共查询到20条相似文献,搜索用时 46 毫秒
1.
The process of amorphous silica clusters impact on a crystal silicon substrate is studied by molecular dynamics simulation,
focusing on the energy transfer between clusters and the substrate under different impact conditions such as cluster size,
impact velocity, and incidence angle. The impact process is divided into cluster deformation stage, cluster resilience stage,
and cluster rebound stage according to the courses of energy change during the impact process. The simulation elucidates that
the time of impact process of every cluster is only related to cluster size and is independent of impact velocity and incidence
angle. The translational energy loss of the cluster and the potential energy increment of the substrate during cluster deformation
stage, and the dissipation energy of system are independent of cluster size under the same impact energy and incidence angle.
And the translational energy loss of the cluster during cluster rebound stage changes from energy absorption to energy release
after the incidence angle becomes more than 60°. The rotational energy of the cluster may be omitted when the incidence angle
is less than 15°. The ratios of the rotational energy increment of the cluster, the kinetic energy increment, and the potential
energy increment of the substrate to the translational energy loss of the cluster are obviously influenced by impact conditions.
And the ratios of the increment of the other categories of energy to the translational energy loss of the cluster are not
sensitive to impact conditions. 相似文献
2.
S. Zimmermann H. M. Urbassek 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2006,39(3):423-432
Using molecular-dynamics simulation, we study the processes occurring
after impact of clusters on a rigid wall. Comparing the impact of model
clusters consisting of 13 atoms, or of 13 diatomic molecules with varied
bond strength, the systematics in the results of the collision process
are investigated. Four regimes of impact-induced cluster fragmentation
are identified: intact reflection, shattering into large fragments,
complete fragmentation, and molecule dissociation. The effect of the
number of degrees of freedom activated in the collision on the
translational and internal energies of the reflected fragments is
discussed in detail. As a rule, with increasing number of degrees of
freedom which can be activated in the collision, the translational
energy sinks. On the other hand, for weak intramolecular bonding,
intramolecular vibrations are easily excited at small impact energies,
reducing the resulting translational energy. The presence of even a very
weak attractive well epsilonw at the surface has a major influence
on the sticking behavior of the clusters — and hence also on the
absolute reflected energies — even at impact energies E0 ≫
epsilonw. 相似文献
3.
W. Christen U. Even 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2003,24(1-3):283-286
Size-selected, protonated water cluster cations
(H2O)nH+,
4 n 32, are scattered at
normal incidence from the surface of a diamond-coated silicon
wafer at collision energies 0 E
coll 500 eV. The size distribution of
collision-induced fragment-ions and the ion yield of scattered
particles are analyzed, using a secondary time-of-flight mass
spectrometer, as a function of the cluster size,
n, and the collision energy,
E
coll. Even at low impact energies only
very small fragment-ions can be detected, with a maximum
fragment size of 35% of the colliding parent cluster ions. For
clusters consisting of more than 10 molecules, the protonated
water dimer
(H2O)2H+
becomes the predominant fragment-ion. The total charge survival
yield obeys a nonlinear increase with cluster size; for the
largest clusters investigated, more than 35% of the impacting
ions survive the surface collision in the cationic charge state. 相似文献
4.
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
5.
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
6.
7.
Beam depletion spectroscopy has been used to measure absolute total inelastic electron-sodium cluster collision cross sections in the energy range fromE0.1 toE6 eV. The investigation focused on the closed shell clusters Na8, Na20, and Na40. The measured cross sections show an increase for the lowest collision energies where electron attachment is the primary scattering channel. The electron attachment cross section can be understood in terms of Langevin scattering, connecting this measurement with the polarizability of the cluster. For energies above the dissociation energy the measured electron-cluster cross section is energy independent, thus defining an electron-cluster interaction range. This interaction range increases with the cluster size. 相似文献
8.
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
9.
