Pure-shear Failure of Thin Films by Laser-induced Shear Waves

Abstract

The measurement of mode-dependent thin film interfacial properties is important in evaluating the quality of the interfaces between thin films and substrates. Previous work has proved that tensile and mixed-mode strength of a thin film/substrate interface can be evaluated using a laser-induced thin film spallation technique. To further examine the application regime of this technique and identify the individual roles of the tensile and shear stress in the resulting interfacial failure, a special sample design is adopted in the current work to realize pure-shear loading at the thin film/substrate interface. Our result demonstrates that for sufficiently high stress amplitude, interfacial failure can be induced solely by the in-plane shear stress and the stress can be quantitatively determined from optical interferometric measurements. Together with the previous tensile and mixed-mode studies, a complete picture of the mode-dependent thin film interfacial strength can now be reliably determined using the laser-induced thin film spallation techniques.