金纳米结的原子流变学
Atomic rheology of gold nanojunctions
摘要：
尽管在微米和纳米尺寸的金属样品中的耗散和变形过程的广泛研究，在具有最终分子尺寸的系统的变形期间起作用的机制仍然难以捉摸。虽然通过将金属线拉伸到原子水平而获得的金属纳米结是探索原子尺度接触的选择系统，但到目前为止还不可能在这种尺度下提取物质的完全平衡和平衡外流变流动性质。本文利用石英音叉型原子力显微镜（TF-AFM），结合电学和流变学的测量，研究了埃量级金结的非线性流变特性。通过提交的交界处增加亚纳米变形，我们发现从一个纯粹的弹性制度的过渡到一个塑料，并最终到一个粘性的流化制度，类似于软屈服材料的流变学，虽然数量级的长度尺度的差异。此外，流化状态突出了毛细吸引力，如对于液体毛细桥所预期的。这种剪切流化不能被捕获的经典模型的原子平面之间的摩擦，指向意想不到的耗散行为的无缺陷的金属结在最终的尺度。因此，原子流变学是探测原子接触的结构重组的有力工具。
英文摘要：
Despite extensive investigations of dissipation and deformation processes in micro- and nano- sized metallic samples, the mechanisms at play during deformation of systems with ultimate, molecular size remain elusive. While metallic nanojunctions, obtained by stretching metallic wires down to the atomic level are a system of choice to explore atomic scale contacts, it has not been possible up to now to extract the full equilibrium and out of equilibrium rheological flow properties of matter at such scales. Here, by using a quartz-tuning fork based Atomic Force Microscope (TF-AFM), we combine electrical and rheological measurement on angström-size gold junctions to study the non linear rheology of this model atomic system. By submitting the junction to increasing sub-nanometric deformations we uncover a transition from a purely elastic regime to a plastic, and eventually to a viscous-like fluidized regime, akin to the rheology of soft yielding materials, though orders of magnitude difference in length scale. The fluidized state furthermore highlights capillary attraction, as expected for liquid capillary bridges. This shear fluidization cannot be captured by classical models of friction between atomic planes, pointing to unexpected dissipative behavior of defect-free metallic junctions at the ultimate scales. Atomic rheology is therefore a powerful tool to probe the structural reorganization of atomic contacts.
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