双层石墨烯中的位错,Nature

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双层石墨烯中的位错
Nature ( IF 50.5 ) Pub Date : 2013-12-18 , DOI: 10.1038/nature12780
Benjamin Butz ₁ , Christian Dolle ₁ , Florian Niekiel ₁ , Konstantin Weber ₂ , Daniel Waldmann ₃ , Heiko B Weber ₃ , Bernd Meyer ₂ , Erdmann Spiecker ₁

Affiliation

位错代表了材料科学中最引人入胜和最基本的概念之一。最重要的是，位错是晶体材料塑性变形的主要载体。此外，它们可以强烈影响半导体和离子晶体的局部电子和光学特性。在小尺寸材料中，它们会经历广泛的图像力，将它们吸引到表面以释放应变能。然而，在石墨等层状晶体中，位错运动主要限于基面。因此，位错无法逃脱，从而将它们限制在只有两个单层那么薄的晶体中。为了在这种极端边界条件下探索位错的性质，选择的材料是双层石墨烯，可以限制这种线性缺陷的最薄的准二维晶体。源自碳化硅上的高质量外延石墨烯的均匀且坚固的石墨烯膜为其研究提供了理想的平台。在这里，我们报告了使用透射电子显微镜对独立双层石墨烯中基面位错的直接观察及其通过衍射对比分析和原子模拟的详细研究。我们的调查揭示了两个惊人的尺寸效应。首先，由于双层石墨烯的独特性质——堆叠故障能量的缺失，导致了特征位错模式，该模式对应于堆叠顺序的交替 AB AC 变化。第二，我们的实验结合原子模拟揭示了双层石墨烯膜的明显屈曲，这是直接由应变调节引起的。事实上，屈曲改变了双层石墨烯的应变状态，对其电子特性至关重要。我们的发现将有助于理解位错及其在双层和少层石墨烯的结构、机械和电子特性中的作用。

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Dislocations in bilayer graphene

Dislocations represent one of the most fascinating and fundamental concepts in materials science. Most importantly, dislocations are the main carriers of plastic deformation in crystalline materials. Furthermore, they can strongly affect the local electronic and optical properties of semiconductors and ionic crystals. In materials with small dimensions, they experience extensive image forces, which attract them to the surface to release strain energy. However, in layered crystals such as graphite, dislocation movement is mainly restricted to the basal plane. Thus, the dislocations cannot escape, enabling their confinement in crystals as thin as only two monolayers. To explore the nature of dislocations under such extreme boundary conditions, the material of choice is bilayer graphene, the thinnest possible quasi-two-dimensional crystal in which such linear defects can be confined. Homogeneous and robust graphene membranes derived from high-quality epitaxial graphene on silicon carbide provide an ideal platform for their investigation. Here we report the direct observation of basal-plane dislocations in freestanding bilayer graphene using transmission electron microscopy and their detailed investigation by diffraction contrast analysis and atomistic simulations. Our investigation reveals two striking size effects. First, the absence of stacking-fault energy, a unique property of bilayer graphene, leads to a characteristic dislocation pattern that corresponds to an alternating AB AC change of the stacking order. Second, our experiments in combination with atomistic simulations reveal a pronounced buckling of the bilayer graphene membrane that results directly from accommodation of strain. In fact, the buckling changes the strain state of the bilayer graphene and is of key importance for its electronic properties. Our findings will contribute to the understanding of dislocations and of their role in the structural, mechanical and electronic properties of bilayer and few-layer graphene.

更新日期：2013-12-18

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