Surface modification by nanosecond laser ablation of copper substrate for the growth behavior of tantalum as hydrogen diffusion layer within AB-BNCT target system

Abstract

To mitigate stress accumulation of tantalum (Ta) hydrogen diffusion layers in accelerator-based boron neutron capture therapy (AB-BNCT) target system, this study employed nanosecond laser ablation (NLA) to modify copper (Cu) substrates before Ta deposition. Finite element method was conducted to simulate the NLA on Cu surfaces, analyzing the evolution of the surface temperature field during a single laser pulse and the effects of different laser parameters on ablation depth. The influence of NLA induced microstructures on the surface morphology, chemical composition, and crystal structure of the deposited Ta layer was then investigated. The growth mechanism for Ta layers on laser ablated Cu surfaces was proposed, three representative Cu surface states were identified: severe ablation surface, ablation track surface, and mild ablation surface. Mild ablation surfaces promoted more uniform Ta growth, reduced stress accumulation, and facilitated the formation of continuous layers, making them promising for AB-BNCT target applications. At a Ta thickness of 20 μm, eight diffraction peaks were detected, with α-Ta(110) predominating, while the increased contribution of α-Ta at larger thicknesses was accompanied by an evolution of the stress state. This study offers valuable insights for the design and fabrication of high-performance hydrogen diffusion layers in AB-BNCT target systems.