共查询到20条相似文献,搜索用时 31 毫秒
1.
K. J. Daun T. A. Sipkens J. T. Titantah M. Karttunen 《Applied physics. B, Lasers and optics》2013,112(3):409-420
The capabilities of time-resolved laser-induced incandescence (TiRe-LII), a combustion diagnostic used almost exclusively to measure soot primary particles, could potentially be extended to size aerosolized metal nanoparticles. In order to do this, however, it is necessary to characterize the thermal accommodation coefficient, α, which specifies the heat conduction rate between the laser-energized nanoparticles and the surrounding gas. This paper extends a molecular dynamics (MD) methodology to calculate α for Fe/He, Fe/Ar, Mo/He, and Mo/Ar systems. A comparative analysis of the results shows that α is most strongly influenced by the potential well between the gas molecule and nanoparticle surface. Finally, the MD-derived value for α is used to recover the nanoparticle size distribution for TiRe-LII measurements made on molybdenum nanoparticles in argon. 相似文献
2.
T. A. Sipkens R. Mansmann K. J. Daun N. Petermann J. T. Titantah M. Karttunen H. Wiggers T. Dreier C. Schulz 《Applied physics. B, Lasers and optics》2014,116(3):623-636
This paper describes the application of time-resolved laser-induced incandescence (TiRe-LII), a combustion diagnostic used mainly for measuring soot primary particles, to size silicon nanoparticles formed within a plasma reactor. Inferring nanoparticle sizes from TiRe-LII data requires knowledge of the heat transfer through which the laser-heated nanoparticles equilibrate with their surroundings. Models of the free molecular conduction and evaporation are derived, including a thermal accommodation coefficient found through molecular dynamics. The model is used to analyze TiRe-LII measurements made on silicon nanoparticles synthesized in a low-pressure plasma reactor containing argon and hydrogen. Nanoparticle sizes inferred from the TiRe-LII data agree with the results of a Brunauer–Emmett–Teller analysis. 相似文献
3.
C. Carbogno A. Groß M. Rohlfing 《Applied Physics A: Materials Science & Processing》2007,88(3):579-586
Based on potential–energy curves that were derived from ab initio calculations within the framework of many-body perturbation
theory, mixed quantum–classical simulations have been performed to understand the dynamics of the photodesorption process
of iodine from KI(100). Dissipation and recoil processes were included by adding a surface oscillator to the ab initio potentials.
Using this approach, we reproduce and explain qualitatively the desorption spectrum and the kinetic energy distribution of
the desorbing iodine.
PACS 68.43.Bc; 31.15.Qg; 31.50.Gh 相似文献
4.
Based on the Collins integral formula and the Hermite–Gaussian expansion of a Lorentz function, an analytical expression for
the Wigner distribution function (WDF) of Lorentz and Lorentz–Gauss beams through a paraxial ABCD optical system is derived. The properties of the WDF of Lorentz and Lorentz–Gauss beams propagating in free space are demonstrated.
The normalized WDFs of Lorentz and Lorentz–Gauss beams at the different spatial points are depicted in the several observation
planes. The influences of the beam parameters on the WDF of Lorentz and Lorentz–Gauss beams in free space are also analyzed
at different propagation distances. The special WDF of a Lorentz beam results in its higher angular spreading than the Gaussian
beam. 相似文献
5.
Derivation of a temperature-dependent accommodation coefficient for use in modeling laser-induced incandescence of soot 总被引:1,自引:0,他引:1
H. A. Michelsen 《Applied physics. B, Lasers and optics》2009,94(1):103-117
This paper presents a derivation of an expression to estimate the accommodation coefficient for gas collisions with a graphite
surface, which is meant for use in models of laser-induced incandescence (LII) of soot. Energy transfer between gas molecules
and solid surfaces has been studied extensively, and a considerable amount is known about the physical mechanisms important
in thermal accommodation. Values of accommodation coefficients currently used in LII models are temperature independent and
are based on a small subset of information available in the literature. The expression derived in this study is based on published
data from state-to-state gas-surface scattering experiments. The present study compiles data on the temperature dependence
of translational, rotational, and vibrational energy transfer for diatomic molecules (predominantly NO) colliding with graphite
surfaces. The data were used to infer partial accommodation coefficients for translational, rotational, and vibrational degrees
of freedom, which were consolidated to derive an overall accommodation coefficient that accounts for accommodation of all
degrees of freedom of the scattered gas distributions. This accommodation coefficient can be used to calculate conductive
cooling rates following laser heating of soot particles. 相似文献
6.
