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1.
M. Gaudry J. Lermé E. Cottancin M. Pellarin B. Prével M. Treilleux P. Mélinon J.-L. Rousset M. Broyer 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,16(1):201-204
Optical properties of mixed clusters (AuxAg
1 - x
)
n
and (NixAg
1 - x
)
n
, produced by laser vaporization and embedded in an alumina matrix, are reported. The size effects are investigated for different
concentrations (x
= 0.25, 0.5 and 0.75) in the diameter range 2-4 nm. For alloyed clusters (AuxAg
1 - x
)
n
of a given size an almost linear evolution of the surface plasmon frequency ω
s
with the concentration is observed (between those of pure gold and pure silver clusters). Moreover the blue-shift and the
damping of the resonance with decreasing size is all the more important as the gold concentration in the particles increases.
Such results are in agreement with theoretical calculations carried out in the frame of the time-dependent local-density-approximation
(TDLDA) including an inner skin of ineffective screening and the porosity of the matrix. The optical response of (NixAg
1 - x
)
n
clusters exhibits a surface plasmon resonance in the same spectral range as the one observed for pure silver clusters, but
considerably damped and broadened. For a given mean cluster size 3.0 nm, a blue-shift of the resonance is observed when increasing
the nickel concentration (between x
= 0.25 and x
= 0.75). The results are in good qualitative agreement with classical predictions in the dipolar approximation, assuming a core-shell
geometry.
Received 21 November 2000 相似文献
2.
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
3.
Metastable fragmentation of silver bromide clusters 总被引:2,自引:0,他引:2
J.-M. L'Hermite F. Rabilloud L. Marcou P. Labastie 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,14(3):323-330
The abundance spectra and the fragmentation channels of silver bromide clusters have been measured and analyzed. The most
abundant species are AgnBrn - 1
+ and AgnBrn + 1
- and Ag14Br13
+ is a magic number, revealing their ionic nature. However, some features depart from what is generally observed for alkali-halide
ionic clusters. From a certain size, AgnBrn - 1
+ is no more the main series, and AgnBr n - 2, 3
+ series become almost as important. The fast fragmentation induced by a UV laser makes the cations lose more bromine than
silver ions and lead to more silver-rich clusters. Negative ions mass spectra contain also species with more silver atoms
than required by stoichiometry. We have investigated the metastable fragmentation of the cations using a new experimental
method. The large majority of the cations release mainly a neutral Ag3Br3 cluster. These decay channels are in full agreement with our recent ab initio DFT calculations, which show that Ag+-Ag+ repulsion is reduced due to a globally attractive interaction of their d orbitals. This effect leads to a particularly stable trimer (AgBr)3 and to quasi-planar cyclic structures of (AgBr)n clusters up to n = 6. We have shown that these two features may be extended to other silver halides, to silver hydroxides (AgOH)n, and to cuprous halide compounds.
Received 9 November 2000 and Received in final form 25 January 2001 相似文献
4.
J. Zhao Y. Luo G. Wang 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,14(3):309-316
Tight-binding model is developed to study the structural and electronic properties of silver clusters. The ground state structures
of Ag clusters up to 21 atoms are optimized by molecular dynamics-based genetic algorithm. The results on small Agn clusters (n = 3-9) are comparable to ab initio calculations. The size dependence of electronic properties such as density of states, s-d band separation, HOMO-LUMO gap, and ionization potentials are discussed. Magic number behavior at Ag2, Ag8, Ag14, Ag18, Ag20 is obtained, in agreement with the prediction of electronic ellipsoid shell model. We suggest that both the electronic and
geometrical effect play significant role in the coinage metal clusters.
Received 7 August 2000 相似文献
5.
F. Calvo F. Spiegelman M. A. Gaveau M. Briant P. R. Fournier J. M. Mestdagh J. P. Visticot 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2003,24(1-3):215-218
The finite temperature optical spectroscopy of
CaArn clusters in the range
6
n
146
is investigated using a Diatomics-In-Molecule (DIM) Hamiltonian
and classical parallel tempering Monte Carlo simulations. The
absorption spectrum is calculated in the vertical approximation
at various temperatures between 2 K and 50 K. Several typical
situations are reported. CaAr6 shows a
strong thermal broadening and shift of the spectral lines,
possibly associated with isomerization.
CaAr13 only shows some broadening.
CaAr37 exhibits features corresponding to
coexisting isomers at low temperature. Finally, the abrupt
changes in the absorption spectrum in
CaAr146 at about 20 K are indicative of
surface diffusion. 相似文献
6.
