Mixed-mode interfacial adhesive strength of a thin film on an anisotropic substrate |
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| Authors: | Rajesh Kitey Nancy R Sottos |
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| Institution: | a Department of Aerospace Engineering, Beckman Institute for Advanced Science and Technology, University of Illinois at Urbana-Champaign, IL 61801, USA
b Department of Materials Science and Engineering, Beckman Institute for Advanced Science and Technology, University of Illinois at Urbana-Champaign, IL 61801, USA |
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| Abstract: | The mixed-mode interfacial adhesion strength between a gold (Au) thin film and an anisotropic passivated silicon (Si) substrate is measured using laser-induced stress wave loading. Test specimens are prepared by bonding a fused silica (FS) prism to the back side of a 〈1 0 0〉 Si substrate with a thin silicon nitride (SixNy) passivation layer deposited on the top surface. A high-amplitude stress wave is developed by pulsed laser ablation of a sacrificial absorbing layer on one of the lateral surfaces of the FS prism. Due to the negative non-linear elastic properties of the FS, the compressive stress wave evolves into a decompression shock with fast fall time. Careful selection of the incident angle between the pulse and the FS/Si interface generates a mode-converted shear wave in refraction, subjecting the SixNy/Au thin film interface to dynamic mixed-mode loading, sufficient to cause interfacial fracture. A detailed analysis of the anisotropic wave propagation combined with interferometric measurements of surface displacements enables calculation of the interfacial stresses developed under mixed-mode loading. The mixed-mode interfacial strength is compared to the interfacial strength measured under purely tensile loading. |
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| Keywords: | Dynamic wave propagation Laser spallation Mixed-mode loading Thin film Decompression shock |
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