Electron-Beam Radiolysis of Ultrathin AlF3 Films on Graphite: Secondary-Electron Effects and Self-Limiting Kinetics

The mechanisms governing electron-induced decomposition in aluminum trifluoride (AlF3), a wide-band-gap ionic material with potential applications as an inorganic electron-beam resist, remain poorly understood. This study investigates the radiolysis of ultrathin AlF3 films on graphite substrates through a combination of experimental characterization and Monte Carlo simulations. We identify a nonmonotonic dependence of electron-beam-induced radiolysis efficiency on film thickness and growth regime, which correlates with thickness-dependent changes in the internal secondary electron spectrum. The decomposition follows power-law kinetics with an exponent ≈−1/3, consistent with self-limiting, evolving radiolysis kinetics. We propose a defect-mediated, self-limiting mechanism in which irradiation-induced defect states provide alternative lower-energy relaxation pathways that may progressively reduce further bond-breaking events as irradiation proceeds. This framework is also consistent with independent radiolysis data for cryolite (Na3AlF6). Furthermore, we provide a validated dielectric model for AlF3 implemented in the Monte Carlo-based Geant4 MicroElec framework, enabling accurate simulation of electron-beam interactions in this material for broader nanofabrication and radiation effect studies.