Frictional characteristics of nano-confined water mediated hole-doped single-layer graphene on silica surface

Abstract

We have investigated the frictional properties of single-layer graphene (SLG) coated rough silica substrate under the influence of nano-confined hydration layer underneath SLG. Through the friction and surface potential measurements by atomic force microscopy (AFM), we found polygonal features in AFM images of SLG-protected silica surface that exhibit simultaneously larger friction and higher surface potential as compared to their surrounding areas due to water layers confined under SLG. Nano-confined water layers at the SLG-silica interface can induce the hole-doping effect in SLG, resulting in a more positively-charged and hydrophilic surface that favors adsorption of ambient water molecules. Therefore, during friction measurements, nanoscale capillary bridges can form within the interstices of AFM probe-SLG contact, leading to larger adhesion and friction. The friction forces were found to respectively have negative and positive dependence on the sliding velocity inside and outside the polygonal regions due to different surface wettability. Hence, it is possible to manipulate the frictional properties of SLGcoated silica by the amount of hydration layer confined underneath SLG. Our results may find applications in friction control for future nano-devices.

Recent advances in probing two-dimensional materials confined water by scanning probe microscopy

“…此外, 在针尖施加压力诱导石墨烯限域冰状水分 子层融化的过程中, 由于水分子的无序性和动态性增 强, 针尖与石墨烯的摩擦力逐渐增大 [55] . 对于石墨烯-硅体系, 限域水分子同样会导致单层石墨烯摩擦力的 增大 [81] . 研究认为这是由于限域水分子层对单层石墨 .…”

Influence of cutoff radius and tip atomic structure on energy barriers encountered during AFM tip sliding on 2D monolayers

“…Since the seminal discoveries of superlubricity in graphite and MoS 2 [1][2][3], the frictional characteristics of two-dimensional (2D) materials have been extensively investigated [4][5][6][7][8][9][10][11][12][13][14][15]. A recent combined experimental and computational study conclusively demonstrates that the frictional contrast observed by atomic force microscopy (AFM) between MoS 2 and graphene, two representative 2D materials, originates from difference in the energy barriers experienced by the sliding tip [16].…”

“…The LJ potential is often chosen for low loads and non-metallic systems [20,21]. The LJ potential between two atoms separated by a distance r is given by: U LJ (r) = 4ε (σ/r) 12 − (σ/r) 6 .…”