Hydrodynamic instabilities in laser pulse-produced melts of metal films

被引:15
作者
Bostanjoglo, O
Nink, T
机构
[1] Optisches Institut, Technischen Universität Berlin, Berlin 10623
关键词
D O I
10.1063/1.362499
中图分类号
O59 [应用物理学];
学科分类号
摘要
The dynamics of melts, as induced by 7 ns laser pulses in Al and Au films, were investigated by in situ time-resolved transmission electron microscopy. Melting, motion of the liquid, and crystallization were observed by tracing the image intensity with a photomultiplier (space/time resolution 100 nm/3 ns) and by streak imaging (streak times 15 ns-4 mu s). Films with native oxides/adsorbed atmospheric contaminations and films purified by pulse melting were found to show a completely different behavior of their melts. The melts of purified films either remained almost flat (Al) or revealed a gradual pileup of liquid in cold regions within 500 ns (Au), caused by thermocapillarity with the negative thermal coefficient of the surface tension of pure metals. In contrast, contaminated films showed three distinctly different types of perturbations: (1) a fast expulsion of the melt from the center of the laser spot within 20 ns after the laser pulse; (2) a gradual contraction of liquid at the center within 0.5-1 mu s; (3) thickness oscillations with frequencies of 5-10 MHz and time constants of 500 ns. These effects are explained by recoil from evaporating contaminations, by thermocapillary flow with a positive thermal coefficient of the surface tension, caused by surface active impurity atoms, and by thermocapillary waves. (C) 1996 American Institute of Physics.
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页码:8725 / 8729
页数:5
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