SIZE EFFECTS ON NONEQUILIBRIUM LASER-HEATING OF METAL-FILMS

被引:140
作者
QIU, TQ
TIEN, CL
机构
[1] Department of Mechanical Engineering, University of California, Berkeley, CA
来源
JOURNAL OF HEAT TRANSFER-TRANSACTIONS OF THE ASME | 1993年 / 115卷 / 04期
关键词
CONDUCTION; THERMOPHYSICAL PROPERTIES;
D O I
10.1115/1.2911378
中图分类号
O414.1 [热力学];
学科分类号
摘要
Picosecond and sub-picosecond lasers have become important tools in the fabrication and study of microstructures. When the laser pulse duration becomes comparable with or less than the characteristic time of energy exchange among microscopic energy carriers, the excited carriers are no longer in thermal equilibrium with the other carriers, creating a nonequilibrium heating situation. The presence of interfaces in metals provides additional scattering processes for electrons, which in turn affects the nonequilibrium heating process. This work studies size effects, due to both surface scattering and grain-boundary scattering, on the thermal conductivity and the energy exchange between electrons and the material lattice. A simple formula is established to predict the influence of film thickness, grain size, interface scattering parameters, and the electron and lattice temperatures on the effective thermal conductivity of metal thin films. Predictions of the analysis agree with the available experimental data. A three-energy-level model is developed to characterize the energy exchange between electrons and the lattice. This study shows that the size effect reduces the effective thermal conductivity and increases the electron-phonon energy exchange rate. The results are useful for improving processing quality, interpreting diagnostic results, and preventing thermal damage of thin films during short-pulse laser heating.
引用
收藏
页码:842 / 847
页数:6
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