It was noted that the access to X-rays, of third-generation synchrotron radiation sources, permitted studies to be made of dynamics in metallic systems at grazing incidence. By combining grazing-incidence reflection of X-rays with the nuclear resonant scattering of synchrotron radiation, it was possible to make depth-selective investigations of hyperfine parameters and diffusion phenomena in Fe and its compounds. An unique feature of this method was its sensitivity to the near-surface motion of atoms. The depth sensitivity could be varied from 2 to 10nm. A 300nm-thick 57Fe sample, grown by molecular beam epitaxy onto a cleaved MgO(001) substrate, was investigated. The diffusion coefficient for Fe in the near-surface (about 2nm) layer was almost 2 orders of magnitude greater than that in bulk body-centered cubic Fe at the same temperature.

Enhanced Iron Self-Diffusion in the Near-Surface Region Investigated by Nuclear Resonant Scattering. M.Sladecek, B.Sepiol, M.Kaisermayr, J.Korecki, B.Handke, H.Thiess, O.Leupold, R.Rüffer, G.Vogl: Surface Science, 2002, 507-510, 124-8