Multilayer systems at nanometre scale have been applied as spectroscopic elements for wavelengths >1 nm and optical reflection systems in the short-wavelength region (<100 nm). Main requirements are a high optical contrast for the multilayer components in the wavelength region of application and a density profile with sharp interfaces between the components. Two sources are responsible for interface roughness, the development of surface roughness during deposition of the multilayer components and intermixing of these components at the interfaces. Etching a freshly deposited layer by low-energy ions has demonstrated to be successful in reducing the surface roughness of W on C, Ni on C and Si on Mo. Implantation of low-energy N+ ions into Si has been applied to reduce the chemical reactivity at the interface with Ni. Formation of a carbide interlayer by implantation of Si with C+ ions successfully prevented intermixing of the Mo on Si interfaces, improving the thermal stability of Mo/Si multilayers. Finally, a combination of implantation and annealing was applied to form Si/SiC multilayers.

Verhoeven, J. (2007). The role of energetic ions in the development of multilayered x-ray reflection optics : an overview. Vacuum, 81, 1466–1471. doi:10.1016/j.vacuum.2007.04.016