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.
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Size Effects on Nonequilibrium Laser Heating of Metal Films
T. Q. Qiu,
T. Q. Qiu
Department of Mechanical Engineering, University of California, Berkeley, CA 94720
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C. L. Tien
C. L. Tien
Department of Mechanical Engineering, University of California, Berkeley, CA 94720
Search for other works by this author on:
T. Q. Qiu
Department of Mechanical Engineering, University of California, Berkeley, CA 94720
C. L. Tien
Department of Mechanical Engineering, University of California, Berkeley, CA 94720
J. Heat Transfer. Nov 1993, 115(4): 842-847 (6 pages)
Published Online: November 1, 1993
Article history
Received:
October 1, 1992
Revised:
January 1, 1993
Online:
May 23, 2008
Citation
Qiu, T. Q., and Tien, C. L. (November 1, 1993). "Size Effects on Nonequilibrium Laser Heating of Metal Films." ASME. J. Heat Transfer. November 1993; 115(4): 842–847. https://doi.org/10.1115/1.2911378
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