Suppression of secondary recoil cascade damage in high-Z/low-Z heterostructures: a mechanism-driven FIB strategy

The integration of low-dimensional materials (LDMs) with high-k dielectrics and heavy metal contacts is fundamental to the development of next-generation nanoelectronics. However, preparing low-damage cross-sections of high-Z/low-Z heterostructures using focused ion beam (FIB) milling is challenging, as fragile buried channels often undergo structural collapse. We identify the secondary recoil cascade as the dominant failure mechanism. Heavy atoms from the overlayers act as secondary projectiles, triggering structural failure at depths far exceeding the direct ion range. Using a HfO₂/CNT array model system, we propose a mechanism-driven strategy to suppress this damage. By optimizing the grazing angle and applying a multi-step energy reduction sequence (30 keV down to 500 eV), we effectively confined the interaction volume and removed inherited damage. Additionally, a raster scanning pattern was used to facilitate thermal relaxation. This approach achieved a 95 % structural retention (303 CNT μm⁻¹) compared to the total loss observed in conventional protocols. The established framework is transferable to various LDM-based heterostructures (e.g., graphene, MoS₂) where high-Z overlayers are present, providing a reliable metrology solution for preserving the intrinsic features of challenging interfacial material stacks.