Since W. von Laue discovered X-ray diffraction using a zinc sulfide single crystal in 1912, single crystals including Si, Ge, LiF, etc. have been used as analyzing crystals for X-ray analysis. However, as the research and applications of X-rays advanced, the wavelength region also extended significantly. Analyzing crystals made of single crystals can no longer cover all X-ray analysis requirements. A new type of analyzing crystals is each made of a periodic layer structure with a period longer than the wavelength of X-rays. For example, if two different kinds of thin layers are overlaid alternately to form a periodic multilayer structure, the multilayer can be used as an analyzing crystal for X-ray analysis. In fact, such a structure was proposed a long time ago after the discovery of X-ray diffraction. However, it was not until the 1970s that scientists were able to make multilayer devices because of the advances of sophisticated ultra thin-film deposition techniques such as electronbeam evaporation, sputtering deposition, etc. The development of multilayer X-ray optical devices has advanced rapidly since the 1970s. In 1980s, the Osmic, Inc. (now Rigaku Innovative Technologies, RIT) in the US commercialized multilayer devices for X-ray fluorescence analysis under the brand name of “Ovonyx”. The multilayer optical devices have now been widely used in X-ray diffraction, X-ray fluorescence, and X-ray projection/ imaging technologies.
A multilayer optical device is also called “artificial lattice,” “artificial multilayer film”, or “artificial stacked film”. In this article, we call it “multilayer optics,” or simply, “multilayer.”