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Intercalation of metal atoms into the interface of graphene and its supporting substrate has become an intriguing topic for the sake of weakening the interface coupling and constructing metal atomic layers under inert covers. However, this novel behavior has rarely been reported on the analogous hexagonal boron nitride (h-BN) synthesized on metal substrates. Here, we describe a comparative study of Mn intercalation into the interfaces of graphene/Rh(111) and h-BN/Rh(111), by using atomically-resolved scanning tunneling microscopy (STM) and density functional theory (DFT) calculations. The intercalation was performed by annealing as-deposited Mn clusters, and the starting temperature of Mn intercalation into h-BN/Rh(111) was found to be ∼80 °C higher than that for graphene/Rh(111). Moreover, the intercalated islands of h-BN/Mn/Rh(111) usually possess more irregular shapes than those of graphene/Mn/Rh(111), as illustrated by temperature-dependent STM observations. All these experimental facts suggest a stronger interaction of Mn with h-BN/Rh(111) than that with graphene/Rh(111). Open image in new window

Due to strong interactions between epitaxial graphene and SiC(0001) substrates, the overlayer charge density induced by the interface charging effect is much more attenuated than that of exfoliated graphene on SiO2. We report herein a quantitive detection of the charge properties of few-layer graphene by surface potential measurements using electrostatic force microscopy (EFM). A minor difference in surface potential is observed to mediate a sequential assembly of metal-free phthalocyanine (H2Pc) on monolayer, bilayer and trilayer graphenes, as demonstrated by scanning tunneling microscopy (STM). In order to understand this, we further executed density functional theory (DFT) calculations which showed higher adsorption energies for Pc on thinner graphenes. In this case, we attribute the unique growth behavior of Pc to its variable adsorption energies on few-layer graphene, and in turn the layer charge variations from the viewpoint of energy minimizations. This work is expected to provide fundamental data useful for related nanodevice fabrications.

Graphene growth on the same metal substrate with different crystal morphologies, such as single crystalline and polycrystalline, may involve different mechanisms. We deal with this issue by preparing graphene on single crystal Ni(111) and on ∼300 nm thick Ni films on SiO2 using an ambient pressure chemical vapor deposition (APCVD) method, and analyze the different growth behaviors for different growth parameters by atomically-resolved scanning tunneling microscopy (STM) and complementary macroscopic analysis methods. Interestingly, we obtained monolayer graphene on Ni(111), and multilayer graphene on Ni films under the same growth conditions. Based on the experimental results, it is proposed that the graphene growth on Ni(111) is strongly templated by the Ni(111) lattice due to the strong Ni-C interactions, leading to monolayer graphene growth. Multilayer graphene flakes formed on polycrystalline Ni films are usually stacked with deviations from the Bernal stacking type and show small rotations among the carbon layers. Considering the different substrate features, the inevitable grain boundaries on polycrystalline Ni films are considered to serve as the growth fronts for bilayer and even multilayer graphene.

Microscopic features of graphene segregated on Ni films prior to chemical transfer—including atomic structures of monolayers and bilayers, Moire patterns due to non-AB stacking, as well as wrinkles and ripples caused by strain effects-have been characterized in detail by high-resolution scanning tunneling microscopy (STM). We found that the stacking geometry of the bilayer graphene usually deviates from the traditional Bernal stacking (or so-called AB stacking), resulting in the formation of a variety of Moire patterns. The relative rotations inside the bilayer were then qualitatively deduced from the relationship between Moire patterns and carbon lattices. Moreover, we found that typical defects such as wrinkles and ripples tend to evolve around multi-step boundaries of Ni, thus reflecting strong perturbations from substrate corrugations. These investigations of the morphology and the mechanism of formation of wrinkles and ripples are fundamental topics in graphene research. This work is expected to contribute to the exploration of electronic and transport properties of wrinkles and ripples. Open image in new window