Four-dimensional electron microscopy: Ultrafast imaging, diffraction and spectroscopy in materials science and biology

Abstract

Understanding the ultrafast evolution of atomic and electronic rearrangements under nonequilibrium conditions in organic, inorganic and biological materials plays a fundamental role in deciphering the mechanism governing chemical and biological functions. With direct visualization, the technological development of future innovative devices on the nanoscale becomes feasible. Although an enormous effort has been devoted to the comprehension and improvement of these materials and devices, the capability of investigating their dynamic behavior is hindered by the difficulty of simultaneously studying their evolution in space and time at the appropriate scales. The traditional characterization techniques and the steady-state theoretical models

Charge dynamics in aluminum oxide thin film studied by ultrafast scanning electron microscopy

“…Excitation, lifetime and decay pathways of excited states of the most common oxygen vacancies in alumina have been studied by photoluminescence [12] and cathodoluminescence [13]. The development of femtosecond electron sources [14,15] makes it now possible to study ultrafast electron dynamics by a novel technique called Ultrafast Electron Microscopy [16][17][18], which combines the spatial resolution of an Electron Microscope (EM) and the temporal resolution typical of an ultrafast optical pump-probe configuration: the sample is excited by two ultrashort pulses, one optical and one electronic, and the effect on typical electron microscope probes, such as SE, is measured as a function of the delay between the two pulses. The nanometer escape depth of the SE probe [19,20] gives the potential to address dynamics at surfaces and interfaces of today's nano-scale devices, where many applications rely on the interplay between semiconductors and insulators.…”

Scanning ultrafast electron microscopy: A novel technique to probe photocarrier dynamics with high spatial and temporal resolutions

“…Ultrafast electron microscopy [6][7][8][9][10][11] is a paradigm-shifting technique that adds nanosecond to sub-picosecond temporal resolution to the conventional electron microscopy. With a probe beam consisting of ultrashort electron pulses generated by illuminating a photocathode with ultrafast laser pulses [12][13][14], photo-induced dynamic processes [15], such as phase transition [16][17][18], structural dynamics [19,20] and electromagnetic response [21][22][23][24] etc.…”

Ultrafast generation and control of an electron vortex beam via chiral plasmonic near fields

“…S1 in the SI and also detailed in Ref. (26) and (27). Femtosecond electron pulses are generated by photoemission from a UV-irradiated LaB6 cathode, accelerated to an energy E0 = 200 keV along the z axis and then directed onto the specimen surface with parallel illumination.…”

“…This is achieved by having ultrashort single-electron wavepackets interacting with an optically-excited femtosecond chiral plasmonic near field. This interaction induces an azimuthally varying phase shift on the electron's wave function, as mapped via ultrafast transmission electron microscopy (26,27). With respect to static approaches using passive phase masks, this method offers a higher degree of scalability to small length scales and a highly efficient dynamic phase control, as inherited from the ability to manipulate the ultrafast plasmonic field.…”