Study on fabrication of hard X-ray Pd/B₄C multilayer film mirrors using refurbished coating

To facilitate the reusability of Pd/B₄C multilayer film mirrors for synchrotron hard X-rays applications, a multilayer film incorporating a 5 nm chromium (Cr) buffer layer was fabricated on silicon substrates. The Cr buffer layer was removed using an etching solution, allowing the successful detachment of the Pd/B₄C multilayer film from the silicon substrate. X-ray reflectivity curves were generated for samples etched for various durations. Subsequent theoretical analyses and experimental validations were carried out, with white light profilometry used to assess surface roughness of samples after various etching times. A new Pd/B₄C multilayer film with a Cr buffer layer was subsequently redeposited onto the etched substrate. The results revealed that after 2 h of etching, the surface roughness of the samples (0.38 nm) was comparable to that of a new substrate (0.35 nm). The oxidation layer formed on the etched substrate had no significant impact on the interface roughness of the newly deposited Pd/B₄C multilayer film, thereby demonstrating that the etched substrate can be effectively refurbished for reuse. This study offers a valuable reference for the sustainable reusability of multilayer film monochromator substrates in synchrotron X-ray optics.