I. I. Bubukina N. F. Zobov O. L. Polyansky S. V. Shirin S. N. Yurchenko 《Optics and Spectroscopy》2011,110(2):160-166
A semiempirical potential energy surface is obtained for the major isotopologue of the water molecule H2
16O that allows the vibration-rotation energy levels in the range of 0–26000 cm−1 to be calculated with an accuracy almost equal to the average experimental accuracy of measurements in the infrared and visible
ranges. Variational calculations using this potential energy surface reproduce the experimental energy values of more than
1500 vibration-rotation levels of H2
16O with the total angular momentum quantum number J = 0, 2, and 5 in the indicated range with a standard deviation of 0.022 cm−1. The potential was obtained by optimizing a starting ab initio surface using a combination of two approaches, i.e., (1) the
multiplication of the starting ab initio surface by a morphing function whose parameters were optimized and (2) the optimization
of parameters of the ab initio surface using both the experimental values of energy levels and the results of quantum-chemical
electronic structure calculations. 相似文献
7.
本文基于无任何可调参数的势模型计算了碱土金属原子(Be、Mg、Ca、Sr、Ba)与Ne原子间相互作用势,得到的势能曲线及势阱位置和深度与现有的从头计算结果符合较好.本文的计算结果进一步验证了碱土金属原子与稀有气体原子间交换能主要来自碱土金属原子最外层s电子与稀有气体原子最外层p电子之间的交换作用. 相似文献
8.
Accurate double many-body expansion potential energy surface of HS_2(A~2A') by scaling the external correlation
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A globally accurate single-sheeted double many-body expansion potential energy surface is reported for the first excited state of HS_2 by fitting the accurate ab initio energies, which are calculated at the multireference configuration interaction level with the aug-cc-pVQZ basis set. By using the double many-body expansion-scaled external correlation method,such calculated ab initio energies are then slightly corrected by scaling their dynamical correlation. A grid of 2767 ab initio energies is used in the least-square fitting procedure with the total root-mean square deviation being 1.406 kcal · mol~(-1).The topographical features of the HS_2(A_2A') global potential energy surface are examined in detail. The attributes of the stationary points are presented and compared with the corresponding ab initio results as well as experimental and other theoretical data, showing good agreement. The resulting potential energy surface of HS_2(A_2A') can be used as a building block for constructing the global potential energy surfaces of larger S/H molecular systems and recommended for dynamic studies on the title molecular system. 相似文献
9.
S. Besner A. V. Kabashin F. M. Winnik M. Meunier 《Applied Physics A: Materials Science & Processing》2008,93(4):955-959
Inorganic nanoparticles offer novel promising properties for biological sensing and imaging, as well as in therapeutics. However,
these applications are often complicated by the possible toxicity of conventional nanomaterials, arising as a result of inadequate
purification procedures of nanoparticles obtained via synthetic pathways using toxic or non-biocompatible substances. We review
novel femtosecond laser-assisted methods, which enable the preparation of metal nanomaterials in clean, biologically friendly
aqueous environment (“green” synthesis) and thus completely solve the toxicity problem. The proposed methods, including laser
ablation and fragmentation, make possible the production of stable metal colloids of extremely small size (∼2 nm) with a low
coefficient of variation (15–25%). Those nanoparticles exhibit unique surface chemistry and can be used for bio-imaging, cancer
treatment and nanoparticle-enhanced Raman spectroscopy. 相似文献
10.
A quantitative modeling of the contributions of localized surface plasmon resonance (LSPR) and interband transitions to absorbance
of gold nanoparticles has been achieved based on Lorentz–Drude dispersion function and Maxwell-Garnett effective medium approximation.
