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The growth of graphene on insulating materials is always a focused issue in the field of multifunctional nanomaterials. To investigate the atomistic mechanism of graphene growth on bicrystal diamonds, we initially investigated the process of in situ growth of graphene on bi-crystal diamonds in the presence of a nickel catalyst and further explored the diamond grain boundary (GB) effect on the graphene growth by reactive molecular dynamics (MD) simulations. The detailed dynamic evolution of graphene growth, the counterdiffusion of catalytic nickel atoms/ GB carbon atoms, and the consequent amorphization of GB were observed. The study demonstrated that the presence of GB assists graphene growth, namely, the amorphous C GB atoms participate in the growth of graphene as supplementary carbon atoms, which is in good qualitative agreement with experimental observations. In addition, we demonstrated that the amorphization of GB is caused by the increase of energy at GB driven by the catalysis of nickel atoms. The results further indicate that the diffusion behavior of the amorphous C GB atom in the nickel lattice involves irregular lateral migration instead of pure upward diffusion. In contrast, in the absence of GB, the kinetics of nickel catalyst-induced amorphization of diamond structures is drastically impaired, resulting in lower graphene coverage.

The physical performance of a heterostructure is strongly influenced by the adhesion properties. The study of adhesion properties between graphene and diamond lattice is an inescapable issue in the development of diamond-based graphene multifunctional nanodevices. Herein, a series of adhesion intensities have been theoretically examined, and the optimum facet of diamond and theoretically recommended orientation angle were obtained, respectively. Moreover, the atomistic peeling behavior and the effect of three typical graphene topological defects on adhesion intensity were explored. The study demonstrated that the presence of double-vacancy defects impairs the adhesion strength due to the reduction of the contact area. In contrast, the presence of Stone-Wales defects is conducive to enhancing the adhesion strength. Interestingly, the effect of single-vacancy defects mainly depends on the delicate competition between single-atom removal and single-atom attraction enhancement. Meanwhile, the effects of diamond surface morphology on graphene adhesion were systematically elaborated by the modeling of one-dimensional and two-dimensional surfaces, and randomly rough surfaces. The adhesion details of graphene on regularly tunable diamonds were explored, and the relations of adhesion intensity and graphene morphology with the random roughness of a diamond surface were further revealed in depth. Since the mechanical and electrical performance of a graphene–diamond heterostructure is sensitively influenced by the adhesion intensity, our findings provide insight into the substrate design of graphene–diamond hybrid devices.

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Graphene on polycrystalline surfaces, such as stainless steel, exhibits frictional strengthening properties during nanofriction. The adsorption state of graphene is directly related to the nanofriction behavior, and graphene's adsorption state is affected by substrate grain boundaries. However, the mechanism of the influence of the substrate grain boundaries on the adsorption state of graphene is not clear. Herein, the adsorption states of graphene on different stainless-steel grain boundary surfaces are analyzed, and the mechanism of the substrate grain boundaries regulating the surface graphene bulge is revealed. The notion that graphene bulges are related to the type of substrate grain boundaries has been confirmed. Moreover, we demonstrate that the difference in the crystal surfaces on both sides of the grain boundaries and the gradient of adsorption energy are the key factors regulating the graphene bulge. Graphene bulging can only be caused by the existence of crystal surface differences in the grain boundary structure; therefore, the tilt grain boundaries are unable to cause graphene bulging. In addition, the adsorption energy distribution within the grain boundary will also influence graphene bulging if there is a grain surface difference in the grain boundary structure. When the direction of the adsorption energy gradient is perpendicular to the grain boundary, such a grain boundary structure favors the appearance of graphene bulges. In contrast, graphene bulging is suppressed when the direction of the adsorption energy gradient is parallel to the grain boundary. It provides a theoretical basis for explaining graphene's nanofriction on polycrystalline substrates such as stainless steel. It is important for the use of graphene for the nano-lubrication of stainless-steel components in microelectromechanical systems.

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