Probing graphene grain boundaries with optical microscopy
Probing graphene grain boundaries with optical microscopy
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DOI：
10.1038/nature11562
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发表时间：
2012-10-11
期刊：
影响因子：
64.8
通讯作者：
Lee, Young Hee
中科院分区：
文献类型：
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作者：
Dinh Loc Duong;Han, Gang Hee;Lee, Young Hee
石墨烯中的晶界是在初始生长阶段通过岛的连接形成的，并且这些边界控制传输特性和相关的器件性能（1，2）。尽管可以使用透射电子显微镜（3，4）和扫描隧道显微镜（2，5 -8）获得关于石墨烯晶界处的原子重排的信息，但是关于石墨烯晶界分布的大规模信息并不容易获得。在这里，我们使用光学显微镜直接观察大面积石墨烯（生长在铜箔上）的晶界，而无需转移石墨烯。这种成像技术是通过选择性地氧化下面的铜箔通过石墨烯晶界功能化与O和OH自由基产生的紫外线照射在富含水分的环境条件下实现的：通过OH功能化的缺陷位点的氧自由基的选择性扩散的密度泛函计算证明。大面积石墨烯的薄层电阻随着石墨烯晶粒尺寸的增加而降低，但与先前的报道（9）相反，没有揭示与铜的晶粒尺寸的强相关性。此外，石墨烯晶界对裂纹扩展（通过弯曲初始化）和终止的影响使用我们的技术清楚地可视化。我们的方法可以作为一个简单的协议，用于评估其他二维层状结构，如氮化硼和剥离粘土的晶界。
Grain boundaries in graphene are formed by the joining of islands during the initial growth stage, and these boundaries govern transport properties and related device performance(1,2). Although information on the atomic rearrangement at graphene grain boundaries can be obtained using transmission electron microscopy(3,4) and scanning tunnelling microscopy(2,5-8), large-scale information regarding the distribution of graphene grain boundaries is not easily accessible. Here we use optical microscopy to observe the grain boundaries of large-area graphene (grown on copper foil) directly, without transfer of the graphene. This imaging technique was realized by selectively oxidizing the underlying copper foil through graphene grain boundaries functionalized with O and OH radicals generated by ultraviolet irradiation under moisture-rich ambient conditions: selective diffusion of oxygen radicals through OH-functionalized defect sites was demonstrated by density functional calculations. The sheet resistance of large-area graphene decreased as the graphene grain sizes increased, but no strong correlation with the grain size of the copper was revealed, in contrast to a previous report(9). Furthermore, the influence of graphene grain boundaries on crack propagation (initialized by bending) and termination was clearly visualized using our technique. Our approach can be used as a simple protocol for evaluating the grain boundaries of other two-dimensional layered structures, such as boron nitride and exfoliated clays.