The contributions are well modeled with three Lorentz oscillators. Influence of the structural properties of the gold nanoparticles
on the LSPR and interband transitions has been examined. In addition, the dielectric function of the gold nanoparticles has
been extracted from the modeling to absorbance, and it is found to be consistent with the result yielded from the spectroscopic
ellipsometric analysis. 相似文献
11.
Ali Safaei 《Journal of nanoparticle research》2010,12(3):759-776
The size dependency of the cohesive energy of nanocrystals is obtained in terms of their averaged structural and energetic
properties, which are in direct proportion with their cohesive energies. The significance of the effect of the geometrical
shape of nanoparticles on their thermal stability has been discussed. The model has been found to have good prediction for
the case of Cu and Al nanoparticles, with sizes in the ranges of 1–22 nm and 2–22 nm, respectively. Defining a new parameter,
named as the surface-to-volume energy-contribution ratio, the relative thermal stabilities of different nanoclusters and their
different surface-crystalline faces are discussed and compared to the molecular dynamic (MD) simulation results of copper
nanoclusters. Finally, based on the size dependency of the cohesive energy, a formula for the size-dependent diffusion coefficient
has been presented which includes the structural and energetic effects. Using this formula, the faster-than-expected interdiffusion/alloying
of Au(core)–Ag(shell) nanoparticles with the core–shell structure, the Au-core diameter of 20 nm and the Ag-shell thickness of 2.91 nm, has been
discussed and the calculated diffusion coefficient has been found to be consistent with its corresponding experimental value. 相似文献
12.
A method is presented for calculating electron-hole pair excitation due to an incident atom or molecule interacting with a metal surface. Energy loss is described using an ab initio approach that obtains a position-dependent friction coefficient for an adsorbate moving near a metal surface from a total energy pseudopotential calculation. A semiclassical forced oscillator model is constructed to describe excitation of the electron gas due to the incident molecule. This approach is applied to H and D atoms incident on a Cu(111) surface, and we obtain theoretical estimates of the "chemicurrents" measured by Nienhaus et al. [Phys. Rev. Lett. 82, 446 (1999)] for these atoms incident on the surface of a Schottky diode. 相似文献
13.
14.
Y. H. Zhang R. S. Qin Y. H. Sun R. W. Barber D. R. Emerson 《Journal of statistical physics》2005,121(1-2):257-267
Gas flow in microchannels can often encounter tangential slip motion at the solid surface even under creeping flow conditions.
To simulate low speed gas flows with Knudsen numbers extending into the transition regime, alternative methods to both the
Navier–Stokes and direct simulation Monte Carlo approaches are needed that balance computational efficiency and simulation
accuracy. The lattice Boltzmann method offers an approach that is particularly suitable for mesoscopic simulation where details
of the molecular motion are not required. In this paper, the lattice Boltzmann method has been applied to gas flows with finite
Knudsen number and the tangential momentum accommodation coefficient has been implemented to describe the gas-surface interactions.
For fully-developed channel flows, the results of the present method are in excellent agreement with the analytical slip-flow
solution of the Navier–Stokes equations, which are valid for Knudsen numbers less than 0.1. The present paper demonstrates
that the lattice Boltzmann approach is a promising alternative simulation tool for the design of microfluidic devices. 相似文献
15.
Dj. M. Maric S. Vogel P. F. Meier T. A. Claxton S. F. J. Cox 《Hyperfine Interactions》1991,64(1-4):567-572
The molecular orbital model for bond-centred hydrogen or muonium in the III–V compound semiconductors is developed with the
help of ab initio cluster calculations. The influence of the loss of symmetry in going from the elemental (group IV) to the
compound (III–V) materials on the electronic structure is studied. The equilibrium configurations, potential energy surfaces
and electronic structures of hydrogen or muonium near the bond-centred site in GaAs, GaP and InP are calculated at the ab
initio HF level in the clusters Ga4As4H18 and the corresponding one for GaP and InP using a split-valence basis set and ab initio pseudopotentials for the core orbitals.
First results of the calculations using a large Ga22As22H42 cluster are discussed. Preliminary results for InP indicate that ionization of the bond-centre defect may be considerably
easier than in the other III–V compounds. which would explain why μSR-signals corresponding to the neutral Mu* state have not been detected in this material. 相似文献
16.
