Development of the crystal structure refinement in ultrafast photoexcited dynamics by four-dimensional precession electron diffraction

Ultrafast transmission electron microscopy, which integrates transmission electron microscopy and photoelectron pulses, has accelerated the investigation of the photoinduced dynamics of materials. In particular, ultrafast electron diffraction (UED) has provided qualitative insights into the dynamics of crystal structure, such as photoacoustic generation and photoinduced structural phase transitions. However, the quantitative refinement of nonequilibrium crystal structures based on diffraction intensities is challenging due to the inherent limitations of electron diffraction, such as multiple scattering and sensitivity to sample inhomogeneity.

In this study, we developed an ultrafast four-dimensional precession electron diffraction (4D-PED), which enables the crystal structure refinement in the photoexcited states. Precession electron diffraction significantly suppresses the effect of multiple scattering and sample inhomogeneity and, therefore, can be directly compared with electron diffraction simulation. As a demonstration, the dynamics of a photoinduced transition material VTe₂ are investigated by 4D-PED. The ultrafast dissolution of the characteristic V-V bond structure in VTe₂ is quantitatively revealed.