Department of Chemistry and Centre for Advanced 2D Materials (CA2DM), National University of Singapore , 3 Science Drive 3, Singapore 117543, Singapore.
NUS Graduate School for Integrative Sciences and Engineering, National University of Singapore, Centre for Life Sciences , #05-01, 28 Medical Drive, Singapore 117456, Singapore.
ACS Nano. 2016 Jan 26;10(1):1681-9. doi: 10.1021/acsnano.5b07662. Epub 2015 Dec 31.
Chemical vapor deposition (CVD) is one of the most promising growth techniques to scale up the production of monolayer graphene. At present, there are intense efforts to control the orientation of graphene grains during CVD, motivated by the fact that there is a higher probability for oriented grains to achieve seamless merging, forming a large single crystal. However, it is still challenging to produce single-crystal graphene with no grain boundaries over macroscopic length scales, especially when the nucleation density of graphene nuclei is high. Nonetheless, nanocrystalline graphene with highly oriented grains may exhibit single-crystal-like properties. Herein, we investigate the spectroscopic signatures of graphene film containing highly oriented, nanosized grains (20-150 nm) using angle-resolved photoemission spectroscopy (ARPES) and high-resolution electron energy loss spectroscopy (HREELS). The robustness of the Dirac cone, as well as dispersion of its phonons, as a function of graphene's grain size and before and after film coalescence, was investigated. In view of the sensitivity of atomically thin graphene to atmospheric adsorbates and intercalants, ARPES and HREELS were also used to monitor the changes in spectroscopic signatures of the graphene film following exposure to the ambient atmosphere.
化学气相沉积（CVD）是扩大单层石墨烯生产规模最有前途的技术之一。目前，人们强烈希望在 CVD 过程中控制石墨烯晶粒的取向，这是因为取向晶粒更有可能实现无缝融合，形成大单晶。然而，在宏观长度尺度上生产无晶界的单晶石墨烯仍然具有挑战性，特别是当石墨烯核的成核密度较高时。尽管如此，具有高取向晶粒的纳米晶石墨烯可能表现出单晶样的性质。在此，我们使用角分辨光电子能谱（ARPES）和高分辨率电子能量损失谱（HREELS）研究了含有高取向纳米晶粒（20-150nm）的石墨烯薄膜的光谱特征。研究了狄拉克锥的稳健性及其声子的色散，以及它们与石墨烯晶粒尺寸的关系，以及在薄膜合并前后的关系。鉴于原子级薄石墨烯对大气吸附物和插层剂的敏感性，还使用 ARPES 和 HREELS 来监测石墨烯薄膜在暴露于环境气氛后的光谱特征变化。
