Au@Ag core-shell nanoparticles have emerged as promising platforms for photonic applications due to their synergistic integration of gold’s biocompatibility and silver’s exceptional plasmonic properties. And Nanoparticles with sharp corners exhibit electron accumulation at the tips under electromagnetic fields, generating enhanced localized electric fields. This phenomenon facilitates their applications in surface-enhanced Raman spectroscopy (SERS) and strong coupling interactions, among other fields. So, when Au@Ag core-shell nanoparticles coupled with sharp corners, there will be outstanding performance in trace molecule detection, biosensing and catalytic applications. This study systematically investigates the seed-mediated synthesis of Au@Ag nanocuboids with tunable morphology, size and surface plasmon resonance (SPR) by using gold nanorod (AuNR) seeds with different dimensions and adjusting the volume of silver precursors. Key synthesis parameters, including AuNR diameters, aspect ratios and AgNO₃ volumes, are modulated to achieve morphological, size and optical control. In experiments adjusting the size of AuNR seeds for synthesizing Au@Ag nanocuboids, as the diameter of AuNR decreases from 136.5±5 nm to 11.2±2 nm and the aspect ratio increases from 1.39 to 8.20, the aspect ratio of Au@Ag nanocuboids increases from 1.18 to 2.69. Notably, when the diameter of AuNR is below 100 nm, the sharpness of the corners of Au@Ag nanocuboids progressively improves with increasing diameter and decreasing aspect ratio of the AuNRs. However, when the AuNR diameter exceeds 100 nm, the corners of the synthesized Au@Ag nanocuboids exhibit truncation. Meanwhile, the extinction spectrum reveals that, apart from the broadened and indistinct peaks caused by the size effect, Au@Ag nanocuboids can primarily excite the longitudinal plasmon resonance mode, transverse plasmon resonance mode, and octupolar plasmon resonance modes. Furthermore, the plasmon resonance peaks exhibit corresponding shifts in response to changes in the size and morphology of Au@Ag nanocuboids. Meanwhile, neither the characterization results of high-resolution transmission electron microscopy (HRTEM) nor selected area electron diffraction (SAED) can observe {111} crystal planes, indicating that the Au@Ag nanocuboids with the sharpest corners remains untruncated and exhibits an exceptional morphology. And high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) combined with energy-dispersive X-ray spectroscopy (EDS) characterization reveals that the silver shell exhibits anisotropic growth features on the gold core, with its transverse thickness being significantly greater than the longitudinal thickness. Besides, Au@Ag nanocuboids dimensions are linearly regulated by the volume of AgNOO₃ (100 mM) from 5 μL to 30 μL, yielding tunable lengths (110.3 ±7.8 nm to 141.3 ±5.5 nm), widths (59.7 ±2.1 nm to 103.7 ±5.6 nm), aspect ratios (1.85 to 1.36) and corresponding plasmon resonance peaks as validated by SEM and extinction spectrum. The simulation results of their extinction spectra are in better agreement with the experimental measurements, and for the nanocuboid with aspect ratio of 1.45, the strength of the electric field at the corners shows a tendency to be enhanced and then weakened with the decreasing of the sharpness of the top corners (r/L = 0.2% - 11.5%), in which the strength of the electric field enhancement is greatest at r/L = 0.5%.
This work synthesizes Au@Ag nanocuboids with controllable sharpness of corners and dimension by adjusting the size and aspect ratio of AuNRs or changing the amount of silver precursors. The method proposed in this study for synthesizing sharp-cornered Au@Ag nanocuboids provides possibilities for customized fabrication of Au@Ag nanocuboids, thereby expanding their application prospects in nanophotonics, catalysis, sensing, photothermal therapy and other fields.