1：Experimental Design and Method Selection:

A seed-mediated growth approach was used, involving the synthesis of 5-nm Au spherical seeds followed by the overgrowth of Cu shells using glucose as a reducing agent and hexadecylamine (HDA) and Cl- as capping agents. The synthesis was conducted at 100°C to facilitate reduction while minimizing self-nucleation.

2：Sample Selection and Data Sources:

Au seeds were synthesized in two steps: formation of Au clusters using NaBH4 reduction and growth into 5-nm spheres. Cu(II) precursor (CuCl2·2H2O) was used for shell growth. Samples were characterized at various reaction times and precursor concentrations.

3：List of Experimental Equipment and Materials:

Chemicals included HAuCl4·3H2O, CuCl2·2H2O, NaBH4, HDA, glucose, ascorbic acid, CTAB, CTAC, ethanol, and deionized water. Equipment included TEM (Hitachi HT7700), HAADF-STEM (Hitachi HT2700), SEM (Hitachi SU8230), UV-vis spectrometer (Cary 60), ICP-MS (NexION 300Q), XRD (X'Pert PRO Alpha-1), XPS (Thermo K-Alpha), and software for DDA calculations (DDSCAT 7.3, LAMMPS, VMD).

4：3, LAMMPS, VMD). Experimental Procedures and Operational Workflow:

4. Experimental Procedures and Operational Workflow: Au seeds were added to an aqueous solution containing HDA, glucose, and CuCl2. The mixture was stirred, purged with argon, heated to 100°C for 1 hour, and products were collected by centrifugation, washed, and re-dispersed in ethanol. Variations included different reaction times, amounts of Au seeds, and concentrations of Cu(II) precursor.

5：The mixture was stirred, purged with argon, heated to 100°C for 1 hour, and products were collected by centrifugation, washed, and re-dispersed in ethanol. Variations included different reaction times, amounts of Au seeds, and concentrations of Cu(II) precursor. Data Analysis Methods:

5. Data Analysis Methods: TEM, STEM, EDX, SEM, UV-vis spectroscopy, ICP-MS, XRD, and XPS were used for characterization. DDA simulations were performed to model optical properties.