Dynamically tuning friction at the graphene interface using the field effect

Abstract

Dynamically controlling friction in micro- and nanoscale devices is possible using applied electrical bias between contacting surfaces, but this can also induce unwanted reactions which can affect device performance. External electric fields provide a way around this limitation by removing the need to apply bias directly between the contacting surfaces. 2D materials are promising candidates for this approach as their properties can be easily tuned by electric fields and they can be straightforwardly used as surface coatings. This work investigates the friction between single layer graphene and an atomic force microscope tip under the influence of external electric fields. While the primary effect in most systems is electrostatically controllable adhesion, graphene in contact with semiconducting tips exhibits a regime of unexpectedly enhanced and highly tunable friction. The origins of this phenomenon are discussed in the context of fundamental frictional dissipation mechanisms considering stick slip behavior, electron-phonon coupling and viscous electronic flow.

Experimental Decoding and Tuning Electronic Friction of Si Nanotip Sliding on Graphene

“…Note that, due to the simplifications made in the DFT calculation model and the introduction of significant strain (see Section 7 of the SI for details), the constructed Si(111)/graphene/ h -BN exhibits metallic properties (Figure S7). This will induce a substantial charge transfer (Figure S8a) between Si(111) and graphene/ h -BN, and further cause a weakening of polarization thereby reduce the dependence of friction on the electric field, as discussed in prior research . This could offer an explanation for the observed discrepancy in the electric-field-dependent friction between DFT calculations and experiments.…”

“…Additionally, the adhesion force between the AFM tip and sample has been reported to exhibit a significant parabolic increase with electric field, even when its direction is reversed. − , The estimated contribution caused by electronic friction alone is too low to explain the above results. The electric-field- or current-controlled adhesion and friction of graphene, , graphene/Ru(0001), Si 3 N 4 /Si, Pt/MoS 2 , and Ir/MoSe 2 interfaces have also been observed in AFM experiments. Specially, Greenwood et al have investigated the effects of insulating, conducting and semiconducting AFM tips on electric voltage controlled friction between them and monolayer graphene, revealing the different microscopic mechanisms of friction including electrostatic attraction, charge transfer eliminating polarization and electronic excitations via electron–phonon coupling.…”

“…The electric-field- or current-controlled adhesion and friction of graphene, , graphene/Ru(0001), Si 3 N 4 /Si, Pt/MoS 2 , and Ir/MoSe 2 interfaces have also been observed in AFM experiments. Specially, Greenwood et al have investigated the effects of insulating, conducting and semiconducting AFM tips on electric voltage controlled friction between them and monolayer graphene, revealing the different microscopic mechanisms of friction including electrostatic attraction, charge transfer eliminating polarization and electronic excitations via electron–phonon coupling. Lang et al investigated the friction between monolayer graphene and conducting tips under the applied electric voltage, revealing the electrochemical oxidation of graphene leading to the rapid increase of friction with the reversed electric field.…”

“…This will induce a substantial charge transfer (Figure S8a) between Si(111) and graphene/h-BN, and further cause a weakening of polarization thereby reduce the dependence of friction on the electric field, as discussed in prior research. 42 This could offer an explanation for the observed discrepancy in the electric-field-dependent friction between DFT calculations and experiments.…”

“…In a subsequent experiment on GaAs and MoS 2 , a similar friction and adhesion force tuning effect by the application of forward and reverse V G was also observed. Especially, Greenwood et al demonstrated that the adhesion between a conductive AFM tip and monolayer graphene becomes approximately constant once the electric voltage increases to a threshold, while the friction presents unignorable variations. These previous experiments indicate that the friction tuning cannot be simply attributed to the adhesion force or to the electronic friction.…”