Temporal resolution in transmission electron microscopy using a photoemission electron source.

Temporal resolution in transmission electron microscopy has progressed to the sub-picosecond level with the stroboscopic method using a photoemission mechanism with an ultrafast laser for the electron gun. Time-resolved transmission electron microscopy in conjunction with a photocathode-type electron source pumped by a pulsed laser has been actively developed to exceed sub-nanosecond time resolution. Here, we provide an overview of the trends in this field and discuss the measurement targets that can be obtained by time-resolved measurements. Furthermore, we consider the types and characteristics of photocathode materials and their related physical quantities for evaluation of the electron beam properties. Experimental results obtained with time-resolved transmission electron microscopy using a semiconductor photocathode that has a surface with a negative electron affinity are presented, and application results based on quantum mechanics are given. We also describe new techniques for improving the time-resolution and new applications of pulsed electron beams in electron microscopy, and discuss the measurement targets that are expected for time-resolved electron microscopy.