Reconstruction of evolving nanostructures in ultrathin films with X-ray waveguide fluorescence holography

摘要

In the normal XFH mode , an emitting atom (i.e. emitter) gives out a spherically outgoing X-ray fluorescence wave. An object wave is formed when this outgoing wave is scattered by a nearby atom (i.e. scatterer) and then interferes with the unperturbed outgoing reference wave, producing a spatially distributed hologram. Lines in blue and gold colors represent waves of elastic and fluorescence energies, respectively. In the inverse XFH mode , the exciting wave at the emitter is a result of interference of the unperturbed incident wave and the scattered incident wave from the scatterer. The hologram is constructed by scanning the incident wave and recording the integrated fluorescence intensity at a fixed detector position. In the mixed-mode X-ray waveguide fluorescence holography (XWFH) at grazing-incidence and exit angles, X-ray standing waves are created within the waveguide for both the elastic and fluorescence energies. The intensity of fluorescence leaving the waveguide concentrates at discrete exit angles, producing a concentric cone-like hologram whose axis of rotation is perpendicular to the film surface. The forward elastic scattering is also modulated by the waveguide and its angular dependence is measured via grazing-incidence small-angle X-ray scattering (GISAXS).