Modelling adhesion of defective graphene interfaces

Abstract eng:
We develop a homogenous spring model to characterize the influence of surface defects on the adhesion properties of graphene interfaces. The modeled correlation between cohesive energy and interfacial separation of graphene silicon-dioxide interface is compared with molecular dynamics simulations, and the results are in good agreement. The exceptional electromechanical properties of graphene have facilitated the development of the next generation of nanodevices. These state-of-the-art nanodevices, such as sensors and transistors, have profound impacts in numerous engineering disciplines, ranging from biomedicine to aerospace [1]. Recent experiments show that graphene could also be used as an ultra-strong reinforcement for composite materials [2]. Using graphene as reinforcement provides an excellent opportunity to transfer the superior electromechanical properties of graphene, across multiple length scales, up to the macroscopic level. In both graphene-based nanodevices and composite materials, graphene is in contact with adjoining materials, creating mechanically weak interfaces between graphene and the other materials. On the other hand, during the fabrication of graphene-based systems, defects such as surface impurities are unavoidable. These defects could highly deteriorate the mechanical properties of graphene [3-6], which will ultimately influence the performance of graphene-based systems. Therefore, understanding the effects of defects on the mechanical properties of both graphene and graphene interfaces is critically important in designing reliable graphene-based systems. In this paper, we develop a homogenous spring model to characterize the influence of surface defects (e.g., vacancies, adatoms) on the adhesion properties of graphene interfaces. Discrete nature of this interface model allow us to investigate the influence of point defects such as vacancies and adatoms, which breaks the continuity of the interface; therefore, the continuum-based models (e.g., [7-9]) cannot be employed. We use the adhesion properties of graphene-silicon-dioxide (SiO2) interface, which is one of the most widely studied interfaces [9,10], obtained using molecular dynamics (MD) simulations to validate the proposed model. We modelled the interfacial adhesion of graphene-SiO2 system using Lennard-Jones (LJ) potential, and the adhesion between carbon atoms of graphene and the SiO2 substrate is represented by nonlinear springs. Fig. 1(a) graphically demonstrates the graphene-SiO2 system, and Fig. 1(b) shows the proposed spring model characterizing the interaction between graphene and SiO2 substrate. One end of the springs are attached to carbon atoms of graphene and the other ends are connected to the substrate, which is assumed infinitely rigid considering the magnitude of van der Waals force and the stiffness of SiO2 and other typical substrate materials. During the delamination process, graphene sheet is assumed to be conforming completely to a flat SiO2 substrate. The separation distance between graphene and SiO2 substrate is l, and the dimensions of the SiO2 substrate are considered infinitely large. Energy stored in a nonlinear spring, U(l), can be expressed in terms of the van der Waals energy between a carbon atom and the SiO2 substrate as (

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