Ultrafine Ag-coated Cu nanoparticles less than 20 nm in diameter were fabricated.
Different Ag precursor concentrations influenced thickness and density of Ag shell.
Excessive Ag precursor concentrations induced formation of surplus fine pure NPs.
Ag dewetting behavior and Cu oxidation in Cu4@Ag1 nanoparticles were observed.
Electrical resistivities of sintered Cu4@Ag1 films were 2.70–4.96 × 10−3 Ω cm.