• PNAS Anthropology Portal
  • Sign-up for PNAS eTOC Alerts

Dynamics and control of gold-encapped gallium arsenide nanowires imaged by 4D electron microscopy

  1. Ahmed H. Zewaila,2
  1. aPhysical Biology Center for Ultrafast Science and Technology, Arthur Amos Noyes Laboratory of Chemical Physics, California Institute of Technology, Pasadena, CA 91125;
  2. bAustralian National Fabrication Facility, Research School of Physics and Engineering, The Australian National University, Canberra, ACT 2601, Australia;
  3. cDepartment of Electronic Materials Engineering, Research School of Physics and Engineering, The Australian National University, Canberra, ACT 2601, Australia
  1. Edited by Charles M. Lieber, Harvard University, Cambridge, MA, and approved October 26, 2017 (received for review May 26, 2017)


Imaging chemical/physical reaction dynamics at nanoscale interfaces of a composite nanostructure requires resolutions in both space and time. Using single-pulse methodology, we directly and visually capture the irreversible eutectic-related phase reactions of a single, same metal/semiconductor nanowire at nanometer–nanosecond spatiotemporal resolution by 4D electron microscopy. With a nondestructive free-standing sample preparation free from environmental disturbance that is important for statistical investigation, we have both qualitatively and quantitatively elucidated the transient phase reactions and obtained important physical properties of the newly formed phases, such as latent heat and specific heat. Our work provides an efficient way of quantitatively determining physical properties of a nanoscale object with a tiny small quantity, especially when not available in bulk counterparts.


Eutectic-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 free-standing 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.


  • ?1To whom correspondence may be addressed. Email: bchen5{at}caltech.edu or jautang{at}caltech.edu.
  • ?2Deceased August 2, 2016.

  • Author contributions: B.C. and A.H.Z. designed research; B.C., X.F., and M.L. performed research; B.C., J.T., and A.H.Z. contributed new reagents/analytic tools; B.C., X.F., J.T., M.L., H.H.T., C.J., and A.H.Z. analyzed data; and B.C., X.F., J.T., M.L., H.H.T., C.J., and A.H.Z. wrote the paper.

  • The authors declare no conflict of interest.

  • This article is a PNAS Direct Submission.

  • This article contains supporting information online at www.danielhellerman.com/lookup/suppl/doi:10.1073/pnas.1708761114/-/DCSupplemental.

Online Impact

                                    1. 99132880 2018-01-23
                                    2. 802899879 2018-01-23
                                    3. 295573878 2018-01-23
                                    4. 352668877 2018-01-23
                                    5. 984633876 2018-01-23
                                    6. 545928875 2018-01-23
                                    7. 976569874 2018-01-23
                                    8. 871324873 2018-01-23
                                    9. 263462872 2018-01-23
                                    10. 577161871 2018-01-23
                                    11. 255603870 2018-01-23
                                    12. 117346869 2018-01-23
                                    13. 90982868 2018-01-23
                                    14. 663415867 2018-01-23
                                    15. 793874866 2018-01-23
                                    16. 843582865 2018-01-23
                                    17. 864971864 2018-01-22
                                    18. 258841863 2018-01-22
                                    19. 957295862 2018-01-22
                                    20. 553518861 2018-01-22