Chen, BinFu, XuewenTang, JauLysevych, MykhayloTan, Hark HoeJagadish, ChennupatiZewail, Ahmed H2021-06-092021-06-090027-8424http://hdl.handle.net/1885/236980Eutectic-related reaction is a special chemical/physical reaction involving multiple phases, solid and liquid. Visualization of a phase reaction of composite nanomaterials with high spatial and temporal resolution provides a key understanding of alloy growth with important industrial applications. However, it has been a rather challenging task. Here, we report the direct imaging and control of the phase reaction dynamics of a single, as-grown freestanding gallium arsenide nanowire encapped with a gold nanoparticle, free from environmental confinement or disturbance, using four-dimensional (4D) electron microscopy. The nondestructive preparation of as-grown free-standing nanowires without supporting films allows us to study their anisotropic properties in their native environment with better statistical character. A laser heating pulse initiates the eutectic-related reaction at a temperature much lower than the melting points of the composite materials, followed by a precisely time-delayed electron pulse to visualize the irreversible transient states of nucleation, growth, and solidification of the complex. Combined with theoretical modeling, useful thermodynamic parameters of the newly formed alloy phases and their crystal structures could be determined. This technique of dynamical control aided by 4D imaging of phase reaction processes on the nanometer-ultrafast time scale opens new venues for engineering various reactions in a wide variety of other systems.This work was supported by Air Force Office of Scientific Research Grant FA9550-11-1-0055S in the Gordon and Betty Moore Foundation for Physical Biology Center for Ultrafast Science and Technology at California Institute of Technology. M.L., H.H.T., and C.J. thank the Australian Research Council for support and the Australian National Fabrication Facility for access to the epitaxial facilities used in this work.application/pdfen-AU© 2017 The Authorshttps://creativecommons.org/licenses/by/4.0/phase reactionAu/GaAs nanowiresstructural dynamicseutectic dynamics4D electron microscopy201710.1073/pnas.17087611142020-11-23Creative Commons Attribution licence