippler I. Shyjumon B. M. Smirnov 《Journal of Experimental and Theoretical Physics》2008,107(6):1009-1021
We analyze scanning electron microscopy measurements for structures formed in the deposition of solid silver clusters onto
a silicon(100) substrate and consider theoretical models of cluster evolution onto a surface as a result of diffusion and
formation of aggregates of merged clusters. Scanning electron microscopy (SEM) data are presented in addition to energy dispersive
X-ray spectrometry (EDX) measurements of the these films. Solid silver clusters are produced by a DC magnetron sputtering
source with a quadrupole filter for selection of cluster sizes (4.1 and 5.6 nm or 1900 and 5000 atoms per cluster in this
experiment); the energy of cluster deposition is 0.7 eV/atom. Rapid thermal annealing of the grown films allows analysis of
their behavior at high temperatures. The results exhibit formation of cluster aggregates via the diffusion of deposited solid
clusters along the surface; an aggregate consists of up to hundreds of individual clusters. This process is essentially described
by the diffusion-limited aggregation (DLA) model, and thus a grown porous film consists of cluster aggregates joined by bridges.
Subsequent annealing of this film leads to its melting at temperatures lower than to the melting point of bulk silver. Analysis
of evaporation of this film at higher temperatures gives a binding energy in bulk silver of ɛ0= (2.74 ± 0.03) eV/atom.
The text was submitted by the authors in English. 相似文献
19.
We report a systematic study of island adsorption and single-adatom diffusion on free silver nanoclusters, and discuss the consequences on the growth. In our calculations, silver is modelled by semiempirical many-body potentials. We consider magic non-crystallographic structures at different sizes: icosahedra (Ih) at 55, 147 and 309 atoms; Marks-truncated decahedra (m-Dh) at 75, 146 and 192 atoms. We calculate the map of adsorption sites and the energy barriers for the different diffusion processes. We find that, due to purely geometrical reasons, medium-size (from 6–8 to 30–40 atoms depending on the cluster) islands on the cluster (1 1 1) facets prefer the hcp stacking on both Ih and Dh structures, while both smaller and larger islands are better placed on fcc stacking. Interfacet diffusion is easy on both Dh and Ih, indicating that large islands are easily grown; in particular, there are multi-atom diffusion processes which allow fast diffusion among the two caps of Dh clusters. For Dh clusters, islands on hcp stacking may lead to the appearance of new fivefold symmetry points, and to the transformation of the cluster into an icosahedron. 相似文献
20.
Bozanić DK Djoković V Blanusa J Nair PS Georges MK Radhakrishnan T 《The European physical journal. E, Soft matter》2007,22(1):51-59
Silver (Ag) and silver sulfide (Ag2S) nanoparticles were synthesized in a sago starch matrix. The resulting nanocomposites were investigated using structural,
optical and thermal methods. XRD spectra of the nanocomposites confirmed the presence of nanostructured silver (cubic phase)
and silver sulfide (monoclinic phase) in the matrix. TEM micrographs showed that the nanoparticles are mostly spherical in
shape. Analyzes of the optical properties of the silver nanocomposite aqueous dispersions/solutions of various concentrations
were carried out. The results and the theoretical considerations suggested that at high concentrations there is a release
of silver nanoparticles from the composite in the water environment. Further dilution produces homogeneous solution in which
silver nanoparticles are capped with starch macromolecules. TGA analysis revealed reduced thermal stability of the nanocomposites
with respect to pure starch matrix. 相似文献