†Department of Materials, University of Oxford, Parks Road, Oxford OX1 3PH, U.K.
‡Nanotube Research Center, Advanced Institute for Industrial Science and Technology, Tsukuba 305-8561, Japan.
ACS Nano. 2015 May 26;9(5):4786-95. doi: 10.1021/acsnano.5b01130. Epub 2015 Apr 16.
We examine the temperature dependence of graphene edge terminations at the atomic scale using an in situ heating holder within an aberration-corrected transmission electron microscope. The relative ratios of armchair, zigzag, and reconstructed zigzag edges from over 350 frames at each temperature are measured. Below 400 °C, the edges are dominated by zigzag terminations, but above 600 °C, this changes dramatically, with edges dominated by armchair and reconstructed zigzag edges. We show that at low temperature chemical etching effects dominate and cause deviation to the thermodynamics of the system. At high temperatures (600 and 800 °C), adsorbates are evaporated from the surface of graphene and chemical etching effects are significantly reduced, enabling the thermodynamic distribution of edge types to be observed. The growth rate of holes at high temperature is also shown to be slower than at room temperature, indicative of the reduced chemical etching process. These results provide important insights into the role of chemical etching effects in the hole formation, edge sputtering, and edge reconstruction in graphene.
我们使用配备有像差校正透射电子显微镜的原位加热支架，在原子尺度上研究了石墨烯边缘末端在温度依赖性方面的情况。在每个温度下，我们从超过 350 个帧中测量了扶手椅型、锯齿型和重构锯齿型边缘的相对比例。低于 400°C 时，边缘主要由锯齿型末端控制，但高于 600°C 时，情况发生了急剧变化，边缘主要由扶手椅型和重构锯齿型边缘控制。我们表明，在低温下，化学刻蚀效应占主导地位，导致系统热力学发生偏离。在高温（600 和 800°C）下，石墨烯表面的吸附物会蒸发，化学刻蚀效应会显著降低，从而能够观察到边缘类型的热力学分布。高温下孔的生长速率也比室温下慢，表明化学刻蚀过程减少。这些结果为化学刻蚀效应在石墨烯中的孔形成、边缘溅射和边缘重构中所起的作用提供了重要的见解。
