No abstract

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.

Purpose The purpose of this paper is to reveal the mechanism of graphene low-temperature friction and provide a theoretical basis for the application of graphene. Design/methodology/approach A probe etching model of graphene on the copper substrate was established to obtain the friction pattern of graphene with different layers in the temperature interval from 100 to 300 K. The friction mechanism was also explained from a microscopic perspective based on thermal lubrication theory. Low-temperature friction experiments of graphene were carried out by atomic force microscopy to further verify the graphene low-temperature friction law. Findings Graphene nanofriction experiments were conducted at 230–300 K. Based on this, more detailed simulation studies were performed. It is found that the combined effect of thermolubricity and thermal fluctuations affects the variation of friction. For monolayer graphene, thermolubricity is the main influence, and friction decreases with increasing temperature. For multilayer graphene, thermal fluctuations gradually become the main influencing factor as the temperature rises, and the overall friction becomes larger with increasing temperature. Originality/value Graphene with excellent mechanical properties provides a new way to reduce the frictional wear of metallic materials in low-temperature environments. The friction laws and mechanisms of graphene in low-temperature environments are of great significance for the expansion of graphene application environments.

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.

No abstract