NSLS-II   |   Brookhaven National Laboratory

Recent Advances in Cathode Lens Microscopy

Rudolf Tromp, IBM T.J. Watson Research Center

The key characteristic of Low Energy Electron Microscopy (LEEM) and Photo Electron Emission Microscopy (PEEM) is the use of a cathode objective lens, in which the sample is immersed in a strong electric field to extract the low energy electrons from the sample into the image forming electron optical column. Traditionally, the spatial resolution has been limited by the combination of chromatic and spherical aberrations of this cathode lens. In most PEEM experiments (in particular when performed with synchrotron radiation) chromatic aberration dominates, while in LEEM spherical aberration is more important. Recently, the correction of these leading aberrations by combination of the cathode lens with a catadioptric system (electron lens + electron mirror) has been demonstrated experimentally, setting a record resolution in LEEM below 2 nm, just a few times the electron wavelength [1]. In PEEM, 5 nm resolution has been achieved. The most advanced microscopes also incorporate an imaging electron energy filter that allows for spectroscopic imaging, as well as angle- and energy-resolved electron spectroscopy from micrometer-sized selected sample areas. Thus, these new instruments open up new areas of research, in particular when combined with powerful new light sources. In this talk, I will review these recent advances, and discuss the potential for additional future developments.