排序方式: 共有43条查询结果,搜索用时 15 毫秒
41.
Dynamics of the plume formation and parameters of the ejected clusters in short-pulse laser ablation 总被引:2,自引:0,他引:2
L.V. Zhigilei 《Applied Physics A: Materials Science & Processing》2003,76(3):339-350
The dynamics of the early stages of the ablation plume formation and the mechanisms of cluster ejection are investigated in
large-scale molecular dynamics simulations. The cluster composition of the ablation plume has a strong dependence on the irradiation
conditions and is defined by the interplay of a number of processes during the ablation plume evolution. At sufficiently high
laser fluences, the phase explosion of the overheated material leads to the formation of a foamy transient structure of interconnected
liquid regions that subsequently decomposes into a mixture of liquid droplets, gas-phase molecules, and small clusters. The
ejection of the largest droplets is attributed to the hydrodynamic motion in the vicinity of the melted surface, especially
active in the regime of stress confinement. Spatially resolved analysis of the dynamics of the plume formation reveals the
effect of segregation of the clusters of different sizes in the expanding plume. A relatively low density of small/medium
clusters is observed in the region adjacent to the surface, where large clusters are being formed. Medium-size clusters dominate
in the middle of the plume and only small clusters and monomers are observed near the front of the expanding plume. Despite
being ejected from deeper under the surface, the larger clusters in the plume have substantially higher internal temperatures
as compared to the smaller clusters. The cluster-size distributions can be relatively well described by a power law Y(N)∼N-τ with exponents different for small, up to ∼15 molecules, and large clusters. The decay is much slower in the high-mass region
of the distribution.
Received: 13 October 2001 / Accepted: 18 July 2002 / Published online: 25 October 2002
RID="*"
ID="*"Corresponding author. Fax: +1-434/982-5660, E-mail: lz2n@virginia.edu 相似文献
42.
Heating and explosive destruction of the near surface volume of metal with initial micro-porosity under nanosecond laser pulse is simulated. It is shown that presence of initial micro-porosity may influence and modify the ejection mechanisms from melt and from solid phase. Thermal and gas dynamic processes in a gas bubble growing in laser irradiated melt are analysed. Experiments show rather different surface morphology defined by micro-explosions and melt ejection for different metals. Possible explosion of micro-pores and solid particles release under nanosecond laser irradiation is analysed for metals with high melting point. It is shown that the stress attains the values that are close to the damage threshold. 相似文献
43.
The mechanism of nanobump formation in femtosecond pulse laser nanostructuring of thin metal films 总被引:1,自引:0,他引:1
Dmitriy S. Ivanov Baerbel Rethfeld Gerard M. O’Connor Thomas J. Glynn Alexey N. Volkov Leonid V. Zhigilei 《Applied Physics A: Materials Science & Processing》2008,92(4):791-796
The physical mechanisms responsible for the formation of nanobump structures on a surface of a thin metal film irradiated
by a tightly focused femtosecond laser pulse are investigated in a large-scale molecular dynamics simulation. The simulation
is performed with a combined atomistic-continuum model adapted for an adequate representation of laser-induced processes at
the length-scale of the entire laser spot. The relaxation of the compressive stresses generated by the fast laser heating
is identified as the main driving force responsible for the separation of the metal film from the substrate and formation
of the nanobump. The kinetics of the transient melting and resolidification, occurring under conditions of the fast cooling
due to the two-dimensional electron heat conduction, defines the shape of the nanobump. The predictions of the simulation
are related to the surface structures observed in femtosecond laser nanostructuring. 相似文献