Perturbation to the resonance modes by gold nanoparticles in a thin-film-based x-ray waveguide

We demonstrate, for the first time, that the resonance modes in a thin-film-based x-ray waveguide are extremely sensitive to the electron density distribution in the thin film. The resonance modes can be effectively altered by diffusion of a gold nanoparticle submonolayer embedded in the waveguide. Such a perturbation can be observed with dramatic change in x-ray reflectivity and fluorescence data in the low-angle (< 0.5 degrees) resonance regime. Conversely, the quantitative analysis of the perturbation to the resonance modes, x-ray reflectivity, as well as the resonantly excited x-ray fluorescence from gold nanoparticles can be exploited to accurately determine the absolute gold distribution within the profile of the thin-film-based waveguide with subnanometer resolution.