M. Vogel K. Hansen A. Herlert L. Schweikhard 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,16(1):73-76
The decay pathway competition between monomer and dimer evaporation of photoexcited cluster ions Au
+
n, n = 2-27, has been investigated by photodissociation of size-selected gold clusters stored in a Penning trap. For n > 6 the two decay pathways are distinguished by their experimental signature in time-resolved measurements of the dissociation.
For the smaller clusters, simple fragment spectra were used. As in the case of the other copper-group elements, even-numbered
gold cluster ions decay exclusively by monomer evaporation, irrespective of their size. For small odd-size gold clusters,
dimer evaporation is a competitive alternative, and the smaller the odd-sized clusters, the more likely they decay by dimer
evaporation. In this respect, Au
+
9 shows an anomalous behavior, as it is less likely to evaporate dimers than its two odd-numbered neighbors, Au
+
7 and Au
+
11. This nonamer anomaly is typical for copper-group cluster ions M
+
9 (M = Cu, Ag, Au) and a similar behavior is found in the anionic heptamers M
-
7. It is discussed in terms of the well-known electronic shell closing at n
e = 8 atomic valence electrons.
Received 2 November 2000 相似文献
7.
P. Parneix 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2003,23(3):375-383
The isomerization and evaporation processes in the neutral homogeneous (CH3CN)n molecular clusters (n
= 2-7) have been investigated using classical molecular dynamics simulations. The evaporation rate constants and the kinetic energy
release in the dissociation have been analysed as a function of the cluster size and as a function of the internal energy
in the parent cluster. The competition between monomer and dimer ejections has been also carefully studied. All the dynamical
properties in these dissociative processes have been discussed in relation to the static properties of the clusters involved
in the dissociation and also in relation to the solid-liquid like transition which appears in these homogeneous molecular
clusters.
Received 19 November 2002 / Received in final form 5 February 2003 Published online 29 April 2003
RID="a"
ID="a"e-mail: pascal.parneix@ppm.u-psud.fr
RID="b"
ID="b"Laboratoire associé à l'université Paris-Sud. 相似文献
8.
D. Ievlev I. Rabin W. Schulze G. Ertl 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,16(1):157-160
The Pick Up technique allows continuous formation of high density metal cluster beams in the otherwise hardly accessible size
range Me2 to about Me50. With an apparatus based on the use of cryo-condensation pumps, Ar as inert gas for production of the host clusters by adiabatic
expansion and silver as metal we demonstrate how the various source parameters influence the composition and mean size of
the resulting cluster distributions. The analysis in the gas phase by means fluorescence spectroscopy allows to conclude that
an Ar shell encapsulates the metal clusters.
Received 30 November 2000 相似文献
9.
J. Lermé B. Palpant B. Prével E. Cottancin M. Pellarin M. Treilleux J.L. Vialle A. Perez M. Broyer 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》1998,4(1):95-108
The optical response of free and matrix-embedded gold metal clusters AuN is investigated in the framework of the time-dependent local-density-approximation (TDLDA). The characteristics of the surface
plasmon resonance are carefully analyzed as a function of the model parameters and the particle radius. The strong influence
of the frequency-dependence of the 5d core-electron dielectric function in the vicinity of the interband threshold is emphasized. The size evolution of the Mie-frequency
in free gold clusters exhibits a noticeable blue-shift trend as the particle size decreases, much stronger than in silver
clusters. The width and shape of the resonance, essentially ruled by the decay via the interband transitions, are found closely correlated to the imaginary component of the core-electron dielectric function.
In presence of a surrounding matrix the blue-shift trend is largely rubbed out. Agreement with recent experimental results
on size-selected gold clusters embedded in an alumina matrix may be achieved by taking into account the porosity effects at
the metal/matrix interface. The comparison with the predictions of classical models is also provided.
Received: 9 March 1998 / Revised: 5 June 1998 / Accepted: 3 July 1998 相似文献
10.
M.-H. Schaffner F. Patthey U. Heiz W.-D. Schneider O. Kuffer H.-V. Roy P. Fayet J.K. Gimzewski R. Berndt 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》1998,2(1):79-82
The emission of photons in the visible wavelength range from mass-selected Ag+
n, Cu+
n, Pt+
n and Pd+
n () clusters is observed. Photons are detected 10-4 s after the cluster generation in a sputter source. The emission intensities display distinct variations with cluster size
and material. The observations are interpreted in terms of the decay of metastable states which are excited during the high-energy
sputtering process used for the generation of these clusters.
