Ion-Bombardment of X-Ray Multilayer Coatings - Comparison of Ion Etching and Ion Assisted Deposition

The effects of two forms of ion bombardment treatment on the reflectivity of multilayer X-ray coatings were compared: ion etching of the metal layers, taking place after deposition, and ion bombardment during deposition, the so-called ion assisted deposition. The ion beam was an Ar+ beam of 200 eV, and the multilayer coatings studied were W-C, Ni-C and W-Si. Cu K-alpha reflection measurements (lambda = 0.154 nm) of Ni-C and W-C multilayer coatings having ion etched metal layers showed considerably higher reflectivities than those of coating having as-deposited layers; a factor 2.5 and 4, respectively. Ion etching of tungsten layers in W-Si coatings did not result in enhanced reflectivities. We applied ion assisted deposition to nickel in Ni-C multilayer coatings. We observed enhanced in-situ soft X-ray reflectivities of ion assisted deposited nickel layers with respect to as-deposited layers. However, the observed increases were less than those obtained by ion etching, which we ascribe to bombardment-induced intermixing at the underlying Ni-C interfaces. Finally we demonstrate that during ion assisted deposition and ion etch rates are not additive, but that the ion etch rate increases. The indicates that during deposition a number of atoms are temporarily loosely bound to the surface.