Secondary electron emission (SEE) is a fundamental surface phenomenon, but its accurate experimental characterization remains challenging due to the high sensitivity to surface conditions and environmental factors. This study utilizes the Monte Carlo simulation method to investigate the SEE process induced by medium- and low-energy heavy ions incident on thin foils, aiming to provide theoretical guidance for the design and application of SEE-based beam diagnostic detectors in accelerator facilities. Taking the thin foil detector for the Xi’an 200MeV Proton Application Facility (XiPAF) as the application background, we utilize the recently extended MicroElec module of Geant4 to quantitatively study the secondary electron yield (SEY), energy spectra, and angular distributions from carbon foils bombarded by heavy ions in the energy range of 1–10 MeV/u. The relationships between SEY and foil thickness, linear energy transfer (LET), and incident angle are systematically explored. Key findings are as follows:
（1）The evolution of forward and backward SEY with foil thickness, as well as their asymmetry, is dominated by δ electron transport. In particular, forward SEY increases rapidly up to ~600 nm and then saturates, while backward SEY saturates at a smaller thickness (~300 nm), consistent with the different escape depths of δ electrons.
（2）For a 100 nm carbon foil, the total SEY exhibits an approximately linear dependence on the incident ion’s LET over three orders of magnitude (0.1–100 keV·cm²·μg^-1). After normalizing the simulated yields with SRIM‑calculated energy deposition, the fitted SEY‑LET coefficient deviates by less than 30% from the experimental data compiled by Rothard et al., which is well within the reported experimental uncertainty (a factor of two).
（3）With increasing incident angle, both forward and backward SEY increase monotonically, but their sensitivities differ: power-law fitting yields f=0.95 for forward emission and f=1.12 for backward emission in γ(φ)=γ(0)∙(cos⁡φ)^-f. This disparity originates from the forward-peaked angular distribution of δ-electrons and their asymmetric transport in the foil, corroborated by the depth distribution of emitted-electron track vertices.
The simulated electron energy spectra and angular distributions agree well with theoretical expectations. The energy deposition calculated by MicroElec shows a deviation from SRIM results (up to 23% for low energy heavy ions), which is attributed primarily to the different effective charge models adopted by the two codes.
This study demonstrates that the Geant4 MicroElec module is an effective tool for simulating heavy ion induced SEE in the medium and low energy regime. The systematic data and physical insights obtained here provide valuable references for the design of thin foil detectors, particularly for online monitoring of low energy heavy ion beams.