M. Becker S. Crampin R. Berndt 《Applied Physics A: Materials Science & Processing》2007,88(3):555-557
We present a theoretical many-body analysis of the electron–electron (e–e) inelastic damping rate Γ of electron-like excitations
in the Shockley surface state band of Ag(111). It takes into account ab initio band structures for both bulk and surface states.
Γ is found to increase more rapidly as a function of surface state energy E than previously reported, thus leading to an improved
agreement with experimental data.
PACS 73.20.At; 68.37.Ef; 72.15.Lh 相似文献
17.
Nadezhda M. Bulgakova Alexei N. Panchenko Alexei E. Tel’minov Mikhail A. Shulepov 《Applied Physics A: Materials Science & Processing》2010,98(2):393-400
We report the formation of microtower structures, observed on multishot nanosecond laser irradiation of liquid metals (Ga,
In, Sn–Pb alloy, Wood’s metal). Ablation in a reactive ambient gas (air, nitrogen, sulfur hexafluoride, nitrogen trifluoride)
is shown to lead to a tower-like structure growing on the irradiated surface at a rate of 3–20 μm per pulse depending on laser
fluence and the types of metal and ambient gas. The interplay between different processes in the heat-affected zone of the
irradiated samples is analyzed, including ablation, thermal expansion, temperature variations of viscosity, surface tension,
thermal stresses, capillary effects, and surface chemistry. A clear picture of microtower origin has been established, and
qualitative modeling can explain the formation mechanism. 相似文献
18.
Manuj Nahar Ignacio F. Gallardo Kristofer L. Gleason Michael F. Becker John W. Keto Desiderio Kovar 《Journal of nanoparticle research》2011,13(8):3455-3464
A continuous aerosol process has been studied for producing nanoparticles of oxides that were decorated with smaller metallic
nanoparticles and are free of organic stabilizers. To produce the oxide carrier nanoparticles, an aerosol of 3–6 μm oxide
particles was ablated using a pulsed excimer laser. The resulting oxide nanoparticle aerosol was then mixed with 1.5–2.0 μm
metallic particles and this mixed aerosol was exposed to the laser for a second time. The metallic micron-sized particles
were ablated during this second exposure, and the resulting nanoparticles deposited on the surface of the oxide nanoparticles
producing an aerosol of 10–60 nm oxide nanoparticles that were decorated with smaller 1–5 nm metallic nanoparticles. The metal
and oxide nanoparticle sizes were varied by changing the laser fluence and gas type in the aerosol. The flexibility of this
approach was demonstrated by producing metal-decorated oxide nanoparticles using two oxides, SiO2 and TiO2, and two metals, Au and Ag. 相似文献
19.
D. Music J. Burghaus T. Takahashi R. Dronskowski J. M. Schneider 《The European Physical Journal B - Condensed Matter and Complex Systems》2010,77(3):401-406
We have explored the bulk modulus and the thermal
expansion of PdFe3N (space group Pm[`3] mPm\overline 3 m) using ab initio phonon
dynamics within the quasiharmonic approximation in the temperature range
from 50 to 1000 K. PdFe3N possesses a linear thermal expansion
coefficient common for typical ceramics. The calculated average linear
thermal expansion coefficient of 6.4 × 10-6 K-1 is
consistent with the average measured coefficient of 6.7 × 10-6 K-1. We have shown here that the thermal behavior of this compound can
be understood based on the electronic structure and the lattice dynamics
thereof. PdFe3N exhibits both metallic as well as covalent-ionic
bonding. The Fe–N covalent-ionic bonding suppresses the lattice vibrations
of the PdFe3 matrix. The bulk modulus of 188 GPa for PdFe3N
decreases by 15% in the temperature range studied, which is expected due
to presence of stiff Fe–N bonds. 相似文献
20.
The dependence of energy accommodation coefficients of inert gases on clean metal surfaces is analyzed in the framework of classical lattice theory. It is found that a Knudsen layer must exist next to the surface to adjust the gas molecular velocity distrivution to surface conditions. At energies below the well-depth, the accommodation coefficient slope is inversely proportional to the square root of the temperature; at energies above the welldepth, the accommodation coefficient is independent of surface temperature. 相似文献