With improved optics and intensity, X-ray reflectivity can now provide subnanometre vertical resolution of surface features.
Imaging surfaces with atomic resolution is usually the domain of surface scanning probes. However, these techniques are not always well suited to real-time measurements or harsh chemical environments — in some cases the scanning tip can react with the underlying surface. Although X-ray imaging techniques can meet many of these challenges, they typically lack the spatial resolution.
Now, Paul Fenter and co-workers1 from Argonne National Laboratory in the USA show that X-ray reflectivity can be pushed to image subnanometre defects on a surface. In Fenter’s experiment, X-rays are tightly focused onto a surface and the reflected X-rays are collected by a charge-coupled device camera. On perfectly smooth surfaces, there is no change in the reflected intensity as the beam moves across the surface. However, when the beam hits a surface bump or defect, some of the reflected X-rays have a slightly different path length and the intensity changes, which allows the surface topography to be mapped.
Surface growth or chemical reactions often occur at ‘steps’ in a partially completed monolayer. This X-ray imaging technique could be used to monitor real-time step growth, both non-invasively and in reactive chemical environments.
Fenter, P. et al. Nature Phys. (2006). 10.1038/nphys419