Tribological Properties of Graphene and Boron-Nitride Layers: A Fully Atomistic Molecular Dynamics Study
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Tribological Properties of Graphene and Boron-Nitride Layers: A Fully Atomistic Molecular Dynamics Study Ricardo P. dos Santos1,2, Leonardo D. Machado2, Sergio B. Legoas3, and Douglas S. Galvao2 1
Physics Department, IGCE, State University of São Paulo (Unesp), Rio Claro, SP, 13506-900, Brazil 2 Applied Physics Department, Campinas State University, Campinas, SP, 13083-970, Brazil 3 Physics Department, CCT, Roraima Federal University, Boa Vista, RR, 69304-000, Brazil ABSTRACT Graphene has been one of the most important subjects in materials science in the last years. Recently, the frictional characteristics of atomically thin sheets were experimentally investigated using atomic force microscopy (AFM). A new mechanism to explain the enhanced friction for these materials, based on elastic compliance has been proposed. Here, we have investigated the tribological properties of graphene and boron-nitride (single and multi-layers) membranes using fully atomistic molecular dynamics simulations. These simulations were carried out using classical force fields, as implemented in the Large-scale Atomic/Molecular Massively Parallel Simulator (LAMMPS) code. The used structural models contain typically hundreds of thousands of atoms. In order to mimic the experimental conditions, an artificial AFM tip was moved over the membranes and the tribological characteristics determined in terms of forces and energies. Our results are in good agreement with the available experimental data. They show that the observed enhanced tribological properties can be explained in terms of out-of-plane geometrical distortions and elastic waves propagation. They validate the general features of the model proposed by Lee et al. (Science 328, 76 (2010). INTRODUCTION With the advent of nanotechnology, the physical properties of nanomaterials and nanostructures have been investigated by a great variety of techniques to address their unique electronic, optical, thermal and vibrational properties. In particular, there is a renewed interest in tribology, in order to investigate the origin of nanofriction and some unusual tribological properties observed for nanomaterials [1-3]. Tribological phenomena arise when the objects make contact [1]. At nanoscale, the surface effects become very important and some technological applications can be critically limited by the tribological behavior of these materials [2]. Some aspects that are very important at macroscale (such as, gravity and inertia) become insignificant at nanoscale, where surface-related features (such as, van der Waals forces, capillary, etc.) become dominant [1-2]. Some fundamental aspects of nanofriction remain not fully understood and more research along these lines is necessary. In the last years graphene has emerged as one of the most important and studied materials from theoretical and experimental perspectives [4]. Graphene is a two dimensional array of hexagonal units of sp2 bonded carbon atoms. Because of its unique electronic properties, graphene is considered one of the most promising mate
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