Adhesion and Friction at Graphene/Self-Assembled Monolayer Interfaces Investigated by Atomic Force Microscopy
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© 2017 American Chemical Society. The functional implementation of graphene as a solid boundary lubricant requires the ability to control its frictional response across a variety of interfaces. This is challenging, as being a single atomic layer thick, the nanotribological properties of graphene depend highly on the competing interaction strengths with the converse sides of the top and bottom contacts of the interfaces it is placed in between. One method to modulate these interactions is to tune the surface chemistry (of one or both counter-faces) with self-assembled monolayers (SAMs). To fully understand the effects on the graphene/SAM (G-SAM) composite interfaces formed, however, first necessitates a basic understanding of graphene-SAM interactions. To explore graphene-SAM adhesive and frictional interactions over a range of chemical functionalities, SAMs were used to functionalize atomic force microscopy (AFM) tips with varying terminal end-groups (-NH2, -CH3, and -phenyl, compared to unfunctionalized -OH terminated reference tips). AFM pull-off force measurements and thermal gravimetric analysis (TGA) were used to evaluate the work of adhesion (mJ/m2) and interaction energy (kcal/mol) of the functionalized tips with graphene. Friction force microscopy (FFM) measurements were performed with the same functionalized AFM tips to examine the graphene-molecule frictional response. Tip-graphene interaction strength was increased for hydrophobic and aromatic functional groups. The frictional response was found to depend on a balance of graphene-molecule adhesion and shear strain. (Figure Presented).
author list (cited authors)
Elinski, M. B., Menard, B. D., Liu, Z., & Batteas, J. D.