Fig. 2. Fabrication process of silver SSC.

(A) After electron beam lithography and surface treatment with 2 M HF, the sample is immersed in HF/AgNO₃ aqueous solution, where Ag⁺ is reduced to silver metal through a redox reaction chain. (B) In nanowells (reduction surface), silver growth follows a spherical symmetry and generates three spheres of appropriate diameter and interdistance. (C) Redox reactions inside a nanowell starting from the silicon surface. (D) SSC architecture and 2D map of electric field. Evidence of external laser polarization along the chain axis. The electric hotspot is localized in the smallest gap. (E to H) SEM images of silver SSCs and possible combinations in monomer, dimer, trimer, and tetramer. Scale bars, 50 nm. PMMA, polymethyl methacrylate.