Elucidating the Growth and Shape Evolution Mechanisms of Gold Decahedral Nanocrystals by <i>In Situ</i> Liquid Cell Transmission Electron Microscopy

Fivefold twinned noble-metal nanocrystals (NCs), particularly decahedral (Dh) structures, are of significant interest owing to their crystallographic structures and physicochemical properties. However, the precise and high-yield synthesis of Dh NCs remains a challenge, as they can adopt multiple shapes (<i>e.g.</i>, star, Marks, pentagonal rod, Ino, and regular Dh) with comparable formation energies. In this study, we used <i>in situ</i> liquid cell transmission electron microscopy (LCTEM) to directly visualize the growth and shape evolution of gold Dh by systematically tuning experimental parameters including electron dose rate, precursor concentration, and ligand additives. By modulating the relative growth rates along the vertices (<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msub><mml:mover><mml:mi>v</mml:mi><mml:mo>¯</mml:mo></mml:mover><mml:mi>v</mml:mi></mml:msub></mml:math>) and the twin boundaries (<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:msub><mml:mover><mml:mi>v</mml:mi><mml:mo>¯</mml:mo></mml:mover><mml:mi>t</mml:mi></mml:msub></mml:math>) of 5-fold twinned seeds, we achieve controllable structural transformation between star and regular Dh. Furthermore, the introduction of different surfactants leads to the structural transformation from Dh to a truncated or elongated pentagonal nanorod, respectively. Statistical quantitative analyses reveal a critical size threshold for the shape evolution of Dh, dependent on the growth rate, surfactant type, and concentration. Our study details the structural transformation routes among different Dh shapes, thereby deepening the understanding of their growth and shape evolution mechanisms.