14.5% near-normal incidence reflectance of Cr/Sc x-ray multilayer mirrors for the water window

Abstract

$\mathrm{Cr}/\mathrm{Sc}$ multilayer mirrors, synthesized by ion-assisted magnetron sputter deposition, are proved to have a high near-normal reflectivity of $R=14.5\%$ at a grazing angle of 87.5° measured at the wavelength $\lambda =3.11 \mathrm{nm}$, which is an improvement of more than 31% compared with previously published results. Elastic recoil detection analyses show that the mirrors contained as much as 15 at. % of N and traces of C and O. Soft x-ray reflectivity simulations reveal interface widths of $\sigma =0.34 \mathrm{nm}$ and an exceptionally small layer thickness drift of $\sim 1.6\times {10}^{-5} \mathrm{nm}/\mathrm{multilayer}$ period throughout the stack. Simulations show that a reflectivity of $R=25.6\%$ is attainable if impurities and layer thickness drift can be eliminated. The abrupt interfaces are achieved with ion assistance with a low ion energy of 24 eV and high ion-to-metal flux ratios of 7.1 and 23.1 during Cr and Sc sputter deposition, respectively. In addition, a near-normal incidence reflectivity of 5.5% for the C VI emission line $\left(\lambda =3.374 \mathrm{nm}\right)$ from a laser plasma source was verified.

© 2003 Optical Society of America