Bayani Amirhossein, Larsson Karin
Department of Chemistry-Ångström Laboratory, Uppsala University, Uppsala 752 37, Sweden.
ACS Omega. 2020 Jun 11;5(24):14842-14846. doi: 10.1021/acsomega.0c01985. eCollection 2020 Jun 23.
The process of Au intercalation into a SiC/buffer interface has been theoretically investigated here by using density functional theory (DFT) and the nudged elastic band (NEB) method. Energy barriers were at first calculated (using NEB) for the transfer of an Au atom through a free-standing graphene sheet. The graphene sheet was either of a nondefect character or with a defect in the form of an enlarged hexagonal carbon ring. Defects in the form of single and double vacancies were also considered. Besides giving a qualitative prediction of the relative energy barriers for the corresponding SiC/buffer interfaces, some of the graphene calculations also proved evidence of energy minima close to the graphene sheet. The most stable Au positions within the SiC/buffer interface were, therefore, calculated by performing geometry optimization with Au in the vicinity of the buffer layer. Based on these NEB and DFT calculations, two factors were observed to have a great influence on the Au intercalation process: (i) energy barrier and (ii) preferential bonding of Au to the radical C atoms at the edges of the vacancies. The energy barriers were considerably smaller in the presence of vacancies. However, the Au atoms preferred to bind to the edge atoms of these vacancies when approaching the buffer layer. It can thereby be concluded that the Au intercalation will only occur for a nondefect buffer layer when using high temperature and/or by using high-energy impacts by Au atoms. For this type of Au intercalation, the buffer layer will become completely detached from the SiC surface, forming a single layer of graphene with an intact Dirac point.
本文利用密度泛函理论（DFT）和推挤弹性带（NEB）方法，从理论上研究了金插入SiC/缓冲层界面的过程。首先计算了（使用NEB）金原子通过独立石墨烯片转移的能垒。石墨烯片要么是非缺陷性质的，要么具有扩大的六边形碳环形式的缺陷。还考虑了单空位和双空位形式的缺陷。除了对相应SiC/缓冲层界面的相对能垒进行定性预测外，一些石墨烯计算还证明了在石墨烯片附近存在能量极小值的证据。因此，通过在缓冲层附近对金进行几何优化，计算出了SiC/缓冲层界面内最稳定的金位置。基于这些NEB和DFT计算，观察到两个因素对金的插入过程有很大影响：（i）能垒和（ii）金与空位边缘的自由基C原子的优先键合。在有空位的情况下，能垒要小得多。然而，金原子在接近缓冲层时更倾向于与这些空位的边缘原子结合。由此可以得出结论，当使用高温和/或通过金原子的高能撞击时，金的插入只会发生在无缺陷的缓冲层上。对于这种类型的金插入，缓冲层将完全从SiC表面分离，形成具有完整狄拉克点的单层石墨烯。
