Probing porosity at buried interfaces using soft x-ray resonant reflectivity

The optical constants of electron beam evaporated boron carbide are measured near boron K-absorption edge. Near the edge, the dispersion part of refractive index shows a sign reversal. Simulated reflectivity profiles near the absorption edge of boron are used to show the utility of soft x-ray resonant reflectivity as a sensitive tool for probing selected buried interfaces. This is due to high and tunable scattering contrast. The simulated resonant reflectivity profiles are sensitive to porosity and position of the porous layer containing the resonating atom. This is experimentally demonstrated through soft x-ray resonant reflectivity measurements of B4C-on-Fe bilayer structure.