The Role of Contact Adhesion in Friction and Wear of Graphene under Sliding Conditions
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The Role of Contact Adhesion in Friction and Wear of Graphene under Sliding Conditions Emil J. Sandoz-Rosado1 and Elon J. Terrell1 1
Department of Mechanical Engineering, Columbia University, 500 West 120th St Room 220, New York, NY 10027. ABSTRACT In this study, the failure mechanisms of graphene under sliding are examined using atomistic simulations. A 6nm diameter diamond tip is slid (at a controlled normal load) over a graphene monolayer that is adhered to a semi-infinite silicon substrate. The impact of tip adhesion on the wear and frictional behavior of graphene is studied by comparing two diamond tips, one of which has been hydrogen-passivated and the other which is bare carbon. By contrasting the passivated and unpassivated tips, the interplay of adhesive and abrasive wear on the graphene membrane can also be compared. The results of this work indicate that chemical bonding between the tip and the graphene greatly exacerbates tearing in the graphene monolayer by plowing ahead of the indenter, causing material build-up and increasing effective contact area. INTRODUCTION However, despite the attention to nanoscale friction, wear of lamellar atomically-thin materials, particularly of graphene, has received less attention since the problem is more complex. Nanotribological studies have been conducted for bulk graphite, diamond and diamond-like carbon (DLC) among other materials[1-3]. For amorphous carbon, wear can be characterized as a continuous phenomenon due to the three-dimensional structure of the material (since wear volume can be more readily calculated, as opposed to a two-dimensional structure where volume is more ambiguous)[4]. Conversely, wear of atomically-thin layers is not well defined (e.g. cannot be defined by worn volume), and has only been explored in a limited fashion. In previous work, the authors exclusively examined abrasive wear in graphene monolayers as well as multi-layer graphene and benchmarked their performance against DLC coatings[5]. In the previous study, tri-layer tribological tests graphene compares favorably to 86% sp3 content DLC of the same film thickness (1.0 nm). The graphene withstood as much as 8.5 times the normal load of the latter during indentation and as much as twice the normal load during sliding and tearing, showing great potential as a nanoscale solid lubricant. Despite the exploration of abrasion in the previous aforementioned work, the nanotribological characteristics of graphene have not been fully explored. Where the previous study had a purely-repulsive indenter and a rigid substrate, a full atomistic substrate and indenter were simulated in this work to examine the impact of tip-membrane adhesion, as well as compliant substrate contributions to wear.
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Corresponding author email: [email protected]
NUMERICAL EXPERIMENT DETAILS To investigate the impacts of adhesion and substrate deflection on the failure of graphene sheets, a molecular dynamics algorithm[6] was used to simulate a 6nm diameter, single-crystal diamond hemisphere sliding over a graphene
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