Unraveling Structural Information of Turkevich Synthesized Plasmonic Gold–Silver Bimetallic Nanoparticles

For the synthesis of gold–silver bimetallic nanoparticles, the Turkevich method has been the state‐of‐the‐art method for several decades. It is presumed that this procedure results in a homogeneous alloy, although this has been debatable for many years. In this work, it is shown that neither a full alloy, nor a perfect core–shell particle is formed but rather a core–shell‐like particle with altering metal composition along the radial direction. In‐depth wet‐chemical experiments are performed in combination with advanced transmission electron microscopy, including energy‐dispersive X‐ray tomography, and finite element method modeling to support the observations. From the electron tomography results, the core–shell structure can be clearly visualized and the spatial distribution of gold and silver atoms can be quantified. Theoretical simulations are performed to demonstrate that even though UV–vis spectra show only one plasmon band, this still originates from core–shell type structures. The simulations also indicate that the core–shell morphology does not so much affect the location of the plasmon band, but mainly results in significant band broadening. Wet‐chemistry experiments provide the evidence that the synthesis pathway starts with gold enriched alloy cores, and later on in the synthesis mainly silver is incorporated to end up with a silver enriched alloy shell.