共查询到20条相似文献,搜索用时 15 毫秒
1.
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
2.
P. C.R. Rodrigues F. M.S. Silva Fernandes 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2006,40(1):115-123
Molecular dynamics simulations of the melting, freezing and nucleation are presented for unconstrained nanoclusters of KCl
with a number of ions between 512 and 10648. The maximum extent of the probed liquid supercooling is analysed to the light
of theoretical predictions and compared with experimental data. The fraction of the solid-like ions in the supercooled liquid
is used as an indicator of heterogeneities within the liquid. Induced nucleation by seeding the supercooled liquid indicates
that solid-liquid coexistence is stable, and sustained during the lifetime of the clusters, relatively to the supercooled
liquid. A phenomenological analysis on the relaxation times of the crystal growth process is made. Critical nuclei sizes computed
from the effectiveness of the seeds in the heterogeneous nucleation of the supercooled liquid, and from the residual crystallites
in clusters not totally melted, are presented as a function of the temperature. The behavior of the systems is followed through
various properties such as liquid and solid molar fractions, enthalpies of melting, heat capacities, self-diffusion coefficients
and relaxation times related to the freezing process. The consistency of the simulation results for the heterogeneous nucleation
is assessed by means of a classical nucleation model, from which an estimate of the interfacial surface tension is also worked
out and compared with experimental data. 相似文献
3.
SIMULATION OF MULTIPLE FRACTAL AND COMPACT GROWTH OF ULTRA-THIN FILMS ON HEXAGONAL SUBSTRATE 总被引:2,自引:0,他引:2 下载免费PDF全文
The multiple cluster growth of ultra-thin films with different deposition rate and different substrate temperature has been studied by kinetic Monte-Carlo simulation. With increasing diffusion rate along cluster edges (corresponding to an increasing substrate temperature), pattern structures change smoothly from fractal islands, compact islands with random shapes, to regular islands, and the average branch width of clusters increases continuously up to some constant value in the compact island limit. The formation of the multiple fractal and compact clusters can be described quantitatively by multifractal. The results of multifractal analysis show that with pattern change from fractal to compact islands, the Hausdorff dimension D0, the information dimension D1, and the correlation dimension D2 decrease, while the width and height of the multifractal spectra increase. 相似文献
4.
A. Lando N. Kébaïli Ph. Cahuzac C. Colliex M. Couillard A. Masson M. Schmidt C. Bréchignac 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2007,43(1-3):151-154
Preformed clusters carrying surfactant are used as primary blocks for the building of nano structures. Self assembly of silver
atom based clusters, soft landed on a HOPG surface, generates a large variety of new architectures depending on the nature
and on the concentration of the impurities. Fractal shapes fragmented into multiple compact like islands, and chain like structures
might be formed. A strong local enhancement of the silver atom mobility at the surface of islands is responsible for those
morphology changes. 相似文献
5.
Bréchignac C Cahuzac P Carlier F Colliex C Leroux J Masson A Yoon B Landman U 《Physical review letters》2002,88(19):196103
Formation and evolution of fragmentation instabilities in fractal islands, obtained by deposition of silver clusters on graphite, are studied. The fragmentation dynamics and subsequent relaxation to the equilibrium shapes are controlled by the deposition conditions and cluster composition. Sharing common features with other materials' breakup phenomena, the fragmentation instability is governed by the length-to-width ratio of the fractal arms. 相似文献
6.
A. M. Panich A. I. Shames H.-M. Vieth E. Ōsawa M. Takahashi A. Ya. Vul' 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,52(3):397-402
We report on a nuclear magnetic resonance (NMR) study of
ultrananocrystalline diamond (UNCD) materials produced by detonation
technique. Analysis of the 13C and 1H NMR spectra, spin-spin and
spin-lattice relaxation times in purified UNCD samples is presented. Our
measurements show that UNCD particles consist of a diamond core that is
partially covered by a sp
2-carbon fullerene-like shell. The uncovered
part of outer diamond surface comprises a number of hydrocarbon groups that
saturate the dangling bonds. Our findings are discussed along with recent
calculations of the UNCD structure. Significant increase in the spin-lattice
relaxation rate (in comparison with that of natural diamond), as well as
stretched exponential character of the magnetization recovery, are
attributed to the interaction of nuclear spins with paramagnetic centers
which are likely fabrication-driven dangling bonds with unpaired electrons.
We show that these centers are located mainly at the interface between the
diamond core and shell. 相似文献
7.
