Twinned Gold Nanoparticles under Growth: Bipyramids Shape Controlled by Environment

Abstract

The structure of (Au) bipyramids, very promising for their specific plasmonic properties, is fully analyzed for gradual stages of growth. From combined use of HRTEM (high resolution transmission electronic microscopy) in specific conditions and SAED (selected area electronic diffraction) analysis, the atomic structure of these elongated objects of different sizes is extracted (from 2 to 60 nm). In the case of silver(I)-assisted growth from citrate capped seeds, a clear pentatwinned structure, made by the superimposition of specific pairs of crystallographic zones is found for the different size nanoparticles representing the different steps of the growing bipyramids. The experimental results were analyzed in the framework of a recent atomistic approach developed for metal−environment interactions to account for the stability of multitwinned nanorods or bipyramids in a complex environment. Efficient in describing the multitwinned nanoparticles and the drastic effects of environment on the stabilization of elongated multitwinned shapes, this model supports the experimental features of bipyramids and nanorods formation from citrate seeds as a function of the nature of the surface chemical ligands: citrate seeds in a growth solution prepared without silver(I) yields the formation of a few pentatwinned nanorods, while the silver(I)-assisted growth process mainly leads to pentatwinned bipyramids. The conservation of a bulk pentatwinned structure inherited from isotropic decahedral (i-Dh) seeds all along the growth is retrieved by this approach for two different environments.

Role of the environment in the stability of anisotropic gold particles

“…Before concluding, we would like to point our that, very recently, the present model has successfully accounted for the existence of different types of elongated MT gold particles (either nanorods or bipyramids), synthesized in a CTAB solution in the presence or in the absence of silver(I), by an adequate choice of parameters e and p. 38…”

Seed‐Mediated Growth of Colloidal Metal Nanocrystals

“…In contrast to singly twinned species,t he incorporation of multiple twin boundaries results in strain energies that increase with particle size,t hus making them only stable at relatively small sizes. singly twinned NR NR [63,81,189] [ 80,190] [60e] [191] decahedron NR [192] [ 89, 90, 185b, 193] [204] NR [194] icosahedron NR [195] [ 89-91, 93, 185b, 196] [87] These growth processes are driven by an inhomogeneous distribution of strain and twin defects.…”

“…Whereas single-crystal and singly twinned seeds can be readily made with {111}, {100}, or {110} facets on the surface by controlling the experimental conditions,multiply twinned seeds are,w ith very few exceptions,t ypically enclosed by {111} facets. [87d] 80,190] [60e] [191] decahedron NR [192] [ 89, 90, 185b, 193] [204] NR [194] icosahedron NR [195] [ 89-91, 93, 185b, 196]…”

Rapid synthesizing of gold nanobipyramids

“…As shown by e.g. Canbek et al silver(I)assisted growth will favor the formation of pentatwinned bipyramids [16] and, as furthermore explained by Liu et al during the formation of GBPs, the absorption of Br − on certain facets of gold seeds inhibits the growth in the corresponding direction [21]. In the present work, we synthesize GBPs with a CTAB concentration of 40%, in which hexagonal liquid crystal is the major phase.…”

“…Our method utilizes a hexagonal liquid crystal (40% CTAB solution) as a template growth frame [15], which suggests that the formation of bipyramids is the result of a liquid crystal accelerated growth process. Several reports of synthesis of gold NPs using CTAB water solution, with typical processing times of the order of 12 h, exist [16][17][18], however the method of synthesizing GBPs as presented here has to our knowledge previously not been reported.…”