Received: 28 October 1997 / Revised: 5 January 1998 / Accepted: 30 January 1998 相似文献
11.
The geometrical and magnetic properties of bimetallic clusters (CoPt)n(1?n?5) have been studied by using the generalized gradient correction spin density formalisms. In general, the ground state structures of (CoPt)n clusters are the three-dimension structures. We found that both the binding energy and magnetism per (CoPt) unit are increasing consistently with the size of the Co–Pt cluster (n). However, as the n increases, the magnetism shows a trace of convergence while the binding energy shows a linearly increasing pattern. Generally, Co average magnetic moment is enhanced when alloyed with Pt atoms than that in pure Co clusters. 相似文献
12.
S. Rubin M. Holdenried H. Micklitz 《The European Physical Journal B - Condensed Matter and Complex Systems》1998,5(1):23-28
Well-defined granular Co/Ag films have been prepared by the co-deposition of in-beam prepared Co clusters and Ag atoms. In
this way we were able to study the giant magnetoresistance (GMR) as a function of mean Co cluster size for a fixed Co cluster volume fraction vcl as well as a function of vcl for a fixed . Mean Co cluster size has been varied between and 6.9 nm, Co cluster volume fraction between 5 and 43%. The GMR was measured in-situ at T=4.2 K in magnetic fields 1.2 T. The analysis of the GMR data obtained from these studies clearly shows that spin-dependent scattering at the Co-cluster/Ag-matrix
interface is the only relevant scattering mechanism causing the GMR in our well-defined samples.
Received: 21 April 1998 / Received in final form: 17 May 1998 /
Accepted: 18 May 1998 相似文献
13.
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
14.
A. Rytkönen M. Manninen 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2003,23(3):351-357
The effect of melting transition on the ionization potential has been studied for sodium clusters with 40, 55, 142, and 147
atoms, using ab initio and classical molecular dynamics. Classical and ab initio simulations were performed to determine the ionization potential of Na142 and Na147 for solid, partly melted, and liquid structures. The results reveal no correlation between the vertical ionization potential
and the degree of surface disorder, melting, or the total energy of the cluster obtained with the ab initio method. However, in the case of 40 and 55 atom clusters, the ionization potential seems to decrease when the cluster melts.
Received 1st November 2002 Published online 24 April 2003
RID="a"
ID="a"e-mail: ar@phys.jyu.fi 相似文献
15.
V. Tevekeliyska Y. Dong M. Springborg V. G. Grigoryan 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2007,43(1-3):19-22
In this work we present results from a theoretical study on the properties of sodium clusters. The structures of the global
total-energy minima have been
determined using two different methods. With the parameterized
density-functional tight-binding method (DFTB) combined with a genetic-algorithm we investigated the properties of NaN clusters with cluster size up to 20 atoms, and with our own Aufbau/Abbau algorithm together with the embedded-atom method (EAM) up to 60 atoms. The two sets of results from the
independent calculations are compared and a stability function is studied as function of the cluster size. Due to the electronic
effects included in the DFTB method and the packing effects included in the EAM we have obtained different global-minima structures
and different stability functions. 相似文献
16.
R. von Pietrowski K. von Haeften T. Laarmann T. Möller L. Museur A. V. Kanaev 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2006,38(2):323-336
The electronic and geometric structure of rare gas clusters doped with
rare-gas atoms Rg = Xe, Kr or Ar is investigated with fluorescence excitation
spectroscopy in the VUV spectral range. Several absorption bands are
observed in the region of the first electronic excitations of the impurity
atoms, which are related to the lowest spin-orbit split atomic 3P1
and 1P1 states. Due to influence of surrounding atoms of the
cluster, the atomic lines are shifted to the blue and broadened
(“electronical cage effect”). From the known interaction potentials and
the measured spectral shifts the coordination of the impurity atom in
ArN, KrN, NeN and HeN could be studied in great detail.
In the interior of KrN and ArN the Xe atoms are located in
substitutional sites with 12 nearest neighbours and internuclear distances
comparable to that of the host matrix. In NeN and HeN the cluster
atoms (18 and 22, respectively) arrange themselves around the Xe impurity
with a bondlength comparable to that of the heteronuclear dimer. The results
confirm that He clusters are liquid while Ne clusters are solid for N≥
300. Smaller Ne clusters exhibit a liquid like behaviour. When doping is
strong, small Rgm-clusters (Rg = Xe, Kr, Ar, m≤10 2) are formed
in the interior sites of the host cluster made of Ne or He. Specific
electronically excited states, assigned to interface excitons are observed.
