Microstructure, Stress and Optical Properties of Ge/C Multilayers

Abstract

Recent studies of x-ray multilayers have focused on understanding and controlling the roughness at the interfaces to achieve high reflectivity. In general, the structure at the interfaces depends on the microstructure inside the layers, and on the interactions between the layer materials. Presumably, in systems in which the components do not react with each other, such as Ru/C and Ge/C, minimum intermixing and diffusion should allow relatively sharp and well-defined interfaces. For this reason, the germanium and carbon pair is studied as a potential candidate for the x-ray multilayer mirrors. Some early materials studies showed that no compounds of Ge and C were detected up to 3170 °C [1]. Early measurements also indicated virtual insolubility of C in Ge, or Ge in graphite [2]. These materials science properties suggest that Ge/C may be able to form sharp multilayer interfaces and hence may provide significant specular x-ray reflectance, especially at wavelengths just above the carbon K edge (4.4 nm), where interfacial microstructure and morphology play a critical role in the determination of reflectivity. In this paper, we present results from a systematic study of the microstructure, stress, and optical properties of as-prepared and annealed Ge/C multilayers having periods and relative individual layer thicknesses typical for soft x-ray applications.