First Principles Study Of Graphene/Nickel System And Its Oxygen Intercalations

The discovery of graphene has aroused great concern in condensed matter physics. Recent studies show that graphene has wide application potential, which intrigues the urgent need for large-scale synthesis and production of high quality graphene. The chemical vapor deposition method has received a lot of attention since it can be used to prepare the large-scale and high-quality graphene cheaply. Understanding the interaction between the graphene and metal substrate is a basic step to optimize and control the chemical vapor deposition growth of graphene.Because the lattice mismatch between graphene and Ni (111) is only 1%, a simple (lxl) surface adsorption phase can form on the surface. Graphene/Ni (111) has been studied extensively as a typical example of lattice-matched system for graphene/metal. However, the stable structure of graphene forming on Ni (111) surface remains debated. Early experiments suggested the top_fcc structure as the most stable phase, while recent experiments have found other structures such as bridge_top can coexist with top_fcc. On the other side, the commonly used LDA and GGA can not reasonably consider van der Waals interactions, leading to the conflict results with experiment. For example, GGA results show that graphene cannot be stable on a nickel surface. How to consider van der Waals interactions effectively is crucial for understanding the graphene/Ni (111).In this paper, we have investigated the grapheme/Ni (111) system, in which the vdW interaction was considered by optB88-vdW functional. And the PBE calculations were also performed for comparison. Accurate potential energy surface showed graphene can be stable on Ni (111) surface, top_fcc, bridge_top and top_hcp have very closed energy, which suggests the three phases coexistence. This is also in good agreement with experiment. Meanwhile, the physical and chemical adsorption can be found at all stable configurations. Dirac points of graphene in chemisorption state on all stable configurations are destroyed. Further analysis showed that the change and hybridization in the symmetry of C atoms induced by and the substrate led the energy gap appearing near K. The bonding mechanism of grapheme/Ni (111) surface are analyzed by the differential charge density and simulated STM.Due to the interaction of graphene and the substrate, the graphene loses its original particular electronic structure on metal surface. Numerous studies confirm that intercalation can effectively relieve the impact of substrate on grapheme. However, the intercalation elements are only limited to metal at present. In this paper, taking oxygen as an example we study the non-metallic element intercalation on grapheme/Ni (111) surface. We studied and discussed in detail the structural stability, electronic structure, the differential charge and STM images of intercalation systems with different coverage. The results show that the insertion the appreciate non-metallic element layer can effectively increase the distance between the graphene and substrate, thereby lift the influence of nickel on graphene, which leads to restore of the original electronic structure in graphene. A strong chemical bonding between oxygen atom and substrate Ni atoms formed during intercalation, which is different from the case of metal.