Very Low Energy Scanning Electron Microscopy of Free-Standing Ultrathin Films

Instrument and methodology is presented for very low energy scanning transmission electron microscopy. The detector system provides simultaneous acquisitions of total reflected and transmitted electron fluxes. Introductory experiments incorporated examination of ultrathin foils of gold, carbon and graphene flakes. Extremely sensitive thickness contrast obtained at units of eV is demonstrated. The phenomenon of electron transmissivity apparently exceeding 100% owing to the contribution of secondary electrons released near to the exit surface is described and discussed. [doi:10.2320/matertrans.MC200915]