Understanding and Preventing Lubrication Failure at the Carbon Atomic Steps

Area of Science:

• Materials Science
• Tribology
• Nanotechnology

Background:

• Two-dimensional (2D) lamellar materials offer excellent low-friction properties at the nanoscale.
• High friction at step edges hinders macroscale superlubricity and limits applications of 2D materials.
• Graphene's step edges, particularly zigzag (ZZ) types, exhibit significantly higher friction than basal planes.

Purpose of the Study:

• To investigate the friction behavior of different graphene step edge structures.
• To develop a method for reducing friction at detrimental ZZ step edges.
• To enable macroscale superlubricity applications for graphene.

Main Methods:

• Comparative friction analysis of armchair (AC) and zigzag (ZZ) graphene step edges.
• Mechanical exfoliation and grinding to produce step edges.
• Thermal annealing in an inert gas environment to reconstruct ZZ step edge structure.

Main Results:

• AC step edges have a minor effect on friction; ZZ step edges increase friction by two orders of magnitude.
• Mechanically produced step edges predominantly exhibit the high-friction ZZ structure.
• Thermal annealing successfully reconstructs ZZ edges to a less-frictional, azulene-like structure, achieving superlubricity.

Conclusions:

• Not all graphene step edges are detrimental to superlubricity; AC edges are less impactful.
• A novel thermal annealing method can transform high-friction ZZ edges into a superlubricious state.
• This breakthrough facilitates the industrial application of graphene superlubricity where step edges are unavoidable.