Observation of zero coefficient of friction above a critical pressure

TL;DR

This paper reports the first experimental observation of self-superlubricity in microscale graphite, achieved by surpassing a critical pressure that induces full contact with a rough gold substrate, with implications for microsystem technology.

Contribution

It demonstrates the first experimental evidence of pressure-induced self-superlubricity in microscale graphite and establishes a dimensionless criterion for the critical pressure needed.

Findings

Self-superlubricity observed in graphite on gold substrate above critical pressure.

Full contact and zero friction achieved without additional pressure on sapphire.

Theoretical analysis links substrate roughness and pressure to contact transition.

Abstract

Self-superlubricity is a highly anticipated phenomenon where certain solid pairs in contact, without lubricant, exhibit zero wear and virtually null static friction and coefficient of friction (CoF). We present the first experimental observation of self-superlubricity in a microscale single-crystalline graphite flake in contact with a nanoscale-rough Au substrate, achieved when the applied normal pressure exceeds a critical threshold. Theoretical analysis revealed that substrate roughness impedes full contact at low pressures, but increasing the pressure induces a transition to full contact, enabling self-superlubricity. We established a dimensionless criterion for this critical pressure, further validated by observing self-superlubricity between graphite and an atomically smooth sapphire substrate without requiring additional pressure. This breakthrough introduces a transformative principle for next-generation microsystems such as micro/nanoscale generators, motors, oscillators, sensors, etc., enabling reduced power consumption and extended operational lifetimes in applications such as 6G communication, humanoid robotics, and unmanned aerial vehicles.