Multilayer Fresnel Zone Plate with High-Diffraction Efficiency: Application of Composite Layer to X-Ray Optics

Abstract

Composite materials are widely utilized in a number of fields, such as materials science, metallurgy, polymer science, interface science, mechanical engineering and aerospace engineering. In this chapter, as an application of a composite material layer (thin film) produced by co-sputtering to the hard X-ray focusing optical technique, a multilayer Fresnel zone plate (ML-FZP) with high diffraction efficiency is described. X-rays in the energy region of 100 – 2,000 eV (2 keV) are called soft X-rays (Snigirev & Snigireva, 2008), while those with higher energy are called hard X-rays. Soft X-rays, especially in the “water window” region (Spiller, 1994), are mainly used in the field of biotechnology. On the other hand, hard X-rays are used in various research fields, including materials science, environmental science and medical science. High brilliant hard X-ray beams with submicronor nanometre-scale spot sizes generated by third-generation synchrotron radiation (SR) facilities such as the APS (USA), ESRF (France) or SPring-8 (Japan), especially for use in the high-energy region, have great potential for use in various fields of research. They are remarkably powerful tools. Recently, higher energy (shorter wavelength) X-ray beams above 20 keV have been utilised in a number of applications, including residual stress measurement in metal matrix composites at 40 keV (Korsunsky & Wells, 2000), local strain measurement within bulk materials at 52 and 90 keV (Lienert et al., 2000), a novel experimental scheme for high-resolution X-ray analysis of deeply buried interfaces at 71.3 keV (Reichert et al., 2003), study of the ice–SiO2 model interface, using X-ray transmission–reflection scheme at 71.3 keV (Engemann et al., 2004), mapping of Sr in (Ba,Sr)TiO3 dielectric ceramics using Ka fluorescence X-rays at 25 keV (Takeuchi et al., 2005), micro-XRF (X-ray fluorescence) analysis of heavy metals in the cells of hyperaccumulator plants at 37 and 75 keV (Terada et al., 2004; Terada et al., 2005), non-destructive imaging of integrated circuits (ICs) at 25 keV, and imaging of Au mesh by three types of X-ray microscopy at 82 keV (Awaji et al., 2003; Suzuki et al., 2006). In addition, microscopic imaging of Au mesh at 200 keV has also been reported (Kamijo et al., 2009). Many types of focusing optics have been developed for hard X-rays and their focusing abilities have been improved over the past two decades. Especially within the last several years, there have been dramatic changes in the performances of focusing optics. The main types of focusing optics and their performances are shown in Fig. 1.