U. Busolt E. Cottancin H. Röhr L. Socaciu T. Leisner L. Wöste 《Applied physics. B, Lasers and optics》1999,68(3):453-457
n
+ clusters (n=2-9)deposited onto highly oriented pyrolytic graphite (HOPG) substrates at liquid nitrogen temperatures. The
deposition was carried out with variable kinetic energies of the clusters. Clusters deposited with high kinetic energy (up
to 60 eV/cluster) become fragmented upon impact. For low deposition energies (1–4 eV/cluster) the size dependence of the photoelectron
spectra reveals a pronounced odd/even effect, which is well known for gas phase silver clusters. This indicates that the soft
deposited clusters retain their size and identity on the sample. The phase of the odd/even effect suggests that transient
negatively charged cluster ions serve as an intermediate step in the two-photon photoemission process. The lifetime of the
anions rises with cluster size. This is attributed to an increasing electronic density of states for larger clusters.
Received: 26 October 1998 / Revised version: 16 December 1998 相似文献
10.
Low-energy cluster beam deposition was used to deposit mass-selected Aun clusters (n = 4, 6, 13 and 20) on amorphous carbon (a-C) substrates. The resulting samples were stored at room temperature under ambient conditions for time periods up to 32 months to analyze the coarsening behaviour of the clusters. Cluster-size distributions were measured in regular time intervals by transmission electron microscopy (TEM). The TEM experiments show a significant increase of the average cluster size with time analogous to classical surface Ostwald ripening (OR). The coarsening of Au clusters can be well described by steady-state diffusion-limited kinetics. The derived surface mass-transport diffusion coefficients at room temperature range between 1.1 and 3.8·10−25 m2 s−1 for our samples. A detailed analysis of values suggests that, the rate of the surface OR for mass-selected Aun clusters increases with the cluster size in the sequence: Au4 ≈ Au6 < Au13 < Au20 for the investigated range of Au clusters. Given that the initial, on-surface cluster-size distributions are nominally monodisperse, classical OR with cluster coarsening based only on the Gibbs-Thomson effect cannot explain the observed coarsening. The activation of the coarsening process is rationalized by initial variations of the cluster sizes due to the deposition process itself and/or the interaction of the clusters with the substrate. Moreover, the presence of initial deposited Au clusters as different isomers with slightly different chemical potential on the substrate, may also initiate the coarsening by surface OR. Furthermore, we find that the coarsening is most pronounced for the paucidispersed sample with Aum (10 ? m ? 20) clusters. A possible explanation of this behaviour is the presence of an initial distribution of different cluster sizes directly after deposition. 相似文献
11.
Vahedi Tafreshi H. Piseri P. Barborini E. Benedek G. Milani P. 《Journal of nanoparticle research》2002,4(6):511-524
We describe a simulation of the nanoparticle trajectories in a pulsed cluster beam source. Clusters, formed by condensation of atomic vapor in a helium bath, and considered here as rigid spheres having a diameter of 1.5nm, were tracked during their travel inside the source cavity, an aerodynamic lens, and a cylindrical nozzle. Steady state supersonic laminar flow of helium is considered in an axi-symmetric geometry aiming to simulate, within some limitations, the conditions under which cluster formation takes place in a pulsed microplasma cluster source. In spite of the unsteady nature of the pulsed source, the time scale characterizing particle motion in the flow field is significantly smaller than the characteristic time constant for the evolution of gas pressure in the source. For this reason, a steady simulation can shed some light on the understanding of processes governing nanoparticle motion in a pulsed vaporization source. The extent to which the Brownian diffusion can affect the particle extraction from the source is investigated. Simulations have shown that the Brownian motion perturbs the clusters from the trajectories dictated by the carrier gas and increases the rate of cluster deposition on the source internal walls. However, it does not hinder the aerodynamic focalization produced by the lens even in nano-size cluster regime. This result is qualitatively confirmed by experiment. 相似文献
12.
J. Westergren S. Nordholm A. Rosén 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2003,22(1):81-97
The cooling of the metal cluster Pd13 in an atmosphere of rare gas has been studied by means of computer simulation. By simulation, the average energy transfer
in collisions between one cluster and one gas atom has been obtained. Emphasis has been placed on conditions when the temperatures
of the colliding species are almost equal. All modes of motion, inclusive the translation, must be considered in order to
obtain vanishing energy transfer at equilibrium. A simulation scheme is presented by which the energy transfer is zero to
the cluster when the gas and the cluster temperatures are equal. At equilibrium the energy transfer does however not vanish
for all impact parameters. In the collisions with Pd13, the cluster is heated by collisions with a small impact parameter but equally cooled by collisions with a large impact parameter.
