HiPIMS deposition method unlocks higher X-ray reflectance in ultra-short-period multilayer mirrors

The efficiency of multilayer (ML) mirrors with ultra-short periods, essential for X-ray science and applications, remains severely limited by interface imperfections at sub-nanometric scale. We demonstrate a breakthrough in interface quality of ultra-short-period W/SiC MLs using optimized high-power impulse magnetron sputtering (HiPIMS) compared to standard magnetron sputtering. By combining synchrotron-based X-ray reflectometry at multiple photon energies and diffuse scattering measurements, we show that HiPIMS reduces interfacial roughness in W/SiC MLs by a factor of two, from ∼0.4 nm to ∼0.2 nm. This results in a significant increase in peak reflectivity, from 63% up to 79% at 40 keV, and in a broader bandwidth. These results highlight the potential of HiPIMS to overcome the nanoscale period thickness limit due to interfacial defects, thus enabling important applications in the soft and hard X-ray ranges.