Adding depth sensitivity to photoelectron microscopy using the standing wave/wedge method

Photoelectron microscopy (PEEM) is by now a well-established technique for studying many types of multilayer or multicomponent structure, including samples of relevance to spintronics, semiconductor technology, and polymer-based materials. The lateral resolution in such microscopes is typically 20 nm, but with the prospect of going down to ca. 1 nm in the near future. However, resolution perpendicular to the surface is not inherent in PEEM measurements, and we here discuss a novel method for providing this at sub-nm resolution, by exciting the photoelectrons with a standing wave created by soft x-ray reflection from a multilayer substrate, and growing one layer of the sample in a wedge form. This standing wave/wedge method has been demonstrated for the first time in measurements with a PEEM located at BESSY in Berlin.