Origin of the rich polymorphism of gold in penta-twinned nanoparticles

TL;DR

This study reveals how the crystallographic structure of gold nanoparticles varies with shape and size, showing deviations from the typical fcc lattice due to elastic distortions in penta-twinned forms.

Contribution

It demonstrates the dependence of gold's crystallographic phases on nanoparticle geometry, highlighting the role of elastic distortions in structural polymorphism.

Findings

Decahedra exhibit body-centered tetragonal structure

Rods and bipyramids show body-centered orthorhombic structure

Structural variations are driven by elastic lattice distortions

Abstract

We report on the crystallographic structure of penta-twinned gold nanoparticles. Although gold typically exhibits a face-centered cubic (fcc) lattice, other phases have been reported in some nanoscale systems. We show that the crystallographic system and the lattice parameters of the gold unit cell strongly depend on the nanoparticle geometry, for a wide size range. Specifically, we show that decahedra exhibit a body-centered tetragonal structure (I4/mmm), whereas rods and bipyramids exhibit a body-centered orthorhombic structure (Immm). These changes in the crystallographic structure are explained by the elastic lattice distortions required to close the mismatch gap in penta-twinned nanoparticles, with respect to fcc single-crystal gold nanoparticles. The effects of nanoparticle shape and size on the surface pressure and the subsequent distortions are additionally discussed.