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The method of ultrafast electron crystallography makes it possible to investigate transient nonequilibrium structures, which yield decisive information about the phase transitions and coherent dynamics of the nuclei in the solid state, on the surface, and in macromolecular systems. This approach has been developed intensively to study the dynamics of nano-objects in the laser radiation field. In recent years, the electron bunch path length in the apparatus diminished significantly, while the accelerating voltage increased considerably. As a consequence, femtosecond electron pulses were obtained. A technique of radio-frequency (RF) grouping of electrons was proposed to increase the electron pulse brightness. The method of electron field emission was used to increase the spatial coherence, and ponderomotive wave front acceleration was applied to reduce the mismatch between the velocities of the light and electron pulses and to contract the electron bunches. These achievements have opened up new possibilities for studying the coherent structural dynamics of the nanomaterials with femtosecond temporal resolution. The chapter describes the experimental setups for ultrafast electron crystallography (UEC) and ultrafast electron nanocrystallography (UEnC), the theory and data analysis, and sample preparation. The presented examples include the investigation of the structural dynamics of condensed phase, surfaces, and crystals, the conversion of graphite into diamond, the behavior of molecular ensembles of fatty acid crystal bilaers, and the melting dynamics of gold nanoparticles. The results of several internationally renowned research groups are included and cited. |
