Nanometer Resolution Holography with the Low Energy Electron Point Source Microscope

Abstract

Holography with the low energy electron point source (LEEPS) microscope has been explored for imaging of unstained biomolecules. DNA ropes are prepared on microfabricated sample supports and imaged with coherent 40 eV electrons emitted from a W(111) point source. We reconstruct the electron wave front and show that the correct source-to-object distance can be determined by analyzing the focus of the reconstruction. Upon variation of the source position, the reconstruction shows reproducible object features with an object focus located at the correct tip-to-object distance with a depth of sharpness of ∼40 nm. It is argued that reconstruction artifacts can be identified by their focus behavior and that only features in the first focus – coming from the screen – truly relate to the object's structure.