Iridium/Iridium Silicide as an Oxidation Resistant Capping Layer for Soft X-ray Mirrors

摘要

Rust on a sword, tarnish on the silverware, and a loss in reflectivity for soft x-ray mirrors are all caused by oxidation that changes the desired characteristics of a material. Methods to prevent the oxidation have varied over the centuries with the default method of a protective coating being the most common. The protective coating for x-ray mirrors is usually a self-limiting oxidized layer on the surface of the material that stops further oxidation of the material by limiting the diffusion of oxygen to the material underneath. The oxidation of an iridium on silicon capping layer was measured. A uniform molybdenum (Mo)/silicon (Si) multilayer stack was used to create a reflected standing wave of 13.4 nm light. A Si spacer and iridium (Ir) gradient were deposited on the uniform multilayer stack. The Ir gradient allowed for a range of Ir thickness (dIr) values to be measured. Atomic force microscopy (AFM), energy dispersive x-ray spectroscopy (EDS), sputtering auger electron spectroscopy (SAES) and grazing angle x-ray diffraction (GAXRD) were used to measure the surface roughness, contamination of the deposited iridium, and depth profiles.