COMMUNICATION pubs.acs.org/JACS 4D Scanning Ultrafast Electron Microscopy: Visualization of Materials Surface Dynamics

ABSTRACT: The continuous electron beam of conven-tional scanning electron microscopes (SEM) limits the temporal resolution required for the study of ultrafast dynamics of materials surfaces. Here, we report the devel-opment of scanning ultrafast electron microscopy (S-UEM) as a time-resolved method with resolutions in both space and time. The approach is demonstrated in the investigation of the dynamics of semiconducting and metallic materials visualized using secondary-electron images and backscatter-ing electron diffraction patterns. For probing, the electron packet was photogenerated from the sharp field-emitter tip of the microscope with a very low number of electrons in order to suppress spacecharge repulsion between elec-trons and reach the ultrashort temporal resolution, an improvement of orders of magnitude when compared t