PNNL

Abstract

Morphology control of anisotropic metal nanocrystals plays an important role in tuning shape-dependent physicochemical properties for various applications, but underlying understanding of their anisotropic growth mechanism remains a great challenge. Here, we investigate the formation of Au penta-twinned nanorod by in situ liquid cell transmission electron microscopy (LC-TEM). It is found that a truncated-decahedron forms in the absence of cetyl-trimethyl ammonium bromide (CTAB), whereas in the presence of CTAB a reentrant groove appears in decahedron to relieve strain during the nanorod formation, which induces the formation of {100} facets. The growth dynamics of penta-twinned nanorod implies that CTAB molecules can promote the nanorod growth by selectively inhibiting atom addition to {100} facets. Density functional theory (DFT) simulations confirm that the partial relieve of strain energy of decahedron nanoparticle is caused by the adsorption of Br- ions. Moreover, the selective adsorption of CTAB lowers the surface energy of {100} facets, resulting in the nanorod growth along the [110] direction. Based on the appearance of reentrant groove and growth dynamics unraveled by LC-TEM, the synergy of strain and surface energy tuning by additives is discovered. The study provides an in-depth insight into the anisotropic growth of nanorods and lays foundations for controlled synthesis of nano-materials.