Disappearance of stress singularity at interface edge due to nanostructured thin film |
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Authors: | Takashi Sumigawa Hiroyuki Hirakata Shohei Matsumoto Takayuki Kitamura |
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Affiliation: | a Department of Mechanical Engineering and Science, Kyoto University, Kyoto 606-8501, Japan b Department of Mechanical Engineering, Osaka University, Suita, Osaka 565-0871, Japan c Department of Micro Engineering, Kyoto University, Kyoto 606-8501, Japan |
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Abstract: | The purpose of this study is to examine the stress distribution near the interface between a nanostructured thin film and a solid body. We focus on a nanostructured thin film that consists of Ta2O5 helical nanosprings fabricated on a Si substrate by dynamic oblique deposition. The mechanical properties of the thin film are obtained by vertical and lateral loading tests using a diamond tip built into an atomic force microscope. The apparent shear and Young’s moduli, G′ and E′, of the thin film are 2-3 orders of magnitude lower than those of a conventional solid Ta2O5 film. Moreover, the thin film shows strong anisotropy. A finite element analysis for two types of components with different interface edges between the thin film and an elastic solid body is conducted under uniform displacement. One has a free edge where the surface-interface angle is 90°-90°, and the other has a short interface crack. These analyses indicate the absence of not only stress singularity but also high stress concentration near the free edge and the interface crack tip. The characteristic stress distributions near the interface are due to the nanoscopically discrete structure of the thin film. |
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Keywords: | Nanosprings Thin film Stress concentration Interface Stress reduction Free edge Crack tip Singularity Dynamic oblique deposition |
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