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
8.
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
9.
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
10.
H.I. Hidmi D.H.E. Gross H.R. Jaqaman 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2002,18(1):87-92
The fragmentation of multiply charged atomic sodium clusters of mass 200 is investigated using the Micro-canonical Metropolis
Monte Carlo (MMMC) statistical technique for excitation energies up to 200 eV and for cluster charges up to +9e. In this work we present caloric curves and charged and uncharged fragment mass distributions for clusters with charges 0,
2, and 4. The caloric curves show a dip at the critical point implying a negative specific heat, as expected for finite systems,
while the fragment mass distributions corroborate the picture of a phase transition from one dominant liquid-like cluster
to complete vaporization.
Received 7 November 2001 / Received in final form 4 April 2002 Published online 28 June 2002 相似文献
11.
M. Dubiel H. Hofmeister G. L. Tan K.-D. Schicke E. Wendler 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2003,24(1-3):361-364
Silver particles in soda-lime glass, less than 10 nm in
size, were prepared by ion implantation. The implantation dose
was in the range of 0.5 to 2×1016 Ag
ions/cm2 and the beam current density
was varied from 0.5 to 2A/cm2. Here,
the beam current density strongly influences ion diffusion and
particle precipitation as well as compressive stress generation
around the particles due to thermal effects resulting from the
deceleration of silver ions. Stress relaxation can be achieved
by increased dose rates or thermal processing at elevated
temperatures. Based on RBS and HREM results, a possible route to
homogeneous distribution of Ag nanoparticles within the glass is
discussed with respect to their interesting optical properties. 相似文献
12.
K. Akamatsu K. Nakahashi S. Ikeda H. Nawafune 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2003,24(1-3):377-380
Formation and structure of composite layer consisting of
polyimide films containing Ni nanoparticles were investigated.
The preparation method relies on KOH treatment on polyimide film
to form carboxyl acid groups and adsorption of Ni ions by ion
exchange followed by hydrogen reduction. The amount of Ni ions
adsorbed in polyimide films were found to be systematically
controlled by changing initial KOH concentration, subsequent ion
exchange time, pH and temperature. Cross-sectional TEM
observation revealed that Ni nanoparticles with 3-5 nm in
diameter were homogeneously dispersed in the surface modified
polyimide layer after heat treatment above 250
°C in H2
atmosphere. The size and distribution of the Ni nanoparticles
were strongly dependent on the heat treatment temperature,
indicating that this method allows microstructural tuning of
metal/polymer nanocomposites. 相似文献
13.
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
14.
H. Nabika S. Deki 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2003,24(1-3):369-372
The effect of colloidal dispersion of silver on the
luminescent properties of Eu (III) complex with
pyridine-3,5-dicarboxylic acid (PyDC) was investigated. The
luminescence from Förster type europium complex was enhanced
several times with the presence of Ag colloid and the
enhancement factor showed Ag concentration dependence. The
observed enhancement effect was discussed in view of
surface-enhancement effect and optical absorption due to surface
plasmon resonance, both arising from excitation of surface
plasmon polariton. The coordination structure around Eu (III)
ion was also affected with the presence of Ag colloid, which
induced the change in the intensity ratio between two emission
bands of
5
D
0
7
F
1
and
5
D
0
7
F
2
transitions of Eu (III) ion. 相似文献
15.
I. Popov T. Kunze S. Gemming G. Seifert 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2007,45(3):439-446
The preferred adsorption sites and the propensity for a self-organised growth of the molybdenum sulfide cluster Mo6S8 on the Au(111) surface are investigated by density-functional band-structure calculations with pseudopotentials and a plane
wave basis set. The quasi-cubic cluster preferentially adsorbs via a face and remains structurally intact.
It experiences a strong, mostly non-ionic attraction to the surface
at several quasi-isoenergetic adsorption positions. A scan of the potential energy surface exhibits only small barriers between
adjacent strong adsorption sites. Hence, the cluster may move in a potential well with degenerate local energy minima at room
temperature. The analysis of the electronic structure reveals a negligible
electron transfer and S-Au hybridised states, which indicate that the cluster-surface
interaction is dominated by S-Au bonds, with minor contributions from
the Mo atom in the surface vicinity. All results indicate that Mo6S8 clusters
on the Au(111) surface can undergo a template-mediated self-assembly to an ordered inorganic monolayer, which is still redox
active and may be employed as surface-active agent in the integration of noble metal and ionic or biological components within
nano-devices.
