Electron optics for dual-beam low energy electron microscopy

Dual-beam low energy electron microscopy (LEEM) is a novel imaging technique that extends LEEM applications to non-conductive substrates. In dual-beam LEEM, two flood beams with opposite charging characteristics illuminate the field of view in order to mitigate the charging effects occurring when substrates with insulating or floating surfaces are imaged in a LEEM. The negative charging effect, created by a partially absorbed mirror beam, is compensated by the positive charging effect of either a higher energy electron beam with an electron yield exceeding 1, or a photon beam. The electron-optical designs of existing and novel dual-beam LEEM approaches are reviewed and compared.