Characterization of Pd/Y multilayers with B₄C barrier layers using GIXR and X-ray standing wave enhanced HAXPES

Pd/Y multilayers are high-reflectance mirrors designed to work in the 7.5–11 nm wavelength range. Samples, prepared by magnetron sputtering, are deposited with or without B₄C barrier layers located at the interfaces of the Pd and Y layers to reduce interdiffusion, which is expected from calculating the mixing enthalpy of Pd and Y. Grazing-incident X-ray reflectometry is used to characterize these multilayers. B₄C barrier layers are found to be effective in reducing Pd–Y interdiffusion. Details of the composition of the multilayers are revealed by hard X-ray photoemission spectroscopy with X-ray standing wave effects. This consists of measuring the photoemission intensity from the samples by performing an angular scan in the region corresponding to the multilayer period and an incident photon energy according to Bragg's law. The experimental results indicate that Pd does not chemically react with B nor C at the Pd–B₄C interface while Y does react at the Y–B₄C interface. The formation of Y–B or Y–C chemical compounds could be the reason why the interfaces are stabilized. By comparing the experimentally obtained angular variation of the characteristic photoemission with theoretical calculations, the depth distribution of each component element can be interpreted.