Cr/Sc/Mo multilayer for condenser optics in water window microscopes

We developed a high-reflectance wide-reflection-band multilayer for application in condenser optics in microscopes working in the water window soft X-ray region. Grazing incidence 20 period Cr/Sc multilayers suffered damage when they were deposited on toroidal substrates, possibly because of the compressive stress of the thick Sc layers present in them. To avoid such damages, we minimized the Sc layer thickness by using a Cr/Sc/Mo 10 tri-layer structure. The resulting multilayer had a periodic thickness of 9.8 nm to reflect 310 eV soft X-ray at an angle of incidence of 77.2°. The multilayers were successfully deposited on Si wafers and concave BK7 substrates by ion beam sputtering with no damage. The peak height, angular acceptance, and spectral width of the measured reflectance of the Cr/Sc/Mo 10 tri-layer were 27.4%, 1.5°, and 35 eV, respectively, showing that it was suitable for condenser optics of broadband high- Z plasma soft X-ray sources.