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.
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.
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.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.