Multimodal characterization of epitaxial graphene on SiC revealing layer-dependent friction and spectroscopic fingerprints

Abstract

Understanding friction in graphene is essential for its applications in nanoelectromechanical systems and solid lubrication. However, establishing a direct relationship between tribological properties and local graphene properties requires correlative measurements using multiple experimental techniques. Here, we investigate the thickness-dependent tribological behavior of epitaxial graphene on SiC by combining atomic force microscopy, low-energy electron microscopy, and Raman spectroscopy. LEEM enables unambiguous identification of monolayer, bilayer, and trilayer graphene domains, while Raman spectroscopy provides statistical characterization of the same regions. Raman analysis reveals layer-dependent spectral fingerprints, including systematic variations in 2D${}_{FWHM}$, $I_{2D}/I_G$, and strain-dominated correlations between the G and 2D band positions. AFM friction measurements show a monotonic decrease in the friction coefficient from monolayer graphene to trilayer graphene. This decreasing friction trend is accompanied by a layer-dependent evolution of the Raman-derived strain state, while the measured RMS roughness and D band area remain approximately constant. The combined AFM–LEEM–Raman approach reveals a spatial correlation between graphene thickness, Raman spectroscopic signatures, and nanoscale friction in epitaxial graphene on SiC.