Effect of substrate modification by Al2O3 sandblasting on Ta layer growth via pulsed DC magnetron sputtering for AB-BNCT targets

Accelerator-based Boron Neutron Capture Therapy (AB-BNCT) is an innovation oncological treatment, facing critical target challenges: hydrogen induced blistering from proton penetration into Cu substrates, thermal management issues, and mechanical failures (e.g., cracking, delamination) of magnetron sputtering Ta hydrogen diffusion layers due to intrinsic stresses, particularly at micrometer scale thicknesses. This study investigates Al2O3 sandblasting induced substrate modification effects on Ta layers deposited via pulsed DC magnetron sputtering for AB-BNCT targets. Cu substrates were sandblasted with 500–100 μm Al2O3 particles, followed by Ta deposition to 1, 5, and 20 μm. To comprehensively characterize the microstructural, compositional, and mechanical properties of the samples, a suite of analytical techniques was employed, including scanning electron microscopy, laser scanning confocal microscopy, x-ray diffraction, x-ray photoelectron spectroscopy, and stress analysis. Key results show that smaller particles (e.g., 100 μm) reduced substrate roughness (Sa = 3.26 μm) and improved Ta layer uniformity by mitigating shadowing effects. Ta crystallite size showed an “increase-decrease” trend with thickness: 9.9–12.1 nm at 1 μm (nucleation), 22.3 nm at 5 μm (via competitive growth and β → α phase transformation), and 20.6 nm at 20 μm (secondary nucleation). Reducing particle size lowered residual stress, with 150 μm sandblasting yielding the lowest stress (0.54 GPa) at 20 μm. Sandblasting induced nanostructures promoted α-Ta (111) as the dominant phase, improving crystallinity and reducing defects. This work demonstrates that regulating Al2O3 sandblasting particle size enables Ta layers balancing hydrogen diffusion, thermal conductivity, and mechanical stability, providing a critical optimization strategy for high performance AB-BNCT targets.