Their absorption bands appear and shift towards lower energy when the
cluster size m increases, according to the Frenkel exciton model. The
characteristic bulk excitons appear in the spectra, only when the cluster
radius exceeds the penetration depth of the interface exciton, which can be
considerably larger than that in free Rgm clusters. This effect is
sensitive to electron affinities of the guest and the host cluster. 相似文献
17.
A. Heidenreich I. Last J. Jortner 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2008,46(1):195-202
We present a theoretical and computational study of the properties and the
response of the nanoplasma and of outer ionization in Xen clusters (n =
55–2171, initial cluster radius R0 = 8.7–31.0 ?) driven by
ultraintense near-infrared laser fields (peak intensity IM = 1015–1020 Wcm-2, temporal pulse length τ= 10–100 fs, and frequency ν= 0.35 fs-1). The positively charged high-energy nanoplasma produced by inner ionization nearly follows the oscillations of
the fs laser pulse and can either be persistent (at lower intensities of IM = 1015–1016 Wcm-2 and/or for larger cluster sizes, where the electron energy distribution is nearly thermal) or transient (at higher intensities
of IM = 1018–1020 Wcm-2 and/or for smaller cluster sizes). The nanoplasma is depleted by outer ionization that was semiquantitatively described by
the cluster barrier suppression electrostatic model, which accounts for the cluster size, laser intensity and pulse length
dependence of the outer ionization yield. The electrostatic model was further utilized for estimates of the laser intensity
and pulse
width dependence of the border radius R0
(I) for the attainment of complete outer ionization at
,
while at R0 > R0
(I) a persistent nanoplasma prevails. R0
(I)
establishes an interrelationship between electron dynamics and nuclear Coulomb explosion dynamics in ultraintense
laser-cluster interactions. 相似文献
18.
G. Martinet M. Chabot K. Wohrer S. Della Negra D. Gardès J. A. Scarpaci P. Désesquelles V. Lima S. Díaz-Tendero M. Alcamí P.-A. Hervieux M. F. Politis J. Hanssen F. Martín 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2003,24(1-3):149-152
We report on experimental and theoretical efforts designed
to understand the fragmentation of small carbon clusters.
Experimentally, a new detection system for high velocity
fragments has been recently developed allowing the fragmentation
of high velocity clusters to be totally recorded [1]. Results
for the branching ratios of deexcitation of
C5 and C9 formed
by electron capture in high velocity
collisions are presented. Theoretically, the dissociation
dynamics of C5 has been investigated
using a kinematical model based on the statistical theory of
Weisskopf. In this model various structural quantities
(geometries, dissociation energies, harmonic frequencies), are
required for both the parent cluster and the fragments. They
have been calculated within DFT and coupled-cluster formalisms
for Cn up to n = 9.
In all cases, a strong correlation between measured branching
ratios and calculated dissociation energies is observed. 相似文献
19.
M. Dubiel R. Schneider H. Hofmeister K.-D. Schicke J. C. Pivin 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2007,43(1-3):291-294
The formation of argentic clusters and very small Ag
nanoparticles of 0.5 to 2 nm size in commercial soda-lime glass silver-doped
by Ag/Na ion exchange in a mixed nitrate melt has been studied by electron
microscopy and EXAFS. Particles formation was induced already during the ion
exchange procedure, or by subsequent ion irradiation with 1.5 MeV He+
or 3 MeV Au+. The presence of nanoparticles was also macroscopically
revealed by their surface plasmon resonance. The structural characterization
indicates that specific configurations of silver oxide-like structures,
so-called argentic clusters, are involved in the initial stage of
nanoparticles formation. 相似文献
20.
S. Neukermans N. Veldeman E. Janssens P. Lievens Z. Chen P.v.R. Schleyer 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2007,45(2):301-308
We report a combined experimental and computational
investigation of small AlnOm species (n ≤20, m ≤
12), produced in a laser vaporization cluster source. The oxygen
content in the clusters was tuned by varying the oxygen
concentration in the carrier gas. Ionization energies are
bracketed using different ionizing photon energies in the energy
range between 5.37 and 7.89 eV. Among the singly doped AlnO
species, Al3O and Al15O are found to have relatively low
ionization energies, which can be related to the magic character
of the corresponding cations. Peculiarly low ionization energies
also are observed for specific oxygen rich species (m > 1),
suggesting the formation of ionically bound subunits. The
structures and ionization energies of singly doped AlnO0,+
(n = 1 - 7) clusters were determined using density functional
theory (B3LYP/6-311+G(d)).
Electronic supplementary material Supplementary Online Material 相似文献