Therefore, a classical potential model was developed on the basis of the DFT data,
which allows to study larger cluster assemblies on the Au(111). 相似文献
16.
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
17.
P.I. Gaiduk J. Lundsgaard Hansen A. Nylandsted Larsen 《Applied Physics A: Materials Science & Processing》2001,73(6):761-763
Semi-spherical SiGe/Si nano-structures of a new type are presented. Epitaxial islands of 30–40 nm in base diameter and 11 nm
in height and having a density of about 6×1010 cm-2 were produced on (001) Si by molecular beam epitaxial growth of Si/Si0.5Ge0.5 layers with in situ implantation of 1-keV As+ ions. It was found by cross-section transmission electron microscopy that the islands have a complicated inner structure
and consist of a micro-twin nucleus and semi-spherical nano-layers of various SiGe compositions. The nature of the surface
patterning is interpreted by stress relaxation through implantation-induced defects.
Received: 12 July 2001 / Accepted: 4 September 2001 / Published online: 2 October 2001 相似文献
18.
M. Iwamoto K. Kuroda V. Zaporojtchenko S. Hayashi F. Faupel 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2003,24(1-3):365-367
Recently, production methods of metal nanoparticles have
been investigated extensively, not only for a research use in
laboratory, but also for an industrial use. However, it is
difficult to obtain metal nanoparticles in high amounts and
concentrations with simple methods. In this study, a gold
nanoparticle-polymer composite was prepared with a simple
procedure using a gold salt and a melted polymer. The composite,
which is in a wax state at room temperature, was highly soluble
in water and lower alcohols, moreover the composite was melted
at about 50
°C. 相似文献
19.
Sabín J Prieto G Ruso JM Sarmiento F 《The European physical journal. E, Soft matter》2007,24(2):201-210
We present a study of the fractal dimension of clusters of large unilamellar vesicles (LUVs) formed by egg yolk phosphatidylcholine
(EYPC), dimyristoylphosphocholine (DMPC) and dipalmitoylphosphocholine (DPPC) induced by Ca2+ . Fractal dimensions were calculated by application of two methods, measuring the angular dependency of the light scattered
by the clusters and following the evolution of the cluster size. In all cases, the fractal dimensions fell in the range from
2.1 to 1.8, corresponding to two regimes: diffusion-limited cluster aggregation (DLCA) and reaction-limited cluster aggregation
(RLCA). Whereas DMPC clusters showed a typical transition from the RLCA to the DLCA aggregation, EYPC exhibited an unusual
behaviour, since the aggregation was limited for a higher concentration than the critical aggregation concentration. The behaviour
of DPPC was intermediate, with a transition from the RLCA to the DLCA regimes with cluster sizes depending on Ca2+ concentration. Studies on the reversibility of the aggregates show that EYPC and DPPC clusters can be re-dispersed by dilution
with water. DMPC does not present reversibility. Reversibility is evidence of the existence of secondary minima in the DLVO
potential between two liposomes. To predict these secondary minima, a correction of the DLVO model was necessary taking into
account a repulsive force of hydration. 相似文献
20.
R. Neffati J. Rault 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,21(2):205-210
By differential Scanning Calorimetry (DSC), at low heating rate and using a technique of fractionation, we have measured the
equilibrium DSC signal (heat flow) J
q
0 of two families of porous glass saturated with water. The shape of the DSC peak obtained by these techniques is dependent
on the sizes distribution of the pores. For porous glass with large pore size distribution, obtained by sol-gel technology,
we show that in the domain of ice melting, the heat flow Jq is related to the melting temperature depression of the solvent, ΔT
m , by the scaling law: J
q
0∼ΔT
m
- (1 + D). We suggest that the exponent D is of the order of the fractal dimension of the backbone of the pore network and we discuss the influence of the variation
of the melting enthalpy with the temperature on the value of this exponent. Similar D values were obtained from small angle neutron scattering and electronic energy transfer measurements on similar porous glass.
The proposed scaling law is explained if one assumes that the pore size distribution is self similar. In porous glass obtained
from mesomorphic copolymers, the pore size distribution is very sharp and therefore this law is not observed. One concludes
that DSC, at low heating rate ( q? 2°C/min) is the most rapid and less expensive method for determining the pore distribution and the fractal exponent of a porous
material.
Received 23 July 1999 and Received in final form 16 February 2001 相似文献