Argon and krypton are found to cool Pd13 equally efficiently while neon and helium are less efficient cooling agents.
Received 28 September 2001 / Received in final form 8 August 2002 Published online 12 November 2002
RID="a"
ID="a"e-mail: JanW@phc.gu.se 相似文献
13.
R. F. Snider 《Journal of statistical physics》1995,80(5-6):1085-1117
An important property of the classical Boltzmann equation is that kinetic energy is conserved. This is closely connected to the fact that the Boltzmann equation describes the nonequilibrium properties of an ideal gas. Generalizations of the Boltzmann equation to higher density involve, among other things, allowing the colliding particles to be at different positions. This spatial nonlocality is known to contribute to the density corrections of gas transport properties. For soft potentials such a spatial separation of the particles also leads to a conversion between kinetic and potential energy. In evaluating these effects the classical dynamics of the whole collision trajectory must be taken into account, involving also the time for the collision process. The resulting time nonlocality has usually been reinterpreted in terms of a spatial nonlocality. However, for a homogeneous system this is not possible and only the time nonlocality remains, this then being responsible for the conversion between kinetic and potential energy. This paper aims to clarify these properties of the nonlocal corrections to the classical mechanical Boltzmann collision term. Comments on the corresponding problem for the quantum Boltzmann equation are also made. 相似文献
14.
利用分子动力学模拟系统研究了低能Pt38,Pt141和Pt266原子团簇与Pt(001)表面的相互作用过程,详细分析了初始原子平均动能为0.1,1.0和10eV的原子团簇的沉积演化过程及其对基体表面形貌的影响.研究表明,初始原子平均动能是描述低能原子团簇的重要参量.当团簇的平均原子动能较低时,团簇对基体表层原子点阵损伤较小,基本属于沉积团簇;随着入射团簇的原子平均动能的增加,团簇对表层原子点阵结构的破坏能力增强,当团簇的原子平均动能增加到10eV时,团簇已经显现出注入特征.低能原子团簇对基体表面形貌的影响
关键词:
分子动力学模拟
低能原子团簇
载能沉积 相似文献
15.
Qiaomu Liu 《Applied Surface Science》2009,255(20):8611-8615
Nb coatings were prepared on a SiC substrate by low pressure chemical vapor deposition using NbCl5. Thermodynamic calculations were performed to study the effect of temperature and partial pressure of NbCl5 on the final products. The as-deposited coatings were characterized by scanning electron microscopy, X-ray diffraction, and energy dispersive spectroscopy. The Nb coatings are oriented and grow in the preferred (2 0 0) plane and (2 1 1) plane, at 1173 K and 1223-1423 K, respectively. At 1123-1273 K, the deposition is controlled by the surface kinetic processes. The activation energy is found to be 133 kJ/mol. At 1273-1373 K, the deposition is controlled by the mass transport processes. The activation energy is found to be 46 kJ/mol. The growth mechanism of the chemical vapor deposited Nb is also discussed based on the morphologies and the deposition rates. 相似文献
16.
H. R. Siekmann E. Holub-Krappe Bu. Wrenger Ch. Pettenkofer K. H. Meiwes-Broer 《Zeitschrift für Physik B Condensed Matter》1993,90(2):201-206
Lead clusters grown in a pulsed arc cluster ion source (PACIS) are soft-landed under UHV conditions on cooled polycrystalline silver targets. VUV-photoelectron spectroscopy with light from the synchrotron BESSY applied to mass-selected clusters on cold (160 K) substrates shows that the Pb 5d core level binding energies depend on cluster size and-only beyond a critical amount of deposited clusters-on the coverage . A decreasing particle size induces a core level shift towards lower binding energy with respect to the bulk value, the maximum shift being –0.33 eV. The same value is achieved by atom deposition and can be explained by a Born-Haber cycle. The limits for small two-dimensional and large three-dimensional clusters will qualitatively be discussed by the same model. Deposition on a warm substrate, however, leads-at least for small systems-to a gradual line shift with . 相似文献
17.
