Abstract
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.
Highlights
Large-scale production of graphene is very challenging for various types of industrial applications
For the Au intercalation process, through the carbon buffer layer and into the SiC(0001)/buffer interface, different types of buffer layers have been considered in the present study
More qualitative values of the intercalation energy barriers were instead obtained by examining the penetration of an Au atom through a graphene sheet
Summary
Large-scale production of graphene is very challenging for various types of industrial applications. Intercalation methods based on thermal annealing have been shown to be a promising way to produce graphene sheets in large sizes.[1−3] It has been experimentally shown that intercalation with different types of elements (such as H,4 Li,[5] Ge, F,7 Au,[8] Pt, and Cu10), followed by thermal annealing, is a suitable way to fabricate high-quality single-layer graphene on SiC substrates. Different theoretical studies have focused on the mechanism of intercalation with either Li11 or Cu,[12] into the SiC/buffer interface. To the best of our knowledge, the mechanism of intercalation with Au atoms has not yet been theoretically addressed. Previous theoretical studies have only dealt with the energy barrier in the atom intercalation process. The complete optimization of the geometrical interface structure (especially after the intercalation process) still needs to be addressed
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