Kinetic and spectroscopic analysis of AlF₃ film growth on graphitic substrates: Flux and microstructure effects on intercalation and surface adsorption

Abstract

We present a detailed investigation of the intercalation and adsorption of aluminum fluoride (AlF3) on highly oriented pyrolytic graphite (HOPG) using Auger electron spectroscopy (AES) and reflection electron energy loss spectroscopy (REELS). Thin AlF3films were thermally evaporated under ultra-high vacuum on two HOPG substrates (grades 2 and 3) differing in crystalline quality and defect density. AES measurements revealed a two-stage sorption mechanism. At low molecular flux (thermodynamic regime), AlF3 molecules gradually incorporated into sub-surface graphitic regions, consistent with interlayer intercalation, as evidenced by the exponential attenuation of the CKLL signal, while at higher coverage the process shifted to surface adsorption. Under high molecular flux (kinetic regime), surface films grew rapidly with limited intercalation. The kinetics was analyzed through a bi-exponential attenuation model of the carbon signal, distinguishing fast surface diffusion from slower interlayer penetration. Differences between HOPG grades underscored the role of structural defects in facilitating intercalation. Complementary REELS data provided insight into the electronic structure evolution of AlF3, showing gradual band-gap formation in defective HOPG and faster stabilization in more ordered substrates. These findings demonstrate that deposition kinetics and substrate crystallinity jointly determine the growth and structural characteristics of AlF3 intercalated layers, providing guidance for the controlled fabrication of two-dimensional heterostructures.