A REFLECTION ELECTRON-MICROSCOPE FOR IMAGING OF FAST PHASE-TRANSITIONS ON SURFACES

A reflection electron microscope for ultrashort-time imaging of laser-induced processes on surfaces was developed. The instrument is based on a conventional transmission electron microscope modified for high-energy electron reflection, and, in addition, equipped with a laser-pulsed high-brightness electron gun, an interaction chamber, and a tilting unit. Images with exposure times of ≤20 ns of transient surface processes can be obtained. The spatial resolution depends on the exposure time and is limited by a compromise between shot noise in the electron image, chromatic aberration of the objective lens, and radiation damage due to the illuminating electron beam. The performance of the microscope is demonstrated by short exposure time images of laser pulse treated bulk GaAs and Au films on Si showing evaporation, flow, and capillary waves, proceeding within 10-500 ns.