Perspective: 4D ultrafast electron microscopy—Evolutions and revolutions

Abstract

In this Perspective, the evolutionary and revolutionary developments of ultrafast electron imaging are overviewed with focus on the “single-electron concept” for probing methodology. From the first electron microscope of Knoll and Ruska [Z. Phys. 78, 318 (1932)], constructed in the 1930s, to aberration-corrected instruments and on, to four-dimensional ultrafast electron microscopy (4D UEM), the developments over eight decades have transformed humans’ scope of visualization. The changes in the length and time scales involved are unimaginable, beginning with the micrometer and second domains, and now reaching the space and time dimensions of atoms in matter. With these advances, it has become possible to follow the elementary structural dynamics as it unfolds in real time and to provide the means for visualizing materials behavior and biological functions. The aim is to understand emergent phenomena in complex systems, and 4D UEM is now central for the visualization of elementary processes involved, as illustrated here with examples from past achievements and future outlook.

Structural Chemistry: The Last 50 Years as Seen by an X‐ray Crystallographer

“…Zewail has developed ultrafast electro diffraction (UED) to produce such movies, for example, for breaking bonds in molecules in the gas phase. Similarly, with ultrafast electron crystallography (UEC), phase transitions in crystals have been delineated and transient structures characterized; the latter are not accessible by equilibrium methods ,. These techniques are also about to become available for X‐rays at free‐electron laser facilities.…”

Tipping solutions: emerging 3D nano-fabrication/ -imaging technologies

“…If 3D nanoscale imaging could be taken for granted using electron-based scanning tunneling microscopy (STM), transmission electron microscopy (TEM), and SEM, the next advancements are expected with the addition of a 4th time dimension [127]. Nanoscale processes are fast and require ultra-short laser technologies to provide resolutions down to a single optical cycle.…”

From structure to structural dynamics: Ahmed Zewail's legacy

“…Zewail devoted the last 10 years or so of his life to applying and further developing this method 154 . A striking example of ultrafast real-time and real-space imaging using UEM and UEC is his work on gold and graphite 155 .…”

“…A striking example of ultrafast real-time and real-space imaging using UEM and UEC is his work on gold and graphite 155 . He went on developing new tools, which each by itself could, and in some case did, evolve into a separate new field 154 . One of the last studies he conducted prior to his passing was carried out in conjunction with one of us on the study of 4DEM in the study of single-site Ti photocatalysists, 156 measuring the trapping time of the electron at pentacoordinated Ti centres 157 .…”