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Compression of freestanding gold nanostructures: from stochastic yield to predictable flow

机译：独立式金纳米结构的压缩：从随机产量到可预测的流量

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摘要

Characterizing the mechanical response of isolated nanostructures is vitally important to fields such as microelectromechanical systems (MEMS) where the behaviour of nanoscale contacts can in large part determine system reliability and lifetime. To address this challenge directly, single crystal gold nanodots are compressed inside a high resolution scanning electron microscope (SEM) using a nanoindenter equipped with a flat punch tip. These structures load elastically, and then yield in a stochastic manner, at loads ranging from 16 to 110 mu N, which is up to five times higher than the load necessary for flow after yield. Yielding is immediately followed by displacement bursts equivalent to 1-50% of the initial height, depending on the yield point. During the largest displacement bursts, strain energy within the structure is released while new surface area is created in the form of localized slip bands, which are evident in both the SEM movies and still-images. A first order estimate of the apparent energy release rate, in terms of fracture mechanics concepts, for bursts representing 5-50% of the structure's initial height is on the order of 10-100 J m(-2), which is approximately two orders of magnitude lower than bulk values. Once this initial strain burst during yielding has occurred, the structures flow in a ductile way. The implications of this behaviour, which is analogous to a brittle to ductile transition, are discussed with respect to mechanical reliability at the micro-and nanoscales.
机译：对孤立的纳米结构的机械响应进行表征对于诸如微机电系统（MEMS）的领域至关重要，在该领域中，纳米级触点的行为可以在很大程度上决定系统的可靠性和使用寿命。为了直接解决这一难题，使用配备了扁平冲头的纳米压头在高分辨率扫描电子显微镜（SEM）中压缩单晶金纳米点。这些结构在16到110μNN的负载范围内弹性加载，然后以随机方式屈服，这比屈服后流动所需的载荷高五倍。屈服后紧随位移爆发，其等于初始高度的1-50％，具体取决于屈服点。在最大的位移爆发期间，结构内的应变能被释放，同时以局部滑移带的形式创建了新的表面积，这在SEM电影和静止图像中均很明显。根据断裂力学的概念，表观能量释放速率的一阶估算值是表示结构初始高度的5-50％的爆裂，其阶次约为10-100 J m（-2），约为两个数量级。数量级低于批量值。一旦在屈服过程中发生了这种初始应变破裂，结构便会以延展的方式流动。讨论了这种行为的含义，类似于脆性到延性的转变，涉及了微米和纳米级的机械可靠性。

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