Fabrication and characterisation of ultra-thin tungsten–carbon (W/C) and platinum–carbon (Pt/C) multilayers for X-ray mirrors

Abstract

Ultra-thin tungsten–carbon (W/C) and platinum–carbon (Pt/C) multilayers were fabricated using dc magnetron sputtering. The bilayer period and the total number of layers were varied for both systems to ascertain the X-ray reflectance response. As a preliminary investigation, in situ resistance measurements were made to determine the minimum continuous single layer thickness that could be produced for W and Pt. We used X-ray reflectivity to monitor the reflectance from the first order peaks and the number of layers in the multilayered structures. X-ray photoelectron spectroscopy showed that a distinct intermixing layer develops in both W/C and Pt/C. A repeating four-layer model was developed to characterise the X-ray reflectivity patterns with mixed interface layers. The model accounts for all the essential features in the observed reflectivity data with particular attention given to layer thickness and interfacial roughness. Assessment of the films by indentation indicated that they are mechanically reliable with no cracking events or delamination obvious from the load–displacement curves indicating excellent adhesion. An anomalous improvement in hardness and Young’s modulus with increasing number of layers was observed. The present results indicate that high-quality ultra-thin W/C and Pt/C tailored multilayer films produced by dc magnetron sputtering show considerable promise as mirrors for high energy X-ray applications.