GEANT4 Study of Secondary Electron Emission in ZnO Nanorod Arrays under 10-100 MeV Oxygen Ion Irradiation

Abstract

Computational study of secondary electron emission (SEE) from ZnO nanorod arrays deposited on Au/Si₃N₄ substrates under irradiation with ¹⁶O ions in the 10–100 MeV energy range was performed. Using a combination of SRIM and GEANT4 Monte Carlo simulations, the mechanisms of electronic stopping, electron excitation, and secondary electron yield (SEY) were systematically analyzed as functions of ion energy, nanorod radius, and substrate coverage. The results show that the dominant energy loss channel of oxygen ions in ZnO is electronic stopping, peaking at 20 MeV, which defines the optimal energy range for efficient SEE. ZnO nanorod arrays demonstrated significant advantages over continuous ZnO films, providing twice increase in SEY due to their high surface-to-volume ratio, anisotropic geometry, and local field enhancement at nanorod tips, which collectively improve both electron generation and escape. The study identified that nanorods with radii of 0.5–1.0 µm and moderate substrate coverage (35-50%) yield the best performance, achieving a favorable balance between interaction volume and electron escape probability. The findings highlight the importance of nanostructure engineering for tailoring SEE efficiency and provide predictive guidelines for the rational design of nanostructured emitters. In particular, ZnO nanorod arrays emerge as promising candidates for high-performance SEE-based detectors and diagnostic devices in plasma physics, ion-beam technologies, and space applications operating in the MeV energy regime. This work demonstrates the potential of advanced computational modeling in accelerating the development of optimized nanomaterials for electron emission and radiation detection.