Abstract
A study of the materials properties of WC/SiC multilayer coatings is presented. We investigated the dependence of interface and surface roughness, intrinsic stress, microstructure, chemical composition, and stoichiometry as a function of multilayer period and in some cases compared these to W/SiC multilayer systems. The WC/SiC material pair forms multilayers with extremely smooth and sharp interfaces and both materials remain amorphous over a wide range of thicknesses. These properties are desirable for multilayer-based high-resolution diffractive x-ray optics, such as multilayer Laue lenses (MLLs), which require very thick films in which the layer spacing varies considerably. Thermal and structural stability studies show that WC/SiC multilayers have exceptional thermal stability, making this an extremely robust and favorable material pair for MLLs and other multilayer-based X-ray optical elements.
Highlights
Multilayers are “artificial crystals” that can be designed and optimized for specific X-ray optical applications
We explore the properties of the tungsten carbide/silicon carbide (WC/SiC) multilayer system, which has remarkably low interfacial roughness and can form nanometer or even sub-nanometer period multilayers [2,3]
Previous studies showed that replacing tungsten with tungsten carbide and silicon with silicon carbide further improves the quality of layer interfaces, which in turn allows for fabrication of ultra-short period multilayer coatings pushing the operative working range to photon energies higher than 200 keV [2,3,15]
Summary
Multilayers are “artificial crystals” that can be designed and optimized for specific X-ray optical applications. We explore the properties of the tungsten carbide/silicon carbide (WC/SiC) multilayer system, which has remarkably low interfacial roughness and can form nanometer or even sub-nanometer period multilayers [2,3] This material pair was investigated as a potential coating for hard X-ray telescopes, which require ultra-thin periods. A MLL focuses X-rays only in one direction so two MLLs with slightly different focal lengths are needed to produce a focused spot, analogous to two crossed cylindrical lenses These two MLLs are produced from multilayers made in two separate deposition runs. W/SiC multilayers, in particular the study of their properties (interface roughness, microstructure, chemical composition, stoichiometry and stress) as a function of multilayer period Their stability as a function of temperature and annealing time is investigated as well
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