The molecular dynamics (MD) computer simulation technique was used to simulate the deposition and cluster growth processes of Pt on a vitreous silica surface. Using a combination of a modified Born-Mayer-Huggins potential (for the substrate) and a Lennard-Jones potential (for the adatoms), the structural features of clusters resulting from four different deposition processes were analyzed and compared to EXAFS results of a similar system. Two of the four deposition processes allowed cluster growth with little interaction with the substrate (by physical separation) and showed comparable results to the EXAFS data. In the two remaining deposition processes, cluster formation occuring with increasing interaction with the substrate resulted in smaller, less three-dimensional particles. This result is in accordance with experimental and theoretical calculations suggesting limited mobility of metal atoms to diffuse once in contract with the amorphous surface. 相似文献
18.
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
19.
Blum J. Tymiak N. Neuman A. Wong Z. Rao N.P. Girshick S.L. Gerberich W.W. McMurry P.H. Heberlein J.V.R. 《Journal of nanoparticle research》1999,1(1):31-42
Nanostructured silicon carbide films have been deposited on molybdenum substrates by hypersonic plasma particle deposition. In this process a thermal plasma with injected reactants (SiCl4 and CH4) is expanded through a nozzle leading to the nucleation of ultrafine particles. Particles entrained in the supersonic flow are then inertially deposited in vacuum onto a temperature-controlled substrate, leading to the formation of a consolidated film. In the experiments reported, the deposition substrate temperature Ts has ranged from 250°C to 700°C, and the effect of Ts on film morphology, composition, and mechanical properties has been studied. Examination of the films by scanning electron microscopy has shown that the grain sizes in the films did not vary significantly with Ts. Micro-X-ray diffraction analysis of the deposits has shown that amorphous films are deposited at low Ts, while crystalline films are formed at high Ts. Rutherford backscattering spectrometry has indicated that the films are largely stoichiometric silicon carbide with small amounts of chlorine. The chlorine content decreases from 8% to 1.5% when the deposition temperature is raised from 450°C to 700°C. Nanoindentation and microindentation tests have been performed on as-deposited films to measure hardness, Young's modulus and to evaluate adhesion strength. The tests show that film adhesion, hardness and Young's modulus increase with increasing Ts. These results taken together demonstrate that in HPPD, as in vapor deposition processes, the substrate temperature may be used to control film properties, and that better quality films are obtained at higher substrate temperatures, i.e. Ts700°C. 相似文献
20.
H. A. Marzouk J. S. Kim P. J. Reucroft R. J. Jacob J. D. Robertson C. Eloi 《Applied Physics A: Materials Science & Processing》1994,58(6):607-613
Thin films of pure copper have been deposited on glass and Si(100) substrates using copper acetylacetonate [Cu(acac)2] and copper HexaFluoroAcetylacetonate [Cu(HFA)2] sources. A thermal, cold-wall, reduced pressure (3325–5985 Pa) Metal-Organic Chemical Vapor Deposition (MOCVD) process was employed. The effect of H2O vapor on the grain size, deposition rate, and resistivity was examined. Electrical resistivities of 2.4 cm for copper films deposited on Si(100) and 3.44 cm for copper films deposited on glass at substrate temperatures of 265° C and a [Cu(acac)2] source temperature of 147° C with the use of H2O vapor were measured. When [Cu(HFA)2] was used, the substrate temperature was 385° C and the source temperature was 85° C. An activation energy for the copper film deposition process was calculated to be 22.2 kJ/mol in the case of the [Cu(acac)2] source. A deposition rate of 11 nm/min was obtained with Cu(acac)2 as the source and the rate was 44.4 nm/min with the Cu(HFA)2 source; both were obtained with the use of H2O vapor. No selectivity was observed with either source for either substrate. The deposited films were fully characterized using XRD, LVSEM, SAXPS, and RBS. 相似文献