The technique of photo-electron emission microscopy (PEEM) is based on imaging of photo excited electrons from a surface. Typically ultra violet (UV) light above the work function of a metal will cause electrons to be emitted from a surface. Since photo excited electrons originate very near to the surface, they essentially reflect the electronic structure of the surface. These electrons may be accelerated and imaged, and the image will reflect the properties of the surface.While the PEEM technique has been understood in a basic sense for many years, it has been limited by the lack of high intensity UV light sources. The most crucial part of the electron imaging system for PEEM, the objective lens, is essentially the same as for the sister technique of low energy electron microscopy (LEEM), and advances in electron optics capabilities have been exploited both for LEEM and for PEEM.
Theory of ballistic electron emission microscopy