Fabrication of Nickel/Gold Multilayered Shells on Polystyrene Bead Cores by Sequential Electroless Deposition Processes

Core-shell conductive beads composed of a polystyrene (PS) core and a metallic shell of nickel-gold were investigated to identify the metal-polymer interface and the electromechanical response under a large deformation. Using dispersion polymerization, the average PS bead diameter was controlled to between 1.5 μm and 4.1 μm by adjusting the water and initiator concentrations, to give a monodispersed particle size distribution. In the electroless deposition processes of Ni followed by gold, the Ni-P shell was initially formed with a thickness of 43 nm, part of which was replaced by gold to give Ni-P and Au shell layers with thicknesses of 39 nm and 43 nm, respectively, as confirmed by transmission electron microscopy (TEM) observation. The electromechanical indentation test of a single core-shell bead showed that its resistance was 9.8 Ω/bead at a compressive deformation of 35%.