Structure and properties of Ta–Ti binary layer as anti-hydrogen embrittlement layer within neutron production target for accelerator-based boron neutron capture therapy (AB-BNCT)

Tantalum (Ta), as the antihydrogen embrittlement layer in the neutron production target of accelerator-based boron neutron capture therapy (AB-BNCT), can effectively slow down and prevent protons from penetrating the copper substrate, thereby decreasing the risk of hydrogen embrittlement in the target system. However, when a Ta film is deposited on the copper substrate using magnetron sputtering, stress accumulation can easily lead to bulging, cracking, and even delamination, which negatively impacts the stability of the target system. Because the introduction of titanium (Ti) can relieve stress, in this study, a series of Ta–Ti binary antihydrogen embrittlement layers were prepared by varying the movement speed of the sample holder using pulsed DC magnetron sputtering and then characterized by physicochemical methods. It was found that the movement speed, to adjust the atomic ratio of Ta and Ti, had a great influence on the deposition speed, surface morphology, structure, and grain size of Ta–Ti binary layers. When the movement speed was set to 15 mm/s, the prepared film exhibited no obvious aggregation particles with a flat surface and the lowest stress value of 13.09 GPa. Moreover, the change of the movement speed induced the transformation of crystal type and fine grain. Moreover, according to the simulation by Monte Carlo methods (SRIM and PHITS), the introduction of Ti was not expected to significantly affect the neutron yield, while it served to decrease the local hydrogen concentration and vacancies. By applying bias pressure, the roughness is reduced and the quality of the film is improved. These results enrich the composition of the AB-BNCT target material and provide reliable theoretical support and practical basis for the AB-BNCT target system.