石墨微片的自收缩运动
Self-Retracting Motion of Graphite Microflakes
摘要：
我们报告观察到一种新的现象，石墨的自收缩运动，其中微小的石墨片，在被移位到各种悬浮位置后，从高度定向的热解石墨的岛屿，在没有外部影响的情况下回缩到岛屿上。我们反复探测和观察这种不同尺寸的薄片表明存在临界尺寸的薄片，大约35微米，在该临界尺寸以上，在操作下不会发生自缩回运动。这有助于解释石墨的自收缩运动尚未被报道的事实，因为天然石墨的样品通常大于该临界尺寸。事实上，在任何种类的单晶的文献中都没有发现这种现象的报道。一个模型，包括静态和动态剪切强度，范德华力的相互作用，和边缘悬挂键相互作用的影响，被用来解释所观察到的现象。这些发现可能有助于创造具有从兆赫兹到千兆赫兹的广泛机械工作频率的纳米机电系统。
英文摘要：
We report the observation of a novel phenomenon, the self-retracting motion of graphite, in which tiny flakes of graphite, after being displaced to various suspended positions from islands of highly orientated pyrolytic graphite, retract back onto the islands under no external influences. Our repeated probing and observing such flakes of various sizes indicate the existence of a critical size of flakes, approximately 35 micrometer, above which the self-retracting motion does not occur under the operation. This helps to explain the fact that the self-retracting motion of graphite has not been reported, because samples of natural graphite are typical larger than this critical size. In fact, reports of this phenomenon have not been found in the literature for single crystals of any kinds. A model that includes the static and dynamic shear strengths, the van der Waals interaction force, and the edge dangling bond interaction effect, was used to explain the observed phenomenon. These findings may conduce to create nano-electromechanical systems with a wide range of mechanical operating frequency from mega to giga hertzs.
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