Elucidating the role of graphitization in laser-induced superlubricity of amorphous carbon films

Graphitization is widely recognized as a key to understanding the low-friction behavior of carbon films. However, its specific features and roles in laser-induced superlubricity of amorphous carbon (a-C) films have not been well clarified. Here, we systematically investigate the top surface of a-C film wear tracks under in situ laser-induced robust macroscale superlubricity using multi-mode atomic force microscopy. Conductive atomic force microscopy and nanoscratch tests show that nanographene islands (tens of nm in diameter, ∼3 atomic layers thick) are dispersed on the superlubricious wear track, covering ∼20% of the area. Electrostatic force microscopy and nano-friction tests confirm that nanographene islands are critical for enriching photoelectrons and significantly reducing friction force under in situ laser irradiation. These findings reveal that electron-enriched nanographene islands are the essential origin of laser-induced superlubricity, offering novel insights into superlubricity control.