Preparation and characterization of sub-20 nm Cu_X@Ag₁ core-shell nanoparticles by changing concentration of silver precursor

Ultrafine Ag-coated Cu (Cu@Ag) nanoparticles (NPs) less than 20 nm in diameter were prepared. After synthesizing ultrafine Cu NPs using a solvothermal method to serve as the core particles, Cu@Ag NPs were fabricated with different initial Ag precursor concentrations, resulting in different thicknesses, densities, and uniformities of Ag shells. The average thickness and density of the Ag shell increased with increasing initial Ag precursor concentration in a Cu:Ag atomic ratio from 6:1 to 1:1. However, excessive Ag precursor concentrations induced homogeneous nucleation and growth of surplus fine pure NPs. Ag dewetting behavior and Cu oxidation in the Cu₄@Ag₁ NPs were observed, they occurred during heating at 200 and 250 °C, respectively. The electrical resistivities of sintered Cu₄@Ag₁ films decreased with increasing temperature from 200 to 240 °C. The resistivity after washing the OA and sintering for 60 min at 240 °C in air was measured to be 4.96 × 10⁻³ Ω cm. The film was sintered in nitrogen using the ink containing non-washed Cu₄@Ag₁ NPs indicated the lower resistivity of 2.70 × 10⁻³ Ω cm owing to the non-oxidation atmosphere, although the chemically capped oleylamine in the core-shell NPs hindered the sintering behavior.