Very-low-primary-energy secondary-electron emission: A surface-dominated quantum regime

At very-low-primary-energy regime, secondary-electron emission enters a regime where classical bulk-transport models break down, and emission becomes governed by quantum surface physics. The incident electron wavelength approaches interatomic distances, elastic scattering dominates over inelastic losses, and the surface potential barrier controls both injection and escape. This review synthesizes the physical mechanisms, material-dependent behavior, and advanced experimental techniques that define this very-low-primary-energy regime. We show how electronic band structure, surface states, work function, and electron affinity collectively determine emission yields and energy distributions across metals, semiconductors, insulators, and two-dimensional materials. The limitations of conventional three-step models are analyzed, and quantum-mechanical frameworks, including dielectric response theory and one-step coherent emission models, are presented as necessary alternatives. Finally, we discuss how understanding very-low-primary-energy secondary-electron emission enables rational surface engineering for applications in electron microscopy, spacecraft charging mitigation, and high-frequency accelerator technologies.