While the 3D static atomic structure of materials is important to understand their functionality, there exists significant interest to reveal the structure and dynamics of materials at 4D atomic resolution to study processes such as nucleation and growth. We developed 4D (the three dimensions of space plus the fourth dimension of time) atomic electron tomography to directly image the dynamics of structural changes at the atomic scale.

Nucleation is the process by which tiny clusters of atoms or molecules (called “nuclei”) begin to coalesce. Nucleation plays a critical role in phenomena as diverse as the formation of clouds and the onset of neurodegenerative disease. Using FePt nanoparticles as a model system, Zhou et al. have recently studied the dynamics of early stage nuclei in an ex-situ AET experiment. The initiation of nucleation on the surface of the nanoparticles is observed and the structure and dynamics of the same nuclei undergoing growth, fluctuation, dissolution, merging and/or division is captured. These results not only show a never-before-seen view of nucleation but also indicate that a theory beyond classical nucleation theory is needed to describe early-stage nucleation at the atomic scale. This experiment adds a new dimension (time) to AET (i.e. 4D AET), capturing atomic motion in materials in four dimensions, which is currently not accessible by any other experimental methods.

4D AET will potentially serve as a powerful tool in studying many fundamental problems such as phase transitions, atomic diffusion, grain boundary dynamics, interface motion, defect dynamics and surface reconstruction.

Reference

1. J. Miao, P. Ercius and S. J. L. Billinge,  Atomic electron tomography: 3D structures without crystals, Science, 353, aaf2157 (2016).

2. Y. Yang*, J. Zhou*, F. Zhu*, Y. Yuan*, D. Chang, D. S. Kim, M. Pham, A. Rana, X. Tian, Y. Yao, S. J. Osher, L. Hu, P. Ercius, J. Miao. Determining the three-dimensional atomic structure of an amorphous solid. Nature, 592, 60–64 (2021).

3. J. Zhou*, Y. Yang*, Y. Yang, D. S Kim, A. Yuan, X. Tian, C. Ophus, F. Sun, A. K. Schmid, M. Nathanson, H. Heinz, Q. An, H. Zeng, P. Ercius, J. Miao. Observing crystal nucleation in four dimensions using atomic electron tomography. Nature, 570, 500–503 (2019)