A parametric study of laser induced thin film spallation |
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Authors: | Junlan Wang Richard L Weaver Nancy R Sottos |
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Institution: | (1) Department of Theoretical and Applied Mechanics, University of Illinois at Urbana-Champaign, 61801 Urbana, IL, USA |
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Abstract: | We report parametric studies of elastic wave generation by a pulsed laser and associated spalling of thin surface films by
the corresponding high stresses. Two different substrate materials, single crystal Si (100) and fused silica, are considered.
Spallation behavior of Al thin films is investigated as a function of substrate thickness, film thickness, laser energy, and
various parameters governing the source. Surface displacement due to the stress wave is measured by Michaelson interferometry
and used to infer the stresses on the film interface. Consistent with previous studies, the maximum stress in the substrate
and at the film/substrate interface increases with increasing laser fluence. For many of the conditions tested, the substrate
stress is large enough to damage the Si. Moreover, the maximum interface stress is found to increase with increasing film
thickness, but decrease with increasing substrate thickness due to geometric attenuation. Of particular significance is the
development of a decompression shock in the fused sillica substrates, which results in very high tensile stresses at the interface.
This shock enhances the failure of thin film interfaces, especially in thicker samples. |
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Keywords: | Laser spallation thin film interface adhesion stress wave decompression shock |
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