INTRODUCTION: Control of friction and wear is a ubiquitous challenge in numerous machined interfaces ranging from biomedical implants, to engines, to nano- and micro-scaled electromechanical systems (MEMS) devices.1 Central to developing boundary lubrication schemes for such applications is how to reduce wear at the rough surfaces of such devices, where nanoscaled asperities dominate the interfacial contacts. The robust mechanical properties and general chemical inertness of two-dimensional (2D) nanomaterials, such as graphene and MoS2, has made them of interest for modifying surface frictional properties. While single layer graphene and MoS2 can readily adapt to surface structure on the atomic scale, when deposited on substrates with nanoscopic roughness of ~ 10 nm rms (as is common in many machined interfaces) a conformal coating generally cannot be fully formed, due to competition between adhesion to the substrate nanoscopic asperities and the bending rigidity of the material.2,3 This often leaves a mixture of supported and unsupported regions which respond differently to applied load, with spatial variations in mechanical properties and chemical bonding. Increased strain in these materials on rough surfaces has also been seen to increase their chemical reactivity.4 Modification of the frictional properties may also be tuned by controlling substrate interactions using self-assembled monolayers.5 Here, we describe a combination of AFM nanomechanical, confocal Raman microspectroscopic and near field IR scattering studies of graphene and MoS2 on silica surfaces with controlled nanoscopic roughness, to examine the how this impacts their frictional properties, and alters their electronic properties and chemical reactivity, where strain dependent reactions can be driven by applied forces.
REFERENCES: 1. Spear, Nano Today (2015), 2. Elinski, J. of Phys. D: Appl. Phys. (2017), 3. Spear, Nanoscale (2015), 4. Raghuraman, Nano Lett. (2017), 5. Elinski, J. Phys. Chem. C (2017).