Essential Role of Icosahedral Symmetry in the 3D Shape of AuAg Plasmonic Nanostars With High Aspect‐Ratio Legs

ABSTRACT Plasmonic nanoparticles play an essential role in improving the sensitivity of different optical methods, and multibranched nanostars are predicted to show the highest enhancement factor for several applications in the near infrared region. The structural complexity of these particles represents a serious challenge with respect to gathering precise knowledge of atomic arrangement and 3D star morphology, making it difficult to accurately predict their optical response and to devise new synthetic methods addressing various applications. Here, we have used 4D‐STEM diffraction mapping and a thorough crystallographic analysis to determine leg configuration in space, so that a better understanding of plasmonic properties and growth mechanism can be obtained. Our results show that although electron microscopy images may show a certain shape diversity with stars displaying 4‐ 5‐ or 6 branches, the orientation of these legs in space follows the positions associated with the apexes of an icosahedral core. The direct application of the measured star structures has been used as quantitative structural input in optical simulations, which show excellent agreement with experimental measurements. This evidence confirms the crucial role of icosahedral symmetry for explaining the growth mechanism and plasmonic response of gold nanostars with high‐aspect‐ratio legs.