Ultralow friction of ink-jet printed graphene flakes

TL;DR

This study demonstrates that inkjet-printed few-layer graphene flakes exhibit ultralow friction comparable to exfoliated graphene, with potential applications in micro- and nano-electromechanical systems lubrication.

Contribution

It shows that liquid phase exfoliated graphene can be inkjet printed to achieve ultralow friction, enabling scalable and high-throughput production for technological applications.

Findings

Printed FLG shows ultralow friction similar to exfoliated graphene.

Ultralow friction persists in flakes as small as 2 nm thick.

Surface step edges exhibit higher friction, indicating edge-related dissipative processes.

Abstract

We report the frictional response of few-layer graphene (FLG) flakes obtained by liquid phase exfoliation (LPE) of pristine graphite. To this end, we inkjet print FLG on bare and hexamethyldisilazane-terminated SiO2 substrates, producing micrometric patterns with nanoscopic roughness that are investigated by atomic force microscopy. Normal force spectroscopy and atomically resolved morphologies indicate reduced surface contamination by solvents after a vacuum annealing procedure. Notably, the printed FLG flakes show ultralow friction comparable with micromechanically exfoliated graphene flakes. Lubricity is retained on flakes with lateral size of a few tens of nanometres, and with thickness as small as ~ 2 nm, confirming the high crystalline quality and low defects density in the FLG basal plane. Surface exposed step edges exhibit the highest friction values, representing preferential sites for originating secondary dissipative processes related to edge straining, wear or lateral displacement of the flakes. Our work demonstrates that LPE enables fundamental studies on graphene friction to the single-flake level. The capability to deliver ultralow-friction-graphene over technologically relevant substrates, using a scalable production route and a high-throughput, large-area printing technique, may also open up new opportunities in the lubrication of micro- and nano-electromechanical systems.