Mobile metal adatoms on single layer, bilayer, and trilayer graphene: An ab initio DFT study with van der Waals corrections correlated with electron microscopy data
Mobile metal adatoms on single layer, bilayer, and trilayer graphene: An ab initio DFT study with van der Waals corrections correlated with electron microscopy data
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DOI：
10.1103/physrevb.87.195430
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发表时间：
2013-05-17
影响因子：
3.7
通讯作者：
Scott, A. J.
中科院分区：
文献类型：
--
作者：
Hardcastle, T. P.;Seabourne, C. R.;Scott, A. J.
用平面波密度泛函理论程序CASTEP，结合Tkatchenko-Scheffler van der Waals修正格式和Perdew，Burke，Ernzerhof广义梯度近似(GGA PBE)，计算了Au，Cr，Al原子在单层石墨烯的扶手椅和锯齿形边结合位，以及在单层、双层和三层石墨烯的高对称性吸附位上的结合能.所有的边位结合能都比所有金属的吸附能高很多。然后计算了原始单层、双层和三层石墨烯上最低能量迁移路径的吸附原子迁移活化势垒，发现它们在室温下都小于或在k(B)T的数量级内，这意味着所有被研究的吸附原子都有很高的迁移率。这表明，蒸发到石墨烯样品上的金属原子在显微镜下表征之前，会迅速跨越晶格并结合到能量有利的边缘位置。然后，我们用扫描电子显微镜(STEM)图像证明了Al和Au在石墨烯上的这一概念，扫描电子显微镜(STEM)图像显示，这些原子只在边缘位置观察到，也在碳氢化合物污染的区域观察到，在那里晶格的原始区域完全没有吸附原子。此外，我们还回顾了在石墨烯/吸附原子体系几何优化计算中确定选定原子位置的问题，并为未来的研究提出了指导原则。
The plane-wave density functional theory code CASTEP was used with the Tkatchenko-Scheffler van der Waals correction scheme and the generalized gradient approximation of Perdew, Burke, and Ernzerhof (GGA PBE) to calculate the binding energy of Au, Cr, and Al atoms on the armchair and zigzag edge binding sites of monolayer graphene, and at the high-symmetry adsorption sites of single layer, bilayer, and trilayer graphene. All edge site binding energies were found to be substantially higher than the adsorption energies for all metals. The adatom migration activation barriers for the lowest energy migration paths on pristine monolayer, bilayer, and trilayer graphene were then calculated and found to be smaller than or within an order of magnitude of k(B)T at room temperature, implying very high mobility for all adatoms studied. This suggests that metal atoms evaporated onto graphene samples quickly migrate across the lattice and bind to the energetically favorable edge sites before being characterized in the microscope. We then prove this notion for Al and Au on graphene with scanning transmission electron microscopy (STEM) images showing that these atoms are observed exclusively at edge sites, and also hydrocarbon-contaminated regions, where the pristine regions of the lattice are completely devoid of adatoms. Additionally, we review the issue of fixing selected atomic positions during geometry optimization calculations for graphene/adatom systems and suggest a guiding principle for future studies.