Electron Beam-Assisted Au Nanocrystal Shear and Rotation.

Understanding metastable structural transitions under beam irradiation is essential for the phase engineering of nanomaterials. However, in situ studies of beam-induced structural transitions remain challenging. This work uses an electron beam in aberration-corrected high-angle annular dark-field scanning transmission electron microscopy to irradiate Au nanocrystals at room temperature. The electron beam-induced thermal spike is estimated by electron energy loss spectroscopy and the two-temperature model. The thermal spike drives a transition in the Au lattice from nonclose-packed (311) and (220) planes to close-packed (111) planes through nonrandom lattice rotation. This transition is attributed to the gradient distribution of shear strain at the grain boundaries, with a critical shear strain of approximately 0.2 for the shift from the (220) to the (111) planes. These insights reveal the origins of nanocrystal shear and rotation under electron beam irradiation, providing strategies for precise nanocrystal manipulation using beam-assisted techniques.