Four-Dimensional Electron Microscopy

Abstract

Ultrafast Imaging: Optical microscopy is generally limited in resolution by the wavelength of light incident on the substrate. Because these wavelengths, even in the ultraviolet, are on the order of hundreds of nanometers, electron beams have long been used instead to probe structural detail at the smallest scale. While offering exceptional spatial resolution, electrons repel one another and so cannot be compressed in time as easily as a pulse of light. Electron microscopy has thus traditionally been a comparatively static characterization method. Zewail (p. 187 ) reviews recent technological developments in stripping down the electron pulses used for imaging that have been able to introduce time resolution of trillionths of a second to this spatially precise technique. Local transformations ranging from graphite film oscillations to iron phase transitions have been tracked in this manner.