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Intrinsic Compressive Stress in Polycrystalline Films is Localized at Edges of the Grain Boundaries

机译:多晶膜中的固有压缩应力位于晶粒边界的边缘

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The intrinsic compression that arises in polycrystalline thin films under high atomic mobility conditions has been attributed to the insertion or trapping of adatoms inside grain boundaries. This compression is a consequence of the stress field resulting from imperfections in the solid and causes the thermomechanical fatigue that is estimated to be responsible for 90% of mechanical failures in current devices. We directly measure the local distribution of residual intrinsic stress in polycrystalline thin films on nanometer scales, using a pioneering method based on atomic force microscopy. Our results demonstrate that, at odds with expectations, compression is not generated inside grain boundaries but at the edges of gaps where the boundaries intercept the surface. We describe a model wherein this compressive stress is caused by Mullins-type surface diffusion towards the boundaries, generating a kinetic surface profile different from the mechanical equilibrium profile by the Laplace-Young equation. Where the curvatures of both profiles differ, an intrinsic stress is generated in the form of Laplace pressure. The Srolovitz-type surface diffusion that results from the stress counters the Mullins-type diffusion and stabilizes the kinetic surface profile, giving rise to a steady compression regime. The proposed mechanism of competition between surface diffusions would explain the flux and time dependency of compressive stress in polycrystalline thin films.
机译:多晶薄膜在高原子迁移率条件下产生的固有压缩归因于在晶界内插入或捕获了原子。这种压缩是由于固体缺陷导致的应力场的结果,并导致热机械疲劳,据估计,这是造成当前设备机械故障的90%。我们使用基于原子力显微镜的开创性方法直接测量纳米级多晶薄膜中残余固有应力的局部分布。我们的结果表明,与预期不符的是,压缩不是在晶粒边界内部产生,而是在边界截取表面的间隙边缘产生。我们描述了一个模型,其中该压应力是由Mullins型表面向边界扩散所引起的,从而产生了与机械平衡轮廓不同的动力学表面轮廓(通过Laplace-Young方程)。如果两个轮廓的曲率不同,则会以拉普拉斯压力的形式产生内在应力。由应力引起的Srolovitz型表面扩散抵消了Mullins型扩散并稳定了动力学表面轮廓,从而产生了稳定的压缩状态。拟议的表面扩散竞争机制将解释多晶薄膜中压应力的通量和时间依赖性。

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  • 来源
    《Physical review letters》 |2017年第25期|256102.1-256102.5|共5页
  • 作者

    Vasco Enrique; Polop Celia;

  • 作者单位

    CSIC, Inst Ciencia Mat Madrid, Sor Juana Ines de la Cruz 3, Madrid 28049, Spain;

    Univ Autonoma Madrid, Inst Nicolas Cabrera & Condensed Matter Phys Ctr, Dept Fis Mat Condensada, E-28049 Madrid, Spain;

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